DE2436718A1 - METHOD AND PRINTER FOR CONTACT-FREE PRINTING - Google Patents

Description

Patent attorneys

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65-22.985P (22.986H) July 30, 1974

The Carter's Ink Company, Cambridge (Mass.), V. St. A.

Method and printer for non-contact printing

The invention relates to a method and a printer for contactless Rapidly printing an image on a receiving surface in which an electric pulse field passes through the receiving surface and an adjacent encoder surface is created, the encoder surface is movable Has electrically conductive pressure particles, which are in a high-resistance medium on the side of the donor surface adjacent to the receiver surface are distributed, the field is applied between a form electrode and a base electrode, the form electrode a pressure surface and has sides protruding therefrom and the printing surface is in the shape of the image to be printed.

65- (387 347) -Me-r (BD 9808/0813 *

² "2A36718

It is common to use high-speed non-contact or non-contact printing by applying an electrical pulse field between a pair of electrodes Via a printing forme or donor or donor surface and a printing material arranged close to it or a pick-up or To carry out the receiving area (see, for example, US Pat. No. 3,550,153 by Haeberle including a "). The side of the donor area contains that of the receiver area is closest, electrically conductive particles of a printing material, which are distributed in a hoci, ohmic medium. The electric Impulse field is applied to selectively charge the pressure particles on the transducer surface. The charged particles are then on the adjacent side of the receiving surface transferred under the influence of the applied field.

The Haeberle printer uses a usable charging technique, whereby a charge is applied to the pressure particles for a short period of time, and hence a considerable accelerating force on the Particles are exerted and high-speed printing is enabled. This useful charging technique is achieved primarily by using an electric High-amplitude pulse field allows that has a potential difference between the electrodes, which in various modifications of the printer can range from several hundred volts to more than 1000 volts.

Controls the spatial distribution of the applied electric field, when the field passes through the donor and receiver surfaces, the formed image created by the deposition of the pressure particles on the receiver surface formed. According to Haeberle, the distribution of the electric field is mainly controlled by the shape of the tip or Pressure surface of a profile or shaped electrode that is close to the receiver

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area is arranged. The components of the generated by the electrode electric field are spatially limited by a base or ground electrode, which is large in comparison to the form electrode is. The base electrode lies next to the transducer surface, so that the electrical pulse field generated by surface charges on the form electrode goes out, completely through the donor and reception area.

Printers working according to the Haeberle method can be designed in this way be that the field shape electrode is an alphanumeric character, or that a print head has several shape electrodes arranged in a matrix, each electrode e.g. B. may have a circle printing area. In the matrix structure, each form electrode is arranged in such a way that that selected ones in the matrix can be energized to form an eventual sequence of points (i.e., deposits of printing particles) in the form of an alphanumeric character.

However, such a printing device has significant disadvantages because the formed electric field emanating from the shaped electrode, both a component of surface charges on the printing surface of the Form electrode as well as an undesirable edge or scattering component of surface charges on the side or sides of the form electrode owns. By the effect, the edge component increases Area of the donor and receiver area through which the field passes. Through the resulting distribution of the dejected Pressure particles through the edge component of the electric momentum field there are considerable limits for the resolution when printing, which can be achieved when using the printing technique according to Haeberle is.

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It is the object of the invention to provide an improved method and To provide an improved printer for high-speed, non-contact printing of high resolution characters.

The object is achieved according to the invention in that the spatial Distribution of the applied electric field through a shield electrode is limited, the shield electrode insulated from the form electrode, placed around it and at such a high electrical level The potential is kept so that the electric field components emerging on the sides of the electrode shape do not pass through the transducer surface run to the receiver surface, while electric field components from the print surface pass through it.

According to the invention, the sharpness and clarity and thus the resolution in non-contact high-speed printing are improved, namely by adding a conductive shield, shield or protective electrode, which is connected to the individual electrode in the Print head is united. The shield electrode is from the form electrode isolated and in the simplest case on the same ground reference potential like the ground electrode. The shield electrode acts as a delimitation of the electric field lines that are caused by surface charges on the The sides of the shaped electrode emerge and therefore serves as a protective shield to protect the electrical field from the transmitter and receiver surfaces occurs, to be limited so that it comes only from the pressure surface of the form electrode.

In a more complex design with a suitable geometry, a pulse with a blocking property is applied to the shield electrode. In such an embodiment, the blocking or in-

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hibitor pulse lower amplitude than that placed on the form electrode Pressure pulse and is polarized in the opposite direction.

