Yubin Liu

Development of a Bionic Hexapod Robot for Walking on Unstructured Terrain

This paper reports the design methodology and control strategy in the development of a novel hexapod robot HITCR-II that is suitable for walking on unstructured terrain. First, the entire sensor system is designed to equip the robot with the perception of external environment and its internal states. The structure parameters are optimized for improving the dexterity of the robot. Second, a foot-force distribution model and a compensation model are built to achieve posture control. The two models are capable of effectively improving the stability of hexapod walking on unstructured terrain. Finally, the Posture Control strategy based on Force Distribution and Compensation (PCFDC) is applied to the HITCR-II hexapod robot. The experimental results show that the robot can effectively restrain the vibration of trunk and keep stable while walking and crossing over the un-structured terrains.

Biomimetic Design and Optimal Swing of a Hexapod Robot Leg

Biological inspiration has spawned a wealth of solutions to both mechanical design and control schemes in the efforts to develop agile legged machines. This paper presents a compliant leg mechanism for a small six-legged robot, HITCR-II, based on abstracted anatomy from insect legs. Kinematic structure, relative proportion of leg segment lengths and actuation system were analyzed in consideration of anatomical structure as well as muscle system of insect legs and desired mobility. A spring based passive compliance mechanism inspired by musculoskeletal structures of biological systems was integrated into distal segment of the leg to soften foot impact on touchdown. In addition, an efficient locomotion planner capable of generating natural movements for the legs during swing phase was proposed. The problem of leg swing was formulated as an optimal control procedure that satisfies a series of locomotion task terms while minimizing a biologically-based objective function, which was solved by a Gauss Pseudospectral Method (GPM) based numerical technique. We applied this swing generation algorithm to both a simulation platform and a robot prototype. Results show that the proposed leg structure and swing planner are able to successfully perform effective swing movements on rugged terrains.

Development of the hexapod robot HITCR-II for walking on unstructured terrain

The purpose of this paper is to describe the design and development of the hexapod robot HITCR-II for walking on unstructured terrain. The leg and joint with modularized structure have been designed, and an objective function has been made up to further optimize the parameters of structure, thereby enhancing the motion performance of this robot; The 3-D.O.F force sensor in the foot end and joint torque sensors have been designed into the structure of leg, thus the leg has the omnidirectional perception of force, and the robot is also equipped with pose sensor, joint position sensor and binocular vision, so it can apperceive its own state and external environment; A highly integrated electric system has been developed, and finally the shell of the robot has been designed to make the robot more beautiful as well as better wrap-around.

A Diagonal Recurrent CMAC Model Reference Adaptive Control for Parallel Manipulators Trajectory Tracking

A method for a model reference adaptive control structure using a diagonal recurrent cerebellar model articulation controller (DRCMAC) is proposed to control the parallel manipulators. In order to achieve high-precision position control and guarantee the convergence of tracking error, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning-rate parameters of the DRCMAC. The good stability and accuracy can be obtained because of the powerful on-line learning capability of the DRCMAC. Finally, the effectiveness of the proposed control method is verified by simulation results in the presence of 6-PRRS parallel manipulators

Singularity Analysis of a 6-PRRS Parallel Robot Based on Geometrical Method

Three types of singularities have been analyzed for a 6-PRRS parallel robot in this paper, i.e., the forward, inverse, and combined singularity. Conventional analysis method of a parallel robot is based on the whole Jacobian matrix, so it needs complex process and computation. The singularity analysis in this paper focuses on the geometrical character of one motion chain, and every chain is processed by the same method, so the complexity of singularity analysis is significantly reduced. Using the product-of-exponential formula, the kinematics equations possess algebraic character so that the inverse singularity analysis algorithms can be readily and systematically formulated. By analyzing the instantaneous mobility of the moving platform, the necessary and sufficient geometrical conditions for the forward singularity configurations are identified. It has shown that these methods can be used for singularity analysis of various parallel robots

On the utility of leg distal compliance for buffering landing impact of legged robots

