D Scanners

2. 3D SCANNERS

A 3D scanner is a device that analyzes a real-world object or environment to collect data on its shape and possibly its appearance (i.e. color). The collected data can then be used to construct digital three-dimensional models.

3D laser scanning developed during the last half of the 20th century in an attempt to accurately recreate the surfaces of various objects and places. The technology is especially helpful in fields of research and design. The first 3D scanning technology was created in the 1960s. The early scanners used lights, cameras and projectors to perform this task. Due to limitations of the equipment it often took a lot of time and effort to scan objects accurately. After 1985 they were replaced with scanners that could use white light, lasers and shadowing to capture a given surface.

3D scanners are very analogous to cameras. Like cameras, they have a cone-like field of view, and like cameras, they can only collect information about surfaces that are not obscured. While a camera collects color information about surfaces within its field of view, a 3D scanner collects distance information about surfaces within its field of view. The "picture" produced by a 3D scanner describes the distance to a surface at each

point in the picture. This allows the

three dimensional position of each point in

the picture to be identified.

For most situations, a single scan will not produce a complete model of the subject. Multiple scans, even hundreds, from many different directions are usually required to obtain information about all sides of the subject. These scans have to be brought in a common reference system, a process that is usually called alignment or registration, and then merged to create a complete model. This whole process, going from the single range map to the whole model, is usually known as the 3D scanning pipeline (Fausto Bernardini, et al, 2002).

2.1 Brief History of 3D Scanners

3D laser scanning developed during the last half of the 20th century in an attempt to accurately recreate the surfaces of various objects and places. The technology is especially helpful in fields of research and design. The first 3D scanning technology was created in the 1960s. The early scanners used lights, cameras and projectors to perform this task. Due to limitations of the equipment it often took a lot of time and effort to scan objects accurately. After 1985 they were replaced with scanners that could use white light, lasers and shadowing to capture a given surface.

With the advent of computers, it was possible to build up a highly complex model, but the problem came with creating that model. Complex surfaces defied the tape measure. So in the eighties, the toolmaking industry developed a contact probe. At least this enabled a precise model to be created, but it was so slow. The thinking was, if only someone could create a system, which captured the same amount of detail but at higher speed, it will make application more effective. Therefore, experts started developing optical technology. Using light was much faster than a physical probe. This also allowed scanning of soft objects, which would be threatened by prodding.

At that time, three types of optical technology were available:

Point, which is similar to a physical probe in that it uses a single point of reference, repeated many times. This was the slowest approach as it involved lots of physical movement by the sensor.

Area, which is technically difficult. This is demonstrated by the lack of robust area

systems on sale.

Stripe, the third system – was soon found to be faster than point probing as it used a band of many points to pass over the object at once, which was accurate too. So it matched the twin demands for speed and precision.

So stripe was clearly the way forwards, but it soon became apparent that the challenge was one of software. To capture an object in three dimensions, the sensor would make several scans from different positions. The challenge was to join those scans together, remove the duplicated data and sift out the surplus that inevitably gathers when you collect several million points of data at once.

One of the first applications was capturing humans for the animation industry. Cyberware Laboratories of Los Angeles developed this field in the eighties with their Head Scanner. By the mid-nineties they had developed into a full body scanner as shown in figure. This is where 3D Scanners appeared.

In 1994, 3D Scanners launched REPLICA – which allowed fast, highly accurate scanning of very detailed objects. REPLICA marked serious progress in laser stripe scanning. Meanwhile Cyberware were developing their own high detail scanners, some of which were ableto cature object colour too, but despite this progress, true three-dimensional scanning – with these degrees of speed and accuracy – remained elusive. One company – Digibotics – did introduce a 4-axis machine,which could provide a fully 3D model from a single scan, but this was based on laser point

not laser stripe – and was thus slow. Neither did it have the six degrees of freedom necessary to cover the entire surface of an object, neither could it digitise color surface. While these optical scanners were expensive, Immersion and Faro Technologies introduced lowcost manually operated digitisers. These could indeed produce complete models, but they were slow, particularly when the model was detailed. Again, they could not digitise color surface.

In 1996, 3D Scanners took the key technologies of a manually operated arm and a stripe 3D scanner – and combined them in ModelMaker. This incredibly fast and flexible system is the world's first Reality Capture System.It produces complex models and it textures those models with color. Color 3D models can now be produced in minutes.

2.3 3D Scanners Techniques

There are varieties of technologies for digitally acquiring the shape of a 3D object. A well established classification (Brian Curless, 2000) divides them into two types: contact and noncontact 3D scanners . Non-contact 3D scanners can be further divided into two main categories, active scanners, and passive scanners. There are varieties of technologies that fall under each of these categories.

