Patent Application
20080112732
This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for dispensing magnetic developer containing marking particles onto a developer roller of a magnetic brush development system.
In general, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is imagewise exposed to light to discharge selected portions of the charged photoconductive surface and create an electrostatic latent image on the photoconductive surface. The latent image is developed by bringing developer material into contact therewith. Two-component developer material comprises toner particles adhering triboelectrically to carrier granules. The carrier particles are usually magnetic. The toner particles are attracted from the carrier granules to form a powder image on the photoconductive member. The powder image is subsequently transferred to a receiver and heated to permanently affix the powder image to the receiver. With the advent of single-component development, magnetic toner particles are employed to develop the latent image. Generally, these toner particles are dispensed directly onto the developer roller, which transports the magnetic toner particles to the latent image recorded on the photoconductive surface. In this way, a single component developer material is employed to develop the latent image.
Commonly assigned U.S. Pat. No. 6,385,415, issued on May 7, 2002, in the names of Hilbert et al. discloses a magnetic brush development station that includes a reservoir of developer material. A transport mechanism brings the developer material into the field of a plurality of magnets within a sleeve (commonly referred to as a developer roller, toning roller, or magnetic brush). The transport mechanism includes a transport roller (also known as a feed roller) located between the reservoir and the developer roller. The transport roller includes a rotatable, non-magnetic tubular member and a magnet or magnets fixedly disposed interiorly of tubular member to attract the developer material from the reservoir to the transport roller using the force on the developer resulting from the magnetic field of the magnets inside the transport roller.
In early designs, the magnets of the transport roller included three alternating magnetic poles in the region of the transport roller adjacent to the reservoir, and the magnetic flux lines from the North to the South poles attracted the developer material to the transport roller. However, it was quickly determined that the three poles did not exhibit sufficient magnetism to pull enough developer material from the reservoir. Subsequently, the design was changed to include four alternating magnetic poles in the region of the transport roller adjacent to the reservoir, and the magnetic pull was sufficient for commercial use.
Although four alternating magnetic poles in the region of the transport roller adjacent to the reservoir caused sufficient developer material to adhere to the transport roller, much of that material was not being transferred to the developer roller and was being returned to the reservoir region as the non-magnetic tubular member continued to rotate. In accordance with the present invention, it has been determined that the use of four alternating magnetic poles in the region of the transport roller adjacent to the reservoir results in the existence of undesirable magnetic flux lines extending around the transport roller across the region of the developer roller. These flux lines resulted in a substantial amount of developer material sticking to the transport roller and not being transferred to the development roller.
Even though the four alternating magnetic poles were known to provide sufficient magnetism to pull enough developer material from the reservoir, by the present invention additional magnetic poles are supplied so that there is an odd number of alternating magnetic poles in the region of the transport roller adjacent to the reservoir. By so doing, it is assured that the magnetic poles on the ends of the assembly of poles are of the same polarity. This prevents the existence of a magnetic flux line extending around the transport roller across the region of the developer roller. When these flux lines are eliminated, the amount of developer material sticking to the transport roller and not being transferred to the development roller is greatly reduced, thereby increasing the efficiency of the development station.
Accordingly, it is a feature of the present invention to provide a development station for a reproduction apparatus that includes a housing forming a reservoir, a developer roller for delivering developer material to a development zone, and a transport roller for moving developer material from said reservoir to said developer roller. The transport roller includes a rotating shell and a stationary core having an odd number of alternating North and South magnetic poles, wherein the number of magnetic poles is at least five. In one preferred embodiment of the present invention, the transport roller consists of five alternating North and South magnetic poles.
Referring now to the accompanying drawings,
As described above, the developer material may be single-component or two-component, but in this illustrative embodiment, it is two-component. As such, a plurality of augers 28 are provided, and have suitable mixing paddles for stirring the developer material within a reservoir 12a of housing 12. A developer roller 14, mounted within development station housing 12, includes a rotating (counterclockwise in
A quantity of developer material is delivered by a transport roller 30 from the reservoir portion of housing 12 to developer roller 14. The amount of developer material delivered to development zone 20 is controlled by a metering skive 22 positioned parallel to the longitudinal axis of developer roller 14, at a location upstream in the direction of shell rotation prior to development zone 20. To provide for selective movement of the metering skive 22, as shown in
A conventional transport roller 30 is shown in
Although four alternating magnetic poles 40, 41, 42 and 43 cause sufficient developer material to adhere to the transport roller, the magnetic force from flux field 47 detrimentally tends to hold a portion of the developer material on the transport roller rather than allow it to be attracted onto development roller shell 18 by forces associated with the magnetic field of core magnet 16. That portion of the developer material is returned to the reservoir 12a as non-magnetic tubular member 34 continues to rotate.
Referring to
Several experiments were conducted comparing the efficiency of transfer rollers having five magnetic poles to conventional transfer rollers having four magnetic poles. Various parameters were varied during the experiments to ensure that the results were universal regardless of the set up of the test apparatus. Such parameters included mixer speed, transport roller speed, core speed of the developer roller, and spacing between the various elements. In every experiment run, the transfer roller having five magnetic poles transferred about 30% more developer mix to the developer roller than was transferred by the transfer roller having only four magnetic poles.
Even though the illustrative embodiment includes five alternating magnetic poles in the region of the transport roller adjacent to the reservoir, the benefits obtained by present invention are extendable to any odd number of magnetic poles greater than three. Three magnetic poles are not considered to be useful because three poles do not exhibit sufficient magnetism to pull enough developer material from reservoir 12a.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
