Design, control and implementation of a ball on plate balancing system

Abstract

The ball balancing system in a 2-degree of freedom platform is of unique importance in understanding the control system applications. It is a platform to test and identify different aspects of controls, as the non-linearities increases with the degree of freedoms. So far many techniques have been applied to sense the position of the ball on a plate in real time, most common of them is touchpad and audio video camera system. This paper describes the design, development and control strategy of balancing a ball on a plate using low cost phototransistor sensors. These Phototransistors are triggered by monochromatic sharp beams of laser light. The plate area is 1sq. foot and an array of 11 sensors each 1 inch apart is used on each axis making total of 121 points on the plate. To balance the ball, two motors are used one for each axis. The ground motor is fixed, while to control the other axis second motor is fixed on top of the ground motor. Hence the system utilizes two sets of independent control mechanisms, each operating in isolation for each axis. ATMEGA16 microcontroller is used which is an Atmel AVR family controller with a flash memory of 16 kb. Since it has two independently switched PWM channels, therefore, it makes this controller ideal for the purpose. Dynamic modeling of the system yields the digital controller capable of balancing the ball in any of the desired positions out of 121 points, on the plate. Although the system becomes quite discrete but still it provides sufficient basis for implementing different control strategies and investigating different system parameters such as actuation mechanism, sensors, controller design and experimental testing, under the predefined condition of the ball diameter.