A developing apparatus

Abstract: A developing apparatus comprises a developing roller which conveys developer on the surface thereof by rotation in a predetermined direction, the developer being conveyed thereon to develop a latent image formed on an image-holding means. A supply roller rotates keeping contact with the developing roller and by its rotation the developer is supplied to the developing roller A regulating member regulates the amount of the developer to be conveyed on the surface of the developing roller. As a result, the supply roller is so disposed that the axis thereof is positioned lower than that of the developing roller while the top thereof is also positioned lower than that of the developing roller.

Description: The present invention relates to a developing apparatus which is used in an electrophotographic copying machine or the like. A known kind of developing apparatus comprises: a developing roller, mounted for rotation in a predetermined direction about its central axis, for conveying a layer of developer to an image-holding means, thereby to develop a latent image formed on the said image-holding means, a supply roller, mounted for rotation about its central axis, which axis is parallel to that of the said developing roller, the two rollers being maintained in contact with one another so that, when the developing roller rotates in the said predetermined direction, developer in a space defined between the two rollers, above their mutually-contacting surface regions, is conveyed by the said developing roller upwardly from the said space to the top of that roller and thence to the said image-holding means, and a regulating member extending adjacent to an upper surface region of the developing roller so as to restrict the thickness of the said layer of developer conveyed by the developing roller to the said image-holding means. Such an apparatus will be referred to hereinafter as an apparatus of the aforesaid kind. Japanese Laid-Open Patent Publication No. 61-267771 describes one example of an apparatus of the aforesaid kind. In this example the supply roller is higher than the developing roller and rotates in the direction opposite to that of the developing roller. In use of such a developing apparatus it is found that developer kept back by the said regulating member, so as to restrict the thickness of the said layer of developer, tends to accumulate on an upper region of the developing roller, and this accumulated developer may collect into a lump and block the desired flow of the developer. An object of the present invention is to reduce this tendency, and the associated danger of developer blockage, in a developing apparatus of the aforesaid kind. According to the present invention there is provided a developing apparatus of the aforesaid kind, characterised in that the said axis of the supply roller is positioned lower than the said axis of the developing roller, and the top of the said developing roller is higher than that of the said supply roller so that a plane that is tangential to the developer roller near the top thereof and is also tangential to the said supply roller near the top thereof is inclined at an angle between 20° and 40° to the horizontal, and in that the said supply roller also rotates in the said predetermined direction of rotation when the apparatus is in use, so that the said respective mutually-contacting surface regions of the two rollers move in opposite directions from one another and developer in the said space is conveyed by the said supply roller in the direction from the top of that roller towards the said developing roller. A developing apparatus embodying the present invention, as compared with a prior apparatus of the aforesaid kind, is found to suffer significantly less from the above-described problem of accumulation of developer kept back by the regulating member and the resulting danger of blockage of the desired flow of developer. Incidentally, JP 59-231560 describes a developing apparatus comprising a developing roller and a control roller mounted for rotation in the same direction about their respective central axes, the said control roller being lower than and parallel to the developing roller and the two rollers being maintained closely adjacent to one another so that respective mutually-adjacent surface regions thereof move in opposite directions from one another. However, this is not an apparatus of the aforesaid kind, the direction of rotation of the rollers being opposite to that required in an apparatus of the aforesaid kind. Thus, in the apparatus of JP 59-231560, developer in the space defined between the two rollers, above their said respective mutually-adjacent surface regions, tends to be conveyed by the said control roller away from the developing roller, and the developing roller conveys the developer downwards in that space. Furthermore, this prior apparatus (JP 59-231560) does not employ a regulating member as required by an apparatus of the aforesaid kind. Instead, the thickness of the layer of developer conveyed to the image-holding means is apparently dependent on such factors as pressure between the two rollers, their relative speeds of rotation, and their surface qualities, since the said layer emerges downwardly from between the two rollers. The emerging layer is initially conveyed downwardly by the developing roller to the bottom of that roller, and thence upwardly to the image-forming means. Thus the principles of operation of this prior apparatus are markedly different from those of an apparatus of the aforesaid kind, and it is not readily apparent that it will suffer from similar problems. Reference will now be made, by way of example, to the accompanying drawing which shows a diagrammatic sectional view of a developing apparatus embodying the present invention. The illustrated developing apparatus 1 serves to develop an electrostatic latent image, formed on a photosensitive drum 3 that serves as an image-holding means and rotates in the direction shown by arrow A. The apparatus comprises a developing roller 7 facing the photosensitive drum 3, and a supply roller 11 disposed in contact with the developing roller 7. It will be appreciated that the respective central axes (5, 9) of the developing roller and the supply roller are parallel to one another. As seen in the drawing, the developing roller 7 rotates anticlockwise about its central axis (5) so that the surface of the roller conveys developer T, in the space defined between the two rollers and above their mutually-contacting surface regions, upwardly to the top of that roller (7). From there the roller 7 conveys a layer of the developer downward to develop the latent image on the drum 3. The supply roller 11 rotates anticlockwise about its central axis (9) so that its surface conveys developer, in the said space, in the direction from the top of the supply roller 11 towards the developing roller 7. A regulating member 15 extends adjacent to an upper surface region of the developing roller 7, so as to restrict the thickness of the layer of developer conveyed, on the surface of the developing roller 7, downwardly towards the drum 3. The developing roller 7, which may be made of stainless steel coated with silicone resin, rotates in the direction (shown by arrow B) opposite to that (shown by arrow A) of the photosensitive drum 3. Thus respective mutually-facing surface regions of the developing roller 7 and the photosensitive drum 3 move in the same direction. The supply roller 11, which may be made of urethane rubber coated with fluorocarbon resin, is so disposed that its axis is positioned lower than that of the developing roller 7 by a distance ℓ. The supply roller 11 rotates in the same direction (shown by arrow C) as the developing roller 7. Thus, the respective mutually-contacting surface regions of the supply roller 11 and the developing roller 7 move in opposite directions from one another. The top of the supply roller 11 is positioned lower than that of the developing roller 7 in such a manner that a plane, indicated by line 17, which touches the surfaces of both these rollers tangentially at respective points near the tops thereof makes an angle ϑ of approximately 20 to 40 degrees with the horizontal plane indicated by line 19. The regulating member 15 which regulates the amount of developer to be conveyed on the surface of the developing roller 7 is located slightly away from the top of the developing roller 7 in the direction of the photosensitive drum 3. The regulating member 15, which is made of phosphor bronze, urethane rubber, silicone rubber, or the like, regulates the amount of developer to be conveyed on the surface of the developing roller 7 so as to form a thin layer of the developer with a predetermined thickness on the surface of the developing roller 7. The developer to be formed in a thin layer on the surface of the developing roller 7 is charged through friction with the regulating member 15. In the developing apparatus 1 of the above construction, the developer is supplied onto the surface of the developing roller 7 by the rotation of the supply roller 11, and is conveyed on the surface of the developing roller 7 in the direction shown by arrow 20 to the regulating member 15. The regulating member 15 prevents further transportation of some of the developer being conveyed in the direction of arrow 20, so that an appropriate amount of the developer is delivered in the direction of the photosensitive drum 3. The developer delivered from the regulating member 15 is formed into a thin layer of a predetermined thickness to be conveyed on the surfaces of the developing roller 7. Developer T prevented by the regulating member 15 from being further conveyed on the surface of the developing roller 7 falls down by gravity and flows toward the supply roller 11 as shown by arrow 21. The developer T is stirred with other developer which is newly supplied by the supply roller 11 onto the surface of the developing roller 7 to be conveyed on the surface of the developing roller 7 toward the regulating member 15. This serves to reduce the possibility that developer kept back by the regulating member 15 will accumulate on the upper part of the developing roller 7 and thereby cause blocking of the developer flow.

