JP2005107458A - Magnet roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet roller capable of suppressing an adverse effect on an image at an end of the magnet roller of a short shaft insertion type formed by press-fitting at least one shaft into a hole section disposed at the end surface of a body section by suppressing the increase of the magnetic force at the end. <P>SOLUTION: The wall thickness in the body section around the hole section of the magnet roller is made smallest in the circumferential position corresponding to the magnetic pole of the maximum magnetic force. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention comprises a cylindrical main body portion made of a resin material in which magnetic powder is mixed and dispersed in a resin binder, and respective shaft portions disposed on both end faces of the main body portion, and at least one of the shaft portions is The present invention relates to a magnet roller that is press-fitted into a hole provided in an end surface of a main body, and particularly relates to an improved magnetic force distribution in the longitudinal direction.

  A magnet formed by a resin magnet in a rotating sleeve as a developing method for visualizing an electrostatic latent image on a latent image holding body such as a photosensitive drum in an electrophotographic apparatus such as a copying machine or a printer, or an electrostatic recording apparatus. A roller is provided, and the toner carried on the surface of the sleeve is caused to fly onto the latent image holding body by the magnetic characteristics of the magnet roller, and the toner is supplied to the surface of the latent image holding body by a jumping phenomenon to visualize the electrostatic latent image. Development methods are known.

  When manufacturing the magnet roller, a resin material in which a magnetic powder such as ferrite is mixed and dispersed in a binder of a thermoplastic resin such as nylon or polypropylene is injected into the magnetic field of the mold cavity, and the magnetic powder is injected. It is widely practiced to produce a cylindrical magnet roller main body portion by orientation.

  In addition, regarding the formation of the shaft portion, both the shaft portion and the shaft portion are formed by injection molding at the same time, a method of forming a so-called shaft-integrated magnet roller, and both the shafts are composed of a single metal shaft. The resin material is injected into a cavity into which a shaft is inserted to form a so-called magnet roller with a gold shaft, and a main body having a hole formed at least at one end of the main body is injection-molded. A method of forming by inserting a shaft is known, and this short shaft insertion method has a feature that a highly accurate shaft portion can be obtained at a low cost (see, for example, Patent Document 1).

  On the other hand, the axial magnetic force distribution of the magnetic poles of the magnet roller is preferably as uniform as possible for image formation by a printer or a copier. Generally, the magnetic force at the end of the magnet roller is the magnetic pole adjacent to the circumferential direction. In addition to the magnetic lines of force from the magnetic field lines, the magnetic field lines from the axial direction end also tend to increase, so that there is a tendency to increase compared to the central part in the axial direction. It was. FIG. 1 is an axial magnetic force distribution diagram of the magnetic poles for explaining this problem. The horizontal axis represents the position in the length direction of the magnet roller, and the position from the center. The vertical axis represents the magnetic force of the magnetic pole of the magnet roller at a predetermined distance, for example, 1 mm, radially outward from the magnetic pole. This is expressed by the magnitude of the magnetic flux density in the radial direction at a distant position.

In FIG. 1, when the magnetic force effective range in which the magnetic force of the magnet roll affects the image is a distance d ₀ from the center in the length direction, and the magnetic force at the center position is Fmin, the magnetic force at the position d ₀ is Fmax. Within this range, the change (variation) of the magnetic force in the length direction of the magnetic force distribution G is (Fmax−Fmin). In order to suppress the influence on the image due to the magnetic force variation, it is necessary to suppress the increase of the end magnetic force as the magnetic distribution G ′ and set the magnetic force at the position d ₀ to Fmax ′.
Japanese Patent Laid-Open No. 7-230216

The present invention has been made in view of such problems, and in a short shaft insertion type magnet roller in which at least one shaft portion is press-fitted into a hole portion provided in an end surface of a main body portion,
Provided is a magnet roller that can suppress an increase in end magnetic force and suppress an adverse effect on an image at the end.

(1) The present invention comprises a cylindrical main body portion made of a resin material in which magnetic powder is mixed and dispersed in a resin binder, and respective shaft portions disposed on both end faces of the main body portion, and at least one shaft The part is press-fitted into a hole provided in the end surface of the main body, and in the magnet roller in which a plurality of magnetic poles are arranged along the circumferential direction,
The magnet roller is configured such that the thickness of the main body around the hole is minimized at a circumferential position corresponding to the magnetic pole having the maximum magnetic force.

