Patent Publication Number: US-6901820-B2

Title: Device for detecting width of sheet-like medium, and image formation apparatus

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to a device (hereinafter “width detecting device”) for detecting a width of a sheet-like medium for use, for example, in a paper feeder of an image formation apparatus such as a copying machine, a printer, a facsimile, or the like. 
   2) Description of the Related Art 
   A width detecting device for detecting a width of a sheet-like medium (i.e., a paper) has been disclosed in, for example, Japanese Patent Application Laid Open No. 5-43058. When it is assumed that the paper has a paper length direction and a paper width direction, then in this width detecting device, two limiting members are disposed parallel to the paper width direction and facing with each other on a base for placing the paper. These limiting members are arranged so as to move towards each other or away from each other, along the paper width direction via an interlocking unit. The limiting members are moved so that they make a contact with the respective edges of the paper, and a detecting unit detects the position of the limiting members to thereby detect the width of the paper. 
   The detecting unit includes a plurality of resistors having different resistances positioned at predetermined positions in the base along the paper width direction, and one contact element is positioned in each of the limiting plates. When the limiting plates are moved, the contact elements in the limiting plates make an electrical contact with the resistors in the base, and an electrical path is created. The detecting unit further includes a voltmeter that measures the voltage of this electrical path. Based on the voltage, it is possible to decide with which resistors the contact elements have made the electrical contact and thereby it is possible to decide the width of the paper because the positions of the resistors are known. 
   In this configuration there is a problem that the contact (hereinafter “contact pressure”) between the resistor and the contact element varies depending upon variation in the size of the parts, conditions at the time of assembly, and environmental conditions. 
   If the contact pressure is strong, the limiting plates may move because of the contact pressure, or it may become difficult to move the limiting plates because of the contact pressure. If the contact pressure is weak, an error may be generated in the detection of the width of the paper. If it is incorrectly detected, for example, that the paper is wider, an unnecessary portion is developed so as to increase the load on a cleaning device or excessive consumption of a toner can be generated. Moreover, since a relatively large resistor area is needed, the miniaturization of the width detecting device is not satisfied. 
   As a sensor for detecting an amount of movement (hereinafter “moving amount”) of a subject, a rotation angle detection type sensor that converts the moving amount into an angle and generates a signal corresponding to the angle is known. Some prior arts have used the rotation angle detection type sensor in combination with the limiting plates described above to detect the width of the paper. In that case, the rotation angle detection type sensor converts the amount of movement of the limiting plates into angles and determines the width of the paper. 
   The rotation angle detection type sensor can accurately detect the width of the paper when the angle is less than 360°, but can not properly detect the width when the angle is more than 360°. Because, since the pattern of the signal output by the rotation angle detection type sensor when the angle is less than 360° is the same as when it is greater than 360°, it is impossible to distinguish whether the angle is less than 360° or greater than 360°. 
   A width detecting device of manual feeding paper base is disclosed in, for example, Japanese Patent Application Laid Open No. 11-130271. This width detecting device has a rotation type variable resistor whose resistance varies according to a rotation angle of a shaft section. This width detecting device detects the paper width based on the resistance output by the rotation type variable resistor. 
   Generally, a paper of size A3 or smaller is used in the image formation device. It is possible to detect the width of the A3 size paper with the rotation angle detection type sensor or the rotation type variable resistor because the angle corresponding to the A3 size paper is less than 360°. 
   However, recently, there is an increasing demand to increase the paper size that can be handled in the image formation apparatus. If the size of the paper is increased, then the angle corresponding to that paper is greater that 360°, and the conventional rotation angle detection type sensor or the rotation type variable resistor do not give proper results. To get proper results, a gear used in the rotation angle detection type sensor should be made larger. If the gear is made larger, then extra space is required to accommodate the gear. Moreover, the number of switches used in the rotation angle detection type sensor increase. This leads to cost increase. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a width detecting device capable of detecting the width of a wider sheet-like medium in a compact configuration. 
   The width detecting device according to one aspect of the present invention comprises a placing base for placing a sheet-like medium having a first side and a second side perpendicular to a width direction of the sheet-like medium; a first limiting member situated on the first side and a second limiting member situated on the second side of the sheet-like medium; an interlocking unit that moves the first limiting member and the second limiting member along the width direction; a rotation angle detection sensor that detects an angle based on positions of the first limiting member and the second limiting member and outputs an angle signal based on the angle; and an auxiliary sensor that judges any one of presence and absence of the first limiting member and the second limiting member in a moving range of the first limiting member and the second limiting member and outputs a presence/absence signal based on the judgment; and a width detection sensor that detects the width of the sheet-like medium based on the angle signal and the presence/absence signal. 