Claims: A developing apparatus comprising a developing roller (7), mounted for rotation in a predetermined direction (B) about its central axis, for conveying a layer of developer (T) to an image-holding means (3), thereby to develop a latent image formed on the said image-holding means, a supply roller (11), mounted for rotation about its central axis, which axis is parallel to that of the said developing roller, the two rollers being maintained in contact with one another so that, when the developing roller rotates in the said predetermined direction, developer in a space defined between the two rollers, above their mutually-contacting surface regions, is conveyed by the said developing roller (7) upwardly from the said space to the top of that roller (7) and thence to the said image-holding means, and a regulating member (15) extending adjacent to an upper surface region of the developing roller (7) so as to restrict the thickness of the layer of developer conveyed by the said developing roller to the said image-holding means, characterised in that the said axis of the supply roller (11) is positioned lower than the said axis of the developing roller (7), and the top of the said developing roller (7) is higher than that of the said supply roller (11) so that a plane that is tangential to the developer roller near the top thereof and is also tangential to the said supply roller near the top thereof is inclined at an angle between 20° and 40° to the horizontal, and in that the said supply roller (11) also rotates in the said predetermined direction (B) of rotation when the apparatus is in use, so that the said respective mutually-contacting surface regions of the two rollers move in opposite directions from one another and developer in the said space is conveyed by the said supply roller (11) in the direction from the top of that roller (11) towards the said developing roller (7).

Inventors: HORI SETSUO, KUROYANAGI SATOSHI, SAKAE MASAHIKO, TSUJI KIKUNOSUKE, UEHARA YOSHIYUKI, WATANABE TAKESHI, HORI, SETSUO, KUROYANAGI, SATOSHI, SAKAE, MASAHIKO, TSUJI, KIKUNOSUKE, UEHARA, YOSHIYUKI, WATANABE, TAKESHI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: G03G15
IPC codes: G03G15