GB841682A - Improvements in or relating to machine tools having automatic control equipment - Google Patents

Abstract

841,682. Photo-electric control systems. BIRMINGHAM SMALL ARMS CO. Ltd. Feb. 28, 1956 [March 1, 1955], No. 5988/55. Class 40(3). [Also in Group XXII] A machine tool comprises an interpreting device 13 for a code element, means controlled by the interpreting device to effect relative positioning between tool and work supports 17, 1, the means comprising at least one datum member, 7(5), a co-operating pointer 15 and means for effecting relative movement between them, and means in the interpreting device to initiate relative positioning between the supports to dimensions controlled by the code element only on contact between the pointer and member. The interpreting device 13 is connected via relays and servo-mechanisms to the tool-support 17, to tool-movement measuring devices 9, 11 and via wheatstone bridge circuits 20, including oscillators 23, to the datum members 5, 7. Each measuring device comprises a fixed ruled diffraction grating 27, a movable grating 29 and a photo-electric cell 39 connected via an electric counter to the interpreting device 13. Each datum member includes a transducer 40 connected to one of the circuits 20 and comprising a variable rheostat, the cursor of which is coupled to the datum surface. In operation, the tool 15 is advanced until contact with the datum member 7 causes the transducer to affect the current in its circuit 20, thus exciting the oscillator 23 which sends a signal to the interpreting device 13. The interpreting device signals the withdrawal of the tool 15 and causes the measuring device 9 to be coupled to the support 17. Movement of the grating 29 in the device 9 produces a MoirÚ fringe effect which causes the photo-cell 39 to transmit a series of impulses to the electronic counter which records the tool movement. The tool is then positioned against the datum member 5 and its withdrawal movement recorded. By code-element signals the tool can then be positioned at any distance from the axes represented by the datum members. Before codesignals are applied, the tool may first be returned to a position where the counter registers zero in both co-ordinates. Tool deflection may be compensated by arranging for the oscillators to be actuated only after a predetermined movement of the datum members. Alternatively, the datum surfaces may be hydraulically loaded as in Fig. I, or spring-loaded as in Fig. 4, or the variable resistors 19 and/or the capacitors 21 in the bridge circuits may be pre-set. If the tool is of rotary instead of single-edge type, it is rotated during the setting-up operations, and the datum members then have a ceramic surface to avoid damage thereto or have a freely rotatable surface as on a roller 7a, Fig. 4. Alternatively, a pointer representing the tool may be used for setting up, and may operate a photo-cell instead of making tangible contact with a datum member. The machine may have several tools and the code element may control stopping and starting, and the loading or feeding and discharging of the workpiece. The code element may also control taper and internal turning, boring, planing, or milling operations. The work and/or the tool may be movable.