Proiect De Licenţă [304678]

Sisu Nicoleta Denisa

Design and ergonomics for underarm crutches

DIPLOMA PROJECT

Study program: Industrial Design

2017

Introduction

Disability affects 15-20% of every country's population. There are at least 650 million people with disabilities worldwide. Conflict and poverty continue to cause high rates of disability in the less developed world. The incidence of disability is increasing in the industrialised world as populations age.

[anonimizat] 1980 to 1990. Crutch and cane use also increased by 14 percent and 53 percent, respectively, over this period. Growth in the usage of these devices continued from 1990 to 1994 , far exceeding what could be attributed to the aging of the population. It is likely that improved survival of trauma patients has also contributed to the growth in mobility device use.

[anonimizat]. [anonimizat] 1% of the population is in need of a wheelchair and an additional 5,6% of people need some kind of walking aid.

The proportion of the population using mobility devices increases sharply with age. While only 0.2 percent of children under age 18 [anonimizat], to 1.5 percent, among those of working age. [anonimizat] 14.0 percent overall rate of mobility device use is almost a factor of 10 [anonimizat]. Just under 40 percent of persons aged 85 or over use mobility devices.

Loss of motor abilities (manipulation and locomotion) [anonimizat] a [anonimizat]. Whereas 31% of the male population aged 75-84 [anonimizat] 52%.

About half of people or their families pay for devices solely on their own.

With the above taken into consideration in order to develop an innovative solution I designed a pear of underarm crutches that fulfills the needs of a lot of people. This involved a large research into the initials designs of crutches. Discovering what has been done in the past and how it worked or didn’t helped made to design a successful product.

1. CHOOSING THE THEME

1.1 Establishing the project objective

The project objective is developing a unique product which ameliorate the problems that the users have when using a regular crutch. By designing this product several aspects were taken into acount:

Applying the ergonomics principle;

Easy usage;

Lightweight;

Functionality: the product must function properly for the intended purpose;

Productivity: the product must be produced with a required quantity and quality at a defined and feasible cost;

Cost effectiveness: the product must be cost effective. It must be manufactured in the most cost effective environment.

1.2 [anonimizat]:

Documentation: bibliographic and photographic

Free hand sketches

Concept Making

Developing the Idea

Materials

3D [anonimizat]

1.3 Gantt Chart

A [anonimizat], is one of the most popular and useful ways of showing activities displayed against time.

Below is a Gantt diagram showing an estimated time schedule for the project regarding all the parts and their duration from its start until the presentation date.

Fig.1- Gantt chart using smartsheet

2. DOCUMENTATION. BIBLIOGRAPHIC AND PHOTOGRAPHIC

2.1 Psychosocial Study: The User

In order to design a succesfull product, I chose a large user group: young, aged, elderly people. It conducted me to make a primary research in order to understand their wants and needs.This was important because it allowed me to understand the user and it helped me to design a product suitable for them at a convenient price.

The first step was to conduct interviews to evaluate current crutch shortcomings. The interviews with crutch users helped to generate a list of design requirements as follows:

-How long do you expect a pair of crutches to last? (26 votes)

-Which aspect is the most important to you in a walking aid? (27 votes)

-How did you pay for your last purchase of a walking aid? (11 votes)

Overall summary of collected opinions from these studies:

1. Support the weight of the user and provide him/her stability: This is of utmost importance for maintaining safety, whether the user is standing, walking, running or climbing stairs.

2. Employ both shock absorption and energy return: The crutches should have a means of absorbing shock and also have a way to return energy to the user (mostly common to long-term users.

3. Durable: This correlates strongly with the weight-bearing capability of the crutch and also the robustness of the interfaces between parts.

4. Lightweight: The crutch must be lightweight to allow ease of maneuverability and low energy consumption. (The weight of a crutch has to be different according to a user’s weight: the heavier user is, the heavier crutch she/he needs.)

5. Maximum mobility: The crutch cannot be bulky, must allow the user to easily move the crutch tip in any direction, and must easily detach from the user in case of a fall.

6. Ease of object reach: The crutch must remain attached to the user while he or she is reaching for an object, opening a door, or shaking hands.

7. Comfort: Comfort between the arm and the cuff or cradle, and the hand and the grip are important.

8. Silent operation: One of users' biggest concerns with present crutches is that the pivoting elbow cuff and adjustment holes become loose and produce loud noises (mostly common to long-term users).

9. Support user self-esteem: The crutch should be attractive and stylish so that it is a personal accessory the user is proud of.

10. Natural Grip should be implemented in the crutches.

11. Larger tip is needed to ensure good touch with the ground.

2.2 Who is the beneficiary /user of the product

The beneficiaries are people who experienced various kinds of injuries, during rehabilitation period (usually having injured leg, foot or hip, have orthoses, have a surgical procedure on a lower limb, or suffer a stroke, etc.) and disabled and elderly people, who are switching from other walking aids to crutches every so often (osteoarthritis, polyarthritis, rheumatism, orthopaedic impairments, late effects of injury, amputees).

It is generally known and has often been shown that on average, males are stronger and faster than females. At 30 years a woman’s strength is approximately 2/3 that of a man, it declines more rapidly with age and at 50 years a woman is about half as strong as a man. Moreover, the body mass center of man and woman differs man's is in his chest, while woman's – in the lower part of the abdomen.

All this means that it is much harder to use crutches and support body weight with an upper part of a body for woman than for man.

And, it is important to note that products that are designed for the lower percentiles of the population (where forces are concerned, these are the weaker persons) can be easier to use or operate by the average user.Those products may sell even better to 'normal' users than standard products, because they too appreciate clear, simple features and light operation. Unless, of course, these products get stigmatized as being specially made for the disabled and the elderly. Neither strong nor weak users want to be seen with a product that visibly classifies them as weak. If this negative image can be avoided, products designed for the weak can be a (commercial) success with everyone.

2.3 User scenario

If you break a bone in your leg or foot, have a procedure on your knee or lower leg, or suffer a stroke, your doctor may recommend that you use a walking aid while you are healing or recovering. Using crutches can help keep your weight off your injured or weak leg, assist with balance, and enable you to perform your daily activities more safely.

When you are first learning to use your crutch, you may wish to have a friend or family member nearby to help steady you and give you support. In the beginning, everything you do may seem more difficult. With just a few tips and a little practice, though, most people are able to quickly gain confidence and learn how to use a walking aid safely.

Making some simple safety modifications to your home can help prevent slips and falls when using your walking aid:

Remove throw rugs, electrical cords, food spills, and anything else that may cause you to fall.

Arrange furniture so that you have a clear pathway between rooms.

Keep stairs clear of packages, boxes, or clutter.

Walk only in well-lit rooms and install a nightlight along the route between your bedroom and the bathroom.

In the bathroom, use nonslip bath mats, grab bars, a raised toilet seat, and a shower tub seat.

Simplify your household to keep the items you need within easy reach and everything else out of the way.

Carry things hands-free by using a backpack, fanny pack, or an apron with pockets.

If your injury or surgery requires you to get around without putting any weight on your leg or foot, you may have to use crutches.

Proper Positioning

When standing up straight, the top of your crutches should be about 1-2 inches below your armpits.

The handgrips of the crutches should be even with the top of your hip line.

Your elbows should be slightly bent when you hold the handgrips.

To avoid damage to the nerves and blood vessels in your armpit, your weight should rest on your hands, not on the underarm supports.

How to walk with crutches:

Place both crutches under your arms, and place your hands on the hand grips of the crutches. Place your crutches slightly in front of you.

The top of the crutches should be about 2 fingers side-by-side (about 1½ inches) below your armpits. Place your weight on your hands. The top of the crutches should not press into your armpits.

If you have one leg that is injured, keep it off the floor by bending your knee.

