bluuebunny/crossref_metadata_2025 huggingface dataset:
Inelastic Strain Accumulation in Cortical Bone During Rapid Transient Tensile Loading
Authors: Fondrk M. T. , Bahniuk E. H. , Davy D. T.
Published: February 2008

An experimental study examined the tensile stress-strain behavior of cortical bone during rapid load cycles to high strain amplitudes. Machined bovine and human cortical bone samples were subjected to loading cycles at a nominal load/unload rate of ±420 MPa/s. Loads were reversed at pre-selected strain levels such that load cycles were typically completed in 0.5-0.7 seconds. Axial strain behavior demonstrated considerable nonlinearity in the first load cycle, while transverse strain behavior was essentially linear. For the human bone 29.1 percent (S.D. = 4.7 percent), and for the bovine bone 35.1 percent (S.D. = 10.8 percent) of the maximum nonlinear strain accumulated after load reversal, where nonlinear strain was defined as the difference between total strain and strain corresponding to linear elastic behavior. Average residual axial strain on unloading was 35.4 percent (S.D. = 1.2 percent) for human bone and 35.1 percent (S.D. = 2.9 percent) of maximum nonlinear strain. Corresponding significant volumetric strains and residual volumetric strains were found. The results support the conclusions that the nonlinear stress-strain behavior observed during creep loading also occurs during transient loading at physiological rates. The volume increases suggest that damage accumulation, i.e., new internal surfaces and voids, plays a major role in this behavior. The residual volume increases and associated disruptions in the internal structure of bone provide a potential stimulus for a biological repair response.
Localized Damage in Vertebral Bone Is Most Detrimental in Regions of High Strain Energy Density
Authors: Kopperdahl D. L. , Roberts A. D. , Keaveny T. M.
Published: February 2008

It was hypothesized that damage to bone tissue would be most detrimental to the structural integrity of the vertebral body if it occurred in regions with high strain energy density, and not necessarily in regions of high or low trabecular bone apparent density, or in a particular anatomic location. The reduction in stiffness due to localized damage was computed in 16 finite element models of 10-mm-thick human vertebral sections. Statistical analyses were performed to determine which characteristic at the damage location — strain energy density, apparent density, or anatomic location — best predicted the corresponding stiffness reduction. There was a strong positive correlation between regional strain energy density and structural stiffness reduction in all 16 vertebral sections for damage in the trabecular centrum (p < 0.05, r2 = 0.43–0.93). By contrast, regional apparent density showed a significant negative correlation to stiffness reduction in only four of the sixteen bones (p < 0.05, r2 = 0.47 – 0.58). While damage in different anatomic locations did lead to different reductions in stiffness (p < 0.0001, ANOVA), no single location was consistently the most critical location for damage. Thus, knowledge of the characteristics of bone that determine strain energy density distributions can provide an understanding of how damage reduces whole bone mechanical properties. A patient-specific finite element model displaying a map of strain energy density can help optimize surgical planning and reinforcement of bone in individuals with high fracture risk.
Convergence Behavior of High-Resolution Finite Element Models of Trabecular Bone
Authors: Niebur G. L. , Yuen J. C. , Hsia A. C. , Keaveny T. M.
Published: February 2008

The convergence behavior of finite element models depends on the size of elements used, the element polynomial order, and on the complexity of the applied loads. For high-resolution models of trabecular bone, changes in architecture and density may also be important. The goal of this study was to investigate the influence of these factors on the convergence behavior of high-resolution models of trabecular bone. Two human vertebral and two bovine tibial trabecular bone specimens were modeled at four resolutions ranging from 20 to 80 μm and subjected to both compressive and shear loading. Results indicated that convergence behavior depended on both loading mode (axial versus shear) and volume fraction of the specimen. Compared to the 20 μm resolution, the differences in apparent Young’s modulus at 40 μm resolution were less than 5 percent for all specimens, and for apparent shear modulus were less than 7 percent. By contrast, differences at 80 μm resolution in apparent modulus were up to 41 percent, depending on the specimen tested and loading mode. Overall, differences in apparent properties were always less than 10 percent when the ratio of mean trabecular thickness to element size was greater than four. Use of higher order elements did not improve the results. Tissue level parameters such as maximum principal strain did not converge. Tissue level strains converged when considered relative to a threshold value, but only if the strains were evaluated at Gauss points rather than element centroids. These findings indicate that good convergence can be obtained with this modeling technique, although element size should be chosen based on factors such as loading mode, mean trabecular thickness, and the particular output parameter of interest.
A Procedure to Determine Equilibrium Postural Configurations for Arbitrary Locations of the Feet
Authors: Gonzalez L. J. , Sreenivasan S. V. , Jensen J. L.
Published: February 2008

