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Unified Force and Motion Adaptive-Integral Control of Flexible Robot Manipulators

Carlos R. de Cos, José Ángel Acosta

TL;DR

This work tackles the challenge of controlling flexible robot manipulators in environments with mixed contact and non-contact phases. It proposes a unified, adaptive force–motion controller based on integral inverse kinematics and adaptive laws for unknown contact stiffness and link deflections, with stability guaranteed by Lyapunov analysis. The controller enables seamless switching between position- and force-control modes without explicit switches, and is validated both theoretically and on a low-cost microcontroller with a multi-DoF, flexible-joint manipulator. The results demonstrate robust force and position tracking, effective disturbance rejection, and practical applicability to tasks like sensor installation and surface inspection in uncertain environments.

Abstract

In this paper, an adaptive nonlinear strategy for the motion and force control of flexible manipulators is proposed. The approach provides robust motion control until contact is detected when force control is then available--without any control switch--, and vice versa. This self-tuning in mixed contact/non-contact scenarios is possible thanks to the unified formulation of force and motion control, including an integral transpose-based inverse kinematics and adaptive-update laws for the flexible manipulator link and contact stiffnesses. Global boundedness of all signals and asymptotic stability of force and position are guaranteed through Lyapunov analysis. The control strategy and its implementation has been validated using a low-cost basic microcontroller and a manipulator with 3 flexible joints and 4 actuators. Complete experimental results are provided in a realistic mixed contact scenario, demonstrating very-low computational demand with inexpensive force sensors.

Unified Force and Motion Adaptive-Integral Control of Flexible Robot Manipulators

TL;DR

This work tackles the challenge of controlling flexible robot manipulators in environments with mixed contact and non-contact phases. It proposes a unified, adaptive force–motion controller based on integral inverse kinematics and adaptive laws for unknown contact stiffness and link deflections, with stability guaranteed by Lyapunov analysis. The controller enables seamless switching between position- and force-control modes without explicit switches, and is validated both theoretically and on a low-cost microcontroller with a multi-DoF, flexible-joint manipulator. The results demonstrate robust force and position tracking, effective disturbance rejection, and practical applicability to tasks like sensor installation and surface inspection in uncertain environments.

Abstract

In this paper, an adaptive nonlinear strategy for the motion and force control of flexible manipulators is proposed. The approach provides robust motion control until contact is detected when force control is then available--without any control switch--, and vice versa. This self-tuning in mixed contact/non-contact scenarios is possible thanks to the unified formulation of force and motion control, including an integral transpose-based inverse kinematics and adaptive-update laws for the flexible manipulator link and contact stiffnesses. Global boundedness of all signals and asymptotic stability of force and position are guaranteed through Lyapunov analysis. The control strategy and its implementation has been validated using a low-cost basic microcontroller and a manipulator with 3 flexible joints and 4 actuators. Complete experimental results are provided in a realistic mixed contact scenario, demonstrating very-low computational demand with inexpensive force sensors.
Paper Structure (9 sections, 2 theorems, 25 equations, 8 figures, 2 tables)

This paper contains 9 sections, 2 theorems, 25 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Background and framework
  3. Force and motion modeling
  4. Unified control strategy
  5. Main stability result
  6. Experimental validation results
  7. Contact force scenario (force control)
  8. Mixed scenario (unified position and force control)
  9. Conclusions

Key Result

Theorem 1

Consider the uncertain error system (eq:errordot) and assume $\mathrm{rank}[J_q] = S$ and $\mathrm{rank}[J_{p,\gamma}] = S_p$ together with the design conditions $N\geq S$ and $N \geq S_{p}$. Define the function $\rho$ of $\mathrm{Proj}(\cdot,\rho)$ in eq:keperphatdot convex and such that $| \hat{k}

Figures (8)

  • Figure 1: Lightweight flexible RM with force capabilities, highlighting the spring mechanism and the contact point.
  • Figure 2: Phases of the complex task: inspection/installation of a sensor on an interface with multi-axis force demands.
  • Figure 3: Definition of the DoF of the RM.
  • Figure 4: Definition of the contact parameters.
  • Figure 5: Control scheme: integral IK (blue, inner position loop); force-oriented change of references (green, outer force loop); and adaptive laws (orange). Equations in brackets.
  • ...and 3 more figures

Theorems & Definitions (7)

  • Remark 1
  • Remark 2
  • Theorem 1: Force control
  • proof
  • Corollary 1: Unifying property
  • proof
  • Remark 3