Showing papers in "IEEE-ASME Transactions on Mechatronics in 2003"

A new type of fish-like underwater microrobot

Abstract: This paper presents a new prototype model of an underwater fish-like microrobot utilizing ionic conducting polymer film (ICPF) actuator as the servo actuator to realize swimming motion with three degrees of freedom. A biomimetic fish-like microrobot using ICPF actuator as a propulsion tail fin and a buoyancy adjuster for the swimming structure in water or aqueous medium is developed. The overall size of the underwater prototype fish shaped microrobot is 45 mm in length, 10 mm in width, and 4 mm in thickness. It has two tails with a fin driven respectively, a body posture adjuster, and a buoyancy adjuster. The moving characteristic of the underwater microrobot is measured by changing the frequency of input voltage from 0.1-5 Hz in water and the amplitude of input voltage from 0.5-10 V. The experimental results indicate that changing the amplitude and frequency of input voltage can control the swimming speed of proposed underwater microrobot.

Dynamics and control of redundantly actuated parallel manipulators

Abstract: It has been shown that redundant actuation provides an effective means for eliminating singularities of a parallel manipulator, thereby improving its performance such as Cartesian stiffness and homogeneous output forces. Based on this concept, several high-performance parallel manipulator prototypes have been designed. A major difficulty that prevents application of the vast control literature developed for the serial counterparts to redundantly actuated parallel manipulators is the lack of an efficient dynamical model for real-time control. In this paper, using the Lagrange-D'Alembert formulation, we propose a simple scheme for computing the inverse dynamics of a redundantly actuated parallel manipulator. Based on this approach, four basic control algorithms, a joint-space proportional derivative (PD) control, a PD control in generalized coordinates, an augmented PD control, and a computed-torque control, are formulated. A two-degrees-of-freedom redundantly acutated parallel manipulator designed for a high-speed assembly task is used to verify the simplicity of the proposed approach and to evaulate the performance of the four control algorithms.

Nonlinear coupling control laws for an underactuated overhead crane system

Abstract: In this paper, we consider the regulation control problem for an underactuated overhead crane system. Motivated by recent passivity-based controllers for underactuated systems, we design several controllers that asymptotically regulate the planar gantry position and the payload angle. Specifically, utilizing LaSalle's invariant set theorem, we first illustrate how a simple proportional-derivative (PD) controller can be utilized to asymptotically regulate the overhead crane system. Motivated by the desire to achieve improved transient performance, we then present two nonlinear controllers that increase the coupling between the planar gantry position and the payload angle. Experimental results are provided to illustrate the improved performance of the nonlinear controllers over the simple PD controller.

Large deflection dynamics and control for planar continuum robots

Abstract: This paper focuses on a class of robot manipulators termed "continuum" robots - robots that exhibit behavior similar to tentacles, trunks, and snakes. In previous work, we studied details of the mechanical design, kinematics, path-planning and small-deflection dynamics for continuum robots such as the Clemson "tentacle manipulator". In this paper, we discuss the dynamics of a planar continuum backbone section, incorporating a large-deflection dynamic model. Based on these dynamics, we formulate a vibration-damping setpoint controller, and include experimental results to illustrate the efficacy of the proposed controller.

An exoskeletal robot for human shoulder joint motion assist

Abstract: We develop exoskeletal robots to assist the motion of physically weak persons such as elderly persons or handicapped persons. In our previous research (2001), a prototype of a two degree of freedom exoskeletal robots for shoulder joint motion assist have been developed. In this paper, we propose an effective fuzzy-neuro controller, a moving mechanism of the center of rotation (CR) of the shoulder joint of the exoskeletal robot, and an intelligent interface in order to realize a practical and effective exoskeletal robot for shoulder joint motion assist. The fuzzy-neuro controller enables the robot to assist a person's shoulder motion. The moving mechanism of the CR of the robot shoulder joint is used to fit the CR of the robot shoulder joint to that of the physiological human shoulder joint during the shoulder motion. The intelligent interface is realized by applying a neural network and used to cancel out the effect the human subject's arm posture change. The effectiveness of the proposed method was evaluated by experiment.

