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
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
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
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
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
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
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.
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.
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.
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®.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
