Patent GB-998817-A (GB)
Title: Speed control system
Inventor: PRESCOTT EDWARD HORACE ALBERT
IPC: B23Q15/10
Filed: 1961-01-13
Abstract: 998, 817. Automatic speed control. PYE Ltd. April 12,1962 [Jan. 13,1961], No. 1564/61. Heading G3R. The speed of rotation of a workpiece held in the headstock of a lathe is varied to maintain the linear speed of travel of a tool relative to the workpiece substantially constant with variations of the position of the tool due to its movement in two independent directions, the tool being mounted on a profiling slide which is in turn mounted on a crossslide. The headstock is driven by an induction coupling 1 having coil 2 which is controlled by a closed loop system with a reference voltage representing speed. Potentiometers P1, P2, are adjusted in response to movements of the cross-slide and profiling slide respectively, and are adapted to provide a voltage which is a summation of the two movements, this voltage being amplified to afford the reference voltage which is compared with a voltage derived from tachometer generator 3 driven by the output shaft of the coupling. The voltage derived from the potentiometers P1, P2, is amplified in a transistor amplifier comprising two Class A stages TR1, TR2, and a Class B pushpull stage TR3,TR4, a control voltage being fed to the amplifier through section S3A of switch S3. This switch allows for selection to be made between manual, pre-set, and automatic speed control for five different profiling angles. Section 3A selects the input voltage from any one of potentiometers P3, P4, or P5 according to whether the switch is set for manual, pre-set, or automatic operation. Sections S3B, S3C, are operable on the manual and pre-set positions to insert a fixed amount of feedback in series with the input to the amplifier from resistors R4, R5, across feedback winding 10 on transformer T3. In the zero position, only the feedback dependent on the position of potentiometer P1 is inserted in series with the amplifier input, whilst, on the remaining positions the feedback dependent on both potentiometers P1, P2, is effective. In the manual and preset positions, section S3D connects resistor R6 in series with potentiometer P1 to maintain the impedance across winding 10 constant. In the other positions, this switch connects potentiometers P1, P2 together, with one position for reversing the connections. Sections S3E, S3F, provide series-shunt combinations of resistance across potentiometers P2 in different profiling positions to maintain constant impedance for winding 10. The output voltage across potentiometer P2 is proportional to the sine of the profile angle. The output of the amplifier is developed across resistor R1 in opposition to the tachometer voltage, the difference being applied as bias to thyratrons V1, V2, to control the energization and speed of the coupling. Switch S2 is coupled to the gear lever on the lathe so that the input voltage to the transistor amplifier is varied according to the gear ratio whereby the spindle speed remains constant when the coupling shaft speed has varied to suit the gear ratio selected. When the coupling 1 is energized, a voltage developed across resistor R3 is applied to transistor TR5, so de-energizing coil L1 and releasing a brake on the output shaft of the coupling. Specifications 929,622 and 948,467 are referred to.