Method and apparatus for control of current in a motor winding

Claim 2

In a method for controlling the flow of current in an inductive load to cause the current to follow a certain command waveform having a rapidly decaying portion, comprising the steps of: connecting the inductive load across a power supply for flow of current through the inductive load in a first direction; connecting first and second current modulators in series with said inductive load and on opposite sides of said load, for modulating the flow of current through the inductive load; connecting a first diode in parallel with the series connection of the inductive load and said second current modulator, and in reverse polarity to the first direction of current flow, for allowing the current to circulate through the inductive load and the second current modulator in the first direction when the current flow to the inductive load from the power supply is interrupted by said first current modulator; connecting a second diode in parallel with the series connection of the inductive load and said first current modulator, and in reverse polarity to the first direction of the current flow, for allowing the current to circulate through the inductive load in the first direction, and through the power supply and the first diode in the opposite direction, when the current is interrupted by both said first and second current modulators, whereby the circulating current in said inductive load is caused to decay rapidly; sensing the flow of current through said second current modulator; sensing the flow of current through said first diode; comparing the sensed currents with the command waveform to derive an error signal; controlling said first current modulator in response to the error signal, derived from the comparison of the sensed current flow through said second current modulator so as to cause the modulating current to follow the command waveform; sensing loss of current control when the first current modulator can no longer cause the current through the inductive load to decay rapidly enough to follow the decaying portion of the command waveform; and cutting off the current flow through both of said first and second current modulators in response to sensing loss of current control, to cause the current to circulate through the power supply in the opposite direction, and through the inductive load in the first direction, whereby the current in the inductive load in the first direction is caused to decay rapidly.

Claim 3

The method of claim 1 wherein said first current modulator pulse width modulates the current flow therethrough in response to the error signal.

Claim 4

The method of claim 1 wherein the step of cutting off the current flow through both of said first and second current modulators includes cutting off the current flow through said first current modulator while cyclically interrupting the current flow through said second modulator in response to the error signal derived from a comparison of the sensed flow of current through said first diode.

Claim 5

The method of claim 1 wherein said second current modulator pulse width modulates the current flow therethrough in response to the error signal.

Claim 6

The method of claim 1 wherein the step of sensing loss of current control comprises sensing a loss of modulation of the current flow through the inductive load.

Claim 7

The method of claim 1 wherein the inductive load comprises a winding of a motor.

Claim 8

In a motor-drive circuit for causing the current in the motor winding to follow a certain command waveform having a rapidly decaying portion comprising current supply means for supplying a flow of current in a first direction; a motor winding connected across said current supply means for flow of current from said current supply means through said motor winding for driving said motor; first and second current modulator means connected in series with said motor winding and on opposite side of said winding for modulating the flow of current through said winding; a first diode means connected in parallel with the series connection of said motor winding and said second current modulator means, and in reverse polarity to said first direction of current flow, for allowing current to circulate through said motor winding and said second current modulator means in the first direction when the current flow to said motor winding from said power supply means is interrupted by said first current modulator means; a second diode means connected in parallel with the series connection of said motor winding and said first current modulator means and in reverse polarity to the first direction of current flow for allowing the current to circulate through said motor winding in the first direction, and through said power supply means and said first diode means in the opposite direction, when the current is interrupted by both said first and second current modulator means, whereby the circulating current in said motor winding is caused to decay rapidly; first sensing means for sensing the flow of current through said second current modulator means to derive a first sensed output; comparator means for comparing said first sensed current output with the command waveform to derive a first error signal output; said first current modulator means being responsive to said first error signal output, for causing the current flowing through said motor winding and said second current modulator means to follow the command waveform; control sensing means including means for sensing loss of control over the current in said motor winding and means for producing a loss of control output when said first current modulator means can no longer cause the current through said motor winding, to decay rapidly enough to follow the rapidly decaying portion of the command waveform; and said second current modulator means being responsive to said loss of control output, for modulating current flow therethrough and for causing current to circulate through said motor winding in the first direction, through said second diode, power supply means, and first diode means in the opposite direction, and to cause the circulating current in said motor winding to decay rapidly.

Claim 9

In a motor-drive circuit for causing the current in the motor winding to follow a certain command waveform having a rapidly decaying portion comprising current supply means for supplying a flow of current in a first direction; a motor winding connected across said current supply means for flow of current from said current supply means through said motor winding for driving said motor; first and second current modulator means connected in series with said motor winding and on opposite side of said winding for modulating the flow of current through said winding; a first diode means connected in parallel with the series connection of said motor winding and said second current modulator means, and in reverse polarity to said first direction of current flow, for allowing current to circulate through said motor winding and said second current modulator means in the first direction when the current flow to said motor winding from said power supply means is interrupted by said first current modulator means; a second diode means connected in parallel with the series connection of said motor winding and said first current modulator means and in reverse polarity to the first direction of current flow for allowing the current to circulate through said motor winding in the first direction, and through said power supply means and said first diode means in the opposite direction, when the current is interrupted by both said first and second current modulator means, whereby the circulating current in said motor winding is caused to decay rapidly; first sensing means for sensing the flow of current through said second current modulator means to derive a first sensed output; comparator means for comparing said first sensed current output with the command waveform to derive a first error signal output; said first current modulator means being responsive to said first error signal output, for causing the current flowing through said motor winding and said second current modulator means to follow the command waveform; control sensing means including means for sensing loss of control over the current in said motor winding and means for producing a loss of control output when said first current modulator means can no longer cause the current through said motor winding, to decay rapidly enough to follow the rapidly decaying portion of the command waveform; and said second current modulator means being responsive to said loss of control output, for modulating current flow therethrough and for causing current to circulate through said motor winding in the first direction, through said second diode, power supply means, and first diode means in the opposite direction, and to cause the circulating current in said motor winding to decay rapidly.

Claim 10

The motor driver circuit of claim 7 including: second sensing means for sensing the flow of current through said first diode means to derive a second sensing output; comparator means for comparing the command waveform with the second sensing output to derive a second error signal; and said second current modulator means being responsive to said second error signal for modulating the current flow therethrough so as to cause the current flow through said motor winding to follow the command waveform in the rapidly decaying portion thereof.

Claim 11

The motor drive circuit of claim 7 wherein said first and second current modulator means are pulse width modulators.

Claim 12

The motor drive circuit of claim 7 wherein said control sensing means further includes an activity sensor means for sensing the current modulation produced by said first current modulator means, and when the sensed current modulation drops below a certain threshold level said activity sensor means produces the loss of control output.