Developing apparatus

Abstract

A developing apparatus for developing an electrostatic latent image on an electrostatic latent image carrier includes a toner tank for storing toner, a developing roller, toner and a blade for supplying the toner from the toner tank to the developing roller. The apparatus further includes a regulation member having one end portion fixedly supported and the other end portion being slidingly held in contact with the outer surface to define a contacting area. The regulating member is bent at an angle .alpha. outwardly from the outer surface to define a bent portion such that the bent portion is located closely adjacent the developing roller with respect to the contacting area.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a developing apparatus for in use an electrophotographic copying apparatus, a printer or the like.

2. Description of the Prior Art

Many of the patents issued in various countries disclose a developing apparatus having a regulation member, which is pressed slidingly against a developing roller for the supply of the toner towards the developing process directory or indirectly. The regulation member is operable to form an electrically charged toner layer on the peripheral surface of a developing roller.

For example, Japanese Patent Application SHO 62-17774, published Jan. 26, 1987, discloses a regulation blade having a generally orthogonally bent end. An outer surface of the bent corner is pressed slidingly against a developing roller. However, because this blade is brought into a line contact with the developing roller, a nip (contact) width between the bent corner of the regulation blade and the developing roller is so small as to result in insufficient electric charging of toner. Furthermore, it is impossible to form a uniform thin layer of toner stably in service over a long time because of the influence which would be brought about by the adhesion of toner to the regulating portion of the blade.

Furthermore, U.S. Pat. No. 4,566,402 discloses the use of two regulation blades of different constructions. One blade is constructed by two pieces of elastic plates bonded at one end with each other. The other blade is constructed by a single elastic plate which is bent at center portion thereof. Both blades are slidingly pressed against the developing roller at their end portion apart from the bonded or bent portion respectively. However, each of these blades can not contact uniformly the developing roller over the entire length of the roller over because the respective blade is flexible and deformable. Therefore this hampers the uniform formation of toner layer and hence results in a varying density of copied image.

SUMMARY OF THE INVENTION

The present invention has been developed with a view to substantially eliminating the above discussed problem inherent in the prior art developing apparatus and is intended to provide an improved developing apparatus effective to provide copies of uniform image quality over a long term.

According to the present invention, a developing apparatus for developing an electrostatic latent image on an electrostatic latent image carrier comprising developer carrier means having an outer surface for carrying developer thereon and being provided rotatably, and regulating means having an end portion so disposed to oppose said developer carrier means in its rotating direction, said end portion having a contacting portion which is in area contact with the surface of said developer carrier means and a bent portion following said contacting portion which is so bent away from said developer carrier means with a curvature formed at its bent corner.

Because regulation member is brought into plane contacts with developing roller, the contact pressure per unit area is reduced and a thin layer of toner is uniformly formed with less occurrence of undesirable toner adhesion, even after a long term of use, thus after passing through the contacting area uniform thickness of thin toner layer is obtained. Thus, uniform amount of toner per unit area can be transported along the entire contact width.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of the present invention will readily be understood from the following description taken in conjunction with preferred embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a developing apparatus according to the present;

FIG. 2 is a fragmentary view showing, on an enlarged scale, a portion of regulation member of FIG. 1;

FIG. 3 is a fragmentary view showing, on an enlarged scale, a portion of regulation member of the prior art;

FIG. 4 is a graph showing relationship between length of the regulation member and amount of toner adhering to the toner support member of the present invention;

FIG. 5 is a fragmentary perspective view of one side portion of a developing apparatus, particularly showing regulation members and side sealings for concealing toner;

FIG. 6 is a fragmentary perspective view of another side portion of a developing apparatus, particularly showing regulation members for concealing toner; and

FIG. 7 is a fragmentary perspective view according to a modification of the developing apparatus shown in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, there is shown in FIG. 1, a developing apparatus 1 for in use an electrophotographic copying apparatus, or in a printer, or the like apparatus. The developing apparatus 1 is disposed adjacent to a photosensitive drum 10 driven in a direction indicated by an arrow d.

The developing apparatus 1 includes a casing 1a, a support member 30 located at upper end corner of casing 1a, and a partition 4 which separates the casing into a toner tank 2 for storing toner To and a buffer room 5 for regulation of toner amount for developing.

Provided in the toner tank 2 is an agitator 3 for stirring the toner and sending the same to buffer room 5 as it rotates in a direction indicated by an arrow c.

