Electrostatic Document Feeders: an example of pure research

    Static electricity feeds the paper

In the article on Roller-type document feeders, it was described how static electricity can cause problems. Human ingenuity being what it is, attempts have been made to develop systems that take advantage of static electricity!

As everyone knows, two items bearing electric charges of the same kind (positive or negative) will repel each other. This principle can be employed to move paper.

An electrostatic motor has several components: a Stator layer, a Slider layer, power supply, and supporting and electrical elements. The Slider layer is a low-conductivity surface which retains electrical charges where they are applied and with similar intensity. The Stator layer contains electrodes of various sorts which can very quickly change their polarization and intensity: thus the intensity can vary from zero to maximum and the polarization from positive to negative. (Of course these terms are simplifications, to make the explanations comprehensible to those untrained in electronic theory!) The Stator layer stays put, thus "stat-ic", and the Slider layer moves.

The motor works something like this: an initial electrical charge pattern and intensity is generated in the Stator layer. This is transferred by natural inductance to the Slider layer (which must be close enough to the Stator layer so that the intervening air doesn't act as an insulator); in doing so the polarity is reversed. The Slider layer being of low conductivity does not lose the charge pattern or the intensities in any significant amount. Once the pattern is established on the Slider layer, a new pattern is applied in the Stator layer, one in which the polarization is opposite to the initial one. Again, the pattern will be transferred to the Slider layer, but as this transfer takes a perceptible amount of time, there will be a period in which the charge on the Stator and Slider layers are the same polarity and will therefore repel each other. The Stator layer can't move, so the Slider layer must; and it is set up so that it can move only in one direction - so thus it moves. It will take a short time to establish the charges on the Slider layer in the same configuration as the new ones on the Stator layer: then the process can be repeated. Thus a continuous Slider layer motion will result.

The pattern and intensity in the Stator layer are determined by the electrical components embedded in it. Thus the physical pattern and the intensity can be varied as required. As well, with proper design the Stator layer can be made in multiple levels, thereby increasing the forces as desired.

In practice, the paper is the Slider layer. Paper isn't a good conductor - in fact it is more of an insulator - so it will hold the charge and the pattern and will not propagate either through itself to the next paper on the stack.

Electrostatic paper movers are compact and can handle very thin and very low-friction paper. However the driving force is small and the entire process is very sensitive to the humidity and temperature of the environment. In fact, it is not certain if any commercial document feeders employ this technology.

(The machines described here are the result of Japanese research in the early 1990's, by Egawa, Niino, Higuchi, and others).

Document Feeder Article Index