US3469911A

US3469911A - Electromagnetic pumping apparatus for use in electrophotography

Info

Publication number: US3469911A
Application number: US612684A
Authority: US
Inventors: Roger G Olden
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1967-01-30
Filing date: 1967-01-30
Publication date: 1969-09-30
Anticipated expiration: 1986-09-30

Description

Sept. 30, 1969 R. G. OLDEN 3,459,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY Filed Jan. 30, 1967 3 Sheets-Sheet 1 O W Y j; /4 I 16 '25 [I I I M v A/ro,e Wi 6 0w,

P 0, 1969 R. s. OLDEN 3,469,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY Filed Jan. 30, 1967 3 Sheets-Sheet 2 q I 14 u E 12 I 1 Q g I] X 5 g1! 41 1 2 I a j I I v v j I I m Fig I h I A I v Z4 1 IOQOO O'OOOI Sept. 30, 1969 R. G. OLDEN 3,469,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY Filed Jan. 30, 1967 3 Sheets-Sheet 3 v Mum/r52" v ,ggv' m/. 51 4 iaeu'r' United States Patent 3,469,911 ELECTRQMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY Roger G. Olden, Princeton, N.J., assignor to RCA Corporation, a corporation of Delaware Filed Jan. 30, 1967, Scr. No. 612,684 Int. Cl. G03g 15/02 US. Cl. 355-3 1 Claim ABSTRACT OF THE DISCLOSURE An electromagnetic pumping apparatus for transporting a powdered developer of iron and toner particles from a reservoir to a developing station in an electrostatic printing machine. The pump comprises a thin-walled tube of nonmagnetic material surrounded by a number of electric coils which are energized in sequence. As the coils are sequentially energized the developer is caused to move along the tube, from the reservoir to the developing station. The switching device that energizes the coils is such that two adjacent coils are always energized at any particular time and the last coil in the sequence is energized for a period shorter than that of the other coils.

Background of the invention This invention relates generally to improved means for circulating a magnetic developer material through an electrostatic printing machine or the like, and more particularly to improved apparatus for conveying magnetic developer material from a reservoir to a developing station in such machines.

In electrophotography it is common to apply a uniform electrostatic charge to the surface of a photoconductive layer. The charge on selected areas is then dissipated by exposing the surface to a light image. Finely divided developer particles which adhere to the charged areas of the surface by electrostatic attraction are applied to the resulting pattern of charges, rendering the pattern visible. A magnetic brush including a mixture of magnetic carrier particles and nonmagnetic developer particles is a con- Venient way to develop the electrostatic image. Permanent visible images can be obtained, for example, by using thermoplastic developer particles which can be heat fused to the photoconductive layer.

The powder developer used in many electrostatic printing machines consists of finely divided iron particles and thermoplastic toner particles. Methods presently used to transport this developer from a reservoir to the area where the electrostatic image is developed involve various problems. Mechanical conveyors cause dusty operation and consume a large amount of space. Screw feeds necessitate locating the reservoir close to the developing area, are limited in capacity and slow machine operation. Both of these methods of moving developer are mechanically complicated and therefore present maintenance problems. A gravity feed is mechanically simpler and consumes no power but it necessitates placing the developer reservoir high in the machine, and such an arrangement limits the size of the reservoir. This method also necessitates locating the reservoir close to the developing area.

Experience has shown that clear, crisp electrostatic prints can be obtained when the electromagnetic developer is continually supplied with fresh developer material. This can be done if the magnetic developer material is circulated from a fairly large reservoir, and the unused portion is returned to the reservoir to be recirculated.

Summary of the invention The invention comprises an electromagnetic pumping apparatus to transport magnetic developer material from a reservoir to a developing station in an electrostatic printing machine or the like. The novel magnetic pumping apparatus includes a hollow tube of a nonmagnetic material surrounded by a plurality of electric coils spaced along its length. When the coils are energized in succession by a rotating switch, the magnetic developer material is moved along the tube. One end of the tube extends into the reservoir of developer material and the other end is disposed adjacent to the electromagnetic developing area. The magnetic pump supplies a developer mixture consisting of iron and toner particles to a magnetic brush which applies the toner particles to an electrostatic image.

