Control Of Walking Robot Research Articles

Controlling flat-foot limit cycle walkers with compliant joints based on local stability variation.

This study investigates local stability of a four-link limit cycle walking biped with flat feet and compliant ankle joints. Local stability represents the behavior along the solution trajectory between Poincare sections, which can provide detailed information about the evolution of disturbances. The effects of ankle stiffness and foot structure on local stability are studied. In addition, we apply a control strategy based on local stability analysis to the limit cycle walker. Control is applied only in the phases with poor local stability. Simulation results show that the energy consumption is reduced without sacrificing disturbance rejection ability. This study may be helpful in motion control of limit cycle bipedal walking robots with flat feet and ankle stiffness and understanding of human walking principles.

Walking control of semi-passive robot via a modified Q-learning algorithm

The analysis and control of stability of passive biped robot has been the subject of an in-depth study because of its unique characteristics. This work gives a new perspective aiming at a force applied on foot of collision phase of walking process of passive robot, which is a completely new way of applying impulse force that is different from the previous. Therefore, the new equation has been derived due to this force which is not parallel to the support leg to provide further analysis for the study. Besides, this paper combines the characteristics of passive walking with the process of reinforcement learning, and an improved algorithm thus was designed to calculate the value of the control force. The simulation results show that control method designed in this article can not only make the unsteady passive robot achieve stable walking, but also have a quick control speed. Furthermore, the selection range of initial values is expanded by using this method, which provides a convenient reference for the later research work.

Control of Dynamic Biped Walking Robot

The objective of this article is to present control algorithms of biped dynamic walking robot. A mathematical model of the walking robot is compiled. The construction of the robot is based on minimalist design principles - absolutely solid body with two legs. Analytical dependencies between six coordinates of the body, coordinates of the left and right legs and absolute coordinates of the feet are defined. The block diagram of control system is presented. Differential equations of walking are compiled. The dynamic stability of biped walking robot near the required trajectory is provided by discrete control of the parameters: «when and where to put foot». To define these parameters, it is proposed to use an inverted mathematical pendulum as an ideal mechanism. Its linearized differential equations allow present the feet coordinates according to the measured initial and final parameters (at the begging and at the end of the step). The article paid particular attention to results of such control method with various walking modes. The coordinates of the robot body, its velocities and accelerations, angles of rotation were investigated. Calculations confirmed the small deviations of the proposed model of walking from the ideal one. The developed methodology allows improve the construction and control system of biped dynamic walking robots at the design stage. Some of the tasks, it can be used: design machines simulating human walking, with high speed and maneuverability, with point feet and synchronized with natural uncontrolled movements.

A Trajectory Control for Bipedal Walking Robot Using Stochastic-Based Continuous Deep Reinforcement Learning

A Trajectory Control for Bipedal Walking Robot Using Stochastic-Based Continuous Deep Reinforcement Learning

МОДЕЛИРОВАНИЕ ПОЛУАВТОМАТИЧЕСКОГО РЕЖИМА УПРАВЛЕНИЯ ДВИЖЕНИЕМ ДВУНОГИХ ШАГАЮЩИХ РОБОТОВ В СИСТЕМАХ ВИРТУАЛЬНОГО ОКРУЖЕНИЯ

The paper considers methods and approaches for semi-automatic motion control of bipedal walking robots in virtual environment systems. The proposed solutions include generating a walking pattern, calculating inverse kinematics, and synthesis of PD-controllers with feedback based on the angle sensor readings. To ensure the static and dynamic stability of the walking robot, generating its movement trajectories is implemented using the criterion of zero mo-ment point (ZMP) and the inverse pendulum model with virtual height. In this case, the walking pattern is generated by solving the problem of inverse kinematics using the Leven-berg-Marquardt method to calculate the rotation angles in the robot joints. To implement semi-automatic motion control of a walking robot in a virtual environment, an approach based on the technology of functional diagrams and virtual control panels is used. Testing the proposed methods and approaches is carried out in the VirSim virtual environment software package and shows their adequacy and efficiency for modelling a walking robot movement while maintaining its balance.

