Image forming apparatus

Abstract

An image forming apparatus includes a stacking unit, a pickup roller, a conveying roller, a transfer unit, a motor, a determiner, and a velocity adjuster. The conveying roller conveys, in a conveying direction, a sheet fed by the pickup roller from the stacking unit. The determiner determines a value of a parameter corresponding to a load torque applied to a motor rotor. Based on a length between a front end of the sheet and a nip position of the conveying roller at a first timing when the determined value changes from a value smaller than a predetermined value to a value greater than the predetermined value, and a length between the nip position and a predetermined position downstream of the conveying roller and upstream of an image forming position in the conveying direction, the velocity adjuster adjusts a conveying velocity at which the sheet is conveyed to the predetermined position.

What is claimed is: 
     
         1 . An image forming apparatus comprising:
 a stacking unit on which a sheet is to be stacked;   a pickup roller configured to feed the sheet stacked on the stacking unit;   a first conveying roller configured to convey the sheet fed by the pickup roller;   a transfer unit configured to transfer an image onto the sheet at an image forming position downstream of the first conveying roller in a conveying direction in which the sheet is conveyed;   a motor configured to drive the first conveying roller;   a determiner configured to determine a value of a parameter corresponding to a load torque applied to a rotor of the motor; and   a velocity adjuster configured to, based on a length between a position of a front end of the sheet and a nip position of the first conveying roller at a first timing when the value of the parameter determined by the determiner changes from a value smaller than a predetermined value to a value greater than the predetermined value, and a length between the nip position of the first conveying roller and a predetermined position downstream of the first conveying roller and upstream of the image forming position in the conveying direction, adjust a conveying velocity at which the sheet being conveyed at a predetermined velocity by the first conveying roller is conveyed to the predetermined position.   
     
     
         2 . The image forming apparatus according to  claim 1 , further comprising an acquisition unit configured to acquire information regarding a type of the sheet to be conveyed,
 wherein the velocity adjuster adjusts the conveying velocity based on the information acquired by the acquisition unit.   
     
     
         3 . The image forming apparatus according to  claim 1 ,
 wherein, in a case where a grammage of the sheet to he conveyed is a first grammage, the velocity adjuster adjusts the conveying velocity using a first length as the length between the position of the front end of the sheet and the nip position at the first timing, and   wherein, in a case where the grammage of the sheet to be conveyed is a second grammage greater than the first grammage, the velocity adjuster adjusts the conveying velocity using a second length greater than the first length.   
     
     
         4 . The image forming apparatus according to  claim 1 , further comprising:
 a second conveying roller provided upstream of the image forming position and downstream of the first conveying roller in the conveying direction; and   an abutment member that is provided upstream of the image forming position and downstream of the second conveying roller in the conveying direction and that the front end of the sheet conveyed by the second conveying roller abuts,   wherein a skew of the sheet is corrected by abutment of the front end of the sheet with the abutment member, and   wherein the predetermined position is a position between the first and second conveying rollers.   
     
     
         5 . The image forming apparatus according to  claim 1 , further comprising a controller configured to start and stop rotational driving of the pickup roller at predetermined time intervals,
 wherein the velocity adjuster adjusts the conveying velocity based on (i) time from a second timing when the rotational driving of the pickup roller is started to a third timing when the sheet is to reach the predetermined position, (ii) time from the second timing to the first timing, and (iii) the length between the position of the front end of the sheet and the nip position and the length between the nip position and the predetermined position at the first timing.   
     
     
         6 . The image forming apparatus according to  claim 1 , further comprising:
 a swinging member configured to move up and down the pickup roller that is rotationally driven; and   a controller configured to control the up-and-down movement of the swinging member,   wherein the velocity adjuster adjusts the conveying velocity based on (i) time from a second timing when the rotational driving of the pickup roller is started to a third timing when the sheet is to reach the predetermined position, (ii) time from the second timing to the first timing, and (iii) the length between the position of the front end of the sheet and the nip position and the length between the nip position and the predetermined position at the first timing.   
     
