GB2268334A

GB2268334A - Electromagnetic actuators

Info

Publication number: GB2268334A
Application number: GB9313207A
Authority: GB
Inventors: Martin Greuer; Richard Maier; Johann Stempfle
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1992-06-26
Filing date: 1993-06-25
Publication date: 1994-01-05
Also published as: DE4221272A1; FR2693830A1; DE4221272C2; GB9313207D0

Abstract

An electromagnetic actuator for adjusting the position of a stop disc 9 in a wire matrix printer comprises a rotatable permanent magnet 13 secured to a shaft 12. When a coil 17, located between-low retentivity rings 15, 18 is energised, the magnet 13, which has multiple radial poles, undergoes limited rotation. The rotary movement is converted into axial movement by an assembly (20) Fig 4 on the shaft 12 thereby axially displacing the stop disc 9. <IMAGE>

Description

1 22649334 POSITIONING MEMBER FOR COMPONENTS IN OFFICE MACHinno This

invention relates to office machines and in particular to a member for positioning components in of f ice machines.

It is known to form a positioning member from a central permanent magnet with a plurality of electromagnet coils distributed over the periphery thereof. Such an arrangement, however, obviously requires a considerable amount of space, and cannot be used in office machines. The continuing miniaturisation of components, such as wire matrix print heads, completely prevents use of a construction such as is conventional in other branches of technology, e.g. for solenoid valves.

It is amongst the objects of this invention to provide a positioning drive which meets the requirements for relatively small drive paths in office machines, which can be produced in the suitable dimensions and which applies the required drive power.

A positioning member for components in office machines, in accordance with the invention, comprises a basically disc-shaped permanent magnet attached to a central swivel pin, the periphery of which magnet is polarised, alternating periodically, such that magnetic poles of the same polarity and of opposite polarity are radially opposed on the periphery, a first low-retentivity ring surrounding the permanent magnet, having claw-like ring segments, the number of which corresponds to half the number of permanent 'magnet poles, an electromagnet coil surrounding the first low-retentivity ring and a second low-retentivity ring surrounding the electromagnet coil having claw-like ring segments the radially inner periphery thereof, the number of which corresponds to half the number of permani-,,nt magnet poles.

The advantages achieved with the positioning member include satisfaction of the requirements of sufficiently large positioning paths, small dimensions and sufficiently large drive force. One particular advantage is that the member is economical to produce, which permits the use of 2 such a positioning drive in office machines.

The positioning member is particularly suitable for use with matrix print heads of the hinged-armature type in which a damping plane is adjustable.

Advantageously, an element for converting rotary movement into an axial movement is provided on the swivel pin. This widens the range of application of the positioning member in office machines and allows gearing of it to the problems which occur in a given case.

Economic production is further ensured in that fixed stops are provided which engage in recesses in the permanent magnet, so that the possible angle of rotation is smaller than the pole distances of the permanent magnet and, in the two end positions of the permanent magnet, the positions of a permanent magnet pole and a ring segment are equidistant from one another. This means further that clearly determined paths of movement can be provided.

Alternatively, the stops are provided on the permanent magnet and the recesses are formed on a cover part which is arranged -on the end face of the permanent magnet.

In this case, advantageous production techniques can be used with the permanent magnet being made from a plastics material filled with hardmagnetic material in an injection-moulding process. Such a production method is worthwhile for large quantities, such as occur in the field of printer technology.

Economic production is also enhanced if the permanent magnet and the swivel pin are made of one piece.

Production is further simplified if the first and the second lowretentivity rings are of identical shape.

Suitably, the positioning member is actuated by a flow of current. in the electromagnet coil for a switching operation which consists of a plurality of successive pulses. This increases the switching load.

To allow a wider range of possible uses the element for converting rotary movement into an axial movement may consist of a sleeve with an internal thread, the sleeve 3 being prevented externally from rotating.