In one embodiment of the invention the magnetic pump deposits the developer material on a rotating brush which in turn brushes the developer particles onto the electrostatic image. An electromagnet mounted behind the electrostatic image completes the magnetic developer brush. In another embodiment the magnetic pump cascades the developer material directly across the electrostatic image which has an electromagnet mounted behind it to form a magnetic developing brush. After passing through the magnetic developing brush in both embodiments, excess developer material falls back into the reservoir where it can be recirculated by the magnetic pump.

The magnetic pump involves no moving parts thereby decreasing maintenance problems. It allows the reservoir to be placed in any convenient location within an electro static printing machine since it can transport the magnetic developer material to a developing area above the reservoir and at any distance from it. The pumping apparatus can be built with a sufiicient capacity to supply developer material at any practical rate to the magnetic developer. Dust is kept at a minimum since the powder developer moves through an enclosed tube. Since the invention can raise the developer mixture to a developing area at a higher level, gravity can be utilized to return excess developer to the reservoir allowing a circulation of the developer and the reuse of the iron particles. When a large reservoir is employed, individual particles of developer are rested between circulations for a far greater period of time than they are in use, so that the developer mixture is always fresh at the developing area. This freshness is important in producing clean, crisp prints from an electroprinting machine.

Brief description of the drawings FIG. 1 is a cross-sectional side view of the novel magnetic pumping apparatus with a partial schematic diagram of its accompanying electric circuit;

FIG. 2 is a cross-sectional side view of one embodiment of the invention; and

FIG. 3 is a cross-sectional view of a second embodiment of the invention.

Description of the preferred embodiments Referring to FIG. 1 of the drawings the novel magnetic pumping apparatus 8 comprises a thin-walled tube 10 of nonmagnetic material surrounded by a number of coils, such as

coils

12, 14 and 16. The intake end 18 of the tube 10 extends into a reservoir 20 of magnetic developer material. The exhaust end 22 of tube 10 is located adjacent to and in operative relation with a magnetic developer station. The tube '10 can be of any desired crosssectional configuration.

The coils, for example coils 12, 14 and 16, are spaced equally along the length of the tube 10. Each coil consists of a plurality of turns of electrically conducting wire. Spacers 24 separate the coils the desired distance and prevent electrical contact between them. The spacers 24 are constructed of electrically nonconducting material and may have any suitable shape. A nonmagnetic and nonconducting housing 25 encases the

coils

12, 14 and 16, thereby preventing iron particles from coming into contact with them. The housing 25 is a tube having a diameter which is large enough to enclose the magnetic pump tube and its surrounding coils. The housing has the same shape as tube 10 and is closed at

ends

18, 22 by a disk of nonconducting material 26 having an aperture 27 to allow access to tube 10. The

coils

12, 14 etc. are completely enclosed in the space between the walls of tube 10 and housing 25.

The reservoir may be fabricated from any material having suflicient structural strength. It can be made in any convenient shape but should be large enough to hold an adequate supply of developer material 28. Magnetic pump tube 10 with its surrounding coils -12, 14 and 16 and housing extends into reservoir 20 to a point near the bottom to insure that all of developer material 28 is periodically circulated through tube 10 to the remainder of the apparatus.

Coils

12, 14 and 16 are energized by a switch 30. The switch 30 has a number of fixed switch contacts 12a, 14a, for example, arranged in a circle around the circumference of the switch. The switch contacts are small metallic disks having terminals to which wires 31 are attached. The wires 31 link the fixed switch contacts 12a, 14a, etc. to the corresponding coils 12, 14, etc. that they energize. A rotating switch arm 32 is mounted on a shaft which extends through the center of the switch 30. A rotating contact 34 is attached to the end of the switch arm 32 so that contact 34 passes across fixed switch contacts 12a, 14a, etc. Rotating contact 34 is wide enough to engage two adjacent switch contacts, such as 12a and 14a, simulaneously. Fixed switch contact 16a is narrower than the other switch contacts 12a, 14a, etc. and is offset from the circle of switch contacts and placed closer to the center of switch 30 so that the rotating contact 34 does not engage it. A second rotating contact 36 is mounted on the rotating arm 32. Contact 36 is located closer to the center shaft of the switch 30 than the rotating contact 34 so that it will engage fixed contact 16a. Contact 36 is narrower than contact 34 so that fixed contact 16a is only engaged for a short time.

