Small sized fixing device capable of securing a heat generation area, and image forming apparatus equipped therewith

A fixing device comprising:

• (a) a cylindrical fixing roller to be heated;
• (b) a coil supporting member disposed along an inside of the fixing roller;
• (c) a heat applying coil formed by winding a wire around a circumference of the coil supporting member for heating the fixing roller by inducing an induced current in the fixing roller;
• and
• (d) a pressing roller for forming a nip portion with the fixing roller, and for conveying a transfer material which is gripped by the nip portion between the fixing roller and the pressing roller, so that a toner image formed on the transfer material is fixed by heat energy from the fixing roller, wherein the heat applying coil is formed by winding the wire in a longitudinal direction of the coil supporting member so as to have a shape which has parts lying parallel to the longitudinal direction of the coil supporting member and parts lying along the circumference of the coil supporting member, and so that a winding density of the parts lying along the circumference of the coil supporting member is made higher than a winding density of the parts lying parallel to the longitudinal direction of the coil supporting member;
• and
• wherein a number of stacked layers of the heat applying coil are different between the parts lying parallel to the longitudinal direction of the coil supporting member and the parts lying along the circumference of the coil supporting member, and the number of stacked layers in the parts lying along the circumference of the coil supporting member is made greater than the number of stacked layers in the parts lying. parallel to the longitudinal direction of the coil supporting member.

An image forming apparatus in which a uniformly charged photoreceptor drum is imagewise exposed, a latent image is formed on the photoreceptor drum, the latent image is developed to form a toner image, and the toner image is transferred onto a transfer material and fixed thereon, the image forming apparatus including a fixing device comprising:

• (a) a cylindrical fixing roller to be heated;
• (b) a coil supporting member disposed along an inside of the fixing roller;
• (c) a heat applying coil formed by winding a wire around a circumference of the coil supporting member for heating the fixing roller by inducing an induced current in the fixing roller;
• and
• (d) a pressing roller for forming a nip portion with the fixing roller, and for conveying a transfer material which is gripped by the nip portion between the fixing roller and the pressing roller, so that a toner image formed on the transfer material is fixed by heat energy from the fixing roller, wherein the heat applying coil is formed by winding the wire in a longitudinal direction of the coil supporting member so as to have a shape which has parts lying parallel to the longitudinal direction of the coil supporting member and parts lying along the circumference of the coil supporting member, and so that a winding density of the parts lying along the circumference of the coil supporting member is made higher than a winding density of the parts lying parallel to the longitudinal direction of the coil supporting member;
• and
• wherein the wire of the heat applying coil has a cross-sectional shape such that a length of a major axis and a length of a minor axis intersecting each other perpendicularly at a center of the cross-sectional shape are different from each other, and the heat applying coil is formed by winding the wire so that adjoining major axes of the cross-sectional shape face each other in the parts lying parallel to the longitudinal direction of the coil supporting member, and so that adjoining minor axes of the cross-sectional shape face each other in the parts lying along the circumference of the heat applying coil.

An image forming apparatus in which a uniformly charged photoreceptor drum is imagewise exposed, a latent image is formed on the photoreceptor drum, the latent image is developed to form a toner image, and the toner image is transferred onto a transfer material and fixed thereon, the image forming apparatus including a fixing device comprising:

• (a) a cylindrical fixing roller to be heated;
• (b) a coil supporting member disposed along an inside of the fixing roller;
• (c) a heat applying coil formed by winding a wire around a circumference of the coil supporting member for heating the fixing roller by inducing an induced current in the fixing roller;
• and
• (d) a pressing roller for forming a nip portion with the fixing roller, and for conveying a transfer material which is gripped by the nip portion between the fixing roller and the pressing roller, so that a toner image formed on the transfer material is fixed by heat energy from the fixing roller,
• wherein the heat applying coil is formed by winding the wire in a longitudinal direction of the coil supporting member so as to have a shape which has parts lying parallel to the longitudinal direction of the coil supporting member and parts lying along the circumference.of the coil supporting member, and so that a winding density of the parts lying along the circumference of the coil supporting member is made higher than a winding density of the parts lying parallel to the longitudinal direction of the coil supporting member;
• and
• wherein a number of stacked layers of the heat applying coil are different between the parts lying parallel to the longitudinal direction of the coil supporting member and the parts lying along the circumference of the coil supporting member, and the number of stacked layers in the parts lying along the circumference of the coil supporting member is made greater than the number of stacked layers in the parts lying parallel to the longitudinal direction of the coil supporting member.