Clamping apparatus with datum function

A clamping apparatus with a datum function aligning a movable member (M) with a reference member (R) to have a supported surface (T) of the movable member (M) fixed to a supporting surface (S) of the reference member (R), the clamping apparatus comprising:

• a positioning hole (12) provided by opening the supported surface (T) of the movable member (M);
• a pull rod (13) having an engaged portion (13b) and being connected to the movable member (M) substantially coaxially with the positioning hole (12) within the positioning hole (12);
• an annular plug portion (21) having a cylindrical hole (21a) and projecting from the reference member (R) so that it is inserted into an annular space defined between the positioning hole (12) and the pull rod (13);
• a shuttle member (23) which has a tapered surface (28) being arranged between the plug portion (21) and the positioning hole (12), and diametrically expanding and contracting, the shuttle member (23) being supported by one of the plug portion (21) and the positioning hole (12) axially movably within a predetermined range and making a tapering engagement with the other, the tapered surface (28) for the tapering engagement being formed so that it narrows toward an inner portion of the positioning hole (12);
• a resilient member (24) urging the shuttle member (23) in such a direction that the tapering engagement is made tightly;
• a transmission sleeve (31) having a cylindrical hole (31a) and an outer peripheral surface (31b), and being axially movably inserted into the cylindrical hole (21a) of the plug portion (21), the cylindrical hole (31a) of the transmission sleeve (31) receiving the engaged portion (13b) of the pull rod (13);
• an engaging member (34) supported by the transmission sleeve (31) so that it engages with and disengages from the engaged portion (13b);
• a supply port (41) for cleaning fluid provided in the reference member (R);
• and
• a flow passage (43, 45) formed in at least one of a space defined between the cylindrical hole (21a) of the plug portion (21) and the outer peripheral surface (31b) of the transmission sleeve (31), and a space inside the cylindrical hole (31a) of the transmission sleeve (31), the flow passage (43, 45) communicating with the supply port (41).