Patent GB-1041289-A (GB)
Title: Web length control device for a web-receiving apparatus such as a rotary printing press
IPC: B65H23/188
Filed: 1964-08-20
Abstract: 1,041,289. Feeding webs. SMITH R.P.M. CORPORATION. Aug. 20, 1964 [Sept. 11, 1963; July 31, 1964], No. 34121/64. Heading B6B. [Also in Division G3] Apparatus for causing a constant length of web to be fed per machine cycle to a machine, such as a rotary printing machine, comprises a member rotated by the web movement, and a member driven directly from the main drive-shaft, means being provided to sense relative variations in the speed of the members caused by small variations in the demand of the machine due, for example, to the use of a web of a different thickness, and thereby to control a variable transmission gear between the main shaft and a web-feeding couple so that the speed of the couple is decreased if the web demand increases and vice versa. In one embodiment, the web 4 is fed from a roll 2, Fig. 1, over a dancer roller 9 which controls a constant tension brake mechanism 11 of known kind, then passes (a) between a wheel 34, and roller 35, rotated by the web, (b) a web feeding and releasing arrangement 95 comprising two driven rollers 90, 91 and a co-operating roller 94, and (c) finally to the printing machine 23. A motor 28 drives the printing machine 23, its shaft 29 being coupled also to the input shaft of a variablespeed transmission unit 60. The output shaft 62 of the unit 60 drives the rollers 90, 91. The input shaft drives through toothed belts and gearing 70 ... 75, Fig. 4, a shaft 76 carrying a disc 78 with two apertures 79, 80. The disc 78 makes one revolution for each ten revolutions of the input shaft. The wheel 34 rotated by the web has a circumference exactly equal to that of the printing cylinders 26 of the machine and is mounted on a shaft 44 carried by spring-pressed arms 47. A disc 52 with a cut-away part 54 is fixed in the shaft 44. The discs 78, 52 are closely adjacent to one another and the size of the cut-away part 54 is such that when it is situated centrally between the two apertures 79, 80 in the disc 78 the apertures are just covered by the adjacent parts of the disc 52. Two light sources 82, 83 are situated so that once during every revolution of disc 78 they are aligned with the apertures 79, 80, and if the position of cutaway part 54 permits, the light can pass through one of the apertures to impinge on a corresponding photo-electric cell 84. In operation, if the wheel 34 is being rotated by the web at the same speed as it is desired the printing cylinders should draw in the web, the disc 78 once at each revolution thereof will have the apertures 79, 80 opposite the cut-away part 54 but they will be obscured by the disc 52. At the same time the rollers 90, 91, 94 will be releasing the web at the same rate as it is being taken by the printing machine. If, however, due for example to a thicker web being used, the printing cylinders 26 start to take a longer length of web per revolution, the speed of wheel 52 will increase relatively to that of disc 78, and at intervals the aperture 80 will be unobscured and its corresponding photo-electric cell energized. This through a relay circuit causes a reversible motor 63 to be energized to alter the transmission unit so that rollers 90, 91 are driven at a slower speed to cause the length of web taken by the cylinders to remain constant. Similarly if the cylinders 26 begin to take less web, aperture 79 will pass light at intervals and energize its cell so as to cause the motor 63 to rotate in the reverse direction and speed up the rollers 90, 91. In one modified construction, a web-driven wheel corresponding to wheel 34 drives another wheel at the same peripheral speed, and the latter wheel applies a mark to the web at predetermined intervals. Just beyond where the mark is applied a pair of photo-electric sensing devices spaced lengthwise of the web are provided. Pulses produced by a counter mechanism actuated by the drive-shaft of the printing machine are applied to the sensing devices at timed intervals. If the web is being fed at the desired length for each printing- cylinder rotation, the mark is situated between the sensing devices at the time the pulses are applied thereto and neither device is energized. Should, however, the printing press demand increase or decrease, one or other of the sensing devices will sense a mark and cause actuation of the motor 63 controlling the variable transmission unit 60 so as to decrease or increase the speed of the rollers 90, 91. In a further modified construction two adjacent discs similar to discs 52, 78 are driven respectively from the wheel 34 and the input shaft to the transmission unit 60. In this case, however, the two discs are normally rotating at the same speed, i.e. if the web is being fed at the desired length for each printing-cylinder rotation. One of the discs carries a single contact and the other carries two contacts, the single contact being midway between the two contacts during normal working. If, however, web demand by the printing machine increases or decreases the single contact on the one disc engages one or other of the two contacts on the other disc and through slip-rings on the discs and a suitable circuit operates the motor 63 to effect the necessary adjustment of the variable transmission unit 60.