Conveyance device and image forming apparatus

Abstract

A conveyance device includes a sheet stacker, a pickup roller, a feed roller, a first drive source, a first encoder, a first drive controller, a separation roller, a second drive source, a second encoder, a second drive controller, a separation pressure provider, and a torque estimation device. The torque estimation device estimates a torque of the second drive source with an applied voltage to the second drive source from the second drive controller after calculating a turning angle speed from a rotation amount of the second drive source detected by the second encoder based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the second drive source and a torque of the second drive source.

What is claimed is: 
     
         1 . A conveyance device comprising:
 a sheet stacker on which sheets are stacked;   a pickup roller configured to contact a top sheet of the sheets stacked on the sheet stacker and to rotate in a sheet conveyance direction;   a feed roller configured to rotate to feed the sheet in the sheet conveyance direction;   a first drive source configured to rotate the pickup roller and the feed roller;   a first encoder configured to detect a rotation amount of the first drive source;   a first drive controller configured to control a speed or a position of the first drive source based on the rotation amount detected by the first encoder;   a separation roller configured to nip a sheet with the feed roller;   a second drive source configured to rotate the separation roller;   a second encoder configured to detect a rotation amount of the second drive source;   a second drive controller configured to perform torque control of the second drive source, the torque control rotating the separation roller with rotation of the feed roller in the sheet conveyance direction when a force having a predetermined value or more is applied to the separation roller from the feed roller in direct contact with the separation roller or nipping a sheet with the separation roller, and rotating the separation roller in a direction opposite the sheet conveyance direction when a force having a value less than the predetermined value is applied from the feed roller to the separation roller, to return an excess sheet to the sheet stacker if sheets are multi-fed;   a separation pressure provider configured to provide a pressure by which the separation roller is pressed against the feed roller; and   a torque estimation device configured to estimate a torque of the second drive source with an applied voltage to the second drive source from the second drive controller after calculating a turning angle speed from the rotation amount of the second drive source detected by the second encoder based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the second drive source and a torque of the second drive source.   
     
     
         2 . The conveyance device according to  claim 1 , further comprising a multi-sheet feed detector configured to monitor a rotation speed of the second drive source while the sheet is being fed and to determine that sheet separation is to be started as sheets are multi-fed if the rotation speed is lower than a predetermined value,
 wherein the multi-sheet feed detector is configured to cause the second drive controller to increase a target torque for the torque control, if the multi-sheet feed detector determines that sheet separation is to be started as sheets including the sheet are multi-fed.   
     
     
         3 . The conveyance device according to  claim 1 , further comprising a multi-sheet feed detector configured to monitor a torque estimation value of the second drive source while the sheet is being fed and to determine that sheet separation is to be started as sheets are multi-fed if the torque estimation value is lower than a predetermined value,
 wherein the multi-sheet feed detector is configured to cause the second drive controller to increase a target torque for the torque control, if the multi-sheet feed detector determines that sheet separation is to be started as sheets including the sheet are multi-fed.   
     
     
         4 . The conveyance device according to  claim 2 , wherein the multi-sheet feed detector is configured to cause the second drive controller to maintain the increased target torque until the sheet being conveyed passes, if the multi-sheet feed detector determines that sheet separation is to be started as sheets are multi-fed. 
     
     
         5 . The conveyance device according to  claim 1 , further comprising a sheet type input device configured to receive an input of a sheet type,
 wherein at least one of a predetermined value of rotation speed or torque estimation value, a target torque, and a value of target torque at a time of multi-sheet feeding is changeable depending on the sheet type input from the sheet type input device.   
     
     
         6 . The conveyance device according to  claim 2 ,
 wherein the multi-sheet feed detector is configured to:
 continue to monitor a rotation speed of the second drive source after determining that sheet separation is to be started as sheets are multi-fed; and 
 determine that the sheet separation is completed if the rotation speed of the second drive source exceeds a predetermined value, and 
   wherein the first drive controller is configured to:
 stop driving of the first drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and 
 resume driving the first drive source if the multi-sheet feed detector determines that the sheet separation is completed. 
   
     
     
         7 . The conveyance device according to  claim 3 ,
 wherein the multi-sheet feed detector is configured to:
 continue to monitor a torque estimation value of the second drive source after determining that sheet separation is to be started as sheets are multi-fed; and 
 determine that the sheet separation is completed if the torque estimation value of the second drive source exceeds the predetermined value, and 
   wherein the first drive controller is configured to:
 stop driving of the first drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and 
 resume driving the first drive source if the multi-sheet feed detector determines that the sheet separation is completed. 
   
     
     
         8 . The conveyance device according to  claim 2 ,
 wherein the first drive controller is configured to:
 reduce driving of the first drive source to a predetermined speed if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed; and 
 return a speed of the first driving source to a normal speed if the multi-sheet feed detector determines that the sheet separation is completed. 
   
     
     
         9 . The conveyance device according to  claim 2 , further comprising:
 a conveyance roller pair configured to nip a sheet fed from the conveyance device;   a third drive source configured to rotate the conveyance roller pair;   a third encoder configured to detect a rotation amount of the third drive source;   a third drive controller configured to control a position or a speed of the third drive source;   a sheet detector configured to detect presence or absence of a sheet in a position of the conveyance roller pair or a position downstream of the conveyance roller pair in the sheet conveyance direction; and   a conveyance-roller-pair sheet nipping determiner configured to determine whether the conveyance roller pair has nipped a sheet based on detection performed by the sheet detector,   wherein the conveyance roller pair, the third drive source, the third encoder, the third drive controller, the sheet detector, and the conveyance-roller-pair sheet nipping determiner are arranged downstream of the feed roller in the sheet conveyance direction in the conveyance device, and   wherein the third drive controller is configured to:
 stop driving of the third drive source if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed after the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet; and 
 resume driving the third drive source if the multi-sheet feed detector determines that the sheet separation is completed. 
   
     
     
         10 . The conveyance device according to  claim 2 , further comprising:
 a conveyance roller pair configured to nip a sheet fed from the conveyance device;   a third drive source configured to rotate the conveyance roller pair;   a third encoder configured to detect a rotation amount of the third drive source;   a third drive controller configured to control a position or a speed of the third drive source;   a sheet detector configured to detect presence or absence of a sheet in a position of the conveyance roller pair or a position downstream of the conveyance roller pair in the sheet conveyance direction; and   a conveyance-roller-pair sheet nipping determiner configured to determine whether the conveyance roller pair has nipped a sheet based on detection performed by the sheet detector,   wherein the conveyance roller pair, the third drive source, the third encoder, the third drive controller, the sheet detector, and the conveyance-roller-pair sheet nipping determiner are arranged downstream of the feed roller in the sheet conveyance direction in the conveyance device, and   wherein the third drive controller is configured to:
 reduce driving of the third drive source to a predetermined speed if the multi-sheet feed detector determines that sheet separation has been started as sheets are multi-fed after the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet; and 
 return a speed of the third drive source to a normal speed if the multi-sheet feed detector determines that the sheet separation is completed. 
   
     
     
         11 . The conveyance device according to  claim 9 ,
 wherein the first drive controller is configured to stop driving of the first drive source if the conveyance-roller-pair sheet nipping determiner determines that the conveyance roller pair has nipped a sheet.   
     
     
         12 . The conveyance device according to  claim 9 , wherein the second drive source is a direct current motor. 
     
     
         13 . An image forming apparatus comprising the conveyance device according to  claim 1 .