EP0653077B1 - Developer station for an electro-photographic printer or copier - Google Patents

Abstract

A developer station for an electro-photographic printer or copier has a developer chamber (12), a mixing chamber (13) and a developer station basin (14) connected to both chambers. Two developer mixture circuits are generated in the developer station, viz: one circuit to accept fresh toner and one for the actual development in a developer slit (18). A paddle roller (37) arranged in the developer station basin (14) generates a vortex in the mixture in the outlet region of the mixing chamber (13) which is enriched with fresh toner and is taken from the continuous developer mixture for the development process. The vortex essentially acts as a buffer store to compensate for heavy toner requirements in development and, in conjunction with the mixing chamber (13), for the tribo-electric activation of the developer mixture.

Description

In electrophotographic printing or copying machines, an optical character generator, e.g. can be an LED character generator, generates a latent charge image and then this charge image is colored with toner particles in a developer station. The black and colored toner particles are electrostatically charged and continuously brought up to the photoconductor in a developer gap. The positively charged toner, for example, is attracted to the exposed areas of the charge image, and the unexposed positively charged areas repel it.

If "negative toner" is used, the photoconductor layer is also negatively charged and exposed with the characters to be developed. Both applications are called reverse development.

So that the toner particles adhere to the charge image, they are charged triboelectrically. This triboelectric charging takes place primarily in a triboelectric manner by friction of the particles against one another in the developer station. The quality of the later typeface essentially depends on this interplay of electrostatic and Van der Waal forces. Therefore, the development process including toner supply and control with the toner materials used as well as the design of the developer station are among the most complex structures in an electrophotographic printing or copying machine.

The most frequently used developer mixture is a two-component mixture of toner and ferromagnetic carrier particles. The two components are mixed in the developer station and brought to the photoconductor in the developer nip via a developer roller designed as a magnetic roller. With the special properties of the toner and the carrier material, the mixing process causes a charging of the toner caused by frictional electricity (triboelectricity). The development process can be supported by an additional preload in the area of the developer gap.

Developer stations of the type mentioned are e.g. known from US-A-5 023 664 or US-A-4 952 279.

There are also described in EP-A-0 430 098 and GB-A-2 226 156 developer stations which have a developer chamber with developer rollers arranged therein, via which developer mixture is fed to a developer nip in a pressure toner concentration. The developer stations also contain a mixing chamber, in which excess developer is mixed with fresh toner, and a developer station sump with a mixing roller arranged therein, via which emaciated developer mixture and enriched developer mixture are mixed to form a developer mixture in pressure toner concentration.

If such developer stations are used in electrophotographic printing devices, in which images of different image density and composition have to be colored in any sequence, a problem is, among other things, the inadequate long-term stability of the toner mixture and the fluctuating triboelectricity due to the strongly fluctuating toner consumption during the coloring. In electrophotographic printing equipment For example, with the help of a test toner mark on the photoconductor, the degree of coloration of the charge image is determined and fresh toner is fed to the developer station as a function of the toner consumption. However, the addition of fresh toner worsens the triboelectric charging of the developer mixture. Another problem is the strongly fluctuating toner consumption, for example when large image areas suddenly have to be colored. This can lead to a sudden depletion of the toner concentration in the developer station before the toner concentration is increased and stabilized again by adding fresh toner.

The object of the invention is to design a developer station for an electrophotographic printing or copying machine in such a way that the toner concentration in the developer zone is as constant as possible regardless of the operating load and the toner consumption.

With regard to triboelectric charging of the developer mixture, the long-term stability should be guaranteed, regardless of the toner consumption.

This object is achieved in a developer station of the type mentioned in accordance with the features of the main claims.

Advantageous embodiments of the invention are characterized in the subclaims.