The positioning member may also be geared more specifically to individual applications by providing the swivel pin with an external thread, the swivel pin being capable of being turned relative to the permanent magnet and then f ixed again in position relative thereto. This allows different starting positions for axial movement of the sleeve part to be defined.

This invention will now be further described by way of example only with reference to the accompanying drawings in which:- Figure 1 is an axial section through a matrix print head; Figure 2 is an axial section of a rotating mechanism and housing forming part of the print head; Figure 3 is a radial section corresponding to Figure 2; Figure 4 is a similar view to Figure 3 showing a mechanism_for axial movement with an enlarged view of the central part; and Figures Sa, 5b, 5c illustrate the rotating mechanism of Figure 2 in a f irst end, middle and second end position.

A positioning member is required for components in of f ice machines in which positioning movements in the peripheral direction and/or in the axial direction have to be performed.

In wire matrix print heads 1 of the hinged armature type shown in Figure 1, there is a wire guidance housing 2 with a ribbon guide 3. A wire drive housing 4 succeeds this, and the entire wire matrix print head 1 is closed off by means of a cover 5. In the interior of the wire drive housing 4, a plurality of magnet yokes 6 (e.g. up to 24) are distributed evenly across the periphery. Each magnet yoke 6 has a hinged armature 7 for actuating an associated print wire 8. The stroke of the hinged armature 7 4 determines the impact force of the print wires 8 on the ribbon and hence on the paper on which printing is to be carried out. In order to change the impact force or the stroke, a stop disc 9 is axially adjusted. A driving coil 10 is associated with each magnet yoke 6. For adjusting the stroke, therefore, a positioning member 11 is necessary, which will be described below.

The positioning member 11, see Figures 2 to 5c, comprises a swivel pin 12, which is arranged centrally, and a permanent magnet 13 which is discshaped in its basic form and is attached to the swivel pin 12. The periphery 14 of the permanent magnet 13 is magnetised, alternating periodically with north and south poles, and therefore forms permanent magnet poles 13a. The permanent magnet 13 is surrounded by a first lowretentivity ring 15, on which claw-like ring segments 16 are formed. The number of ring segments 16 corresponds to half the number of the permanent magnet poles 13a. An electromagnet coil 17 surrounds the firs t low-retentivity ring 15 and is itself surrounded by a second, "radially outer, low-retentivity ring 18. A radially inner periphery 18a is formed with claws 18b like ring segments 16. All the parts are enclosed and held together by means of a positioning-member housing 19. In the illustrated case, the low-retentivity ring 18 itself forms a closure as shown in Figure 2.

A limited, smaller angle of rotation of the permanent magnet 13 serves to generate a holding moment and a higher starting torque.

An element 20 for converting a rotary movement into an axial movement may also be located on the swivel pin 12 if required as is discussed further below.

Stops 21 (or recesses) are worked or formed into the permanent magnet 13, which stops or. recesses engage in fixed recesses (or stops) see Figure 3. The possible angle of rotation 23 is thus smaller than the pole distances 24 of the permanent magnet 13. In the two end positions 25a and 25b of the permanent magnet 13, the positions of each permanent magnet pole 13a and of the associated ring segment 16 are equally spaced apart.

As soon as a current flows through the electromagnet coil 17, magnetic poles form on the claw-shaped ring segments 16, which poles attract or repel the corresponding permanent magnet poles 13a and in so doing produce a rotary movement of the permanent magnet 13 together with the swivel pin 12.

The direction of rotation of the permanent magnet 13 is altered by reversing the polarity of the current in the electromagnet coil 17. In the current-free state, however, a torque acts on the permanent magnet 13 which moves it to one or other side dependent on the position. This results in a holding moment in the end positions 25a, 25b. The switching member (the permanent magnet 13) is bistable.