     
         7 . The image forming apparatus according to  claim 1 , further comprising a feeding roller provided upstream of the first conveying roller in the conveying direction and configured to convey the sheet fed by the pickup roller downstream,
 wherein a conveying path which is provided between the feeding roller and the first conveying roller and in which the sheet is guided is curved.   
     
     
         8 . The image forming apparatus according to  claim 7 ,
 wherein the feeding roller is adjacent to the first conveying roller, and   wherein a peripheral velocity of the first conveying roller is faster than a peripheral velocity of the feeding roller.   
     
     
         9 . The image forming apparatus according to  claim 1 , wherein, in a case where a state where the value of the parameter determined by the determiner is smaller than the predetermined value continues for a predetermined time, the conveyance of the sheet is stopped. 
     
     
         10 . The image forming apparatus according to  claim 1 , wherein the determiner is a first determiner, the image forming apparatus further comprising:
 a second determiner configured to determine a rotational phase of the rotor of the motor; and   a controller configured to control a driving current flowing through a winding of the motor so that a deviation between the rotational phase determined by the second determiner and an instruction phase indicating a target phase of the rotor becomes small.   
     
     
         11 . The image forming apparatus according to  claim 10 , wherein the controller controls the driving current based on a torque current component that is a current component represented in a rotating coordinate system based on the rotational phase of the rotor determined by the second determiner and is also a current component that causes the rotor to generate a torque. 
     
     
         12 . The image forming apparatus according to  claim 1 , wherein the determiner is a first determiner, the image forming apparatus further comprising:
 a second determiner configured to determine a rotational velocity of the rotor of the motor; and   a controller configured to control a driving current flowing through a winding of the motor so that a deviation between the rotational velocity determined by the second determiner and an instruction velocity indicating a target velocity of the rotor becomes small.   
     
     
         13 . The image forming apparatus according to  claim 12 , further comprising a third determiner configured to determine a rotational phase of the rotor of the motor,
 wherein the controller controls the driving current based on a torque current component that is a current component represented in a rotating coordinate system based on the rotational phase of the rotor determined by the third determiner and is also a current component that causes the rotor to generate a torque.   
     
     
         14 . The image forming apparatus according to  claim 1 , further comprising a detector configured to detect driving current flowing through a winding of the motor,
 wherein the determiner determines the value of the parameter based on the driving current detected by the detector.   
     
     
         15 . An image forming apparatus comprising:
 a stacking unit on which a sheet is to be stacked;   a pickup roller configured to feed the sheet stacked on the stacking unit;   a first conveying roller configured to convey the sheet fed by the pickup roller;   a transfer unit configured to transfer an image onto the sheet at an image forming position downstream of the first conveying roller in a conveying direction in which the sheet is conveyed;   a motor configured to rotationally drive the first conveying roller;   a determination unit configured to determine a value of a parameter corresponding to a load torque applied to a rotor of the motor;   an acquisition unit configured to acquire information regarding a grammage of the sheet to be conveyed; and   a velocity adjustment unit configured to, according to a change of the value of the parameter determined by the determination unit changes from a value smaller than a predetermined value to a value greater than the predetermined value, adjust a conveying velocity at which the sheet conveyed at a predetermined velocity by the first conveying roller is conveyed to a predetermined position downstream of the first conveying roller and upstream of the image forming position in the conveying direction,   wherein, in a case where the acquisition unit acquires information indicating that the grammage of the sheet to be conveyed is a first grammage, the velocity adjustment unit adjusts the conveying velocity to a first velocity, and   wherein, in a case where the acquisition unit acquires information indicating that the grammage of the sheet to be conveyed is a second grammage greater than the first grammage, the velocity adjustment unit adjusts the conveying velocity to a second velocity faster than the first velocity.   
     
