IROS2019國際學(xué)術(shù)會議論文集 1599

Abstract This paper developed a 4 degree of freedom cable driven upper limb rehabilitation robot and proposed a control algorithm of the passive training for this robot Comparing with the conventional cable driven rehabilitation robot the workspace of this robot is increased by optimizing the distribution of the cable attachment points and by improving the mechanical design The rotation structure of the upper arm module can change the distribution of the attachment points as needed by which the cable tension planner can be satisfied in almost all cases At the meantime the internal external rotation of shoulder joint can be achieved without the change of the cables configuration which is also important for increasing the workspace and comfortability of utilization The activities of daily living ADLs training can be achieved well without any manual adjustment The related controller for passive training is designed which includes a higher controller for trajectory tracking and a lower controller for keeping cable tension as the output of the tension planner in real time The passive training experiments are conducted on five healthy subjects of different body size The results demonstrated that the passive training can be achieved well on different subjects and the cable tension controller is also working effectively I INTRODUCTION Due to the aging of population some accidents and other reasons many people suffer from the strokes in the world 1 After stroke the patient s advanced central nervous system is damaged resulting in partial or complete disorder of motor control and sensory seriously affecting patients daily life Studies have shown that rehabilitation training can promote brain damage or redundant nerves to re learn and restore human function 2 Usually the rehabilitation training is operated by a professional therapist Due to the high cost and lack of personnel the economic pressure of the patients as well as the inconvenience of rehabilitation training is increased Over the years the robot industry has developed rapidly and the use of robots for rehabilitation training has become more and more popular Relevant research also shows that robotic rehabilitation training has a good effect and can significantly reduce the cost of treatment 3 After many years of development the upper limb rehabilitation training robot can be divided into two types the end effector type robots and the arm exoskeletons The end effector type robots such as MIT Manus 4 and the Arm Guide 5 are fixed to the end of the human arm and drive the limb The structure is usually simple and does not cause the joint misalignment problems but its workspace is limited and Research supported by the National Key Research and Development Program of China No 2017YFB1303201 the National Natural Science Foundation of China No 91648206 and the Key Research and Development Program of Jiangsu Province No BE2018004 4 Ke Shi Aiguo Song Ye Li Dapeng Chen and Huijun Li are with the School of Instrument Science and Engineering Southeast University Nanjing 210096 China e mail a g song the movement flexibility is relatively poor the exoskeleton robots such as ARMin 6 L Exos 7 and robots proposed in 8 9 have better flexibility and larger workspace than the end effector robots but their structures are more complicated generally and it is more difficult to meet the requirements of the joint alignment in the shoulder joint without a fixed rotation center Some researchers have adopted a more complex redundant degree of freedom mechanism to meet this requirement but the simplicity of the structure and the stability of the system are still sacrificed 10 The above problems usually occur more on traditional rigid robots In recent years flexible exoskeleton robots have been developed Compared with rigid robots flexible robots are more adaptive to the human body using cables or artificial muscles to simulate human muscle contraction 11 12 At the same time since the human body itself is usually a part of the robot the problems of joint misalignment and limb length adaptation are avoided The CAREX developed by the University of Delaware is driven by cables so that there is no joint misalignment problem in the human robot system and the patient s load is light which makes the inertia small during the movement After years of development they design a series of rehabilitation robots from four to seven degrees of freedom DOFs and related algorithms which has opened up a new field for the development of rehabilitation training robots 11 13 15 In addition Professor Yang of Nanyang Technological University designed a seven DOFs cable driven rehabilitation robot and made corresponding analysis on the workspace which also gave a great inspiration to the research in related fields 16 17 Shao and others also carried out certain analysis and design of the cable driven robot and conducted relevant experiments all of which achieved good results 18 20 Compared with the traditional rigid exoskeleton robot including the robots using cables in their transmissions but composed of rigid mechanical rods and conventional joints the cable driven exoskeleton rehabilitation training robot has many advantages light weight simple structure no joint misalignment and good adaptability no need to adjust according to different limb lengths However the characteristic that cables can only pull but not push makes it difficult to achieve a large workspace like the traditional exoskeleton CAREX 7 is the latest robot of the CAREX research team and its theoretical workspace still cannot completely satisfy the requirement of ADLs training 14 Although the workspace of some robots such as CAREX 7 can satisfy ADLs training requirement to a certain extent there is still a noticeable gap with the complete ADLs space especially in abduction adduction and internal external rotation of shoulder joint It is difficult to carry out a wide range of rehabilitation training and the