Patent GB-772683-A (GB)
Title: Improvements in a machine tool for copying from a template
IPC: B23Q35/12
Filed: 1954-12-29
Abstract: 772,683. Copy-milling. EKSTROM, CARLSON & CO. Dec. 29, 1954 [Jan. 8, 1954], No. 37548/54. Class 83 (3). [Also in Groups XXXIV and XXXVII] A machine-tool comprises a control member 87 movable radially in several directions to control movement in the same direction of a tool 31 by actuation of first and second powermeans 85, 86 connected to first and second relatively-movable members 25, 27, the degree of movement of the control member controlling the rate of movement of the tool. The pattern 35, Fig. 11, is secured to the work-blank 33 which is itself secured to the worktable 34, spacers 36 being interposed between them. The cutter 31 on a spindle 29 is rotated by a motor 30 carried on a head 28 moved vertically by a piston 51 between limits 47. The cutter can be retracted through the bore of a concentric follower 32, to prevent it fouling the template, by a piston 65 attached to the motor 30. The head 28 is lowered and the cutter then moved axially downwards by depression of a single push-button by means of sequenceswitches LS1, LS2 controlling solenoid-operated valves. The head is carried by the outer-arm 27, Fig. 7, pivoted on an inner-arm 25, which is pivoted on the base 26. The outer-arm is attached to its pivot 41 which is rotated by a reversible variable-speed D.C. motor 86 driving through gearing 113, 110, 116. A similar motor 85 rotates the inner-arm 25 through gearing 105. Electromagnetically-operated clutches 121, 122, energized with the motors, permit slipping of both drives under overload, the direct current to the coils being adjusted by rheostats to required values. Furthermore, electromagnetically-operated brakes 132, 133 are energized partially during movement of the arms, the movement being under the control of a single "joy-stick" 87, Fig. 9, which selectively energizes one or both motors 85, 86. The brakes 132, 133 exercise a resistance to rotation of the arms to prevent the follower from leaving the template after sudden changes of direction or speed. When the " joy-stick " is central it actuates a switch 149 to energize the brakes 132, 133 fully to lock the arms in position. Such locking also occurs when the cutter is raised from the work by a push-button which is similar to that which lowers the cutter, and which also de-energizes the driving-clutches 121, 122 so that the tracer is not pressed against the template. The " joy-stick " 87, Figs. 8 and 9, is mounted by a ball-and-socket 91, 95 and carries a ball 167 engaging a plate 165 engaged by spring-pressed rods 156, 157. The plate 165 and the " joy-stick " are centralized by springs 170. The plate is shaped so that movement of the " joy-stick produces movement of the tool in the same direction, but additionally, the sides 175, 176 are inclined so that the follower is held against the pattern as it is traversed, the inclinations being arranged so that the follower may move clockwise round the inside of a template or counterclockwise round the outside. Furthermore, the greater the movement of the "joy-stick" in any direction, the faster is the movement of the tool in that direction. Movement of the rod 156 controls the motor 85, Fig. 21, through a phase-shifting and discriminating network 185 including a core 181 in an inductance coil 182, the output of the network being a minimum when the core is at one end of the coil and a maximum at the other. The motor 85 is a shunt-wound D.C. motor, the voltages through the armature windings and the stabilizing-series-windings being varied according to movement of the core, and the voltage through the shunt-field-winding 187 being constant from a D.C. source. The voltage for the motor 85 is developed by a continuously-driven generator 189 according to the direction and magnitude of the signal of the reactor 179, which corresponds to the output of the network 185. The output-voltage of the generator 189 is varied by changing the field in response to movement of the core, so that the output varies from zero when the core is central to maxima of opposite polarities at the ends of its movement. The field comprises a winding 191 supplied from the constant D.C. source so that the output-voltage of the generator is a maximum of one polarity when this winding only carries current. The second winding 192 has an opposing current varied by movement of the core 181. The windings have equal turns so that when the voltages are equal the generator output is zero. The voltage in the winding 192 is controlled through a regulator 193 fed from the network 185 according to the setting of a potentiometer 194. A similar potentiometer controls a biasing-signal whereby the voltage of the generator is adjusted to zero for the neutral position of the " joystick ". A resistor 197, connected to the output of the generator in parallel with the armature of the motor 85, compensates for varying loads on the tool. A resistor 207 limits the regulator output to prevent the armaturecurrent in the motor 85 from exceeding a certain value. To prevent the motor 85 from starting at a high voltage, switch 2VR-1 is provided, which is opened whenever there is an output from the generator 189. The circuits described for the motor 85 are duplicated for the motor 86. In a modification, the follower 32<SP>1</SP>, Fig. 22, is movable into contact with an overhead-template 35 by fluid-pressure means 84.