GB2102347A - Printer comprising a guide device for a record carrier - Google Patents

Abstract

In a printer, for example, an ink jet printer comprising a guide device for a record carrier (2), the record carrier is fed by means of a transport roller (1) to an adjoining supporting surface (5) along which a printing head (6) is displaceable. The supporting surface extends in a plane which segmentally intersects the path of the record carrier around the transport roller. At the area of the supporting surface, a ruler (26) presses against the record carrier without bringing it directly into contact with the supporting surface, so that the record carrier becomes S-shaped upon passage from its path around the transport roller to the supporting surface. <IMAGE>

Description

SPECIFICATION Printer comprising a guide device for a record carrier The invention relates to a printer comprising a guide device for transporting a record carrier, by means of a transport roller, to a strip-shaped, flat supporting surface which adjoins the transport roller by way of one of its long sides, viewed in the transport direction of the record carrier, and along which a printing head is displaceable, the record carrier being pressed by a ruler from the side of the printing head before it reaches the area of the printing head. In a printer of this kind which is known, for example, from DE-OS 28 29 827, the record carrier should rest as flatly a possible on the supporting surface in order to keep the distance between the record carrier and the printing head as constant as possible; this is important notably when the printing head is an ink jet printing head.

In the printer which is known from said DE-OS 28 29 827, the supporting surface tangentially adjoins the transport roller and the record carrier is pressed against the transport roller by means of a rule directly before the separation from the transport roller. It has been found that the record carrier does not rest flatly on the supporting surface in all circumstances in such a guide device.

It is the object fo the invention to improve a printer of the kind set forth in order to ensure that the record carrier rests completely and perfectly flatly on the supporting surface. To this end, the invention is characterized in that the supporting surface is situated in a plane which segmentally intersects the path of the record carrier around the transport roller, viewed in a cross-sectional view, thereof, the rise of arc of the segment being smaller than half the radius thereof, the ruler pressing against the record carrier at the area of the supporting surface without bringing the record carrier directly into contact with the supporting surface.Thanks to these steps, record carrier becomes S-shaped at the passage from the transport roller to the supporting surface under influence of the forces acting on the record carrier, the record carrier subsequently resting completely and perfectly flatly on the supporting surface, so that always a constant distance between this surface and the printing head is ensured.

A preferred embodiment of the printer in accordance with the invention is characterized in that the transport roller comprises toroidal rings which are spaced apart in its longitudinal direction, and which define the path of the record carrier around the transport roller, the supporting surface comprising groove-shaped recesses at its long side which faces the transport roller, said recesses corresponding to the toroidal rings which project therein. The path of the record carrier around the transport roller is thus determined by the toroidal rings, because the record carrier rests only thereon.Because the toroidal rings project into the groove-shaped recesses in the supporting surface, the supporting surface adjacent the toroidal rings extends as far as the transport roller, so that at these areas the supporting surface is situated slightly below the path of the record carrier at the passage from the transport roller to the supporting surface; this has a favourable effect on the formation of a smooth S-curve in the record carrier upon its passage to the supporting surface, so that the flat positioning of the record carrier on the supporting surface is further improved. It is to be noted that transport rollers comprising toroidal rings which are spaced apart in its longitudinal direction are known to be used in commercially available printers.In the above context however, the use of such a transport roller offers said special advantage that the passage of the record carrier from the transport roller to the supporting surface is very smooth.

In view of the simplicity of the construction, the ruler is preferably formed by a bent end of a shelllike cover element which is arranged around the transport roller at a distance therefrom.

The invention will be described in detail hereinafter with reference to the drawings which show two embodiments in accordance with the invention.

Figure 1 is a partly diagrammatic front view of the most relevant parts of a printer comprising a transport roller with toroidal rings.

Figure 2 is a cross-sectional view of the printer shown in Figure 1.

Figure 3 is a cross-sectional view of a further embodiment comprising a transport roller whose circumferential surface defines the path of a record carrier.

Figure 4 diagrammatically shows the plane of the supporting surface which segmentally intersects the path of the record carrier around the transport roller.

