US3434413A

US3434413A - Print hammer mechanisms for high speed printers

Info

Publication number: US3434413A
Application number: US622604A
Authority: US
Inventors: Ronald Henry Lee; Albert John Keen
Original assignee: International Computers and Tabulators Ltd
Current assignee: International Computers and Tabulators Ltd
Priority date: 1967-01-06
Filing date: 1967-03-13
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25
Also published as: GB1159751A; DE1983302U

Description

March 25, 1969 LEE ET AL 3,434,413

PRINT HAMMER MECHANISMS FOR HIGH SPEED PRINTERS Filed March 15, 1967 Sheet Of 2 uasmr mm KEEN kmxw ATTORNEYS March 25, 1969 R LEE ET AL PRINT HAMMER MECHANISMS FOR HIGH SPEED PRINTERS Sheet i of 2 Filed March 13, 1967 Di m e E O W M wum T N o M w; a w me United States Patent 3,434,413 PRINT HAMMER MECHANISMS FOR HIGH SPEED PRINTERS Ronald Henry Lee, Stevenage, and Albert John Keen,

Letchworth, England, assignors to International Computers and Tabulators Limited, London, England, a British company Filed Mar. 13, 1967, Ser. No. 622,604 Claims priority, application Great Britain, Jan. 6, 1967, 907/67 Int. Cl. B411 9/00 US. Cl. 10193 8 Claims ABSTRACT OF THE DISCLOSURE A multiple print hammer assembly built up by assembling individual print hammer assemblies into a trough-shaped alignment member is disclosed, the hammer assemblies being suitable for use in conjunction with so-called on-the-fiy printing apparatus. Each individual print hammer assembly uses a unitary structure to form an integrated magnetic circuit in conjunction with an armature having an extension having the print hammer itself and electromagnet coils mounted on projections from the structure. Forwardand back-stops are provided. The alignment member may form a heat sink for all the individual hammer assemblies mounted on it. Electrical connections for the energisation of the electromagnet coils are provided by contact pins extending from the unitary structure and the pins are also used for the purpose of locating the individual hammer circuit in the alignment members. For high speed operation the armature may be supported on a low-friction bearing, for example a bearing of polytetrafiuoroethylene, and the armature biassing spring may be separated from the stud upon which it bears by a resilient pad or a pad of low friction material. The forward stop, which is adjustable to limit the travel of the print hammer in response to operation of the armature, may be separated from the print hammer by a pad of resilient material.

Cross-reference to related application The apparatus disclosed herein is also disclosed, in part, in co-pending patent application No. 621,885 filed Mar. 9, 1967, filed by the same inventors and assigned to the same assignee as the present application.

Background of the invention The present invention relates to printing apparatus of the so-called on-the-fiy kind and in particular to print hammer mechanisms suitable for use in conjunction with printers in which a type carrier carrying a repertoire of characters is movable past a printing position and in which a particular character is selected to be printed by the timed operation of a print hammer.

It has previously been proposed to provide on-the-fiy printing apparatus in which a record member, such as a document is positioned adjacent a printing member having, for example, a group of rotating typewheels each carrying a repertoire comprising a sequence of different characters. A transfer medium, such as a typewriter ribbon is interposed between the typewheels and the document, and a group of print hammers, one for each print wheel, is provided on the opposite side of the document from the transfer medium. By selectively energising electromagnets associated respectively with the hammers in timed relationship to the rotation of the typewheels, the hammers are impelled towards the typewheels so that characters carried by the typewheels are caused to be printed on the document, a particular character from any 3,434,413 Patented Mar. 25, 1969 In accordance with the present invention an individual print hammer assembly has a unitary magnetic structure supporting energising coils and a pivot carrying an armature, the armature having an extension carrying the print hammer proper. The armature is normally biassed to a non-operated position by spring means but is moved to an operating position by the application of an electrical pulse to the coils, thereby momentarily moving the print hammer to an operative position, the extent of movement of the hammer being limited by a front stop. This form of construction provides a highly efiicient magnetic circuit for high speed operation of the print hammer.

