GOM Acceptance Test
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Process Description
Acceptance Test according to the Guideline
VDI/VDE 2634 Part 3
GOM mbH
Mittelweg 7-8
D-38106 Braunschweig
Germany
www.gom.com
Tel.: +49 (0) 531 390 29 0
Fax: +49 (0) 531 390 29 15
E-Mail: info@gom.com
Legal Notes
Legal Notes
No part of this publication may be reproduced in any form or by any means or
used to make any derivative work (such as translations, transformations or
adaptations) without the prior written permission of GOM.
GOM reserves the right to revise this publication and change contents from
time to time without obligation on the part of GOM to provide notification of
such revision or change.
GOM provides this manual without warranty of any kind, either implied or
expressed, including, but not limited, to the implied warranties of merchantability and fitness for a particular purpose.
GOM may improve or change the manual and/or the product(s) described
herein at any time.
Copyright © 2014
GOM mbH
All rights reserved
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Table of Contents
Table of Contents
Legal Notes........................................... .....2
6
1
1.1
1.2
Important Notes.................................... .....5
Standard Signal Words................................5
Safety and Health Hazard Notes............ .....5
6.1
6.2
Restriction to the Operation Modes
and Conditions.........................................17
Operation Modes.................................... ...17
Operation conditions..................................18
2
Introduction................................................7
7
Preparing the PSA................................ ...19
3
3.1
General Information about the
Acceptance Test................................... .....9
Used Parameters.......................................10
8
8.1
8.2
4
Guideline VDI/VDE 2634 Part 3............ ...13
5
5.1
5.2
Differences between the Processes... ...15
Used Parameters.......................................15
Sensor Measurement Volume and Total
Measuring Volume.................................. ...15
Test Positions.............................................15
8.2.1
8.2.2
8.3
8.4
8.5
8.6
8.7
Acceptance Test................................... ...21
Creating a New Project with VDI Test........21
Measuring Volumes with Differing Handling........................................................ ...22
Tilting the PSA........................................ ...22
Tilting by 30°........................................... ...23
Execute Measurement Series 1.................23
Execute Measurement Series 2.................26
Execute Measurement Series 3.................27
Evaluating Results.................................. ...27
Export Test Protocol...................................28
5.3
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Safety and Health Hazard Notes
Important Notes
1
1.1
Important Notes
Standard Signal Words
In this publication the following standard signal words can be used:
DANGER!
▶
The label points to an imminent danger. The situation can lead to serious
bodily harm or death!
WARNING!
▶
The label points to a dangerous situation. The situation can lead to serious bodily harm or death!
CAUTION!
▶
The label points to a dangerous situation. The situation can lead to light
bodily harm!
NOTICE
▶
Info
The label points to a situation which can lead to material damages. The
damages can result on the product or in the vicinity of the product!
The label indicates important application notes and useful information.
1.2
Safety and Health Hazard Notes
CAUTION!
Decalibrated sensor
A decalibrated sensor leads to imprecise measuring result.
▶ Calibrate the sensor according to the respective hardware user manual!
▶
Maintain the warm-up time and the calibration limit values!
CAUTION!
Higher measuring uncertainty caused by mechanical vibrations
Mechanical vibrations lead to higher measuring uncertainties.
▶ Measure only in environments which are free of vibrations!
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Safety and Health Hazard Notes
Important Notes
NOTICE
Overexposed measuring areas
In overexposed measuring areas, the sensor does not capture any measuring
data.
▶ Avoid overexposures!
▶
Avoid extremely bright external light sources!
NOTICE
Higher measuring uncertainty caused by fluctuating temperature
Fluctuating temperatures lead to higher measuring uncertainties.
▶ Keep the temperature constant throughout the measurement period!
▶
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The ambient temperature and the temperature of the artifact have to be
identical!
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Introduction
2
Introduction
This manual is intended for qualified personnel who have comprehensive
knowledge of coordinate measuring technology. Basic PC knowledge (windows-based programs and operating systems) is expected.
