EP0188671A1 - Armature construction group manufacturing process for matrix print heads - Google Patents

Abstract

The armature assembly for matrix print heads having a plurality of magnetic drives for a corresponding plurality of print elements is made by providing an annular armature ring and positioning a disc annulus inside the armature ring in a concentric relation thereto; a resilient arm ring is superimposed upon the disc and armature ring so as to establish concentric placement thereto; the arm ring is fastened to the armature ring and the arms of the arm ring to the disc such that the ring arms extend above an annular gap between the armature ring and the disk; subsequent slots are thermally cutting into the disk to obtain individual armature arms, the slots extending into and through said annulus to divide the annulus into individual arms that remain connected to the armature ring on account of the fastening. The disk may have been cut out from the armature ring.

Description

The invention relates to a method for producing an armature assembly for a matrix print head, wherein resilient arm arms are attached to an outer armature ring over the circumference.

Such armature assemblies are used in conjunction with electromagnets or permanent magnets to force the printing element (in the case of serial matrix printing heads this consists of a printing needle, also called printing wire) into the printing position with great force. H. move against an ink ribbon, whereby a pressure point is created on one or more consecutive recording media (paper webs). The pressure element is in this case fastened to a resilient armature which is biased by means of the permanent magnet. The electromagnet is used to temporarily cancel the permanent magnetic field. Such a magnet system is referred to as a pre-tensioned magnet system because the resilient armature arm is held in a tensioned position.

Matrix print heads of this type have meanwhile become a mass article. The large number to be manufactured and the requirements for precise manufacture (serial matrix print heads already achieve a write speed of over 200 characters / sec.) And the required write performance (lifespan) of several million characters require special manufacturing processes.

In the manufacture of an armature assembly for matrix print heads, it is known (DE-PS 30 17 903 or EP-OS 0 009 873) to provide a largely thin armature ring with radial slots, so that resilient armature arms are formed. Elongated parts are placed and fastened on these anchor arms, at the tip of which the pressure needle is arranged. After assembly of the matrix print head, the elongated parts slide in the guide slots of a cover plate. The necessary play between the elongated parts and the guide slots is characterized by tight, expensive tolerances.

It also creates a critical parasitic air gap that becomes problematic due to different slot widths within a printhead. These different slot widths lead to different needle flight times, which results in a poor typeface.

The invention has for its object to produce an armature assembly for a matrix printhead with high accuracy, which is economical to manufacture for mass production (no tight tolerances _. Requires) and still ensures high energy utilization of the electrical energy supply during operation of the matrix printhead.

The object is achieved according to the invention in that a circular anchor ring and a round disc concentrically introduced into the interior of the anchor ring are firmly connected to a spring arm ring placed on the anchor ring by the spring arms covering the annular gap between the anchor ring and round plate being fastened to the round plate and in that only then is the lateral contour of the resilient anchor arms formed on both sides by thermal slitting of the round blank. It is economical first of all that the round blank itself can be worked out of the circular anchor ring, so that advantageously no waste is produced. It has also been shown in the practical implementation that after concentric insertion of the round plate, the concentricity of anchor ring and round plate can easily be fixed very precisely by the connection with the spring arm ring. This condition is now maintained by the fact that the armature arms are only subsequently manufactured, whereby any inaccuracy can be avoided.

In a development of the invention it is provided that the thermal slitting along the contours of the resilient armature arms begins in predetermined recesses in the spring arm ring. The start of the process is therefore in an already free space between the anchor ring and the blank.

The high accuracy of the generation of the resilient armature arms is achieved in that the thermal slitting of the spring arms in the round blank is performed by laser cutting.

In a further development of the invention, it is provided that the anchor ring and the round blank are produced from flat strip magnetic iron in a common operation. Accordingly, the manufacture of the anchor ring and round blank takes place practically simultaneously.

Another improvement of the invention is that a round blank is reworked on its inner diameter and a raw blank on its outer diameter. Due to the post-processing, a highly precise setting of the secondary so-called parasitic air gap mentioned is possible.

If post-processing is to be dispensed with, it is provided according to further features of the invention that the armature ring and the round blank are produced by sintering magnetic powder with a finished size.