  (2) In the present invention, in (1), the cross-sectional shape of the hole is a D-shape in which a part of the circle is cut out at only one place, and the center of the circle is matched with the central axis of the main body. This is a magnet roller in which the cut surface is spaced apart from the circumferential position corresponding to the magnetic pole having the maximum magnetic force.

  (3) In the present invention, in (1), the thickness of the main body around the hole is small at a circumferential position corresponding to a magnetic pole having a large magnetic force, and is increased at a circumferential position of a magnetic pole having a small magnetic force. It is a magnet roller.

  When trying to suppress an increase in end magnetic force at a predetermined circumferential position, reducing the outer diameter of the magnet roller end at this circumferential position increases the distance between the magnet roller surface and the magnetic force measurement position, It is known that the increase in magnetic force can be suppressed, but besides this, the magnetic field lines coming from the end can be reduced by engraving the end face of the main body at this circumferential position, At that time, if the magnetic force of the magnetic pole is strong, more magnetic lines of magnetic force will come in, so the stronger the magnetic force, the greater the reduction effect by this method. It turned out that the reduction effect is so large that the main-body part thickness from the magnet roller surface becomes thin.

  According to the magnet roller of the present invention, the thickness of the main body around the hole is minimized at the circumferential position corresponding to the magnetic pole having the maximum magnetic force. In this case, it is possible to suppress an increase in the end portion magnetic force by suppressing the wraparound of the magnetic lines of force from the end portion.

  Further, when the cross-sectional shape of the hole is a D-shape in which a part of the circle is cut out at only one place, the D-cut surface that is a cut-out flat portion corresponds to the magnetic pole having the maximum magnetic force. In addition to preventing relative rotation of the short shaft inserted into the hole by arranging it apart from the position, in the magnetic pole having the maximum magnetic force, the magnetic lines of force from the thick part corresponding to the D-cut surface are circulated. It is possible to suppress the increase in end magnetic force.

  In addition, by increasing the thickness of the main body around the hole at the circumferential position corresponding to the magnetic pole having a large magnetic force and increasing the thickness at the circumferential position of the magnetic pole having a small magnetic force, While greatly suppressing this, it is possible to suppress the increase / decrease in the magnetic force at the ends of all the magnetic poles in a well-balanced manner by suppressing the increase in the magnetic force at the end portions only slightly.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a perspective view showing the magnet roller of this embodiment in a state before assembling one shaft portion. The magnet roller 1 includes a cylindrical main body 2 made of a resin material in which magnetic powder is mixed and dispersed in a resin binder, and shafts 3 and 4 disposed on both end faces 2a and 2b of the main body 2, respectively. The at least one shaft portion 3 is press-fitted into a hole portion 5 provided in the end surface 2 a of the main body portion 2.

  The cross-sectional shape of the hole 5 is a D-shape in which a part of the circle is cut out, the center of the circle is aligned with the center axis of the main body, the D-cut surface 5a is provided, and the D-cut surface 5a is connected to the shaft 3 Is inserted into the hole 5 so as to function as a rotation stop means for preventing the relative rotation between them.

  FIG. 3 is a magnetic force distribution diagram showing the distribution of magnetic force in the circumferential direction of the magnet roller 1 corresponding to the D-shaped hole by the petal projection method. The magnet roller 1 has four magnetic poles, N1, S1, N2, and S2. Among these, N1 is a magnetic pole having the maximum magnetic force, that is, the peak magnetic force N1max of N1 is different from that of the other magnetic poles. It means that it is larger than any of the peak magnetic forces. At this time, the body thickness t around the hole 5 is configured to be minimum at the circumferential position corresponding to the magnetic pole N1. Actually, in the example shown in FIG. 3, the magnetic pole N1 is disposed directly opposite to the D-cut surface 5a, and the main body around the hole 5 except the circumferential portion corresponding to the D-cut surface 5a. The wall thickness t is the same, but in any case, the wall thickness t at the circumferential position corresponding to the magnetic pole N1 is the smallest.

  FIG. 4 is a side view showing the shape of the hole of the magnet roller of another embodiment having the same magnetic force distribution as that shown in FIG. 3 and having the shape of the hole at the end different from that of FIG. The magnetic force distribution is also shown. The cross-sectional shape of the hole 15 of the magnet roller 11 is a shape in which three circles are cut out. At the circumferential position corresponding to the magnetic pole N1 having the highest magnetic force, there is no notch and the arc 15a is the outer peripheral surface of the hole. The wall thickness t1 around the hole 15 is the smallest here.

