Structural Synthesis And Design Of Novel Three-Degree-of-Freedom Differential Gear Train

As manufacture process became more and more intelligent and versatile, the three-fingered underactuated robotic gripper which can handle objects with irregular shapes has been used very widely. To improve the transmission capability of the gripper, many people started to study the drive component(three-degree-of-freedom differential gear train) of the gripper. At present, the most popular three-degree-of-freedom differential gear train in the international adopts bevel gears. Both radial force and axis force are put on the bevelr gears when they are in mesh, so the shafts suffer both torque and bending moment. Because of this, the running of the system is not calm, and it brings noise and decrease the life of the system. Besides, it is not easy to process the bevel gears than the spur gears, and the assembly of the bevel gears is discommodious. So, studing and exploring novel three-degree-of-freedom differential gear train is still important problem to solve.To improve the transmission capability of the gripper, this paper presents the design and synthesis of novel three-degree-of-freedom differential gear train based on the research of the abroad. It begins with changing the bevel gear train presented by foreigner into spur gear train. As we all know, only radial force is put on the spur gears when they are in mesh, there is no axis force, so the shafts suffer only torque. Because of this, the running of the system is very calm, it reduces the noise and prolongs the life of the system. Besides, it is more easy to process the spur gear than the bevel gear, and the assembly of the spur gear is more convenient.We have accomplished the structural synthesis of the novel three-degree-of-freedom differential gear train. First, we selected the structure form based on the trait of the gear train and ascertained the diameter relations between all gears through movement analysis. Afterwards, we got the sketch of the gear train based on the structure form and the diameter relations between all gears. Second, we have calculated the parameters of the novel three-degree-of-freedom differential gear train, selected the tooth number for all gears, and choosed the addendum modification coefficient for gears needing addendum modification. Aside, we validated that the gears satisfied with assembly condition and calculated the asymmetry coefficient of the load distribution.We have worked out the intension condition and the efficiency of the novel three-degree-of-freedom differential gear train. We protracted the three-dimensional modeling of the gear train and carried out it's kinematics emluation. The paper gives out the following conclusion by emulating the kinematics of the three-degree-of-freedom differential gear train. The three output shafts are absolute, the input torque is distributed equally among all the output shafts. The speeds of the output shafts may very, but the output torques remain the same. Under the conditions of the input power be equal to the out put power, the sum of the three output speeds is three times of the input speed. Through the emulation, it proves that the transmission of the three-degree-of-freedom differential gear train accords with our demand.