EP0514377B1 - Transport device for recording media in printers and photocopiers - Google Patents

Abstract

A device for transporting recording media (100), useful in particular in the fixing section of a printer or photocopier, has a counter-roll (201) and a feed roll (205) movably arranged in relation to the counter-roll (201), between which the recording medium (100) is transported by friction. A guide bar (214) is arranged as a balance beam parallel to and spaced from the feed roll (205) so as to pivot around an axis of rotation (216) in relation to the feed roll (205). In order to press the feed roll (205) against the counter-roll, so as to compensate according to need any forces that may arise, spring elements (218) are arranged on the guide bar (214) on both sides of the axis of rotation and are coupled to bearing elements (206) of the feed roll (205). The guide bar may be moved by a servomotor (224) in order to control the position of the recording medium (100) between the rolls (201, 205).

Description

The invention relates to a device for transporting a record carrier in a printing or copying device and the use of such a device in a fixing station of a printing or copying device.

In the case of non-mechanical printing devices with a high printing speed, which work according to the electrophotographic or magnetic principle, it is common to use continuous paper with transport perforations. The continuous paper is drawn off from a stack, transported through a transfer printing station with the help of tractors engaging in the peripheral perforations and coated with a toner layer depending on the character. The toner layer on the recording medium is then thermo-pressure fixed in a fixing station. Such a fuser is such. B. is known from US Pat. No. 4,147,922. For this purpose, the fixing station contains in the usual way an electrically heated fixing roller and a pressure roller that can be pivoted on and off the fixing roller. The record carrier must be guided exactly through the fixing station without moving relative to the fixing roller.

In order to prevent such a relative movement, it has turned out to be necessary to ensure a uniform pressure force of the pressure roller on the fixing roller along the length of the roller. If there are different pressing forces along the length of the roller, there is a risk that the paper web will move horizontally in the fixing station during printing. This can lead to tension in the paper web and to paper tear at high transport speeds.

For pivoting a pressure roller against a counter roller In a fixing station it is known from DE-C2-27 17 260 to arrange the pressure roller on rockers and to pivot them over cam disks. The counter roller is fixed in place.

If the pressure roller is not guided and swiveled exactly parallel to the counter roller, different pressure forces act along the rollers. Although the elastic sheathing of the pressure roller ensures a certain force balance, it has been shown that this force balance is not sufficient.

A fixing device for copying machines is known from EP-A-0 002 303, which has a fixing roller and a pressure roller that can be pivoted on and off the fixing roller. The pressure roller is pivotally mounted in a carrier cage on which an eccentric engages. Via a device measuring the deflection of the carrier cage, the pressure force of the pressure roller on the fixing roller is measured. The pressure force of the pressure roller along the fixing roller can be changed or adjusted by pivoting the eccentric. Pressure fluctuations of the pressure roller on the fixing roller can thus be compensated for.

Furthermore, the recording media used can be of different thicknesses across their width, or the recording media serve as carriers for credit cards to be printed, etc.

Non-mechanical printing devices can also be designed so that they can process recording medium webs of different widths. It is therefore necessary to design the fusing station with the rollers arranged therein in accordance with the largest recording medium width. Areas of the fusing roller or the pressure roller in the fusing station that do not come into contact with the recording medium heat up more locally than the actual contact regions with the recording medium because the recording medium extracts heat from the fusing roller in the fusing area. This leads to a heat-dependent different diameter of the pressure roller consisting of elastic material. The recording medium is thereby deflected horizontally.

It has therefore proven to be advantageous to monitor the lateral position of the recording medium exactly when the fusing station is run in, in order to be able to intervene in a regulating manner if necessary by means of a control arrangement.

The problem of the exact controllable management of record carriers is not only available for electrophotographic printing and copying machines. Also with other printing devices, the z. B. work with ink printing units, it is necessary to position the record carrier exactly at least in the printing area.

To position the recording media in printing devices, it is customary to use mechanically adjustable mechanical guide elements in the paper channel of the printing device, the actual position of the recording media also being scanned via mechanical contact elements.

For the positional scanning of the recording media, it is known from IBM Technical Disclosure Bulletin Vol. 23, No. 7a, December 1980 and from EP-Bl-0 031 137 to use optoelectronic scanning devices.

