Swavik Spiewak

High Accuracy, Low-Invasive Displacement Sensor (HALIDS)

Sub-micron accuracy and precision in measuring unconstrained, spatial motion is pivotal in science and engineering. It imposes stringent requirements on the accuracy, reliability, and invasiveness of sensing devices (including lasers, lidar sensors, or optical scales). While the capabilities of these devices have seen dramatic improvements in the last decades, the needs for sub-micron accuracy, low-invasive sensors greatly outpace the available solutions. The root cause of measurement difficulties is a conflict between the very nature of motion (simultaneous translations and rotations relative to a chosen reference base) and the fundamental requirement of measurement accuracy known as the Abbe principle.Small and accurate Microsystems Technology based inertial sensors (accelerometer and gyroscopes) can alleviate, or at least significantly mitigate, many of the current difficulties. If contained in small Inertial Measurement Units (IMU) and equipped with a wireless signal transmission, they can be placed on or very close to the objects whose motion is to be measured.Furthermore, as long as the IMU, its fixture, and some region of this object around the fixture can be considered as rigid, coordinate transformation rules facilitate converting signals measured by IMU into translations and rotations of any point in this rigid region. Consequently, a virtual 6-DOF sensor can be created. Its dimensions are infinitesimally small, and it can be “placed” anywhere within the above rigid region. In particular, it can be placed such that it is collinear with the displacements of the cutting tool or robot’s end effector, and satisfies the Abbe principle.We present a High Accuracy, Low-Invasive Displacement Sensor (HALIDS) for application in manufacturing and in engineering design. The sensor is capable of measuring simultaneously 6-degrees-of-freedom displacements of objects. Its short term resolution is down to 0.1 nanometer and accuracy better than 1 micron. The sensor can be built small, light and wireless. Results from experimental evaluation of two prototype versions are presented.Copyright

Prediction of Temperature in Vacuum Arc Remelting in the Presence of Strong Disturbances

Abstract A system for predictive, noninvasive temperature measurement in a broad class of manufacturing processes is presented. The system employs a comprehensive, three-tier signal processing algorithm to achieve high accuracy and reliability in the presence of strong disturbances. Temperature estimates are generated by ‘unstructured, shallow knowledge’ based algorithms. The estimation process employs a set of robust features obtained by signal processing that involves constitutive models representing ‘deep knowledge’ about the process dealt with. The application of these models is combined with ‘structured, shallow knowledge’ based techniques. Results obtained in application to the investment casting of titanium, which employs the vacuum arc remelting (VAR) process, are presented.

A Test Setup for Evaluation of Harmonic Distortions in Precision Inertial Sensors

Steadily improving performance of inertial sensors necessitates significant enhancement of the methods and equipment used for their evaluation. As the nonlinearity of sensors decreases and gets close to that of the exciters, new challenges arise. One of them, addressed in this research, is a superposition of errors caused by the nonlinearity of tested devices with nonlinear distortions of excitation employed for experimental evaluation. This can lead to a cancellation, at least partial, of the effects of both imperfections and underestimation of the actual distortions of the evaluated sensors. We implement and analyze several system architectures and evaluate components of applicable motion generation systems from the viewpoint of satisfying the relevant, often conflicting requirements posed by the evaluation of high performance inertial sensors. Robust mechanical integration of the guidance, actuation, and measurement functions emerges as a key factor for achieving the needed quality of generated test patterns. We find precision air bearing stages, such as ABL1500 series (Aerotech) most suitable for implementing the needed experimental setup. We propose an architecture with two reciprocating stages, implement and evaluate its core components, and illustrate its performance with experimental results.

