Design and implementation of a control system for a powered reciprocating gait orthosis
The University of Salford has developed a program in order to improve the control of lower limb orthotics thus improving the ability of paraplegics to walk. Although the system is greatly needed for rehabilitation it is hoped that the final system would enable paraplegics to walk in the community. The present project, which is based on previous designs such as the R. G. O (Reciprocating Gait Orthbsis), strives to add external power at the hips of the R. G. O. The constructed prototype is made of a mechanical skeleton with each leg driven by a brushless motor and a lead screw. The main purpose of this project is to design a control system to control the motion of the legs. The first step in achieving this task was to model the various components of the system separately and then derive a model using system identification that will describe the behaviour of the whole system. The starting point was a mechanical device with two motors mounted one at either hip. A full mathematical analysis of the system is carried out. Once a mathematical model is derived for the RG. O with the two motors it can be used to carry out real time simulations using MATLAB. Once the model is derived it must be validated to make sure it is actually a mathematical representation of the system. The identified model is usually very accurate as it is based on the actual system performance. Then real time simulations of the theoretical and the identified model are compared. If the theoretical model behaves in the same way as the identified model then it is validated and may be used for further work. The models derived using system identification were validated and gave a good comparison when compared to real data. A pole placement controller was designed and tested based on these models. The controller performance was tested with the orthosis unloaded, loaded with artificial loads (a plaster leg weighing 10 Kg). The controller managed to follow the pre-set trajectory reasonably well. The orthosis was then tested with a volunteer in it. Again the performance was very encouraging. The fmal Project will be P. C driven System with the possibility of using NiCAD Batteries as the power source. The main tools, which will be used in order to carry out simulations and comparisons of theoretical and practical results, are MATLAB. The software used was C.