GB2066740A

GB2066740A - Moving coil type printing head

Info

Publication number: GB2066740A
Application number: GB8038775A
Authority: GB
Original assignee: Seikosha KK
Current assignee: Seikosha KK
Priority date: 1979-12-07
Filing date: 1980-12-03
Publication date: 1981-07-15
Also published as: FR2471279B1; DE3046105A1; GB2066740B; IT1127938B; DE3046105C2; FR2471279A1; IT8050324A0

Abstract

A moving coil type printing head comprises a cantilevered printing lever (9) provided with a printing element (15), for example a hammer. The printing lever has a base portion (10) supported by a holding member (5), resilient leg portions (12) integrally extending from the base portion, a triangular lever portion (13) integral with the leg portions and carrying a moving coil (28) and a tongue portion (16) integral with and extending from the base of the lever portion towards the base portion. A plate member (25) is mounted on the holding member (5) and extends above the tongue portion (16). A fulcrum member (21) is secured to the tongue portion (16) and is in contact with the plate member (25). <IMAGE>

Description

SPECIFICATION Moving coil type printing head This invention relates to moving coil type printing heads.

Attempts have been made in recent years to develop a printing head for an impact type dot printer employing one or more moving coils.

However, known moving coil type printing heads have, in the present stage of development, several technical problems which must be resolved with respect to performance, response and reliability.

For example, if a cantilevered printing lever driven by means of the moving coil is reduced in weight to enable it to be driven at a higher speed, it is subject to distortion and/or deflection so that its operation is unstable and thus its response speed actually falls. In addition, if a large current is applied to the moving coil in order to form a clear dot, an excessive bending moment acts on the printing lever as the printing element strikes a platen, so that the response of the printing lever becomes abnormal.

According to one aspect of the present invention there is provided a moving coil type printing head comprising: a cantilevered printing lever provided with a printing element, said printing lever having a base portion supported by a holding member, two resilient leg portions integrally extending from said base portion, a triangular lever portion intregral with said leg portions and carrying a moving coil, and a tongue portion integral with and extending from the base of said lever portion toward said base portion; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil; a plate member mounted on said holding member and extending above said tongue portion; and a fulcrum member secured to one of said tongue portion and said plate member, and being in contact with the other of said tongue portion and said plate member.

In the preferred embodiment said holding member has a portion which is inclined away from the direction in which the printing lever moves during a printing operation, and to which the base portion of said printing lever is secured.

Said holding member may be releasably mounted on a carrier plate which carries said magnetic flux generating means.

Preferably said lever portion has flange portions at opposite lateral edges thereof to increase the 'stiffness.

Said printing lever may be symmetrical with respect to its centre line.

In one embodiment said fulcrum member is arranged at a position substantially corresponding to one-third of the total length of said leg portions from said base portion.

According to a further aspect of the present invention there is provided a moving coil type printing head comprising a cantilevered printing lever provided with a printing element; a moving coil carried on said printing lever; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil and comprising a centre yoke member, an annular outer yoke member surrounding said centre yoke member, an air gap formed between said centre and outer yoke members, said moving coil being disposed in said air gap, and an annular permanent magnet sandwiched between said outer yoke member and a portion integral with said centre yoke member so as to magnetize oppbsiteíy said centre and outer yoke members; and at least one air passageway extending through the centre yoke member to the exterior.

Preferably said centre yoke member has control means adjustably mounted thereon so as to restrict the range of displacement of said printing lever, Said control means may be an abutment screw adjustably screwed to said centre yoke member through said printing lever, a flange integrally formed from an intermediate part of said abutment screw so as to determine a rest position of said printing lever, and a nut adjustably screwed to the abutment screw so as to reduce or prevent overdeflection of said printing lever.

A guide member for an inked ribbon may be disposed adjacent the printing element. Said guide member may have a longitudinal groove for locating the printing element in a rest position of said printing lever.

According to another aspect of the present invention there is provided a printer having a moving coil type printing head as recited above.

In one embodiment the printer has a platen and the printing element is a knife-like hammer member for cooperating with the platen, the platen having, on its outer periphery, a plurality of projections extending substantially parallel to the axis thereof and selectively positionable so as to intersect said hammer member upon rotation of the platen.

Said hammer member preferably has an arcuate striking surface whose radius of curvature corresponds to the radius of said projections.

Said hammer member may be located between said flange portions.