Lift the crutches and move them a step ahead of you. Put the rubber ends of the crutches firmly on the ground. Move the foot that is not injured between the crutches. Place that heel down first.

If you are using your crutches for balance, move your right foot and left crutch forward. Then move your left foot and right crutch forward. Keep walking this way.

How to go up stairs with crutches:

Face the stairs. Put the crutches close to the first step.

Push onto the crutches and put your uninjured leg on the first step.

Put your weight on your uninjured leg that is on the first step. Bring both crutches and the injured leg onto the step at the same time.

When you hold onto a railing with one arm, put both crutches under the other arm. Use the railing to help you go up stairs.

How to go down stairs with crutches:

Stand with the toes of your uninjured leg close to the edge of the step.

Bend the knee of your uninjured leg. Slowly lower both crutches along with the injured leg onto the next step.

Lean on your crutches. Slowly lower your uninjured leg onto the same step.

Place both crutches under one arm while you hold onto the railing with the other arm.

How to sit in a chair with crutches:

Turn and back up to the chair until you feel the edge of it against the back of your legs. Keep your injured leg forward.

Take your crutches out from under your arms. Sit while bending your uninjured knee.

How to get up from a chair with crutches:

Sit on the edge of your chair.

Push up with your hands using the crutches or arms of the chair. Put your weight on your uninjured foot as you get up.

Keep your injured leg bent at the knee and off the floor.

Crutch-Walking Gaits

The client’s strength and type of disability are guides to the best possible crutch-walking gait or style of walking. The client should use the muscles and joints as much as possible. A healthcare provider and a physical therapist will determine the gait that is best for each client to use.

In two-point gait, the client is partially weight-bearing on both legs. (A crutch and the opposite leg are considered one “point.” The other crutch and leg are the second “point.”) The client puts his or her body weight on one leg and on the contralateral (opposite side) crutch. The client then brings the other crutch and leg forward together, and shifts the weight to them. This gait is faster and more like walking than the others, and the client can change the gait as muscle power improves. This gait is used following spinal cord injury; when both legs have about the same strength; and when a client is learning to walk again.

In three-point gait, each crutch and only one leg support weight. (Each is considered a “point.”) The other leg is non-weight-bearing. The person moves the non-weight-bearing leg and both crutches forward together, balancing the weight on the unaffected leg, while supporting the weight on the crutches and weak leg. He or she then steps forward with the weight-bearing leg. Steps should be of equal length and timed so that no pauses occur. This gait is best when one leg is disabled and the other is strong enough to bear all the client’s weight. This gait keeps most or all of the weight off the weak leg. However, sometimes the client may place a small amount of weight on the weak leg if partial weight-bearing is allowed. This gait is one means of strengthening the weak leg without endangering the client.

In four-point gait, each crutch and each leg move separately. (Each of the four “points” supports weight.) The client places one crutch forward, and then advances the contralateral foot; he or she then brings the second crutch forward, and the other foot follows. Rhythmic, short, and equal steps are important. Counting helps to develop rhythm: one, right crutch forward; two, advance left foot; three, left crutch forward; four, advance right foot. This gait is the easiest and the safest to use (the client always has three points of support). The client must be able to bring each leg forward and clear the floor with each foot. Those who are partially paralyzed, have fractures of both legs, or have arthritis often can safely use this gait.

In swing-through or tripod gait, the client stands on the strong leg, moves both crutches forward the same distance, rests his or her weight on the palms, and swings forward slightly ahead of the crutches. The client then rests the weight again on the good leg and balances for the next step. Because this gait is fast, the client should learn to balance before attempting it. This gait is often used following a fracture, when no weight-bearing is allowed on one leg. It also is used following amputation, when the prosthesis is not in place (particularly for young people). The client who is allowed to put weight on only one leg must hold up the other leg, bending the knee (not bending at the hip). Rationale: It is important to prevent hip contracture, which can occur rapidly. A contracture is an abnormal shortening of muscles, which can lead to permanent deformity. This technique also improves balance. Bending the knee is tiring, and the client should rest frequently with the leg elevated. In some cases, a strap is applied to hold the affected leg up.

2.4 Prospectologic study: The product

Walking sticks have aided bi-pedal man since the dawn of our evolution. Since antiquity humans have fashioned support devices to hold themselves up when they became sick or injured. Such devices are dated to 2830 B.C. A carving on the entrance of an Egyptian tomb depicts a figure leaning on a crutch like stuff. The walking stick has served well as an assist to climbing, an aid to steadying people themselves, as a reaching tool, a weapon, as weight-bearing device to facilitate ambulating when debilitated and for some it was a matter of fashion.

As we became more sophisticated our walking sticks developed specialized functions for individual needs such as hook shaped top to herd sheep or a T shaped top to nestle in the pit of the underarm for a rudimentary crutch.

Crutch design has evolved from the basic "T" to aluminium braces with ice-gripping tips or energy storing tips that function as shock absorbers. For lower-limb injuries, crutches remain useful today to decrease discomfort, reduce recovery time, and assist walking. The form was driven by its need to function and was shaped for the individuals needs.

Many companies in the world currently manufacture all types of crutches. These mass-produced crutches have many similar attributes in common. They are mostly made out of aluminium tubing with adjustment holes above and below the handgrip so that one size fits all. The arm cuffs are made of metal and the handgrips and crutch tips are made of solid elastomers.

Unfortunately an attempt to make an inexpensive crutch to accommodate the needs of everyone ends up not meeting the needs of anyone effectively.

A crutch must do 2 things:

– Reduce weight load on one of your legs;

– Broaden your support base to improve your balance and stability.

The support also should assist upright movement and transmit sensory cues through the hands. A crutch allows people with paralysis the benefits of upright posture and lets them manoeuvre in places they cannot go with a wheelchair.

A crutch becomes necessary when a person cannot walk, or walks with extreme difficulty. Any person with leg or foot pain or injury, weak muscles, or an unstable gait may benefit from using a crutch or crutches. Regaining upright body movement aids circulation, assists kidney and lung functions, and helps prevent calcium loss from your bones.

Crutches shift the force of upright movement from your legs to your upper body.You must have sufficient arm strength, balance, and coordination to use them effectively.

Sizing a forearm crutch

Fig.8- Forearm measuring

The "X" measurement will determine the position of the underarm piece in relation to the handgrip on the final crutch or crutches. It is the distance from your elbow, leaving ~ 8 cm, and your handgrip.

The "Y" measurement will determine the distance between your handgrip and the bottom of the crutch tip. The measurement must be taken when the elbow is flexed not more than 30 degrees.

Sizing an underarm crutch

Fig.9- Underarm measuring

The "X" measurement will determine the position of the underarm piece in relation to the handgrip on the final crutch or crutches. It is the distance from your underarm to your handgrip when elbow is flexed not more than 30 degrees.

The "Y" measurement will determine the distance between your handgrip and the bottom of the crutch tip (the same distance as measuring the forearm crutch).

The “Z” measurement will determine the length of the cradle. This measurement depends on the thickness of users arm, but practically it is always a standard.

2.5 Similar existing products on the market

It is important to understand the function of a crutch to differentiate between the three major types. Crutches bear the weight of the body when walking. It can therefore also reduce pressure on the legs which can aggravate pain even in the absence of muscle weakness. It should, however, by the nature of its design not be used for supporting the body weight when standing for long periods of time

There exists three types of crutches in the market:

Axillary (Underarm) crutch

These crutches rest under the arm, hence the name axillary crutches or underarm crutches. The body weight is transferred from the armpit to the floor and in this manner it can bear up to 80% of the body weight. The hands should grasp on the handles during walking but can be freed momentarily when standing, only if the hands need to be used and the entire body weight will not be rested on a single crutch during this time. However, users need to be aware of the dangers of using these crutches as ongoing pressure on the armpit area can cause compression of the nerves running through it. Therefore, crutch users are discouraged from resting their entire weight on the crutch for long periods like when standing.

