JPH0367667A - Constituent body of electrostatic printer head and stylus shape - Google Patents

Abstract

PURPOSE: To decrease an amplitude of fluctuation of an electric voltage being necessary for providing an image with high quality on a print medium by using a stylus with specified shape, thickness and substance as a printer head. CONSTITUTION: Each of styli is formed into a rectangular cross section and the thickness of the stylus is selected such that background noises are removed or substantially decreased and a stylus driving voltage swing with a small amplitude is usable. By decreasing thickness of the stylus, the thickness of the stylus approaches to the dimension of surface unevenness (an irregular shape) for generating accidental discharge. When the stylus itself approaches the same dimension as the dimension of the surface unevenness, mean electric voltage for stylus discharge approaches mean electric voltage generated by the discharge of the surface unevenness and in this instance, a region where background is generated is decreased. When a copper stylus 72a is used and the thickness is made at most approximately 0.0005 inch, a sharp, clear and high density printing is generated and the difference in electric voltage being necessary for generating an unwanted printing with no accidental discoloration is decreased.

Description

TECHNICAL FIELD The present invention relates to electrostatic printers, and more particularly - to the field of electrostatic printing; The present invention relates to an electrostatic printhead that uses a stylus with a unique cross section that reduces ground noise.

Prior Art Electrostatic printers are known in the art. This kind of printer is
For example, U.S. Pat. No. 4,672.339;
2,400, No. 4.731. It is described in No. 542. Electrostatic printers use a printhead with an electrically conductive stylus. Typically, these styluses are circular in cross-section, disposed closely together, and separated by an insulating material. When media passes by these styli and a voltage is applied to a selected stylus, an electrostatic charge is placed on the media adjacent to the selected stylus so that it subsequently attracts and retains toner. At that time, the charge image is made visible. This mechanism is known in the art. A stylus with a rectangular cross-section to ensure that the print on the media is dense and that it is possible to print the media at an optimal speed so that the resulting image quality is the desired one. A rectangular cross-section stylus is selected to have an aspect ratio of approximately 1:1 (ie, the width to length ratio of the cross-section is approximately 1:1). Rectangular styluses have also been used, the thickness of which is significantly less than the width. See, for example, U.S. Pat.
c Pr1nter of Video Bi
tures with Gray Tones
) J discloses a write head with an electrode having a substantially elongated cross-sectional shape, the width dimension being significantly smaller than the length dimension. However, the stylus of this patent requires a significant sacrifice in the speed at which the media moves past the stylus of the electrostatic printhead when used in a multiplexed arrangement.

Electrostatic printing typically uses two power supplies to print. One power source can be described as a bias source, but it does not mean that the voltage between the stylus and the print medium is at a level below that required to cause charge transfer between the stylus and the print medium. Generate a difference. This bias voltage is typically applied to the print media through a conductive backplate arrangement to the conductive layer of the media as known in the art.

A bias voltage is further applied to the medium via capacitive coupling from the pair of front plates. Such an arrangement is described, for example, in US Pat. No. 3,611,419. On the other hand, it is also possible to apply a DC bias voltage directly to the stylus.

In either case, the additional voltages required to effectuate the printing are selected via additional electrical pulsing circuits controlled in such a manner as to produce the desired image on the print medium. Supplied to the stylus.

One of the problems with conventional styli is that because a DC bias voltage below the voltage at which printing is applied to the head stylus, an accidental discharge from either stylus to the print media can occur, which can be harmful during subsequent development. , random discolorations occur on the media that have no relation to the image desired to be formed on the media. This "background noise" is undesirable and must be reduced to a very low level, if not completely eliminated.

To do so, the DC bias voltage must be reduced to a lower level, and therefore the pulse circuit used in conjunction with the DC bias circuit to supply the required printing voltages to the various styli in the printhead is , so that larger voltage swings than were previously necessary are possible. This means that
It increases cost and complicates the electronics and reduces printhead life due to deterioration of the insulating material between the styli due to the new higher voltage between adjacent styli.

OBJECTS The present invention has been made in view of the above points, and it is an object of the present invention to eliminate the drawbacks of the prior art as described above and to provide an electrostatic print head that uses a stylus of a novel shape.

CONFIGURATION The novel stylus configuration in the present invention makes it possible to reduce the amplitude of the voltage swings required to give a high quality image on the print medium, and therefore to reduce the amplitude of the voltage swings used to drive the stylus. This makes it possible to reduce the complexity and size of electronic components and lower costs. Furthermore, the lower pulse voltages required by the present invention reduce the deterioration of the insulating material between the styli in the electrostatic printhead, thus reducing electrostatic pressure using a stylus constructed in accordance with the present invention. Extending the operating life of the print head. Because of this low pulse voltage, the present invention allows printhead configurations with styli positioned more closely together than previously possible.

According to the invention, each stylus is formed to have a rectangular shape, and the thickness of the stylus eliminates or substantially reduces background noise and is smaller than in the prior art. It has been chosen to allow the use of stylus drive voltage swings of amplitude.

The inventors have discovered that the background noise that appears on the print media is, to a large extent, a function of the roughness of the stylus surface and edges.

