Patent GB-1331601-A (GB)
Title: Relative motion control means
IPC: H02P5/52
Filed: 1969-07-16
Abstract: 1331601 Automatic speed control COVENTRY GAUGE & TOOL CO Ltd and COLLEGE OF AERONAUTICS REGISTERED GOVERNORS OF 12 Oct 1970 [16 July 19691 35836/69 Heading G3R [Also in Division H2] A grinding wheel 10 is driven by a synchronous motor 1 associated with a rotary encoder 11 comprising a glass disc 14 with a radial line grating for co-operation with reading heads 15. Each head has a fixed reference grating and photosensitive cells responsive to light passing through the gratings. Rotation of the disc 14 produces Moire fringes whereby the cells develop a signal which is converted to a train of square wave pulses whose frequency represents the speed of the wheel 10. The signals from the heads 15 are processed by a unit 17 to eliminate the effects of eccentricity of the disc 14. The pulse train is then fed to a frequency changer 18 comprising a multiplier and divider. A workpiece 20 such as a gear blank is driven by a D.C. motor 2 associated with a rotary encoder 22 similar to the encoder 11, a unit 27 compensating for eccentricity of the disc 24. The unit 18 is set initially so that the frequency of the pulse train is equal to the frequency of the train produced by the encoder 22 when the workpiece is running in correct engagement with the grinding wheel. The two pulse trains are fed to a reversible counter 19 to increment and decrement the counter respectively, the count oscillating by one digit on either side of a specific number. The output of the counter is connected through a digital-analogue converter 26 and amplifiers 28 to the motor 2 whereby the system operates as a phase servo. The gain of a discriminator 29 is adjusted so that the system operates at any demand speed with zero output from the converter 26. After this adjustment, the system operates at all speeds with zero servo error. When gear grinding, the angle of inclination of the axis of the wheel 10 to the axis of the workpiece 20 is modified by the spiral angle of the workpiece 20, the angle being set by a sine bar assembly 46. In addition, the speed of the workpiece is modified in accordance with the lead of the workpiece and the rate of cross feed relative to the wheel 10. A linear encoder 44 co-operates with sine bar 46 and its frequency depends on the speed of cross feed of the support 21 by the motor 4 and the modified spiral angle. A reversible counter 39 receives pulse trains from the encoder 44 and from a rotary encoder 33, the output of the counter being applied to a D.C. motor 3 which drives the encoder disc 34 as well as a carrier for the reading heads 25 of the encoder 22. The rotary motion of the workpiece 20 is thus modified to compensate for the spiral angle. In another arrangement the encoder 33 is incorporated with the encoder 22 by providing further reading heads to the disc 24 mechanically distinct from the heads 25, Fig. 2 (not shown). In a further modification, the output from the linear encoder 44 is fed to a gate and thence to the counter 19. The gate accepts pulse trains from the units 18, 27, and adds the pulses from the encoder 44 to either of these trains, depending on whether the spiral angle of the workpiece is right or left-hand, Fig.3 (not shown). A warning device 8 indicates excessive acceleration of the wheel 10, while indicators 9, 49, show when grinding can commence. Manual control is provided at 12 and 42 for the motors 1 and 3 respectively.