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Research on Prosthetic Hand Modeling Based on ADAMS and MATLAB Xu zhuojun Tian yantao Liyang School of communication engineering School of communication engineering School of communication engineering Jilin University Jilin University Jilin University Changchun, China Changchun, China Changchun, China xuzhuojun tianyt AbstractIn this paper, we use ADAMS to design a model of intelligent prosthetic hand, which has the high humanoid shape, its weight and size are similar to adults hand. The proposed model has 16 degrees of freedom (dofs), which are split into 14 dofs for the five fingers, and 2 dofs for the wrist. The model allows the execution of Activities of Daily Living (ADLs) like grasp, wrist turn and so on. in order to the research the control algorithm of the prosthetic hand , Integration of ADAMS with MATLAB for designing and developing prosthetic hand system is presented in this paper. The model can complete simple movements by proportional control algorithm. Keywords-virtual prosthetic hand; ADAMS; modeling; grasp I. INTRODUCTION Intelligent prosthetic hand is a substitute for the integral part of the amputees. The intelligent prosthetic hand using surface Electromyography (EMG)-controlled has become a mainstream class of external powered prosthetic hand. The control system of intelligent prosthetic hand is given in Figure 1. The information source of EMG control is EMG signal which detect from the remnants of the muscles of residual limb by surface electrodes. EMG collection module sent EMG signal into the movement decision module. The signal will be carried out feature extraction, classification and then complete the action decision-making in movement decision module. The movement implement module make the prosthetic hand do corresponding movement according to the result which obtained from movement decision module. There are two parts included in the movement implement module, one is control algorithm design and the other is prosthetic devices design. Figure 1. control system of intelligent prosthetic hand. Now many studies are carried out around the prosthetic devices design. To date there are no prosthetic hand is available to replace human hands that fully simulates the various human-like operations of moving, grasping, lifting, twisting and so on 1. Moreover, most of the market available hand prostheses do not have the conditions for secondary development. The research on intelligent prosthetic hand will be limited if only around the product. The model of intelligent prosthetic hand we present can solve this problem precisely. It provide a platform for design and development of prosthetics products. The model can simulate a variety of hand movements, and can monitor data in real time as velocity, acceleration, torque, angle and so on. In ADAMS and MATLAB simulation environment, different control algorithms can be attempted and verified. Automatic Dynamic Analysis of Mechanical Systems (ADAMS) is a analysis software about virtual prototype which is developed by Mechanical Dynamics Inc. ADAMS create fully parametric geometric model of the mechanical system use the interactive graphical environment. Its solver using Lagrangian equations method of multi-rigid-body system dynamic theory to establish the system dynamic equations for make the statics, kinematics and dynamics analysis of the virtual prototype system. This paper presents design and simulation of a virtual prosthetic hand model in the 3-dimensional environment in ADAMS/VIEW. The dynamics simulation on the hand model is implemented on the platform integration of ADAMS with MATLAB. Virtual model design process is then given with details in Section II on settings required for ADAMS environment. Kinematic simulation results in Section III verify the rationality of hand model. Section IV tested model under a closed loop controller, Simulation results show that the model can do simple action under control like grasp. II. VIRTUAL PROSTHETIC HAND MODEL The hands, the eyes which can feel 3-dimensional space, the brain which can handle information coming from eye-hand are three vital organs make human has a highly intelligence. It can be attributed to a complex structure of hand that human can put different gestures by bending the fingers. Human beings have five fingers on each hand, including three phalanxes of the index finger, middle finger, ring finger, little finger, and only two phalanxes of the thumb. Fingers can bend inward, and make a slight swing to left and right. The models degrees of freedom we designed in this paper are given in Figure2. The deformation of palm contributes little in ADLs, so degree of freedom is not assigned to the palm in the model. This paper is supported by the Key Project of Science and Technology Development Plan for Jilin Province (Grant No.20090350), funding by Jilin university 985 project engineering bionic technology innovation platform and supported by doctoral student interdisciplinary research project fund of Jilin University ?No.2011J009). 1635978-1-4577-0321-8/11/$26.00 2011 IEEE (a) (b) (c) (d) Figure 2. Kinematic structure of model. The proposed model as shown in Figure 3 is composed by rigid bodies, the size of palm and fingers is similar to adults right hand according to the anatomical description. It reflected physical properties of the human hands. The model is the default steel structure in ADAMS, weigh 500 grams. 1 -14 marked in the Figure 3 is joint angle between each adjacent phalanx, e.g. 1 is the joint angle between the first phalanx and the second phalanx of the index finger from the tip to the root. The controller in Section IV makes the model complete movement by control these joint angles. Figure 3. Prosthetic hand model. In the initial state, fingers and palm are in the same plane which consists of X axis and Y axis in the 3-D environment in ADAMS. The last four fingers all have three phalanxes, the position connect to the palm and the length of these twelve phalanxes are all different. Thumb has two phalanxes, and almost at right angle with the other four fingers in the initial state. As the hand movements are more emphasis on the direction of relative movement between the thumb and other four fingers. Reference to the shape of the intelligent prosthesis product-Cyber Hand 2, we set the position of thumb lower than it in the actual human hand. The thumb in the model we proposed is into a 130 angle with other four fingers and palm. The hand model in this paper has 16 dofs, thumb has 2 dofs, each other four fingers has 3 dofs, since the number of the phalanxes they have, and the wrist has 2 dofs. In ADAMS we select the link part in the rigid body library for the fingers, and the extrusion part which can be shaped into irregular shape in the rigid body library for the palm. Revolute joint is added in each joint of each finger, and spherical joint is added in the root of palm to reflect the degree