In principle, the developer station according to the invention has two developer circuits. A circuit is used to take up fresh toner in the developer station or to mix fresh toner into the developer mixture contained in the developer station. A second circuit is used to actually color the charge images in the developer zone on the photoconductor. The circuits are not completely separate from one another, but there are in principle two areas of contact in which the circuits merge into one another or are mixed with one another. In the area of the developer station sump, a vortex is generated below the mixing chamber receiving the fresh toner, in which developer mixture is swirled essentially with a pressure toner concentration with developer mixture which has an excess of toner. 1 area of the paddle roller is a mixture of emaciated developer mixture from the developer gap with developer mixture of pressure toner concentration.

Any high toner consumption is compensated for in the short term by the excess toner in the vortex, which has the function of a buffer memory, among other things.

Because the developer station essentially has two developer circuits, the developer mixture is more strongly activated and, as a result, the triboelectric charging is faster and higher.

A long-term constancy of the triboelectric charge results, among other things, from the compensation of a possibly higher toner consumption from the vortex, in which the carrier particles and toner particles are already partially triboelectrically activated and which only partly contains fresh, non-activated toner.

Sudden toner consumption is compensated for by the consumption of the excess toner in the vortex below the mixing chamber. As a result, the toner delivery system is not overloaded for a short time.

In the developer station, an electrically conductive two-component developer mixture of toner particles with ferromagnetic carrier particles with a predetermined breakdown field strength value can advantageously be used. This makes it possible to apply an electric field in the developer gap, the field strength of which exceeds the breakthrough field strength value of the developer mixture, with the result that the developer becomes conductive. This improves the coloring of large areas. This process is described in US-A-4,076,857.

• Figur 1 eine schematische Schnittdarstellung der erfindungsgemäßen Entwicklerstation in einer elektrofotografischen Druckeinrichtung und
• Figur 2 eine schematische Darstellung, teilweise im Schnitt, einer in der Entwicklerstation verwendeten Schaufelwalze.

An embodiment of the invention is shown in the drawings and is described in more detail below, for example. Show it

• Figure 1 is a schematic sectional view of the developer station according to the invention in an electrophotographic printing device and
• Figure 2 is a schematic illustration, partly in section, of a paddle roller used in the developer station.

A photoconductor drum 10 is arranged as the charge image carrier in a printing device, which is not shown in detail here and works according to the electrophotographic principle. A charge image is applied to this photoconductor drum 10 in a known manner by means of an exposure device which is controlled as a function of the character, and this charge image is then colored using the developer station shown. The coloring takes place according to the reverse development principle, in which the areas of the charge image discharged by exposure are colored with the aid of a developer mixture 11 consisting of toner particles and carrier particles. After passing through the developer station, the toner images produced by coloring the charge image are transferred to a recording medium in the usual way. The developer station essentially consists of a developer chamber 12, which is arranged in the region of the photoconductor 10, as well as a mixing chamber 13 adjoining the developer chamber 12 and a developer station sump 14 formed below the developer chamber and the mixing chamber.

Developer chamber

The developer chamber 12 contains two magnet rollers 15/1 and 15 which are arranged next to one another in the usual way 15/2. They contain a permanent magnet core 16 and a rotatable roller 17 surrounding the permanent magnetic core. By aligning the ferromagnetic carrier particles of the developer mixture 11 along the field lines of the magnetic rollers, a developer mixed brush is formed which, according to the selected direction of rotation of the magnetic rollers, has a tip between the magnetic rollers 15/1 and 15/2 and the photoconductor drum 10 located developer gap 18 passes. The tips of the brushes touch the photoconductor drum 10 and thus transfer the toner particles onto the surface of the photoconductor 10 in accordance with the charge image applied there. Since the direction of movement of the magnetic rollers 15/1 and 15/2 is chosen opposite to the direction of movement of the photoconductor drum 10 (arrows FIG. 1), this type of development is referred to as counter-directional development. The developer chamber 12 is closed off from the mixing chamber 13 by a shielding plate 19 made of ferromagnetic material. The shielding plate 19 is arranged at a distance from the magnetic rollers 15/1 and 15/2 forming a feed channel 20. The feed channel 20 opens opposite the developer station sump 14 in an access area 21 for the developer mixture, which is fed via the access area 21 to the magnetic rollers 15/1 and 15/2. In the entrance area to the developer gap 18 between the magnetic roller 15/2 and the photoconductor drum 10 there is a metering device which defines the width and the thickness of the developer mixture supplied to the developer gap in the form of a mixed carpet. The metering device contains lateral wipers 22 arranged on both sides of the magnetic roller 15/2, which, with their wiping lips, determine the width of the mixed carpet along the circumference of the magnetic roller 15/2 and a metering roller 23 made of translucent plastic with internal red light source 24 (LED Stripes). The metering roller has two functions:

