Tip Position Error Research Articles

Development of Multisegment Steering Mechanism and 3-D Panorama for Automated Bladder Surveillance System

A cystoscope is an invaluable tool for bladder cancer surveillance and lower urinary tract pathology diagnosis. The performance of cystoscopy can be improved by automating the procedure to ensure rapid and complete inspection, having a predicted pathway for imaging. This paper proposes a versatile, wire-driven, multisegment mechanism for steering an imaging probe to follow optimal, preprogrammed scan trajectories. A novel flexible imaging probe scanning fiber endoscope (SFE) of 1.2 mm in diameter generates high-quality reflectance or fluorescent images. A 3-D panoramic reconstruction view of the bladder is generated by custom software to confirm comprehensive surveillance and improve clinical efficiency. The kinematics and controllability of the proposed mechanism are analyzed. The multiple degrees-of-freedom of the mechanism provide the advantage of maintaining the camera perpendicular to the bladder wall with a safety distance. The measured experimental results show 8.1% and 5.1% tip position and orientation errors, respectively, to the theoretical simulation predictions. Within a synthetic bladder phantom made from patient-specific geometry information, the apparatus is able to generate a 3-D panorama of about 60% of the bladder's inner surface, while accepting 50% image overlap between adjacent images. The novel imaging capability of the SFE, combined with a robotized multisegment steering mechanism and an image stitching software, proposes potential advancements to the multimodal 3-D panorama of the bladder.

Identification and compensation for offset errors on the rotary axes of a multi-axis Magnetorheological Finishing machine tool

In this paper, offset errors in rotary axes of a multi-axis Magnetorheological Finishing (MRF) machine tool are identified using a “trial cut” method and compensated in postprocessor for MRF figuring process. Kinematic model considering the offset errors of the multi-axis MRF machine tool UPF700-7 is built, utilizing homogenous transformation matrices theory. Then, a trial cut method by acquiring removal functions (RFs) in given positions of a sphere workpiece is proposed to identify the offset errors, in which only one rotary axis and two translational axes move simultaneously to obtain a circular trajectory. The maximum material removal position of the RFs is defined as the actual tool tip position in MRF process. The difference between ideal and actual tip tool position is applied to determine the relation between actual tool tip position and offset errors. The relations between them are derived with a linear equation, and offset errors are calculated using the least squares method. Finally, figuring correction experiments are performed on an off-axis aspheric mirror to validate the feasibility of the improved technology in an integrated MRF figuring process, in which offset errors are compensated in a postprocessor.

Posture estimation of hose-shaped robot by using active microphone array

Hose-shaped rescue robots have been developed for searching narrow spaces such as under collapsed buildings. The posture estimation independent of the past history is critical, because conventional inertial-sensor-based posture estimation has two main problems; a cumulative error problem peculiar to inertial sensors, and a sudden posture change problem caused by external forces. For coping with the two problems, we developed a novel posture estimation method by putting an active microphone array, a set of microphones and loudspeakers, on the robot. The method calculates the time difference of arrival (TDOA) of the reference signal emitted from one loudspeaker, and estimates the posture from the distance obtained by TDOA. This concise method still has three problems: (1) external noise, (2) reverberation and reflection, and (3) obstacles. These problems are tackled by (1) TSP signal, (2) GCC-PHAT and a threshold-based onset detection, and (3) rejecting incorrect onset times, respectively. Experiments with simulated sounds and actual recordings demonstrate that the method attains the performance of estimation comparable to that of conventional methods, that is, less than 20 cm of the tip position error. Even without historical data, the method attains the similar performance while conventional methods fail.

Fiber-Bragg-grating-based ultrathin shape sensors displaying single-channel sweeping for minimally invasive surgery

We report on the development of a highly flexible, thin shape sensor that can be integrated into minimally invasive surgery systems. Three optical fibers are arranged in a triangular shape and epoxy molded to produce a sensor diameter of less than 900μm, ensuring high-bending operation up to 90°. Each fiber contains four fiber Bragg gratings (FBGs) operating at different wavelengths. With simultaneous detection of all the grating signals, the overall curvatures and torsions are interpolated and used for three-dimensional shape reconstruction. Three FBGs located at the same axial location also enables temperature compensation. Real-time shape monitoring with a sampling rate of 3.74Hz is realized. The average tip position error was 1.50% of the total sensor length.

