Patent GB-725199-A (GB)
Title: Electro-optical measuring, testing or grading apparatus
Inventor: MILLS JOHN PENROSE
IPC: B07C5/16
Filed: 1953-04-13
Abstract: 725,199. Photo-electric control system. BRITISH TIMKEN, Ltd. April 13, 1953, No. 9945/53. Class 40 (3). In a device for operating one of a number of controls in response to the degree of movement of a member, the member is arranged to deflect a light beam, a cyclical scanning device being provided to permit the passage of the beam to a photo-cell at a point in the scanning cycle dependent on beam deflection, a switch member operative in synchronism with the scanning member to render successively each of the controls responsive to the photo-cell so that depending on beam deflection the appropriate cell is actuated. The invention is described with reference to sorting gudgeon pins into a number of boxes according to their diameter and to plotting the temperature-time curve of a furnace by means of a large number of pins each marking a particular temperature on a moving chart. As shown gudgeon pins 2 are placed separately under a gauging bar 7 by a pushing member 3, this bar being arranged to rotate a mirror 9 joined to a pivoted lever 9 so as to deflect a light beam from a source 11 through the periphery of a rotating chopping plate 41 on to a fixed inclined mirror 17, thence to a curved mirror 18 and on to a photo-electric cell 19. Fixed mirror 17 is situated in the centre of a rotating scanning drum 21 in the curved face of which are helically arranged apertures 24. Thus the extent of beam deflection determines the aperture of the scanning drum through which the beam passes to the photocell. Rotating in synchronism with the scanning drum is a rotating switch arm 32. Photocell 19 feeds an amplifier 31 and the output of the amplifier is connected by the rotating arm to each of a number of relays 35 in turn each associated with a magnet 36. Thus photo-cell 19 when energized by the light beam operates the magnet with which it is instantaneously associated by the switch arm and raises a flap on one of a number of receptacles 5. Pusher 3 then rolls the gudgeon pin over the flaps so that it falls into the appropriate open box. In the device for plotting temperature of a furnace (Fig. 7, not shown) a thermocouple inside the furnace positions the moving element of a moving-coil meter, this element carrying a mirror. Instead of magnets 36 operating flaps each magnet is associated with a key which presses an inked band into contact with a continuously moving chart driven by a synchronous motor. Circuits (Fig. 3).-An A.C. amplifier may be used for the photo-cell output since the light beam has been chopped by toothed wheel 41 the teeth of which are so shaped as to modulate the light beam sinusoidally. The amplifier consists of three resistance-capacity coupled stages comprising a pentode 42 and double triode 46. The bias voltage applied to the cathode of the left-hand triode of valve 46 is such that the valve is cut off unless the light reaching the cell is at least 50 per cent of the area of the beam. This is to prevent operating of two magnets when the light beam overlaps two apertures. A filter tuned to the photo-cell chopping frequency is provided to reduce interference. Relays 35 each consists of a thyratron having an anode relay with associated contacts. These thyratrons are provided with a common automatic biasing resistance so that when the first thyratron fires the bias becomes such that no other thyratron can. Thus as the photo receives exactly equal illumination through successive scanning areas only the first thyratron energized is able to fire. The thyratrons are restored by cam-operated contacts 67 in their anode circuits and this cam is also arranged to operate and energize a magnet 16 which moves a shutter 18 out of the light path when the gudgeon pin is being gauged. In the case of the furnace a further magnet is parallelled with magnet 16 to operate a brake to clamp the meter movement when the measurement is being made.