The object of the invention is therefore to provide a device for transporting recording media in printing or copying devices with a roller arrangement with counter-roller and pressure roller and in between by friction-guided recording medium, which is designed such that the pressure roller on the recording medium or the counter-roller with a longitudinal uniform roller pressure is applied to the roller length.

Another object of the invention is to design the device in such a way that the recording medium can be positioned between the rollers.

The device is said to be particularly suitable for installation in a fixing station of an electrophotographic printing or copying device.

This object is achieved according to the features of claims 1 and 6.

Advantageous embodiments of the invention are characterized in the subclaims.

Due to the arrangement of a guide bar mounted in a beam-like manner, which engages with spring elements on the bearing elements of the pressure roller, the pressure roller is pressed against the counter roller over its entire roller length with a uniform pressure force. Any different pressure forces that occur are compensated. The record carrier is thus transported between the rollers safely and without distortion. Relative displacements of the record carrier to the rollers are avoided. The device is thus particularly suitable for fixing stations in electrophotographic printing and copying devices in which a toner image is thermo-pressure fixed on a recording medium.

In an advantageous embodiment of the device, the force-balancing effect can be influenced with the aid of an adjusting device. This makes it possible to control the position of the record carrier between the rollers.

• Figur 1 eine schematische Schnittdarstellung einer Fixierstation einer elektrofotografischen Druckeinrichtung mit der darin angeordneten Transportvorrichtung und
• Figur 2 eine schematische Darstellung der Fixierstation der Figur 1 mit einem Blockschaltbild einer Regelungsanordnung zur seitlichen Positionierung des Aufzeichnungsträgers.

Embodiments of the invention are shown in the drawings and are described in more detail below, for example. Show it

• Figure 1 is a schematic sectional view of a fixing station of an electrophotographic printing device with the transport device and arranged therein
• Figure 2 is a schematic representation of the fuser of Figure 1 with a block diagram of a control arrangement for lateral positioning of the record carrier.

A printing device operating on the principle of electrophotography contains a fixing station for fixing a toner image on a recording medium in the form of an endless paper web 100. The recording medium 100 is exposed to heat and pressure in the fixing station and thus a firm connection of the toner image to the recording medium is achieved. For thermal printing fixing, the fixing station contains a fixing roller 201 with a heat radiator 202 arranged therein in the form of a halogen lamp. The fixing roller 201 is mounted on a frame 203 of the printing device and is driven by a motor 204. The fixing roller 201 usually consists of an aluminum tube coated with plastic. A pressure roller 205 made of a steel tube encased with rubber is mounted on and can be pivoted away from the fixing roller 201. The pressure roller 205 is mounted on two lateral bearing elements 206. The bearing elements 206 are mounted in the frame 203 of the printing device so as to be pivotable about a fixed axis of rotation 207. In order to pivot the pressure roller 205 onto and off the fixing roller 201, which acts as a counter roller, two cam disks 209, which are rotatable via an electric motor 208 (FIG. 2), are arranged, which bear against guide projections 210 (rotatable rollers) of the bearing elements 206. Two tension springs 211 engaging laterally on the bearing elements 206 serve as return springs for the bearing elements 206 and press the bearing elements 206 against the cam disks 209 via the guide lugs 210. The cam disks 209 are mounted on lever-like oscillators 212 with an axis of rotation 213 assigned to the frame 203 of the pressure device. A guide rod 214, which has approximately the length of the pressure roller, is arranged at a distance parallel to the pressure roller. It is pivotally mounted approximately in the center with respect to the pressure roller in a bearing piece 215 and specifically about an axis 216 which runs approximately perpendicular to the longitudinal extent of the pressure roller. The guide rod 214 has adjustable fastening elements (adjusting screws) 217 at its ends, in which springs 218 connected to the rockers 212 are suspended. The springs 218 in connection with the centrally mounted guide rod 214 form a kind of balance beam for balancing the pressure of the pressure roller of the pressure roller 205 to the fixing roller 201 over the length of the pressure roller. To limit the swinging range of the rockers 212, adjustable stops 219 are arranged in the bearing area for the cam disks 209. The motor 208 is coupled to the cam disks via a cross coupling 220. It enables the cam disks 209 to be pivoted about the axis of rotation 213 in accordance with the direction of the arrow shown in FIG. 2 and thus a relative movement to the stationary via fastening elements (screws etc.) 221 on the frame 203 of the pressure device attached motor 208.

