Research On The Wearable Power Assist Robot

The wearable power assist robot is a new research field in recent years, which belongs to special robot category. Power assist robot represents a high integration of robotics, ergonomics, control engineering, technology of sensor, communication, signal processing and etc. The power assist robot is designed for normal human lower limb power augmentation, and it has its potential applications for elderly people, handicapped, succor, care-worker, soldier and fireman. The power assist system includes the fundamental exoskeleton, actuator, controller and many sensors for obtaining user motion information. The all devices constitutes a robot system to improve ability of human walking and increase load to human body, and it also constitutes a local area network similar to human nervous system. It becomes a humachine system.Supported by the National Nature Science Foundation of China and based on multi-joint mechanical operator, this thesis focuses on the research and development of a novel power assist system which is a combination of the human motion intention recognition, contact force sensor, pseudo-compliance control. The main research contents are as follows: analyze and calculation feature of body and exoskeleton; successful power assist prototype development including exoskeleton machine, human-robot kinematics and dynamics, contact force sensor; judgment of human motion intention using multi-sensor data fusion; a control method of pseudo-compliance is proposed, through which we can adjust the coefficient of mass, damp and spring to change user movement intensity during walking.The whole thesis has a thorough knowledge of theoretical analysis and the technology realization, and it involves many research fields manifested in following several aspects:1. The robot that we proposed is for assisting activities of daily life without affecting the user to walk normally. So, the system must have many DOFs like human, however, it is impossible to include all the DOFs of human legs in consideration of design complexities. Here, our mechanical structure consists of a 12 DOFs mechanism (6 DOFs for each leg) based on ergonomics, anatomy and mechanism design technology. The hip structure has 3 DOFs in total. They perform function of flexion/extension, abduction /adduction and internal rotation/external rotation, realizes the function of straight walking, balance adjustment, and walking direction change respectively. At the knee joint, there is 1 DOF, which perform the flexion /extension. Comparing to other joint motion, the flexion/extension of hip and knee is the most important to normal walking and its energy consumption is also most. So, only the motion of flexion/extension at hip and knee are currently powered. To avoid the motion collision between the WPAL exoskeleton and the user, the designed joint axes and human joint axes must be on an identical axis. So, the length of the designed exoskeleton links can be changed according to the real length of user thigh and lower leg, even for metal waistband. Through analyzing power assist system kinematics and dynamics, and combining simulation software, we can carry on the design optimization; simultaneously, it provides the reference for the motor selection.2. A novel thought about the judgment of human motion intention based on multi contact force sensor is proposed. After analyzing the motion recognition method based on image resolution and surface electromyographic (sEMG), we proposed a method using multi-dimensional force guidance information. The two-dimension force sensors are equipped on thigh and lower thigh respectively for each exoskeleton leg, which detect the force caused from the motion difference between WPAL and the user. And they contact directly with normal person leg through bundles. Floor reaction force (FRF) sensors are developed to measure FRF which are generated in front and rear parts of footboard. Using modern technology of signal processing and data fusion, we can finish the judgment of user motion intention. This method is different from existing method used in foreign power assist system.3. Through the theoretical analysis and the technical realization, we developed a prototype having 12 DOFs and four motor-driven. After study on the control method of foreign power assist device, we proposed a novel method named pseudo-compliance according to its own unique feature and our research level. We can adjust the coefficient of mass, damp and spring to change power assist supply for user during walking. And, we changed the multi-DOF robot control to equivalent several independent control way.