bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibration and Application of an Intra-articular Force Transducer for the Measurement of Patellar Tendon Graft Forces: An in Situ Evaluation
Authors: Fleming B. C. , Good L. , Peura G. D. , Beynnon B. D.
Published: February 2008

The objective of this study was to evaluate two calibration methods for the “Arthroscopically Implantable Force Probe” (AIFP) that are potentially suitable for in vivo use: (1) a direct, experimentally based method performed by applying a tensile load directly to the graft after it is harvested but prior to implantation (the “pre-implantation” technique), and (2) an indirect method that utilizes cadaver-based analytical expressions to transform the AIFP output versus anterior shear load relationship, which may be established in vivo, to resultant graft load (the “post-implantation” technique). The AIFP outputs during anterior shear loading of the knee joint using these two calibration methods were compared directly to graft force measurements using a ligament cutting protocol and a 6 DOF load cell. The mean percent error ((actual – measured)/(actual) * 100) associated with the pre-implantation calibration ranged between 85 and 175 percent, and was dependent on the knee flexion angle tested. The percent error associated with the post-implantation technique was evaluated in two load ranges: loads less than 40 N, and loads greater than 40 N. For graft force values greater than 40 N, the mean percent errors inherent to the post-implantation calibration method ranged between 20 and 29 percent, depending on the knee flexion angle tested. Below 40 N, these errors were substantially greater. Of the two calibration methods evaluated, the post-implantation approach provided a better estimate of the ACL graft force than the pre-implantation technique. However, the errors for the post-implantation approach were still high and suggested that caution should be employed when using implantable force probes for in vivo measurement of ACL graft forces.
A Cellular Solid Criterion for Predicting the Axial-Shear Failure Properties of Bovine Trabecular Bone
Authors: Fenech C. M. , Keaveny T. M.
Published: February 2008

In a long-term effort to develop a complete multi-axial failure criterion for human trabecular bone, the overall goal of this study was to compare the ability of a simple cellular solid mechanistic criterion versus the Tsai–Wu, Principal Strain, and von Mises phenomenological criteria—all normalized to minimize effects of interspecimen heterogeneity of strength—to predict the on-axis axial-shear failure properties of bovine trabecular bone. The Cellular Solid criterion that was developed here assumed that vertical trabeculae failed due to a linear superposition of axial compression/tension and bending stresses, induced by the apparent level axial and shear loading, respectively. Twenty-seven bovine tibial trabecular bone specimens were destructively tested on-axis without end artifacts, loaded either in combined tension-torsion (n = 10), compression-torsion (n = 11), or uniaxially (n = 6). For compression-shear, the mean (± S.D.) percentage errors between measured values and criterion predictions were 7.7 ± 12.6 percent, 19.7 ± 23.2 percent, 22.8 ± 18.9 percent, and 82.4 ± 64.5 percent for the Cellular Solid, Tsai–Wu, Principal Strain, and von Mises criteria, respectively; corresponding mean errors for tension-shear were –5.2 ± 11.8 percent, 14.3 ± 12.5 percent, 6.9 ± 7.6 percent, and 57.7 ± 46.3 percent. Statistical analysis indicated that the Cellular Solid criterion was the best performer for compression-shear, and performed as well as the Principal Strain criterion for tension-shear. These data should substantially improve the ability to predict axial-shear failure of dense trabecular bone. More importantly, the results firmly establish the importance of cellular solid analysis for understanding and predicting the multiaxial failure behavior of trabecular bone.
Low-Frequency Acoustic Sweep Monitoring of Bone Integrity and Osteoporosis
Authors: Panteliou S. D. , Abbasi-Jahromi H. , Dimarogonas A. D. , Kohrt W. , Civitelli R.
Published: February 2008

We developed a noninvasive method to evaluate bone structural integrity. It is based on the measurement of the dynamic characteristics of the bone using sweeping sound excitation in the range of acoustic frequencies. The Quality Factor (a measure of material damping) has been used as an indicator of the tendency of the bone to fracture. Results of animal studies have supported this hypothesis since linear correlations were observed between bone density, quality factor, and impact strength. A vibration excitation in the form of an acoustic sweep signal is applied to a bone to measure the quality factor. Rat bones were tested, obtained from animals with osteoporosis age-dependent (tested in vitro) or ovariectomy-induced (tested in vivo), and compared with bones of healthy (control) rats. The change in damping was, on average, equal or greater to the change in density. Moreover, excellent correlation of the quality factor was obtained with bone fracture energy measured with an impact test. During a vibration cycle, the changing strain results in temperature changes due to the reciprocity of temperature and strain. Nonreversible conduction of heat due to the unequal temperature change results in entropy production that is enhanced due to the stress concentration about the voids associated with bone porosity. Damping is a measure of the production of entropy. Its measure, the quality factor, represents a potentially useful tool for monitoring bone integrity, which is deteriorating in diseases characterized by disruption of the trabecular architecture, such as osteoporosis. A computational model yielded results that are in good correlation with the experimental results.
A Fuzzy Decision System for Fault Classification Under High Levels of Uncertainty
Authors: Chen Yubao
Published: February 2008

