Patent GB-864505-A (GB)
Title: Improvements in and relating to a machine-tool
IPC: B23B47/06
Filed: 1957-12-24
Abstract: 864,505. Drilling-machine details. SOC. GENEVOISE D'INSTRUMENTS DE PHYSIQUE. Dec. 24, 1957 [Sept. 13, 1957], No. 40037/57. Class 83 (3). In a machine-tool comprising means for braking a rotary member, and electromagnetic safety-devices, the braking-action is terminated before the rotary member stops rotating, but the safety-devices remain operative until rotation stops. As illustrated, the rotary member is the motor spindle of a jig-borer, which is braked by reversing the current to the motor 10. The safety-devices comprise electromagneticallyoperated pins 32, 33, 60, projected against the spindle-sleeve 16 and into the path of a changespeed lever 9a, respectively, to restrict movements of the sleeve and lever 9a while a spindledriving pulley 11, driven by the motor, rotates. As depicted, the pulley is rotating but not driving the spindle 15, which is retained safely by engagement of the pins 32, 33, in grooves 16a, 16b, in the spindle-sleeve 16, with its upper sleeve-end 21 out of engagement with clutch teeth 23 rotating with the pulley and with stationary teeth 36b on the casing 8a. Rotation of the pulley must cease before the pins 32, 33 withdraw, freeing the spindle for movement by the lever-operated rack-and-pinion gear 19, 20, either to engage the clutch-teeth 23 for rotation of the spindle, or the teeth 36a, 36b, for holding the spindle during rotation of the draw-spindle 29 by a worm-gearing 30a, 30b. The motor (not shown), driving this gearing is started by a switch 35 operated by a rod 34 moved by the draw-spindle as this is engaged in a driving- socket of the worm-wheel 30a. The driving clutch-teeth 23 are provided in a ring 24 splined within the pulley 11 but movable axially against the action of a spring 27. The drive from the motor to the gear-box 9 (Fig. 1, not shown), and from the latter to the pulley, is by belts, and a knob 9b is operable to select the drive when the clutch-lever 9a is in its neutral positions. Control of the duration of the braking-effect, and of the release of the pins 32, 33, 60, is by an alternator 38 and the discharge from a condenser 47, Fig. 6, the rotor 39 of the alternator being driven by the shaft of the motor 10 and slotted at 90 to vary the reluctance of the magnetic field. Operation and electric control.-The pins 32, 33, 60, are operated by coils 32a, 33a, 60a, connected to a D.C. supply 43. Coils 50, 51, 52, 54, 55, control contacts 50a-50c, 51a-51c, 52a- 52b, 54a-54b, 55a-55c, respectively, in the circuit, and energization of coil 53 reverses the current to the spindle motor 10. A bridgecircuit 44 rectifies the A.C. from alternator 38. The motor 10 is started by closing a switch 45, which energizes all the coils except 53, which is maintained inactive by the opening of contact 54b. To stop the motor, switch 45 is opened, thus de-energizing coils 54, 55, which reverse the settings of their contacts, including the closing of contact 54b, which energizes coil 53 and reverses the current to motor 10. Coil 50 remains energized, by the voltage from the bridge 44, until this falls below the necessary minimum due to the braking-effect on the motor. De-energization of the coil 50 opens contact 50a, terminating the braking-effect, and closes contact 50c, which permits condenser 47 to discharge through coil 51, thus maintaining this coil, and through it coils 32a, 33a, 60a, energized until the motor has had time to stop. When the condenser has discharged, coil 51 de-energizes, opening contacts 51a-51c and de-energizing coils 32a, 33a, 60a, to withdraw pins 32, 33, 60. Instead of the above electric control, one which is wholly or partly mechanical may be used. The condenser 47 may be replaced by a time-delay relay or a dash-pot.