The centre of curvature may deviate from the axis of said platen when the hammer member is in a rest position and the centre of curvature substantially coincides with the axis of said platen during a printing operation.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a front elevational view of a moving coil type printing head according to the present invention; Figure 2 is a cross-sectional view taken along the line Il-Il of Figure 1; Figure 3 is a front elevational view of a printing lever of the printing head of Figure 1; Figure 4 is a cross-sectional view taken along the line IV--IV of Figure 3; and Figure 5 illustrates deflection of the printing lever.

In the following description reference to "upper", "lower", "front", "rear", etc. refer to the directions as seen in the drawings.

Referring to Figures 1 and 2 there is illustrated a moving coil type printing head according to the present invention having a carrier plate 1 with an L-shaped cross-section and a transverse bent portion 2 supported on a carriage (not shown) of a printer which is adapted to be scanned in a direction transverse to a direction 4 of advance of paper 3 on which printing is to be formed. The carrier plate 1 carries a holding member or plate 5 on its lower front surface. The holding plate 5 is secured to the carrier plate 1 by means of screws 6 and has an upper portion 7 inclined backward at a predetermined angle, e.g. 5 , in a direction opposite to the direction of moven,ent of a cantilevered printing lever 9 during a printing operation.In addition, the upper portion 7 of the holding plate 5 is inserted into a rectangular opening 8 formed in the carrier plate 1. The printing lever 9 is secured to the upper portion 7 of the holding plate 5 by means of caulking pins 11.

As best shown in Figure 3, the printing lever 9 has a rectangular base portion 10 which is secured to the upper portion 7 of the holding plate 5, resilient leg portions 12 which are integral with and extend from the base portion 10, and a triangular lever portion 13 which is integral with the resilient leg portions 12. The printing lever 9 is symmetrical about its centre line and is made as a body from thin leaf spring material in order to reduce its weight, and the lever portion 13 is provided at its lateral edges with flange portions 14 which are folded forward at right angles to the plane of the lever portion 13 in order to increase the stiffness thereof. In consequence, any deflection of the printing lever 9 substantially takes place at the resilient leg portions 12. The lever portion 1 3 carries a knife-like printing hammer 1 5 at its free end.The printing hammer 15 is sandwiched between the upper ends of the flange portions 14 and fixed therebetween by means of, for example, adhesive or spot welding.

In addition, the lever portion 13 has an integral tongue portion 16 which extends towards the base portion 10 from the lever portion 13 between the resilient leg portions 12. A reinforcing member 17 is fixed to the tongue portion 1 6. The base portion 10 has two holes 18 through which the pins 11 pass. A hole 20 for securing a disc-shaped bobbin holder 19 (Figure 2) is formed in the lever portion 13 at its central part. Furthermore, the tongue portion 1 6 and the reinforcing member 1 7 each has a hole 22 through which a fulcrum member in the form of a pin 21 (Figures 1 and 2) loosely passes, and a hole 24 through which the rear end of a post-like member 23 (Figures 1 and 2) is forced.

As clearly seen in Figure 2, an arm-like plate member 25 is secured to the holding plate 5 by means of a caulking pin 26, and a pin 21 is secured to the tongue portion 1 6 so as to be in contact with the plate member 25 in the following manner. Initially, the pin 21 is passed through the hole 22 (see Figure 3) and then it is movable axially. Thereafter, the plate member 25 is secured to the holding plate 5 and thus the pin 21 cannot be removed from the hole 22. At this time the carrier plate 1 carries nothing on its rear surface, and a coil spring 27 is located in an aperture in the carrier plate 1 at a position corresponding to the, pin 21, this aperture being closed by an annular outer yoke member 30 which is secured to the carrier plate 1 on its rear surface.In consequence, the pin 21 is biased toward the plate member 2,5 by virtue of the force exerted by the coil spring 27 and contacts with the plate member 25. Adhesive is introduced under the headed portion of the pin 21, and thus the latter is secured to the tongue portion 1 6 and the reinforcing member 17 when the adhesive hardens. Thus even though the plate member 25 is positioned relatively inaccurately, the pin 21 can be secured to the tongue portion 16 and the reinforcing member 17 so as to contact surely the plate member 25, thus no adjustment of the position of the pin 21 nor the plate member 25 is required. In this embodiment, the pin 21 is arranged to contact the plate member 25 at a position substantially corresponding to one-third of the total length of the resilient leg portions 12.

