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A Ferrofluid Servo Inertial Sensor for High Reliability and High Accuracy Measurement

IP.com Disclosure Number: IPCOM000187568D
Original Publication Date: 2009-Sep-25
Included in the Prior Art Database: 2009-Sep-25
Document File: 6 page(s) / 183K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Inclination and acceleration of dynamic and continuous measurement in high-speed objects, such as cars, trains, or aircrafts, require inertial sensors with high accuracy and high reliability. The open-loop inertial sensors with compact structure and low cost are applied in a wide variety of industrial and research environments. However, the accuracy and the robustness against shock and vibration are imperfect, especially in spring-and-mass inertial sensor. Each element of the open-loop sensor contributes the total measurement error. Both the spring of the coefficient and the pick-off scale factor change with deflection, temperature, and time, resulting in nonlinearity and repeatability. Another limitation of the open-loop sensor is the tradeoff between sensitivity and response speed. Reducing (spring stiffness) to obtain a sizeable sensitivity results in a reduction of the response speed.

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A Ferrofluid Servo Inertial Sensor for High Reliability and High Accuracy Measurement

Idea: Yanling Lin, CN-Shanghai; Zhao Hui, Ph.D., CN-Shanghai; Qiran Zhang, Ph.D., CN-Shanghai

Inclination and acceleration of dynamic and continuous measurement in high-speed objects, such as cars, trains, or aircrafts, require inertial sensors with high accuracy and high reliability. The open-loop inertial sensors with compact structure and low cost are applied in a wide variety of industrial and research environments. However, the accuracy and the robustness against shock and vibration are imperfect, especially in spring-and-mass inertial sensor. Each element of the open-loop sensor contributes the total measurement error. Both the spring of the coefficient and the pick-off scale factor change with deflection, temperature, and time, resulting in nonlinearity and repeatability. Another limitation of the open-loop sensor is the tradeoff between sensitivity and response speed. Reducing (spring stiffness) to obtain a sizeable sensitivity results in a reduction of the response speed.

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In order to promote the performances of the devices and resolve the confliction between sensitivity and response time, servo-type inertial sensor using force-balance configuration are proposed. Since the elastic suspension element's only function is to suspend and guide the inertial mass, it is designed to be as weak as possible, and its restoring force is replaced by an electromagnetic balancing force. There are some inertial sensors using servo architectonics referenced below.

An existing solution is a servo acceleration sensor comprising a pendulum assembly composed of a pendulum made up of a torque coil provided on one side of a metal plate, a free end section from which the pendulum is suspended, a base end section, alongside a pair of plate springs connecting the free end section and the base end section. It also has a permanent magnet placed away from the metal plate and a pendulum assembly support frame that supports the pendulum assembly with the base end section being secured. In addition there is also a displacement sensor that senses the displacement of the pendulum and outputs it in the form of an electric signal. Lastly it includes a sensing circuit that supplies power to the torque coil on the basis of the electric signal and thereby generates magnetic force to return the pendulum to the original position allowing it to also sense acceleration.

Generally, the servo acceleration sensor reduces the amount of open-loop sensor errors, as well as the speed limitation. However, the pair of plate springs used as the elastic suspension of the mass suffers from stability problems characteristic of the elastic elements such as residual stress and stress relief over time; dimensional change due to temperature, shock and vibration; and so forth....