Mechatronics

Published by Elsevier
Online ISSN: 0957-4158
Publications
Conference Paper
In this paper, we consider the output feedback control problem for dynamically positioned surface vessels when uncertainties related to the system parameters are present. Specifically, by applying Lyapunov techniques, we design a nonlinear model based adaptive output feedback controller that achieves global asymptotic tracking and compensates for the parametric uncertainties associated with nonlinear ship dynamics despite the lack of velocity measurements. Simulation results are included to illustrate the performance of the proposed control law
 
Conference Paper
We design a control strategy for a rotating unbalanced disk. The control strategy is composed of a control torque and two control forces. The control strategy regulates disk displacement while ensuring that the unbalanced disk tracks a desired angular velocity trajectory. Specifically the control uses a desired compensation adaptation law (DCAL) and a gain adjusted forgetting factor to achieve exponential stability despite the lack of knowledge of the imbalance-related parameters provided a mild persistency of excitation condition is satisfied
 
Conference Paper
This paper describes motion planning of computer controlled automata (CCA). We consider two steps for the motion planning; (1) Create rough patterns of motion. (2) Modify the patterns iteratively and create a desired motion. A real time planning method for a robot task, which has been developed by authors, is applied as the first step. Using this method, a human operator can generate a trajectory of the CCA while monitoring the actual motion by operating a joystick. For accurately modifying inadequate motion in the second step, a CAD system is developed. Tools for the CAD system are described and, then, the effectiveness is shown in an experimental example
 
Conference Paper
Summary form only given. An online sensor is required for real-time control of penetration depth in robotic welding. Currently, no online techniques exist for direct penetration depth measurement. The development of a penetration control system will significantly reduce the costs associated with repairing or scrapping defective welds. Laser array generated ultrasound is a noncontact, nondestructive method that can potentially be used to measure weld penetration. This paper will discuss the design and implementation of an automated system that was used to measure the depth of simulated solidified welds. The system consists of a laser array generation source and an electromagnetic acoustic transducer (EMAT) receiver. Measured penetration results for the simulated weld is compared with the exact results. Experimental results will also be shown for array gain measurements in order to demonstrate the power of the array. This automated system is being modified in readiness for use in actual robotic welding
 
Conference Paper
Summary form only given. This paper proposes a localization method of indoor mobile robot using vision and color signboard. The color signboard is placed in the environment as landmark to decide the robot's absolute position. The signboard is also attached to each robot for localization among robots. The color signboard is designed such that the robot can perform three key functions: the signboard detection, identification and localization. Autonomous navigation of mobile robots in wide area as well as cooperative operations requires many signboards with unique identification pattern. The color coding method allows us to make many distinct signboards. Several mobile robots hovering in the same environment may cause the unforeseen obstruction to the viewing of the signboards. Our color signboard allows the robot to verify its own position when the signboard is visible entirely in the field of view. The absolute positioning algorithm for mobile robot using the color signboard is described, where the vision and odometric dead reckoning information is combined by the extended Kalman filter
 
Conference Paper
In this paper, a path tracking algorithm is proposed to compensate path deviation due to torque bound. For this, a disturbance observer is applied to each joint of an n degrees of freedom manipulator to obtain a simple equivalent robot dynamics (SERD) being represented as an n independent double integrator system. For an arbitrary trajectory generated for a given path in Cartesian space, whenever the saturation of any actuators is met, the desired acceleration of the nominal trajectory in Cartesian space is modified online by using SERD. Also an integral action with respect to the difference between the nominal and the modified trajectories is utilized in nonsaturated region of actuators to reduce the path error. To verify the effectiveness of the proposed algorithms, numerical simulations and real experiments are performed for two degrees of freedom SCARA type direct-drive arm
 
Conference Paper
This paper is concerned with the design problem of the robust control for a networked control system (NCS) with time-varying communication delays. It has been known that time delays may not only degrade the system performance, but also destabilize the controlled plant. To alleviate the influence resulting from time delays while maintaining performance, a mixed fuzzy-PID/neural network compensating scheme is applied to pneumatic systems with uncertain communication delay. The experimental results verify effectiveness and superiority of our proposed approach.
 
Article
We consider in this paper the design and implementation of a dual-stage actuated hard disk drive (HDD) servo system, in which an additional piezoelectric actuator is mounted on top of the conventional voice-coil-motor (VCM) actuator to provide a faster and finer response. More specifically, the dual-stage actuated HDD servo system consists of a primary VCM actuator and a secondary suspension piezoelectric microactuator. The VCM actuator is used to quickly move the read/write (R/W) head of the HDD servo system to a target track, whereas the microactuator is used to fine-tune the R/W head position when it is getting closer to the target. In our design, the primary actuator is controlled by a newly developed composite nonlinear feedback (CNF) control law, which has fast rise time and small overshoot, and the microactuator is controlled through a simple static gain together with a low-pass filter and a notch filter. Simulation and implementation results show that in track following, the dual-stage actuated HDD servo system has outperformed the single-stage actuated counterpart by more than 47% in settling time and by 39% in position error signal (PES) tests.
 