HAPTR2: Improved Haptic Transformer for legged robots’ terrain classification

The haptic terrain classification is an essential component of a mobile walking robot control system, ensuring proper gait adaptation to the changing environmental conditions. In practice, such components are a part of an autonomous system and thus have to be lightweight, provide fast inference time, and guarantee robustness to minor changes in recorded sensory data. We propose transformer-based HAPTR and HAPTR2 terrain classification methods that use force and torque measurements from feet to meet these requirements. For reliable comparison of the proposed solutions, we adapt two classical machine learning algorithms (DTW-KNN and ROCKET), one temporal convolution network (TCN), and use the state-of-the-art CNN-RNN. The experiments are performed on publicly available PUTany and QCAT datasets. We show that the proposed HAPTR and HAPTR2 methods achieve accuracy on par or better than state-of-the-art approaches with a lower number of parameters, faster inference time, and improved robustness to input signal distortions. These features make HAPTR and HAPTR2 excel in terrain recognition tasks when considering real-world requirements.

Integrated inverted pendulum and whole-body control design for bipedal robot with foot slip

Low-friction ground surfaces present a particular challenge for control of bipedal walking robots. The onset of foot slip changes the robot dynamics and the commonly designed walking controllers assuming non-slip conditions cannot maintain balance and prevent the walker from falling. We present a two-level robot controller for bipedal walker under foot slip. The high-level control is built on a two-mass linear inverted pendulum (TMLIP) model to generate the appropriate step location such that the robot walker maintains dynamic balance through multiple planned steps. The specified stepping tasks are fed to the low-level control that is based on a whole-body operational space (WBOS) framework. The WBOS controller uses the dynamic model of the multi-link bipedal walker and generates joint torques to maintain balance and follow the given stepping task in the presence of foot slip. Performance of the integrated TMLIP-WBOS control algorithm is demonstrated through extensive simulation studies of a 5-link robotic walker.

The Walking Robot Control System that is Adaptive to Changes in the Kinematics

The walking mobile robots (WMR) have recently become widely popular in robotics. They are especially useful in the extreme cases: search and rescue operations; cargo delivery over highly rough terrain; building a map. These robots also serve to explore and describe a partially or completely non-deterministic workspace, as well as to explore areas that are dangerous to human life. One of the main requirements for these WMR is the robustness of its control system. It allows WMR to maintain the operability when the characteristics of the support surface change as well as under more severe conditions, in particular, loss of controllability or damage of the supporting limb (SL). We propose to use the principles of genetic programming to create a WMR control system that allows a robot to adapt to possible changes in its kinematics, as well as to the characteristics of the support surface on which it moves. This approach does not require strong computational power or a strict formal classification of possible damage to the WMR. This article discusses two main WMR control modes: standard, which accord to a serviceable kinematics, and emergency, in which one or more SL drives are damaged or lost controllability. As an example, the structure of the control system of the WMP is proposed, the kinematics of which is partially destroyed in the process of movement. We developed a method for controlling such robot, which is based on the use of a genetic algorithm in conjunction with the Mealy machine. Modeling of modes of movement of WMR with six SL was carried out in the V-REP program for two cases of injury: absent and not functioning limb. We present the results of simulation of emergency gaits for these configurations of WMP and the effectiveness of the proposed method in the case of damage to the kinematic scheme. We also compared the performance of the genetic algorithm for the damaged WMR with the standard control algorithm.