   The image formation apparatus according to another aspect of the present invention employs the width detecting device according to the present invention. 
   These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view that shows a width detecting device according to one embodiment of the present invention; 
       FIG. 2  is an enlarged plan view of a portion in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view viewed from the arrows B—B of  FIG. 2 ; 
       FIG. 4  is a cross-sectional view viewed from the arrows A—A of  FIG. 1  (partially including the cross-section viewed from the arrows B—B); 
       FIG. 5  is a view of a portion in  FIG. 4 ; 
       FIG. 6  is an exploded perspective view that explains the coupling relationship between a first limiting member and a first rack member; 
       FIG. 7  is a cross-sectional view viewed from the arrows C—C of  FIG. 1  that explains the coupling relationship between the first limiting member and the first rack member; 
       FIG. 8  schematically explains the positional relationship between the first limiting member and sensors; 
       FIG. 9  is an essential part cross-sectional view that explains the positional relationship between a sensor and a rack member when a transmission type auxiliary sensor is used; 
       FIG. 10  is a perspective view that explains the positional relationship between the sensor and the rack member when the transmission type auxiliary sensor is used; 
       FIG. 11  schematically explains the positional relationship between a first limiting member and sensors when a plurality of auxiliary sensors is used; 
       FIG. 12  shows an example of the configuration of an image formation apparatus; 
       FIG. 13  is a plan view that shows a width detecting device according to another embodiment of the present invention; 
       FIG. 14  is an enlarged plan view of a portion of  FIG. 13 ; 
       FIG. 15  is a cross-sectional view viewed from the arrows B′—B′ of  FIG. 14 ; 
       FIG. 16  schematically explains the positional relationship between a first limiting member and sensors; and 
       FIG. 17  schematically explains the positional relationship between a first limiting member and sensors when auxiliary sensors are used. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments of the width detecting device for detecting a width of the paper according to the present invention are explained below with reference to accompanying drawings. The invention is by no means limited to these embodiments. 
   FIG.  1  and  FIG. 2  show a width detecting device according to one embodiment of the present invention. This width detecting device comprises a first limiting member  2 R and a second limiting member  2 L disposed facing with each other on a placing base  5  for placing a paper. The first limiting member  2 R and a second limiting member  2 L can move towards or away from each other via an interlocking unit  1  so as to make a physical contact with respective edge of the paper. 
   A paper is placed on the placing base  5  and the first limiting member  2 R and the second limiting member  2 L are moved in the width direction W so as to make a physical contact with the respective edges of the paper. In this state, a sensor detects the position of any one of the first limiting member  2 R and the second limiting member  2 L. 
   As the sensor, a rotation angle detection type sensor  3 S for converting the moving amount of the first limiting member  2 R (or the second limiting member  2 L) into an angle and generating a signal corresponding to the angle, and an auxiliary sensor  4 S capable of judging existence or absence of the first limiting member  2 R in the moving range of the first limiting member  2 R are provided so that the paper width size can be detected based on the output from the sensors  3 S,  4 S. 
   An interlocking unit  1  comprises a first rack member  10 R, a second rack member  11 L, a motion transmitting pinion  6 G, or the like. The first rack member  10 R having a longitudinal rectangular bar-like shape is provided integrally with the first limiting member  2 R as well as it comprises a first rack  10 R- 1  in the width direction W. 
   The second rack member  11 L having a longitudinal rectangular bar-like shape is provided integrally with the second limiting member  2 L as well as it comprises a second rack  11 L- 1  formed in the width direction W, facing the first rack  10 R- 1 . The motion transmitting pinion  6 G is disposed between the first rack  10 R- 1  and the second rack  11 L- 1  so as to be engaged commonly with the first rack  10 R- 1  and the second rack  11 L- 1 . 
   For the first rack member  10 R, a paper width detecting rack  10 R- 2  is formed on the rear side of the first rack so as to be engaged with a gear  3 G of the rotation angle detection type sensor  3 S via an interlocking gear  7 G engaged with the width detecting rack  10 R- 2 . 
   The structure of the members and the coupling relationship of the members with each other are explained in further details. 
   The first limiting member  2 R comprises a portion provided upright in the vertical direction as shown in the cross-section in  FIG. 1 , and a supporting section  2 R- 1  bent in the 90° direction with respect to the section shown in the cross-section, for supporting the paper width direction end. For the second limiting member, the section is referred to as the numeral  2 L- 1 . 
   In  FIG. 3  as a cross-sectional view viewed from the arrows B—B of  FIG. 2 , the width direction W is the direction orthogonal to the paper surface of FIG.  3 . The placing base  5  is a plate-lime member for placing a paper on the upper surface thereof. As shown also in  FIGS. 1 and 2 , a guide groove  9  is formed parallel to the width direction W. 
   The guide groove  9  is pierced through by an interlocking shaft  10  slidably. The upper portion of the interlocking shaft  10  is provided integrally with the supporting section  2 R- 1 , and a one end side of the first rack member  10 R is fixed with the lower part thereof. The relationship of these members is shown further apparently in  FIGS. 4 and 5 . 
