GB607790A - Improvements in web tensioning apparatus - Google Patents

Abstract

607,790. Fluid-pressure servomotor-control systems. WOOD NEWSPAPER MACHINERY CORPORATION. Nov. 17, 1945, No. 30937. Convention date, Feb. 26. [Class 135] A fluid-pressure servomotor system for maintaining a substantially constant tension in a web being fed to a web-consuming apparatus, e.g. a roll of paper to a printing press, comprises a movable web engaging roller biassed by fluid pressure to press against the web to control the tension therein, which tension reacts on a pilot valve to vary the pressure of fluid supplied to a fluid link in a web-retarding endless belt which contacts the web. As shown, the web 8, Fig. 1, passes from a roll 5 over an idler roller 9 and a floating roller 10 carried by pivoted arms 11 to the printing press. The roller 10 is biassed through a link 14 by a diaphragm 13 subjected to air pressure in a line 16 which may be adjusted by a manuallyactuated control unit C to adjust the web tension to any desired value. The arms 11 carry a second link 39 attached to a lever 38 to which is secured a cam 35 whose co-operating roller coacts with the spindle 34 of a pilot valve 31 supplied with compressed air from a main 29, via a pressure regulating valve 30 and line 32, to vary the outlet pressure therefrom. The latter pressure acts on the upper surface of the diaphragm 45 of a spring-biassed boost valve 40 to control the flow of compressed air from the pressure-regulating valve 30 to a cylinder 26 to operate a piston 25 whose rod 27 carries a pulley 21 over which passes an endless belt 17 in frictional contact with the web roll 5 and driven in the same direction as, and at a slightly lower speed than, the web roll by a chain-and-sprocket drive 23. The boost valve 40 is controlled by a solenoidactuated valve 42 whose solenoid 53 is operated by a switch 54 which, in one position, energizes the solenoid to open the valve 42 whilst the press is running, and in another position closes a press stopping circuit and de-energizes the solenoid 53 to close the valve 42 and reduce the frictional forces on the web. To apply the maximum possible retarding force to the web roll in an emergency, such as the breaking of a web roll, a solenoid-actuated shuttle lift valve 48 is positioned in the line between the boost valve 40 and the cylinder 26 which, under normal working conditions, opens communication between these members, but in an emergency by the operation of a switch 51 energizes a solenoid 49 to cut out the boost valve 40 and open the cylinder 26 to the maximum possible regulated pressure, and at the same time closes a press stopping circuit. To ensure -smooth working, a double-acting dashpot 56 is connected to the arms 11 by a link and lever 58, 57. In operation, as the roll 5 decreases in size, the frictional retarding force of the belt 17 decreases with consequent reduction in the web tension which results in the arms 11 being moved in an anticlockwise direction which moves the cam 35 to operate the spindle 34 to increase the outlet pressure from the pilot valve 31 which increases the load on the piston 25 and hence the retarding force in the web to readjust the tension therein to its desired value. If for any reason the web tension should increase, the arms 11 will move clockwise to operate the cam 35 to decrease the outlet pressure from the pilot valve and hence reduce the web retarding force and again readjust the web tension to its desired value.