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Method and Apparatus for Three-Dimensional Position Measurement

IP.com Disclosure Number: IPCOM000043092D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Smith, GM: AUTHOR

Abstract

In robot or other position testing it is necessary to measure actual coordinates at various reference points in the working volume. This should preferably use a non-contact sensing method and give a linear measurement of position error in three dimensions. This is achieved by comparing and measuring the light received by four photocells arranged in a horizontal cross when illuminated from above by a point source of light carried by the moving member, the position of which is to be checked, and partially obscured by a disc also carried by the member. Fig. 1 shows the light source 1 and obscuring disc 2 supported fixed relative to each other on a moving member (not shown).

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Method and Apparatus for Three-Dimensional Position Measurement

In robot or other position testing it is necessary to measure actual coordinates at various reference points in the working volume. This should preferably use a non-contact sensing method and give a linear measurement of position error in three dimensions. This is achieved by comparing and measuring the light received by four photocells arranged in a horizontal cross when illuminated from above by a point source of light carried by the moving member, the position of which is to be checked, and partially obscured by a disc also carried by the member. Fig. 1 shows the light source 1 and obscuring disc 2 supported fixed relative to each other on a moving member (not shown). With the arrangement shown, the ring of light from the source is centered on the cross of photocells 3 illuminating an equal predetermined portion of each only when the moving member is exactly at the reference point. The respective outputs from the four cells, which are arranged as shown in Fig. 2 with two cells aligned in the X direction and two in the Y direction, representing the amount of illumination received, are amplified by identical amplifiers 4. The amplified signals from the cells in the X direction are supplied as inputs to differential amplifier 5, and from the two cells in the Y direction as inputs to differential amplifier 6. All four cell outputs are supplied as inputs to summing amplifier 7. In operation, any moveme...