Teleoperated touch feedback from the surfaces at the nanoscale: modeling and experiments

Abstract: In this paper, a teleoperated nanoscale touching system is proposed, and continuum nanoscale contact mechanics models are introduced. The tele-nanorobotic system consists of a piezoresistive nanoprobe with a sharp tip as the nanorobot and force-topology sensor, a custom-made 1-degree-of-freedom haptic device for force-feedback, three-dimensional (3D) virtual reality (VR) graphics display of the nano world for visual feedback, and a force-reflecting servo type scaled teleoperation controller. Using this system, one-dimensional and 3D touching experiments and VR simulations are realized. Scaling of nano-forces is one of the major issues of the scaled teleoperation system since nanometer scale forces are dominated by surface forces instead of inertial forces as in the macro world. As the force scaling approach, a heuristic rule is introduced where nano-forces are linearly scaled with an experimentally determined scaling parameter. Simulation results and preliminary experiments of touching silicon and InAs quantum dot nanostructures show that adhesion forces at the nanoscale can be felt repeatedly at the operator's hand, and the proposed system enables the nanoscale surface topography and contact/noncontact nano-force feedback.

GA-based multiobjective PID control for a linear brushless DC motor

Abstract: This paper presents a robust output tracking control design method for a linear brushless DC motor with modeling uncertainties. Two frequency-domain specifications directly related to the mixed sensitivity function and control energy consumption are imposed to ensure stability and performance robustness. With regard to time-domain specifications, the rise time, maximum overshoot and steady-state error of the step response are considered. A generalized two-parameters proportional, integral, and derivative (PID) control framework is developed via a genetic searching approach ensuring the specifications imposed. The proposed design method is intuitive and practical that offers an effective way to implement simple but robust solutions covering a wide range of plant perturbation and, in addition, provides excellent tracking performance without resorting to excessive control. Extensive experimental and numerical results for a linear brushless motor confirm the proposed control design approach.

Design and control of a novel spherical permanent magnet actuator with three degrees of freedom

Abstract: The paper describes the design and control of a new version of a spherical permanent magnet actuator, which is capable of three degrees of freedom and a high specific torque. Based on an analytical magnetic field distribution, the torque vector and back-emf are derived in closed forms. An optimal design procedure is proposed to achieve maximum output torque or maximum acceleration for a given payload. The control of the actuator, whose dynamics are similar to those of robotic manipulators, is facilitated by the establishment of a complete actuation system model and the application of the computed torque control law. The validity of the analysis and design techniques, and the effectiveness of the control strategy, are confirmed by measurements.

Design and energetic characterization of a liquid-propellant-powered actuator for self-powered robots

Abstract: This paper describes the design of a power supply and actuation system appropriate for position or force controlled human-scale robots. The proposed approach utilizes a liquid monopropellant to generate hot gas, which is utilized to power a pneumatic-type actuation system. A prototype of the actuation system is described, and closed-loop tracking data are shown, which demonstrate good motion control. Experiments to characterize the energetic performance of a six-degree-of-freedom actuation system indicate that the proposed system with a diluted propellant offers an energetic figure of merit five times greater than battery-powered DC motors. Projections based on these experiments indicate that the same system powered by undiluted propellant would offer an energetic figure of merit in an order of magnitude greater than a comparable battery-powered DC motor actuated system.

Force sensing microinstrument for measuring tissue properties and pulse in microsurgery

Abstract: Miniaturized and "smart" instruments capable of characterizing the mechanical properties of tiny biological tissues are needed for research in biology, physiology, and biomechanics, and can find very important clinical applications for diagnostics and minimally invasive surgery (MIS). We are developing a set of robotic microinstruments designed to augment the performance of surgeons and clinicians during MIS. These microtools are intended to restore (or even enhance) the finger palpation capabilities that the surgeon exploits to characterize tissue hardness and to measure pulsating vessels in traditional surgery, but which are substantially reduced in MIS. This paper describes the main applications and the performance of a prototype miniature robotic instrument consisting of a microfabricated microgripper, instrumented with semiconductor strain-gauges as force sensors. The experimental set-up used for the in vitro tests reported in this paper consists of the microprobe mounted on a workstation and teleoperated. A haptic interface provides force feedback to the operator. We have demonstrated that the system can discriminate, both qualitatively and quantitatively, tiny skin samples based on their different elastic properties, and "feel" microvessels on the basis of pulsating fluid flowing through them.