Article
This paper describes the use of pneumatic muscle actuators in rehabilitation robotics. The history and application of this type of actuator is reviewed, and the design of an electric wheelchair mounted rehabilitation robot, utilizing a new form of pneumatic muscle actuator, the flexator, is discussed. The theory of controllable compliance is detailed and experimental results based on the flexator actuator are given to support this theory.
 
Article
To achieve robust linear position driving control with contactless and low mechanical friction, this paper presents the development of a magnetic suspension positioning stage directly driven by an inverter-fed linear permanent magnet synchronous motor (LPMSM). First, an experimental linear positioning system is established. In which, the LPMSM is fed by a properly designed current-controlled inverter having accurate and quick current tracking response, and the magnetic suspended supporting mechanism is employed. In addition, to enhance the driving control performance, the laser position sensing system and personal computer-based controller are also properly set up. The dynamic model of the whole drive system is estimated from the measurements. And accordingly, a two-degrees-of-freedom control scheme consisting of a command feedforward controller and an H∞ feedback controller is designed firstly to fulfill the specified positioning control requirements at nominal case. Then, a simple model following controller is further added to preserve the desired control performance as the operating condition and parameter changes occur. Some simulated and experimental results reveal that quantitative and robust position control performances are obtained by the proposed controller.
 
Article
At the present time, actuators with several degrees of freedom (Dof) are being used more and more frequently. In order to yield viable devices, it is necessary to ensure high performance, as well as keeping the cost low. This paper deals with the modeling and control of a 2Dof permanent magnet planar actuator. A prototype dedicated to theoretical conclusion validations is presented and its operation explained. A model, based on a permeance network, is introduced. The simulation results are compared to measurements obtained using a manufactured prototype. Three Hall effect sensors are then used to obtain the x–y position of the moving part. From these signals, simulations of a scalar control are obtained using Matlab Simulink®.
 
Article
This paper presents the design, manufacture, and implementation of a dual-stage tip-tilt steering mechanism driven by ultra-high strain piezoelectric stacked actuators for coarse and fine motion control. The design of motion control systems often requires a compromise between range and bandwidth response. Consequently, for a given dynamic response, as range increases so too will following errors If advanced information is available, these errors may often be minimized by using feedforward techniques. In recent years, dual-stage systems which incorporate serially connected fine and coarse stages have demonstrated promising results. Related efforts (employing dual-stage methods) have addressed variants on designs using PZT elements, voice coils, or linear motors. The dual-stage uses a fine motion platform (with high frequency response and short range) to actively reduce following errors of the coarse platform which has a lower bandwidth response. This paper presents a dual-stage (also referred to as a multi-coaxial) tip-tilt mechanism with 6 degree of freedom (DOF) comprising two 3 DOF stages connected in series. The ultimate purpose of the mechanism is to position a 300 mm diameter mirror, hence it is referred to as a fast steering mirror. Also described is the nested control algorithm that is used to derive the drive signals for both the fine and coarse platforms. The algorithm provides a method by which the fine platform is actively driven to a commanded offset (usually its mid-range setting) by the coarse platform. Concurrently, the fine platform actively responds to the demand to reduce rapidly changing following errors. Finally, an experimental program is overviewed to assess the closed loop response for the fine, coarse, and dual-stage controllers. In one experiment, a sinusoidal input of amplitude ±300 μrad was employed at 10 Hz. The coarse controller generated a following error up to ±100 μrad at 10 Hz. In contrast, the dual-stage mechanism equipping both the coarse and fine controller reduced the following error to ±5 μrad. Frequency response plots of the closed loop control system are also presented and, with further optimization, indicate potential bandwidth improvements with small following errors and minimal phase lags up to 70 Hz.
 
Article
Magnetic levitation is a good choice for high precision micromanipulation. Several magnetic levitation systems have been proposed and shown to be effective for precision positioning. Most of these systems work with small air gaps and have a small movement range for levitated objects. Increasing the air gap will introduce uncertainty into the modeling and control of the system but is required for specific applications, such as micromanipulation. This paper investigates regulation methods and the control of a large gap magnetic field for non-contact manipulation. A two dimensional magnetic field analysis is performed on a system consists of two electromagnets. In order to increase the uniformity of the magnetic field and have control over the distribution of the field, the electromagnet poles are connected together through a soft magnetic iron called pole piece. The effect of pole piece is investigated through both finite element analysis and mathematical modeling. Definition of a working envelop through magnetic filed distribution is discussed. The results of 2D modeling are discussed and are extended into the 3D case. A number of pole piece profiles are proposed and their effect on the magnetic field investigated. An experimental setup is used for 3D levitated movement of a small permanent magnet. It is shown that manipulation of objects can be performed using an appropriate configuration of electromagnets, a special pole piece, and a yoke.
 
