Patent GB-925235-A (GB)
Title: Improvements in or relating to electrically operated automatic platform scales
IPC: G01G13/02
Filed: 1960-04-25
Abstract: 925,235. Weighing-machines. MANUFACTURE DE BETHUNE. April 25, 1960 [April 30, 1959], No. 14438/60. Addition to 880,740. Class 143. [Also in Group XXXVIII] The platform scales of the parent Specification are modified by mounting the transmitter on a disc driven by a motor through a gear-box and electromagnetic clutch, so that the transmitter stator and rotor can be rotated together to bring the pointer(s) to zero. This provides a method of weighing objects in a container which is an alternative to the methods described in the parent Specification, and also facilitates weighing out a predetermined quantity of material. In Fig. 1 the transmitter 39 is fixed to a disc 501 resting on three rollers 503, 504, 505, and can be driven by a gear 607. The transmitter shaft 502 carries a pinion 37 which can be driven from either a high-speed motor 606 or a low-speed motor 32 by means of electromagnetically-operated' flexible gears 35, 36 as in the parent Specification. A similar flexible gear 604 and pinions 601, 602, 605 enable the transmitter casing to be rotated by a knob 619 or the high-speed motor 606 when the appropriate electromagnetic clutches are energized, as described below. Each gear-pinion combination gives a step-up or step-down speed ratio of 2 to 1. The shaft 502 drives a pointer 519 directly, and the pinion 37 carries fingers 512 which engage slots in a further pinion 516 on a concentric hollow shaft 518. The end of the latter is milled to drive a gear 522 on a shaft 523 carrying a further pointer 524 which moves one division on its scale for each revolution of the pointer 519. A further pinion 517 meshing with the pinion 516 drives a printer. The pinion 37 is connected to the transmitter casing by an electromagnetically-operated friction clutch 613 (details in Fig. 2, not shown). Cancelling weight of container.-After the container has been weighed, and is still on the platform, the clutch 613, gear-engagement magnet 609 and brake-release magnet 611 are energized by means not shown. The knob 619 is then turned by hand, and by means of the gear-train 604, 601 and 607 drives the transmitter casing, shaft, and pointers until the latter stand at zero. The clutch and magnets are then de-energized. Alternatively, the motor 606 can be used for this purpose in the following way. Button 620 is pressed to energize relay 621 which locks on via the back contacts 636 and 625 of the unenergized relays 635 and 622 respectively. Contacts 629, 630 and 631 energize the gear-engagement magnets 609, 610, clutch 613 and brake-release magnet 611 respectively, and contact 628 starts the motor 606. Since pointer 524 is not at zero, contacts 627 are closed, and relay 623 is energized, so that contacts 626 are included in the holding circuit of relay 621. When pointer 524 approaches zero one of the contact bushes 627 falls into a notch on the disc 627 and the contacts open, de-energizing relay 623. Pointer 519 carries on its shaft a disc 631 of which one quadrant is conductive and engages a pair of sliding contacts 632a. When the pointer approaches zero these contacts are bridged by the quadrant and energize a relay 622. Contacts 625 then open and break the holding circuit of relay 621, which falls off after a slight delay so that the motor 606 stops with the pointers at zero. The scales can then be used to indicate and print the net weight of articles in the container. Returning pointers to zero for normal weighing. When the container has been removed from the platform the pointers will show a negative value, and are put back to zero by using the knob 619 as above, or by using the motor 606 as follows. The weighing operation of the parent Specification is carried out with nothing on the platform, so that the counterpoise moves back to zero from its position where it balanced the weight of the container. As the pointers pass through zero towards their negative value a second pair of sliding contacts 634a engages the conductive quadrant 631 and energizes relay 633. This holds on at 642, and by its contacts 634 energizes another relay 635, which in turn reverses the connections to the motor 606 by its contacts 637, 638. When the counterpoise and pointers come to rest, button 620 is pressed and motor 606 drives the pointers as before, but in the opposite direction. At the zero point, relay 635 falls off, but this is delayed so that the motor overshoots and is reversed to approach zero always from the same direction. Alternative mounting of transmitter 39 (Fig. 3). The transmitter casing 1039 rotates on ballbearings 1051 in an outer casing 1050, electrical connection being made via slip rings 1043. The casing 1039 is driven by gear 607 on a shaft 1053 which is also mounted on ball-bearings 1052. Further slip rings 1047 carry current to the clutch 613. A gear 1054 on the casing 1039 drives a pinion 1055 and gear 1056 to rotate a scale 1059 on shaft 1057. A sleeve 1060 is driven from this via the reduction gearing shown and carries another scale 1062. The upper part of each scale is visible through a hole in a mask 1066. The end view of this arrangement is in Fig. 4 (not shown). Weighing out predetermined quantity.-The above procedure for setting the pointers to zero is used to bring them to a position representing the desired weight, starting from zero with the container on the platform. The motor 606 is used for approximate setting, and the drive is via the gear-train 605, 604, 602, 35, 37 with clutches 610, 608 and 90 energized. For exact balance, clutches 608, and 90 only are energized, and the gear-train 602, 35, 37 is turned by the knob 619. The casing of the transmitter has remained undriven, so that rotation of the shaft 502 has caused (by normal selsyn action) the counterpoise to advance to a position where it will balance the combined weight of the container and the predetermined amount of contents. The beam has therefore dropped and the armature 702 of an E-type transformer 703 (Fig. 6), is in a central position. Button 704 is now pressed and held, and this supplies A.C. to the primary of the transformer and a meter 705 to the differentially-connected secondaries. As filling of the container proceeds balance will be approached, the beam starts to rise and the meter pointer starts to move, giving a warning to the operator. At balance, the meter pointer reflects light from a lamp 2006 to a photo-cell 2005, which operates a relay 707 to light a warning lamp 708 and stop the feed of material to the container.