role of related movement in the rehabilitation process is also very important They adopted a manually adjusted method for the attachment Cable Driven 4 DOF Upper Limb Rehabilitation Robot Ke Shi Aiguo Song Ye Li Dapeng Chen Huijun Li 2019 IEEE RSJ International Conference on Intelligent Robots and Systems IROS Macau China November 4 8 2019 978 1 7281 4003 2 19 31 00 2019 IEEE6465 points according to tasks in order to satisfy the workspace which is inconvenient and could bring errors to a certain extent during the adjustment Therefore how to increase the workspace of the cable driven robot is one of the problems that need to be solved The main work of rehabilitation robots is to assist the patient to complete some movements along desired trajectories which consists of passive training and active training Passive training means that the patient is carried by the robot to move passively along predefined trajectories which is mainly used for the completely disable patient Active training means that the robot follows the movement of the patient and use an external assist force as needed It is usually applied for the patient who has been treated for a very long time and has fundamental exercise capacity In the existing research there is rare mention of the passive training function of the cable driven exoskeleton rehabilitation robot The importance of passive training in the early stage of rehabilitation training is unquestionable so how to make the cable driven robot meet the requirements of both active and passive training is also one of the problems to be solved 21 Moreover the human robot interaction comfortability is also important For example if the human robot connection is not stable and comfortable enough it will have a great influence on the control precision of the robot and also affect the patient s rehabilitation experience The design of friendly human robot interaction component is also one of the problems Aiming at the above problems this paper designs a cable driven 4 DOF upper limb rehabilitation training robot and proposes a passive training control algorithm for it The robot keeps a series of excellent features of the cable driven robot which are lightweight simple structure and free from joint misalignment Moreover by using the innovative rotation structure the workspace has been greatly increased which can achieve almost the complete ADLs space and can provide a wide range of active and passive rehabilitation training with 3 DOFs of the shoulder joint and 1 DOF of the elbow joint By optimizing the design of the structure and utilization of the air bag the wearable comfortability is increased the stability of the connection is improved By the series structure of the forearm and upper arm components the relative independence of the shoulder and elbow joints movement is realized which reduces the calculation and control complexity and also plays an important role in the extension of the workspace The actuators can be placed anywhere by the utilization of the Bowden cables which increases mobility in actual use The rest of this paper is organized as following Section II describes the whole mechanism of the robot including the mechanical structure the dynamic analysis and the workspace optimization Section III proposes the PID control algorithm which achieves the position control based on the cable tension Section IV presents the passive training experiment on the healthy subjects and the analysis of the results finally the conclusions are made in Section V II SYSTEM CONCEPT It can be seen from the existing researches that most of the cable driven robots belong to the parallel robots 14 16 22 23 According to the relevant researches of the cable driven robot the n DOF robot requires at least n 1 cables to drive 24 25 Moreover besides the number of cables the distribution of the cable attachment points also greatly affects the workspace Yang et al have designed and simulated the cable driven 7 DOF rehabilitation robot and the theoretical workspace is pretty large but there are too many cables six cables for the shoulder and wrist joints respectively in the system and the prototype has not been built 16 CAREX can adjusts the distribution of the cable attachment points manually according to training tasks to satisfy the requirement of the workspace 11 14 But it is not convenient and may causes more errors during the adjustment In addition Shao et al also optimized the workspace of the cable driven robot for shoulder rehabilitation but it is based on the fact that the shoulder joint has only two DOFs ignoring the internal external rotation of the shoulder joint 20 However the rotation DOF is very important especially for the passive training because in the case where the elbow joint is not at the initial position such as elbow flexion 50 a moment of internal rotation direction is generated on the shoulder joint due to the gravity of the forearm component under the active training model or the forearm under the passive training model This moment is obviously difficult to compensate for cable driven robots In fact since the cable can only provide pulling force in the direction of the cable in similar structures it is difficult for the robot to generate large forces in all directions simultaneously The schematic shown in Fig 1 is a typical cable driven spherical joint structure which is utilized widely in rehabilitation exoskeleton robot for the shoulder or wrist During the rotation following the direction of arrow ignoring the movement of other two DOFs increases and the tension must increase to generate enough moment as needed When is 90 it is the singularity of the rotation movement And cannot be too small because the cables must avoid collision with the other cables or the limb These causes that it is difficult for the rotation angle to satisfy the requirement of ADLs training In addition the rotation changes the configuration of cables which affects the force and movement in the other two