Control of ionic polymer metal composites

Abstract: Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined through the unblocked maximum displacement and blocked force output. An open-loop position control and closed-loop position proportional-integral-derivative (PID) control are then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).

The Tricept robot: dynamics and impedance control

Abstract: The Tricept is a novel industrial robot characterized by a hybrid kinematic design featuring a three-degrees-of-freedom (3-DOF) structure of parallel type and a 3-DOF spherical wrist. In this work the authors focus on the derivation of a dynamic model to be used for both simulation and control purposes. Two different approaches are discussed and compared in terms of inverse dynamics computation. Then, a model-based control is derived aimed at enforcing a 6-DOF impedance behavior at the end effector to manage interaction with the environment. Simulation results are presented to evaluate the accuracy of an approximate dynamic model computation as well as to test the effectiveness of the proposed impedance control strategy.

Settling control and performance of a dual-actuator system for hard disk drives

Abstract: This paper presents a settling control of a dual-actuator system for hard disk drives. The dual-actuator system consists of a voice coil motor (VCM) as a first stage actuator and a push-pull-type piezo-electric transducer (PZT) as a second-stage actuator. The settling controller is designed in three steps. In the first step, the VCM controller is designed so that the VCM feedback loop has basic performance and appropriate stability. In the second step, the PZT controller and a decoupling filter are designed in order to achieve superior performance of the dual-actuator system. The decoupling filter, which is placed between the PZT controller output and the VCM controller input, is a PZT output estimator so that the PZT actuator output is canceled at the VCM controller input. In the third step, the reference trajectory is designed for fast and smooth settling. In this study, the closed-loop sensitivity function is used as a performance index, and the gain and phase margins of the open-loop characteristic are used as stability measures. Experimental results show that the dual actuator system with the proposed settling controller achieves better performance than a single actuator system with the same VCM and a conventional settling controller.

Full-state tracking and internal dynamics of nonholonomic wheeled mobile robots

Abstract: In the paper, the stable full-state tracking problem is investigated for nonholonomic wheeled mobile robots under output-tracking control laws. Dynamics of such wheeled mobile robots are nonholonomic and pose challenging problems for control design and stability analysis. The dynamics formulated in terms of full-state tracking errors offer some properties that allow better understanding of the internal and zero dynamics of the tracking-error system and more insights to the trajectory tracking stability. Output functions are chosen as virtual reference points for various types of wheeled mobile robots in aid of output controller designs. Sufficient conditions are derived to ensure the stable full-state trajectory tracking under output-tracking control laws. A type (1,1) mobile robot of car-like configuration is studied in detail and further numerical analysis provides more results which are beyond the reach of analytical means. An example and simulation results are presented to confirm the theory and observations.

Piezoelectrically actuated four-bar mechanism with two flexible links for micromechanical flying insect thorax

Abstract: In this paper, a piezoelectrically actuated four-bar mechanism with two flexible links is proposed to be used in a micromechanical flying insect robot wing thorax for stroke amplification. PZT-5H- and PZN-PT-based unimorph actuators are utilized at the input link of the four-bar for a compact and lightweight thorax transmission mechanism. The kinematics and dynamics of the proposed wing structure with two parallel four-bar mechanisms are analyzed, optimal four-bar link size selection method is introduced, and quasistatic forces generated at the wing are computed for evaluating the feasibility of the design. Using laser micromachining and folding techniques, prototype four-bar structures are constructed. In the experiments, for a 10/spl times/1/spl times/0.12 mm/sup 3/ PZT-5H actuator-based four-bar mechanism, the stroke amplification of around 20 - 25 is held, and an attached polyester wing is resonated at 29 Hz with around 90/spl deg/ flapping motion. These results match closely with the predicted theoretical values.

