Servo system, servo motor driving device, safety unit and method for controlling servo system

A servo motor driving device for driving a servo motor, the servo motor driving device comprising:

• a servo driver configured to generate an instruction value for an operation of the servo motor using an instruction signal for controlling driving of the servo motor sent by a controller and a feedback signal for detecting the operation of the servo motor sent by an encoder, and drive the servo motor in accordance with the instruction value;
• and
• a safety monitor configured to generate a stop signal which is sent to the servo driver in order to stop an output of torque from the servo motor when the operation of the servo motor is in an abnormal condition,
• wherein the servo driver controls the servo motor as a result of receiving the stop signal from the safety monitor such that the servo motor stops an output of torque, and
• the safety monitor acquires from the servo driver the instruction value and a feedback value that is obtained based on the feedback signal as a result of the servo motor having been driven in accordance with the instruction value, and generates the stop signal when a determination value calculated with the instruction value and the feedback value is in a first abnormal condition or when the determination value is not in the first abnormal condition and at least one of the instruction value and the feedback value is in a second abnormal condition.

A safety monitor used in a servo system,

• wherein the servo system comprises:
• a servo motor;
• a controller configured to output an instruction signal that controls driving of the servo motor;
• an encoder configured to detect an operation of the servo motor and generate a feedback signal representing the detected operation;
• and
• a servo driver configured to generate an instruction value for the operation of the servo motor by using the instruction signal from the controller and the feedback signal from the encoder, and drive the servo motor in accordance with the instruction value, the servo driver controlling the servo motor as a result of receiving a stop signal from the safety monitor such that the servo motor stops an output of torque,
• the safety monitor comprising:
• a determiner configured to determine whether a determination value calculated with the instruction value and the feedback value is in a first abnormal condition or when the determination value is not in the first abnormal condition, whether at least one of the instruction value and the feedback value being in a second abnormal condition;
• and
• a signal generator configured to generate the stop signal when the determiner determines that the determination value calculated with the instruction value and the feedback value is in the first abnormal condition or when the determination value is not in the first abnormal condition, the at least one of the instruction value and the feedback value is in the second abnormal condition.

A method for controlling a servo system,

• the servo system having:
• a servo motor;
• a controller configured to output an instruction signal which controls driving of the servo motor;
• an encoder configured to detect an operation of the servo motor and generate a feedback signal representing the detected operation;
• a servo driver configured to generate an instruction value for the operation of the servo motor using the instruction signal from the controller and the feedback signal from the encoder, and drive the servo motor in accordance with the instruction value;
• and
• a safety monitor configured to control the servo driver such that the servo motor stops an output of torque when the operation of the servo motor is in an abnormal condition,
• the servo driver being configured such that the output of torque from the servo motor is inhibited as a result of receiving a stop signal from the safety monitor,
• the control method comprising:
• determining whether a determination value calculated with the instruction value and the feedback value is in a first abnormal condition or when the determination value is not in the first abnormal condition, whether at least one of the instruction value and the feedback value is in a second abnormal condition;
• and
• generating the stop signal when it is determined that the determination value calculated with the instruction value and the feedback value is in the first abnormal condition or when the determination value is not in the first abnormal condition, the at least one of the instruction value and the feedback value being in the second abnormal condition.