In this study, we develop a hydraulically-driven soft robotic hand for handling heavy vegetables in a vegetable factory and report its experimental validations. The working population in agriculture is decreasing worldwide, creating a lot of demands for the robotic automation in harvest and trans-portation of agricultural produces. In particular, a vegetable factory deals with large and heavy vegetables, e.g., cabbages, with 2–3 kg weight and 20–30 cm diameter. A soft robot hand is suitable for handling a food or vegetable; however, most of existing soft robot hands cannot generate necessary output because they are usually actuated by the air-pressure. Therefore, we employ the hydraulic actuation for our soft hand to generate 1 or 2 MPa pressure. Using the developed soft hand, we report experimental validations including basic control performance evaluation and grasping experiments assuming a vegetable factory environment.

Industrial robots require force controllability and impact resistance to ensure safe physical interactions. An electro-hydrostaic actuator (EHA) is expected to be suitable for such applications because it has high backdrivability which improve both force controllability at contact and impact resistance. However, EHAs had been rarely used in multi-axes robotic systems. The previous works validated the force controllability of the EHA-driven robot Hydra. However, the impact resistance of an EHA-driven robot is still unclear. In order to evaluate the impact resistance of the high-power EHA-driven robot, we developed high-pressure EHAs employing ceramics as rigid material to reduce internal leakage, and developed the EHA-driven 6-DOF robot arm Hydracer as the platform for the evaluation. This paper describes the mechanism of Hydracer especially on the base 3-DOF mechanism, and conducts the backdrivability measurement and the impact resistance evaluation.

6-DOF robot manipulator Hydracer was developed to gain high output torque and high backdrivability by adopting electro-hydrostatic actuators, however control of overall system of Hydracer is not yet conducted. To achieve flexible force control of Hydracer, we worked on the system improvements: enhancement of reliability of ceramics components, reduction of internal leakage by considering the property of hydraulic oil, and the identification of inertial parameters to improve its controllability. By using identified parameters, flexible force control of Hydracer by zero-torque control with gravity compensation was realized which reveals the potential of safe human-robot interaction.