Article
This paper presents a method to automate the process of surface scanning using optical range sensors and based on a priori known information from a CAD model. A volumetric model implemented through a 3D voxel map is generated from the object CAD model and used to define a sensing plan composed of a set of viewpoints and the respective scanning trajectories. Surface coverage with high data quality and scanning costs are the main aspects in sensing plan definition. A surface following scheme is used to define collision free and efficient scanning path trajectories. Results of experimental tests performed on a typical industrial scanning system with 5 dof are shown.
 
Article
The design and analysis of a miniature electromagnetic actuator for use in a novel virtual tactile display is described. The actuator operates in repulsive mode so that it can be used for vibro-tactile stimulation of a human fingertip. Pulsed current and permanent magnet based approaches are investigated and compared. Four frequencies (10, 50, 100, and 150 Hz) were used to test the perception limit of three human subjects. The results indicated that the perception is not strongly dependent on frequency in the test range. The required stimulation energy of individual pulses was estimated to be below 57 micro-Joules, while the average peak-force needed for reliable stimulation was 59 milli-Newtons. The perception of simple test shapes was also tested by attaching the actuator onto the fingertip of the human subjects and turning it on and off as a function of its position.
 
Article
This paper describes the application of a stereo algorithm with novel variable windows to the measurement of three-dimensional (3D) shapes. Due to heavy variations of disparities within a rectangular window, previous area-based stereo algorithms have given rise to relatively large matching errors around depth discontinuities. In this paper, a new correlation function based on a robust estimator is formulated to improve matching accuracy in the area with depth discontinuities. Four-direction line mask including a rectangular window is devised not only to reduce noise effects but also to improve matching accuracy. The connectivity of match candidates selected by the correlation function is investigated to include the physical sense that disparities near an interested pixel are constant, and then integer disparities are estimated by finding the disparity plane with maximum connected match candidates. A novel variable window derived from a set of maximum connected candidates with positive intensity-gradient based similarity is used to minimize matching ambiguity of existing area-based methods. In addition, sub-pixel disparity estimation is performed to reduce local deformation effects of the variable windows resulting from projective distortion. Experiments confirm that the proposed method estimates accurate and robust results in the vicinity of depth discontinuities as well as in continuously smooth areas.
 
Article
Loads from vehicles alter the functional and structural characteristics of road pavements that directly affect the loss of resistance of the pavement and the users’ comfort and safety. Those alterations require constant observation and analysis of an extensive area of road surface with high precision. For such it was developed a new scanning prototype machine capable of acquiring the 3D road surface data and characterize the road texture through two algorithms that allows calculate the Estimated Texture Depth (ETD) and Texture Profile Level (L) indicators. The experimental results obtained from nine road samples validate the developed algorithms for the texture analysis and showed good agreement between the scanning prototype equipment and the traditional Sand Patch Method.
 
Article
The paper presents an educational view on the concept of mechatronics as a logical development of rationalization and integration across the traditional subject disciplines of mechanical engineering, electrical engineering and computer technology. Examples of case studies, project investigations and research activities are included as illustrations of current mechatronics teaching practice within the mechanical engineering department at the Dundee Institute of Technology.
 
Article
The vehicle dynamics and control play an important role in an automated highway system for passenger cars. This study addresses the problem of designing active controllers for four-wheel-steering (4WS) vehicles. We first obtain a set of linear maneuvering equations representing the four-wheel steering motions and independent wheel torques for lateral/directional plus roll dynamics. We then formulate simultaneous H2 and H∞ (sub)-optimal controls with a desired pole assignment via linear matrix inequalities (LMIs). The steering angles are actively controlled by steering wheel commands through the actuator mechanisms for the lateral/directional and roll motions. Further the wheel power and braking are directly controlled by independent torques. Numerical simulations are performed on a complex vehicle model in order to evaluate the vehicle performance (noise and disturbance attenuation), stability, and robustness under a given class of uncertainty. Finally, the presented autopilot controller provides greater maneuverability and improved directional stability for passenger vehicles.
 