The protrusions protruding from the surface and edges of each stylus act as points of increased electric field experienced by a smooth surface stylus between the stylus and random points on the print medium to be imaged. Breakdown occurs in the atmosphere at lower voltage levels than in the atmosphere. Such a random breakdown is required because the difference between the stylus voltage and the printing media voltage is required to produce a sustained breakdown over the entire surface of the stylus for high density printing. This occurs when the voltage on the stylus is at the previous bias voltage level. When such random breakdowns occur, electrons are transferred to portions of the media surface directly adjacent to the protrusions on the stylus, creating areas of accidental charge images on these portions of the media. do. These charge images are later developed by a suitable development device to form visible incidental images. Therefore, as the media moves past a stylus maintained at a DC bias voltage, undesirable discoloration and streaks may appear on the surface of the media adjacent the stylus.

In experiments conducted by the inventors, styli of a considerable width but of various selected thicknesses were connected to a voltage source. The voltage applied to each stylus was then increased linearly with time between two selected values. Typically, starting with -100V applied to the stylus, the voltage on the stylus was varied to -600V over a period of about 5 minutes. At the same time, the print media was moved past the stylus. Thus, as the print medium moved past the stylus, the voltage on the stylus changed (ie, increased or decreased) as a function of time. As time passes and the voltage on the stylus increases, the voltage on the print media adjacent to the stylus increases before the voltage on the stylus reaches the voltage level necessary to form a sharp, clear, and dense image. Small discoloration and streaks appeared on the surface. The first example of such discoloration is
A stylus of the same thickness as that used in prior art heads was used to print on the electrostatic medium. The portion labeled "background" in FIG. 1a represents the discoloration of the print media that occurs as a result of unidirectional partial discharge of the stylus. The portion shown as "linearity" in Figure 1a represents the charge on the print medium (i.e.
Figure 2 shows the charge imparted by the stylus on the print medium in such a way that the voltage (voltage) increases linearly with subsequent increases in stylus voltage. In this portion of the drawing, the amount of charge imparted to the portion of the print media adjacent to the stylus is directly (ie, linearly) proportional to the incremental increase in voltage on the stylus.

FIG. 1b shows the coloration on the print medium obtained by applying voltage to a stylus constructed in accordance with an embodiment of the present invention in the same manner as applied to a prior art stylus. . The white area represents no discharge from the stylus to the media when the voltage on the stylus is below the threshold for linearity.

The dark area on the right side of FIG. 1b is the printed image corresponding to a voltage on the stylus sufficient to cause a discharge from the stylus to the printing medium, varying linearly as a function of changes in stylus voltage. It should be noted that the print media as shown in Figures 1a and 1b is being transported to the left (i.e., as shown in Figures 1a and 1b).
time increases to the right in both figures) and the horizontal bands shown in Figures 1a and 1b are each about 0
．． It was formed by one expandable stylus with a width of 5 inches (1.27 cm).

One embodiment of the present invention employing a copper stylus in which the stylus is formed to a thickness of 0.0005 inches (0.0127 mm) or less provides a sharp and sharp pulse voltage that is lower than the pulsed voltage used in the prior art. It is possible to use pulsed voltages to form high-density images in order to provide a signal with significantly reduced background noise on the imaged medium.

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description is for illustrative purposes to provide detailed explanation of the present invention, and is not intended to limit the technical scope of the present invention.

FIG. 2 shows protrusions 11a formed on the stylus surface;
A stylus 10 of circular cross-section with a 17 i
for Use in Staggered R
No. 4,419,679, entitled "ecoding Head)" (one of a plurality of styli in an electrostatic print head), such as that disclosed in U.S. Pat.

Print media 12 is shown moving past surface 11 of stylus 10 to the left. Stylus 10
When a voltage is applied to the protrusion on the stylus (e.g.
lla, llb, 1lc) are believed to act as sites for incidental discharge (these projections are exaggerated and not shown to scale). When such accidental discharges occur, background noise of the type shown as "background" in FIG. 1a is generated on print media 12.

Since the electric field is higher at the ends of the stylus (whether circular or square), accidental breakdown occurs first at the ends of the stylus rather than at the center of the stylus. This is known in the art.

This same accidental breakdown is believed to be initiated at some small local stylus surface irregularity. The inventors have found that as the dimensions of such irregularities decrease, the probability of accidental breakdown occurring increases. However, at some point, as the dimensions of such irregular shapes are further reduced, the probability that an accidental discharge will occur no longer changes.

The inventors have determined that by making each stylus a rectangular cross-section and then decreasing the thickness of the stylus, the thickness of the stylus will ultimately approach the dimensions of the surface asperities (irregular shapes) that generate accidental discharges. The experiment was conducted based on the assumption that As the stylus itself approaches dimensions equal to the dimensions of the surface asperities, the average voltage for the stylus discharge approaches the average voltage at which the surface asperity discharge occurs, thereby reducing the area where background occurs. In order to verify this, the inventor conducted an experiment on the discharge characteristics of a stylus with a rectangular cross section as a function of thickness. Figures 3-5 show some results of this experiment. Third
The figure shows a portion of this experiment in which a voltage A increasing over time is applied to the stylus, and the voltage induced on the moving print medium above the stylus is shown as voltage B. At time TO, a voltage A increasing linearly with respect to time is applied to the stylus.

