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Miniature dumbbell bars are as well successfully used for the verification of CMMs with Video Autofocus (vertical axes). We believe that our miniature dumbbell method is the most suited one. Previous approches with gage blocks or stair step standards bring problems with them as weigt influence and measurement not only in Z-direction.
To our best knowledge there is no other comparable commercial (standard) product: Scales of near zero thermal expansion material and a fame of carbon fibre which has as well a near zero thermal expansion and a very good long term stability.
This is our standard product for optical CMM verification:
A line scale consisting of a chromium grating on vitro-ceramic; the vitro-ceramic plate is supported by a carbon fibre composite frame. This frame protects and maintains the thin vitro-ceramic plate flat, even when changing from horizontal to diagonal positions. Checking the CMM in diagonals is more and more demanded in CMM performance verifications and supported by the ISO 10360-7 (2011).
Alternatively one can use these small "Mini Escalon Bars" with 3mm spheres.
Such small spheres can be excellently probed by tactile and by vdeo systems.
Calibration can be by tactile measurement and the use of the bars can be for verifying video CMMs....
These bars are as well suited as reference artefacts for tomography, including for dental tomography systems.
Courtesy Quality Vision Japan
ISO 1036-7 verification of CMM in ISM3D (7 lines in 3D)
A circle standard plate (chromium-on-glass) is available.
The layout is shown here on the left with the diameters.
Such a reticule is required for ISO 10360-7 CMM verification. The circles are required to be larger than the field of view. Therefore several circle sizes are on our reticules.
10 mm to 200 mm length.
2mm or 3 mm balls.
Miniature Dumbbell Ball Bars on stand
These dumbbells here are mainly made for tomography system verification and calibration.
They serve as well as for small laser scanners and fringe projection systems if furnished with mat spheres.
On the right : different elastic fixtures for miniature dumbbells. Note that for tomography the fixture might cause problems if too thick or of materials with high atomic weight (relative to the "real object"). The thin clamps and the spheres of ruby on the dumbbells have proven particularly suitable.
White mat balls with near zero volume scattering
Here we have Dumbbell Ball Bars with balls of very low volume scattering ceramics and of aluminium balls with mat white paint coating.
The latter is a unique product feature of us.
These dumbbells are used for VDI 2634 verification of
laser scanners and fringe projection systems.
"Normal" ceramics smeer any projected image "downhill" and thus falsify the measurement results, in some cases by more than 0.1 mm.
Different diameters and lengths are possible.
The largest white and not-volume-scattering balls we make
are 160 mm in diameter;
their form error is typically <10 µm.
There is probably no competing product world wide.
The new ISO 10360-8 on verification of optical measurement systems
asks for more lengths to be measured than the VDI/VDE 2634.
Thus here on the left one sees our corresponding
ball beam made with either "normal" spheres or mat steel spheres
or low volume scattering ceramic spheres.
For fringe projection the latter is indispensible.
3D artefacts as well are supplied
with low-volume-scattering ceramic spheres.
VDI 2634 verification and ISO 10360-8 verification of optical measurement systems
both ask for reference flats in the tests. The size of these flats must be 66% of the measuring
range of the instrument.
We deliver aluminum flats with lapped laque surface, up to 500 mm x 500 mm.
This is an almost non-volume scattering surface. The flatness is htypically
up to 200mm x 200mm: 5-6 µm
up to 300mm x 300mm: 7-8 µm.
up to 500mm x 500mm: 11-13 µm.
The advantage of our photogrammetry reference bars is that the targets are on the one hand in the symmetry line of the bar (negligible influences of bending on length) and that on the other hand the white circles are concentrical with the cylinders on which they are painted (allowing both: tactile and optical measurement).
The white circles are co-lanar with the black surfaces. The edge roughness is better than that of retroreflecting targets.
These graphs on the left describe the philosophy of the standards on optical CMM testing: the test lengths must be measured bi-directionally, this includes in the errors the probing errors when measuring from different sides :
the "probe tip diameter error" in case of tactile measurement or
the "edge finding error" when measuring by video sensor.
There is a remedy if no bi-direcional standards of length are available:
Measure centre distances and add the probing size error.
This probing error can be determined by measuring a line width or a circle diameter.
This remedy is important if for example mini ball beams are used where only the centre distances are calibrated.