Article
A control method which drives the permanent magnet A.C. servo motor without the detection of the rotor position by the absolute position transducer such as an absolute encoder or a resolver is described. Only an incremental encoder is coupled to the motor shaft in order to obtain information about electrical commutation, motor speed, and motor position. A fuzzy algorithm is developed in order to estimate the absolute rotor position which is essential to electrical commutation. The center of gravity method defuzzifies the output variables of the fuzzy rules to generate the current command for estimation. A pulse interval measurement method is discussed, which enables the measurement of the motor speed and the motor position with the same resolution from a standstill to the rated speed. A digital current control method is proposed, which makes the permanent magnet A.C. servo motor fed by impressed currents.The entire control algorithm is implemented on the control system consisting of a digital signal processor (DSP) ADSP2101. Experimental results show that the proposed control scheme can be effectively used in controlling the permanent magnet A.C. servo motor with only an incremental encoder as a position transducer with high dynamic performance.
 
Article
This paper employs a PI observer to detect abnormal information in an auto-balancing two-wheeled cart caused by actuator faults and steering load torques. A fault diagnosis scheme which contains the strategies of both fault-detection and fault-evaluation is proposed in this paper. Analysis and design of the PI observer are then discussed in detail. A statistical threshold that has the benefits of improving decision-making reliability is investigated for diagnosing a possible abnormal operation and/or a serious actuator malfunction. Illustrated examples are given for evaluating the performance and feasibility of the presented fault diagnosis strategy.
 
Article
The design and construction of a dynamic absorber incorporating active vibration control is described. The absorber is a two-degree-of-freedom spring-lumped mass system sliding on a guide pillar, with two internal vibration disturbance sources. Both the main mass and the secondary absorber mass are acted on by D.C. servo motors to suppress the vibration amplitude. A fuzzy control algorithm is used to control this multi-input/multi-output (MIMO) system. According to the characteristics of the system dynamics, the membership fuctions and the fuzzy rules are decided. Then a conventional fuzzy controller and a decoupling fuzzy controller for the MIMO vibration system are designed. Finally, the results of some experiments are presented. The experimental results show that the system is effective in suppressing vibration. The performance of this control strategy for position tracking control is evaluated based on experimental data.
 
Article
Work on innovative interfaces has led to the development of optopneumatic systems, which can receive an optical control signal and produce a pneumatic output signal. Specifically, the interface discussed here employs what is known as the “photothermic effect” to convert light power into a pneumatic signal. This is crucial in developing actuators that are suitable for use in areas involving explosion hazards or electromagnetic interference problems, where electrical devices are not recommended or must be avoided. In this case, the system converts an optical signal into a pneumatic signal thanks to a light absorption body interposed between the optical source and the operating gas. The investigation was carried out using both theoretical and experimental methods. Essentially, its goals were to compare the behavior of light absorption bodies in a photothermic cell, using different materials that ensure a durable, repeatable coating with little sensitivity to disturbance, and to determine the influence of varying the photothermic cell’s geometric dimensions.
 
Article
In a didactic approach to mechatronics, the academic subject can be defined according to four dimensions: identity, legitimacy, selection and communication. A result of defining the legitimacy of mechatronics as functional is that the ultimate identity can be viewed as thematic. Following this, a model is proposed to describe the evolution of mechatronics, from a disciplinary identity towards a thematic. The move from a disciplinary identity to a thematic is divided into six stages, each represented by a characteristic view and academic practice of the subject. To further illustrate this evolutional process examples from various universities in northern Europe are given. The universities analysed for this purpose presents examples for stages 3–5 in the model; stages represented by a change in courses (stage 3), a change in curricula (stage 4) and by a change in organization (stage 5).
 
Article
The present approach to teaching control system design as a stand-alone course offered late in the undergraduate curriculum, with little discussion of hardware, implementation, or integration through design, is ineffective in preparing students for engineering practice. Control systems must be integrated into the design from the beginning and not be simply after-thought add-ons. Based on the authors' extensive experience teaching mechatronics to university students and professional engineers, an integrated mechatronic approach to teaching controls is proposed. This approach will seriously address the deficiencies in the present-day skills of working professionals, as observed by the authors in teaching professional engineering workshops. These deficiencies are a direct result of how we presently teach controls and related topics.
 
Article
Methods of increasing the bandwidth of a telescope servo system have been investigated. The results of this research, both via simulation and practical evaluation, have shown that the application of acceleration feedback can increase the position servo loop bandwidth by a factor of 4. Acceleration feedback has been applied successfully to the servo system of a real machine. This has been achieved both by the use of accelerometers and by software-based acceleration calculation and state estimation techniques. The performance of the software-based techniques matches that of the accelerometer if the sampling rate of the servo system is high enough.
 
