Patent ID: 7839111

Claim:
A stepper motor control apparatus comprising: condition determination device determining a first condition to satisfy both of equations (1) and (2) below, and a second condition to satisfy an equation (3) below; reference step number calculation device calculating, if the first condition is satisfied, the number of reference steps which is a reference value for a rotational direction and a step amount of a stepper motor as a value larger by one step than the number of reference steps of a previous processing cycle in an approaching direction in which a difference between an angle obtained by accumulating the numbers of reference steps and a target angle of the stepper motor is reduced, calculating, if the second condition is satisfied, the number of reference steps as a value smaller by one step than the number of reference steps of the previous processing cycle in the approaching direction, and calculating, if neither of the first and second conditions is satisfied, the number of reference steps as a value equal to the number of reference steps of the previous processing cycle, for each passage of an update period which satisfies an equation (4) below; (| V ( N− 1)|+1)*(| V ( N− 1)|+2)/2≦|DISTANCE| (1), | V ( N− 1)|< V _MAX (2), | V ( N− 1)|*(| V ( N− 1)|+1)/2>|DISTANCE| (3), t ≧(θ k/a _MAX)^(½) (4), where V(N−1) is number of reference stops of previous processing cycle, DISTANCE is a value obtained by subtracting angle obtained by accumulating numbers of reference steps from target angle of stepper motor and represented by step unit, V_MAX is a maximum step amount which enables rotation of stepper motor at one update period, t is an update period, θk is an angle of one step, a_MAX is maximum response acceleration of stepper motor; and stepper motor driving device rotating, for each passage of the update period, the stepper motor by a step amount indicated by the number of reference steps of a current processing cycle in a direction indicated by the number of reference steps of the current processing cycle.