Capacitive vs piezoresistive MEMS gyroscopes: a theoretical and experimental noise comparison

AbstractThis work aims both at theoretically formalizing a comparison between piezoresistive (PZR) and capacitive (CAP) gyroscopes in terms of resolution limits, and at validating the predictions through experimental measurements on MEMS devices of both types. As predicted by the developed theory, PZR gyroscopes, well immune to parasitic capacitances and void of feedback resistance noise, show 10-fold better angle random walk (ARW) than CAP gyroscopes for the same nominal mode-split value, the same drive-motion amplitude and the same electronic noise density

APPROXIMATION OF HYSTERESIS DENSITY FUNCTION IN STRETCH SENSOR

Stretch SensorTM developed by Images Scientific Instruments Inc, USA, is a unique polymer component that changes resistance when stretched. When sensor is stretched and released it exhibits hysteresis and large relaxation time. For identification of hysteresis and relaxation, Preisach model is a very well-known method. Experiments are carried out using tension tester and the experimental data is used for identification. Modified Preisach model is used for relaxation identification and the experimental data is discretized for analysis of relaxation. Identification is based on first reversal curve of major hysteresis loop and noise error of sensor. It has been observed that if sensor is used in pre-stretch conditions, relaxation time is reduced. Also more the iterations of stretch, hysteresis is reduced and sensor output error is also reduced. Hysteresis and relaxation time cannot be eliminated because they are inherent properties of polymer but can be compensated under specific conditions. Compensation is useful for calibration of the sensor

Study and Design of a Multi-range Programmable Sensor for Temperature Measurement

In this paper, a wide-range high-precision sensor has been designed in order to accurately measure the temperature in a medium with arbitrary temperature variation and the implementation of a wide-spectrum temperature measurement system with a self-selected multi-sensor has been realized. This multi-sensor core is made up of different sensors combined to measure different temperature ranges. This concept can be used for high-precision temperature measurement in electrical capacitance tomography applications. The proposed technique is well suited for temperatures in boilers, industries, and everywhere high temperature measurement sensitivity is needed by using different combined temperature sensors of high precision

Improvements to a Thermally Actuated MEMS Viscosity Sensor

Being able to measure and monitor the viscosity of a fluid accurately and in real-time can provide insights and prevent field failures of lubricated mechanical elements. A micro electro mechanical system (MEMS) viscosity sensor that measures the properties of liquids through thermal vibrations of a silicon membrane has been previously developed. The device measures viscosity through three different characteristics: the frequency, amplitude and the quality factor of the vibrating membrane. The membrane is actuated via a short pulse of heat delivered by the heater resistor provided by an external voltage. The pulse width is controlled by a waveform generator and a power MOSFET. The movement of the membrane is measured with an in-situ piezoresistor Wheatstone bridge, which is powered by an external voltage source, and amplified with and instrumentational amplifier before the resulting vibrating signal is analyzed in LabView. The end goal of this work is to characterize the sensitivity and real-time response of a thermally actuated MEMS viscosity sensor. In addition, a process modification to include a deep reactive ion etch instead of a KOH etch, has been developed. As viscosity is dependent on temperature, when the membrane is actuated by heat, the effects of locally changing the fluid temperature will affect the sensitivity of the sensor. Optimized test bias condition results were, Wheatstone bridge bias voltage when increased over 7 V, the natural frequency of vibration of the sensor is modified. Pulse width and heater bias value can be adjusted for optimum sensor response. With these established bias conditions, the real-time response of the system was investigated. Epoxy was used to cover the sensor perimeter, protect the 25 - micron aluminum wire bond connections to a copper PCB and to glue the sensor onto the PCB. Test result show a spike in frequency and amplitude when different oils were added. As shown with additional tests, the spike is mainly caused by slight temperature variations that are introduced with new oil and how they affect the sensor packaging. Spikes were reduced by lowering the bridge bias voltage from 7 V to 3 V, which minimized the sensor heating. Furthermore, addition of oil in very small quantities, in the µL range, reduced the changes in temperature. Figure 1 shows frequency and amplitude response with varying viscosities without agitation. During testing, when oil is added, the amplitude shows an immediate overdamped response which takes about 1-2 minutes to stabilize, whereas frequency is characterized by an underdamped response with response time 5-7 minutes. Frequency response time was slower as it is very dependent on intrinsic stresses of both sensor and packaging, whereas amplitude of oscillations seems to be more independent to these properties changing and shows faster response

