US 3656818 A
A vibration resistant guide for an ink jet printing head that moves back and forth across a paper web, comprising a flat rail supported at opposite ends and having guideways extending along opposite edges to guide the printing head, the center of the rail having a recess in its under surface. A damping bar composed of a rubber matrix with lead shot embedded therein is disposed in the recess to damp out vibrations of the rail. The damping bar fits loosely within the recess, and is retained therein by a diaphragm that covers the recess.
Description (OCR text may contain errors)
United States Patent Bischoff et al.
 SELF -DAMPED GUIDE RAIL  Inventors: Vincent E. Bischoff, Rivergrove; Paul S.
Colecchi, Des Plaines, both of II].  Assignee: A. B. Dick Company, Chicago, Ill.  Filed: May 8, 1970 21 App1.No.: 35,717
 U.S. Cl ..308/3, 188/1 B  Int. Cl. ..Fl6c 29/00  Field ofSearch ..308/3,3A;108/102,137;
312/341 NR, 330, 334, 348; 248/15, 20, 358 R; 188/1 B;267/136, 141
 References Cited UNITED STATES PATENTS 3,088,561 5/1963 Ruzicka ..l88/l B 2,375,818 5/1945 Peters ....l88/1 B 2,272,639 2/1942 Jack ..1 18/1 B [151 3,656,818 [451 Apr. 18, 1972 3,239,185 3/1966 SweeneyetaL ..267/141 FOREIGN PATENTS OR APPLICATIONS 920,586 9/1960 Great Britain ..188/l B Primary Examiner-Martin P. Schwadron Assistant Examiner-Ronald H. Lazarus AttorneySamuel Lindenberg and Arthur F reilich  ABSTRACT A vibration resistant guide for an ink jet printing head that moves back and forth acrossa paper web, comprising a flat rail supported at opposite ends and having guideways extending along opposite edges to guide the printing head, the center of the rail having a recess in its under surface. A damping bar composed of a rubber matrix with lead shot embedded therein is disposed in the recess to damp out vibrations of the rail. The damping bar fits loosely within the recess, and is retained therein by a diaphragm that covers the recess.
8 Claims, 4 Drawing Figures PATENTEBAPR 18 m2 YMJCEM 7' 5f BISCHOF PAUL 5 1 COLECCH/ BY 4 Erma/WW AfEs s 1 SELF-DAMPED oumr: RAIL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to ticularly, head rail.
2. Description of the Prior Art An ink jet printing machine generally employs a printing head that moves back and forth across a web of paper. While moving in the forward direction across the paper, a stream of minute ink droplets is projected at the paper and deflected so that the stream creates letters on the paper. The printing head can be guided in lateral motion across the paper by an elongated guide bar or rail. In order to maintain good printing fidelity, the printing head must be free from mechanical vibrations. It has been found that the guide rail is subject to resonant vibrations of large amplitudes as the printing head is thrust rapidly back and forth along it. Various methods have been tried in an effort to reduce vibrations of the guide rail, including the use of viscous or elastic materials to support the rail, and the use of rails of various shapes and materials supported at various locations. None of these attempts have proven successful.
OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide a guide for a printing head, which effectively resists vibrations.
Another object is to provide an ink jet printing machine of good printing fidelity.
In accordance with one embodiment of the invention, an ink jet printing machine is provided which includes a guide along which the printing head reciprocates, wherein the guide is compact and economical to produce and effectively resists vibrations. The guide is an elongated flat rail with opposite edges forming guide tracks along which the printing head moves. A recess is formed at the center of the rail, and a small bar of rubber with lead shot embedded therein is positioned within the recess. The recess is covered by a thin diaphragm of flexible material to retain the rubber-lead matrix therein. The effect of the rubber-lead dampening bar is similar to that of a weight attached by a spring to the center of the guide rail, that counteracts vibrations to damp them.
The novel features of the invention are'set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an ink jet printer constructed in accordance with the present invention;
FIG. 2 is a bottom view of the guide rail in the apparatus of FIG. 1;
FIG. 3 is a sectional view taken on and FIG. 4 is a sectional view taken on the line 4-4 of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an ink jet printer includes a printing head that can move laterally across a guide rail 12 while a jet of ink droplets 14 is projected at a web of paper 16. The printing head includes electrodes 18 for charging the ink droplets, charged deflector plates 20 for deflecting the droplets in accordance with their charge, and a catching device 22 for catching the droplet stream when no character is to be printed on the paper. The printing head 10 is supported by four slider bearings or shoes 24 that move along opposite edges 26, 28 of the guide rail. A servo motor 30 moves a cable 32 that is attached to the printing head to thrust the head back and forth along the guide rail.
The printing machine is capable of printing at high speeds, so that the printing head 10 moves at a rapid rate in a forward printing apparatus and, more parto apparatus for damping vibrations of a printing the line 33 of FIG. 2;
direction across the paper and is rapidly accelerated to an even higher speed during its return to the left edge of the paper to start a new printing line. Rapid acceleration of the printing head by the cable driving system results in shocks being transmitted to the guide rail, and these shocks can result in vibrations of the rail and of the printing head, which reduce printing fidelity. The guide rail 12 is supported by fasteners 34 that project through holes at opposite ends of the rail, and into rail supports 35. This manner of support which leaves the center portion of the rail unsupported to allow the printing head to move therealong, allows vibrations of the rail that are primarily of one frequenc which is determined by the length of the rail. In order to damp these vibrations, a cavity or recess 36 is formed in the lower face of the guide rail, and a damping bar is held therein.
