Des ign, Control and Implementation of a BaIlon Plate Balancing System A. Zeeshan*, N. Nauman**,M. Jawad Khan** * Department of Mechatronics College of E& ME, National University of Sciences and Technology Rawalpindi, Pakistan, ** Department of Mechatronics Air University, Islamabad, Pakistan 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-Iinearities 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 Isq. 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 ixed, while to control the other axis second motor is ixed 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 A VR family controller with a lash 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 suicient basis for implementing diferent control strategies and investigating different system parameters such as actuation mechanism, sensors, controller design and experimental testing, under the predeined condition of the ball diameter. I. Introduction "The ball on plate problem is a benchmarkfor testing control algorithms. " The ball and plate system is one of the most enduringly popular and important laboratory models for teaching control systems engineering [1]. The control of unstable systems is critically important to many of the most dificult control problems. Since the system is Open Loop Unstable that is the system output (the ball position) increases without limit for a ixed input (plate angle) so the control of such a system is signiicantly important [2]. The purpose of designing such a system is to build a model capable to test and veriY different control systems aspects such as non-linearities and compensator design. To control the ball on plate system, a servo control system is required. Such a system is one of the most important and widely used forms of control systems. The job of servo motor here is to maintain a speciic angle 978-1-4577-1929-5/12/$26.00 ©2011 IEEE corresponding to the ball position until the ball reaches its desired position. The control loop of the servo mechanism is shown in Figl.l. FB c=SP-FB Signal"onditioning, Linearization and ampliication ifrcq Figure 1.1: Control loop of the mechanism Considering all the above mentioned factors, the design was developed to have following features: a. Quick sensing mechanism for the position of the ball. b. Eficient and light weight design. c. High performance actuators/ motors. d. Control mechanism using PID algorithm. The irst requirement was to sense the position of the ball in real time. For that purpose different techniques were considered. These are enlisted below with their limitations [3]. a. Touch pad. Costly. Complicated integration technique with the design in hand. b. Over head camera and image processing. Cumbersome to develop a standalone system using this technique. c. Resistive plate, a kind of 2-dimensional potentiometer. Complicated mechanism and limited information was available. d. Grid of sensors for each axis. Although the mechanism required excessive wiring and provided limited resolution but due to low cost it was chosen to develop an experimental model. II. Mechanical Design The mechanical structure of any control systems model is the most crucial element of the entire design, which needs immense contemplation in dynamics [4] [5]. A. Degrees of Freedom In the proposed design the system requires two separate motors to be acting on the plate independently at the same time, hence making it a 2-DOF system. Avoiding conlict between two such motors was a major design problem. To overcome this problem an additional platform between Proceedings of 2012 9th International Bhurban Conference on Applied Sciences & Technology (IBCAST) 22 Islamabad, Pakistan, 9th - 12th January, 2012