Patent ID: 7493847

Claim:
A fluid pressure cylinder with a position detecting device comprising a cylinder tube, a piston linearly moving in the cylinder tube by the action of a fluid pressure, and the magnetostriction type position detecting device for detecting an operating position of the piston, wherein the position detecting device comprises a magnetostrictive line extending along the cylinder tube and a permanent magnet moving in the cylinder tube in synchronism with the piston, and when a current pulse is supplied to the magnetostrictive line, the operating position of the piston is detected from ultrasonic oscillation generated to the magnetostrictive line at a position corresponding to the permanent magnet, the fluid pressure cylinder characterized in that: the cylinder tube is formed of a non-magnetic conductive material, a hole-or groove-shaped hollow portion extending in parallel with a moving direction of the permanent magnet is formed to the cylinder tube, the magnetostrictive line comprising a ferromagnetic material is inserted into the hollow portion, and the extreme end of the magnetostrictive line is electrically connected to the cylinder tube, thereby the cylinder tube is also used as a current feedback conductor, wherein the hollow portion is a groove, the groove comprises a groove inlet to open on an outer surface of the cylinder tube, and the groove inlet is covered by a lid.