A multiple print hammer assembly is built up by assembling a number of the individual print hammer assemblies into an aligning member, each individual assembly carrying means for locating it in the required position in the aligning member. Using this form of structure, the individual print hammer assemblies are secured in position in good thermal contact with the aligning member which then serves as a heat sink to aid in dissipating heat generated by the electrical impulses applied to the coils, thus allowing high current pulses to be used for the operation of the individual print hammers. In addition the means carried by the individual assemblies for locating the assemblies in the alignment member also provides electrical contacts for the supply of energising pulses to the electromagnet coils.

Further refinements of construction which assist in enabling high speed operation of print hammers in assemblies made in accordance with this invention include: a low friction bearing for the armature, a resilient or low friction pad interposed between the armature spring and that particular member against which it works and a resilient pad interposed between the front stop and the print hammer.

view of a group of print hammer assemblies and their operational relationship.

Description of the preferred embodiments Referring now to FIGURE 1, a print hammer assembly has a unitary structure 1 of magnetic material. The unitary structure 1 comprises a foot portion 2, a head portion 3 spaced away from the foot portion 2 and a web 4 joining the foot and

head portions

2 and 3. The general configuration of the structure 1 is such that the web 4 is arranged at one end of the foot and

head portions

2 and 3 so that these portions both extend from the web in the same direction. The web 4 is thinner than the foot and

head portions

2 and 3 and has two parallel projections 5 extending into the space between the foot and

head portions

2 and 3. The projections 5 are arranged to form cores for a pair of electromagnet coils 6.

Each coil 6 is formed by a winding about a thin paper former 7, the winding and former 7 being encapsulated in an epoxy resin after the winding has been completed, so that an entire coil is slid over one of the projections 5. The windings are connected in series by conventional flying leads from the coils to a pair of contact pins 8. The contact pins are held in the foot portion 2 of the unitary structure 1 and are electrically insulated from the structure 1 by means of insulating sleeves 9, the pins 8 projecting beyond the sleeves 9 outside the foot portion 2 of the structure 1.

A block 10 is secured by means of a screw 11 to the head portion 3 of the unitary structure 1. The block 10 carries a pivot pin 12, and an armature 13 is supported by the pivot pin 12. The armature is arranged so that in operation it is attracted in response to energisation of the magnet coils 6 to move to a position bridging the ends of the projections 5. An extension 14 is provided on the armature 13 and a print hammer 15 is mounted on the end of the extension 14. The extension 14 is arranged generally at right angles to the direction in which the armature 13 extends, so that the extension lies within the space between the foot and

head portions

2 and 3. The print hammer is shaped so that its extremity projects above and at one end of the head portion 3 as shown in the figure, and is moved by movement of the armature 13 into the bridging position so that this projection is increased. The head portion 3 of the unitary structure 1 carries a screw 16 which is positioned so that it limits this movement of the print hammer 15. Thus, the screw 16 forms an adjustable front stop for the print hammer.

The armature 13 is biassed by means of a spring member 17 so that it is normally maintained in a non-operated position spaced away from the ends of the projections 5 by a small distance. The spring member 17 is a fiat spring secured by means of a block 18 to one end of the armature 13. The free end of the spring 17 acts against a stud 19 in the web 4 of the unitary structure 1.

As shown in FIGURE 3, a multiple print hammer assembly is built up by aligning a group of the assemblies described above in side-by-side relationship so that the extremities of all the print hammers 15 are arranged in line. A further group of assemblies are similarly mutually aligned and the two groups are arranged with respect to each other so that the print hammers of the first group are interleaved between those of the second group, thus forming a single line of print hammers. In order to prevent stray magnetic fields from one hammer assembly from affecting adjacent assemblies, each assembly carries a shield 20 of magnetic material (FIGURES l and 3). The shield 20 is conveniently supported by an adhesive layer applied to the outer surface of the magnetic coils 6.

