EP0357860A1 - Wire matrix print head of the flap armature type - Google Patents

Abstract

In a wire matrix print head of the flap armature type, each printing needle (1) is assigned a flap armature (3), a magnet yoke (10) is located opposite each flap armature (3), one of the two magnet yoke legs (10a, 10b) being surrounded by an electromagnetic spool (2), the flap armature (3) is mounted between the magnet yoke (10) and a support bearing (14) located opposite for swivel positions which correspond to the retracted and front position of the printing needle (1), and the flap armature (3) or the printing needle (1) each being held in the retracted position by means of a leg spring (16), a first spring leg (16a) being supported against a print head or on the flap armature (3) and a second spring leg (16b) being supported on a print head housing side (4). <??>In order to provide the flap armature (3) or the printing needle (1) with a more advantageous guiding by an improved design of the leg spring (16) in each case, it is proposed that all the leg springs (16) be connected to each other and form an integral spring cage (17). <IMAGE>

Description

The invention relates to a matrix needle printhead of the hinged armature type, with each hinged armature associated with the hinged armature, with each hinged armature arranged opposite magnet yoke, one of the two magnet yoke legs being surrounded by an electromagnetic coil, the hinged armature between the magnet yoke and an opposite support bearing for pivoted positions, which is the retracted and correspond to the front position of the pressure needle and the hinged armature or the pressure needle are each held in the retracted position by means of a leg fender, a first spring leg being supported against a pressure needle head or on the hinged armature and a second spring leg being supported on a printhead housing side.

Such hinged anchor systems are critical with regard to the accuracy of the manufactured parts and the resulting functional accuracy. Economic production requires relatively large tolerances in dimensions. In addition, the assembly based on this entails more or less fixed costs. In operation, however, the hinged anchor system should be functionally accurate and durable. These conflicting requirements continually lead to new efforts to look for system improvements that not only reduce manufacturing costs and facilitate assembly, but also increase the service life. In addition, increases in speed, i.e. the actuation frequency required.

A hinged anchor system of the type described is known from DE 32 43 475 C2. The known solution uses generic hinged anchors of the generic type between the magnetic yoke and an opposite elastic O-ring as a support bearing, with each pressure needle between a guide bush and a pressure needle head by means of a helical spring is pressed against the hinged armature so that it is in the rest position, ie in the retracted position, as long as the electromagnet coil is not energized. Such a design leads to the fact that the pressure needles between the guide bush and the anchor point of attack are completely free and can perform uncontrolled movements, which is disadvantageous.

Another known solution, which comes closest to the generic type mentioned in one embodiment, is known from DE-GM document 78 27 095. Although this solution already provides leg springs instead of helical springs on the print head, the lateral guidance of the print head is still very soft.

In relation to this state of the art, the object of the invention is to provide the hinged anchor or the pressure needle with more advantageous guidance in each case by an improved design of the leg spring.

The stated object is achieved according to the invention in that all leg springs are connected to one another and form a one-piece spring cage. The connection of all leg springs leads to stiff spring legs and a high positional accuracy of the spring engagement points on the pressure needle or on the hinged anchor. The production of only one one-piece workpiece is favorably opposed to 9, 18 or 24 individual leg springs. The assembly of the hinged anchor is also considerably cheaper if the workpiece is only one piece. The spring force can be provided uniformly for all printing needles. As a result, the impressions of the individual printing needles are much more uniform than before.

In an embodiment of the invention it is provided that the spring cage is fixed at least radially on the inside and at least with the second spring leg on the inside of a pressure needle guide housing. This makes assembly easier, more accurate and faster than before. In addition, the group of 7, 9, 12, 18 or 24 printing needles is fixed more precisely and guided precisely over the entire stroke during operation.

An improvement of the invention is that the first spring leg is provided with a U-shaped guide comprising the armature cross section. The spring cage is therefore also suitable for the various types of needle fasteners, in which the pressure needle either lies loosely on the hinged anchor with the pressure needle head or is rigidly connected to the hinged anchor without a pressure needle head. The spring cage can thus be used for different needle attachments on the hinged anchor.

The spring cage is advantageously produced from a one-piece, round, stamped part. With a sheet thickness of e.g. From 0.05 to 0.3 mm it is possible in a common tool to punch out the spring legs and then bend them in the appropriate direction. From a diameter dependent on the elongated diameter of the spring legs, therefore, only a metal strip of the stated thickness and width is required, which can be punched and bent in a follow-up cutting tool, so that the spring basket is finally conveyed out at the end of the tool.

Following this, the functions of the spring cage in the installed state can also be taken into account during manufacture by the U-shaped guide on the first spring leg being bent up on the flat stamped part and by the first spring leg being executed with the finished U-shaped guide to the second spring leg is bent.

• Fig. 1 einen axialen Längsschnitt als Halbschnitt durch den betriebsbereiten Matrixnadeldruckkopf,
• Fig. 2 einen Teilschnitt aus Fig. 1 in vergrößertem Maßstab im Bereich des Federkorbes,
• Fig. 3 eine Seitenansicht zu Fig. 2 auf den Federkorb mit den Drucknadeln von hinten,
• Fig. 4 die Herstellung des Federkorbs aus einem Stanzteil in vergrößertem Maßstab mit über den Umfang verteilten Herstellschritten,
• Fig. 5 einen Querschnitt durch Fig. 4 in Richtung V - V und
• Fig. 6 einen Querschnitt durch Fig. 4 in Richtung VI - VI.

