GB2037620A

GB2037620A - Developing electrostatic images using magnetic toner

Info

Publication number: GB2037620A
Application number: GB7847388A
Authority: GB
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 1978-12-06
Filing date: 1978-12-06
Publication date: 1980-07-16
Also published as: GB2037620B

Abstract

Apparatus for feeding magnetic toner to a drum 5 having an electrostatic image thereon comprises a toner supply 3; a rotating non-magnetic cylindrical sleeve 1 for transporting the toner from the toner supply to the light- sensitive surface; a magnet roll within the sleeve for attracting toner to the sleeve, the roller having an array of an even-number of radially-spaced permanent magnets, of which adjacent magnets have opposite polarity, the magnetic roller rotating in the same direction as the sleeve, so that excess toner accumulating in advance of the development nip is caused to recirculate (arrows d, e) back toward the supply. A plate 7 can be provided to partition the toner flowing to the light-sensitive surface (arrow b) from the excess toner being removed and recirculated. <IMAGE>

Description

SPECIFICATION Improvement relating to an electronic reproducing machines using magnetic toner The present invention relates to an improved method and apparatus for feeding magnetic toner material in electronic image reproducing machines.

One type of conventional toner feed apparatus used in electronic image reproducing machines, is shown in Figure 1 of the accompanying drawings.

The magnetic toner 4 is fed from a toner supply tank through a feed gap d, defined by a non-magnetic circular sleeve and is transported in the direction of an arrow (b) either by securing the non-magnetic sleeve 1 and rotating a magnet roll 2 in the direction of an arrow (a) or by securing the magnet roll 2 and rotating the non-magnetic sleeve 1 in the direction of an arrow (b). The physical phenomenon of the net transport of magnetic material in a direction opposite to the movement of a series of magnetic poles in such toner feeder mechanisms is described in Japanese Patent Publication 37-14798, published September21, 1962.

With reference to Figure 1, the delivery gap d2 between a light sensitive drum 5 rotating in the direction of an arrow (c) and the sleeve 1 typically is made equal to or smaller than the gap d1 to allow excess toner to be fed from supply tank 3 in order to accumulate a supply 6 of the magnetic toner 4. There is, therefore, a substantial area of sliding contact between the toner 4 and the light sensitive drum 5 so that electrostatic latent images on the surface of the light sensitive drum 5 are completely developed by the magnetic toner 4. However, since the gap d2 the balance between the amount of the magnetic toner 4 transported through the gap d1 and that passing through the gap d2 and recycled to the supply tank 3 through passage 9 often can not be maintained and the accumulation of excess toner at 6 becomes unstable.Also as the excess magnetic toner 4 coagulates with the elapse of time, it becomes impossible to maintain continuous and stable development. Solution to those problems have been proposed but have been largely unsuccessful. For example recesses have been provided in a part of the surface of the light-sensitive drum 5 or the developing apparatus has been moved periodically so as to enlarge the gap d2.

One object of the present invention is to avoid these problems by improving feeding of magnetic toner material in electronic image-reproducing machines to enable continuous and stable development.

According to the present invention, we propose apparatus for feeding magnetic toner to a lightsensitive surface, the apparatus comprising: a magnetic roller having opposite polarity, said roll being rotatable in a given direction; a non-magnetic cylindrical sleeve surrounding the roller, the sleeve and the light-sensitive surface defining therebetween delivery gap, and the sleeve being rotatable in the same direction as the roller, means for feeding toner into the magnetic field of the roller, for rotation with the sleeve toward the delivery gap; and means under counter-rotation forces induced by the rotating magnetic roller for removing excess toner accumulating at the delivery gap, the removing excess toner accumulating at the delivery gap, the removing means including a path opposite to the given dire(,tion.

Preferably, the feeding means includes a toner supply and the removing means includes means for recirculating the excess toner to the toner supply.

It is also preferred that the removing means includes partition means separating the path from the toner being carried to the delivery gap by the sleeve.

It is also preferred that the sleeve and the magnetic roller are independently rotatable and that the magnet roll is rotated faster than the sleeve.

