Pradip N. Sheth

Characterization of Infrared Range-Finder PBS-03JN for 2-D Mapping

This paper presents a characterization study of the HOKUYO PBS-03JN Infrared range-finder and compares it to the characterization of the SICK LMS-200 laser range-finder for use in indoor 2-D mapping. Many parameters that could affect the performance of the sensor including warm-up time, divergence of the detection beam, usable detection range in the azimuth, target surface, color, and size properties, incidence angle at the target, and the mixed pixels problem have been studied. This characterization, quantification of errors, and 3-D confidence in the distance readings of the sensor is vital for practical applications. These characteristics are compared to the counterpart characteristics of the laser range-finder. The PBS-03JN is a cost effective alternative to laser range-finders in indoor environments. The sensor is attractive due to lower power consumption, and its lightweight.

Passive derivation of basic walker-assisted gait characteristics from measured forces and moments

This work describes a method that passively assesses basic walker-assisted gait characteristic, including heel strikes, toe-off events, as well as stride time, double support and right & left single support phases using only force-moment measurements from the walkers handles. The passively derived gait characteristics were validated against motion capture gait analysis and showed good correlations. This research is part of an effort that aims to identify user intent, from measuring forces and moments exerted on the handles of the walker as well as from perceiving the environment, and to incorporate identified intent into a passive shared steering control system for the walker. The primary focus of the work leading to This work is to identify the double support phase, and to engage the steering control at the beginning of this phase to maximize the users stability. However, the application of the method presented and the instrumented walker can be extended to longitudinal outside the lab Gait assessment.

Modal reduction of geared rotor systems with general damping and gyroscopic effects

The presence of damping, gyroscopic behavior, and gearing complicates traditional vibration analysis. This paper presents a methodology for conducting modal reduction on a geared rotor dynamic system under the influences of general damping and gyroscopic effects. Based on the first-order, state-space methodology, a coordinate transformation is presented for diagonalizing the state equations of motion for each substructure in the system. A modal synthesis procedure assembles the system equations from the individual substructures. The substructures are coupled via gear-mesh interactions. Using this technique, the size and complexity of a model can be reduced without incurring significant loss of accuracy. The reduced model allows for traditional methods of system analysis to include eigen-solution analysis, and frequency response. Validation occurs through application to a simple geared system widely discussed in the literature. The results of the modal reduction match closely with the full finite element model. A transmission system is also analyzed to illustrate the method’s usefulness to a complex system model of multiple shafts and gear interactions. Considerations arising from the analysis of geared systems are also discussed.

A physics-based model for predicting user intent in shared-control pedestrian mobility aids

This paper presents a physics-based model approach to infer navigational intent of the user of a walker, based on measuring forces and moments applied to the walkers handles. Our experiments use two 6-DOF force/moment sensors on the walkers handles, a 2-D kinematic-dynamic model of the walker and a digital motion capture system to trace the path of the walker. The motion capture system records the path the walker follows while the 6 DOF sensors record the handle forces used to guide the walker along that path. A dynamic model of the walker that determines user navigational intent from force/moment data was developed and validated against the motion capture data streams. This paper describes the development and validation of the model as well as plans for using the model as a path predictor. The inferred user intent is incorporated into a passive shared steering control system for the walker.

Physics-based modeling strategies for diagnostic and prognostic application in aerospace systems

This paper presents physics-based models as a key component of prognostic and diagnostic algorithms of health monitoring systems. While traditionally overlooked in condition-based maintenance strategies, these models potentially offer a robust alternative to experimental or other stochastic modeling data. Such a strategy is particularly useful in aerospace applications, presented in this paper in the context of a helicopter transmission model. A lumped parameter, finite element model of a widely used helicopter transmission is presented as well as methods of fault seeding and detection. Fault detection through diagnostic vibration parameters is illustrated through the simulation of a degraded rolling-element bearing supporting the transmission’s input shaft. Detection in the time domain and frequency domain is discussed. The simulation shows such modeling techniques to be useful tools in health monitoring analysis, particularly as sources of information for algorithms to compare with real-time or near real-time sensor data.

Multibody Dynamics Integrated With Muscle Models and Space-Time Constraints for Optimization of Lifting Movements

A multibody dynamics model integrated with space-time constraints based optimization is presented in this paper for generating optimal trajectories of human lifting movements. “Space-time constraints” is a two-point boundary value dynamic optimization technique developed for animation of computer graphics characters and has a significant potential for biomechanics and other mechanical movement based dynamic optimization problems. Optimization results demonstrate the ability to consider different preferences for minimizing the loading of specific joints such as an ankle, or a knee, or a shoulder during the lifting motion and the resulting lifting trajectories are shown to be different. Lumped muscle models to generate the joint torques are incorporated at five joints to model the actuation effects of the muscular system during the dynamic movement. The dynamic optimization is then based on the muscle activation parameters instead of the traditionally used joint torques. The muscle activation model optimization is shown to correlate better with the actual motion tests conducted by the VICON video capture and test data analysis system.Copyright