As shown in Figure 2, the bobbin holder 19 which is secured to the hole 20 (see Figure 3) holds a cylindrical bobbin 29 around which a moving coil 28 is wound. The moving coil 28 is adapted to cooperate electromagnetically with a magnetic flux generating means which is constituted by the outer yoke member 30, a centre yoke member 31 positioned in a central opening of the outer yoke member 31, and an annular permanent magnet 33 sandwiched between the outer yoke member 30 and a rear disc-shaped portion 32 integral with the centre yoke member 31. The outer and centre yoke members 30,31 are made of a magnetic material having a high magnetic permeability and are magnetized to have opposite magnetic poles by virtue of the permanent magnet 33.The moving coil 28 is disposed in an air gap between the outer and centre yoke members 30,31 and the magnetic flux is generated radially across the moving coil 28 in the air gap. The outer yoke member 30, the permanent magnet 33 and the centre yoke member 31 are fixed to one another by means of, for example, adhesive, and the outer yoke member 30 is fixed on the rear surface of the carrier plate 1 by means of screws 34 as seenin Figure 1, thereby the whole of the magnetic flux generating means is carried on the carrier plate 1.

The centre yoke member 31 is provided at its centre with an abutment screw 35 to restrict the range of displacement of the printing lever 9. The abutment screw 35 has a rear screw portion which is screwed into the centre yoke member 31 so as be adjustably positioned, and an integral intermediate flange 36 in contact with the rear surface of the bobbin holder 1 9, so that the rest position of the printing lever 9 is determined. In this rest position, the printing lever 9 is bowed at its resilient leg portions 12 due to the inclination of the upper portion 7 of the holding plate 5 on which the printing lever 9 is supported. Therefore, the bobbin holder 1 9 is in contact with the flange 36 at a suitable predetermined contact pressure.

In addition, the abutment screw 35 has a front screwed portion around which a nut 37 is screwed so as to be adjustably positioned, and the range of displacement or swing of the printing lever 9 is restricted by the nut 37.

The centre yoke member 31 is provided with an air passageway 38 which is in communication with the air gap in which the moving coil 28 is disposed. This air passageway extends through the centre yoke member 31 to the exterior. The bobbin 29 and the bobbin holder 19 are also provided with an air passage way 39 as seen in Figure 1. The air passageway 39 communicates with an air-tight space which is formed between the bobbin holder 19 and the centre yoke member 31 as shown in Figure 2.

As shown in Figures 1 and 2, a ribbon guide 41 is secured to the outer yoke member 30 by means of screws 40 and is located behind the printing hammer 15. The ribbon guide 41 has a longitudinal groove 42 formed at its central portion, and as the printing lever 9 is positioned in the rest position, its free end is in light contact with a bottom surface 43 of the groove 42. In other words, the ribbon guide 41 also acts as an abutment to determine the rest position of the printing lever 9. The ribbon guide 41 is provided at both sides of the groove 42 with guide grooves 44 by which an inked ribbon 45 arranged between the paper 3 and the printing hammer 1 5 is conducted.

A flexible flat cable 46 is arranged to apply a driving current to the moving coil 28, and a plate member 47 is affixed on a rear surface of an end of the cable 46 by means of, for example, adhesive. This end of the cable 46 is attached to the pin 23 through a nut 48. The cable a6 is provided with thin film conductors 49, 50 having respective terminals 49a, 50a from which lead wires 51, 52 for connection to the moving coil 28 are connected.

A platen 53 of the printer and illustrated by a broken line in Figure 2, is disposed opposite to the printing hammer 15, and a plurality of projections 54 are integrally formed parallel to its axis equidistantly around its periphery. Corresponding to the projections 54, the printing hammer 1 5 has an arcuate front surface whose radius of curvature is equal to the radius of the projections 54. When the printing lever 9 lies in the rest position as shown in Figure 2, the centre of curvature of the front surface of the printing hammer 1 5 deviates from the axis of the platen 53 by an amount corresponding to displacement of the printing lever 9 during a printing operation.

The centre of curvature is positioned above the centre of the platen 53. However, as the printing hammer 1 5 collides with one of the projections 54 in order to form a dot on the paper 3, the centre of curvature of the front surface of the printing hammer 1 5 will be moved to coincide substantially with the axis of the platen 53.

In the above-described embodiment of the present invention, all the parts except the outer and centre yoke members 30, 31 and the permanent magnet 33 are respectively made of a suitable non-magnetic material such as stainless steel, phosphor bronze, brass or plastics material.

