GB1578648A

GB1578648A - Printer

Info

Publication number: GB1578648A
Application number: GB46229/77A
Authority: GB
Original assignee: Facit AB
Current assignee: Facit AB
Priority date: 1976-11-10
Filing date: 1977-11-07
Publication date: 1980-11-05
Also published as: NL7712345A; CH625070A5; SE7612497L; DE2750318A1; JPS5363125A; IT1090431B; FR2370591B1; FR2370591A1; SE403325B

Abstract

The high-speed printer is provided with a moving print head (15) which is arranged on a movable carriage (17). The movement of the print head (15) is determined by an expandable bladder (14) which acts on the print head and which is pneumatically connected to a second bladder via an air hose (12). The second bladder (20) is in this case arranged to be fixed with respect to the printer frame (27) and can be compressed by means of an electromagnet (23). This allows a high printing speed with small moving mass. <IMAGE>

Description

(54) AN IMPROVED PRINTER (71) We, FACIT AKTIEBOLAG, a Swedish joint stock company of S-597 00 Atvidaberg, Sweden, do hereby declare the invention, for which we pray that a patent .may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a printer having a printing head provided with printing needles and arranged on a movable carriage, the carriage being arranged to move along a recording medium, and the printing head being movable in relation to the carriage so that the distance between the printing needles and the medium is variable.

High speed printers having the above features and having printing heads movable in a direction perpendicular to the recording medium are known, the movable heads allowing, for example, the use of different thicknesses of recording medium.

Generally, one or more springs are used to press the printing head against the recording medium. The drawback of this is that the printing head is continously subjected to a force directed towards the medium, which inter alia makes changing and feeding of the medium more difficult. To avoid this drawback it is also known to produce the pressing force by means of an electromagnet mounted on the carriage, whereby interruption of the current to the magnet results in the printing head being withdrawn from the medium. Locating the electromagnet on the carriage, however, leads to further drawbacks, in that (a) more space is required and, more importantly (b) the increased mass of the carriage results in slower carriage movements and hence a lower printing speed.

It is an object of this invention to provide for the moving of the printing head in a direction to or from the medium but at the same time to avoid the drawbacks of the known constructions.

According to this invention a printer has a printing head, which head has printing needles and is attached to a carriage, the carriage being movable relative to a frame of the printer to move the head along a recording medium, wherein the head is movable relative to the carriage so that the distance between the needles in their rest position and the medium is variable, the said distance being charged by an expansible first fluid containing device which acts on the head and which is connected to a second fluid containing device, the latter being mounted on the frame and operable by an electromagnet, to cause expansion of the first fluid containing device.

An embodiment of the invention will now be described by way of example with reference to the drawing, in which the Figure is a diagrammatic side elevation of a printing head and a control device.

The apparatus shown in the Figure can be divided into three parts, viz. a printing head part 10, a control device 11 and a hose 12 connecting the two. For clarity the control device 11 is drawn to a larger scale than the rest of the Figure.

In addition to a hose connection 13, which is shown only diagrammatically, the part 10 includes a first fluid containing device in the form of a hollow, elongate bladder 14, for example of rubber, arranged to act upon the rear of a printing head 15.

The printing needles of the head are indicated diagrammatically at 16, the carriage carrying the printing head at 17 and the recording medium at 18. During printing of each separate line, the carriage is arranged to move along the medium 18, i.e.

in a direction perpendicular to the plane of the drawing. The printing head is pivotably attached to the carriage, by leaf springs, one of which is shown at 19.

The interior of the bladder 14 is connected by the hose 12 to a second fluid containing device in the form of a bellows 20 in the control device 11. The bellows 20 is secured to a disc 21 and is compressible between this disc and a movable disc 22 which is connected to the armature 24 of an electromagnet 23. When the electromagnet is disconnected from its supply, a spring (diagrammatically shown at 25) holds the armature 24, and thus the disc 22, away from the bellows 20. The latter has an opening 26 so that operation of the pneumatic system, unlike a closed system, is not affected by changes in the ambient temperature and atmospheric pressure.

Unlike the movable printing head part 10, the control part 11 is fixed and is secured to the printer frame 27. This is made possible by the flexible hose 12.

