Wheel Actuator Research Articles

Optimal Trajectory Tracking Control for Automated Guided Vehicles

This work presents a control strategy for the trajectory tracking problem of an Automated Guided Vehicle (AGV). In contrast to the current methods, this design strategy remains invariant and flexible to arbitrary number of wheels. A three-stage cascade control strategy is proposed in which the control design for the vehicle chassis is separated from the wheel-tire modules. For a given vehicle reference trajectory, the outer controller determines the required forces and moment inputs to the vehicle chassis in a time-receding fashion. At the second stage, the required forces and moment inputs are optimally allocated for each wheel and tire. At each wheel-tire module, a nonlinear controller is used to determine the actual control input for the wheel actuators. The performance of the presented control strategy is illustrated through simulation results with a realistic driving scenario for a six-wheeled vehicle. We demonstrate that the proposed controller architecture is configurable for an arbitrary number of wheels and capable of handling large steering angles efficiently.

Dynamic Air-Bearing Hardware-in-the-Loop Testbed to Experimentally Evaluate Autonomous Spacecraft Proximity Maneuvers

Ground-based testbeds are critical to develop and test different elements of spacecraft guidance, navigation, and control subsystems. This paper provides an in-detail description of a state-of-the-art air-bearing testbed used to develop guidance, navigation, and control methods for close-proximity operations. Test vehicles, representing spacecraft, float via air bearings over a horizontally leveled granite monolith and move with two translational degrees of freedom and one rotational degree of freedom under the effect of thrusters and reaction wheel actuators. This setup achieves a quasi-frictionless and low residual acceleration dynamic environment. The testbed experimental setup as well as the vehicle hardware and software architectures are discussed in detail. Characterization of different testbed elements is provided. Finally, a test campaign is used to showcase its capabilities and to illustrate the testbed operations.

Empirical Modeling of Steering System for Autonomous Vehicles

To design an automatic steering controller with high performance for autonomous vehicle, it is necessary to have a precise model of the lateral dynamics with respect to the steering command input. This paper presents an empirical modeling of the steering system for an autonomous vehicle. The steering system here is represented by three individual transfer function models: a steering wheel actuator model from the steering command input to the steering angle of the shaft, a dynamic model between the steering angle and the yaw rate of the vehicle, and a dynamic model between the steering command and the lateral deviation of vehicle. These models are identified using frequency response data. Experiments were performed using a real vehicle. It is shown that the resulting identified models have been well fitted to the experimental data.

Reaction Wheel Actuation for Improving Planar Biped Walking Efficiency

Reaction wheel systems (RWSs) are beneficial in improving bipedal walking stability, and theoretical work has shown that they can also improve the efficiency of preplanned walking motions. This work provides the first demonstration of RWS-related efficiency improvements on a physical robot and identifies the energy-saving paradigm. Gaits for a five-link planar biped are generated via trajectory optimization with and without reaction wheels. Comparisons of the resulting system behavior show a 5–10% efficiency advantage for robots with an RWS under typical walking conditions and a larger advantage near regions of marginal dynamic feasibility. The savings are mainly accomplished by enabling trajectories with better joint motor utilization, not by minimizing impact losses or acting as a kinetic energy recovery system. The RWS also improves centroidal angular momentum regulation, with the reduction in centroidal angular momentum amplitude reaching 30% at high speeds. Simulations and experiments with a five-link planar biped validate the efficiency improvements seen in optimization. This demonstrates the viability of using efficient inertial actuators to improve the efficiency of complex walking robots.

A robust adaptive tracking control method for a rehabilitative walker using random parameters

ABSTRACTThe present paper investigates stochastic modelling and a new nonlinear reliable tracking control method for a rehabilitative training walker. The stochastic model is constructed by considering random parameters. A new nonlinear tracking method against actuator fault is proposed based on redundant degree of freedom and a state feedback controller is designed by exploiting an adaptive control technique. It is proved that the mean square of the trajectory tracking error can be made arbitrarily small by choosing appropriate design parameters. As an application, simulation results confirm the effectiveness of the proposed method and verify that the walker with random parameters can provide safe sequential motion when one wheel actuator is at fault.

