GB1000659A - Apparatus for controlling tension in a running web - Google Patents

Abstract

1,000,659. Fluid-pressure brakes. CAMERON MACHINE CO. May 22, 1963 [May 23, 1962], No. 20434/63. Heading F2F. [Also in Division B6] Variations in web tension detected by a roller 12 are hydrostatically communicated from a chamber 18 through a pipe 20 to a tensionsensing valve 22, the output of which is directly proportional to variations of the web tension. The air pressure outlet of the tension valve 22 is first modulated in a modulator 26, Fig. 3, to remove transient tension variations, and is then applied to a ratio valve 30, Fig. 4, via pipe 28. The output of the ratio valve, which is inversely proportional to web tension, is applied via a relay 34 and a brake supply valve 38 to the pneumatic applied, spring returned brake 10 acting on a web-roll spindle 10a. In the modulator 26, Fig. 3, unmodulated air enters from the output of the tension valve 22 via a pipe 24 into a chamber 172. A duct 186 allows air to enter a chamber 182 formed between diaphragms 174 and 176 via a throttle valve 188 which has the effect of maintaining a general equality of pressures in chambers 172 and 182 while preventing momentary pressure changes from passing from one chamber to the other. Since diaphragm 176 has a larger area than diaphragm 174, the effect is to bias the flat end of a spacing bolt 178 against a fixed nozzle 184 to control bleed communication of air pressure through the latter. The modulator 26 has at its lower end a chamber 26 S.P. connected to a compressed air supply by a pipe 54. The chamber 26 is connected to a chamber 26 B.P. above a diaphragm 190 by a restricted duct 189. Air may bleed from chamber 26 B.P. through nozzle 184 into a chamber 199 underneath diaphragm 176, thence through a duct 196 to the chamber 26 MP. from which modulated pressure is carried by pipe 28 to the ratio valve 30. The diaphragm 190 comprises two flexible plates 198 and 200 spaced apart by a layer of metal mesh which enables the chamber formed therebetween to vent to atmosphere via ports 204. The lower plate 200 has a valve seat 206 co-operating with a valve element 208. The valve element also includes a ball valve member 210 spring biased against valving passage 214 to control the flow of air from chamber 26 S.P. to chamber 26 M.P. In the modulator 26 the operation of its valve members 208, 210 is controlled by the bleed pressure in chamber 26 B.P. from which chamber bleeding is controlled by the nozzle 184 controlled by diaphragm 176 which in turn is controlled by the modulated pressure in chamber 182. In the ratio valve 30, Fig. 4, the lower part is of similar construction to the lower part of the modulator 26. To maintain the desired brake controlling pressure in chamber 30 B.C.P., air is either vented to atmosphere from the latter through valve seat 228 and port 226 or charged into said chamber by opening of the ball valve 232 to pass higher pressure air from chamber 30 S.P. into chamber 30 B.C.P. and/or by opening of nozzle 224 to pass higher pressure air from chamber 30 B.P. to a chamber 238, thence through ducts 240 and 240a into chamber 30 B.C.P. Flexing of the diaphragm 222 is caused by variation in the throttling effect through nozzle 224 which variations are controlled by a differential between the pressures present in chamber 238 and a resultant or mean of the modulated air pressure derived from the tension sensing valve 22 and a datum or desired tension air pressure separately established as the pressure needed for proper brake operation to maintain a desired web tension. This is achieved with a triple diaphragm assembly comprising diaphragms 242, 244 and 246 rigidly interconnected and spaced by a bolt 248 also serving as a valve element for the nozzle 224. The modulated air pressure from tension sensing valve 22 enters the chamber 252 formed between diaphragms 242 and 246 via pipe 28. The datum pressure enters the chamber 256 formed between diaphragm 244 and 246 via pipe 258. Chamber 238 is in direct contact with the brake control pressure in chamber 30 B.C.P. via ducts 240a and 240. The chamber 254 above the top diaphragm 242 is in direct contact with the brake control pressure via adjustable throttle valve 280 and ducts 240b and 240 and is also connected via a restriction 286 with a chamber 288. This chamber 288 is also connected by restriction 290 and ducts 218c and 218 to chamber 30 S.P. and may vent to atmosphere via duct 295 under control of diaphragm 292. A reset-controlling chamber 294 is in communication with the brake control pressure in chamber 30 B.C.P. via ducts 240 and 240c and adjustable throttle valve 296. The datum pressure is achieved by controlling the pressure in a chamber 268. Air is supplied to the chamber 268 from chamber 30 S.P. via ducts 218 and 218b and restriction 270. Pressure in chamber 268 is under control of diaphragm 266 cooperating with nozzle 272 which bleeds to atmosphere. The chamber above diaphragm 266 is open to atmosphere and the spring 264 applies the necessary force to maintain the datum pressure. This force may be adjusted with the screw knob 262 to alter the datum pressure and therefore alter the set tension in the web. Specification 843,898 is referred to.