GB1356014A - Web transport apparatus - Google Patents

Abstract

1356014 Automatic control of line printers; programmed control HONEYWELL INFORMATION SYSTEMS Inc 19 April 1971 [24 March 1970] 20264/71 Headings G3N and G3R Web transport apparatus includes a plurality of web tractors, each driven by a retroactively controlled motor receiving a signal representing a velocity waveform and produced by a controlled function generator. In the system shown, Fig. 2, motors 1, 3 drive shafts for tractors which move a paper web through a line printer under control of a computer 31. The motor shafts are associated with tachometers 25, 27 and position transducers 21, 23 which feed signals to summing junctions 43, 45 for comparison with a velocity demand signal on line 37. The transducers 21, 23 produce a multiple null output for each revolution corresponding to positions of print lines on the paper web. Resistors 63, 65 measure the currents in motors 1, 3 and compare the current difference with a reference valve 71 so as to maintain a constant current difference and thus a desired paper web tension, thus allowing web movement in either direction. In operation, when the motors 1, 3 are stationary, the output on line 37 is zero, and switches 47, 49, 77, which may be FET's, are closed so that the shafts are held at predetermined positions with the web under the desired tension. Because of the tension signal, the transducer 21 is slightly displaced from a null position. The computer now indicates a desired movement of a certain number of print lines. This number is placed in a line counter 83, Fig.3, which produces a first output 79 to open switches 47, 49, 77 and a second output 85 which energizes a voltage level generator 87. A ramp generator 91 now produces a velocity demand signal on line 37 which is followed by motors 1, 3. The sinusoidal outputs from transducers 21, 23 are squared in amplifiers 51, 52, and a comparator 53 adjusts the motor drives to maintain accurate phase synchronism. Each null from transducer 21 is detected by a circuit 82 which decrements the counter 83 thus causing the level of the function generator output to decrease stepwise. When the count reaches zero, switches 47, 49, 77 are closed by output 79 and the shafts move to their desired positions under the control of transducers 21, 23 and the tension control. The ramp generator 91, Fig.4, converts a step voltage input to a series of levels alternating with ramps of controlled slope. With a zero level input, Zener diodes 105, 107, 117, 127 control transistors 121, 131 to conduct equal, constant currents so that no current flows on line 123 and a zero output signal results. If the input voltage level suddenly increases, transistor 131 is cut off, and the current in transistor 121 charges capacitor 135 to produce a steadily increasing output voltage on line 37. When the output voltage reaches the input level, feedback to input amplifier 113 causes transistor 131 to turn on again and the voltage on capacitor 135 remains constant until the input level changes again. Decrease in the input level similarly turns off transistor 121 to discharge capacitor 135 until the new voltage level is reached.