On the one hand, the distance between the metering roller 23 and the magnetic roller 15/2 defines a metering gap 25 which defines the thickness of the mixed carpet, on the other hand the red light source 24 discharges the parts of the photoconductor drum 10 which have not been colored with toner and thus facilitates the transfer printing of the toner images onto the recording medium.

The developer mixture which has become leaner due to the development from the developer gap 18 is fed to the developer station sump 14 via an outlet region 26 of the developer chamber 12. In the exit area 26 there is a doctor blade 27 with a doctor blade which wipes off the developer mixture adhering to the magnetic roller 15/1 and a front mixing device 28 consisting of baffles which ensures transverse mixing of the developer mixture by inclined baffles.

Mixing chamber

The mixing chamber 13 adjacent to the developer chamber 12 is delimited on the one hand by a housing wall 29 of the developer station and on the other hand by the shielding plate 19. It is coupled in its upper part to the developer chamber 12 via an overflow channel 30 and furthermore also has an inlet opening 31 for fresh toner in the upper part on. Compared to the metering roller 23, it is closed off by an elastic sealing lip 32. The mixing chamber contains a rear mixing device 33 in the form of transverse or inclined mixing plates 34 and guide plates 35 coupled to the mixing plates 34 for the developer mixture. The mixing device 33 of the mixing chamber mixes, via the overflow channel 30, developer mixture taken over from the developer chamber 12 in pressure toner concentration with fresh toner taken over via the feed opening 31 and feeds the resulting mixture to the developer station sump 14, with the Mixing chamber 13 to developer station sump 14, a mixture vortex 36 is formed, the function of which will be explained later.

Developer station swamp

To generate the mixture vortex 36 and to convey the developer mixture 11 to the access area 21 of the developer chamber 12, a paddle roller 37 is arranged within the developer station sump. This paddle roller 37 is driven by an electric motor and extends over the entire width of the developer station and essentially consists of two lateral web wheels 38 with plate-like blade elements 39 arranged thereon. Inside the blade elements 39 arranged on the circumference of the paddle roller 37 there is one with the web wheels 38 coupled transport helix 40 in the form of a transport screw. The direction of inclination of the transport helix 40 serving as conveying elements is selected such that the developer mixture penetrating between the blade elements 39 and laterally via the land wheels 38 is transported to the center of the developer station, where it emerges again from the blade roller 37 between the blade elements 39. As a result, the developer mixture is mixed transversely in the area of the developer sump 14.

Function of the developer station

In principle, the developer station creates two developer mixture circuits, namely a first developer circuit, which is used to absorb fresh toner into the developer mixture, and a second developer circuit, in which the actual development of the solution image takes place. In principle, this results in three developer mixtures, namely a first developer mixture, which is identified by chain lines, with pressure toner concentration, and a second developer mixture, characterized by a thin continuous line consisting of fresh toner and a third developer mixture, characterized by a thick line consisting of a slightly emaciated developer mixture.