Dynamic walking characteristics and control of four-wheel mobile robot on ultra-high voltage multi-split transmission line

High-voltage lines are an important channel for power transmission, and multi-split transmission lines are the main strength of power transmission. Compared with double-wheel single-wire maintenance robots, ultra-high-voltage multi-split transmission lines and four-wheel mobile robots have a wider application range and greater demand. The maintenance of multi-split transmission lines relies on the stable walking and control of four-wheel mobile robots on heterogeneous multi-split transmission lines. However, uncertain disturbance factors such as wind load in the complex field environment cause vibration of double-split and quad-split lines. The slight change in the line spacing causes the line contact to the edge of the robot’s walking wheel, which increases the friction during the robot’s walking. It also directly hinder the movement of the robot on the multi-split transmission line, thus restricting the completion of the robot’s maintenance operation. Based on the analysis, this paper establishes a mathematical model of the external force disturbance influence on the spacing of the double-split lines. At the same time, the robot walking mechanics characteristics model under the change of the line space has been established. Three different forms of the robot walking online have been obtained through abstraction processing. A method of side friction identification based on fuzzy control has been proposed, through the online monitoring of the friction between line and edge of the walking wheel, the robot walking wheel motor walking force can be intelligently controlled in real time, and effectively avoids the “wheel-line” jam phenomenon under the external uncertain factors in the field environment. Finally, the feasibility and engineering practicability of the method have been verified through MATLAB/ADAMS simulation and field operation experiments. Therefore, the automation and intelligence level of the operation and the transmission system maintenance management has been improved.

Variable-time-interval trajectory optimization-based dynamic walking control of bipedal robot

AbstractBipedal robots by their nature show both hybrid and underactuated system features which are not stable and controllable at every point of joint space. They are only controllable on certain fixed equilibrium points and some trajectories that are periodically stable between these points. Therefore, it is crucial to determine the trajectory in the control of walking robots. However, trajectory optimization causes a heavy computational load. Conventional methods to reduce the computational load weaken the optimization accuracy. As a solution, a variable time interval trajectory optimization method is proposed. In this study, optimization accuracy can be increased without additional computational time. Moreover, a five-link planar biped walking robot is designed, produced, and the dynamic walking is controlled with the proposed method. Finally, cost of transport (CoT) values are calculated and compared with other methods in the literature to reveal the contribution of the study. According to comparisons, the proposed method increases the optimization accuracy and decreases the CoT value.

From Neural Command to Robotic Use: The Role of Symmetry/Asymmetry in Postural and Locomotor Activities

This article deepens a reflection on why and how symmetry/asymmetry affects the motor and postural behavior from the neural source, uterine development, child maturation, and how the notion of symmetry/asymmetry has been applied to walking robot design and control. The concepts of morphology and tensegrity are also presented to illustrate how the biological structures have been used in both sciences and arts. The development of the brain and the neuro-fascia-musculoskeletal system seems to be quite symmetric from the beginning of life through to complete maturity. The neural sources of movements (i.e., central pattern generators) are able to produce both symmetric or asymmetric responses to accommodate to environmental constraints and task requirements. Despite the fact that the human development is mainly symmetric, asymmetries already regulate neurological and physiological development. Laterality and sports training could affect natural musculoskeletal symmetry. The plasticity and flexibility of the nervous system allows the abilities to adapt and compensate for environmental constraints and musculoskeletal asymmetries in order to optimize the postural and movement control. For designing humanoid walking robots, symmetry approaches have been mainly used to reduce the complexity of the online calculation. Applications in neurological retraining and rehabilitation should also be considered.

Adaptive tracking control for underactuated mechanical systems with relative degree two

The adaptive tracking state-feedback control for underactuated mechanical systems with outputs characterized by global relative degree equal to two is addressed. A new control technique called virtual control is proposed. Fictitious control inputs and outputs are introduced to achieve full actuation: the key step is to find the reference signals for the fictitious outputs so that the resulting virtual adaptive controls are zero. The adaptive control of an underactuated three-link walking robot with unknown torso mass is designed according to the proposed control strategy. Simulations show that adaptation is crucial for stable walking.