This research was directed toward predicting postural equilibrium configurations in normal humans for asymmetric locations of the feet. The objective of the study was to identify trends in the variation of the location of ground center of pressure (COP) with increasing levels of asymmetry in the foot placement. The procedure developed here minimized the muscular effort (active torques) in the lower extremities while maximizing postural stability margins for given foot locations. Minimizing muscular effort led to fully extended knees, and maximal stability margin led to the COP moving toward the rear foot in asymmetric stance. A combined analytical-numerical optimization scheme was used to avoid singularities that can arise due to the fact that at equilibrium postural configurations, the torso lies at or near the workspace boundary of the lower extremities. Experiments were conducted and the results obtained were in keeping with the model predictions. This basic understanding of asymmetric stance is important for studying asymmetric postural mechanics in the presence of external disturbances, and for extending the results from normal subjects to humans at both ends of the life span.
Dynamic Feedback Linearization for Electrohydraulically Actuated Control Systems
Authors: Vossoughi Gholamreza , Donath Max
Published: February 2008

Using the dynamic inversion principal, a globally linearizing feedback control law is developed for an electrohydraulic servo system. The proposed control law is implemented on a rotational joint driven by a linear actuator. The results from experiments indicate that better uniformity of response is achieved across a wider range of operating conditions than would otherwise be possible. Improved symmetry is obtained for the extension and retraction phases of motion for an asymmetric actuator under various loading conditions and actuator positions. As a result of the improvements in linearity, significantly better performance is achieved when using linear controllers. To incorporate the effects of parametric uncertainties on the feedback linearization, a state space linear fractional representation of the parametrically uncertain linearized system is also developed. This uncertainty model is specifically suited for the design of robust control systems using the μ-synthesis and H∞ based approach.
Feedforward Controllers and Tracking Accuracy in the Presence of Plant Uncertainties
Authors: Zhao Yongdong , Jayasuriya Suhada
Published: February 2008

In the absence of plant parameter uncertainty feedforward controllers can be synthesized to achieve perfect continuous tracking. When plant has uncertainties it is, in general, impossible to achieve such perfect tracking. Investigated in this paper is the role played by feedforward controllers in the presence of plant uncertainties. We show that the use of feedforward controllers cannot improve the tracking error beyond what is achievable with a properly designed feedback loop, over all plant uncertainties. Including preview in the feedforward will not alter the situation either. We present two methods of designing robust compensators so that the tracking error due to uncertainties will be made small in some sense in the frequency domain and will have zero error in the steady state.
Adaptive Forced Balancing for Multivariable Systems
Authors: Beale S. , Shafai B. , LaRocca P. , Cusson E.
Published: February 2008

Active magnetic bearing (AMB) actuators support rotors without friction but require feedback control for stabilization and performance. Autobalancing compensation causes AMBs to spin a rotor about its inertial axis to eliminate synchronous force transmission from mass unbalance. Because mass unbalance constitutes a sinusoidal sensor disturbance within the bandwidth, conventional methods can either cause instability or fail to preserve desired bandwidth. We introduce a new method called adaptive forced balancing (AFB) which overcomes these problems. We consider AFB with a frequency tracking capability for SISO systems (i.e., single-end AMB suspensions) and show how to extend it for the MIMO case as applied to a double-end AMB suspension.
Tunable Active Vibration Absorber: The Delayed Resonator
Authors: Olgac Nejat , Holm-Hansen Brian
Published: February 2008

This paper elaborates upon a novel concept, the Delayed Resonator, a tunable active vibration absorber. This technique uses a control which has a time delayed feedback of the absorber mass displacement. The substance of this process is in that the absorber completely removes oscillations from the primary structure. Two very strong features that should be mentioned are: (a) the excitation frequency range can vary over a semi-infinite interval, and (b) the absorber can be tuned in real time. These are the unique characteristics of the technique distinguishing it from the others. Stability issues of the primary system combined with the Delayed Resonator are addressed following Nyquist and root locus methods. In particular, the absorption performance for cases with time varying excitation frequency is studied. The primary focus of this paper is on the analysis of transient absorption behavior of the Delayed Resonator during its tuning. An example case is provided which considers a step change in the excitation frequency. A well-pronounced manifestation of the tunability feature of the Delayed Resonator is observed. The superiority of the Delayed Resonator absorber over the conventional a priori tuned absorbers is also demonstrated.
On the Use of an Elastic-Plastic Contact Law for the Impact of a Single Flexible Link
Authors: Yigit A. S.
Published: February 2008

An elastic-plastic contact law is proposed for modeling impact of a single flexible link. This contact law allows continuous transition between contact and noncontact phases and is capable of predicting impact force histories. The impact model parameters can readily be obtained from the material and geometric properties. Excellent agreement with the experimental results has been obtained for both elastic and rigid body motion of the link. The impact force histories are also obtained and compared for perfectly elastic and elastic-plastic impact models. It is shown that a perfectly elastic impact assumption is not realistic for most impacts of flexible links.
An Algorithm for Obtaining Proper Models of Distributed and Discrete Systems
Authors: Wilson B. H. , Stein J. L.
Published: February 2008

