The demand for collaborative robots is expected to increase in the future due to their high adapt-ability. However, most of collaborative robots available in the market are driven by a combination of electromagnetic motors and reduction gears, and thus the weight of the arm itself tends to become larger in order to increase its payload. This study focuses on the hydraulic robot arm, which has an advantage in the force/weight ratio, as a means of realizing collaborative robots for heavy objects. This paper proposes a robot arm that reduces its tip speed while maintaining the maximum force by limiting the flow rate to each motor of the arm. This paper also confirmed the applicability of hydraulic robot arm to actual collaborative work by conducting a demonstration experiment in which an operator attaches a 20 kg steel plate to the target position using the developed robot arm.
