Patent GB-895887-A (GB)
Title: Improvements in the automatic control of weighing and feeding machines
Inventor: LLOYD ARTHUR KENNETH
IPC: G01G13/00
Filed: 1960-02-10
Abstract: 895,887. Weighing apparatus. IMPERIAL CHEMICAL INDUSTRIES Ltd. Jan. 23, 1961 [Feb. 10, 1960], No. 4751/60. 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) adjusting means comprising a piston 26 carrying the nozzles 17, 18 and movable in a cylinder 25, pressure in the upper part of the cylinder being maintained constant and pressure in the lower part varying with said back pressure whereby the nozzles 17, 18 and the flat metal strip 14 are altered in position to restore the beam and the nozzles to a zero position and offset any weight carried by the weighing machine, (iii) locking means to prevent further changes in pressure in the lower part -of the cylinder 25 when the piston 26 is at rest after adjustment. A, pneumatic system is thus used to tare the weighing machine as well as to control the feed. The weighing beam 1 carries a support 8 for a container .into which material can be fed from the device 9 and on the same side of the fulcrum 2 are a spring 3 which functions as counteracting mechanism and a platform 7 for a standard weight W. Air is supplied to the upper part of the cylinder 25 through a restrictor R 2  and maintained at constant pressure by a vent through a restrictor R 4 . At the operation of a push button, shown in Fig. 1, valves D and B are vented and also the lower part of a cylinder 21, the consequent descent of the piston 22 thus lowering the weight W on to the -platform 7. The valve B, when de-energized, connects the lower part of the cylinder 25 to a relay N. This is of known construction, having a space divided 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, the effect thus being that the pressure below the piston 26 varies according to the position of the beam, since the control pressure is governed by the action of the pneumatic measuring device 13. If there is any change in tare weight when a new container is placed on the support 8 the beam will be displaced from zero and the back pressure in the device 13 will be greater or less than the pressure above the piston 26 according to whether the tare weight has increased or decreased. The piston 26 will therefore move, carrying the nozzles 17, 18 nearer to, or further from, the strip 14, and so on moving until the back pressure equals the pressure above the piston 26. The pressure below the piston 26 is then at the correct value to operate precision relays P 1 , P 2  since, with the constant pressure at 15 lbs. per sq. inch,. P 1  -operates at pressures above 15 lbs. per sq. inch and P 2  operates at pressures below 16 lbs. per sq. inch. As a result, valve A is operated. With the piston 22 at the bottom of its stroke a switch G is operated so that air is fed through the ports of relays P 1 , P 2  and valves G, A to a valve C and, through a restrictor R D  to valves D and B. This operation of valve B introduces a pressure below the piston 26 equal to that above it (15 lbs. per sq. inch) and therefore locks it in position. The operation of the valve D introduces air pressure in the bottom of the cylinder 21 and the weight W is lifted, whereupon the opposite end of the beam falls and the beam remains tilted because the cylinder 25 is now disconnected from the relay N, consequent on the last operation of the valve B. Operation of the valve C also energizes a valve E, at which the operation of the sleeve valve 9 is controlled by the back pressure in the device 13, via the relay N and a similar relay V. When the back pressure reaches the pre-set value of 15 lbs. per sq. inch the relay P 1  is energized, causing the valve A, and in turn the valve C, to be de-energized, whereupon the valve E is vented and full pressure is impressed on the sleeve valve 9, ensuring a tight shut-off of the feed. When the filled container is removed, the back pressure falls, causing the relay P 1  to be de-energized and the pneumatic system to be restored to its condition at the beginning of the weighing cycle. In modifications, the air from the nozzles in the pneumatic measuring device may impinge directly on the weighing beam; the feed control may include an electric circuit, and a vibrating feeder may be used.