EP0081809A2 - Wire printer with a convenient construction, and its method of manufacture - Google Patents

Abstract

A needle printing device having a plurality of printing needles mounted in electromagnets with a permanent magnet operating through a yoke to retain a spring upon which the needles are mounted against the core of the electromagnet, the spring having an armature thereon which is released when the electromagnet is energized to permit the needles to be driven into printing position by operation of the spring. The particular features of the invention involve a construction wherein the yoke means is formed in two parts, with the first part having a surface which is formed in a common plane with a surface of the core of the electromagnet, the second part of the yoke having a surface which lies in a common plane with a surface of the armature when the electromagnetic is de-energized with the armature held against the core of the electromagnet.

Description

The invention relates to a dot-matrix printing system which is designed in such a way that it has a structure which is as easy to assemble as possible. It also relates to a method for producing such a dot-matrix printing system.

In US-PS 4 225 25o a mosaic printhead is described in a compact design, in which the printing elements are held in a rest position not cooperating with the recording medium by a segmented permanent magnet, the printing elements being resiliently biased, and in which the printing elements are then held by the Excitation of an electromagnet can be shot into the printing position by canceling the corresponding field of the permanent magnet. In this case, the recording or drain elements are welded onto the individual segments of an armature disk provided with slots and move in slot-shaped recesses of a yoke part which closes the print head upwards in the form of a front plate.

Since the printing elements on the pressure hammers carrying them - segments of the armature disk - do not have a clear, structurally predetermined position, it is extremely difficult to attach the printing elements to the segments in production in such a way that the tips of the printing elements lie in the desired printing position on the recording medium - in one or two rows vertically one above the other - that, on the other hand, they are also guided in the recesses of the segmented front panel in such a way that even air gaps remain between the pressure elements and the slots in the segmented front panel. If these air gaps are missing, the pressure elements obviously cannot move because the front plate is magnetized and holds it in place. The correct fastening becomes particularly difficult supply of the printing elements on the segmented armature disk, if a certain position of the printing elements is to be achieved relative to the recording medium, that is if the printing elements must all be arranged exactly in one or two rows, which is usually required in dot matrix printers. In this case, it is almost impossible to create a faceplate that is designed so that its tolerances force the pressure elements to be attached to the segments of the anchor plate in the correct position.

In addition, there is the difficulty of correctly maintaining the air gap between the segments of the armature plate and the cores of the electromagnets. In this case, it is necessary to individually adjust the individual cores of the electromagnets so that when the electromagnet is not energized, the segments of the armature plate bear tightly against the core of the electromagnet under the action of the permanent magnet. Even slight differences not only in the air gaps between the core of the excited electromagnet and its armature, but also an inclined position of the armature relative to the core of the electromagnet have a performance-reducing effect.

A further disadvantage of the known arrangement is, in particular, that if one of the pressure elements, which, as is known, is not all actuated equally often, is worn out, so that pressure is no longer applied, the entire anchor plate must be replaced with the pressure elements. In contrast, the object of the invention is to provide a printing system of this type which can be assembled as cheaply as possible with a basically similar construction. The systems should also be designed so that they can either be combined into a needle print head, in which the needles are arranged in one or more rows one below the other, or can also be arranged in a row to build a line printer. It is also an object of the invention to construct the dot-matrix printing system so that individual needles that are subject to particularly heavy wear and tear, in particular to be able to individually replace the needles, which are mainly used for printing medium lengths, in order to create cheaper repair options for the needle printing systems.

Accordingly, the invention consists of a needle printing system consisting of a base plate made of magnetic material and one or more permanent magnets individually or jointly assigned to the printing needles and electromagnets individually assigned to each printing needle, each with a core, yoke parts for bridging the air gaps between the poles of the permanent magnet (s) and the electromagnet, the permanent magnets pulling an armature with the spring under tension against the core of the non-energized electromagnet and the spring allowing the armature to snap forward with the pressure needle when the electromagnet is excited into the pressure position, and is characterized in that, on the one hand, the pole ends of the first yoke parts, the partially bridge the air gap between the permanent magnets and the electromagnets, and the pole ends of the cores of the electromagnets lie in one plane and that on the other hand the armatures are arranged in a further yoke part and that the pole ends of this further yoke part and the pole end of the armature also lies in one plane in its pretensioned position when the electromagnet is not energized.

