Patent GB-918071-A (GB)
IPC: B65H23/08
Abstract: 918,071. Feeding webs. MIEHLE-GOSS-DEXTER Inc. June 2, 1959 [June 23, 1958], No. 18831/59. Class 100 (1). An apparatus for controlling the tension in a web drawn from a supply roll comprises a controller having a control member and means for providing an output signal proportional to the net input force on the member, means responsive to changes in web tension for applying a correspondingly changing first input force to the control member, means for applying a second input force to the member which opposes the first force and which decreases as the rate of change of the output signal increases, and means for applying a braking force to the supply roll which is proportional to the output signal. As shown, braking force is applied to a supply roll 20, Fig. 1, supplying a printing press 21, by a strap 24 fixed at its ends 24a, 24b. The strap 24 is engaged by a roller 26 carried by a piston rod of a pneumatic actuator 28 supplied with air under pressure from a pressure booster 58 connected to an accumulator 59a and a pressure source 54. Web tension is sensed by a roller 30 movements of which about a pivot 32 cause vertical movements of a rod 86 and a control rod 49 of a fluid pressure controller 45 which controls the supply of fluid pressure to the actuator 28 in proportion to displacement of the roller 30 from a reference position, thereby varying the braking action on the supply roll 20. The controller 45 controls the operation of a regulating valve 50 which produces a regulated output pressure proportional to the net input force in a downward direction. The valve 50 has an input chamber 51 supplied with air under pressure through a conduit 52 and an output chamber 55 which supplies the booster 58. Should the controller 45 have a large flow capacity the booster may be omitted. A plunger 61 has a valve 61a co-operating with a valve seat 62 for controlling the flow of air between the chambers 51 and 55. The upward force on the valve 61a is counterbalanced by downward force due to air pressure acting on a flange 64 and a diaphragm 65. A tube 66 supplies air under pressure to a first balancing chamber 68 and through a conduit 69 to a second balancing chamber 70. Pressure in the chambers 68, 70 causes upward and downward forces respectively to act on a piston 71 fixed to the rod 49, the upward force balancing the total downward forces acting on rod 49. A pilot valve 61b, 71a opens after downward movement of the plunger 61, caused by an increase in downward pressure on the rod 49, and pressure in the chamber 68 has lifted the piston 71 slightly. Consequently, air passes into chambers 76 and 78 to raise the plunger 61 and close the valve 61a. Under normal operating conditions, the roller 30 is urged in a counterclockwise direction by a loading cylinder 38 supplied with air under pressure by a load controller 100 generally similar in construction to the controller 45 and supplied through a regulator 116 the setting of which determines the loading of the cylinder 38 and thus the value of web tension to be maintained constant. Rapid fluctuations in web tension, e.g. caused by an out of round supply roll, high rates of acceleration and deceleration, rapid change of supply roll diameter consequent upon a splicing operation are counteracted by increasing the response or " gain " of the controller 45. A chamber 130 closed by diaphragms 131, 132 is connected by a conduit 56 having a restricted orifice to the chamber 55. The flow through the orifice 134 varies directly with the pressure differential on either side thereof, such that the pressure in the chamber 130 equals that in chamber 55 when the output pressure changes slowly, but tends to isolate the chamber from the chamber 55 when that pressure changes rapidly. Thus, the chamber 130 does not assist chamber 68 in restoring equilibrium to the rod 49 in the case of rapid tension fluctuations as in the case of normal fluctuations. By suitably choosing the net effective area of the chambers 68, 70 on which output pressure urges the rod 49 upwardly and the effective area within the chamber 130 upon which output pressure acts upwardly, the relative gain ratio for normal and rapid rates of tension changes may be of the order of 1 : 8. A chamber 140 is connected to a three-way valve 145 controlled by a solenoid 145b energized with the press motor M, such that the plunger 145a takes up the position shown in Fig. 1 to vent the chamber 140 to atmosphere. When the press is jogged or decelerated during an emergency stop, the plunger 145a moves to the Fig. 6 (not shown) position. Thus, air is supplied from a stop regulator 146, Fig. 1, to the chamber 140 thus causing an additional downward force to act on the rod 49. The net input force on the rod 49 is increased, thereby increasing the output force and the pressure supplied by the booster 58 to the actuator 28 which in turn increases braking force on the roll 20. In the event of an emergency stoppage of the press is initiated by opening one of a number of push buttons e.g. S1, Fig. 4 (not shown) to deenergize the motor M, Fig. 1, and close switch S 2 , Fig. 4 (not shown), to energize a stop relay SR through time delay relay contacts TDR1, while contacts SR 2  close to energize solenoids 118a, 170b Fig. 1, of solenoid valves 118, 170 respectively. Energization of solenoid 118a causes plunger 118b to disconnect regulator 116 from load controller 100 and connect stop regulator 146 in its place, thus increasing the pressure acting downwardly on load control rod 104. Consequently, the pressure in conduit 106 leading to cylinder 38 is rapidly increased to increase the loading force applied to the roller 30. Energization of solenoid 170b causes plunger 170a to connect chamber 171 in load controller 100 with conduit 56 to create an upward force on control rod 104 to oppose the downward force exerted in the chamber 115. The solenoids 118a, 170b are maintained energized during stopping by a time delay relay, not shown. Specifications 918,072, 918,073 and 918,074 are referred to. Reference has been directed by the Comptroller to Specification 748,829.