Patent GB-895924-A (GB)
Title: Improvements in the automatic control of weighing and feeding machines
Inventor: LLOYD ARTHUR KENNETH
IPC: G01G5/00
Filed: 1960-02-10
Abstract: 895,924. Weighing apparatus. IMPERIAL CHEMICAL INDUSTRIES Ltd. Jan. 23, 1961 [Feb. 10, 1960], No. 4750/60. Class 143. An automatic feed weigher comprises (i) a pneumatic measuring device 13, in which air issues from nozzles 17, 18 and impinges on a flat metal strip 14 projecting from the weighing beam 1 whereby relative movement between the beam and the nozzles, resulting in a reduction of free space around the nozzles, causes an increase in back pressure which controls a feeding device 9 to stop the feed at a predetermined pressure, (ii) oil-filled bellows 6 which act on a lever 4 whereby change of pressure in the bellows produces a force which effects displacement of weight counterbalancing means ina direction to restore balance position, a communicating connection maintaining a fixed pressurerelationship between said back pressure and the pressure in the bellows during adjustment, adjustment ceasing when said force balances the force produced by any weight causing departure from the balance position and (iii) means under control of said back pressure to lock the adjustment means so that no further adjustment takes place with a further change in weight. A pneumatic system is thus used to tare the weighing machine as well as to control the feed. The pneumatic circuit, Fig. 1, is shown with the mechanism that operates each valve separate from the valve and the port connections of each valve in the deenergized position. At the end of a weighing cycle, air at 25 lbs. per sq. inch keeps a piston 22 raised with a standard weight W clear of its platform 7. The filled container is removed from the support 8 and the left hand of the beam 1 (as seen in Fig. 1) tilts down. The strip 14 therefore uncovers the holes 17, 18 so that the back pressure in the nozzles 13 is reduced. A new, empty, container is put on the support. The weight-counterbalancing means comprises a spring 3 attached at its lower end to the beam 1 and at its upper end to the lever 4 which is supported at one end by a pivot and at the other end by the bellows 6. A push button is operated and, moving from the Fig. 1 position, vents valves D and B (energized at the end of the last weighing cycle) to atmosphere, causing the bellows 6 to be connected to an oil separator 20 and the lower part of the cylinder 21 to be vented. The system starts to re-balance by oil flowing in or out of the bellows 6 to equalise the pressures in the bellows and in the nozzle device 13, while the piston 22 lowers the weight W on to the platform 7. The left hand side of the beam rises and causes the back pressure in the nozzles 13 to increase. A relay N of known type, having a space divided into two by a diaphragm and operable to cause air to be passed on at a pressure which is at a fixed ratio to the control pressure, operates so that the pressure in the bellows rises and the position of the beam is readjusted until the force due to the bellows balances the downward force of the spring. Any change in the weight of the empty container is thus compensated for variation between certain limits. For tare weights outside those limits the locking device ensures that weighing cannot proceed further. P 1  is a relay which operates above 15 lbs. per sq. inch and P 2  a relay which operates below 16 lbs. per sq. inch and when balance is established and the back pressure is at the predetermined value of 15 lbs. per sq. inch, P 1  and P 2  operate, thus energizing a valve A. The arrival of the piston 22 at its bottom position operates a valve G and establishes connection from the 25 lbs. per sq. inch supply through the ports of P 1 , P 2 , G and A to valve C and also through a restrictor R D  to valves D and B. The valve C remains energized by its own connection to the supply. The operation of the valve B disconnects the bellows 6, which are therefore locked, while D raises the piston 2 and weight W. Also, since B cannot operate without P 1  and P 2 , the apparatus will only accept containers with tare weights within the limits. When the piston 22 reaches its top position, valve F de-energizes valve A but, since valve C remains energized, a valve E causes a relay V, which is similar to the relay N, to operate a sleeve valve 9. This consists of an elastic or compressible tube section 10 surrounded by a rigid tube 11 to form a chamber 12 into which air can be fed under high pressure to compress the sleeve valve and so reduce, and ultimately stop, the flow of material through it. The operation of the sleeve valve is controlled, through the relay V, by the back pressure and when the standard weight W is lifted off the back pressure first falls, allowing the pressure in the sleeve valve 9 to fall and therefore the feed of material to the container 8 to start. As the back pressure increases the compression in the sleeve valve 9 increases, thus reducing the rate of feed to the container. When the predetermined value of 15 lbs. per sq. inch is reached, P 1  is energized, causing A to be de-energized, which in turn causes C to be de-energized through connections A, G and F. E is then vented to atmosphere and the full air supply is fed to the sleeve valve, ensuring a tight shut-off. In modifications, the feed control may include an electric circuit and a vibrating feeder may be used.