DOFs a b Fig 1 The schematic of a typical cable driven spherical joint structure a the overall view b the top view S0 is the center of the shoulder joint U0 is the center of the upper arm module Si i 1 2 3 and 4 is the cable attachment point of the shoulder module Ui i 1 2 3 and 4 is the cable attachment point of the upper arm module 6466 Therefore based on the above analysis this paper proposes a new mechanical structure by which the distribution of the cable attachment points can be changed automatically and the robot workspace is greatly increased It is completely controlled by the controller according to the current arm posture during training without manual adjustment which undoubtedly increases the convenience of utilization The robot structure and workspace analysis will be introduced as following 2 1 Mechanical design As shown in Fig 2 there are the 3D model and the prototype of the 4 DOF upper limb rehabilitation training robot The robot system includes a driving box a base frame a shoulder bracket an upper arm module and a forearm module The shoulder bracket is fixed on the frame and the frame is placed on the ground The shoulder bracket is made of aluminum alloy with the Bowden cable fixing devices on the surface and the holes through which the cables can pass The shoulder bracket is connected to the upper arm module by four cables Considering the influence of the attachment points on the workspace as described above the placement of the shoulder bracket and the upper arm module cable attachment points is optimized and the optimization is described in the following section The robot has some special designs in the mechanical structure As shown in Fig 2 c the upper arm module is made of nylon material by 3D printing It is divided into two parts the inner and outer rings There are four cable attachment points on the outer ring and the shoulder bracket respectively When connected the inner ring can be rotated relative to the outer ring The contact surface has grooves for mounting small steel balls which are installed therein and lubricated to reduce the friction A cable groove on the outer surface of the inner ring is used for winding and fixing the cable and the two ends of this cable are combined with the Bowden cable through the holes of the outer ring thereby controlling the rotation of the inner ring The rotation between the inner and outer rings is driven by one motor This mechanism has two functions 1 When the current placement of the cable attachment points cannot provide enough positive pull force to meet the tension control strategy the rotation changes the relative position of the attachment points to meet the strategy Through the change of the attachment points distribution during the movement combined with the points distribution optimization strategy the ADLs workspace can be realized almost 100 the calculation is shown in the next section 2 By adding the rotation structure the internal external rotation of the shoulder joint can be independent of the flexion extension and abduction adduction reducing the coupling between the joint motions so that the four cables will not collide with the arm or the cables themselves even under a wide range of motion such as external rotation 60 In the rotation process the cable attachment points on the upper arm module rotate in real time which can ensure a wide range of rotation motion without changing the configuration of the cables between the shoulder module and the upper arm module The configuration of cables will not be distorted which is critical to increase the robot s workspace Because the robot is designed to provide both active and passive training modes that is even if the patient is in the initial stage of rehabilitation and the muscle strength is very weak the passive training can be done with the robot assistance So the protection of the patient with weak muscles is very important The inner ring of the upper arm module is connected with one end of the lateral support rod and the other end of the rod is connected with the forearm module to ensure the support for the patient s arm during the internal external rotation In order to adapt limbs of different length and avoid the joint misalignment the support rod is designed as a redundant DOF structure as shown in Fig 2 c There is no restriction on the center of the elbow joint during utilization and there is no need to adjust the limbs for different length the inner side of the inner ring is fixed with an air bag which has silicone material surface to increase the friction When the patient wears the device the air bag is inflated to an appropriate size so that the patient s arm and the upper arm module are stably connected the extension rod the air bag the air bag the forearm module the support rod the inner ring the outer ring the upper arm module a b c d the shoulder bracket the tension sensor the IMU sensor the Bowden cable Fig 2 a the prototype of this robot worn by the user b the 3D model of this robot c the 3D model of the components worn on the arm d the overall view of the driver box The upper arm and forearm module are also connected by two cables for controlling the flexion extension of the elbow joint The starting point of one cable is placed on the extension rod of the upper arm module so the collision between the cables and the limb can be avoided The inner side of the forearm module is an air bag similar to the upper arm module for fixing the human arm The utilization of 3D printing technology enables this series of complex mechanical structures to be realized at low cost light weight and high strength This also makes the robot system can be costume made according to the patient s body size it usually can adapt to normal body size but the special body size needs custom made modules The six cables except the one for the rotation are equipped with tension sensors to 6467 detect the cable tension ensuring the safety of the rehabilitation process and the active and passive