First developer mixing cycle:

The majority of the developer mixture is located in the developer station sump 14, which consists of a trough-shaped shape of the housing. There it is mixed by the paddle roller 37. Sixteen paddle elements 39 (strips) of the paddle roller 37 transport it via the access area 21 into the feed channel 20 of the developer chamber 12. This takes up part of the developer mixture with the aid of the magnetic rollers 15/1 and 15/2, while the excess developer mixture onto the transport helix 40 The bucket roller falls and is conveyed to the center of the developer station. Due to the rotary movement of the roller of the magnetic roller 15/1, the developer mixture is transported to the magnetic roller 15/2 and taken over by it. The rotor (roller) of the magnetic roller 15/2 conveys the developer mixture to the side wipers 22. By wiping off the superfluous developer mixture, the width of the mixture carpet is determined, which then flows into the developer gap (developer zone) 18. The thickness of the mixed carpet is determined via the metering roller (23). The developer mixture is pressed through the metering gap 25 and reaches the developer gap (18) (development zone) as a mixture carpet that is precisely defined in width and thickness, while the excess, separated developer mixture reaches the mixing device 33 via the shielding plate 19 and the guide plates 35. Fresh toner is fed through the overlying feed opening 31 via a corresponding conveying device as a function of the determined toner concentration in the developer mixture of the mixing chamber 13 and through the mixing device 33 mixed with their mixing plates 34 with the stripped excess developer mixture. The developer mixture mixed in this way reaches the area of the paddle roller 37; on the one hand, the mixing vortex 36 arises from the feed direction of the developer mixture from the mixing chamber into the developer sump and through the movement of the paddle roller 37.

The shielding plate 19 is arranged as a separating element between the developer chamber 12 and the mixing chamber 13 so that the developer mixture stream can trickle freely in the mixing device 33. The field lines of the magnetic rollers 15/1 and 15/2 close via the ferromagnetic shielding plate 19 and thus no longer influence the developer behind it.

Second developer mixture circuit

In the second developer mixture circuit, developer mixture with a pressure toner concentration is removed from the mixture vortex 36 via the paddle roller 37 and fed to the magnetic rollers 15/1 and 15/2 as described. After dosing via the dosing device and passing through the developer gap 18, the developer mixture is stripped off via the doctor blade 37 and the developer mixture trickles into the front mixing device 28, where it is mixed transversely in order to compensate for possible uneven consumption of toner along the width of the developer station . The developer mixture which has leaned through the passage through the developer gap 18 trickles out of the front mixing device 28 into a region of the paddle roller 37, is picked up by this and is mixed in the manner described with the developer located in the developer station sump 14.

• Ein Entwicklergemisch mit geringfügig hoher Konzentration im Bereich der hinteren Mischeinrichtung 33 bis zur Schaufelwalze 37;
• ein Entwicklergemisch in Drucktonerkonzentration im Bereich Schaufelwalze 37, Magnetwalzen 15/1, 15/2, Dosierwalze 23 bzw. hinterer Mischeinrichtung 33;
• weiterhin ein Entwicklergemisch mit geringerer Tonerkonzentration im Ausgangsbereich der Magnetwalzen 15/1, 15/2 im Bereich der vorderen Mischeinrichtung 28 und der Schaufelwalze 37.

As already described, developer mixtures with three different toner concentrations are created in the developer station:

• A developer mixture with a slightly high concentration in the area of the rear mixing device 33 up to the paddle roller 37;
• a developer mixture in pressure toner concentration in the area of the paddle roller 37, magnetic rollers 15/1, 15/2, metering roller 23 or rear mixing device 33;
• furthermore a developer mixture with a lower toner concentration in the output region of the magnetic rollers 15/1, 15/2 in the region of the front mixing device 28 and the paddle roller 37.

In order to mix these three types of developer mixture defined according to their toner concentration, there are in principle two joints: namely the mixture vortex 36 under the shielding plate 19 - here developer mixture with pressure toner concentration is mixed with that with a higher toner concentration - and a joint in the area of the paddle roller 37. Here is Developer mixture with pressure toner concentration mixed with a developer mixture that has become slightly leaner due to the development process.

A constant toner concentration in the developer gap 18 is achieved via the two developer mixing circuits and joints, both geometrically viewed over the width of the developer station and over time.