Design, Construction, and Rough-Terrain Locomotion Control of Novel Hexapod Walking Robot With Four Degrees of Freedom Per Leg

Multi-legged walking robots are suitable platforms for unstructured and rough terrains because of their immense locomotion capabilities. These are, however, redeemed by more sophisticated control and energy-demanding motion in comparison to wheeled robots. Particularly, electrically actuated multi-legged walking robots suffer from the adverse ratio between the robot body weight and payload capacity. Moreover, the locomotion speed and endurance ratio is far from what can be achieved with wheeled robots. In this paper, we focus on six-legged walking robots with statically-stable gait. Based on the analysis of existing solutions, we propose a novel construction of the affordable electrically actuated robot with substantial improvements in its motion capabilities, locomotion speed, reliability, and endurance. The proposed design is implemented in a Hexapod Ant Robot (HAntR) that is accompanied by the developed locomotion control approach to improve its rough terrains negotiation capabilities by the active distribution of the robot weight to the legs in the stance phase. Properties of the robot have been experimentally verified in extensive deployments, and based on the experimental benchmarking of the built prototype, HAntR is capable of locomotion for over an hour with the payload of 85% of its weight, and its maximum crawled distance per one second is 87% of its nominal length. HAntR represents significant improvements not only regarding the robots with identical actuators but also in comparison to other existing platforms. Therefore, we consider HAntR represents a step further towards a wide range of future applications and deployments of six-legged walking robots.

Energy-Efficient Locomotion Generation and Theoretical Analysis of a Quasi-Passive Dynamic Walker

This Letter presents a robot walking control method, which we call “quasi-passive dynamic walking.” The method is targeted at underactuated legged robots and applied to obtain energy-efficient limit cycle gait on level ground. To achieve efficient locomotion, as well as to overcome the underactuation of the system, two key points are implemented into this method to positively utilize the passive dynamics of the system. The first one is to initialize the walker at the fixed Poincaré section obtained from passive dynamic walking on a gentle downhill. The second one is to indirectly excite the hip angle by periodically oscillating a wobbling mass, which is attached to the body frame. The walker is, therefore, able to step forward on level ground without any torque actuation. Moreover, the phase diagram of the generated gait is entrained to limit cycle by the periodical oscillation of the wobbling mass. Numerical simulations and theoretical analysis are conducted to evaluate the efficiency as well as the local stability of the gait. Our control method enables underactuated legged robots to walk extremely efficiently on level ground with only one actuator, which provides the easiness for implementation on real machines.

A Stabilization Method Based on an Adaptive Feedforward Controller for the Underactuated Bipedal Walking with Variable Step-Length on Compliant Discontinuous Ground

Both compliance and discontinuity are the common characteristics of the real ground surface. This paper proposes a stabilization method for the underactuated bipedal locomotion on the discontinuous compliant ground. Unlike a totally new control method, the method is actually a high-level control strategy developed based on an existing low-level controller meant for the continuous compliant ground. As a result, although the ground environment is more complex, the calculation cost for the robot walking control system is not increased. With the high-level control strategy, the robot is able to adjust its step-length and velocity simultaneously to stride over the discontinuous areas on the compliant ground surface. The effectiveness of the developed method is validated with a numerical simulation and a physical experiment.

Using Neural Networks to Predict the Normal Reactions of a Walking Robot

Purpose of reseach . This work is devoted to solving one of the problems associated with the control of walking robots based on their dynamic mathematical model − the presence in it of obvious mechanical bonds due to reactions of bonds with the supporting surface. To solve this problem, it is proposed to use a fully connected neural network to evaluate the forces of normal reactions between the surface and the feet of a bipedal walking machine during its implementation of one step. Methods. The paper considers two neural network architectures based on fully connected layers with ReLU activation functions. The architecture of the neural network includes five fully connected layers (input, output and three hidden), and an alternative architecture includes a thinning layer after each fully connected layer. The input data for the network are the state of the robot and the required control actions, and the output is the predicted reaction forces. The training sample is generated by modeling a complete dynamic model of the robot. The network is built and trained using machine learning libraries Keras and TensorFlow. Results. The generation of training sample for neural network is described here, and it is carried out the training of two architectures of neural networks. Based on the simulation data, it was established that both trained neural networks are able to accurately predict the values of normal reactions using the values of generalized coordinates and velocities, as well as control actions as input, however, a static prediction error is observed. Conclusion . The results obtained within the framework of the article can be further used to control the movement of bipedal walking machines on various types of surfaces.

