Electromagnetic Drive

Abstract

An electromagnetic drive for the needle of a needle printer comprising a pair of cylindrical magnet pole shoes disposed within a cylindrical magnet coil and connected with the needle.

Description

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to needle printing devices and more particularly to electromagnetic drive for the needle of such devices.

II. Description of the Prior Art

Electromagnetic drives are used for causing a needle moved by them to stroke an ink support so that ink is transferred to a record support inserted behind the ink support. Mosaic-like arrangement and selective triggering of several electromagnetic drives allows the recording of characters.

Needle printers are often used in data processing machines to print data on a record support. It frequently happens, especially in the case of bookkeeping machines, that the same needle printer has to record consecutively on record supports of different thickness. For example, a blank form can be arranged on one side of the printing area and a copybook on the other side whereby records are to be made on both record supports.

In the case of known needle printers, the quality of the record depends upon the distance between the printing tips of the needles and the record support as well as upon the force exerted each time on the needle. Furthermore, the speed of the printing process depends upon the speed with which the drive for the needles responds so that the recording frequency is limited by the type of the respective drive.

SUMMARY OF THE PRESENT INVENTION

The present invention has as its object the design of an improved electromagnetic drive for the needle of a needle printer which without change of its setting, applies records of equal quality to record supports of different thickness and which has an increased operating frequency as compared to known arrangements.

To achieve this object, an electromagnetic drive according to the invention is so designed that within a cylindrical magnet coil, opposed in the longitudinal direction of the magnet coil, there are arranged two cylindrical magnet pole shoes, displaceable in the longitudinal direction of the magnet coil, connected with the needle, and having the end that is remote from the needle pressed against a damping element by a spring when the magnet coil is without current.

The spring cooperating with the damping element urges the armature into cylindrical magnet pole shoes so as to prevent vibrations during the return motion from the operating position to the resting position. Thereby, the damping element absorbs the total energy acting during the return motion of the armature. On the other hand, the spring can be so dimensioned that different deflections are possible which essentially are determined by the distance between the record support and the printing tip of the needle which is connected with the armature. Then, it is advantageous to use as spring a helical spring having, for the most part, constant tension over different lengths of deflection. Thus, the use of an electromagnetic drive according to the invention makes it possible to print on record supports of different thickness in a basic position. The arrangement of the armature within cylindrical pole shoes makes possible a very simple assemblage of the drive, for essentially, only the magnet pole shoes and the armature have to be installed in the interior space of the magnet coil; thereby, the adjustment of these individual elements in relation to each other is not critical since the final setting is determined by the arrangement of the spring and the damping element. However, this final setting can be easily obtained by external setting elements. Thus, an electromagnetic drive according to the invention is excellently suitable for mass production.

According to a further embodiment of the invention, the armature of the drive can consist of a segment having magnetic conductivity and a segment not having magnetic conductivity whereby each segment is disposed within one respective magnet pole shoe when the magnet coil is without current. Then, the magnetically non-conductive segment performs the function of providing an air gap in which the magnetic field moving the armature becomes effective. Besides, this segment can advantageously serve for guiding the armature because its connection with the magnetically conductive segment and its disposition in the other magnet pole shoe can ensure that the longitudinal movement of the total armature takes place free from canting and without interference. When a helical spring is used, the magnetically nonconductive segment can be so designed that it forms a chamber receiving the helical spring. Thereby, the helical spring is firmly enclosed, and the motion of the total armature within the magnet coil attains further precision.

