EP0022480B1 - Electromagnetic print hammer actuator mechanism - Google Patents

Abstract

An electro-magnetic print hammer comprises a single magnetic hammer element in which an impact mass is coupled to a pivotted armature by flexible stem. The hammer-stem has (N+1/2) periods of oscillation at its resonant frequency during the free flight time of the hammer mass. A permanent magnet with a strong magnetic force which decays rapidly with distance holds the hammer element fixed upon motion of the armature until the armature torque exceeds the magnet holding force to cause the hammer mass to break loose with a snap action. Stop means prevents armature impacts with the operating pole piece of a stator core. The visco-elasticity of the armature stop matches the rebound characteristics of the print medium when impacted by the hammer mass.

Description

The invention relates to an electromagnetically operable printing hammer drive, consisting of a two-armed lever pivotable about an axis, the first arm of which can be flexurally oscillated, is made of magnetizable material and carries the printing hammer head at its upper end and the second arm of which can be acted upon by an electromagnet, whereby for one of the two lever arms a stop limiting the rotation of the lever with an elastic material on the stop surface and a holding device for the print hammer lever is provided in its rest position.

From US-A-3 747 521 an electromagnetically operable print hammer drive is known, which consists of a two-armed lever pivotable about an axis. One arm of this lever carries the print hammer head at its upper end; the other arm of the lever can be acted upon by an electromagnet. The lever carrying the print hammer head is able to vibrate in a flexible manner. For this reason, when the movement of the lever moved by the electromagnet is stopped, the lever carrying the print hammer head will spring forward elastically in the printing direction.

From US-A-3 705 370 an electromagnetically operable printing hammer drive is also known, but which consists of a two-armed, rigid lever which can be pivoted about an axis. In the holding state, the arm of the lever carrying the print hammer head rests on a permanent magnetic holding magnet, from which, however, it is released when an electromagnet acting on the other lever arm is excited.

US Pat. No. 3,711,804 also describes an electromagnetically operable printing hammer drive which consists of a two-armed lever which can be pivoted about an axis, the rest and pressure position of which is determined by a magnetic flux acting on this lever. With this arrangement, too, it can be assumed that the print hammer lever arm has no elastic properties.

With the structures described above, a further increase in the printing speed is problematic. The rigid pressure hammer structures are too heavy to have a short contact time; They require a lot of energy, which (could be used for printing) is lost on return springs or stop elements. With elastic hammers, on the other hand, energy is lost due to the elastic deformation of the hammer before impact. In addition, the impact of the armature on the stop or pole piece in the working air gap of the electromagnet leads to a reduction in the elastic and non-magnetic properties of the material over a long period of time. This ultimately leads to improper operation of the hammers and affects print quality.

In the elastic hammer structure, as described above in US-A-3 747 521, the kinetic energy of the moving lever arm carrying the print hammer head is used in order to bring about a corresponding increase in the impact speed during the printing process when the other lever arm strikes. However, this requires relatively long flight times since the print head moves relatively slowly before increasing its speed.

The object of the invention is to provide an improved printing hammer drive, in particular for use in high-speed printers, which, in addition to a short flight time, delivers a high impact energy of the printing hammer.

In addition, it should be easy to manufacture with great precision in mass production, have a very short contact time, avoid double stops and have a long service life.

This object of the invention is achieved in an advantageous manner in that a holding magnet for the first lever arm is provided as the holding device, that in the holding state this lever arm lies against the holding magnet untensioned, as long as the electromagnet is not actuated for a printing process, and that the holding force of the holding magnet in Compared to the pull-out force of the electromagnet is dimensioned so that the actuation of the electromagnet by tensioning the first lever arm causes energy storage in the same before the print hammer head moves in the printing direction, and that the first lever arm then moves in the tensioned state when the holding force of the holding magnet is exceeded releases the holding magnet in the direction of pressure.

Advantageous developments of the invention can be found in the dependent claims.

• Bei Erregung des Elektromagneten müßte der den Druckhammerkopf tragende Hebel (falls er nicht biegeelastisch wäre und zunächst nicht von einem Haltemagneten zurückgehalten würde) bereits eine Schwenkbewegung in Druckrichtung ausführen. Diese Schwenkbewegung setzt anfangs jedoch nicht ein, weil der Hebel vom Haltemagneten zurückgehalten wird ; dabei wird er aufgrund seiner Biegeelastizität vorgespannt und erfährt somit eine Energiespeicherung.

In summary of the invention described in detail later, the following is stated:

• When the electromagnet is excited, the lever carrying the print hammer head (if it were not flexible and would not initially be held back by a holding magnet) would already have to perform a pivoting movement in the pressure direction. However, this pivoting movement does not begin at the beginning because the lever is held back by the holding magnet; it is pretensioned due to its elasticity and thus experiences energy storage.