These crutches can be made of wood, aluminum or titanium. They are manufactured to fit children and adults and have adjustable heights. The very top of the crutch is usually covered with a material with a high coefficient of friction to decrease movement under the arms.  The handle of the crutch is covered with a cushioned material to protect the user's palm. The tip of the crutch is usually made out of rubber to ensure traction.

Potential Users

Underarm crutches can be used by any patient who needs extra stability or balance, especially if a limb needs to be offloaded. Common examples of underarm crutches users include those with fractures of the lower extremity, those with soft tissue damage to the lower extremity and unilateral lower limb amputees. The soft tissue in the axillae and chest should be in good condition and the user should have sensation in their hands and chest.

Forearm crutches

These crutches transfer the body weight through the foream and down to the floor. It is essentially a cane with a handle along its length, rather than at the top as is seen with a traditional walking stick. It may have a forearm cuff at the top which provides greater support.

Forearm crutches are made of aluminum or titanium and have a vinyl covered steel forearm cuff. The height and cuff position of the crutch are adjustable. The open end of the cuff is placed on the lateral aspect of the forearm to permit elbow flexion and grasping without dropping the crutch. The top of the crutch is angled at 20° to provide a comfortable, stable fit. Many people prefer forearm crutches to underarm crutches because ambulation is safer and easier, the forearm support stabilizes the wrist during weight bearing, the user's hands are free to perform various tasks while the individual's body weight is supported through the forearm by the forearm cuff pivots and the patient does not have to worry about dropping the crutches. A leather cuff can also be used.

Potential Users

This design was originally developed for patients with poliomyelitis. It is especially appropriate for patients who have good proximal upper limb strength but weak distal strength and who are unable to hold and control the orthosis effectively.. It is able to transfer up to 50% of the body weight down to the floor.

Platform crutch

Platform crutches have a trough for the forearm to fit into at the very top. A vertical handgrip is placed at the end of the platform. Velcro straps are applied around the forearm to keep it in place.

Potential Users

This design is specifically for patients who can't support their weight through their wrists and hands, who have severe deformities of the wrist or fingers or below elbow amputation and who are unable to extend one or both elbows passively

For design purposes, the weakest users are often relevant than the strongest, and beginners more than experienced users. This is one of the reasons why the chosen target group of this product is temporary users (short-term users).

2.6 Identifying and defining critical problems

Current crutch designs present some problems for users, especially for those proportions of patients who use crutches for the life-time. Extensive researches have been done about these problems. We argue that most important problems can be classified as below:

High-energy expenditure

It takes about twice as much energy to ambulate with swing-through crutch gait as it does for normal ambulation. This is due both to the upper body's reaction to the shock of impact and to the vertical movement needed to clear the feet in swing phase by users wearing knee-ankle-foot or those with locked knees. The user essentially is doing a body push-up with every step.

Injuries caused by repetitive loads on the hands, wrists, and arms during ambulation

These injuries affect many users and are simply stress injuries to the upper limb caused by constant use of crutches. If users have arthritis or other conditions affecting the upper limb, then the effect is compounded. Also some diseases may occur; Users of crutches are susceptible to carpal tunnel syndrome due to the awkward angle of the hands. Carpal tunnel syndrome occurs when tendons or ligaments in the wrist become enlarged, often from inflammation, after being aggravated. The narrowed tunnel of bones and ligaments in the wrist pinches the nerves that reach the fingers and the muscles at the base of the thumb. On occasion, forearm crutches have been observed to cause or lead indirectly to multiple injuries and disorders despite their ability to transfer weight and despite the fact that they are often somewhat less intrusive than traditional full-length crutches. Each repetition of usage of the crutch may be injurious and can produce micro-trauma to the tissues and joints of the body. Although the human body has enormous self-repair abilities, continued exposure to such activities can outweigh these abilities, which then results in injury.

Problems created by not standing and walking

If people do not use crutches because they tire easily or acquire hand/arm problems, there are possible consequences. There are many reasons (physiological and psychological) why it is good to stand and walk rather than sit and use wheeled mobility. These reasons include improved bone growth, improved blood circulation, reduced bladder infections, reduced pressure sores, and prevention of contractures . Most permanent users utilize forearm crutches, whereas most temporary users utilize underarm crutches. Many designs were tested with users and compared with standard forearm crutches.

2.7 Ergonomics

Ergonomics is a science focused on the study of human fit, and decreased fatigue and discomfort through product design. Ergonomics applied to office furniture design requires that we take into consideration how the products we design fit the people that are using them. At work, at school, or at home, when products fit the user, the result can be more comfort, higher productivity, and less stress. Ergonomics can be an integral part of design, manufacturing, and use. Knowing how the study of anthropometry, posture, repetitive motion, and workspace design affects the user is critical to a better understanding of ergonomics as they relate to end-user needs.

The crutch is an object that has not kept pace “ergonomically” with the ever-changing world of modern medicine. Static overloading results when muscles, especially those of the hand and the extensor muscles of the wrist, are traumatized or overstressed repeatedly over time. Injuries common to crutch use include carpal tunnel syndrome, wrist tendonitis, medial or lateral elbow epicondylitis, and rotator cuff muscle strains and tears. These injuries result from cumulative stresses on tissues and joints and excessive muscular contraction that impedes blood flow. Other parts of the body, such as the back and the shoulders, are also adversely effected by unnatural stress and increased loads. In addition, use of crutches causes fatigue and discomfort, for its users, when it has to help them in their everyday life.

If crutches are not ergonomically designed, their users run the risk of serious injury. Modern medicine needs an ergonomically designed, comfortable, user-friendly crutch.

The muscle groups most important for crutch walking include:

The shoulder muscles that stabilize the upper extremity and those that hold the top of the crutch against the chest wall.

The arm muscles (at the shoulders) must be able to move the crutches forward, backward, and sideways.

Other muscle groups that must be strong enough to support the patient include:

The forearms, to help prevent flexion or buckling. These muscles are important in raising the body for a swinging gait.

The wrist muscles, to enable weight-bearing on the hand pieces of the crutches;

The finger and thumb muscles, to grasp the hand piece.

From a biomechanics perspective, as a load is applied to the palmar side of the fingers in grasping a tool, lever, or material, load moments result at each of the finger and wrist joints.

Underarm crutches Forearm crutches

Fig.13- The mostly stressed body parts using different kinds of crutches [6]

Different body parts are stressed when using different kind of crutches (Fig.13). So changing a kind of crutch every so often would give user a possibility to rest his/her wrists and elbows (when changing from forearm to underarm crutch), armpits (when changing from underarm to forearm crutch).

Altering the posture of the arm will have a great effect on the moments at the elbow and shoulder, but will have no effect on the external reactive forces since they have remained as a parallel force system .

Person's endurance is measured by investigating spontaneous changes in posture. It means, that when a person feels tired (himself in a whole or in specific body part) he wants to change his posture. That gives him relaxation

Moreover, different kind of crutches could be used in different situations. According to physiotherapists and some users, it is much easier to start using underarm crutch, but it is harder to use it for long walks and it is harder to learn how to use forearm crutch correctly, but much easier to use it for a long walks/ longer time. In standing position and using arms, underarm crutch is more comfortable. Also, in the start of using crutches, underarm crutches give better feeling of safety and stability, and, according to some users, it do not stand out as much as forearm crutches. And this is very important for a period of adaptation.

2.8 List of requirement (specifications) for the new product

When preparing a detail requirements list it is essential to state whether the individual items are demands or wishes.

Demands are requirements without which fulfilment the solution is not acceptable. They can be established qualitatively or as against some limits.