Pipe inspection using a laser-based transducer and automated analysis techniques

Abstract: This paper presents a new sensing methodology for the automated inspection of pipes. Standard inspection systems, as they are for example used in waste pipes and drains, are based on closed-circuit television cameras which are mounted on remotely controlled platforms and connected to remote video recording facilities. Two of the main disadvantages of such camera-based inspection systems are: 1) the poor quality of the acquired images due to difficult lighting conditions and 2) the susceptibility to error during the offline video assessment conducted by human operators. The objective of this research is to overcome these disadvantages and to create an intelligent sensing approach for improved and automated pipe-condition assessment. This approach makes use of a low-cost lighting profiler and a camera which acquires images of the light projections on the pipe wall. A novel method for extracting and analyzing intensity variations in the acquired images is introduced. The image data analysis is based on differential processing leading to highly-noise tolerant algorithms, particularly well suited for the detection of small faults in harsh environments. With the subsequent application of artificial neural networks, the system is capable of recognizing defective areas with a high success rate. Experiments in a range of waste pipes with different diameters and material properties have been conducted and test results are presented.

Intelligent control of quadruped gallops

Abstract: In this paper, a new intelligent control approach for high-speed quadruped bounding and galloping gaits is presented. The controller is capable of learning the leg touchdown angles and leg thrusts required to track the desired running height and velocity of a quadruped in only one stride. Training of the controller is accomplished not with a mathematical model, but with simple rules based on a heuristic knowledge of the quadruped mechanics. The result is a controller that produces better velocity and height tracking characteristics than a Raibert-based controller and is robust to modeling errors. Additionally, by making use of the natural dynamics of the system, gait characteristics comparable to biological quadrupeds result. The status of a legged machine being constructed for demonstration of the control approach and further study of the characteristics of galloping is also presented.

The reduction of stick-slip friction in hydraulic actuators

Abstract: The stick-slip friction phenomenon is observed near zero relative velocity, during the transition from static to dynamic friction, when static friction is greater than dynamic friction. This nonlinear change in friction force over a small change in velocity results in difficulties in achieving accurate and repeatable position control. In some cases, the actuator position controller reaches a limit cycle (hunting effect). Friction compensation at low speeds has traditionally been approached through various control techniques. This paper proposes an alternative solution, namely, friction avoidance. By rotating the piston and rod, the Stribeck region of the friction-velocity curve is avoided and the axial friction opposing the piston movement is approximately linearized. Simulation and experimental results are presented to validate this approach.

Optimized binary modular reconfigurable robotic devices

Abstract: Binary robotic devices with large degrees of freedom have been proposed by a number of researchers. However, experimental implementations of these concepts have been built with conventional components. These physical systems are heavy, complex and far from being practical devices. In this paper, a lightweight, compliant mechanism driven by optimized magnet-coil actuators is proposed and developed as an element for modular hyper-redundant degrees of freedom robotic systems. Such elements could be used in a number of applications and would replace conventional, complex, and heavy components. The device has a parallel kinematic structure. Its binary actuation simplifies its control architecture.

The 100 G capturing robot - too fast to see

Abstract: This paper discusses the capturing robot with the maximum acceleration of 100 G in design specification. We aim find the combination of the arm with a mass of 0.1 kg and the spring capable of producing the initial compressed force of 100 N, in order to achieve the 100 G. To reduce the total capturing time, we propose an arm/gripper coupling mechanism where the spring energy initially accumulated in the arm is transferred to the kinetic energy of the arm and continuously to the kinetic energy for closing the gripper at the capturing point without any time lag. The experimental results show the maximum acceleration of 91 G and the capturing time of 25 ms were achieved. Experiments on capturing a dropping ball were also executed with the assistance of the 1 ms-vision.