Only when the force of the holding magnet is no longer sufficient does the pretensioned lever tear off the holding magnet and advance in the pressure direction. As a result, it achieves a very high impact speed for the printing process with a short flight time.

In one embodiment of the invention, a stop is provided which prevents damage to the yokes at the air gap. This is the Provide anchors with a nose, the movement of which is limited by a stop. The stop is such that the anchor is stopped at the same time as the hammer strikes the pressure medium or shortly before. The stop can also consist of a passive pole of the electromagnetic yoke. In any case, the stop is provided with a cushion, the elastic properties of which are selected so that they essentially match the rebound properties of the printing medium. If the stop is designed so that it stops the movement of the armature at the beginning of the impact of the hammer head on the pressure medium, the hammer bounces back and reverses its direction of movement. However, due to the flexibility of the shaft, the print hammer head can move a little further forward and penetrate the print medium while the armature reverses its direction of movement before the print hammer head reverses upon rebounding. Then the print hammer head follows the movement of the armature and moves away from the print medium, eliminating the possibility of double impact. This also keeps the contact time between the print hammer head and the print medium very short. Where the rebound properties of the cushion and print medium are matched to one another, the rebound movement of the print hammer head and the armature takes place essentially together, so that double stops are prevented. Since the anchor moves back a little earlier than the hammer head, the anchor also helps to reduce the contact time of the hammer.

• Figur 1 eine Seitenansicht der erfindungsgemäßen Druckhammereinheit,
• Figur 2 eine Vorderansicht mehrerer Druckhammereinheiten gemäß Fig. 1,
• Figur 3 eine Draufsicht der in Fig. 2 gezeigten Anordnung,
• Figur 4 eine Seitenansicht des in Fig. 1 dargestellten Hammerelementes,
• Figur 5 eine Vorderansicht des in Fig. 4 gezeigten Hammerelementes,
• Figur 6 eine perspektivische Ansicht des Magnetjoches nach Fig. 1 und
• Figur 7 Zeitdiagramme zur Darstellung der Verschiebung des Aufschlagteiles und des Ankers des Druckhammerelementes gemäß Fig. 1 während eines Arbeitszyklus.

An embodiment of the invention is shown in the drawings and will be described in more detail below. Show it :

• FIG. 1 shows a side view of the printing hammer unit according to the invention,
• FIG. 2 shows a front view of a plurality of printing hammer units according to FIG. 1,
• FIG. 3 shows a top view of the arrangement shown in FIG. 2,
• FIG. 4 shows a side view of the hammer element shown in FIG. 1,
• FIG. 5 shows a front view of the hammer element shown in FIG. 4,
• Figure 6 is a perspective view of the magnetic yoke of Fig. 1 and
• 7 shows time diagrams to show the displacement of the impact part and the anchor of the print hammer element according to FIG. 1 during a working cycle.

1, the printing hammer unit contains a U-shaped magnetic yoke 10. The working winding 11 is located on the lower leg 12 and extends beyond the pole face 13, which forms a working air gap with the armature. The upper leg 14 is bevelled with its pole face 15 towards the end of the working winding 11. The working winding 11 is electrical via the connections 16 and 17. connected to an external power source (not shown).

The print hammer unit further comprises a hammer element 18 which is pivotally mounted on the shaft 19 in addition to the pole face 15 of the upper yoke leg 14. The armature 20 of the hammer element 18 has a projection 21 which is aligned with the lower leg 12 of the yoke 10. This projection 21 is located essentially within the winding 11 and forms with the pole face 13 of the lower leg 12 a working air gap, which lies completely inside the working winding 11 during the rotary movement of the armature 20. A second air gap is formed between the bevel 22 of the armature 20 and the beveled pole face 15 of the upper leg 14. The bevel 22 extends parallel to the pole face 15 in the most advanced position of the armature 20. A hole 40 (FIG. 4) in the upper end of the armature 20 receives a rotary shaft 19. A stop lug 24 at the lower end of the armature 20 works on an armature stop, which preferably consists of a fixed block 25 with an arm 26. The anchor stop is designed to limit the rotation of the armature 20 clockwise and to allow the armature to bounce back counterclockwise. The block 25 lies in such a way that the projection 21 of the armature 20 cannot touch the pole face 13 of the lower leg 12.

A stop pad 27 made of a suitable material such as polyurethane is attached to the end of the arm 26. When the armature 20 rotates clockwise, the stop lug 24 hits this cushion 27, the elastic properties of which should essentially match the pressure medium 31 with the rebound characteristic. The anchor 20 and the hammer head 29 begin to bounce back essentially simultaneously when the impact on the cushion 27 and the pressure medium 31 takes place simultaneously.