Possibly. Suddenly high toner consumption due to sudden large-area coloring is compensated for by the consumption of the excess toner in the mixture vortex 36 under the rear mixing device 33. Thereby the toner delivery system is not overloaded for a short time. With low toner consumption, only a little toner is fed into the developer station and the toner concentration gradually balances out.

The first developer mixture circuit, which essentially serves to hold fresh toner, also serves for the additional triboelectric activation of the developer mixture. This results in a triboelectric charging of the developer mixture that is almost independent of toner consumption.

In addition, the developer station above the metering roller in the exit region of the photoconductor drum 10 from the developer station contains a carrier catching roller 41 which has a permanent magnet with a rotating roller jacket. The carrier capture roller 41 may detach carrier particles adhering to the photoconductor drum 10 and throw them back into the developer station.

The constant movement and mixing of the developer mixture creates toner dust inside the developer station. Protective devices are provided in the developer station so that it does not pollute the environment as it emerges. These essentially consist of the sealing lip 32, which seals off the fresh toner supply area against the photoconductor drum 10. Furthermore, there is a suction opening 42 in the upper area of the developer station, which sucks off the toner dust that has arisen in the upper area of the developer station with the aid of a suction device. A similar suction device is arranged in the area of the front mixing device 28. It sucks off the toner dust that arises in the area of the mixing device 28.

In the embodiment of the developer station described above, two magnetic rollers are provided as developer rollers. However, it is also possible to use a single larger magnetic roller or a plurality of magnetic rollers arranged next to one another. It is also conceivable to use other mechanical means of application, e.g. Blade elements or short pile brushes to be replaced. A paddle roller is provided in the developer sump as a vortex-generating agent. The paddle roller can optionally be replaced by a magnetic roller or by other mechanical swirling and transport means, e.g. in the form of a pin roller or other rollers with a rough surface that transports the developer mixture. As far as the photoconductor is concerned, it is designed as a photoconductor drum in the exemplary embodiment. However, a photoconductor tape can also be used as the photoconductor. Instead of the two-component developer mixture, one-component developer mixture can also be used.

The developer station is particularly suitable for the use of two-component developer mixture of high conductivity with a low resistance of about 10 ^{8 to} 10 ⁹ ohms, has aas a predetermined breakdown field strength value. In this case, an electric field is applied in the developer gap 18 via a bias voltage, the field strength of which exceeds the breakthrough field strength value of the developer mixture. This phenomenon is described in detail in US-A-4,076,857.

Reference list

10 =

Photoconductor, photoconductor drum

11 =

Developer mix, two component developer mix, developer

12 =

Developer chamber

13 =

Mixing chamber

14 =

Developer station sump, developer tray

15/1, =

Magnetic roller

15/2 =

Magnetic roller

16 =

Permanent magnet core, permanent magnet arrangement

17 =

rotatable roller, magnetic roller cover

18 =

Developer gap, developer zone

19 =

Shielding plate

20 =

Feed channel

21 =

Access area

22 =

lateral scraper elements, elements determining the width of the mixed carpet

23 =

Dosing roller

24 =

Red light source, LED bar

25 =

Dosing gap

26 =

Exit area of the developer chamber

27 =

Doctor blade, doctor element

28 =

front mixing device

29 =

Housing wall of the developer station

30 =

Overflow channel, connecting channel

31 =

Feed opening for fresh toner

32 =

Sealing lip

33 =

rear mixing device

34 =

Mixing plates

35 =

Baffles

36 =

Mixture vortex

37 =

Paddle roller

38 =

Stegrad, spoke wheel

39 =

Blade elements, strips

40 =

Transport helix, transport screw

41 =

Carrier capture roller

42 =

Extraction openings for toner dust

Claims (13)

1. Developer station for an electrophotographic printing or copying machine for the development of charge images generated on a photoconductor (10), with

   - a developer chamber (12) which is arranged in the region of the photoconductor (10),
   the developer chamber (12) having:

   - at least one developer roller (15/1, 15/2) with a clearance relative to the photoconductor (12), said clearance forming a developer gap (18);

