Wenqiang Wu

A Modular Biped Wall-Climbing Robot With High Mobility and Manipulating Function

High-rise tasks such as cleaning, painting, inspection, and maintenance on walls of large buildings or other structures require robots with climbing and manipulating skills. Motivated by these potential applications and inspired by the climbing motion of inchworms, we have developed a biped wall-climbing robot-W-Climbot. Built with a modular approach, the robot consists of five joint modules connected in series and two suction modules mounted at the two ends. With this configuration and biped climbing mode, W-Climbot not only has superior mobility on smooth walls, but also has the function of attaching to and manipulating objects equivalent to a “mobile manipulator.” In this paper, we address several fundamental issues with this novel wall-climbing robot, including system development, analysis of suction force, basic climbing gaits, overcoming obstacles, and transiting among walls. A series of comprehensive and challenging experiments with the robot climbing on walls and performing a manipulation task have been conducted to demonstrate its superior climbing ability and manipulation function. The analytical and experimental results have shown that W-Climbot represents a significant advancement in the development of wall-climbing robots.

Autonomous Pose Detection and Alignment of Suction Modules of a Biped Wall-Climbing Robot

Vacuum adsorption is a simple but effective attaching method widely used in many fields including robotic wall climbing. It is required that the sucker is aligned well with the target surface to form airtight chamber for vacuum generation. For applications in biped wall-climbing robots, automatically aligning the sucker with the wall is beneficial and important to enhance the efficiency and effectiveness of vacuum adsorption. Especially, such a function is essential for autonomous intelligent climbing. To this end, we propose a novel and low-cost approach to perform autonomous alignment of a sucker (suction module) based on noncontact sensors. We first develop a sensing system to detect the configuration of the swinging suction module with respect to the target surface, and then present an algorithm to compute the configuration transformation and control the robot to drive the suction cups toward the target surface with a well-aligned configuration for adherence. In this paper, the basic theory for autonomous pose detection and alignment of the suction module for wall climbing with a biped robot is presented. Specifically, the key configuration of the swinging suction module for adsorption is analyzed, and the pose detection model, the conditions for forming airtight chamber, and the autonomous alignment algorithm are introduced. Calibration of the sensing system and experiments with our biped wall-climbing robot W-Climbot is conducted. The results have verified the feasibility, effectiveness and applicability of the proposed sensing system, theoretical analysis and the algorithm for autonomous pose detection and alignment of the suction modules.

Climbot: A modular bio-inspired biped climbing robot

High-rise tasks in agriculture, forestry and building industry requires robots possessing climbing function. Motivated by these potential applications and inspired by the climbing motion of animals such as inchworms, we have developed a novel biped climbing robot - Climbot. Built with a modular approach, the robot consists of five 1-DoF joint modules connected in series and two special grippers mounted at the ends. With this configuration, Climbot is able not only to climb a variety of media, but also to grasp and manipulate objects, and hence is a “mobile” manipulator. In this paper, we first introduce the development of this novel robot, and then illustrate three climbing gaits based on the unique configuration of the robot. Experiments of climbing poles are carried out to verify the climbing functions and to demonstrate potential application of the proposed robot.

Stability of biped robotic walking with frictional constraints

Tipping-over and slipping, which are related to zero moment point (ZMP) and frictional constraint respectively, are the two most common instability forms of biped robotic walking. Conventional criterion of stability is not sufficient in some cases, since it neglects frictional constraint or considers translational friction only. The goal of this paper is to fully address frictional constraints in biped walking and develop corresponding stability criteria. Frictional constraints for biped locomotion are first analyzed and then the method to obtain the closed-form solutions of the frictional force and moment for a biped robot with rectangular and circular feet is presented. The maximum frictional force and moment are calculated in the case of ZMP at the center of contact area. Experiments with a 6-degree of freedom active walking biped robot are conducted to verify the effectiveness of the stability analysis.

The superior mobility and function of W-Climbot — A bio-inspired modular biped wall-climbing robot

W-Climbot is an inchworm-like biped wall-climbing robot we developed with a modular approach. Consisting of five joint modules and two suction modules, the robot is actually a mobile 5-DoF manipulator with dual sucking end-effectors at the two ends. With this kinematic structure and biped climbing mode, W-Climbot has superior wall-climbing function (great ability to omni-directional locomotion, to negotiate obstacles on the walls and to transit between walls) and manipulation function. In this paper, the robot system is first introduced, suction force in one critical case is analyzed for climbing reliability and safety, and three climbing gaits are presented. To illustrate its superior 3-D mobility, a series of experiments (climbing on a vertical exterior surface with different gaits, negotiating obstacles, and transiting among interior surfaces) are carried out. Performing a pick-and-place task on a wall is also demonstrated as one of its the potential applications. The results show that W-Climbot is a significant advancement in development of wall-climbing robots.

