GB1385415A - Devices for stopping the work spindle of a machine tool - Google Patents

Abstract

1385415 Liquid-friction and full-face-disc brakes; stopping by detent in definite positions ZAHNRADFABRIK FRIEDRICHSHAFEN AG 18 Sept 1972 [16 Sept 1971] 43088/72 Heading F2E A device for stopping the work spindle of a machine tool in a predetermined angular position comprises a hydrostatic pump or motor 2 (optionally with a friction brake 3) rotationally associated with the spindle (not shown), a valve assembly 6, 7, connected to the inlet and outlet pipes 4, 5, of the pump or motor 2 and serving to control the outlet, a pin 11 attached to the slidable valve member 7, and an index plate 15 attached to the spindle, the plate 15 having one or more slots 14 for receiving the pin 11 and having cams 16 and bevels 20 for purposes referred to below; the pin 11 has a catch 12 co-operable with a pawl 13 for locking the pin. As shown, and in operation, when the spindle is rotating normally the valve member 7 is in a position somewhat above that shown in Fig. 1 but represented symbolically in Fig. 2 at A. To stop the spindle, a valve 44, Fig. 2, is opened, whereupon hydraulic liquid is admitted to cause actuation of a multi-plate full-face disc brake 3 whose "inner" discs rotate with the work spindle and whose outer discs are connected to the rotor of the hydrostatic device 2. Hydraulic liquid is also admitted to the device 2 and to the valve casing 6. Initial actuation of brake 3 causes driving of the outer discs by the inner discs, with slip, so device 2 acts as a pump, pressurizing outlet pipe 5. At a certain pressure a by-pass valve 22 disconnects pipe 5 from pipe 4, whereupon the pressure in pipe 4 attains a value of, e.g. 16 to 24 atm. gauge, while that in pipe 5 attains a value of, e.g. 80 atm. gauge. Pump 2 acting through the brake 3 exerts a braking action on the work spindle and when eventually the disc speeds in brake 3 are equal, further braking occurs. Consequently hydrostatic device 2 runs slower, so the pressure in outlet pipe 5 drops, and in turn the pressure exerted thereby on the inside of valve member 7. The continuing inlet pressure acting through orifice 24 on the top 9 of valve member 7 moves it downwards to position B, the position shown in Fig. 1, where pin 11 is temporarily prevented from further descent by engagement of catch 12 with pawl 13. Upon rotation of index plate 15 to a position where cams 16 on one of its faces can move pawl 13 away from catch 12, pin 11 and valve member 7 are freed for further downward movement. The lower end of pin 11 (by roller 17) now comes in contact with a bevel 20 in the edge of disc 15 whereupon valve member and pin move down to position C. At this phase, flow into the valve casing 6 from outlet pipe 5 is being throttled at 18, Fig. 1, and flow outward therefrom is being restricted by one or more orifices on the right hand side. Pressure in pipe 5 therefore increases, producing further braking action. During movement of pin 11 on bevel 20 throttle 18 becomes smaller in area until the index plate 15 is brought to rest as slot 14 reaches pin 11. Control of throttle 18 is governed by the slope of bevel 20. The spindle may be re-started after valve 44 has been closed again. For machine tools the work spindles of which are rotated only in timed sequence, friction brake 3 and valve 22 may be omitted; then, for part of the cycle, apparatus 2 is driven as a motor by hydraulic liquid through (open) valve 44.