Evolutionary computing approaches to optimum design of fuzzy logic controller for a flexible robot system

Abstract This paper presents the design of a Fuzzy Logic Controller (FLC) whose parameters are optimized by using Genetic Algorithm (GA) and Bacteria Foraging Optimization (BFO) for tip position control of a single link flexible manipulator. The proposed FLC is designed by minimizing the fitness function, which is defined as a function of tip position error, through GA and BFO optimization algorithms achieving perfect tip position tracking of the single link flexible manipulator. Then the tip position responses obtained by using both the above controllers are compared to suggest the best controller for the tip position tracking.

Robotic System for Closed-Bore MRI-Guided Prostatic Interventions

This paper reports on the development of a new closed-bore magnetic resonance imaging (MRI) compatible robotic system for image-guided prostatic interventions: ablation, brachytherapy, and biopsy. The first stage of development addresses only laser-based ablation. The robot actuators are ultrasonic motors. The first physical robot prototype was manufactured and tested in the MRI with an ablation tool. The tests covered magnetic resonance (MR) compatibility, tool visualization, and robot control accuracy. Robot tip position error is less than 2 mm at points closer than 0.5 m to the isocenter. A method to control ultrasonic motors for MRI-compatibility is reported.

GPU based real-time instrument tracking with three-dimensional ultrasound

Real-time three-dimensional ultrasound enables new intracardiac surgical procedures, but the distorted appearance of instruments in ultrasound poses a challenge to surgeons. This paper presents a detection technique that identifies the position of the instrument within the ultrasound volume. The algorithm uses a form of the generalized Radon transform to search for long straight objects in the ultrasound image, a feature characteristic of instruments and not found in cardiac tissue. When combined with passive markers placed on the instrument shaft, the full position and orientation of the instrument is found in 3D space. This detection technique is amenable to rapid execution on the current generation of personal computer graphics processor units (GPU). Our GPU implementation detected a surgical instrument in 31 ms, sufficient for real-time tracking at the 25 volumes per second rate of the ultrasound machine. A water tank experiment found instrument orientation errors of 1.1 degrees and tip position errors of less than 1.8mm. Finally, an in vivo study demonstrated successful instrument tracking inside a beating porcine heart.

Relationships between straightness and angular kinematic errors in machines

The software compensation approach for the improvement of machine tool and coordinate measuring machine accuracy depend to some extent on machine error modelling and measurement methodologies. The currently established methodology is based on the derivation of tool position error (for machine tools) or stylus tip position error (for coordinate measuring machines) by the combination of individual axis joint kinematic error parameters. The purpose of this paper is to propose a machine error analysis based on error classification. This taxonomic approach forms a conceptual basis for an analysis of machine errors with a deeper understanding of error mechanisms at more fundamental levels. The relevance of this approach is investigated through the case study of the coupling mechanism between joint kinematic angular and straightness errors of machine linear axes. The limitations of the joint kinematic straightness and angular error modelling based on purely abstract mathematical dependence principles are explored through simulations and experiments.

End-effector Trajectory Control in a Two-Link Flexible Manipulator Through Reference Joint Angle Values Modification by Neural Networks

The basic difficulty in the control of flexible link manipulators stems from the fact that the link deflections cannot be controlled directly. Since the number of control inputs, applied by the actuators, is less than the total number of variables to be controlled, control approaches aiming at the suppression of deflections and vibrations are generally insufficient. Another possible approach is to determine new joint trajectories to minimize the error of the end-effector in the operational space. In this paper, a neural network is designed to compute incremental changes for the reference values of the joint angles to achieve successful tip tracking in the operational space. Tip position errors in the x-and y-directions are utilized as inputs to the neural network. The cost function, which is minimized in training the neural network, is also chosen as the sum of squares of the tip position error in both directions. Joint angle control is provided by a PD controller. Simulations are carried out to evaluate the performance of the neural-network-based trajectory tracking method, and the results are depicted in both joint and operational spaces.