The useful effect of the shield electrode lies in the provision of a controllability or regulation of the spatial distribution of the remaining ones electric field components in the area of the transmitter and receiver surfaces when printing is desired. The remaining components of the electrical impulse fields that pass through the surfaces emanate from · the pressure surface of the form electrode. The spatial distribution the residual field components in the pressure area is essentially the same as the distribution of the field components that are exerted by the pressure area of the Form electrode run out, the amplitude of the field decreasing with a relatively steep gradient around the area in which printing is desired is. As a result, a relatively sharp transition is produced between a printed area and a non-printed area, as a result of which a high-resolution image is achieved.

The invention thus provides a method and a printer for high-resolution, non-contact printing. An electrical impulse field is applied between a shaped and a base electrode by a donor surface and a closely adjacent receiver surface for transferring electrically conductive printing material particles from the donor surface to the receiver surface. The shape of the resulting Precipitation of the printing material particles on the receiver surface depends on the spatial distribution of the components of the electrical Impulse field that pass through the transmitter and receiver surfaces. The distribution of these components is mainly regulated or controlled by the shape of the pressure surface of the mold electrode. - A shield electrode is around the outer contour or circumference of the

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Arranged pressure surface of the electrode form and extends along the sides of the electrode to eliminate the effect of edge components of the electrical impulse field, which emanate from points on the surface of the formula electrode outside the printing surface.

The invention is explained in more detail with reference to the embodiments shown in the drawing. Show it:

Fig. 1 is a semi-schematic structure of a printer according to the invention,

FIG. 2 shows a cross section through the structure according to FIG. 1,

3 shows a cross section of the electric field distribution in a construction of a conventional printer;

4 shows a cross section through the electric field distribution a printer according to the invention,

Fig. 5 shows a structure of a matrix-arranged printer according to the invention.

A high speed non-contact printer in accordance with the invention is shown in FIGS. In Fig. 1 are an electric field forming electrode 12 and a base electrode 14 separated from one another by a pressure gap 15. An encoder surface 17 is located in the pressure gap 15 and a receiving surface 19. The relative dimensions of the printer assembly according to FIG. 1 are for a better understanding in comparison to those of the surface 17 and 19 shown exaggerated. The side of the

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Surface 17, which is closest to the receiving surface 19, has many electrically conductive particles of a printing material or pigment, which are distributed in a high-resistance medium.

The dimensions of the printer structure and the transmitter and receiver surfaces 17 and 19 and their arrangement in the pressure gap 15 are chosen so that the structure works according to the teaching of Haeberle, i.e., a pulsed electric field is applied between electrodes 12 and 14 across pads 17 and 19 for selective charging of pressure particles distributed in the transducer surface 17 * The electrical impulse field also acts to transfer the charged particles to the adjacent side of the receiver surface 19. A visible image becomes therefore formed by the deposition of the charged pressure particles on the surface 19. The electric field is generated by a generator 21 by a pulse signal applied to the formula electrode 12. The base electrode 14 is held at ground reference potential.

In Figs. 1 and 2 there is also a cylindrical shield electrode shown having an electric. Contains conductor and is distributed around the sides of the electrode 12 form. The shield electrode 23 is from the shaped electrode 12 separated by a screen gap 27 by means of an electrical insulating material 25. As shown in FIG the shield electrode 23 is held at ground reference potential. In the Embodiment described is the shield electrode 23 by the Insulating material 25 held together with the shaped electrode 12.

Of course, the formula electrode 12 represents the main device for forming the image formed by the deposition of the printing particles on the receptor surface 19. In the illustrated

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In the tenth embodiment, the image is round; H. essentially the same the pressure area of the form electrode 12, d. i. the surface section of the electrode 12 that is closest to the encoder surface 17. According to According to the invention, the screen gap 27 between the shaped electrode 12 and the screen electrode 23 depending on the dimensions of the printing nip 15 is selected so that when the shield electrode 23 is held at a suitable potential, essentially all edge components of the electric field which emanate from surface charges on the sides of the electrode shape 12, from surface charges on the shield electrode 23, and practically no edge component coming from the sides of the forming electrode 12 exits, runs through the surfaces 17 and 19 to the base electrode 14. In this way, a structure is created according to the invention of a printer in which the electric field components which reach the base electrode 14 are essentially only those which emerge from the side of the electrode 12 that is the receiving surface 19 is closest, i.e. H. from the printing area. Edge field components, which emerge from the sides of the shaped electrode 12 are taken up or limited or terminated by the shielding electrode 23. As a result, the field amplitude at surface 19 decreases with a relatively steep gradient around the area in which printing is desired is.