Wishes are those requirements that are taken into consideration whenever possible. They may be formulated as options with the stipulation that they only warrant limited increases in cost. It is advisable to classify wishes as being of major, medium or minor importance.

Even before a certain solution is adopted, a list of demands and wishes should be drawn up and the quantitative and qualitative aspects differentiated.

Quantitative: all data that include numbers and magnitudes, such as number of items required, maximum weight, power out put, volume flow, rate etc.

Qualitative: all data involving permissible variations or special requirements such as waterproof, corrosion proof, shockproof etc.

If possible, the requirements should be quantified and defined in the clearest possible terms. Special indications of important influences, intentions or procedures may also be included in the requirements list, which is thus an internal digest of all the demands and wishes expressed in the language of the various departments involved in the design process. As a result, the requirements list not only reflects the initial position but also serves as an up-to-date working document.

The first step in clarifying the task is the establishment the necessary functions and the specific constrains (for example: safety, ergonomics, production, quality control, assembly, transport, maintenance, manipulate).

In order to make easier the requirements list making, it is useful to consult a checklist, which can be structured on categories, or sub-systems (functions and assemblies).

Table.1- Requirement list

Critical areas: Geometry, Kinematics, Forces, Material, Safety, Ergonomics

Requirements of the crutches:

Geometry: – clear dimensions
– cradle and grip suitable for anthropometric dimensions – diameter, length

– reduced weight

Kinematics: additional forward velocity, relative to traditional axillary crutches

Forces: The crutches must sustain the weight of an average men.

Material: light, durable, eco-friendly

Safety: walking, going up and down the stairs

Ergonomics: – easy to use, user-adapted-weight, handling, convenience

– pleasant to the eye

– suitable for a certain category of clients

Production: series, unique layout

Assembly: ease of assembly, adjustability

Operation: maximizing: pushing, displacement

Maintenance: simple to clean, with removable parts

Recycling: recyclable materials(steel, aluminum, plastics, rubber), low wear replacement parts

Costs: low cost of materials, low loss (suitable technology), cheap technology solutions, reuse, recycling

Design, general: minimalist design, accent on functionality, pleasant appearance, shapes and attractive colors.

Considering this data, the crutches must follow a fundamental law: in order to make a design product successful, you have to find a balance between ergonomics, aesthetics and functionality.

If a product simply looks good but has no functionality, it will have no market value and make the target clients question your credibility as a designer/ manufacturer or seller.

Same goes if a product is fully functional but does not look as good as it should be looking. Clients do not tend to buy functional products that do not look good for the simple fact that humans are not set up to enjoy things that are not beautiful in any way.

However, a designer should keep in mind the fact that all human minds are different and someone’s garbage may be another one’s treasure. Same goes with the comparison between good and bad looking.

3. PRESENTATION OF CONCEPT IDEAS

The fist step of the design phase was to find the shape of the crutch. Below are some examples of the Brainstorming.

Fig.14- Free hand sketches

In order to comply with the design specification, three different concept ideas have been put into practice through sketches in order to analyze what concept is the best out of the three.

All three ideas have a couple of things in common, such as:

Applying the ergonomics and aerodynamics principles

Easy usage

Pleasant appearance

Minimalist design

3.1 First concept idea

The first concept idea was inspired by the double curve resembling the letter S. This type of curve can be found in nature, in several art objects and in many things which surrounds us.

The underarm cradle is made of foam and keeps the underarms from getting sore and reduce friction eliminating rashes. This type of foam increse the comfort of the user and provides a better stability and durability. It also have handle adjustment holes.

3.2 Second concept idea

After coming up with the first concept idea, the second concept was of creating another crutch which has a fixed grip and 2 adjustments levels, meaning that it has 3 different pipe diameters which go one into each other.

3.3 Third concept idea

The third concept is a combination between the previous variants and provides a realistic approach to the technical details.

This concept has a large comfortable underarm cradle that enhances stability and reduces underarm fatigue and soreness. The ergonomic grip is designed for repetitive and vigorous use, allowing proper blood flow and nerve conduction. This reduces carpal tunnel syndrome and wrist tendonitis. The grip has a soft sculptured foam handle for comfortable palm support.

Regarding the diameter of the pipes, i have made a modification compared to the previous concept, meaning that the entire crutch has the same pipe diameter except the two rods that enter in the pipes which allows to make adjustments( one on the upper part and one on the bottom part).

3.4 Multi-criteria analysis

The multi-criteria analysis is a tool generally used when a decision has to be made regarding a complex problem. For designers and engineers it is especially useful when having multiple solutions for one problem and trying to find the best answer. It is a fairly objective method as it uses different criteria which have different importance, obtained through calculus. The reason why it isn’t entirely objective is because the criteria are chosen by the person performing the analysis and sometimes his/her personal preferences or other motives may intervene when making this choice.

Therefore, the first step when performing a multi-criteria analysis is to choose the elements by which the product will be evaluated. After this step, the method becomes objective as the importance of the criteria is computed using specific formulas. Two types of evaluation matrixes will then be performed through specific methods and by using the established criteria with their corresponding importance. These are rough evaluation and fine evaluation.

For this project, the three crutches conceptual variants presented in the previous sub-chapters will be evaluated using the multi-criteria analysis-both rough and fine evaluation. As it was previously stated, the first step is to choose the criteria by which the evaluation will be made. In order to be as objective and relevant as possible, the criteria I will choose for evaluation will be selected based on common evaluation tables of crutches which can be found on the internet.

Considering the discussed aspects, the criteria for the analysis are:

Aesthetic= AE

Ergonomics= ER

Safety= ST

Time to assemble= TA

Reliability= RB

Weight= W

Manufacturing= MF

Maintenance= MT

These are the most important points that need to be taken into consideration when it comes to the overall design of the crutches.

All these are represented in the matrix below and the criterion is assigned as follows:

If criterion a is more important than criterion b = 1

If criterion a is of equal importance as criterion b = 0.5

If criterion c is less important than criterion b = 0

Table 2- Computation values for the relative weight of criteria using FRISCO formula

Where:

k = 1…n, the order number of the current criterion

Pk = the global grade of criterion k, which is the sum of grades from row k of the matrix n x n = 8 x 8

Lk = the top based on the count of Pk

Sk = no of criteria which have global grades inferior to the global grade of the current selection

Wk = absolute coefficient of weight of the current selection computed with the FRISCO Formula:

Wk = ;

Pmax = max Pk;

Pmin = min Pk;

and their relative values (wk):

wk = , k = 1…n.

Table 3- The variants evaluated according to FRISCO formula

Using the FRISCO formula we find a more precise order of the variants. According to it the best solution is the third variant. We will focus on developing the best solution.

3.5 Detailed description of the chosen concept

Several sketches were made in order to established the details of the product.

The underarm cradle: 
– Provides for better sense of stability in use 
– As the walking movement proceeds, the front position of the underarm cradle gives the user forward arm and shoulder support 
– Consequently, there is less reliance on the direct underarm pressure 
– Larger area enhances sense of walking stability and reduces underarm fatigue and soreness

The ergonomic grip:

– It is designed for repetitive and vigorous use

– Allows proper blood flow

– Reduces carpal tunnel syndrome and wrist tendinitis

– Has a comfortable palm support

The Clip sits around the tube and a centrally located pin is meant to push through a pre-punched hole in the tube offering a locking mechanism. It will open up to suit the tube diameter.

Extended Range:
– Adaptable to multiple end users 
– Fits a large range of height

The chosen tip is the the last one. It has a special integrated damper and swivel 360 degrees that absorbs impact and shock in a lasting way, by not passing on the user impacts and dramatically decreases pain in the hands, wrists and shoulders, as it reduces tension and the load on the joints.

