Patent GB-775765-A (GB)
Title: Electrolytic grinding apparatus
IPC: B23H5/08
Filed: 1954-02-24
Abstract: 775,765. Automatic control systems for electrolytic grinders. NORTON GRINDING WHEEL CO., Ltd. Feb. 24, 1954 [March 16, 1953], No. 5415/54. Class 38 (4). The invention relates to the automatic limitation of load current and control of applied voltage in an electrolytic grinder. The circuit of the work-piece W, Fig. 7, and a single conducting ring CR1 on the grinding wheel is supplied over conductors 104, 105 from the D.C. output of a magnetic amplifier MA2 having its power windings PW energized over three-phase lines P1-P3 from an A.C. source. The biasing windings BW of amplifier MA2 are energized over a resistor R8 from the output of a rectifier bridge RB connected through a transformer T1 and a voltage stabilizer VS across one phase of the A.C. supply, the tapping on resistor R8 being adjusted to bias the amplifier somewhat above cut-off to give a desired output voltage across the load circuit. Inductive windings 106, wound on cores CO, associated with the conductor 104 carrying the D.C. load current, are connected in series with a rectifier bridge RB1 across a transformer T2 energized through stabilizer VS from the A.C. supply. Control windings RW of amplifier MA2 are energized in the same sense as windings BW over a tapped resistor R3 connected across the output of bridge RB1, so that, if an increased load current is called for, the resulting tendency for cores CO to saturate causes a rise in output of bridge RB1 and an increased current in the windings, thereby increasing the output voltage of the amplifier to compensate for the inherent drop due to increased current demand. Control windings CW of amplifier MA2 are energized in opposition to windings BW over conductors 93, 94 from the D.C. output of a second magnetic amplifier MA1 having power windings PW1 supplied from lines P1-P3 and biasing windings BW<SP>1</SP> energized over a resistor R9 from the output of bridge RB, the tapping on resistor R9 being adjusted to bias amplifier MA1 below cut-off in the absence of other control signals. Control windings VW of amplifier MA1 are in series with a voltage reference resistor R8 supplied from the bridge RB, or rectifier UV and the work-wheel interface W-CR1, so that, if the interface voltage exceeds the reference, rectifier UV permits energization of the windings in opposition to that of windings BW1. The resulting output of amplifier MA1 to the windings CW of amplifier MA2 tends to reduce the output of the latter to restore the required interface voltage. Control windings IW of amplifier MA1 are in series with a load-currentreference resistor R7 supplied from the bridge RB, a rectifier UV1 and a resistor R2 supplied from the current-responsive bridge RB1, so that, if the interface current exceeds the reference, rectifier UV1 permits energization of the windings in opposition to that of windings BW1. The resulting output of amplifier MA1 to windings CW of amplifier MA2 tends to reduce the latter's output to and thus reduce the interface current. A load resistor R1 connected across the interface prevents an unduly high open-circuit voltage appearing across the output of amplifier MA2 if the work is removed from the grinding-wheel. In a modification, Fig. 8, a plurality of conducting rings CR2- CR4 coact with the work W, and the interfaces are connected in parallel circuits across the output conductors 104, 105 of amplifier MA2. In order to limit the individual interface currents to safe values, inductive windings 106a-106c, associated with the separate parallel load circuits, are in series with rectifier bridges RB2-RB4 respectively. With a switch SW thrown to the right, the outputs of these bridges across resistors R22-R24 respectively are separately compared with a current reference set on resistor R7, so that, if any interface current exceeds the reference, one of windings IW2-IW4 of amplifier MA1 is energized to modify the output of amplifier MA2 as already described. If the total load current is substantially equally shared between the interfaces, a single inductive winding CO in series with a bridge RB1 may detect this total load current. By throwing switch SW to the left, the output of bridge RB1 across a resistor R2 is compared with a total current reference on resistor R7, so that an excessive current results in the energization of winding IW4 of amplifier MA1. Specification 761,483 is referred to.