   As shown in  FIGS. 6 and 7 , the supporting section  2 R- 1  and the first rack member  10 R are integrated by locking with pawl members  15 ,  16  via shafts  13 ,  14  for determining the interval between the supporting section  2 R- 1  and the first rack member  10 R and fixing them in addition to the fixing shaft  10 . 
   As shown in  FIG. 6 , in order to support the pawl member  15 , the shaft  13 , the interlocking shaft  10 , the shaft  14 , the pawl member  16 , or the like, in the first rack member  10 R, a through opening  15   h , a boss hole  13   b , a hole with the bottom  10   h , a boss hole  14   b  and a through opening  16   h  are formed in the first rack member  10 R. The supporting section  2 R- 1  and the first rack member  10 R are integrated via the pawl member  15 , the shaft  13 , the interlocking shaft  10 , the shaft  14 , the pawl member  16 , or the like. 
   In  FIG. 6 , in the first rack member  10 R, a convex portion  10 R- 3  is formed as a section to be detected for having the existence or absence thereof detected by the sensor  4 S. The convex portion  10 R- 3  is provided integrally with the first rack member  10 R, however, for the explanation convenience, it is shown independently from a rack forming section  10 R- 4  in FIG.  6 . The first rack member  10 R is produced integrally by a resin molding process. 
   A groove  10 R 3   a  is formed in the longitudinal direction end of the convex portion  10 R such that the pawl member  15 , the shaft  13 , the interlocking shaft  10 , the shaft  14 , the pawl member  16 , or the like are fixed with the rack section  10 R- 4  via the groove  10 R- 3   a . Moreover, for smooth movement in the width direction W of the first limiting member  2 R, a guide groove  90  is provided in addition to the guide groove  9 . 
   Based on the coupling relationship between the first rack member  10 R and the supporting section  2 R- 1 , the second rack member  11 L and the supporting section  2 L- 1  are coupled, however, explanation is omitted. Moreover, as those corresponding to the guide grooves  9 ,  90 , guide grooves  9 ′,  90 ′ are provided such that the second limiting member  2 L is moved, interlocking with the first limiting member  2 R via the guide grooves  9 ′,  90 ′. 
   As shown in  FIGS. 3  to  5 , a retainer plate  12  is provided below the plate-like placing base  5  with an interval. The retainer plate  12  is a plate-like member integrated with or provided integrally with the placing base  5  via a column member (not shown), having the rigidity. 
   As shown in  FIGS. 4 and 5 , the rotation angle detection type sensor  3 S is fixed on the rear surface of the placing base  5 , and the motion transmitting pinion  6 G and the interlocking gear  7 G are pivoted by shafts J 1 , J 2  provided on the rear surface of the placing base  5 . 
   The shafts J 1 , J 2  for supporting the motion transmitting pinion  6 G and the interlocking gear  7 G stably support the motion transmitting pinion  6 G and the interlocking gear  7 G by having the lower ends thereof supported by the retainer plate  12 . 
   According to the configuration, by grasping the first limiting member  2 R (or the second limiting member  2 L) with a hand and moving in the width direction W, the second limiting member  2 L (of the first limiting member  2 R) is moved by the same amount in the opposite direction with respect to a mark  160  that shows the center so as to be disposed at a position contacting with the side portion of the paper placed on the placing base  5 . 
   Since both the first rack  10 R- 1  and the second rack  11 L- 1  are engaged with the motion transmitting pinion  6 G, the first limiting member  2 R and the second limiting member  2 L are moved by the same distance in the opposite directions. Therefore, regardless of the paper size, the center position in the width direction W of the placed paper is always provided constantly at the mark  160  position. 
   In this embodiment, scale lines and the size names representing the same are printed on the placing base  5  in the width direction W with respect to the mark  160  at positions representing the sizes of postcard, B6, A5, B5, A4, A3, B3, A2. 
   In the first limiting member  2 R and the second limiting member  2 L, projections  17 R,  17 L are provided for representing the scale lines. For example, when the projection  17 R of the first limiting member  2 R is aligned with the scale line of the postcard, the interval between the first limiting member  2 R and the second limiting member  2 L provides the postcard size. The same is applied to the other sizes. The same effect can be achieved by aligning the projection  17 L of the second limiting member  2 L. 
   The movement of the first rack member  10 R is transmitted to the gear  3 G via the interlocking gear  7 G so that the rotation amount is converted to an angle by the rotation angle detection type sensor  3 S for outputting a signal corresponding to the angle. That is, four signals are changed according to the rotation angle of the gear  3 G. 
   According to the present invention, the paper size is detected by the signal detection results of the rotation angle detection type sensor  3 S and the auxiliary sensor  4 S. For example, when a paper is placed on the placing base  5  provided as a paper manual feeding base and the paper is interposed between the first limiting member  2 R and the second limiting member  2 L in the width direction W, the first rack  10 R- 1  and the second rack  11 L- 1  are moved. According to the movement of the first rack  10 R- 1 , the interlocking gear  7 G to be engaged with  10 R- 2  is rotated and the gear  3 G of the rotation angle detection type sensor  3 S is rotated as well. 
   According to the gear rotation angle, the output signal from the rotation angle detection type sensor  3 S is changed. Moreover, the auxiliary sensor  4 S is disposed at a position capable of detecting the first rack member  10 R- 1  provided integrally with the first limiting member  2 R. By detecting the output signals from the rotation angle detection type sensor  3 S and the auxiliary sensor  4 S, the paper width of the placed paper can be found. 
   The relationship between the paper sizes and the output signal from the rotation type switch with a gear  9  and the reflection type sensor  10  is shown in the following table 1. 
   [Table 1] 
   Relationship between the paper size and the rotation angle detection type sensor and the auxiliary sensor 
   
