Quasi Sliding Mode Control: An application to Heart Rate Regulation

Regular physical activity prevents many physical and mental illnesses. To achieve a healthy heart-rate profile and to prevent over exercise, it is important to select the exercise intensity properly for training sessions. Heart rate is easy to measure compared to other important parameters related to acute exercise. So various training tools provide some features to produce a user defined heart rate profile as a reference by adjusting the workload. In this paper a long duration exercise on a treadmill is explained and a nonlinear heart rate profile model is used to meet predefined control objectives. A nonlinear dynamic model of the human heart rate response is used [1] and the control objective is to make the heart rate track a predefined reference trajectory. The design of a first order Sliding Mode controller (SMC) is first attempted here. But due to the presence of a discontinuous signum function in the control signal, undesired phenomenon of `chattering' is occurred. To avoid the chattering, a Quasi Sliding Mode Controller (QSMC) is designed where discontinuous signum function is replaced by continuous sigmoid function. The performance of the proposed controller is also compared with the existing one [1] by simulation study.