The problem of high levels of uncertainty existing in machine diagnosis is addressed by an approach based on fuzzy logic. In this approach, multiple sensors/channels are used, and the uncertainty is treated by membership functions in different stages of the signal processing. The concepts of fuzziness, fuzzy set, and fuzzy inference are described, particularly for the development of a practical procedure for machine diagnosis. The membership functions are established through a learning process based on test data, rather than being selected a priori. The information-gain weighting functions are also introduced in order to improve the robustness and reliability of this method. As a result, a framework of a Fuzzy Decision System (FDS) is proposed and applied to a machining process. Experiment verification with an optimistic success rate of 97.5 percent was achieved.
Extended Bond Graph Reticulation of Piezoelectric Continua
Authors: Lee Fu-Shin , Moon Tess J. , Masada Glenn Y.
Published: February 2008

Extended Bond Graph (EBG) reticulations for general and linear piezoelectric continua are developed in this paper. The EBG formulation is especially advantageous for modeling the distributed coupled electromechanical effects of these materials and for combining this representation with other discrete models. The electromechanical coupling effects are represented by a multiport C-element for the general piezoelectric material. For linear constitutive properties, the coupling effects are represented by two multiport C-elements; one for the strain energy and the other for the capacitance storage, and a transformer that converts the power flows between the two energy domains. Details of the developments of the general formulation and of the specific models are provided. This work represents the first application of EBGs to electric fields.
Turbocharged Diesel Engine Modeling for Nonlinear Engine Control and State Estimation
Authors: Kao Minghui , Moskwa John J.
Published: February 2008

Engine models that are used for nonlinear diesel engine control, state estimation, and model-based diagnostics are presented in this paper. By collecting, modifying, and adding to current available engine modeling techniques, two diesel engine models, a mean torque production model and a cylinder-by-cylinder model, are summarized for use in the formulation of control and state observation algorithms. In the cylinder-by-cylinder model, a time-varying crankshaft inertia model is added to a cylinder pressure generator to simulate engine speed variations due to discrete combustion events. Fuel injection timing and duration are control inputs while varying engine speed, cylinder pressure, and indicated torque are outputs from simulation. These diesel engine models can be used as engine simulators and to design diesel engine controllers and observers.
Adaptive Computed Reference Computed Torque Control of Flexible Robots
Authors: Lammerts I. M. M. , Veldpaus F. E. , Van de Molengraft M. J. G. , Kok J. J.
Published: February 2008

This paper presents a motion control technique for flexible robots and manipulators. It takes into account both joint and link flexibility and can be applied in adaptive form if robot parameters are unknown. It solves the main problems that are related to the fact that the number of degrees of freedom exceeds both the number of actuators and the number of output variables. The proposed method results in trajectory tracking while all state variables remain bounded. Global, asymptotic stability is ensured for all values of the stiffnesses of joints and links. To show the characteristics of the proposed control law, some simulation results are presented.
On-Line Preload Monitoring for Anti-Friction Spindle Beatings of High-Speed Machine Tools
Authors: Tu Jay F. , Stein Jeffrey L.
Published: February 2008

Catastrophic and premature bearing failure caused by excessive thermally-induced bearing preload is a major design problem for spindle bearings in high-speed machine tools. Due to a lack of low cost and easy to maintain on-line preload measuring techniques, the traditional solution is to limit the maximum spindle speed and the initial bearing preload. This solution is incompatible with the trend of high-speed machining, which requires increasing both spindle speed and spindle stiffness. Therefore, it would be valuable if thermally-induced preload can be monitored on-line for regulating bearing thermal behavior at high speeds. This paper proposes using a dynamic state observer based on a preload model to estimate the spindle bearing preload via low cost thermocouples attached to the bearing outer ring and the spindle housing. The observer is based on a state-space model capable of describing the transient preload behavior of the spindle bearing. The temperatures of the outer ring and housing are used as the feedback signals for the preload observer. The observer gains are determined systematically to account for modeling errors, unknown parameters, nonlinearities, and measurement noise. In particular, the modeling errors due to unexpected factors such as bearing skidding, wear, and lubricant deterioration are compensated by a Modeling Error Compensator (MEC). By using the MEC, the error dynamics of the observer can be converted into a form suitable for applying existing observer techniques such as the Extended Kalman Filter (EKF). This preload observer has been successfully validated on two different bearing configurations operated at different speeds. The results show that the model-based monitoring technique, which combines the measurement of outer ring and housing temperature and a robust state observer, can be an effective and low-cost solution for preload monitoring in high-speed machine tools.
Lyapunov Direct Design of Robust Control for Electrical-Mechanical Systems Composed of Cascaded Nonlinear Uncertain Subsystems
Authors: Qu Zhihua , Dawson Darren M.
Published: February 2008

