GB2118899A

GB2118899A - Cleaning unit for an electrophotographic device

Info

Publication number: GB2118899A
Application number: GB08306195A
Authority: GB
Inventors: Ryoichi Tsuruoka; Masayoshi Katch
Original assignee: Fuji Xerox Co Ltd
Current assignee: Fujifilm Business Innovation Corp
Priority date: 1982-03-17
Filing date: 1983-03-07
Publication date: 1983-11-09
Also published as: JPS58159567A; GB8306195D0

Abstract

A cleaning blade 3 is held by a holding member 4 for pivotal movement about an axis O, and contacts the surface of a photosensitive member 1 at a contact point Q. A spring 8 acts at a point P to urge the cleaning blade 3 into engagement with the photosensitive member 1. The distance I1 between the point P and the pivot axis O is chosen in relation to the distance I2 between the pivot axis O and the contact point Q such that 1</=I2/I1, and preferably such that: 1.5</=I2/I1</=2.5. <IMAGE>

Description

SPECIFICATION Cleaning unit for an electrophotographic device This invention relates to a cleaning unit for an electrophotographic device, which is used to remove non-transferred toner from a photosensitive member.

Conventional cleaning units of this type can be classified into two groups, as indicated respectively in Figures 1 and 2 of the accompanying drawings. Each of these cleaning units comprises a cleaning blade 30 which forms an angle (hereinafter called the pressing angle) with a side of a photosensitive member 31 which has not yet been cleaned, the member 31 being turned in use in the direction of arrow a. In the first group of cleaning units (Figure 1), the pressing angle is an obtuse angle fl,. In the second group (Figure 2), the pressing angle is an acute angle 02.In Figures 1 and 2, reference characters t and 2 respectively denote the point at which the cleaning blade 30 contacts the surface of the photosensitive member 31, while X1 andX2 respectively designate tangents to the surface of the member 31 at the points t and 2- In the first group of cleaning units, the cleaning efficiency is high because the cleaning blade 30 is pressed against the photosensitive member 31 at an obtuse angle. However, a difficulty exists in that the cleaning blade 30 and its holder (not shown) tend to vibrate because the frictional force between the blade and the member 31 cannot satisfactorily be absorbed. The edge of the blade 30 where the frictional force is locally concentrated may be torn off as a result.

This difficulty is not experienced with cleaning units of the second group because any frictional force generated is immediately released by deformation of the cleaning blade 30. However, the cleaning action is lessened because the frictional force cannot be utilized as a cleaning force.

Cleaning units of the type shown in Figure 2 therefore have a lower cleaning effect than units of the type shown in Figure 1. Accordingly, the angle and the pressing force of the cleaning blade 30 should each be in a range which is close to a prescribed value.

It is an object of the present invention to overcome the above-described difficulties.

According to the invention, there is provided a cleaning unit for an electrophotographic device, comprising a cleaning blade for cleaning the surface of a photosensitive member, a holding member pivotably holding the cleaning blade in such a manner as to permit the latter to move away from and into contact with the photosensitive member, and means for pressing the cleaning blade against said surface of the photosensitive member, the length It of a segment between a pivot axis of the cleaning blade and a biasing force application point, and the length 12 of a segment between said pivot axis and the contact point of said cleaning blade with the photosensitive member being selected so as to satisfy the following expression:: 1 Al2/l t With such a construction, the cleaning blade can make satisfactory contact with the surface of the photosensitive member, while at the same time minimising the fluctuations in the pressing force required for cleaning the photosensitive member, thereby maintaining a satisfactory cleaning effect.

The invention will now be further described, by way of example only, with reference to Figure 3 of the accompanying drawings, which is a diagram of a cleaning unit according to the present invention.

The cleaning unit shown in Figure 3 forms part of an electrophotographic device having an image-bearing member D in the from of a drum 1 which rotates in the direction of the arrow. The cleaning unit (referenced 2) is composed of a body 23 having a rotary shaft 11 on which a holding member 6 is rotatably mounted. The holding member 6 is coupled by means of a pivot screw 5 to a further holding member 4 which holds a cleaning blade 3. The members 4 and 6 together form holding means B.

At one end of the holding member 6 there is provided a shaft 7 which protrudes to the outside of the body 23 through a window 25 formed in the latter. The shaft 7 has fastened thereto a lower end of a pressure-applying spring 8, an upper end of the spring 8 being fastened to a supporting portion 26 on the body 23 by way of a spring engaging shaft 9. These components together form pressing means C.

Blade separating means E is provided outside the body 23. Upon excitation of a solenoid 15, the blade separating means E operates a lever 10 so that the latter pushes the shaft 7 and thereby turns the cleaning blade 3.

A toner conveying mechanism 24 is provided below the body 23 and includes a toner guiding paddle 13 and a toner conveying auger 14.

Assume now that the rotation axis of the shaft 11 (i.e. the centre of rotation of the cleaning blade 3) is at a point 0, the central part of the locking portion of the shaft 7 to which the pressureapplying spring 8 is fastened (i.e. the point of force) is at P, and the contact point of the cleaning blade 3 with the surface of the photosensitive member 1 (i.e. the point of action) is at Q. Assume also that a segment OP between the point of force P and the fulcrum 0 has a length It, and a segment OQ between the point of action Q and the fulcrum 0 has a length 12.According to the present invention, these lengths satisfy the requirement that: 12zit i.e. 19161, so that the variation in the pressing force of the contact blade 3 on the photosensitive member 1 is lessened in the event that the contact point 0 becomes displaced from a prescribed position.