Provided in the buffer room 5 are a developing roller 7 located below the support member 30, a sealing block 12 positioned beneath the developing roller 7, and a regulation member 8 having one end fixedly held by the support member 30 and other end slidingly pressed against the outer surface 7a of developing roller 7 for regulating the thickness of a toner layer on the roller surface 7a as will be described in detail later in connection with FIG. 2. Further provided in the buffer room 5 is a rotating blade 6 driven in a direction indicated by an arrow b for stirring and sending the toner towards the roller surface 7a.

Referring to FIG. 2, the regulating member 8 has its low end portion bent at an angle .alpha., which is about 90.degree. in this embodiment, to provide an upright portion 8x which extends at about tangent direction with respect to the roller surface 7a and a bent portion 8y which extends at about radial direction outwardly from the roller surface 7a. A lower end portion of the upright portion 8x is held slidingly pressed against roller surface 7a so as to make a contacting area 9.

In operation, as agitator 3 rotates in direction c, the toner To stored in toner tank 2 is fed into buffer room 5 over the partition 4. In buffer room 5, the toner is delivered to roller surface 7a by the rotating blade 6 and is held on the roller surface 7a. Then, as the developing roller 7 rotates in the direction a, the toner adhered on roller surface 7a is carried and brought to the contacting area 9, at which the top portion of the toner is scraped off by the regulation member 8. Therefore, after the contacting area 9, the toner remaining on the roller surface 7a is spread with a uniform thickness to define a toner layer entirely across the roller surface 7a along the axial-wise direction.

More specifically, since the regulating member 8 is held in contact with the roller surface 7a, not in line but in area, the toner passing through the contacting area 9 is charged by the contact with the regulation member 8 and, at the same time is adhered to the roller surface 7a. Thus, on the roller surface 7a that have passed the contacting area 9, a thin layer of charged toner is formed.

Furthermore, the regulation member 8 has the bend portion 8y located further towards the end from the contacting area 9. Therefore, a high linearity of the regulating member 8 particularly at the contacting area 9 in the axial direction of roller 7 can be obtained. Thus, at the contacting area 9, the regulating member 8 contacts the roller surface 7a with a uniform pressure along the axial-wise direction of the developing roller 7. Also, since the regulating member 8 is held in contact with the roller surface 7a at contacting area 9 not in a line but in an area, the contacting pressure per a unit area between the regulating member 8 and roller surface 7a is relatively small, thereby avoiding rigid adhering of toner on the regulating member 8 or the roller surface 7a which may occur if the roller contacting pressure is greater than the appropriate pressure. Furthermore, with such an appropriate contacting pressure between the regulating member 8 and the roller surface 7a, the thin toner layer formed after passing through the contacting area 9 can be maintained constant in the axial-wise direction and also in the roller advancing direction. Thus, a constant and stable toner supply can be effected during the life time of the developing apparatus.

As noted above, the regulating men%her 8 makes an area contact with developing roller 7 at the contacting area 9. At this contacting area 9, the low end portion of the regulating member 8 extends for the length of .DELTA.L from the central point A which is substantially the middle way of the area contact which the member makes at the contacting area. The bent portion 8y thus then further extends from the length .DELTA.L to form a regulating passage for toner.

By the rotation of developing roller 7, the toner layer To formed at the contacting area 9 is transferred to a developing station 11 at which the roller surface 7a is so provided as to confront with the photosensitive drum 10. At the developing station 11, the electrically charged toner adhering on roller surface 7a is attracted by the electrostatic latent imaged formed on the surface of the photosensitive drum 10 by the electrostatic force to form a visible toner image which is thereafter transferred to a copy paper in a known manner.

In the meantime, the toner To remaining on the roller surface 7a passes through the sealing block 12 and is returned back to the buffer room 5. In the buffer room 5, the toner To consumed at the developing station is compensated to form again the thin toner layer at the contacting area 9.

Referring to FIG. 4, test results are shown for the comparison between the developing apparatus of the present invention and that of the prior art. The tests are carried out to find out the change of the toner amount M (mg/cm.sup.2) adhering on a unit area of roller surface 7a immediately after passing through the contacting area 9 with respect to the change of the length .DELTA.L. The prior art developing apparatus used in the tests is shown in FIG. 3 which includes a regulation member 8' of straight plate having no bent portion. The length .DELTA.L for the prior art developing apparatus is measured from central point A of contacting area to the free end of regulating member 8'. In FIGS. 2 and 3, O is the center of roller 7. The developing apparatus of the present invention used in the tests has a metallic regulating member 8 with a thickness being between 0.05 mm and 0.15 mm, the curvature radius R being less than 0.3 mm, the bent angle .alpha. being approximately 90.degree., and the distance from the bent corner to the end of the bent portion being 2 mm.

