The Design Of Compliant Constant-Force Gripper

Compliant mechanism is a kind of mechanism that utilizes its partial or its entire elastic member to stored energy and release energy. In the process it can obtain the mechanical force, displacement or motion according to the design requirements. This type of mechanism is no need to assemble and easy to be formed. It also has advantages of no friction, no wear and long fatigue life. What's more, it has the characteristics of high positioning accuracy and easy matching with non-mechanical transmission. Therefore, compliant mechanism has get people's favor in the mechanism design. The compliant constant-force mechanism is designed based on the above considerations in this thesis. The constant-force mechanism for grasping fragile objects and can be automatically regulated according to the size of the grasping object. It can achieve an approximate constant-force without the help of sensor or precise control.Firstly, this thesis gives a brief introduction to compliant mechanisms and realizes the research on the compliant mechanisms of the domestic and international in recent years. Several major application areas of compliant mechanisms are introduced. Then the author learns the compliant gripper and the pseudo rigid body model method. Secondly, this thesis summarizes the constant-force mechanism of the concept, classification, application and design method. And it verifies the constant-force characteristics of a compliant four bar slider constant-force mechanism. The author uses particle swarm optimization algorithm(PSO) to research the optimization design of four bar constant-force mechanism based on the previous study. Then the constant-force was found from five bar mechanism, a dynamic compliant constant-force gripper is designed. It achieves the grasping, moving and releasing under a single input. The methods of minimum energy and motion coefficient are used to calculate and compare the output force, and the optimal design of the mechanism is carried out. Then, a compliant symmetrical gripping mechanism with constant-force can be designed without the need of sensor and the need of precise input control. The input displacement is only in the range of design, no matter how large; the output force is always approximate constant. In which the mechanism of the different conditions of the multiple optimization design, and simulate the optimization of the mechanism for Workbench, simulation results are analyzed and compared, and produced the entity model. Then, the large output range of the mechanism is improved by increasing the optimized parameters, which makes the mechanism to reach a constant output value when the input displacement reaches a fixed value. Lastly, the method of design compliant constant-force mechanism is discussed and summarized, and then the future work is specified.The design of two compliant constant-force mechanism based on the five-bar mechanism in this thesis have some characteristics such as simple input, no need precise control and without sensor. At the same time, it also has some advantages of flexible mechanism. They can be widely used in the screening qualified product, grasping fragile items, grasping variable size targets also can be used to clip cells and other living objects. The design method of the constant-force mechanism proposed by this thesis can be extended to other planar mechanism.