     
       
         
             
             
             
             
             
             
             
             
           
             
                 
             
             
                 
                 
                 
               Sig- 
               Sig- 
               Sig- 
                 
                 
             
             
                 
                 
               Gear 
               nal 
               nal 
               nal 
               Signal 
               Signal 
             
             
               NO 
               Paper size 
               angle 
               1 
               2 
               3 
               4 
               5 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
               1 
               Postcard 
                0° 
               H 
               L 
               L 
               L 
               L 
             
             
                 
               (100 mm) 
             
             
               2 
               B6 (128 mm) 
                40.5° 
               H 
               H 
               L 
               L 
               L 
             
             
               3 
               A5 (148 mm) 
                71.3° 
               H 
               H 
               L 
               L 
               L 
             
             
               4 
               B5 (182 mm) 
               119.9° 
               L 
               H 
               H 
               L 
               L 
             
             
               5 
               A4 (210 mm) 
               184.7° 
               L 
               L 
               H 
               L 
               L 
             
             
               6 
               B4 (257 mm) 
               231.3° 
               L 
               L 
               H 
               H 
               L 
             
             
               7 
               A3 (297 mm) 
               288.1° 
               L 
               L 
               L 
               H 
               L/H 
             
             
               8 
               B3 (364 mm) 
               351.6° 
               L 
               L 
               L 
               L 
               H 
             
             
               9 
               B3 (364 mm) 
               360° 
               H 
               L 
               L 
               L 
               H 
             
             
               10 
               B3 (364 mm) 
                40.5° 
               H 
               H 
               L 
               L 
               H 
             
             
               11 
               B3 (364 mm) 
                71.3° 
               L 
               H 
               L 
               L 
               H 
             
             
               12 
               A2 (420 mm) 
               119.9° 
               L 
               H 
               H 
               L 
               H 
             
             
                 
             
             
               Note 1: The signals 1 to 4 are the output from the rotation angle detection type sensor, and the signal 5 is the output from the auxiliary sensor.  
             
             
               Note 2: The gear angles in Nos. 10 to 12 are the output from the rotation angle detection type sensor in the second rotation.  
             
             
               Note 3: The auxiliary sensor outputs L and H in No. 7 are both detected as the A3 size.  
             
          
         
       
     
   
   In the table 1, the gear angles in Nos. 10 to 12 in the table 1 show the values in the second rotation of the rotation angle detection type sensor  3 S. Moreover, the signals  1  to  4  are the outputs from the rotation angle detection type sensor  3 S, and the signal  5  is the output from the auxiliary sensor  4 S. 
   In this embodiment, a SSS-31 type rotary switch (produced by Shinmei Electric Co., Ltd.) is used as the sensor  3 S. 
   The sensor  3 S used is of a type outputting four kinds of the signals from the signal  1  to the signal  4  according to the gear angle without distinction of the outputs exceeding one rotation of the gear from the outputs detected within the one rotation. 
   The sensor of this type has been used in a conventional width detecting device as the detection subject of a relatively small size, and it is adopted as it is so that the configuration is simple and it is advantageous in terms of the cost. 
   For example, it is adjusted such that the gear angle of the sensor  3 S is 0° when the projection  17 R is aligned with the postcard scale. At the time, from the sensor  3 S, combination signals of H (high level) as the signal  1  (hereinafter the same is applied), L (low level) as the signals  2  to  4   8 hereinafter the same is applied), that is, H, L, L, L are output. By inputting the outputs into detector such as a CPU, it is judged that a postcard size paper is placed on the placing base  5 . 
   Similarly, the detection outputs of No. 2 to No. 8 in the table 1 are as follows:
     B6 size: gear angle 40.5°: H, H, L, L in the order of the signal  1  to the signal  4     A5 size: gear angle 71.3°: L, H, L, L   B5 size: gear angle 119.9°: L, H, H, L   A4 size: gear angle 184.7°: L, L, H, L   B4 size: gear angle 231.3°: L, L, H, H   A3 size: gear angle 288.1°: L, L, L, H   B3 size: gear angle 351.6°: L, L, L, L.
 
Since the gear angles from the postcard size to the B3 size have a less than 360° gear angle, the detection outputs corresponding to each paper size are of different combinations, and thus the sizes can be distinguished theoretically.
   