Both in the finishing of the anchor ring on its inner diameter and the round plate on its outer diameter as well as in the manufacture of the anchor ring or the round plate by sintering, it is advantageous according to further features of the invention that the annular gap between the anchor ring and the round plate has the values of one required uncritical, parasitic air gap of the biased electromagnetic permanent magnet system used in matrix printheads is dimensioned. In such a system, such an uncritical air gap arises radially between the armature ring and the rear face of the armature arms.

An embodiment of the invention is shown in the drawing and will be described in more detail below.

• Fig. 1 einen Matrixdruckkopf der vorgespannten Bauart halb Schnitt, halb Ansicht,
• Fig. 2 den Matrixdruckkopf gemäß Fig. 1 in Ansicht auf die Druckelemente mit mehreren Teil schnitten in aufeinanderfolgenden Ebenen des Querschnittes gemäß Fig. 1:
  • Schnitt I in der Schnittebene gemäß Fig. 2,
  • Schnitt II in der Schnittebene gemäß Fig. 2,
  • Schnitt III in der Schnittebene gemäß Fig. 2,
  • Schnitt IV in der Schnittebene gemäß Fig. 2,
• Fig. 3 eine Vorderansicht der Ankerbaugruppe bestehend aus Ankerring, Ronde, Federarmring (teilweise weggelassen),
• Fig. 3a einen senkrechten Achsenschnitt durch die Ankerbaugruppe gemäß Fig. 3,
• Fig. 4 eine Vorderansicht auf die Ankerbaugruppe nach dem Schlitzen der Ronde,
• Fig. 4a einen senkrechten Querschnitt durch die Ankerbaugruppe gemäß Fig. 4,
• Fig. 5 einen Rohling für den kreisförmigen Ankerring, vor dem Ausschneiden der Ronde,
• Fig. 6 den kreisförmigen Ankerring nach dem Ausschneiden der Ronde,
• Fig. 7 die aus dem kreisförmigen Ankerring gemäß Fig. 6 gewonnene Roh-Ronde,
• Fig. 8 die Ronde nach dem Nachbearbeiten,
• Fig. 9 der kreisförmige Ankerring nach einer Nachbearbeitung des Innendurchmessers und
• Fig. 10 das Einbringen der nachbearbeiteten Ronde in den nachbearbeiteten.kreisförmigen Ankerring in konzentrischer Stellung vor dem Auflegen des Federarmrings.

Show it:

• 1 is a matrix printhead of the pretensioned type half section, half view,
• 2 shows the matrix print head according to FIG. 1 in a view of the printing elements with several parts cut in successive planes of the cross section according to FIG. 1:
  • Section I in the sectional plane according to FIG. 2,
  • Section II in the sectional plane according to FIG. 2,
  • Section III in the sectional plane according to FIG. 2,
  • Section IV in the sectional plane according to FIG. 2,
• 3 is a front view of the armature assembly consisting of armature ring, round plate, spring arm ring (partially omitted),
• 3a shows a vertical axis section through the armature assembly according to FIG. 3,
• 4 is a front view of the armature assembly after the round blank has been slit,
• 4a is a vertical cross section through the armature assembly of FIG. 4,
• 5 is a blank for the circular anchor ring, before cutting the blank,
• 6 shows the circular anchor ring after the round blank has been cut out,
• 7 shows the raw round blank obtained from the circular anchor ring according to FIG. 6,
• 8 the round blank after reworking,
• Fig. 9 of the circular anchor ring after finishing the inner diameter and
• 10 shows the introduction of the reworked round blank into the reworked circular anchor ring in a concentric position before the spring arm ring is placed on it.

FIGS. 1 and 2 serve to explain the functions of a (serial) matrix printhead as an example in order to precede the interaction of an armature assembly with other function groups within the overall matrix printhead of the description of the manufacturing method of the armature assembly.