For operating the system optimally, the ability to visualize in 3D and a color
vision ability are assumed.
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General Information about the
Acceptance Test
3
General Information about the Acceptance Test
The acceptance test is performed in line with the GOM Acceptance Test
according to the guideline VDI/VDE 2634 Part 3.
The inspector creates the measured values for defined parameters using the
process which is described in this process description. The inspector always
performs the process in the same way. The inspector compares the measured
values with the corresponding limit values. The limit values are determined by
GOM and define the maximum permissible measurement error for the test.
For the test, the inspector uses a sphere artifact which is produced by GOM.
The sphere artifact with the name Probing / Spacing Artifact, short PSA
(see Fig. 1), consists of several matching, homogeneous sphere pairs with different diameters and spacings. On behalf of GOM, the metric sizes (diameter
of each sphere and centers of each sphere pair) are determined highly precisely in an external calibration. There are the calibration standards “manufacturer's calibration” and DAkkS calibration (DAkkS = Deutsche Akkreditierungsstelle GmbH is Germany's national accreditation body) available.
Fig. 1: PSA400 (front) with 9 sphere pairs, PSA900 (back) with 4 sphere pairs
If a sensor has several measuring volumes, the inspector tests each measuring volume in combination with the sensor in a separate acceptance test. In
each acceptance test, the inspector measures one pair of spheres consisting
of two spheres with the same nominal diameter size. The sphere pair to be
used depends on the sensor to be tested and the used measuring volume.
You find the assignment of the sphere pair to the sensor and measuring volume in the acceptance test protocol.
In line with the acceptance test, the inspector measures three measurement
series with ten individual measurements. The positioning and aligning of the
sphere pair with respect to the sensor measuring volume is defined exactly for
each individual measurement. The positioning and aligning not repeated
within a complete acceptance test. The software carries out the transformation and fine-alignment of the individual measurements for each measurement
series. From the measurements, the software computes a polygonized mesh.
Subsequently, the inspector derives the values for the parameters.
The inspector can export the results of the acceptance test as a PDF protocol.
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Used Parameters
General Information about the Acceptance
Test
3.1
Used Parameters
To estimate the measuring accuracy, the software uses the following parameters:
● Probing error form (sigma)
● Probing error size
● Sphere spacing error
● Length measurement error
To determine the corresponding current parameter values, the software calculates for a sphere pair the best-fit spheres from the measuring data. For the
calculation, the software uses the method of least squares. The parameter
probing error form (sigma) corresponds to the standard deviation. The standard deviation is calculated from the radial distance of all measured points of a
sphere with respect to the corresponding fitting sphere with a freely estimated
diameter (see Fig. 2).
The parameter probing error size is the difference between the measured
diameter and the calibrated diameter of the respective sphere (see Fig. 2).
Fig. 2: Schematic representation of the calculation
Probing error form
Probing error size
The parameter sphere spacing error is the resulting difference between the
measured sphere spacing of both centers of the fitted spheres and the corresponding calibrated spacing (see Fig. 3).
Fig. 3: Schematic representation of the sphere spacing error calculation
The length measurement error is the difference between the measured length
of two opposite points and their corresponding calibrated spacing. The measurement has to be carried out via a bidirectional probing from opposite direc-
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General Information about the
Acceptance Test
Used Parameters
tions on nominal parallel surfaces perpendicular to one of the surfaces (see
Fig. 4).
Fig. 4: Schematic representation of the length measurement error calculation
Info
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The ATOS measuring system measures full-field undifferentiated points. Due
to this process, defined individual points cannot be determined specifically.
Therefore, the single points which lie exactly on the connecting axis of both
sphere center points and and point towards the outside on each sphere cannot be measured directly.
That way, the parameter length measurement error can be determined only
via an indirect combined measurement and evaluation. According to the
guideline VDI/VDE 2634 - Part 3, the software determines the parameter
length measurement error using Method C.