The development of automated modeling software requires strategies for synthesizing mathematical models of systems with distributed and discrete characteristics. A model order deduction algorithm (MODA) is developed to deduce a Proper System Model by selecting the proper complexity of submodels of components in a system subject to a frequency based metric. A Proper Model in this context means that (1) the system model has the minimum spectral radius out of all possible system models of equivalent or greater complexity, and (2) any increase in the model complexity will result in spectral radius beyond a specific frequency range of interest. Proper Models are also defined to have physically meaningful parameters. Proper Models are intended to be useful for design, where mapping the relationship between design parameters and dominant system dynamics is critical. While MODA is illustrated using the application of machine-tool drive systems, it is readily applicable to other modeling applications.
Display of Feel for the Manipulation of Dynamic Virtual Objects
Authors: Yoshikawa Tsuneo , Yokokohji Yasuyoshi , Matsumoto Tomoharu , Zheng Xin-Zhi
Published: February 2008

A system for displaying feel information, while manipulating virtual objects, which takes their dynamic behavior into account is introduced. The display is realized using multiple link mechanisms. New concept of impedance display and two ways of its realization, “measuring force and displaying motion” and “measuring motion and displaying force,” are proposed. Calculation algorithms for the driving input to the display device for the operation of both single-body and multi-body virtual objects are established. The validity of the proposed method is verified experimentally using a newly developed two-finger display device.
Contact/Impact in Hybrid Parameter Multiple Body Mechanical Systems
Authors: Barhorst A. A. , Everett L. J.
Published: February 2008

The multiple motion regime (free/constrained) dynamics of hybrid parameter multiple body (HPMB) systems is addressed. Impact response has characteristically been analyzed using impulse-momentum techniques. Unfortunately, the classical methods for modeling complex HPMB systems are energy based and have proven ineffectual at modeling impact. The problems are exacerbated by the problematic nature of time varying constraint conditions. This paper outlines the reformulation of a recently developed HPMB system modeling methodology into an impulse-momentum formulation, which systematically handles the constraints and impact. The starting point for this reformulation is a variational calculus based methodology. The variational roots of the methodology allows rigorous equation formulation which includes the complete nonlinear hybrid differential equations and boundary conditions. Because the methodology presented in this paper is formulated in the constraint-free subspace of the configuration space, both holonomic and nonholonomic constraints are automatically satisfied. As a result, the constraint-addition/deletion algorithms are not needed. Generalized forces of constraint can be directly calculated via the methodology, so the condition for switching from one motion regime to another is readily determined. The resulting equations provides a means to determine after impact velocities (and velocity fields for distributed bodies) which provide the after collision initial conditions. Finally the paper demonstrates, via example, how to apply the methodology to contact/impact in robotic manipulators and structural systems.
Inverse Kinematic Control Algorithms With a Reduced Coriolis Component for Use in Motion Simulators
Authors: Repperger D. W.
Published: February 2008

A motion simulator is studied within the framework of a multilink robotic manipulator and a class of inverse kinematic algorithms are investigated. Human subjects, for this motion simulator, sit at the end effector and are subjected to all relative motions of the respective links. From the perspective of the subject, one undesired artifact of this simulation occurs when Coriolis accelerations are induced at the end effector as a consequence of a coordinate frame moving relative to another moving frame. This paper adapts the inverse kinematic solution to those which have a minimum Coriolis component and can be used to control the motion simulator. A simple feedback control law is derived which, it turns out, has an additional interpretation as the solution of a related linear quadratic optimization problem.
A Novel Vibratory Device for Angular Rate Measurement
Authors: Netzer Ehud , Porat Itzhak
Published: February 2008

A vibratory angular rate sensor includes a vibrating element instead of a rotating element as in gyroscopes. The vibratory sensor can withstand high accelerations, has long operating life, and is not costly. A new configuration for a vibratory sensor is proposed and analyzed. The proposed scheme has high mechanical gain and low sensitivity to changes in its parameters. An experimental prototype was built and tested, and the results show good agreement with the analysis.
Trajectory Planning of Tracked Vehicles
Authors: Shiller Zvi , Serate William
Published: February 2008

This paper presents a method for computing the track forces and track speeds of planar tracked vehicles, required to follow a given path at specified speeds on horizontal and inclined planes. It is shown that the motions of a planar tracked vehicle are constrained by a velocity dependent nonholonomic constraint, derived from the force equation perpendicular to the tracks. This reduces the trajectory planning problem to determining the slip angle between the vehicle and the path tangent that satisfies the nonholonomic constraint along the entire path. Once the slip angle has been determined, the track forces are computed from the remaining equations of motion. Computing the slip angle is shown to be an initial boundary-value problem, formulated as a parameter optimization. This computational scheme is demonstrated numerically for a planar vehicle moving along circular paths on horizontal and inclined planes.
Extended Pole Placement Method With Noncausal Reference Model for Digital Servo-Control
Authors: Chen Chwan-Hsen , Van Brussel Hendrik , Swevers Jan
Published: February 2008

