JPH02267577A - Developing device - Google Patents

Abstract

PURPOSE:To decrease the number of turns of a coil and to miniaturize the device by providing a back yoke member on the outside of a cylindrical member of a developing sleeve, and reducing a reluctance of the periphery of the cylindrical member in a magnetic field generated by an armature coil. CONSTITUTION:On the outside on the outside peripheral surface of a cylindrical member 11 of a developing sleeve 10, a cylindrical back yoke member 40 consisting of a soft magnetic material is provided by separating it by a clearance through which a developer T moves, and on a part of the member 40, an opening part 41 for replenishing the developer and for supplying the developer to an image carrying body is provided. In this state, in the case when a prescribed magnetic field is generated in the periphery of the member 11 by bringing armature coils 12, 13 to electric conduction, its magnetic flux passes through the inside of the member 40, and comparing with the case when its magnetic flux passes through in the air, a reluctance becomes smaller.

Description

Detailed Description of the Invention (Industrial Application Field) For example, in a copying machine that uses electrophotography, an electrostatic latent image formed on a photosensitive drum, which is an image carrier, is developed by a developing device. , it is necessary to visualize this by developing it. In order to develop the electrostatic latent image, it is necessary to supply the developer (toner) in the developing device toward the electrostatic latent image through the developing device, and the developing device performs this function. This is the developing sleeve inside. #Developing sleeves are generally made by rotating a multi-pole magnetized permanent magnet inside a cylindrical member made of non-magnetic material, and utilizing the fact that the leakage magnetic field from the permanent magnet moves with the rotation of the permanent magnet. A device that supplies magnetic toner along the outer peripheral surface toward an adjacent photosensitive tram is often used.

However, the method of rotating a permanent magnet to generate a rotating magnetic field on the outer surface of a cylindrical member requires a bearing device to rotationally support the permanent magnet, a motor, a belt, a reduction gear, etc. for rotating the permanent magnet, and the structure The developing device is complex and generates rotational noise due to the rotation of the permanent magnet, so the applicant has proposed a developing device that generates a rotating magnetic field electrically instead of rotating the permanent magnet.

This consists of arranging two or three sets of armature coils shifted by a predetermined electrical angle inside a cylindrical member made of non-magnetic material.
By applying two-phase or three-phase alternating current to the armature coil, an alternating rotating magnetic field is generated on the outer circumferential surface of the cylindrical member, and the rotating magnetic field causes the magnetic toner to approach the outer circumferential surface of the cylindrical member. There is something that supplies the photosensitive drum.
By this, the electrostatic latent image on the photosensitive drum is developed and
IJfII! The electrostatic latent image can be converted into a toner image.

(Problem to be Solved by the Invention) However, even if a rotating magnetic field is generated on the outer circumferential surface of the cylindrical member by the armature coil described above, it takes a large ampere turn to obtain a magnetic field of several hundred Gauss necessary for conveying toner. This causes the problem of heat generation in the coil due to the large current, and the problem of increasing the size of the device due to an increase in the number of turns of the coil.

The present invention has been made in view of the above problems, and its purpose is to generate a rotating magnetic field electrically without requiring a large current, and without making the device internal. It is an object of the present invention to provide a developing device which can fully exhibit its developing ability.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a two-phase or three-phase A rotating magnetic field is generated on the outer circumferential surface of the cylindrical member by passing an alternating current into the phase, and the rotating magnetic field moves the magnetic developer toward the adjacent image carrier along the outer circumferential surface of the circular tt1 member. In the developing device for developing the electrostatic latent image on the image carrier, a cylindrical back yoke member made of a soft magnetic material is disposed above the outer circumferential surface of the cylindrical member and spaced apart by a gap through which the developer moves. Further, the back yoke member is characterized in that a part thereof is provided with an opening for replenishing the developer and for supplying the developer to the image carrier.

(Function) Since the back yoke member made of soft magnetic material is disposed outside the cylindrical member, when the armature coil is energized to generate a predetermined magnetic field around the cylindrical member, the magnetic flux is transferred to the back yoke. When the magnetic flux passes through the member, the magnetic resistance can be made smaller than when the flux passes through the air. Therefore, even when generating a rotating magnetic field around a cylindrical member,
The required excitation ampere turns can be reduced, and the number of coil turns and current value of the armature coil can be reduced.

(Embodiment) An embodiment of the present invention will be described below with reference to the accompanying drawings, taking a copying machine that employs electrophotography as an example.

First, an overview of image formation by a copying machine will be explained with reference to FIG. 1. In the figure, l is a photosensitive drum which is an image bearing member, and around the photosensitive drum l are primary chargers 2. IJl image device 3
, a transfer charger 4, and a cleaning device 5 are provided.