2.3.1 Contact technique

3D contact scanners, generally calibrated to operate on a fixed platform, often contain a probelocated at the end of an articulated mechanical arm. The arm may be robotically or manually manipulated over the part's surface. As the probe contacts the object's surface the scanner records the X,Y,Z position of the probe by taking positional measurements of the armature. The recorded positions form a point cloud, which can be used to calculate a 3D mesh. Some highly accurate 3D scanners called Coordinate Measuring Machines (CMMs) are often used by the manufacturing industry to inspect parts for early indications of assembly problems. 3D contact scanners suffer from slow scan rates and may not be ideal for delicate objects, such as precious artworks, as physical contact may damage or deform the surface.

Contact 3D scanners probe the subject through physical touch. A CMM (Coordinate Measuring Machine) is an example of a contact 3D scanner. A coordinate measuring machine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, amongst others.

It is used mostly in manufacturing and can be very precise. The disadvantage of CMMs though, is that it requires contact with the object being scanned. Thus, the act of scanning the object might modify or damage it. This fact is very significant when scanning delicate or valuable objects such as historical artifacts. The other disadvantage of CMMs is that they are relatively slow compared to the other scanning methods. Physically moving the arm that the probe is mounted on can be very slow and the fastest CMMs can only operate on a few hundred hertz. In contrast, an optical system like a laser scanner can operate from 10 to 500 kHz. Other examples are the hand driven touch probes used to digitize clay models in computer animation industry.

The typical CMM is composed of three axes, an X, Y, and Z. These axes are orthogonal to each other in a typical three-dimensional coordinate system. Each axis has a scale system that indicates the location of that axis. The machine will read the input from the touch probe, as directed by the operator or programmer. The machine then uses the X,Y, Z coordinates of each of these points to determine size and position with micrometre precision typically.

2.3.2 Non-Contact Technique

Non-contact 3D scanners, as the name implies, do not make physical contact with an object surface. Instead, noncontact 3D scanners rely on some active or passive techniques to scan an object. The end result is a highly accurate cloud of points that can be used for reverse engineering, virtual assembly, engineering analysis, feature and surface inspection or rapid prototyping.

Active scanners emit some kind of radiation or light and detect its reflection in order to probe an object or environment. Possible types of emissions used include light, ultrasound, or x-ray.

3D Laser Scanning or 3D Laser Scanners can generally be categorized into three main categories: time of flight, phase shift, and laser triangulation. Some technologies are ideal for short-range scanning, while others are better for mid- or long-range scanning. These laser scanning techniques are typically used independently but can also be used in combination to create a more versatile scanning system.

2.3.2.1 Short-Range (less than 1 meter focal distance)

2.3.2.1.1 Laser Triangulation 3D Scanners

Laser triangulation scanners use either a laser line or single laser point to scan across an object. A sensor picks up the laser light that is reflected off the object, and using trigonometric triangulation, the system calculates the distance from the object to the scanner.

The distance between the laser source and the sensor is known very precisely, as well as the angle between the laser and the sensor. As the laser light reflects off the scanned object, the system can discern what angle it is returning to the sensor at, and therefore the distance from the laser source to the object’s surface.

2.3.2.1.2 Structured Light (White or Blue Light) 3D Scanners

Structured light scanners also use trigonometric triangulation, but instead of looking at laser light, these systems project a series of linear patterns onto an object. Then, by examining the edges of each line in the pattern, they calculate the distance from the scanner to the object’s surface. Essentially, instead of the camera seeing a laser line, it sees the edge of the projected pattern, and calculates the distance similarly.

2.3.2.2 Mid- and Long Range (more than 2 meters focal distance)

2.3.2.2.1 Laser Pulse-based 3D Scanners

Laser pulse-based scanners, also known as time-of-flight scanners, are based on a very simple concept: the speed of light is known very precisely, so if we know how long a laser takes to reach an object and reflect back to a sensor, we know how far away that object is. These systems use circuitry that is accurate to picoseconds to measure the time it takes for millions of pulses of the laser to return to the sensor, and calculates a distance. By rotating the laser and sensor (usually

via a mirror), the scanner can scan up to a full

360 degrees around itself.

2.3.2.2.2 Laser Phase-shift 3D Scanners

Laser phase-shift systems are another type of time-of-flight 3D scanner technology, and conceptually work similarly to

pulse-based systems. In addition to pulsing the

laser, these systems also modulate the power

of the laser beam, and the scanner compares

thephase of the laser being sent out and then

returned to the sensor.

