Abstract
In the development of a wearable robot, compact volume size, high energy efficiency, and a high load capacity linear actuator system are necessary. However, conventional hydraulic actuator systems are difficult to apply to wearable robots. Also, they have nonlinearities because of the presence of hydraulic fluid in a single rod cylinder. Electric linear actuators resolve the problems of hydraulic systems. However, due to their low load capacity, they are not easy to apply to wearable robots. In this paper, a pump-controlled electro-hydraulic actuator (EHA) system that considers the disadvantages of the hydraulic actuator and electric actuator is proposed for a wearable robot. Initially, a locking circuit design is considered for the EHA to give the system load holding capacity. Based on the developed model, the adaptive sliding mode control (ASMC) scheme is designed to resolve the nonlinearity problem of changes in the dynamic system. The ASMC scheme is then modeled and verified with Simulink. In order to verify the performance of the proposed adaptive control with the model, experiments are conducted. The proposed EHA verifies that the ASMC reaches the target value well despite the existence of many model uncertainties.
Highlights
Conventional hydraulic actuators have commonly been used in plenty of heavy equipment applications
It is important for more studies to focus on increasing muscular strength using actuators, such as with wearable robots for rehabilitation training, in military applications, and in commercial applications
An adaptive sliding mode control scheme is developed in order to minimize the model uncertainties for the pump-controlled electro-hydraulic actuator (EHA) system using Equation (17)
Summary
Conventional hydraulic actuators have commonly been used in plenty of heavy equipment applications. Controlled pumps have slow responses because the contained volumes are large, and the pressure must be built up initially. On the other hand, controlled valves offer rapid responses because the contained volumes are small. Regardless of the load pressure, the energy efficiency is low because the supply pressure is constant, and internal leakages occur when changing the direction of the fluid in the valve [6,7]. Despite these disadvantages, the conventional hydraulic system is widely used in heavy industries due to its high
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