DE2916881A1 - INKJET PRINTER - Google Patents

Description

T.F.E. Taylor 14-8-3-3- Z3 Ib8ö1

Inkjet printing unit

The invention relates to an inkjet printing unit a print head through which a writing fluid flows and has a nozzle, from which at pulsed Excitation of the writing head, ink droplets are ejected, which are taken from the writing fluid flowing through are, a storage container with writing fluid, the connected to the print head via a ring-shaped circulation system is, and two pumps, which are arranged to the right and left of the print head in the circulation system.

State of the art

A general problem with inkjet printing units is the risk of the writing fluid drying out during the process longer writing pauses. In printing units of the aforementioned type, the writing fluid is indeed during the pause intervals kept in circulation. The liquid in the spray nozzle is not included. This is therefore exposed to the risk of drying out or solidifying, so that the nozzle during the subsequent Recording cycle may be clogged. This problem is attempted with slowly drying writing fluid to meet. However, such liquids tend to flow before they have dried, so that the typeface does not meet high quality requirements.

? .5 task and solution

The object of the invention is to increase the operational reliability of inkjet printing units.

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This object is given by that in claim 1

Features solved. The subclaims show advantageous

Refinements of the subject matter of the invention.

advantages

The advantages achieved by the invention consist mainly - Special in the fact that even when using fast-drying writing fluid the clogging of the spray nozzle is reliably avoided by ink that has dried on or on.

Description of the invention

The invention is explained in more detail below in conjunction with the drawings on the basis of two exemplary embodiments. It shows:

Figure 1 in a schematic representation of the basic structure of an inkjet printing unit,

FIG. 2 shows a first embodiment of a reversing valve for reversing the delivery direction of a pump,

FIG. 3 shows a second embodiment of a reversing valve applied to an arrangement according to FIG. 2.

The inkjet printing unit shown schematically in FIG. 1 has a print head 1. This consists of a Head part 1B, in which a spray nozzle 1A is inserted, the is in direct connection with a channel 1C penetrating the head part. One end of this channel is over a pipe 2A with a first feed pump 3A and the other end of this channel is via a pipe 233. connected to a second feed pump 3B. The two

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Pumps 3A and 3B are for their part via pipelines 2C and 2D with a storage container 4 with writing fluid in connection. During the printing operation, the pump 3A conveys the writing fluid via the lines 2C and 2A to the print head 1 and presses it through the channel 1G shown in dashed lines, the liquid the nozzle 1A passes and flows off again via the line 2B or is sucked off by the pump 3B as the liquid is delivered by the pump 3A. The writing fluid is supplied via the pump 3B fed back to the storage container 4 via the line 2D. The write head 1 is known per se and therefore not shown designed so that it is under an electrical control from the in the channel 1C withdraws a small amount of writing fluid flowing through the nozzle 1A and against a recording medium ejects.

If there is a longer pause in the recording process, the pressure pump 3A can be reversed in its direction of action will. As a result, both pumps 3A and 3B act as suction pumps as seen from the print head 1. This has to The result is that air is sucked in via the nozzle 1A and ultimately the nozzle 1A and the channel 1C are completely filled with writing fluid are emptied. There is thus the risk of the nozzle clogging due to the writing fluid drying out prevented in printhead 1.

In the case of the two pumps 3A and 3B, it is important that they deliver equal amounts of liquid in order to avoid overpressure or underpressure in the print head 1. A pump arrangement with which this requirement is met is shown in FIG. 2, in which two screw pumps arranged in tandem operation on a drive shaft of a motor

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are provided. However, this design does not allow the direction of rotation of a pump to be reversed on its own / as the handling described above makes it necessary. For this reason, a reversing valve 2X is included in the line system, by means of which a one-sided reversal of the conveying direction in the area of the print head 1 is made possible. In the illustrated position of the reversing valve 2X, the writing fluid is caused to flow through the print head 1, flowing through intersecting connecting sections 2L and 2M of the reversing valve. In the other possible position of the reversing valve 2X, the connections of the line sections 2A ¹ and 2A "or 2C and 2C" are separated. Instead, the line ^{sections 2A 1} and 2C ″ or 2A ″ and 2C are now connected to one another by connecting sections 2K and 2N. In this position of the reversing valve 2X, the writing fluid is sucked out of the print head via the pump 3A in operative connection with the pump 3B, as was previously described in connection with FIG.

The reversing valve described above can be replaced by an embodiment according to FIG. The pumps 3 and the lines, the print head 1 and the storage container 4 are only shown schematically in this drawing, but correspond to those of FIG. 2. The reversing valve 5 is shown partially in section. It consists of a fixed body 5A, which has four cross bores 5K / 5W, 5L / 5X, 5M / 5Y, 5N / 5Z arranged one below the other. These bores are interrupted by a core 5B which is rotatably and precisely fitted in the body 5A. The core has a corresponding transverse hole 5P, 5Q, 5R and 5S at the level of the transverse bores. These are arranged in such a way that when the core 5B is in a rotational position, the holes 5P and 5S are aligned with the transverse bores 5K / 5W or 5N / 5Z (as shown

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set), while in a position of the core 5B rotated by 90, the holes 5Q and 5R on the associated Cross bores 5L / 5X or 5M / 5Y are aligned. A quarter turn of the core 5B around the is thus sufficient To reverse pump operation.

The illustration in FIG. 3 provides intermediate lines 2K ^l and 2M ^l , 2M "and 2N ⁿ , 2L ¹ and 2N ¹ as well as 2K" and 2L "in order to connect the reversing valve 5 to lines 2A ¹ , 2A", 2C ^l and 2C " Of course

it is conceivable to integrate these intermediate lines in the form of channels in a correspondingly larger valve body, as indicated by the dashed line
Area 5A ^{1 is} outlined. Such a valve body would then only have four connections for the external connections.

2 sheets of drawings

Claims (1)

Patent attorney ^ 9 16 881 Dipl.-Phys. Leo Thul Stuttgart T.F.E. Taylor-V.N.Bansal-P.T.C.Raby 14-8-3 INTERNATIONAL STANDARD ELECTRIC CORPORATION, New York Claims [1.] Inkjet printing unit with a print head through which a writing fluid flows and has a nozzle from which, when the writing head is pulsed, ink droplets are ejected, which are taken from the writing fluid flowing through, a storage container with writing fluid, which is circulated via an annular system is connected to the print head, and two pumps which are arranged to the right and left of the print head in the circulation system, characterized in that the conveying direction of the pump (3A) working towards the print head (1) is reversible. 2. Inkjet printing unit according to claim 1, in which two pumps driven in tandem via a common motor are provided, characterized in that the pump (3A) working towards the print head (1) is in the supply and discharge line (2C, 2A) a reversing valve (2X, 5) is switched on which, in the reversing position, interchanges the connection of the inlet and outlet lines (2C, 2A) to the pump (3A). 3. Inkjet printing unit according to claim 2, characterized in that the reversing valve (5) consists of a fixed body (5A) and a rotatable in this body April 19, 1979 - / - vHy / mü 909846/0622 T.F.E. Taylor 14 - 8 - 3 - 2 - and accurately mounted core (5B) that the body (5A) has four bores (5K / 5W, 5L / 5X, 5M / 5Y, 5N / 5Z) that is interrupted by the core (5B) and that the core (5B) is provided with four transverse holes (5P, 5Q, 5R, 5S) in alignment with the transverse bores, which are arranged in pairs (5P / 5S and 5Q / 5R) offset from one another by 90 ° in the core (5B). 909846/0622