Development of a robotic system for the analysis of the mechanical function of biological joints

为了确定生物关节的力学功能，研制了一种由六轴机械臂、伺服电机控制器和控制计算机组成的机器人系统。机械手各轴均由交流伺服电机驱动。假定生物关节的运动学用6自由度关节坐标系表示。采用雅可比变换描述关节的位置/姿态和力/力矩。在IBM CP/Q操作系统上，采用C语言对一个可同时执行多任务的闭合位置/力反馈进行编程。根据位置/力数据，机械手移动，将关节的位置/力控制在规定的水平。为了确定施加在软组织上的力，采用了UFS法。初步测试结果表明，在胫骨钳施加500 N载荷时，位移误差小于120 mm，机械手刚度大于310 N/mm。利用该系统对膝关节运动、膝关节韧带和半月板的力学功能进行了实验分析。我们发现1)前交叉韧带的受力分布取决于膝关节屈曲角度，2)交叉韧带主要抵抗膝关节平移，而半月板主要抵抗膝关节旋转，3)半月板的功能既取决于关节压缩力，也取决于交叉韧带损伤，4)双窝ACL重建在术后关节稳定性方面优于传统重建方法。最后，我们发现该系统具有分析关节力学功能的能力。

A robotic system, consisting of a 6 axis manipulator, servo motor controllers, and a control computer, has been developed to determine the mechanical function of biological joints. All the axes of the manipulator are driven with AC servo motors. Kinematics of biological joints was assumed to be represented with a 6 degreeof freedom joint coordinate system. Jacobian transformation was used for the description of the position/posture and force/moment of the joints. C language was employed for the programming of a closed position/force feedbackloop on an operating system, IBM CP/Q which is capable of performing multi tasks simultaneously. Based on position/force data, the manipulator moves to control position/force of the joint at a prescribed level. To determine the force applied to soft tissues, the UFS method was employed. A preliminary test to assess the system performance showed that error in displacement was less than 120 mm under the application of 500 N of load to the tibial clamp, and that the stiffness of the manipulator was higher than 310 N/mm.An experimental analysis of knee motion and mechanical functions of knee ligaments and menisci has been performedusing the developed system. We have found 1) force distribution in the anterior cruciate ligament depends on knee flexion angle, 2) the cruciate ligaments primarily resist to knee translation, while the menisci primarily resist to knee rotation, 3) the function of the menisci depends on both joint compressive force and cruciate ligaments injury, and 4) Bi-socket ACL reconstruction has an advantage in postoperative joint stability over traditional reconstruction methods. Finally, we have found that the system has the capability for the analysis of joint mechanical function.