Force Control Method for the Variable Robot Payload in Metal Slag Removal Operation

To achieve accurate force control during slag removal operations in the metallurgical industry, the impedance control strategy is commonly employed. A robot designed for slag removal operation has been developed to handle oxidized slag suspended on the surface of molten metal. However, the oxidized slag typically adheres to the end-effector over time, altering the end-effector's weight and impacting the force control's precision. This paper proposes a novel force control strategy to realize the re-identification of variable parameters of the end-effector without stopping the operation of the robot. First, a six-dimensional force sensor is installed between the robot flange and the end-effector. The paper calibrates and calculates the end-effector's parameters, reducing the influence of the end-effector's gravity on force perception. Secondly, a real-time parameter updating algorithm, termed MRLS (Modified Recursive Least Squares Method), is designed specifically for parameter re-identification of variable robot payload. Finally, experimental results demonstrate that the error of the measured weight of the tool to the true value is 1.64%. When the robot is in the slag removal movement process, the error of the contact force estimated is within 0.13N.