The special design and arrangement of the armature which so-to-speak, is suspended between both end positions results in a very fast response of the drive. The responding motion is practically free from vibrations since the armature is supported on one side by the spring. The fast response can be even improved when the space surrounding the armature between the magnet pole shoes is filled with a material having electric conductivity. Eddy currents arise in this material, when the magnet coil is switched on, hence, this material causes concentration of the magnetic field to the range of the armature whereby an increased action of force is exerted on the armature. A further measure for fast build-up of the magnetic field consists in that the magnet coil is surrounded by a metal sheath which is slotted in the longitudinal direction of the magnet coil and which is connected with spool flanges which have magnetic conductivity and connect the metal sheath with the magnet pole shoes. The metal sheath serves for returning the magnetic flux via the spool flange. The slotting in the longitudinal direction of the magnet coil prevents the formation of eddy currents in the metal sheath so that the magnetic field build-up in the interior of the coil is not delayed because of eddy currents.

In order to make possible adjustment of the resting position and the operating position of the armature within the magnet coil, the needle can be introduced into the magnetic coil passing through a threaded pin which makes possible adjustment of the range of movement of the armature and serves as an outer support for the spring. Adjustment of the threaded pin adjusts the degree of compression of the spring so that this adjustment makes it possible to attain an optimal adaptation of the working stroke of the armature to the various record supports of different thickness on which records have to be made. A further possibility of adjustment arises when as a damping element, there is provided a damping disk, the position of which can be adjusted by a threaded pin arranged on the magnet coil end that is remote from the needle. This makes possible an adjustment of the damping element which avoids any reflection when the recoiling armature is struck.

In the case of the last-named mode of carrying out the invention, it is expedient to provide the damping disk with a central opening which communicates with the outer space of the drive via a central boring of the threaded pin supporting the damping disk. This produces an air channel which during a fast return motion of the armature, avoids any elasticity that could be caused by compressed air.

DESCRIPTION OF THE DRAWING

An example for carrying out the invention is subsequently described with the aid of the drawing which depicts a cross-section of an electromagnetic drive according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The magnetic drive illustrated in the drawing has a magnet coil 1 which is cylindrically formed. The magnet coil 1 is seated on a coil body consisting of two pole shoes 2 and 3 which are arranged in the interior of the magnet coil 1 and which are opposed by a certain distance. An armature is guided in the pole shoes 2 and 3 and consists of two segments 4 and 4a. The segment 4 is constructed of a material having magnetic conductivity while the segment 4a is constructed of a material not having magnetic conductivity, e.g., plastic. The end of a needle 5 is attached to the armature and is passed through the segment 4a which is not magnetically conductive. The segment 4a is inserted into the magnetically conductive segment 4 and joined with it, for example, by cementing. During the same manufacturing operation, the end of needle 5 can be likewise cemented whereby at the same time, it can be jammed between the two segments 4 and 4a in the interior of segment 4.

The segment 4a is designed cylindrically and to form a chamber for receiving a helical spring 6, the other end of which strikes a threaded pin 12. The threaded pin 12 is provided with a projection which corresponds to the inner diameter of the helical spring 6 so that during compression, the cylindrical form of the helical spring 6 is maintained by the chamber of the armature segment 4a as well as by the projection of threaded pin 12. Outside of the magnet coil 1, the threaded pin 12 is provided with set nut 17 which permits adjustment of the threaded pin 12 within the magnet coil 1. Such an adjustment also changes the position of the helical spring 6 so that the working stroke of the armature 4, 4a can be adjusted.

The magnetically conductive piece 4 of the armature has a frontal area which is remote from the magnetically non-conductive segment 4a and which lies against a damping disk 7. The damping disk 7 is provided with a central opening 14. In turn, the disk 7 lies on an additional threaded pin 13 which can be adjusted outside of the magnet coil 1 by set nut 18. Thus, also at that end of the armature, it is possible to adjust the range of its motion. The threaded pin 13 is provided with a central bore 15 which communicates with the outer space of the drive and permits escape of the air compressed by the return motion of the armature.