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Guideline VDI/VDE 2634 Part 3
4
Guideline VDI/VDE 2634 Part 3
The guideline VDI/VDE 2634 Part 3 with the title “Optical 3D measuring systems - Multiple view systems based on area scanning” contains a description
on procedure and calculation for acceptance and reverification test of imaging
systems with area-based sampling in several single scans. This group of systems includes especially fringe projection systems like the ATOS sensors
which capture and evaluate an object using multiple individual measurements
transformed into each other.
The guideline was created by the committee of experts 3.32 “Optische 3DMeßtechnik” (Optical 3D Measuring Technique) and published in December
2008. The committee of experts 3.32 “Optische 3D-Meßtechnik” is a joint
committee of VDI (Verein Deutscher Ingenieure = Association of German
Engineers) and DGPF (Deutsche Gesellschaft für Photogrammetrie und Fernerkundung e.V., Arbeitskreis Nahbereichsphotogrammetrie = German Society for Photogrammetry, Remote Sensing and Geoinformation).
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Differences between the Processes
5
Test Positions
Differences between the Processes
GOM developed the GOM Acceptance Test from the guideline VDI/VDE
2634 - Part 3. The main purpose was the creation of a procedure which enables an exact and reliable statement with respect to the achievable measuring
accuracy under realistic conditions. Furthermore, GOM kept the test as simple
and stable as possible. As a result, there are several differences between
both processes.
5.1
Used Parameters
The acceptance test according to the guideline VDI/VDE 2634 Part 3 in line
with the GOM Acceptance Test includes the following parameters:
● Probing error form (sigma)
● Probing error size
● Sphere spacing error
● Length measurement error
The guideline VDI/VDE 2634 - Part 3 uses the same parameters. However,
the probing error form is evaluated with the statistical size range.
The result label and the protocol contain all results for both processes. That
way, the test can be performed in compliance with the GOM Acceptance
Test as well as with the guideline VDI/VDE 2634 Part 3.
5.2
Sensor Measurement Volume and Total Measuring Volume
The guideline VDI/VDE 2634 Part 3 differs between the sensor measuring volume and the total measuring volume. The guideline VDI/VDE 2634 Part 3
understands the sensor measuring volume as the maximum measuring volume that is captured in one single scan. Usually, the sensor measuring volume is smaller as the total measuring volume which consists of all combined
sensor measuring volumes of all single scans. According to the guideline
VDI/VDE 2634 Part 3, the spatial diagonal of the total measuring volume is at
least double as long as the one of the sensor measuring volume if nothing
else was agreed on.
Since the sensor measuring volume and total measuring volume are identical
in the acceptance test in line with the GOM Acceptance Test, the correspondingly shorter distances are used for the normal.
5.3
Test Positions
In line with the acceptance test according to the guideline VDI 2634 Part 3,
the inspector places the artifact in different, defined places of the reference
scene. The inspector measures the artifact with several single scans. In the
process, the artifact is to be found in different positions with respect to the
sensor measuring volume. For the probing error form and probing error size,
the inspector measures at least three positions in the reference scene with at
least five single scans each. For the sphere spacing error and length measurement error, the inspector measures seven defined positions. The number
of single scans is not defined.
In one single scan, the inspector measures only one of both test spheres if
possible.
The acceptance test in line with the GOM Acceptance Test differs in these
points. The inspector tests the parameters in three measurement series with
ten single scans each. Since the test spheres as well as the reference points
are attached to the PSA base plate, the test spheres cannot be moved with
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Test Positions
Differences between the Processes
respect to the reference points. Almost always, the inspector measures both
test spheres simultaneously.
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Restriction to the Operation Modes
and Conditions
6
Operation Modes
Restriction to the Operation Modes and Conditions
The guideline VDI/VDE 2634 Part 3 recommends defining the operation
modes and conditions for the acceptance test. Only under the defined requirements the corresponding limit values are authoritative for an acceptance test.
According to the guideline VDI/VDE 2634 Part 3 the operation modes are the
adjustment and configuration possibilities of the optical 3D measuring system.