As apparent from the graph of FIG. 4, the solid line test results of the developing apparatus 1 according to the present invention showed relatively small change of the toner amount M (mg/cm.sup.2) adhering on a unit area of roller surface 7a immediately after passing through the contacting area 9 with respect to the change of the length .DELTA.L. On the contrary, the dotted line test results of the developing apparatus according to the prior art showed relatively large change of the toner amount M (mg/cm.sup.2) adhering on a unit area of roller surface 7a immediately after passing through the contacting area 9 with respect to the change of the length .DELTA.L.

As apparent from these test results, according to the present invention, even if the length .DELTA.L should vary among the manufactured developing apparatuses or within a developing apparatus after a long period of use, the toner amount M (mg/cm.sup.2) will not be changed greatly, resulting in unchanged and stable supply of toner to the developing station 11.

The regulation member 8 according to the preferred embodiment of the present invention may be made either by a metallic blade or a resinous blade. For the metallic type regulation member 8, stainless steel or phosphor bronze may be used. If the regulation member 8 is made by a resinous material, a synthetic resin capable of being electrostatically charged to the polarity opposite to that of the toner may be used, or alternatively a synthetic resin capable of being electrostatically charged to the same polarity as that of the toner may be used. In the latter case, the position on the triboelectric charging order table for the synthetic resin and that for the toner should be spaced away.

Furthermore, according to a preferred embodiment, the regulation member 8 has a curvature radius R of about 0.5 mm or less. If the curvature radius R is set greater than a permissible range, the amount of toner captured under the regulating member 8, i.e., at the contacting area 9, will be increased. In order to avoid such an increase of the captured toner, the contacting pressure of regulating member 8 against the roller surface 7a should be increased, but which in turn results in undesirable rigid adhering of toner layer on the roller surface 7a.

The bending angle .alpha. should preferably be between 60.degree. and 100.degree.. If the bending angle .alpha. is made greater than the preferable range, the amount of toner captured under the regulating member 8 will be increased, and therefore, the problem similar to that described above occurs.

The bent distance between the bent corner to the free end of the bent portion 8y should be between 0.5 mm and 5 mm, and preferably be between 0.5 mm and 1.5 mm. If the bent distance is made smaller than the permissible range, it will be difficult to form a uniform bent corner. If the bent distance is made longer than the permissible range, the circulation of toner in the buffer room 5 as effected by the rotating blade 6 is interrupted, resulting in collection of densely packed toner against bent portion 8y, in turn resulting in rigid adherence of toner on the regulating member 8.

Referring to FIGS. 5 and 6, a modification is shown. In this modification, the regulation member 8 has a recess 8a formed at each opposite end of the bent portion 8y so as to pressure fittingly insert an elastic block 8b made of an elastic material such as "molt plane" in the recess 8a, as best shown in FIG. 6, so as to conceal and prevent toner from flowing through the clearance between side sealing 20 and the side edge of regulation member 8. At the recess 8a, the reduced bent distance between the bent corner to the bottom edge of the recess 8a should preferably be between 0.3 mm and 1 mm. If the reduced bent distance is made greater than the above range, the clearance between the regulation member 8 and elastic block 8b becomes relatively large to permit the toner to pass therethrough freely. If the reduced bent distance is made smaller than the above range, the bending at the bottom of the recess may not be properly effected such that the edge at the bottom of the recess may directly contact the roller surface 7a resulting in damage, torque increase or rotation trouble of the roller 7.

Referring to FIG. 7, another modification of the present invention is shown. In the modification of FIG. 7, a circular film 21 having a size slightly greater than the circumference of the roller 7 is applied. The regulating member 8 is held in contact with the film 21.

The present invention is also applicable to the developing apparatus utilizing a developing roller with carriers provided on the roller surface 7a to receive toner from the toner source, wherein the toner is mixed with and adhered to the carriers, and regulation is effected on the carriers.

As is clear from the foregoing description, since the regulating member 8 is held in contact with the roller surface 7a at the predetermined contacting area 9, the charging level and the thickness of the toner layer after the contacting area 9 can be obtained with less variation.

Furthermore, since the contacting pressure per unit area at the contacting area 9 can be made relatively low, the toner may not be rigidly adhered to the roller surface 7a.

Also, since the bent portion 8y is formed, the linearity along the contacting area 9 in the axial-wise direction can be obtained. Thus, the thickness of the toner layer as formed by the regulating member 8 can be maintained constant throughout the axial-wise direction on the roller surface 7a.