A New Helicopter Transmission Model for Condition-based Maintenance Technologies Using First Principles

This paper presents a new helicopter transmission model in support of CBM initiatives. The model uses the first principles approach to analyze the rotating shafts and gear couplings using rotor dynamic analysis techniques. The helicopter transmission is presented, followed by a discussion of the finite element formulation to include gear mesh modeling methodologies. System natural frequencies and mode shapes are discussed, along with the model’s validation procedure. The model’s primary purpose is to simulate multiple operating conditions to include faults. One such fault condition simulates the wear of gear tooth contact surfaces. The nature of the fault and its modeling techniques are discussed. Simulation results are presented in the time domain using a conventional vibration diagnostic parameter. A new diagnostic parameter, the FE2, is also introduced for detecting faults in the frequency domain. Additional considerations and further research points are also discussed. The results demonstrate the potential of physics-based, mathematical models in providing a key technology enabler for improving health monitoring and prediction capabilities of CBM strategies.

A New Fluid Film Bearing Test Rig for Oil and Water Bearings

Ever-increasing demands on the turbomachinery industry result in faster, lighter machines with higher rotational speeds and power densities. Modern, well-established thermoelastohydrodynamic (TEHD) analyses predict static and dynamic bearing characteristics in the presence of a turbulent lubricant and reduced lubricant flows. Proper design of tilting-pad journal bearings (TPJB) is required for successful operation of rotating machinery. Bearing static effects include pad temperature, bearing pressure profile, and static operating position. Bearing dynamic effects include stiffness, damping, and added mass coefficients. The current body of experimental data does not include the entire range of speed and load for which TEHD analyses are thought to be valid or where industrial machines operate. Experimental data for both oil-lubricated and water-lubricated bearings is desired. Oil lubricated bearings are used in high-speed turbomachinery. Water bearing data are of interest for applications that use the process fluid as the bearing lubricant. This paper describes a new Fluid Film Bearing Test Rig (FFBTR) which is being designed to experimentally verify the TEHD analyses, both in the laminar and in the turbulent regime, and support industrial needs. Static bearing characteristics will be measured with temperature probes, pressure probes, and displacement measurements. The dynamic bearing coefficients will be identified by rotor perturbation with active magnetic bearing force actuators. The rotational speed range of the FFBTR will be 9000–22000 rpm. The test bearing size is 127 mm, giving a range of surface speeds of 60–146 m/s. The range of bearing length-to-diameter (L/D) ratios that can be tested will be 0.5–0.75. Separate lubrication systems for water-lubricated and oil-lubricated bearings will be provided. Two magnetic bearings will be used as non-contact force actuators for rotorbearing system perturbation. The designed capacity for the magnetic force actuators is 13 kN/exciter, for a total static plus dynamic load of 26 kN that can be applied to the test bearing. The actuators are designed to apply forces to the test rotor at non-synchronous frequencies up to 560 Hz. Bearing static characteristics will be measured. Static measurements will include lubricant pressure profile, lubricant and pad temperatures, and static eccentricity. During dynamic testing, test shaft and bearing tilting pad motion will be measured. Dynamic bearing stiffness, damping, and added mass coefficients will be identified from force and displacement measurements. The frequency dependence in tilting-pad journal bearing coefficients will be investigated. The combination of static and dynamic measurements will be used to validate the TEHD analyses and provide design information to industry.Copyright

Generalized Stiffness Gear-Mesh Matrix Including EHD Stiffness

This paper presents a method to compute gear mesh stiffness based on the EHD behavior by combined finite element solution of the Reynolds Equation with the elastic contact model. It is shown that this solution requires iterative procedure to balance the computed pressure profile with the external nominal transmission load. This mesh stiffness is load dependent and therefore is a nonlinear phenomenon. The nominal stiffness value is utilized to model a full (12×12) gear mesh matrix for a linear dynamic model of rotor bearing systems including gears to evaluate system dynamics and coupling between lateral/torsional vibrations.Copyright

A finite elements approach for analysis and design of pumps

Abstract The reliability and performance of any pump system can be directly affected by its vibration characteristics. In this paper a finite elements approach for vibration analysis and design of centrifugal pump systems is developed. The procedure uses an assemblage of building blocks to predict the dynamic characteristics of each of the major pump components and the whole pump system. Preprocessing, analysis, and postprocessing capabilities of the ansys program are used extensively in the development of the procedure. The accuracy of the approach and the adequacy of modeling the pump components are verified by correlating the natural frequencies obtained using the procedure with the experimentally measured frequencies. The ability of the procedure to evaluate changes in system dynamics such as the addition of vibration control elements is demonstrated.