The reference numeral 1 in the Figures 1 and 2 denotes a transport roller which serves for the transport or the line-wise feeding of, for example, a sheet-like record carrier 2 which is shown only in Figure 2. Viewed in the transport direction of the record carrier (denoted by an arrow 3), the record carrier proceeds from a guide surface 4 to the transport roller 1 and subsequently to a stripshaped flat supporting surface 5 along which a printing head 6, for example, an ink yet printing head is displaceable. To this end, the printing head 6 is mounted on a carrier 7 which is displaceable in the line direction on two guide rods 8 and 9. The drive for such a displacement of the printing head is not shown herein but may be realized in a customary manner, for example, by means of a motor with a drive belt, a toothed belt or similar.

The transport roller 1 of this embodiment comprises toroidal rings 10 which are spaced apart in its longitudinal direction and which are situated in corresponding grooves; these rings are often also referred to as O-rings. Because the toroidal rings 10 project from the circumferential surface of the transport roller 1, they define the path of the record carrier around the transport roller.Two pressure rollers 11 and 12 which are consecutively arranged along the path of the record carrier around the transport roller cooperate with each each of the toroidal rings 10, each of said pressure rollers being journalled on Ushaped supports 1 3 and 14 which themselves are mounted on a shaft 1 5. The shaft 1 5 is supported by two levers 1 6 and 1 7 which are pivotable together about a stationary shaft 18, so that the pressure rollers can be pivoted towards and away from the toroidal rings by displacement of the levers 16 and 17.The pressure rollers 11 and 12 then pass through corresponding openings 1 9 and 20, respectively, which are provided in a shell-like cover element 21 which surrounds the transport roller at a distance, thus forming a guide for the record carrier 2. When the pressure rollers 11 and 12 are lifted off the toroidal rings 10, the record carrier can be slid by hand from the guide surface 4 and around the transport roller 1 until it reaches the supporting surface 5; it can also be pulled out of the printer by hand. However, when the pressure rollers 11 and 12 contact the toroidal rings 10, the record carrier is transported further by rotation of the transport roller.To this end, the transport roller can be rotated either by means of a handwheel 22 connected thereto or by means of a motor 23, via a gearwheel drive with gearwheels 24 and 25.

In a printer of this kind it is very important that the record carrier 2 rests flatly on the supporting surface 5 in order to ensure that its distance from the printing head 6 is always the same, regardless of the position of the head with respect to the record carrier, because printing is correct only when this distance is the same. A constant distance between the printing head and the record carrier is required in several types of printing heads, for example, printing heads of daisy-wheel printers, stylus printers or ink jet printers. Notably in the case of ink jet printers it is important that this requirement is satisfied, because a comparatively small, constant distance between the printing head and the record carrier is to be maintained, because otherwise the print becomes irregular and incomplete.

In order to ensure that the record carrier rests exactly flat on the supporting surface 5, the supporting surface 5 is situated in a plane which segmentally intersects the path of the record carrier 2 around the transport roller 1, viewed in a cross-sectional view; a ruler 26 presses the record carrier at the area of the supporting surface 5 without bringing the record carrier directly into contact with the supporting surface 5. Thus, at the passage of the record carrier from the path around the transport roller to the supporting surface, the record carrier becomes S-shaped in order to ensure that the record carrier is indeed completely flatly positioned on the surface 5 at the area of the printing head.

The segmental intersecting of the path of the record carrier around the transport roller by the plane of the supporting surface is diagrammatically shown in Figure 4, the arc of circle 27 indicating the path of the record carrier around the transport roller, whilst the stroke/dot line 28 indicates the plane of the supporting surface. The segment which is cut off is denoted by heavy lines. The position of the ruler 26 is indicated by an angle. It is clearly shown that the dimensions of the segment and the position of the ruler determine the shape of the S-shape of the record carrier 2 at its passage from the path around the transport roller to the plane of the supporting surface. Experiments have demonstrated that in order to ensure suitable flat positioning of the record carrier on the supporting surface, the rise of h to be one eighth of the radius r.The required position of the ruler 26 follows from the choice of the dimensions of the segment, because the ruler must be situated at such a distance from the plane 28 of the supporting surface that the record carrier becomes (preferably lightly) S-shaped, without being brought directly into contact with the supporting surface; this is clearly shown in Figure 4.

