A new approach for hybrid (PID + MRAC) adaptive controller applied to two-axes McKibben muscle manipulator: a mechanism for human-robot collaboration

Purpose This paper aims to present a new approach, called hybrid model reference adaptive controller or H-MRAC, for the hybrid controller (proportional-integral-derivative [PID + MRAC]) that will be used to control the position of a pneumatic manipulator. Design/methodology/approach It was developed a McKibben muscle using nautical mesh, latex and high-density polyethene connectors and it was constructed an elbow manipulator with two degrees of freedom, driven by these muscles. Then it was presented the H-MRAC control law based on the phenomenological characteristics of the plant, aiming at fast response and low damping. Lyapunov's theory was used as the project methodology, which ensures asymptotic stability for the control system. Findings It was developed a precise control system for a pneumatic manipulator and the results were compared to previous research. Research limitations/implications In collaborative robotics, human and machine occupy the same workspace. This research promotes the development of safer and more complacent mechatronic systems in the event of collisions. Practical implications As a practical implication, the research allows the substitution of electric motors by McKibben muscles in industrial robots with high accuracy. Social implications The pneumatic manipulator will make the human-robot physical interaction safer as it can prevent catastrophic collisions causing victims or equipment breakdown. Originality/value When compared to results in the literature, the present research showed a 37.51% and 36.74% lower global error in position tracking than MRAC and Adaptive proportional-integral-derivative (A-PID), respectively, validating its effectiveness.

Model Predictive Displacement Control Tuning for Tap-Water-Driven Muscle By Inverse Optimization with Adaptive Model Matching and Analysis of Contribution

The tap-water-driven McKibben muscle has many advantages and is expected to be applied in mechanical systems that require a high degree of cleanliness. However, the muscle has strong asymmetric hysteresis characteristics that depend on the load, and these problems prevent its widespread use. In this study, a novel control method - model predictive control with servomechanism based on inverse optimization with adaptive model matching - is applied to the muscle based on a high-precision mathematical model employing an asymmetric Bouc-Wen model. The experimental results show that the proposed approach achieves a high tracking performance at a reference frequency of 0.3 Hz, with a mean absolute error of 0.13 mm in the steady-state response. Furthermore, an easier controller tuning can be achieved. Additionally, the authors evaluate the contributions of the elements of the proposed method. The results show that the contribution of the adaptive system is higher than that of the servo system. Furthermore, the effectiveness of adaptive model matching is reconfirmed.

Model Predictive Displacement Control Tuning of Tap Water Driven Muscle With Adaptive Model Matching: Numerical Study

The tap water driven McKibben muscle possesses several merits of the water hydraulic system, including high flexibility, low weight, and high power density. These aspects enable the application of this muscle system to mechanical systems that require high cleanliness. However, the muscle shows strong asymmetric hysteresis characteristics depending on the applied load, which blocks its effective application. This study presents an appropriate modelling of the hysteresis characteristics of the muscle using an asymmetric Bouc-Wen model along with a control strategy, based on the model predictive control with servomechanism (MPCS). Subsequently, an inverse optimisation is proposed by applying an adaptive model matching to make the compensated system match the prespecified predictor to reduce the time-consuming routine for obtaining proper weight matrices in the evaluation function of the model predictive control. The numerical simulation results show that the proposed approach works well, and easier controller tuning can be achieved.

Segmentation of a Soft Body and its Bending Performance using Thin McKibben Muscle

In recent years, soft actuator has been extensively developed in robotic research. This type of robot is expected to work with human with its flexible and adaptable advantage. The actuator material is soft, light, safe and high compliant. Due to these factors, soft McKibben is of interest as an actuator for this research for bending application. This paper introduces a variant bending analysis of a soft body manipulated using soft McKibben actuators. A series of 1.80 mm width with the length of 120.0 mm McKibben actuator is used to control the bending motion. The design consists of four McKibben actuators arranged in parallel and compacted in a soft body. The bending behavior was evaluated using an experimental test with a variety of pneumatic input pressure and length section on the actuator. The experiment showed that the bending angle was influenced by the segmentation length of the actuator, where the segmentation length and increased input pressure also allow more bending on the actuator. The actuator with lot of section gave more bending response compared to the actuator with lesser section. With the performance exhibited from this study, McKibben actuator can be applied in a wider use for continuum manipulator.

Hybrid Pneumatic-Hydraulic Actuator with Adaptable Stiffness

This work presents a method to control the stiffness of a hybrid actuator. The resulting stiffness is required to meet the conditions of real life applications, such as human prosthetics, human-robot interaction, and delicate robot interaction. The hybrid actuator is basically a pneumatic-hydraulic muscle, which can operate simultaneously in both pneumatic and hydraulic modes. The main challenge in this work is to manage the switching between pneumatic and hydraulic modes. In pneumatic mode when a load is applied to the actuator, air in the tank is allowed to compress resulting in muscle extension. While in hydraulic mode, the fluid is pressurized and the resultant system stiffness is higher. In both cases, the McKibben muscle is full with hydraulic fluid. It has been shown that the performance of the actuator is mostly the same in terms of response and bandwidth in both modes of operation. The use of different types of controllers to improve the system performance is investigated. It is found that the parallel configuration combined with PID controller is the best solution for achieving the required muscle performance.