As shown in FIGS. 2-4, the chamber or recess 36 is largely filled by a damping bar 38. The damping bar 38 is formed from a predetemrined mass of lead shot uniformly dispersed in a soft, live rubber compound. The damping bar 38 is constructed to fit loosely in the recess so that it is free to shift position slightly therein. The damping bar is held in place by a diaphragm 40 that covers the recess. The diaphragm 40 includes an outer sheet 42 of foil tape which completely covers the recess, and an inner sheet 44 of masking tape which is cut to a size that allows it to be received within the recess. The foil tape 42 has pressure-sensitive adhesive on its upper face for sticking to the guide rail 12, while the masking tape 44 is free from adhesive on its upper surface so that it can serve to prevent sticking of the damping bar to it.
The damping bar 38 and diaphragm 40 operate to damp vibrations in somewhat the same manner as a weight attached by a spring to the center of a vibrating beam that is supported at opposite ends in a manner that causes the center of the beam to have the greatest amplitude of vibrations. If the spring and weight have a natural frequency of oscillation equal to that of the vibrating beam, then the weight will tend to oscillate out of phase with the beam and reduce the amplitude of vibrations. The damping bar 38 largely serves as a combined spring and weight, the weight being embedded in the spring. Furthermore, the rubbery matrix material in which the lead shot weight is embedded, is a good vibration absorber. The combined weight of the rubber matrix and lead shot also serves as a weight, and the diaphragm 40 which couples the damping bar to the guide rail serves as a spring. By locating the recess 36 in the bottom face of the guide rail and allowing the damping bar to rest on the diaphragm, the design assures that the damping bar will be resting on the diaphragm at the beginning of any vibration period, to begin damping the vibrations immediately.
One ink jet printing machine that was constructed included a guide rail 12 of extruded aluminum, with a width of 1 inch, height of five-sixteenths inch and unsupported length of 18 inches along which the printing head moved. A damping bar construction which was found highly effective in reducing vibrations, included a matrix of Dow-Corning type 732RTV silicone rubber with one-sixteenth inch diameter lead shot uniformly dispersed therein. The damping bar was composed of 3 parts lead shot by weight to 1 part rubber, and the entire damping bar had a weight of approximately 15 grams. The bar had a height of approximately eleven sixty-fourths inch and was held in a recess in the guide rail of approximately onefourth inch. The outer sheet 42 of the diaphragm was formed from 0.0075 inch thick aluminum foil with pressure-sensitive adhesive on one side thereof. The masking tape sheet 44 of the diaphragm was formed from ordinary masking tape having a thickness of about one sixty-fourth inch.
It has been found that a guide rail having a cavity filled with loose particles of a relatively high specific gravity at least that of iron, is also resistant to vibrations. However, by embedding the particles in a resilient matrix, particularly one of elastomeric material, additional dampening reduction is obtained while permitting easier handling of the damping material during construction. Both in the case of a guide rail recess filled with only loose particles and in the case of a guide rail recess filled with particles that are embedded in an elastomeric matrix, good dampening is obtained while retaining compactness of the flat guide rail.
Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.
What is claimed is:
l. A guide for a printing head comprising:
an elongated member having an unsupported portion for guiding a printing head back and forth across a printing medium; and
a damping member which includes a multiplicity of items of a material at least about the density of iron embedded in elastic material, said clamping member coupled to said unsupported portion of said elongated member.
2. The guide described in claim 1 wherein:
said elongated member comprises a substantially flat bar with guides extending along opposite edges, and with a recess formed in one face; and
said damping member is disposed in said recess; and includa diaphragm of flexible material disposed to cover said recess to hold said matrix therein.
3. The guide described in claim 2 wherein:
said bar is oriented with one face facing primarily downward, and said recess is formed in said downward facing face of said bar.
4. A guide for a printing head comprising:
an elongated member having a center portion for guiding a printing head back and forth across a printing medium, and having end portions;
means for supporting said end portions of said member;
means defining a chamber at said center portion of said member;
a resilient material disposed in said chamber; and
a multiplicity of particles embedded in said resilient material, so that said resilient material can couple said particles to said center portion of said elongated member, said particles having a higher specific gravity than said resilient material.
5. The guide described in claim 4 wherein:
an elongated guide member having end portions and having a center portion for guiding a printing head in back and forth motion;
means for supporting said end portions of said member;
means defining a recess in a lower surface of said member;
a first material disposed in said recess free of attachment to said elongated member; and
a diaphragm mounted on said elongated member and extending under said recess to support said first material, said diaphragm constructed of a thin resilient material to springingly support said material on said member so that said material can deflect downwardly with respect to said member.
7. A printing machine comprising:
means for holding a printing medium;
an elongated guide bar having opposite end portions and having a recess at least in center portion thereof;
means for supporting said opposite end portions of said guide bar so that it extends across said means for holding a printing medium;
a printing head;
. means for supporting said printing head in movement along said guide bar;
a first material of specific gravity at least about as great as that of iron disposed in said recess; and
a block of rubber-like material fixed to said first material and coupling it to said guide bar, to permit movement of said first material relative to said center portion of said guide bar.
8: The printing machine described in claim 7 wherein:
said recess is formed on an underside of said guide bar, and
including a diaphragm extending across said recess and having opposite ends mounted on said bar, said diaphragm constructed of a thin resilient material to permit downward deflection of said first material and block relative to said bar.