Patent GB-372574-A (GB)
Title: Improvements in and relating to control systems for machines operating upon lengths of material such as paper
IPC: B41F13/02
Filed: 1931-05-29
Abstract: 372,574. Feeding webs. BRITISH THOWSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees) of King, W. R.; 1146, Parkwood Boulevard, Schenectady, New York, U.S.A.) May 29, 1931, No. 15775. Convention date, May 30, 1930. [Class 109 (i).] In a machine having an element adapted to perform an operation such as cutting or printing upon a length of material at predetermined points, control mechanism is provided for correcting any lack of register of the points at which the operation is to be performed including a light-sensitive device co-operating with a light source and control areas upon the material, to pass electric impulses to one or other of two relays, one being actuated thereby to effect an increase in the rate of operation of the machine element and the other to effect a decrease therein, together with means for returning each relay to normal after a time delay determining the amount of the correction, and a contact-making device actuated in accordance with the rate of operation of the machine element and arranged to pass an impulse to the appropriate relay only when the relationship between the machine element and the material varies from the normal by a certain amount. The invention is described with reference to a machine for cutting wrappers from a web 10, which is fed at constant speed to the rotary cutter 15, the speed of which can be varied by an electric circuit including a light-sensitive cell 39, amplifier 52, electric discharge devices 41, 42, and their corresponding coils 43, 44, which when energized attract their respective armatures to close contacts 34 or 35 and thus energize one or other of the differentially-wound field windings 32, 33 to drive a pilot motor 29 in the appropriate direction for varying the speed of the cutter 15 through variable speed gear 24. A rotary switch 40 is provided, fixed to and rotating with the shaft of the cutter 15, and comprises two insulated conducting parts 40a, 40b, and a nonconducting member 67. Two insulated conducting rings 68, 69 make contact respectively with the parts 40a, 40b, and each ring is joined as shown to the grid of one of the electric discharge devices 41, 42, each of which preferably comprises a three-electrode mercury vapour relay, of the type wherein the starting of the arc is controlled by the grid and its interruption is obtained by breaking the output circuit. When a control area 37 enters the beam from the light source 50, the current in the circuit of the cell 39 falls, resulting in an increased potential of the plate of the amplifier 52, which is preferably of the gridcontrolled three-electrode type. This plate is connected by a wire 80 to a contact member 81 bearing as shown upon the rotary switch 40. If the material 10 is in register with the cutter 15 at this instant, the member 81 engages with the insulating strip 67 and neither of the valves 41, 42 is operated. If, however, the material is in advance of the cutter 15, the member 81 makes contact with the part 40a and thence through the conducting ring 68 to the grid 71. The increased potential of the grid 71 starts the current in the anode circuit of the valve 41, thus energizing the coil 44, which attracts its armature, closes the contact 34, and drives the motor 29 in a suitable direction. A similar action takes place if the cutter 15 is in advance of the material, the member 81 then making contact with the part 40b to start a current in the valve 42, whereby the coil 44 is energized to start the motor 29 in the opposite direction. The motor continues to operate until the anode circuit of the valve 41 or 42 is interrupted ; this is effected by a second rotary switch 78 on the shaft of the cutter 15, which is provided with an insulating strip 79. The anode circuits of the valves 41, 42 are both completed through a brush engaging the edge of the disc 78 so that the circuit is broken once in each revolution by the insulating strip 79.