Starting from anchor 20, shaft 28, which carries a hammer head 29, runs upwards. The front of the hammer head 29 has an impact surface 30 with which the medium 31 is struck against characters on a character carrier (eg a type tape).

A protrusion 32 above the hammer surface 30 causes a mass distribution so that the center of the effective impact mass and the shaft mass coincide more closely with the impact center. This makes the hammer less sensitive to double impacts and the rear part 33 serves to guide the hammer head 29.

The shaft 28 is substantially reduced in depth compared to the anchor 20 and is slightly beveled from the anchor 20 to the base of the hammer head 29. The shaft 28 is designed to be flexible and permits bending in the axis of rotation of the armature 20. The extent and degree of the bending can change depending on the operating parameters of the hammer system.

The degree of flexibility means that the on Impact mass (ie hammer head 29) follows anchor 20 with a delay and also swings relative to anchor 20. The oscillation period of the resonance frequency of the arrangement Hammer / SChaft / Aufschlagrnasse is chosen so that it is N + 1/2 oscillation periods during the time of free flight. This ensures that the impact mass hits the printing medium 31 when the hammer head 29 moves at the highest possible speed and thus delivers the greatest printing energy.

4 and 5 it can be seen that the hammer element 18 is made from a piece of magnetizable material. The hammer head 29, the shaft 28 and the armature 20 are integrated into one part. As can best be seen from FIG. 5, in addition to the width, the depth of the shaft 28 with respect to the anchor 20 is also reduced. The total weight of the hammer element 18 is thus reduced and, in addition, the possibility is given to give the shaft 28 the desired flexibility in order to allow the shaft to bend and the hammer head to move independently of the anchor mass 20.

• Schaftflexibilität ca. 4,45 kg/mm
• Äquivalente Aufschlagkopfmasse = 1,2 g
• Abstand Drehpunkt/Hammerkopf = 35 mm
• Abstand Drehpunkt/Anker = 14,2 mm
• Abstand Drehpunkt/Polster = 24,5 mm
• Polfläche = 10,2 x 0,24 mm
• Ampere-Windungszahl der Spule maximal 1 000 Ampere/Windungen
• Pulszeit = ₁,₂ ms
• Polster = Polyurethan, Härtegrad 90
• Polsterdicke = 0,355 mm

Furthermore, a holding device in the form of a permanent magnet 34 is provided, which is attached to a fixed carrier piece 35. The magnet 34 is preferably located between the hammer head 29 and the shaft 19. Since the shaft 28 is made of magnetizable material, the magnet 34 exerts a counterclockwise torque on the hammer element 18 and thus acts on the armature 20 when the winding 11 is excited counterclockwise developed torque. If the winding 11 is not energized, the magnet 34 holds the hammer element in the rest position, in which the shaft 28 is not bent. In the rest position, the pole face 13 is separated from one another by the lower leg 12 of the yoke 10 and the projection 21 of the armature by the largest working air gap. The stop lug 24 is then separated from the pad 27 on the arm 26 of the block 25. The rear part 33 of the hammer head 29 rests on the upper stop 36, which is held on the support rod 35 by an adjusting screw 37. In order to print with the described one-piece hammer element, the winding 11 is excited with a short-term pulse 46 (see FIG. 7). As the magnetic field builds up in the air gap, the. Projection 21 is drawn to the lower leg 12 so that the armature moves clockwise. Due to the holding force of the permanent magnet 34, however, the hammer head 29 does not start to move immediately. The shaft 28 bends and stores elastic energy as the armature 20 moves ahead of the hammer head 29 as shown by the two curves 50 and 51 and FIG. 7. When the separating force reaches the holding force of the permanent magnet 34, the shaft 28 and hammer head 29 snap away, and the hammer head 29 is accelerated in free flight to strike the print medium 31. During flight, the shaft 28 and the hammer head 29 vibrate with a predetermined resonance frequency. As already mentioned, there are N + 1/2 oscillation periods of the shaft and the hammer head during the flight time. The hammer head 29 hits the print medium 31 at the highest possible speed. At the same moment, however, the stop stop 24 of the armature 20 also hits the stop cushion 27. When it hits this cushion 27, the armature 20 bounces back and begins to turn counterclockwise. Since the pad 27 has essentially the same elastic property as the pressure medium 31, the armature 20 and hammer head 29 bounce back at essentially the same moment. Without an exact adaptation of the elastic properties of the cushion 27 and the pressure medium 31, the reversal of the movement can take place at more or less slightly different moments. Since the shaft 28 is designed to be flexible, the anchor 20 and the hammer head 29 move to a certain extent independently of one another after the impact. In some cases the hammer head 29 may bounce back slightly in front of the anchor 20, in other cases a little later. In this case, the timing is such that the armature 20 bounces back before the hammer head 29 can reverse its direction of movement after the bouncing back. He cannot hit the print medium 31 more than once. After rebounding, the shaft 28 returns to a position in which it is held by the permanent magnet 34 until the next excitation pulse is applied to the winding 11. The following information applies to a manufactured model:

