Stepping motor controller

A stepping motor controller comprising;

• current sensors that detect respective motor currents of corresponding phases,
• an inverter containing a current control means for feeding stepped currents to motor windings,
• a coordinate transformer that transforms said motor currents in a fixed coordinates system detected by said current sensors into currents in a first rotational coordinates system composed of a d axis being in the direction of a magnetic flux direction and a q axis being perpendicular to said d axis,
• an angle calculator that transforms an external command pulse for causing said motor to make a stepping rotation into a command angle,
• wherein a second rotational coordinates system composed of a dp axis and a qp axis being perpendicular to said dp axis is determined from said command angle,
• a command current on said dp axis is set to be a value corresponding to a motor current amplitude,
• another command current on said qp axis is set to be zero,
• said motor current is projected on said dp axis and said qp axis,
• said motor current is controlled so as to make a component of said motor current on said dp axis coincide with said command current on said dp axis and to make a component on said qp axis coincide with said another command current on said qp axis, and
• said motor is caused to make a stepping rotation by rotating said second rotational coordinates system by a predetermined angle at each time when said external command pulse is applied.