A source of electrical energy is connected to the rotating switch arm 32 so that the switch contacts 12a, 14a, etc. are energized as the contact 34 moves across them. Electrical energy is conducted from the fixed switch contacts through the wires 31 to the

coils

12, 14, etc. When the coil 12 is energized, a magnetic field is produced which draws a slug 40 of magnetic developer material into tube 10 and holds it at the center of the coil 12. Contact 34 on revolving arm 32 is wide enough to contact two adjacent switch contacts simultaneously so that the next coil on tube 10, coil 14, is energized before the magnetic field of coil 12 has collapsed and the slug 40 moves up the tube 10toward coil 14 rather than falling back toward the reservoir 20. As the rotating arm 32 moves across the other switch contacts in switch 30, the corresponding coils are energized and the resulting magnetic fields move the slug 40 of developer along tube 10. When the narrow contact 36 on rotating arm 32 engages contact 16a, coil 16, the last of the series of coils, is energized. Since both the revolving contact 36 and the switch contact 1611 are narrow, they touch for a short period of time and the coil 16 is only energized momentarily so that the slug 40 does not stop within its magnetic field but instead the slug 40 is ejected through discharge end 22 of tube 10. The magnetic pump 8 can deliver a continuous supply of magnetic developer material if a plurality of rotating arms are used in the switch 30.

A magnetic pump, similar to that shown in FIG. 1, was constructed having a tube diameter of inch and an over-all length of 8 inches. Twelve coils /2 inch in width 4 were arranged equidistantly along its length with each coil containing approximately 2500 turns of number 35 wire. A current of about .820 ma. flowed through the coils. The coils were energized successively by a rotating switch arm similar to that shown in FIG. 1. This device pumped a standard developer material, consisting of toner and iron particles, well, raising it about 6 inches vertically and ejecting it through a curved portion of the tubing as shown in FIG. 1.

FIG. 2 shows an embodiment of the invention which is utilized in an electrostatic printing machine. The intake end 18 of the magnetic pump 8 extends into the reservoir 20 of magnetic developer material 28. The discharge end 22 of the tube 10 is disposed adjacent to a rotating brush 42. A trough 44 attached to the discharge end 22 of the tube 10 extends partially around the rotating brush 42. The trough 44 is placed close to the surface of the rotating brush 42 and conforms closely to the shape of the brush. The cross-sectional configuration of tube 10 can be made to correspond to the cross-sectional area of the rotating brush 42. The shape of the entire magnetic pumping apparatus 8 is made to conform to the space available in the electrostatic printing machine but the magnetic pumping apparatus is otherwise the same as described above in reference to FIG. 1. The brush 42 consists of a solid central disk of suitable material with a shaft through its center to allow rotation. The circumference of the brush 42 is covered with a nonconducting material such as nylon velour. The brush 42 rotates at a speed about one half the speed at which the paper 46 moves across it in the same direction as the paper is moving.

Magnet 48 is an electromagnet which is mounted closely behind a platen 50 and directly above the brush 42. The poles of magnet 48 form a magnetic developing brush with the rotating brush 42. The platen 50 consists of a fiat metal plate placed between the paper 46 and the electromagnets 48 and 51.

Brushes

52 and 54 are smaller than brush 42 but are otherwise similar in construction. The brush 52 rotates in a counterclockwise direction while brush 54 rotates clockwise in a direction opposite to the motion of the paper. The second electromagnet 51 which is similar to magnet 48 is mounted behind the platen 50 and above brushes 52 and 54 so that it forms two additional magnetic brushes with

brushes

52 and 54.

Magnetic pump 8 transports magnetic developer material 28 from the reservoir 20 and deposits it on the rotating brush 42. The trough 44 prevents the developer from falling back into the reservoir 20 and causes it to be picked up by the brush 42. As the brush rotates, the powdered developer is brushed against the paper which has an electrostatic image on the side facing the brush 42. The platen 50 holds the paper flat and insures uniform contact between the paper and the rotating brush so that developer is spread across all areas of the electrostatic image. Electromagnet 48 completes a magnetic developing brush with rotating brush 42 and attracts the magnetic developer to the paper 46 increasing the probability that toner particles will adhere to the charged areas of the electrostatic image.

