Abnormal load detection method

Abstract

A method for accurately detecting an abnormal load caused, e.g., by adhesion of the distal end of a spot gun. A flag F2 is set to "1" when a move command is outputted to move a movable part of a machine and is reset to "0" upon lapse of a predetermined very short period of time, and, while the flag F2 remains "0" during stoppage of the movable part, a disturbance torque T0, estimated by a disturbance estimation observer, is stored and successively updated. When a move command is thereafter outputted, and the flag F2 is set to "1", an estimated disturbance torque T1 is obtained, and if the absolute value .vertline.T1-T0.vertline. of the difference between the disturbance torque T1 and the disturbance torque T0, estimated immediately before the movable part is moved, is greater than a reference value Ts, it is determined that an abnormal load is applied, whereupon an alarm is outputted, a flag F1 is set to "1", and the motion is stopped. The disturbance torque T0 estimated during stoppage indicates a value of the load then acting on the movable part, such as gravity. Consequently, the value .vertline.T1-T0.vertline. represents a disturbance torque during movement of the movable part, which is free from the influence of gravity, and a comparison between this value and the reference value Ts permits accurate detection of a force acting on the movable part, not including gravity or frictional force, whereby the occurrence of adhesion or the like can be accurately detected.

Dependencies are inferred from the claim text.