Actuator and method of adjusting actuator

1. An actuator comprising:

a shaft capable of reciprocating in an axis direction;

a driver to drive the shaft to reciprocate;

a magnet that reciprocates in synchronization with a reciprocating motion of the shaft;

a magnetic detector to detect magnetic flux densities in two directions of a magnetic field which vary with a reciprocating motion of the magnet;

a storage to store both correction values at three or more correction points which are predetermined in a relative angle range within which the magnet can reciprocate with respect to the magnetic detector, and a function to calculate an interpolated correction value between correction points by using the correction values as parameters; and

an arithmetic operator to calculate a relative angle of the magnet with respect to the magnetic detector by using the magnetic flux densities in the two directions which are detected by the magnetic detector, and to correct a linearity error in the relative angle by using the interpolated correction value calculated from either the correction values or the function which is stored in the storage,

wherein the storage stores, as a correction value at an outermost correction point in the relative angle range, a correction value causing an absolute value of an outermost extremum out of plural extremums in the relative angle range to be equal to or less than an absolute value of another extremum out of the plural extremums which is located inwardly next to the outermost extremum, the plural extremums being exhibited by a linearity error in a relative angle which is corrected by using an interpolated correction value calculated from the function which uses the correction values as parameters.

2. The actuator according to claim 1 , wherein the storage stores, as a correction value at an outermost correction point at one end of the relative angle range, a first correction value causing an absolute value of an outermost extremum out of the plural extremums at the one end of the relative angle range to be equal to or less than an absolute value of another extremum out of the plural extremums which is located inwardly next to the outermost extremum, and also stores, as a correction value at an outermost correction point at another end of the relative angle range, a second correction value causing an absolute value of an outermost extremum out of the plural extremums at said another end of the relative angle range to be equal to or less than an absolute value of another extremum out of the plural extremums which is located inwardly next to the outermost extremum.

3. The actuator according to claim 2 , wherein the first correction value and the second correction value are different from each other.

4. The actuator according to claim 1 , wherein the actuator includes metallic stoppers to restrict a range within which the shaft reciprocates.

5. An actuator adjusting method of writing correction values in the storage which the actuator according to claim 1 includes, the actuator adjusting method comprising:

in a measurement device, measuring a position of the shaft;

in a control device, operating the actuator to move the shaft in one direction, and using both the position of the shaft measured by the measurement device and the relative angle calculated by the arithmetic operation unit while the shaft is being moved, to calculate correction values at three or more correction points which are predetermined in the relative angle range; and

in a writing device, after the movement of the shaft is completed, writing the correction values at the correction points which are calculated by the control device in the storage at one time.

6. The actuator adjusting method according to claim 5 , wherein, by the control device, moving the shaft multiple times, and calculating a correction value at an outermost correction point in the relative angle range by using positions of the shaft and relative angles which have been determined multiple times.