The extended pole placement (EPP) method extends the well-known pole placement method to digital servo-control with known control inputs. A servo-control system designed using the EPP method achieves an accurate command response through the use of a noncausal reference model and an accurate approximation of nonminimum-phase zeros. The phase error of the command response between the desired output and the actual output may be made arbitrarily small, while its gain extends uniformly to a selectable bandwidth. A selectable feedforward bandwidth is important in controlling flexible structures where unmodeled resonances might be excited by rough feedforward inputs. Experimental results on a machine tool slide show that a controller designed by the EPP method yields better servo performance for cornering and contour tracking tasks than an E-filter-enhanced zero phase error tracking controller.
The Modeling and Simulation of a Proportional Solenoid Valve
Authors: Vaughan N. D. , Gamble J. B.
Published: February 2008

A nonlinear dynamic model of a high speed direct acting solenoid valve is presented. The valve consists of two subsystems; a proportional solenoid and a spool assembly. These two subsystems are modeled separately. The solenoid is modeled as a nonlinear resistor/inductor combination, with inductance parameters that change with displacement and current. Empirical curve fitting techniques are used to model the magnetic characteristics of the solenoid, enabling both current and magnetic flux to be simulated. The spool assembly is modeled as a spring/mass/damper system. The inertia and damping effects of the armature are incorporated in the spool model. The solenoid model is used to estimate the spool force in order to obtain a suitable damping coefficient value. The model accurately predicts both the dynamic and steady-state response of the valve to voltage inputs. Simulated voltage, current, and displacement results are presented, which agree well with experimental results.
Adaptive Control of an Industrial Robot Retrofitted With an Open-Architecture Controller
Authors: Zhou Yuchen , de Silva Clarence W.
Published: February 2008

A PUMA 560 industrial robot has been retrofitted with an open-architecture controller. An adaptive control scheme that incorporates actuator dynamics has been implemented on this robot testbed. The overall low level control scheme is based on the complete robot-actuator dynamics, and consists of a modified regressor-based adaptive algorithm and a feedforward compensation scheme for actuator dynamics. It is shown by a Lyapunov-like analysis that, under this control scheme, the tracking error of a general robot is bounded. Experiments carried out show that the performance of the robot, with the adaptive control scheme, is significantly improved when properly compensated for actuator dynamics.
Exploration of a Mobile Robot Based on Sonar Probability Mapping
Authors: Min Byung-Kwon , Cho Dong Woo , Lee Sang-Jo , Park Young-Pil
Published: February 2008

This paper suggests a new exploration strategy of an autonomous mobile robot in an unknown environment. Determination of a temporary goal based on a representation of work area named exploration quadtree is proposed. The exploration quadtree provides the information on quality of the regions concerned in a robot’s workspace. Using this quadtree the robot easily finds the next temporary goal that makes exploration more efficient. The quadtree is made up from a sonar probability map that is constructed by sonar range sensing and Bayesian probability theory. We then propose a method that plans a path between the determined temporary goals based on a probability map. The developed methods were implemented on a real mobile robot, AMROYS-II, which was built in our laboratory, and shown to be useful enough in a real environment that can be projected onto a two-dimensional space.
Stabilization of Nonlinear Singularly Perturbed Multiple Time-Delay Systems by Dither
Authors: Hsiao Feng-Hsiag , Hwang Jiing-Dong
Published: February 2008

Dither is a high frequency signal injected into nonlinear systems for the purpose of improving their performance. Stability of the dithered nonlinear singularly perturbed multiple time-delay system is investigated by deriving its corresponding dithered reduced-order model and by using the relaxed method to analyze stability of the dithered reduced-order model when the frequency of dither is sufficiently high. Moreover, if the singular perturbation parameter is sufficiently small, then stability of the relaxed model would imply stability in finite time of the dithered nonlinear singularly perturbed multiple time-delay system.
Dynamic Modeling and Control of a Ball-Joint-Like Variable-Reluctance Spherical Motor
Authors: Lee Kok-Meng , Roth Ronald B. , Zhou Zhi
Published: February 2008

