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

Abstract

To prevent disalignment of the edges of a folded sheet by smoothly feeding the sheet to a packaging unit while keeping tension fluctuations to a minimum when the sheet is unwound from a paper roll set in a paper feed unit even though the paper roll diameter decreases gradually as the sheet is unwound. A sheet length measuring sensor or rotary encoder is provided in the paper feed path through which the packaging sheet is fed toward the packaging unit. An angle sensor is provided which includes Hall element sensors provided on a support shaft and magnets provided on a core pipe of the paper roll. Any change in the signals from one of these sensors relative to the signal from the other sensor is used to calculate the paper roll winding length, and the sheet tension is adjusted to an optimum, constant level by controlling the sheet braking force stepwise according to the roll diameter measured by the sensors.

What is claimed is: 
     
      
       1. A roll sheet assembly for use with a drug packaging device including a sheet feed unit comprising a fixed shaft, a first rotary shaft rotatably mounted around the fixed shaft and carrying said roll of sheet material, a first brake means for applying a braking force to the first rotary shaft, and feed rollers for feeding the sheet material from said roll, a second brake means for producing a constant braking force between the first rotary shaft and said roll of sheet material, a packaging unit comprising a triangular plate for folding the sheet material in half so as to form a valley in the sheet material, a hopper for dropping drugs into the valley formed in the sheet, and heating rollers for heat-sealing the sheet material in a width direction at predetermined intervals and along top edges thereof to form a plurality of bags with the drugs sealed therein, 
       
         the sheet feed unit further comprising a sheet length sensor for measuring a feed length of the sheet in a sheet feed path leading to the packaging unit, a first angle sensor for detecting a rotation angle of said roll of sheet material, and a control unit for calculating a current sheet length on said roll of sheet material and the diameter of said roll of sheet material based on the sheet length measured by the sheet length sensor and the rotation angle measured by the angle sensor, and controlling a direct-current voltage applied to the first brake means, 
         said roll sheet assembly comprising a cylindrical second rotary shaft having a cylindrical outer periphery and a cylindrical inner periphery, sheet material wound on said cylindrical outer periphery of said second rotary shaft, and at least one magnet provided on said cylindrical inner periphery of said second rotary shaft. 
       
      
     
     
      
       2. The roll sheet assembly as claimed in  claim 1 , wherein said at least one magnet comprises four magnets circumferentially spaced at equal intervals. 
      
     
     
      
       3. The roll sheet assembly as claimed in  claim 1 , wherein said magnet is detachably mounted on said inner cylindrical periphery of said second rotary shaft. 
      
     
     
       4. An assembly comprising:
 a hollow core pipe having a predetermined length, said hollow core pipe comprising a cylindrical inner periphery and a cylindrical outer periphery;   a sheet of drug packaging paper wound around the cylindrical outer periphery of said hollow core pipe to form a sheet roll; and   a plurality of magnets provided on the cylindrical inner periphery of said hollow core pipe at circumferential intervals such that a sheet length and a diameter of the sheet roll can be calculated by an angle sensor provided on a fixed shaft,   wherein said plurality of magnets are provided such that the circumferential intervals are arranged in a way that detection of said plurality of magnets is carried out at equal angular intervals while said hollow core pipe makes one revolution, and said plurality of magnets are rotatable together with the sheet roll.   
     
     
       5. The assembly of claim 4, wherein the equal angular interval is 22.5°. 
     
     
       6. The assembly of claim 4, wherein the plurality of magnets comprises four magnets positioned at angular intervals of 67.5° around an axis of the hollow core pipe. 
     
     
       7. The assembly of claim 4, wherein the plurality of magnets comprises two magnets positioned at angular intervals of 22.5° around an axis of the hollow core pipe. 
     
     
       8. The assembly of claim 4, wherein the plurality of magnets comprises eight magnets positioned at angular intervals of 45° around an axis of the hollow core pipe. 
     
     
       9. The assembly of claim 4, wherein the plurality of magnets comprises sixteen magnets positioned at angular intervals of 22.5° around an axis of the hollow core pipe.