  The S1 pole and the S2 pole are magnetic poles having substantially the same magnetic force, and are lower than the N1 pole but higher than the N2 pole. The circumferential positions of the hole 15 corresponding to these magnetic poles are notched to form cut surfaces 15b and 15c, and the thicknesses t2 and t3 here are larger than t1. The N2 pole has a lower magnetic force than any of the poles, and the hole 15 is deeply cut out at a circumferential position corresponding to the N2 pole to form a cut surface 15d, where the wall thickness t4 is t1 to t3. Greater than either. In this way, by increasing or decreasing the thickness according to the magnitude of the magnetic force of the magnetic pole, it is possible to configure the magnet roller 11 that hardly increases or decreases the magnetic force with the central portion in the axial direction in all the poles.

  As an example, the magnet roller 1 having the circumferential magnetic force distribution shown in FIG. 3 and a D-shaped hole 5 having a D-cut surface 5a on the opposite side of the magnetic pole having the maximum magnetic force in the magnetic force distribution is used as an example. A magnet roller having a distribution and having the same outer shape, that is, a magnet roller in which the shaft portion is integrally injection-molded with the same material as that of the main body portion, has the same magnetic force distribution and D-shape as in Comparative Example 1. Although the hole 5 and the magnet roller formed by matching the circumferential position of the magnetic pole N1 having the maximum magnetic force with the position of the D-cut surface 5a of the hole 5 are referred to as Comparative Example 2, Examples, Comparative Example 1, In addition, the increase amount of the end magnetic force with respect to the central magnetic force was compared between the magnetic pole N1 having the maximum magnetic force and the magnetic pole N2 positioned almost diagonally to the magnetic pole N1 in Comparative Example 2. Table 1 shows a comparison result corresponding to the magnetic pole N1, and Table 2 shows a comparison result corresponding to the magnetic pole N2.

In Table 1, Fmax and Fmin respectively indicate the magnetic force in the effective magnetic field range d ₀ in FIG. 1 and the magnetic force at the center in the length direction. In Examples, Comparative Example 1 and Comparative Example 2, the outer diameter of the magnet roller is 16 mm, the shaft radius r ₁ is 4 mm, and the distance d ₁ from the rotation center of the D-cut surface 5a is 2 mm. The same applies to the shaft-integrated magnet roller of Comparative Example 1. Moreover, the depth of the hole part 5 in an Example and the comparative example 2 is 5 mm.

  As is clear from Tables 1 and 2, the effect of suppressing the increase in the end magnetic force is small just by providing a hole as in Comparative Example 2 with respect to Comparative Example 1, but the magnetic pole with the maximum magnetic force is D The increase rate can be largely suppressed by disposing it on the opposite side of the D-cut surface away from the cut surface, and the effect is particularly remarkable with a strong magnetic pole.

  According to the magnet roller of the present invention, the thickness of the main body around the hole is minimized at the circumferential position corresponding to the magnetic pole having the maximum magnetic force. In the magnetic pole, an increase in the end magnetic force can be suppressed by suppressing the wraparound of the magnetic lines of force from the end.

It is a perspective view which shows the axial direction magnetic force distribution of a magnet roller. It is a perspective view which shows the magnet roller of embodiment which concerns on this invention. It is a magnetic force distribution figure which shows the circumferential direction magnetic force distribution of a magnet roller. It is a front view of the hole of the magnet roller of other embodiments.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnet roller 2 Main part 2a, 2b End face of main part 3 Axis 4 Axis 5 Hole 5a D cut surface 11 Magnet roller 5 Hole 5a Arc 5b-5d Cut surface

Claims (3)

A cylindrical main body portion made of a resin material in which magnetic powder is mixed and dispersed in a resin binder, and respective shaft portions disposed on both end surfaces of the main body portion. At least one of the shaft portions is an end surface of the main body portion. In a magnet roller that is press-fitted into a hole provided in a plurality of magnetic poles arranged along the circumferential direction,
A magnet roller configured such that the thickness of the main body around the hole is minimized at a circumferential position corresponding to the magnetic pole having the maximum magnetic force.   The cross-sectional shape of the hole is a D-shape in which a part of the circle is cut out at only one place, the center of the circle is matched with the central axis of the main body, and the D-cut surface is a circumference corresponding to the magnetic pole having the maximum magnetic force. The magnet roller according to claim 1, wherein the magnet roller is disposed apart from the directional position.   2. The magnet roller according to claim 1, wherein the thickness of the main body around the hole is small at a circumferential position corresponding to a magnetic pole having a large magnetic force and large at a circumferential position of the magnetic pole having a small magnetic force.

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