Sheet feeder, document reader, and image forming apparatus

A sheet feeder for sequentially picking up sheets from a sheet stack and continuously transporting the sheets along a sheet transport path, the sheet feeder comprising:

• a transport unit that transports the sheets along the sheet transport path one by one;
• a gap occurrence detection unit that detects, within a predetermined section of the sheet transport path, occurrence of a gap between the trailing edge of a preceding sheet and the leading edge of a following sheet;
• and
• a controller that controls a timing at which the transport unit starts transporting the following sheet according to a result of the detection by the gap occurrence detection unit,
• the gap occurrence detection unit including:
• a light emitting element that is disposed on a first side of the sheet transport path and emits diffused light at least toward the predetermined section;
• a first light receiving element that is disposed on the first side of the sheet transport path;
• a converging reflector that is disposed on a second side of the sheet transport path opposite the first side and converges, onto the first light receiving element, light that is emitted by the light emitting element and reaches the converging reflector by travelling across the predetermined section;
• and
• a second light receiving element that is arranged so as not to (i) receive the light emitted by the light emitting element and regularly reflected by the converging reflector and (ii) detect light emitted by the light emitting element and reflected by a sheet passing through the predetermined section, wherein
• the gap occurrence detection unit detects occurrence of the gap based on outputs from the first light receiving unit and the second light receiving unit while the preceding sheet and the following sheet are passing through the predetermined section.

A sheet feeder for sequentially picking up sheets from a sheet stack and continuously transporting the sheets along a sheet transport path, the sheet feeder comprising:

• a transport unit that transports the sheets along the sheet transport path one by one;
• a gap occurrence detection unit that detects, within a predetermined section of the sheet transport path, occurrence of a gap between the trailing edge of a preceding sheet and the leading edge of a following sheet;
• and
• a controller that controls a timing at which the transport unit starts transporting the following sheet according to a result of the detection by the gap occurrence detection unit,
• the gap occurrence detection unit including:
• a first light emitting element that is disposed on a first side of the sheet transport path and emits diffused light at least toward the predetermined section;
• a light receiving element that is disposed on the first side of the sheet transport path;
• a converging reflector that is disposed on a second side of the sheet transport path opposite the first side and converges, onto the light receiving element, light that is emitted by the first light emitting element and reaches the converging reflector by travelling across the predetermined section;
• and
• a second light emitting element arranged such that light emitted by the second light emitting element and reflected by a sheet passing through the predetermined section is detected by the light receiving element,
• the sheet feeder further comprising:
• a lighting switching unit that switches between lighting by the first light emitting element and lighting by the second light emitting element;
• and
• an output sampling unit that obtains a first output corresponding to the first light emitting element and a second output corresponding to the second light emitting element by sampling an output from the light receiving element according to the switching by the lighting switching unit, wherein
• the gap occurrence detection unit detects occurrence of the gap based on the first and second outputs obtained by the output sampling unit while the preceding sheet and the following sheet are passing through the predetermined section.

A sheet feeder for sequentially picking up sheets from a sheet stack and continuously transporting the sheets along a sheet transport path, the sheet feeder comprising:

• a transport unit that transports the sheets along the sheet transport path one by one;
• a gap occurrence detection unit that detects, within a predetermined section of the sheet transport path, occurrence of a gap between the trailing edge of a preceding sheet and the leading edge of a following sheet;
• and
• a controller that controls a timing at which the transport unit starts transporting the following sheet according to a result of the detection by the gap occurrence detection unit, wherein
• the gap occurrence detection unit includes:
• a light emitting element that is disposed on a first side of the sheet transport path and emits light at least toward the sheet transport path;
• a light receiving element that is disposed on the first side of the sheet transport path;
• and
• a converging reflector that is disposed on a second side of the sheet transport path opposite the first side and converges, onto the light receiving element, light that is emitted by the light emitting element and reaches the converging reflector by travelling across the predetermined section, wherein
• the sheet transport path and the set of the light emitting element, the light receiving element, and the converging reflector are arranged such that reflection light of the light emitted by the light emitting element that is regularly reflected by the sheet being transported along the predetermined section of the sheet transport path is not received by the light receiving element.