| 摘要 |
1,205,446. Position finding. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 3 Oct., 1967 [6 Oct., 1966], No. 44895/67. Heading H4D. [Also in Division G1] In a machine tool control system in which the image of a fixed grating is projected on to a movable grating connected for movement with the machine tool and in which the image is given a periodic lateral motion by reflecting the image beam in a rotating light-reflective polyhedron, the reflected beam is bifurcated to produce two relatively reversed images on a movable grating. As shown light from a lamp 1 is reflected at a fixed curved mirror 2 and impinges on a fixed grating 4. The image formed by the light passing through this grating passes through a pair of lenses 3 and 6 and a semi-transparent mirror 5 and is reflected in a rotating polyhedron 7. The reflected beam passes back through the lens 6 and is reflected by the semi-transparent mirror 5 towards a mirror 8. Half of this beam misses the mirror and impinges on the movable grating 9 where it is reflected on to a photo-cell 11, while the other half is reflected at the mirror 8 and is reflected by the movable grating as at C, D on to another photo-cell 10. While the grating 9 is stationary the two images A, B and C, D of the fixed grating appear to move in the direction of the arrows with a velocity proportional to the rate of rotation of the polyhedron 7. The frequencies of the resulting pulsating outputs of the two photo-cells being equal. If the grating 9 is moving it adds to the apparent velocity of one image and subtracts from the other. The resulting difference in frequency in the outputs of the two photo-cells 10 and 11 is proportional to the velocity of the grating 9 and thus of the machine tool and is independent of irregularities in the polyhedron 7. The displacement of the grating can be derived from the difference in phase of the two outputs. In another form (Fig. 2, not shown) a semi-transparent mirror formed of two plane parts at an obtuse angle to each other are used. These two parts additionally split the beam into two paths one either side of a vertical plane through the system and extending at 45 degrees to the plane. In each of these paths is a detector arrangement generally similar to that formed by the components 8 to 11 except that two internally reflecting prisms replace the mirrors 8 and a single point grating 9 is used for both arrangements. Thus movements in two perpendicular directions can be measured. |
