Researchers dream of developing autonomous humanoid robots which behave/walk like a human being. Biped robots, although complex, have the greatest potential for use in human-centered environments such as the home or office. Studying biped robots is also important for understanding human locomotion and improving control strategies for prosthetic and orthotic limbs. Control systems of humans walking in cluttered environments are complex, however, and may involve multiple local controllers and commands from the cerebellum. Although biped robots have been of interest over the last four decades, no unified stability/balance criterion adopted for stabilization of miscellaneous walking/running modes of biped robots has so far been available. The literature is scattered and it is difficult to construct a unified background for the balance strategies of biped motion. The zero-moment point (ZMP) criterion, however, is a conservative indicator of stabilized motion for a class of biped robots. Therefore, we offer a systematic presentation of multi-level balance controllers for stabilization and balance recovery of ZMP-based humanoid robots.
Table of Contents
1. Introduction
2. Gait cycle
3. Stability
3.1 Zero-Moment Point (ZMP)
3.2 Centroidal angular momentum
3.3 Footstep-based criteria
4. ZMP-based control
5. High-level control
5.1 Online reference walking patterns
5.2 Balance control
6. Low-level control
7. Conclusions
Research Objectives and Themes
This paper aims to provide a systematic overview of multi-level control strategies for ZMP-based humanoid robots, addressing the challenges of stabilizing biped locomotion in complex, human-centered environments. It explores various stability criteria, walking pattern generators, and balance recovery methods to bridge the gap between theoretical modeling and practical implementation.
- Analysis of stability criteria for bipedal mechanisms.
- Evaluation of online reference walking pattern generation methods.
- Classification and description of multi-level balance control strategies.
- Investigation of low-level control techniques for tracking angular joint trajectories.
- Comparison of reactive and proactive balance mechanisms.
Excerpt from the Book
3. Stability
The biped mechanism is unstable during the SSP. One of the challenges in the design and control of biped robots is to maintain their balance while walking in different kinds of environment. The reason for the instability is under-actuation owed to the passive joint of the foot-ground contact. This means that control of the feet is dependent on control of the mechanism above the feet. Common stability theories such as analysis of eigenvalues, gain and phase margins, and Lyapunov stability can be applied to particular modes of biped robot gait but cannot guarantee biped stability for all modes of motion.
In general, there are two types of stability criteria that the trajectories of a biped mechanism depend on: static stability and dynamic stability. Static stability restricts the vertical projection of the centre of the mass of the biped to the inside of the support polygon. The support polygon is defined as the area represented by the stance foot during the SSP and the bounded area between the supported feet during the DSP. This type of stability leads to slow gait and biped robots with large feet.
Summary of Chapters
1. Introduction: Discusses the motivation for developing autonomous humanoid robots and outlines the inherent mechanical and control challenges, such as nonlinearity and under-actuation.
2. Gait cycle: Defines the two primary phases of human walking, the double-support phase (DSP) and the single-support phase (SSP), which are fundamental to bipedal locomotion.
3. Stability: Examines stability criteria for bipedal systems, focusing on static vs. dynamic stability and detailing methods like the Zero-Moment Point (ZMP), centroidal angular momentum, and footstep-based criteria.
4. ZMP-based control: Explains the hierarchical control approach for biped robots, emphasizing the necessity of multi-level control systems to manage external and internal perturbations.
5. High-level control: Details strategies for motion planning and balance control, specifically focusing on generating online reference walking patterns and regulating the biped's posture.
6. Low-level control: Investigates the tracking of desired angular joint trajectories during different walking phases, including the specific dynamics of the SSP, impact phase, and DSP.
7. Conclusions: Summarizes the key findings, emphasizing the importance of considering computational complexity and the need for a comparative study of control architectures.
Keywords
Biped robot, Stability, Zero-moment point, Balance, Multi-level control, Humanoid locomotion, Gait cycle, Motion planning, Centroidal angular momentum, Footstep-based criteria, Reactive control, Proactive control, Low-level control, Dynamics, Trajectory generation
Frequently Asked Questions
What is the primary focus of this research?
The work provides a systematic overview and presentation of multi-level balance controllers used for the stabilization and balance recovery of biped humanoid robots based on the ZMP criterion.
What are the central thematic fields?
The paper covers bipedal stability theories, walking pattern generation, hierarchical control architectures, and specific techniques for managing balance during different gait phases.
What is the core research goal?
The goal is to bridge the gap in existing literature by offering a unified background on balance strategies and control, helping designers understand how to stabilize biped robots in various environments.
Which scientific methods are primarily analyzed?
The study analyzes methods such as the Zero-Moment Point (ZMP), centroidal angular momentum, footstep-based stability margins, and multi-level hierarchical control including reactive (feedback) and proactive (feedforward) mechanisms.
What topics are discussed in the main part of the paper?
The main part covers the classification of stability criteria, the generation of online reference walking patterns, the design of multi-level balance controllers, and low-level joint trajectory tracking.
Which keywords characterize the work?
The work is characterized by terms such as biped robot, stability, ZMP, balance, multi-level control, humanoid locomotion, and gait cycle.
How does the ZMP criterion influence bipedal control?
The ZMP serves as a conservative indicator of stability; if the ZMP remains within the support polygon, the system is considered dynamically stable.
What role does the gait cycle play in the proposed control strategies?
The control laws change during transitions between the single-support and double-support phases, necessitating different dynamic models and control approaches for each phase.
Why is multi-level control necessary for these robots?
Because biped robots interact with complex, unknown environments, simple local controllers are often insufficient; multi-level systems allow for robust adaptation to internal and external perturbations.
What is the significance of the footstep strategy?
The footstep strategy is used as a reactive mechanism to recover balance when the velocity of the center of mass makes other internal balancing methods insufficient.
- Quote paper
- Hayder Al-Shuka (Author), 2017, An Overview on Balancing and Stabilization Control of Biped Robots, Munich, GRIN Verlag, https://www.grin.com/document/375226