The voltage B on the moving print medium (typically dielectric coated paper) opposite the stylus remains approximately zero until time T1. During the period between T1 and T2, in the portion of curve B shown as "C" in FIG. It shows the "noise" that is reflected. This is due to the accidental intermittent breakdown of the atmosphere between the stylus and print media, as discussed above. This accidental breakdown is assumed to be caused by surface portions of the stylus having high electric fields due to imperfections such as protrusions 11a, 11b, llc, etc. on the surface 11 of the stylus 10 shown in FIG. Conceivable. Time T2
At , the voltage A on the stylus reaches the value A2.

After time T2, voltage B on the print medium increases approximately linearly with time at substantially the same rate as voltage A on the stylus. This is a linear part of the system's operation. When voltage A on the stylus reaches A3, voltage B on the print medium reaches 83, and subsequent development forms a sharp, clear, and dense image on the medium.

Figure 3 was obtained as part of an experiment to determine at what point background noise occurs on the print media when the voltage is increased relatively slowly across the stylus. . In actual operation, the stylus operates in a digital manner and it is on (in which case the voltage on the stylus is at point A
3) or off (in which case the voltage on the stylus is typically that at point A4, chosen below A1 to completely eliminate background noise). ).

- It is desirable to have a minimum voltage swing in the membrane between turning on and turning off the stylus. To achieve this, the voltage difference A3-A4 on the stylus should be as small as possible. The voltage on the print media corresponding to the stylus in the on state is
The voltage shown as B3 and the voltage on the print media when the stylus is off is the voltage shown as B4, which is essentially O. In conventional heads driven by conventional electronics, when the stylus is turned on, the stylus voltage increases rapidly over time (it typically takes 1 to 10 microseconds to rise from A4 to A3). Meanwhile, the time during which the voltage on the stylus is on (ie, point A3) is typically 80 microseconds. From point A3 to point A4
The voltage drop time on the stylus is also rapid (typically 1 to 10 microseconds). Looking at Figure 3, the voltage on the stylus when the stylus is off is A1
If the level is somewhat higher than the level indicated by and varies somewhat over time due to the presence of voltage A on the stylus. Naturally, the voltage B on the print medium is the third
Voltage B4 on the left side of area C on the curve shown in the figure
The off-voltage on the stylus is set to A4 so that no background noise is formed on the print media.
It is possible to lower it to However, doing this increases the voltage difference (A3-A4) between print and non-print, and the drive circuitry is forced to move due to the larger voltage swing required. It becomes more complex and expensive.

Of course, even if the voltage difference A3-Al is used by the stylus to print, the required voltage swing to be provided by the electronics is necessary to reduce background noise on the print media and to print. Voltage difference A that does not contribute to forming a sharp, clear, dense image on the media
2-Al is included. Therefore, this is not desirable. Of course, the goal to minimize cost and complexity is to make the "print" to "non-print" voltage swing as small as possible. An additional purpose is to provide a sharp, clear and dense image on the media during printing.
When the printing voltage B3 is generated and printing is not in progress,
The objective is to apply a "non-printing" voltage of Ov on the print medium without causing background discoloration on the print medium.

This problem is compounded in conventional electrostatic printheads where printing is controlled by a multiplexed series of drive voltages.

In such multiplexed systems, a plurality of styli, evenly spaced from each other, are connected in a number of groups so that one stylus of a particular group is selected for printing and When pulsed, all corresponding styli in other groups are pulsed as well. The actual printing is performed by a second pulsed voltage coupled to the print media through a series of backplates. This second pulsed voltage is applied locally to the print media and serves to establish a "bias" voltage in a spatially defined area around a particular group of styli. When one stylus in one group is energized, the corresponding styli in each of the other groups are similarly energized and thus selected, even if the backplates associated with the styli in the other groups are not activated. The styli in the group that did not print will not print sharp, clear, high-density images on the print media. The level of the pulse operating voltage on the stylus is A1 in Figure 3.
and A2, a thin image often referred to as a "ghost" is formed on the print media on the underside of the styli of these other non-selected groups. This ghosting phenomenon is described in US Pat. No. 3,792,495, issued February 12, 1974. Ghosts may also form if the electrical characteristics of the print media are incorrect. If the resistance of the print media's conductive layer is not optimal, the locally applied "bias" voltage from the selected backplate will spread unduly and affect the styli outside the selected stylus group. , causing the voltage difference between the print medium and the corresponding selected stylus in an unselected group near the selected group to be within a range between A1 and A2.

To eliminate or reduce this ghosting phenomenon,
The pulsing voltage applied to the backplate can be increased and the pulsing voltage applied to the stylus can be used to reduce the charge on the print media to a third
It is possible to make the voltage A1 or less in the figure. However, increasing the voltage for pulsing on the backplate adjacent to the selected group of styli causes the styli in the selected group to not print on the print media to
The connection between the stylus and the print medium such that it experiences a voltage difference between itself in the area between A voltage difference is generated between the two. Such benefit considerations are known in the art.

As will become apparent from the detailed description of the invention, the use of copper beryllium or another material with equivalent properties in the stylus eliminates or minimizes ghosting and accidental writing as described above, while It is possible to construct an electrostatic print head that allows a wider range of stylus voltages and backplate voltages to be used in conventional multiplexed printing systems. Such a conventional multiplexing configuration is shown in FIG.

