GB2049558A - Printing device - Google Patents

Abstract

A printing device comprising a support (e.g. daisy wheel) 6, 7, 20 carrying characters 8 which are selectively contactable with a, preferably cylindrical, platen 5 under the action of a striker member, usually a hammer 11. This hammer 11 is displaced by a striker device 13, 17, 18, 19, against the force of a return device such as a spring 16, in the direction of a writing surface 5. So as to obtain a striking force adapted to the actual printing surface of each character 8 the printing surface of each character 8 forms part of an imaginary surface P corresponding, in use, to the writing surface 5, the spacing between the surface P and the support surface 21 contactable by the hammer is a function, preferably proportional to the printing surface size of that character. <IMAGE>

Description

SPECIFICATION Printing device The present invention relates to a printing mechanism comprising a support member for supporting characters which are selectively movable into contact with a writing surface under the action of a striker member. The striker member is displaced by a striker device against the action of return means. The striker member may be initially accelerated and then decelerated towards the support member or may be continuously accelerated. The actual printing surface of each character forms part of an imaginary surface corresponding to the writing surface when the character is in contact therewith.

A single striker member is usually provided in known printing devices of this type and one of the inherent problems of such devices is to obtain a striking force which is appropriate for the size of the printing surface of the characters, that is to say, is substantially proportional to the actual printing surface area. This problem can be readily seen by the fact that the actual printing surfaces of the characters may vary by a factor of the order of 20 to 30 as is the case in comparing the size of a punctuation mark with a capital letter.

Known printing devices, which are generally mounted on a carriage displaced along a cylindrical platen, are provided with a striker device permitting the displacement of the striker member at two or more different speeds corresponding to two or more different levels of striking force. Such devices are, however, complex and costly, because it is necessary to provide information associated with each character as to the required striking force, to read this information and to transmit it to the striker device before the printing of the character takes place. These steps are effected automatically.

Nevertheless, the high cost of such devices has caused manufacturers to produce devices which generally only have two levels of striking force. This, of course, does not permit the striking force to be changed in an analog manner in dependence upon the size of the printing surface of the characters.

The present invention seeks to provide a printing device which permits a striking force adapted to the size of the printing surface of each individual character to be attained without incurring excessive manufacturing costs.

In accordance with the present invention, there is provided a printing device comprising a support member on which a plurality of characters are provided, the characters being selectively displaceable into contact with a writing surface under the action of a striker member, the striker member being displaced by means of a striker device biassed into a rest position by resilient return means, the printing surface of each character forming part of an imaginary surface corresponding to the writing surface when the character is in contact therewith wherein the spacing between said imaginary surface and the surface of the support contactable by said striker member is a function of the size of the printing surface of the character.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. lisa side view of part of a printing device in accordance with the present invention, the device including a printing disc, Figs. 2 and 3 each show an elevational view of a detail of the printing disc, and Fig. 4 is a view similar to Figs. 2 and 3, but showing a modified detail.

Since printing devices of the type are generally well known in the art, the following description will be limited solely to those features which are essential for an understanding of the invention.

In Fig. 1, there is shown a printing device 1 for a typewriter. The device 1 is mounted on a carriage 2, which carriage is slidably displaceable along a rod 3 and a bar 4. The axis of the rod 3 and bar 4 extend to the axis of the cylindrical platen 5 of the typewriter.

The printing device 1 comprises a disc 6 having a plurality of arms 7 extending radially therefrom, the free ends of each arm being provided with a character 8 in relief.

The printing disc 6 is fixedly mounted on the end of a rotatable selector shaft 9 driven by a motor 10.

The characters 8 can be selectively brought into contact with the cylindrical platen 5 or a sheet of writing material located therearound by rotating the shaft 9 and striking the rear face of the free end of the selected arm 7 by a striker member such as a ham mew 11.

The hammer 11 is of a generally cylindrical form and includes a circular bearing shoulder 12 against which a pivotal lever 13 is caused to strike. The hammer 11 is located at the free end of an arm 14 pivotally mounted on the carriage 2 and is biassed into contact with an abutment member 15 by a return spring 16 in its rest position.

The lever 13 is integrally formed with a plate 17, the plate being pivotally mounted on the carriage 2 and being so located as to be attracted by an electromagnet 18. A spring 19 maintains the plate 17 in its rest position at a predetermined spacing from the electromagnet 18.