The serial matrix print head shown in the drawing has an electromagnetic coil assembly 1, which consists of a magnetic flux guide plate 2, magnetic pole cores 3 fastened to it with electromagnetic coils 4 and a permanent magnet plate 5. The electromagnetic coil assembly 1 is opposite an armature assembly 6, which consists of an armature ring 7, (in the drawing) to the left and to the right according to FIG. 1 armature arms 8, the armature arms 8 each by means of relatively short spring arms 9 with the Anchor ring 7 are connected. The number of magnetic pole cores 3 of the electromagnetic coils 4, the armature arms 8 and the spring arms 9 corresponds, as usual, to the number of pressure elements 10, which in the exemplary embodiment are designed as relatively long pressure needles and are stored in a mouthpiece 11. In the present exemplary embodiment there are 2 x 12 = 24 pressure elements within the electrically or magnetically non-conductive housing 12, which is composed of the two housing parts 12a and 12b and is held together by means of screws 13 distributed over the housing circumference.

The pressure elements 10 are guided around the pressure path (approx. 0.3 to 0.6 mm) essentially axially movable in a guide housing 14 in bearings 15. Supplements 17 are located between the housing 12 and the guide housing 14 in order to determine the exit length of the pressure elements 10 from the guide housing 14 and also to be able to change them later. The guide housing 14 serves at the same time for fastening the matrix print head on a carriage (not shown) or the like, which is moved back and forth in front of a pressure abutment. A flange 14a and at least two dowel pins 14b are provided for fastening.

Current is applied to the electromagnetic coils 4 by connection to a character generator (not shown further), which is located on a circuit board circuit, by means of plug connections 18 and 19.

An uncritical, parasitic air gap 20 is provided, the size of which, with the slightest deviations, can have a negative influence on the magnetic flux density and thus on the energy transmission and the build-up and breakdown of the electromagnetic fields or the permanent magnetic fields. The air gap 20 is not critical when the air is optimally magnetized. Such an optimal magnetization of the air gap 20 is present when the air gap is dimensioned so large that on the one hand no tight tolerances for the manufacture of the anchor ring 7 or the anchor arms 8 have to be required and on the other hand the field line density is indeed large enough to accommodate the pretensioning force the spring arms 9 to keep the balance, but on the other hand is not too high to hinder a rapid breakdown of the permanent magnetic field when the electromagnetic coils 4 are switched on. This practically ideal case can be realized by manufacturing the armature assembly according to the invention as described below. An intermediate plate 24 arranged between the magnetic flux guide plate 2 and the armature ring 7 forms a uniform plane 25 with its end face 24a (Fig. 2), wherein the armature ring 7 rests against the intermediate plate 24 in this plane 25 when the housing parts 12a and 12b are connected.

The armature arms 8 lie in the retracted position (as shown in FIG. 1) at a slight angle to the plane 25 and rest on the associated magnetic pole cores 3. Here, the thickness of the anchor ring 7 corresponds approximately to the thickness of the anchor arms 8, including the relatively small thickness of the spring arms 9, which are connected to the anchor arms 8 and the anchor ring 7. The very short spring arm 9 is given a shortened clamping length by a step 7a, so that the remaining anchor ring surface 7b is available for the connection. The gradation 7a additionally creates a freedom of bending for the armature arm 8. The gradation 7a may a continuation of the air gap 20.

However, it is possible to make the short spring arms 9 of antimagnetic material, e.g. Chromium-nickel steel, so that no magnetic field lines can run over the spring arms 9 or over the space of the gradation 7a.

A further limitation of stray fluxes or a concentration of the magnetic field lines is carried out by the magnetic flux guide plate 2, which ends opposite the side of the pressure elements 10 approximately at the level of the magnetic pole cores 3.

First, the prepared anchor ring 7 and a round 27, which is introduced concentrically into the interior 26, are connected to an already prepared spring arm ring 28, which has relatively short spring arms 9. The anchor ring 7 and the spring arm ring 28 are preferably exactly concentric over their respective outer diameters. The round blank 27 is introduced into the interior 26 to the anchor ring 7 and spring arm ring 28 exactly concentrically. Then, for example by spot welding or by pinning, the spring arms 9 firmly connected to the round blank 27. The spring arms 9 now project beyond the annular gap 29 and form a rigid connection between the anchor ring 7 and the round plate 27 (FIGS. 3 and 3a).

