Optics: measuring and testing – By configuration comparison – With comparison to master – desired shape – or reference voltage
Patent
1995-03-15
1997-06-03
Evans, F. L.
Optics: measuring and testing
By configuration comparison
With comparison to master, desired shape, or reference voltage
348130, 348132, G01B 1102
Patent
active
056360312
DESCRIPTION:
BRIEF SUMMARY
This invention concerns an assembly and a method to measure the dimensions of an object.
In traditional optical measuring machines, the camera is equipped with a lens and a CCD sensor allowing an electronic analysis of the object's outlines, so asking for the object to be moved under the camera's lens; and risking to move the object on the support, due to vibrations induced by the support's moving mechanisms. Moreover, it is well known that lenses give distorted images; and because of that, measuring machines-cannot work with enough accuracy. All optical lenses show a chromatic aberration, which results in that the focal plane and the dimensions of the image change with a light wavelength variation. Until now, it has been tried to minimise these effects by correcting of the lenses. Nevertheless, even using corrected lenses it is possible to notice a residual chromatic aberration, which has a bad impact on the image quality and lowering the measurements accuracy.
This invention wants to supply a solution to improve the measurement accuracy, as well as to overcome the disadvantages of known realisations.
According to this invention, this aim is reached by means of a method, whose characteristics are the following: table, it by means of a video camera so that to compare the obtained shape with other ones stored into a computer and to choose the stored image having the same shape, determine a coordinates system related to the position of the object, of a probe, whose displacement is driven by the stored image, having previously turned the main axes according to the direction of the ones of the object on the table, detected by the probe are then determined.
The assembly to make use of the method is characterized by a stationary horizontal transparent table for supporting the objects to be measured with at least a video camera and a light source, one of them being placed over and the other one under the said table, mounted on a bridge movable on two slides, for moving the camera and/or the light source.
The annexed drawings show, as an example, the proposed assembly:
FIG. 1 is a global view of the invention, showing only the characteristic elements,
FIG. 2 is a view from above of the bridge supporting two cameras,
FIG. 3 is the same view as of FIG. 2, but with one camera and two lenses, and
FIG. 4 is a partial view of the assembly showing another position for the light source.
FIG. 1 shows the assembly with a transparent support 1, fixed on a bearing arm 11 and holding some objects to be measured 7, one of which is visible on the drawing. A video camera 2 and a light source 3 are fixed on a bridge 4. The camera 2 is placed over the support 1, while the light source is placed under it. Of course, it would be possible as well to exchange the position between the camera 2 and the light source 3. The bridge 4 is mounted movable on two slides 5 X and Y, the control axes of which are not showed.
The camera 2, equipped with a lens and a CCD sensor 6 with a narrow field of view can be freely displaced up and down with respect to the support 1, on which one or more objects to be measured 7 can be placed in an undetermined position.
So as to facilitate the interpretation of the measurements, the bridge 4 can be provided with two cameras 2A and 2B as in FIG. 2. The first camera 2A could have a large field of view allowing to electronically store the position of the object(s) to be measured, as well as their angular displacement. The second camera 2B with a narrow field of view can be automatically moved from one object to another and proceed to the required measurement analyses.
A single camera 2 with two lenses 6, one of them having a large field of view while the other one has a narrow field of view are showed in FIG. 3. The lenses are mounted on a transversal slide 8 placed on the bridge 4. According to the different measurement tasks, one of the two different field of view will be used.
FIG. 4 shows another arrangement of the light source 9, which is horizontally or obliquely mounted but by side of the optical axis of
REFERENCES:
patent: 4711579 (1987-12-01), Wilkinson
patent: 4918627 (1990-04-01), Garcia et al.
patent: 5184217 (1993-02-01), Doering
patent: 5231675 (1993-07-01), Sarr et al.
TM Technisches Messen, vol. 57, No. 2, Feb. 1993, Munchen, DE pp. 71-77, T. Pfeifer, F.-J. Czuka `Messsystem zur 100%-Kontrolle von Stanzteilen im Produktionstakt` see p. 73, paragraph 3--p. 77, paragraph 5; figures 3,4.
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