     
         16 . The image forming apparatus according to  claim 15 , further comprising:
 a second conveying roller provided upstream of the image forming position and downstream of the first conveying roller in the conveying direction; and   an abutment member that is provided upstream of the image forming position and. downstream of the second conveying roller in the conveying direction and that the front end of the sheet conveyed by the second conveying roller abuts,   wherein a skew of the sheet is corrected by abutment of the front end of the sheet with the abutment member, and   wherein the predetermined position is a position between the first and second conveying rollers.   
     
     
         17 . The image forming apparatus according to  claim 15 , further comprising a control unit configured to start and stop rotational driving of the pickup roller at predetermined time intervals,
 wherein the velocity adjustment adjusts the conveying velocity based on (i) time from a third timing when the rotational driving of the pickup roller is started to a second timing when the sheet is to reach the predetermined position, (ii) time from the third timing to the first timing, and (iii) the length between the position of the front end of the sheet and the nip position and the length between the nip position and the predetermined position at the first timing.   
     
     
         18 . The image forming apparatus according to  claim 15 , further comprising:
 a swinging member configured to move up and down the pickup roller that is rotationally driven; and   a control unit configured to control the up-and-down movement of the swinging member,   wherein the velocity adjustment unit adjusts the conveying velocity based on (i) time from a third timing when the rotational driving of the pickup roller is started to a second timing when the sheet is to reach the predetermined position, (ii) time from the third timing to the first timing, and (iii) the length between the position of the front end of the sheet and the nip position and the length between the nip position and the predetermined position at the first timing.   
     
     
         19 . The image forming apparatus according to  claim 15 , further comprising a feeding roller provided upstream of the first conveying roller in the conveying direction and configured to convey the sheet fed by the pickup roller downstream,
 wherein a conveying path which is provided between the feeding roller and the first conveying roller and in which the sheet is guided is curved.   
     
     
         20 . The image forming apparatus according to  claim 19 ,
 wherein the feeding roller is adjacent to the first conveying roller, and   wherein a peripheral velocity of the first conveying roller is faster than a peripheral velocity of the feeding roller.   
     
     
         21 . The image forming apparatus according to  claim 15 , wherein, in a case where a state where the value of the parameter determined by the determination unit is smaller than the predetermined value continues for a predetermined time, the conveyance of the sheet is stopped. 
     
     
         22 . The image forming apparatus according to  claim 15 , wherein the determination unit is a first determination unit, the image forming apparatus further comprising:
 a second determination unit configured to determine a rotational phase of the rotor of the motor; and   a control unit configured to control a driving current flowing through a winding of the motor so that a deviation between the rotational phase determined by the second determination unit and an instruction phase indicating a target phase of the rotor becomes small.   
     
     
         23 . The image forming apparatus according to  claim 22 , wherein the control unit controls the driving current based on a torque current component that is a current component represented in a rotating coordinate system based on the rotational phase of the rotor determined by the second determination unit and is also a current component that causes the rotor to generate a torque. 
     
     
         24 . The image forming apparatus according to  claim 15 , wherein the determination unit is a first determination unit, the image forming apparatus further comprising:
 a second determination unit configured to determine a rotational velocity of the rotor of the motor; and   a control unit configured to control a driving current flowing through a winding of the motor so that a deviation between the rotational velocity determined by the second determination unit and an instruction velocity indicating a target velocity of the rotor becomes small.   
     
     
         25 . The image forming apparatus according to  claim 24 , further comprising a third determination unit configured to determine a rotational phase of the rotor of the motor,
 wherein the control unit controls the driving current based on a torque current component that is a current component represented in a rotating coordinate system based on the rotational phase of the rotor determined by the third determination unit and is also a current component that causes the rotor to generate a torque.   
     
     
         26 . The image forming apparatus according to  claim 15 , further comprising a detector configured to detect driving current flowing through a winding of the motor, wherein the determination unit determines the value of the parameter based on the driving current detected by the detector.