Examination of existing joint designs for robot wrist applications has indicated that a spherical wrist motor offers a major performance advantage in trajectory planning and control as compared to the popular three-consecutive-rotational joint wrist. The tradeoff, however, is the complexity of the dynamic modeling and control. This paper presents the dynamic modeling and the control strategy of a three degree-of-freedom (DOF) variable-reluctance (VR) spherical motor which presents some attractive possibilities by combining pitch, roll, and yaw motion in a single joint. The spherical motor dynamics consist of the rotor dynamics and a torque model. The torque model is described as a function of coil excitations and a permeance model in terms of the relative position between the rotor and the stator. Both the forward dynamics which determine the rotor motion as a result of activating the electromagnetic coils and the inverse model which determines the coil excitations required to generate the desired torque are derived in this paper. The solution to the forward dynamics of the spherical motor is unique, but the inverse model has many solutions and therefore an optimization is desired. Experimental results verifying the dynamic model are presented. The control of a VR spherical motor consists of two parts; namely, the control of the rotor dynamics with the actuating torque as system input, and the determination of the optimal electrical inputs for a specified actuating torque. The simulation results and implementation issues in determining the optimal control input vectors are addressed. It is expected that the resulting analysis will serve as a basis for dynamic modeling, motion control development, and design optimization of the VR spherical motor.
Predicting the Behavior of Slipper Pads in Swashplate-Type Axial Piston Pumps
Authors: Harris R. M. , Edge K. A. , Tilley D. G.
Published: February 2008

This paper describes a dynamic model for slipper-pads that allows lift and tilt behavior to be predicted, including the effects of possible contact with the swashplate or slipper retaining plate. This model has been incorporated in the Bathfp simulation package and used to examine the dynamic stability of slipper-pads over the pumping cycle, and to compare the behavior over a range of pump speeds. The centripetal tilting moments acting on the slipper-pad increase with speed and as a consequence can lead to contact between the slipper and the swashplate at high speed. This is particularly likely to occur as the piston makes the transition between suction and delivery, where the pressure forces acting on the piston-slipper assembly change abruptly. The predicted nature of the swashplate contacts at high speeds correspond closely with witness marks on a dismantled pump. The model presented may also be used for predicting slipper behavior in other types of pump, for example, wobble-plate type pumps, or in piston motors.
Vibration Control of an Axially Moving String by Boundary Control
Authors: Lee Seung-Yop , Mote C. D.
Published: February 2008

The stabilization of the transverse vibration of an axially moving string is implemented using time-varying control of either the boundary transverse motion or the external boundary forces. The total mechanical energy of the translating string is a Lyapunaov functional and boundary control laws are designed to dissipate the total vibration energy of the string at the left and/or right boundary. An optimal feedback gain determined by minimizing the energy reflected from the boundaries, is the radio of tension to the propagation velocity of an incident wave to the boundary control. Also the maximum time required to stabilize all vibration energy of the system for any initial disturbance is the time required for a wave to propagate the span of the string before hitting boundary control. Asymptotic and exponential stability of the axially moving string under boundary control are verified analytically through the decay rate of the energy norm and the use of semigroup theory. Simulations are used to verify the theoretically predicted, optimal boundary control for the stabilization of the translating string.
Damage-Mitigating Control of a Reusable Rocket Engine: Part I—Life Prediction of the Main Thrust Chamber Wall
Authors: Dai Xiaowen , Ray Asok
Published: February 2008

The goal of damage-mitigating control in reusable rocket engines is to achieve high performance without overstraining the mechanical structures; and the major benefit is an increase in structural durability with no significant loss of performance. This sequence of papers in two parts investigates the feasibility of damage mitigating control of a reusable rocket engine similar to the Space Shuttle Main Engine (SSME). The challenge here is to characterize the thermo-mechanical behavior of the structural materials for damage prediction in conjunction with dynamic performance analysis of the thermo-fluid process in the rocket engine, and then utilize this information in a mathematically and computationally tractable form for synthesizing decision and control algorithms. This paper is the first part and investigates the damage phenomena in the coolant channel ligament of the main thrust chamber of a rocket engine that are characterized by progressive bulging-out and incremental thinning leading to eventual failure by tensile rupture. A creep damage model is analytically derived based on the theories of sandwich beam and viscoplasticity. The objective of this model is to generate a closed-form solution of the wall thin-out in real time where the ligament geometry is continuously updated to account for the resulting deformation. The creep damage model has been examined for both single-cycle and multi-cycle stress-strain behavior, and the results are in agreement with those obtained from the finite element analyses and experimental observation. Due to its computational efficiency, this damage/life prediction model is suitable for on-line applications of decision and control, and also permits parametric studies for off-line synthesis of damage mitigating control systems. The second part, which is a companion paper, develops an optimal policy for damage mitigating control of the rocket engine.
Damage-Mitigating Control of a Reusable Rocket Engine: Part II—Formulation of an Optimal Policy
Authors: Dai Xiaowen , Ray Asok
Published: February 2008