Also according to this invention, we propose a method offeeding magnetic toner to a light sensitive surface comprising: attracting the toner toward the surface of a cylindrical sleeve surrounding a magnetic roller, the roller having an even number of permanent magnets radially spaced within the circumference, adjacent magnets having opposite polarity, the sleeve and the light-sensitive surface defining therebetween a delivery gap; rotating the sleeve and the roller in the same direction, thereby transporting toner along with the sleeve toward the delivery gap in the direction of rotation; and removing excess toner accumulating at the delivery gap using circulation forces induced in the toner the rotating magnetic roller.

Preferably, the toner is attracted from a toner supply and the removing step includes recirculating the excess toner to the toner supply by the counterrotation forces.

It is also preferred that the removing step includes providing a path opposite to the given direction, the excess toner being removed along the path.

It is also preferred that the removing step includes partitioning the path from the toner being carried to the delivery gap on the sleeve.

And it is also preferred that the sleeve and the magnetic roller are independently rotatable, the magnetic roller being rotated roll faster than the sleeve.

Embodiments of the present invention will now be described by way of example with reference to Figures 2 and 3 of the accompanying drawings of which: Figure 2 is a side view of one embodiment of toner feed apparatus according to the present invention and Figure 3 is a side view of another embodiment of the present invention.

In the drawing, reference numerals 1 to 6,9 and d1 and d2 correspond respectively to those components and dimensions mentioned above with reference to the prior art apparatus shown in Figure 1.

In the two embodiments of toner feed apparatus shown in Figures 2 and 3, a magnetic roller 2 having a non-magnetic sleeve 1 is used to attract toner 4 from a supply tank 3 in the conventional manner.

The sleeve 1 is rotated by conventional drive means 10 in a given direction (b) so as to transportthe toner adhering thereto, through a feed gap d1 toward a delivery gap d2 defined between the sleeve 1 and the rotating image-bearing drum 5. Feed gap d1 is made equal to or greater than delivery gap d2so that more toner can be deposited on the drum than is able to flowthrugh delivery gap d2, and on past delivery gap d2 back to toner supply tank 3 via path 9. There is a tendancy for excess toner to accumulate as indicated at 6 up-stream of delivery gap d2 as in the conventional apparatus but in, the apparatus shown in Figures 2 and 3 the excess toner is recirculated to the supply tank 3.In each embodiment the magnetic roller 2 is driven in the same direction but preferably at a higher speed than, the non-magnetic sleeve 1 by means 10, which can be any convenional drive mechanism, such as direct motor drive, gears, pulleys, etc., which is used to rotate.

The supply tank is closed to define a path 8 along which excess toner in the accumulated mass 6 circulates in a direction opposite to the direction of rotation of the sleeve 1.

With reference to the embodiment of Figure 2, the accumulation of magnetic toner in the reservoir space 6 tends to recirculate in the direction of an arrow (d) due to the moving magnetic field of the magnetic roll 2 rotating in the direction of the arrow (a). In the vicinity of sleeve 1, the frictional drag forces of the moving sleeve 1 overcome this tendency to recirculate so that the net flow is toward the delivery gap d2 whereas in the accumulated mass of excess toner in space 6 remote from the surface of sleeve 1, the recirculation forces dominate. This recirculation of the excess magnetic toner 4 in the direction of the arrow (d) eliminates coagulation in the accumulated mass of toner in the reservoir space 6 and preventss undersirable deposition of excess magetic toner on the light-sensitve drum 5 thereby improving developing efficiency and enabling high quality development.

In addition to the mechanism described above, recirculation is also assisted by partitioning the recirculating flow of excess toner from the toner being transported from supply tank 3 toward the gap d2. A partition plate 7, as shown in Figures 2 and 3 of the drawing, is disposed in a plane parallel to the axes of sleeve 1 and magnetic roller 2 and is spaced from the non-magnetic sleeve 1 to define between the plate 7 and sleeve 1 a gap equivalent to the gap d1 ofthe conventional apparatus in Figure 1. When the amount toner in the mass 6 gradually increases and rises above the partition plate 7, the excess magnetic toner is forced out in the direction of an arrow (e) by the recirculation forces along the path 8 defined between the partition plate 7 and the wall of supply tank 3, to the supply tank 3.The undesirable accumulation of toner is thus suppressed, the amount of excess toner being constant, and forming a stable mass, thereby improving developing efficiency.