In FIG. 8, four drive circuits Dl to D4 are used to drive each of the four sets of styli 71, 72, 73, 74 that constitute the stylus in one electrostatic print head.
is used. Respective field plates (or back plates) 751.75-2.75-3.75-4.75 in contact with the conductive backside of print media 76
Five additional driver circuits B1 to B5 are schematically shown to drive each driver -5. Print media is
It is of a type known in the electrostatic printing art. Although field plates 75-1 through 75-5 are shown on the back side of print media 76, this is not essential. As known in the art, plate 7
5-1 to 75-5 can be placed on the same side of the print medium 76 as the stylus, and the potential on the plates 75-1 to 75-5 is the same as the conductive layer on the back side of the print medium 76. The print medium 76 is capacitively coupled to the print medium 76 through the dielectric layer. To explain the operation, when a selected stylus such as the stylus 71-1 performs printing, the stylus of the group 71 in which the stylus 71-1 is located (i.e., the stylus 71-1) prints.
1.71-2.71-3.71-4.71-5) is the selected driving voltage E3 (typically -2
75V) and backplate 75-1 is driven to voltage E4 (typically 275V). Therefore, the voltage difference between the stylus in group 71 and the conductive layer of print media 76 in the region near backplate 75-1 is such that it imparts a charge on the print media adjacent to stylus 71-1. . If the other styli in group 71 is desired to print, after back plate 75-1 returns to zero, In order to print the selected styli in the group 71, the back plates 75-2 to 75 are arranged opposite to these other styli.
-5 must be activated in order. In fact, all styli adjacent to a given backplate, such as backplate 75-1, selected to print on print media 76 are simultaneously driven by their appropriate driver circuits. Ru. Therefore, when backplate 75-1 is activated and raised to voltage E4, all styli 71-1, 72 adjacent to backplate 75-1 selected for printing
-1.73-1.74-1 actually does that.

After that, the group 7 adjacent to the back plate 75-2
The selected styli within 1 through 74 are activated simultaneously, so that when backplate 75-2 is raised to voltage E4, the stylus selected to print will actually do that. The remainder of the styli adjacent to the remaining backplates are similarly activated, and the selected stylus is connected to the backplate 75, 3.75-4.
．． It is driven to perform printing in conjunction with the sequential activation of 75-5.

Voltage AI (shown in Figure 3 as the voltage on the stylus at which background noise on the print media begins), voltage A2 (the charge deposited on the print media in response to increasing voltage on the stylus is linear). Voltage on the stylus that is the target) and Voltage A3 (voltage on the stylus where the stylus operates normally to impart a charge on the print media such that subsequent application of toner produces a sharp and dense image on the print media) Experiments were conducted to determine the effect of stylus thickness on the voltage of the stylus. It should be noted that voltage A2 is essentially 0V (B2) on the print media, so theoretically,
Although there is no image on the print medium, a subsequent increase in the voltage on the stylus above voltage A2 causes a corresponding increase in the voltage on the print medium, thus increasing the image density on the print medium.

Referring to FIG. 4, the benefits of reducing the thickness of a stylus used in an electrostatic printhead in accordance with the present invention are conceptually illustrated.

FIG. 4 shows that by decreasing the thickness of the stylus, A
3 (the voltage on the stylus where a sharp, clear, high-density image is formed) and Al (the voltage on the stylus where no background image is formed) is shown to be reduced. There is. The lower curve A1 corresponds to the voltage on the stylus as a function of stylus thickness when background noise begins to appear on the print media. The thickness of the stylus is point F in Figure 4.
As it decreases below 1, the threshold voltage A1 for background phenomena increases.

Curve A3 corresponds to the voltage on the stylus at which the desired image density is formed on the print media.

This voltage A3 is relatively constant. FIG. 4 shows that by reducing the stylus thickness, the difference between these voltages (Al and A3) is significantly reduced. Curve A2 in FIG. 4 represents the voltage on the stylus at the point where charge begins to be applied linearly onto the print media. At this point, the two voltages A1 and A2 are approximately the same.

For a stylus thickness Dl corresponding to a dot, it is assumed that the stylus thickness is of the order of magnitude of the protrusion dimension that causes accidental charge transfer. Therefore, for a stylus with a thickness D1 or less, if the stylus voltage A (Figure 3) is somewhat lower than the threshold (A2) when performing linear printing, accidental streaks or defects may occur on the print media. Substantially no desired marks are generated. At this point, voltage A2 is substantially equal to voltage A1.

Therefore, the voltage difference A3-Al is minimized. In one example, a copper stylus was used. The stylus thickness Fl at the point in FIG. 4 where the two curves A1 and A2 begin to approach each other (point F on curve A1) was 0.0005 inches (0.0127 mm). Therefore, about 0.00
For stylus thicknesses of 0.05 inches or less, the voltage difference A3- required to produce a sharp, clear, dense print and free of undesired and accidental discoloration.
Al is reduced.

EXPERIMENTAL EXAMPLE 1 FIG. 7 schematically depicts the apparatus used to determine the effect of stylus thickness on the image formed on print media.