Robust control design of nonlinear uncertain systems is investigated. A system under consideration consists of finite nonlinear systems which are cascaded and have significant uncertainties. Such a system arises naturally from many real physical systems, especially mechanical systems. An important feature of these systems is that they do not satisfy the assumption of the standard matching conditions required by most existing robust control results. General classes of cascaded uncertain systems are identified for which robust controllers are obtained explicitly in terms of the bounding functions of the uncertainties. The resulting robust controllers guarantee stability of global uniform ultimate boundedness or global exponential convergence to zero. The controls are designed by a two-step systematic design procedure. First, design fictitious robust controllers for input of individual subsystem as if every subsystem had an independent control. Then, a recursive mapping is proposed which maps the individual fictitious controls recursively into the only control of the overall system.
Stabilizability of Unstable Linear Plants Under Bounded Control
Authors: Zhao Yongdong , Jayasuriya Suhada
Published: February 2008

Considered in this paper is the problem of stabilizing a linear unstable plant under bounded control. It is shown that a linear strictly unstable plant can never be globally stabilized under bounded control, and a linear unstable plant can never be globally stabilized under bounded linear feedback control. Hence, any stabilizing controller {be it linear or nonlinear) for a strictly unstable plant can only be locally stabilizing. Consequently, it is important to estimate the domain of attraction achievable with a locally stabilizing control under a prespecified control bound. Since, it is difficult to construct the domain of attraction, we use the domain within which the control is not saturated to approximate it. The relation between these two domains are characterized and computable expressions for the biggest stability ball and the biggest stability polytope that lie inside the domain of nonsaturating control are given.
Variable Structure Control of a Pneumatic Actuator
Authors: Tang J. , Walker G.
Published: February 2008

In an effort to overcome the nonlinerities associated with a pneumatic system the variable structure control (VSC) technique has been employed to control the position of a pneumatic actuator. To accomplish this a model of a pneumatic actuator was developed to allow the control systems to be studied via simulations. The results from the simulations indicated that the VSC technique can position the actuator rapidly, via first-order trajectory, in response to a step input. An experimental study of the VSC control system was then performed. These experiments verified the simulation work, and demonstrated that inherent system delays and the quantisation of the control signals can cause and uncontrollable oscillatory behaviour; stability limits were established for three of the system parameters. It was also found, that the actuator could be placed within ±5 mm of the desired position.
Friction Modeling and PD Compensation at Very Low Velocities
Authors: Dupont Pierre E. , Dunlap Eric P.
Published: February 2008

It is a well-known empirical result that stick-slip can often be eliminated from a system by stiffening it. More recently, it has been shown that for a negatively-sloped friction-velocity curve, a frictional lag must be present for machine/controller stiffness to produce this stabilizing effect. In this paper, experiments involving dry and lubricated line contacts of hardened tool steel are described which demonstrate the existence of frictional lag in boundary lubrication. It is also shown that a single-state-variable friction model provides a good representation of the actual friction dynamics. The model and associated parameter values provide a means for computing lower bounds on the machine stiffness and PD gains necessary for steady motion at velocities on the order of microns per second.
A Frequency Domain Criterion for Robustly Stabilizing a Family of Interval Plants
Authors: Zhao Yongdong , Jayasuriya Suhada
Published: February 2008

Considered in this paper is the problem of robust stabilization of a family of interval plants by a single fixed compensator. A frequency domain sufficient condition determines the closed-loop stability. In particular if a specially constructed frequency function does not, at any frequency ω ∈ [0, ∞], intersect the box [−1, 1] × [−1, 1] in the complex plane then the entire closed loop family is stable. Also identified is a class of interval plants for which the sufficient condition in fact does become necessary.
Optimal Tracking Control of Multi-Zone Indoor Environmental Spaces
Authors: Zaheer-uddin M. , Patel R. V.
Published: February 2008

Optimal control of indoor environmental spaces is explored. A physical model of the system consisting of a heating system, a distribution system and an environmental zone is considered and a seventh order bilinear system model is developed. From the physical characteristics and open-loop response of the system, it is shown that the overall system consists of a fast subsystem and a slow subsystem. By including the effects of the slow subsystem in the fast subsystem, a reduced order model is developed. An optimal control law is designed based on the reduced order model and it is implemented on the full order nonlinear system. Both local and global linearization techniques are used to design optimal control laws. Results showing the disturbance rejection characteristics of the resulting closed-loop system are presented. The use of optimal tracking control to implement large changes in setpoints, in a prescribed manner, is also examined. A general model to describe environmental zones is proposed and its application to multi-zone spaces is illustrated. A multiple-input optimal tracking control law with output error integrators is designed. The resulting closed-loop system response to step-like disturbances is shown to be good.
Study on a Surface-Motor Driven Precise Positioning System
Authors: Tomita Yoshiyuki , Koyanagawa Yasushi
Published: February 2008

