Mass Estimation of Self-Contained Linear Electro-Hydraulic Actuators and Evaluation of the Influence on Payload Capacity of a Knuckle Boom Crane

Self-contained linear hydraulic drives are characterized by having integrated the hydraulic power unit e.g. electrical prime mover, hydraulic pumps etc. and the hydraulic cylinder in a single compact unit. Compared to the hydraulic cylinder itself, the mass of the self-contained linear actuator is significantly larger. For some applications, e.g. crane manipulators the additional mass of the actuators compared to conventional valve-controlled hydraulics, may reduce the payload capacity, which is a central performance parameter. As a case study, a medium sized two link knuckle boom crane is modelled and by assuming the force capability of the hydraulic cylinders to be the limiting factor, the reduction in payload capacity is examined if replacing the knuckle boom cylinder with a self-contained hydraulic cylinder drive. By focusing on seven different hydraulic circuit architectures, this study estimates the mass of compact pump-controlled actuators and investigates to what extent the choice of system topology affects the mass of the actuator, and thus payload capacity of the crane. The results show that the choice of hydraulic circuit architecture may affect both the required amount of installed power and the mass of the self-contained actuator. For the considered knuckle boom crane the estimated mass of the needed 59 kW selfcontained actuator ranges from 2300 kg to 2521 kg depending on the hydraulic circuit architecture. The mass of the hydraulic cylinder itself used for conventional valve actuation is estimated to 1674 kg. If the entire working range is considered, installing the heavier self-contained actuator reduces the payload capacity with up to 3 % compared to conventional valve actuation.