   - an access region (21) receiving developer mixture (11) having the printing-toner concentration;

   - metering means (22, 23) for the developer mixture (11), the metered developer mixture being fed to the developer gap (18) via at least one of the developer rollers (15/1, 15/2) and excess developer divided off during metering being diverted out of the developer chamber (12) via an overflow channel (30);

   - an outlet region (26) for diverting the developer mixture depleted as a result of the development out of the developer chamber (12),

   - a mixing chamber (13) which is coupled to the overflow channel (30) and which has an access region (31) for fresh toner, the mixing chamber (13) containing means (33) which mix the excess developer with fresh toner and which thus produce an enriched developer mixture,

   - a developer-station sump (14) which receives the enriched developer mixture from the mixing chamber (13) and which is coupled to the access region (21) and to the outlet region (26) of the developer chamber (12) and contains vortex-generating means (33, 37) via which a vortex swirling the depleted developer mixture together with the enriched developer mixture and intermediately storing it is generated in a space which is not occupied by the means (33, 37) and from which developer mixture having the printing-toner concentration is extracted and is fed to the developer chamber.
2. Developer station according to Claim 1, with developer rollers which are designed as magnetic rollers (15/1, 15/2) having a direction of run in the developer gap (18) which is opposite to the direction of movement of the photoconductor (10).
3. Developer station according to one of Claims 1 or 2, with a shielding plate (19) separating the developer chamber (12) from the mixing chamber (13) and consisting of ferromagnetic material.
4. Developer station according to one of Claims 1 to 3, with lateral stripping elements (22) and a metering roller (23) which are arranged as metering means in a region of feed of the developer mixture to the developer gap (18).
5. Developer station according to one of Claims 1 to 4, with guide elements (34, 35) arranged in the mixing chamber (13) for the transverse intermixing of excess developer and fresh toner.
6. Developer station according to one of Claims 1 to 5, with guide elements (28), arranged in the outlet region (26) of the developer chamber (12), for the transverse intermixing of the depleted developer mixture, and with a stripping element (27) for the associated developer roller (15/1).
7. Developer station according to one of Claims 1 to 6, with a paddle roller (37), arranged in the developer-station sump (14), as a vortex and transport means, with paddle elements (39) arranged on its circumference.
8. Developer station according to Claim 7, with a paddle roller (37) having an internal transport helix, which is designed in such a way that the developer mixture in the paddle roller (37) is moved in the axial direction relative to the paddle-roller middle.
9. Developer station according to one of Claims 1 to 8, with a device (32) sealing off the mixing chamber (13) relative to the photoconductor (10).
10. Developer station according to one of Claims 1 to 9, with a suck-off device (42) for toner dust.
11. Developer station according to one of Claims 1 to 10, with an electrically conductive two-component developer mixture (11) of toner particles with ferromagnetic carrier particles, which has a predetermined breakdown field-strength value.
12. Developer station according to Claim 11, with means for generating in the developer gap (18) an electrical field, the field strength of which exceeds the breakdown field-strength value of the developer mixture.
13. Process for the development of charge images generated on a photoconductor in an electrophotographic printing or copying machine, having the following features:

    - in a developer-station sump (14), a mixture vortex (36) serving as a developer-mixture buffer store is generated by vortex-generating means (33, 37), in a space not occupied by the means (33, 37), from a developer mixture enriched with fresh toner and from a developer mixture depleted as a result of the development process,

    - developer mixture is extracted continuously from the mixture vortex (36),

    - the extracted developer mixture is transformed by metering (22, 23) into a mixture carpet of predetermined width and thickness,

    - the mixture carpet is guided through a developer gap (18) adjacent to the photoconductor (10) and is introduced as a depleted developer mixture into the developer-station sump (14),

    - if appropriate, the excess developer mixture separated during the metering (22, 23) is enriched with fresh toner in dependence on the toner consumption and is fed to the developer-station sump (14).

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