A 0.0005 inch thick copper film 72 (see FIG. 7) was formed on a printed circuit (PC) board electrically insulating substrate 71. Regions 73a and 7 of this laminated PCC board are made of copper acid, glass-epoxy material.
3b adjacent to the copper PC board laminate structure.
It was installed between epoxy laminates. This stylus 72A
A top surface 7 of a composite glass epoxy copper substrate laminate having
4 was rounded to give a radius of approximately 2 to 3 inches (this radius is not particularly critical for this experiment).
. Print media 75 (type 2089 insulating paper, supplied by James River Graphics, Inc., South Hadley, Mass.) is then inserted into the stylus 72a (the end of the conductive material 72) as shown in FIG. surface). Then, the voltages AI, A2°A3 as shown in FIGS. 3 and 4 are applied.
It was determined. This means that the insulating paper is 0. 5 inches/
A Wavetic function generator (Model 601, available from Trek Incorporated, Medina, New York) was connected to a TREK high voltage operational amplifier (Model 601, available from Trek Incorporated, Medina, New York) while moving adjacent to and past the stylus at a speed of 1.2 seconds. (Model 801, available from Wavetic, Inc., Sun Diego, State), from a normal voltage (sometimes 0, other times a voltage other than 0, e.g. 200V) in the negative direction. This was done by linearly increasing the stylus voltage. This experimental apparatus is used, for example, in U.S. Pat. No. 4,731,5
It was installed in a device as described in No. 42. The back side of the print media was contacted with a conductive transition commercially available from Schliegel Corporation of Rochester, NY, which acted to press the print media against the stylus laboratory apparatus, imparting a normal force to the print media. to maintain the print media at an average distance of 10 microns from the stylus. This is conventionally known. Measure the voltage B on the insulating paper using an electrostatic voltmeter (TREK model 5).
65).

Voltage B was then plotted along with voltage A on the stylus as a function of time. The results are shown in FIG. A 0.0005 inch thick copper stylus (approx.
5 inches wide), voltage A1 was about 235V and A2 was about 360V. Therefore, the difference between the voltage A1 at which a background phenomenon is evident on the insulating paper and the voltage A2 at which the charge imparted on the paper is linear is approximately 125 volts. Therefore, in order to avoid background phenomena, the voltage A on the stylus must be dropped below 235V (voltage A1) when the stylus is "off" and to produce a dense print. The necessary additional voltage must be increased above 360v (voltage A2). The additional voltage required to produce high density printing is typically 150V. The voltage A3 required to produce high density printing is shown in FIG. 3 and corresponds to voltage B3 on the print media. Therefore, a voltage swing of about 275 volts is required on the stylus to go from no printing on the print media to a dense, acceptable print on the print media. Such large voltage swings require expensive electronics.

Further, the electrostatic printhead includes a plurality of styli, each stylus being closely spaced and separated from an immediately adjacent stylus by an insulating material. For example, if a voltage such as A3 is applied on one stylus to print as shown in FIG. The sub-voltage condition creates a large voltage difference between these two adjacent styli. Voltage difference A
3-Al may generate current flow between two directly adjacent styli. This is illustrated in FIG. In FIG. 9, the stylus 90 includes Al(
(see Figure 3) is applied with a voltage substantially equal to
Therefore, stylus 90 does not print on medium 95. Stylus 91 has a voltage applied to it substantially equal to A3 so that it provides sufficient charge transfer to media 95 to produce a sharp, clear, high density image. The voltage difference A3-Al is the voltage difference between the stylus 91 and the medium 9.
A current flow is generated between the styli 91 and 90 in the presence of an electric field generated by the discharge between the styli 91 and 90. This electric field is trapped between electrostatic printhead 96 and media 95. Due to the magnitude of the voltage difference A3-Al, the current flowing from stylus 91 to stylus 90 degrades insulating material 98 and creates a pitting area 94 between styli 91 and 90, thus impairing the performance of printhead 96. It is at a level that would have a negative impact on the In response to the phenomenon in electrostatic printhead performance caused by this pitching, conventional styli have been placed further apart from each other by necessity, thus increasing the separation distance. The desired current flow is reduced thereby increasing printhead life. The increased distance requirements limit the resolution achievable in the print head and the prior art stylus selected for printing and forming a white area between the colored images of two adjacent styli. This limits the spot size produced by the image, thereby limiting the density of the image produced. This effect is described in US Patent Nos. 3,798,609 and 3,157,456.

In FIG. 10A, several rows of styli (101-1
04) is illustrated. In low resolution printers, the stylus 101 is large and the distance d between the styli
is, for example, a small fraction of the total area printed when two adjacent styli are printed simultaneously. In higher resolution printers, it is necessary to maintain the same distance d between the styli to limit undesired currents between the styli, but the printhead is smaller for a given head length. By having a large number of styli (ie, higher resolution), the area between the styli becomes a greater proportion of the total print area, and the resulting print density or density is reduced. This effect is evident in the stylus 103, where the desired resolution is closely related to the distance d required between the styli to reduce unwanted currents. This problem, of course, is compounded by the need for two-, three-, and even four-line styli to manufacture printheads that simultaneously provide high-resolution, high-density, or high-density image printing with long printhead life. This resulted in the creation of a prior art printhead configuration.

