GB2081650A - Wire matrix printing apparatus - Google Patents

Abstract

In a wire matrix printing head a ring of wire-selection electromagnets are grouped about the wire guiding arrangement 17, the electromagnets each having a yoke assembly 3 with a pair of limbs each able to support a separate energising coil 5. The electromagnet armatures 14 are supported by a common frame 9 having a finger 10 for each armature, on which the armatures are respectively pivoted. The printing wires 22 are spring loaded into their restored positions and are there supported by an individually adjustable resilient backstop 31. The printing wires 22 are supported in guides so that they are arranged in two columns, both the columnar pitch and the pitch of nominally adjacent wires in the columns being of the order of the wire diameter. Control of wire selection from the two columns is arranged to prohibit a further selection of any one wire for printing unless the printing head has moved along the printing line for a distance equal to twice the columnar pitch. <IMAGE>

Description

SPECIFICATION Wire matrix printing apparatus The- present invention relates to a wire matrix printing apparatus employing a wire printing head and to a method of selection of wires in the head to print a line of characters.

Wire printers have previously been proposed in which, for example a wire printing head is carried along a print line across a record and in which wires of the head are selected to be driven towards the record in order to pring characters in the line. Particular forms of such apparatus have employed a group of wires whose ends are gathered into a single vertical column to form styli facing the record, selected ones of these styli being impelled towards the record at each of a number of predetermined columnar positions forming a character printing area, so that the outline of a required character is progressively formed by dot impressions as the head advances over the character area.The impulsion for each of the styli is derived by the delivery of a blow to the opposite end of the wire, usually by an electromagnet armature, and a convenient form of print head has its electromagnets arranged in a circle at a position adjacent the ends of the printing wires. The selection of the required magnets to be energised is accomplished conventionally by the comparison of a stored character representation with the character required for each character printing area and the consequential selection of the required printing magnets at each of the predetermined columnar positions within this area. Typically a printing head would have seven wires or styli in a column and five columnar positions would be arranged within each character printing area so that a character is represented by a matrix containing 7 x 5 permissible dot printing positions.

When used in conjunction, for example, with data processing apparatus, it is found that as the effective speed of such apparatus is progressively increased, there is a requirement for a corresponding increase in the operating speed of printing apparatus and a primary limitation on the operating speed of previously proposed wire matrix printers is the operating time of the driving electromagnets. The present invention contemplates improvements both in the structure of the printing head and in its mode of operation in printing the characters in order to increase its effective operating speed.

According to the present invention, matrix printing apparatus includes a printing head having a base plate arranged to support a ring of U-shaped yoke assemblies each with a pair of parallel limbs extending in a direction substantially perpendicular to one side of the base plate, the limbs each being arranged to support a coil assembly; means for supporting in spaced relationship substantially to said one side of the base plate a non-magnetic spacer for each yoke assembly overlying the ends of the limbs and a frame having a plurality of fingers, one for each yoke assembly, each carrying a pivot support lug, the disposition of each finger relative to a corresponding one of the yoke assemblies being such as to support an armature pivoted on the lug carried by the respective finger to co-operate with the yoke assembly; a nose piece centrally disposed with respect to the ring of yoke assemblies and arranged to carry wire guides, the nose piece being positioned to project from that side of the base plate opposite said one side; and a plurality of printing wires supported in said wire guides, each wire having a printing end projecting from the nose piece and a second end engageable with and arranged to be impelled in a printing movement by operation of an associated one of the armatures. The frame may include a resilient backstop for the armatures and such a backstop may comprise for each armature a separate adjustable resilient member. The print head may include two columns of printing wires spaced at a pitch of an order of mangitude similar to the wire diameter.Printing wire selection control means may then include provision for regulating the successive selection of a single wire no more frequently than at an interval corresponding to movement of the head along a printing line by a distance at least equal to twice the pitch spacing.

Apparatus embodying the present invention will now be described, by way of example, with reference to the accompanying drawings, in which, Figure 1 is a diagrammatic exploded view of a printing head, Figure 2 iilustrates, partly in section, an assembled print head, Figure 3 is an explanatory illustration of the disposition of printing wires forming styli, and Figure 4 shows an example of the structure of printed characters.

