1. Field of the Invention
The present invention relates to a document end detecting unit for detecting a front-end or rear-end of a document moving relatively to a light source, a document reading unit which reads a document moving relatively to a light-receiving section, and a facsimile apparatus equipped with a document reading unit.
2. Description of the Related Art
An electronic equipment for processing an image such as a facsimile apparatus is equipped with a document reading unit for optically reading a document. A document reading unit comprises a light-receiving section for reading a document, a light source, and a moving system for moving a document relatively to the light-receiving section. For reading a document, it is ideal that the light source illuminates a point to be read of the document from a direction forming an angle of 45xc2x0 with the surface of the document and the light-receiving section reads the surface of the document from a perpendicular direction to the surface of the document. When a document is illuminated from one direction slanting to the surface of the document, a shade caused by the thickness of the document appears in close to either the front-end or rear-end of the document. A front-end of a document is an end on the downstream side in the document moving direction, and a rear-end of a document is an end on the upstream side in the document moving direction. In the case where the light source locates on the upstream side in the document moving direction from the light-receiving section, a shade caused by a front-end of a document appears. In the case where the light source locates on the downstream side in the document moving direction from the light-receiving section, a shade caused by a rear-end of a document appears. When a shade of the front-end or rear-end appears, the light-receiving section reads the shade, so that an unnecessary black line is inserted into an image which is a result of reading.
A first method of preventing insertion of a black line caused by a shade is to place light sources both on the downstream side and the upstream side in the document moving direction from the light-receiving section and illuminate a document from both the sides of the light-receiving section. In this case, it is difficult to completely delete both shades of the front-end and rear-end of a document at a time. Moreover, since a plurality of light sources need to be placed, the production cost of a document reading unit increases.
A second method of preventing insertion of a black line caused by a shade is to accurately detect a front-end or rear-end of a document causing a shade and, based on a result of detection, eliminate a shade of the front-end or rear-end of the document from an image which is a result of reading. In view of economy, the second method is appropriate for an electronic equipment such as a facsimile apparatus as a method of preventing insertion of a black line caused by a shade. In the second method, it is necessary to accurately detect a shade of a front-end or rear-end of a document when reading the document.
In Japanese Examined Patent Publication JP-B2 2898453, the applicant of this invention discloses a document reading unit which detects a front-end of a document based on a change of outputs of reading means caused by a shade of the front-end of the document. The document reading unit disclosed in JP-B2 2898453 detects a change of outputs of reading means caused by cutting off light reflected from a white backboard whose end on the downstream side in the document transferring direction is flat, transfers the document a predetermined distance from a point in time of detecting the change of outputs, and thereafter starts to read the document.
Japanese Unexamined Patent Publication JP-A 8-214108 (1996) discloses a method of detecting a front-end of a document in a document reading unit which moves a document with a light-receiving section fixed. The document reading unit disclosed in JP-A 8-214108 further comprises a white member, which is a roller for transferring a document. The light-receiving section of the document reading unit has a portion working as a light-receiving portion for detecting a front-end other than a portion working as a light-receiving portion for reading a document. The white member is opposed to the light-receiving portion for reading a document and the light-receiving portion for detecting a front-end. The surface of the white member is white, and in order to make the light reflectivity of part of the surface of the white member lower than that of the remainder, the part of the surface of the white member has a slot or a black-colored portion. The light-receiving portion for detecting a front-end is placed on the same board as the light-receiving portion for reading a document, on the upstream side in the document moving direction from the light-receiving portion for reading a document, and opposed to the slot or the colored portion. When a document starts to move, the light-receiving portion for detecting a front-end receives light reflected from the slot or the colored portion, and when the document comes between the slot or colored portion and the light-receiving portion for detecting a front-end, receives light reflected from the document. The document reading unit determines the difference between a color of the slot or colored portion and the white color of the background color of the document based on a change over time of the amount of the reflected light, and detects the front-end of the document based on the difference.