Article
Accurate position control and its related dynamics have been under research for industrial robotics and CNC machinery applications. Several works have developed techniques to fulfil the trajectory planning and profile generation from the CADCAM point of view, however, there is a lack in the mathematical foundations on computationally efficient profile generation for implementation in digital systems. This paper shows a novel approach for acceleration–deceleration profile generation based on polynomials at the discrete-time domain which is computationally efficient and easy to implement in most digital system available technologies. Results in the form of simulations and a servomotor driving the axis position on a CNC milling machine are presented to show the procedure efficiency and jerk reduction. It is shown that the proposed parameterisation of polynomial based profile generation requires half the operations to be computed, compared with the currently available methodologies for direct polynomial evaluation. Furthermore, the proposed procedure is multiplier free which means that almost every low-cost processor or embedded digital system can easily perform the generation task.
 
Article
Maneuverability is the measure of the dynamic performance of a manipulator in a specific posture or configuration, and acceleration radius is one of the most utilized indices of it. Acceleration radius can be utilized as the reference to judge whether further dynamic analysis should be performed when evaluating the controllability and feasibility of the manipulator following the prescribed path with assigned kinematic and kinetic requirements in the planning phase. When utilizing acceleration radius as the dynamic reference in the planning phase, it can prevent wasting the calculation cost due to these non-necessary dynamic analyses, and it can also be utilized as the benchmark in the on-line control.However, the existence of the configuration errors is inevitable in reality, and it deteriorates the dynamic performance of a manipulator with the ideal configuration parameters and leads to the potential risk of failing to achieve an assigned dynamic task. To investigate the adverse behavior caused by the configuration errors and to provide some clues to avoid or reduce their influence, this article proposes a novel and systematic method which can be used to evaluate the maneuverability deterioration of a non-redundant serial manipulator system due to the influence of configuration errors, and it also provides an index, deterioration rate, to quantitate this kind of deterioration. Deterioration rate can be utilized to quantitate the maneuverability deterioration due to the influence of configuration errors in a prescribed workspace or region and can also be treated as the safety or derating margin when proceeding with the control or path planning.
 
Article
In order to make industrial robots and computer numerical control (CNC) machine tools perform tasks efficiently, many techniques for the acceleration and deceleration of industrial robots and CNC machine tools have been proposed. Polynomial technique can generate velocity profiles of various acceleration and deceleration characteristics, but it requires a lot of computations. Digital convolution technique can generate efficiently velocity profiles, but it cannot generate velocity profiles with some kinds of acceleration and deceleration characteristics. This paper proposes an efficient approach for generating velocity profiles that cannot be generated by previous techniques as well as velocity profiles generated by them. Based on the proposed approach, an acceleration and deceleration circuit for industrial robots and CNC machine tools is designed by using the VHDL and it is implemented with a FPGA. A velocity profile generated by the acceleration and deceleration circuit will be applied to one single-axis control system.
 
Article
In this paper, we present a technique of acceleration control which can be used as a fast inner loop to enhance the disturbance suppression capabilities of permanent magnet brushless D.C. (PM BLDC) drives when used in typical position control applications. The proposed technique has the advantage of simplicity which should make it of considerable appeal to many practising engineers. In the paper, the technique is carefully described, and then evaluated and compared with an alternative control system design which uses standard state-feedback techniques only. The superiority of the proposed technique is demonstrated in simulation experiments, and also in a real-time implementation for position control using a PM BLDC drive.
 
Article
Angular acceleration estimation and its application in acceleration feedback control are investigated experimentally in the paper. In combination of Newton Predictor (NP) with Kalman Filter (KF), a new predictive estimator for angular acceleration, called Newton Predictor Enhanced Kalman Filter (NPEKF) is proposed. This estimator provides a wide bandwidth and a small phase lag of the estimated acceleration while attenuating noises. Based on the estimated acceleration an acceleration feedback control (AFC) is presented for multiple degree-of-freedom (DOF) mechatronic system. The design of AFC is specified in terms of its stability and ability in suppressing dynamic disturbances. Experiments are conducted on a 2-DOF direct-drive manipulator. The frequency responses of the acceleration estimated by NP, KF and NPEKF are compared with those of the measured acceleration via linear accelerometer. The performance of AFC using the estimated acceleration is assessed against that using the measured acceleration. This study has shown that the proposed NPEKF estimator is able to supply the AFC with reliable required acceleration.
 
Article
A new application for accelerometers is presented and evaluated instead of using it to measure the linear acceleration of the vehicle, which is usually performed with traditional odometry. In the present case, a dual orthogonal axis accelerometer is vertically aligned in the center of a wheel. Then the rotational position of the wheel can be detected and RPM can be counted based on the accelerometer angular position. A microcontroller is used to measure the value of each accelerometer axis, and with a proper algorithm 12 wheel positions are detected combining the x-axis and y-axis values. The wheel position is transmitted by means of a wireless link to another microcontroller or computer located on board of the vehicle to estimate the traveled distance. This embedded wireless device is now named accelodometer. Field results on a pick-up tested at up to 40 km/h and with an autonomous robotic vehicle showed that this accelodometer presented advantages with respect to both usual accelerometer and incremental encoder, avoiding the accumulative error due to the sensor drift.The repeatability of the device was established within the 0.01% in 4 km path. A resolution of 1/12 of the wheel perimeter was determined.
 