Redundant Input Safety Tracking for Omnidirectional Rehabilitative Training Walker with Control Constraints

AbstractThis study proposes a nonlinear safety tracking method based on redundant degrees of freedom with control constraints to protect against actuator faults that may occur in robotic rehabilitative walkers. A redundant input model with uniform actuator faults is constructed by separating the corresponding columns of the control matrix, and an adaptive robust control method is presented to deal with the separated term that is considered in relation to the extrinsic bounded interference that occurs on robotic walker systems. Based on the backstepping technique, an adjustable control law can be designed to maintain stability in terms of solving linear matrix inequality. The trajectory tracking error performance and the velocity tracking error performance are derived simultaneously. As an application, simulation results confirm the effectiveness of the proposed method and verify that the walker can provide safe sequential motions even when one wheel actuator fails.

Slip Ratio Reduction and Moving Balance Control of a Ball-bot using Mecanum Wheel

This paper proposes a robust balance and driving control for omni-directional ball robot(generally called ball-bot) with two axis mecanum wheel. Slip between ball and mecanum wheel actuator inevitably occurs along diagonal axis due to its instantaneous strong torque. In order to reduce and saturate slip, exact distance calculation scheme especially for rotational movement is essential. So this research solved Euler-Lagrange dynamics for proposed two axis ball robot based on practical mechanical modeling. Robust balance control was carried out by PID controller according to the pitch and roll angles of ball robot by using sensor fusion between AHRS and wheel encoder. Proposed PID controller enhances stability by reducing steady state error and settling time. Proposed slip control algorithm for omni-directional ball robot has been demonstrated by experiments for balance control and arbitrary driving control.

An optimal wheel-torque control on a compliant modular robot for wheel-slip minimization

SUMMARYThis paper discusses the development of an optimal wheel-torque controller for a compliant modular robot. The wheel actuators are the only actively controllable elements in this robot. For this type of robots, wheel-slip could offer a lot of hindrance while traversing on uneven terrains. Therefore, an effective wheel-torque controller is desired that will also improve the wheel-odometry and minimize power consumption. In this work, an optimal wheel-torque controller is proposed that minimizes the traction-to-normal force ratios of all the wheels at every instant of its motion. This ensures that, at every wheel, the least traction force per unit normal force is applied to maintain static stability and desired wheel speed. The lower this is, in comparison to the actual friction coefficient of the wheel-ground interface, the more margin of slip-free motion the robot can have. This formalism best exploits the redundancy offered by a modularly designed robot. This is the key novelty of this work. Extensive numerical and experimental studies were carried out to validate this controller. The robot was tested on four different surfaces and we report an overall average slip reduction of 44% and mean wheel-torque reduction by 16%.

Redundant input guaranteed cost non-fragile tracking control for omnidirectional rehabilitative training walker

In this study, the problem of guaranteed cost non-fragile tracking control on the omnidirectional rehabilitative training walker is examined. The nonlinear redundant input method is proposed when one wheel actuator fault occurs. The aim of the study is to design an asymptotically stable controller that can guarantee the safety of the user and ensure tracking on a training path planned by a physical therapist. The guaranteed cost control and the asymptotically zero state detectable concept of the walker are presented, and the model of redundant degree is constructed. The cost performance index is defined to restrain initial oversize input forces. On the grounds of LMI, a controller with gain variations that can satisfy asymptotic stability is obtained using a common Lyapunov function for admissible uncertainties resulting from an actuator fault. Simulation results confirm the effectiveness of the proposed method and verify that the walker can provide safe sequential motion when one wheel actuator is at fault.

Development of a spherical reaction wheel actuator using electromagnetic induction

A spherical reaction wheel is a novel three-axis induction motor consisting of a spherical rotor and electromagnets. The electromagnets allow the rotor to levitate and to rotate about any desired axis without mechanical contact. A benefit of the actuator is to control the satellite for three-axis attitude using the single spherical reaction wheel. In this study, a prototype model of the spherical reaction wheel with a single rotating axis is developed, and a feasibility study on the actuator is conducted. The actuator system is designed through electromagnetic field analyses of the spherical rotor in order to evaluate the levitation force and torque. Dynamic performance tests are carried out under electromagnetic rotation and levitation conditions, and torque-speed characteristics are investigated. Using the test data, torque modeling and velocity control simulations are also performed. Finally, closed loop speed control tests are conducted on the experimental model. The model shows that the maximum torque and speed are 0.7 N m and 13,500 rpm, respectively, and the speed control error is less than 4%.

