In order to identify the key parameters of flexible joint model with harmonic driver, an off-line identification method by integrating several sensors is proposed. The key parameters can be identified by the experimental data of motor position sensors, current sensors and joint torque sensors. Firstly, the flexible joint model is established, which uses the flexspline as the output in the harmonic driver. Then, the motor torque coefficient is identified by running in forward and inverse directions with different loads. In the no-load condition, joint friction and motor friction are identified from the joint torque and motor output torque. Finally, the stiffness and damping parameters are identified by the knocking method, while the nonlinear relationship between stiffness and joint torque is obtained by progressively increasing the motor output torque under the condition that the joint position is hold. Several experiments are repeated, and the results show a high repeatability, which verifies the proposed method.
 张奇, 谢宗武, 刘宏, 等.基于无源性理论的柔性关节控制器设计[J].机器人, 2013, 35(1):23-31.Zhang Q, Xie Z W, Liu H, et al. Flexible joint controller design based on passivity theory[J]. Robot, 2013, 35(1): 23-31. Albu-Schaffer A, Eiberger O, Grebenstein M, et al. Soft robotics[J]. IEEE Robotics & Automation Magazine, 2008 15(3): 20-30. Albu-Schaffer A, Ott C, Hirzinger G. A unified passivity-based control framework for position, torque and impedance control of flexible joint robots[J]. International Journal of Robotics Research, 2007, 26(1): 23-39.  Mehling J S, Strawser P, Bridgwater L, et al. Centaur: NASA's mobile humanoid designed for field work[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA: IEEE, 2007: 2928-2933. 周军, 余跃庆.考虑关节柔性的模块机器人动力学参数辨识[J].机器人, 2011, 33(4):440-448.Zhou J, Yu Y Q. Dynamic parameter identification of modular robot with flexible joints[J]. Robot, 2011, 33(4): 440-448. da Silva A R. Parameters identification and failure detection applied to space robotic manipulators[D]. Sao José dos Campos, Spain: Instituto Nacional De Pesquisas Espaciais, 2002. Kircanski N M, Goldenberg A. An experimental study of nonlinear stiffness, hysteresis, and friction effects in robot joints with harmonic drives and torque sensors[J]. International Journal of Robotics Research, 1997, 16(2): 214-239.  Albu-Schaffer A, Hirzinger G. Parameter identification and passivity based joint control for a 7 DOF torque controlled light weight robot[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA: IEEE, 2001: 2852-2858. Zhang Q, Xie Z W, Cai H G, et al. FPGA-implementation of passivity-based control for elastic-joint robot[C]//IEEE International Conference on Robotics and Biomimetics. Piscataway, USA: IEEE, 2012: 271-276. Zhang Q, Xie Z W, Ni F L, et al. A high performance FPGA-based joint controller with hardware/software co-design method[C]//IEEE International Conference on Mechatronics and Automation. Piscataway, USA: IEEE, 2012: 1109-1114. Ott C, Albu-Schaffer A, Kugi A, et al. On the passivity-based impedance control of flexible joint robots[J]. IEEE Transactionson Robotics, 2008, 24(2): 416-429.  Ruderman M, Hoffmann F, Bertram T. Modeling and identification of elastic robot joints with hysteresis and backlash[J]. IEEE Transactions on Industrial Electronics, 2009, 56(10): 3840-3847.