Article
For a limited, but increasing, number of surgical procedures, robots can provide the surgeon with valuable assistance. They can help theatre staff to avoid the hazard of X-radiation by assisting during those parts of operations requiring the use of X-rays; they can remain stationary for longer than the human and this may help where precision and immobility are desirable; they can find access to difficult sites for inspection or repair. Surgical assist robots pose a different set of design constraints to those of their industrial counterparts. Patient safety is paramount and this makes very stringent demands on the command interface between the surgeon and the robot. In particular, command disambiguation is essential. After describing some significant experimental systems in use world-wide, a novel fully-integrated system for minimal access surgery called DUMASS is discussed together with some operational features.
 
Article
A Virtual Access Laboratory (VAL) for undergraduates is currently being built at Georgia Tech. This laboratory will house a three-degree of freedom, hydraulically actuated device resembling a fork lift truck. Experiments with the hydraulic equipment can be run remotely via the Internet. Such an experimental apparatus will give students exposure to hydraulics, technology that is used expansively in industry, yet lightly treated in most US undergraduate engineering curricula. The software responsible for providing the user interface and controlling the manipulator is comprised of both client and server programs that communicate via the Internet. The client code is written in Java and features a Graphical User Interface to provide a user-friendly environment for students. Code for the server is written in C++ to run on Windows NT with Hyperkernel for deterministic real-time control. This code will offer the students the ability to run experiments such as system identification, PID control, and trajectory planning. A camera monitors the system and provides students with visual data.
 
Article
A large Stewart platform for fine tuning of the feed source tracing is presented in this paper. The model of kinematics control is developed with coordinate transformation, and a quasi-static load analysis is made by virtual work principle with Jacobian matrix because the tracing speed is slow. The kinematics accuracy model is derived by position vector analysis, and the kinematics accuracy results are provided. It has shown that the designed Stewart platform can satisfy the requirement of feed source trajectory control of large spherical radio telescope.
 
Article
In this article, computer aided methods and tools for improving the accuracy of a mechanism's dynamic model used in the Matlab/Simulink simulation environment are presented. This is done by a simple but exact method with the support of a high-level CAD system Pro/Engineer that allows the analysis of mass properties and the dynamics of complicated spatial mechanisms. These tools can serve for a synthesis of the control system based on Lagrangian dynamics and following a simulation of the whole mechatronic system behavior.
 
Article
Odometry provides fundamental pose estimates for wheeled vehicles. For accurate and reliable pose estimation, systematic and nonsystematic errors of odometry should be reduced. In this paper, we focus on systematic error sources of a car-like mobile robot (CLMR) and we suggest a novel calibration method. Kinematic parameters of the CLMR can be successfully calibrated by only a couple of test driving. After reducing deterministic errors by calibration, odometry accuracy can be further improved by redundant odometry fusion with the extended Kalman filter (EKF). Odometry fusion reduces nonsystematic or stochastic errors. Experimental verifications are carried out using a radio-controlled miniature car.
 
Article
This paper describes an accurate continuous path controller and its application to accurate control of a flexible one-link robot equipped with an optical link deflection sensor. The controller consists of: (1) feedforward, and (2) feedback of the difference between desired and measured states. The feedforward calculation aims at zero tracking errors; it is based on the inverse open loop model of the system, and therefore independent of the feedback calculation. The feedback term compensates for disturbances and modelling inaccuracies. The sensor system is called DIOMEDES (Laser ode ptical System for asuring Structural flection), and measures in real time the spatial structural deflections of the flexible link. The experimental test case is a flexible one-link robot. The model, on which the controller is based, is the result of experimental frequency domain identificaton. An accurate model is obtained by dividing the total system into two submodels, and by identifying the submodels separately. The experiments show that this control approach, in combination with the use of an accurate optical link deflection sensor, allows very accurate tracking, provided that an accurate model of the system is available.
 
Article
An advanced continuous path tracking controller and its application to accurate control of two different linear synchronous motor machine tool axes are described. The controller consists of state feedback, feedforward, and motor ripple compensation. The feedforward aims at zero tracking errors and consists of inverse model pre-filtering. Ripple compensation is implemented in the position control loop and based on an experimentally identified first order approximation of the motor ripple. Both cogging (magnetic ripple) and force ripple (electro-magnetic ripple) are considered. Experiments carried out on the two machine tool axes show that a simple ripple compensation method is necessary and sufficient in order to achieve acceptable tracking errors.
 