   This rotary switch outputs the same combination signals in a constant range of the gear angle such as the combination signal of No. 1 in the table 1 when the gear angle is “0°” to “less than 40.5°”, the combination signal of No. 2 in the table 1 when the gear angle is “40.5°,” to “less than 71.3°” (hereinafter it is same in the table 1). 
   Regarding the case of using only the rotation angle detection type sensor  3 S as the sensor, when the gear angle corresponding to B3 is 360°, the combination signals is H, L, L, L as shown in the table 1. Since it is the same as the combination signals for the postcard size, the size cannot be distinguished. 
   In this embodiment, the auxiliary sensor  4 S is provided such that the detection output is changed at an optional position whereat before the gear angle corresponding to the moving amount of the first limiting member  2 R converted by the rotation angle detection type sensor  3 S exceeds 360° as the boundary. Thereby, the size can be detected also for a wide width paper. 
   Although it is possible to provide another rotation angle detection type sensor as the auxiliary sensor  4 S, a binary output type sensor such as an on-off sensor, capable of judging existence or absence of the first limiting member  2 R in the moving range of the first limiting member  2 R is used in this embodiment instead of using the rotation angle detection type sensor as the auxiliary sensor. As a sensor of this type, a so-called reflection type sensor of a non contact type and a transmission type sensor are well known, and they can be used. In addition thereto, as it is described later, a contact type sensor for switching on or off the electric contact according to the operation of an actuator (contact), such as a mechanical type micro switch can be used as well. 
   A reflection type sensor may be used as the auxiliary sensor in a combination with a rotation angle detection type sensor. When the reflection type is used as the auxiliary sensor  4 S, a light emitter-receiver  4 S 1  (see  FIGS. 2 ,  3 ) is disposed at a position aligned with the A3 scale line. Moreover, the end of the convex portion  10 R- 3  as the section to be detected is aligned with the projection  17 R. Thereby, the detection output from the auxiliary sensor  4 S is changed when the projection  17 R represents the A3 scale line as the boundary. The light emitter-receiver  4 S 1  is aligned with the A3 scale line and the detection end by the auxiliary sensor  4 S is provided at the A3 size position for improving the total detection result reliability by adding the detection result of the auxiliary sensor  4 S before the 360° gear angle position for avoiding the risk of the detection error by providing the same thereat. 
   In the table 1, a detection signal by the auxiliary sensor  4 S is shown as a signal  5 . As to the output from the auxiliary sensor  4 S, a light output from the light emitter-receiver  4 S 1  is reflected by the convex portion  10 R- 3  so as to be input to the light receiver again via the light emitter-receiver  4 S 1 . From the postcard size to the A3 size, L is output. Then, from more than the A3 size to the B3, A2 wide size, since the convex portion  10 R- 3  as the section to be detected is outside the light emitter-receiver  4 S 1 , due to the absence of the reflected light, H is output. 
   In the table 1, since there is a detection error in the vicinity of the A3 size, in either case of L or H, it is judged to be the A3 size in combination with the output from the rotation angle detection type sensor. 
   In the table 1, Nos. 8 to 10 are in the range with the gear angle from 351.6° to 71.3° in the second rotation via 40.5° in the second rotation. In consideration of the error in which the operator positions the projection  17 R at the scale position manually in about the range, since the positioning error is ordinarily generated to this extent, for a signal combination in the range, it is judged to be the B3 size in combination with the signal  5  in either case. 
   As to the A2 size set as the maximum size, as shown in  FIG. 1 , since the moving limit of the first limiting member  2 R is limited by a stopper STP, at the time of the gear angle 119.9° in No. 12, it is judged to be the A3 size by the combination of the outputs L, H, H, L of the signals  1  to  4  and the output H of the signal  5 . 
   Since the reflection type sensor is used as the auxiliary sensor  4 S of the rotation angle detection type sensor  3 S, miniaturization of the detecting unit can be realized. Furthermore, since the movement of the first limiting member  2 R can be transmitted to the rotation angle detection type sensor  3 S via the width detecting rack  10 R- 2  and the interlocking gear  7 G, slippage cannot be generated in the motion transmitting path. Therefore, the detection accuracy for the position of the first limiting member  2 R (second limiting member  2 L) is high as well as the detection accuracy for the paper width is high. 
   The interlocking gear  7 G disposed between the gear  3 G of the rotation angle detection type sensor and the width detecting rack  10 R- 2  is provided for enabling engagement of both of them via the interlocking gear when the gear  3 G and the width detecting rack  10 R- 2  have different heights from the same reference plane, and thus the interlocking gear  7 G can be eliminated when direct engagement is feasible, for example, when the heights from the same reference plane is same, the engagement position can be matched by changing the shapes of the gear  3 G and the width detecting rack  10 R- 2 , or the like. In this case, the width detecting rack  10 R- 2  and the gear  3 G of the rotation angle detection type sensor can be engaged directly. 
   As shown in  FIGS. 9 and 10 , a transmission type sensor may be used as the auxiliary sensor  4 S in a combination with a rotation angle detection type sensor. 
   The auxiliary sensor  4 S′ comprises a light emission section  4 S′- 1  and a light receiver  4 S′- 2  facing with each other with an interval therebetween, with a section to be detected  10 R′- 4  as a part of a first rack member  10 R′ provided based on the first rack member  10 R, disposed in the space portion of the interval. In the first rack member  10 R′, the first rack  10 R′- 1  and the width detecting rack  10 R′- 2  each correspond to the first rack  10 R- 1  and the width detecting rack  10 R- 2  in the first rack member  10 R. As in this embodiment, the same effect can be obtained by using the transmission type as the auxiliary sensor  4 S instead of the reflection type. 
   A contact type sensor may be used as the auxiliary sensor in a combination with a rotation angle detection type sensor. The contact type sensor is, for example, a micro switch.  FIGS. 13  to  16  show an embodiment thereof.  FIG. 13  corresponds to  FIG. 1 ,  FIG. 14  corresponds to  FIG. 2 ,  FIG. 15  corresponds to  FIG. 3 , and  FIG. 16  corresponds to  FIG. 8 , respectively. In  FIGS. 13  to  16 , the micro switch as the auxiliary sensor is shown by the numeral  4 S. Since the other component members are same as those shown in  FIGS. 13  to  16 , the same numerals are applied and explanation is omitted as much as possible. 
