A clamping mechanism (1) for machine tools (2), equipped with a power-operated chuck (5) and an electric drive motor (11) with a changeover function for triggering clamping movements, a motion converter (31) for converting the adjustment movements into the axial movements of a draw rod (7) as well as a force accumulator (41), is configured as a play and slip-free functional unit, and to determine the axial adjustment movements of the draw rod (7) when clamping and unclamping a workpiece (10), an electronic rotary encoder (101) in a stationary arrangement is allocated to one of the components (53; 54) that is involved in the force transmission. Due to this embodiment, it is possible to configure the clamping mechanism (1) with inherent rigidity, having neither play nor slip, as a result of which both the axial adjustment movements of the draw rod (7) and consequently the particular operating positions of the clamping jaws (6) of the power-operated chuck (5) can be used without restrictions. The machine tool (2) can be controlled without problems in this way with great accuracy without having to accept inaccuracies.