面向柔顺装配装夹的机器人手腕变刚度机理研究

在柔顺装配装夹过程中，不同工序对机器人手腕刚度要求不同。在刚性定位工序中，大的手腕刚度可保证机器人搬运工件定位到作业位置的精度。在装配装夹工序中，小的手腕刚度可柔顺补偿机器人装配装夹工件的位姿误差。提出了一种大范围变刚度的五自由度手腕，可实现工件的翻转、俯仰、偏转和平移。研究通过调节弹性张力改变手腕刚度的机理，实现手腕关节刚度随弹性张力的增加而线性增加。分析手腕弹性张力和几何参数对手腕变刚度特性和刚度分布的影响，通过设计手腕关节的几何参数实现手腕刚度分布保持不变。研究变刚度手腕刚性定位与柔顺装配装夹的机理，建立手腕装配装夹过程中的形变位姿模型和补偿工件位姿误差的空间模型，得到手腕刚度随手腕位姿的变化模型，实现手腕克服阻力完成装配装夹作业。实验结果表明机器人手腕可大范围变刚度，满足刚性定位与柔顺装配装夹要求。

Research on Variable-stiffness Mechanisms of Robot Wrists for Compliant Assembling-clamping

The stiffness requirements of robot wrists vary with processes during automatic assembling-clamping of robots. The precision of robots moving workpieces to operating positions in the process of rigid localization is achieved if robot wrists equip with a large stiffness. The pose errors of workpieces in the process of compliant assembling-clamping can easily be compensated if robot wrists with a low stiffness is utilized. A 5-DOF (degrees of freedom) robot wrist with a large stiffness variation is proposed, and the rotations of the workpieces around X axis, Y axis and Z axis and the translations along X axis, Y axis can be realized. The stiffness variation mechanisms of the wrist modulating pretension and the mechanisms of both rigid localization and compliant assembling-clamping are studied. The stiffness of wrist joints increase linearly with the increase of pretension of elastic elements. The influences of pretensions and geometrical parameters on the variable-stiffness characteristics and the stiffness distribution of a wrist are researched. By designing geometric parameters of wrist joints, the stiffness distribution of the wrist is obtained and remains constant in the process of modulating wrist stiffness. The pose models of wrists caused by deformations during assembling-clamping and the models of compensating posture errors of workpieces are established. The models of wrist stiffness varying with wrist positions and postures are obtained, the assembly operations and clamping operations can be obtained by the wrist overcoming resistances. The results show that the stiffness of the wrist can be modulated largely, the requirements of both rigid localization and compliant assembling-clamping can be satisfied.