Weiliang Xu

Tracking control of uncertain dynamic nonholonomic system and its application to wheeled mobile robots

Considers the tracking problem of dynamic nonholonomic systems with unknown inertia parameters. A new controller is proposed. The proposed controller not only ensures the entire state of the dynamic system asymptotically track the desired trajectory, but also is characterized by low dimension and the absence of singular points. Simulation results show that the proposed controller is effective.

Adaptive tracking control of uncertain nonholonomic dynamic system

This note considers the tracking problem of nonholonomic dynamic systems with unknown inertia parameters. A new controller is proposed relying on newly defined tracking errors and the passivity property of the nonholonomic dynamic system. The proposed controller ensures that the entire state of the system asymptotically tracks the desired trajectory. Simulation results show effectiveness of the proposed controller.

Sensor-based fuzzy reactive navigation of a mobile robot through local target switching

Fuzzy reactive control, incorporating a local target switching scheme, is applied to the automatic navigation of an intelligent mobile robot in an unknown and changing environment. Sensed-ranging signals and relative target position signals are input to the fuzzy controller. The steering angle and the velocity change are inferred to drive the mobile robot. A reactive rule base governing the robot behavior is synthesized from the human heuristics with respect to various situations of environment. A local target switching scheme is proposed to serve as a front-end processor of the fuzzy active controller and to deal with the local trapping and wandering cycle problem in the navigation of a behavior based mobile robot. The algorithm is described, together with some particular considerations about implementation. Efficiency and effectiveness of the proposed approach are verified through simulation and experiments conducted on a Nomad 200 mobile robot.

Design of a Biologically Inspired Parallel Robot for Foods Chewing

To quantitatively assess food texture changes and/or masticatory efficiency during chewing, the jaw movements and chewing/biting forces must be measured. For this purpose, a robotic solution has been proposed to reproduce the human chewing behavior. The chewing robot of parallel mechanism is based on the biological finding that the mandible is pivoted at the temporomandibular joints and driven by groups of muscles for opening and closing of the mouth. This paper reviews the biomechanics of the mastication system, defines the kinematical mechanism of the chewing robot, and describes the design of the actuation systems. With a linear actuator for a muscle group of mastication, its spatial placement between the mandible or moving plate and the maxilla or ground plate follows the line of action and attachment sites of the muscle. The design requirements for each actuation system are mainly specified as the actuation range, velocity, and acceleration, and the actuation force, which are determined by inverse kinematics analysis via a simulation software and the jaw force analysis via Pythagorean theorem, respectively. A design of the physical linear actuation, which is made up of a rotary motor, a gear reduction train, and a leadscrew, is presented, whereas the challenges are discussed for building the entire chewing robot.

Bond-rupture immunosensors—A review

It has long been the goal of researchers to develop fast and reliable point-of-care alternatives to existing lab-based tests. A viable point-of-care biosensor is fast, reliable, simple, cost-effective, and detects low concentrations of the target analyte. The target of biosensors is biological such as bacteria or virus and as such, the antibody-antigen bond derived from the real immune response is used. Biosensor applications include lab-based tests for the purposes of diagnostics, drug discovery, and research. Additional applications include environmental, food, and agricultural monitoring. The main merits of the bond-rupture method are quick, simple, and capable of discriminating between specific and non-specific interactions. The separation of specific and non-specific bonds is important for working in real-life complex serums such as blood. The bond-rupture technique can provide both qualitative results, the detection of a target, and quantitative results, the concentration of target. Bond-rupture achieves this by a label-free method requiring no pre-processing of the analyte. A piezoelectric transducer such as the quartz crystal microbalance (QCM) shakes the bound particles free from the surface. Other transducers such as Surface Acoustic Wave (SAW) are also considered. The rupture of the bonds is detected as electronic noise. This review article links diverse research areas to build a picture of a field still in development.

Vibration control for a flexible-link robot arm with deflection feedback

The use of flexible links in a robot inevitably causes the elastic deflection and vibration of the endpoint of the robot during high-speed operations. The deflection and vibration will tend to degrade the positioning performance of the robot. In this paper, an optical sensing system consisting of a laser diode and a position sensitive detector is introduced for the real-time measurement of the dynamic deflection. Utilising a non-linear, coupled and measurement-based dynamic system model, a Lyapunov-type controller based on the deflection feedback is then proposed to damp out the tip oscillations and regulate the endpoint of the flexible robot. Experimental tests are conducted for a flexible one-link robot arm with a payload mass at the tip. The results demonstrate the effectiveness of the proposed measuring and control schemes.

Variable structure exponential stabilization of chained systems based on the extended nonholonomic integrator

Abstract In this paper, a new variable structure control strategy for exponentially stabilizing chained systems is presented based on the extended nonholonomic integrator model, the discontinuous coordinate transformation and the “reaching law method” in variable structure control design. The proposed approach converts the stabilization problem of an n-dimensional chained system into the pole-assignment problem of an (n−3)-dimensional linear time-invariant system and consequently simplifies the stabilization controller design of nonholonomic chained systems.

Point-to-Point trajectory planning of flexible redundant robot manipulators using genetic algorithms

The paper focuses on the problem of point-to-point trajectory planning for flexible redundant robot manipulators (FRM) in joint space. Compared with irredundant flexible manipulators, a FRM possesses additional possibilities during point-to-point trajectory planning due to its kinematics redundancy. A trajectory planning method to minimize vibration and/or executing time of a point-to-point motion is presented for FRMs based on Genetic Algorithms (GAs). Kinematics redundancy is integrated into the presented method as planning variables. Quadrinomial and quintic polynomial are used to describe the segments that connect the initial, intermediate, and final points in joint space. The trajectory planning of FRM is formulated as a problem of optimization with constraints. A planar FRM with three flexible links is used in simulation. Case studies show that the method is applicable.

Maximum-dynamic-payload trajectory for flexible robot manipulators with kinematic redundancy

High payload-to-mass ratio is one of the advantages of flexible robot manipulators. For a given point-to-point task, the maximum dynamic payload-carrying capacity of a flexible redundant robot manipulator (FRM) is established in the paper. A finite-element model is presented for describing the dynamics of the system considering the added payload and the flexibility of the FRM. Different from rigid-body manipulators, vibration deformation, which is due to lightweight and high operation accelerations, is considered as constraint for the system optimization. The kinematic redundancy is integrated into the optimization formulation. The maximum-dynamic-payload trajectory is determined through optimization in which a planar FRM is employed as an example. This method is useful especially for FRMs performing repeated point-to-point operations.

Kinematics and Experiments of a Life-Sized Masticatory Robot for Characterizing Food Texture

A life-sized masticatory robot, which is intended to chew foods in a human way while the food properties are evaluated, of a 6RSS parallel mechanism is discussed in this paper. A robotic mechanism is proposed, and its kinematic parameters are defined according to the biomechanical findings and measurements of the human masticatory system. For a given mandibular trajectory to be tracked, the closed-form solution to inverse kinematics of the robot is found for joint actuations, whereas differential kinematics is derived in Jacobian matrices. Major features of the robot, including the motion control system, are presented. Experimental results for free chewing, soft-food chewing, and hard-food chewing are given where the foods are simulated by foam and hard objects, and crank actuations and driving torques (an indication of muscular activities) required are compared for the chewing of different foods.