Patent Publication Number: US-2003227126-A1

Title: Document sensor and sensing method

Description:
BACKGROUND OF INVENTION  
       [0001] 1. Field of Invention  
       [0002] The present invention relates to the document sensor of a sheet feed scanner. More particularly, the present invention relates to a document sensor that can be fabricated at a considerably reduced cost.  
       [0003] 2. Description of Related Art  
       [0004] Due to rapid progress in the electronic manufacturing industry, high performance computing systems are produced en-mass. With the proliferation of electronic products in the market, many of them are used in our daily life. In recent years, processing speed and storage capacity of computer products has also increased at a tremendous pace leading to higher performance for many types of graphic processors. Consequently, different types of image processing products such as optical scanners and digital cameras are constructed.  
       [0005] According to the document scanning method, optical scanners can be classified as belonging to: a packet scanner, a sheet feed scanner, a drum scanner or a flatbed scanner. As an example, a sheet feed scanner can have an optical resolution in excess of 600 dpi and almost all of them have a scanning structure that employs contact image sensors (CIS). In fact, the sheet feed scanner occupies such a small volume that they are routinely carried along with a notebook computer.  
       [0006] In general, a document sensor is installed on a sheet feed scanner so that the presence of any document in the sheet feeder can be detected. FIG. 1 is a front view showing a document sensing system in a conventional sheet feed scanner. As shown in FIG. 1, the document sensor  100  includes an optical sensor  110 , a light emitter  120 , a rocking lever  130  and a key peg  140 . The optical sensor  110  and the light emitter  120  are attached to the sheet feeder (not shown) on each side of the rocking lever  130 . The key peg  140  is also attached to the sheet feeder after passing through a hole in the rocking lever  130 . Thus, the rocking lever  130  is free to rotate using the key peg  140  as a pivot. The light emitter  120  is positioned in such a way that a beam of light  122  from the light emitter  120  will go straight into the optical sensor  110  unimpeded.  
       [0007] Before a document (not shown) is fed into the sheet feeder, one end of the rocking lever  130  will cut across the path of the beam  122 . Hence, the light beam  122  can never reach the optical sensor  110 . Without receiving any light, the light sensor  110  will transmit a signal to a circuit chip (not shown) so that the chip jumps to a “no document” logic state.  
       [0008]FIG. 2 is a side view of the document sensing system in FIG. 1. When a document  150  is fed in direction  152  into the sheet feeder, the document  150  pushes the rocking lever  130  and swings its upper end to one side so that the light beam  122  is able to project straight ahead to the optical sensor  110  unimpeded. On picking up the light beam  122 , the optical sensor  110  transmits another signal to the circuit chip so that the chip switches to a “document present” logic state.  
       [0009] As shown in FIGS. 1 and 2, the presence or absence of a document  150  in the sheet feeder depends on the light emitter  120 /light sensor  110  system. The demand for a light emitter and a light sensor increases production cost of the optical scanner.  
       SUMMARY OF INVENTION  
       [0010] Accordingly, one object of the present invention is to provide a document sensor for a sheet feed scanner that does not require the incorporation of a light emitter and an optical sensor. Hence, overall production cost of the document sensing system is greatly reduced.  
       [0011] To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a document sensor for detecting the presence or absence of a document in a sheet feeder. The document sensor mounts on the sheet feeder. The document sensor at least includes a printed circuit board, a key peg and a rocking lever. The printed circuit board is attached to the sheet feeder. The printed circuit board contains a first lead wire and a second lead wire. The first lead wire and the second lead wire are separate from each other. The key peg passes through a hole in the rocking lever before attaching to the sheet feeder so that the rocking feeder may rotate using the key peg as a pivot. A conductive element is attached to the rocking lever so that the first lead wire and the second lead wire may be electrically connected together through a rotary motion of the rocking lever.  
