Motor control system with control amplifier stage having antiundershoot circuit

Claim 2

An energizing system for an electrical motor in which electrical energy is passed to the motor through a power circuit having at least one semiconductor switch, the motor energization being regulated by a control signal which regulates the conduction time of the semiconductor switch, which system comprises: a control amplifier stage including an operational amplifier having first and second input connections and an output connection; an output conductor coupled between the operational amplifier output connection and the power circuit to regulate the on and off times of the semiconductor switch in accordance with the conduction level of the operational amplifier, means for providing a speed command signal and for applying the speed command signal to one of the operational amplifier input connections, a feedback capacitor coupled between the output conductor and an input connection of the operational amplifier, and means for applying to said output conductor a first bias potential of a level to effect near saturation conduction of the operational amplifier when the speed command signal calls for a very low speed and thus produces a low ontime of the semiconductor switch, and to insure that an increasing speed signal applied to the operational amplifier reduces the conduction level of the operational amplifier toward zero, such that speed reduction signals applied to the operational amplifier will not provide excess charge on the feedback capacitor and produce speed undershoot in the system.

Claim 3

A motor-energizing system as claimed in claim 1 in which said operational amplifier includes an additional connection, and means for applying a second bias potential to said additional connection, to insure that a zero output voltage is provided in the output circuit of the operational amplifier when a zero input signal is applied to both the first and second input connections.

Claim 4

A motor-energizing system as claimed in claim 1 and further comprising a firing circuit coupled to the semiconductor switch to regulate its turn-on time, and a variable semiconductor switch, coupled between the firing circuit and the output conductor which is coupled to the operational amPlifier, which variable semiconductor switch is normally conducting to transfer the control signal to the firing circuit, and means for providing an override signal to said variable semiconductor switch for turning the variable semiconductor switch off and interrupting power transfer to the motor upon sensing a motor overload condition.

Claim 5

An energizing system for a DC motor in which three-phase electrical energy is rectifier in a power circuit including three SCR''s to energize the motor, and in which three firing circuits are connected to regulate the turn-on times of the respective SCR''s in accordance with a received control signal, comprising: a control amplifier stage, including an operational amplifier having first and second input connections and an output connection, and an output conductor coupled between the output connection and the firing circuits to regulate the turn-on times of the SCR''s in accordance with the conduction level of the operational amplifier, means for providing a signal related to the motor terminal voltage to the first input connection of the operational amplifier, means for providing a speed reference signal to the second input connection of the operational amplifier, a feedback capacitor coupled between the output connection and the first input connection of the operational amplifier, and means for applying to said output conductor a first bias voltage of a level to effect near saturation conduction of the operational amplifier when the speed reference signal applied to the second input connection signals a very low speed and thus produces a low ontime of the SCR''s, and when an increase-speed reference signal is applied to the second input connection provides a reduction in the conduction level of the operational amplifier toward zero, such that a reduce speed reference signal applied to the second input connection of the operational amplifier will not produce excess charge on the feedback capacitor with consequent speed undershoot as the motor coasts to the new, lower speed.

Claim 6

An energizing system for a DC motor in which three-phase electrical energy is rectifier in a power circuit including three SCR''s to energize the motor, and in which three firing circuits are connected to regulate the turn-on times of the respective SCR''s in accordance with a received control signal, comprising: a control amplifier stage, including an operational amplifier having first and second input connections and an output connection, and an output conductor coupled between the output connection and the firing circuits to regulate the turn-on times of the SCR''s in accordance with the conduction level of the operational amplifier, means for providing a signal related to the motor terminal voltage to the first input connection of the operational amplifier, means for providing a speed reference signal to the second input connection of the operational amplifier, a feedback capacitor coupled between the output connection and the first input connection of the operational amplifier, and means for applying to said output conductor a first bias voltage of a level to effect near saturation conduction of the operational amplifier when the speed reference signal applied to the second input connection signals a very low speed and thus produces a low ontime of the SCR''s, and when an increase-speed reference signal is applied to the second input connection provides a reduction in the conduction level of the operational amplifier toward zero, such that a reduce speed reference signal applied to the second input connection of the operational amplifier will not produce excess charge on the feedback capacitor with consequent speed undershoot as the motor coasts to the new, lower speed.

Claim 7

A motor-energizing system as claimed in claim 4, in which the means for applying the first bias voltage to the output conductor includes a potentiometer.

Claim 8

A motor-energizing system as claimed in claim 4 in which the operational amplifier includes an additional connection, and means is provided for applying a second bias voltage to this additional connection, to insure that a zero output voltage is provided in the output circuit of the operational amplifier when a zero input signal is applied to both the first and second input connections.

Claim 9

A motor energizing system as claimed in claim 6 in which the means for applying the second bias voltage includes a potentiometer to facilitate adjustment of the operational amplifier circuit.