Motor control system with current limit circuit

Claim 2

An energizing system for an electrical motor in which electrical energy is passed to the motor through a power circuit including at least one semiconductor switch, comprising: a voltage-divider circuit connected to provide a signal related to the motor terminal voltage, a control-amplifier stage, having an output connection connected to regulate operation of the semiconductor switch and thus regulate energization of the motor, and having an input connection coupled to the voltage divider circuit to receive the signal related to the motor terminal voltage, and a current limit stage, including an input circuit connected to receive a control signal related to the level of current flow through the motor armature, an output circuit coupled to said voltage-divider circuit, and a constant current circuit connected to pass a substantially constant current over said output circuit through a portion of the voltage-divider circuit to modify the motor terminal voltage signal passed from the voltage-divider circuit to said control-amplifier stage.

Claim 3

A motor-energizing system as claimed in claim 1 in which said current limit stage further comprises an operation amplifier having first and second input terminals and an output terminal, means for coupling the output terminal of said operational amplifier to regulate conduction of the constant current circuit, means including said input circuit for applying said control signal to the first input terminal of the operational amplifier, which control signal is of a given polarity, and means for supplying a reference signal, of a polarity opposite of said given polarity, which is summed with said control signal to provide a resultant sum signal which is applied to said first input terminal, such that the resultant sum signal changes polarity when the control signal indicates the motor current has exceeded the level indicated by the reference signal.

Claim 4

A motor-energizing system as claimed in claim 2, in which said constant current circuit includes a first transistor connected to operate as a constant current source.

Claim 5

A motor-energizing system as claimed in claim 3 and further comprising a second transistor, coupled between the output terminal of the operational amplifier and the constant current source, for increasing the conduction of said constant current source as the output signal of the operational amplifier indicates the motor armature current exceeds the level required to enter the current limit mode of operation.

Claim 6

A motor-energizing system as claimed in claim 3 and further comprising circuit means coupled in the emitter-collector circuit of the first transistor to complete a path for current flow through at least said portion of the voltage-divider circuit, the emitter-collector path of the first transistor and the circuit means, and a diode, coupled between the base and the emitter of said first transistor, To insure that the constant current source transistor is just at the point of conduction to provide rapid system operation.

Claim 7

A motor-energizing system as claimed in claim 4 and further comprising a feedback potentiometer, coupled between the emitter of said second transistor and the second input connection of the operational amplifier, to adjust the amount of feedback in the current limit stage and correspondingly regulate the slope of the motor current-speed characteristic beyond the point at which the system enters the current limit mode.

Claim 8

A motor-energizing system as claimed in claim 3 and further comprising a feedback circuit, including a resistor and a capacitor, coupled between the first input connection of the operational amplifier and a common connection between the first and second transistors.

Claim 9

An energizing system for a DC electrical motor in which electrical energy is passed to the motor through a power circuit which includes a plurality of SCR''s regulated by at least one firing circuit, comprising: a voltage divider circuit connected to provide a signal related to the motor terminal voltage, a control-amplifier stage, having an output circuit connected to regulate operation of the firing circuit and thus regulate energization of the motor, and having an input circuit coupled to the voltage-divider circuit to receive the motor terminal voltage signal, and a current limit stage, including an operational amplifier having first and second input connections and an output connection, a transistor connected as a constant current source for increasing its conduction in response to a signal provided by said operational amplifier to provide a substantially constant current flow over an output conductor and through at least a portion of said voltage divider circuit to modify the motor terminal voltage signal passed to the control-amplifier stage, means coupled to said first input connection of the operational amplifier for providing a control signal of given polarity and related to the level of motor armature current flow, and means including a potentiometer for providing an adjustable reference signal of a polarity opposite said given polarity to said first input connection of the operational amplifier, such that an increase of the motor armature current above a level represented by the setting of said potentiometer effects a transition of the operational amplifier output signal and places the system in the current limit mode of operation.

Claim 10

An energizing system for a DC electrical motor in which electrical energy is passed to the motor through a power circuit which includes a plurality of SCR''s regulated by at least one firing circuit, comprising: a voltage divider circuit connected to provide a signal related to the motor terminal voltage, a control-amplifier stage, having an output circuit connected to regulate operation of the firing circuit and thus regulate energization of the motor, and having an input circuit coupled to the voltage-divider circuit to receive the motor terminal voltage signal, and a current limit stage, including an operational amplifier having first and second input connections and an output connection, a transistor connected as a constant current source for increasing its conduction in response to a signal provided by said operational amplifier to provide a substantially constant current flow over an output conductor and through at least a portion of said voltage divider circuit to modify the motor terminal voltage signal passed to the control-amplifier stage, means coupled to said first input connection of the operational amplifier for providing a control signal of given polarity and related to the level of motor armature current flow, and means including a potentiometer for providing an adjustable reference signal of a polarity opposite said given polarity to said first input connection of the operational amplifier, such that an increase of the motor armature current above a level represented by the setting of said potentiometer effects a transition of the operational amplifier output signal and places the system in the current limit mode of operation.