There are many types of 3D scanners and 3D scanning
technologies. Some are ideal for short range scanning while others are better
suited for mid or long range scanning. The 3D scanner and technology needed to
3D scan a very small object is very different from the best 3D scanner to 3D
scan a large aircraft.
Here is a brief
outline of the 3D scanning technologies and types of 3D Scanners.
Short Range 3D
Scanners
Short Range 3D scanners typically utilize a Laser
triangulation or Structured Light technology.
Laser based 3D Scanners
Laser based 3D scanners use a process called trigonometric
triangulation to accurately capture a 3D shape as millions of points. Laser
scanners work by projecting a laser line or multiple lines onto an object and
then capturing its reflection with a single sensor or multiple sensors. The
sensors are located at a known distance from the laser's source. Accurate point
measurements can then be made by calculating the reflection angle of the laser
light.
Laser scanners are very popular and come in many designs.
They include handheld portable units, arm based, CMM based, long range, and
single point long range trackers.
Benefits of 3D Laser Scanners
- · Able to scan tough surfaces, such as shiny or dark finishes
- · Less sensitive to changing light conditions and ambient light
- · Often more portable
- · Simpler design – easier to use and lower cost
Projected or
Structured Light 3D Scanners
Historically known as “white light” 3D scanners, most
structured light 3D scanners today use a blue or white LED projected light.
These 3D scanners project a light pattern consisting of bars, blocks or other
shapes onto an object. The 3D scanner has one or more sensors that look at the
edge of those patterns or structure shapes to determine the objects 3D shape.
Using the same trigonometric triangulation method as laser scanners the
distance from the sensors to the light source is known. Structured light scanners
can be tripod mounted or hand held.
Benefits of
Structured light 3D Scanners
- · Very fast scan times – as fast as 2 seconds per scan
- · Large scanning area – as large as 48 inches in a single scan
- · High resolution – as high as 16 million points per scan and 16 micron (.00062”) point spacing
- · Very high accuracy – as high as 10 microns (.00039”)
- · Versatile – multiple lenses to scan small to large parts in a single system
- · Portable – hand held systems are very portable
- · Eye safe for 3D scanning of humans and animals
- · Various price points from low cost to expensive depending on resolution and accuracy
Medium and Long Range
3D Scanners
Long range 3D
scanners come in two major formats - Pulse based and phase shift – both of
which are well suited for large objects such as buildings, structures,
aircraft, and military vehicles. Phase shift 3D scanners also work well for
medium range scan needs such as automobiles, large pumps and industrial
equipment. These scanners capture millions of points by rotating 360 degrees
while spinning a mirror the redirects the laser outward towards the object or
areas to be 3D scanned.
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. Thus, if the length of
time a laser takes to reach an object and reflect back to a sensor is known,
the distance from sensor to object is known. 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.
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 the phase of the laser sent out and
returned to the sensor. Phase shift measurements are typically more accurate
and quieter but are not as flexible for long range scanning as pulse-based 3D
scanners. Laser pulse based 3D scanners can scan objects up to 1000m away while
phase shift scanners are better suited for scanning objects up to 300m or less.
Benefits Long Range
3D Scanners
- · 3D Scan millions of points in a single scan – up to 1 million points per second
- · Large scanning area up to 1000 meters
- · Good accuracy and resolution based on object size
- · Non-contact to safely scan all types of objects
- · Portable
Coordinate Measuring
Machine (CMM)
A coordinate measuring machine (CMM) is used primarily to
inspect parts. The machine can be controlled manually or through controlled
offline through software and computers. Measurements are defined by attaching a
probe to the machine. The probe typically has a small ball at the end of a
shaft of a known diameter. The CMM is then programed to contact the part. When
the machine senses contact of the probe tip a measurement value in taken in XYZ
space.
The most common type of CMM is a bridge type which has 3
axis X, Y & Z. The probing system that is attached many times can rotate
providing an additional 3 axis for a total of 6 degrees of freedom (DOF).
To very accurately measure parts to a few microns, CMM’s are
typically deployed in a very controlled inspection room that includes a
reinforced floor, controlled humidity and temperature, and isolation from
vibration and other forces that could affect the accuracy. In addition, most
CMM’s have a large granite table surface that is perfectly level. Parts are fixture
onto the granite table so that there is no movement during the measuring
process.
Benefits of CMM’s
- · One of the most accurate ways of measuring an object
- · Small to large parts can be measured with the proper machine
- · Industry standards and certifications for measurements and software exist
- · Many styles and sizes of machines exist from many manufactures
Arm based 3D Scanners
and Probe systems
An armed based 3D
scanning or probing system is similar to a coordinate measuring machine (CMM)
in the fact it can use a touch probe to measure a part. In addition to the
probe, many arm based systems also have an attachable 3D laser scanner for
collecting large amount of points. Software keeps track of the joint movements
of the arm to know where it is in 3D space at all time.
Arm based systems
work by attaching the articulated arm to either a table or sturdy base. Then
the arm is held by a hand grip at the end and moved around to probe or scan.
The main advantage of these systems is they are much more portable then a CMM
and can be used in a shop floor environment.
Benefits of Arm based 3D Scanners and Probe systems
- · Portable system
- · Good accuracy on small to medium size parts
- · Ability to probe and scan a single part
Optically tracked 3D
Scanners and Probe Systems
Optically tracked 3D
scanning and probing systems use a set of cameras to track the location of the
3D scan head or probe in 3D space. These systems offer advantages over arm
based systems including freedom of movement, better accuracy over distance, and
the ability to include “dynamic referencing”. Dynamic referencing systems work
by attaching targets or led lights to the object you are scanning or probing.
This allows the camera system to track the part and scan or probe head
separately from each other. The net result is the part can be moving even while
scanning and no loss of accuracy or data quality occurs. In addition, the
camera system can also be moved around allowing you to scan large parts in one
setup.
Benefits of optically
tracked 3D scanning and probing systems
- · 3D scanning and probing in the same system
- · Freedom of movement
- · Large 3D scanning volume
- · Ability to probe and scan even while the part is moving with no loss of accuracy
- · Very portable