That is, when the photosensitive drum l uniformly charged by the primary charger 2 is exposed to image light from a document (not shown), an electrostatic latent image is formed on the photosensitive drum l according to the image light. The electrostatic latent image is transferred to the developing device 3 as the photosensitive drum l rotates.
The toner image is developed by the developer (magnetic toner containing a magnetic material, hereinafter referred to as toner) in the developing device 13, visualized, and converted into a toner image.

This toner image is then transferred via a transfer charger 4 onto a transfer paper P that is conveyed from a paper feed system (not shown).The transfer paper P carrying the 0-order toner image is transferred to a fixing device (not shown). The toner image is fixed as a permanent image on the transfer paper P, and the photosensitive drum L after the transfer is cleaned of residual toner by the cleaning device 5, and the same operation is repeated successively. An image is formed on the transfer paper P.

Here, the developing device a13 includes a developing device main body 3a having toner therein, and is accommodated in the developing device main body 3a, and supplies the toner in the developing device main body 3a toward the photosensitive drum l. It is composed of a developing sleeve 10, etc., which converts the electrostatic latent image on the top into a toner image. The developing sleeve lO
The part exposed outward from the developing device main body 3a is disposed close to the photosensitive drum l, and the toner in the developing device main body 3a is moved to the proximal portion 10a to the photosensitive drum l. It is made to stick to the electrostatic latent image on 1.

Next, the principle of conveying toner by the developing sleeve 1O will be explained based on FIGS. 2 to 5.

FIG. 2 is a diagram conceptually showing a cross section of the developing sleeve IO, in which a first armature coil 12 is disposed on the inner surface of a thin cylindrical member 11 made of a non-magnetic material.

A second armature coil 13 is arranged inside.

1st. The second armature coils 12 and 13 each have 18 single coils a or b wound around a predetermined laminated core and arranged at equal intervals in the circumferential direction of the cylindrical member 11,
Each wheel coil a (or b) is electrically connected to alternately generate magnetic fields of opposite polarity. That is, the two magnetic poles are N
, S, for example, if the odd-numbered single coil a l+ a31 "" a ty of the m-th child coil 12 generates N magnetic poles on the radially outer side of the cylindrical member 11, Even numbered single coil a * * 84 * ””a 1
M generates a magnetic pole S on the radially outer side of the cylindrical member 11, and similarly the odd numbered single coil b+ of the second armature coil
+b3+...bl? If N magnetic poles are generated on the radially outer side of the cylindrical member 11, then it is an even numbered single coil b.

bl, . . . b, a generate magnetic poles S on the radially outer side of the cylindrical member 11.

Further, the first armature coil 12 and the second armature coil 13 are arranged to be shifted from each other by half the pitch of the single coil a (or b), that is, by 90 degrees in electrical angle.

Here, to explain the electrical connection method between each single coil 8 of the first armature coil 12 with reference to FIG. 3, the current flows in from the right side of the single coil a14 and flows out from the left side of the single coil a13. The single coil ats and the single coil a14 are electrically connected so that the air flows in and flows out from the right side. After that, other single coil a13. ... are also connected in the same way,
The current finally flows out from the right end of the single coil all, and the right ends of the single coils a14 and ass serve as input terminals Pa of the power supply. Therefore, when an alternating current is applied to the input terminal Pa, the magnetic fields of the adjacent single coils a have opposite polarities. Note that pb is an input terminal for the power supply of the second armature coil 13, and the electrical connection between each single coil 5 of this second armature coil 13 is also the same as that of the first armature coil. shall be taken as a thing.

Also number 1. As shown in FIG. 5, the second armature coils 12 and 13 receive 5 alternating currents having a frequency f whose phases are shifted by 90 degrees, that is, Icos2πft.

It is necessary to supply l5in2πft, which is the fourth
As shown in the figure, a power supply 20 and first and second armature coils 1
2.13 power supply input terminal Pa.

This is realized by connecting a predetermined drive circuit 21 between pb and pb.

Next, the first. The action of the second armature coil 12.13 will be explained.

The first and second armature coils 12 and 13 each have a phase of 9.
When an alternating current with a frequency f shifted by 0 degrees is applied, the first .
A rotating magnetic field is generated around the second armature coil 12, 13, which will be expressed below using an equation.

First, when a unit current is passed through the armature coil 12, 1' is 1.
The magnetic field Ha generated in the radial direction of the cylindrical member 11 is a single coil a.
If the number is 2P, the circumferential angle from the predetermined position to the outer circumferential surface of the cylindrical member 11 is θ (see FIG. 2), and the constant is Hv, it is expressed as HaxHv-sinPθ. Further, when a unit current is passed through the second armature coil 13, the magnetic field Hb generated in the radial direction of the first cylindrical member 11 is expressed as Hbwl(v·cosPθ) as described above.

