JPH02748Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to the improvement of a long permanent magnet roll for electrostatic development of 400 mm or more that performs magnetic brush development. The present invention relates to a permanent magnet roll for electrostatic development which has a structure and prevents uneven development by alleviating a decrease in magnetic flux density at a joint portion.

In electrostatic transfer type electrophotographic copying machines, various permanent magnet rolls for electrostatic development (hereinafter referred to as magnet rolls) that prevent uneven development have been proposed. In both cases, the permanent magnets that make up the magnet roll are formed as a single piece of magnet with no seams in the axial direction, and those that use rubber magnets, resin magnets, or cylindrical hard ferrite magnets that are made using a rubber press method. , there is one that uses a monolithic rectangular rod-shaped anisotropic ferrite magnet that is seamless in the axial direction.

However, rubber magnets and the like have low magnetic properties and are unsuitable especially when high coercive force is required, and rubber press magnets are difficult to reduce in weight and cannot be called efficient magnet rolls. Furthermore, the monolithic square bar type anisotropic ferrite magnet had a maximum length of about 400 mm due to its manufacturing method. In large copying machines that require a long magnet roll of 400 mm or more, for example, the only way to construct a long permanent magnet is by joining multiple block magnets, and this is due to the inevitable air gaps at the joints of the magnets. The unevenness of development had become a major problem.

This idea is aimed at a permanent magnet roll for electrostatic development with a length of 400 mm or more.The long permanent magnet is composed of multiple block magnets, and the reduction in magnetic flux density at the joint is alleviated to reduce uneven development. The purpose is a permanent magnet roll for electrostatic development that prevents

In other words, this invention is an electrostatic development system in which a magnet assembly in which a plurality of long integral permanent magnets are arranged in the axial direction at radial positions from the shaft center is built in a non-magnetic cylindrical sleeve so as to be relatively freely rotatable. A permanent magnet roll for electrostatic development, characterized in that the permanent magnet roll is composed of a plurality of block magnets, each of which is a long integral permanent magnet, and the joining end surface of the block magnets is an inclined surface whose thickness decreases temporarily in the axial direction. It is.

In this invention, the permanent magnet used in the magnet structure housed in a long magnet roll is made longer by joining a plurality of, for example, square bar-shaped block magnets in the axial direction of the magnet structure. The joint end face of the block magnet is made into an inclined end face whose thickness in the axial direction decreases temporarily at an angle θ, and this is combined with a block magnet having an equivalent inclined end face to form a joint part, and a long piece integrated into a square rod shape is formed. By assembling the permanent magnet into a permanent magnet, the decrease in magnetic flux density at the joint can be minimized. This angle θ may be appropriately selected in consideration of the dimensions and magnetic properties of the block magnet, the required length of the integral permanent magnet, the number of block magnets, and the like. Further, the same effect can be obtained regardless of the direction of the inclined surface of the joint in the axial direction.

Examples of this invention will be described below based on the drawings. FIG. 1 is a perspective view of a magnet structure according to this invention, and FIG. 2 is a perspective view of an elongated integral permanent magnet according to this invention.

The magnet structure 1 includes a magnet holding member 2 made of a cylinder made of synthetic resin, a metal fitted with an insert mold at the axis center of both end faces of the magnet holding member 2, here a rotating support shaft 3 made of a non-magnetic metal, and a magnet holding member 2. It is comprised of long permanent magnets 4, 5, and 6 in the form of integral rectangular rods that are fitted into three axial grooves provided on the outer circumferential surface of the member 2.

The long permanent magnets 4, 5, and 6 are anisotropic ferrite magnets with dimensions of 640 mm length x 12 mm width x 15 mm height.
Each block magnet is composed of three block magnets, and the inclined end faces constituting the joints of the block magnets are each at an angle of 45°, and the thickness of the joints is gradually reduced in the axial direction.

A magnet roll was made by housing and supporting the magnet structure constructed above in a non-magnetic sleeve, and the magnetic flux density on the sleeve surface was measured and found to be 1000.
Obtained a value greater than Gauss.

In addition, when three block magnets made of rectangular parallelepipeds were joined with their joint surfaces perpendicular to the axial direction to have the same dimensions as the long permanent magnet 4 described above, and the magnetic flux density at the joint was measured, it was found that the magnetic flux density was 15% or more. Although a decrease in magnetic flux density was observed, in the case of the long permanent magnet 4 according to this invention, the decrease was only 2 to 3%.

Furthermore, a second magnet with one of the two joining surfaces of the long permanent magnet 4 having an inclined surface angle of 45 degrees in the opposite direction.
An elongated permanent magnet 7 in the form of a solid rectangular bar as shown in the figure was manufactured, but the decrease in magnetic flux density at the joint surface of the block magnet was exactly the same as that of the elongated permanent magnet 4 in Fig. 1.

[Brief explanation of drawings]

Figure 1 is a perspective view of the magnet structure according to this invention.
FIG. 2 is a perspective view of a long integral permanent magnet according to this invention. 1... Magnet structure, 2... Magnet holding member, 3...
... Rotating shaft, 4, 5, 6, 7... Long permanent magnet.

Claims (1)

[Scope of utility model registration request] In a permanent magnet roll for electrostatic development, a permanent magnet roll for electrostatic development has a relatively rotatable magnet structure in which a plurality of long integrated permanent magnets are arranged in the axial direction at radial positions from the shaft center within a non-magnetic cylindrical sleeve. 1. A permanent magnet roll for electrostatic development, characterized in that the integral permanent magnet is composed of a plurality of block magnets, and the joining end surfaces of the block magnets are inclined surfaces whose thickness gradually decreases in the axial direction.