ExoBike : mechanical component development

Muitas das vezes o processo de reabilitação é monótono e desmotivador devido à repetibilidade dos exercícios e falta de feedback ou ferramentas que permitam avaliar o progresso. Assim, tendo em conta que o exercício de bicicleta é muito utilizado para a reabilitação dos membros inferiores, foi criado o projeto ExoBike. De modo a combater tais fatores, a ExoBike consiste numa bicicleta equipada com sensores de força nos principais pontos de interação entre bicicleta e paciente. Assim é possível adquirir dados importantes para avaliar o progresso do paciente, bem como estabelecer metas e ajustar os exercícios conforme as necessidades do paciente. Alem desta componente de aquisição de dados, o projeto ExoBike engloba ainda uma vertente de realidade virtual, que junta com a componente de aquisição de dados, proporciona ao paciente uma experiência mais imersiva, tornando assim a prática de exercício para reabilitação mais divertida e motivadora. Este documento foca-se no desenvolvimento dos dispositivos mecânicos instalados na bicicleta para a aquisição dos dados do paciente. Para tal foi desenvolvido um selim capaz de analisar a postura do paciente, um guiador que caracteriza a força que o paciente realiza com os membros superiores, uns pedais capazes de analisar o movimento de pedalada e uns punhos que adquirem a força de preensão que o paciente é capaz de efetuar. Sendo que as metodologias de aquisição de dados dos dispositivos se baseiam em células de carga, extensometria elétrica por resistência e inteligência artificial. Os dispositivos foram desenvolvidos e otimizados com recurso a programas de desenho computacional, analisados através de métodos numéricos e analíticos, ensaiados através de prototipagem rápida com impressão 3D e produzidos com recurso a máquinas de fabrico subtrativo com controlo numérico. De modo a garantir o correto funcionamento dos dispositivos, estes foram sujeitos a uma serie de calibrações e testes funcionais com grupos de 3, 5 e 31 voluntários para corroborar as metodologias adotadas e avaliar as capacidades das mesmas. Sendo que os dipositivos indicaram uma correlação de 0.7, entre a postura do voluntario e a sua altura, e uma correlação elevada de 0.9 entre a massa do voluntario e a força exercida pelos membros inferiores. Entre outro tipo de correlações, os dipositivos foram ainda capazes de determinar, com uma fiabilidade 95%, o efeito de recalcamento psicológico quando os voluntários foram sujeitos a uma reação de defesa induzida nos membros inferiores. Considerando assim, que as metodologias e dispositivos desenvolvidos se encontram mais do que aptos para o objetivo pretendido de avaliação e monitorização do processo de reabilitação dos membros inferiores com recurso a bicicleta estátic

Design, simulation, and fabrication of a flow sensor for an implantable micropump

The design, simulation, and fabrication of a flow sensor to be integrated into an implantable micropump is presented. The flow sensor operates by the method of thermal anemometry, in which heat is dissipated from a resistive element held in the flow of the fluid. The rate at which heat is carried away is dependent on the flow rate and is directly related to the thermal conductance. A control circuit utilizing the constant-temperature anemometry mode of operation is used to generate a change in voltage in response to change in thermal conductance, and subsequently, flow rate. A mathematical expression describing the sensor sensitivity based on thermal effects is proposed, based on the thermal spreading resistance and basic heat transfer laws. The mathematical model is refined using finite-element analysis, and a complete formulation for the effect of sensor area, length-to-width ratio, and fluid velocity on thermal spreading resistance is determined. The refined thermal spreading conductance equation can be used to replace assumptions made in initial mathematical analysis. An original fabrication process is presented and investigated, in which a p-doped polysilicon bridge is encapsulated in silicon oxide and silicon nitride using surface micromachining techniques. A sacrificial polysilicon layer and KOH etching are used to form half of the complete fluid channel in the bulk of the silicon wafer. When the fluid channel is sealed with a complementarily etched wafer, the sensor bridge is situated in the middle of the fluid channel, optimally placed for maximum sensitivity. The fabrication process yields functional sensor bridges, with even the most fragile sensor shape withstanding the process

Sensorized Tools for Haptic Force Feedback in Computer Assisted Surgery

Structural engineerin

A biologically inspired joint model using engineering methods to enhance understanding of muscle activity

Compliant actuators and control methods have been known to exhibit similarities in human musculoskeletal systems. In order to better understand and improve the effects of force optimization under closed- loop conditions, a physical joint model was constructed with an agonist and an antagonist muscle operating under linear control. Utilizing LabVIEW software, compliant McKibben air muscles and Merlin stretch sensors, the author was able to incorporate a Bang-Bang controller and propose the inclusion of pulse width modulation (PWM) as well as a Proportional-Integral-Derivative (PD) controller to study the reflex loops under various levels of feedback sensitivity. The feedback mechanism, similar to proprioceptive muscle spindle feedback, will be based on the input given from the stretch sensors to achieve a desired movement. Motions are controlled by the Central Nervous System (CNS). Demonstration of an open-loop muscle model working in conjunction with an inertial system would be extremely difficult. However, understanding the control process of a muscle can be demonstrated through the closed-loop control method. This was accomplished by constructing a linear bang-bang controlled computer program to simulate a musculoskeletal model that incorporates proprioceptive feedback. Simulink software was also utilized to show how the damping and stiffness coefficients, as in human muscle spindle and Golgi Tendon Organ feedback loops, can be adjusted to optimize stability

Characterization of a Low-Cost Millinewton Force Sensor for Ionic Polymer Metal Composite Actuators

Ionic polymer-metal composites (IPMCs) have become an area of interest in the past decade for their unique properties as actuators. Conventional IPMCs require the use of rare earth metals for electrodes making the fabrication of these materials expensive, time consuming to produce, and not suitable for large scale manufacturing. Due to the low actuational forces, in the millinewton scale, characterization of IPMCs is costly and often requires expensive force sensors and data acquisition (DAQ) systems. This thesis explores the capabilities of a low cost, two dimensional millinewton force sensor fabricated out of nitinol #1 wire and orthogonally mounted strain gauge pairs in half bridge configurations. An Arduino microcontroller based DAQ system and a modular test stand were developed to facilitate calibration of the force sensor and testing of IPMCs. The overall system cost, approximately $200 USD, was able to achieve a force resolution of 0.49 mN. Calibration of the force sensor was accomplished gravimetrically and the data was processed in an Arduino-LabVIEW™ interface. An ionic polymer-carbon composite (IPCC) fabrication concept was also developed that utilizes buckypaper (BP) electrodes, electrospun nanofibrous Nafion mats, and EMI-Tf ionic liquid for hydration. The IPCC concept has the potential to achieve faster actuation rates, larger deflections, and longer operations in air compared to IPMCs. The IPCC fabrication process developed takes a fraction of the time compared to conventional IPMC fabrication and can be applied to IPMC fabrication for production on an industrial scale