Patent GB-1339314-A (GB)
Title: Measuring machine
IPC: G01B11/00
Filed: 1971-08-02
Abstract: 1339314 Positioning systems SOC GENEVOISE D'INSTRUMENTS DE PHYSIQUE 2 Aug 1971 [2 Sept 1970] 36155/71 Heading G4H [Also in Division G1] In an apparatus for measuring or monitoring displacement, e.g. of a movable machine part 2 relative to a fixed bed 1, an initial coarse measurement is effected by a digital system including a photo-electric pulse generator 19 while the final fine measurement is carried out by an analog system 33-41 which reads a scale 12 attached to the member 2, there being a commutation arrangement (17, Fig. 3, not shown) which ensures that the two measuring systems are not operative simultaneously. The member 2 is moved up or down by a servo-controlled motor 9 which receives either one of the outputs from the two measuring systems. Rotational movement of the shaft 10 is translated into vertical movement of the member 2 by a gearing arrangement 7, 8. The shaft 10 is connectible to the shaft 20 by means  of an electromagnetic coupling 21.  The optical pulse generator comprises a disc 19 attached to the shaft 20 and a plurality of  light source/detector combinations. One rotation of the shaft 20 corresponds to a displacement of the member 2 equal to the spacing between two graduations on the scale 12, and generates a fixed number of pulses.  The analog system includes an incandescent lamp 33, beam splitter 34, vibrating mirror 36 and a field diaphragm 42, having a helical slot  40, attached to the shaft 20.  In operation, the counter (22) of the digital  system is set to a desired value, corresponding  to the desired displacement of the member 2. As soon as the counter assumes this non-zero  state, a control signal from its output engages the electromagnetic coupling and also actuates the commutator (17) so that the servomotor receives the output from the counter, after conversion to analog form (26). The member 2 is thus moved into position under control of the digital system until the counter thereof reaches a zero state. At this point, the counter produces another control signal to disengage the coupling 21 and switch the commutator so that the servomotor receives the output from the  photo-cell 41 of the analog system. The mirror  36 is vibrating so that the image of the desired scale mark is scanned across the diaphragm 42. If the two extreme positions of this image are not symmetrical with respect to the helical slot 40, the shaped (31, 32) output signal from the photo-cell actuates the motor to correct this. The apparatus may be used under manual control. In this case the operator sets the counter to zero and engages the coupling 21. A manual speed control (43) is provided, and this is operated to drive, via the commutator, the servomotor until the counter reading indicates that the desired position has almost been achieved. The counter is then re-set to zero, thereby disengaging the coupling 21 and setting the commutator so that the servomotor receives the output from the analog system. Fine adjustment is achieved by rotating the knob 44, which also rotates the field diaphragm and hence causes movement of the member 2. The magnitude of this fine adjustment is recorded on the counter. Each switching element (48, 49) of the commutator device is provided with its own relay. Movement of a machine part in three orthogonal directions may be monitored by having one apparatus for each direction of movement.