This sequence of papers in two parts investigates the feasibility of damage-mitigating control of a reusable rocket engine similar to the Space Shuttle Main Engine (SSME) where the objective is to increase structural durability without any significant loss of performance. To this effect, a fatigue damage model of the turbine blades has been reported in earlier publications, and a creep damage model of the main thrust chamber coolant channel has been formulated and tested in the first part. This paper, which is the second part, synthesizes an optimal policy for open loop control of up-thrust transients of the rocket engine. Optimization is based on the integrated model of the plant, structural and damage dynamics under the constraints of fatigue and creep damage in the critical components. The results are presented to demonstrate the potential of life extension of reusable rocket engines via damage mitigating control. The concept of damage mitigation, as presented in this paper, is not restricted to control of rocket engines. It can be applied to any system where structural durability is an important issue.
Part I: Modeling of a One-Degree-of-Freedom Active Hydraulic Mount
Authors: FitzSimons P. M. , Palazzolo J. J.
Published: February 2008

There is a diverse range of applications for active hydraulic mounts such as vibration absorbers, flight simulators, and industrial test rigs. The purpose of the mount considered here is to make a mass that is driven by an external force and a hydraulic actuator behave as if it were a prescribed mechanical impedance driven solely by the external force. We develop a model of this mount that includes the effects of servovalve dynamics and fluid compressibility and will be used in the future design of a robust control system. Then the conic sector bound method, which is readily amenable to the application of established robust control methodologies, is used to describe a family of linear time-varying plants that could be used to represent the nonlinear behavior of the system.
Modeling and Test of an Electropneumatic Servovalve Controlled Long Rodless Actuator
Authors: Lin X. , Spettel F. , Scavarda S.
Published: February 2008

The usual way of modeling an electropneumatic servodrive system consists of supposing the homogeneity of the flow parameters in the cylinder. In order to study the influence of the transmission line effects on the dynamic behavior of a long pneumatic rodless cylinder, a generalized one-dimensional distributed parameter cylinder model is presented. The proposed numerical scheme combining the finite difference and the “characteristics” method enables the simulate of a long rodless cylinder by taking into account the servovalve boundary conditions and the piston movement. The simulated results are compared with experimental results.
Modeling and Diagnosis of Motion Error of Multi-Axis Machines Using a Ball Bar Test
Authors: Jeng Shyr-Long , Chieng Wei-Hua , Lee An-Chen
Published: February 2008

The contouring accuracy of a multi-axis machine has a critical effect on the quality of many advanced technology products. One of the best approaches to assessing the contouring performance of machine tools is through double ball bar measurement. During circular interpolation motion, the machine traverses, with two axes at a time, a circular trajectory, with each axis subject to sinusoidal changes in acceleration, velocity, and position. The motion error is measured by detecting the relative distance between a point on the spindle nose and another point on the machine table and plotting this distance in polar coordinates. The present paper derives mathematical models and diagnosis procedures for first and second-order motion error resulting from the active degrees of freedom of a multi-axis machine. The theoretical results are verified by both computer simulation and double ball bar testing experiments.
Synthesis of Hybrid Impedance Control Strategies for Robot Manipulators
Authors: Pelletier Michel
Published: February 2008

This paper presents a new method to automatically synthesize robot compliant motions based on hybrid impedance control. The scheme relies on decoupled linear impedance models of the robot and the environment, in which the errors due to control, task frame estimation, as well as environment uncertainty are explicitly taken into account. The technique consists of selecting appropriate manipulator impedances to match the environment dynamics and satisfy all the task goals. Two experimental examples of this methodology are presented.
In-Situ Identification of Active Magnetic Bearing System Using Directional Frequency Response Functions
Authors: Lee Chong-Won , Ha Young-Ho , Joh Chee-Young , Kim Cheol-Soon
Published: February 2008

Complex modal testing is employed to obtain the directional frequency responses of a four-axis active magnetic bearing system. In the test, magnetic bearings are used as exciters while the system is in operation. The directional frequency response estimates are then used to effectively identify the parameters of the active magnetic bearing system. Experimental results show that the directional frequency response function, which is properly defined in the complex domain, is a powerful tool for identification of bearing as well as modal parameters of the system.
System Simulation and Control of Batch-Fed Solid Waste Incinerators
Authors: Kuo Jing T.
Published: February 2008

Frequently, due to the irregularities in fuel properties of the wastes and variations in feed rates, the operation of a batch-fed incinerator may encounter pressure surges and transient flue gas leakages. A lumped model to simulate the flow, pressure, and temperature behavior of an incineration system was developed, according to the fundamental conservation laws governing the overall balances of flow and thermal-mechanical energies of the system components. The system dynamic responses to flow control and waste burning variations were analyzed numerically. Qualitatively, the results correctly reflected the observed operational characteristics of batch-fed incinerators. The lumped system model can serve as a tool to design control algorithms. The concepts and approaches adopted in this work can be used as the basis for further expansion in details toward the development of an incinerator system simulator for operator training purposes.
An Operational Method for Nonparametric Analysis of Feedback Control Systems
Authors: Pan Jianhua , Van de Vegte J. , Mills J. K.
Published: February 2008

