Patent GB-1324445-A (GB)
Title: Electromagnetic actuator having regulation of the force on the armature
IPC: G05F7/00
Filed: 1971-04-20
Abstract: 1324445 Hydraulic motor control circuits VOITH GETRIEBE KG 20 April 1971 [22 April 1970] 10296/71 Heading F1P [Also in Divisions G3 and H1] An electromagnetic actuator 1 comprises a coil 2 surrounded by iron cladding 3, 3<SP>1</SP> and an armature 4 axially movable therein in opposition to a projecting polepiece 5 against a spring 7; a fieldstrength sensitive resistor 8 being fixed to the face of 5 and connected in a resistor bridge circuit 8, 14, 15, 16 energized from source 11 and having an adjustable slider 165 between 15, 16. The voltages at bridge points 148, 165 are compared over in series resistors 23, 24 at inputs + E, - E of amplifier V and are initially equal, so that a fall of resistance of 8 produces a rise of voltage at 148 and at the amplifier output to open transistor T 1  and to drive power transistor T 2  to excite coil 2 from the source and impel the armature against spring 7. Buildup of field increases resistance of 8 and reduces voltage at 148, so that the amplifier output becomes increasingly negative related to zero, and closes transistor T 1  and power transistor T 2  to de-energize coil 2. Bypass diode D across the coil allows exponential decay of the resultant field, spring 7 expands, the flux in 8 is reduced, and consequently coil 2 is again energized, to initiate a continuous squarewave on-off pulsation of the coil energization whose frequency is dependent on the difference between the voltage drop across 8 and the pre-set value set by sliders 65, so that the field is stabilized at a pre-set value. In a modification, Fig. 2, resistors 15, 16 are fixed and the amplifier receives the voltage from point 148 of the bridge in opposition to voltage from a tacho generator, or from a generator of e.g. a sinusoid or ramp function on receipt of e.g. a trigger signal. The actuator operates the piston 4<SP>1</SP> of a hydraulic limit valve having control lands 18, 19 restricting the volumetric flow of pump 20; the pressure fluid being connected to, the inner end face of the armature through bores 4<SP>1</SP> to act against the pull-in thereof. A reducing pin 7<SP>1</SP> on core 5 slides pressure tightly in bore 4<SP>1</SP> to limit the pull in, and the system operates to control and limit the delivery pressure. In a modification, Fig. 3 (not shown) the armature field excites a Hall plate to generate a flux voltage to excite the amplifier in opposition to a pre-set voltage, and to energize or deenergize the field through a series diode to produce similar pulsating energization, and a function voltage generator may furnish the Hall plate excitation. In a further modification, Fig.4 (not shown) an auxiliary winding of the field coil may produce voltage proportional to armature flux change which is integrated by a capacitance feedback amplifier to represent total field flux. The field coil itself represented by inductance in series with resistance may produce across the latter a direct voltage superimposed on a voltage representing the rate of change of the field, which is CR differentiated to reverse DC and double integrated in capacitance feedback amplifiers to produce voltage dependent on total field flux, which as before is composed with a pre-set or function voltage to control the pulsating field energization, Fig. 5 (not shown).