Sheet conveyor and image forming system

Abstract

A sheet conveyor includes: a holder that detachably holds a sheet roll; a conveyance roller that conveys, by rotation, a sheet pulled out from the sheet roll; a first motor that rotates the conveyance roller; a second motor that rotates the sheet roll along with the conveyance of the sheet; a tension estimator that estimates tension of the sheet conveyed by the rotation of the conveyance roller; a measuring device that measures a physical quantity related to rotary motion of the conveyance roller; and a controller. The controller estimates acceleration torque of the second motor required for rotating the sheet roll depending on acceleration of the conveyance roller, based on rotation acceleration of the conveyance roller specified by the physical quantity measured by the measuring device, and calculates a feedforward control input for the second motor based on the acceleration torque estimated.

What is claimed is: 
     
         1 . A sheet conveyor, comprising:
 a holder configured to detachably hold a sheet roll;   a conveyance roller configured to convey, by rotation, a sheet pulled out from the sheet roll;   a first motor configured to rotate the conveyance roller;   a second motor configured to rotate the sheet roll along with conveyance of the sheet;   a tension estimator configured to estimate tension of the sheet conveyed by the rotation of the conveyance roller;   a measuring device configured to measure a physical quantity related to rotary motion of the conveyance roller; and   a controller,   wherein the controller is configured to:
 estimate acceleration torque of the second motor required for rotating the sheet roll depending on acceleration of the conveyance roller, based on rotation acceleration of the conveyance roller specified by the physical quantity measured by the measuring device; 
 calculate a feedforward control input for the second motor based on the acceleration torque estimated; 
 calculate a feedback control input for the second motor based on target tension and estimated tension as the tension estimated by the tension estimator; 
 control the second motor based on at least one of the feedback control input calculated and the feedforward control input calculated; and 
 control the second motor at least based on the feedforward control input from among the feedback control input and the feedforward control input, under a condition that the conveyance roller is accelerated. 
   
     
     
         2 . The sheet conveyor according to  claim 1 ,
 wherein the controller is further configured to:   calculate a control input for the first motor based on a deviation between a target rotation velocity and a rotation velocity of the conveyance roller specified by the physical quantity measured by the measuring device; and   control the first motor based on the control input calculated.   
     
     
         3 . A sheet conveyor, comprising:
 a holder configured to detachably hold a sheet roll;   a conveyance roller configured to convey, by rotation, a sheet pulled out from the sheet roll;   a first motor configured to rotate the conveyance roller;   a second motor configured to rotate the sheet roll along with the conveyance of the sheet;   a tension estimator configured to estimate tension of the sheet conveyed by the rotation of the conveyance roller;   a measuring device configured to measure a physical quantity related to rotary motion of the conveyance roller; and   a controller,   wherein the controller is configured to:
 control the first motor based on the physical quantity measured by the measuring device, such that the conveyance roller rotates in accordance with a velocity profile, 
 estimate acceleration torque of the second motor required for rotating the sheet roll depending on acceleration of the conveyance roller, based on target rotation acceleration of the conveyance roller specified by the velocity profile; 
 calculate a feedforward control input for the second motor based on the acceleration torque estimated; 
 calculate a feedback control input for the second motor based on target tension and estimated tension as the tension estimated by the tension estimator; 
 control the second motor based on at least one of the feedback control input calculated and the feedforward control input calculated; and 
 control the second motor at least based on the feedforward control input from among the feedback control input and the feedforward control input, under a condition that the conveyance roller is accelerated. 
   
     
     
         4 . The sheet conveyor according to  claim 1 , wherein the controller is configured to:
 determine a diameter of the sheet roll; and   estimate the acceleration torque based on the diameter of the sheet roll.   
     
     
         5 . The sheet conveyor according to  claim 1 , wherein the controller is configured to:
 determine a diameter of the sheet roll;   calculate inertia in a rotary coordinate system of the sheet roll based on the diameter of the sheet roll; and   estimate the acceleration torque based on the inertia and rotation acceleration of the conveyance roller.   
     
     
         6 . The sheet conveyor according to  claim 3 , wherein the controller is configured to:
 determine a diameter of the sheet roll;   calculate inertia in a rotary coordinate system of the sheet roll based on the diameter of the sheet roll; and   estimate the acceleration torque based on the inertia and the target rotation acceleration of the conveyance roller.   
     