An operational method of analysis using nonparametric impulse response models is proposed for the nonparametric analysis and design of feedback control systems. It is based on the algebra of convolution quotients, and represents common results such as closed-loop transfer functions in symbolic forms, which closely resemble those for conventional parametric analysis. In design applications, controllers are also expressed symbolically by means of convolution quotients. A deconvolution algorithm is proposed to compute the convolution quotients, and permits these symbolic forms to be evaluated and applied to nonparametric analysis and design.
Experimental Approach to Selecting H∞ Weighting Functions for DC Servos
Authors: Yang Ciann-Dong , Tai Hung-Chun , Lee C. C.
Published: February 2008

This paper proposes an experimental solution for selecting H∞ weighting functions by exploiting an experimental planning method which is widely used in quality control. Conducting matrix experiments via orthogonal array, free parameters in H∞ weighting functions can be determined efficiently so that the resulting controller is able to satisfy all the design specifications. Velocity controller design of DC servomotors is demonstrated to show the superior servo performance provided by the experimental H∞ design. All specifications of robust stability and robust performance are validated by hardware experiments. The resulting controller tends to uniform and lower μ curve, which is a reminiscence of μ controller.
A Uniform Bound for the Jacobian of the Gravitational Force Vector for a Class of Robot Manipulators
Authors: Ghorbel F. , Gunawardana R.
Published: February 2008

In this paper, we study the boundedness of the Jacobian of the gravitational force vector of serial link robot manipulators with respect to the generalized coordinate vector. The uniform bound of this matrix plays an important role in the stability analysis and design of many control systems. In order to insure the existence of a uniform bound, it is typically assumed that manipulators under consideration have only revolute joints. We therefore propose a larger class of manipulators, referred to as class BD manipulators, for which a uniform bound exists. This bound can easily be computed using basic link parameters including the link masses, the Denavit-Hartenberg link parameters, and the link center of mass locations.
Robust Controller Design for Discrete Uncertain Multiple Time-Delay Systems
Authors: Hsiao Feng-Hsiag , Pan Shing-Tai , Teng Ching-Cheng
Published: February 2008

We derive a variety of succinct criteria of robust stability for discrete uncertain systems which contain multiple delays and a class of series nonlinearities. Each result is expressed by a brief inequality and corresponds to compromise between simplicity and sharpness. The properties of norm are employed to investigate robustness conditions that guarantee asymptotic stability rather than ultimate boundedness of trajectories. It is shown that the uncertainties, nonlinearities, and delays are the factors of instability of the overall system, between which some compromise is necessary.
On the Emulation of Stiff Walls and Static Friction With a Magnetically Levitated Input/Output Device
Authors: Salcudean S. E. , Vlaar T. D.
Published: February 2008

This technical brief addresses issues of mechanical emulation of stiff walls and stick-slip friction with a 6-DOF magnetically levitated joystick. In the case of stiff wall emulation, it is shown that the PD control implementation commonly used severely limits achievable wall damping and stiffness. It is also shown that the perceived surface stiffness can be increased without loss of stability by applying a braking force pulse when crossing into the wall. For stick-slip friction, Karnopp’s model was implemented using a PD controller within the stick friction threshold. Even though the PD controller allows some motion during the stick phase, the haptic feedback provided is remarkably similar to stick-slip friction.
Nonstationary Random Dynamics of a Mobile Robotic Manipulator
Authors: Akpan U. O. , Kujath M. R.
Published: February 2008

The paper presents results from a study of the structural motion of a flexible mobile manipulator, and specifically, it discusses the time-dependent statistics and the deterministic response of this motion. The manipulator is mounted atop a vehicle which is supported by a suspension system. The vehicle accelerates uniformly on a rough surface generating a nonstationary random excitation and a deterministic excitation. The system response is separated into deterministic and stochastic components. The covariance Liapunov’s equation for the manipulator stochastic joint responses is developed. Further, expressions for the covariance matrices of the manipulator tip motion are developed and the transformation necessary to relate them to various Cartesian coordinate frames is derived. Expressions for the principal variances of the tip motion are developed by means of the singular value decomposition. The effects of damping, vehicle acceleration, surface roughness coeffifients, and manipulator configuration on the tip responses are explored.
A Frequency Domain Identification Scheme for Control and Fault Diagnosis
Authors: Mallory G. , Doraiswami R.
Published: February 2008

A robust scheme to estimate a set of models for a linear time-invariant system, subject to perturbations in the physical parameters, from a frequency response data record is proposed. The true model as well as the disturbances affecting the system are assumed unknown. However, the physical parameters are assumed to enter the coefficients of the system transfer function multilinearly. A set of models is identified by perturbing the physical parameters one-at-time and using a frequency domain identification technique. Exploiting the assumed multilinearity, the estimated set of models is validated. The proposed scheme is evaluated on a number of simulated systems, and on a physical robot manipulator arm.
Prototype of a Microtesting System Made by the LIGA Process to Measure the Young’s Modulus in Cantilever Microbeams
Authors: Ruther P. , Bacher W. , Feit K. , Maas D. , Menz W.
Published: February 2008

