EP0195761A1

EP0195761A1 - Paper feed in printers

Info

Publication number: EP0195761A1
Application number: EP19860850056
Authority: EP
Inventors: Bror Gösta Helmfrid; Leif Helmer Andersson
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1985-03-20
Filing date: 1986-02-19
Publication date: 1986-09-24
Also published as: SE447224B; SE8501357D0; JPS61229582A; SE8501357L

Abstract

Paper feed arrangement for a printer provided with tractor feed and a cylindrical platen. The platen is driven at a somewhat higher peripheral rate than the advancing rate of the tractor feed. Friction can be enabled or disabled between the platen and paper web. For enabled friction the tension in the paper web is limited by a deflecting means over which the paper web runs.

Description

TECHNICAL FIELD

The present invention relates to a paper feed arrangement in printers which are provided with a cylindrical platen and advancing means for advancing a printing medium in the form of a paper web or the like, engagement between the advancing means and the paper web taking place either in front of, or both in front and behind, the platen with respect to the advancing direction of the web.

BACKGROUND ART

For rapid printers and similar equipment, which are used, inter alia, as output means in computer systems, the printing medium is usually a paper web with perforations at its edges for advancing the web. The movement of the latter in relation to the print position of the printer is obtained by advancing means provided with teeth cooperating with the perforations in the paper such as to advance the web forwards or backwards relative the print position. Advancing means of this type, so-called tractor feeders, are usual on the market and are known, inter alia, from the US patent specification 3 825 162.
Tractor feed is mainly of two types, single or push-pull traction. With the former the paper web is moved with the aid of the tractor feeder via conducting means past a cylindrical or flat platen, against which printing is performed. In push-pull traction the feed to the print position takes place in the same way as for single traction, but down-stream of the print position the perforations in the paper web are brought into engagement with an other section of the feeder where the teeth move in the opposite direction to those advancing the paper web towards the print position, thus obtaining an advance away from the position as a supplement to the paper advance in a single- traction feeder.
When using a matrix printer in combination with the tractor feeders discussed above it is difficult to achieve good printing guality. This is due to the attempt to obtain low friction between the paper web and platen, for reasons of operational reliability, resulting in that the paper has a tendency to move transverselyin the directions the matrix printing head moves. The problem is most noticeable when a line is written with a reciprocating movement of the printing head, which is usual in near letter quality (NLQ) printing.

DISCLOSURE OF INVENTION

The object of the invention is to solve the above problem by providing between paper web and platen sufficient friction to prevent relative movement therebetween when a line is being printed.

BRIEF DESCRIPTION OF DRAWING

The invention, with its characterizing features disclosed in the following claims, will now be described in detail with reference to the accompanying drawing, the figure on which depicts in side elevation the parts of a printer of interest with reference to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The parts of a printer, which are only schematically illustrated in Figure 1, include a tractor feeder 1 which advances a paper web 2 via a deflecting means 3 and two conducting members 4 and 5 to a cylindrical platen 6. The web 2 accompanies the rotation of the platen 6 to a print position 7 with the aid of two counter-pressure rollers 8 and 9 and two conducting members 10 and 11. The web 2 is then advanced out of the printer between two conducting plates 12 and 13.
An unillustrated drive means includes a motor driving the platen via spur gearing. The means also drives the tractor feeder 1 via second spur gearing between the platen and feeder. The ratio between the two sets of spur gearing is selected such that the peripheral rate of the platen is somewhat higher than the advancing rate of the feeder, the difference being about 0,2 %.
The two counter-pressure rollers 8 and 9 constitute parts of a friction means. They are mounted in two U-shaped cheek plates 14, which are kept together by a shaft 15. The shaft is radially guided by two projections 16 and 17 on the conducting member 10. The friction means further includes an unillustrated operating means for determining the position in height of the shaft 15 via a rod 18. In an upper position the two rollers 8 and 9 engage against the platen 6 with a force such that the friction force between the paper web and the platen prevents any relative movement between them. This force is equal to zero in a lower, unillustrated position of the shaft 15. The operating means functions so that the shaft 15 normally assumes its upper position. By controlling a printer carriage associated with the printer such that it moves to an extreme position outside the printing area the operating means is actuated to move the rod 18 downwards, the force between the rollers and the platen thus becoming zero. The printer carriage is controlled by a computer connected to the printer such as to assume the extreme position at about every 30th line shift.
For line shifts where the carriage does not assume the extreme position, the platen advances the paper web somewhat further than the tractor feeder does. The length of paper web between the tractor feeder and platen is thus shortened, resulting in a tensional force in the paper web. This force is limited by the spring bias in a spring 19 co-acting with the deflecting means 3, which includes a bar disposed substantially transverse the advancing direction of the paper web and mounted on a shaft 20, such that the bar turns clockwise about the shaft at a line shift.
When a line shift occurs where the printer carriage assumes the extreme position, the counter-pressure rollers 8 and 9 are no longer urged against the platen 6, thus allowing the deflection means 3 to be turned back into its original position by the bias in the spring 19, to pull the paper web a corresponding distance backwards.

Claims

1. Paper feed arrangement for a printer provided with a cylindrical platen (6) and advancing means (1) for advancing a paper web (2), engagement between the means and paper web taking place solely up-stream, or up-stream and down-stream of the platen, in the advancing direction of the web, characterized in that drive means are arranged to drive the platen at a somewhat higher peripheral rate than the advancing rate of the advancing means (1), and in that friction means are arranged to prevent relative movement between the web (2) and the platen (6) when said friction means are urged towards the platen, a deflection means (3), over which the web runs, being arranged to shorten the length of the web between the advancing feeder and the platen when said friction means is urged against the platen, by rotational displacement of the deflection means (3) on exceeding a tensional limit for the paper web.

2. Paper feed arrangement as claimed in claim 1, characterized in that said friction means includ at least one counter-pressure roller (8,9) and an operating means which, in a first position biases the roller towards the platen (6), and in a second position causes the roller to be released from said bias.

3. Paper feed arrangement as claimed in claim 1, characterized in that said deflection means (3) includes a bar which is rotatably mounted on a shaft (20) substantially transverse the advancing direction of the paper web, said bar being biased with the aid of a spring (19) to an initial position, the bar turning about its shaft in response to the tension in the paper web such that the length of the web between said advancing means (1) and said platen (6) is shortened.