       [0012] In one embodiment of this invention, the rocking lever has a linear shape and the conductive element is positioned at one end of the rocking lever. The conductive element may be an electroplated conductive layer on the rocking lever or a conductive plate attached to the rocking lever through rivets. Furthermore, the entire rocking lever may be made from a conductive material. One major design criteria of the rocking lever is the capacity to join up the first lead wire and the second lead wire selectively.  
       [0013] This invention also provides a method for sensing the presence or absence of a document inside a sheet feeder. The document sensing method includes the following steps. In step one, a document sensor is provided. The document sensor is attached to the sheet feeder. The document sensor comprises a first lead wire, a second lead wire and a driven element. The first lead wire and the second lead wire are detached from each other but are electrically connected together through the driven element. In step two, a document is fed into the sheet feeder. The entrance of a document pushes the driven element away from either the first lead wire or the second lead wire, breaking the electrical connection between the first and the second lead wire. Hence, the presence of a document in the sheet feeder can be detected. In step three, the document is pulled away from the sheet feeder. The driven element moves back to the original position and reforms the electrical connection between the first lead wire and the second lead wire. Hence, the absence of a document in the sheet feeder can be detected.  
       [0014] This invention also provides an alternative method for sensing the presence or absence of a document inside a sheet feeder. The document sensing method includes the following steps. In step one, a document sensor is provided. The document sensor is attached to the sheet feeder. The document sensor comprises a first lead wire, a second lead wire and a driven element. The driven element is detached at least from either the first lead wire or the second lead wire. In step two, a document is fed into the sheet feeder. The entrance of a document pushes the driven element to make an electrical connection between the first lead wire and the second lead wire. Hence, the presence of a document in the sheet feeder can be detected. In step three, the document is pulled away from the sheet feeder. The driven element moves back to the original position, breaking contact with at least either the first lead wire or the second lead wire again. Hence, the absence of a document in the sheet feeder can be detected.  
       [0015] In brief, by attaching a conductive element to the rocking lever or fabricating the rocking lever with conductive material, an electrical connection or disconnection between the first lead and the second lead wire can be selected through a rotation. Ultimately, internal logic states of a silicon chip can be controlled. The document sensing system has a simple structure and circuit design and hence the production cost is low.  
       [0016] It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0017] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
     [0018]FIG. 1 is a front view showing a document sensing system in a conventional sheet feed scanner;  
     [0019]FIG. 2 is a side view of the document sensing system in FIG. 1;  
     [0020]FIG. 3 is a front view showing a document sensing system in a sheet feeder according to one preferred embodiment of this invention;  
     [0021]FIG. 4 is a side view of the document sensing system in FIG. 3;  
     [0022]FIGS. 5 and 6 are side views showing the positions of a rocking lever inside a document sensing system according to a second preferred embodiment of this invention; and  
     [0023]FIGS. 7 and 8 are side views showing the positions of a rocking lever inside a document sensing system according to further another preferred embodiment of this invention. 
    
    
     DETAILED DESCRIPTION  
     [0024] Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
     [0025]FIG. 3 is a front view showing a document sensing system in a sheet feeder according to one preferred embodiment of this invention. The document sensor  200  in FIG. 3 is used for detecting the entrance of a document (not shown) into a sheet feeder (not shown). The document sensor  200  is mounted on the sheet feeder. The document sensor  200  comprises a printed circuit board  210  and a driven element  220 . The printed circuit board  210  is attached to the sheet feeder. The printed circuit board  210  at least includes a first lead wire  212  and a second lead wire  214 . The first lead wire  212  and the second lead wire  214  are detached from each other. That means the first lead wire  212  and the second lead wire  214  are electrically isolated. The driven element  220  comprises a rocking lever  230  and a key peg  240 . The key peg  240  passes through a hole in the rocking lever  230  before attaching to the sheet feeder so that the rocking lever  230  is free to rotate using the key peg  240  as a central pivot. The rocking lever  230  has a linear shape. A conductive member  250  (shaded portion in the figure) is attached to one end  232  of the rocking lever  230 . The conductive member  250  is a conductive layer formed on the surface of the rocking lever  230  either by electroplating or by riveting. Through rotation of the rocking lever  230 , the first lead wire  212  and the second lead wire  214  may be electrically connected or separated by moving the conductive member  250  towards or away from the lead wires  212  and  214  through rocking motion of the lever  230 .  
