A clamp pallet (2) as a reference member is fixed to a table (1) of a machining center. A tapered positioning hole (12) is opened in a lower surface of a work pallet (3) as a movable member. An annular central pillar (21) is projected upward from the clamp pallet (2), and an intermediate member (22) is arranged between the central pillar (21) and the positioning hole (12). The intermediate member (22) is composed of a shuttle member (23), which is diametrically expandable and contractible and supported on the central pillar (21) vertically movably, and a tapered cylinder (26), which is attached to an outer periphery of the shuttle member (23) and makes a tapering engagement with the positioning hole (12). The shuttle member (23) is urged upward by means of an elastic member (24).

In a clamping apparatus for fixing a work piece carrier with a clamping pin in a clamping chuck, the clamping chuck is provided with a central opening for receiving the clamping pin and with a clamping mechanism firmly keeping the clamping pin in the central opening. The central opening has a conical inserting portion, and the clamping pin comprises a rear section with exposed aligning surfaces, engaging the conical inserting portion, to align the clamping pin with regard to the clamping chuck in X- and/or Y-directions. Circular seat portions on top of the clamping chuck constitute the Z-stop for the work piece carrier. For pneumatically cleaning the exposed aligning surfaces, the conical inserting portion is provided with gas outlet openings, located corresponding to the arrangement of the exposed aligning surfaces. The surface areas of the work piece carrier that will rest on the seat portions are pneumatically cleaned by gas outlet openings located in the center of the seat portions.

A work pallet (3) has an under surface opened to provide a positioning hole (12). The positioning hole (12) has an upper wall which supports a pull rod (13) diametrically movably. A clamp pallet (2) projects an annular plug portion (21), onto which a shuttle member (23) is externally fitted. The shuttle member (23) makes a tapering engagement with the positioning hole (12). The plug portion (21) has a cylindrical hole (21a), into which a transmission sleeve (31) is inserted. The transmission sleeve (31) supports an engaging ball (34), which engages with an engaged portion (13b) of the pull rod (13). Defined between the cylindrical hole (21a) and an outer peripheral surface (31b) of the transmission sleeve (31) is a flow passage (43) through which cleaning compressed air passes.

Two positioning devices (4, 5) are horizontally spaced apart from two clamping devices (6, 6) at a predetermined interval. Each of the positioning devices (4, 5) includes a positioning hole (23) provided by opening a work pallet (2), a plug portion (27) projecting from a clamp pallet (1), and an intermediate member (30) vertically movably supported by the plug portion (27). The intermediate member (30) is urged upwards by a coned disk spring (31) and has a tapered surface (33) which makes a tapering engagement with the positioning hole (23). The clamping device (6) fixes the work pallet (2) to the clamp pallet (1).

A coupling device with two coupling members, which are to be connected coaxially together, and a tension rod, which penetrates the first coupling member and is to be coupled with the second coupling member. To minimize the effect of the cross forces on the positioning of the second coupling member, it is provided that the end, facing the head of the tension rod, penetrates into a passage borehole of the second coupling member with a radial clearance; and a connector, resting against a shoulder of the second coupling member, can be attached to the end, thus resulting in radial clearance between connector and second coupling member. Furthermore, a connector is described whose periphery has a contour, which prevents a turning action inside the coupling member, whereby the connector can also be moved in the coupling member and exhibits an axial contact surface, which is adequately small to enable a swivelling motion without generating a counteracting moment of flexion.