Load Reconstruction Technique UsingD-Optimal Design and Markov Parameters

This paper develops a technique for identifying dynamic loads acting on a structure based on impulse response of the structure, also referred to as the system Markov parameters, and structure response measured at optimally placed sensors on the structure. Inverse Markov parameters are computed from the forward Markov parameters using a linear prediction algorithm and have the roles of input and output reversed. The applied loads are then reconstructed by convolving the inverse Markov parameters with the system response to the loads measured at optimal locations on the structure. The structure essentially acts as its own load transducer. It has been noted that the computation of inverse Markov parameters, like most other inverse problems, is ill-conditioned which causes their convolution with the measured response to become quite sensitive to errors in system modeling and response measurements. The computation of inverse Markov parameters (and thereby the quality of load estimates) depends on the locations of sensors on the structure. To ensure that the computation of inverse Markov parameters is well-conditioned, a solution approach, based on the construction ofD-optimal designs, is presented to determine the optimal sensor locations such that precise load estimates are obtained.

An Inverse Approach on Load Identification From Optimally Placed Accelerometers

This paper presents an inverse approach for estimating dynamic loads acting on a structure from acceleration time response measured experimentally at finite number of optimally placed accelerometers on the structure. The structure acts as its own load transducer. The approach is based on the standard equilibrium equation of motion in modal coordinates. Modal model of a system is defined by its modal parameters — natural frequencies, corresponding mode shapes and modal damping factors. These parameters can be estimated experimentally from measured data, analytically for simple problems, or from finite element method. For measurement of the acceleration response, there can be a large number of combinations of locations on the structure where the accelerometers can be mounted and the results may be quite sensitive to the locations selected for accelerometer placements. In fact, the precision with which the applied loads are estimated from measured acceleration response depends on the number of accelerometers utilized and their location on the component. Implementation of a methodology to determine the optimum set of accelerometer locations, based on the construction of D-optimal design, is presented to guide the selection of number and locations of accelerometers that will provide the most precise load estimates. A technique based on model reduction is proposed to reconstruct the input forces accurately. A numerical validation that helps to understand the main characteristics of the proposed approach is also presented. The numerical results reveal the effectiveness and utility of the technique.

Examination of Knee Joint Moments on the Function of Knee-Ankle-Foot Orthoses During Walking

The goal of this study was to investigate clinically relevant biomechanical conditions relating to the setup and alignment of knee-ankle-foot orthoses and the influence of these conditions on knee extension moments and orthotic stance control during gait. Knee moments were collected using an instrumented gait laboratory and concurrently a load transducer embedded at the knee-ankle-foot orthosis knee joint of four individuals with poliomyelitis. We found that knee extension moments were not typically produced in late stance-phase of gait. Adding a dorsiflexion stop at the orthotic ankle significantly decreased the knee flexion moments in late stance-phase, while slightly flexing the knee in stance-phase had a variable effect. The findings suggest that where users of orthoses have problems initiating swing-phase flexion with stance control orthoses, an ankle dorsiflexion stop may be used to enhance function. Furthermore, the use of stance control knee joints that lock while under flexion may contribute to more inconsistent unlocking of the stance control orthosis during gait.

Input Force Identification in Time Domain Using Optimally Placed Accelerometers

A technique in time domain is presented that aims at identifying dynamic loads acting on a structure from acceleration time response measured experimentally at finite number of locations on the structure. The structure essentially gets transformed into its own load transducer. The approach is based on the standard equilibrium equation in dynamics in time domain. For measurement of the acceleration response, there can be a large number of combinations of locations on the structure where the accelerometers can be mounted and the recovered loads may be quite sensitive to the locations selected for accelerometer placements. In fact, the precision with which the applied loads are estimated from measured acceleration response depends on the number of accelerometers utilized and their locations on the component. Implementation of a methodology to determine the optimum set of accelerometer locations, based on the sparse nature of the mass, damping and stiffness matrices, is presented to guide the selection of number and locations of accelerometers that will provide the most precise load estimates. A numerical validation that helps understand the main characteristics of the proposed approach is also presented. The numerical results reveal the effectiveness and utility of the proposed technique.

The Experiments Study of Polishing Characteristics during Polishing Process

The investigation of experiment becomes more important to increase the understanding of polishing performance. In this paper, a high precision polishing process test bench with in-situ measurement technology was applied to investigate the effects of operating parameters on polishing interfacial phenomena during mechanical polishing with IC1000 pad. The shear force and temperature rise were measured for stainless steel during mechanical polishing process. The surface temperature was measured by T-type thermocouples and the shear force was measured by a load transducer. The shear force for various particle size, applied load and rotation speeds during polishing process was demonstrated. Furthermore, the temperature rise under different slurry concentration was investigated. The experimental results contribute to the understanding of polishing mechanism and also provide an index to end-point-detection.

Load Transducer Design Using Inverse Method With Model Reduction

This paper presents an inverse approach for estimating time varying loads acting on a structure from experimental strain measurements using model reduction. The strain response of an elastic vibrating system is written as a linear superposition of strain modes. Since the strain modes as well as the normal displacement modes are intrinsic dynamic characteristics of a system, the dynamic loads exciting a structure are estimated by measuring induced strain fields. The accuracy of estimated loads is dependent on the placement of gages on the instrumented structure and the number of retained strain modes from strain modal analysis. A solution procedure based on construction of D-optimal design is implemented to determine the optimum locations and orientations of strain gages. An efficient approach is proposed which makes use of model reduction technique, resulting in significant improvement in the dynamic load estimation. Validation of the proposed approach through a numerical example problem is also presented.

Effect of Shear and Thermal Characteristics on Chemical Mechanical Polishing

Chemical mechanical polishing has been widely used to achieve global planarization of wafers. In this paper, an improved designed test rig is used to acquire the signals on chemical mechanical polishing. The shear force and temperature-rise are measured during chemical mechanical polishing process. The polishing temperature is measured by T-type thermocouples screwed behind the polishing interface of the carrier. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head. The parameters including down force, rotation speed, particle size and volume flow rate of slurry are investigated. The experimental results provide a good index to end-point-detection. The theoretical simulation by the average lubrication equation coincides with the experimental results. This study contributes to the understanding of chemical mechanical polishing mechanism.

Thermal and Shear Characteristics Study of Various Mechanical Polishing Materials

Mechanical polishing is a primary technique for planarization of material surface in manufacture fabrication. Because the theoretical polishing mechanism is inadequately understood and because higher levels of polishing performance are desired, the investigation of experiment becomes more important. In this paper, a high precision polishing machine has established. With an improved design, a test rig can be easily used to simulate the mechanical polishing process and acquire the signals of polishing. The temperature-rise and shear force are measured for three different materials (i.e. copper, aluminum and silicon wafer) during mechanical polishing process. For the self-design test rig in the mechanical polishing process, its surface temperature is measured by T-type thermocouples screwed behind the polishing interface of the carrier. And shear force is measured by a load transducer mounted on the lever and connected with the polishing head. Furthermore, the roughness and particle size effects during polishing are demonstrated. The experimental results not only provide a good index to end-point-detection, but also increase the understanding of mechanical polishing process.