ATLAS MOTION PLATFORM MECANUM WHEEL JACOBIAN IN THE VELOCITY AND STATIC FORCE DOMAINS

Conventional training simulators commonly use the hexapod configuration to provide motion cues. While widely used, studies have shown that hexapods are incapable of producing the range of motion required to achieve high fidelity simulation required in many applications. Atlas is a six degree of freedom vehicle operating training simulator motion platform where orienting is decoupled from positioning, and unbounded rotation is possible about any axis. Angular displacements are achieved by manipulating the cockpit contained in a 2.9 metre (9.5 foot) diameter sphere with three Mecanum wheel actuators. The angular velocity Jacobian, Jω, maps the desired angular velocity of the sphere to the required speeds of the three Mecanum wheels, while the static force Jacobian, Jτ, maps the static moment vector required to statically orient the sphere to the static torques required by the three Mecanum wheels. In this paper, the two Jacobians are derived independently, and it is confirmed that , as it must. The implicat...

Dynamics and vibration analysis of the interface between a non-rigid sphere and omnidirectional wheel actuators

SUMMARYThis paper presents analysis of the dynamics and vibration of an orientation motion platform utilizing a sphere actuated by omnidirectional wheels. The purpose of the analysis is to serve as a design tool for the construction of a six-degree-of-freedom motion platform with unlimited rotational motion. The equations of motion are presented taking flexibility of the system into account. The behaviour of the system is illustrated by sample configurations with a range of omnidirectional wheel types and geometries. Vibration analysis follows, and sensitivity to various parameters is investigated. It is determined that the geometry of omnidirectional wheels has a significant effect on the behaviour of the system.

A new model to compute the desired steering torque for steer-by-wire vehicles and driving simulators

This paper deals with the control of the hand wheel actuator in steer-by-wire (SbW) vehicles and driving simulators (DSs). A novel model for the computation of the desired steering torque is presented. The introduced steering torque computation does not only aim to generate a realistic steering feel, which means that the driver should not miss the basic steering functionality of a modern conventional steering system such as an electric power steering (EPS) or hydraulic power steering (HPS), and this in every driving situation. In addition, the modular structure of the steering torque computation combined with suitably selected tuning parameters has the objective to offer a high degree of customisability of the steering feel and thus to provide each driver with his preferred steering feel in a very intuitive manner. The task and the tuning of each module are firstly described. Then, the steering torque computation is parameterised such that the steering feel of a series EPS system is reproduced. For this purpose, experiments are conducted in a hardware-in-the-loop environment where a test EPS is mounted on a steering test bench coupled with a vehicle simulator and parameter identification techniques are applied. Subsequently, how appropriate the steering torque computation mimics the test EPS system is objectively evaluated with respect to criteria concerning the steering torque level and gradient, the feedback behaviour and the steering return ability. Finally, the intuitive tuning of the modular steering torque computation is demonstrated for deriving a sportier steering feel configuration.

Robust Redundant Input Reliable Tracking Control for Omnidirectional Rehabilitative Training Walker

The problem of robust reliable tracking control on the omnidirectional rehabilitative training walker is examined. The new nonlinear redundant input method is proposed when one wheel actuator fault occurs. The aim of the study is to design an asymptotically stable controller that can guarantee the safety of the user and ensure tracking on a training path planned by a physical therapist. The redundant degrees of freedom safety control and the asymptotically zero state detectable concept of the walker are presented, the model of redundant degree is constructed, and the property of center of gravity constant shift is obtained. A controller that can satisfy asymptotic stability is obtained using a common Lyapunov function for admissible uncertainties resulting from an actuator fault. Simulation results confirm the effectiveness of the proposed method and verify that the walker can provide safe sequential motion when one wheel actuator is at fault.

전방향 셀프-밸런싱 로봇휠체어 개발

In this paper, we report a self-balancing robot wheelchair which has the capability of keeping upright posture regardless of the terrain inclination in terms of the three dimensional balancing motion. It has the mobility of five degrees of freedom, where pitching, yawing, and forward motions are generated by the two-wheeled inverted pendulum mechanism and the rolling and vertical motions are implemented by the movement of the tilting mechanism. Several design considerations are suggested for the sliding type vehicle body, wheel actuator module, tilting actuator module, power and control system, and the riding module.