   The auxiliary sensor  4 S is fixed on the retainer plate  12  according to the embodiment of the auxiliary sensor  4 S such that the actuator  4 SS- 1  thereof is slid against the width detecting rack  10 R- 2  according to the movement of the first limiting member  2 R. In the sliding state (contact), the auxiliary sensor  4 S is switched on, and the output at the time is provided as the L output here with regard to the table 1. Then, when the actuator  4 SS- 1  is in the state displaced from the width detecting rack  10 R- 2  (non contact), the auxiliary sensor  4 S is switched off, and the output at the time is provided as the h output with regard to the table 1. 
   In this embodiment, as shown in  FIG. 16 , the auxiliary sensor  4 SS position is positioned on the retainer plate  12  such that the actuator  4 SS- 1  is provided at a positioned aligned with the A3 scale line. Moreover, the end of the width detecting rack  10 R- 2  as the section to be detected is set at a position coinciding with the projection  17 R or a position slightly outer side thereof. 
   Thereby, the detection output by the auxiliary sensor  4 SS is changed at the time the projection  17 R of the first limiting member  2 R points out the A3 scale line as the boundary. The actuator  4 SS- 1  is aligned with the A3 scale line and the detection end by the auxiliary sensor  4 S is provided at the A3 size position for improving the total detection result reliability by adding the detection result of the auxiliary sensor  4 SS before the 360° gear angle (corresponding to B3) for avoiding the risk of the detection error by providing the same thereat. 
   When the projection  17 R of the first limiting member  2 R points out from the postcard size to the A3 size, the actuator  4 SS- 1  of the auxiliary sensor  4 SS is pressured by the width detecting rack  10 R- 2  so that “L” is output from the auxiliary sensor  4 SS. Then, for a wide size of more than A3, that is, B3 and A2, since the end of the width detecting rack  10 R 02  as the section to be detected is displaced from the actuator  4 SS- 1  so as not to be contacted with the section to be detected, “H” is output. As in this embodiment, the same effect can be obtained by using the contact type sensor as the auxiliary sensor  4 SS instead of the non contact type sensor. In contacting the actuator  4 SS- 1  with the width detecting rack  10 R- 2 , since the module of the rack is smaller than the curvature of the tip end of the actuator  4 SS- 1 , detection error is not generated. 
   Moreover, the sliding portion of the actuator  4 SS- 1  as the section to be detected is not limited to the rack section, and one comprising a flat section to be detected can be used. For example, a convex portion  10 R- 3  can be used as well. In contrast, when the width detecting rack  10 R is used as the section to be detected, a configuration without the convex portion  10 R- 3  can be employed as well. 
   Since the first rack member  10 R is integrated with the supporting section  2 R- 1  only on the one end side thereof, as to the engaging relationship between the first rack  10 R- 1  and the motion transmitting pinion  6 G, it is provided as the so-called cantilever support. Since there is a distance between the integrated portion and the motion transmitting pinion  6 G, the risk is involved in that the engaging state can be unstable derived from departure of the first rack  10 R- 1  from the motion transmitting pinion  6 G due to the force applied between the rack and the pinion at the time of transmitting the motion. Then, in order to stably support the engaging relationship, a tooth skipping preventing unit is provided. The same is applied to the second rack member  11 L. 
   As shown in  FIGS. 1 ,  6 ,  8 , or the like, as to the first rack member  10 R, the tooth skipping preventing unit comprises a component portion with a fin-like small piece  20  projecting outward from the side portion of the free end on the opposite side with respect to the integrated portion of the rack member  10 R with the first limiting member  2 R, and a slider  21  provided by bending the small piece  20  upright in an L shape on the end part of the retainer plate  12  in the moving range of the small piece  20  to be moved with the first rack member  10 R such that the small piece  20  is slide against the slider  21  while being pressured by the elastic force. 
   Since the first rack member  10 R is pressured by the motion transmitting pinion  6 G by the elastic force of the small piece  20 , skipping of a tooth can be prevented. As to the first rack member  10 R, the width detecting rack  10 R- 2  on the opposite side of the motion transmitting pinion  6 G is engaged with the interlocking gear  7 G and the interlocking gear  7 G is supported between the placing base  5  and the retainer plate  12 , the interlocking gear  7 G serves also as a tooth skipping preventing unit. As shown in  FIG. 5 , the upper surface portion of the retainer plate  12  is made thicker at a position of receiving the free end side of the first rack member  10 R for providing a receiver  12   a  for preventing sagging of the first rack member  10 R by its self weight. 
   Similarly, as to the second rack member  11 L, as shown in  FIGS. 1 ,  5 , or the like, a fin-like small piece  22  is provided on the free end of the second rack member  11 L, and a slider  23  is provided by bending the side portion of the retainer plate  12  upright in an L shape in the moving range of the small piece  22  to be slid against the slider  23  for serving as a tooth skipping preventing unit. Moreover, the upper surface portion of the retainer plate  12  is made thicker at a position of receiving the free end side of the second rack member  11 L for providing a receiver  12   b  for preventing sagging of the first rack member  10 R by its self weight. 
   According to the tooth skipping preventing units, furthermore, since the auxiliary sensor  4 S (or the auxiliary sensor  4 S′,  4 SS) is supported by the retainer plate  12 , the operation of the first rack member  10 R, the second rack member  11 L, and the motion transmission accompanying the same are stabilized so that engagement of the interlocking gear  7 G or the gear  3 G of the rotation angle detection type sensor  3 S and detection by the auxiliary sensor  4 S (or the auxiliary sensor  4 S′,  4 SS) can be highly accurate so that the paper width can be detected further accurately. 
   In the above mentioned embodiments, the paper widths of various sizes from the postcard size to the A2 size are detected by switching the output of the auxiliary sensor  4 S (or the auxiliary sensor  4 S′,  4 SS) between L and H at a position immediately before having the gear  3 G of the rotation angle detection type sensor  3 S exceeding 360 degrees (one rotation), and combining the output from the auxiliary sensor  4 S (or the auxiliary sensor  4 S′,  4 SS) and the output from the rotation angle detection type sensor  3 S. 
