Abstract
A method for measuring the two-dimensional position of the center of gravity of a plane figure is described.
Its principle consists in repetitive determinations of the center of gravity of an object as in balancing a rod. As this method utilizes the phenomenon that the center of gravity of an object is the null point when it is brought into equilibrium, it may be designated a null method.
The system is implemented through the use of a video camera as a sensor and an analog circuit as a processor of the video signal. The center of gravity of an object contrasted against the background is detected in voltage. The major devices involved in the processor are around fifteen ICs consisting of operational amplifiers, analog gates, dividers, comparators, and logic SSIs.
The closed loop configuration of the circuit dictated by the null method is effective in the elimination of errors resulting from simple design and crude elements, thus achieving high accuracy of measurement. Having a linear characteristic and being independent of the properties of any object to be measured, the loop makes a rapid response beyond the reach of the conventional null methods. Another prominent feature of the system is high noise immunity afforded by the integrator used in the signal path.
Experiments performed with an ITV camera demonstrated an overall accuracy of position of ±0.5% FS and a response time in the order of 30ms.
