FLUID PRESSURE DRIVE APPARATUS WITH DISPLACEMENT DETECTOR

摘要

A fluid pressure drive apparatus in which a strong scale is formed easily on the surface of a movable member without increasing the size and damage to a packing seal due to protrusions and recesses of the scale is eliminated. A predetermined part of a piston rod (13) is irradiated with a laser beam and the temperature at the irradiated part is raised. Consequently, the irradiated part of the piston rod (13) deteriorates and an oxide film (22) is formed. Between adjacent oxide films (22), an unprocessed portion (25) in pure state is formed on a piston rod (13) having a different reflectivity. Consequently, the man-hour required for forming a scale can be reduced and the scale is not peeled off nor rusted easily because a strong oxide film is employed as the scale. Since the protrusions and recesses of the scale are very small, damage to a rod packing can be reduced, and an increase in size can be avoided because the scale is formed on the piston rod itself as a movable member.