The arrangement of the pole ends of a first yoke part and the cores of the electromagnets in one plane has the advantage that no tolerances can occur here. The same applies to the second component, the second yoke part with its anchor. No tolerances can occur here either, so that an exact air gap results in the excited position of the electromagnet. If the electromagnet is not energized, the armature lies flat on the core of the electromagnet when the spring is tensioned, without any tilting of the armature occurring. This will be an optimal one System performance achieved and at the same time clearly defined for the assembly of the geometric location of the various points that are decisive for the determination of the air gaps. The permanent magnetic force is hereby exploited to the maximum, and the service life and functional reliability of the individual dot-matrix printing systems are substantially increased, because the armature always hits the core of the electromagnet in a flat manner.

In a further embodiment of the invention, the damping stop for damping the kinetic energy of the spring and the armature in the rest position is also arranged in one plane with the pole ends of the first yoke parts and the cores of the electromagnets, so that no tolerance possibilities arise from the arrangement of the damping stop result and no settings are required.

In order to also have the possibility of replacing individual needles that are particularly susceptible to wear, according to a further feature of the invention, each armature is individually assigned the further yoke part, so that individual systems can be installed separately here.

During assembly, there is the possibility of premounting the base plate with the cores of the electromagnets, with the permanent magnets, with the electromagnets and the first yoke parts and grinding them flat so that the pole ends of the yoke parts and the cores lie exactly in one plane. If the damping stop is also to be in one plane with these pole ends of the yoke parts and the cores, then the damping stop is also ground to this plane at the same time.

In the manufacturing process, it is then provided that the armature, when the spring is tensioned, is ground in the yoke part individually assigned to it so that the underside of the yoke part and the armature likewise form a plane such that when the electromagnet is not energized, the armature is positioned precisely without any tilting on the cores of the electromagnets.

This method has the additional advantage that the armature can be mounted in the yoke part assigned to it without the force of the permanent magnet having a disadvantageous effect here.

Further advantages and details of the invention result from the following description of various embodiments of the invention.

• FIG. 1 einen Schnitt durch ein erfindungsgemäß ausgebildetes Nadeldrucksystem,
• FIG. 2 ist eine teilweise geschnittene Draufsicht auf den Anker in seinem Jochteil,
• FIG. 3 zeigt in Explosivdarstellung die Art und Weise, wie eine Vielzahl von Nadeldrucksystemen gemäß FIG. 1 zu einem Nadeldruckkopf vereinigt sind,
• FIG. 4 zeigt die Anordnung einer Mehrzahl von Nadeldrucksystemen in einer Reihe zur Konstruktion eines Zeilendruckers.

In the drawings shows

• FIG. 1 shows a section through an inventive needle printing system,
• FIG. 2 is a partially sectioned plan view of the anchor in its yoke part,
• FIG. 3 shows in an exploded view the manner in which a large number of needle printing systems according to FIG. 1 are combined to form a needle print head,
• FIG. 4 shows the arrangement of a plurality of dot matrix printing systems in a row for the construction of a line printer.