The spring force of the springs 218 is significantly greater than the spring force of the return springs 211 on the pressure roller 205. When the pressure roller 205 is pressed on (FIG. 1), the rockers 212 are pivoted away from the stops 219. The cam disks 209 press the pressure roller 205 against the fixing roller 201 according to their deflection. The pressure force is essentially determined by the spring force of the springs 218 in connection with the geometric structure of the rocker 212 and the degree of deflection of the cam disks 209.

To pivot away, the cam disks 209 are rotated back via the motor 208. As a result, the rocker 212 first moves under the action of the spring force 218, without the pressure roller 205 being pivoted away from the fixing roller 201, and specifically until the rockers 212 engage the stops 219 with their lower pivot arms. This absorbs the spring force of the spring elements 218. When the cam disks 219 are rotated further to completely pivot the pressure roller 205, the pressure roller 205 is then lifted off the fixing roller 201 under the action of the return spring 211. In this actual pivoting process, the bearing elements 206 rest against the cam disks 209 via their projections 210. The swivel range and thus the range of rotation of the cam disks 209 is limited by an attachment 222 on the cam disks which, when the cam disks 209 are rotated completely, swivels against the guide attachments 210 of the bearing elements creates. The pressure roller 205 is thus in the pivoted-off state and the recording medium 100 can be threaded into the fixing station. The pressure roller 205 is pivoted towards the fixing roller 201 in the opposite direction. First, the pressure roller 205 is brought into contact with the fixing roller 201 by rotating the cam disks 209 and against the spring force of the return springs 211. When the cam disks 209 are turned further, the rockers 212 then lift off the stops 219 and the spring force of the springs 218 is increased fully effective. The beam-like construction of the pressure mechanism for the pressure roller 205 with guide rod 214 and spring elements 218 in connection with the rockers 212 ensures a force balance of the pressure force of the pressure roller 205 along the fixing roller 201 and thus for a uniform fixing force on the recording medium 100. This is important for one uniform fixation result, especially when recording media 100 of different widths are used.

As already mentioned at the beginning, the fixing station in the electrophotographic printing device serves to fix the toner image applied to the recording medium in a transfer printing station by heat and pressure on the recording medium 100. For this purpose, the recording medium 100 is brought into contact with the fixing roller 201 with its toner layer side upwards via a fixing saddle 223 which can be pivoted on and off. It wraps around the fixing roller 201 at a wrap angle Z and is heated there (preheated). The actual fixing then takes place in a fixing gap FX, namely the pressure area between fixing roller 201 and pressure roller 205. For fixing, the recording medium 100 in the fixing area from the wrap angle Z and fixing gap FX has to be heated from room temperature to fixing temperature of greater than 110 ° C. To achieve good print quality, it is therefore necessary to precisely guide the recording medium 100 in the fixing station.

It is common in electrophotographic printing or copying machines To use recording media of different widths or different formats. In order to be able to ensure continuous printing operation, the individual units of the printing device must be designed in such a way that it is possible to switch between different paper formats or different recording medium widths without pronounced cooling phases. The fixing roller 201 and the pressure roller 205 are therefore designed with respect to their length for the widest possible recording medium format. If a recording medium with a width that is less than the maximum possible recording medium width is fixed between the fixing roller 201 and the pressure roller 205, the pressure roller 205 heats up locally differently. The heating in the area of the recording medium is less than in the area of the pressure roller 205 which is not covered by the recording medium, since the recording medium absorbs and dissipates heat during the fixing process.

It has now been found that the different heating of the pressure roller areas leads to different expansion of the pressure roller in the case of recording media of different widths. This results in a different diameter of the pressure roller 205 in the area of the recording medium and in the area not covered by the recording medium. This in turn leads to the recording medium being deflected horizontally in the fixing gap FX. The result is smearing of the toner image and thus disturbances of the printed image.

Furthermore, such a lateral deflection of the recording medium leads to a tensioning of the recording medium in the paper guides of the printing devices. This can result in tearing of the paper.

It is therefore advantageous to regulate the horizontal position of the recording medium 100 in the fixing gap FX during the fixing process, in particular when recording media of different widths are used. The positioning itself is carried out by changing the pressure force of the pressure roller 205 on the fixing roller 201 over its length.

