CSEM Scientific and Technical Report 2008

Low Cost Micro Metrology Concept
P. Glocker, G. Gruener, R. Wyss, U. Zbinden
The project shows a solution for economic geometrical dimension measurements of microparts. Based on the CSEM PocketDelta Robot and
standard low cost camera systems and optics a compact metrology system was developed for application in the watch or precision punching
industry. The measuring algorithm is robust against optical distortions.
The quality of micro mechanical system is often based on the
conformity of the assembled single parts. The 100%
measurements of microparts generate significant extra costs.
With the pocket measuring robot a concept is demonstrated
for economic quality controls of micro parts. Based on the
CSEM PocketDelta a metrology system for plane micro parts
(Figure 1) was developed:
Figure 1: Measuring sample "platine"
The hardware (Figure 2) is divided into four subsystems: Work
piece carrier, vision sensor, illumination and manipulator. The
target is to have lowest set up costs for the application and
robustness.
Figure 2: Pocket measuring robot
The task of the work piece holder is reduced to guarantee the
approximate position (e.g. ±1 mm). For the above sample
"platine" two simple pins will do the job. For the illumination a
backlight module is used. The backlight illumination gives the
best results for image processing and is uncritical to use in an
industrial environment. The vision system which is used as a
contactless probe is equipped with low cost optics with plastic
lenses and is available as OEM module with integrated USB
102
driver. The manipulator, a CSEM PocketDelta [1] , is responsible
for moving the vision system to the measuring position.
The implemented software includes interactive graphical user
interface (Figure 3) and was developed within the
collaboration with HSLU of Canton Luzern. It offers a tool for
specification of the measuring position and sequence, as well
as the classification. The image processing universal pattern
identifier has been created based on the library Intel Open
CV [2] , to be used without any adjustment e.g. to auto detect
bearing or insertion pin position of different diameters without
adding any metric information.
The only inputs from the operator are the theoretical positions
of the objects to be measured and the nominal value of the
distance to be checked. The software will automatically
generate the measuring movements for the robot and classify
the results according to the tolerances.
The control architecture is based on a virtual server concept
and will allow integration of any robot kinematics. For
calibration reasons the robot movement must be highly
repetitive and needs to be calibrated with a reference grid.
Figure 3: Pocket measuring system
Typical specification for a Pocket Measuring Robot:
• Measuring area 50 x 50 mm
• Resolution in X, Y 0.001 mm
• Accuracy 0.005 mm
• Measuring speed up to 2 points per second
The sensor works in a real absolute measuring mode and
needs no reference cycle.
[1] S. Perroud, et al., "New pocket and Delta robots with integrated
controllers", CSEM Scientific and Technical Report 2006,
page 80
[2] Learning OpenCV: Computer Vision with the OpenCV Library
G. Bradski; A. Kaehler, 2008