Next, Ico is applied to the above first and second armature coils 12 and 13.
s2wft, summer 5in2πft 2 with a 90 degree phase difference
When the alternating current of each phase is applied, the first. The composite magnetic field H due to the second armature coil 12.13 is )1=)i3-1cos2rft +Hblsin2πft =Hv-1sin(Pθ+:2rft), and one composite magnetic field H is two sine waves traveling in the direction of θ at frequency f. This results in an alternating rotating magnetic field. Note that I is the amplitude of the alternating current.

In addition, since a rotating magnetic field can be generated on the outer circumferential surface of the cylindrical member 11 in the developing sleeve 1O, the toner is moved in the circumferential direction of the cylindrical member 11, and the electrostatic charge of the photosensitive tram 1 is reduced by the toner. This allows the latent image to be developed.

As shown below, 1st. 2nd armature coil 12° 13 to 90
The cylindrical member 11 is
Since a rotating magnetic field can be generated on the outer circumferential surface of the cylindrical member 11, the toner can be moved toward the photosensitive tram 1 along the outer circumferential surface of the cylindrical member 11 without mechanically rotating the permanent magnet.
By adsorbing toner to the electrostatic latent image on the photosensitive tram 1, the electrostatic latent image can be developed into a toner image. In addition, although the case where two-phase alternating current is applied to two sets of armature coils has been described above, each single coil of three sets of armature coils each having a different electrical angle of 120 degrees is arranged alternately,
Exactly the same effect can be obtained even when three-phase alternating current is applied to this.

Next, we will explain the specific structure and operation of the developing sleeve 10, which generates a rotating magnetic field by passing two-phase alternating currents having a phase difference of 90 degrees to the first and second armature coils 12 and 13, and its operation. This will be explained with reference to FIGS. 10 to 10.

As shown in FIG. 7, this developing sleeve 10 is disposed close to the bottom of the photosensitive drum l, and is located inside a thin cylindrical member 11 made of a non-magnetic material. Second armature coil 12
．． 13, and also has a back yoke member 40, a tray 50, etc. on the outside of the cylindrical member 11. 1st
, the second armature coil 12.13 has four salient poles 30a formed at equal intervals on the outer periphery of a core 30 made of a laminated iron core.
,... to the coil 31. The first armature coil 12 is composed of single coils a, , a, each having an electrical angle of 180 degrees. .

The second armature coil 13 is also composed of single coils b+ and b* having an electrical angle of 180 degrees. And the adjacent single coils al, a, b,.

b, respectively have an electrical angle of 90 degrees from each other.

The back yoke member 40 is made of a soft magnetic material such as iron, and the toner T transport path 14 is connected to the outer peripheral surface of the cylindrical member 40.
That is, it is a cylindrical member disposed concentrically outside the cylindrical member 11 with a gap t in between. As shown in FIG. 7, an opening 4 extends in the axial direction of the photosensitive drum 1 by approximately the same length as the image forming portion in the axial direction.
1 is formed, toner T is replenished around the cylindrical member 11 through the opening 41, and the toner T held on the outer peripheral surface of the cylindrical member 11 is transferred from the opening 41 to the photosensitive tram l.
will be supplied to

As shown in FIG. 7, the tray 50 has a plate portion 51 disposed at a certain inclination angle on one end side of the opening 41 of the back yoke member 40, that is, on the side farther away from the photosensitive tram l.
and a support portion 52 fixed to the outer peripheral portion of the back yoke member 40, and new toner T can be replenished via the plate portion 51 of the tray 50.

In addition, 32 in FIG. 6 is the 1st. 2nd armature coil 12.13
This is the power supply cable for the

So, first. When alternating currents with different phases of 90 degrees are applied to the second armature coils 12 and 13, one cylindrical member 1
A rotating magnetic field is generated on the outer circumferential surface of the cylindrical member 11, and the toner T is moved counterclockwise in the drawing w47 along the outer circumferential surface of the cylindrical member 11, that is, along the conveyance path 14 by the rotating magnetic field. This means that it can be supplied to the photosensitive drum l.

Here, since the back yoke member 40 is disposed outside the cylindrical member 11, the first
When the first armature coil 12 is energized, the magnetic flux generated by the first armature coil 12 passes through the single coil a and the magnetic paths ml and m2 in the air to the hack yoke member 40.
After passing through the back yoke member 40, the toner passes through the gap t in the toner transport path 14 and returns to the single coil a2.