In the case of optically detecting a front-end or rear-end of a document causing a shade, the shorter a distance from the light-receiving portion for reading a document to the light-receiving portion for detecting a front-end is, the smaller an error in detection of a front-end or rear-end caused by transfer of a document is. The smaller an error in detection of a front-end or rear-end is, the more accurately a shade caused by a front-end or rear-end is eliminated from an image which is a result of reading. The best construction of a document reading unit is the one that the light-receiving portion for reading a document also works as the light-receiving portion for detecting a front-end. In the document reading unit disclosed in JP-A 8-214108, the light-receiving portion for reading a document and the light-receiving portion for detecting an end of a document are disposed separately. Moreover, since the document reading unit of JP-A 8-214108 does not detect a shade and has the slot for lowering the light reflectivity of part of the white member, the object thereof is different from that of the invention. In the case where instead of the slot a colored portion is provided on the surface of the white member in order to lower the light reflectivity, as described in JP-A 8-214108, it becomes difficult to detect the shade.
In a document reading unit, output data showing a light-receiving result of a light-receiving section are often subjected to shading correction. In shading correction, an output waveform showing a distribution of output data from light-receiving elements with respect to positions of the light-receiving elements composing a light-receiving section is compared with a reference waveform which is set in advance, and the output waveform is corrected in accordance with the reference waveform. The reference waveform is set individually in every document reading unit. For example, in a state where a light source illuminates a white member opposed to a light-receiving section for reading a document, the light-receiving section receives light reflected from the white member, whereby in accordance with an output waveform of data outputted as a result of light-reception, a reference waveform is formed. In the document reading unit of JP-A 8-214108 mentioned before, the white member has the slot or colored portion, so that the amount of light reflected from the white member is largely different depending on a place where light is reflected. Therefore, in the document reading unit of JP-A 8-214108, it is difficult to use an output waveform of data showing the amount of light reflected from the white member as a reference waveform.
An object of the present invention is to provide a document end detecting unit which is capable of optically detecting a front-end or rear-end of a document with accuracy, a document reading unit, and a facsimile apparatus.
The invention provides a document end detecting unit which detects one of an upstream end and downstream end in a moving direction of a document moving relatively to a predetermined reference position, the document end detecting unit comprising:
a light source for illuminating the reference position from a downstream side or upstream side in the moving direction of the document;
light-receiving means for receiving reflected light coming through the reference position;
a back member opposed to the light-receiving means and the light source across the reference position; and
detecting means for detecting the one end of the document,
wherein a slot whose longitudinal direction is substantially parallel to the moving direction of the document is provided on a surface of the back member, and
the detecting means detects a shade of the one end of the document appearing at the slot of the back member based on a light-receiving result of the light-receiving means, and detects the one end of the document based on a result of detecting the shade.
According to the invention, the document end detecting unit detects a shade appearing at the slot of the back member due to an end of a document, and detects either end of the document based on a result of detecting the shade. This allows appearance and disappearance of a shade to be detected with reliability, so that reliability on detection of either end of a document in the document end detecting unit according to the invention is increased enough to be more practicable than a conventional document end detecting unit which uses a back member having no slot.
In the document end detecting unit of the invention it is preferable that the detecting means detects disappearance timing of a shade of the downstream end in the moving direction of the document and regards the detected disappearance timing as timing when the downstream end in the moving direction of the document reaches the reference position.
According to the invention, in the document end detecting unit, the detecting means regards a detected disappearance timing of a shade of a downstream end in the moving direction of a document as timing when the end reaches the reference position. Timing when the downstream end in the moving direction of the document reaches the reference position coincides with disappearance timing of a shade. This enables the document end detecting unit to most reliably detect the downstream end in the moving direction of a document based on a shade appearing at the slot of the back member.
In the document end detecting unit of the invention it is preferable that the detecting means detects appearance timing of a shade of the downstream end in the moving direction of the document and regards a point in time when the document has relatively moved a predetermined distance from a position thereof at the detected appearance timing as timing when the downstream end in the moving direction of the document reaches the reference position.
According to the invention, in the document end detecting unit, the detecting means detects timing when the downstream end in the moving direction of the document reaches the reference position based on only appearance timing of shade of the downstream end in the moving direction of the document. This simplifies the construction for detecting a shade of a document end, so that the entire construction of the document end detecting unit is simplified.