This can be more readily understood by considering the converse situation where li/li < 1, i.e. where the fulcrum is shifted to a position 0' or 0". Any change in the position of the contact point 0 will result in an amplified change in position of the point of force P, so that the pressing force will change by a comparatively large amount.

To give a numerical example, the pressure necessary for satisfactory cleaning is typically between 1 and 3 g/mm, preferably 1.5 g/mm+0.15 g/mm (i.e. +10%). Suppose that the lengths It and 12 are set such that 12/lit=0.5. In the event that the contact point Q is shifted from 1 mm from its prescribed position, then the point of force P will be displaced 2 mm from its prescribed position. For a spring 8 having an elastic constant k of 100 g/mm, this will mean a change in pressing force of as much as 200 g. If the entire length of the cleaning blade 3 is 390 mm, then the resultant change in cleaning pressure will be 0.67 g/mm, i.e. more than the permitted tolerance.

On the other hand, displacement of the contact point Q can cause the cleaning blade 3 to press on the photosensitive member 1 more than is required. As a result, the cleaning blade quickly becomes worn and fatigued, i.e. the cleaning characteristic rapidly deteriorates. Thus, displacement of the contact point Q by as little as 1 mm will be sufficient to cause a poor cleaning characteristic.

To illustrate the advantage given by the invention, suppose that in the same numerical example as given above the lengths It and 12 are set such that 12/lit=2. Now, a shift of 1 mm in the position of the contact point Q will result in a displacement of only 0.5 mm for the point of action P. This will cause a change in pressing force of 50 g and a change in the cleaning pressure of 0.13 g/mm, the latter being within the permitted tolerance of +0.15 g/mm.

Variations in the position of the contact point 0 give rise to the following effects: (1) a dimensional error in the direction of cutting of the cleaning blade 3, and (2) a variation in the friction between the cleaning blade 3 and the photosensitive member 1.

As explained previously, effect (2) may also result from the structure of the cleaning unit, being of the type shown in Figure 2. The effects on the pressing force of the variation in position of the contact point Q can be minimised by choosing the lengths It and 12 such that 12 > 1t, as described previously. A more desirable stable condition can be obtained if the following relationship is satisfied: 1 .5612../l tA2-5 If 12/lit were to be made greater than 3, then it would be necessarv to use a spring 8 having a large elastic constant in order to obtain a large enough pressing force for cleaning. If the elastic constant is extremely high, then an excessively large force is required to separate the cleaning unit 2 from the photosensitive member 1.In other words, it will be necessary to replace the solenoid 1 5 with one of a larger capacity.

In the arrangement prescribed above, the distance 12 between the centre of rotation 0 and the contact point Q of the cleaning blade 3 on the photosensitive member 1 is relatively large, and accordingly even when the contact point 0 is shifted from the set value the pressing angle 0 is relatively small. In the same manner as does the pressing force, the pressing angle 0 greatly affects the cleaning characteristic, and therefore it is desirable that the cleaning unit be so designed that the pressing angle 0 is substantially maintained unchanged.

As is apparent from the above description, in the cleaning unit of the invention the length It of the segment between the centre of rotation of the cleaning blade 3 (i.e. the fulcrum 0) and the point where the cleaning blade 3 is pressed against the photosensitive member 1, (i.e. the point of force P) is smaller than the length 12 of the segment between the fulcrum 0 and the contact point 0 of the cleaning blade 3 on the photosensitive member 1. Therefore, the cleaning blade 3 is satisfactorily contacted with the surface of the photosensitive member 1, whereby fluctuations in the pressing force required for cleaning are minimised. Thus, the cleaning unit of the invention has an excellent cleaning characteristic.

Claims

1. A cleaning unit for an electrophotographic device, comprising a cleaning blade for cleaning the surface of a photosensitive member, a holding member pivotably holding the cleaning blade in such a manner as to permit the latter to move away from and into contact with the photosensitive member, and means for pressing the cleaning blade against said surface of the photosensitive member, the length It of a segment between a pivot axis of the cleaning blade and a biasing force application point, and the length 12 of a segment between said pivot axis and the contact point of said cleaning blade with the photosensitive member being selected so as to satisfy the following expression: 1 612/l t

2.A cleaning unit as claimed in Claim 1, wherein the holding member includes a protruding portion, and spring means is attached to the protruding portion so as to provide said biasing force.

3. A cleaning unit as claimed in Claim 1 or 2, wherein the holding member includes a blade holding portion and a base portion, the base portion being supported for pivotal rotation about said pivot axis.

4. A cleaning unit as claimed in Claim 1, 2 or 3, wherein the holding member holds the cleaning blade in relation to a plane tangent to the photosensitive member such that an acute angle is formed between the cleaning blade and said plane on a side of the cleaning blade which faces an uncleaned surface of the photosensitive member.

5. A cleaning unit as claimed in any preceding claim, wherein the lengths It and 12 are related such that: 1.5Qd1,2.5

6. A cleaning unit for an electrophotographic device, substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

7. A cleaning unit for an electrophotographic device, comprising a cleaning blade for cleaning the surface of a photosensitive member and adapted to contact said photosensitive member at a contact point, a holding member which holds the cleaning blade for pivotal movement about a pivot axis towards and away from said surface of the photosensitive member, and biassing means acting on the cleaning blade or the holding member at a force application point to bias the cleaning blade towards the surface of the photosensitive member, the distance It between the pivot axis and the force application point being related to the distance 12 between the pivot axis and the contact point such that: 1 6i2/lt