Patent GB-780419-A (GB)
Title: Method and means of recording and reproducing displacements for the control of manufacturing machines
IPC: B23Q35/12
Filed: 1953-01-26
Abstract: 780,419. Photo-electric control systems for machine tools. NEERGAARD, L. E. DE. Jan. 26, 1953, No. 2242/53. Class 40 (3). [Also in Groups XXII, XXXVII and XXXVIII] A record member for controlling the rate and direction of movement of a machine element comprises a parallel sided strip carrying plural spaced parallel lanes, or a circular disc carrying plural spaced concentric lanes, which are distinguished from the background by differential transmissibility to luminous flux; and relative movement is produced between such record member and a photo-electrically sensitive pickup member in the direction of the boundaries of the strip or disc; whereby the direction and rate of angular displacement perpendicularly to such boundaries generates electrical signals corresponding thereto in amplitude and phase sense which are applied to actuate control mechanism responsive thereto for the regulation of the power-actuated movement of a machine tool holder or flame cutter. In a two-dimensional device (Figs. 6, 7, 8) for recording control displacements which are subsequently applied to regulate the movements of a tool, a plane base 12 carries parallel to its surface a spaced tubular longitudinal support 14 along which is slidable a T-member 18 carrying a boom 16 parallel to the surface and at right angles to the support. A stylus 24 following a pattern is carried by a crosshead 23 sliding on the boom which is attached to a flexible non-expansible endless metal metering ribbon 22 surrounding a spring-loaded tension pulley 19 at the boom end and two fixed pulleys on the T-member. A similar but stationary tensioned non-expansible metal metering ribbon 31 is stretched parallel to support 14 and base 12 to traverse parallelly to ribbon 22 the surface of a photographic film 36 which is motor driven at constant speed between reels 28 and 29 fixed to the T-member in a direction at right angles to the metering ribbons, along the centre of each which extends a chain of equally spaced and identical rectangular apertures 35, 35a (Figs. 4, 5) which move across the film surface carried by apertured polished guide 37 as the crosshead and stylus are moved over the pattern in the X and Y directions by motors 38, 39 driving pinions which engage racks 14a, 14b on the boom and support. Staggered light beams are projected respectively through the apertures in ribbons 22-31 to record on the film surface two groups of parallel opaque traces 36 corresponding respectively to the X and Y co-ordinates of stylus movement. When the stylus is stationary in a co-ordinate direction, the traces are disposed parallelly to the film motion while displacement of the stylus produces inclination of the traces to the direction of movement at an angle proportional to the velocity of displacement. For tool control, the recorded film is motor driven at constant speed between reels 28, 29 mounted on the T-member 18 of a similar apparatus wherein the crosshead 23 carries in place of the stylus, e.g. a cutting torch for movement over the work mounted on base 12 in response to variable excitation of motors 38, 39 driving the rack and pinion mechanisms referred to above. The perforated metering ribbons 22, 31 travers the recorded surface at right angles in accordance with the movements of the crosshead and T member, and the film passes over an apertured support 37 (Fig. 9) where light passes respectively through the recorded traces and apertures of the meter ribbons corresponding to the X and Y co-ordinates of motion to illuminate photo-cells 120, 121. Each photo-cell is connected (Fig. 10) to the input of an inverter pentode amplifier 136 whose outputs bias in opposite senses the control grids of pentodes 129, 130 whose anode currents energize the secondaries 133, 134 of transformers whose primaries 127, 128 are connected in series with the shading pole windings 125, 126 of the corresponding motor 38 or 39 whose field 124 is continuously A.C. energized. At a critical illumination of the photo-cell the input is effective to excite both pentodes 129, 130 whereby the shading coils are both de-energized and the motor is stationary, while a rise or fall of the input from the critical value selectively unbalances the anode currents of the pentodes until at full current operation one shading coil is effectively open-circuited while the other is effectively short-circuited so that the motor rotates at full speed in the appropriate direction. When the tool is in coincident at any instant with its required position as recorded, the apertures of the metering ribbon for the appropriate positional co-ordinate are symmetrically disposed with regard to the opaque and transparent portions of the appropriate recorded trace (Figs. 11, 12, not shown), so that 50 per cent of the possible light passes and the illumination is adjusted so that the photo-cell output has the critical value at which the appropriate co-ordinate movement motor is at rest. Deviations of the respective control traces produce corresponding modulations of the illuminations of the photo-cells and of the inputs of the associated motor control amplifiers, so that the speeds and rotational directions of the appropriate motors are controlled to shift the cross-head and tool in X and Y co-ordinates of motion to a position at which the tool position corresponds to that dictated by the record and the apertures of the metering ribbons are disposed synmetrically to the recorded opaque traces, and the motors are at rest. Thus the tool is continuously adjusted in position in accordance with the pre-recorded movements of the stylus over the pattern. The apparatus is extensible to control movements in three dimensions by the use of three groups of recorded traces respectively controlling three separate photo-cell motor control circuits. The perforated metering ribbons may be replaced by transparent discs bearing opaque spirals which are rotated by the appropriate movable member in the path of the light traversing the recording film to the photo-cell, whereby the light is modulated as described according to the deviation between the tool position and the required position dictated by the record. Electric or hydraulic servo systems may be interposed between the photo-electrically controlled motors and the mechanical members to be traversed. The record traces may be imposed by a cutting comb (Figs. 1 to 3, not shown) movable mechanically across the moving film in response to each co-ordinate movement of the stylus whereby groups of plural parallel grooves are impressed on the film in accordance with the stylus movement and are filled with an opaque pigment and covered with a transparent plastic layer.