In both end positions 25a, 25b, the holding position of the permanent magnet may be at different distances from the claw-shaped ring segments 16, in order to obtain a higher starting torque in the direction of rota tion, in which, in the starting position, the permanent magnet 13 is further removed from the claw-shaped ring segments 16 or the claws 18b (Figures 5a to 5c).

The return path of the claw-shaped ring segments 16 or of the claws 18b may be provided by two symmetrical lowretentivity rings 15 and 18, which are mounted, offset by a divider, against one another.

The permanent magnet 13 and the swivel pin 12 may be made of one piece. The permanent magnet 13 may also form the stops 22, and the recesses may be provided on a cover part 26 arranged on the end face of the permanent magnet 13. The permanent magnet 13 may also be produced from a plastics material f illed with hard-magnetic material in an injection-moulding process. It is also very economic to shape the first and the second lowretentivity rings 15 and 18 identically, i.e. to manufacture effectively only one single ring type.

Furthermore, it is advantageous if the current flowing 6 through the electromagnet coil 17 for a switching operation comprises a plurality of successive pulses in order to increase the switching load.

The element 20 for converting the rotary movement into an axial movement comprises a sleeve part 27 with an internal thread 28, the sleeve part 27 forming an external gap 27a in which a tappet 19a of the positioningmember housing 19 engages and prevents the sleeve part 27 from rotating on the outside.

The swivel pin 12 is provided with an external thread 29 which engages the internal thread 28 of the sleeve part 27.

The swivel pin 12 can therefore be turned relative to the permanent magnet 13 and fixed again, in order to define a different starting position for an axial movement of the sleeve part 27. Such a case is provided for the positioning member of Figure 1 so that the stop disc 9 adopts a changeable basic position.

W, 7

Claims

A positioning member f or components in of f ice machines comprising a basically disc-shaped permanent magnet attached to a central swivel pin, the periphery of which magnet is polarised, alternating periodically, such that magnetic poles of the same polarity and of opposite polarity are radially opposed on the periphery, a f irst low-retentivity ring surrounding the permanent magnet having claw-like ring segments, the number of which corresponds to half the number of permanent magnet poles, an electromagnet coil surrounding the first low-retentivity ring and a second' low-retentivity ring surrounding the electromagnet coil having claw-like ring segments on the radially inner periphery thereof, the number of which corresponds to half the number of permanent magnet poles.
2. A positioning member as claimed in Claim 1, wherein an element for converting rotary movement into.an axial movement is arranged on the swivel pin.
3. A positioning member as claimed in Claim 2, wherein the element for converting rotary movement into an axial movement comprises a sleeve formed with an internal thread and external means f or preventing the sleeve from rotating.
4. A positioning member as claimed in Claim 3, wherein the swivel pin is f ormed with an external thread and wherein the relative rotation positions of the swivel pin and the permanent magnet can be adjusted to def ine different starting position (s) for axial movement of the sleeve.
5. A positioning member as claimed in any preceding Claim, including fixed stops or recesses arranged to cooperate respectively with recesses provided in or fixed 8 stops provided,on the magnet so that the possible angle of rotation is less than the pole distances of the permanent magnet and, in the two end positions of the permanent magnet, the permanent magnet poles are equidistant from the associated ring segments.
6. A positioning member as claimed in Claim 5, wherein the permanent magnet is provided with stops and cooperating recesses are formed in a cover arranged on the end face of the permanent magnet.
7. A positioning member as claimed in any preceding Claim, wherein the permanent magnet and the swivel pin are integral.
8. A positioning member as claimed in any preceding Claim, wherein the permanent magnet is made from plastics material filled with hard-magnetic material in an injection-moulding process.
9. A positioning member as claimed in any preceding Claim, wherein the first and second low-retentivity rings are of identical shape.
10. A.positioning member as claimed in any preceding Claim, wherein the positioning member is actuated by a current flowing in the electromagnet coil of a plurality of successive pulses.
11. A positioning member substantially as hereinbefore described and illustrated in the accompanying drawings.