Moreover, since the variation of the length .DELTA.L may not change the toner amount M (mg/cm.sup.2) adhering on a unit area of roller surface 7a immediately after passing through the contacting area 9, the regulating member 8 can be formed with less preciseness, resulting in simple manufacturing steps.

Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.

Claims

1. A developing apparatus for developing an electrostatic latent image on an electrostatic latent image carrier comprising:

developer carrier means having an outer surface for retaining an electrostatically charged developer thereon and being provided rotatably; and

regulating means formed by a bending plate which has a supporting portion, a bent portion and a bent corner having a curvature radius of 0.5 mm or less formed between the supporting portion and the bent portion, said supporting portion defining a rear end of said bending plate, said bent portion and bent corner defining a forward end of said bending plate, said supporting portion fixedly disposed at said rear end and having a substantially flat contacting portion which is substantially flat in a rear-to-front direction of said plate and is in area contact with the surface of said developer carrier means and is disposed close to the bent corner, said bent corner formed with a round curvature shape having a predetermined curvature radius and having a bent angle of 60.degree.-90.degree., said bent portion being bent with respect to said substantially flat contact portion in a direction away from the developer carrier means, said front end of said bending plate which contains said bent portion and said bent corner being located upstream of said supporting portion with reference to a direction of rotation of said developer carrier means, the entirety of said bent portion being situated farther from said surface than said bent corner.

2. A developing apparatus as claimed in claim 1, wherein said developer carrier means is a developing roller.

3. A developing apparatus as claimed in claim 1, wherein said developer carrier means comprises a driving roller and a circular film having a size slightly greater than the circumference of said driving roller, said circular film being mounted on said driving roller.

4. A developing apparatus as claimed in claim 1, wherein said bent portion terminates in a free end and ha a length between 0.5 mm and 5 mm measured from the bent corner to the free end.

5. A developing apparatus as claimed in claim 1, further comprising a support member located adjacent to said developer carrier means for fixedly holding one end of said regulating means.

6. A developing apparatus for developing an electrostatic latent image on an electrostatic latent image carrier comprising:

developer carrier means having an outer surface for carrying an electrostatically charged developer thereon and being provided rotatably;

rotatable means for supplying a toner to the developer carrier means disposed close to the developer carrier means; and

regulating means formed by a bending plate having a supporting portion, a bent portion and a bent corner formed between the supporting portion and the bent portion, said supporting portion being fixedly disposed at one end and having a substantially flat contacting portion which is substantially flat in a rear-to-front direction of said plate and is in area contact with the surface of the developer carrier means and disposed close to the bent corner, said bent corner formed with a round curvature shape and having a curvature radius no greater than 0.5 mm, and said bent portion being bent with respect to said substantially flat contacting portion in a direction away from the developer carrier means and having a length of 0.5 to 5 mm measured from the bent corner to the free end, an end of said bending plate which contains said bent portion and said bent corner being located upstream of said supporting portion with reference to a direction of rotation of said developer carrier means.

7. A developing apparatus as claimed in claim 6, further comprising a support member located adjacent to said developer carrier means for fixedly holding one end of said regulating means.

8. A developing apparatus as claimed in claim 6, wherein said developer carrier means is a developing roller.

9. A developing apparatus as claimed in claim 6, wherein said developer carrier means comprises a driving roller and a circular film having a size slightly greater than the circumference of said driving roller, said circular film being mounted on said driving roller.

10. A developing apparatus for developing an electrostatic latent image on an electrostatic latent image carrier comprising:

developer carrier means having an outer surface for carrying an electrostatically charged developer thereon and being provided rotatably; and

regulating means formed by a bending plate which has a supporting portion, a bent portion and a bent corner having a curvature radius of 0.5 mm or less formed between the supporting portion and the bent portion, said supporting portion being fixedly disposed at one end and having a contacting portion which is substantially flat in a rear-to-front direction of said plate and is in area contact with the surface of said developer carrier means and is disposed close to the bent corner, said bent corner formed with a round curvature shape having a predetermined curvature radius, said bent portion being bent with respect to said substantially flat contacting portion in a direction away from the developer carrier means, said regulating means being formed with a recess at each opposite end of said bent portion, an end of said bending plate which contains said bent portion and said bent corner being located upstream of said supporting portion with reference to a direction of rotation of said developer carrier means.

11. A developing apparatus as claimed in claim 10, wherein said recess has a length between 0.3 mm and 1 mm measured from the bent corner to the bottom edge of the recess.

12. A developing apparatus as claimed in claim 10, further comprising an elastic block fittingly inserted in said recess.