Abstract
This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution is proposed at the valve-controlled actuator and hydraulic power system interaction level. The energy consumption of the widely popular valve-controlled load-sensing (LS) and constant-pressure (CP) systems is effectively minimised through cost functions formulated in a discrete-time dynamic programming (DP) approach with minimum state representation. A prescribed end-effector path and important actuator constraints at the position, velocity and acceleration levels are also satisfied in the solution. Extensive field experiments performed on a forestry hydraulic manipulator demonstrate the performance of the proposed solution. Approximately 15–30% greater hydraulic energy consumption was observed with the conventional methods in the LS and CP systems. These results encourage energy-optimal redundancy resolution in future robotic applications of hydraulic manipulators.
Highlights
Hydraulic loaders are powerful, typically 4-degrees-of-freedom (4-DOF) manipulators, that are used for heavy-duty material handling on mobile machines, such as trucks and forest forwarders.Currently, hydraulic loaders are predominantly operated by humans, but loader manufacturers are interested in diversifying their offerings through robotic functionality to remain competitive.On the research side, and in the industry, subjects dealing with reducing reliance on the expertise of human operators in loader control have received much attention
DIDO (LS); the proposed CP cost (43), which is minimised according to dynamic programming (DP) (CP); the proposed CP cost, which is minimised according to DIDO (CP); a positive actuator energy cost, which is solved according to DP
This paper addressed the open problem of global energy-optimal redundancy resolution of 4-DOF
Summary
Typically 4-degrees-of-freedom (4-DOF) manipulators, that are used for heavy-duty material handling on mobile machines, such as trucks and forest forwarders. Several next-generation robotic semi-automated approaches, for example, have been proposed to help alleviate the operator’s workload by automating the repetitive work tasks that would normally be the operator’s responsibility [1,2] On one hand, these semi-automated approaches discuss closed-loop control, and on the other hand, they involve redundancy resolution because hydraulic loaders are typically kinematically redundant. Both problems are important, it is safe to estimate that redundancy resolution of hydraulic manipulators has received less and too little interest in academia in relation to the importance of redundancy resolution compared to closed-loop control problems This is probably because so many different types of redundancy resolutions [3,4,5,6,7,8,9] have been proposed for general.
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