An image forming apparatus is provided. The image forming apparatus includes a print engine to be used to perform an image forming job, a motor to start the print engine, a driving circuit to supply a power to the motor and to include a sensor to sense a size of current of the power supplied to the motor during an operation to perform the image forming job, and a processor to detect an occurrence of jam based on a size of current sensed by the sensor in a first time interval while the motor is driven and a size of current sensed by the sensor after a determined time from the first time interval.

A sheet conveyance device includes a transmitter circuit, a receiver circuit, an integrator circuit which performs charging of electric charge outputted from the transmitter circuit and outputs a judgment voltage, a drive circuit, and a control circuit. The drive circuit feeds a drive signal to the transmitter circuit. At a lapse of a wait time after changing a level of a transmission instruction signal to a level instructing to feed the drive signal to the transmitter circuit, the control circuit makes the integrator circuit start to perform charging. When adjusting the wait time, the control circuit performs processing for adjustment a plurality of times. The control circuit makes the wait time different in each execution of the processing for adjustment. The control circuit determines a new wait time based on a magnitude of the judgment voltage recognized in each execution of the processing for adjustment.

A medium conveying apparatus includes a conveying roller to convey a medium, a first magnet to generate a first magnetic force for attracting a magnetic material moving with the medium conveyed by the conveying roller, and a second magnet to generate a second magnetic force for attracting the magnetic material attracted to the first magnet.

According to one embodiment, there is provided an image processing apparatus including a sheet storage unit, a pickup roller, a paper feed roller, a separation roller, a roller drive unit, a roller pressing unit, and a drive control unit. The pickup roller picks up a sheet from the sheet storage unit. The paper feed roller conveys the sheet picked up by the pickup roller. The separation roller is disposed to face the paper feed roller. The roller drive unit drives the separation roller. The roller pressing unit presses the separation roller against the paper feed roller. The drive control unit controls the roller drive unit so as to generate a conveying force for conveying the sheet and a returning force for pushing the sheet back in a direction opposite to a conveyance direction.

A medium transport device includes a feeding roller that feeds a recording medium, a transport roller that transports the recording medium toward a recording head, and a transport motor which is a common driving source for the feeding roller and the transport roller. The medium transport device includes a power transmission mechanism that transmits power of the transport motor to the feeding roller, and a control section that controls a current of the transport motor. The control section measures a current value flowing through the transport motor during driving as a measured current value, and adds a predetermined offset value to the measured current value to set a second limit value as a limit value of the current supplied to the transport motor.

A medium transport device includes a feeding roller that feeds a recording medium, a transport roller that transports the recording medium toward a recording head, and a transport motor which is a common driving source for the feeding roller and the transport roller. The medium transport device includes a power transmission mechanism that transmits power of the transport motor to the feeding roller, and a control section that controls a current of the transport motor. The control section measures a current value flowing through the transport motor during driving as a measured current value, and adds a predetermined offset value to the measured current value to set a second limit value as a limit value of the current supplied to the transport motor.

A sheet size detecting mechanism includes a sheet guiding module, a sensing module and a control unit. The sensing module includes a contact element and a circuit board. The circuit board includes a first conducting part, a second conducting part and plural fixed resistors. The first conducting part includes plural conductive segments. The plural conductive segments are connected with the corresponding fixed resistors, respectively. While the sheet guiding module is moved relative to the sheet input tray, the contact element is moved with the sheet guiding module. When the electric connection between a first conductive segment and the second conducting part is established through the contact element, the corresponding fixed resistor provides a resistance value, and the circuit board issues a sensing signal according to the resistance value. The control unit acquires the size of the paper sheet according to the sensing signal.

A sheet size detecting mechanism includes a sheet guiding module, a sensing module and a control unit. The sensing module includes a contact element and a circuit board. The circuit board includes a first conducting part, a second conducting part and plural fixed resistors. The first conducting part includes plural conductive segments. The plural conductive segments are connected with the corresponding fixed resistors, respectively. While the sheet guiding module is moved relative to the sheet input tray, the contact element is moved with the sheet guiding module. When the electric connection between a first conductive segment and the second conducting part is established through the contact element, the corresponding fixed resistor provides a resistance value, and the circuit board issues a sensing signal according to the resistance value. The control unit acquires the size of the paper sheet according to the sensing signal.

A post-processing unit includes a stapler, a driving section, and a controller. The stapler is moved in a Y direction and executes a stapling process on a paper sheet. The driving section moves the stapler in the Y direction. The controller controls an operation of the stapler and an operation of the driving section. The controller executes first control to supply a set current or a set voltage to the driving section, second control to supply, to the driving section, the same supply current as the set current or the same supply voltage as the set voltage, and third control to stop the supply of the supply current or the supply voltage. When the stapler executes the stapling process a plurality of times, the controller repeatedly executes the second control and the third control and causes the stapler to execute the stapling process during the execution of the second control.

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.