Many legged robots have compliant mechanisms in the distal segments of their legs called distal compliance. One important function of such characteristic is to buffer landing impact at touchdown. However, there is still no general design strategy for it. In particular, nonlinear compliance behaviors are supposed to be more beneficial than linear ones, yet it is open what type of nonlinearity is a good fit. From this perspective, we used a simple spring–mass model performing free drop to investigate the design principles of distal compliance. The model includes damping and preload in spring and realistic limitations on spring compression, therefore gives a straightforward correspondence with actual hardware systems. We confirmed the benefits of using distal compliance over purely stiff structures, in terms of landing impact buffering. By assessing the relative influences of a variety of compliance configurations through numerical simulations, we found that for compliance behaviors of the same average stiffness, nonlinearities had little effect on the impact magnitude (<1u2009N), but stiffening compliance behaviors were able to provide better buffering performance by extending the impact time. It was also noticed that stiffening compliance behaviors were inevitably accompanied by a larger amplitude of spring compression, indicating that necessary trade-off has to be made for those systems concerning torso stationarity. The experimental data with our hexapod robotic platform agreed well with the results found with the proposed model, confirming that the spring–mass model could be a template to provide a useful guide for the design of distal compliance in legged robots.

Discrete sliding mode control with fuzzy adaptive reaching law on 6-PRRS parallel robot

Applying distributed control strategy, a discrete sliding mode controller (DSMC) with fuzzy adaptive reaching law is proposed to tracking the trajectory of 6-PRRS parallel robot. The detailed design procedure of the DSMC system with fuzzy adaptive reaching law is presented. The disturbances prediction, which guarantees the stability of the control system, is developed In order to attenuate the chattering phenomena, reaching law is actively tuned according fuzzy rule. Simulation study has been carried out to evaluate the performance of the proposed controller, and the results showed that the proposed controller has achieved a performance with minimum reaching time and smooth control actions. In addition, the results have also proven the effectiveness and robustness of the trajectory tracking of parallel robot characterized under disturbances and parameter uncertainties

Optimization of a frog inspired robot powered by pneumatic muscles

Study on frog swimming mechanism is an interesting topic, and a frog inspired robot has been designed with the pneumatic muscles as the driver. To improve the design and trajectory planning, the optimization of the robot was studied in this paper. For the robot structure, the limb size was optimized in ADAMS and joint parameters of the bionic robot are optimized by particle swarm optimization (PSO) method. Meanwhile, the trajectory during propulsive phase is also optimized in Matlab. Simulations in ADAMS verified the feasibility of the proposed optimization for the frog inspired robot.

Surface Defect Edge Detection Based on Contourlet Transformation

In order to preferably capture the surface defect edge information of strip steel, and provide more accurate data for subsequent defect analysis, this paper researches on the principle and implementation method of Contourlet transformation, analyzes the multi-directional and anisotropic characteristics, and proposes the image edge detection algorithm based on Contourlet transformation. This paper uses Laplacian Pyramid filter and directional filter for combination to realize Contourlet filter bank, and extracts the image edge information by the way of detecting the method of modulus maximum of Contourlet sub-band coefficient. The comparative experiments of the edge detection algorithm based on wavelet transformation and Sobel algorithm prove that the defect edge extracted by this algorithm is closer to the true edge of surface defect.

An indirect stiffness estimation of flexible joint based on system function approximation

We propose an indirect stiffness estimation method of flexible joint based on system function approximation in this paper. At first, an alternative system function is constructed. Then a system function estimation method based on saturation function is introduced to estimate its output. Taking the estimated system function as prior model, the least square method is finally introduced to identify the joint stiffness. Meanwhile, another system estimation method based on RBF neural network is also introduced to verify the efficiency of the former one. There are two advantages of the new proposed stiffness estimation method. Firstly, it is more robust to environmental noise, since no basic version or filter version of angle acceleration is maintained in the estimation process. Secondly, its easy to apply because only measurements of joint angle on motor side, joint velocity on motor side and joint angle on link side is needed.