2.3.3 Scanning solutions

Portable 3D Scanners: HANDYSCAN 3D

The HandySCAN 3D™ handheld scanners of new generation have been optimized to meet the needs of product development and engineering professionals on the lookout for the most effective and reliable way to acquire 3D measurements of physical objects.

Creaform’s flagship metrology-grade scanners underwent a complete re-engineering, building on its core assets. They are now more portable and they are faster at delivering accurate and high resolution 3D scans while remaining overly simple to use. Yet, it is their true portability that has changed the rules and set a whole new trend in the 3D scanning market.

Portable 3D Scanners: Go!SCAN 3D

The Go!SCAN 3D™ product line offers an easy portable 3D scanning experience, providing fast and reliable measurements. With these handheld 3D scanners, even 3D data in full color can be captured

The Go!SCAN 3D™ were designed for simplified, quick, and accurate 3D scanning. Through a very efficient process, these self-positioning systems can be used by anyone without requiring any prior experience or background, and provide visual guidance as you are scanning. Their innovative technology bypasses preparation steps and specific setups, provides a very fast measurement rate, and does not require manual data post-processing.

Highly versatile, they can be used for a wide range of applications, helping professionals throughout the entire product development process.

Optical CMM 3D Scanner: METRASCAN 3D

Creaform’s portable optical CMM 3D scanner, the MetraSCAN 3D, solves the issues of unexpected costs, production and part approval delays from non-conformities. The system addresses reverse engineering and dimensional inspection of production tools, jigs, assemblies, sub-assemblies or final products ranging from 1 to 3.5 m (3.3 to 11.5 ft.) with an accuracy of up to 0.064 mm (0.0025 in.). Optical metrology provides measurement accuracy that is insensitive to the instabilities of the environment, making the MetraSCAN 3D Optical CMM an excellent choice for shop-floor quality control metrology. Free of any rigid measurement set up, it maintains the same level of performance regardless of the environment instabilities.

Portable coordinate measuring machine: HandyPROBE Next

Manufacturers and production managers can use portable measurement technologies to enable considerably greater flexibility and efficiency in performing quality control (QC) operations directly on the production floor. The HandyPROBE Next™ portable CMM provides measurement accuracy that is insensitive to the instabilities of any environment. Free of any rigid measurement setup, the portable CMM outperforms traditional portable CMMs on the shop floor.

The complete HandyPROBE Next system has the unique ability to perform real-time dynamic referencing of its scanning and probing devices as well as on targets of the object that is being inspected. The C-Track optical tracker and wireless probe can be moved at any time during the measurement sequence and generate the same high-quality data.

2.4 Areas of application and capabilities

Short-range 3D scanning

3D scanning of objects of any size, colour, texture (even shiny materials)

3D archiving

Competitive analysis

Preparation for prototyping (with/out colour)

Long-range 3D scanning

3D scanning of large and oversized structures

As-built re-engineering and surveys

Topographical surveys

Engineering and detail surveys

High-definition surveying

Structural deformation & volumetric analysis

Plant layouts

Clash detection

Forensic / crime scene digitizing

Areas of use

Automotive

Aerospace

Manufacturing

Consumer products

Heavy industries

Medical

Research

Oil and gas

Arts and architecture

Virtual reality

Prototyping in engineering

In engineering, 3d scanning is very useful in conception, designing, prototyping, proper engineering, production, quality control.

3D scanning can be applied at the prototype phase in many ways; the most common is actually to reduce the number of prototype design cycles necessary. A part designed using 3D scan data often only requires one or no prototypes since it is designed utilizing precise measurements of the physical world. 3D scanning can also be used in combination with prototyping to scale physical objects.

Reverse engineering

It is used to generate 3D CAD models from existing objects (as-built), whether to determine the original design intent, to modernize manufacturing processes or to design a new part to fit to a legacy part, for instance.

Parametric 3D modeling in generic and native formats

Hybrid modeling (2D and 3D scan data)

Reconstruction from 3D scanning data, probing, 2D drawings, sketches, etc.

Design modification from actual objects

Data preparation for digital simulation

3D modeling of objects of all sizes

2.5 Model reconstruction and Software

2.5.1 Model reconstruction from point clouds

The point clouds produced by 3D scanners can be used directly for measurement and visualization in the architecture and construction world. Most applications, however, use instead polygonal 3D models, NURBS (Non-Uniform Rational B-Splines) surface models, or editable feature-based CAD models (aka Solid models).