• Shaft flexibility approx.4.45 kg / mm
• Equivalent service head mass = 1.2 g
• Distance pivot point / hammer head = 35 mm
• Distance pivot point / anchor = 14.2 mm
• Distance pivot point / cushion = 24.5 mm
• Pole area = 10.2 x 0.24 mm
• Ampere number of turns of the coil maximum 1 000 ampere / turns
• Pulse time = _{1, 2} ms
• Upholstery = polyurethane, degree of hardness 90
• Upholstery thickness = 0.355 mm

The hammer unit described above can also be used in a hammer bank. A stator block 38, which is preferably cast from plastic, is provided to accommodate several (in this case 5 pieces) yokes 10 at the same distance from one another. The distance between the yokes 10 corresponds to the distance between the printing positions in a line printer. On the underside of the carrier piece 35, carrier arms 39 are arranged between the upper leg 14 of the yokes 10. The support arms 39 are made of non-magnetic material such as. B. aluminum. Circular grooves 40 in the support arms 39 form a recess 40 for the shaft 19. Vertical flanges 41 above the cover plate 42, which are also made of non-magnetic material, are aligned with the support arms 39 and hold the shaft 19 in the recess 40 when fastened by means of screws 43 to the block 35. Each hammer element 18 is thereby mechanically separated and magnetically isolated within the assembly. An upper guide piece 44 attached to the carrier piece 35 has flanges 45 for guiding the rear part 33 during the rotation of the hammer element 18 about the shaft 19. Such assemblies consisting of several hammers can be assembled in modules on a carrier frame (e.g. for line printers).

Claims (9)

1. Electro-magnetically operable print hammer drive, consisting of a two-arm lever (18) pivotable round an axis, whose first arm (28) can oscillate flexibly, consists of magnetizable material, and carries the print hammer head (29) at its upper end, and whose second arm (20) can be applied with energy by an electro-magnet (10/11), where for one of the two lever arms (20, 28) a stop (26) limiting the rotation of the lever, with elastic material (27) at the impact surface, and a holding device for the print hammer lever in its stationary position are provided, characterized in that as a holding device a holding magnet (34) for the first lever arm (28) is provided, that in the stationary state this lever arm (28) is placed without tension against the holding magnet (34) as long as the electro-magnet (10/11) is not controlled for a printing process, and that the holding force of the holding magnet (34) compared with the power of attraction of the electro-magnet (10/11) is such that the control of the electro-magnet (10/11), by the tensioning of the first lever arm (28), first effects the storing of energy therein before the print hammer head moves in the printing direction, and that subsequently when the holding force of the holding magnet (34) is exceeded the first lever arm (28) is disengaged in the tensioned state from the holding magnet (34).

2. Print hammer drive as claimed in claim 1, characterized in that the holding magnet (34) is a permanent magnet.

3. Print hammer drive as claimed in claim 1, characterized in that the electro-magnet (10/11) comprises a U-shaped magnetic core acting with at least one pole face (13, 15) on the second lever arm (20).

4. Print hammer drive as claimed in claim 3, characterized in that a core face (14) associated to the upper part (22) of the second lever arm (20) is bevelled compared with a core face (13) associated to the lower part (21) of the second lever arm (20), and that the second lever arm (20) is of a shape adapted to this core face (13,15) design to form narrow working gaps.

5. Print hammer drive as claimed in claim 4, characterized in that the bevel (15, 22) of the upper pole face (14), or its associated part of the second lever arm (20) extends over axle (19) into the region of the first lever arm (28).

6. Print hammer drive as claimed in any one of claims 1 to 5, characterized in that the impact of the print hammer head (29) during printing takes places substantially shortly before or after the arrival of the lever arm on the stop (26), or coincides with the arrival of the lever arm on the stop.

7. Print hammer drive as claimed in claim 6, characterized in that the elastic material (27) to avoid an undesired double impact of the print hammer (29) is adapted to the rebound characteristics of the printing medium.

8. Print hammer drive as claimed in any one of claims 1 to 7, characterized in that after the release of the print hammer drive and the disengaging of the first lever arm (28) from the holding magnet (34), the first lever arm (28) executes up to its impact to produce an imprint, free oscillations in and against the printing direction, and that at the time of its impact the print hammer head (29) has reached a maximum speed.

9. Print hammer drive as claimed in any one of claims 1 to 8, characterized in that for approaching the center of the effective impact mass and the lever mass to the point of impact of the print hammer head (29) an additional mass (32) is. provided at the upper end of the first lever arm (28).

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