Sheet mass measuring unit

Abstract

A mass measuring unit includes two driving rollers vertically separate from each other and intersecting the direction of conveyance of a mail matter. Servo motors for driving the driving rollers are connected to torque detection units. A control unit controls motor control units to cause them to impart a rate difference between the driving rollers to rotate the mail matter during its conveyance, and to cause the torque detection units to detect the torque values of the servo motors. The control unit compares the thus detected torque values with the torque values of the servo motors detected when the servo motors are idling without rotating the mail matter, thereby measuring the mass of the mail matter using a calculation unit.

1 . A mass measuring unit for measuring a mass of a sheet of paper, comprising:
 a conveyor path configured to convey a sheet of paper;   a rotation mechanism configured to rotate and forward the sheet of paper along the conveyor path;   a torque detection unit configured to detect torque of the rotation mechanism; and   a calculation unit configured to calculate a mass of the sheet of paper, based on torque of the rotation mechanism that is detected by the torque detection unit when the rotation mechanism rotates the sheet of paper, and torque of the rotation mechanism that is detected by the torque detection unit when the rotation mechanism rotates no sheet of paper.   
     
     
         2 . The mass measuring unit according to  claim 1 , wherein the rotation mechanism rotates the sheet of paper at substantially a same conveyance rate before and after rotating the sheet of paper. 
     
     
         3 . The mass measuring unit according to  claim 1 , wherein the rotation mechanism rotates the sheet of paper at substantially a same conveyance rate and attitude before and after rotating the sheet of paper. 
     
     
         4 . A mass measuring unit for measuring a mass of a sheet of paper, comprising:
 a conveyor path configured to convey a sheet of paper;   a rotation mechanism including a driving roller configured to rotate in contact with the sheet of paper conveyed by the conveyor path, and a motor configured to accelerate and/or decelerate the driving roller to rotate and forward the sheet of paper along the conveyor path;   a torque detection unit configured to detect torque of the motor; and   a calculation unit configured to calculate a mass of the sheet of paper, based on torque of the motor that is detected by the torque detection unit when the rotation mechanism rotates the sheet of paper, and torque of the motor that is detected by the torque detection unit when the rotation mechanism rotates no sheet of paper.   
     
     
         5 . The mass measuring unit according to  claim 4 , wherein the rotation mechanism further includes a driven roller configured to be rotated by the driving roller and cooperate with the driving roller to hold therebetween the sheet of paper conveyed by the conveyor path. 
     
     
         6 . The mass measuring unit according to  claim 4 , wherein the driving roller rotates the sheet of paper, kept in contact with a portion of the sheet of paper deviated from an imaginary center line that extends in a direction of conveyance and passes through the center of gravity of the sheet of paper conveyed by the conveyor path. 
     
     
         7 . The mass measuring unit according to  claim 4 , wherein the torque detection unit monitors a current supplied to the motor to detect the torque of the motor. 
     
     
         8 . The mass measuring unit according to  claim 4 , wherein the rotation mechanism rotates the sheet of paper at substantially a same conveyance rate before and after rotating the sheet of paper. 
     
     
         9 . The mass measuring unit according to  claim 4 , wherein the rotation mechanism rotates the sheet of paper at substantially a same conveyance rate and attitude before and after rotating the sheet of paper. 
     
     
         10 . A mass measuring unit for measuring a mass of a sheet of paper, comprising:
 a conveyor path configured to convey a sheet of paper;   a rotation mechanism including a first driving roller, a second driving roller, a first motor, and a second motor, the first driving roller rotating in contact with a surface portion of the sheet of paper conveyed by the conveyor path, the second driving roller being vertically aligned with and separate from the first driving roller, the second driving roller rotating in contact with another surface portion of the sheet of paper conveyed by the conveyor path, the first and second motors independently accelerating and/or decelerating the driving rollers such that the driving rollers rotate at different rates, thereby rotating and forwarding the sheet of paper along the conveyor path;   a torque detection unit configured to detect torque values of the first and second motors;   a storing unit configured to beforehand store torque values of the first and second motors detected by the torque detection unit when the rotation mechanism is idling under same conditions as when rotating the sheet of paper, with no sheet of paper conveyed by the conveyor path; and   a calculation unit configured to calculate a mass of the sheet of paper, based on torque values of the first and second motors that are detected by the torque detection unit when the rotation mechanism rotates the sheet of paper during conveyance thereof, and the torque values of the first and second motors stored in the storing unit.   
     
     
         11 . The mass measuring unit according to  claim 10 , wherein the rotation mechanism further includes a first driven roller and a second driven roller configured to be rotated by the first and second driving rollers, respectively, and to cooperate with the first and second driving rollers to hold therebetween the sheet of paper conveyed by the conveyor path. 
     
     
         12 . The mass measuring unit according to  claim 10 , wherein the torque detection unit monitors currents supplied to the first and second motors to detect the torque values of the first and second motors. 
     
     
         13 . The mass measuring unit according to  claim 10 , wherein in the rotation mechanism, the first and second driving rollers are accelerated and decelerated to rotate the sheet of paper at substantially a same conveyance rate before and after rotating the sheet of paper. 
     
     
         14 . The mass measuring unit according to  claim 10 , wherein in the rotation mechanism, the first and second driving rollers are accelerated and decelerated to rotate the sheet of paper at substantially a same conveyance rate and attitude before and after rotating the sheet of paper.