     [0026] Before the entrance of a document (not shown) into the sheet feeder, the first lead wire  212  and the second lead wire  214  are electrically connected together through the conductive path  250 . Since a closed circuit is formed through the wires  212  and  214 , a circuit chip connected to the wires  212  and  214  will jump to a “no document” logic state.  
     [0027]FIG. 4 is a side view of the document sensing system in FIG. 3. When a document  260  is fed into the sheet feeder in direction  262 , the document  260  pushes the rocking lever  230  and moves the conductive member  250  away from the first lead wire  212  and the second lead wire  214 . Hence, an open circuit is formed between the first lead wire  212  and the second lead wire  214 . The breaking of the circuit will initiate a signal that informs the circuit chip to jump to a “contain document” logic state.  
     [0028] As shown in FIGS. 3 and 4, this invention relies on the attachment of a conductive member  250  to the rocking lever  230  and the selective breaking of electrical connection between the first lead wire  212  and the second lead wire  214  through rotation to signal a change of logic state inside a circuit chip. This type of document sensor  200  has a simple structural design and uses a simple circuit. Hence, fabrication cost of the sensor is low.  
     [0029] In the first embodiment, conduction between the first lead wire and the second lead wire indicates a “document absent” logic state while an open circuit between the first and the second lead wire indicates a “document present” logic state. However, the aforementioned configuration of the logic states is not the only permissible one. logic states may also be used to control the circuit chip. FIGS. 5 and 6 are side views showing the positions of a rocking lever inside a document sensing system according to a second preferred embodiment of this invention.  
     [0030] As shown in FIG. 5, before the passing of a document into the sheet feeder, the first lead wire  312  and the second lead wire  314  are in an open circuit state. Hence, the circuit chip will jump to a “no document” logic state. On the other hand, when a document  360  is fed into the sheet feeder in direction  362  as in FIG. 6, the document  360  pushes the rocking lever  330  to make an electrical connection between the first lead wire  312  and the second lead wire  314 . Hence, a closed circuit is formed and the circuit chip will switch to a “document present” logic state.  
     [0031] In the aforementioned embodiments, a conductive member is attached to the rocking lever by electroplating or riveting. However, this invention also permits the entire rocking lever to be made from a conductive material so that the first lead wire and the second lead wire may be electrically connected through motion of the rocking lever.  
     [0032] Furthermore, in the foregoing embodiments, the first lead wire and the second lead wire are disposed on a printed circuit board. However, the invention is not limited in the foregoing applications. As shown in FIGS. 7 and 8, they are side views showing the positions of a rocking lever inside a document sensing system according to another preferred embodiment of this invention. The first lead wire  412  is disposed on the printed circuit board  410  but the second lead wire  414  is disposed on the rocking lever  430 . The second lead wire  414  is electrically connected to the conductive members  450 , so that when the rocking lever  430  is rotated to printed circuit board  410 , the conductive members  450  would cause the first lead wire  412  and the second lead wire  414  to be connected. Then, it can be judged whether or not the sheet is fed into the sheet feeder. The method to judge it is similar as foregoing descriptions and is not further described here. The method using the structure. as shown in FIG. 7, to judge whether or not the sheet is fed into the sheet feeder can refer to the descriptions for FIGS. 5 and 6. The method using the structure. as shown in FIG. 7, to judge whether or not the sheet is fed into the sheet feeder can refer to the descriptions for FIGS. 3 and 4.  
     [0033] In conclusion, this invention relies on the attachment of a conductive member to the rocking lever and the selective breaking of electrical connection between a first lead wire and a second lead wire through rotation to signal a change of logic state inside a circuit chip. This type of document sensor has a simple structure and employs a simple control circuit. Hence, fabrication cost of the sensor is considerably lower than the conventional light emitter/optical sensor system.  
     [0034] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.