Patent GB-1179447-A (GB)
Title: Power Press Acceleration Control System
Inventor: HEIBERGER FRANCIS E
IPC: B30B15/14
Filed: 1967-06-02
Abstract: 1,179,447. Controlling clutches. DANLY MACHINE CORP. 2 June, 1967, No. 25528/67. Heading F2L. [Also in Divisions B3 and G3] The acceleration control system of a power press comprising a press drive motor 28 driving a flywheel 41 through an electrically responsive coupling 43, e.g. an eddy current clutch, which flywheel drives a press drive shaft 46 through a main clutch 47, e.g. pneumatically operated, comprises a signal supply 107 providing a speed control signal having a magnitude representative of the desired flywheel speed, a speed control circuit 101 responsive to the control signal for energizing the coupling 43 to transmit sufficient torque to rotate the flywheel at the desired speed, and control signal regulating means operable prior to the engagement of the main clutch 47 to increase the magnitude of the control signal to a maximum predetermined press starting speed level and, subsequent to the engagement of the clutch 47, to increase the magnitude of the control signal to a higher press operating speed level, the rate of change of the magnitude of the control signal subsequent to the engagement of the clutch 47 being sufficiently low that the press motor 28 is capable of providing a press acceleration related to that rate of change. 1st Embodiment. General.-As shown in Figs. 3 and 4, two presses A and B having their own speed control circuits 101, 102 are supplied with speed control voltage by a variable auto transformer 107, the primary circuit of which is coupled across an A.C. input between lines L 1  and L 2 , and its variable secondary is coupled between a slide 108 and line L 2  in parallel with the primary windings 105, 106 of two identical transformers 103, 104 forming the inputs of the respective speed control circuits for the presses A and B. Press control system.-To control the maximum starting speed, acceleration, and operating speed of presses A and B, the voltage and rate of change of voltage developed across the secondary of transformer 107 by moving the slide 108 are regulated by a reversible D.C. motor 109 connected to drive the slide 108, a comparator circuit 111 providing an output signal to indicate that a change in the magnitude of the speed control signal is required, a gate circuit 112 activated in response to the comparator output signal, and a motor energization circuit 113 which responds to activation of the gate circuit 112 to energize the motor 109 to drive the slide 108 in the required direction. The comparator circuit 111 includes a transformer 121, the primary winding thereof being in parallel with the primary windings 105, 106 so that the voltage across the secondary winding 123 is proportional to the instantaneous voltage applied to the speed control circuits 101, 102. The proportional voltage (the proportionality is herein considered to be unity) is converted to a D.C. voltage by a bridge rectifier 124 and smoothed by a filter capacitor 125 and dropped across a resistor 126. A second transformer 131 has its primary winding 132 connected between lines L 1 , L 2  and its secondary winding across a bridge rectifier 134, the D.C. output of which is similarly smoothed by a capacitor 135 and dropped across a resistor 136. The comparator circuit also includes two potentiometers, a press starting speed potentiometer 137 and a press operating speed potentiometer 138, the manual settings of the slides 141 and 142 of which establish the press starting and operating speed reference voltages. Prior to the depression of a press starting pushbutton 114 closing contacts S 9  to engage clutch 47, contacts S 1 -S 4  are closed, and contacts S 5 -S 8  are open so that, if the voltage dropped across resistor 126 is greater than the press starting speed reference voltage developed across potentiometer 137, a path including diodes 145, 146 and contacts S 1  is poled to provide firing bias to the gate-cathode circuit of a silicon controlled rectifier 147, and the signal applied to the speed control circuits 101, 102 is automatically reduced to a safer starting speed level. Similarly, subsequent to the engagement of clutch 47, when contacts S 1 -S 4  are open and contacts S 5 -S 8  are closed, if the comparison, signal across resistor 126 is less than the operating speed reference voltage provided by potentiometer 138, a path including diodes 151, 152 and contact S 5  is poled to provide firing bias to the controlled rectifier 147. On firing of the rectifier 147, a relay ACC connected in the anode-cathode circuit is energized and a normally open contact set ACC 1  in the motor energization circuit 113 is closed to connect a bridge rectifier 161 in the circuit 113, the connection being made through either an auto transformer 162 and contacts S 2  before the clutch 47 is engaged or through an auto transformer 164 and contacts S 6  subsequent to the clutch 47 being engaged, the current flowing