High Performance Isolation and Excitation of Vibration for Enhanced Identification of Inertial Sensors

Microsystems Technology based inertial sensors offer important advantages in low-invasive measurement of spatial motion with sub-micron accuracy. However, their successful implementation hinges upon achieving very low distortion and noise at the low end of the frequency spectrum. Therefore the investigations that lead to the enhancement of inertial sensors require environments free of the ambient vibrations to the maximum possible extent.This research focuses on developing a hybrid vibration isolation system. It comprises a custom built pre-isolation stage supporting a small size, high performance commercial vibration isolation platform. Our objective is to reduce the ambient vibrations present in typical research laboratories, usually strongly affected by the “cultural noise”, down to a level of the super quiet sites, i.e., close to the level defined by New Low Noise Model (NLNM). Performance of the developed system is illustrated with experimental results.Copyright

Vibration Rectification and Thermal Disturbances in Ultra Precision Inertial Sensors

Advanced inertial MEMS sensors facilitate achieving superb precision and resolution in measuring translational and rotational displacements, down to femtometers and milli-arcseconds. At present such performance is possible only in measurements of a very short duration, typically below 1 second. As this duration increases, the precision rapidly deteriorates. However, experimental accelerometers indicate the possibility of measurements with sub-micron precision for up to 30 seconds. For longer measurements, e.g., up to 5 minutes, the errors increase. However they still remain below 100 μm. The main cause of errors is a strong amplification of low frequency disturbances and distortions introduced by the sensors. It occurs when acceleration and angular rate are converted to the translational and angular displacement, i.e., during the integration. Thus, the key to maximizing the performance of inertial displacement sensors is a reduction of their low frequency disturbances. In the top tier sensors the key components of the disturbances include (1) the inherent thermodynamic and electrical noise, (2) chaotic mechanical phenomena, and (3) nonlinear distortion. The presented research is concerned with these three areas. It focuses on the identification and correction of errors which deteriorate a stability of the sensors’ bias, in particular on the vibration rectification error (VRE) and temperature variations due to the actuation in servo accelerometers. The investigated accelerometers are high performance sensors, digital and analog, whose total harmonic distortion is in the range from 1% down to a few parts-per-million (i.e., <0.001%). The objective is to develop on-line corrective filters capable of reducing the overall low frequency distortion below 0.00001%.Copyright

Non-invasive mapping of fluid temperature and flow in microsystems

Currently available temperature and fluid flow measurement methods have shown limitations in microscale systems. This research concerns the development of a non-invasive optical measurement technique and sensor for mapping two-dimensional temperature fields and, ultimately fluid flows. The system is based on the Shack-Hartmann wave-front sensor. Analytical considerations underlying the mapping technique and preliminary experimental results are presented. Two experimental rigs involved in this study are also discussed.

Investigation of Chaotic Dynamics in MST Based Precision Sensors

This paper is concerned with the accuracy and signal detection limits in ultra precision, Microsystems Technologies based inertial sensors. It focuses on conditions that lead to chaotic dynamics, detection of such dynamics. Development of the needed constitutive-empirical, scale-able models is presented and illustrated by example of axially preloaded microflexures. To eliminate uncertainties caused by the accumulation of numerical errors in commonly used engineering software we employ arbitrary precision computations. We detect chaotic dynamics in the investigated systems by means of Poincare map technique to show the evolution of phase space from deterministic to chaotic behavior.1 Copyright

Dynamics of Mechanically Over-Constrained Inertial Sensors

Microsystems Technology based inertial sensors offer important advantages in low-invasive measurement of spatial motion with sub-micron accuracy. Their successful implementation hinges upon achieving very low distortion and noise at the low end of the frequency spectrum. Of particular importance is the Vibration Rectification Error (VRE) — an apparent shift in the signal bias that occurs when inertial sensors are subjected to vibration. A common approach to the reduction of VRE is assuring a highly symmetrical mechanical structure of sensors. Furthermore, a low cross-axis sensitivity is desirable. In accelerometers these properties are achieved by employing multiple flexures supporting the seismic mass. However, this may lead to mechanical over-constraining and multiple local equilibria rather than a single global one. Multiple equilibria combined with the nonlinearity of flexures create conditions for chaotic behavior, which can greatly degrade the sensors’ performance. We investigate representative architectures of high performance servo accelerometers, study the impact of over-constraining, and develop comprehensive dynamic models accounting for the presence of this condition. Given the complexity of spatial motion of the proof mass and resulting deformations in the flexures, we employ computer aided generation of constitutive, symbolic and scaleable models of the investigated sensors. We illustrate analytical investigations with numerical simulations and experimental results.Copyright