A newly developed precise positioning system incorporating a surface-motor (SFM) drive unit is presented and its advantageous features, operation principles, electromagnetic drive force design, and some experimental results are described. The stage of our “SFM positioning system” is levitated on a base plate by three air bearing pads; being driven by three brushless-type linear DC motors in three degrees of freedom. The guidance and positioning of the stage’s planar motion are achieved via the simultaneous operation of three identical proportional-integral-derivative (PID) servo-control systems, each having a laser-interferometer position feedback loop. The electromagnetically produced drive forces are analyzed by employing magnetic permeability theory, with good correspondence being obtained between calculated and experimental results. Additionally discussed is the closed-loop dynamic behavior, including the motion caused by three axis-interference. Evaluations of experimental tests indicate that a positioning resolution of 10–20 nm and yaw angle accuracy less than ±0.08 µrad are successfully achieved for an x-y travel range of 10 mm.
Slewing Maneuvers and Vibration Control of Space Structures by Feedforward/Feedback Moment-Gyro Controls
Authors: Yang Li-Farn , Mikulas M. M. , Park K. C. , Su Renjeng
Published: February 2008

This paper presents a momentgyro control approach to the maneuver and vibration suppression of a flexible truss arm undergoing a constant slewing motion. The overall slewing motion is triggered by a feedforward input, and a companion feedback controller is employed to augment the feedforward input and subsequently to control vibrations. The feedforward input for the given motion requirement is determined from the combined CMG (Control Momentum Gyro) devices and the desired rigid-body motion. The rigid-body dynamic model has enabled us to identify the attendant CMG momentum saturation constraints. The task for vibration control is carried out in two stages; first in the search of a suitable CMG placement along the beam span for various slewing maneuvers, and subsequently in the development of LQ control algorithms for CMG spin-stabilization. Both analytical and numerical results are presented to show the effectiveness of the present approach.
Inverse Force and Motion Control of Constrained Elastic Robots
Authors: Yim Woosoon , Singh Sahjendra N.
Published: February 2008

We treat the question of position and force control of a three-axis elastic robotic system on a constraint surface based on nonlinear inversion of an input-output map and linear feedback stabilization. Unlike the rigid robots, the feedback linearizing control of end point motion gives rise to unstable zero dynamics. Instability of zero dynamics is avoided by controlling a parameterized output vector corresponding to a point close to the end point of the arm. Zero dynamics are stable or almost stable as long as the parameter in the output vector does not exceed a critical value. Using the inverse controller, the control of the force and the position of the end point is possible while the end effector moves on the constraint surface. However, this excites the elastic modes. For the final capture of the terminal state and vibration suppression, a linear stabilizer is designed. Simulation results are presented to show that in the closed-loop system trajectory and force control on the constraint surface is accomplished.
The Discrete Event Modeling and Trajectory Planning of Robotic Assembly Tasks
Authors: McCarragher B. J. , Asada H.
Published: February 2008

A new approach to process modeling, task synthesis, and trajectory planning for robotic assembly is presented. Assembly is modeled as a discrete event dynamic system incorporating both discrete and continuous aspects of the process. The discrete event nature of assembly due to contact state transitions is modeled using Petri nets. The Petri net modeling enables a compact graphical description of causal contact state transitions and provides a coherent mathematical representation of both the discrete and continuous dynamics. In contrast to the traditional contact state network, the Petri net modeling also incorporates causality. Using discrete event modeling, an efficient assembly strategy is found. A discrete event trajectory is determined using dynamic programming to minimize the path length and the uncertainty during assembly. Lastly, an optimal event trajectory is calculated to demonstrate the method. This paper lays the foundation of discrete event modeling for robotic assembly. An new avenue for the analysis and synthesis of significant aspects of the assembly process is opened.
CMAC Neural Network Control for High Precision Motion Control in the Presence of Large Friction
Authors: Larsen G. A. , Cetinkunt S. , Donmez A.
Published: February 2008

Precision requirements in ultra-precision machining are often given in the order of micrometers or sub-micrometers. Machining at these levels requires precise control of the position and speed of the machine tool axes. Furthermore, in machining of brittle materials, extremely low feed rates of the machine tool axes are required. At these low feed rates there is a large and erratic friction characteristic in the drive system which standard PID controllers are unable to deal with. In order to achieve the desired accuracies, friction must be accurately compensated in the real-time servo control algorithm. A learning controller based on the CMAC algorithm is studied for this task.
Single-Loop QFT Design for Robust Performance in the Presence of Non-Parametric Uncertainties
Authors: Chait Yossi , Borghesani Craig , Zheng Yuan
Published: February 2008

