Location detector device

A location detector comprising:

• a magnetic field generating body having a polar surface of N-pole, and a polar surface of S-pole on its reverse side, and attached to a reciprocating drive shaft to move in directions perpendicular to a magnetic pole direction in which the N and S poles are aligned;
• a first stationary magnetic body having a curved portion, and disposed opposite to one of the polar surfaces of the magnetic field generating body;
• a second stationary magnetic body disposed at a position opposite to the other of the polar surfaces of the magnetic field generating body, and having a linear portion that is parallel to the moving directions of the magnetic field generating body, said linear portion being opposite to the curved portion of the first stationary magnetic body with the magnetic field generating body interposed therebetween;
• a third stationary magnetic body disposed side by side with the first stationary magnetic body at a position opposite to the second stationary magnetic body;
• a magnetic sensor placed in a state sandwiched between opposite surfaces of the first stationary magnetic body and the third stationary magnetic body, said sensor detecting a location of the magnetic field generating body due to the fact that when a distance in the magnetic pole direction between the magnetic field generating body and the first stationary magnetic body varies according to a reciprocating movement of the drive shaft, a magnetic flux passing therethrough is changed;
• and
• a permanent magnet placed between opposite surfaces of the second stationary magnetic body and the third stationary magnetic body in such a manner that zero is included in a detection range in magnetic flux density thereof when the magnetic flux passing through the magnetic sensor is changed.