Patent GB-1339468-A (GB)
Title: Method and device for immobilisation of a machine shaft in a pre determined angular position
IPC: D05B69/26
Filed: 1971-10-26
Abstract: 1339468 Stopping machines at definite positions; electric and speed control QUICKROTAN BECKER & NOTZ KG 26 Oct 1971 [5 Nov 1970] 49801/71 Heading F2E [Also in Division G3] A machine shaft 4, Fig. 1, or a shaft connected to it, is stopped in a predetermined angular position by an electromagnetically-actuatable brake 5, 8, 9, under the control of a regulator circuit 10 provided with an appropriate braking signal for controlling the braking torque; stopping in the predetermined position is ensured by deriving the braking signal, at least during the final part of the braking action, in the following manner: (a) measuring (continuously) at 11 the rotational speed of the machine shaft, (b) calculating at 14 the angle of rotation required for the shaft to come to rest from the then speed under a braking torque less than the maximum of which the brake is capable, (c) measuring at 15 the angular displacement of the shaft from the desired stopping position and (d) comparing the two angular values at 16. As shown, apparatus for maintaining constant a given speed of revolution of shaft 4, and stated to be known, comprises a motor 1 having a shaft 2 and flywheel 3 rotating constantly at the maximum speed, and an output shaft 4 carrying a clutch plate 5 and a driving pulley 6. The clutch plate may be brought into engagement with the flywheel 3 by energization of a clutch winding 7, and into engagement with a braking abutment 9 by energization of a brake winding 8. The desired rotational speed of a machine shaft driven by output shaft 4 is selected on a rotational speed "transmitter" 12, and its output signal is compared in a comparator 13 with that from the rotational speed-measuring circuit element 11. According to the invention, circuit elements 14 to 16 are added, element 14 making use of the signal from speed-measuring element 11. To stop the machine shaft, "transmitter" 12 is set to zero, and circuit elements 14, 15 are brought into action. The signal from comparator 13 deriving from elements 11, 12, initiates braking, at first powerful, of shaft 4. The influence of the output signal of comparator 16 on regulator 10 increases as the actual speed of revolution approaches the zero speed selected. The shaft is decelerated until the output signals of elements 11, 12, are equal, and those of elements 14, 15, are correspondingly equal, the output of comparator 13 being now zero. Fig. 3 shows a more sophisticated arrangement which also includes provision for stopping the machine a second time at a position spaced less than 360 degrees (e.g. 180 degrees), from the first. Starting with the machine-shaft idle, when a desired speed of rotation is selected at "transmitter" 12, a signal through stage 30 to flip-flop 31 causes an unblocking signal along path 38 to release gate 19 so that signals from a summing amplifier 26 reach regulator 10. Flipflop 32 driven by a signal from 12 operates a stage 29 to block the path of signals from a circuit 27 (associated with the second stop) to summing amplifier 26. Stage 28 is unblocked along path 41, but gate 17 (part of the circuitry for the first stop) at this time blocks any signals from comparator 16 (a summing amplifier). The actual shaft speed is signalled by a differentiating stage 24 which receives a signal from the anglemeasuring device 15 and takes the place of circuit element 11. Initially the difference between the signals from 12 and 24 is large, so amplifier 26 causes regulator 10 to energise clutch-winding 7, whereby shaft 4 is accelerated. Device 15 (see below) now delivers a sawtooth voltage whose longer slope is measured in stage 24. When the difference, at amplifier 26, between the desired and actual speed signals becomes zero, clutch winding 7 is de-energized. Thereafter, the speed is maintained constant as outlined in the second paragraph. To stop the machine shaft in the first position, "transmitter" 12 is set to zero. A blocking signal along path 39 disappears, but gate 17, controlled by circuit element 18, still blocks signals from amplifier 16. Thus only a large signal representing the difference between the high actual shaft speed and zero desired speed reaches regulator 10, so brake winding 8 is fully energized. The shaft is thus braked with maximum braking torque independently of the output of 16. When the actual speed has dropped to a predetermined value, element 18 unblocks gate 17. whereupon elements 14 to 16 are brought into play, and through 28, 26 and 19 serve to reduce the energization of brake winding 8 until the shaft comes to rest. A switching element 35 now delivers a signal (to) from element 15 to input e2 of flip-flop 31, resetting it, thereby blocking gate 19 alongpath 38. Regulator 10 is thereby disconnected from amplifier 26, and the windings 7, 8 are de-energized. The machine shaft may now be turned freely by hand. The second stopping position circuit 27 compares the actual angle signal of the anglemeasuring element 15 to a reference voltage U B . As long as the actual angle signal is smaller than the reference voltage, comparator 13 receives a signal causing energization of clutch winding 7. The machine shaft thus begins to turn again. As soon as the actual angle signal equals the reference voltage, circuit 27 issues a braking order to regulator 10 through unblocking stage 29, summing amplifier 26 and gate 19. The machine shaft is thus braked and held in the second position. An angle-measuring element is shown in Figs 8 and 9 and incorporates a rotor 60 to be secured to the machine shaft, pole plates 80, 81, and a measuring head 65 incorporating a Hale generator. In a modification (not accompanied by a drawing) the speed of revolution of the machine shaft is determined by a tacho-generator, and the actual angle turned through is obtained from an integration stage following the tachogenerator.