better design through measurement: contact vs. non-contact technologies
TRANSCRIPT
Better Design Through Measurement: Contact vs. Non-Contact Technologies
This webinar will be available afterwards at
designworldonline.com & email
Q&A at the end of the presentation
Hashtag for this webinar: #DWwebinar
Before We Start
Moderator
Leslie Langnau Design World
Presenter
Ryan Dant FARO Technologies
Better Design Through Measurement: Contact vs. Non-Contact Technologies
Ryan Dant, Applications Engineer, FARO Technologies
• Introduction
• Single Point Repeatability and Volumetric Accuracy
• Contact Measurements
o Strengths and Weaknesses
• Non-Contact
o Strengths and Weaknesses
• How can You Benefit?
• Q and A
Agenda
In terms of articulated arm CMM’s, contact measurement includes any probes that
require the probe to be physically touching the surface of the part being digitized.
• This includes hard probes and touch-trigger probes
What Is Contact Measurement
A type of digitization that uses lasers or light systems
to capture data without touching the part.
• Includes white and blue light systems, as well as laser line
probes, used with portable CMM’s.
• We will focus on those types of probes that can be used in
tandem with an articulated arm (e.g. Laser Line Probes (LLPs)
Non-Contact Measurement
Single Point Repeatability and Volumetric
Accuracy Two ways to compare different measurement methods:
• Single Point Repeatability, or precision, is how close the same
measurements are together.
• Volumetric Accuracy: How close a point can be in 3D space to
it’s nominal (or correct) position.
Contact Measurement
Hard Probing
Touch-Trigger Probing
Contact Measurement: Hard Probing
• Hard Probing is a subset of those types
of probes that require contact with the
desired surface and a manual trigger.
• Hard probes come in a variety of
different shapes and sizes, ranging from
large ball-type probes down to a needle
point.
Contact Measurement:
Hard Probing - Calibration
• When a probe is switched it is important to “teach” the arm the location of the
tip (point probe), or the center of the sphere (ball probe).
o Known as calibration
• There are different types of calibration, each used for a specific case of probe
type. Videos available at www.faro.com/site/resources/supportvideos
Contact Measurement:
Hard Probing – Ball Compensation
• When measuring a surface with a ball probe, the radius of the probe (4) must be considered.
• This is because the point is taken at the center of the probe (3) which was found during compensation.
• But the ball contacts the surface at the tangent point (2).
Contact Measurement:
Hard Probing - Accuracy
• The accuracy of a hard probe is entirely
determined by the accuracy of the articulated
arm CMM that it is mounted to.
• Modern “Arms” range in accuracy from <.001” to
around .005”
Contact Measurement:
Hard Probing – Capturing Data
When capturing data with a hard probe, the probe is placed up against the desired surface
and a manual trigger is depressed which records the 3D location of the probe at the moment
of the trigger.
Single Point – Trigger for every reading
Interval – Press and hold for either distance
based or time based readings
Contact Measurement:
Hard Probing – Points Taken vs. Accuracy
To accurately represent a feature,
enough points must be taken to
improve the best fit.
How many is enough?
Contact Measurement:
Best Fit
• When accurate readings for surface inspection are needed it is important to
take a high volume of points to account for any deviation on the surface of the
part.
• It can be a lengthy process to cover a surface in a high volume of points
necessary for detailed surface inspection.
Hard Probing
• Accurate
o As high accuracy as .0005”
• Low volume of points
• Quick Measurement of Geometric
Primitives
Contact Measurement:
Touch Trigger Probes
• With a touch-trigger probe the articulated arm will record a point when the
probe contacts the surface.
o Thus, the x,y,z data of the point will be recorded at very low pressures.
• This can be beneficial when measuring parts consisting of material that
deflects under low amounts of pressure.
o e.g. Molded or formed plastic, sheet metal
Non-Contact
Measurement Laser Line Probes
Non-Contact Measurement:
What is an LLP?
• (1) Laser Emitter
• (2) Camera
• (3) Calibration Plate
Non-Contact Measurement:
LLP Calibration
As with the hard probe, we need to teach the
arm the 3D distance from the laser emitter
to the points being taken.
Non-Contact Measurement:
Calibration Considerations
• When calibrating a laser probe, it is first necessary to use a properly
calibrated contact probe to define a feature.
• When dealing with an attached LLP the accuracy of the LLP must be added
to the accuracy of the Arm; the resultant “system” accuracy will be what is
measured to.
Non-Contact Measurement:
Acquiring Data
Takes ~45,000 points per second along a line
Non-Contact Measurement: Point Clouds
A scan with an LLP will produce a point cloud, which is just a large 3D group of
points that correspond to the geometry measured.
• Point clouds can be exported to CAD and turned into models
• They can also be used for inspection
Non-Contact Measurement:
Point Cloud Color Contour Map
Laying a point cloud over a CAD model we can obtain
a color map that shows us the deviation of the part
scanned.
Non-Contact Measurement:
Measurement Considerations
• Part Color
o The easiest colors to capture start at white and the difficulty increases as the
color darkens.
• Darker colors absorb more light
• Part Reflectivity
o As a part reaches a certain threshold of reflectivity, the part will scatter the laser
and make reading hard to acquire
o e.g. high machine finish and chrome parts
Non-Contact Measurement:
Resolving the Reflectivity Problem
• Paint the part.
• Coat the part in a solvent, which can
counteract the effects of reflectivity.
How Can You Benefit? Industry Comparison & Conclusions
Conclusions:
Hard Probing
Good for doing simple measurements quickly on rigid parts.
• Machine Shops
• Fabrication Shops
• Welding
Conclusions:
Touch-Trigger Probes
Applications where simple feature based
measurements suffice, but material will deform if
pressed on by a hard probe.
• Plastics
• Formed Sheet Metal
Conclusions:
Laser Line Probe
• Ideal for complete reverse engineering projects
o Point Clouds can be exported into CAD and turned into
IGES, STP, or X_T (to name a few)
• Inspection of complex geometry not suited for feature
based inspection
o Can compare to CAD and provide color contour maps
Thank You
For more information: www.faro.com
Questions?
Design World Leslie Langnau [email protected] Phone: 440.234.4531 Twitter: @DW_RapidMfg
FARO Technologies Ryan Dant [email protected] Phone: 630.862.4752 - Can call or text
Thank You
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