The printing head described above operates as follows. When a current driving pulse is applied to the moving coil 28 through the conductors 49, 50 of the cable 46 and the printing lever 9 is in the rest position as shown in Figure 2, the moving coil 28 generates a magnetic field which interacts with the magnetic flux in the air gap between the outer and centre yoke members 30, 31 and the printing lever 9 is displaced leftward against the resilient force of the resilient leg portions 12.

Since the lever portion 13 has a high degree of stiffness by virtue of the flange portions 14 and the pin 21 secured to the tongue portions 16 and the reinforcing member 17 is in contact with the plate member 25, the printing lever 9 is pivoted about the pin 21, i.e. about the line lV-IV in Figure 3, as indicated by the reference numeral 9' in Figure 5. The printing hammer 1 5 makes a perfect circular motion substantially about the pin 21 so the inked ribbon 45 and the paper 3 impact against one of the projections 54 and thus a dot is formed on the paper 3 when the printing hammer 1 5 strikes the projection 54.After the printing hammer 15 has collided with the corresponding projection 54, the intermediate portion of the printing lever 9 is still deflected due to inertia, but the front end of the bobbin holder 1 9 is in contact with the nut 37 and therefore such inertial deflection is restricted and so a relatively large bending moment or deflecting force is not applied to the printing lever 9. The printing lever 9 is returned to the rest position by the resilient leg portions 12. On the other hand, the printing head is scanned also in a direction transverse to the direction of advance of the paper 3 at the same time as the printing lever 9 is actuated and the platen 53 is continuously rotated as indicated by an arrow 55 as seen in Figure 2 by means of a driving motor (not shown).In consequence, positions where the printing hammer 1 5 crosses or intersects with the projections 54 are moving in vertical and horizontal directions in accordance with the scanning of the printing head and the rotation of the platen 53. The printing lever 9 is actuated at a suitable selected position and timing and therefore desired characters, graphs, pictures etc. are formed by a dot matrix. Detailed description of the printing operation is omitted because it has no relation to the invention directly.

However, the printing operation has been disclosed in detail in Japanese Application No.

119506/79.

The effects and advantages of the particular construction of the printing lever 9 illustrated in the drawings will be clearly understood from the following description. If the tongue portion 16, the reinforcing member 17, the pin 21 and the plate member 25 were not employed, when the printing lever 9 receives an abrupt actuating force upon energisation of the moving coil 28, it would be distorted in the region of the resilient leg portions 12 as indicated by the reference numeral 9" in Figure 5 due to the inertia of the printing hammer 1 5. Only subsequently would the lever portion 13 start to move leftward. In this case, the actuation of the printing hammer 15 would be delayed and the response of the printing lever 9 would be inferior and consequently it would be difficult to actuate the printing lever 9 at a high speed.Such advantages are increased if the lever portion 13 does not have the flange portions 14 at its lateral edges. On the other hand, the construction of the printing lever 9 shown in Figure 3 prevents abnormal distortion of the resilient leg portions 12 and thus the printing lever 9 can be actuated stably at relatively high speed and a constant printing force can be produced.

In addition, since the air passageways 38, 39 are opened in the centre yoke member 31, the bobbin 29 and the bobbin holder 19, the moving coil 28 is subject to little air resistance when actuated and therefore it can be actuated at a high speed. Since the cable 46 having the terminals 49a, 50a for connection to the lead wires 51, 52 is attached to the printing lever 9 through the pin 23 and the nut 48 so as to move together with the printing lever 9, there is no relative motion between the moving coil 28 and the end of the cable 46. Consequently, the lead wires 51, 52 receive no repeated stress and can have a long life although the printing lever 9 is repeatedly actuated at a high speed for a long period of time.

Moreover, if the ribbon guide 41, which functions as an abutment to restrict undesirable motion of the printing hammer 1 5 after it has just returned to the rest position after a printing operation, is made of soft plastics material, shocks may be absorbed so that the vibration or rebound of the printing lever 9 may be damped rapidly and noise reduced. To reduce noise and undesired vibration of the printing lever 9, a damping member such as an elastic rubber or sponge can be arranged between the bobbin holder 19 and the flange 36.

If desired, a printing wire can be used as the printing element instead of the knife-like printing hammer 1 5. However, in the case of a printing wire, the platen 53 should be modified to be stationary and to form a flat surface opposite to the printing wire. The holding plate 5 can be formed integrally from the carrier plate 1, however, considering assembly or maintenance of the printing lever 9, this may not be convenient. In addition, means for restraining the abnormal distortion of the printing lever 9 can be modified.

