Sheet feeding device and sheet feeding method

A sheet feeding device that sequentially feeds a sheet from each of a first roll and a second roll around which the sheet is wound, and supplies the sheet to a predetermined processing device at predetermined conveyance speed using a supply mechanism, the sheet feeding device comprising:

• a first support shaft that is rotatable while supporting the first roll at its center position;
• a second support shaft that is rotatable while supporting the second roll at its center position;
• the supply mechanism that supplies the sheet fed from the first roll or the second roll as the first support shaft or the second support shaft rotates to the processing device at the predetermined conveyance speed;
• a storage mechanism that is disposed upstream of the supply mechanism to store the sheet fed from the first roll or the second roll, and is configured to be able to change a sheet storage amount;
• a joining mechanism that is disposed upstream of the storage mechanism, and is capable of switching a roll of sheet to be supplied to the processing device by performing joining processing of joining the sheet of the first roll and the sheet of the second roll;
• a calculation unit that calculates an outer diameter of the first roll or the second roll and a sheet remaining amount that change as the sheet is supplied to the processing device by the supply mechanism;
• and
• a shaft control unit that controls rotation operation of the first support shaft and the second support shaft,
• wherein when the sheet of the second roll is continuously supplied after the sheet of the first roll is supplied to the processing device,
• the shaft control unit
• performs steady control of adjusting rotation speed of the first support shaft to cause the first roll to have peripheral speed equal to conveyance speed by maintaining the storage amount of the sheet of the first roll in a first storage amount as a reference using the storage mechanism in a steady state in which the sheet of the first roll is supplied to the processing device at the conveyance speed, and
• performs storage amount adjustment control of, when the sheet remaining amount of the first roll becomes a first remaining amount obtained by adding a predetermined length to a predetermined target remaining amount, accelerating the rotation speed of the first support shaft to cause the first roll to have the peripheral speed faster than the conveyance speed until the storage amount of the sheet of the first roll using the storage mechanism reaches a predetermined second storage amount that is larger than the first storage amount, and after the storage amount of the first roll reaches the second storage amount, adjusting the rotation speed of the first support shaft to cause the first roll to have the peripheral speed equal to the conveyance speed,
• the joining mechanism performs the joining processing when the sheet remaining amount of the first roll reaches the target remaining amount after the shaft control unit performs the storage amount adjustment control, and
• the calculation unit
• calculates a first outer diameter as the outer diameter of the first roll based on the conveyance speed and a number of rotations of the first support shaft, and calculates a sheet thickness from a decrease amount of the first outer diameter per rotation of the first roll, to calculate the sheet remaining amount based on the first outer diameter of the first roll and the sheet thickness, when the shaft control unit performs the steady control, and
• calculates a second outer diameter as the outer diameter of the first roll based on the first outer diameter immediately before switching to the storage amount adjustment control, the calculated sheet thickness, and the number of rotations of the first support shaft, to calculate the sheet remaining amount based on the second outer diameter of the first roll and the sheet thickness, when the shaft control unit performs the storage amount adjustment control.