In the document end detecting unit of the invention it is preferable that the color of the surface of the back member and the inner wall of the slot is white;
the light-receiving means is composed of a plurality of light-receiving elements arranged in parallel to a direction which is substantially orthogonal to the moving direction of the document;
light reflected from the slot of the back member and light reflected from the surface of the back member excluding the slot are respectively received by one or more light-receiving elements; and
the detecting means:
(1) judges whether the surface of the document is dark color or not based on the amount of reflected light received by a light-receiving element which should receive the light reflected from the surface of the back member excluding the slot, and
(2) when the surface of the document is dark color, detects timing when the amount of reflected light received by the light-receiving element which should receive the light reflected from the surface of the back member excluding the slot becomes less than a predetermined light amount, and regards the detected timing as timing when the downstream end in the moving direction of the document reaches the reference position.
According to the invention, in the document end detecting unit, when the surface of the document is dark color, the detecting means regards timing when the amount of light reflected from the surface of the back member excluding the slot becomes less than a predetermined light amount as timing when the downstream end in the moving direction of the document reaches the reference position. This enables the document end detecting unit to detect a document end even when it is difficult to distinguish a shade from the surface of a document because the surface of the document is dark color.
In the document end detecting unit of the invention it is preferable that the back member has a plurality of slots, and
the detecting means performs detection of a shade of a document end and detection of a position of the document end individually at points where the slots of the back member are formed.
According to the invention, in the document end detecting unit, detection of a shade of either end of a document and detection of a position of either end of a document are performed at the plurality of slots on the surface of the back member, respectively. As a result, a plurality of results of detecting the position of either end of the document can be found, so that it is possible to increase the precision in a position of one end and detect a skew of the document by using the detection results.
The invention provides a document reading unit comprising:
the document end detecting unit mentioned above;
moving means for moving at least one of the light-receiving means and the document to be read so that the document moves relatively to the light-receiving means in the document end detecting unit while passing through the reference position;
data accumulation means for accumulating data of reflected light amount from the light-receiving means as data of density of pixels composing an image; and
accumulation control means for causing the data accumulation means to start and finish accumulation of data in accordance with timing when the detecting means of the document end detecting unit detects either end of the document.
According to the invention, the document reading unit uses the document end detecting unit which uses a shade of either end of a document. Since the light-receiving means used for detection of a document end also works as light-receiving means for optically reading a document, an error in detection of a document end due to movement of the document is minimized, and a component count of the document reading unit is decreased. Since a data accumulation timing is controlled based on a result of detecting a document end by using a shade appearing at the slot of the back member, a shade of the document end is reliably eliminated from an image which is a result of reading a document at a point in time that data are accumulated in the data accumulation means. This increases the quality of an image in the data accumulation means.
In the document reading unit of the invention it is preferable that thee document reading unit further comprises reference waveform producing means for producing a reference waveform used for shading correction; and shading correction means for subjecting data of the reflected light amount from the light-receiving means to shading correction using the reference waveform, that the light-receiving means is composed of a plurality of light-receiving elements arranged in parallel to a direction substantially orthogonal to the moving direction of the document, and that the reference waveform producing means causes the light-receiving means to receive light reflected from a surface of the back member and regards an output waveform showing a relation between the reflected light amounts outputted from the respective light-receiving elements and positions of the respective light-receiving elements as the reference waveform.
According to the invention, the document reading unit performs shading correction using the reference waveform when reading a document. An output waveform obtained as a result of causing the light-receiving means to receive the light reflected from the surface of the back member is used as a reference waveform. This facilitates production of a reference waveform in consideration of variations in property of individual light-receiving means. In the case where such a reference waveform is used, the shading correction means is capable of performing shading correction with accuracy.
In the document reading unit of the invention it is preferable that an inclination angle of a side wall of the slot of the back member to a bottom surface of the slot is more than and less than 90xc2x0.
According to the invention, in the document reading unit, the gradient of the side wall of the back member slot is gentle, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes the reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that a surface of a border portion between a side wall of the slot of the back member and the bottom surface of the slot is curved.
According to the invention, in the document reading unit, an angle of a portion where a side wall of the slot of the back member rises from the bottom surface of the slot is gently curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes a reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that a surface of a border portion between a side wall of the slot of the back member and a surface of the back member is curved.