Article
Many hydraulically-operated process such as machining, injection molding and metal forming process are usually represented by a hydraulic actuator-load system whose dynamic characteristics are complex and highly nonlinear. Due to these characteristics, the conventional approach to the controller design for these systems may not guarantee accurate tracking control performance. Taking into account the repetitive nature of the operations in those processes, a discrete iterative learning control algorithm is proposed to realize an accurate hydraulic servo system. In the algorithm, the control input sequence for next operation is determined by utilizing the tracking error as well as information of the dynamic characteristics obtained from the past operations such that the output trajectory tracks the given desired trajectory as closely as possible. To investigate gradual improvement of tracking performance in consecutive operations, the proposed algorithm is implemented to the hydraulic servo system. A series of experiments was performed for the position tracking control of the system. The experimental results show that regardless of inherent nonlinearities and uncertainties associated with hydraulic system, an accurate tracking control performance is obtained using the proposed learning control algorithm characterized by recursive operations.
 
Article
A software tool based on bond graphs is presented together with a hardware-in-the-loop experimental rig. These are designed to be used as aids in the planning, simulation, implementation and testing of control systems containing multiple actuators with sensory feedback.The windows-based, object-orientated (OO) development tool ACE (Adaptive Control Environment) enables the user to build up a graphical representation of the system by selecting objects from a library of system elements and/or mini systems. Each of these objects, although viewed as a graphical drawing of the selected element on this level, contains data representing an acausal bond graph. As the model is built up containing several of these objects, ACE has a view of the overall interconnecting acausal bond graph of the system.For hardware-in-the-loop simulation, ACE divides the core system model into three parts, representing:•the hardware-in-the-loop objects — that is the hardware under test (e.g. an electrical motor and sensors);•the controller — whose function it is to control the afore mentioned hardware;•an applied loading. It is from the last two of these sub-systems that control code may be generated for operation and testing on a specially developed DAP (Data Acquisition Processor) controlled test-rig.
 
Article
Recently a substantial amount of research has been done in the field of dextrous manipulation and hand manoeuvres. The main concern has been how to control robot hands so that they can execute manipulation tasks with the same dexterity and intuition as human hands. This paper surveys multi-fingered robot hand research and development topics which include robot hand design, object force distribution and control, grip transform, grasp stability and its synthesis, grasp stiffness and compliance motion and robot arm-hand coordination.Three main topics are presented in this article. The first is an introduction to the subject. The second concentrates on examples of mechanical manipulators used in research and the methods employed to control them. The third presents work which has been done on the field of object manipulation.
 
Article
Today Surface Acoustic Wave (SAW) devices are used in many electronic products, e.g. as filters in communications applications or for signal processing in radar systems. Due to the dependence of the propagation characteristic of the microacoustic wave on many physical parameters (e.g. temperature or strain) it is possible to build SAW sensors for a great variety of physical, chemical and biological parameters. SAW sensors are not only small, rugged and show small aging rates, they also can be used as wirelessly interrogable and completely passive sensors for many hostile environments. In this contribution the SAW device principles, design procedures and technological issues as well as examples of their use in certain measurement and identification applications are reviewed.
 
Article
The design of a bistable electro-pneumatic interface based on laminar-to-turbulent jet transition is herein presented. This principle, used in the past to produce air stream controlled fluidic turbulence amplifiers, is now applied to a new interface driven by acoustic waves and controlled through very low power electrical signals. The study was performed experimentally, attempting to find the optimum interface geometry and analysing its sensitivity to acoustic signals in a frequency range from 2 to 20 kHz and at different excitation levels. A piezo-electric buzzer was used as sound source, resulting in a device with electric power consumption of less than 5 mW, able to switch common low/high pressure pneumatic valves.
 
Article
The lack of reliable non-contact, non-destructive, online sensors with the ability to detect defects as they form and with the capacity to operate at high temperatures and in harsh environments is a big obstacle to fully automated robotic welding. This paper presents a non-contact automated data acquisition system for monitoring a robotic gas–metal arc welding process based on laser ultrasonic technology. While a robot welds between two 1040 steel strips, a Nd:YAG Q-switched pulse laser generates ultrasound on one side of the weld by ablation, and a non-contact electro-magnetic acoustic transducer (EMAT) placed on the opposite side of the weld detects ultrasound transmitted through the weld bead. Ablation is employed because high temperature specimens require strong signals to compensate for attenuation within the bulk of the material. The data is then analyzed to determine the time required for ultrasound to travel from the laser source to the EMAT, termed as the time of flight (ToF). When experimental ToF is compared to theoretical ToF, it is determined that surface waves are detected by this system. Therefore, this system can measure weld bead reinforcement distance. In most cases, weld bead geometry is an indication of the weld quality, and can be used as feedback to control a welding process.
 