Referring now to Figures 1 and 2 of the drawings, a printing head 1 is carried on a main mounting plate 2. The plate 2 carried a number of U-shaped electromagnet yoke assemblies 3, each built up from a number of laminations, the bases of the U-shapes being held in apertures 4 in the plate 2. A coil assembly 5 is positioned on each limb of the yoke assemblies 3. An end plate 6 is spaced away from the main plate 2 by spacers 7 and the plate 6 carries, by means of dowel pins 8, an armature support frame 9. A fixing screw 33 secures the frame 9 to the plate 6. The frame 9 has a number of peripheral fingers 10, one for each yoke 3 and the fingers 10 each have a pair of recessed lugs 11, turned inwardly to face the yokes 3.The recesses 12 in the lugs 11 accommodate projecting pivots 13 of armatures 14, the arrangement of the frame 9 being such that each armature 14 is pivoted adjacent a corresponding one of the yokes 3. Each armature 14 has a projection 1 5 carrying an ear 16.

A nose piece 1 7 is secured to the main plate 2 and projects outwards on the opposite side of the plate 2 from the yokes 3, being secured to the plate 2 by screws 1 8. The nose piece carries a pair of intermediate wire guides 19 and a terminal wire guide 20. The guides 19 and 20 have a number of guide holes 21 for printing wires 22, the terminal guide 20 having its guide holes in a double columnar arrangement, as will be described with reference to Figure 3, and the intermediate guides 19 have wire guide holes arranged in a suitable configuration to permit the wires 22 to be aligned at one end each with the ear 16 of a corresponding one of the armatures 14, the other ends of the wires 22 projecting from the terminal guide 20.

That end of each wire 22 adjacent the ear 1 6 of the corresponding armature 14 is fitted with a ferrule 23 which bears against the ear 1 6 under the influence of a return spring 24, so that the effect of energising the electromagnet coils 5 is to cause the appropriate armature to drive its associated printing wire 22 from its retracted position into a printing position at which it strikes a conventional record member 25 (as best seen in Figure 2) through a transfer medium such as a printing ribbon 26, to make a mark on the record.

Once the coils 5 are de-energised, the return spring 24 restores the wire 22 into its retracted position.

A non-magnetic member 27 is provided, having a projecting ear 28 corresponding to each coil position within the head, each ear 28 being interposed between the ends of the yoke assemblies 3 and the associated armature 14 to provide a conventional residual non-magnetic gap spacer. The end plate 6 is provided with a ring of threaded holes 29 each aligned with a corresponding hole 30 in the armature support frame 9. A resilient plug 31, carried in each of the holes 30, forms a backstop damper for each of the armatures. Screws 32 in the holes 29 of the end plate 6 are provided for the adjustment of the dampers 31. The rear of the head assembly is protrected by a cover 34.Connectio.-s to the coils 5 are conveniently arranged by the use of a printed wiring board 35 which is secured to the main plate 2 by rivets 36 and spacers 37, the board 35 being formed at one edge with connection fingers to receive a suitable socket (not shown).

The arrangement and control of the wires 22 will now be described in greater detail with reference to Figure 3. As noted earlier, one wellknown representation of characters by a stylus or wire-printer is based on a matrix of dots arranged in a 7 x 5 configuration, and this configuration will be used as an example to illustrate the operation of the present apparatus.

Thus a character may be printed by the selective operation of seven styli arranged in a single column as the column traverses a "five-dot-wide" character space. It is also apparent that to draw a vertical line, all the styli of the column are required to be energised simultaneously, while to draw a horizontal line, a single stylus is required to be operated successively at each of the five notional dot positions of the character space as it is traversed by the head. This latter requirement sets the limitation of printing speed at the maximum rate at which successive dot positions of a horizontal line can be printed by the same stylus.