In the drawing, an embodiment of the invention is shown schematically and is explained in more detail below. Show it:

• 1 shows an axial longitudinal section as a half section through the ready-to-use matrix needle print head,
• 2 shows a partial section from FIG. 1 on an enlarged scale in the area of the spring cage,
• 3 shows a side view of FIG. 2 of the spring cage with the pressure needles from behind,
• 4 shows the manufacture of the spring cage from a stamped part on an enlarged scale with manufacturing steps distributed over the circumference,
• Fig. 5 shows a cross section through Fig. 4 in the direction V - V and
• Fig. 6 shows a cross section through Fig. 4 in the direction VI - VI.

A matrix needle printhead of the hinged armature type is equipped with an electromagnetic coil 2 assigned to each pressure needle 1 and a hinged armature 3. The printing needles 1 are arranged in printing needle gaps with 7, 9, 2 times 9, 12 or 2 times 12 printing needles and are guided in a printing needle guide housing 4 in a guide mouthpiece 5, which is located at a stroke distance in front of a pressure abutment 6. An ink ribbon (not shown) (perpendicular to the plane of the drawing) is moved in front of the printing needles 1 and a recording medium 7 is guided over the printing abutment 6, on which characters or images are generated.

In a rear housing part 8, which is closed with a cover 9, the electromagnetic coil 2 and each folding armature 3 are each assigned a magnetic yoke 10. The electromagnetic coil 2 surrounds one of the magnetic yoke legs 10a or 10b. The magnet yokes 10 are seated in a base plate 11 which is further developed towards the central axis 12 towards a hub 13.

Each hinged armature 3 is pivotally mounted between a magnetic yoke 10 and an opposite support bearing 14, consisting of an elastic O-ring 14a. A damping ring 15 is also arranged on the hub 13, against which the hinged armature 3 with its radially inner hinged armature arm 3a facing the pressure needle 1 bears in the retracted pivot position.

In this retracted position, each hinged anchor 3 is held by means of a leg spring 16, which are connected to a one-piece spring cage 17. In the event that the pressure needle 1 (FIGS. 2 and 3) is connected to the hinged armature 3 or the radially inner hinged armature arm 3a via a bore 18 with weldings 19, the pressure needle 1 (with a pressure needle head, not shown) is not underneath, but the hinged arm 3a itself.

The leg spring 16 as a member of the spring cage 17 each has a first spring leg 16a and a second spring leg 16b. While the first spring leg 16a forms a U-shaped guide 20 which includes the hinged armature 3 (FIGS. 2 and 3), the spring cage 17 lies at least radially (FIG. 1) on a projection 4a of the pressure needle guide housing 4 and lies with the second Spring legs 16b on the inside 4b of the pressure needle guide housing 4. The spring cage 17 is adjusted and fixed over all of these contact points. The U-shaped guide 20 corresponds to the armature cross section 3b dimensioned so that a single anchor 3 can advantageously be mounted and fixed in the guide 20.

The spring basket 17 (FIGS. 4 to 6) is produced from a one-piece, round-shaped stamped part 21. After a first process step, arms 22 are punched out with projections 23 shaped on both sides. On the arms 22, the projections 23 to the guides 20 are first bent up in a U-shape, then in a further process step (upper quarter of FIG. 4) the first spring legs 16a are formed from the arms 22 by vertical raising, which are in a last process step are completely bent inwards against a central circular opening 24 (lower right quarter of Fig. 4), so that the spring cage 17 is thus completed. The spring cage 17 is thus in a configuration over the entire circumference, as shown in the lower right quarter of FIG. 4.

Claims (5)

1.Matrix needle printhead of the hinged armature type, with each hinged arm associated with each pressure needle, with each hinged armature arranged opposite magnet yoke, one of the two magnet yoke legs being surrounded by an electromagnetic coil, the hinged armature between the magnet yoke and an opposing support bearing for pivot positions which is in the retracted and forward position correspond to the pressure needle and the hinged armature or the pressure needle are each held in the retracted position by means of a leg fender, a first spring leg being supported against a pressure needle head or on the hinged armature and a second spring leg being supported on a printhead housing side,
characterized,
that all leg springs (16) are connected to one another and form a one-piece spring cage (17). 2. matrix needle printhead according to claim 1,
characterized,
that the spring cage (17) is fixed at least radially on the inside and at least with the second spring leg (16b) on the inside (4b) of a pressure needle guide housing (4). 3. matrix needle printhead according to claims 1 and 2,
characterized,
that the first spring leg (16a) is provided with a U-shaped guide (20) encompassing the armature cross section (3b). 4. matrix needle printhead according to claims 1 to 3,
characterized,
that the spring cage (17) is made from a one-piece, round, stamped part (21). 5. matrix needle printhead according to claims 1 to 4,
characterized,
that on the flat stamped part (21) the U-shaped guide (20) is bent up on the first spring leg (16a) and that the first spring leg (16a) is executed with the finished U-shaped guide (20) towards the second spring leg (16b) is bent.

Images