GB1281576A - Method and device for braking and stopping a machine - Google Patents

Abstract

1281576 Stopping machines at definite positions BOWE BOHLER & WEBER KG 31 Oct 1969 [6 Nov 1968] 53570/69 Heading F2E A machine 6, Fig. 1, e.g. a feed device for a paper cutter, driven so as to provide repeated conveying cycles, e.g. for a web of paper 8, has its speed reduced gradually from a high value V 1 to a low value V 2 by a coupling 4 shortly before a stopping position is reached, and the period between the moment when a predetermined reduced speed is reached and the moment when the stopping position is reached is indirectly measured and, at the next cycle, the time of switching of the coupling 4 to initiate the speed reduction is automatically changed, if necessary, in such a sense that the next period above referred to corresponds to a desired value, due allowance being made for the ratio of the lower speed to the higher speed. Preferably, the desired value only slightly exceeds zero. As shown, during normal running, coupling 4 is positioned so that motor-driven shaft 3, rotating at the higher speed V 1 , drives shaft 5. A toothed wheel 12 on shaft 5 generates pulses through a magnetic head 13 which are recorded in a counter 14. At time BF, Fig. 2, determined by the counter (the beginning of the " braking interval " BI), when the machine is nearing the end of its cycle, an output signal BI<SP>1</SP>, Fig. 1, is supplied by the counter to a logic element 19 (the signal being maintained to the end of the braking interval); element 19 in turn applies a signal to a ramp generator H, the voltage from which increases with time and is compared in a comparator 22 with the voltage appearing for the time being in a store C (see below). When the rising voltage from generator H equals that in store C, a signal from comparator 22 sets a flip-flop 23 so that coupling 4 is switched, via relay 24 and electromagnet 25, to connect notor-driven shaft 2 rotating at the lower speed V 2 to shaft 5. This occurs at time B, Fig. 2, an interval T 0 after BF. Simultaneously, flip-flop 23 re-sets logic element 19 (and a flip-flop 18), generator H being thereby also re-set. The time elapsing during the ensuing speed reduction (see the inclined part of speed curve 27) is slightly greater than T 1 . At a speed Vg (slightly in excess of V 2 ), the pulses from pulse generator 12, 13, being conveyed from counter 14 to a ramp generator 15, are so infrequent that the sawtooth height in differential amplifier 16 (such height being dependent on pulse spacing in ramp generator 15), is above the minimum value, 17, necessary for provision of an output signal to flip-flop 18. In turn, flip-flop 18 supplies a signal to another logic element 20, which is at this time also receiving the continuous signal BI<SP>1</SP>. In consequence, logic element 20 supplies a signal to the store C, whereupon the voltage in store C begins to increase with time from its initial value. This situation continues until the end of the braking interval, denoted by line BG in Fig. 2, at which instant signal BI<SP>1</SP>, Fig. 1, ceases, and a signal BG<SP>1</SP> from counter 14 passes to a third logic element 21. The time interval from attainment of speed Vg to the emission of signal BG<SP>1</SP> is nearly T 2 , Fig. 2. Logic element 21 is already receiving also an inverted signal from flip-flop 18. In consequence, logic element 21 supplies a signal (opposite in character to that from element 20) to the store C, whereupon the voltage in store C begins to decrease with time, but only briefly, because there soon follows at time VE, Fig. 2, a signal (indicated by VE, Fig. 1), which energizes electromagnet 10 to engage pawl 11 with ratchet wheel 9. Shaft 5 is thereby arrested. The signal VE also re-sets flip-flop 23, so the coupling 4 re-connects shaft 3 to shaft 5. While shaft 5 is at rest there are no signals from counter 14 to elements 20 and 21; store C is of such a character that in the absence of input signals the voltage already generated in it remains constant. The apparatus is now set for another cycle of operation, and the voltage now appearing in store C, which may differ from its value at the beginning of the cycle just completed, will determine the magnitude to which the voltage in generator H will rise when signal BI<SP>1</SP> is next emitted by counter 14. Hence, also, the time of rise is determined, this being the new value of T 0 which may differ from the earlier value. Since the interval BI is constant, T 2 may also have a new value. Curve 27 thus moves towards position 28, Fig. 2, and for reasons of safety T 0 may be increased in small steps, by appropriate choice of capacities and/or charging currents in the circuit, particularly in generator stage H. If the curve is initially to the right of position 28, Fig. 2, it means that the critical speed V g is not reached before signal BG<SP>1</SP> is emitted from counter 14. Thus, no signal is received by store C along path 16, 18, 20, but the signal from 21 initiated by signal BG<SP>1</SP> causes the voltage in store C to fall progressively until time VE. Thus, the new C-voltage is definitely less than formerly, T 0 is correspondingly reduced, and curve 27 is moved leftwards. The value of speed V g may be varied by varying the voltage 17 to be attained at stage 16. Store C may be re-set (e.g. to zero) through line 29; the rate of change in it may be varied by choice of circuit parameters.