Optimally distributed actuator placement and control for a slewing single-linkflexible manipulator

A method is proposed for determining the optimal placement and controller designfor multiple distributed actuators to reduce the vibrations of flexible structures. Inparticular, application of piezoceramic patches to a horizontally-slewingsingle-link flexible manipulator modeled using the assumed modes method isinvestigated. The optimization method uses simulated annealing and allowsplacement of any number of distributed actuators of unequal length, althoughpiezoceramics of fixed equal lengths are used in the example. It also designs anlinear-quadratic-regulator controller as part of the optimization procedure. Themeasures of performance used in the investigation to determine optimalityare the total mass of the system and the time integral of the absolutevalue of the hub and tip position error. This study also varies the relativeweightings for each of these performance measures to observe the effects on thecontroller designs and piezoceramic patch positions in the optimized solutions.

Inversion-based sliding control of a flexible-link manipulator

In this paper a control strategy based on nonlinear inversion is considered for a class of multi-link, structurally flexible manipulators to achieve small tip-position tracking errors while maintaining robust closed-loop performance. This is accomplished by defining new outputs near the end points of the arms. Motivated by the concept of a sliding surface in variable structure control (VSC), a robustifying term is developed to drive the nonlinear plant's error dynamics onto a sliding surface. On this surface the error dynamics are guaranteed to be independent of parametric uncertainties. In order to avoid over-excitation of higher frequency flexural modes due to control chattering, the discontinuous functions normally used in classical VSC are replaced by saturation nonlinearities at the outset. This also facilitates analysis by the standard Lyapunov techniques. The controller performance is demonstrated by simulation on a two-link manipulator with the second link flexible and with considerable parametric uncertainty. In the absence of the sliding controller, the inversion-based controller results in instability when subjected to parametric uncertainty.

Tracking Control of a Miniature Flexible Arm Using Piezoelectric Bimorph Cells

A theoretical and experimental study is presented for the end- point control of a slender flexible arm driven by piezoelectric bimorph cells. A discrete-time formulation is presented for the arm-cell system and applied to the problem of moving the arm so that the tip closely tracks the fluctuation of target. The tip displacement (versus time) is compared with the target fluctuation, and the tip position error is used, together with other estimated system states, as the basis for applying control voltage to the cells. Both simulation and experimental results show that the PID control using the piezoelectric cells as the actuators is sufficient to make the arm tip follow the fluctuation of target precisely.

Temperature perturbation effects in a high precision CMM

Two definitive temperature perturbations were introduced into the environment of a high precision Leitz PMM-866 coordinate measuring machine (with scale temperature compensation) using heaters arranged to simulate aspects of horizontal and vertical temperature gradients in the Y–Z plane. A 250 mm ULE and Zerodur ball-bar was repeatedly measured by the CMM. The CMM itself was used to probe the specimen table as a reference plane during the course of the temperature change. A vertical temperature gradient of up to 9°C across the granite lintel comprising the probe-carriage slideway produced an approximately linear change of apparent ball-bar length with time at a rate averaging about 1 μm deg −1 C. Changes of slideway straightness and apparent specimen table height were also measured. However, a similar temperature rise of one steel bridge supporting column relative to the other produced a variable small effect, without change of apparent ball-bar length. It is shown that the effect of introducing the vertical gradient can be predicted assuming a curvature of the portal beam giving rise to a gradient of pitch along the slideway and resulting in probe tip position errors which, to a first approximation, vary linearly with duration of the temperature gradient. A finite element thermal stress analysis technique is employed to explore the measured distortion of the slideway beam.

Position error compensation of robotic contour end-milling

Three-dimensional cutting force dynamics of end-milling is developed, and position error sources of robotic machining is studied. A strategy to compensate cutting force in force/motion control of robotic machining is established in order to achieve better positioning accuracy. Position error is analysed in the cutting process through reference points by using force sensor. The tip position error estimated with the aid of wrist-force sensor is compensated in feedforward control form. The quantitative results are obtained from the digital computer simulations of the dynamic model of the studied system.