For example, the pin 21 may be secured to the plate member 25 and then the pin member 21 is in contact with the tongue portion 1 6 at the position of the line IV-IV of Figure 3.

The moving coil type printing head described above has good performance, response and reliability. The printing lever 9 can make a substantially perfect circular motion about the pin 21 without being subject to abnormal deflection or distortion in the region of the resilient leg portions 12 even if a large current is applied to the moving coil 28 so as to provide the printing lever with a sufficient displacement force. Therefore, the printing lever is actuable at a relatively high' speed and produces a sufficient printing force to enable clear dots to be formed on the paper 3. In addition, since the printing lever is supported by the upper portion 7 of the holding plate 9 so that a suitable biasing return force is applied to it, it can be returned speedily toward the rest position after a printing operation and can be located stably at that rest position. Further, since the printing lever is releasably mounted on the carrier plate 1 by means of the holding plate 5, its assembly and maintenance is easy. Since the printing lever can have a sufficient stiffness by virtue of the flange portions 14 formed at the opposite edges of the lever portion 13, it can surely transmit the printing force to the printing element. Further because of the provision of the air passageway 38 the moving coil can be actuated at a high speed. Further, the range of displacement of the printing lever can be controlled by the abutment screw 35 and thus it can be actuated in a stable manner without introducing undesirable deflection or distortion.

The moving coil type printing head described above can be manufactured to be light weight and of compact size at low cost.

Claims

1. A moving coil type printing head comprising: a cantilevered printing lever provided with a printing element, said printing lever having a base portion supported by a holding member, two resilient leg portions integrally extending from said base portion, a triangular lever portion integral with said leg portions and carrying a moving coil, and a tongue portion integral with and extending from the base of said lever portion toward said base portion; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil; a plate member mounted on said holding member and extending above said tongue portion; and a fulcrum member secured to one of said tongue portion and said plate member, and being in contact with the other of said tongue portion and said plate member.

2. A moving coil type printing head as claimed in claim 1 in which said holding member has a portion which is inclined away from the direction in which the printing lever moves during a printing operation, and to which the base portion of said printing lever is secured.

3. A moving coil type printing head as claimed in claim 1 or 2 in which said holding member is releasably mounted on a carrier plate which carries said magnetic flux generating means.

4. A moving coil type printing head as claimed in any preceding claim in which said lever portion has flange portions at opposite lateral edges thereof to increase the stiffness.

5. A moving coil type printing head as claimed in any preceding claim in which said printing lever is symmetrical with respect to its centre line.

6. A moving coil type printing head as claimed in any preceding claim in which said fulcrum member is arranged at a position substantially corresponding to one-third of the total length of said leg portions from said base portion.

7. A moving coil type printing head comprising a cantilevered printing lever provided with a printing element; a moving coil carried on said printing lever; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil and comprising a centre yoke member, an annular outer yoke member surrounding said centre yoke member, an air gap formed between said centre and outer yoke members, said moving coil being disposed in said air gap, and an annular permanent magnet sandwiched between said outer yoke member and a portion integral with said centre yoke member so as to magnetize oppositely said centre and outer yoke members; and at least one air passageway extending through the centre yoke member to the exterior.

8. A moving coil type printing head as claimed in claim 7 in which said centre yoke member has control means adjustably mounted thereon so as to restrict the range of displacement of said printing lever.

9. A moving coil type printing head as claimed in claim 8 in which said control means is an abutment screw adjustably screwed to said centre yoke member through said printing lever, a flange integrally formed from an intermediate part of said abutment screw so as to determine a rest position of said printing lever, and a nut adjustably screwed to the abutment screw so as to reduce or prevent over-deflection of said printing lever.

10. A moving coil type printing head as claimed in any of claims 7 to 9 in which a guide member for an inked ribbon is disposed adjacent the printing element.

11. A moving coil type printing head as claimed in claim 10 in which said guide member has a longitudinal groove for locating the printing element in a rest position of said printing lever.

12. A moving coil type printing head substantially as herein described with reference to and as shown in the accompanying drawings.

13. A printer having a moving coil type printing head as claimed in any preceding claim.

14. A printer having a moving coil type printing head as claimed in any preceding claim.

14. A printer as claimed in claim 13 having a ,platen, the printing element being a knife-like hammer member for cooperating with the platen, the platen having, on its outer periphery, a plurality of projections extending substantially parallel to the axis thereof and selectively positionable so as to intersect said hammer member upon rotation of the platen.

