Closed-loop position control system using LabVIEW

Abstract

A closed-loop DC motor control system is developed using National Instrument's (NI) data acquisition (DAQ) board (Model MIO 6040E), LabVIEW software package, and DAQ signal accessory board for smooth and accurate positioning. The motor can be rotated either clockwise (CW) or counterclockwise (CCW) as needed. A linear feedback that employs a potentiometer provides the current position of the motor. The LabVIEW software is used to develop a virtual instrument (VI) that includes a front panel and a functional diagram. The VI reads the desired position of the motor entered by the user on the front panel and the current motor position via feedback, and determines its amount and direction of rotation. A smooth cubic polynomial that is continuous and has a continuous first and second derivative is utilized to represent the angular position of the motor. The VI uses the polynomial to generate a velocity profile which in turn is converted into a voltage profile for the motor armature through a conversion formula. This conversion formula is determined through the use of motor speed-voltage characteristics obtained from laboratory experiments. Reading the motor position and sending voltage to the motor circuit are accomplished via the DAQ's input and output ports respectively. The system is tested in the laboratory for different angular displacements and initial positions of the motor. Initial results are found to be satisfactory. This initiative is a preliminary work towards the development of a control system of one of the Radio Telescopes (called Smiley) at Pisgah Astronomical Research Institute (PARI) in Rosman, North Carolina.