Method of adjusting tension applied to sheet, and device for the same

A sheet tension adjusting device comprising:

• a fixed shaft (1b);
• a first rotary shaft (1c) rotatably mounted on said fixed shaft;
• a second rotary shaft (P) rotatably mounted on said first rotary shaft for supporting a roll of sheet;
• a brake means (20) engaging said first rotary shaft for applying a variable braking force to said first rotary shaft so as to feed the sheet to a sheet processing station provided along a sheet feed path while maintaining a predetermined tension in the sheet;
• a first angle sensor (24, 25) for detecting the rotation angle of said second rotary shaft;
• a sheet length sensor for measuring the feed length of the sheet in the sheet feed path to the sheet processing station;
• a second angle sensor (26, 27) for detecting the rotation angle of said first rotary shaft, and
• a control unit for calculating the current paper length on the roll or the diameter of the roll based on the sheet length measured by said sheet length sensor or the rotation angle measured by said first angle sensor;
• adjusting the tension in the sheet being fed to said sheet processing station by applying a DC voltage to said brake means to control the braking force of said brake means in a stepwise manner and constantly in each step according to the diameter of the roll;
• and detecting any relative rotation between said first rotary shaft and said second rotary shaft based on disagreement between signals from said first and second angle sensors.