Fusing device, a heating device, and a method for fusing a toner image onto a sheet

A fusing device for fusing toner images onto a sheet, comprising:

• pressing means for pressing the sheet at a pressing position with a force F (kg) along a predetermined sheet path;
• heating means located at an upstream side of said pressing means with respect to a direction of sheet transportation for heating the sheet;
• wherein the force F and the heating means are set so as to satisfy the following formula:
• 0<F<0.5.theta..sup.2 +0.05.theta.,
• wherein .theta. is defined as an angle between a first line from said heating means to said pressing position and a second line defined by said predetermined path.

A method for fusing a toner image onto a sheet, comprising the steps of:

• pressing a pair of rollers against each other at a contact position with a force F (kg);
• transporting the sheet to the contact position between said rollers along a predetermined path;
• heating the sheet at a heating position upstream of the rollers with respect to a transporting direction of the sheet with a heater that is facing a surface of the sheet on which the toner image is held;
• and
• setting the force F and the heating position so as to satisfy the following formula:
• <
• F<0.5.theta..sup.2 +0.05.theta.,
• wherein .theta. is an angle defined by a first line from said heating position to said contact position and a second line defined by said predetermined path.

A fusing device for fusing a toner image onto a sheet, comprising:

• a pair of members which are in contact with each other at a contact position with a force F (kg) along a predetermined sheet path;
• a flat heating device located at an upstream side of said pair of members with respect to a direction of transportation of the sheet, said heating device facing the predetermined sheet path;
• a line from an upstream edge of said heating device with respect to the direction of transportation to said contact position and a second line defined by said sheet path makes an angle .theta.2;
• a line from a downstream edge of said heating device with respect to the direction of transportation to said contact position and the second line defined by said sheet path makes an angle .theta.1;
• wherein the force F and an orientation of the heating device are set so as to satisfy the following formula:
• 0<F<0.5(.theta..sub.x).sup.2 +0.05(.theta..sub.x);
• wherein (.theta..sub.x) is a smaller of .theta.1 and .theta.2.