A Novel Framework for a Systematic Integration of Pneumatic-Muscle-Actuator-Driven Joints into Robotic Systems Via a Torque Control Interface

Abstract

In this paper, two different torque control approaches for PMA-driven (PMA = Pneumatic muscle actuator) revolute joints are presented and tested. In previous work controllers for PMA-driven robots are typically customized for the use on a specific robotic system. In contrast, the proposed controllers define a general control interface for every robot that is actuated by PMA-driven joints. It will be shown that controlling the torque of a PMA-driven joint enables the use of standard robotic motion control frameworks, because the torque represents the natural input of the robotic equation of motion. Therefore, both proposed torque control approaches are interconnecting PMAs and their challenging characteristics on the one hand and “conventional” motion control strategies for robots on the other hand. After a detailed discussion of two different torque control approaches, we show that a torque controller handles all characteristics and dynamics of a PMA-driven joint internally, which implies that only its bandwidth and its static torque characteristic must be taken into account for the design of the outer motion control loop. This feature simplifies the integration of PMA-driven joints in robotic systems enormously, as will be demonstrated by a design of a cascade-structured, flatness-based motion controller for an exemplary robot with one degree of freedom.

A Review on the Development of Pneumatic Artificial Muscle Actuators: Force Model and Application

“…Nowadays, Shadow Group of Companies from the U.K. [104] and Festo AG & Co. from Germany [105] are manufacturing various kinds of PAM for industrial robotics and medical applications [106]. The PAMs are very much suitable for multiple applications like exoskeletons along with rehabilitation assistance [6,107,108], grasping and handling delicate objects with complex geometry [109][110][111], a robotic mechanism where multiple sophisticated movements are required [112][113][114][115][116], and industrial and service robotics [6,[117][118][119]. PAMs are mainly used as robotic actuators in applications where compliance and low powerto-weight ratio are essential.…”

A Current-Mode Analog Front-End for Capacitive Length Transducers in Pneumatic Muscle Actuators

“…For the patient’s safety and control of their interaction with these mechanical apparatus, force, length, and pressure sensors must be employed for the real-time control and actuation of the artificial muscles. In this sense, small force and pressure lightweight sensors are commercially available; in contrast, length sensors are typically bulky and not so easy to install in wearable devices [ 9 , 10 , 11 , 12 , 13 ]. However, several solutions have been reported in literature aimed to embed length sensors in pneumatic muscles [ 14 , 15 , 16 , 17 ].…”