According to the invention, in the document reading unit, the portion where the slot falls from the surface of the back member is gently curved, so that it is possible to treat the back member as a member with almost uniform reflectivity. This makes the reference waveform produced based on light reflected from the back member more accurate, so that the shading correction means is capable of performing shading correction with more accuracy.
In the document reading unit of the invention it is preferable that the reference waveform producing means corrects the shape of the output waveform to a shape to be obtained in the case where the back member has no slot, and regards the corrected output waveform as a reference waveform.
According to the invention, in the document reading unit, when a reference waveform for shading correction is produced, part of the output waveform corresponding to the slot is corrected to obtain an output waveform in the case of no slot, so that a more accurate reference waveform is produced. With such a corrected reference waveform, it is possible to adopt such an ideal method as integrating light-receiving means for reading a document and light-receiving means for detecting a document end, and perform shading correction using the reference waveform with more accuracy.
In the document reading unit of the invention it is preferable that the reference waveform producing means corrects part of the output waveform corresponding to the slot by interpolation of both sides of the part of the output waveform.
According to the invention, in the document reading unit, the output waveform is corrected by interpolating the part of the output waveform corresponding to the slot by both the sides of the part of the output waveform. This allows a reference waveform to be corrected with ease and reliability by using only the output waveform.
In the document reading unit of the invention it is preferable that the document reading unit further comprises standard waveform storing means which previously stores a standard falling waveform showing a standard relation between the amount of light reflected from a back member having a slot and positions of the light-receiving elements and a standard reference waveform showing a standard relation between the amount of the light reflected from the back member having no slot and positions of the respective light-receiving elements, and that the reference waveform producing means corrects the output waveform based on the standard falling waveform and the standard reference waveform.
According to the invention, in the document reading unit, a reference waveform for shading correction is produced based on a result of reading the light reflected from the surface of the back member and the content stored in the standard waveform storing means. In producing a reference waveform, part of the output waveform corresponding to the slot is corrected, so that a more accurate reference waveform is produced.
In the document reading unit of the invention it is preferable that the accumulation control means sets timing of starting to accumulate data in the data accumulation means later than timing when either end of a document reaches the reference position, detected by the detecting means.
According to the invention, in the document reading unit, timing of starting to accumulate data is set later than timing when a document end reaches the reference position, detected by the document end detecting unit. This reliably removes a shade caused by a document end from an image which is a result of reading a document, so that the quality of an image is increased still more.
In the document reading unit of the invention it is preferable that the back member has a plurality of slots, the detecting means performs detection of a shade of a document end and detection of a position of either end of the document individually at points where the plurality of slots of the back member are formed, and the accumulation control means calculates the amount of skew of the document based on the difference in position of the document end detected at the plurality of slots, and sets timing of starting to accumulate data in the data accumulation means later than timing detected by the detecting means that either end of a document reaches the reference position, by a period of time corresponding to the calculated amount of skew.
According to the invention, in the document reading unit, timing of starting to accumulate data is set later than timing detected by the document end detecting unit that a document end reaches the reference position, by a period of time corresponding to the amount of skew of a document. This allows a front-end portion of the document which is not seen in an image due to removal of a shade to be reduced still more, thereby preventing a lack of information on a document due to removal of a shade in an image.
In the document reading unit of the invention it is preferable that the back member is a roller which is capable of rotating about a rotation axis, and the moving direction of a document is orthogonal to an axial direction of the rotation axis.
According to the invention, the document reading unit is constructed in such a manner that the light source and the light-receiving elements are fixed and a document moves. Since the back member is a roller, the back member is capable of working as one of the members of a document moving system. This makes it possible to downsize the document reading unit and decrease a component count. Therefore, the producing cost of the document reading unit is reduced.
The invention provides a facsimile apparatus comprising:
the document reading unit mentioned above; and
a communication unit for sending data of an image accumulated in the data accumulation means of the document reading unit to a communication unit capable of receiving data of an image.
According to the invention, the facsimile apparatus comprises the document reading unit equipped with the document end detecting unit which uses a shade of a document end. With such a document reading unit, the precision in detection of a document end is increased, so that the facsimile apparatus is capable of performing a process associated with detection of a document end with more precision.