Linear gauge

A linear gauge for measuring displacements of a surface of a workpiece, the linear gauge comprising:

• a contact member having a lower tip to be positioned facing the workpiece;
• an air slider including a cylinder having an inner supporting wall that surrounds an outer side wall of the contact member with a clearance left between the inner supporting wall and the outer side wall, and configured to eject air from the inner supporting wall such that the contact member is supported movably in a vertical direction;
• a scale that detects a height position of the contact member;
• a casing accommodating therein the contact member, the air slider, and the scale;
• an evacuation portion formed in an upper portion of the cylinder such that the ejected air is evacuated into the casing;
• and
• a communication channel communicating an inlet formed in an upper portion of the contact member and an outlet formed in the lower tip of the contact member with each other inside the contact member, the communication channel not being open to a space between the contact member and the inner supporting wall of the cylinder that surrounds the outer side wall of the contact member,
• wherein the air evacuated from the evacuation portion into the casing is introduced from the inlet into the communication channel and is allowed to blow out from the outlet to provide a clearance between the lower tip of the contact member and the surface of the workpiece, to thereby enable contactless measurement of the displacements of the surface of the workpiece.