In the embodiment shown in the Figures 1 and 2, the ruler is simply formed by the bending of the end 29 of the shell -like cover element 21 which is situated near the supporting surface 5, the edge thus bent over performing the function of the ruler.

The distance between the ruler 26 and the supporting surface 5 can then be simply adjusted by adjustment of the shell-like cover element.

The Figures 1 and 2 also show that at the area of its long side 30 which faces the transport roller 1 the supporting surface 5 comprises groove-like recesses 31 which correspond to the toroidal rings 10 and in which the toroidal rings project. The portions of the supporting surface 5 adjacent the toroidal rings thus reach as far as the transport roller 1, so that at these areas the surface is situated slightly below the path of the record carrier at the passage from the transport roller to the surface. A kind of air cushion is thus formed underneath the record carrier; it has been found that this has a particularly favourable effect for a smooth S-shaped passage from the record carrier to the supporting surface, so that the flat positioning of the record carrier on the supporting surface is further enhanced.

The embodiment shown in Figure 3 utilizes a transport roller 1 whose entire circumferential surface, for example, formed by a top layer of an elastic material, is used for the transport of the record carrier. Also provided are pressure rollers 11 and 12 which in this case co-operate directly with the circumferential surface of the transport roller 1 and which adjustable with respect thereto in the same manner as in the embodiment shown in the Figures 1 and 2. Similarly, there is provided a shell-like cover element 21 which comprises openings 19 and 20 for the pasage of the pressure rollers 11 and 12, respectively. The supporting surface 5 whose long side 30 adjoins the circumferential surface of the transport roller 1 again extends in a plane which segmentally intersects the path of the record carrier around the transport roller, said path being defined by the circumferential surface of the transport roller in said embodiment. In said embodiment a ruler 26 is provided as a separate, strip-shaped component. The free end of the ruler again presses the record carrier at the area of the supporting surface 5, without bringing the record carrier directly into contact with the supporting surface.

The choice of the dimensions of the segment cut off from the path of the record carrier around the transport roller by the plane of the supporting surface again determines the distance between the free end of the ruler 26 and the supporting surface 5 so that upon its passage from the transport roller to the supporting surface 5 the record carrier becomes S-shaped as previously described with reference to Figure 4.

The record carrier 2 is thus absolutely flatly positioned against the supporting surface 5, so that it is ensured that the distance between the printing head 6 and the record carrier is always constant.

Obviously, the steps in accordance with the invention can also be taken for printers having a record carrier transport device of a type other than the described type. For example, in the case of a record carrier comprising edge perforations, a drive with so-called tractors can be provided for this purpose. In such a case the transport roller itself may be formed as a so-called spiked roller.

Claims (4)

1. A printer comprising a guide device for transporting a record carrier by means of a transport roller, to a strip-shaped, flat supporting surface which adjoins the transport roller by way of one of its long sides, viewed in the transport direction of the record carrier, and along which a printing head is displaceable, the record carrier being pressed by a ruler from the side of the printing head before it reaches the area of the printing head, characterized in that the supporting surface is situated in a plane which segmentally intersects the path of the record carrier around the transport roller, viewed in a cross-sectional view thereof, the rise of arc of the segment being smaller than half the radius thereof, the ruler pressing against the record carrier at the area of the supporting surface without bringing the record carrier directly into contact with the supporting surface.

2. A printer as claimed in Claim 1, characterized in that the transport roller comprises toroidal rings which are spaced apart in its longitudinal direction, and which define the path of the record carrier around the transport roller, the supporting surface comprising groove-shaped recesses at its long side which faces the transport roller, said recesses corresponding to the toroidal rings which project therein.

3. A printer as claimed in Claim 1 or 2, characterized in that the ruler is formed by a bent end of a shell-like cover element which is arranged around the transport roller at a distance therefrom.

4. A printer substantially as herein described with reference to the accompanying drawings.