A microtesting system manufactured by the LIGA process (Becker et al, 1986) combined with a new sacrificial structure technique is presented. The system is used for bending experiments to determine the Young’s modulus of electroplated materials used in the LIGA process. The force needed to bend the specimen is generated by a pneumatically driven microactuator. This actuator is able to produce forces in the range of several 10 mN and displacements of 50 μm and more. Bending of the specimen is detected optically. With a trap for adhesive, adhesive bonding can be applied to cover the actuator chamber with a glass platelet. For the fluidic supply of the actuator, hoses are bonded into microtunnels (140 μm diameter) running parallel to the substrate and passing through the sidewalls of the actuator housing. The microtunnels are produced by the sacrificial structure technique.
Componentwise Bounded Controllers for Robust Exponential Convergence
Authors: Corless M. , Leitmann G.
Published: February 2008

This paper presents controllers for a class of nonlinear uncertain systems when each control input is subject to an upper bound on its magnitude or norm. The proposed controllers ensure that all closed loop state trajectories which originate in a bounded region exponentially converge to a desired neighborhood of the origin with a desired rate of convergence. The results are illustrated by applying them to the stabilization of a spacecraft subject to bounded control and disturbance torques.
Robust Nondiagonal Controller Design for Uncertain Multivariable Regulating Systems
Authors: Franchek M. A. , Herman P. , Nwokah O. D. I.
Published: February 2008

Presented in this paper is a robust controller design methodology for a class of uncertain, multivariable, regulating systems required to maintain a prespecified operating condition within hard time domain tolerances despite a vector of step disturbances. The design methodology is a frequency domain approach and is based on sequential loop design where a Gauss elimination technique facilitates the various design steps. The specific class of systems addressed are those which can be modeled as square, multivariable systems with parametric uncertainty. One restriction imposed is that the system and its inverse are stable for all plant parameter combinations. The key features of this design methodology include (i) the design of a fully populated controller matrix, (ii) the ability to design for system integrity, and (iii) the direct enforcement of hard time domain tolerances through frequency domain amplitude inequalities.
A Digital Robust Controller for Cutting Force Control in the End Milling Process
Authors: Rober S. J. , Shin Y. C. , Nwokah O. D. I.
Published: February 2008

In this work, a digital robust controller is designed via Quantitative Feedback Theory (QFT) to maintain a constant cutting force in the presence of parametric uncertainty for a time varying end milling process. The QFT controller is designed using the delta transform method for discrete systems. The controller is designed to limit the overshoot and settling time of the cutting force levels over a range of cutting parameters. Models are presented for the cutting process and machine dynamics including parametric uncertainty, and these models are used to develop a controller which meets given tracking and regulation specifications for all plant values. Experimental results are obtained by implementing the controller on a milling machine.
Lobing Behavior in Centerless Grinding—Part I: Stability Estimation
Authors: Zhou S. S. , Gartner J. R. , Howes T. D.
Published: February 2008

This two-part paper addresses the lobing behavior associated with centerless grinding. Part I establishes a system model (the lobing loop) for lobing analysis and develops methodologies for lobing stability analysis, and Part II investigates lobing characteristics and proposes remedies for lobing suppression. The lobing loop shows that lobing behavior is of kinematic nature, caused by the interaction between the geometric rounding mechanism and regenerative cutting mechanism. A bidiagram-matical method is subsequently developed for lobing stability estimation. It was found that lobing is inherently unstable, and the characteristic roots of the lobing loop are limited within their respective root neighborhoods in the u-plane. This leads to: (1) a method of lobing stability estimation using the growth rate boundaries, and (2) an efficient way of solving for the characteristic roots using a Taylor’s series approximation. The availability of growth rate boundaries and characteristic root distribution provides an effective tool for the control of lobing in centerless grinding.
Design of Optimal MIMO DIVSC Systems and Its Application to Idle Speed Control of Spark Ignition Engine
Authors: Chern Tzuen-Lih , Chuang Chin-Wen
Published: February 2008

An optimal multi-input multi-output (MIMO) discrete integral variable structure control (DIVSC) rule is proposed in this paper. This approach can achieve accurate and robust dynamic responses. The modified existence conditions are introduced to assure the existence of the discrete non-ideal sliding motion. The design procedures are clearly developed in this paper. Use optimal LQ method to decide the coefficients of the sliding surfaces and integral gains. On the basis of the nonideal sliding motions, the control functions can be found out to satisfy the modified existence conditions. The idea of boundary layer is used to smoothing the control functions. Furthermore, take the engine idle speed control as an example. Simulation results will demonstrate the potential of the proposed approach.