Patent GB-810838-A (GB)
Title: Improvements in or relating to tracing apparatus and method
IPC: B23Q35/12
Filed: 1955-12-21
Abstract: 810,838. Copy-milling. CINCINNATI MILLING MACHINE CO.' Dec. 21, 1955 [Dec. 28, 1954], No. 36684/55. Class 83 (3). [Also in Groups XXIX and XXXVIII] A copy milling machine comprises an hydraulically-fed milling head and work-table controlled by a feeler associated with a threedimensional template, displacement of the feeler in the horizontal and vertical directions relative to the template producing corresponding variations in output from two E-type transformers with normally balanced secondary windings, the horizontal signal being split into components to produce the correct direction of movement, the electrical signals controlling hydraulic servo valves and motors causing the feeler to follow the template, and to be followed by a locally-associated cutting tool. The machine may be adjusted for two-dimensional automatic control, or for manual control. The machine comprises a work-table 21, Fig. 1, horizontally movable on a bed 20 in one direction, and a column 22 mounting a cross-slide 23 movable in the perpendicular horizontal direction, the cross-slide carrying a tool head 25 and tool 27 capable of vertical movement. Adjustably associated with the tool 27 is a feeler 34, and on the worktable 21 are mounted the work 28 and the template 35. When the machine is set for manual control, the work-table is moved by a hand-wheel 40, horizontal movement of the cross-slide 23 is produced by a hand wheel 41, and vertical movement of the tool 27 by hand wheel 42 or 43. A control-box 45 may be operated to convert the machine to automatic operation, when the manual control hand wheels are made ineffective. Hydraulic-feed mechanism.-The servomotor for the table 21 comprises an hydraulic cylinder 50, Fig. 2, containing a piston 51 bolted to the table and moved by admitting fluid to either end of the cylinder. The cross-slide 23 is similarly moved by an hydraulic servomotor comprising a cylinder 53 and piston 54 attached to the cross-slide, and vertical movement of the tool head 25 by an hydraulic cylinder 56 attached to the head and having a piston 57 bolted to the cross slide 23. Actuation of the hydraulic servomotors is effected manually or automatically as determined by a selector valve 68 which, as shown, is in the manual control position. The pressures in the two parts of servomotor 50 are determined by a valve 65 whose plunger is operated by a feed-screw 95 bolted to the table 21 and driven by the handwheel 40 when a half-nut 96 is engaged with the screw. Similarly, servomotor 53 is actuated by valve 66 controlled by hand-wheel 41, and motor 56 by valve 67 controlled by hand wheel 42 or 43. Feeler construction and operation.-The feeler 34, Fig. 3, extends from a sleeve 119 in a casing 115, and is attached to a plunger 123 mounted for longitudinal sliding movement on ball bearings 124, 125, and has a lateral extension 127 carrying a soft-iron armature forming part of a differential transformer 164. The top of sleeve 119 has a conical seat for a ball 131, and resting on the ball is a spring-biased sleeve 132 mounted for longitudinal sliding movement on ball bearings 134, 135 and having a lateral extension 138 carrying a soft-iron armature forming part of a differential transformer 146. Thus vertical displacement of the feeler 34 produces a signal from transformer 164 and lateral displacement a signal from transformer 146. A signal from transformer 164 is amplified and phase-rectified by valves, whose anodes are also supplied with a 1000 c.p.s. signal in opposition, to produce a proportional D.C. potential of appropriate-polarity which, after further amplification, causes energization of one or other coil of a servo valve 307, Fig. 2, which controls the vertical servomotor 56, 57. Similarly, transformer 146 operates a servo valve 375 to control an hydraulic motor 376 which, through gearing, rotates the shaft of a resolver comprising a sinecosine potentiometer with two sliders. A D.C. voltage is applied across the two parallel windings, and the voltages at the sliders are the component direction-signals for steering the table and cutter head in the horizontal direction. A further horizontal displacement signal is applied to a second resolver whose two sliders are displaced by 90 degrees with respect to the previous sliders, to produce the component direction signals required to bring the feeler back to its null position. The two pairs of component signals are combined electrically and amplified separately to drive hydraulic servo valves 477, 485 respectively. Facilities are provided for decreasing the component signals when the feeler is subjected to a sudden change in direction.