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Dynamic Motion/Force Control of Mobile Manipulators via Extended-UDE

Songqun Gao, Wendi Ding, Maotong Cheng, Qinyuan Ren, Ben M. Chen

TL;DR

This work tackles the challenge of dynamic coupling in mobile manipulators by introducing a dynamic-coupling-integrated model that combines base kinematics with manipulator dynamics, avoiding full-body modeling. An extended uncertainty and disturbance estimator (extended UDE) is developed to separately estimate dynamic coupling $\mu_c$ and other unmodeled uncertainties $\mu_u$, providing a feedforward compensation of coupling and a feedback path for disturbances within an impedance-control framework. The authors prove global stability under full motion control and dissipativity under motion/force control, and demonstrate improved transient response and robot-environment interaction (REI) performance. The approach is validated through simulations and wall-cleaning experiments, showing significant improvements in motion and especially force tracking when the base experiences high dynamics, with remaining limitations identified for compliant environments. Overall, the proposed framework offers a practical, velocity-based control scheme that enhances dynamic interaction capabilities of mobile manipulators in real-world tasks.

Abstract

Mobile manipulators are known for their superior mobility over manipulators on fixed bases, offering promising applications in smart industry and housekeeping scenarios. The dynamic coupling nature between the mobile base and the manipulator presents challenges for force interactive tasks of the mobile manipulator. However, current strategies often fail to account for this coupling in such scenarios. To address this, this paper presents a dynamic coupling-integrated manipulator model that requires only the manipulator dynamics and the mobile base kinematics, which simplifies the modeling process. In addition, embedding the dynamic model, an extended uncertainty and disturbance estimator (UDE) is proposed for the mobile manipulator, which separately estimates the dynamic coupling terms and other unmodeled uncertainties, incorporating them into the feedforward and feedback control loops, respectively. The proposed approach increases the speed of response of the system and improves the dynamic robot-environment interaction (REI) performance of the mobile manipulator. A series of simulations and experiments of a wall-cleaning task are conducted to verify the effectiveness of the proposed approach. Ablation studies demonstrate that the proposed approach significantly improves the motion/force tracking performance when the mobile base is in dynamic motion.

Dynamic Motion/Force Control of Mobile Manipulators via Extended-UDE

TL;DR

This work tackles the challenge of dynamic coupling in mobile manipulators by introducing a dynamic-coupling-integrated model that combines base kinematics with manipulator dynamics, avoiding full-body modeling. An extended uncertainty and disturbance estimator (extended UDE) is developed to separately estimate dynamic coupling and other unmodeled uncertainties , providing a feedforward compensation of coupling and a feedback path for disturbances within an impedance-control framework. The authors prove global stability under full motion control and dissipativity under motion/force control, and demonstrate improved transient response and robot-environment interaction (REI) performance. The approach is validated through simulations and wall-cleaning experiments, showing significant improvements in motion and especially force tracking when the base experiences high dynamics, with remaining limitations identified for compliant environments. Overall, the proposed framework offers a practical, velocity-based control scheme that enhances dynamic interaction capabilities of mobile manipulators in real-world tasks.

Abstract

Mobile manipulators are known for their superior mobility over manipulators on fixed bases, offering promising applications in smart industry and housekeeping scenarios. The dynamic coupling nature between the mobile base and the manipulator presents challenges for force interactive tasks of the mobile manipulator. However, current strategies often fail to account for this coupling in such scenarios. To address this, this paper presents a dynamic coupling-integrated manipulator model that requires only the manipulator dynamics and the mobile base kinematics, which simplifies the modeling process. In addition, embedding the dynamic model, an extended uncertainty and disturbance estimator (UDE) is proposed for the mobile manipulator, which separately estimates the dynamic coupling terms and other unmodeled uncertainties, incorporating them into the feedforward and feedback control loops, respectively. The proposed approach increases the speed of response of the system and improves the dynamic robot-environment interaction (REI) performance of the mobile manipulator. A series of simulations and experiments of a wall-cleaning task are conducted to verify the effectiveness of the proposed approach. Ablation studies demonstrate that the proposed approach significantly improves the motion/force tracking performance when the mobile base is in dynamic motion.
Paper Structure (14 sections, 1 theorem, 31 equations, 13 figures, 2 tables)

This paper contains 14 sections, 1 theorem, 31 equations, 13 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Dynamic Modeling of Manipulator on the Mobile Base
  3. Motion/Force Control Approach via Extended UDE
  4. Extended UDE Design
  5. Stability Analysis
  6. Dynamic Performance Analysis
  7. Simulation and Experiment
  8. Simulation Configuration
  9. Validation of Dynamic Coupling Terms
  10. Dynamic Interaction Results
  11. Experiment Setup
  12. Experimental Results and Analysis
  13. Discussion
  14. Conclusion

Key Result

Theorem 1

Suppose that the system's uncertainty and external disturbance are bounded, as shown in (uncertainty), and that the system dynamics and disturbances are constrained below the given frequency $\omega_c$. Under the control law given by (f_all): the manipulator system on the mobile base (dynamics3) is globally asymptotically stable in the full motion control mode. Furthermore, it remains stable and

Figures (13)

  • Figure 1: (a) Composite images of the wall-cleaning demonstration of the mobile manipulator at different time steps: $t_0,t_1,t_2$ and $t_3$. (b) The mobile manipulator platform is described using three frames of reference under the Cartesian coordinate system: the inertial frame $\{i\}$, the body frame $\{b\}$, and the end effector frame $\{ee\}$.
  • Figure 2: Control diagram of the dynamic motion/force control of mobile manipulators through extended UDE. In the extended UDE, the dynamic coupling term is compensated in the feedforward control loop, while other unmodeled system uncertainties are compensated in the feedback control loops.
  • Figure 3: Comparison of measured dynamic coupling terms in $x$-axis and $y$-axis and estimation using the dynamic coupling model.
  • Figure 4: The high-dynamic forward $\eta_1$, lateral $\eta_2$, and yaw $\eta_6$ motion trajectory of the mobile base.
  • Figure 5: Comparative motion tracking results with the mobile base in low-dynamic motion.
  • ...and 8 more figures

Theorems & Definitions (2)

  • Theorem 1
  • proof