On the other hand, as shown in FIG. 8, if there is no back yoke member 40, the magnetic flux emitted from the single coil a1 will flow through the magnetic path m3 in the air.
．． m, and return to the single coil a2, the length of the magnetic path of the magnetic flux in the air will be extremely different depending on whether the back yoke member 40 is present or not. That is, the magnetic resistance to the magnetomotive force generated by the coil current is much smaller when the back yoke member 40 made of a soft magnetic material is provided than when the back yoke member 40 is not supported. 40 requires smaller ampere turns to generate the same magnetic flux.

Therefore, by providing the hack yoke member 40, Ia!
Since the number of turns of the J magnetic current and the single coils a, . . . can be reduced, unnecessary heat generation to the device can be prevented, and the device can be made smaller.

Further, for example, the single coil a1 of the first armature coil 12 is disposed at a position slightly to the right in the circumferential direction in FIG. 10 from the center of the opening 41 of the back yoke member 40. , from the distance 1+ between the right edge part a1-1 of the single coil at and the right axial end 41a of the opening 41, the left edge part a1-2 of the single coil at and the left axial end 41b of the opening 41
The distance between fax and fax is longer. Further, the photosensitive drum 1 is also disposed at a position closest to the cylindrical member 11 near the right edge portion a, -1 of the single coil a1.

Therefore, if the exciting current is applied to the first t-th armature coil 12,
As shown in Figure 1O, the left edge part a of the single coil a1
The magnetic flux M2 generated from the 1-2 side toward the left axial end 41b of the opening 41 of the hack yoke member 40 is generated from the right edge a of the single coil a1, and from the -1 side toward the right axial end 41b of the opening 41. The magnetic flux M generated toward the portion 41a can generate a stronger magnetic flux density. For this reason, the photosensitive drum
Thus, a large amount of toner T can be collected in the vicinity of the cylindrical member 11, and toner T without uneven density can be supplied to the photosensitive tram l.

Furthermore, since the plate portion 51 of the tray 50 is disposed on the side of the opening 41 of the back yoke member 40 where the magnetic flux density is weak, it becomes easy to collect excess toner T and prevent the toner T from scattering. .

It should be noted that the above description has been made with reference to a copying machine that employs electrophotography.The developing device according to the present invention is not limited to one that uses electrophotography, but may simply develop an electrostatic latent image with a magnetic developer. Of course, it can be applied to anything.

(Effects of the Invention) As is clear from the above description, according to the present invention, a hack yoke member is disposed outside one cylindrical member, and the magnetic resistance of the magnetic field generated by the armature coil around the cylindrical member is suppressed to a small level. As a result, the ampere-turns required in the armature coil to obtain the required magnetic field strength can be reduced.

Therefore, the number of turns of the armature coil can be reduced, and the device can be made smaller. In addition, the current value of the armature coil can be reduced, and the problem of heat generation due to large currents can be solved, and power consumption can also be kept low.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining image formation by a copying machine, FIG. 2 is a sectional view for explaining the operation of a developing sleeve, and FIG. 3 is a diagram showing the wiring state of an armature coil. Figure 4 is a diagram explaining the power supply to the armature coil, Figure 5
The figure is an explanatory diagram of two alternating currents with a 90 degree phase difference.
The figure is a perspective view of the developing sleeve, FIG. 7 is a sectional view taken along line A-A in FIG. 6, and FIG. , FIG. 10 is a diagram for explaining the distribution of magnetic flux density of the developing sleeve. 1... Image carrier (photosensitive drum), 11... Cylindrical member, 12° 13... Armature coil, 40... Back yoke member. 41...Opening, t...Gap, T...Developer (toner)

Claims (3)

[Claims] (1) A two-phase or three-phase alternating current is applied to two or three sets of armature coils that are arranged inside a thin cylindrical member and are composed of a plurality of single coils, so that the In a developing device that generates a rotating magnetic field and uses the rotating magnetic field to move a magnetic developer toward an adjacent image carrier along the outer peripheral surface of a cylindrical member to develop an electrostatic latent image on the image carrier. , a cylindrical back yoke member made of a soft magnetic material is disposed above the outer circumferential surface of the cylindrical member outwardly, separated by a gap through which the developer moves; A developing device comprising an opening for supplying developer to an image carrier. (2) The developer according to claim 1, wherein the opening is disposed on the upper side of the back yoke member, and a tray for replenishing the developer and preventing the developer from scattering is provided around the opening. Device. (3) One of the single coils is disposed slightly closer to one of the opening ends than the center of the opening, and an image is carried on the edge side of the single coil that is closer to the adjacent opening end. 2. The developing device according to claim 1, wherein the developing devices are arranged so that their bodies are substantially opposed to each other.