# Model-free Friction Observers for Flexible Joint Robots with Torque Measurements

## TL;DR

This paper introduces a model-free friction observer for flexible joint robots that improves stability and passivity by using the nominal motor-side signal, enabling effective stiction compensation without a friction model.

## Contribution

It proposes a novel friction observer that uses the nominal motor-side signal feedback, maintaining stability and passivity while providing better stiction compensation in a model-free context.

## Key findings

- Validated through simulations and experiments.
- Achieves stable and passive control without friction models.
- Effectively compensates for stiction in flexible joint robots.

## Abstract

This paper tackles a friction compensation problem without using a friction model. The unique feature of the proposed friction observer is that the nominal motor-side signal is fed back into the controller instead of the measured signal. By doing so, asymptotic stability and passivity of the controller are maintained. Another advantage of the proposed observer is that it provides a clear understanding for the stiction compensation which is hard to be captured in model-free approaches. This allows to design observers that do not overcompensate for the stiction. The proposed scheme is validated through simulations and experiments.