| This section describes the Amazing Ball, a ball-on-plate balancing system. The realization of the system was obtained with the simultaneous consideration towards constraints like cost, performance, functionality, extendibility, and educational merit.
A complete system description for the ball-on-plate system is presented.
PHYSICAL SYSTEM DESCRIPTION
The physical system consists of an mechanical plate, two actuation mechanisms for tilting the plate about two axes, a ball position sensor, instrumentation for
signal processing, and real-time control software/hardware. The entire system is mounted on a mechanical (steel) base plate and is supported by four vertical springs and a central joint.
The motors are operated in angular position mode for ease of modeling and controls. A pulse-width modulated signal is employed for this purpose. The servos are powered by a 6V DC power supply.
A resistive touch sensitive glass screen (hantouch.com) that is actually meant to be a computer touchscreen was used for sensing the ball position. It provides an extremely reliable, accurate, and economical solution to the ball position sensing problem. The screen consists of three layers: a glass sheet, a conductive coating on
the glass sheet, and a hard-coated conductive topsheet.
An external DC voltage is applied to the four corners of the glass layer. Electrodes spread out the voltage on the glass layer creating a uniform
voltage field. When the top layer is pressed by the weight the ball, the top sheet gets compressed into contact with the conductive coating on the glass layer. As a result, current is drawn from each side of the glass layer in proportion to the distance of the touch from the edge. This generates a set of four voltages at the corners of the glass-sheet. These four voltages are filtered and subsequently
used for computing the ball position coordinates using simple linear relationships. The response time of this sensor is 8-15 ms which is fast enough for this application. The ball rolls on this touch-screen, which in turn is mounted on the
The system can be used as an excellent test-bed for testing various control schemes. An optimal controller using full-state feedback can be designed to achieve yet better performance. Although controllers based on the linear model perform extremely well, it will interesting to apply the principles of non-linear controls and seek any further improvements in the system performance.
The system is distributed with a pre-loaded PID control system for an easier approach.
A brief guide to unpack the Amazing Ball system package:
The following tutorials show how to tune the control algorithm of the Amazing Ball system: