Patent GB-1384391-A (GB)
Title: Synchronized operation of three or more cyclically operating machines
IPC: H02P5/50
Filed: 1971-12-02
Abstract: 1384391 Control of several A.C. motors AIDA ENG Ltd 2 Dec 1971 [21 Dec 1970] 55889/71 Heading H2J [Also in Division G3] Three or more separately driven, cyclically operating machines are synchronized by periodically detecting the relative phases of the machines and utilizing the machine which is then lagging in phase relative to all of the others as a reference, all those machines whose phase difference relative to the lagging machine is greater than a predetermined value being slowed relative to the lagging machine. In the described embodiment, the machines are presses M-1, M-2, M-3 and a blank feeder M-4, each being provided with a respective pulse generator A-1, A-2, A-3, A-4 producing a predetermined number of pulses during each cycle of operation of a machine part such as a crank and with a respective signal generator J-1, J-2, J-3, J-4 producing an output signal at an equivalent first predetermined point in the operating cycle of each machine part. These generators are connected as shown to an arrangement of flip-flops C-1 ... C-4 and N-1 ... N-4, resistors R-1 ... R-4, AND, NOT and OR gates AND-1 ... AND-4, NOT-1 ... NOT-4 and  OR-1 ... OR-4, OR-P, OR-K and counters D-1 ... D-4. In a typical cycle of operation from rest, electric motors driving the machines are started simultaneously so that the machines move together from an equivalent second predetermined point relative to the first, the resultant pulses produced by generators A-1 ... A-4 being isolated from the counters D-1 ... D-4 by short-circuiting of resistors R-1 ... R-4 and the state of the logic gates and flip-flops. As the three fastest machines reach their first predetermined points, the appropriate ones of the generators J-1 ... J-4 allow the outputs of the corresponding generators A-1 ... A-4 to reach the (+) inputs of the respective counters D-1 ... D-4 by operation of the relevant gates and flip-flops, the attainment by the third fastest machine of its first predetermined point removing the short-circuit from resistors R-1 ... R-4 and actuating an appropriate one of the flip-flops N-1 ... N-4 to pass to gates OR-P and OR-K the output of that one of the generators A-1 ... A-4 associated with the fourth or slowest machine, which is thus identified. When its associated signal generator J-1 ... J-4 is actuated by the fourth machine reaching its first predetermined point, the gate OR-K passes the output of its associated generator A-1 ... A-4 to the (-) inputs of all the counters D-1 ... D-4, which then produce respective outputs corresponding to the difference between the count accumulated since the associated generator J-1 ... J-4 was actuated and the pulses from the generator A-1 ... A-4 of the slowest machine. According to the values of the outputs of the counters associated with the three fastest machines, the respective driving motor is left energized or de-energized and allowed to coast or braked, for example by supplying D.C. to the motor if it is of A.C. type. If any counter output exceeds a predetermined high value all four motors are stopped. Except for the latter action, the various motor control operations are initiated and terminated by the counter output during each cycle of the machine parts, the various components in Fig. 1 being cleared or reset at the end of the cycle irrespective of whether the control operation has achieved its desired effect. A scanning circuit L scans the flip-flops C-1 ... C-4 with a high speed pulse train from oscillator OSC to enable the system to correctly identify the lagging machine even when the time differential of the signals from any two of the generators J-1 ... J-4 is less than the period of one pulse of the generators A-1 ... A-4.