An Intelligent Robust Tracking Control for a Class of Electrically Driven Mobile Robots

This paper addresses the problem of designing robust tracking control for a class of uncertain wheeled mobile robots actuated by brushed direct current motors. This class of electrically-driven mechanical systems consists of the robot kinematics, the robot dynamics, and the wheel actuator dynamics. Via the backstepping technique, an intelligent robust tracking control scheme that integrates a kinematic controller and an adaptive neural network-based (or fuzzy-based) controller is developed such that all of the states and signals of the closed-loop system are bounded and the tracking error can be made as small as possible. Two adaptive approximation systems are constructed to learn the behaviors of unknown mechanical and electrical dynamics. The effects of both the approximation errors and the unmodeled time-varying perturbations in the input and virtual-input weighting matrices are counteracted by suitably tuning the control gains. Consequently, the robust control scheme developed here can be employed to handle a broader class of electrically-driven wheeled mobile robots in the presence of high-degree time-varying uncertainties. Finally, a simulation example is given to demonstrate the effectiveness of the developed control scheme.

Unified Treatment of the Kinematic Interface Between a Sphere and Omnidirectional Wheel Actuators

This paper presents a general approach to the kinematics of an orientation motion platform utilizing a sphere actuated by omnidirectional wheels. The number and type of the omnidirectional wheels, as well as their position and orientation relative to the sphere are arbitrary, provided they are distinct. In this paper, the general kinematics are presented and illustrated by sample configurations with a range of omnidirectional wheel types and quantities. Moreover, no-slip conditions are identified, and the resulting expressions and their implications on the design of such a mechanical system are demonstrated by means of several benchmark examples.

Piezoresistive encoders for ratcheting actuation systems

Abstract This paper introduces piezoresistive encoders that can provide information on the performance of ratcheting actuation systems, and may be useful in future applications that require position determination. One unique feature of the encoders is that they gain their piezoresistance from the bulk properties of polycrystalline silicon without additional fabrication steps. In this study, two encoders are considered: a parallel-guiding encoder in an on-chip Wheatstone bridge, and a piezoresistive microdisplacement transducer (PMT) encoder in an on-chip Wheatstone bridge. In tests, the encoders each generated measurable signals, with the PMT encoder providing the best sensitivity. The PMT encoder operated at actuation frequencies up to 920 Hz and produced a signal between 2 V and 3.2 V (applied gain of 1000). The PMT encoder produced unique signals corresponding to distinct ideal and non-ideal behaviors of a ratchet wheel actuation system.

Resistance torque control for steer-by-wire system to improve human–machine interface

A steer-by-wire system, which has no mechanical constraints between steering wheel and front wheel, is expected to improve steering performance. The mechanical resistance torque is not transmitted from the front wheel to the steering wheel, and it is essential to simulate the torque around the steering wheel for better human-machine interface. Previous studies investigated resistance torque control originating from vehicle behaviour variables such as yaw rate and lateral acceleration. However, other variables such as steering wheel angle and front wheel actuation force are also good candidate sources to generate resistance torque. In this paper, first, four general guidelines are introduced to evaluate three types of resistance torques, i.e., the steering wheel angle origin, the steering force origin and the vehicle behaviour origin. First two guidelines are for ‘driver-made’ phase to make a turn, while the third guideline is for ‘vehicle-made’ phase to return to straight driving and the fourth one is the applicability guideline. Satisfaction of these guidelines by each of the three resistance torques is examined by the actual vehicle experiment. A necessity of combining these three types of resistance torques is indicated as a future subject.

Adaptive Control of an Electrically Driven Nonholonomic Mobile Robot via Backstepping and Fuzzy Approach

This paper investigates the tracking control of an electrically driven nonholonomic mobile robot with model uncertainties in the robot kinematics, the robot dynamics, and the wheel actuator dynamics. A robust adaptive controller is proposed with the utilization of adaptive control, backstepping and fuzzy logic techniques. The proposed control scheme employs the adaptive control approach to design an auxiliary wheel velocity controller to make the tracking error as small as possible in consideration of uncertainties in the kinematics of the robot, and makes use of the fuzzy logic systems to learn the behaviors of the unknown dynamics of the robot and the wheel actuators. The approximation errors and external disturbances can be efficiently counteracted by employing smooth robust compensators. A major advantage of the proposed method is that previous knowledge of the robot kinematics and the dynamics of the robot and wheel actuators is no longer necessary. This is because the controller learns both the robot kinematics and the robot and wheel actuator dynamics online. Most importantly, all signals in the closed-loop system can be guaranteed to be uniformly ultimately bounded. For the dynamic uncertainties of robot and actuator, the assumption of ldquolinearity in the unknown parametersrdquo and tedious analysis of determining the ldquoregression matricesrdquo in the standard adaptive robust controllers are no longer necessary. The performance of the proposed approach is demonstrated through a simulation example.