This note focuses on the robust performance control design problem in single-loop systems from the viewpoint of the Quantitative Feedback Theory (QFT) method. Unlike the more general setup for QFT which allows arbitrary plant uncertainty description (i.e., value sets or templates), we assume that the plant uncertainty is described by multiplicative perturbation. A set of quadratic inequalities is developed for the robust performance problem in general, and, in particular, for the robust complimentary sensitivity problem. The so-called QFT bounds can be computed in a closed-form from these quadratic inequalities.
Analysis of Induction Plasma Deposition Dynamics for Control
Authors: Narendra K. S. , Smith C. W. , Gevelber M. A.
Published: February 2008

Plasma torches are used in a variety of different applications including forming corrosion and wear resistant coatings, near net shape manufacture, and production of metal matrix composites. The dynamics of a low order nonlinear dynamic model of the process are analyzed to obtain insight into developing an appropriate control structure.
Vibration Control Experiment of a Slewing Flexible Beam
Authors: Liu Y. C. , Yang S. M.
Published: February 2008

Two high-authority control/low-authority control algorithms are presented and experimentally validated on a fast slewing beam system. The first one termed the constrained motion method in two-stage (CMM-TS) accomplishes the rigid-body motion control and the optimal control of vibration suppression by a stepping motor. Another termed the constrained motion method in combination (CMM-CO) combines both the optimal control from stepping motor and active damping control from piezoelectric actuator for vibration suppression. Experimental results show that these algorithms are concise in formulation, efficient in hardware realization, and effective in vibration suppression.
A Quantitative Investigation of Structure-Function Relationships in a Tendon Fascicle Model
Authors: Derwin K. A. , Soslowsky L. J.
Published: February 2008

These studies sought to investigate quantitative relationships between the complex composite structure and mechanical properties of tendon. The isolated mouse tail tendon fascicle was chosen as an appropriate model for these so-called “structure-function” investigations. Specifically, collagen fibril diameters and mechanical properties were measured in fascicles from immature (3 week) control, adult (8 week) control, and adult (8 week) Mov13 transgenic mice. Results demonstrated a moderate correlation between mean fibril diameter and fascicle stiffness (r = 0.73, p = 0.001) and maximum load (r = 0.75, p < 0.001), whereas a weak correlation with fascicle modulus (r = 0.39, p = 0.11) and maximum stress (r = 0.48, p = 0.04). An analysis of pooled within-group correlations revealed no strong structure-function trends evidenced at the local or group level, indicating that correlations observed in the general structure-function analyses were due primarily to having three different experimental groups, rather than significant correlations of parameters within the groups.
Dynamic Contact of the Human Fingerpad Against a Flat Surface
Authors: Pawluk D. T. V. , Howe R. D.
Published: February 2008

This paper investigates the dynamic, distributed pressure response of the human fingerpad in vivo when it first makes contact with an object. A flat probe was indented against the fingerpad at a 20 to 40 degree angle. Ramp-and-hold and sinusoidal displacement trajectories were applied to the fingerpad within a force range of 0–2 N. The dynamic spatial distribution of the pressure response was measured using a tactile array sensor. Both the local pressure variation and the total force exhibited nonlinear stiffness (exponential with displacement) and significant temporal relaxation. The shape of the contact pressure distribution could plausibly be described by an inverted paraboloid. A model based on the contact of a rigid plane (the object) and a linear viscoelastic sphere (the fingerpad), modified to include a nonlinear modulus of elasticity, can account for the principal features of the distributed pressure response.
Interrelation of Creep and Relaxation: A Modeling Approach for Ligaments
Authors: Lakes R. S. , Vanderby R.
Published: February 2008

Experimental data (Thornton et al., 1997) show that relaxation proceeds more rapidly (a greater slope on a log-log scale) than creep in ligament, a fact not explained by linear viscoelasticity. An interrelation between creep and relaxation is therefore developed for ligaments based on a single-integral nonlinear superposition model. This interrelation differs from the convolution relation obtained by Laplace transforms for linear materials. We demonstrate via continuum concepts of nonlinear viscoelasticity that such a difference in rate between creep and relaxation phenomenologically occurs when the nonlinearity is of a strain-stiffening type, i.e., the stress-strain curve is concave up as observed in ligament. We also show that it is inconsistent to assume a Fung-type constitutive law (Fung, 1972) for both creep and relaxation. Using the published data of Thornton et al. (1997), the nonlinear interrelation developed herein predicts creep behavior from relaxation data well (R ≥ 0.998). Although data are limited and the causal mechanisms associated with viscoelastic tissue behavior are complex, continuum concepts demonstrated here appear capable of interrelating creep and relaxation with fidelity.
A Validated Three-Dimensional Computational Model of a Human Knee Joint
Authors: Li G. , Gil J. , Kanamori A. , Woo S. L.-Y.
Published: February 2008

