This paper proposes the replacement of the control implemented in the hydraulic boom cylinder of a hydraulic excavator with a ball screw actuator. The hydraulic system controls the flow rate and pressure of the hydraulic pump, so the extension and contraction speed of the cylinder is controlled by the set command flow rate of the pump. Therefore, in the case the boom cylinder is replaced with the ball screw, the hybrid control of speed and force is required. Additionally, because ball screws are vulnerable to impact forces, impact force relaxation control is required. Conventional impact force mitigation control stops operation after contact with the environment and but generates a large subsequent impact force. This issue is solved using, a controlled acceleration approach, which applies an acceleration command in the same direction as the impact force exerted due owing to the contact with the environment. Thus, this proposed method reduces the impact force. This paper explains the soft boom cylinder control using a disturbance-observer-based equivalent hydraulic system for an electric excavator. The validity of the proposed soft impact force control is verified from experimental results obtained using the actual electric excavator.
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