Patent GB-1285823-A (GB)
Title: A method of controlling a machine at different working speeds and a control system for performing the method
IPC: B30B13/00
Filed: 1970-06-10
Abstract: 1285823 Timing; date indicating SCHUMAG SCHUMACHER METALLWERKE GmbH 10 June 1970 [18 June 1969] 28145/70 Heading B3P [Also in Division G3] A machine tool capable of operating at different working speeds starts its operating cycle each time a moving element of the machine reaches a particular starting position, the operating cycle having been triggered at an instant preceding the start of the cycle by a fixed time interval called the "machine time constant", this "time constant'' being the same for all working speeds. The trigger signal is initiated by the moving element at an instant in time preceding the generation of that signal and thus during the time period extending from that instant to the commencement of the operating cycle. The moving machine element travels through different distances corresponding to the different working speeds. The control system of the invention causes the time interval extending from the instant of initiation to the generation of the trigger signal to be automatically adjusted in relation to the working speed so that the moving machine element is always at its starting position at the start of the operating cycle. As shown, Fig. 1, the machine 1 is a draw machine having two draw carriages 2, 3 reciprocated by cams 4, 5 driven by a shaft 6, the shaft also carrying arcuate members 7, 8 for actuating, respectively, switches 9, 10. The switches 9, 10 are associated, respectively, with the carriages 2, 3. A step-up gear-box 12 driven by-the shaft 6 rotates a disc 13 having an outer circle of perforations 14 sensed by photo-cells 16<SP>1</SP>, 16<SP>11</SP> and an inner circle of perforations 15 sensed by photocells 17<SP>1</SP>, 17<SP>11</SP>, Fig. 3. The control cycle is initiated by the closing of switch 9 or 10 by the leading end of member 7 or 8 and a desired fixed measuring time interval, e.g. 50 ms., is determined by counting the pulses from the circles 14, 15. When the required number of pulses, e.g. 30, have been counted the trigger signal is generated. The spacing of the perforations 14 is such that the 30 pulses are counted exactly by the end of the fixed measuring time interval of 50 ms. when the machine is operating at its maximum speed and the trigger signal is given at this instant and no pulses are counted from the circle 15. If the machine is operating at a speed lower than the maximum so that 30 pulses are not counted within the fixed measuring time interval, pulses are counted from the circle 15 until the total of 30 is reached when the trigger signal is given. The circle 15 has fewer perforations than the circle 14 in the ratio fmt : tft where fmt is the fixed measuring time of 50 ms. and tft is the total fixed time which equals fmt + the "machine time constant". The machine "time constant" may equal 130 ms. so that tft equals 180 ms. Thus, if circle 14 has 160 holes, circle 15 has Thus, the slower the machine operates so the instant of the trigger signal is progressively delayed whereby the moving machine element is always at its starting position at the beginning of the operating cycle. In the draw machine described this position corresponds to the gripping of the work by jaws on the carriages 2, 3 As shown in Fig. 4, on closure of switch 9 or 10 pulses from photo-cells 16<SP>1</SP>, 16<SP>11</SP> pass through gates 28, 29, 24 or gates 30, 31, 24 to counters 25, 26 which, when 30 pulses are counted, activate an AND gate 32 to produce the trigger signal. Gates 28 ... 31 are NAND gates and gate 24 is a NOR gate. The gates 28, 30 are enabled through a bi-stable stage 21 which also activates an astable stage 22 generating pulses at 100 c./s. These pulses are counted by a counter 23 functioning as a time switch such that at the end of the fixed measuring time interval of 50 ms. a pulse is sent to monostable stage 27 which resets stage 21 and zeroizes the counter. If at the end of the 50 ms. interval 30 pulses have not been sent by the photo-cells 16<SP>1</SP>, 16<SP>11</SP>, pulses from the photo-cells 17<SP>1</SP>, 17<SP>11</SP> are sent via gates 29, 31, 24 to the counters 25, 26 until the total of 30 is attained. The trigger signal from AND gate 32 activates monostable stage 33 which resets bistable stages 34, 35. Through gate 37 for switch 9 and gate 36 for switch 10 the corresponding electromagnetic valve 39 or 38 is excited and the associated carriage 2 or 3 takes over.