The shock absorber allows to automatically adjust the angle of support with the ground by maximizing the contact area, consequently the support and grip on the ground increase.
The special design also helps to keep the tip clean. .

4. PRODUCT DEVELOPMENT

4.1 Stages for the constructive design

The objective of the constructive design stage is to transform the concept developed in the previously stage, into a project. This involves taking some steps in choosing the necessary materials and the most appropriate technological processes for their processing. The adopted solutions will be permanently verified from a technical and economic point of view.

4.2 Dimensioning

The purpose of dimensioning is to provide a clear and complete description of an object. 
A complete set of dimensions will permit only one interpretation needed to construct the part. Dimensioning should follow these guidelines:

Accuracy: correct values must be given;

Clearness: dimensions must be placed in appropriate positions;

Completeness: nothing must be left out, and nothing dupicated;

Readability: the appropriate line quality must be used for legibility.

The dimesions and specifications of crutches are based around the weight and height of an average man.

The dimensioning body height (5th to 95th percentiles) of women in Europe varies between 156,2 and 178,9 cm. The lowest woman's height is 147,5 cm and the highest – 186,0 cm . The dimensioning body height (5th to 95th percentiles) of men in Europe varies between 166,9 cm and 190,2 cm.The lowest man's height is 156,8 cm and the highest – 197,0 cm. The shoe height (+2,5 cm) must be taken into account.

Fig.22- Different body heights

Below we can see some of the general dimensions of the main components of this project.

Fig.23- Minimum height Fig.24- Maximum height

4.3 Material choice

Material is a wide term for the (chemical) substance, or a mixture of substances that constitute an element. There are concerns to think about when choosing materials (in order of importance) are:

Meeting the performance requirements

Easy to process

Ecological concern

Aesthetics properties

Most products need to satisfy some performance targets, which we determine by considering the design specification (for example: they must be cheap, or stiff, or strong, or light, or perhaps all of these criteria). Where selection charts are really useful is in showing the trade-off between 2 properties, because the charts plot combinations of properties.

With the criteria mentioned before, we need to choose the proper materials for the product’s component. Following is a list of these materials per item.

In order to achieve the overall look and functionality of the crutches, aluminum alloy is the main material used for this concept idea.

The total independent parts used for this design, made of aluminum alloy are:

The bottom pipe

The middle pipe

The underarm pipe

The upper rod

The bottom rod

In order to achieve comfort, there are two foam handles places on the cradle and on the grip. Both handles are made of polyethylene foam, which is a soft, easily mantained and hygienic material. Polyethylene is closed-cell foam, meaning its structure is made of millions of tiny bubbles, sealed off from each other. This provides a resistance to water, in addition to a strength and rigidity not present in open-cell foams. It is also resistant to solvents, petroleum products, and is antimicrobial as well, inhibiting the growth of mold, mildew, and bacteria. A resilient material, polyethylene returns to form after compression, while still yielding enough to provide cushion and security where it is needed. It is these characteristics, combined with its versatility and customization possibilities, that make it useful in so many applications.

The tip of the crutches it’s made from the following materials:

A stainless steel damper

A stainless steel spring

Two rubber caps

A rubber cover

The clips which helps to adjust the crutches are made from PVC and steel.

4.4 Material Analysis

4.4.1 Aluminum alloy

After iron, aluminium is now the second most widely used metal in the world. The properties of aluminium include: low density and therefore low weight, high strength, superior malleability, easy machining, excellent corrosion resistance and good thermal and electrical conductivity are amongst aluminium’s most important properties. Aluminium is also very easy to recycle.

Properties of aluminium

Weight

One of the best known properties of aluminium is that it is light, with a density one third that of steel, 2,700 kg/m3. The low density of aluminium accounts for it being lightweight but this does not affect its strength.

Strength

Aluminium alloys commonly have tensile strengths of between 70 and 700 MPa. The range for alloys used in extrusion is 150 – 300 MPa. Unlike most steel grades, aluminium does not become brittle at low temperatures. Instead, its strength increases. At high temperatures, aluminium’s strength decreases. At temperatures continuously above 100°C, strength is affected to the extent that the weakening must be taken into account.

Linear expansion

Compared with other metals, aluminium has a relatively large coefficient of linear expansion. This has to be taken into account in some designs.

Machining

Aluminium is easily worked using most machining methods – milling, drilling, cutting, punching, bending, etc. Furthermore, the energy input during machining is low.

Formability

Aluminium’s superior malleability is essential for extrusion. With the metal either hot or cold, this property is also exploited in the rolling of strips and foils, as well as in bending and other forming operations.

Conductivity

Aluminium is an excellent conductor of heat and electricity. An aluminium conductor weighs approximately half as much as a copper conductor having the same conductivity.

Joining

Features facilitating easy jointing are often incorporated into profile design. Fusion welding, Friction Stir Welding, bonding and taping are also used for joining.

Reflectivity

Another of the properties of aluminium is that it is a good reflector of both visible light and radiated heat.

Screening EMC

Tight aluminium boxes can effectively exclude or screen off electromagnetic radiation. The better the conductivity of a material, the better the shielding qualities.

Corrosion resistance

Aluminium reacts with the oxygen in the air to form an extremely thin layer of oxide. Though it is only some hundredths of a (my)m thick (1 (my)m is one thousandth of a millimetre), this layer is dense and provides excellent corrosion protection. The layer is self-repairing if damaged.

Anodising increases the thickness of the oxide layer and thus improves the strength of the natural corrosion protection..

Aluminium is extremely durable in neutral and slightly acid environments.
In environments characterised by high acidity or high basicity, corrosion is rapid.

Non-magnetic material

Aluminium is a non-magnetic (actually paramagnetic) material.

Zero toxicity

After oxygen and silicon, aluminium is the most common element in the Earth’s crust. Aluminium compounds also occur naturally in our food.

4.4.2 Polyethylene foam

Polyethylene foam is a durable, lightweight, resilient, closed-cell material. It is often used for packaging fragile goods due to its excellent vibration dampening and insulation properties. It also offers high resistance to chemicals and moisture.

Polyethylene foam is easy to process and fabricate. It has high load bearing characteristics that help manufacturers reduce packaging costs as they can use thinner and smaller amounts of foam yet still protect their products.

Polyethylene Foam Material Characteristics:

Closed-Cell

Very lightweight

Non-abrasive

Easy to fabricate

Non-Dusting

Superb strength and tear resistance

Excellent shock absorption & vibration dampening properties

Flexibility

Impervious to mildew, mold, rot, and bacteria

Resistant to water, chemicals, solvents & grease

CFC free

Odorless

Excellent buoyancy

Very cost-effective

Excellent thermal insulation properties

4.4.3 Stainless steel

Stainless steel is an iron-containing alloy—a substance made up of two or more chemical elements—used in a wide range of applications. It has excellent resistance to stain or rust due to its chromium content, usually from 12 to 20 percent of the alloy. There are more than 57 stainless steels recognized as standard alloys, in addition to many proprietary alloys produced by different stainless steel producers.

Stainless steels are made of some of the basic elements found in the earth: iron ore, chromium, silicon, nickel, carbon, nitrogen, and manganese. Properties of the final alloy are tailored by varying the amounts of these elements. Nitrogen, for instance, improves tensile properties like ductility. It also improves corrosion resistance, which makes it valuable for use in duplex stainless steels.

4.4.4 Rubber

Natural rubber consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water.  Forms of polyisoprene that are used as natural rubbers are classified as elastomers.

Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms, it has a large stretch ratio and high resilience, and is extremely waterproof.

