Encoder abnormality detecting method, operation control device, robot, and robot system

An operation control device for controlling a motor that drives an output shaft of an operation system, the device comprising:

• a controller configured to output a speed command designating a rotational position of the motor, and commanded position information indicating the rotational position of the motor according to the speed command;
• a driver configured to receive the speed command output from the controller and an output signal output from an encoder for sensing the rotational position of the motor, and to control drive of the motor based on the speed command and the output signal;
• an abnormality detection device configured to detect an abnormality of the encoder;
• a damping filter for removing a vibration component of the operation system from the commanded position information;
• a delay control filter for compensating the commanded position information for a time delay caused by a delay in drive control of the motor;
• the damping filter including a set of a plurality of damping filters with filter constants different from each other;
• the delay control filter including a set of a plurality of delay control filters with time constants different from each other;
• the controller including
• an applicable damping filter determiner configured to select one of the plurality of damping filters which has one of the filter constants corresponding to a weight of an attachment load held by the operation system;
• and
• the abnormality detection device including
• a first receiver configured to receive the output signal from the encoder,
• a second receiver configured to receive the commanded position information from the controller or receive corrected position information via the one of the damping filters selected by the applicable damping filter determiner and the delay control filter, and
• a determiner configured to compare the corrected position information with detected position information on the motor calculated based on the output signal, and determine that the encoder has the abnormality, if there is a difference greater than or equal to a predetermined value between the corrected position information or the commanded position information and the detected position information.