This paper presents a three-dimensional finite element tibio-femoral joint model of a human knee that was validated using experimental data. The geometry of the joint model was obtained from magnetic resonance (MR) images of a cadaveric knee specimen. The same specimen was biomechanically tested using a robotic/universal force-moment sensor (UFS) system and knee kinematic data under anterior-posterior tibial loads (up to 100 N) were obtained. In the finite element model (FEM), cartilage was modeled as an elastic material, ligaments were represented as nonlinear elastic springs, and menisci were simulated by equivalent-resistance springs. Reference lengths (zero-load lengths) of the ligaments and stiffness of the meniscus springs were estimated using an optimization procedure that involved the minimization of the differences between the kinematics predicted by the model and those obtained experimentally. The joint kinematics and in-situ forces in the ligaments in response to axial tibial moments of up to 10 Nm were calculated using the model and were compared with published experimental data on knee specimens. It was also demonstrated that the equivalent-resistance springs representing the menisci are important for accurate calculation of knee kinematics. Thus, the methodology developed in this study can be a valuable tool for further analysis of knee joint function and could serve as a step toward the development of more advanced computational knee models.
Robust Composite Control for Singularly Perturbed Systems With Time-Varying Uncertainties
Authors: Chen Y. H. , Chen J. S.
Published: February 2008

A two-time-scale linear system with uncertain time-varying parameter is to be stabilized. A class of robust composite controls is proposed. The control renders the system practically stable regardless of the true value of the parameter. The control scheme consists of linear and nonlinear parts. The linear part is designed via a two-level optimization setting. No matching condition is needed for the linear control. The nonlinear part is of continuous saturation type. Matching condition is needed for the nonlinear control. However, it can be achieved by choosing the boundary layer model appropriately.
A New Matching Condition for Nonlinear Robust Control Design
Authors: Chen Y. H.
Published: February 2008

We study the control design problem for uncertain nonlinear systems. A new matching condition is presented. The main idea is to explore the route through which the (worst case) uncertainty may affect the stability. This route is then used to establish the new matching condition. Compared with the previous case, the current matching condition prescribes the route nonlinearly while the early matching condition is a special case of the linear description. A class of robust controls, which guarantees practical stability, can be designed based on this new matching condition. The size of the uniform ultimate boundedness ball can be made arbitrarily small by an appropriate choice of a design parameter.
Robust Tool Wear Estimation With Radial Basis Function Neural Networks
Authors: Elanayar Sunil , Shin Yung C.
Published: February 2008

In this paper, a unified method for constructing dynamic models for tool wear from prior experiments is proposed. The model approximates flank and crater wear propagation and their effects on cutting force using radial basis function neural networks. Instead of assuming a structure for the wear model and identifying its parameters, only an approximate model is obtained in terms of radial basis functions. The appearance of parameters in a linear fashion motivates a recursive least squares training algorithm. This results in a model which is available as a monitoring tool for online application. Using the identified model, a state estimator is designed based on the upperbound covariance matrix. This filter includes the errors in modeling the wear process, and hence reduces filter divergence. Simulations using the neural network for different cutting conditions show good results. Addition of pseudo noise during state estimation is used to reflect inherent process variabilities. Estimation of wear under these conditions is also shown to be accurate. Simulations performed using experimental data similarly show good results. Finally, experimental implementation of the wear monitoring system reveals a reasonable ability of the proposed monitoring scheme to track flank wear.
Integrated Structure/Control Design of High Speed Flexible Robots Based on Time Optimal Control
Authors: Rai Sudhendu , Asada Haruhiko
Published: February 2008

This paper presents the integrated structure/control design of high speed single link robots based on time-optimal control and finite element analysis. First, the solutions of a time optimal control problem are analyzed with respect to the arm link inertia and its structural flexibility. A new technique is developed to further reduce the optimal traveling time by redesigning the arm structure through the trade-off analysis between the arm inertia and its natural frequency. In the latter half of the paper, the design criterion is extended to multiple indices by considering residual vibrations, load bearing capacity and other design constraints. For suppressing residual vibrations, a simple feedback control is designed and its dynamic performance with respect to pole-zero locations is improved along with other criteria through mechanical structure modification. The finite element method is used as a modeling tool and the shape of the arm geometry is modified as design parameters. An arm is designed which performs much better as compared to the design which is done without considering the interactions between physical structure and control. The newly designed arm is tested by constructing an experimental setup. The results show significantly improved performance.
Frequency Domain Control of Flexible Beams With Piezoelectric Actuator
Authors: Yang S. M. , Liu Y. C.
Published: February 2008