Subsequently, the lateral contour 30 is carried out by baking, melting or the like. Slits 31 in an approximately radial direction (FIGS. 4 and 4a), so that peaks 32 and individual resilient armature arms 8 are produced with a predetermined slot width. The tips 32 lie here on a predetermined closed line 33. The center of the disk is designated 33a. The thermal slitting is advantageously started as a starting position due to the predetermined recesses 9a of the spring arm ring 28 in the annular gap 29.

After the slitting operation, the armature assembly is finished with the highest precision and only requires the installation according to FIG. 1. Such a precise manufacture of the spring arms 9 is carried out by laser cutting.

The preparatory method steps are described below in order to be able to produce the anchor ring 7 and the round blank 27 with sufficient accuracy.

The round plate 34 is produced from a magnetic iron flat strip (for example in the follow-up cutting process) by punching. Instead of a stamping operation, eroding or a similar process can also be used. This creates the raw diameter "D" (Fig. 5). In a further process step, the round blank 27a is obtained from the round plate 34 without any significant waste occurring (FIG. 6). The raw circular blank 27a has the diameter dl.

The raw circular blank 27a can, however, already be produced with the smaller diameter d2 (FIG. 7). In the first case, the anchor ring 7 is widened to its finished dimension by reworking its inner diameter dl to dl '(FIG. 9), and the raw round blank 27a with its outer diameter dl or d2 is widened to its finished dimension d2' (FIG. 8) is brought.

However, the anchor ring 7 and the round plate 27 can also be produced by sintering magnetic powder to the finished dimensions D, dl 'and d2' (FIGS. 8, 9 and 10). The parts produced in this way correspond to FIG. 10.

The parts according to FIG. 10 thus each form the starting basis for the manufacturing method described for FIGS. 3, 3a and 4, 4a.

The phase shown in FIG. 10 therefore takes into account that the annular gap 29 between the armature ring 7 and the round plate 27 is dimensioned to the values of the described, necessary, non-critical, parasitic air gap 20 according to FIG. 1 of the pretensioned electromagnet-permanent magnet system used in matrix print heads becomes.

The parts made by stamping or sintering, i.e. the anchor ring 7 and the round plate 27 can, under certain conditions, also be produced by investment casting to the specified finished dimensions D, dl 'and d2'. 3, 3a and 4, 4a, spring arms 9 and armature arms 8 are positioned in an extremely precise manner. Positional accuracy is the basic prerequisite for armature assemblies equipped with flat spring arms 9 and thick armature arms 8, such Anchor assemblies work without special guides for the anchor trough 8.

Claims (7)

1. Method for producing an armature assembly for a matrix print head, resilient arm arms being attached to an outer armature ring over the circumference,
characterized,
that a circular anchor ring (7) and in the interior (26) of the anchor ring (7) concentrically introduced Ronde (27) with a spring arm ring (28) placed on the anchor ring (7) are firmly connected by the spring arms (9) Annular gap (29) between anchor ring (7) and blank (27) covering are fastened to the blank (27) and only then is the lateral contour (30) of the resilient anchor arms (8) formed on both sides by thermal slitting of the blank (27) becomes. 2. The method according to claim 1,
characterized,
that the thermal slitting along the contours (30) of the resilient armature arms (8) in predetermined recesses (9a) of the spring arm ring (28) is started. 3. The method according to claims 1 and 2,
characterized,
that the thermal slitting of the spring arms (9) in the round blank (27) takes place by laser cutting. 4. The method according to claims 1 to 3,
characterized,
that the anchor ring (7) and the circular blank (27) are made in a common operation from flat ribbon magnetic iron. 5. The method according to claims 1 to 4,
characterized,
that a round plate (34) on its inside diameter and a raw blank (27a) on its outside diameter are reworked. 6. The method according to claims 1 to 5,
characterized,
that the armature ring (7) and the round plate (27) are produced by sintering magnetic powder with finished dimensions (D, dl 'and d2'). 7. The method according to claims 1 to 6,
characterized,
that the annular gap (29) between the armature ring (7) and the round blank (27) is dimensioned to the values of a required uncritical, parasitic air gap (20) of the pretensioned electromagnetic permanent magnet system used in matrix print heads.

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