# Calibration-free per-finger force-feedback slip control for grasping by anthropomorphic hand with tri-axial tactile sensors

## TL;DR

This paper introduces a real-time slip control system for robotic hands that works without calibration or complex sensors, making it suitable for grasping unknown objects in practical settings.

## Contribution

A novel calibration-free slip-recovery controller for robotic hands using tri-axial tactile sensors and localized per-finger force adjustments.

## Key findings

- The system rapidly detects and recovers from slip using baseline-subtracted tangential force changes.
- Experiments showed effective re-stabilization on objects with varying rigidity, weight, and surface texture.
- Localized per-finger correction improved grasp efficiency by minimizing unnecessary force increases.

## Abstract

This paper addresses the challenge of detecting and recovering from slip during robotic grasping of unknown objects, with the objective of establishing a robust no on-site or per-object calibration slip-recovery controller for an anthropomorphic hand. This hand is equipped with tri-axial piezoresistive tactile force sensors on each finger, and the proposed approach is validated through experimental analysis. The proposed methodology eliminates the need for object- or pose-specific calibration, explicit friction modelling, dense tactile arrays, line-of-sight vision, and a data-hungry learning process, enabling real-time implementation with minimal computation and integration effort. Using a commonly acquired online baseline from initial readings, slip is detected from relative changes between consecutive samples of the baseline-subtracted resultant tangential force, and object engagement is determined when the normal force reading deviates from a no-slip baseline beyond a preset threshold. Upon detecting slip, each finger increases its gripping force in closed-loop control until the slip stops, while enforcing motor-current protection in finger control to prevent actuator overload and object damage. Experiments were conducted on objects with different rigidity, weight, and surface textures, including an aluminium tube, a plastic water bottle, and a sponge. Additionally, the response time and variations in gripping force were evaluated. The results demonstrate rapid slip response via localized per-finger correction, good object conformability, and effective re-stabilization under different lifting speeds and sudden external disturbances. The per-finger design utilizes the minimum necessary correction at the offending finger, reducing unnecessary force increases on other fingers and improving grasp efficiency. This approach represents a practical solution for warehouse picking, human–robot collaboration, and in situ manipulation where task-specific calibrations, visual access, or training datasets are impractical.