Design and development of a novel redundant and fault-tolerant actuator unit for heavy-duty parallel manipulators

Abstract

This paper proposes a novel dual-input/single-output actuator unit, called a redundant and fault-tolerant actuator (RFTA), designed for heavy-load parallel manipulators. After the definitions of redundant and fault tolerance are given, the principle of the proposed RFTA is described using its two working processes. According to the derived kinematics, 12 fault modes caused by two different input velocities are developed and classified, and the physical meanings are represented correspondingly. Mechanical transmitting properties of the proposed RFTA are analysed respectively. On the other hand, RFTA, as a dual-module hot spare architecture to achieve high reliability and safety, with its complete redundant structure can be called Multiple Births Structure (MBS) and is different form the traditional partial redundant structures – Siamesed Births Structure (SBS). The reliability models show that RFTA is more reliable than SBS. Three guidelines – the select guideline, the design guideline, and the operation guideline – are suggested. Those design guidelines are useful to designers and users. A prototype of RFTA and its control system are developed and the relevant experiments are carried out. The experimental results demonstrate that RFTA is able to not only supply double driving force but also tolerate some local faults caused by out-of-syncs. RFTA provides heavy-duty equipment, especially large-scale parallel manipulators, with a new probability in changing their drive mode, from the hydraulic power supply to the motor drive. Furthermore, this paper also demonstrates that RFTA has some potential applicable prospects under heavy-duty environments, such as a large-scale parallel earthquake simulator and an electric press with heavy duty cycles.