A Prognostics Model for Detecting the

A Prognostics Model for Detecting the - 2008 INTERNATIONAL...

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2008 INTERNATIONAL CONFERENCE ON PROGNOSTICS AND HEALTH MANAGEMENT A Prognostics Model for Detecting the Irreversibility Margin of Non-Reversible Electromechanical Actuators Giovanni Jacazio, Stefano Pastorelli, and Massimo Sorli, Member, IEEE Abstract- This paper presents a prognostics model that was developed for detecting how far an inherently non-reversible ACME screw actuator is from the reversibility limit. The model makes specific reference to an actuator comprised of a dc electric motor, a gear reducer and a power screw with an ACME thread converting rotary into linear motion, but it could be adapted to different actuators configurations. The prognostics model is based on an algorithm that only needs the information on motor current and ambient temperature without the need of specific additional sensors. By comparing the differences between the motor electric currents for two different directions of actuator motion, and fusing that information with those ofthe components physical characteristics while taking into account the temperature effects, it is possible to detect a decrease of the irreversibility margin and generate an alert when such margin becomes dangerously low. Index Terms- Electromechanical actuator, irreversibility, non-reversible actuator, prognostics algorithm, screw actuator. I. NON-REVERSIBLE ACTUATORS Many actuation systems are required to be non-reversible, which means that they must operate upon receiving a command from their controller, but remain stationary while subjected to the external loads when no command is given. Non-reversible actuation systems are found in several applications: hoists, parking brakes and secondary flight controls are some examples of systems using non-reversible actuators. The irreversibility function can be obtained in three different ways. A frrst solution is to provide the actuation system with a brake which is engaged when no command is given to the motor; electric motors often include a brake that is normally engaged and it is released when supply voltage is applied. Similarly, actuation systems powered by hydraulic motors can be equipped with a pressure-off brake. A second solution is to fit a no-back device into the actuator; the no- back device is released when driven by the motor, thereby allowing the mechanical power flow from the motor to the G. Jacazio is with the Department of Mechanics, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy (e-mail: giovanni.jacazio@polito.it) S. Pastorelli is with the Department of Mechanics, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy (e-mail: stefano.pastorelli@polito.it) M. Sorli is with the Department of Mechanics, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy (e-mail: massimo.sorli@POlito.it) 9778-1-4244-1936-4/08/$25.00 © 2008 IEEE load, but it automatically engages preventing an actuator blowback when the motor operation stops. A third alternative is to use actuators that are inherently non-reversible as a result
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A Prognostics Model for Detecting the - 2008 INTERNATIONAL...

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