Polygon mesh models: In a polygonal representation of a shape, a curved surface is modeled as many small faceted flat surfaces (think of a sphere modeled as a disco ball). Polygon models—also called Mesh models, are useful for visualization, for some CAM (i.e., machining), but are generally "heavy" (i.e., very large data sets), and are relatively uneditable in this form. Reconstruction to polygonal model involves finding and connecting adjacent points with straight lines in order to create a continuous surface. Many applications, both free and non free, are available for this purpose (e.g. MeshLab, kubit PointCloud for AutoCAD, JRC 3D Reconstructor, imagemodel, PolyWorks, Rapidform, Geomagic, Imageware, Rhino etc.).

Surface models: The next level of sophistication in modeling involves using a quilt of curved surface patches to model our shape. These might be NURBS, T Splines or other curved representations of curved topology. Using NURBS, our sphere is a true mathematical sphere. Some applications offer patch layout by hand but the best in class offer both automated patch layout and manual layout. These patches have the advantage of being lighterand more manipulable when exported to CAD. Surface models are somewhat editable, but only in a sculptural sense of pushing and pulling to deform the surface. This representation lends itself well to modeling organic and artistic shapes. Providers of surface modelers include Rapidform, Geomagic, Rhino, Maya, T Splines.

Solid CAD models: From an engineering/manufacturing perspective, the ultimate

representation of a digitized shape is the editable, parametric CAD model. After all, CAD isthe common "language" of industry to describe, edit and maintain the shape of the

enterprise's assets. In CAD, our sphere is described by parametric features which are easilyedited by changing a value (e.g., center point and radius).

These CAD models describe not simply the envelope or shape of the object, but CAD models also embody the "design intent" (i.e., critical features and their relationship to other features). An example of design intent not evident in the shape alone might be a brake drum's lug bolts, which must be concentric with the hole in the center of the drum. This knowledge would drive the sequence and method of creating the CAD model; a designer with an awareness of this relationship would not design the lug bolts referenced to the outside diameter, but instead, to the center. A modeler creating a CAD model will want to include both Shape and design intent in the complete CAD model.

Vendors offer different approaches to getting to the parametric CAD model. Some export the NURBS surfaces and leave it to the CAD designer to complete the model in CAD (e.g., Geomagic, Imageware, Rhino). Others use the scan data to create an editable and verifiable feature based model that is imported into CAD with full feature tree intact, yielding a complete, native CAD model, capturing both shape and design intent (e.g. Geomagic, Rapidform). Still other CAD applications are robust enough to manipulate limited points or polygon models within the CAD environment (e.g., Catia).

2.5.2 Model reconstruction from a set of 2D slices

CT, industrial CT, MRI, or Micro-CT scanners do not produce point clouds but a set of 2D slices (each termed a "tomogram") which are then 'stacked together' to produce a 3D representation. There are several ways to do this depending on the output required:

Volume rendering: Different parts of an object usually have different threshold values or greyscale densities. From this, a 3-dimensional model can b constructed and displayed on screen. Multiple models can be constructed from various different thresholds, allowing different colors to represent each component of the object. Volume rendering is usually only used for visualisation of the scanned object.

Image segmentation: Where different structures have similar threshold/greyscale values, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image. Image segmentation software usually allows export of the segmented structures in CAD or STL format for further manipulation

Image-based meshing: When using 3D image data for computational analysis (e.g. CFD and FEA), simply segmenting the data and meshing from CAD can become time consuming, andvirtually intractable for the complex topologies typical of image data. The solution is calledimage-based meshing, an automated process of generating an accurate and realistic geometrical description of the scan data.

2.5.3 Geomagic Capture for Scan-Based Design

Geomagic Capture scanners work flawlessly with SOLIDWORKS® via a software plugins and connects via Geomagic Design X to Siemens® NX™, Solid Edge®, Creo®, Pro/ENGINEER® and Autodesk Inventor®. With the power to take scan data directly into CAD, there can be designed highly complex parts faster via one seamless workflow.

The ultra-compact Geomagic Capture scanners capture precise data using state-of-the-art blue LED technology. The amazing devices capture almost one million points in 0.3 seconds to create detailed models of physical objects, accurate to 0.034-0.118 mm.

Geomagic Capture portable scanners and flexible software make it a perfect fit for a variety of applications, from heavy-duty manufacturing to industrial design to automotive to jewelry. The new method of Scan-Based Design empowers designers across all industries to swiftly create the type of innovative products that customers demand.

With Geomagic Capture scanners you get one easy-to-use, affordable solution that bridges hardware, software and CAD for your convenience. Because it’s a complete plug-and-play system, there is no need to burn time incorporating multiple products from multiple vendors into your workflow.