The operation conditions contain the environmental influences on the optical
3D measuring system.
In line with the GOM Acceptance Test, GOM defines the following operation
modes and conditions. The acceptance test of a system is performed according to this process description, observing the restrictions of the operation
modes and conditions. The acceptance test protocol contains a reference to
this process description. Due to that fact, the following operation modes and
operation conditions are also part of the protocol.
6.1
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Operation Modes
The sensor and its parts are factory-adjusted. Check before a reverification measurement whether the settings comply with the specifications.
If the settings do not comply with the specifications, set up the sensor
according to the respective User Manual Hardware. This approach is not
valid for ATOS Core sensors.
Calibrate the sensor. Maintain the warm-up time and the calibration limit
values.
Carry out the measurements with the quality setting High and the resolution setting Full resolution.
Choose the exposure time such that the measuring images are well
exposed. Avoid overexposures.
Polygonize the single scans to a mesh using the setting Standard.
For calculating the spheres, the software uses only measurement data
which is above a defined plane. This plane is aligned parallel to the artifact base plate. This plane intersects the sphere at the latitude 10° south.
The software determines the spheres using the least squares method. In
the process, the software rejects 0.3% of the measured values as outliers.
This value corresponds to a setting of 3 sigma.
The software determines the parameter Length measurement error
using Method C (see VDI/VDE 2634 Part 3, page 18).
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Operation conditions
Restriction to the Operation Modes and
Conditions
6.2
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Operation conditions
The artifact, the PSA, includes two spheres fixed to each other with a
base plate. The spheres have the nominal diameters defined in Operations ► Test VDI 2634 - Part 3 ► New... ► Artifact.
The sphere spacing approximates the nominal distance defined in Operations ► Test VDI 2634 - Part 3 ► New... ► Artifact.
The spheres are made from steel. To ensure diffuse reflection, coat the
spheres with a titanium dioxide layer (see 7 Preparing the PSA).
Sphere diameters and sphere spacing are determined by a DAkkS calibration. The corresponding measuring uncertainty has to be very small
compared to the corresponding limit value.
The PSA is equipped with reference point markers, cleaned and sprayed
according to the instructions in ATOS User Manual- Probing Spacing Artifacts (PSA).
Maintain the environmental conditions in accordance with the respective
User Manual Hardware. In particular, the temperature must be kept constant throughout the measurement period.
The ambient temperature and the temperature of the artifact have to be
identical.
The measuring environment must be free of mechanical vibrations.
The ambient light must not vary extensively during the measurement.
Avoid extremely bright external light sources.
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Preparing the PSA
7
Preparing the PSA
Before you can use the PSA, e.g. for an acceptance test, equip the PSA with
reference point markers. The reference points enable the transformation of
the individual measurements into a common coordinate system within one
measurement series.
The size, the number and the distribution of the reference points directly influence the transformation quality and also the measuring results of the acceptance test.
In ATOS User Manual- Probing Spacing Artifacts (PSA), you find detailed
information regarding the handling of the PSA:
● Recommended point pattern for equipping the PSA with reference points
● Recommended sensor test configurations
● Handling of the spray stencil
To be able to evaluate exactly the measuring accuracy of your system, prepare the surface with suitable means. Spray the PSA with titanium dioxide
powder.
In ATOS User Manual- Spraying with the Airbrush System, you find information and tips for handling the airbrush system purchased from GOM:
● Parts of the airbrush system
● General spraying process with the airbrush system
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Creating a New Project with VDI Test
Acceptance Test
8
8.1
Acceptance Test
Creating a New Project with VDI Test
Requirements:
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●
●
●
●
Observe the safety and health hazard notes.
Observe section 6.1 Operation Modes.
Observe section 6.2 Operation conditions.
Perform the acceptance test with an ATOS Professional software, minimum V8.0.
The firmware has to be up to date.
