Design of a variable stiffness flexure mechanism for micromanipulation tasks

In micromanipulation tasks, the interaction force between the manipulator and an object or environment is difficult to control. In the traditional approach, force control is achieved by controlling the displacement of the end-effector during contact with an object, and therefore controlling of force and displacement cannot be decoupled. In this work, we propose to achieve interaction force control by varying the stiffness of the actuating mechanism. To achieve varying stiffness, a flexure mechanism with infinite resolution and no backlash is installed between the end-effector and actuators. The stiffness of a slender flexure element is varied by controlling its internal stress through piezoelectric actuators. The design procedure of the proposed variable stiffness mechanism is presented. Finite element analysis and experiments are conducted to evaluate the performance of the design. The stiffness of the prototype can be precisely controlled within the range of 5 to 25 kN/m.