Lintner, S. (2017). Orientation proportional control of a prosthetic wrist [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2017.48441
E354 - Institute of Electrodynamics, Microwave and Circuit Engineering
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Date (published):
2017
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Number of Pages:
58
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Keywords:
Prothese; Armbewegung; Sensor
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Prosthesis; Arm movements; Sensor
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Abstract:
In the recent years multiarticulated upper limb prosthesis with an increasing amount of degrees of freedom (DOF) were developed. Unfortunately the development of suitable control methods could not keep up with that progress. The conventional control method for prosthesis of the upper limb, which is based on the signals of two surface electro myography (sEMG) electrodes placed on residual muscle groups, allows only for sequential and speed proportional control of the prosthesis. A state machine must be implemented to access all DOF. With an increasing amount of DOF this control method becomes increasingly slower and unintuitive to use. The learning process to master the control method is slow and difficult. In this work a control method for upper limp prosthesis using an inertial measurement unit (IMU) is developed and tested. The movement of the residual lower arm is used to generate an additional control signal. This control signal is being used to control the active wrist rotation of the prosthesis. The control signal generated by this approach allows for a position proportional control of the prosthesis. This control method allows to simultaneously generate a second control signal to control an active wrist extension/flexion. However active wrist extension/flexion is not available for daily life users and therefore it was not in the focus of this work. Based on the works of Mayer [10] and Schlachter [18] an embedded prototype will be created. First an AXON IMU is added to a Michelangelo hand system of the company Ottobock. To generate a position proportional control signal from the IMU data an orientation estimation algorithm is needed. To find the most suitable, different orientation estimation algorithms are compared. The Michelangelo hand system is enhanced by a position proportional controller for control of an active wrist rotator. Finally a suitable switching condition is chosen to activate and deactivate the IMU control method. For evaluation of the IMU control approach clinical user tests are performed. The clothespin relocation test (CRT) and the compound manipulation task (CMT)[1] were chosen to be suitable tests. Three amputee subjects performed the tests first with the IMU control method and then with the conventional EMG control method. A comparison of the task completion times shows that on average the users were able to perform the CRT 25.2% faster and the CMT 2.4% faster with IMU control method. Interviews with the test subjects were held to record their feedback on the IMU control method. Users reported that they felt that the IMU control method is very intuitive and has good suitability for daily life. Users especially emphasised the positive effects of the simultaneous control of opening/closing of the hand and wrist rotation, which opens up new fields of application for the prosthesis. Users also reported that they needed a higher muscular effort or felt muscle fatigue when using the IMU control method. The control method introduced in this diploma thesis showed to be able to overcome the limitations of the EMG control method. Simultaneous control over two degrees of freedom of the prosthetic hand is possible and leads to more natural looking movements. The position proportionality provides intuitive control of the prosthesis and the relative orientation estimation allows the prosthesis to be used in any posture. To further test the full potential of the introduced control method a prototype with active wrist flexion/extension should be developed and tested in clinical user tests. Also a long-term test should be performed to evaluate the full capability of a user handling the IMU control method.
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