Patent GB-647029-A (GB)
Title: Improvements in or relating to indicating devices
Inventor: MOLINS DESMOND WALTER
IPC: G01G23/32
Filed: 1948-07-22
Abstract: 647,029. Weighing apparatus. MOLINS MACHINE CO., Ltd. July 22. 1948, No. 19652. [Class 143] [Also in Group XL(b)] The angular position of a moving member is indicated by reflecting light from a mirror moving with the member to a screen, and a light sensitive device is arranged to control a signalling device when the member is in a particular position. The invention is described with reference to indicating the position of the weighbeam of mechanism for weighing out measured quantities of tobacco for packing. Tobacco on the tray 11 Fig. 1 is fed by the operator into a scale pan 1. Behind the pan is a translucent screen on which a horizontal line of light travels up and down indicating the weight. When the line is between predetermined limits one or other of a pair of photo-cells is activated to illuminate with a distinctive colour the part of the screen on which the line of light is located. The operator then presses a switch pad 4 and the scale pan is tilted and emptied. The weighbeam 15 (Figs. 2 and 3) is suspended on a taut wire 16 and is damped by a copper loop 28 moving between the poles of an adjustable magnet 31. One or more leaf springs 55 may be provided pressing the weighbeam away from the fixed structure so that it starts to move before the pan has the correct weight in it. A conical spring may serve the same purpose. A horizontal beam of light from a projector 50 passes on to a mirror 27 pivoting with the beam, is reflected to a fixed mirror 38, back to mirror 27, to a mirror 37 at the rear of the casing and finally to the back of a translucent screen 3 so that as the weighbeam pivots a line of light moves up and down the screen. A certain zone of the screen within which the line of light must lie if the weight is to fall within the desired degree of tolerance is indicated by lines 48 (Fig. 2) and is illuminated by coloured lamps 52 when the beam of light reaches it. This is accomplished by a pair of photo-electric cells to which light is reflected by a pair of prisms 76 situated beside the translucent screen and crossed by the same beam of light. Timing and pan emptying mechanism.- A continuously driven cam 102 (Figs. 21 and 22) is followed by a roller 108 pinned on the arm of a lever 110 the end of which is formed as a toothed quadrant and engages a gear wheel 114. Each time the roller of the lever 110 rides into a depression on the cam 102 wheel 114 is rotated and drives shaft 87 through a safety spring clutch thereby emptying the pan. The roller however is normally prevented from entering the depression and is only permitted to do so when the energization of a magnet 138 removes armature 134 from the path of a member 138 on the quadrant. A further shaft 94 driven by a pin 123 which is urged against the quadrant arm by a spring 122 lifts a shaft on which the pan is supported and clamps it in inverted V-bearings prior to tilting. Shaft 101 also drives through helical gearing a pointer in an instrument set in the face of the operator's tray, to indicate the position of cam 102. A further cam shaft operates two contact sets at times suitably related to the emptying period. Optical system for photo-cells.-The light projector is shown dotted at 50 in Fig. 2. The filament of a lamp 40 is imaged by a condensing lens on to a slit and then re- Bected by a prism 47 on to the moving mirror 27. A section through the light sensitive cell housing is shown in Fig. 14. This housing is situated beside the translucent screen so that it is traversed by the horizontal beam of light. When the beam is in the selected zone it enters the slit 76 and is reflected by either prism 71 or 72 to photo-cell 69 or 70. The position of these prisms is adjustable by a screw 73 carrying an eccentric spigot which moves the prism carrier. Circuit arrangements.-When the weight on the pan is within the required tolerances, one of the photo-cells 70, 69 is illuminated and the anode relay 60, 61 of the associated pentode pulls up and lights lamps 52 associated with the coloured zone on the indicating screen. The operator then depresses the switch-actuating pad, operating contact 143 to energise 62 which locks up. Shortly afterwards, in normal circumstances, cam operated contact 140 changes over temporarily to actuate counter 58 and, if relay 60 is still actuated, indicating that the weight is substantially exact, counter 59. Contact 139 also is changed over shortly before 140 to energize magnet 138 which allows the cam mechanism to empty the pan. If the switch pad is actuated when the weight is not within the required tolerances or when the contact 140 is in its metering position, 62 is not actuated, the counters are not operated and the scale pan is not emptied. Contact 139 remains off normal for the whole of the emptying period but contact 140 is restored shortly after its beginning. In consequence, if the switch pad is operated late, 62 may operate and 138 may be energized when the cam follower is over the depression in the emptying cam. In these circumstances the magnet is unable to attract its armature because the latch member 135, Fig. 22, is forced against the end of the armature by spring 113 and emptying does not take place. Relay 62 remains locked up, however, at the end of the emptying period and the pan is emptied normally without a further operation of the switch pad when the cam comes round again. If 62 is not operated when 139 changes over, a magnet 147 stops the feed for the wrapping paper. An additional counter magnet 149 is operated by each rotation of the cam shaft.