Although stylus configurations such as the 104 are capable of achieving high resolution while maintaining large spacing between adjacent styli, such heads do not allow accurate alignment of each row of styli during manufacturing. It is necessary and necessary to store information (buffering) between those two lines. This is conventionally known. Considering that each stylus is on the order of 0.0025 inch and the length of the printhead is 36 inches or more, it is difficult to design a head with such a plurality of aligned rows of styli. The difficulty in manufacturing is considerable. This difficulty was solved by the inventor Dogget t, Mi
tchard, Dahj7quist's "Improved Electrostatic Printhead (Improved Ej; 1ec
trostatic Printhead) J.

The stylus of the invention makes it possible to construct a head in which the distance between the styli can be smaller than that of prior art styluses, thereby producing a high optical density print. This makes it possible to provide a head capable of producing higher resolution with a single or multiple row stylus. This is achieved by eliminating or reducing the background region C (see FIG. 3). Reducing the background area C reduces the voltage difference A2-Al (see FIGS. 3 and 4), which reduces the required voltage difference between adjacent styli and therefore the voltage difference between adjacent styli. Unwanted current flow is reduced, which makes it possible to increase the life of the insulating material between the styli and thereby the life of the printhead itself. Therefore, it is desirable that the change in voltage on the stylus from the non-printing state to the printing operation state be as small as possible. According to the present invention, the inventors have found that it is possible to significantly reduce the voltage difference between the styli by making the stylus much thinner than previously considered appropriate in the art. Ta.

Experimental Example 2 The second experiment was carried out by applying a thin chrome adhesive layer to the cafton (
A 1500A thick stylus consisting essentially of copper attached to a Kapton film substrate was used.

In this experiment, conductive layer 72 (Figure 7) consisted of a thin chromium layer (the exact thickness of this layer is not known, but is believed to be approximately 50-100 amps);
A thick copper layer on top of it (the thickness of the copper is such that the overall thickness of the composite layer is considered to be about 1500 mm)
was formed.

The chromium layer between the copper and Kapton is necessary because copper adheres well to chromium but not to Kapton. On the other hand, copper adheres well to chrome. On both sides of the resulting Kapton-chromium-copper laminate,
Glass epoxy composite materials 73a and 73b were formed.

This glass epoxy material 73a, 73b is commonly available from printed circuit board manufacturers and vendors.

The thickness of this material on each side of the stylus was typically on the order of 3/8 inch. The respective ends 71a and 72a of the Kapton and conductive layers forming the test stylus and backing laminate protrude from the glass epoxy material 73a and 73b in the initially laminated state. These edges and adjacent glass epoxy material are
The upper surface 7 of the structure is then smoothed and polished.
A radius of approximately 2 to 3 inches is formed at 4.

This allows the print medium to easily pass over the surface 74 and the test stylus 72a (typically, the print medium is a dielectric material from the same manufacturer used in Example 1). ). Connections to conductive layer 72 are made by alligator clips as in Example 1, and voltage A is applied to layer 72 and insulating paper 75 is varied as in Example 1 while moving past the stylus. Ta. The insulating paper 75 is placed at an average distance of about 10 microns from the stylus 72, either by spacer particles in the surface of the paper or by the average roughness of the paper stock, as is known in the art of manufacturing paper for use in electrostatic printers. was held at

Voltage Al, A2. A3 (Figures 3 and 4) was determined. Voltages A1 and A2 coincided and were about 385 volts, as shown by point 2 on the graph in FIG. Voltage A3 was approximately 535v.

The voltage difference A3-Al was about 150v.

Therefore, the threshold for applying a charge directly onto the media (e.g., an increase in the voltage on the stylus 72 (FIG. 7) increases the charge applied onto the print media 75 linearly) is: Equal to the threshold for background noise formation on print media. Therefore, in practice, there is no voltage region (region corresponding to region C on curve B in FIG. 3) in which a substantial background phenomenon occurs, and therefore a stylus voltage A2 in which a linear increase in charge transfer begins. No background noise is generated on the underlying media.

Thus, region C (FIG. 3) where background phenomena occur on the medium (i.e., the region where there is no linear relationship between the increase in voltage on stylus 72 and the increase in charge imparted on medium 75). has been removed. Note that while in FIG. 3 charge is linearly deposited onto the print media in response to an increase in stylus voltage from A2 to A3, the charge generated by the stylus voltage between A2 and A3 The developed area formed by the stylus voltage will form a lower quality image on the media than the image formed with a stylus voltage substantially equal to A3. In practice, if it is desired to print a stylus image on the media, the voltage on the stylus is quickly increased to voltage A3, and the charge imparted on the print media is sufficient to give a good image. ensure that there is Several other copper thicknesses were investigated and the resulting voltages A1 and A2 are shown in the graph of FIG. The results of this study indicate that styli thinner than 1200 OA exhibit almost no additive phenomena at the voltage difference A2-Al.

Experimental Example 3 0.0 using an intermediate adhesive layer believed to be chromium
A titanium stylus with a thickness of 0.001 finch was formed on Kapton. The resulting structure is identical to that shown in FIG. 7, with the substitution of titanium electrode material 72 for copper.