of freedom of the wrist. It has 3 dofs of the spherical joint in ADAMS, according to the kinetic characteristic of wrist; we locked the degree of freedom along the Z axis. III. KINEMATIC SIMULATION IN ADAMS After design hand model, we will test rationality of the model. We set rotational joint motion command on each joint. Different movements would be done by modifying the parameters in the command. There are two parts in the kinematic simulation, wrist movement simulation and fingers movement simulation. These two kinds of movements can be simulated simultaneously, however, in order to easy to observe results, and the characteristic of the hand movements also be considered that the action are focused on one aspect generally. So, the simulation work is divided into two parts. A. Wrist Movement Figure 4. Wrist turn simulation. Though the wrist part is not appear in this hand model, the freedom of wrist movements is reflected in the forms of movement of palm due to set spherical joint in the palm root, and the orientation of joint is specified as normal to the working grid in ADAMS, so the movement of palm root can completely replace the wrist movement. The wrist mainly completes two kinds of movements which is turn and extension-flexion. In the ADAMS reference coordinate system, these two movements are along the X axis and the Y axis. We choose the axis which movement runs 1636 (a) (b) (c) (d) (a) (b) (c) around and set the rotate speed by 1 degree per second in motion commands, in addition, the movements along the other two axis direction are locked. The simulate results are shown in Figure 4 and 5, each group of pictures is the screenshot from simulation animation of ADAMS in accordance with the order from (a) to (d), where Figure 4 is wrist turn movement; Figure 5 is wrist extension-flexion. The results show that model can complete the movement realistic during kinematic simulation. Figure 5. Wrist extension-flexion simulation. B. Finger Movement One of the most common hands movements is grasping, so it is the most important for the hand model. There are many grasp movement in ADLs, which mainly come in three classes: Power grasp (the shape C is formed between thumb and other fingers, which is usually used to grasp the cylinders, e.g. cups and bottles, etc.)? Lateral grasp (this action requires that thumb and other fingers keep unbend state and the relative motion is effective, the side view of hand is flat, which is usually used to hold the flat objects, e.g. books and credit cards, etc.), Precision grasp (that is the relative motion between thumb, index finger and middle finger, three fingers are tips to tips, which is usually used to grasp the small globular object, e.g. some fruit and Ping pang, etc.) 3. The kinematics simulation of finger movements is mainly for the above three kinds of movements. The size of each phalanxes in each finger is not the same, if they move with the same speed, the simulate results are not satisfactory. In order to achieve a more precise result, we set the different speed for each motion command, and monitoring key joint angle through the sensor in ADAMS to control simulation stop time. The Figure 6 is screenshots of finger movement simulation including wrist freedom has been locked, from (a) to(c) are Power grasp, Lateral grasp, Precision grasp. The results show that the model can achieve three kinds of grasp movements like humans . Figure 6. Finger movement simulation. IV. DYNAMIC SIMULATION IN ADAMS WITH MATLAB It is directly to test rationality of the modeling with kinematics simulation, and can quickly verify the design of the original idea; however, it is not the ultimate goal of our work. The ultimate goal we designed the hand model is to build up a platform which the dynamic simulation for virtual prototyping and the control algorithm research of the intelligent prosthetic hand can be studied on it. Though ADAMS has the capability of implementing a closed loop control of the virtual prototype, its capability is quite restricted. On the other hand, MATLAB is well known for designing control systems. Integrating ADAMS with MATLAB allows us to get the benefit of both. A M-file and some other MATLAB files about the hand model we designed can be generated by ADAMS with all the parameters we set before, and we can set the input and output variables of the MATLAB control system in it. The series files are imported into MATLAB, and then will form an ADAMS module in MATLAB/SIMULINK (Figure 7). 14 input and output variables were set correspond to 14 dofs of fingers in the system. 2 dofs for the wrist is not included in this control system temporarily. A controller should be built on the external of ADAMS module. When the SIMULINK simulation starts, the program will automatically call the ADAMS / VIEW in the simulation window, play the dynamic simulation. Figure 7. ADAMS module in MATLAB/SIMULINK. 1637 (a) (b) (a) (b) (c) (d) We used the controller which reported in 5 to control the model achieve a power grasp movement. We use this control structure to validate the availability of joint simulation system with ADAMS and MATLAB which we set up. A typically proportional controller is shown in Figure 8. Kp is the proportional gain on the error. d is the desired joint angle. n is the measured normal angle with corresponding feedback gain, Kn. Figure 8. Typically proportional controller. There are four controllers with the same diagram but different parameters in control system to control a different joint angle that is shown in Figure 3 in Section II. Which, 1 -4 is a group, 5 8 is a group, 9 -12 is a group, and 1 3, 14 is a group. The screenshots of dynamic simulation is shown in Figure 9 from (a) to (c), and (d) is the front view of the grasp movement. For distinguished from the previous simulation, we render the model in ADAMS/VIEW. As can be seen from Figure 9, the model can do grasp movement under proportional controller. Although the wrist is uncontrolled, as force on the fingers, the wrist get the force indirect is in an extension state naturally. Figure 10 (a) is the curve of 1 measured by SIMULINK during dynamic simulation, The x-axis coordinate is in units of , the joint angle corresponding to the end of the movement time is 137 degree by conversion. Figure 10 (b) is the curve of 1 measured by ADAMS during kinematic simulation in Section ?, the results is generated by finger joints uniform motion under the humanoid ideal state, the joint angle corresponding to the end of the movement time is 140 degree. By comparing the two figures shows that the trends of joint angle changes in dynamics simulation with control and trends in the ideal state are approximate, And the joint angle at the end of the movement is almost the same size. The comparison indicate that the proposed model can be achieved humanoid state under control. V. CONCLUSION Kinematic simulation of prosthetic hand model using ADAMS has been presented in this paper. Seve