Kinematical analysis of an upper limb prosthesis.

Menyhardt, Karoly ; Nagy, Ramona ; Luca, Gheorghe 等

1. INTRODUCTION

The main purpose of this study is to compare the kinematical parameters from the mechanical model (figure 1a), the 3D simulation (SolidWorks/CosmosMotion) and the physical data gathered, with a professional APAS measurement system, from a prosthesis designed (figure 1b) and developed at CMPICSU Research Center from "Politehnica" University of Timisoara by the first author.

The kinematic study was initially done in order to compare the motion of the human upper limb and the prosthesis. Further studies of the mechanical model presented in the current paper helped us understand the motion of the prosthesis.

This study was developed from the necessity of quantifying the basic movements of the prosthesis in order to make it run smoother and more natural, like the human upper limb (Pravin, 2006).

Throughout the literature there are few papers that present the mechanical model and compare it with a physical prosthesis, realized by the authors (Duraisamy et al., 2006), (Jadhav & Krovi, 2003). In most cases, the kinematical analysis is made on an idealized anatomical model where the muscles are replaced by given forces. In the current study the analysis is done on a real mechanical model that is analogue for the developed prosthesis.

A concrete and in detail analysis will permit to specify the conditions for the working regime (Lloyd et al., 2000). In addition, graphics that evaluate the phenomena are traced putting in evidence the validity of the model.

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2. MECHANICAL APPROACH

The stability and motion of the prosthesis is influenced by lots of factors, sometimes even the least significant factor could affect the outcome of the task (Raikova, 1992), (Veeraraghavan et al., 2004).

Because of the difficulties in calculus, the prosthesis was modeled as a two bar mechanism (figure 1a) where OA (the arm) executes a rotation around joint O, due to change in the prosthesis' center of gravity. The AB segment (forearm with hand) executes a planar motion, driven by the connected arm and elbow motor. The angular velocity [[??].sub.2] was considered constant throughout its range of motion (the prosthesis is able to do a 150 degrees flexion in the elbow).

Considering the position for the center of gravity being:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

[[theta].sub.2] was determined as a function of [[theta].sub.2] (2)

Trough various calculus and restraint conditions, e.g. the center of gravity remains ahvays on ms Oy axis, results that its velocity is mat from equation (3) and its curve Fig.2.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)

The acceleration for the center of gravity for the prosthesis' mechanical model is shown in equation (4) and figure Fig.3. prosthesis' mechanical model.

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All the other linear and angular kinematical parameters were determined for each point of the mechanism. These parameters helped in establishing the trajectory and the workspace for the prosthesis in order to assess the possible movements. The kinematical analysis of the movement refers at the quantitative description of body segments without taking into account the forces that generate the movement.

3. RESULTS OF THE ANALYSES

In this paragraph are presented the results of the kinematical analysis from different points of view/interest. In all the studied cases the time needed to perform the prosthesis movement was slightly longer, the artificial "muscles" (DC steppers) being slower than the human muscles. The trajectories and exercises were the same in all cases, generated by computer and by the upper limb prosthesis.

For the time interval [10, 27] seconds the curve from the theoretical model almost overlaps with the curve from the physical model. The differences in the amplitude are due to the simplification of the model (uneven distribution of the masses in the physical model) and the measurement uncertainty. The curves are presented in figures Fig.4 and Fig.5.

The resulted data from the analysis for a movement cycle of the upper limb/prosthesis or for a succession of cycles can be used to analyze the movement pattern (Karamanidis et al., 2003). By evaluating this movement a joint, motor or coordination deficit can be outlined or quantified and efficient strategies of compensation can be made based on these values (Murray & Johnston, 1998). By determining the kinematic parameters (linear and angular acceleration), is possible to know the inertial forces for further dynamical studies.

However, long-term cyclic testing is necessary to ensure reliability and a valid assessment of the efficacy of the prosthesis can only occur by clinical trial.

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4. CONCLUSION

This performed mobility study is useful in outlining the differences between the movement of a human arm and a prosthesis. The gathered results have been filtered out and processed in order to correct and enhance the prosthesis's unnatural movement. Every movement scheme has different solutions based on the forces that appear and the prosthesis' orientation and position. Determining the orientation and position in real time without the use of external equipment brings forward new obstacles that need to be surmounted.

The results validate the physical prosthesis and its behavior in normal load conditions.

Comparing the results from the mathematical approach, mechanical simulation and the measured data from prosthesis and human upper limb, could help us improve the control of the prosthesis' motor by feeding adequate input parameters to the microcontrollers.

The next steps in the research will include sensorial feedback and adaptation of the microcontrollers to these inputs.

5. REFERENCES

Duraisamy, K.; Isebor, O.; Perez, A.; Schoen, M.P.; Naidu, D.S. (2006). Kinematic Synthesis for Smart Hand Prosthesis, Biomedical Robotics and Biomechatronics, BioRob 2006. The First IEEE/RAS-EMBS International Conference on, Volume, Issue, 0-0 0 Page(s):1135-1140

Jadhav, C., and Krovi V. (2003). In-Vivo Estimation of Unknown Upper-Limb Kinematic Parameters, 11th National Conference on Machines and Mechanisms, (NaCoMM-2003), Delhi, India, December 18-19, 2003.

Karamanidis K.; Arampatzis A, Bruggemann G.P. (2003). Symmetry and reproducibility of kinematic parameters during various running techniques, Medicine and science in sports and exercise vol.35, 6, pp. 1009-1016 Lippincott Williams & Wilkins, Hagerstown, ISSN 0195-9131

Lloyd D.G., Alderson J., Elliott B.C. (2000). An upper limb kinematic model for the examination of cricket bowling: A case study of Mutiah Muralitharan, Journal of Sports Sciences, Volume 18, Number 12, 1, pp. 975-982(8)

Murray I.A., Johnson G.R. (1998). Upper limb kinematics and dynamics: the development and validation of a measurement technique, Proceedings of Fifth International Symposium on the 3D Analysis of Human Movement, Chattanooga, Tennessee. 2-5 July.

Pravin N. (2004). Development of Quantitative Measures for Characterization of Upper Limb Dysfunction, M.S. Thesis, Department of Mechanical & Aerospace Engineering, SUNY Buffalo.

Raikova R. (1992). "A General Approach for Modelling and Mathematical Investigation of the Human Upper Limb", Journal of Biomechanics, 25, 857-867.

Veeraraghavan A., Roy-Chowdhury A.K., Chellappa R. (2004). "Role of shape and kinematics in human movement analysis," in Proceedings of the IEEE CVPR '04, Washington, DC, USA, vol. 1, pp. 730-737.