Many printers are currently available for use as output devices in data processing systems and the like. These printers fall into two general categories: non-impact printers, such as laser and thermal devices which are quiet but cannot be used for multicopy forms, and impact printers which can produce fully formed characters (daisy wheel) or arrays of dots (dot matrix) which can produce multiple copies on one pass, but which are noisy.
An example of a non-impact printer is shown in the Hilpert, et al U.S. Pat. No. 4,502,797. This patent teaches the use of electrodes to form dots on an electrosensitive paper. While such a device is quiet, the need for an electrosensitive record medium limits its practicality and increases the cost of producing documents. The Lendl U.S. Pat. No. 4,174,182 is directed to a needle printing head, wherein a dot-matrix printer utilizes a camming operation to drive the print needles towards the paper. Print needles are selected by utilizing a piezoelectric brake which can controllably prevent selected print needles from reaching the record medium. Such a device is noisy because the print needles are fired towards the record medium, thereby creating impact noise. The same noise problem exists in the Goloby U.S. Pat. No. 4,167,343 wherein a combination of an electromagnetic force and stored torsional energy fires print needles toward a record medium.
Japanese Patent 568.20468(A) of 5.2. 1983 to Harada shows a device wherein selected print elements are shifted toward a printing surface with the help of piezoelectric plates and then locked into position by an electromagnet. Thereafter, a rotating cam propels the entire array of print elements toward the surface so that only those elements initially shifted toward the surface actually strike the surface. Again, not only is there impact noise, but there is a two step process in selecting the elements for printing, i.e. a piezoelectric displacing of selected elements followed by an electromagnetic locking of all elements in the print array. An example of non-electromagnetic printer is shown in the Kolm U.S. Pat. No. 4,420,266 which is directed to a piezoelectric printer. This printer, because it relies entirely on the piezoelectric phenomena to perform impact printing, is both noisy and has a complex and expensive layered piezoelectric structure. All of the above-discussed devices print only with one intensity. In other words, they are incapable of printing in "dots of variable size".