Thus, given this limitation, it is apparent that in one case an improvement in printing speed may be obtained by improving the response time for the selection of the styli or printing wires. It is also to be observed that conventional wire printer arrangements have frequently used yoke structures each carrying a single energising coil and, in these cases, the physical size of the coil is a limiting factor in determining the number of wired selection magnets which may be included in a circle of a given size. The size and impedance of such coils also impose severe constraints on the operating characteristics of the wire selection magnets.The form of construction now proposed uses a pair of coils for each electromagnet assembly and this structure permits the reduction of response time of the electromagnet by allowing the application, for example, of an increased electrical current while at the same time allowing greater heat dissipation from the coils so that the entire assembly has an improved performance. At the same time, the physical size of the coils may be reduced so that the provision of the greatest possible number of magnets in a circle becomes a simpler matter.

The arrangement of the printing wires at the terminal guide 20 is indicated in Figure 3 by a dashed outline representing the guide 20 enclosing the guide holes 21 supporting the wires 22. The wires 22 are arranged in two columns, indicated by column axes 40 and 41.

The column 40 contains seven wires 22, while the column 41 contains only five wires 22, one wire 22 being provided at each end of the column 41 as well as a group of three wires 22 occupying adjacent dot positions at the centre of the column.

It is found that the omission of wires 22 from the intermediate positions adjacent the ends of the columns does not affect the representation of a satisfactory character outline, and provides a valuable reduction in the required number of wireoperating arrangements, notably the yokes 3, coils 5 and armatures 14 in order to provide a compact print head.

Previous character representations, as has been, noted, have required the spacing of the printing wires or styli on a 7 x 5 matrix grid in which the pitch of the dot positions is the same for rows and columns, adjacent dot positions being at a pitch of the same order as the diameter of the wires, represented in Figure 3 as a distance P. The extent of a character space is indicated in Figure 3 by a line of broken outline circles 42 extending from the lowermost pair of guide holes 21 as shown in the Figure. Adjacent character spaces are separated by a space equivalent to one dot position, a broken line circle 43 indicating the first dot position for the next character. For the sake of simplicity, it is preferred to regard the columnar dot-printing positions of the character space as being spaced at half the conventional pitch distance, as indicated by distance R.Thus, the character space consists of nine columnar axes 44 at a pitch spacing R, and the conventional horizontal dot spacing is 2R. Because there are effectively two columns of wires 22 in the printing head, it is possible to use different columns to print dots in adjacent ones of the conventional columnar positions, so that, in the case of a horizontal line, a single wire 22 of one of the columns is required to be actuated at a rate consistent with the movement of the head over a distance 4R. Thus, the former limitation on the printing speed is no longer true, the printing speed being effectively double by the use of the present arrangement of printing wires.

Moreover, it is found that the curved appearance of rounded characters may be improved by the selection of horizontal dot positions intermediate those of the conventional matrix, as may be the appearance of angular lines, such as those required for the figure "7" or the limbs of such letters as "M" or "K", for example. In order to use these intermediate positions, as shown in the Figure by the position of broken line circle 45, the conventional print control is modified. Previously matrix proposed printers have used a series of timing pulses to control the energisation of print magnets, the frequency of the timing pulses being arranged to correspond to the movement of the print head through a distance equal to the spacing between adjacent dot positions, so that the timing pulse corresponds to the time taken for the head to traverse the pitchdistance P.The selection of the particular magnets to be energised at these intervals is dependent upon a stored character representation. In the present case the timing pulse frequency is made to correspond to the time taken by the head to traverse the distance R and the stored representation then allows the selection of magnet operation at the columnar positions 44 at this pitch. Thus, it will be seen that the control arrangements for the present apparatus are essentially similar to those previously proposed, but that the stored character representation takes into account the altered timing pulse frequency.It will be understood that the over-riding requirement for energisation of the print magnets is that no one magnet may be selected for reenergisation at a frequency greater than that required by the printing head to traverse a horizontal distance equal to 4R, and it will then be apparent that the same magnet may be reenergised for any position lying on one of the column axes 44 once this distance has been equalled or exceeded. Figure 4 shows a typical set of character representations which may be printed by this arrangement.