The following are the physical properties of rubber:

Specific gravity

Abrasion resistance

Tear resistance

Compression set

Resilience

Elongation

Tensile modulus

Tensile strength

Hardness

4.4.5 PVC

Polyvinyl Chloride (PVC) is one of the most commonly used thermoplastic polymers in the world. It is a naturally white and very brittle plasti. It is used most commonly in the construction industry but is also used for signs, healthcare applications, and as a fiber for clothing.

PVC is produced in two general forms, first as a rigid or unplasticized polymer (RPVC or uPVC), and second as a flexible plastic. Flexible, plasticized or regular PVC is softer and more amenable to bending than uPVC due to the addition of plasticizers like. Flexible PVC is commonly used in construction as insulation on electrical wires or in flooring for homes, hospitals, schools, and other areas where a sterile environment is a priority, and in some cases as a replacement for rubber. Rigid PVC is also used in construction as pipe for plumbing and for siding.

Some of the most significant properties of Polyvinyl Chloride (PVC) are:

Density: PVC is very dense compared to most plastics (specific gravity around 1.4)

Economics: PVC is readily available and cheap.

Hardness: Rigid PVC is very hard.

Strength: Rigid PVC has extremely good tensile strength.

4.5 Technological processes

4.5.1 Aluminum

The process for creating standard aluminum extrusions is the same as the process used for creating custom aluminum extrusions. Raw aluminum materials, which are 99.9 percent recycled aluminum, come to Silver City Aluminum in the form of seven inch diameter billets. These billets are very long, so our crew cuts them down to a more manageable size, depending on the sizes that are requested by the client’s order. The billets are pre-heated before they reach the extrusion station and are then heated to a specific temperature according to the recipe or requirements of the standard extrusion die that will be used.

Using over 10,000,000 pounds of pressure, the aluminum materials are then pushed through the standard extrusion die to create rod and bar aluminum, as well as solid and hollow aluminum tubes and angles. The reason why these are called standard aluminum extrusions is that we use a basic standard shape, size and ratio to create these products, which are commonly requested and used by our clients across the board. Custom aluminum extrusions are created in the same way, but using an extrusion die that is created specifically for client based on their unique manufacturing needs.

The extruded rod and bar aluminum or hollow aluminum tubes are then cooled down on extremely large tables, stretched and then cut, according to the order. The aluminum is also hardened with heat to help bring out the inherent qualities of the metal, such as strength, durability and natural corrosion resistance.

4.5.2 Polyethylene foam

Polyethylene foam, also referred to as PE, is a type of foam that is very rigid and made primarily through an extrusion process. Polyethylene foam is a strong, resilient, closed-cell type of foam. Polyethylene foam, unlike polyurethane foam, has the capability of being reheated in order to change its shape.

Polyethylene foam is the material produced as a result of the polymerization of ethylene. It is lightweight, flexible and resilient to mildew, mold, rot and bacterial growth, making it an extremely popular manufacturing choice in a wide range of applications.

Polyethylene foam is made up of ethylene chains connected by weak forces. It can be created with different densities or material properties, however is usually able to be broken apart without much force as the cell bonds are relatively weak.

Using different catalysts during polymerization will result in slightly adapting the properties of the foam, allowing it to be more useful in certain applications. Most types of foam however are non-abrasive materials and thus are widely used in packaging and protecting goods during storing, transportation and shipping.

Fabricating foam is a relatively easy process. It is typically cut into its desired shape or dimensions using abrasion, heat, water jet cutting or foam cutting blades. Often shapes have to be joined to create the final desired product, and adhesives are used fairly often to achieve this.

Foam, especially polyethylene foam, is one of the cheapest artificially fabricated materials to produce. The investment into the required processing energy is worth the initial costs as the resulting material is extremely versatile and useful.

As with other types of foams, polyethylene foam provides an excellent material for vibration absorption and dampening and so is used in insulation and cushioning of areas. The foam can also be used to minimize static in certain applications by providing a wave absorbing material.

Polyethylene, or PE foam is also CFC-free, recyclable and odorless, therefore providing an environmentally friendly solution for foam and packaging needs. Environmentally friendly choices are becoming increasingly important, even for large scale industrial processes such as foam fabrication.

4.5.3Stainless steel

The manufacture of stainless steel involves a series of processes. First, the steel is melted, and then it is cast into solid form. After various forming steps, the steel is heat treated and then cleaned and polished to give it the desired finish. Next, it is packaged and sent to manufacturers, who weld and join the steel to produce the desired shapes.

Fig.29 [11]

To make stainless steel, the raw materials—iron ore, chromium, silicon, nickel, etc.—are melted together in an electric furnace. This step usually involves 8 to 12 hours of intense heat. Next, the mixture is cast into one of several shapes, including blooms, billets, and slabs.

Fig.30 [11]

The initial steel shapes—blooms, billets, slabs, etc.—are hot rolled into bar, wire, sheet, strip, and plate. Depending on the form, the steel then undergoes further rolling steps (both hot and cold rolling), heat treatment (annealing), descaling Ito remove buildup), and polishing to produce the finished stainless steel. The steel is then sent the end user.

4.5.4 Rubber

Industrial Rubber components are usually manufactured by one of the following methods:

Injection Moulding – Using strip compound produced as previously described.

Compression Moulding – Requires secondary operations to process material into suitable forms of the correct weight and/or shape to suit particular products.

Extrusion – Using strip compound produced as previously described.

Injection and Compression moulding requires highly accurate single or multi-cavity moulds, typically made in high grade steel and designed and made using CAD/CAM programmes.

Injection Moulding:

Injection moulding has a number of elements operating automatically on timed sequences with moulding temperatures usually between 165°C and 200°C.

Moulding cycle:

Mould closes.

A plasticising screw rotates to force the injection of an accurate volume of pre-plasticised rubber compound into the mould.

Material is directed into the mould via a system of runners to each individual cavity, each having small injection ports.

Material is cured for a pre-determined time during which the plasticising screw retracts and plasticises sufficient rubber for the next injection.

Mould opens and parts are removed manually or automatically by robotic or other system.

Cycle is repeated.

During each machine cycle an operator may perform a variety of operations including: Trimming excess rubber (flash), inspection, packaging or assembly. Alternatively, the part may be forwarded for trimming by other methods.

Compression Moulding:

This simpler process is slower in operation than injection moulding in that special uncured preformed and weighed blanks are used. The process employs hydraulic presses with pre-heated platens at (150-170°C) that in turn heat up the mould.

Moulding cycle:

Open mould and remove product from previous cycle.

Load required blanks into each cavity.

Close mould and move into hydraulic press.

Activate hydraulic press. The closing action causes displacement of rubber to fill each mould cavity. To overcome certain conditions, pressure is sometimes released and the mould "bumped" to allow air escape.

Cure – Time is determined as a function of material and cross section of part being moulded.

Remove part(s) manually or automatically after pulling mould from press.

Repeat cycle.

Again the operator may have tasks to perform as described for injection moulding. Compression moulding is generally more suited to low volume production or where tooling costs are to be kept to a minimum. Compression moulding is also not suitable for moulding complex shapes.

Extrusion:

Extrusion is used for either of two functions:

Manufacture of long lengths of cured sections for fabrication of items too large for injection or compression moulding.

The production of blanks for compression moulding.

4.5.5 PVC

Polyvinyl Chloride is made from one of three emulsion processes:

Suspension polymerization

Emulsion polymerization

Bulk polymerization

Vinyl chloride monomer (VCM) is the raw material for all kinds of PVC polymerisation. VCM, which is gaseous under normal conditions, is stored under pressure in order to keep it liquid.

Suspension polymerisation, step by step .
As a first step in the production of suspension PVC, also known as S-PVC, VCM is fed into the polymerisation reactor alongside water and suspending agents. Through high-speed agitation, small droplets of VCM are formed. It is these droplets that eventually become PVC.
As a next step in PVC manufacture, an initiator or catalyst soluble in VCM is fed into the reactor. It is here, under pressure and at temperature ranging from 40 to 60°C, that the VCM droplets are turned into PVC. The PVC obtained through this method is suspended in water and appears as slurry particles of 50~200 μm diameter. .