Mathematical models of binary spherical-motion encoders

Abstract: This paper presents several algorithms that solve the problem of determining the orientation of a freely rotating ball that is partially enclosed in a housing. The ball is painted in two colors (black and white) and the housing has a number of sensors that detect these colors. The question which we attempt to answer is: knowing how the ball is painted, knowing the location of the sensors, and given a complete set of sensor measurements, how does one determine the orientation of the ball to within an acceptable error threshold? The algorithms we present to solve this problem are based on methods and terminology from geometric control theory. Essentially, we generate dynamical systems that evolve on the group SO(3). These dynamical systems are constructed so as to attract the computed orientation of the ball to the actual one being detected by the sensors. Solving this spherical decoding problem is important in applications where the spherical motion must be detected. One such application is the feedback control of spherical motors.

Hybrid fault adaptive control of a wheeled mobile robot

Abstract: A fault adaptive control methodology for mobile robots is presented. The robot is modeled as a continuous system with a supervisory controller. The physical processes of the robot are modeled using bond graphs, and this forms the basis of a combined qualitative reasoning and quantitative model-based estimation scheme for online fault detection and isolation during robot operation. A hierarchical-control accommodation framework is developed for the supervisory controller that determines a suitable control strategy to accommodate the isolated fault. It is shown that for small degradations in actuation effort, a robust controller achieves fault accommodation without significant loss of performance. However, for larger faults, the supervisor needs to switch among several controllers to maintain acceptable performance. The switching stability among a set of trajectory tracking controllers is presented. Simulation results verify the proposed fault adaptive control technique for a mobile robot.

Asymptotic trajectory tracking of manipulators using uncalibrated visual feedback

Abstract: To implement a position-based visual feedback controller for a manipulator, it is necessary to calibrate the homogeneous transformation matrix between its base frame and the vision frame besides intrinsic parameters of the vision system. The accuracy of such a calibration greatly affects the control performance. Substantial efforts must be made to obtain a highly accurate transformation matrix. In this paper, we propose an adaptive visual feedback controller for manipulators when the homogeneous transformation matrix is not calibrated. It is assumed that the vision system can measure the 3D position and orientation of the manipulator in real-time. Based on an important observation that the unknown transformation matrix can be separated from the visual Jacobian matrix, we propose an adaptive algorithm, similar to the model-based adaptive algorithm, to estimate the unknown matrix online. The use of the proposed visual feedback controller greatly simplifies the implementation of a manipulator-vision workcell. This controller is especially useful when such a pre-calibration is not possible. It is proved by Lyapunov approach that the motion of the manipulator approaches asymptotically to the desired trajectory. Simulations and experimental results are included to demonstrate performance of this adaptive visual feedback controller.

On modeling, identification, and control of a heavy-duty electrohydraulic harvester manipulator

Abstract: Focuses on modeling, parameter estimation, and control for a heavy-duty electrohydraulic manipulator of a harvester machine. The linear-graph method is implemented in deriving mathematical models for the swing, boom and stick subsystems. Actuation dynamics are subsequently integrated with manipulator dynamics to result in a complete machine model. Identification procedures employed in estimating physical parameters are discussed in detail and key parameter results supplied. Model validation studies show good agreement between model predictions and experiments. A Cartesian controller for the motion of the manipulator end-point is described and response results are presented. It is shown that the obtained response is very good for the purposes of this harvester machine, resulting in very small relative tracking errors.

A behavior-based mobile robot with a visual landmark-recognition system

Abstract: In this paper, based on behavior-based artificial intelligence we have built a fully autonomous mobile robot. Several modules are developed for the mobile robot to implement different levels of competences and behaviors, where each module itself generates behaviors. New modules can be easily added to the robot system to improve in the competence without changing any existing modules. A vision-based landmark recognition system for robot navigation is developed as the highest layer in the subsumption architecture. A genetic-algorithm-based search method for pattern recognition of digital images is proposed and implemented to recognize artificial landmarks by searching all the predefined patterns. The vision layer is capable of generating the desired behaviors corresponding to various landmarks. A combination of eight ultrasonic sensors is designed to implement obstacle-avoidance behaviors through a set of fuzzy rules. The effectiveness of this behavior-based mobile robot is demonstrated by experimental studies.