An insulating paper 75 was passed over the upper surface 72a of the stylus 72. In this experiment, a voltage A2 of approximately 365v and a voltage A1 of 300v were generated. These results are 0.
The results were approximately similar to those obtained with a copper stylus 0.0001 finch thick (see Figure 5).

In practice, thin styli (on the order of 1200 OA) are difficult to work with and difficult to manufacture. Therefore, the voltage difference A
2-1200O shown in Figure 5 to reduce Al
We considered a configuration that could use a thicker stylus than A and still achieve the phenomenon in background region C (FIG. 3). According to the invention, it is possible to select a stylus thickness that is compatible with the amount of background phenomena and the tolerable complexity and cost of electronics in the system under development.

As shown in FIG. 5, it is possible to identify the magnitude of the acceptable voltage difference A2-Al and then determine the required stylus thickness to obtain that voltage difference. . It is therefore possible to select both the amount of background phenomena that is acceptable and the voltage difference between the styli that is acceptable in the system and then determine the appropriate stylus thickness to achieve the desired result. Considerable flexibility is provided in designing the system.

Factors to consider in determining stylus thickness include the cost of manufacturing the electrostatic printhead, the cost of the electronics used to drive the stylus within the printhead, the lifespan of the printhead, and the media. such as the quality of the image formed on top. The cost of the system has a value for the useful life of the system, which depends on the maximum voltage between adjacent styli. The voltage across this stylus determines the life of the electrostatic printhead. This is because the degradation of the insulating material between adjacent styli is a direct function of the distance between adjacent styli.

Although the voltage A1 shown in FIGS. 3, 4, and 5 is a fairly substantial voltage (this voltage ranges from -200 to -40
0V), this voltage can be applied to all styli and stylus pulsing electronics, so the voltage difference between the styli is A1
and A3, not the absolute value of the voltage applied to the stylus. Of course, the entire circuit could be biased to voltage A1, or a backplate with a biased print medium could be used to bias it to voltage level A1.

Although styli made of titanium and styli made of copper appear to give perfectly compatible results, there are additional concerns regarding styli that appear to be at least in significant part zinc and alternative styli made of aluminum. Tests produced different results. actually,
Zinc and aluminum styli were incompatible with the results obtained with copper and titanium. However, it remains to be determined whether the general shape of the curve obtained using these materials as a stylus is, in fact, similar to the shape of the curve obtained using a copper or titanium stylus. Sufficient testing for these substances (
(i.e., zinc and aluminum).

Tests were conducted using beryllium and beryllium-copper styli. Although we have not obtained complete experimental results over a wide range of thicknesses using beryllium or beryllium copper styli, Figure 5 shows the difference between voltages A2 and A1 for a 0.0003 inch beryllium stylus. It shows. As shown in Figure 5, this difference is approximately 5
It is 5V. Therefore, an electronic circuit for use with an electrostatic printhead with a stylus made from 0.0003 inch beryllium can be used with 150 volts on the surface of an insulating print medium before development.
Requires a voltage swing between the off state and the on state of about 205v. Such a circuit is much less expensive than the circuit used in conventional electrostatic print heads, which require 275V.

Therefore, if a voltage difference of about 55 V is used, A2-Al, it becomes possible to use a 0.0003-inch beryllium stylus in the electrostatic print head, and if copper is used as the stylus material, It is possible to achieve the intended results of the present invention using a thicker stylus than that described. however,
Beryllium is extremely expensive.

0.0005 inch beryllium-copper stylus and 0.0005 inch beryllium-copper stylus
．． A 0.002 inch beryllium-copper stylus similarly produces a voltage difference A2- greater than that obtained using pure copper.
Lower values were achieved for Al. Thus, it is possible to use beryllium-copper styli in accordance with the principles of the present invention to form part of an electrostatic printhead.

Based on the finding that the voltage difference A2-Al associated with beryllium-copper is much lower than that for the same thickness of copper and provides a relatively low cost electronic drive circuit, the inventors found that beryllium-copper is a suitable material for the stylus in an electrostatic printhead according to the invention. Of course, experimental results from a 0.002 inch beryllium-copper stylus show that even if the stylus is thick enough to be effectively square, it still makes an excellent electrostatic printhead. Is possible.

Experimental results obtained from 0.002 inch beryllium-copper indicate that electrostatic printheads constructed by fitting round wire onto a mandrel also provide excellent print quality.

Although specific embodiments of the present invention have been described in detail above, the present invention should not be limited to these specific examples, and various modifications can be made without departing from the technical scope of the present invention. Of course it is. For example, in the embodiments described above, copper, titanium, aluminum, beryllium, and beryllium-copper are used as the stylus material, but materials different from these materials may be used without departing from the technical scope of the present invention. It is also possible to use styli of different thicknesses.