At the final stage of the S-PVC process, the slurry discharged from the polymerisation reactor is stripped of un-reacted VCM; most of the water is removed, usually by centrifugation, and the solid is dried. The end result is PVC in the form of a white powder, or resin, which is non-toxic, odourless and inert. Importantly, all un-reacted VCM is recovered and recycled as raw material.
Emulsion and bulk polymerisation .
Emulsion polymerisation and bulk polymerisation are alternative but far less common technologies to manufacture PVC. Emulsion polymerisation produces finer resin grades with much smaller particles, which are required by certain applications. This type of resin is either known as E-PVC or P-PVC, since it is often used as paste for coating surfaces.
Bulk (or mass) polymerisation yields PVC resin similar to suspension PVC. The difference is that polymerisation occurs in the absence of water. It s primarily used for products that require high transparency and good plasticising properties.

4.6 Human factors and ergonomics

Human factors and ergonomics , also known as comfort design, functional design, and user-friendly systems, is the practice of designing products, systems or processes to take proper account of the interaction between them and the people who use them.

The field has seen contributions from numerous disciplines, such as psychology, engineering, biomechanics, industrial design, physiology and anthropometry. In essence, it is the study of designing equipment and devices that fit the human body and its cognitive abilities. The two terms "human factors" and "ergonomics" are essentially synonymous.

Anthropometry is the branch of ergonomics that deals with body shape and size. People come in all shapes and sizes so you need to take these physical characteristics into account whenever you design anything that someone will use, from something as simple as a pencil to something as complex as a crutch.

When studying anthropometry, we need to take into consideration some design rules:

Decide who you are designing for

Anthropometry tables give measurements of different body parts for men and women, and split into different nationalities, and age groups, from babies to the elderly. So first of all you need to know exactly who you are designing for. The group of people you are designing for is called the user population.

For example if you were designing an office chair, you would need to consider dimensions for adults of working age and not those for children or the elderly. If you were designing a product for the home, such as a kettle, your user group would include everyone except young children (hopefully!).

Decide which body measurements are relevant

You need to know which parts of the body are relevant to your design. For example, if you were designing a mobile phone, you would need to consider the width and length of the hand, the size of the fingers, as well as grip diameter. You wouldn't be too interested in the height or weight of the user (although the weight of the phone might be important!).

Decide whether you are designing for the 'average' or extremes

The variation in the size and shape of people also tells us that if you design to suit yourself, it will only be suitable for people who are the same size and shape as you, and you might 'design out' everyone else.

Percentiles

Percentiles are shown in anthropometry tables and they tell you whether the measurement given in the tables relates to the 'average' person, or someone who is above or below average in a certain dimension.

If you look at the heights of a group of adults, you'll probably notice that most of them look about the same height. A few may be noticeably taller and a few may be noticeably shorter. This 'same height' will be near the average (called the 'mean' in statistics) and is shown in anthropometry tables as the fiftieth percentile, often written as '50th % ile'. This means that it is the most likely height in a group of people. If we plotted a graph of the heights (or most other dimensions) of our group of people, it would look similar to this:

Fig.32- Graph depicting the 5th, 50th, and 90th percentile range in anthropometry [13]

Usually, you will find that if you pick the right percentile, 95% of people will be able to use your design. For instance, if you were choosing a door height, you would choose the dimension of people's height (often called 'stature' in anthropometry tables) and pick the 95th percentile value – in other words, you would design for the taller people. You wouldn't need to worry about the average height people or the 5th percentile ones – they would be able to fit through the door anyway.

With the anthropometric and ergonomic studies done through the project we can design the crutches to meet the needs of as many people as possible.

For ambulant disabled people, it is necessary to consider those users functioning with crutches, canes,etc. All these aids becone, in essence, a functional part of the indicidual’s body. Accordingly, both aid and user should in almost every instance be viewed as a singke entity. For design purpose it is useful to know something not only of the anthropometry involved, but of the total space considerations.

Fig.33 – Crutches [14]

The mode, gait and speed of the user is impeded significantly by the use of crutches. Changes of grade and circulation up or down stairs are extremely difficult and in some situations almost impossible. The limited use of the user’s lower extremities as well as manipulation and placement of crutches significantly limit the leverage that he or she can develop, particularly as may be required in opening or closing doors and getting in and out of seats. The critical dimensions that impact on clearance include crutch swing( A), walking crutch swing(B), standing crutch span(C), body crutch span(D), and body crutch swing(E).

4.7 Dynamics

Crutch walking is a widespread type of gait among elderly and injured people. The main problem of crutch locomotion is its high energy consumption which is between two and three times that of normal walking in terms of metabolic cost. Furthermore, it is highly demanding for the upper-body muscles, which are not suited for such efforts. Despite these inconveniences, the psychological importance for the subjects of being able to stand and walk on their own makes this type of locomotion very common.

The swing-through crutch gait consists of four phases: crutch-stance phase, heel strike, footstance phase and crutch strike. In this work, we pay particular attention on the crutch strike that occurs at the end of foot-stance.This has been reported to be an important cause of energy loss during motion .

A four-segmental planar model of the human body is used to analyze various dynamic aspects of the crutch impact, e.g., kinetic energy redistribution, velocity change and the magnitude of contact impulses. The model and coordinates used are shown in Fig.34, body segment parameters are based on anthropometric data.

Fig.34- Dynamic four-segmental model of the subject with crutches[15]

Let us consider that ti represents the time point when the crutch tip impacts the ground. This event takes place in the [t i- ; t+i ] interval, where t –i and t+i represent the so-called pre- and post-impact instants. This interval is considered very short on the characteristic time scale of the finite motion and, therefore, the configuration of the system can be assumed constant. This event can be characterized by bilateral impulsive constraints. These can be written as

Aq˙ + = 0

where q˙ +is the post-impact array of generalized velocities, and A is the constraint Jacobian matrix. The above constraints define the required topology at t+i , i.e., the tip of the crutch to be in contact with the ground without slipping after the impact. Based on matrix A, the tangent space of the system can be decomposed to two mutually orthogonal subspaces in terms of the mass metric, namely, the Space of Constrained Motion (SCM) and the Space of Admissible Motion (SAM). The decomposition to such subspaces can be accomplished via asymmetric projector operators, Pc and Pa. These are used to project kinematic and kinetic quantities to the SCM and SAM, respectively. Based on them, the kinetic energy of the system can be decoupled as

T = Tc + Ta =1/2 vTc Mvc +1/2 vTa Mva;

where vc = Pcq˙ and va = Paq˙ . Assuming that muscular forces are finite, then the only impulses that need to be considered are the ones developed at the tip due to contact. These impulses are completely projected to the SCM and thus, based on the dynamics analysis one can conclude that the pre-impact kinetic energy of the SCM is completely lost, T+c = 0, and its counterpart associated with the SAM stays in the system after impact, T+a = T-a ≤ T-.

The previous energetic analysis was used to obtain guidelines for optimal crutch selection or crutch-use teaching. These can be applied to reduce energy consumption, which may also lead to a decrease of the muscular fatigue of the subject. The following points summarize some of the results obtained using the presented approach:

A crutch longer than the conventional reduces the energy loss per unit distance and also reduces the magnitude of the contact impulses developed at the tip of the crutch.

A crutch shorter than the conventional facilitates the separation of the feet at post-impact

time and thus, less push-off effort is needed to start the crutch-stance phase.

A small angle θ1 at impact, Fig.34, is better to minimize the energy loss at crutch strike.

