This invention relates to a device for and a method of detecting an overlap in paper being transported. More particularly, this invention relates to such a device and a method capable of dependably informing the user whether or not the detected overlap is of a kind to be avoided or a kind that may be ignored.
When a plurality of sheets of paper to be scanned individually are simultaneously transported in an overlapped condition even partially, it is not possible to carry out an accurate scan. For this reason, many scanners of this type are provided with an overlap detector, or a detector for detecting an overlapped condition of paper sheets being transported such that the transportation of the paper sheets may be stopped temporarily. In other words, scanning by such a scanner is interrupted when the overlap detector detects an overlapped condition.
The scanning operation of a scanner is interrupted also when the overlap detector detects an overlapped condition erroneously, forcing the user to go through the troublesome process of investigating the cause of the interruption and restarting the scanning. Another problem with such a prior art overlap detector is that it always concludes that there is an overlap of the kind for which the transportation of paper should be interrupted whenever two sheets of paper are found to be overlapping. In other words, doubly folded sheets and two sheets of intentionally overlapped paper are both treated as representing an overlapped condition for which the transportation of the paper should be interrupted.
It is therefore an object of this invention to provide a device for and a method of accurately detecting an overlap in paper being transported such that doubly folded paper and two sheets of paper that are intentionally overlapped may be distinguished.
An overlap detecting device according to this invention may be characterized as comprising a detecting means for detecting an overlapped condition in a paper sheet being transported on its transportation path, a data generating device for generating a specified data item on the overlap detected by the detecting means, a level selector for selecting one of a plurality of preliminarily defined levels corresponding to the specified data item generated by the data generating device, and an output device for outputting the selected level by the level selector. Thus, as an overlapped condition of a paper sheet being transported on a path is detected, a specified data item about the overlap is generated, its level is selected from a plurality of preliminarily defined levels and the selected level is outputted to be referenced by the user. The user can thereby determine whether the overlap was of an intentional or unintentional kind. The data generating device and the level selector may each comprise a CPU.
For the detection of the overlap, use may be made of an ultrasonic wave generator for generating ultrasonic waves to be made incident on the path of transportation of the paper sheet, an ultrasonic receiver for receiving the ultrasonic waves generated by the ultrasonic wave generator and a phase difference detector which may comprise a CPU for detecting a phase difference between the ultrasonic waves received by the ultrasonic wave receiver and a predetermined standard phase. An overlap in a paper sheet being transported on the path can be detected from the phase difference detected by the phase difference detector.
The aforementioned data item serves to indicate a possibility of occurrence of the overlap, and the preliminarily defined levels include a first level indicating that the overlap is certainly taking place and a second level indicating that there is a possibility that the overlap is taking place. Thus, if the first level is outputted during a scanning operation, the scanning is interrupted but the scanning can be continued if the output is the second level. In this manner, interruption of the scanning due to an erroneous detection of an overlap can be restrained.
The aforementioned data item may include a cumulative number of times the overlap has been detected by the overlap detector and the level selector may include a first level selector and a second level selector, the first level selector selecting the first level if the cumulative number is equal to or greater than a predefined first threshold value, the second level selector selecting the second level if the cumulative number is equal to or greater than a predefined second threshold value which is smaller than the first threshold value. The first and second level selectors may each comprise a CPU. In this manner, the level of possibility for the occurrence of an overlap can be dependably determined, and these levels can be freely adjusted by the user or by the maker by merely changing the values of the first and second threshold values.
The aforementioned data generating device may reset the cumulative number of times to zero if the paper sheet is on its path of transportation but the overlap has not been detected by the overlap detector. In this manner, the levels for determining the possibility of an overlap can be set more reliably.
There may also be provided a judging device for judging that there is no possibility that an unintentional overlap has occurred if the overlap is detected by the overlap detector over an entire detection range of the paper sheet from its front edge to its back edge. In other words, a doubly folded paper sheet or two intentionally overlapped sheets of paper are not considered to be an unwanted overlap. Thus, a scanner provided with a detecting device of this invention can operate on doubly folded paper sheets and pairs of intentionally overlapped paper sheets. Such a judging device may comprise a CPU which may not be the same as any of the CPUs referred to above but may comprise a CPU of a multi-purpose personal computer.
An overlap detection method of this invention may be characterized as comprising the steps of generating ultrasonic waves to be made incident on the path of transportation of the paper sheet, receiving the ultrasonic waves made incident on the path, detecting a phase difference between the received ultrasonic waves and a predetermined standard phase, detecting an overlap in a paper sheet being transported on the path on the basis of the detected phase difference, generating a specified data item on the detected overlap, selecting one of a plurality of preliminarily defined levels corresponding to the specified data item, outputting the selected level, and judging that there is no possibility of an unintentional overlap if the overlap is detected over an entire detection range of the paper sheet from its front edge to its back edge. When an overlap is detected by a method of this invention, a specified data item is generated on the detected overlap, a level for the specified data item is selected from a plurality of preliminarily defined levels and the selected level is outputted. Thus, the user can easily judge whether or not the detected overlap is an unwanted overlap.