Analog stepping motor control system

Claim 1

In combination, an electric motor of the stepping type having a stator with a set of discrete poles and a rotor having a set of discrete poles with electrical windings on one of said sets of poles so that said rotor has a plurality of natural detent positions in which said rotor poles are aligned with poles of said stator or are between poles of said stator in a symmetrical relationship therewith when various of said windings are energized, means for energizing said windings to apply torque on said rotor in a foreward direction when supplied with a forward energization signal, means for energizing said windings to apply torque on said rotor in a reverse direction when supplied with a reverse energization signal, a first emitter driven by said rotor effective to produce output pulses as said rotor moves through successive increments each of Z* after passing through its desired or home position in the forward direction and producing the same output pulses at the same rotor positions as the rotor moves back in the reverse direction, a second emitter driven by said rotor effective to produce a gradually changing output signal as the rotor rotates having nodes which are substantially farther apart than Z* with rotor rotation, a first control means under the control of the output pulses of said first emitter for providing said reverse energization signal so as to thereby apply torque on said rotor in the reverse direction with constant average currents in said windings when said rotor passes through its home position moving in the forward direction until the point of maximum oscillation of the rotor and the control means including counting means under the control of the output pulses of said first emitter so as to maintain the reverse energization signal and the corresponding constant average currents in said windings producing reverse rotor torque until the rotor returns to a reverse torque termination point which is between said point of maximum oscillation and said home position, said first control means including means effective under the action of said counting means at a forward torque initiating point of rotor rotation lying between said point of maximum oscillation of the rotor and said home position for providing said forward energization signal and thereby applying torque on said rotor in the forward direction with corresponding constant average currents in said windings as said rotor is moving back in the reverse direction from said point of maximum oscillation toward home position. second control means under the control of the gradually changing output signal of said second emitter effective to modulate the currents in said windings while said forward energization signal is applied so as to provide a forward torque on said rotor tending to move the rotor to its home position With said currents in the windings being so modulated that they are greater for greater spacing of said rotor with respect to its home position and are less as the rotor is closer to its home position, and means for switching from said first control means to said second control means under the action of said counting means when said rotor is closer to its said home position than said forward torque initiating point of rotor rotation.