A Variable Stiffness Gripper with Dual Leaf-Spring Mechanism

The variable stiffness grippers predominantly change the stiffness in two ways: 1) incorporating soft materials but suffering from limited repeatability and high sensitivity to environmental changes; 2) utilizing mechanical structures but suffering from limited stiffness modulation range and heavy self-weight. To overcome the aforementioned drawbacks, we propose a novel variable stiffness gripper with dual leaf-spring mechanism. The dual leaf-spring gripper (DLSG) incorporates symmetrical pairs of roller bearings to constrain the leaf-spring's vertical deflection at the point of contact, while the stiffness modulation is achieved by changing the effective length of the leaf spring. Advantages with our design includes: 1) wide range of stiffness modulation, 2) compact mechatronic design, and 3) low self-weight. The stiffness modulation and grasping operation are independently controlled by two DC motors. We have derived the theoretical stiffness modulation equation of DLSG and validate our derivation with hardware experiments. To demonstrate the effectiveness of the DLSG in industrial application, we develop a two-fingered gripper and successfully validate the grasping ability on objects with different surface hardness, ranging from soft and fragile to rigid.