In order to maintain the individual print hammer assemblies in position in the multiple assembly an aligning member 21 is provided. The aligning member is generally trough-shaped and has locating holes 22 provided in the base of the trough to accommodate the connecting pins 8 and their insulating sleeves 9, the pins 8 projecting through the base of the trough. The print hammer assemblies are secured in the aligning member by

screws

23 and 24, the screw 23 passing through a hole 25 in the base into the foot portion 2 of the unitary structure 1 of the assembly and the screw 24 passing through a hole in the head portion 3 into a threaded hole 26 in the aligning member 21.

A series of resilient members 27 are provided arranged along the inner sides of the member 21, each of the members 27 being positioned adjacent one of the armatures. Each of the members 27 is arranged to form a backstop for the armature with which it is associated when the corresponding individual print hammer assembly is secured into position in the trough.

In operation, the multiple print hammer assembly consisting of a number of individual hammer assemblies secured to the aligning member, is supported in relation to a conventional rotary type carrying member, such as a group of print wheels each carrying a repertoire of characters. The arrangement is such that the characters of a single wheel are carried in turn past a print hammer so that a single character is selected to be printed b the timed operation of the print hammer in the conventional manner. It will be appreciated that as the speed of rotation of the typewheels is increased, the time available for the operation of a print hammer is decreased, and it becomes necessary to increase the speed of response and of operation of the print hammer in order to allow a selected character to be printed cleanly and in correct position on a document. The present print hammer assembly, as described above employs an integral magnetic circuit in which the yoke and the magnet cores and pole pieces are all parts of the single unitary structure 1 to provide improved magnetic characteristics. This form of construction provides a high efiiciency magnetic circuit of small size, and since the size is reduced the mass of moving parts may also be reduced, thus allowing faster operation.

The speed of response and operation of the print hammer may also be improved by the use of relatively high energising current pulses applied to the magnet coils 6. However, because the increase in speed of rotation of the typewheels may involve a shorter cycle of operation of the apparatus, the frequency with which operating pulses are applied to the magnet coils also increases. The combined effects of high energising current and faster pulse repetition rate tends to produce an undesirable rise in temperature in the magnet coils 6. In the present apparatus, the use of a thin former 7, preferably of paper, on which the operating coils are wound allows the rapid transfer of heat to the unitary structure 1. By arranging that the meeting faces of the unitary structure and the aligning member 21 are machined to provide a good thermal contact and by making the aligning member of heavy and robust construction, the aligning member provides a heat sink, so that the undesirable local temperature rise in the operating coils of the individual hammer assemblies is greatly reduced.

It is also to be noted that the use of the contact pins 8 and their associated insulating sleeves 9 to locate the individual print hammer assemblies in the aligning member 21 enables a multiple hammer assembly to be built up without the use of conventional spacer combs to separate the individual print hammers, thus reducing the risk that the hammers may touch the combs with a consequent deterioration in speed of response as well as providing a simpler, more easily assembled, and therefore less costly, unit.

The print hammer assembly shown in FIGURE 1 may be modified to further improve its performance, as shown in FIGURE 2. The pivot pin 12 is, in this case, enclosed in a sleeve 28 of a material having a very low coeflicient of friction, such as polytetrafluorethylene. The sleeve 28 then forms a low-friction bearing for the armature 13. The armature spring member 17 is separated from the stud 19 carried by the unitary structure 1 by resilient pad 29. The pad 29 serves to damp out any mechanically induced vibration in the spring which might adversely offset the performance of the assembly. The pad 29 may 31- ternatively be formed from a low-friction member to avoid any frictional losses caused by the spring 17 rubbing the stud 19 carried by the unitary structure 1 by a resilient 15 to bounce on the front stop screw 16, the screw 16 may be separated from metallic contact with the print hammer 15 by a further resilient pad 30.

