Patent GB-500104-A (GB)
Title: Improvements in or relating to automatic machines for machining profiled workpieces
IPC: G06K11/02
Filed: 1937-04-26
Abstract: 500,104. Photo - electric control of copying-machines. VIKHMAN, V. April 26, 1937, No. 29732 /36. [Class 40 (iii)] [Also in Group XXXVIII] An automatic machine for working profiled articles, particularly those having a closed outline, in which a photo-electric cell runs along the outline of a pattern and a tool follows the movement of the cell, such movement being composed of longitudinal and transverse feeds of slides to which the cell and the tool are attached, is characterized in that the said feed movements are produced by separate motors or their equivalents, that the transverse feed, produced by the displacement of the point of light of the photo-electric device from or on to the outline, varies the continuous longitudinal feed until the latter ceases entirely when the line runs at right-angles thereto, and that when the outline " doubles on its tracks," in consequence of the resulting excessive displacement of the point of light from or on to the line the directions of the longitudinal and transverse feeds are simultaneously reversed. The invention is applicable to metalworking machines of various types, such as lathes and milling, grinding or shaping machines. Fig. 7 shows a photo-electric device for scanning a pattern in the form of a black line on a white background. The device comprises a casing containing a lamp 24, a photo-electric cell 29, and an optical system for concentrating a beam of light into a point on the margin of the black outline 3 of the pattern, and collecting the light reflected from the pattern, by means of reflecting surfaces 28, 26, so that it falls on the cell 29. Normally, the spot of light lies half on the black line and half on the white area. In the system shown diagrammatically in Fig. 8, in which 3 represents a line drawing of the profile of the article to be machined, and 11 the work on which a milling tool 12 operates, the photo-electric device 1 is attached to a compound rest consisting of a bed slide 4 and a cross slide 5 adapted to slide transversely in guides in the member 4, which is movable longitudinally. The feed of the slide 5 is effected by the axial movement of a screwed rod 18, rotated continuously by a motor 20 through a worm wheel 60, the screw passing through a worm-wheel nut 61 driven by a motor 19. The screw 18 and nut 61 rotate in the same direction, and axial displacement of the screw, if any, depends upon the relative speeds of revolution of the screw and nut. The photo-electric cell 1 controls an amplifying valve 22, the output of which controls the motors 19, 20, in such a way that with a increase in speed of one the speed of the other correspondingly diminishes, this being effected by connecting the armature of one motor and the field winding of the other in parallel in the output circuit of the valve. With this arrangement, when, due to the longitudinal feed of the photo-electric cell, the point of light tends to shift either off the black line or further on to it, the resulting increase or decrease of current in the valve 22 so changes the speed of the motors 19, 20 that the point of light is brought back to the normal position in relation to the line, the tool 12 being moved correspondingly. The feed of the slide 4, whereby the cell &c. are fed longitudinally, is effected by a screwed rod 7, which is rotated in one direction or the other at a constant speed by a worm wheel 56 splined on the rod and driven by a motor 58. The screw passes through a worm-wheel nut 55 which is driven through a mechanical rectifying device 15 by a pinion 59 operated by a rack 62 on the transverse slide. The purpose of the rectifier 15 which comprises two intergeared pawl and ratchet devices, Fig. 13 (not shown), is to make the direction of rotation of the nut 55 unaffected by a change in the direction of rotation of the pinion 69. Electromagnetic reversing clutches 13 are provided in the transmission to the parts 55, 56, for the purpose described below. By means of the arrangement described, any acceleration or retardation of the transverse feed of the photo-electric cell and tool varies the longitudinal feed inversely. When, in tracing the pattern, the spot of light reaches a point where the curve reverses its direction, it tends to move completely away from or on to the line, and the resulting excessive increase or decrease ef illumination of the photo-electric cell causes an excessive change in the output current of the valve 22. This brings into operation one or other of two relays R<1>, R<2>, the closure of a circuit through either of which energizes a solenoid K. The core of the solenoid serves, through a rack and pinion and ratchet device 49, to actuate commutating switches K<1>, K<2>, the switch K<1> operating to the direction of rotation of the motors 19, 20, and the switch K<2> actu, ating the electromagnetic clutches 13 to change the direction of rotation of the wheels 55, 56. Thus, at a point where the outline of the pattern necessitates a change in the direction of longitudinal feed of the cell and tool, this is effected automatically, together with a reversal of the transverse feed. In a modification, Fig. 12 (not shown), the screwed rods 7, 18 are replaced by screws threading into nuts on the slides 4, 5, the screws being rotated by differential gears which replace the worm wheels shown in Fig. 8. A further modification. Fig. 14 (not shown), embodies hydraulic driving means for' the slides carrying the photo-electric cell and the tool. In this case, pistons working in cylinders are connected to the slides, and are operated by the pressure of oil pumped to the cylinders through valves actuated by solenoids, which are operated by an amplifier associated with the photo-electric cell. Specification 474,992 is referred to.