When a character 8 is selected, it is brought into position by the motor 10, the electromagnet 18 is energised and strongly attracts the plate 17. This causes pivotal movement of the lever 13 which strikes the shoulder 12 of the hammer 11 and causes this latter to move in the direction of the cylindrical platen 5 against the action of the return spring 16.

When the plate 17 contacts the electromagnet 18 the pivotal movement of the lever 13 ceases but the hammer 11 continues to move in the direction of the cylindrical platen 5 under its own momentum. However, it is still subjected to the action of the return spring 16. The hammer 11 is thus initially accelerated towards the cylindrical platen 5 whilst the electromagnet is attracting the plate 17, but then decelerates until the hammer 11 strikes the character 8.

Figs. 2 and 3 show, in detail, different printing characters 8. Each character is carried on the front face of a body portion 20 mounted on the free end of one of the radial arms 7. On the rear face of body portion 20, a heel 21 is provided which co-operates with the hammer 11. The thickness of the heel 2-1 is selected in dependence upon the size of the printing surface of the character 8. More specifically, the largerthe surface of the printing character8the thicker the heel 21.

Thus, it is important that the hammer 11 which, it will be recalled, is decelerating as it approaches the cylindrical platen 5, strikes the heel 21 of the character 8 with a speed which increases as the thickness of this heel 21 increases.

It can thus be seen that to obtain a striking force adapted to the printing surface area of the characters 8 it is sufficient to make the thickness of the heel 21 of each character 8 a function of the printing surface of the character.

Fig. 4 shows a modified arrangement in which the end of each radial arm 7 is provided with two concentric rows of characters 8. The body portion 20 on the free end of the arm carries the two characters 8 in relief on its front face and a heel 21 for each character 8 on its rear face. The thickness of the heels is again dependent upon the size of the printing surface of the character 8 with which it is associated.

Various modifications of the printing device of the present invention can be envisaged. Thus, the relief height of the characters 8, that is to say, the amount they project from the body member 20 may be selected in dependence upon the printing surface size. More generally, a support for the characters 8 may be provided in which, for each character, the spacing between an imaginary surface P, which is the printing surface and corresponds to the writing surface when the character 8 is in contact therewith and the corresponding contact surface of the support which co-operates with the striker member, is a function of the size of the printing surface of the character.

The striker device may be different from that described hereinbefore. Thus, it could, for example, be in the form of a cam co-operating with the arm 14 for displacing the hammer 11.

The support 6 for the characters may be spherical or cylindrical, the striker member acting on a pivot point or a pivotal axis respectively of such support.

In such cases, the spacing referred to herein before is constituted by the spacing of the imaginary surface P for each character from the point or the pivotal axis of the support 6.

A printing device can also be envisaged in which the striking of the characters is effected when the hammer or, more generally, the striker member, is propelled with a progressively increasing speed. In this modification, the thickness of the heel 21 is decreased as the printing surface of the character increases.

Claims (6)

1. A printing device comprising a support member on which a plurality of characters are provided, the characters being selectively displaceable into contact with a writing surface under the action of a striker member, the striker member being displaced by means of a striker device biassed into a rest position by resilient return means, the printing surface of each character forming part of an imaginary surface corresponding to the writing surface when the character is in contact therewith wherein the spacing between said imaginary surface and the surface of the support contactable by said striker member is a function of the size of the printing surface of the character.

2. A device as claimed in claim 1 wherein the striker member is initially accelerated and thereafter decelerated towards the writing surface.

3. A device as claimed in claim 1 wherein the striker member is continuously accelerated towards the writing surface.

4. A device as claimed in any one of claims 1 to 3 wherein the characters contact the writing surface whilst the striker member is submitted to a single action of the return force wherein the spacing between the imaginary surface and the surface of contact is proportional to the size of the printing surface for each character.

5. A device as claimed in any preceding claim wherein the support comprises a printing disc having a plurality of arms extending radially therefrom, a body member being fixedly mounted at the free end of each arm, each body member carrying at least one character on its front face, a heel being provided on the rear face of each body member, the thickness of the heel being proportional to the size of the printing surface of the character associated therewith.

6. A printing device as claimed in claim 1 constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.