Figure 3 shows another embodiment of the present invention wherein the rotating directions of the non-magnetic sleeve 1 and the magnet roll 2 are opposite to those in the embodiment of Figure 2, the accumulated toner in reservoir space 6 being located below the delivery gap d2. In all other respects the two embodiments are identical.

The embodiments of toner feed apparatus shown in Figures 2 and 3 were tested in a copying machine as described below. About 5000 copies were reproduced without intemption. No change in the developing efficiency was detected thus showing the excellent stability in the continuity of the developing efficiency achieved using the method and apparatus of the present invention.

Example Light sensitive selenium drum 5 was rotated at a peripherial speed of about 100 mm/sec. The nonmagnetic sleeve 1 which was made of a stainless sleeve had an outside diameter of 30 mm and was rotated at 70 r.p.m. whereas the magnetic roll 2 which was made of isotropic barium ferrite, had an outside diameter of 29 mm having 8 and was rotated at 1200 r.p.m. It had eight magnetic poles, the magnetic flux density on the surface of nonmagnetic sleeve 1 being about 500 gauss. The mag netic toner 4 constituted 60% magnetite and the balance of resin and carbon particles between 10 30 m in diameter and having 10'2 1012cm ofspecific volume resistivity. The gaps d1 and d2 respectively were 0.7 mm and 0.5 mm.

Claims

1. Apparatus for feeding magnetic toner to a light-sensitive surface, the apparatus comprising: a magnetic roller having an even number of permanent magnets radially spaced within its circumference, adjacent magnets having opposite polarity, said roll being rotatable in a given direction; a non-magnetic cylindrical sleeve surrounding the roller, the sleeve and the light-sensitive surface defining therebetween a delivery gap, and the sleeve being rotatable in the same direction as the roller, means for feeding toner into the magnetic field of the roller, for rotation with the sleeve toward the delivery gap; and means under counter-rotation forces induced by the rotating magnetic rollerfor removing excess toner accumulating at the delivery gap, the removing means including a path oppositeto the given direction.

2. Apparatus according to claim 1 wherein the feeding means includes a toner supply and wherein the removing means includes means for recirculating the excess toner to the toner supply.

3. Apparatus according to claim 1 wherein the removing means includes a partition dividing the said path from the toner being rotated into the delivery gap with the sleeve.

4. Apparatus according to claim 1 wherein the sleeve and the magnetic roller are independently rotatable, the magnetic roller being rotatable faster than the sleeve.

5. A method for feeding magnetic toner to a light-sensitive surface comprising: attracting the toner toward the surface of a cylindrical sleeve surrounding a magnetic roller, the roller having an even number of permanent magnets having opposite polarity, the sleeve and the lightsensitive surface defining therebetween a delivery gap; rotating the sleeve and the roller in the same direction, thereby transporting toner along with the sleeve toward the delivery gap in the direction of rotation; and removing excess toner accumulating at the delivery gap using circulation forces induced in the toner the rotating magnetic roller.

6. A method according to claim 5 wherein the toner is attracted from a toner supply and wherein the removing step includes recirculating the excess toner to the toner supply by the circulation forces.

7. A method according to claim 5 wherein the removing step includes providing a path opposite to the given direction, the excess toner being removed along the path.

8. A method according to claim 7 wherein the removing step includes the step of partitioning the path from the toner being rotated into the delivery gap on the sleeve.

9. A method according to claim 5 wherein the sleeve and the magnetic roller are independently rotatable and wherein the magnetic roller is rotated faster than the sleeve.

10. Apparatusforfeeding magnetictonertoa light-sensitive surface in an electronic image reproducing machine, the apparatus comprising a toner supply; a magnetic roller having an even-number of radially-spaced permanent magnets, adjacent magents having opposite polarity; a non-magnetic cylindrical sleeve surrounding and concentric with the magnetic roller; a toner feed gap bounded in part by the sleeve; a toner delivery gap formed by the sleeve and the light-sensive surface; and a toner reservoir space for accumulating excess toner, the space bounded in part by the light-sensitive surface, the sleeve being rotatable to feed toner through the feed gap from the toner supply to the toner reservoir space and comprising means for removing excess toner from the reservoir in a direction opposite to the direction of the sleeve, the removing means including means for rotating the magnetic roller in the same direction as the sleeve for inducing counterrotation forces in the excess toner.