It will be realised that the choice of a matrix grid of the size referred to above is one that has been commonly used. It is clear, however, that the provision of seven printing wires in a column is not to be regarded as a necessary limitation on the capacity of the print head 1, and that the horizontal character space illustrated is also exemplary, both the total character space and the columnar axes within that space being determined by the timing pulse frequency in relation to the speed of traversal of the head 1 along the printing line of the record to be printed. Equally, the provision of two columns of printing wires 22 in the printing head is related to the time required for operation of a single print-wire actuator and the speed of head traversal. The omission of two wires from the second column of print wires is convenient where the character outline will permit such a simplification, but is not to be regarded as an essential consequence of the provision of such an additional column.

As has been noted earlier, the example described employs an electromagnet structure having two coils and while this form of construction has advantages in the more efficient operation of the printing wires, it will be realised that a structure using only one coil may alternatively be used. In the interest of close packing of the magnets within the head it is also possible, where two-coil structures arranged in a circle are used, to make the inner coils of smaller diameter than the outer coils.

Claims (6)

1. A matrix printing apparatus including a printing head having a base plate arranged to support a ring of U-shaped yoke assemblies each with a pair of parallel limbs extending in a direction substantially perpendicular to one side of the base plate, the limbs each being arranged to support a coil assembly; means for supporting in spaced relationship substantially parallel to said one side of the base plate a non-magnetic spacer for each yoke assembly overlying the ends of the limbs and a frame having a plurality of fingers, one for each yoke assembly, each carrying a pivot support lug, the disposition of each finger relative to a corresponding one of the yoke assemblies being such as to support an armature pivoted on the lug carried by the respective finger to cooperate with the yoke assembly; a nose piece centrally disposed with respect to the ring of yoke assemblies and arranged to carry wire guides, the nose piece bing positioned to project from that side of the base plate opposite said one side; and a plurality of printing wires supported in said wire guides, each wire having a printing end projecting from the nose piece and a second end engageable with and arranged to be impelled in a printing movement by operation of an associated one of the armatures.

2. Matrix printing apparatus as claimed in Claim 1, in which the frame carrying said fingers also includes means for supporting resilient backstop means for each of the armatures.

3. Matrix printing apparatus as claimed in Claim 2 in which said frame includes a plurality of apertures, one for each armature, the apertures being aligned respectively with the armatures and further including a separate resilient backstop member carried in each aperture respectively and an end plate arranged to support said frame, the end plate carrying adjusting screws aligned respectively with said apertures in the frame whereby the resilient backstop members are individually adjustable.

4. Matrix printing apparatus as claimed in Claim 2 in which said frame is a symmetrical hublike member from which the fingers project radially outwards and in which each of said nonmagnetic spacers for the respective yoke assemblies is formed by a projection extending radially outward from an annular member of nonmagnetic material.

5. Matrix printing apparatus as claimed in Claim 1 in which the nose piece extends through the base plate to locate the second ends of the printing wires adjacent their respective armatures for engagement therewith and in which return spring members are provided, one for each printing wire, each return spring member being arranged in engagement with the nose piece to provide a load effective to restore a printing wire and its associated armature to an unoperated state after completion of a printing movement.

6. Matrix printing apparatus as claimed in Claim 5 including means for supporting the printing head adjacent a record, that end of the nose piece from which the printing wires project being so spaced from the record as to permit a print wire moved by operation of its associated armature to print an impression on the record; means for moving the head across the record along a printing line in which characters are required to be printed in succession and means for controlling the selection of printing wires to be operated during such movement, in which the wire guides are arranged to support the wires into two parallel columns, one column at least containing a predetermined number of wires corresponding to the required height of a character to be printed, the wires in said one column being closely spaced at a pitch 2R of the same order of magnitude as the wire diameter, the columns being spaced at a similar pitch distance and in which the selection controlling means is arranged to permit successive selection of a single wire no more frequently than at an interval corresponding to movement of the head along the printing line by a distance at least equal to twice the pitch 2R.