     
         7 . The sheet conveyor according to  claim 5 , wherein the controller is configured to:
 estimate viscous friction torque in the rotary coordinate system of the sheet roll based on the diameter of the sheet roll and the physical quantity measured by the measuring device; and   calculate the feedforward control input for the second motor based on the acceleration torque and the viscous friction torque estimated.   
     
     
         8 . The sheet conveyor according to  claim 6 , wherein the controller is configured to:
 estimate viscous friction torque in the rotary coordinate system of the sheet roll based on the diameter of the sheet roll and the velocity profile; and   calculate the feedforward control input for the second motor based on the acceleration torque and the viscous friction torque estimated.   
     
     
         9 . The sheet conveyor according to  claim 7 , wherein the controller is configured to:
 further estimate dynamic friction torque; and   calculate the feedforward control input for the second motor based on the acceleration torque, the viscous friction torque, and the dynamic friction torque estimated.   
     
     
         10 . The sheet conveyor according to  claim 4 , further comprising a roll diameter measuring device configured to measure the diameter of the sheet roll,
 wherein the controller is configured to determine the diameter of the sheet roll measured by the roll diameter measuring device based on input from the roll diameter measuring device.   
     
     
         11 . The sheet conveyor according to  claim 4 , wherein the controller is configured to:
 calculate the feedback control input based on a value obtained by amplifying an input value by an amount corresponding to a gain, the input value being at least one of a deviation between the estimated tension and the target tension, an integral value of the deviation, and a differential value of the deviation; and   set the gain to a value corresponding to the diameter of the sheet roll.   
     
     
         12 . The sheet conveyor according to  claim 1 , further comprising a roll measuring device configured to measure a physical quantity related to rotary motion of the sheet roll,
 wherein the controller is configured to calculate a control input as the feedback control input, based on a tension deviation and a velocity deviation,   the tension deviation is a deviation between the estimated tension and the target tension, and   the velocity deviation is a deviation between a target rotation velocity of the sheet roll and a rotation velocity of the sheet roll specified by the physical quantity measured by the roll measuring device.   
     
     
         13 . The sheet conveyor according to  claim 3 , further comprising a roll measuring device configured to measure a physical quantity related to rotary motion of the sheet roll,
 wherein the controller is configured to calculate a control input as the feedback control input, based on a tension deviation and a velocity deviation,   the tension deviation is a deviation between the estimated tension and the target tension, and   the velocity deviation is a deviation between a target rotation velocity of the sheet roll based on a target rotation velocity of the conveyance roller specified from the velocity profile and a rotation velocity of the sheet roll specified from the physical quantity measured by the roll measuring device.   
     
     
         14 . The sheet conveyor according to  claim 1 , wherein the controller is configured to:
 control the second motor based on both of the feedback control input and the feedforward control input, under the condition that the conveyance roller is accelerated;   control the second motor at least based on the feedback control input, under a condition that the conveyance roller is rotated at a constant velocity;   calculate the feedback control input based on a value obtained by amplifying an input value by an amount corresponding to a gain, the input value being at least one of a deviation between the estimated tension and the target tension, an integral value of the deviation, and a differential value of the deviation; and   in a case of accelerating the conveyance roller, set the gain to a value lower than a case of rotating the conveyance roller at the constant velocity.   
     
     
         15 . The sheet conveyor according to  claim 1 , wherein the controller is configured to:
 determine an addition value obtained by adding the feedback control input calculated and the feedforward control input calculated, as the control input for the second motor, irrespective of whether the conveyance roller is accelerated; and   control the second motor based on the control input determined.   
     
     
         16 . The sheet conveyor according to  claim 1 , further comprising a tensioner being movable and configured to apply tension to the sheet by contacting with the sheet pulled out from the sheet roll,
 wherein the tension estimator is configured to estimate the tension of the sheet based on a position of the tensioner that is moved by the contact with the sheet.   
     
     
         17 . The sheet conveyor according to  claim 1 , wherein the controller is configured to control the second motor such that the tension of the sheet corresponds to the target tension before driving of the conveyance roller is started by the first motor. 
     
     
         18 . An image forming system comprising:
 the sheet conveyor as defined in  claim 1 ; and   a recording unit configured to form an image on the sheet conveyed by the sheet conveyor.