Importance

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Abstract

When a stepping motor is driven by supplying to the drive coil of the stepping motor a drive current whose amplitude is periodically increased and attenuated with time in a state that the upper peaks of the current variation are limited to be within set values of current being varied stepwise and in a substantially sinusoidal fashion, the drive current to be fed to the drive coil is controlled such that a waveform of the drive current is configured so as to approximate to a sinusoidal waveform over one period of the waveform. To such a current control, each set value is larger than that obtained from a sinusoidal waveform. The drive current may be attenuated, in each step of the related set value, at a first attenuating rate and a second attenuating rate smaller than the first attenuating rate, the first and second attenuating rates being combined at a ratio of n/m (n: a positive integer, m a positive integer except n). In the latter current control, the drive current is attenuated at a first attenuating rate for a first period of time subsequent to the shifting of one step of a set value to the next or second step of another set value, and the drive current is attenuated at a second attenuating rate, which is smaller than the first attenuating rate, for a second period of time ranging from the end of the first period till the second step shifts to the next step of still another set value.

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First Claim