Each system has a base plate 1, which consists of a magnetically conductive material. An electromagnetic core 2 is fastened in this base plate 1. At the edge of the base plate 1, a permanent magnet 3 is arranged, which can be individually assigned to each magnet system, but which, as shown in FIG. Figure 3 shows which can take the form of a ring 30 which is axially magnetized. A first yoke part 4 serves to partially close a magnetic circuit between the core 2 of the electromagnet 5, 6, the base plate 1, the permanent magnet 3 and this yoke part 4. On the base plate 1, a coil carrier 5 is also fastened, on which the electromagnetic coil 6 is wound. A tubular part 7 is arranged on the coil carrier 5 for carrying out the ends of the winding. To fix the second yoke part 8 on the first yoke part 4, retaining bolts 9 are subsequently inserted into recesses in the yoke part 4. The further yoke part 8 can be seen in particular from FIG. It has two recesses 10 for its spatial definition on the first yoke part 4 and has two projecting pole ends 11, which surround an armature 12 on both sides, so that a uniform air gap 13 results between the armature 12 and the two pole ends 11 of the yoke part 8. For this purpose, the armature 12 is made of a particularly easily magnetizable material - Vacoflux - as a square part with a round bore. The spring 14 is made of round steel and its end 15 is inserted into a corresponding recess in the second pole part 8. A pinch 16 of the spring 14 ensures that the spring 14 can bend. At the same time, the pinch also serves to ensure that the armature 12 with the spring 14 in the direction of the two pole ends 11 in the yoke part 8 has the necessary transverse stability so that the armature 12 does not touch these pole ends 11. A further pinch 17 is attached to the spring 14, which runs perpendicular to the pinch 16 and is used for soldering on the pressure needle 18. In between, a smaller pinch ensures that the anchor is stuck.

In order to dampen the oscillation of the pressure needle or the spring when the pressure needle returns to the tensioned rest position, a damping stop 19 is provided, which is fastened on a post 20 in the base plate 1. Two guide stones 21 and 22 are used to feed the printing needles 18 in a manner converging on the printing base.

The drawing also shows that by a certain angling of the spring 14 between the pinch 17 and the armature 12, the pressure needle 18 in the rest position, i.e. that is, in the situation in which the electromagnet 6 is not energized, bears against the damping stop 19. Furthermore, the drawing shows that the armature 12, when the spring 14 is in the relaxed position, extends somewhat obliquely with its pole end. This means that the pole end 23 of the yoke part 8 and the pole end 24 of the armature 12 in the relaxed position of the spring 14 - electromagnet 6 excited - is so beveled that when the armature 12 and the magnetic core 2 are in contact, the armature 12 is not tilted and that the two parts lie snugly on top of each other. As a result, the performance of the permanent magnet is best utilized, which on the other hand also leads to an improvement in the performance of the entire system, since precisely defined currents are required for the electromagnet 6 in order to cancel the force of the permanent magnet and to cause the pressure of the pressure needle 18.

A consideration of FIG. 1 and 2 also shows that the system, consisting of spring 14 and armature 12, is essentially symmetrical in the direction of the axis of the spring, so that there are hardly any tilting moments for the armature.

The needle printing systems are mounted so that the parts 1, 2 3, 4, 5 and 6 and 2o and 19 are preassembled as one part, ie without the bearing bolts 9. Then this preassembled part is ground flat, so that the damping stop 19, the The pole end of the core 2 of the electromagnet 5, 6 and the pole end 25 of the yoke part 4 lie in one plane with zero tolerance. The yoke part 8, the spring 14 and the armature 12 are then preassembled as follows: First, the spring 14 is provided with the pinch 16, and the spring 14 is inserted with its end 15 into the recess in the yoke part 8 until it is firmly seated. Then the anchor 12 by means of its bore Striped over the spring 14 until he is stuck on the pinch 16. Then the spring 14 is as shown in FIG. 1 can be seen slightly bent and the pressure pin 18 soldered onto the pinch 17 then attached. The spring 14 is then tensioned. The result is that the armature 12 emerges from the yoke part 8 to a certain extent unevenly. Now the part 8 is ground with the part 12 so that the underside 24 of the armature 12 lies exactly in one plane with the pole end 23 of the yoke part 8. Here, too, there is a tolerance of zero. As soon as the part 8 is then placed on the subsequently attached bolts 9 on the yoke part 4, the armature 12 lies flat with its underside 24 on the core 2 of the electromagnet 6 without any air gaps, canting or the like remaining. Because the armature 12 is absolutely flat in the tensioned position of the spring and without any air gap or any tilting on the core 2 of the electromagnet 5, 6, erosions between the armature and the core are avoided, which increases the efficiency of the system and at the same time reduces wear. Should wear nevertheless occur, this will take place uniformly over the entire surface and is not impeded by the penetration of the pressure needle 18 at the end 17 of the spring 14 into the damping stop 19. The whole system does not require any special adjustment operations, neither for ensuring the air gaps between the armature 12 and the two arms 11 of the yoke part 8, nor between the armature 12 on the one hand and the core 2 of the electromagnet 5, 6 on the other hand. It works for the assembly of the anchor with the clamping action of the spring. Screw connections are largely avoided when assembling the overall system.

