Patent GB-771052-A (GB)
Title: Improvements in and relating to weighing equipment
Inventor: KENNAWAY ALEXANDER
IPC: G01G13/02
Filed: 1952-02-18
Abstract: 771,052. Electric indicating systems. IMPERIAL CHEMICAL INDUSTRIES, Ltd. Feb. 18, 1953 [Feb. 18, 1952; March 21, 1952; Dec. 8, 1952], Nos. 4221/52, 7339/52 and 31068/52. Class 40 (1). [Also in Group XVIII] Weighing-equipment automatically adjusts itself to give a zero reading when it comes to rest with a container on the weighing platform. Any weight subsequently added to the container is indicated as the net weight. The gross and tare weights may also be indicated. The equipment may control an automatic feed whereby a container may be fed with a predetermined weight of material. When a container is placed on a weighing table 10, Fig. 1, a pointer 11, carried by a driving shaft, indicates the gross weight on a fixed scale 12. An adjustable scale 13 is coupled to the shaft and is carried round with the pointer. The coupling is released when the equipment reaches equilibrium and any further weight added to the container drives the pointer alone. The net weight is indicated on scale 13, the gross weight on scale 12 and the tare weight on scale 12 against the zero of 13. In an alternative arrangement, Fig. 2, the pointer 22 is coupled to the driving shaft 23 when the weighing table 20 comes to rest carrying the container. Material is fed to the container when the pointer and the shaft are coupled. The pointer engages contacts 24a, 24, respectively to change the feed from coarse to fine and to stop the feed. Two pointers may be used. The driving shaft may be coupled to a moving scale or a pointer by a magnetic clutch or by a follow-up system comprising a self-balancing Wheatstone bridge or three-phase servomotors, which also detects equilibrium. The follow-up system may detect equilibrium without driving any parts. In addition to or in place of the pointers and scales, counters may be mechanically coupled to the equipment during a weighing operation. The counters may carry type to print the weights. The equipment may generate electrical pulses, say one for each 1/10 lb., the weight being registered by pulse counters. A circuit for controlling equipment like that shown in Fig. 2 comprises three relays A, B, C, Fig 5. A clutch between the pointer and the driving shaft is controlled by a circuit between terminal 66, 73. Terminals 61, 62 connected to the rotor of the follower in a circuit including terminals 69, 70 receive a signal depending upon the lack of coincidence between follower and transmitter. A contact 64 is momentarily closed when the container is placed on the platform, relay A pulls up, starts the servomotor by connecting terminals 67, 68 and is held by the signal on terminals 61, 62. At equilibrium, the signal on 61, 62 disappears, A falls back, terminals 65, 71 are connected in a coarse feed control circuit and the clutch control circuit 66, 73 is completed. When the pointer brushes contact 76 (24a in Fig. 2), relay B operates and a fine feed circuit is completed over terminal 72. Finally, when. the pointer brushes contact 77 (24 in Fig. 2), relay C operates, the feed is stopped and the clutch is slipped. The pointer is returned to zero by a spring when the container is removed. Red and amber indicating lights are included in the coarse and fine feed circuits. Indicating lamps 74, 75 are white and green. In a modification (Fig. 6, not shown), the servo follower drives the scale 13 of Fig. 1 and is cut out at equilibrium. The transmitter is driven by the shaft carrying pointer 11. Printed records of gross, net and tare weights are provided by the machine shown in Figs. 7 to 9. Material is fed over a shaker platform 124 into a drum 121. When a manual switch is operated, the machine movements are transmitted to an indicator 127 by a servo system including a transmitter 125, a follower 126, a motor 132 and an induction generator 133. The motor 132 may be clutched to gross, tare and net weight counters 134, 135, 136. On the fixed scale 127, pointer 129 follows the drive but 128 does not start until a clutch operates after taring. Coarse feed starts and contacts 130, 131 later engage 128 to change to fine feed and then to stop the feed. The printing mechanism operates to print the weights registered by the counters. The circuit of the clutch which operates the net weight pointer 128 opens at contact 139, Fig. 8, when the pointer returns to the 1 lb. mark and the pointer is then returned to zero by a spring 138. The spring carries a roller 140 which engages a notch 141 in the disc 137. When a container is placed on the platform 120, a platform switch changes over contacts 151, 152, Fig. 9, and relay H operates. Relay I follows and remains operated until the container is removed. Relays J, N are normally operated, the latter operating the gross weight counter clutch over terminal 161. At equilibrium, relays H and J fall back and relay K operates and holds over terminal 164 which is connected to the contact 139 (Fig. 8). Clutch 162 now couples the net weight pointer 128 to the drive and coarse feeding starts. Contacts 153, 154 control the change from coarse to fine feed and stop the feed as described for Fig. 5, relays L, M operating as the contacts are closed. Relay N is tripped by M. The printer is operated in a circuit over terminals 158, 163. Clutches are operated to record tare and net weights over terminals 159, 160 and front and back contacts respectively of relay J which falls back as described after taring. Pulse counters, instead of clutches, may be connected to terminals 159, 160, 161 if contact N2 is connected to a pulse generator driven by the weighing machine. As the weights are printed, the indicator 127 and the clutch 162 may be dispensed with. The contacts 153, 154 may be replaced by contacts in the impulse counters. Indicator lamps are provided as before. Impulse generators. Impulses may be transmitted by means of a brush and an armature with alternate conducting and non-conducting segments. Alternatively, a magnetic tape with alternately magnetized and non-magnetized strips may be driven past a conductor. A disc or a cylinder with alternate opaque and transparent strips may interrupt a beam of light directed on a photo-electric cell. In each case the number of impulses is proportional to the weight to be registered. As described, equilibrium is detected when the lag between the pointer and the follow-up disappear. Equilibrium may also be detected electronically. Pulses from the weighing machine are fed from 216, Fig. 12, to a valve 210 and are repeated to the counter by a relay 212. The pulses repeated by 210 also build up a potential on the grid of 211 to keep it conductive so long as the interval between successive pulses is less than, say, 3 seconds. Relay 214 is then equivalent to relays A, Fig. 5, and H, Fig. 9. In another arrangement, a metallic disc 220, Fig. 13, driven by the weighing machine rotates between the poles of a magnet 221 carrying a light pointer 224 and pivoted at 222. Eddy currents in 220 displace the magnet from its normal position of equilibrium. Return to the position of equilibrium is detected photo-electrically. Hydraulic and pneumatic arrangements of detecting equilibrium are described.