Discrete-Time Fractional Order Integral Sliding Mode Control of an Antagonistic Actuator Driven by Pneumatic Artificial Muscles

Abstract

Recently, pneumatic artificial muscles (PAMs), a lightweight and high-compliant actuator, have been increasingly used in assistive rehabilitation robots. PAM-based applications must overcome two inherent drawbacks. The first is the nonlinearity due to the compressibility of the air, and the second is the hysteresis due to its geometric construction. Because of these drawbacks, it is difficult to construct not only an accurate mathematical model but also a high-performance control scheme. In this paper, the discrete-time fractional order integral sliding mode control approach is investigated to deal with the drawbacks of PAMs. First, a discrete-time second order plus dead time mathematical model is chosen to approximate the characteristics of PAMs in the antagonistic configuration. Then, the fractional order integral sliding mode control approach is employed together with a disturbance observer to improve the trajectory tracking performance. The effectiveness of the proposed control method is verified in multi-scenario experiments using a physical actuator.

Design and control of soft rehabilitation robots actuated by pneumatic muscles: State of the art

“…1 (n)) [38,44,45] with larger assistance output. This high compliant lower limb rehabilitation orthosis is aimed to guide the patient's lower-limb to a designate trajectory and can adapt the compliance according to the patient's disability [46,47], as shown in Fig. 1 (o).…”

Special Issue on “Human Health Engineering”

“…Contributions can focus on sensors, wearable hardware, algorithms, or integrated monitoring systems. We organized the different papers according to their contributions to the main parts of the monitoring and control engineering scheme applied to human health applications, namely papers focusing on measuring/sensing of physiological variables [24][25][26][27][28][29][30][31], contributions describing research on the modelling of biological signals [32][33][34][35][36][37][38], papers highlighting health monitoring applications [39][40][41][42], and finally examples of control applications for human health [43][44][45][46][47][48]. In comparison to biomedical engineering, we envision that the field of human health engineering also covers applications on healthy humans (e.g., sports, sleep, and stress) and thus not only contributes to develop technology for curing patients or supporting chronically ill people, but also for disease prevention and optimizing human well-being more generally.…”

“…Finally, Dao et al [48] investigated pneumatic artificial muscles (PAM) as a basis for antagonistic actuators in assistive rehabilitation robots. They developed a discrete-time second order model describing the dynamic characteristics of PAMs and a fractional order integral sliding mode controller to improve the trajectory tracking performance.…”

Discrete-Time Sliding Mode Control based on Exponential Reaching Law of a Pneumatic Artificial Muscle Actuator

“…It has been acknowledged that sliding mode control (SMC) is an effective robust control strategy for PAMs based systems in the presence of uncertainties and disturbances [11][12][13][14][15][16][17][18]. Nevertheless, with the rapid development of digital controllers, studying the discrete-time sliding mode control (DSMC) design has attracted considerable attention.…”

“…In discrete-type SMC methodology, the control input is updated at the sampling instant only and remains unchanged during the sampling period. Moreover, numerous works of DSMC have been carried out in the literature on many kinds of systems, including the equivalent control approach [15] and the reaching lawbased method [16]. Since the chattering phenomenon is a major problem that degrades tracking accuracy in the application of DSMC, this paper is then concentrated on the reaching-law based control strategy which is considered effective against chattering issues.…”