Patent EP-0078745-B1 (EP)
IPC: B23D36/00
Filed: 1982-10-29
Granted: 1985-04-10
Abstract: 1. Electrical control device for a rotary shear (1), the said shear including two rotors, one above the other (3, 5), each bearing a cutting blade (4, 6) and driven at variable speed by an electric motor (9), and the said device including : - a first device (14, 15) for the continuous measurement of the movement of the strip (2) to be cut upstream of the shear and supplying a train of pulses the number of which is proportional to the said movement, - a second device (29) for the continuous measurement of the angular movement of the rotors also supplying a train of pulses the number of which is proportional to the said angular movement, and dimensioned such that the movement of the strip to be cut corresponding with N pulses from the first measuring device is equal to the length of the arc swept by one of the blades for the transmission of N pulses by the said second measuring device, - a device (31) for marking the position of the rotors immediately preceding the cut, - a logic unit such as a microcomputer (69), - an electronic assembly to create, under the control of the said measuring devices, the said marking device and the said logic unit, the speed reference of the electrical power supply device of the motor, characterized in that the said electronic assembly includes : - a first count up-count down device (36) capable of : 1) being initialized at the time of the marking pulse at a value (Lx - Ny) representing, as a number of pulses of the two measuring devices, the difference between the length of the product to be cut and the circumference of one of the rotors, 2) counting, for example positively, the pulses representing the angular movement of the rotors, in the opposite direction, therefore negatively in this example, those representing the movement of the product to be cut, and finally positively or negatively according to switching controlled by the logic unit, pulses called local created by the said logic unit, - a second count up-count down device (42) connected to a digital-analog converter and to a scaling amplifier (67) providing the speed reference of the motor, or a similar equivalent device capable of : 1) being initialized, at a time defined by the logic unit, at a value M representing the inverse value of the acceleration and deceleration to be given to the rotors in order to result in synchronism with the strip at the moment of cutting, and the value of which is fixed by the following rule : if theta 0 is the angle of rotation of the rotors corresponding to the phase preceding the cut, called the synchronization phase, during which the theoretical angular speed of rotation of the rotors and linear speed of movement of the strip are equal, if theta 1 is the angle of rotation of the rotors during the cutting phase, these angles being expressed in degrees, we will take M = Ny (1 -theta 0 + theta 1/360) 2) counting positively or negatively, according to the same switching as that mentioned above and during the periods defined by the logic unit, the pulses representing the movement of the product to be cut, - a regulating device (64) acting, under the control of the logic unit, on the speed reference, and the input of which is representative of the number contained in the said first count up-count down device (36), and in that the logic device divides up one rotation of the rotor, the start point of which is given by the marking pulse, into four successive phases during which : I. during the first phase, called the cutting phase, and for the angle of rotation of the rotors theta 1, the regulating device is rendered inoperative, the first counter is initialized at the value (Lx - Ny), the second counter is maintained at the value M, and the scaling amplifier is adjusted once and for all such that the theoretical angular and linear speeds of the blades and the product are equal, II. during the second phase, during which the motor is uniformly accelerated or decelerated depending on whether the length of the product to be cut is less than or greater than the development of the rotor : a) the regulator being still inoperative and the output voltage of the digital-analog converter then being by construction proportional to the product of the content of the second counter by the speed of movement of the strip, the said second counter is either incremented or decremented, depending on a sign test applied to the first counter at the moment of transition from phase I to phase II, by as many units as the number of pulses created by the device measuring the movement of the product to be cut, such that the motor is subjected to a constant acceleration or deceleration of value proportional to 1/M, b) the first counter is either incremented or decremented by one unit on the appearance of each local pulse delta u transmitted by the logic unit in response to the reception of each product movement pulse delta x according to the following criterion : if x is the number of delta x pulses, not counting the present pulse, that have been presented since the start of the second phase, and if SIGMA u is the number of local pulses created by the logic unit during the same lapse of time, a pulse delta u will be transmitted if 1/2.(x + 1)**2 /M >=SIGMA u, c) if the second counter reaches zero value, it is maintained at that value such that the motor is stopped, and the transmission of local pulses is also stopped, d) the end of the second phase and the start of the next phase is indicated by the logic unit when the first counter reaches zero value, III. during the third phase, everything happens in such a way as to produce total symmetry with the acceleration or deceleration movement produced in phase II, the logic unit transmitting local pulses theoretically maintaining the first counter at zero, the second counter varying in the opposite direction to its variation in phase II, and also the regulator, rendered operative, also acting in such a way as to effectively maintain the first counter at zero ; the end of phase III, and therefore the start of phase IV, is indicated when the number displayed in the second counter has again become equal to M, the movement of the product to be cut observed during the third phase being equal to that made during the second phase, except for the period in which the motor speed reference is null, IV. the fourth and last phase, called the synchronization phase, is identical with the first phase, but in addition the regulator is left in operation and continues to act in such a way as to effectively maintain the first counter at zero.