Patent GB-1149230-A (GB)
Title: Incrementing apparatus
IPC: G11B15/20
Filed: 1967-11-30
Abstract: 1,149,230. Digital position control. INTERNATIONAL BUSINESS MACHINES CORP. 30 Nov., 1967 [22 Dec., 1966 (2)], No. 54442/67. Heading G4H. A movable member 8 is moved through a predetermined number of steps to a required position by apparatus comprising a register 20 for storing a count of the required number of steps, driving means operable to drive the member either at slow-speed from which the member can be stopped at the required position in response to a zero indication from the register, at high speed, means for reducing the count stored in the register each time the member moves a step, a tachometer 30 for indicating the speed of the member and deceleration control means responsive to the register and to the tachometer to initiate deceleration when the member approaches at high speed within a given number of steps of the required position. The member 8 is driven by motor 10 which is controlled by circuit 12 receiving inputs from a drive latch 14 and from a brake latch 16. The counter is coupled to the driving latch to reset it when it reaches a count of zero. The number of increments required is loaded into the counter and this number is reduced by inputs from gates 22 and 24. A commutator 26 produces pulses, one for each step made by the motor, which pass to gate 22 and to a pulse generator 28 having a fixed pulse rate. The fixed-rate pulses are applied to gate 24, enabled by a signal on lead 32 from a tachometer 30 indicating that the pulse rate from commutator 26 is less than that from generator 28. The generator 28 produces pulses at a rate corresponding to the maximum speed of the motor 10. Inverter 34 blocks gate 22 when gate 24 is open so that motor and counter control is by one pulse train or the other. And gates 41, 42, 44, 48 are connected to outputs of counter 20 representing successively lower counts. The outputs of the gates are coupled to the braking latch 16. The counter is loaded with the number of steps required and the driving latch 14 is set by a signal on terminal 62. The motor 10 starts and pulses for commutator 26 pass through gate 22 to reduce the number in the counter. When the motor has speeded up the tachogenerator energizes lead 32 and gate 24 opens to pass the fixed rate pulses from generator 28 to the counter. After this the motor runs at maximum speed until deceleration becomes necessary. As the motor speed increases the tachometer will mark terminals 51, 52, 54 and 58, and enable corresponding gates 41, 42, 44, 48. Each of these gates corresponds to a motor speed and a number remaining in the counter. If the motor is running at full speed and the counter reaches a value such that gate 48 gives an output the brake latch 16 is set and drive latch 14 reset. When the speed falls below the maximum the tachometer transfers the controls to the pulses from commutator 26. The signal on lead 32 also resets the brake latch and sets the drive latch again so that driving continues at a lower speed. When a given lower member is reached the next gate 44 responds, again applying the brake and resetting the drive latch. The process continues until the zero count terminal is marked when both latches are reset and the motor stops in the desired position. The tachometer comprises an integrator to which the decriminating pulse train is applied. The resulting voltage is sensed by a plurality of threshold level devices, e.g. Schmitt triggers. The system may be adapted for movement in either direction. The system may be a magnetic tape drive control for moving the tape to a desired address. The tape may carry marks which are sensed to provide the variable rate pulse train.