Importance

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Abstract

An open loop control device and method are provided for stepping motors. By energizing a motor so that the rotor motion is the result of a revolving field which is of piecewise constant speed and uniform field strength, the rotor can be brought to a stop at any desired position. Such position can be the same as or different from the conventional full-increment or half-increment detent positions of the motor. This control method and device guarantee that there is no oscillation when the rotor reaches its final position. The field windings are energized in sequential manner and such that the resultant field takes into account the magnetic characteristics of the motor. The revolving field can be initially adapted to produce, in one case, an angular velocity of half the desired speed for purposes of accelerating the rotor. After one-half of a resonant period has elapsed, the rotor is accelerated to the desired speed. At this time, the speed of the field is doubled and the rotor fully synchronized therewith. When the rotor is to be stopped, the field velocity is switched to an angular velocity equivalent to that of the acceleration velocity which is half the constant speed velocity and the rotor therefore overshoots. Half of a resonant time period later, the rotating field is stopped and the rotor comes to a standstill without oscillation since the field is precisely aligned with the rotor at the instant of stopping. Also, a method is provided for establishing current forms or patterns for the windings of a multi-phase stepping motor to provide the uniform revolving field taking into account the magnetic characteristics of the motor. This method comprises, for each of the pairs of windings which are sequentially effective to drive the rotor of the stepping motor, the steps of driving one winding of the pair with maximum running current and measuring rotor stiffness at the resultant detent position, and thereafter passing a relatively small current through the other winding of the pair and reducing the current through the first winding to displace the rotor to a position which is a fraction of a distance towards the next detent position. These two currents are adjusted to obtain a rotor stiffness equal to the first rotor stiffness while maintaining rotor position. Subsequent steps involve sequentially displacing the rotor and repeating the process to obtain a current curve which will generate the aforesaid revolving field with constant velocity and uniform strength despite magnetic characteristics of the components of the stepping motor involved.

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First Claim