手康复机器人钢丝绳–绳套传动系统中的摩擦补偿
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摘要
在手康复机器人的钢丝绳–绳套传动系统中,钢丝绳与绳套之间的摩擦力会引起力控制过程中的动力损失,产生传动死区、滞后等现象,并且带来系统不稳定等问题,因此需要补偿摩擦力.首先推导了手指任意姿态下,钢丝绳中张力的计算公式.然后,1个手指关节上的传动模式简化如下:电动机1以位置控制模式运转,模拟关节运动;电动机2以转矩控制模式运转,补偿钢丝绳上的摩擦力.每根钢丝绳穿过绳套,绳端固定在电动机1和电动机2的输出轮上,钢丝绳两端张力之差即是摩擦力.将摩擦力转化为补偿电动机轴的等效摩擦力矩,补偿电动机以转矩控制模式运转,输出与等效摩擦力矩方向相反的转矩.假设时间间隔足够小、手指运动缓慢,利用t-1时刻的张力计算得到t时刻的等效摩擦力矩.用此迭代方法计算出不同时刻补偿电动机需要输出的补偿力矩,对钢丝绳–绳套中的摩擦力进行补偿.最后在实验平台上进行了主动康复模式实验,实验结果表明,补偿后的阻力只有补偿前的15%,该补偿方法有效.
In cable-conduit transmission system of hand rehabilitation robot, friction between cable and conduit can cause power loss in force control process, sometimes results in dead zone and hysteresis phenomena, even brings other problems such as system instability. Thus, it is needed to compensate the friction. Firstly, the tension in cable is formulated when finger bending in arbitrary shape. Then, the transmission mode of a finger joint is simplified as follows: motor 1 runs in position control mode to simulate the motion of the joint. Motor 2 runs in torque control mode to compensate the friction in cable. Each cable passes through a conduit and the ends of cable are fastened on output pulleys attached to each of the motors. The tension difference between both ends of cable is the friction in cable and conduit. Friction is transformed into equivalent friction torque of motor 2 shaft. The compensation motor runs in the torque control mode, and the direction of its output torque is opposite to the equivalent friction torque. Assuming that time interval is small enough and finger moves slowly, equivalent friction torque at t moment can be calculated by tensions at t- 1 moment. Using this iterative method, compensation torque at different moments that motor 2 should output can be obtained to compensate friction in cable and conduit. Finally, an active rehabilitation experiment is carried out on an experiment setup, and the result shows the resistance reduces to 15% after compensation, which means the method is effective.
In cable-conduit transmission system of hand rehabilitation robot, friction between cable and conduit can cause power loss in force control process, sometimes results in dead zone and hysteresis phenomena, even brings other problems such as system instability. Thus, it is needed to compensate the friction. Firstly, the tension in cable is formulated when finger bending in arbitrary shape. Then, the transmission mode of a finger joint is simplified as follows: motor 1 runs in position control mode to simulate the motion of the joint. Motor 2 runs in torque control mode to compensate the friction in cable. Each cable passes through a conduit and the ends of cable are fastened on output pulleys attached to each of the motors. The tension difference between both ends of cable is the friction in cable and conduit. Friction is transformed into equivalent friction torque of motor 2 shaft. The compensation motor runs in the torque control mode, and the direction of its output torque is opposite to the equivalent friction torque. Assuming that time interval is small enough and finger moves slowly, equivalent friction torque at t moment can be calculated by tensions at t- 1 moment. Using this iterative method, compensation torque at different moments that motor 2 should output can be obtained to compensate friction in cable and conduit. Finally, an active rehabilitation experiment is carried out on an experiment setup, and the result shows the resistance reduces to 15% after compensation, which means the method is effective.
引文
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[15]缪建成,陈关龙,金隼.小直径柔性钢索预紧张力的测量与计算[J].力学与实践,2006,28(2):29-32.Miao J C,Chen G L,Jin S.Measurement and calculation of the pre-tension of a flexible thin cable[J].Mechanics in Engineering,2006,28(2):29-32.
[2]Worsnopp T T,Peshkin M A,Colgate J E,et al.An actuated finger exoskeleton for hand rehabilitation following stroke[C]//10th International Conference on Rehabilitation Robotics.Piscataway,USA:IEEE,2007:896-901.
[3]Fu Y L,Wang P,Wang S G.Design and development of a portable exoskeleton based CPM machine for rehabilitation of hand injuries[C]//4th International Conference on Robotics and Biomimetrics.Piscataway,USA:IEEE,2007:1476-1481.
[4]Agrawal V,Peine W J,Yao B,et al.Control of cable actuated devices using smooth backlash inverse[C]//27th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2010:1074-1079.
[5]Kaneko M,Yamashfia T,Tanie K.Basic considerations on transmission characteristics for tendon[C]//5th International Conference on Robotics and Automation.Piscataway,USA:IEEE,1991:827-832.
[6]Palli G,Melchiorri C.Model and control of tendon-sheath transmission systems[C]//23th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2006:988-993.
[7]Kaneko M,Wads M,Maekawa H,et al.A new consideration on tendon-tension control system of robot hands[C]//5th International Conference on Robotics and Automation.Piscataway,USA:IEEE,1991:1028-1033.
[8]Palli G,Borghesanand G,Melchiorri C.Friction and viscoelasticity effects in tendon-based transmission systems[C]//27th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2010:3890-3895.
[9]Borghesanand G,Palli G,Melchiorri C.Friction compensation and virtual force sensing for robotic hands[C]//28th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2011:4756-4761.
[10]Agrawal V,Peine W J,Yao B.Modeling of transmission characteristics across a cable-conduit system[J].IEEE Transactions on Robotics,2010,26(5):914-924.
[11]Agrawal V,Peine W J,Yao B.Modeling of a closed loop cableconduit transmission system[C]//25th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2008:3407-3412.
[12]Tian F X,Wang X S.The design of a tendon-sheath-driven robot[C]//15th International Conference on Mechatronics and Machine Vision in Practice.Piscataway,USA:IEEE,2008:280-284.
[13]Wang S,Li J T,Zheng R Y,et al.Multiple rehabilitation motion control for hand with an exoskeleton[C]//28th International Conference on Robotics and Automation.Piscataway,USA:IEEE,2011:3676-3681.
[14]王爽.人手运动功能康复机器人控制方法的研究[D].北京:北京航空航天大学,2011.Wang S.Research on the control algorithm of an exoskeleton for hand motor function rebabilitation[D].Beijing:Beihang University,2011.
[15]缪建成,陈关龙,金隼.小直径柔性钢索预紧张力的测量与计算[J].力学与实践,2006,28(2):29-32.Miao J C,Chen G L,Jin S.Measurement and calculation of the pre-tension of a flexible thin cable[J].Mechanics in Engineering,2006,28(2):29-32.