In the following, the FIG. 3 and 4 are discussed to explain how the individual dot-matrix printing systems can now be combined to form an overall system.

FIG. 3 shows in particular a wire dot print head. Dev chend from the needle printing system according to FIG. 1 and 2, only the first yoke part 4 is in the form of a cage 4o, which surrounds all the electromagnets 5, 6. Deviating further, the magnet 3 is not assigned to each individual system, but is designed in the form of a ring magnet 30 which is axially magnetized. Otherwise, the dot-matrix printing system according to FIG. 3 exactly the system, as shown in FIG. 1 and 2 is shown. A housing 39 is used for assembly. The front boundary surface 26 of this housing is provided with a mouthpiece 27 in which the needle guide 22 can be seen at the front. A sensing roller 28 is mounted under the mouthpiece 27 and serves to sense the paper thickness and thus to set the exact printing distance between the front edges of the printing needle 18 and the printing pad. The lower part of the housing is provided with dovetail-shaped ribs 29 with which it can be held in a detent. Ribs 31 and recesses 32 in the housing 39 are intended to ensure the best possible cooling of the system, which heats up over longer working hours.

In the interior of the housing nor a projection 33 is provided which serves to hold the cage member 4 _0, the ring magnet 30 and the base plate 1 by means of recesses 34 in position and to lead. A rubber ring 35 is provided between the housing 39 and the yoke part or the yoke parts 8 of the pressure needle system, which holds the systems elastically. A similar rubber ring 36 is also present under the base plate 1, ie an elastic rubber ring 36 is also present between the base plate 1 and a printed circuit board 37 for leading out the connections 38 of the electromagnets 2, 5, 6. In addition to the magnetic force of the permanent magnet (s) 3, the rubber rings 35, 36 hold the parts in their relative position to one another.

Instead of the cage part 40 of the ring magnet 30, a needle printhead according to FIG. 3 a system can be used, as shown in FIG. 1 and 2 show, that is with individual permanent magnets 3 and individual yoke parts 4. The drawings clearly show that the entire assembly of the needle printhead takes place almost without screw connections. The individual parts are only put together and held in their position relative to one another and to the housing by means of a correspondingly meaningful design.

Because each needle is individually stored and held in a yoke part 8, it is possible to exchange this yoke part with its anchor and the needle if, for example, a needle has broken off or if the wear on the needle is so great that this needle is not prints more.

FIG. 4 shows that the same dot matrix printing systems can also be used to produce a line printer. The base plate 1 is elongated here, and the individual pen pressure systems are arranged next to one another on this base plate at a certain distance from one another. The printing needles 18 act on the printing pad 41. To generate the characters, the entirety of the printing systems must either be moved by the distance between two printing needles 18 or the printing pad must be moved from left to right or from right to left by the same amount. At the same time, of course, transport of the record carrier perpendicular to the line direction is required. One line is printed each time the printing needle systems move by the distance between two printing needles 18.

Without design changes and the like, it is possible to implement various needle strokes with this needle pressure system by making the pressure gap between the armature 12 and the core 2 of the electromagnet 5, 6 somewhat smaller or larger. This is particularly necessary if, such as. B. in a passbook printer, for example on the right side of the book there are more sheets and thus a thicker paper layer is provided than on the left side of the book.