This effect is shown in FIGS. 3 and 4. FIG. 3 shows the conventional structure according to Haeberle and FIG. 4 shows a structure according to the invention. In Fig. 3, the units and tens of the reference numerals of the components of the printer correspond to those of the printer according to FIG. 1. In FIG. 4, the reference numerals correspond to the components of the printer according to FIG. 1.

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In the Haeberle structure according to FIG. 3, a single one is cylindrical Shown electrode 112 with the radius R, the pressure surface of which is separated from the base electrode 114 by the pressure gap 115 (which is 3R wide, i.e. three times the radius of the shape electrode 112). The formula electrode 112 is generated by a generator 121 operated to generate an electrical pulse field between the formula electrode 112 and the base electrode 114. That generated electric field is shown by dash-dot lines in Fig. 3, the density 'of the field lines at one point in Fig. 3 a measure of is the field amplitude at this point (note that Figures 3 and 4 are an electric field representation in embodiments show in which the dielectric material 25 or 125 has the same dielectric constant as the gap area; in embodiments with different dielectric constants in these ranges if the electric field has a discontinuity or a jump point in the normal components at the boundary between the two areas). The field lines emerge from the electrode 112 at a right angle from, run through the receiver surface 119 and the donor surface 117 and terminate at right angles on top of base electrode 114. The edge field components from the sides of form electrode 112 exit parallel to the top of surfaces 119 and 117 and bend then to donor and receiver surfaces 117 and 119 um. It can be seen from the field line density shown in FIG. 3 that the areas 117 and 119 a field of maximum intensity in the area are exposed to the center of the pressure surface of the mold electrode 112 is closest. For the described embodiment must added that the amplitude of the applied electric field is chosen so that for the printer shown and for Geberund Receiver surface 117, 119 the conductive particles of the donor surface

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are transmitted to the receiving surface 119, as described by Haeberle, in order to form a "dark" area where the amplitude of the electric field through the surfaces 117, 119 is 70-100% of the peak value of the electric field Ε ~ is that from the center the printing surface of the electrode 112 is a "gray" area where the amplitude of the electric field passes through the surfaces 117, 119 is 30 - 70% of the peak value of the electric field Eq, and there a "light" (or unprinted) area where the field amplitude is below 30% of the peak value of the electric field Eq lies.

The heavily shaded area 120 a on the underside of the surface 119 reproduces the dark area of an image caused by precipitation is formed by pressure particles on the plate 119, which is caused by the electric field created by the surfaces 117 and 119 occurs (and has an intensity between 70 and 100% of the peak value). The hatched area 120b gives up the gray area of the of the area 119 again. The gray area is representative for the transition between a printed and an unprinted area. It can be seen that the width of the full Image, which includes areas 120a and 120b, is much larger is than the width of the printing area of the form electrode 112. It should also be noted that the main extent of the image around the boundary of the formula electrode 112 due to the edge components of the electrical Field has arisen, which emerge from the sides of the electrode 112 form.

For comparison with FIG. 3, FIG. 4 shows a printer according to FIG Invention and is otherwise the same as the structure according to FIG. 3. In particular

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is a grounded annular shield electrode 23 (the thickness 2R) with a distance 2R arranged from the electrode form 12, so that the ratio of the dimensions of the printing gap 15 and the screen gap 27 is proportional to 3/2. The generator 21 generates a pulse signal, the height of which is such that the tip field in the printing nip 15 is exactly as large as the tip field generated by the generator 121 of FIG in the pressure gap 115. The applied to the electrode 12 form Pulse signal creates an electric field between the formula electrode 12 and the base electrode 14, as shown by the field lines emanating from the formula electrode 12. As in Fig. 3 is the density of the field lines shown at one point is a measure of the field amplitude at this point. For the structure shown in FIG. 4 appears the tip field which passes through the surfaces 17 and 19 at a point which is the center of the pressure surface of the form electrode 12 is closest, as in the structure according to FIG. 3. The edge field lines or components that emerge from the sides of the molded electrode 12 terminate at the shield electrode 23, which is held at ground potential is, and not at the base electrode 14, as the corresponding edge components according to FIG. 3. Consequently, only the field lines reach the of surface charges on the round pressure surface of the mold electrode 12 emerge, donor and receiver surfaces 17, 19 and cause printing.