One of the challenges in structural control is to apply successfully the control law derived from a discrete, reduced-order model to the engineering system of much higher order. Spillover associated with discrete system modeling has been known to lead to closed loop system instability. This paper presents a frequency domain stability criterion for the high/low-authority controller design of flexible beam systems in distributed parameter model. It is shown that the poles of a slewing beam system can be categorized in two groups: one from those of a cantilever beam and the other from those of a high-authority control slewing beam. Stability analysis can thus be conducted in each group independently. Application of piezoelectric actuator is shown to be effective in the vibration control of a slewing beam system. Neither distributed sensing/estimation nor functional gain calculation is required. Furthermore, the spillover problem can be prevented.
On the Stability of Integral Force Control in Case of Contact With Stiff Surfaces
Authors: Ferretti G. , Magnani G. , Rocco P.
Published: February 2008

In this paper the robustness properties of explicit force control with respect to contact stiffness are investigated, considering different control laws applied to an industrial robot affected by joint compliance. A theoretical analysis, performed on the well-known linear fourth-order model of a single joint robot interacting with the environment, shows that, differently from the case of P or PD control, integral control ensures increasing stability with increasing contact stiffness. This result is believed new. In particular, it is shown that through the adoption of an integral control law, force control is actually feasible even in the case of an infinitely stiff environment, which is a quite common situation in real industrial applications (metal working, deburring, etc.). It is also shown that the adoption of a feedback on motor velocity can greatly widen the range of the stabilizing integral gains as well as the achievable bandwidth. Experimental results, obtained with the industrial robot SMART 3S, are provided in order to substantiate the theoretical analysis.
Well-Conditioned Observer Design for Observer-Based Monitoring Systems
Authors: Huh Kunsoo , Stein J. L.
Published: February 2008

Observer-based monitoring systems for machine diagnostics and control are receiving increased attention. These observer techniques can estimate process and machine variables from inexpensive, easy to install remote sensors based on state-space models of the machine structure between the machine variables of interest and the location of the remote sensors. Unfortunately, these observers can be ill-conditioned and this leads to poor performance. The authors have previously shown that observer performance can be represented by a single performance index, the condition number of the eigensystem of the state observer matrix and that there exists an upper bound for the index in non-normal matrices and the bound can be determined by the structure and eigenvalues of the observer matrix. In this paper, a design methodology for synthesizing well-conditioned observers is proposed based on the upper bound of the performance index. The methodology is based on the fact that a small upper bound guarantees small values of the performance index. A well-conditioned matrix form is defined and a block-by block design strategy to produce a well-conditioned observer matrix is presented. A complete design procedure for well-conditioned deterministic state observers is given for the single-output case. The design strategy is illustrated with an example that shows that the proposed well-conditioned observer performs much better than an observer designed with traditional pole placement techniques.
Time Domain State Space Identification of Structural Systems
Authors: Liu Ketao , Miller David W.
Published: February 2008

An integrated time domain state space identification technique for structural systems is presented. This technique integrates the Observability Range Space Extraction identification algorithm, Balanced Realization model reduction algorithm, and Least Square model updating algorithm to generate low order and highly accurate state space models for structural systems based upon time domain data. The algorithms are integrated in such a manner that the Observability Range Space Extraction identification algorithm is used to generate an initial overparameterized state space model and then the Balanced Realization model reduction and Least Square model updating algorithms are used to iteratively reduce and update the model to achieve minimum prediction errors in time domain. We shall present the Observability Range Space Extraction identification algorithm and the Least Square model updating algorithm and discuss the integrated identification technique. The MIT Middeck Active Control Experiment (MACE) is used as an application example. MACE is an active structure control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this technique will be discussed.
Measures of Robustness for Uncertain Time-Delay Linear Systems
Authors: Oucheriah Said
Published: February 2008

Several delay-dependent criteria to test the stability of time-delay systems that were proposed require solving the Lyapunov matrix equation. This can be a troublesome task and often nontrivial. In this note, a delay-dependent sufficient condition that guarantees the robust stability of linear uncertain time-delay systems is presented. The stability test criterion derived in this paper is based on induced norms and matrix measures. The salient feature of the result obtained is its simplicity and ease in testing the robust stability of uncertain time-delay linear systems.
Noncollocated Feedback for the Control of Elastic Structures With Friction in the Actuators
Authors: Richter K.
Published: February 2008