A prerequisite for the regulation is first the detection of the actual position of the recording medium when the recording medium 100 enters the fixing station in the entrance area of the fixing saddle 223. For this purpose, an optoelectronic sensor S is arranged there, which detects the lateral position of the recording medium 100 via its transport holes . Commercially available optoelectronic scanners or mechanical scanning elements or the like can be used as sensors S.

The arrangement shown in FIG. 2 for the lateral positioning of the tape-shaped recording medium 100 contains a sensor S with an associated evaluation circuit AS for converting the sensor signals into position signals UD. Downstream of the evaluation circuit AS is an analog-digital converter W, which converts the position signal UD supplied by the evaluation arrangement AS into a digital signal so that it can be evaluated and processed with the aid of a microprocessor P. The microprocessor P is connected to the actual controller C of the printing device via a data bus. This control (device control) can, for. B. be designed in accordance with US-A-4 593 407, the microprocessor P is a commercially available microprocessor (z. B. microprocessor 8080 Siemens). The microprocessor P is also connected to a program memory M for receiving the control program.

The control signals supplied by the microprocessor P are amplified via an amplifier AP and fed to the control arrangement E for setting the pressure force of the pressure roller 205 on the fixing roller 201 along the fixing roller.

In the exemplary embodiment in FIG. 2, the device E contains a servomotor 224 with an eccentric disk 225 arranged thereon. Instead of a servomotor, however, any other adjustable electronic drive device is also suitable, e.g. B. a solenoid. The eccentric disc 225 is connected to the guide rod 214 via a linkage 226. By twisting the Eccentric disc 225, the guide rod 214 is deflected by the linkage 226 to different degrees about the axis of rotation 216 and thus the pressure force on the bearing elements 206 of the pressure roller 205 is changed. The horizontal position of the recording medium can thus be set in the fixing gap FX.

This setting is carried out via the arrangement described for lateral positioning with the microprocessor P, which the actual positioning signals UD supplied by the sensor S with a z. B. compares the target position stored in the memory M and controls the servomotor 224 as a function thereof via the amplifier AP. The position of the actuator 224, the z. B. can be detected via a scanning device, the microprocessor P is also supplied for evaluation.

The position of the recording medium in the fixing station can be optimized via the control arrangement. The aim of the regulation can be the so-called zero position of the continuous paper, i. H. the positioning of the transport perforations of the continuous paper at a position assigned to the position above the dividing line of the sensor surfaces of the scanner. The aim of the regulation can also be to keep the record carrier available, e.g. if First, very narrow paper is printed and then a change to wide paper is envisaged. The control arrangement takes into account the behavior of the recording medium to be expected in the future and deflects the recording medium a predetermined time before or after the change. The different behavior of the recording media and any necessary reserve can be stored as a program in the memory M of the microprocessor arrangement.

The transport device with counter roller and pressure roller described in connection with a fixing station of an electrophotographic printing device can also be used in other printing devices or copying devices for the transport of recording media. These record carriers can be used as Single sheets or continuous paper webs.

If compression springs 218 are used instead of the tension springs, they engage directly on the lower part of the lever-like rockers 212 in the vicinity of the cam disks 209. The stop 219 which absorbs the spring force of the spring must be arranged in a corresponding position on the upper part of the rockers 212.

It is also possible, instead of the described pivoting mechanism for the pressure roller 205, on the pressure roller 205 a simple pivoting lever with z. B. to completely dispense with a locking mechanism or pivoting. The springs 218 of the guide rod then directly engage the bearing element 206 of the pressure roller 205 if, for example, they are designed as compression springs or via pivotable levers corresponding to the lever-like wings 212.

Reference symbol list

100

Record carrier, continuous paper web

201

Fixing roller, counter roller

202

Radiant heater

203

frame

204

engine

205

Pressure roller

206

Bearing elements

207

stationary axis of rotation

208

Electric motor

209

Cam disks

210

Guiding approach, stop

211

Tension springs

212

Swing, lever

213

Axis of rotation

214

Guide rod

215

Bearing element, bearing piece

216

axis

217

Fastening element, adjusting screw

218

feather

219

attacks

220

Cross clutch

221

Fastener, screws

222

Neck, cam disks

223

Fixation saddle, paper guide saddle

Z

Wrap angle

FX

Fixing gap

E

Device for adjusting the pressure force

S

sensor

AS

Evaluation circuit

W

Analog-to-digital converter

224

Servomotor

225

Eccentric disc

226

Linkage

Claims (10)