Claims (13)

1.Needle printing system consisting of a base plate made of magnetic material and one or more permanent magnets, individually or jointly assigned to the printing needles, and electromagnets, each with a core, individually assigned to each printing pin, yoke parts for bridging the air gaps between the poles of the permanent magnet (s) and the electromagnet, whereby the permanent magnets pull an armature with the spring under tension against the core of the non-energized electromagnet and the spring causes the armature to snap forward into the pressure position with the pressure needle when the electromagnet is excited,
characterized,
that on the one hand the pole ends (25) of first yoke parts (4) which partially bridge the air gap between the permanent magnets (3) and the electromagnets (2, 5, 6) and the pole ends of the cores of the electromagnets (5, 6) lie in one plane and
that on the other hand the anchors (12) are arranged in a further yoke part (8) and
that the pole ends (11) of this further yoke part (8) and the pole end (24) of the armature (12) also lie in one plane in their pretensioned position when the electromagnet (5, 6) is not energized. 2. Needle printing system according to claim 1,
characterized,
that a damping stop (19) for the spring (14) carrying the armature (12) lies in one plane with the pole ends of the cores (2) of the electromagnets (5, 6) and the pole ends (25) of the first yoke parts (4) . 3. Needle printing system according to claim 1,
characterized,
that each armature (12) is individually assigned the further yoke part (8) in which the armature (12) is mounted by means of the spring (14) in such a way that there is an exact air gap between the yoke part (8, surrounding the armature (12) 11) and the anchor (12). 4. Needle printing system according to claim 3,
characterized,
that the spring (14) consists of a round steel bar, which is squeezed several times (16, 17) and the one pinch (16) also serves as suspension and for transverse stabilization of the armature and the spring in a recess of the yoke part (8), while the other pinch (17) is used for soldering the pressure needle (18) and that between the two pinches (16, 17) the armature is also stuck by pressing. 5. needle printing system according to claim 1 and 2,
characterized,
that for assembly to a needle print head, the first yoke parts (4) are arranged on an outer ring and the electromagnets (2, 5, 6) on an inner ring, in the center of which the damping stop (19) is located. 6. needle print head according to claim 1, 2 and 5,
characterized,
that the permanent magnet (3) is a ring magnet (3o) which is axially magnetized. 7. needle printhead according to claim 1, 2 and 5,
characterized,
that the first yoke part (4) surrounding the electromagnet (2, 5, 6) is a cage-shaped part (4o). 8. needle print head according to claim 1, 2 and 5,
characterized,
that a permanent magnet (3) and a first yoke part (4) are individually assigned to each electromagnet (6), the yoke parts overall complementing one another to form a cage (4o). 9. needle printhead according to claim 1, 2 and 5,
characterized,
that in the center of the base plate (1) and the electromagnets (2, 5, 6) the damping stop (19) is arranged, which intercepts the ends (17) of the spring (14) equipped with the pressure needle in the prestressed rest position. 1 ₀ . Dot-matrix printing system according to claims 1 to 4, characterized in that several such systems are arranged in a row to form a line printer. 11. A method for producing a dot-matrix printing system according to claim 1,
characterized,
that the base plate (1) with the cores (2) of the electromagnets (5, 6), with the permanent magnets (3), with the electromagnets (2, 5, 6) and the first yoke part (4) as a part pre-assembled and flat be ground in such a way that the pole ends (25) of the yoke parts (4) and the cores (2) lie exactly in one plane. 12. The method according to claim 1 and 11,
characterized,
that the armature (12) mounted in its yoke part (8) is ground when the spring (14) is under tension so that the undersides of the yoke part (8) and the armature (12) form a plane. 13. The method according to claim 1 and 4,
characterized,
that the spring part (14) is first provided with a pinch (16),
that the spring part (14) is inserted into the recess of the yoke part (8) until it is fixed in the press fit, that the armature (12) is pushed onto the spring part (14) until it is stuck in the press fit and that afterwards the second pinch (17) is carried out and then the pressure needle (18) is soldered.

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