Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Zero Wrench Control via Wrench Disturbance Observer for Learning-free Peg-in-hole Assembly

Kiyoung Choi, Juwon Jeong, Sehoon Oh

TL;DR

This work addresses the challenge of achieving zero wrench control in dynamic, contact-rich manipulation by introducing a Dynamic Wrench Disturbance Observer (DW-DOB) that explicitly accounts for task-space inertia in the disturbance estimation loop. By canceling inertial reactions in the disturbance residual and enforcing a phase-aligned filtering scheme, DW-DOB preserves sensitivity to small external wrenches while maintaining robust stability through a passivity-based analysis. The approach is validated experimentally on a 7-DOF manipulator performing peg-in-hole insertions at industrial tolerances, where DW-DOB yields deeper, more compliant insertions with minimal residual wrenches and outperforms both conventional CWDOB and PD baselines. These results establish a practical, learning-free solution for precise Cartesian wrench control in assembly tasks, with potential broad applicability to other contact-rich manipulation scenarios.

Abstract

This paper proposes a Dynamic Wrench Disturbance Observer (DW-DOB) designed to achieve highly sensitive zero-wrench control in contact-rich manipulation. By embedding task-space inertia into the observer nominal model, DW-DOB cleanly separates intrinsic dynamic reactions from true external wrenches. This preserves sensitivity to small forces and moments while ensuring robust regulation of contact wrenches. A passivity-based analysis further demonstrates that DW-DOB guarantees stable interactions under dynamic conditions, addressing the shortcomings of conventional observers that fail to compensate for inertial effects. Peg-in-hole experiments at industrial tolerances (H7/h6) validate the approach, yielding deeper and more compliant insertions with minimal residual wrenches and outperforming a conventional wrench disturbance observer and a PD baseline. These results highlight DW-DOB as a practical learning-free solution for high-precision zero-wrench control in contact-rich tasks.

Zero Wrench Control via Wrench Disturbance Observer for Learning-free Peg-in-hole Assembly

TL;DR

This work addresses the challenge of achieving zero wrench control in dynamic, contact-rich manipulation by introducing a Dynamic Wrench Disturbance Observer (DW-DOB) that explicitly accounts for task-space inertia in the disturbance estimation loop. By canceling inertial reactions in the disturbance residual and enforcing a phase-aligned filtering scheme, DW-DOB preserves sensitivity to small external wrenches while maintaining robust stability through a passivity-based analysis. The approach is validated experimentally on a 7-DOF manipulator performing peg-in-hole insertions at industrial tolerances, where DW-DOB yields deeper, more compliant insertions with minimal residual wrenches and outperforms both conventional CWDOB and PD baselines. These results establish a practical, learning-free solution for precise Cartesian wrench control in assembly tasks, with potential broad applicability to other contact-rich manipulation scenarios.

Abstract

This paper proposes a Dynamic Wrench Disturbance Observer (DW-DOB) designed to achieve highly sensitive zero-wrench control in contact-rich manipulation. By embedding task-space inertia into the observer nominal model, DW-DOB cleanly separates intrinsic dynamic reactions from true external wrenches. This preserves sensitivity to small forces and moments while ensuring robust regulation of contact wrenches. A passivity-based analysis further demonstrates that DW-DOB guarantees stable interactions under dynamic conditions, addressing the shortcomings of conventional observers that fail to compensate for inertial effects. Peg-in-hole experiments at industrial tolerances (H7/h6) validate the approach, yielding deeper and more compliant insertions with minimal residual wrenches and outperforming a conventional wrench disturbance observer and a PD baseline. These results highlight DW-DOB as a practical learning-free solution for high-precision zero-wrench control in contact-rich tasks.
Paper Structure (20 sections, 1 theorem, 21 equations, 6 figures, 1 table)

This paper contains 20 sections, 1 theorem, 21 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Problem Formulation
  3. Motivation and Problem Definition
  4. Lack of Dynamic Cartesian Wrench Control
  5. Underdevelopment of DOB for Wrench Control
  6. Limitations of Learning-Based Approaches for Peg-in-Hole
  7. Research Gap and Contributions
  8. Dynamic Wrench Disturbance Observer (DW-DOB)
  9. Dynamics Formulation of Manipulator Wrench
  10. Contact Wrench Disturbance Observer (CWDOB)
  11. Proposed Dynamic Wrench DOB (DW-DOB)
  12. Passivity-based Stability Analysis
  13. System without DOB
  14. Contact Wrench Disturbance Observer (CWDOB)
  15. Dynamic Wrench Disturbance Observer (DW-DOB)
  16. ...and 5 more sections

Key Result

Lemma 1

For any $a,b \in \mathbb{R}^n$ and any $\eta>0$, it holds that

Figures (6)

  • Figure 1: Robot performing a manipulation task that requires highly compliant zero wrench control. The insertion force (blue) in a peg-in-hole task and the resulting external wrench (red) are illustrated.
  • Figure 2: Block diagram of the proposed Dynamic Wrench Disturbance Observer (DW-DOB), which incorporates task-space inertia into the disturbance estimation loop for zero wrench control.
  • Figure 3: Experiment setup for peg-in-hole task ($20mm$ H7/h6). Maximum clearance $\Delta_{\max}=0.034mm$.
  • Figure 4: End-effector (a) wrench $(F_x, F_y, T_x, T_y)$ (b) and z-position during insertion, illustrating wrench suppression achieved by DW-DOB compared to the PD controller and CWDOB.
  • Figure 5: (a) Cumulative port energy $E_{\mathrm{port}}(t)$ and (b) Passivity residual $\rho(t)$ during the peg-in-hole insertion with respect to each controllers.
  • ...and 1 more figures

Theorems & Definitions (1)

  • Lemma 1: Cauchy/Young Inequality