[Brief explanation of drawings]

FIG. 1a is an illustration showing an image formed on a print medium by an extended stylus that produces significant background noise below the voltage level for linear printing; FIG. 1b
The figures illustrate images formed on print media by an expandable stylus constructed in accordance with the present invention that generates little or no background noise below voltage levels for linear printing. Figure, 2nd
Figure 1a is a schematic diagram showing rough protrusions on the surface and edges of the stylus that are thought to generate background noise of the type shown in Figure 1a; Figure 3 shows the voltage applied to the stylus with respect to time; The voltage on the stylus is induced by the voltage on the stylus (
A graphical representation of the corresponding voltage appearing on the print medium showing the occurrence of background noise during the period before the voltage on the print medium reaches a point where it becomes linear; FIG. As a function of the thickness of the stylus voltage A3, a sharp, clear and dense image is formed on the print medium, and the stylus voltage A2 is such that the voltage on the print medium is linear and background phenomena occur on the print medium. 5 is an illustration showing in conceptual form the starting stylus voltage A1 and the reduced required stylus pulse operating voltage made possible by the present invention; FIG. Experiments using a copper stylus that showed the difference between the voltage on the stylus at which linear printing begins to appear on the print medium as a function of the thickness of the rectangular cross-section stylus. 6 is a schematic diagram illustrating a stylus formed with a thickness of rtJ to significantly reduce background noise in accordance with the present invention. , FIG. 7 is a schematic diagram showing a test stylus constructed in accordance with the present invention mounted within an insulating material, such as a glass-epoxy laminate, and FIG. FIG. 9 is a schematic diagram illustrating a prior art multiplexing arrangement for selectively forming a predetermined image on a print medium by using the print medium 95 directly adjacent the top surface of the stylus 91.
state of current flowing from a stylus 91 held at a high voltage to an immediately adjacent stylus 90 held at a low voltage when the stylus 91 is driven to a voltage sufficient to impart a charge onto a portion of FIG. 10A is an illustration showing the effect of increased distance between styli on the resolution obtainable with prior art styluses. (Explanation of symbols) 10 Stylus 11: Protrusion 12 Niblint media Engraving of drawing (no change in content) FIGUREla FIGURElb FIGURE2 FIGURE3 FIGURE4 FIGURE9 FIGURE10A Procedure amendment book form) August 22, 1990

Claims (1)

[Scope of Claims] 1. An electrostatic printhead comprising a plurality of styli arranged to apply an electrostatic charge onto a dielectric coated medium, each stylus having a rectangular cross section; The thickness of the cross-section is such that the amount of charge imparted onto the medium increases substantially linearly with increasing voltage on the stylus, and the minimum voltage on the stylus is such that an undesirable background image is formed on the medium. and the lowest voltage on the stylus is selected to be less than or equal to a selected number. 2. The electrostatic printhead of claim 1, wherein the stylus comprises a copper material. 3. The electrostatic printhead of claim 2, wherein the stylus has a thickness of less than about 0.0005 inch. 4. The electrostatic printhead of claim 1, wherein the stylus has a thickness of less than about 0.00006 inch. 5. The electrostatic printhead of claim 1, wherein the stylus comprises titanium. 6. The electrostatic printhead of claim 1, wherein the stylus comprises beryllium-copper. 7. The stylus according to claim 1, wherein the thickness of the stylus imparts a charge on the medium adjacent the stylus in such a manner that an increase in stylus voltage is linearly proportional to the voltage on the stylus. the voltage above is selected to be substantially the same as the voltage at which background noise becomes visible on the medium;
Thus, a stylus where the voltage on one stylus is at a level selected to form an image on an adjacent medium and the voltage on an adjacent stylus is selected not to form an image on an adjacent medium. An electrostatic print head characterized by a minimum voltage difference between the two. 8. The electrostatic printhead of claim 7, wherein the stylus is constructed from beryllium-copper. 9. An electrostatic printhead according to claim 7, wherein the stylus comprises a copper material. 10. The electrostatic printhead of claim 9, wherein the stylus is selected to have a thickness of about 0.00006 inches or less. 11. The electrostatic printhead of claim 7, wherein the stylus comprises titanium. 12. The electrostatic printhead of claim 7, wherein the stylus comprises beryllium-copper. 13. Claim 1, wherein the thickness of the stylus is such that the voltage on the stylus is selected to print an image on media adjacent to the stylus and the voltage on the stylus does not form an image on the media adjacent to the stylus. An electrostatic printhead characterized in that the voltage difference between the voltages on adjacent styli selected as such is selected to achieve a desired lifetime. 14. The electrostatic printhead of claim 13, wherein the stylus comprises a copper material. 15. The electrostatic printhead of claim 13, wherein the stylus comprises a titanium material. 16. The electrostatic printhead of claim 13, wherein the stylus comprises a beryllium-copper material. 17. An electrostatic printhead comprising a plurality of styli, each having a rectangular cross-section and arranged to impart an electrostatic charge onto a dielectric print medium, wherein the thickness of the stylus cross-section is approximately equal to the thickness of the stylus to be printed. The voltage difference between the selected stylus and an adjacent stylus that is selected not to print is selected such that the current flowing between adjacent styli is less than or equal to the selected value. An electrostatic print head characterized by: 18. The electrostatic printhead of claim 17, wherein the stylus comprises a copper material. 19. The electrostatic printhead of claim 17, wherein the stylus comprises a titanium material. 20. The electrostatic printhead of claim 17, wherein the stylus comprises a beryllium-copper material. 21. An electrostatic printer comprising a plurality of styli arranged to apply an electrostatic charge onto a dielectric print medium, wherein the stylus is comprised of an alloy of beryllium.