11. Apparatus according to claim 10 wherein the removing means also includes means for recirculating the excess toner to the toner supply.

12. Apparatus according to claim 12 wherein the magnetic roller are independently rotatable at different speeds.

13. Apparatus according to claim 12 wherein the magnetic roller rotates faster than the sleeve.

14. Apparatus according to claim 10 wherein the light-sensitive surface is the surface of a rotatable cylindrical drum having an axis parallel to the axes of the magnetic roller and the sleeve, wherein the reservoir space is above the delivery gap; and wherein the sleeve rotates in a direction opposite to that of the drum.

15. Apparatus according to claim 10 wherein the light-sensitive surface is the surface of a rotatable cylindrical drum the axis of which is parallel to the axes of the magnetic roller and the sleeve; wherein the reservoir space is above the delivery gap; and wherein the sleeve rotates in the same direction as the drum.

16. Apparatus according to claim 11 wherein the removal means also includes partition means for separating the flows of toner to and from the toner supply respectively from and to the reservoir space.

17. Apparatus according to claim 16 wherein the partitioning means includes a plate positioned parallel to the axes of the magnet roll and sleeve, the plate also being spaced from the sleeve, the spacing between the plate and sleeve defining the feed gap.

18. Apparatus according to claim 17 wherein the width of the feed gap is greater than or equal to the width of the delivery gap.

19. Apparatus according to claim 17 wherein the width of the feed gap is greater than about 0.3 mm and less than about 1.5 mm.

20. A method for feeding magnetic toner from a toner supply, through a feed gap, and to a lightsensitive surface in an electronic image reproducing machine, comprising magnetically attracting the toner from the supply onto a non-magnetic cylindrical sleeve by locating a roller having an even number of radially spaced permanent magnets inside a sleeve, adjacent magnets being of opposite polarity; transporting the toner attracted to the light-sensitive surface, by rotating the sleeve relative to the feed gap and depositing the toner in a reservoir space adjacent thereto, and in sliding engagementwith, the light-sensitive surface, so as to accumulate toner, and comprising removing the excess toner from the reservoir in a direction opposite to the direction in which the sleeve rotates, by rotating the magnetic roll in the same direction as the sleeve thereby inducing circulation forces in the excess toner.

21. A method according to claim 20 wherein the magnet roll is rotated at a higher speed than the sleeve.

22. A method according to claim 21 wherein the removing step includes the step of recirculating the excess tonerto the toner supply by the action of the counter-rotation forces.

23. A method according to claim 20 wherein the removing step further includes the step of partitioning the recirculating excess toner from the flow of toner from the toner supply.

24. A method according to claim 23 wherein the partitioning step includes positioning a plate parallel to the axis of the sleeve, and spacing the plate from the sleeve, the least distance between the sleeve and the spaced plate member contituting the feed gap.

25. A method according to claim 20 wherein the toner reservoir is bounded by the sleeve and the light-sensitive surface and a toner delivery gap is formed at the point of the smallest distance separating the light-sensitive surface and the sleeve wherein the feed gap is greater than or equal to the delivery gap.

26. A method according to claim 20 wherein the feed gap iswiderthan about 0.3 mm and narrower than about 1.5 mm.

27. A method according to claim 20 wherein the light-sensitive surface is the surface of a rotating cylindrical drum the axis of which is parallel to the axes of the magnetic roller and sleeve; wherein the reservoir space is above the smallest distance between the sleeve and the drum; and wherein the sleeve rotates in the opposite direction to the drum.

28. A method according to claim 20 wherein the light-sensitive surface is the surface of a rotating cylindrical drum the axis of which=is parallel to the axes of the magnetic roller and sleeve; wherein the reservoir space is below the shortest distance between the sleeve and the drum; and wherein the sleeve rotates in the same direction as the drum.