In recent years, since image printing technologies have been improved, images can be formed on various media, such as normal sheets, coated sheets, and sheets used for OHP (being an overhead projector). However, these sheets exhibit a higher contacting force between each sheet, so that sheets are not easily separated, and consequently, superposed sheets are too often conveyed. In order to prevent the superposed sheets from being conveyed, a sheet conveyance device has been developed, in which each sheet is puckered so that the sheet is easily separated.
Generally, in the sheet conveyance device, two conveyance rollers, each contacting the sheet, rotate at different rotation times so that the sheets are separated one by one.
In Unexamined Japanese Patent Application Publication No. 7-25,491 (see page 3, and FIG. 1), a sheet conveyance device, featuring a timing pulley, is disclosed. Said device is structured of a first sheet supplying roller, a second sheet supplying roller, a timing belt, and timing pulleys. One of the timing pulleys is attached to the first sheet supplying roller, while the other is attached to the second sheet supplying roller. Around each timing pulley, said timing belt is entrained. A rotation starting time is determined so that when a predetermined time interval has passed after the first sheet supplying roller began to rotate, then the second sheet supplying roller begins to rotate. Due to the time difference between rotation starting times of the first and second sheet supplying rollers, said sheet conveyance device forms a pucker on the sheet contacted to the first and second sheet supplying rollers, whereby each sheet is easily separated.
However, since the above patent application includes the timing pulley to form a pucker on the sheet, the device becomes quite large and complicated. Further, the production cost of the device itself increases.
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