Walking With Confidence: Safety Regulation for Full Order Biped Models

Safety guarantees are valuable in the control of walking robots, as falling can be both dangerous and costly. Unfortunately, set-based tools for generating safety guarantees (such as sums-of-squares optimization) are typically restricted to simplified, low-dimensional models of walking robots. For more complex models, methods based on hybrid zero dynamics can ensure the local stability of a pre-specified limit cycle, but provide limited guarantees. This letter combines the benefits of both approaches by using sums-of-squares optimization on a hybrid zero dynamics manifold to generate a guaranteed safe set for a ten-dimensional walking robot model. Along with this set, this letter describes how to generate a controller that maintains safety by modifying the manifold parameters when on the edge of the safe set. The proposed approach, which is applied to a bipedal RABBIT model, provides a roadmap for applying sums-of-squares techniques to high-dimensional systems. This opens the door for a broad set of tools that can generate flexible and safe controllers for complex walking robot models.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ МЕТОДОВ УПРАВЛЕНИЯ ШАГАЮЩИМИ РОБОТАМИ С НЕЛИНЕЙНОСТЯМИ В СЕНСОРНОЙ СИСТЕМЕ

The work is focused on the control of two-legged walking robots. The robot control task for two-legged walking robots is formulated as a quadratic programming task, which allows consideration of unilateral mechanical constraints in the form of inequality constraints caused by the friction cones and torque limitations of the drives. However, in order to assess the quality of such control approach it is important to analyze this system relative to the alternative methods. Three types of regulators are compared: CTC (Computed Torque Controller), linear quadratic regulator with constraints CLQR restrictions (Constrained Linear Quadratic Regulator) and the controller based on the quadratic programming NQPC (Nested Quadratic Programming-based Controller). Particular attention is paid to the impact of inaccuracies of the sensor system on the quality of the robot control system. The study covers cases where a dynamic observer can be used to compensate for inaccuracies of sensors, as well as cases where restrictions are imposed on the torque values in the robot joints. The simulation results show there is a sensor parameter area in which the quality of the regulator operation is robust with respect to small changes in the nonlinear properties of sensors, and such parameter areas are characteristic for systems with and without an observer, as well as for systems with restrictions on the torque values and without them.

Design and Implementation of Intelligent Robot Walking Control System Based on DSP

In recent years, the aging of the population and the acceleration of urbanization have led to a decrease in labor force, an increase in production costs and a decrease in labor productivity. In order to solve these problems, the degree of mechanical automation is bound to increase. This paper has completed the design and development of the automatic walking robot control system, mainly to realize the functions of visual navigation and walking control of the control system. The experiments prove that the vision navigation system of the automatic walking robot can provide the walking control system with direction identification and identification information of the ridge and furrow extension paths between fields. The designed walking control system can call the motor driver to realize the forward, backward, left forward, right forward, left backward and right backward rotation of the control object according to the path information. After experimental debugging, the automatic walking robot can move according to the direction of the identification image, which greatly improves the real-time and intelligent level of the automatic walking robot.

ORHRO: OPEN Robotics Humanoid RObot - from a mechanical retrofit to a new real time industrial controller based walking robot

The design and control of walking robots is a great issue for researchers (high number of DOFs, coupled phenomena). They could benefit to the biomechanics community as testing beds for bio-inspired...