Dynamics modeling and simulation of constrained robotic systems

Abstract: Dynamic analysis is the basic element of mechanical design and control of mechanisms. This work intends to address dynamic methods relevant to constrained robots and mechanisms from a unified analytical point of view, which is based on differential variational principles. A constrained robotic system is a mechanical system, where we need to consider kinematic constraint conditions explicitly in dynamic modeling and analysis. Important classes of constrained robotic systems include, for example, parallel robots and closed-chain mechanisms where the loop closure conditions can be generally expressed by nonlinear holonomic constraint equations, and mobile robots where the system is subjected to linear nonholonomic constraints. Our primary focus is on systems with nonlinear holonomic constraint equations (e.g., parallel robots, robotic systems with closed kinematic chains). However, the approach and formulation discussed are also applicable for nonholonomic systems. In the framework presented, many approaches can be discussed, and new directions can be highlighted that can contribute to the better understanding of dynamic behavior. Two new approaches for the dynamic analysis and for the simulation of constrained robotic systems are introduced and discussed. The paper also points out some areas and methods where further exploration is necessary to shed light on problems and applications related to constrained robotic systems.

Neurofuzzy control of modular and reconfigurable robots

Abstract: In recent years, the concept of modular and reconfigurable robotics emerged as a means for flexible and versatile automation This concept allows for the execution of many complex tasks that cannot be performed by fixed-configuration manipulators Nevertheless, reconfigurable robots introduce a challenging level of complexity to the problem of design of controllers that can handle a wide range of robot configurations with reliable performance This paper addresses the position control of modular and reconfigurable robots We develop a practical intelligent-control architecture that can be easily used in the presence of dynamic parameter uncertainty and unmodeled disturbances The architecture requires no a priori knowledge of the system-dynamics parameters Adaptive control is provided using fuzzy gain tuning of proportional-integral-derivative parameters in the presence of external disturbances The architecture also provides learning control using feedforward neural networks Moreover, the architecture has the capability of updating the adaptive control under reconfigurability Experiments on a modular robot test bed are reported to validate the effectiveness of the control methodology

A novel dual-axis repulsive Maglev guiding system with permanent magnet: modeling and controller design

Abstract: In this paper, we extend our previous result (1999, 2000) on designing a single-axis Maglev guiding system to a more involved task of designing a novel dual-axis positioning system. First, important issues related to construction of the mechanism of the dual-axis positioning system are addressed. Then, the dynamics of the dual-axis Maglev guiding system are analyzed. According to the derived analytic model, which is subject to unknown system parameters, an adaptive controller that can control the carrier at the desired target point of each axis with full alignment is presented. From the experiment results, a good performance in terms of regulation of the guiding-axis and tracking of the positioning-axis is achieved. This validates the design of the system hardware and demonstrates the feasibility of the developed controller.

Bang-bang impact control using hybrid impedance/time-delay control

Abstract: For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing the control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to first absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is attained. After impact transient, the hybrid impedance/time-delay control algorithm is again utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment, and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm that switches only to zero and maintains the same gains, while other controllers use more than one control algorithm or different control gains. It is shown via experiments that overall performance is superior or comparable to more complicated existing impact force control techniques.

Pinpoint injection of microtools for minimally invasive micromanipulation of microbe by laser trap

Abstract: This paper reports transportation of the target microbe by the laser trapped microtools with minimum laser irradiation to the target. The size of a microtool (MT) is around micrometer. The MTs are manipulated by the focused laser under the microscope to manipulate the target microbe. Here we propose a pinpoint injection method of MTs at the desired location in the microchamber, which is filled with liquid. At first, we classified the injection method of the MTs in four categories. Here we employed a new method to install the MTs inside the microchamber. We developed a MT holding chip to install the MTs. The MTs were injected in the microchamber, and were manipulated successfully by the laser scanning micromanipulator to transport the target microbe for separation. The proposed method is useful for the pinpoint injection of MTs and separation by the indirect micromanipulation.