   Furthermore, in order to enable the size detection of a larger size paper, such as the B2 and A1 sizes, as shown in  FIG. 11 , a first rack member  10 R′ and a second limiting member  11 L′ (not shown) with the length prolonged than the first rack member  10 R and the second limiting member  11 L in the embodiments, and an auxiliary sensor  5 S is provided in addition to the auxiliary sensor  4 S for adding a signal  6  to the table 1 column as the output of the added auxiliary sensor  5 S so that it can be dealt with by switching the output from the auxiliary sensor  5 S at a position immediately before having the gear  3 G of the rotation angle detection type sensor  3 S exceeding 720 degrees (2 rotations) between L and H. 
   Similarly, also in the case of using a transmission type auxiliary sensor  4 S′, although it is not shown, it can be dealt with by adding another transmission type sensor according to the auxiliary sensor  5 S. Furthermore, in the case of a contact type sensor, as shown in  FIG. 17 , an auxiliary sensor  5 SS is provided in addition to the auxiliary sensor  4 SS for providing the same function as that of the auxiliary sensor  5 S. 
   Accordingly, in addition to the non contact type such as the reflection type and the transmission type, by providing an auxiliary sensor of a simple configuration such as a contact type sensor at a position capable of detecting the first rack member by two or in a plurality of three or more as needed, the paper width detectable range can be enlarged in a small space at a low cost so as to increase the number of detections. 
   The width detecting devices according to the above mentioned embodiments can be used in a manual feeding device in a printer, a facsimile, an image formation apparatus, or the like, or an automatic document feeder (ADF) attached to the image formation apparatus. 
   When the width detecting device is used for a manual feeding device, the size of the paper to be fed manually is input to a controlling unit of the image formation apparatus as an electric signal so that the image formation process is executed based on the paper size information. When it is used for an automatic document device, similarly, a signal including the size information is input to a reading controlling unit so that the reading scanning width is set. 
   Hereinafter, with reference to  FIG. 12 , an embodiment of an image formation apparatus comprising a manual feeding device and an automatic document device is explained. 
   In  FIG. 12 , a reference numeral  100  represents a copying machine main body, a reference numeral  200  represents a paper feeding table for placing the same, a reference numeral  300  represents a scanner to be mounted on the copying machine main body  100 , and a reference numeral  400  represents an automatic document device to be mounted further thereon. With these elements assembled together, the image formation apparatus is provided. 
   In the copying machine main body  100 , an endless belt-like intermediate transfer member  26  is provided in the center. 
   As shown in  FIG. 12 , the endless belt-like intermediate transfer member  26  is hung around three supporting rollers  70 ,  72 , and  73  so as to be enable rotation and conveyance in the clockwise direction in the figure. Moreover, an intermediate transfer member cleaning device  74  is provided on the left side of the second supporting roller  72  out of the three rollers for eliminating the residual toner remaining on the intermediate transfer member  26  after the image transfer. 
   On the intermediate transfer member  26  placed between the first supporting roller  70  and the second supporting roller  72  out of the three rollers, four image formation units  18  of black, cyan, magenta and yellow are arranged side by side along the conveyance direction so as to provide a tandem image formation section  25 . As shown in  FIG. 12 , an exposing device  29  is provided on the tandem image formation section  25 . 
   A secondary transfer device  71  is provided on the opposite side of the tandem image formation section  25  with respect to the intermediate transfer member  26 . In this embodiment, the secondary transfer device  71  provided by placing a secondary transfer belt  24  as an endless belt around two rollers  23   a ,  23   b , is provided in the state forced against the third supporting roller  73  via the intermediate transfer member  26  for transferring an image on the intermediate transfer member  26  to a paper. 
   A fixing device  250  is provided on the side of the secondary transfer device  71  for fixing the image transferred on the paper. The fixing device  250  is provided by forcing a pressuring roller  27  against a fixing belt  260  as an endless belt  260 . 
   The secondary transfer device  71  also has a paper conveying function for conveying the paper after the image transfer to the fixing device  250 . Of course a non contact type charger may be disposed as the secondary transfer device  71 . In this case, it is difficult to have the paper conveying function. 
   In this embodiment, a paper inverting device  28  is provided parallel to the tandem image formation section  25  below the secondary transfer device  71  and the fixing device  250  for inverting the paper for recording an image on the both sides of the paper. 
   For copying with the color copying machine, a manuscript is set on a manuscript base  30  of the automatic document device  400 . In the automatic document device, the width detecting device of the present invention is used so that the manuscript width is recognized automatically. Alternatively, a manuscript is set on a contact glass  32  of the scanner  300  by opening the automatic document device  400  and closing the automatic document device  400  for weighting thereby. 
   When a manuscript is set on the automatic document device  400  and a start switch (not shown) is pressed, the manuscript is first conveyed onto the contact glass  32 . In contrast, when a manuscript is set on the contact glass  32 , the scanner  300  is driven immediately so as to run a first running member  33  and a second running member  34 . A light is emitted from a light source by the first running member  33  as well as the reflected light from the manuscript surface is further reflected toward the second running member  34  so as to be reflected by a mirror of the second running member  34  for inputting the same into a reading sensor  36  via an image forming lens  35  for reading the manuscript content. As the manuscript reading device, a type of utilizing a laser beam can be used as well. In any case, the scanning width for scanning the manuscript can be set based on the paper width information from the width detecting device according to the present invention. Moreover, the developing area by the developing unit can be set and the erasure width after photosensitive member primary charging can be set in the image formation unit  18 . 