A torso leaning forward (θ2 > 0, Fig.34) yields less energy consumption per unit distanceand reduces the magnitude of contact impulses.

4.8 Eco Design

Eco-design means designing a product with special consideration for the environmental impacts of the product during its whole lifecycle. In a life cycle assessment, the life cycle of a product is usually divided into procurement, manufacture, use, and disposal.

Eco-design is a growing responsibility and understanding of our ecological footprint on the planet. Green awareness, over population, industrialization and an increased environmental population have led to the questioning of consumer values. It is imperative to search for new building solutions that are environmentally friendly and lead to a reduction in the consumption of materials and energy.

The impact this materials have on the environment is expressed using the EcoIT 99. EcoIT 99 is a damage orientated method used by designers to know the impact assessment of Life Cycle of a product.

Table 4 -The Eco indicators of materials

Fig.35 –Production chart of the materials

Fig.36 –Disposal chart of the materials

4.9 3D Modeling

4.9.1 Introduction to CATIA V5R19

CATIA (an acronym of computer aided three-dimensional interactive application, pronounced ) is a multi-platform software suite for computer-aided design (CAD), computer-aided manufacturing (CAM), computer-aided engineering (CAE), PLM and 3D, developed by the French company Dassault Systèmes.

Commonly referred to as a 3D Product Lifecycle Management software suite, CATIA supports multiple stages of product development (CAx), including conceptualization, design (CAD), engineering (CAE) and manufacturing (CAM). CATIA facilitates collaborative engineering across disciplines around its 3DEXPERIENCE platform, including surfacing & shape design, electrical, fluid and electronic systems design, mechanical engineering and systems engineering.

CATIA facilitates the design of electronic, electrical, and distributed systems such as fluid and HVAC systems, all the way to the production of documentation for manufacturing.

4.9.2 Product modeling

The first step was modeling all the pieces of the crutch.

Fig.37-The upper pipe Fig.38-The upper rod

Fig.39-The middle pipe Fig.40- The bottom rod

Fig.41-The bottom pipe Fig.42-The foam of the middle pipe

Fig.43-The tip

Fig.44-The foam of the upper pipe Fig.45-The clip

After modelling all the components I have made an assembly in order to see how it looks like with the main components.

Fig.46- Assembly of the main components

After the assembly was made I have inserted the materials of the pieces. After that, I have made another assembly containing all the components.

Fig.47- The final assembly Fig.48- Exploded view of the crutch

Fig.49- The tip Fig.50- Exploded view of the tip

Fig.51- Use scenario1 Fig.52- Use scenario2 Fig.53- Use scenario3

4.9.3 Renderings

The renderings of the crutches were made using KeyShot 6.3 sofware.

KeyShot is the fastest and easiest to use 3D rendering and animation software available. In just a few steps you can create amazing looking images from your 3D models that can be used throughout the product development process to make design decisions and quickly create variations of concepts for customer, manufacturing or marketing.

Everything inside KeyShot happens in realtime. KeyShot uses unique rendering technology which makes it possible to see all changes to materials, lighting, and cameras instantly.

KeyShot is built on Luxion’s internally developed, physically correct render engine based on research in the areas of scientifically accurate material representation and global illumination. The result is stunning realism, incredible accuracy and speed that is beyond compare.

Fig.54 Fig.55

Fig.56 Fig.57

Fig.58 Fig.59 Fig.60

Fig.61 Fig.62 Fig.63

4.9.4 Detailed design

All the dimensions necessary for building the crutches can be seen in the 2D execution drawings at the end of the diploma project.

In the 2D drawings one can find detailed drawings and specifications for all the parts present in the assembly of the crutches and these include the following:

Upper pipe

Upper rod

Middle pipe

Bottom rod

Bottom pipe

Clip

Tip assembly

Minimum assembly of the crutch

Maximum assembly of the crutch

4.9.5 FEM Analsysis

Finite Element Analysis was used to find out the stress distribution pattern in the crutch. This analysis gave an estimate of stress values in the new crutch design.

The displacement was fully constrained at the tip to simulate the contact at the ground. The loading applied was chosen such that it satisfies the weight criteria of a healthy adult. Therefore the chosen value of the load is 1176 N.

A distributed load of 1176 N was applied in the perpendicular direction on the grip( 588 N) and on the cradle( 588 N).

Fig.64- Von Mises Stress

Fig.65- Displacement

After the fist analysis was made, the next analysis was performed on one pin of the clip. The value of the load was the same as the value of the crutch.

Fig.66- Von Mises Stress on the tip

Fig.67- Displacement on the tip

4.10 Economical evaluation and estimation of the product

40,00 LEI (one piece)

Dimensions:

-Diameter: 25 mm

-Length: 6000 mm

Thickness: 1,5 mm

Weight: 1,87 kg

34,00 LEI ( one piece)

Dimensions:

-Diameter: 22 mm

-Length: 6000 mm

Thickness: 1,5 mm

Weight: 1,62 kg

$12.00 =48,00 LEI (two pieces)

14,00 LEI (two pieces)

10,00 LEI (two pieces)

8,00 LEI (one piece)

18,00 LEI (one piece)

£0.87= 5,00 LEI ( one piece)

Almost all the materials listed above are availvable on the Romania market, right now.

The calculation for the crutches:

Price= a+ b+ c+ d+ e+ 2* f+ 2* g+ 4* h (1)

Where:

a= diameter 25 pipe

b= diameter 22 pipe

c= underarm foam

d= wrist foam

e=tip

f= cover

g= damper

h= clip

Equation (1) becomes:

Price= 40+ 34+ 48+ 14+ 10+ 2* 8+ 2* 18+ 4* 5= 218,00 LEI

Although the price may appear substantial compared to other products, this is a price calculated using prices for raw materials from private suppliers.

In order to obtain a better manufacturing price, an entire factory is needed, to ensure profit. Also, a contract between a manufacturer and a supplier as well as buying a large amount of the same material, ensures a lower price for the raw material and an overall lower manufacturing price.

This price is calculated only for the raw materials needed in the manufacturing of the crutches and does not include any processing which needs to be applied on the materials, such as cutting, stamping , and so on.

5. THE MOCK-UP

The first step was filling the pexal pipes with fine sand in order to bend it properly. After filling the pipes I started bending the midle pipe, using as guide a round pipe that has a similar diameter to the midle one.

Fig.76

Fig.77 Fig.78

In order to make the adjustments the next step was making the holes.

Fig.79 Fig.80

Fig.81 Fig.82

After all the pieces are made the next step was painting the pipes with a silver spray.

Fig.83 Fig.84

The tip of the crutch was made using a 3D printer. A 3D printer is similar to a 2D printer – to the horizontal plane xy adds another vertical plane on the axis z. The 3d printing software virtually divides the model in hundreds of horizontal layers that are transmitted to the machine. This sets layer over layer of material until the object is finished. The formats that the printer will recognise are: stl, 3ds, wrl, wrml, obj. The printed object results in an unfinished brut form that needs further improvements.

Below are some photos of the process.

Fig.85 Fig.86 Fig.87

Fig.88 Fig.89 Fig.90

Fig.81- The final assembly

Adjusting the crutch height
The pictures below shows how to adjust crutch height using this mechanism.

6. CONCLUSIONS

The overall aim of this project was to make an everyday life for people with reduced mobility better.

The suggested solution fulfills the aim of this project and match the design criteria described in the research part.

This crutch helps its users to perform everyday activities easier and feel more comfortable.

It provides:

better mobility,

better stability,

comfort.

As a final conclusion, these crutches, at least in theory, are able to sustain the total load of an average man or woman, without failing.

As any other product, these crutches can be improved on many levels, from the material used, to the overall shape or even by adding other components. However, given the fact that it is a first concept and in theory, it functions, the goal of the project has been achieved.

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