Bibot-U6: A Novel 6-DoF Biped Active Walking Robot - Modeling, Planning and Control

Most of current biped robots are active walking platforms. Though they have strong locomotion ability and good adaptability to environments, they have a lot of degrees of freedom (DoFs) and hence result in complex control and high energy consumption. On the other hand, passive or semi-passive walking robots require less DoFs and energy, but their walking capability and robustness are poor. To overcome these shortcomings, we have developed a novel active biped walking robot with only six DoFs. The robot is built with six 1-DoF joint modules and two wheels as the feet. It achieves locomotion in special gaits different from those of traditional biped robots. In this paper, this novel biped robot is introduced, four walking gaits are proposed, the criterion of stable walking is addressed and analyzed, and walking patterns and motion planning are presented. Experiments are carried out to verify the locomotion function, the effectiveness of the presented gaits and to illustrate the features of this novel biped robot. It has been shown that biped active walking may be achieved with only a few DoFs and simple kinematic configuration.

A binary approximating method for graspable region determination of biped climbing robots

For a biped pole-climbing robot (BiPCR) with grippers, it is an essential demand to determine the target grasp configuration for climbing and transiting between poles, with the graspable region as a priori knowledge. The graspable region on the target pole is critically important for climbing path planning and motion control. To efficiently compute the graspable region for a BiPCR, we propose a novel binary approximating method in this paper. This method may also be applied to generate the three-dimensional (3-D) workspace of a manipulator with constant orientation. The grasping problem and the concept of graspable region for a BiPCR are first introduced. The binary approximating method and the corresponding algorithms are then presented to generate the graspable region. Additional constraints on a biped climbing robot with five degrees of freedom (DoFs) are presented as a supplement to the algorithm. A series of comprehensive simulations are conducted with the five-DoF and six-DoF climbing robots to verify the effectiveness of the proposed method. Finally, the dexterity of biped climbing robots with different DoFs is discussed. Graphical Abstract

Gripper self-alignment for autonomous pole-grasping with a biped climbing robot

For biped climbing robots to climb poles, trusses or trees with dual grippers, it is required that the grippers are aligned with the target objects before they grasp for climbing or manipulating. However, this requirement is difficult to meet in practice with programming control, teaching-and-playback, or remote control with a joystick, due to the mobility of the base gripper, the manufacturing and control errors of the robot, and other uncertainty. It is hence necessary and significant for the grippers to be autonomously aligned with the target under utilization of sensors. In this paper, we develop a sensing system by integrating multiple sensors including a camera, a laser scanning range finder and two ultrasonic distance sensors to detect the relative configuration of a gripper with respect to the target to grasp, and then present an algorithm based on the sensor information to adjust the gripper configuration for alignment with the grasping target. In the experiments with our biped climbing robot Climbot, the gripper can grasp a static pole autonomously and can even follow a moving pole. The effectiveness and real-time of the sensing system and the self-alignment algorithm have been verified by the experiments.

Task-oriented inverse kinematics of modular reconfigurable robots

Consisting of a set of modules with the same connection interfaces, different configurations of modular robot can be assembled for different tasks, with high adaptation in complicated environments. Because of the variational task and changeable configuration of modular reconfigurable robots, it is very hard to solve the kinematics of all the configurations by traditional algebraic methods. To solve this problem, we present a method to automatically generate the kinematics of modular reconfigurable robot. We first introduce our modular robot system, including the description of the basic modules, the description of topology and the generation of configuration, we then discuss about the task-oriented inverse kinematics with the mixed iteration method and evaluation method. The configurations of modular robots for biped pole-climbing and for manipulating are implemented, with them inverse kinematics as two examples of application of the presented method. The results confirmed the validity and suitability of the algorithm for serial type modular reconfigurable robots.

Dynamic modeling and analysis of junction surfaces of robotic modules

Junction surface plays an important role in the performance of a modular robot in terms of positioning error and system stiffness. In this paper, junction surfaces of robotic modules are modeled and analyzed based on virtual medium. The asperity of a junction surface is first made equivalent to an isotropic virtual medium layer, and the thick surface contact fractal theory is combined with the contact mechanics theory. The analytical dynamic model is thus established, by which the coupling relationship between the asperities of junction surface is successfully simulated. The fractal dimension and the scale coefficient of the equivalent junction surfaces are obtained by surface profilometer and power spectrum analysis, and the dynamic characteristic parameters of the virtual medium are calculated. Comparison result shows that the theoretical and measured modal shapes basically match, and the relative errors between the theory natural frequency and the test natural frequency of every order are less than 7.3%, which verifies the effectiveness of the dynamic model of the module junction surface.