Article
The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. The distance between cantilever tip and sample surface in non-contact AFM is a time-varying parameter even for a fixed sample height, and typically difficult to identify. A remedy to this problem is to directly identify the sample height in order to generate high-precision atomic-resolution images. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Since in most practical applications only the microcantilever deflection is accessible, we will use merely this measurement to identify the sample height. In most non-contact AFMs, cantilevers with high-quality factors are employed essentially for acquiring high-resolution images. However, due to high-quality factor, the settling time is relatively large and the required time to achieve a periodic motion is long. As a result, identification methods based on amplitude and phase measurements cannot be efficiently utilized. The proposed method overcomes this shortfall by using a small fraction of the transient motion for parameter identification, so the scanning speed can be increased significantly. Furthermore, for acquiring atomic-scale images of atomically flat samples, the need for feedback loop to achieve setpoint amplitude is basically eliminated. On the other hand, for acquiring atomic-scale images of highly uneven samples, a simple PI controller is designed to track the desired constant sample height. Simulation results are provided to demonstrate the feasibility of the approach for both sample height identification and tracking the desired sample height.
 
Article
A new reinforcement learning algorithm is introduced which can be applied over a continuous range of actions. The learning algorithm is reward-inaction based, with a set of probability density functions being used to determine the action set. An experimental study is presented, based on the control of a semi-active suspension system on a road-going, four wheeled, passenger vehicle. The control objective is to minimise the mean square acceleration of the vehicle body, thus improving the ride isolation qualities of the vehicle. This represents a difficult class of learning problems, owing to the stochastic nature of the road input disturbance together with unknown high order dynamics, sensor noise and the non-linear (semi-active) control actuators. The learning algorithm described here operates over a bounded continuous action set, is robust to high levels of noise and is ideally suited to operating in a parallel computing environment.
 
Article
Conventional spinal implants are static and rigid structures which underpin the skeleton, not adapted to patient’s post-surgery evolution (e.g. growth in scoliotic children). A new active spinal implant uses mechanical energy from the patient’s body to perform an active, progressive dynamic correction. It is growth-compatible and can be extracted after completion of skeletal amendment. It is non-invasively controlled by means of a transcutaneous transformer.The core of the prosthesis is an internal hydraulic mechanism, which allows the appropriate corrective forces, bending moments and torques to be applied on the spine. The actions of the prosthesis on the skeleton can be periodically modified, under medical supervision, by activating several built-in, remote controlled micro-valves. The power and control signal to transiently activate the intracorporeal microvalves will be obtained by means of a PRC (parallel resonant converter) with a transcutaneous transformer. Telemetry is obtained by adding a slight oscillation in the frequency control circuit, resulting in an AM + FM modulated output signal. This signal is analyzed by a microcontroller in order to activate the selected intracorporeal microvalve.The new implant allows a progressive correction thanks to the non-invasive control of its modifiable geometry and its visco-elastic behaviour.
 
Article
Photostrictive materials, exhibiting light induced strain, are of interest for future generation wireless remote control photo-actuators, micro-actuators, and micro-sensors applications. (Pb, La)(Zr, Ti) O3 (PLZT) ceramics doped with WO3 exhibit large photostriction under uniform illumination of near-ultraviolet light. Using a bimorph configuration, a photo-driven relay and a micro walking device have been demonstrated. However, for the fabrication of these devices, materials exhibiting higher photovoltaic effect and higher response speed must be developed. The present paper reviews a new theoretical model for photovoltaic effect first, then enhanced performance photostrictive materials through sample surface characteristics, finally its potential future applications.
 
Article
One of the greatest challenges facing designers in the mechatronics field is the development of autonomous systems capable of guiding an airborne object along a given trajectory or maintaining its position in a specified location. Nonetheless, developing such ability is essential to support emerging UAV (Unmanned Aerial Vehicle) requirements in the civil and military domains. Accordingly, this study commences by constructing a mechatronic system featuring a manipulator arm actuated by a DC-motor-driven constant-pitch propeller and then develops suitable control schemes to regulate the power supplied to the DC motor such that the manipulator arm is driven through a specified rotational displacement. Three different control schemes are implemented to regulate the displacement of the manipulator arm, namely a fixed gain PID controller, a function-based variable gain PID controller and a fuzzy gain-mixing PID controller. The feasibility of the three control systems is evaluated both numerically and experimentally. It is shown that the fixed gain PID controller results in a significant overshoot of the manipulator arm and leads to a loss of control. However, the function-based variable gain PID controller and the fuzzy gain-mixing PID controller both ensure an accurate tracking performance, even when the manipulator arm is manually perturbed during rotation.
 
Top-cited authors
Kyoung Kwan Ahn
  • University of Ulsan
Mark Jolly
  • LORD Corporation
Mark Lee
  • Aberystwyth University
S. B. Choi
  • Inha University
H. Van Brussel