Design of a miniature Servo Controller for a Flow Control Actuator in Aerospace Application

Author Name(s): Zaki Anwar, Y. Laxminarayana, J.V.Sudheendra, R.V.Naveen Kumar
Author Email: Zaki.Anwar@rcilab.in

Abstract

This paper deals with the design of a miniature servo controller for a short duty flow control actuator. The servo controller is designed for position control of the flow control actuator (FCA) with high accuracy. The flow control actuator in this application demands quick response, fine precision and compact size. The controller is required to be confined and integrated inside the FCA casing wherein space is shared along with the BLDC motor, gears assembly and position sensor. The servo controller is realized and the Tests results are meeting the specifications.

Keywords

Flow Control Actuator, BLDC motor, Servo Controller

Introduction

An actuator, in general, is a device that produces some sort of physical motion by taking energy from a source. The actuators are characterized based on their sources of energy. Hydraulic, pneumatic or electromechanical actuators are more common among others which use liquid, gas or electrical power as their energy source respectively whereas the type of motion these actuators produce can be linear, rotary or any other combination of these motions. In some aerospace vehicle applications, actuators are employed for precise control of opening of vanes for flow of gases thereby controlling the thrust as per requirement of the vehicle. The aerospace vehicle under consideration is thrust controlled by Vane of a flow control mechanism operated by an actuator. The functional block diagram of this flow control actuator (FCA) system is as shown in Fig-1.The FCA is realized as the electromechanical actuation system, owing to very narrow space constraints as shown in Fig2,.In this FCA system, the BLDC motor acts as prime mover and uses electrical energy supplied by battery to drive the vane through gear trains. Gear trains serve speed reduction and the amplification in the torque produced by the motor. The servo controller is very essential and key element of any actuation system as it controls the position of the output depending upon the input command which in turn controls the entire system. Therefore, it is ultimately in charge of entire aerospace vehicle as it closes the inner loop of control system. The servo controller sends required voltage signals to drive circuitry of the motor which are proportionate to the error between the command and the actual position of the vane sensed by the position sensor. The critical requirement of the controller is to have fast response characteristics for position command along with providing the stability. As the brushless (BLDC) dc motor lacks the brushes for commutation, it is the job of controller to execute this commutation function, so it energizes the proper phases of the motor in a sequence calculated by Hall sensors as the rotor moves. The controller implements a PWM (pulse width modulation) scheme to power the motor. The controller eventually performs the closed loop function to execute position control to suit the requirement of FCA system which demands high bandwidth and fast dynamic response.[4][6]

Conclusion

In this paper, design of a compact servo controller using L6235 for rotary actuator control is implemented. The controller IC, L6235 provides high speed PWM. It is a good solution for motor control where acute space constraints exist. The selection of PWM frequency and control logic parameters i.e. gains are critical in designing a servo controller, therefore they need be optimized through experiment. The servo controller for actuator is designed within the compact size, hardware is realized and the system is integrated and tested. The method proposed in this paper is simple and reliable. The hardware test results at no-load and load conditions under different conditions are satisfactory and hence the controller is able to meet the requirements of the servo system for aerospace application.

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