The invention relates to a printing needle apparatus comprising a plurality of printing needles that operate substantially in parallel and are actuatable lengthwise by means of a suitable back and forth moving actuator, for engagement of their tips against a recording medium. In such apparatus, actuating force is applied to each printing needle through a yielding stroke equalizing element, and for each needle there is a selectively controllable blocking device which operates to hold the front end of the needle stationary so that it does not engage the recording medium.

In printing needle technology heretofore known there is difficulty in increasing the printing speed by increasing the number of printing needles that work in parallel, since very much space is taken up on the one hand by the stroke equalizing spring devices and on the other hand by the known control or blocking elements. By reason of this undesirably high space requirement, the individual printing needles--and in a multiple-row device, the individual printing needle rows--cannot be arranged as close to one another as would be desirable.

The object of the present invention is to provide an improved printing needle apparatus of the type just described, wherein the individual printing needles can be arranged substantially more closely beside one another and wherein the yielding stroke equalizing elements do not project out beyond the plane of the side-by-side printing needles of a printing line.

The problem presented is solved according to the invention in that the yielding stroke equalizing elements are a permanent component of printing needles which are formed of resilient material and which, in their rear portions, are of zigzag or wave-shaped form in the plane of the printing line.

Further features of the invention will be apparent as the description proceeds.

In the following, preferred embodiments of the invention are described with reference to the accompanying drawings.

In the drawings:

FIG. 1 is an enlarged section of a printing needle comb in plan view;

FIG. 2 is a side view of FIG. 1;

FIG. 3 is an enlarged section of a blocking elements comb in plan view;

FIG. 4 is a side view of FIG. 3;

FIG. 5 is an illustration of the combination of printing needle comb and blocking element comb in sectional side view;

FIG. 6 is the lower guide for the printing needles on a still larger scale;

FIG. 7 is a schematic much enlarged plan view of a pair of blocking elements; and

FIG. 8 is a section taken on the section line VIII--VIII of FIG. 7, shown in the blocked (a) and unblocked (b) condition.

In printing needle apparatus of the present invention, a plurality of individual needles 2 are spaced apart at regular intervals, lengthwise parallel to one another and lying in a common plane, so that their tips 1 can impress a row of dots upon a recording medium as the needles are moved lengthwise into engagement with it. The printing needles 2 are thus arranged like the teeth of a comb, and the assembly 6 comprising one row of printing needles is sometimes referred to herein as a printing needle comb. In the printing needle comb of the present invention, each stroke equalizing element 4 is formed in one piece with its needle shaft 2.

A section of printing needle comb according to the invention, illustrated in FIGS. 1 and 2 at a scale of about 2:1, can be etched, stamped or manufactured by any of several controlled cutting processes from a springy metal sheet corresponding to the desired thickness of the dots to be printed. The tip 1 of each needle has approximately the width of the metal thickness, so that a square printed dot results. The needle shaft 2 has a sidewardly projecting lug 3 which cooperates with an abutment 8, described hereinafter, to arrest the needle against movement into contact with the recording medium. The yielding equalizing element 4 is so formed, depending upon the spacing between needles and the printing stroke, that upon arresting of one needle and resultant pressing together of the yielding equalizing elements 4, the neighboring needles are not hindered in the printing process. The cross bar 5, with which all of the printing needles of the row are formed in one piece, holds the printing needles together and at the same time serves as a printing beam that is connected with a conventional eccentric drive or the like (not shown) to be movable up and down.

The advantages of this printing needle configuration lie in the very low manufacturing cost, in the extraordinarily compact arrangement, and in the avoidance of interference, so that the printing needles in a multiple row arrangement can cover a surface without overlapping, owing to their square tips.

In FIGS. 3 and 4 there is illustrated on a scale of about 2:1 a section of a blocking element comb comprising a plurality of piezo bending transducers and which in combination with the printing needle comb 6 (FIGS. 1 and 2) can prevent each individual printing needle, under electronic control, from engagement against the recording medium.

The basic material of the blocking element comb is springy sheet metal, and upon the middle region of each of its teeth there is cemented a piezo stratum 9. The outer end of each comb tip 7 is bent through 180° to form, in each case, a hook-like lock 8 for an adjacent printing needle, engageable with the lug 3 thereon. The width of the hook-like tips 7 is such that they can swing between the printing needle shafts 2. A cross bar 10 of the blocking element comb holds the individual blocking elements together and is fastened to a stationary base 13. Through an electrical connection 11 on each piezo blocking element, a voltage potential can be conducted to the individual blocking element, to bring about a bending of it that engages its hook-like tip 7 with the cooperating lug 3. The conduction of the electrical null potential is accomplished through a suitable connection 12 to the cross bar 10.

FIG. 5 shows the general construction of the combination of printing needle comb and blocking element comb in sectionalized side view. The needle tips 1 of the printing needle comb move up and down in guides 14. The blocking elements can thus be selectively swung between the needle shafts 2, and with their abutments 8, which engage against the lug 3, can prevent a downward movement of the needle shafts 2 and needle tips 1. As the needle comb is actuated downward, the yielding equalizing elements 4 of the working printing needles maintain their form according to FIG. 1, but those of the arrested printing needles are deformed to be more acute-angled. Since the needle tips 1 are guided, an embodiment that is very advantageous from the standpoint of production is possible, wherein the yielding stroke equalizing elements 4, which all lie in the plane of the needle shafts 2, extend only to one side of their respective needle shafts, and each has a right-angled apex, to have a half-wave configuration.

A base plate 13 that holds the blocking element comb, which is connected with the drive and guides the printing needle comb, stands at a fixed distance from the printing support 15 upon which the recording medium rests.

FIGS. 7 and 8 show a unit comprising a needle lug 3 and a blocking element 7, the abutment 17 of which projects sidewardly and not in this case forwardly. In this case, therefore, the hook-like bending over of the tip of the blocking element, as in FIG. 4, is unnecessary. FIG. 8a shows the conditions when the piezo bending transducer is blocking, and FIG. 8b shows the released condition. Instead of a sideward lug 3, there could obviously be provided a cutout in the needle shaft 2 into which an abutment could fall.

FIG. 6 shows in side view the configuration of the needle guides. The guide bars 14 are provided with grooves that correspond to the needle width and the needle distance, and the needles are confined in them by means of the cover plate 18, to be thus guided in all transverse directions. The cover plate 18 thus substantially facilitates assembly and eliminates the simultaneous insertion of a plurality of needle tips into respective bores.

The recess 19 under the lower guide bar 14 and the cover 18 can be filled with ink, which then also enters into the needle exit slit 20 but cannot run out of it because of capillary force. In this manner needle points that are wetted with ink can produce printed dots on the print medium.

The previously employed expression "springy sheet metal" is not intended to be limited to steel sheet with resilient properties but includes sheets of other suitable resilient metals.

As the testing of the subject matter of the application has shown, the needle printing apparatus according to the invention operates with extraordinary reliability and accuracy, which is achieved because the arresting of the printing needle in a non-printing position is effected in every case by a form-related cooperation of abutments on the printing needles and on the piezoelectric bending oscillators.

The heretofore employed arresting devices for needle printing apparatus that operate by force blocking have the disadvantage, known from experience, that dirt can cause them to block in non-braking conditions or can result in the application of a braking force of insufficient magnitude so that the printing needles slide through and are not held back.