The space surrounding the armature between the two magnet pole shoes 2 and 3 is filled with a material having electric conductivity. For this purpose, there can be provided, for example, a highly conductive copper ring 8 which upon switching on of the magnet coil 1, causes the formation of strong current eddies in its material. The current eddies concentrate the magnetic field arising between the pole shoes 2 and 3 to be within the range of the armature so that fast response of the drive is ensured. Moreover, the dynamic effect is thereby increased so that if necessary, the current required for feeding the drive can be reduced.

The ends of the two pole shoes 2 and 3 are secured in place by two flange parts 10 and 11 and a metal sheath 9 that surrounds the magnet coil 1 and which is clamped between the flange parts 10 and 11. The metal sheath 9 can be provided with a slot (not shown) running in the longitudinal direction of the magnet coil 1 to prevent the formation of eddy currents.

During assembly of the drive, the ring 8 provided between the pole shoes 2 and 3 permits simple centering and distancing between the pole shoes 2 and 3. Furthermore, this ring determines the position of armature 4, 4a, so that the latter merely has to be inserted into the pole shoes 2 and 3 during assembly of the drive. However, a joint insertion of the pole shoes and the armature into the magnet coil is conceivable.

When the magnet coil 1 is switched on, the armature 4, 4a takes up a position between the two pole shoes 2 and 3 which deviates from the depicted position whereby the magnetically nonconductive segment 4a produces the equivalent of an air gap between the two pole shoes 2 and 3. The non-conductive segment 4a also has the effect of a guiding element which ensures that the total armature moves free from canting in the longitudinal direction of the magnet coil 1. The needle 5 is mounted in a guide 16 that extends into the threaded pin 12 and is displaced against the effect of the spring 6 by the motion of the armature 4, 4a. When the magnet coil 1 is switched off again, the armature 4, 4a returns to its resting position.

The threaded pins 12 and 13 permit adjustment of the working stroke in both limit positions of the armature 4, 4a by simply loosening and tightening the nuts 17 and 18 after corresponding rotation of the threaded pins 12 and 13. These adjustments also affect the operating speed of the drive because greater operating speed results in respectively longer operating time. Furthermore, the tension of the spring 6 is regulated so that adjustment of the threaded pins 12 and 13 can also serve for changing the printing quality at the printing tip of the needle 5.

The above-described magnetically non-conductive elements should preferably be also electrically non-conductive in order to avoid the generation of eddy currents which can delay the build-up of the magnetic field moving the armature.

Claims

Having described our invention, we claim:

1. An electromagnetic drive for the needle of a needle printer, comprising a cylindrical magnet coil, an armature disposed within said coil and operable upon said coil being energized to move said armature axially with respect to said coil, said armature being connected to said needle such that axial, reciprocal movement of said armature produces corresponding movement of said needle, a pair of axially spaced cylindrical pole members disposed intermediate said armature and said coil, an electrically conductive cylindrical member encompassing said armature and disposed intermediate said spaced pole members; and said armature comprising a first member and a second member, said first member being joined to said second member and being magnetically conductive; said second member being magnetically and electrically non-conductive.

2. The device as defined in claim 1 and including spring means urging said armature to a retracted position upon deenergization of said coil.

3. The drive according to claim 1, characterized in that the magnet coil is surrounded by a magnetically conductive metal sheath which is slotted in the longitudinal direction of the magnet coil and connected with magnetically conductive coil flanges which connect the metal sheath with the magnet pole shoes.

4. The drive according to claim 2, characterized in that said spring means is a helical spring.

5. The drive according to claim 4, characterized in that said second member of the armature forms a chamber receiving the helical spring.

6. The drive according to claim 4, characterized in that the needle is passed into the magnet coil through a threaded pin which permits adjustment of the range of motion of the armature and serves as outer support for the spring.

7. The drive according to claim 7, characterized in that there is provided a damping disk, the position of which is adjustable by a threaded pin which is disposed at the end of the magnet coil remote from the needle.

8. The drive according to claim 7, characterized in that the damping disk is provided with a central opening which is connected with the outer space of the drive via a central bore of the threaded pin supporting the damping disk.