After the paper has passed through this first magnetic brush, the magnetic field decreases at point 58 and the excess developer is free to fall back into the reservoir 20. The rotation of brush 42 also tends to remove excess developer from the paper at the limit of the magnetic field of magnet 48.

Brushes

52 and 54 perform a dual function. Together with electromagnet 51 they form a second magnetic developing brush to further fix the image but they also serve as cleanup brushes to remove excess developer from the paper 46. This is especially the function of the brush 54 which rotates in a direction opposite to that of the

brushes

42 and 52 and opposite to the direction in which the paper is moving. Excess developer which is brushed from the page at

points

60 and 62 also falls back to the reservoir 20.

The invention provides a continuous circulation of developer material through the electrostatic printing machine. When the reservoir 20 is large, the time during which individual particles of developer are used becomes small and a supply of fresh developer is always available to the magnetic developing brush.

FIG. 3 shows a second embodiment in which the invention is utilized in an electrostatic printing machine. The electromagnetic pump is similar in construction to that described in FIG. 1. A continuous web of paper 46, which has been treated with a chemical such as zinc oxide to make it photosensitive, it passed through a corona generator 64 and is then exposed to a light image 68. Various methods and apparatus for corona generation and photographic exposure are known in the art and these steps in the electroprinting process are not part of the subject invention.

The paper 46 is passed around two rollers 70 and 72. These rollers are cylinders constructed of any suitable material with shafts through their centers allowing them to rotate. The rollers 70 and 72 are mounted so that the paper surface will slope downward from roller 70 to roller 72. An electromagnet 74 similar to those in FIG. 2 is mounted behind the paper 46 and about midway between the rollers 70 and 72. After the paper has passed around roller 72 the side having the electrostatic image moves across a heater 76. The heater is not a part of the invention and various types are known in the art so a description will not be given.

A continuous web of photosensitive paper is passed through the corona generator 64 which gives it a uniform electrical charge. It is then exposed to a light image by lens 68 which dissipates the electrical charge on the exposed areas of the paper. The paper then passes over the roller 70.

The magnetic pump 8 transports magnetic developer from the intake end 18 of tube 10 to its discharge end 22. The discharge end 22 is disposed so that the magnetic developer is ejected onto the sloping surface of the paper at a point slightly above the electromagnet 74 and below roller 70. The developer particles cascade down the sloping surface of the paper 46 and across the electrostatic image. The combination of the developer particles 80 moving across the paper and the electromagnet 74 mounted behind the paper forms a magnetic developing brush which causes the thermoplastic toner particles to adhere to the electrostatic image.

Excess magnetic developer moves down the sloping paper surface and falls back into reservoir 20 at point 82 in the area of the roller 72. Since the side of the paper having the electrostatic image is facing downward after passing around the roller 72, excess magnetic developer will fall from the electrostatic image into the reservoir 20.

Finally, the developed electrostatic image passes over heater 76 which melts the thermoplastic toner particles and fuses them to the paper surface to form a light-fast image.

In this embodiment as in the previous one, the invention provides a continuous circulation of the magnetic developer through the electrophotographic machine and insures a continuing fresh supply of developer material to the magnetic brush.

What is claimed is:

1. In electrostatic printing apparatus including means for providing an electrostatic image on a recording medium, electromagnetic developing means for said image and a reservoir of electromagnetic developer material, the improvement comprising, electromagnetic pumping means for transporting a part of said developer material from said reservoir to said developing means, means for removing the unused portion of said developer material from said electrostatic image, said electromagnetic pumping means including a tube of nonmagnetic material, a plurality of electric coils surrounding said tube, means for energizing said coils in succession, the intake end of said tube extending into said reservoir of electromagnetic developer material and the discharge end adjacent to, and in operative relation with, said electromagnetic developing means, and said means for energizing said coils in succession comprising switching means which also momentarily energizes two adjacent ones of said coils and which energizes the last one of said successively energized coils for a shorter time than the others of said coils.

References Cited UNITED STATES PATENTS NORTON ANSHER, Primary Examiner D. B. WEBSTER, Assistant Examiner