Understanding Accuracy, Repeatability, and Resolution in Robotiq Grippers

This article explains why Robotiq only documents the position resolution of its grippers, such as the 2F-85, and clarifies common misconceptions about accuracy and repeatability in robotic gripping.

What is Position Resolution?

• Position resolution refers to the smallest detectable movement the gripper can report.

• For the 2F-85, the total stroke (85 mm) is divided into 256 discrete positions, resulting in a position resolution of approximately 0.4 mm.

• This means that if the position feedback increases by one unit, the gripper has moved roughly 0.4 mm.

Why Repeatability Isn’t Specified

• Repeatability was once promoted but is no longer documented for the following reasons:

  • Mechanical wear can degrade repeatability over time.

  • Force-based gripping requires travel: about 5 mm of movement is typically needed to achieve reliable grip force.

  • Real-world conditions like speed and force settings influence positioning precision.

• Because gripping often uses Open/Close commands and requires extra travel for force sensing, the notion of repeatability below 0.4 mm becomes less meaningful.

Feedback Limitations

• The gripper’s position feedback is not intended as a precise measurement system.

• The 0.4 mm resolution is a digital step, not a calibrated reference.

• It should be interpreted as +/-0.2 mm around a nominal position, without a definitive transition point.

Calibrate for Better Accuracy

• Always calibrate the gripper position using a real-world measurement tool (e.g., a ruler).

• The feedback values are best used for coarse positioning or validation, not for precision measurement.

Conclusion: Robotiq grippers offer practical and reliable position feedback, but only resolution is documented due to the complexity and variability of real-world applications. For best results, combine feedback with manual calibration and allow for travel in force-based gripping.