We claim:

1. A print hammer assembly including a unitary structure of magnetic material having a pair of projections;

a magnet coil about at least one of said projections, the coil comprising a winding upon a thin former so d1mensioned to fit closely about the projection;

a pivot;

means for supporting the pivot, the supporting means being secured to said unitary structure;

an armature supported by said pivot and operable in response to energisation of said coil to move towards a position bridging said projections;

spring means between said unitary structure and said armature acting to bias the armature toward a nonoperated position spaced away from said projection; an extension on the armature; a print hammer carried by said extension;

an adjustable front stop carried by said unitary structure to limit movement of said print hammer produced by movement of said armature towards said bridging position; an aligning member having an aperture and means for locating said unitary structure relative to the aligning member including a locating member carried by said unitary structure and engaging in the aperture in the aligning member, an electrical conductor extending through the cating member and electrically insulated from said unitary structure and from said aligning member, and an electrical connection between said electrical conductor and said magnet coil. 2. A print hammer assembly as claimed in claim 1 in which the locating means includes a pair of electrically conductive pins, and a sleeve of insulating material surrounding at least one of said pins. 3. A print hammer assembly including an aligning member; a plurality of unitary structures of magnetic material,

each structure having a pair of projections; means on each unitary structure for locating the respective structures relative to the aligning member; means for securing each said unitary structure to said aligning member in thermally conductive relationship with said aligning member, the aligning member being effective as a heat sink for all said unitary structures; each said unitary structure carrying a magnet coil about at least one of said projections, the coil comprising a winding upon a thin former so dimensioned to fit closely about the projection; a pivot; means for supporting the pivot on the unitary structure; an armature supported by said pivot and operable in response to energisation of said coil to move towards a position bridging the projections; spring means acting between said unitary structure and said armature to bias the armature toward a non operated position spaced away from the projections; an extension on the armature; a print hammer carried by said extension and an adjustable front stop carried by said unitary structure and arranged to limit movement of said print hammer produced by movement of said armature towards the bridging position. 4. A print hammer assembly including an aligning member; a unitary structure of magnetic material having a pair of projections;

means on said unitary structure for engaging the aligning member to locate the structure relative to the aligning member and to secure the unitary structure to the aligning member;

a magnet coil about at least one of said projections, the coil comprising a winding upon a thin former so dimensioned to fit closely about the projection;

a pivot .pin;

means for supporting the pivot pin on the unitary structure;

an armature supported by said pivot pin for rotation about a longitudinal axes of the pivot pin, said armature being responsive to energisation of said coil to rotate in a first direction towards a position bridging said projections;

spring means acting between said unitary structure and said armature tending to rotate the armature in a direction opposite to said first direction away from said projections;

an extension on the armature;

a print hammer carried by said extension and an adjustable front stop carried by said unitary structure effective to limit movement of said print hammer produced by rotation of the armature in the first direction.

5. A print hammer assembly as claimed in claim 4 including a stud on said unitary structure and in which said spring means comprises a leaf spring secured at one end to said armature, the opposite end of the leaf spring engaging the stud.

6. A print hammer assembly as claimed in claim 5 in which the opposite end of the leaf spring includes a pad of resilient material which engages the stud on the unitary structure.

7. A print hammer assembly as claimed in claim 4 including a member of low friction material rotatable about said pivot pin and in which the armature is supported on said member.

8. A print hammer assembly as claimed in claim 4 in which the adjustable front stop includes an element of re silient material arranged to engage the print hammer to limit the movement of the print hammer in the first direction.

References Cited UNITED STATES PATENTS 2,940,385 6/1960 House 101-93 3,110,250 11/1963 Fradkin 101-93 3,177,803 4/1965 Antonucci 101-93 3,183,830 5/1965 Fisher et a1. 101-93 3,200,739 8/ 1965 Antonucci 101-93 3,266,418 8/1966 Russo 101-93 3,314,359 4/1967 Martin 101-93 3,349,696 10/ 1967 Potter 101-93 WILLIAM B. PENN, Primary Examiner.