As in the structure of FIG. 3, a dark area, which the Includes areas where the field amplitude is 70-100% of the peak amplitude is, a gray area in which the field is 30-70% of the peak amplitude, and a light area in which the field is below 30% of the peak amplitude is formed. In Fig. 4 there is the heavily shaded Area 20 a on the surface 19 the dark area and the

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hatched area 20b on surface 19 again represents the gray area. It can be seen that the width of the printing area in Fig. 4 (which comprises the areas 20a and 20b) is much narrower than the corresponding one Area for the structure according to Fig. 3. The areas are mainly defined by those components of the electric pulse field formed, which emerge from the surface area of the form electrode 12 lying closest to the donor surface 17, d. H. the printing area of the form electrode 12. Since the edge components emerging from the sides of the form electrode 12 end on the shield electrode 23, calls none of these components resulted in a deposition of pressure particles on the receptor surface 19.

In addition, the width of the gray area is 20 b of FIG. 4 significantly narrower than the gray area 120b of FIG. 3. Accordingly, the edge sharpness or contour fidelity is that produced according to the invention Image correspondingly better than the image generated according to a conventional method. Therefore, a form electrode can be made Print a comparatively fine point on a thin wire of suitable dimensions with a shield sleeve electrode. For the described exemplary Embodiments, the improvement in resolution is about 3: 2.

According to another embodiment with a shaped electrode shaped according to an alphanumeric character, a shielding sleeve electrode generates the circumferential course of the shaped electrode with distance follows, also a high-resolution character with "sharp" edges. In still other forms of embodiment, the shield electrode 23 can be held at a potential different from the earth potential,

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which provides a possibility of regulating or controlling the edge field for the dimensions of the special print. Such a rule or The possibility of control includes the possibility of widening the field of the printing area by one that is larger than the printing area Generate image. Likewise, a pulse signal can be sent to the shield electrode 23 with a signal that is opposite to that at the formula electrode 12 Polarity (and of a certain amplitude.

Of course, electrodes 112, 12 and 23 are in both 3 and 4 shown as being held in a dielectric medium 125,25. Other arrangements may be used in other embodiments. For example, a printer may have one in a glass capillary tube embedded thin wire included, wherein the outside of the capillary tube has an electrically conductive coating.

In Fig. 5, an embodiment is shown in which sixteen cylindrical field shape electrodes 12 are arranged in a matrix. The shaped electrodes 12 are in a conductive mounting block 35 housed, in which each electrode 12 of the shielding electrode, that is the fastening block 35 here, by means of dielectric material 25 is isolated. In other embodiments, other numbers of shaped electrodes can be used. In further embodiments can several individually protected electrode assemblies can be fixed in a dielectric block. Such an electrode arrangement can e.g. B. a centrally arranged in a glass capillary tube thin Wire included, with the outside of the tube covered with a conductive layer. In the latter arrangement, a separate Inhibitor shield pulse can be selectively applied to the individual energized electrode assemblies.

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A printer in the form of a matrix according to FIG. 5 can be used for facsimile or image printing or for printing alphanumeric Characters are used by many points. The resolution in such a printhead is limited by the envelope or Enveloping surface of the electric field components of the corresponding formula electrodes when the field passes through the receiver and transmitter surfaces.

In a conventional matrix printhead where the mold electrodes are thin wires such as those used for image printing and no shield sleeves are used (e.g. if the shaped electrodes are embedded in an insulating material are) the border field limits the size of the printed dots to at least four times the size of the gap area between Form and base electrodes, regardless of the size of the individual pressure areas of the form electrodes. With all practically used For printers, the printing gap is inevitably considerable, e.g. B. about 0.15 mm (about 0.006 in), as the pressure gap must accommodate the donor and receiver surfaces with the necessary space. Therefore, the smallest radius for the printed point that is generated by one of the shape electrodes in the matrix is limited, since the Edge fields extend the actual pressure to a considerably larger radius. Consequently, when designing a conventional arranged in a matrix print head, the spatial density of the form electrodes is narrowly limited.

¹ In the embodiment of the invention according to FIG. 5, a pulse generator 21 is connected to the various shape electrodes 12 via a character selection logic 41. The logic 41 may take any form known in the art that can control the pulse signals from the

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Generator 21 to the appropriate shape electrodes 12 causes the Formula electrodes to voltage.zu put, so that a certain alphanumeric Character is printed on the surface 19. The generator 21 and logic 41 can be of any known form be and are not part of the invention per se.

