Transport control method, a transport apparatus, and a printing apparatus

Abstract

A transport control method for use in transporting a medium in a predetermined direction by an upstream drive roller and a downstream drive roller, to operate the downstream drive roller by using PID control based on a detection value of a tension sensor disposed downstream of the upstream drive roller and upstream of the downstream drive roller for detecting tension. The transport control method includes a stable state determining step for determining, at time of the operation, whether a difference between the detection value of the tension sensors and a target value is within a stable width to make a stable state which maintains a stability time; and a gain decreasing step for decreasing a gain of the PID control to be less than an initial value when the difference is determined to be in the stable state.

What is claimed is: 
     
         1 . A transport control method for use in transporting a medium in a predetermined direction by an upstream drive roller disposed in an upstream position in a transport direction of the medium, and a downstream drive roller disposed in a downstream position in the transport direction, to operate the downstream drive roller by using PID control based on a detection value of a tension sensor disposed downstream in the predetermined direction of the upstream drive roller and upstream of the downstream drive roller for detecting tension of the medium, the transport control method comprising:
 a stable state determining step for determining, at time of the operation, whether a difference between the detection value of the tension sensor and a target value is within a stable width to make a stable state which maintains a stability time; and   a gain decreasing step for decreasing a gain of the PID control to be less than an initial value when the difference is determined to be in the stable state.   
     
     
         2 . The transport control method according to  claim 1 , further comprising an initial value setting step for setting the gain to the initial value when the upstream drive roller starts to be driven from a stopped state, and when the upstream drive roller starts to be decelerated toward the stopped state. 
     
     
         3 . The transport control method according to  claim 1 , further comprising a gain increasing step for increasing the gain when, after the gain decreasing step, the difference is determined to have deviated from the stable width, or although within the stable width, is in a nonstable state incapable of maintaining the stability time. 
     
     
         4 . The transport control method according to  claim 2 , further comprising a gain increasing step for increasing the gain when, after the gain decreasing step, the difference is determined to have deviated from the stable width, or although within the stable width, is in a nonstable state incapable of maintaining the stability time. 
     
     
         5 . The transport control method according to  claim 1 , wherein the stable state determining step has the stable width in at least two types. 
     
     
         6 . The transport control method according to  claim 1 , wherein the gain decreasing step has a minimum gain set as a lower limit in decreasing the gain to be less than the initial value. 
     
     
         7 . The transport control method according to  claim 1 , wherein the gain increasing step has a maximum gain set as an upper limit in increasing the gain. 
     
     
         8 . The transport control method according to  claim 2 , wherein the gain increasing step has a maximum gain set as an upper limit in increasing the gain. 
     
     
         9 . The transport control method according to  claim 1 , wherein the gain is a proportional gain. 
     
     
         10 . A transport apparatus for transporting a medium in a predetermined direction, comprising:
 an upstream drive roller disposed in an upstream position in a transport direction of the medium;   a downstream drive roller disposed in a downstream position in the transport direction;   a tension sensor disposed downstream in the predetermined direction of the upstream drive roller, and upstream of the downstream drive roller, for detecting tension of the medium;   a drive control unit for operating the downstream drive roller by using PID control based on a detection value of the tension sensor;   a stable state determining unit for determining, at time of the operation, whether a difference between the detection value of the tension sensor and a target value is within a stable width to make a stable state which maintains a stability time; and   a gain adjusting unit for decreasing a gain of the PID control to be less than an initial value when the stable state determining unit has determined that the difference is in the stable state.   
     
     
         11 . The transport apparatus according to  claim 10 , wherein the gain adjusting unit sets the gain to the initial value when the drive control unit starts to drive the upstream drive roller from a stopped state, and when the drive control unit starts to decelerate the upstream drive roller toward the stopped state. 
     
     
         12 . The transport apparatus according to  claim 10 , wherein the gain adjusting unit increases the gain when, after the gain adjusting unit decreased the gain, the stable state determining unit determines that the difference has deviated from the stable width, or although within the stable width, is in a nonstable state incapable of maintaining the stability time. 
     
     
         13 . The transport apparatus according to  claim 11 , wherein the gain adjusting unit increases the gain when, after the gain adjusting unit decreased the gain, the stable state determining unit determines that the difference has deviated from the stable width, or although within the stable width, is in a nonstable state incapable of maintaining the stability time. 
     
     
         14 . The transport apparatus according to  claim 10 , wherein the stable state determining unit has the stable width in at least two types. 
     
     
         15 . The transport apparatus according to  claim 10 , wherein the gain adjusting unit has a minimum gain set as a lower limit in decreasing the gain to be less than the initial value. 
     
     
         16 . The transport apparatus according to  claim 10 , wherein the gain adjusting unit has a maximum gain set as an upper limit in increasing the gain. 
     
     
         17 . The transport apparatus according to  claim 11 , wherein the gain adjusting unit has a maximum gain set as an upper limit in increasing the gain. 
     
     
         18 . The transport apparatus according to  claim 10 , wherein the gain is a proportional gain. 
     
     
         19 . A printing apparatus for performing printing while transporting an elongate printing medium in a predetermined direction, comprising:
 a printing station for printing on the printing medium in a printing area disposed along a transport path of the printing medium;   an upstream drive roller disposed upstream of the printing area;   a downstream drive roller disposed downstream of the printing area;   a tension sensor disposed downstream in the predetermined direction of the upstream drive roller, and upstream of the printing area, for detecting tension of the printing medium;   a drive control unit for operating the downstream drive roller based on a detection value of the tension sensor and by using PID control;   a stable state determining unit for determining, at time of the operation, whether a difference between the detection value of the tension sensor and a target value is within a stable width to make a stable state which maintains a stability time; and   a gain adjusting unit for decreasing a gain of the PID control to be less than an initial value when the stable state determining unit has determined that the difference is in the stable state.   
     
     
         20 . The printing apparatus according to  claim 19 , wherein the gain adjusting unit sets the gain to the initial value when the upstream drive roller starts to be driven from a stopped state, and when the upstream drive roller starts to be decelerated toward the stopped state.