1 5. A printer as claimed in claim 14 in which said hammer member has an arcuate striking surface whose radius of curvature corresponds to the radius of said projections.

16. A printer as claimed in claim 14 or 1 5 when dependent upon claim 4 in which said hammer member is located between said flange portions.

1 7. A moving coil type printing head as claimed in claim 15 in which the centre of curvature of said arcuate striking surface deviates from the axis of said platen when the hammer member is in a rest position and the centre of curvature substantially coincides with the axis of said platen during a printing operation.

18. A moving coil typ'e printing head comprising: at least a cantilevered printing lever made of a leaf spring, and provided at its free end with a printing element opposing to a platen; a moving coil carried on said printing lever; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil; said printing lever being constituted by a base portion supported by a holding member, two or more resilient leg portions integrally extending from said base portion, a triangular lever portion integrally connected to said leg portions and carrying said moving coil at its intermediate part, and a tongue portion integrally extending from the base of said lever portion toward said base portion; an arm like plate member mounted on said holding member, and extending above said tongue portion; a fulcrum member secured to one of said tongue portions and said plate member, and being in contact with the other of said tongue portion and said plate member.

19. A moving coil type printing head comprising: at least a cantilevered printing lever provided at its free end with a printing element; a moving coil carried on said printing lever; a magnetic flux generating means producing a magnetic flux crossing said moving coil; said magnetic flux generating means being constructed by a post-like centre yoke member, an annular outer yoke member surrounding said centre yoke member, an air gap formed between said centre and outer yoke members in order to movably dispose said moving coil therein, and an annular permanent magnet sandwiched between said outer yoke member and a rear discoid portion integrally formed from said centre yoke member so as to magnetize said centre and outer yoke members to opposite magnetic poles respectively; and at least an air loophole opened in said centre yoke member from said air gap toward the external air.

New claims or amendments to claims fiied on 27 March 1981.

Superseded claims 1 to 1 9.

New or amended claims:

1. A moving coil type printing head comprising: a cantilevered printing lever provided with a printing element; a moving coil secured to said printing lever; a magnetic flux generating means for producing a magnetic flux intersecting said moving coil, said printing lever having a base portion supported by a holding member, two resilient leg portions integrally extending from said base portion, a triangular lever portion integral with said leg portions and carrying said moving coil, and a tongue portion integrally extending from the base of said lever portion toward said base portion; and a fulcrum member is attached to one of said tongue portion and a plate member mounted on said holding member so as to be in contact with the other of said tongue portion and said plate member.

2. A moving coil type printing head as claimed in claim 1 in which said printing lever is made of a thin leaf spring in order to reduce its weight.

3. A moving coil type printing head as claimed in claim 1 or 2 in which said lever portion has flange portions at opposite lateral edges thereof to increase the stiffness.

4. A moving coil type printing head as claimed in any preceding claim in which said holding member has a portion which is inclined away from the direction in which said printing lever is actuated, and to which the base portion of said printing lever is secured.

5. A moving coil type printing head as claimed in any preceding claim in which said holding member is releasably mounted on a carrier plate which carries said magnetic flux generating means.

7. A moving coil type printing head as claimed in any preceding claim in which said printing lever is symmetrical with respect to its centre line.

8. A moving coil type printing head as claimed in any preceding claim in which said printing element has a bar shape and is clamped between the proximal ends of said flange portions.

9. A moving coil type printing head as claimed in any preceding claim in which said moving coil has a cylindrical shape, and said magnetic flux generating means comprises a centre yoke member, an annular outer yoke member surrounding said centre yoke member, an annular air gap which is formed between said centre and outer yoke members and in which said moving'coil is disposed, and an annular permanent magnet sandwiched between said outer yoke member and a rear discoid portion integral with said centre yoke member so as to magnetise oppositely said centre and outer yoke members.

10. A moving coil type printing head as claimed in claim 9 in which said centre yoke member has at least one air passageway passing through the exterior.

11. A moving coil type printing head as claimed in claim 9 or 10 in which said centre yoke member has control means adjustably mounted thereon so as to restrict the range of displacement of said printing lever.

12. A moving coil type printing head as claimed in claim 11 in which said control means is an abutment screw adjustably screwed to said centre yoke member through said printing lever, a flange integrally formed from an intermediate part of said abutment screw so as to determine a rest position of said printing lever and a nut adjustably screwed to the abutment screw so as to reduce or prevent overdeflection of said printing lever.

13. A moving coil type printing head substantially as herein described with reference to and as shown in the accompanying drawings.