In the above embodiment with a pressure gap dimension of approx. 0.152 mm (approx. 0.006 in), a shaped electrode made of thin Wire with a diameter of approx. 0.1015 mm (approx. 0.004 in) and a cylindrical shield electrode that is approx. 0.1015 mm (approx. 0.004 in) from With the shape of the electrode removed, there may be a dark spot about 0.1625 mm (about 0.0064 in) in diameter with a gray area of approx. 0.0712 mm (approx. 0.002-8 in) with a pulse of 800 V and 5 u can be printed. A similarly sized dark point that is printed with a conventional printer and is identical Peak field amplitude, but without shield electrodes, has a gray area of approximately 0.10092 mm (approximately 0.0043 in). That 'way looks a printhead according to the invention an improvement in edge sharpness and edge resolution of around 50% compared to comparable conventional ones Devices before

Of course, other modifications are also possible.

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Claims (11)

Claims 1.) Method for non-contact high-speed printing of an image on a receiving surface in which an electrical impulse field passes through the receiver surface and an adjacent donor surface are applied, the donor surface has movable, electrically conductive pressure particles, which are distributed in a high-resistance medium on the side of the transmitter surface adjacent to the receiver surface, the field between a Form electrode and a base electrode is applied, the form electrode has a printing surface and sides protruding therefrom and the printing surface has the shape of the image to be printed, characterized, that the spatial distribution of the applied electric field by a shield electrode (23, 35) is limited, the shield electrode (23, 35) insulated from the formula electrode (12), arranged around it and is maintained at such a high electrical potential that electrical field components emerging on the sides of the shaped electrode (12) do not run through the transmitter surface (17) to the receiver surface (19), while electric field components from the pressure surface run through it. 2. Printer for performing the method according to claim 1, characterized by one arranged around the sides of the electrode shape (12) and shielding electrode (23, 35) which is insulated from it and which is separated from the shaped electrode (12) by a shielding gap (27). 509808/0813 3. Printer according to claim 2, characterized by a generator (21) for applying a first electrical pulse field between the form electrode (12) and the base electrode (14). 4. Printer according to claim 3, characterized by a generator to the shield electrode (23, 35) on such an electrical Maintain potential so that electrical field components that emerge from the sides of the electrode (12) do not pass through the transducer surface (17) and receiving surface (19) extend while electric field components from the pressure surface pass through them. 5. Printer according to one of claims 2-4, characterized by a generator for applying a second electrical pulse field between the shield electrode (23, 35) and the base electrode (14), the second electrical pulse field to the first electrical Pulse field has opposite polarity and is so large that electric field components that emerge from the sides of the form electrode (12), do not run through the transmitter surface (17) and receiver surface (19), while electric field components emanating from the printing surface pass through it. 6. Printer according to one of claims 2-5, characterized in that a plurality of shaped electrodes (12) are arranged in a matrix are and several shield electrodes each surround an associated electrode shape (12) around the sides of the electrode shape (12). 7. Printer according to claim 6, characterized by a device 509808/0813 device for selectively applying the first electrical pulse field between at least one form electrode (12) and the base electrode (14). 8. Printer according to claim 7, characterized by a device for holding the screen electrodes, depending on the electrode shape (12) who have selectively applied the electric field at such a high electric potential that electric field components from the sides of the selected shaped electrodes (12), not through the transmitter surface (17) and the receiver surface (19) while electric field components from the printing surface pass through them. 9. Printer according to claim 7, characterized by a device for the selective application of a second electrical pulse field between the base electrode (14) and those shielding electrodes which around the selected shape electrodes (12) are arranged which have applied the first electrical field, the second electrical pulse field polarity is opposite to the first electric pulse field and is so large that electric field components emanating from the sides of the selected shaped electrodes (12) emerge, do not run through the transmitter surface (17) and the receiver surface (19), while electric field components emanating from the printing surface run through it. 10. Printer according to claim 8 or 9, characterized by a Device for keeping each shield electrode at the same electrical potential. 509808/0813 11. Printer according to one of claims 2 to 10, characterized in that that the ratio of pressure gap (15) and protective gap (27) is proportional to 3/2. 509808/0813 ι * ⁰ · ♦ Blank page