Performance Evaluation of a Low Cost Angular Positioning System

Nowadays, control systems tend to rely on software more and more. Expensive sensors are replaced by smarter programs, which, in many cases, satisfactorily accomplish the same functions traditionally performed by the addition of more complex sensors or a greater number of them. The heavier load on the software side, also allows for greater flexibility and the ability to easily adapt to new requirements. In this paper, the performance of a low cost angular positioning system will be evaluated. This system is used to control a homemade goniophotometer, where mechanical components (including sensors and actuators) are given. The goniophotometer is C-g type. Movement around each axis is powered by induction motors, each with its gear reduction box, driven by frequency variators. Motors are mounted on the shafts of the equipment. Angular position measurements are performed by incremental encoders. The encoders are mounted on the shafts of the goniophotometer, too. The control and data acquisition software resides in a PC computer, equipped with function specific dedicated peripherals. These include an encoder signal processing card and another card to communicate with other instruments. To output control signals to the actuators, the PC parallel port is used. The objective is to determine if the inherent limitations of the system components (mechanical and instrumentation) can be attenuated or eliminated by the control software. Disadvantages associated to the existing equipment will be indicated, as well as the way to overcome them where it is possible; or the conditions that have to be met for this disadvantages to be tolerable, where it is not.