   When the start switch is pressed, one of the supporting rollers  70 ,  72 ,  73  is rotated and driven by the driving motor for driving the other two supporting rollers following thereto so as to rotate and convey the intermediate transfer member  26 . At the same time, the photosensitive member  40  is rotated by each image formation unit  18  for forming a single color image of black, yellow, magenta, and cyan on each photosensitive member  40 . 
   That is, at the time of image formation, while rotating the photosensitive member  40 , first the surface of the photosensitive member  40  is charged uniformly by the charging device, and then a writing light Lb of a laser, by an LED, or the like is irradiated from the exposure device  21  according to the reading content by the scanner  300  for forming an electrostatic latent image on the photosensitive member  40 . Thereafter, a toner is adhered by the developing device that visualizes the electrostatic latent image. 
   According to the conveyance of the intermediate transfer member  26 , the single color images thereof are transferred successively by the primary transfer device  62  so as to form a composite color image on the intermediate transfer member  26 . For the surface of the photosensitive member  40  after the image formation, the residual toner is eliminated for cleaning by the photosensitive member cleaning device, and the charge is eliminated by the charge eliminating device that prepares itself to the next image formation. 
   When the start switch is pressed, one of paper feeding rollers  42  of the paper feeding table  200  is selected and rotated for taking out papers from one of multi stage paper banks  43  provided in a paper feeding cassette  44 , separating the same one by one by a separating roller  45 , introducing to a paper feeding path  46  for conveying by a conveying roller  47 , guiding into a paper feeding path  48  in the copying machine main body  100 , and butting against a resist roller  49  so as to be stopped. 
   Alternatively, papers are taken out from a manual feeding device  51  with the width detecting device of the present invention by rotating a paper feeding roller  50  for separating the same one by one by a separating roller  52 , introducing to a paper feeding path  53 , and similarly butting against the resist roller  49  so as to be stopped. 
   The resist roller  49  is rotated with the timing matched with the composite color image on the intermediate transfer member  26 . A paper is sent into between the intermediate transfer member  26  and a secondary transfer device  71  for transferring by the secondary transfer device  71  so as to form a color image on the paper. 
   The paper after the image transfer is conveyed by the secondary transfer device  71  so as to be sent into the developing device  25 . After fixing the transferred image by applying the heat and the pressure by the fixing device  25 , it is discharged by a discharge roller  56  according to changeover by a switching pawl  55  so as to be stacked on a paper discharge tray  57 . Alternatively, it is input into the paper inverting device  28  according to changeover by the switching pawl  55  so as to be inverted and guided again to the transfer position for recording an image also on the rear side, and it is discharged onto the paper discharge tray  57  by the discharge roller  56 . 
   For the intermediate transfer member  26  after the image transfer, the residual toner remaining on the intermediate transfer member  26  after the image transfer is eliminated by the intermediate transfer member cleaning device  74  for preparing itself to the next image formation by the tandem image formation section  25 . 
   In the tandem type image formation section  25 , as it is known, each image forming unit  18  comprises a charge device, a developing device, a primary transfer device, a photosensitive member cleaning device, a charge eliminating device, or the like around the drum-like photosensitive member  40 . In this embodiment, the photosensitive member  40  is a drum-like rotating member with a photosensitive layer formed on a bare pipe of an aluminum, or the like by coating an organic photosensitive material having the photosensitive property, but it may be an endless belt-like rotating member. 
   In the developing device, a developing sleeve is provided facing the photosensitive member  40  as well as a magnet is fixed in the developing sleeve. Moreover, a doctor blade is provided with the tip end adjacent to the developing sleeve. 
     FIG. 12  merely shows a tandem type full color image apparatus as an embodiment of the image formation apparatus. The width detecting device according to the present invention is not limited to the image formation apparatus shown in  FIG. 12 , and it can be used widely in an apparatus comprising an image formation section for forming an image on a paper, such as an image formation apparatus of a type comprising a manual feeding device, and an image formation apparatus comprising an automatic document device. Needless to say, it can be used also to a manual feeding device and an automatic document device for an electrophotography system image formation apparatus for a black and white image, a printer, a facsimile or the like. 
   According to the first aspect of the invention, the width of a wide size sheet-like medium can be detected in a compact configuration. 
   According to the second aspect of the invention, even in the case of using a rotation angle detection type sensor of a simple configuration, a wide size can also be detected according to a combination with an auxiliary sensor. According to the third aspect of the invention, it can be executed easily by using a simple sensor. 
   According to the fourth aspect of the invention, since the movement of the limiting member is detected by each sensor, utilizing the gear engaging relationship, owing to absence of generation of slippage in the motion transmitting path, a high detection accuracy can be provided. 
   According to the fifth aspect of the invention, the operation of the first and second rack members can be stabilized by preventing tooth skipping so that detection by the sensor utilizing the gear engaging relationship can be highly accurate so that the width can be detected highly accurately. 
   According to the sixth aspect of the invention, the size of a wider sheet-like medium can be detected. 
   According to the seventh aspect of the invention, the width size can be detected automatically in an image formation apparatus comprising a manual feeding device or an automatic document device that handles a wide sheet-like medium. 
   Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.