Procedure:
1. Check whether the prerequisites mentioned above are met.
2. Start an ATOS Professional software.
3. Import the PSA template with the respective nominal values.
Info
If you have purchased the PSA as of May 2013, you have to create manually the template using the corresponding calibration certificate (see
ATOS User Manual- Probing Spacing Artifacts (PSA)). You have to create
the template only once.
a) Open Edit ► Application Settings ► Preferences... ► Templates
► VDI artifacts ►
Import.
Windows explorer opens.
b) Navigate to the PSA template. Open the template.
The software loads the template into the preferences.
c) Finish the import with OK.
4. Create a project.
a) Open File ► New Project.
5. Save the project under any name.
a) Carry out File ► Save.
The software saves the project in the chosen directory.
6. Create a VDI test.
a) Open Operations ► Test VDI 2634 - Part 3 ► New....
b) Complete the dialog according to your requirements.
c) Enter the measurement temperature.
d) Enable (
) the option Change number of test positions and set
the value to 3. For the GOM Acceptance Test, three test positions
(measurements) are required.
e) Choose in Artifact the corresponding PSA template.
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Measuring Volumes with Differing Handling
f)
Acceptance Test
Close the dialog with Create and close.
The software creates three measurement series.
The main toolbar of the workspace Digitize changes. You see additional buttons.
Fig. 5: Additional buttons
Info
To set the active measurement series during the test, use only the buttons
intended for this purpose which are described below.
Using the function Switch To Previous Test Position, you navigate to the
previous measurement series and set it as the active measurement series.
Using the function Calculate Test Position, you start a calculation for the
parameters of the active measurement series.
This function is enabled as soon as you perform at least one measurement in
the active measurement series.
Using the function Switch To Next Test Position, you navigate to the next
measurement series and set it as the active measurement series.
Using the function Export Test Protocol, you export a PDF document containing all relevant measuring results of the GOM Acceptance Test.
8.2
Measuring Volumes with Differing Handling
In line with the acceptance test, you measure three measurement series with
ten individual measurements. The positioning and aligning of the sphere pair
with respect to the sensor measuring volume is exactly defined for each individual measurement.
In step 2 of the respective measurement series, you have to treat the following measuring volumes (see 8.3 Execute Measurement Series 1, 8.4 Execute
Measurement Series 2, 8.5 Execute Measurement Series 3) differently from
the standard process.
8.2.1
Tilting the PSA
In the standard case, you tilt the sensor. During the process, the PSA remains
in horizontal position in its case. With the following measuring volumes, you
tilt the PSA and not the sensor in all three measurement series.
Procedure:
1. Constantly hold the sensor perpendicular to the ground.
2. Tilt the PSA relatively to the sensor.
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ATOS Triple
Scan II
ATOS Triple
Scan III
ATOS Compact
Scan 5M
ATOS Compact
Scan 2M
ATOS Core
MV 38
MV 38
MV 40
MV 35
MV 45
MV 60
MV 60
MV 70
MV 60
MV 80
MV 100
MV 100
-
-
-
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Execute Measurement Series 1
Acceptance Test
8.2.2
Tilting by 30°
In the acceptance test, the tilting angle between the viewing direction of the
sensor and the normal vector of the PSA is per default 45°.
Nevertheless, use for the following measuring volumes the tilting angle of 30°.
8.3
ATOS Triple
Scan II
ATOS Triple
Scan III
ATOS Compact
Scan 5M
ATOS Compact
Scan 2M
ATOS Core
MV 38
MV 38
MV 40
MV 35
MV 45
MV 60
MV 60
MV 70
MV 60
MV 80
Execute Measurement Series 1
Requirements:
●
The project created in 8.1
Procedure:
1. Position the PSA in its case horizontally on a plane and stable surface.
2. Tilt the ATOS sensor by 45° with respect to its support axis (Fig. 6).
Info
If the sensor is attached to a lift or it is a SO measuring volume marked
respectively by GOM (see 8.2.1 Tilting the PSA), tilt not the sensor but
the PSA.
