Control circuit
First Claim
1. In a control system for a d.c. motor, said motor having a predetermined electrical time constant and having power input terminals, said control system having a balanced condition and first and second unbalanced conditions one on each side of said balanced condition, the improvement comprising:
- a. means controllable for generating for application to said power input terminals a first drive signal of first polarity and a second drive signal of opposite polarity, said first drive signal tending to drive said motor from said first unbalanced condition toward said balanced condition and said second drive signal tending to drive said motor from said second unbalanced condition toward said balanced condition,
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Accused Products
Abstract
A control system for a d.c. motor, in which a cyclical d.c. drive signal is applied to the motor power input terminals as the system approaches balance. In each cycle, during at least part of the time interval between drive signal application to the motor terminals, a very low impedance (virtually a short circuit) is applied to the motor terminals. These braking pulses provide progressive braking as the motor approaches its balance point, limiting overshoot and ensuring a return without hunting from an overshoot condition to the balance point. As the system nears its deadband range, each braking pulse exceeds in duration the electrical time constant of the motor and constitutes a substantial portion of its associated cycle.
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Citations
14 Claims
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1. In a control system for a d.c. motor, said motor having a predetermined electrical time constant and having power input terminals, said control system having a balanced condition and first and second unbalanced conditions one on each side of said balanced condition, the improvement comprising:
a. means controllable for generating for application to said power input terminals a first drive signal of first polarity and a second drive signal of opposite polarity, said first drive signal tending to drive said motor from said first unbalanced condition toward said balanced condition and said second drive signal tending to drive said motor from said second unbalanced condition toward said balanced condition, - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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2. b. means controllable for applying a low impedance to said power input terminals,
c. means for sensing the condition of said motor and for controlling said means (a) and (b) for applying to said power input terminals, i. when said motor is in said balanced condition, said low impedance for at least a substantial portion of the time when said motor is in said balanced condition, ii. when said motor nears said balanced condition from said first unbalanced condition, a first composite signal comprising cyclically and sequentially said first drive signal and said low impedance, iii. when said motor nears said balanced condition from said second unbalanced condition, a second composite signal comprising cyclically and sequentially said second drive signal and said low impedance, d. each application of said low impedance to said power input terminals constituting a braking interval and the duration of each braking interval being at least as great as said time constant as said motor nears said balanced condition from either of said unbalanced conditions and when said motor is in said balanced condition, e. said means (c) including means for controlling the ratio of the duration of each braking interval to the duration of its associated cycle so that such ratio increases as said motor nears said balanced condition from either unbalanced condition, and so that the duration of each braking interval is a substantial portion of its associated cycle as said motor nears said balanced condition, whereby to brake said motor progressively as it nears said balanced condition.
Specification