Motor armature current limit system

Claim 2

A control system for a motor having an armature, said control system comprising means combining a control reference voltage and a speed reference voltage to provide a control voltage of selectable magnitude and polarity, means responsive to the magnitude and polarity of an operating voltage to transmit a corresponding current through the armature, current limit means responsive to a predetermined value of said control voltage to produce a current limit voltage having a polarity opposite the polarity of said control voltage and a magnitude substantially equal to the amount by which the magnitude of said control voltage exceeds said predetermined value, and means to combine said control voltage and said current limit voltage to produce said operating voltage, whereby current limit is provided for the armature at stand-still and all speeds of the motor.

Claim 3

A control system as in claim 1 wherein said current limit means comprises first and second signal inverting amplifier means having input and output terminals, negative biasing means for applying a predetermined negative biasing voltage to the input terminal of said first amplifier means to produce a positive amplifier output, positive biasing means for applying a predetermined positive biasing voltage to the input terminal of said second amplifier means to produce a negative amplifier output, a first clamping means for limiting the positive output of said first amplifier means, a second clamping means for limiting the negative output of said second amplifier means, and a first input means for applying said control voltage to the input terminals of said first and second amplifier means.

Claim 4

A control system as in claim 2 wherein each of said first and second amplifier means has a feedback resistor and wherein said first clamping means comprises a unidirectional current conduction means connected in parallel with said first feedback resistor and said second clamping means comprises a unidirectional current conduction means connected in parallel with said second feedback resistor.

Claim 5

A control system as in claim 2 including tachometer means coupled to the armature to produce said speed reference voltage, and wherein said current limit means includes a second input means to apply said speed reference voltage to the input terminals of said first and second amplifier means.

Claim 6

A control system as in claim 4 wherein the system provides motoring and plugging modes for said motor, and wherein said current limit means includes speed reference adjustment means to permit independent adjustment for said speed reference voltage for each of said motoring and plugging modes.

Claim 7

A control system as in claim 5 wherein said speed reference adjustment means comprises first and second adjustable resistance means, said first adjustable resistance means being connected to the input terminal of said first amplifier means through a first unidirectional current conduction means and to the input terminal of said second amplifier means through a second unidirectional current conduction means, said second adjustable resistance means being connected to the input terminal of said first amplifier means through a third unidirectional current conduction means and to the input terminal of said second amplifier means througH a fourth unidirectional current conduction means, and wherein said first and fourth unidirectional current conduction means are poled to transmit one polarity of said speed reference voltage and said second and third unidirectional current conduction means are poled to transmit the other polarity of said speed reference voltage.

Claim 8

A control system as in claim 2 wherein each of said negative and positive biasing means includes adjustable resistance means.