Patent GB-1150057-A (GB)
Title: Improvements in or relating to turret control arrangements for machine tools
Inventor: BURG FRED GEORGE
IPC: G05B19/35
Filed: 1966-06-28
Abstract: 1,150,057. Indexing turrets. HOUDAILLE INDUSTRIES Inc. 28 June, 1966, No. 29047/66. Heading B3C. [Also in Divisions G3 and H2] An apparatus for controlling the indexing of a machine tool turret comprises a selecting device generating a signal indicating the deviation of the turret from a desired position, a bistable device responsive to the signal which changes state when the deviation reduces to a preset value, a control device reducing the speed of an indexing drive on a change of state and a second bi-stable device initiating a further speed reduction at a second preset value. A circular potentiometer R 10 , Fig. 2, has tappings 01-20, equal in number to the turret positions, connected to a decoding matrix 29, set to a desired indexing position of the turret by a tape command or manually. A rotor 30 moves in synchronism with the turret and has wipers 30a, 30b between which a constant direct-potential is impressed; the potential at any tapping being a measure of departure of the turret from the position corresponding to the tapping. The tapped deviation voltage is compared with pre-set reference voltages, derived from tappings S9a, S9b on a reference potentiometer R9, by matching networks 27, 28 controlling relays 1HR, 2HR. The relay 2HR is operated when the tapping voltage falls to the reference voltage at tapping S9a and the relay 1HR is operated when the tapping voltage drops in value to that at tapping S9b. The relays selectively actuate contacts 22- 26, Fig. 1, to apply reducing tapped voltages, from sliders S 3 -S 5  of potentiometers R 3 -R 5  in series across a silicon-controlled rectifier 14, through to a phase-shift R.C. network R 6 -R 8 , C 1 , C 2  controlling the triggering of the rectifier 14. The conduction of the silicon controlled rectifier 14 determines the speed of a motor driving the turret by varying the average voltage applied to the armature M, the field winding F of the motor being connected across lines L1, L2 supplying full-wave rectified current derived from an A.C. source, not shown. The direction of rotation of the motor is determined by contacts 10-13 selectively actuated by relays 17, 18, Fig. 2. When the relays 17, 18 are de-energized contacts 15, 16 are closed and a braking resistor R 1  is connected across the motor; a dynamic braking control relay DBR, responsive to the armature voltage through a tapping 52 on a resistor R 2 , dropping out when the motor speed falls to a set value. During a programmed positioning operation, a tape command 43, 44 is received or a manual push 39, 40 is operated to determine the direction of rotation of the turret, through index relays IMR or IPR, actuating relay 17 or 18 through a contact 35 which is closed by the withdrawal of a turret locking pin, not shown, by a solenoid 31 actuated by a start relay SSR. The initial speed of the turret is controlled by the setting of resistor R 3  through normally closed contacts of relays 1HR, 2HR. As the rotor 30 approaches its desired position, the deviation voltage falls so that relay 2HR is energized which removes the supply from the armature of motor M, through the appropriate index relay, the dynamic braking resistor R 1  becomes effective and further speed control is transferred to resistor R 4 . As the armature slows down the voltage across resistor R 2  decreases until relay DBR opens which establishes a circuit through the contacts of the index minus relay 1MR and the armature coasts until the speed determined by the setting of resistor R 4  is reached. The armature rotates at this speed until the rotor 30 reaches a position at which the relay 1HR is energized so that the setting of resistor R 5  becomes effective, the armature then coasts and subsequently rotates at the determined speed until a switch 38 is opened by the cam 37, driven by the turret, when near the desired index position to render the dynamic braking circuit effective. When switch 38 is closed in the full line position at the desired index positions, a stop index relay S1R is energized and a contact 34 of the now deenergized start relay SSR causes a solenoid 32 to engage the locking-pin at the desired index position of the turret.