1. Device for transporting recording media (100) in printers or photocopiers having

   a) a counter-roll (201) and a feed roll (205), mounted movably relative to the counter-roll (201), between which rolls the recording medium (100) is transported by friction, one of the rolls (201, 205) being driven by electric motor,

   b) lateral bearing elements (206, 203) for the rolls (201, 205),

   c) a guide bar (214) which is arranged in the manner of a balance beam with spacing parallel to the feed roll (205) and so as to be pivotable about an axis of rotation (216) relative to the feed roll (205), and

   d) spring elements (218) which are coupled to the guide bar (214) and the bearing elements (206) of the feed roll (205) and are arranged on both sides of the axis of rotation (216) of the guide bar (214) in order to press the feed roll (205) against the counter-roll (201) in a force-compensating manner, as required.
2. Device according to Claim 1, having rotatably mounted links ( 212 ), coupled to the spring elements (218), having swivel arms for pressing the feed roll (205) onto the counter-roll (201).
3. Device according to Claim 2, having

   - eccentric elements (209), which are arranged on the links (212), can be rotated via an adjusting motor (208) and are supported on the bearing elements (206) of the feed roll (205), for pivoting the feed roll (205) onto and away from the counter-roll (201),

   - a limiting stop (219) assigned to the links (212), and

   - a restoring spring (211) coupled to the bearing elements (206) of the feed roll (205), the above-mentioned elements being arranged relative to one another in such a way that, starting from a pivoted-away position, when the feed roll (205) is pivoted on via the eccentric elements (209) counter to the force effect of the restoring spring (211), the links rest on the limiting stop (219) and thus absorb the spring force of the spring elements (218) until the feed roll (205) is supported on the counter-roll (201).
4. Device according to Claim 3, in which the eccentric apparatus (209) has cam disks.
5. Apparatus according to one of Claims 1 to 4, in which the guide bar (214) is coupled to an adjusting motor (224) in order to deflect the guide bar (214) about the axis of rotation (216) into predeterminable deflection positions and thus to adjust the pressing force of the feed roll (205) onto the counter-roll (201) along its roll length.
6. Fuser station for an electrophotographic printer or photocopier for thermal fusing of a recording medium (100), bearing a toner image, having

   a) a motor-driven, electrically heated fuser roll (201) and a feed roll (205) which can be pivoted onto and away from the fuser roll (201), between which rolls the recording medium (100) is passed for fusing,

   b) lateral bearing elements 206) for the feed roll (205),

   c) a guide bar (214) which can be rotated in the manner of a balance beam about an axis of rotation (216) perpendicular to the longitudinal extent of the feed roll (205), and

   d) spring elements (218), arranged on lateral arms of the guide bar (205), for force-compensating pressing of the feed roll (205) onto the fuser roll (201) via the bearing elements (206) of the feed roll (205).
7. Fuser station according to Claim 6, having links (206) mounted rotatably about a stationary axis of rotation (207) for pressing the feed roll (205) onto the fuser roll (201) via the spring elements (218).
8. Fuser station according to Claim 7, having

   - eccentric elements (209), which are arranged on the links (212), can be rotated via an adjusting motor (208) and are supported on the bearing elements (206) of the feed roll (205), for pivoting the feed roll (205) onto and away from the counter-roll (201),

   - a limiting stop (219) arranged in a stationary manner and assigned to the links (212), and

   - a restoring spring coupled to the bearing elements (206) of the feed roll (205), the abovementioned elements being arranged relative to one another in such a way that, starting from a pivoted-away position, when the feed roll (205) is pivoted on via the eccentric elements (209) counter to the force effect of the restoring spring (211), the links rest on the limiting stop (219) and thus absorb the spring force of the spring elements (218) until the feed roll (205) is supported on the counter-roll (201).
9. Fuser station according to Claim 8, in which the eccentric apparatus has cams (209).
10. Fuser station according to Claims 6 to 9, in which the guide bar (214) is coupled to a drive apparatus (224) in order to deflect the guide bar (214) about the axis of rotation (216) into predeterminable deflection positions and thus to adjust the pressing forces of the feed roll (205) onto the counter-roll (201) along its roll length.

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