Development of an exercise machine for enhanced eccentric training of the muscles : A study of sensors and system performance

Sammanfattning: Currently, there are various training machines that can support training of the muscles while the muscles are lengthened, also known as eccentric training. Training machines that are widely used to train the muscles eccentrically utilize a flywheel to generate load to the user. When training the muscles eccentrically with such a machine, there is a desire to accomplish eccentric overload, which is achieved when the muscles under training are exposed to a very high load during eccentric training of these muscles. To achieve this, the user needs to activate other muscles that are not in the focus of the training or be assisted by another person. In this study, a novel, smart flywheel training machine was developed by implementing electric motor and sensors, which could identify the exercise pattern of the user and help achieve desired eccentric overload. This study focused on how the system performance of such training machine interacting with human beings was affected by various grade of sensor feedback. With an increased resolution of the sensors and a lower sample time, the cost of the system is increased, and it was therefore of interest to study what grade of sensor feedback was required. More exactly, this study evaluated how the system performance was improved when sensor resolution was improved, what resolution and sample time were required for the system to perform correct and safely and last, how noise and disturbances affected the system. The study was conducted in a simulated environment in Matlab and Simulink, and some real tests and experiments were also performed on the existing flywheel training machine. An incremental encoder was implemented in the system and resolution of the encoder, as well as sample time, were tweaked in the simulation to test different combinations of these. The results showed that both resolution and sample time had an impact on the system performance. A higher resolution resulted in a smaller tracking error to some extent, but after a certain value the system became unstable if the sample time was not small enough. Noise and disturbances had a minor impact on the system performance. It was concluded that the best choice of encoder resolution was 0.0314 radians with a sample time of 0.01 ms. Even lower resolution such as 0.628 rad, 0.126 rad or 0.0571 rad with a sample time of 0.1 ms could be allowed and should be considered safe. However, the system might not perform as desired if these alternatives are chosen, although the alternatives might decrease the cost of the system.