| Sit-to-stand motion (STS) is one of the most common postures in daily life.However, it is impossible mission for subjects with paralysis of lower limbs, spinal cordinjuryor weak muscle strength. Assistive standing-up robot is based on rehabilitationtechnology and integrated with control, information, mechanics, medical science andother advanced subjects, which is used to provide patients with STS training.Furthermore physical therapists will be replaced by the routine training robot. STStraining can benefit the motion and sensory function, the increase of muscle volume andso on. Research work is based on assistive standing-up robot. Design of the robot, workprinciple, control mode and dynamic model of STS motion was built and studied.According to the results of simulation and experiment, the robot can assist patients tostand along reference trajectory, control the momentum of center of mass during STSmaneuver and the patient can voluntarily participate the process.Factors caused failed STS motion are presented in the paper. Based on the analysisof merits and drawbacks of the present assistive robot, a new hydraulic servo assistiverobot is presented. Firstly, the mechanical structure and operational principle of therobot are outlined. The position and force control mode can be chose during STSmotion. The composition of hardware system, design and development of softwaresystem are illustrated to explain characteristics of the robot. Dynamic characteristics ofsubjects in STS motion by assistive standing-up robot are analysed, the three-linkagedynamic model of human body was built up in sagittal plane. The model can be usedto predict moments of lower extremities, which combined with the Newton-Eulerinverse dynamic approach, human anthropometric data and data measured by sensorsystem. The simulation was carried out, and the accuracy of the model was verified bycomparison of the simulated and experimental results. In addition, kinematic data wasobtained by experiment and simulation. The force control of the assistive standing-uprobot was achieved by the extended kalman flter algorithm (EKF).The sit-to-stand motion was determined by the trajectory of the two robot joints.So the position control methods of robot motion joints were studied and compared inthe paper. Firstly, kinematic velocity equation of the rotation joint was deduced by thedesign dimension of the assistive standing-up robot and the position of piston. By comparison of feedback control and velocity feed-forward control methods，the resultsshowed that sliding joint got better position accuracy than rotation joint by feedbackcontrol. But position accuracy of sliding and rotation joints was obtained by feed-forward control. The assistive standing-up robot need to track the reference trajectory ofhip joint accurately and keep proper velocity moving along the reference trajectory,otherwise the fast change of velocity or inaccurately trajectory tracking would causefalling down during STS motion. Firstly inverse kinematics was used to deduce thefunction between position of end-effector and the speed of robot motion joints, theinverse Jacobian matrix also obtained. Secondly, trajectory tracking algorithm combinedwith trapezoidal speed in order to assist subjects finish STS rehabilitation training.Simulation studies of different trajectory have been done by writing program andsimulation platform. The simulation and test results showed that it was valid andrational to use trajectory tracking algorithm and trapezoidal speed rate. Programmablecontrol of speed rate and trajectory tracking was realized and also meet patients’requirement of physical difference during rehabilitation exercise.By analysis of assistive force during STS motion, both intact human limbs andneuromuscular system can voluntarily participate in the STS training. Although it isimpossible to complete the STS motion successfully by means of muscular strength ofupper limbs or lower extremity, patients have strong desire to participate the STStraining. The STS training was done passively by traditional method, so it is meaningfulto develop new robot and control method by which the subject can participate actively.The force and moment equilibrium equations were derived by analysis the STS motion.The simulation model and force controller were established by integrating equationswith EKF algorithm. The calculated results are agreed with the experiment results. Therationality and feasibility of the model and controller were validated. The contact forcebetween robot and human body was effectively reduced by the force control mode. Theassistive force provided by robot was quantified and accorded with the demand of STSmotion. It is not only ensured the safety of training, but also maximized muscular forceduring STS motion. Good man-machine integration was realized in the paper. |
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