Roll sheet conveyance device and image forming apparatus incorporating same

Abstract

An image forming apparatus includes an image forming device forming an image on a recording medium wound into a roll, and a roll sheet conveyance device unwinding and conveying the medium to the image forming device. The roll sheet conveyance device includes a roll sheet feed device, a torsion detector, and a control device. The roll sheet feed device includes a drive device including upstream and downstream shafts in a drive transmission direction to rotate the medium, and a feed device to feed the medium. The detection device includes a torsion coil spring provided between the upstream and downstream shafts, and a pair of an encoder and an encoder sensor detecting the torsion amount at the opposite ends of the torsion coil spring. The control device controls the torsion amount on the basis of a signal from the detection device, and applies a given back tension to the medium.

1 . An image forming apparatus comprising:
 an image forming device configured to form an image on a recording medium wound into a roll; and   a roll sheet conveyance device configured to unwind and convey the recording medium to the image forming device,   the roll sheet conveyance device including:
 a roll sheet feed device including a drive device including an upstream shaft and a downstream shaft in a drive transmission direction to rotate the recording medium, and a feed device provided along a conveyance path of the recording medium to feed the recording medium; 
 a torsion detector including a torsion coil spring provided between the upstream shaft and the downstream shaft, and an encoder and an encoder sensor pair configured to detect an amount of torsion at opposite ends of the torsion coil spring; and 
 a control device configured to control the amount of torsion of the torsion coil spring on the basis of a signal output from the torsion detector and apply a given back tension to the recording medium. 
   
     
     
         2 . The image forming apparatus as described in  claim 1 , wherein the encoder of the torsion detector is provided to each of the upstream shaft and the downstream shaft, and faces the corresponding encoder sensor fixed thereto. 
     
     
         3 . The image forming apparatus as described in  claim 1 , wherein the encoder of the torsion detector is provided to either one of the upstream shaft and the downstream shaft, and the corresponding encoder sensor is provided to the other one of the upstream shaft and the downstream shaft. 
     
     
         4 . The image forming apparatus as described in  claim 1 , wherein, upon detection of oblique feeding of the recording medium, the control device rewinds the recording medium while maintaining the given back tension. 
     
     
         5 . The image forming apparatus as described in  claim 4 , wherein, if an amount of oblique feeding of the recording medium exceeds a given amount, the control device sets the amount of torsion of the torsion coil spring to be larger in reverse rotation for rewinding the recording medium than in forward rotation for feeding the recording medium. 
     
     
         6 . An image forming apparatus comprising:
 image forming means for forming an image on a recording medium wound into a roll; and   roll sheet conveying means for unwinding and conveying the recording medium to the image forming means,   the roll sheet conveying means including:
 roll sheet feeding means including drive means for rotating the recording medium, and feeding means for feeding the recording medium; 
 torsion amount detection means including torsion resilience means for generating resilience, and encoder and sensor means for detecting an amount of torsion at opposite ends of the torsion resilient means; and 
 control means for controlling the amount of torsion of the torsion resilient means on the basis of a signal output from the torsion amount detection means, and applying a given back tension to the recording medium. 
   
     
     
         7 . A roll sheet conveyance device configured to unwind and convey a recording medium wound into a roll to an image forming device configured to form an image on the recording medium,
 the roll sheet conveyance device comprising:
 a roll sheet feed device including a drive device including an upstream shaft and a downstream shaft in a drive transmission direction to rotate the recording medium, and a feed device provided along a conveyance path of the recording medium to feed the recording medium; 
 a torsion detector device including a torsion coil spring provided between the upstream shaft and the downstream shaft, and an encoder and an encoder sensor pair configured to detect an amount of torsion at the opposite ends of the torsion coil spring; and 
 a control device configured to control the amount of torsion of the torsion coil spring on the basis of a signal output from the torsion detector and apply a given back tension to the recording medium. 
   
     
     
         8 . The roll sheet conveyance device as described in  claim 7 , wherein the encoder of the torsion detector is provided to each of the upstream shaft and the downstream shaft, and faces the corresponding encoder sensor fixed thereto. 
     
     
         9 . The roll sheet conveyance device as described in  claim 7 , wherein the encoder of the torsion detector is provided to either one of the upstream shaft and the downstream shaft, and the corresponding encoder sensor is provided to the other one of the upstream shaft and the downstream shaft. 
     
     
         10 . The roll sheet conveyance device as described in  claim 7 , wherein, upon detection of oblique feeding of the recording medium, the control device rewinds the recording medium while maintaining the given back tension. 
     
     
         11 . The roll sheet conveyance device as described in  claim 10 , wherein, if an amount of oblique feeding of the recording medium exceeds a given amount, the control device sets the amount of torsion of the torsion coil spring to be larger in reverse rotation for rewinding the recording medium than in forward rotation for feeding the recording medium.