Mechanical Copiers. There are now on the market several mechanical copiers, without the many disadvantages of the copying press, or the defects of the carbon method. One of the most satisfactory and best known is the roller copier. The fundamental principle of the roller copier is that of the clothes wringer; the original letter, with a wet tissue sheet placed against the written side, is passed between rubber rollers, to which just the right amount of pressure is applied.
Working from the clothes-wringer idea as a basis, the inventor of the roller copier set about to remedy the defects of the copying press. It was found that clear copies could be obtained only under certain conditions; the pressure must be absolutely uniform, and the tissue sheet must be moistened evenly.
Fig. 4. Mechanism of the Yawman & Erbe Roller Copier
As to the pressure, it was found that too much or too little resulted in unsatisfactory copies—some faint, others blurred—the very defect that had made the use of the copying press objectionable. This was overcome by using an adjusting screw by which the exact pressure required could be obtained. But, if the pressure were left on all of the time, the rubber rollers would soon be flat. So, an adjustment lever was added, by which the pressure could be thrown on before copying, and thrown off when the machine is not in use.
To adjust a single sheet of tissue paper so that it would lie smooth on the letter, was out of the question. This difficulty was overcome by copying on a continuous roll, and the problem of moistening was solved by passing the paper through water, insuring equal moisture over the entire surface.
The mechanism of the roller copier is shown in Fig. 4. The paper from the roll is passed under the dampening roll in the water tank, then between the large roller and the wringing roller, over the same large roller and between it and the copying roller, thence out over the flanged roller and down to the winding reel. The pressure on the wringing and copying roller is adjusted by the adjusting screws A and B, and the adjustment lever throws the pressure on or off. The letter to be copied is laid face down on the feeding shelf, the edge is placed under the copying roller, pressure thrown on, and a turn of the crank carries the letter through into a receiving basket, leaving a perfect copy. If additional copies are wanted—any number up to a half-dozen—the operation is repeated for each copy.
Fig. 5. General View
of the Yawman & Erbe
Roller Copier