Although the off-road mobility characteristics of wheeled or tracked vehicles are generally recognized as being inferior to those of man and cursorial animals, the complexity of the joint-coordination control problem has thus far frustrated attempts to achieve improved vehicular terrain adaptability through the application of legged locomotion concepts. Nevertheless, the evident superiority of biological systems in this regard has motivated a number of theoretical studies over the past decade which have now reached a state of maturity sufficient to permit the construction of experimental computer-controlled adaptive walking machines. At least two such vehicles are known to have recently demonstrated legged locomotion over smooth hard-surfaced terrain. This paper is concerned with an extension of the present theory of limb coordination for such machines to the case in which the terrain includes regions not suitable for weight-bearing and which must consequently be avoided by the control computer in deciding when and where to successively place the feet of the vehicle. The paper includes a complete problem formalization, a heuristic algorithm for solution of the problem thus posed, and a preliminary evaluation of the proposed algorithm in terms of a computer simulation study.

Adaptive Locomition of a Multilegged Robot over Rough Terrain

Micro-vibration has been a dominant factor impairing the performance of scientific experiments which are expected to be deployed in a micro-gravity environment such as a space laboratory. The micro...

System integration and control design of a maglev platform for space vibration isolation

Design and experiment of a noncontact electromagnetic vibration isolator with controllable stiffness

3-DoF zero power micro vibration isolation via linear matrix inequalities based on H∞ and H2 control approaches

For large bearing capacity and low current consumption of the magnetic suspension platform, a 2-DOF electromagnetic actuator with a new structure of halbach array is proposed to improve driving force coefficients. The structure and the working principle are introduced. An accurate sub domain model of the new structure is established to accurately and rapidly calculate the magnetic field distribution for obtaining the parameters and performance of the electromagnetic actuators. The analytical model results are verified by the finite element method. The force/torque model of the magnetic suspension platform is established based on the proposed 2-DOF electromagnetic actuator. Three position-sensitive detectors and six accelerometers are applied to perceive in real time the posture and vibration acceleration of the platform, respectively. Their hardware information is introduced and measurement models are established based on the layout. Finally, the electromagnetic characteristics of the proposed actuator are investigated and compared with the conventional counterpart by finite element analysis. The results show that the average magnetic field, 0.432 T, horizontal and vertical force coefficient, 92.3 N/A and 30.95 N/A, and torque in x and z direction, 3.61 N·m and 8.49 N·m, of the proposed actuator are larger than those of the conventional one.

/pdf/design-and-analysis-of-a-2-dof-electromagnetic-actuator-with-1jdlo63f.pdf

Design and Analysis of a 2-DOF Electromagnetic Actuator with an Improved Halbach Array for the Magnetic Suspension Platform

Legged robots can pass through complex field environments by selecting gaits and discrete footholds carefully. Conventional methods plan gaits and footholds separately and treat them as a single-step optimal process. However, such approaches cause poor passability in sparse foothold environments. This letter proposes a novel coordinative planning method for hexapod robots. It treats gait and foothold planning as a sequence optimization problem while considering the harshness of the environment as the leg’s fault. The Monte Carlo tree search (MCTS) algorithm is used to optimize the entire traversing motion sequence. A slidingMCTS method is proposed to effectively strike a balance between optimization and search operations by introducing a moving root node and controlling the sampling time. The proposed planning algorithm takes advantage of the fault-tolerant mechanism, lifting legs without valid footholds and planning the contact sequence of the remained legs, to improve the passability of the hexapod robot in harsh terrains. The method has been compared with the RRT-based search method for terrains with different densities of foothold, and experiments on challenging terrains are carried out to verify the efficiency. The results have shown that the proposed method dramatically improves the hexapod robot’s ability to pass through sparse-foothold environments.

/pdf/contact-sequence-planning-for-hexapod-robots-in-sparse-cttccare.pdf

Contact Sequence Planning for Hexapod Robots in Sparse Foothold Environment Based on Monte-Carlo Tree

A magnetic levitation isolation system applied for the active control of micro-vibration in space requires actuators with high accuracy, linear thrust and low power consumption. The magneto-force-thermal characteristics of traditional electromagnetic actuators are not optimal, while actuators with a Halbach array can converge magnetic induction lines and enhance the unilateral magnetic field. To improve the control effect, an accurate magnetic field analytical model is required. In this paper, a magnetic field analytical model of a non-equal-size Halbach array was established based on the equivalent magnetic charge method and the field strength superposition principle. Comparisons were conducted between numerical simulations and analytical results of the proposed model. The relationship between the magnetic flux density at the air gap and the size parameters of the Halbach array was analyzed by means of a finite element calculation. The mirror image method was adopted to consider the influence of the ferromagnetic boundary on the magnetic flux density. Finally, a parametric model of the non-equal-size Halbach actuator was established, and the multi-objective optimization design was carried out using a genetic algorithm. The actuator with optimized parameters was manufactured and experiments were conducted to verify the proposed analytical model. The difference between the experimental results and the analytical results is only 5%, which verifies the correctness of the magnetic field analytical model of the non-equal-size Halbach actuator.

Optimal Design of Magneto-Force-Thermal Parameters for Electromagnetic Actuators with Halbach Array

Payload-agnostic Decoupling and Hybrid Vibration Isolation Control for a Maglev Platform with Redundant Actuation

This paper presents a novel six-DOF positioning and active vibration isolation platform based on magnetic levitation principle, which is intended to be used in space or laboratory environment to obtain an ability of payload precision positioning and vibration attenuation so that a favorable environment for science experiment, precision measurement and material processing can be obtained A maglev actuator scheme is proposed which enable the ability of six-axis motion The transformation and dynamics model of whole system is derived An adaptive robust sliding mode controller and a vibration filter controller combined with acceleration compensation is designed and implemented for different circumstances Extensive simulation and experiments validate the performance of motion range and vibration isolation Further improvements of modeling method and control algorithm are discussed as well

Zhaopei Gong

Papers

System integration and control design of a maglev platform for space vibration isolation

Contact Sequence Planning for Hexapod Robots in Sparse Foothold Environment Based on Monte-Carlo Tree

Optimal Design of Magneto-Force-Thermal Parameters for Electromagnetic Actuators with Halbach Array

Payload-agnostic Decoupling and Hybrid Vibration Isolation Control for a Maglev Platform with Redundant Actuation

Design and control of a novel six-DOF maglev platform for positioning and vibration isolation