Fast Update Rate Research Articles

Real‐time Rigid Body Simulation for Haptic Interactions Based on Contact Volume of Polygonal Objects

Abstract This paper proposes a new method for real‐time rigid body simulations for haptic interactions based on a penalty method regarding contact volume. Analytical methods for calculation of contact forces require too much time to maintain fast update rates for haptic controls. In addition, they prohibit direct connection of haptic interfaces. Penalty methods, which employ spring‐damper models for calculation of contact forces, offer a very rapid rate of iterations. In addition, they permit direct connection of haptic interfaces. Penalty methods are good for haptic interactions. However, previous penalty methods do not regard distribution of contact forces over the contact area. For that reason, they can't calculate normal and friction forces on face‐face contacts correctly. We propose a distributed spring‐damper model on a contact area to solve these problems. We analyze three‐dimensional geometries of the intersecting portion on the polyhedral objects. Then, we integrate forces and torques of distributed spring‐damper models. We implement a proposed simulator and compare it with a point‐based penalty method and constraint method. The comparison shows that the proposed simulator improves accuracy of the simulation of face‐face contact and friction forces and the simulation speed. In addition, we attach a six degree‐of‐freedom (6‐DOF) haptic interface to the simulator. Users can feel 6‐DOF force feedback and input 6‐DOF motions. Categories and Subject Descriptors (according to ACM CCS): I.6.5 [Model Development]: Modeling methodologies, H.5.2 [User Interfaces]: Haptic I/O, I.3.6 [Methodology and Techniques]: Interaction techniques

Real‐time modulation of acoustic gradient noise in interventional MRI

AbstractAcoustic noise is inherent to magnet resonance imaging (MRI) and poses safety risks to patients and interventional radiologists. Although a spectrum of noise reduction techniques has been implemented, new developments further increase sound levels. Silent pulse sequences based on derating gradient currents have been proposed but are limited to slow pulse sequences not suitable for interventional MRI (iMRI). However, iMRI does not continuously require fast imaging with high image update rates. Therefore, the aim of this study was to develop a tool that could remotely derate the gradient currents in real time, operated by the interventionalist. The duration of the derated gradients is increased to retain image resolution [this extends imaging time and echo time (TE)]. The experiment setup consisted of a custom‐built remote controller located in the interventional MR room. A fast spoiled gradient recalled echo (FSPGR) sequence was tested and acoustic recordings were made with a microphone in the magnet bore. An optical link sent data from the remote controller to a computer that was connected to a 1.5‐T cardiovascular MR scanner over ethernet. A software server installed on the MR system received the requests and passed these on to the integrated pulse generator in order to control the real‐time imaging. Slew rate adjustments were accomplished by calculating instruction period changes and adjusted waveform amplitudes accordingly. The experimental setup reduced the slew rate up to 16‐fold, which resulted in a considerable acoustic noise reduction of 21.1 dBA. The remote controller performed well and image quality showed no substantial qualitative changes. We made use of the previously described idea of silent pulse sequence designing. Although derating is at the expense of the image refresh rate, our real‐time slew rate reduction is compatible with the fact that iMRI procedures do not continuously require fast image update rates. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 20B: 34–39, 2004.

Improving Tornado Warnings with the Federal Aviation Administration's Terminal Doppler Weather Radar

Abstract The potential role of the Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR) to supplement the Weather Surveillance Radar–1988 Doppler (WSR–88D) for tornado detection is discussed. Compared to the WSR–88D, the TDWR has a narrower beam, lower scan angles, and faster update rates. The 11 August 1999 Salt Lake City, Utah, tornado is used as an illustration of the utility of the TDWR. The Salt Lake City TDWR was much closer to the tornado than the WSR–88D and the WSR–88D was 750 m higher than the TDWR. Because the tornado developed rapidly upward from a surface convergence line, the TDWR detected the formation earlier than the WSR–88D. Also, the vortex signatures associated with the tornado were much better defined by the TDWR. The enhanced spatial and temporal coverage provided by the TDWR network is shown. A significant improvement in tornado detection, as well as other low–altitude phenomena, would be gained. However, ground clutter and signal attenuation can degrade coverage....

Robust tracking of multiple objects in sector-scan sonar image sequences using optical flow motion estimation

The fast update rate and good performance of new generation electronic sector scanning sonars is now allowing practicable use of temporal information for signal processing tasks such as object classification and motion estimation. Problems remain, however, as objects change appearance, merge, maneuver, move in and out of the field of view, and split due to poor segmentation. This paper presents an approach to the segmentation, two-dimensional motion estimation, and subsequent tracking of multiple objects in sequences of sector scan sonar images. Applications such as ROV obstacle avoidance, visual servoing, and underwater surveillance are relevant. Initially, static and moving objects are distinguished in the sonar image sequence using frequency-domain filtering. Optical flow calculations are then performed on moving objects with significant size to obtain magnitude and direction motion estimates. Matches of these motion estimates, and the future positions they predict, are then used as a basis for identifying corresponding objects in adjacent scans. To enhance robustness, a tracking tree is constructed storing multiple possible correspondences and cumulative confidence values obtained from successive compatibility measures. Deferred decision making is then employed to enable best estimates of object tracks to be updated as subsequent scans produce new information. The method is shown to work well, with good tracking performance when objects merge, split, and change shape. The optical flow is demonstrated to give position prediction errors of between 10 and 50 cm (1%-5% of scan range), with no violation of smoothness assumptions using sample rates between 4 and 1 frames/s.

Use of GPS-Determined Attitude in Combination with Conventional Attitude Sensors

Use of multi antenna GPS equipment for determination of a vessel's attitude holds some promise for the development of accurate and inexpensive attitude systems. An application for such systems might be to provide very accurate roll information for multibeam echo sounders.The present state-of-the-art GPS attitude systems cannot meet the required accuracy and update rate for such applications. GEOTEAM A/S has therefore developed a PC-based system which combines GPS-based attitude with roll and pitch information from a Vertical Reference Unit (VRU) and heading from a gyro compass.In such a combined system, the long-term high accuracy of a GPS-based attitude system is combined with the short-term accuracy and fast update rate of conventional VRUS and gyro compasses in order to achieve a resulting performance that is better than any of the systems. In effect, the GPS attitude is used to calibrate the VRU and the gyro compass in real time.During the past year extensive tests have been performed with a system using a Trimble VECTOR II GPS attitude system with a 1 metre baseline between the antennas, both on a van (with an inertial navigation system as reference) and on a vessel. During November and December 1993 further tests were made with an Ashtech 3DF attitude system with longer baselines (7·5 m). These tests were made on a vessel where the combined GPS/VRU attitude was fed into a multibeam echo sounder. These tests were performed in cooperation with Simrad Subsea A/S, the multibeam echo sounder EM 1000 manufacturer.

A Robust Navigation System for Autonomous Vehicles Using Ultrasonics

A navigation system has been developed for the guidance and control of autonomously guided vehicles using a novel ultrasonic 3D location system in conjunction with traditional ultrasonic rangefinders. This system is most suitable for navigation in structured environments, e.g., factories, hospitals, offices, airplane and space shuttle assembly plants, nuclear power plants and other hazardous areas. The strengths of the system are accuracy (2.54mm), ease of use, self installation/calibration and fast position update rates (>50Hz). A method for automatic modifications of maps has been implemented. An object oriented approach has been used to develop a system that is robust and flexible