What Is JTS Calibration and When Is It Needed?

Article Summary

• Joint Torque Sensor (JTS) Calibration corrects the offset and scale values of each joint's torque sensor to ensure accurate torque and force estimation on Doosan collaborative robots. This article explains what JTS Calibration is, why it matters, and when you should perform it.

   

Applies To

• Product: M-Series, H-Series, A-Series, P-Series, E-Series

• Software: All versions (version-specific notes in the procedure article) 

   

What Is JTS Calibration?

• Joint Torque Sensor (JTS) Calibration is the process of correcting the Offset and Scale values of the torque sensor in each robot joint. Every joint on a Doosan cobot contains a JTS that measures the torque applied during operation. Over time, these sensor readings can drift from the actual torque values. Calibration realigns the sensor output to match the true torque, ensuring accurate force estimation, reliable collision detection, and smooth direct teaching. 

Why Is JTS Calibration Important?

JTS Calibration serves several critical purposes: 

• **Mechanical error correction**: Compensates for manufacturing tolerances and structural changes in the joint to improve torque measurement accuracy. 
• **Encoder reference alignment**: Ensures the home position (homing posture) is reliable and repeatable. 
• **Precision maintenance**: Maintains both repeatability and absolute positioning accuracy over the robot's operating life. 
• **Post-service initialization**: After replacing a motor, reducer, encoder, or joint module, calibration re-establishes the sensor baseline so the robot operates within specification.

When Should You Perform JTS Calibration? 

Perform JTS Calibration in the following situations: 

1. After replacing an encoder, motor, or reducer. 
2. After disassembling and reassembling an arm or joint module. 
3. After a significant collision or crash event. 
4. Before shipping a new robot (factory requirement). 
5. During scheduled maintenance or when a quality issue is detected. 
6. When direct teaching shows "drifting" or "floating" behavior on one or more axes. 
7. When false collision detection or TCP force limit errors occur after extended storage or long-term operation.

What Causes JTS Offset Values to Change? 

Two primary factors contribute to offset drift: 

• **Strain gauge aging**: The JTS uses strain gauges that gradually lose precision over time and repeated use, causing the measured offset to shift. 
• **Structural changes in the module**: Repeated loading cycles can cause micro-level mechanical changes in the joint module and JTS housing, which also affect the offset and scale readings.