When the electromagnet 23 is energised, the magnetic forces pull the armature inwards, i.e. to the left in the Figure. This results in the disc 22 closing the opening 26 and then compressing the bellows 20. The increased pressure within the bellows 20 causes the bladder 14 to expand. This expansion forces the head 15 to hinge on its springs 19 so that the printing needles 16 approach the medium 18. A sensing means 28 in the form of a roller is mounted on the head 15 and is arranged to contact the medium 18 and thus limit the forward movement of the head. The volumes of the bladder 14 and the bellows 20, and the extent of the armature movement are chosen such that compression of the bellows 20 continues after the sensing means 28 has prevented further movement of the head 15.

This results in a further pressure increase within the system, holding the printing head in a steady forward position. The excess force also acts to oppose the total reaction force created during the printing operation, which reaction force would otherwise tend to move the printing needles away from the medium.

When the electromagnet 23 is disconnected, the head 15 will, due to its resilient attachment by the springs 19, force air out of the bellows 14 causing an expansion of the bladder 20. The spring 25 aids rapid retraction of the armature 24 and thus rapid uncovering of the opening 26.

WHAT WE CLAIM IS: 1. A printer having a printing head, which head has printing needles and is attached to a carriage, the carriage being movable relative to a frame of the printer to move the head along a recording medium, wherein the head is movable relative to the carriage so that the distance between the needles in their rest position and the medium is variable, the said distance being changed by an expansible first fluid containing device which acts on the head and which is connected to a second fluid containing device, the latter being mounted on the frame and operable by an electromagnet, to cause expansion of the first fluid containing device.

2. A printer according to claim 1 wherein the first said device is an air containing bladder and the second said device is an air containing bellows.

3. A printer according to claim 2 wherein the electro-magnet has a movable armature which is attached to a disc, the disc being arranged to compress the bellows.

4. A printer according to claim 2 or claim 3 wherein the bellows has an opening which communicates with the surrounding air and is arranged to be closed when the bellows is compressed.

5. A printer according to any of claims 2 to 4, wherein the head is pivotable on the carriage and the bladder is arranged such that its expansion causes that part of the printing head provided with the printing needles to move towards the medium.

6. A printer according to claim 5 wherein the printing head has sensing means arranged to co-operate with the medium and stop motion of the head towards the medium when the distance between the needles and the medium has reached a required value.

7. A printer constructed and arranged substantially as herein described and shown in the drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. opening 26 so that operation of the pneumatic system, unlike a closed system, is not affected by changes in the ambient temperature and atmospheric pressure. Unlike the movable printing head part 10, the control part 11 is fixed and is secured to the printer frame 27. This is made possible by the flexible hose 12. When the electromagnet 23 is energised, the magnetic forces pull the armature inwards, i.e. to the left in the Figure. This results in the disc 22 closing the opening 26 and then compressing the bellows 20. The increased pressure within the bellows 20 causes the bladder 14 to expand. This expansion forces the head 15 to hinge on its springs 19 so that the printing needles 16 approach the medium 18. A sensing means 28 in the form of a roller is mounted on the head 15 and is arranged to contact the medium 18 and thus limit the forward movement of the head. The volumes of the bladder 14 and the bellows 20, and the extent of the armature movement are chosen such that compression of the bellows 20 continues after the sensing means 28 has prevented further movement of the head 15. This results in a further pressure increase within the system, holding the printing head in a steady forward position. The excess force also acts to oppose the total reaction force created during the printing operation, which reaction force would otherwise tend to move the printing needles away from the medium. When the electromagnet 23 is disconnected, the head 15 will, due to its resilient attachment by the springs 19, force air out of the bellows 14 causing an expansion of the bladder 20. The spring 25 aids rapid retraction of the armature 24 and thus rapid uncovering of the opening 26. WHAT WE CLAIM IS:

1. A printer having a printing head, which head has printing needles and is attached to a carriage, the carriage being movable relative to a frame of the printer to move the head along a recording medium, wherein the head is movable relative to the carriage so that the distance between the needles in their rest position and the medium is variable, the said distance being changed by an expansible first fluid containing device which acts on the head and which is connected to a second fluid containing device, the latter being mounted on the frame and operable by an electromagnet, to cause expansion of the first fluid containing device.