Info
For certain SO measuring volumes marked respectively by GOM, use the
tilting angle of 30° instead of 45° (see 8.2.2 Tilting by 30°).
Fig. 6: Positioning sensor and PSA for first measurement series (position
for first measurement)
Standard case
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Execute Measurement Series 1
3.
4.
5.
6.
Acceptance Test
Special case lift with respectively marked SO measuring
volume
Set the height by positioning the center of the measuring volume towards
one of the spheres.
Position the center of the measuring volume centrally towards the center
point of the connecting axis between both spheres.
Carry out eight measurements in this position.
a) For each measurement, rotate the PSA by 45° around the set center
point.
b) Every time, position the center of the measuring volume centrally
towards the center point of the connecting axis between both spheres.
Position the PSA with the outside of the left sphere (outer piercing point of
the connecting axis) into the center of the measuring volume (Fig. 7).
Fig. 7: Positioning sensor and PSA for first measurement series (position for ninth measurement)
Standard case
7.
8.
9.
10.
11.
Special case lift with respectively marked SO
measuring volume
Carry out the ninth measurement.
Rotate the PSA by 180°.
Adjust the position of the PSA until the center of the measuring volume
coincides with the piercing point of the connecting axis on the right outside
of the sphere.
Carry out the tenth measurement.
Click button
Calculate Test Position.
The dialog Calculate Test Position opens.
12. Fill out the dialog. You can determine the spheres also with Ctrl + RMB.
13. Check the preview of the fitting plane and the point selection.
14. If the preview is satisfactory, confirm the calculation with OK.
After a successful computation, the software displays the results in a
result label.
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Acceptance Test
Execute Measurement Series 1
Fig. 8: Result label for the first measurement series
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Execute Measurement Series 2
8.4
Acceptance Test
Execute Measurement Series 2
Procedure:
1.
Click button
Switch To Next Test Position.
The second measurement series is active.
2. Tilt the ATOS sensor from the perpendicular position by 45° in clockwise
direction (Fig. 9).
Info
If the sensor is attached to a lift or it is a SO measuring volume marked
respectively by GOM (see 8.2.1 Tilting the PSA), tilt not the sensor but
the PSA.
Info
For certain SO measuring volumes marked respectively by GOM, use the
tilting angle of 30° instead of 45° (see 8.2.2 Tilting by 30°).
Fig. 9: Positioning sensor and PSA for second measurement series (position for first measurement)
Standard case
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Special case lift with respectively marked SO
measuring volume
3. From here, repeat the steps 3 to 14 of the section 8.3 Execute Measurement Series 1.
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Evaluating Results
Acceptance Test
8.5
Execute Measurement Series 3
Procedure:
1.
Click button
Switch To Next Test Position.
The third measurement series is active.
2. Tilt the ATOS sensor from the perpendicular position by 45° in counterclockwise direction (Fig. 10).
Info
If the sensor is attached to a lift or it is a SO measuring volume marked
respectively by GOM (see 8.2.1 Tilting the PSA), tilt not the sensor but
the PSA.
Info
For certain SO measuring volumes marked respectively by GOM, use the
tilting angle of 30° instead of 45° (see 8.2.2 Tilting by 30°).
Fig. 10: Positioning sensor and PSA for third measurement series (position for first measurement)
Standard case
Special case lift with respectively marked SO
measuring volume
3. From here, repeat the steps 3 to 14 of the section 8.3 Execute Measurement Series 1.
8.6
Evaluating Results
If all measurement series are evaluated successfully, the results for the
parameters are determined. In the column Result, you see each largest deviation of the individual results of a parameter (Fig. 11).
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Export Test Protocol
Acceptance Test
Fig. 11: Result label for all measurement series
If in all three measurement series the sensor meets all limit values for the
parameters viewed, the acceptance test is successful.
8.7
Export Test Protocol
Using the function Export Test Protocol, you export a PDF document containing all relevant measuring results of the GOM Acceptance Test.
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