Investigated are PID-type controllers that use noncollocated sensory feedback for damping vibrations of elastic structures with high friction in the actuators. Based on a two-degree-of-freedom spring-mass system, it is demonstrated how the control-lability of such systems can be considerably improved by feedback of noncollocated measurements. Friction in the actuators leads to undamped, residual vibrations that cannot be controlled because the occurring forces do not suffice to overcome static friction. The boundaries of this uncontrollable domain are derived in the state space. A positive feedback of noncollocated sensory signals renders a stronger coupling of the motions of the actuators to structural deformations, resulting in a considerable reduction of the amplitudes of uncontrollable vibrations. Additionally, steady state errors can be significantly reduced because higher controller gains can be realized. It is shown that the time behavior of the deformations of an elastic structure can be predicted in good approximation by a linear model that neglects friction if the proposed controller is used.
Estimating In-Cylinder Precombustion Mixture Temperatures Using Acoustic Resonances
Authors: Carryer J. E. , Roy R. H. , Powell J. D.
Published: February 2008

The air-fuel ratio of automotive engines during the warm-up period is difficult to control and contributes a substantial portion of the emissions on the EPA test cycle. High bandwidth estimation of the in-cylinder charge temperature provides opportunities for improvement in spark ignition (SI) engine control algorithms. Pressure sensor based algorithms for estimating air-fuel ratio (AFR) have been shown to be improved by bulk temperature information. This paper explores the suitability of using acoustic resonances to estimate charge temperature in the presence of an unknown AFR and without the ‘sharp’ excitation of diesel or knocking SI combustion. A technique that allows for the estimation of the precombustion average bulk charge temperature during a 1-2 ms interval based on acoustic resonance data gathered from a pressure transducer is described. A parameter estimation algorithm suitable for extracting the required frequency information from short data sets is identified. The variation in temperature estimates as a function of AFR has been explored using a computer simulation that accounts for the change in the ratio of specific heats with changing mixture strength. The performance of the acoustic resonance based temperature estimates has been evaluated by comparing them to predictions based on a polytropic compression.
LQR for State-Bounded Structural Control
Authors: Chuang C.-H. , Wu D.-N. , Wang Q.
Published: February 2008

In order to prevent structural damages, it is more important to bound the vibration amplitude than to reduce the vibration energy. However, in the performance index for linear quadratic regulator (LQR), the instantaneous amplitude of vibration is not minimized. An ordinary LQR may have an unacceptable amplitude at some time instant but still have a good performance. In this paper, we have developed an LQR with adjustable gains to guarantee bounds on the vibration amplitude. For scalar systems, the weighting for control is switched between two values which give a low-gain control when the amplitude is inside the bound and a high-gain control when the amplitude is going to violate the given bound. For multivariable systems, by assuming a matching condition, a similar controller structure has been obtained. This controller is favored for application since the main structure of a common LQR is not changed; the additional high-gain control is required only if the vibration amplitude fails to stay inside the bound. We have applied this controller to a five-story building with active tendon controllers. The results show that the largest oscillation at the first story stays within a given bound when the building is subject to earthquake excitation.
Selecting the Performance Weights for the μ and H∞ Synthesis Methods for SISO Regulating Systems
Authors: Franchek M. A.
Published: February 2008

Presented in this paper is a method in which the performance weights W1(s) and W2(s) of the robust performance problem and the H∞ optimization problem can be chosen to directly enforce hard time domain constraints. The class of systems addressed are single-input-single-output (SISO) regulating systems required to maintain the output within a prespecified time domain tolerance despite (i) plant uncertainty, (ii) an external step disturbance, and (iii) actuator output saturation. The performance weights are extracted from the feedback configuration and facilitate performance maximization.
Function Space BFGS Quasi-Newton Learning Algorithm for Time-Varying Recurrent Neural Networks
Authors: Yan Lilai , Li C. James , Huang Tung-Yung
Published: February 2008

This paper describes a new learning algorithm for time-varying recurrent neural networks whose weights are functions of time instead of scalars. First, an objective functional that is a function of the weight functions quantifying the discrepancies between the desired outputs and the network’s outputs is formulated. Then, dynamical optimization is used to derive the necessary conditions for the extreme of the functional. These necessary conditions result in a two-point boundary-value problem. This two-point boundary-value problem is subsequently solved by the Hilbert function space BFGS quasi-Newton algorithm, which is obtained by using the dyadic operator to extend the Euclidean space BFGS method into an infinite-dimensional, real Hilbert space. Finally, the ability of the network and the learning algorithm is demonstrated in the identification of three simulated nonlinear systems and a resistance spot welding process.
Time-Energy Optimal Control of Articulated Systems With Geometric Path Constraints
Authors: Shiller Zvi
Published: February 2008

The motions of articulated systems along specified paths are optimized to minimize a time-energy cost function. The optimization problem is formulated is a reduced two-dimensional state space and solved using the Pontryagin maximum principle. The optimal control is shown to be smooth, as opposed to the typically discontinuous time optimal control. The numerical solution is obtained with a gradient search that iterates over the initial value of one co-state. Optimal trajectories are demonstrated numerically for a two-link planar manipulator and experimentally for the UCLA Direct Drive Arm. The smoother time-energy optimal trajectory is shown to result in smaller tracking errors than the time optimal trajectory.