in the respective direction through the armature of the motor 109 to drive the slide 108 in the required direction. The rate of decrease or increase in the speed control signal is determined by the manual setting of slides 163, 165. Thus, substantially the full capacity of the motor 28 may be used since the rate of change of the speed control voltage, i.e. the press acceleration from starting speed to operating speed, is substantially constant. The speed control circuits for each press A and B, e.g. 101, each comprise a two stage amplifier. Fig. 4, the first stage of which is a conventional magnetic amplifier 200, and the second stage 221 a conventional solid state power amplifier. The speed control signal from the supply of Fig. 3 is converted to a proportional D.C. voltage by a bridge rectifier 201 and smoothed by a capacitor 202 before being applied across the control input or speed voltage input 203 of the magnetic amplifier, a trimming rheostat 205 providing compensation for any irregularities between the transformers 103, 104. Bias for the amplifier is provided by a transformer 207, the primary winding of which is connected across lines L 1 , L 2  and the secondary winding is coupled to the bias input 209 of the amplifier 200 through a rectifier 211 and a lines level setting rheostat 212. The reference or phase voltage input 214 of the amplifier is connected through leads 215, 216 to receive the phase correction of voltage output of a discriminator which forms part of a synchronizing circuit for the presses (to be described later). The second amplifier stage 221 comprises a controlled bridge rectifier comprising two silicon, controlled rectifiers 222, 223 and uncontrolled rectifiers 225, 226, the anodecathode or firing circuit of 222 being connected between the magnetic amplifier output terminals 231, 232, the firing circuit of 223 being connected across the output terminals 233, 234 of amplifier 200, the output of amplifier 221 being fed to the eddy current clutch slip rings 44, 45. As the outputs from the magnetic amplifier increase, the amplifier 221 is biased for conduction for an increasing portion of the positive half-cycle of the signal between lines L 1 , L 2  so that as the speed control signal applied to the amplifier 200 increases, a larger current is permitted to flow through the eddy current clutch 43 and clutch slippage is reduced as more speed is required. A conventional phase error detection system, Fig. 5 (not shown), is used to maintain synchro-. nization between the various presses in the line. The system comprises a transmit-receive synchro arrangement for each of the presses A and B. The rotors of the transmitting synchros TA, TB are energized by the signal between lines L 1 ,L 2 , and the stator windings of the transmitters are connected in star formation with the similarly connected stator windings of the receivers, any lead or lag between the rotor of a receiving synchro and its corresponding transmitting synchro rotor resulting in a signal across the receiving rotor. The rotors of the receiving synchros are coupled for rotation with the drives of presses A and B, whilst, to provide a reference phase, the transmitter rotors TA, TB are rotated by a motor 243 at the instantaneous line speed as determined by the speed control signal fed to circuits 101, 102. The armature current for motor 243 which is directly proportional to the speed control signal is provided by a transformer 270, the primary winding 271 being connected in parallel with primary windings of transformers 103, 104, and the secondary winding 272 providing an input signal for a motor speed control circuit of the two stage amplifier type shown in Fig. 4, the reference voltage being fixed, and the motor is chosen so that for any given speed control signal, the speed of the motor substantially equals the output speed of the clutch 43. The rotor windings of the receiver synchros are connected across the inputs of respective discriminators, the outputs of which are applied across the terminals 215, 216 of their corresponding magnetic amplifier 200 as described. Each discriminator. Fig. 6 (not shown), comprises an input transformer (281) having a centre tapped secondary winding (283) feeding the base-emitter input circuits of a pair of transistors (284), (285). The collectoremitter output circuits of the transistors are energized through respective load resistors (286), (287) and reverse current blocking protective diodes (288), (289) by the voltage developed across the secondary winding of a transformer 292, the primary winding of which is energized by the same signal applied to the rotor winding of the respective transmitting synchros. When the rotors of the transmitting and receiving synchros are out of phase, depending on whether there is a lag or lead, one of the transistors conducts producing a D.C. voltage across its respective resistor, which is applied to the magnetic amplifier to regulate the slippage of clutch 43 accordingly. 2nd Embodiment. General.-In Fig.