GB2076341A

GB2076341A - Paper feeding in printers

Info

Publication number: GB2076341A
Application number: GB8115425A
Authority: GB
Original assignee: Data Recording Instrument Co Ltd
Current assignee: Data Recording Instrument Co Ltd
Priority date: 1980-05-27
Filing date: 1981-05-20
Publication date: 1981-12-02
Also published as: GB2076341B

Abstract

A matrix printer in which the platen 5 is mounted on a vertical axis and moves with the printing head 1 along the print line. The platen is resiliently mounted and one end bears against a flat plate 2 through the record medium 4. The flat plate 2 defines a plane in which printing is to be effected so that, regardless of the thickness of the record medium, the front face of the record medium is always aligned with the printing plane. <IMAGE>

Description

SPECIFICATION Improvements in or relating to paper feeding This invention relates to printing apparatus in which a printing head is moved across a record medium and the printing head is selectively operated during movement across the record medium to effect printing of a line of characters on the record medium.

In such apparatus a platen is provided to extend behind the record medium to support the record medium at least along the line on which printing is to be effected. Hence the spacing between the printing elements of the print head and the front face of the record medium is dependent upon the thickness of the record medium. The quality of printing particularly when using print heads having a plurality of wires as printing elements, the elements being operated in such a manner that required characters are formed by a plurality of dots, is dependent upon the spacing between the printing elements and the front face of the record medium being set within close limits to an optimum value. If the record medium is of uniform thickness the print head can be adjusted to this spacing and this will be satisfactory for a run of printing using the medium.However, in the case where the record medium consists of multi-part stationery in which some parts are of full width whereas other parts are narrower, the thickness of the record medium will vary across its width. Hence a setting of the print head for optimum quality of print in the region of the thickest part of the medium will result in lower quality printing in the other thinner parts of the medium and vice versa.

According to the invention printing apparatus includes a printing head; a platen mounted in opposition to the printing head and effective to support a read face of a record medium interposed between the printing head and the platen; means operable to traverse the printing head and the platen along a printing line; means defining a plane in which printing is to be effected by the printing head; and means operative to sense the thickness of the record medium between the platen and the plane defining means at a position aligned with the printing head in the direction of the printing iine, such sensing means being effective to adjust the position of the platen to maintain in said plane that portion of a front face of the record medium lying between the printing head and the platen.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side view of printing apparatus and Figure 2 is a part perspective view of the apparatus.

Referring to the drawings a printing head 1 is mounted on a carriage (not shown) for movement along a line perpendicular to the plane of Fig. 1 of the drawings. A bar 2 extends parallel to the line of movement of the printing head 1 and provides a guide face 3 for the front face of a record medium 4 on which printing is to be effected. The printing head 1 is a so-called wire printer in which a plurality of wires are arranged with their ends in a line or in matrix formation whereby lengthwise movement of selected wires as the printing head moves across the record medium results in a plurality of dots being printed on the record medium by the ends of the wires and the time of operation of each wire is chosen so that the dots form the outlines of required characters on the record medium.

In order to support the record medium during the printing by the printing head, a platen in the form of a roller 5 having an axis of rotation perpendicular to the line of movement of the printing head 1 is mounted on a carriage (not shown) and caused to move with the print head along the rear face of the record medium. The platen is mounted to be free to move toward and away from the printing head so that the space therebetween may be adjusted for different thicknesses of record medium. The thickness of the record medium at a position aligned with the printing head is sensed by sensing means consisting of an extension of the platen roller 5. The roller 5 is urged by spring means (not shown) toward the guide face 3 of the bar 2 whereby the front face of the record medium is pressed against the guide face 3.Therefore the surface of the platen is continuously positioned, as the print head traverses the record medium, such that with the rear face of the record medium supported by the platen roller 5, the front face of the record medium is maintained co-planar with the guide face 3 and hence at a uniform spacing from the print head regardless of the thickness of the record medium.

In order to prevent any undesirable transverse movement being imparted to the record medium due to the traversal of the platen roller, a thin flexible blade 6 secured at its ends to the frame of the printing apparatus is interposed between the platen roller and the record medium.

The printing head 1 and the platen roller 5 may be mounted on separate carriages driven in synchronism along the line of printing or may be mounted on a common carriage.

Printing apparatus as described above is suitable not only for printing on continuous multi-part stationery in which some of the layers extend over only part of the width and hence the thickness of the multi-part stationery varies across its width but also for printing on the pages of books such as bank pass books where the thickness of the part on which printing is to be effected will vary according to the number of pages and the two halves of the book will usually be of different thicknesses.

Claims

1. Printing apparatus including a printing head; a platen mounted in opposition to the printing head- and effective to support a rear face of the record medium interposed between the printing head and the platen; means operable to traverse the printing head and the platen along a printing line; means defining a plane in which printing is to be effected by the printing head; and means operative to sense the thickness of the record medium between the platen and the plane defining means at a position aligned with the printing head in the direction of the printing line, such sensing means being effective to adjust the position of the platen to maintain in said plane that portion of a front face of the record medium lying between the printing head and the platen

2.Printing apparatus as claimed in Claim 1, in which said plane defining means is provided by a guide face located on a bar extending parallel to and aligned with the printing line.

3. Printing apparatus as claimed in Claim 1 or 2, in which said sensing means includes an extension of the platen engaging the rear surface of the record medium and effective to load the front face of the record medium at the plane defining surface; and spring means effective to urge the platen towards said plane defining means.

4. Printing apparatus as claimed in Claims 1, 2 or 3, including a thin flexible blade extending along said printing line and interposed between the platen and the record medium.

5. Printing apparatus as claimed in Claims 1 to 4, in which the printing head and the platen are mounted on a common carriage driven along the printing line.

6. Apparatus as claimed in Claims 1 to 4, in which the printing head and the platen are mounted on separate carriages driven in synchronism along the printing line.

7. Printing apparatus as claimed in any preceding claim, in which the printing head is a wire printer.

8. Printing apparatus constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.