Patent GB-781280-A (GB)
Title: An apparatus for controlling the rate and direction of movement of a member
IPC: G05B19/35
Filed: 1953-01-26
Abstract: 781,280. Photo-electric machine tool control. NEERGAARD, L. E. DE. Jan. 26, 1953, No. 24604/55. Divided out of 780,419. Class 40 (3). [Also in Groups XXII and XXXVIII] Apparatus for controlling the rate and direction of movement of a movable member in a unidirectional machine tool control system in response to a control record provided with positionally variable discrete indicia representing required movements of the member, comprises means for generating plural variable phase signals one of which is a comparison signal and another of which is generated from the record trace with a phase angle variable in response to positional changes of the indicia, means for maintaining the base frequencies of the signals equal to each other independently of movement of the record, and means for automatically controlling the direction and magnitude of the motion of said machine member in response to the phase difference between the indicial positional change phase variable signal and the comparison signal. Fig. 1 shows apparatus for unidirectional machine tool control in response to a lineal control record bearing thereon plural parallel light modulating traces which are deflectible laterally of the record in proportion to the rate and direction of the required tool movement. A transparent film 407 (Fig. 2, not shown) bears opaque control traces as described and is uniformly traversed through the light path from a lamp 409 to a photo-cell which is also interrupted by a synchronous motor-driven transparent scanning disc 410 bearing an opaque spiral of pitch equal to the distance between adjacent traces. The tool carrier 402 slidable on a guide 404 carries a metering bar 408 having a linear series of rectangular perforations (Fig. 3, not shown) whose pitch is equal to that of the scanning spirals and the control traces, which interrupts light from lamp 420 falling on photocell 421 through a second transparent synchronous motor-driven scanning disc 418 bearing a similar opaque spiral. When the control traces are parallel to the direction of motion of the film and the tool carrier is at rest in its corresponding position, the voltage outputs of the photo-cells alternate at a synchronous frequency. Displacement of the traces in either direction in accordance with a required control action produces a frequency modulation of the photo-cell output which appears as a phase shift proportionate to the control action. A similar modulation of the output of photo-cell 421 follows displacement of the tool support and metering bar by the hydraulic motor 424 and after amplification the photo-cell outputs are supplied to a known phase comparator 423 reversibly energizing the torque motor 432, which operates piston valve 425 controlling the hydraulic motor so that displacement of the control traces produces a corresponding movement of the tool support and metering bar and restores phase coincidence between the outputs of the two photo-cells. Alternatively, modulated control and follow-up signals may be obtained from parallel magnetized traces on a moving control strip of magnetic steel by transversely scanning it by a synchronously rotating threaded magnetic member (Figs. 4, 5, not shown) having a superimposed pick-up coil, the thread pitch being equal to that of the control traces. The member may be of non-magnetic material having plural equally spaced magnetic inserts generating an interrupted helical magnetic thread; the signal output then being at a multiple of the motor synchronous frequency but modulated at the frequency thereof. The control records may be superimposed spirally on a rotating disc and the system is applicable to other forms of process control, and to the control of the direction and rate of rotation of rotary members. Specification 781,281 is referred to.