Patent Publication Number: US-7712988-B2

Title: Sheet feed tray for image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority from Japanese Patent Application No. 2005-373236, filed on Dec. 26, 2005, the entire subject matter of which is incorporated herein by reference. 
   TECHNICAL FIELD 
   Aspects of the present invention relate to a sheet feed tray for an image forming apparatus, which is suitably applicable to an electrophotographic image forming apparatus such as a laser printer. 
   BACKGROUND 
   A recording medium such as a recording sheet or OHP sheet is usually placed in a positioned state by contacting with a wall face such as an outer peripheral wall of a sheet feed tray for an image forming apparatus. 
   In a sheet feed tray capable of placing recording media of various sizes has a wall-shaped regulating wall member, which is made movable to contact with an end portion of the recording medium thereby to position it, and a lock mechanism for regulating a displacement of the regulating wall member (see, for example, JP-A-1-209227). 
   The lock mechanism disclosed in JP-A-1-209227 includes a saw-tooth shaped engaging portion (or a corrugated portion) formed in the sheet feed tray, an engagement pawl disposed at the regulating wall member for engaging with the engaging portion and a coil spring for pushing the engagement pawl onto the engaging portion. The engagement pawl is made movable relative to the engaging portion. 
   When the position of the regulating wall member is to be changed, the engagement pawl is displaced away from the engaging portion to release an engaging state (or a locked state) between the engaging portion and the engagement pawl, and the regulating wall member is moved while holding that released state. Then, the engagement pawl is brought into engagement with the engaging portion and fixes (or locks) the position of the regulating wall member. 
   SUMMARY 
   When an entire sheet feed tray is to be moved, the regulating wall member may impinge against another member or a printer, and an external force may act on the regulating wall member. The external force is received by a contacting face between the engagement pawl and the engaging portion. Thus, a force to release the engaging state (releasing force) may act on the engagement pawl. 
   JP-A-1-209227 discloses to push the engagement pawl onto the engaging portion by an elastic force of the coil spring so as to hold the engaging state between the engagement pawl and the engaging portion (this elastic force for holding the engaging state will be called “holding force”). If the external force acting on the regulating wall member is strong, the releasing force exceeds the holding force and the engaging state is released. In such a case, the regulating wall member may be moved unintentionally. 
   In view of the above, the holding force may be increased by enlarging a spring constant of the coil spring. When the position of the regulating wall member is to be changed, the engaging state has to be released by applying a force exceeding the holding force. If the holding force is increased, a strong force is needed when the position of the regulating wall member is to be changed. Thus, workability of the operation to change the regulating wall member is deteriorated. 
   Aspects of the invention prevent the regulating wall member from moving in case a strong external force acts on the regulating wall member while preventing the workability of the operation to change the position of the regulating wall member from being deteriorated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing the exterior of a laser printer according to an aspect of the invention; 
       FIG. 2  is a sectional side view showing the laser printer; 
       FIG. 3  is a perspective view of an upper face side of a sheet feed tray; 
       FIG. 4  is an exploded perspective view of the sheet feed tray; 
       FIG. 5  is a lower face view of a regulating wall member; 
       FIG. 6  is a lower face view of the regulating wall member; 
       FIG. 7  is an enlarged view of a lock mechanism; 
       FIG. 8  is an enlarged view of the lock mechanism; 
       FIG. 9  is a sectional view taken along line IX-IX of  FIG. 7 ; 
       FIGS. 10A and 10B  are views of the sheet feed tray taken from the upper side with a lock mechanism portion being broken; and 
       FIGS. 11A and 11B  are views of the sheet feed tray taken from the lower side with the lock mechanism portion being broken. 
   

   DETAILED DESCRIPTION 
   General Overview 
   According to a first aspect of the invention, there is provided a sheet feed tray for an image forming apparatus, comprising: a placing tray including a placing portion, on which a recording medium is placed, and a first tray side engagement portion; a regulating wall member which is assembled in a displaceable manner with the placing tray and regulates a position of the recording medium such that a wall portion of the regulating wall member contacts with an end portion of the recording medium; a first engagement member which is disposed on the regulating wall member and includes a first regulating wall member side engagement portion, the first regulating wall member engaging with the first tray side engagement portion and regulates a displacement of the regulating wall member; an elastic unit which is elastically deformable and generates a force for holding an engaging state between the first tray side engagement portion and the first regulating wall member side engagement portion; an elastic deformation regulating unit which regulates a deformation amount of the elastic unit; and a releasing operation unit which releases the engaging state between the first tray side engagement portion and the first regulating wall member side engagement portion. 
   When the position of the regulating wall member ( 94 ) is to be changed, a force exceeding the holding force has to act to release the engaging state. At the same time, the holding force is generated when the elastic unit is elastically deformed. Therefore, either in case the user releases the engaging state or in case a strong external force acts on the regulating wall member ( 94 ) to release the engaging state, the deformation of the elastic unit ( 96   d ) at the time when the engaging state is released is larger than that of the elastic unit ( 96   d ) at the time when the engaging state is held. 
   Thus, if the deformation of the elastic unit ( 96   d ) is regulated by the elastic deformation regulating unit ( 101 ), it is possible to prevent the elastic unit ( 96   d ) from being deformed to such an extent that the engaging state is released. Even if a strong external force acts on the regulating wall member ( 94 ), it is possible to prevent the engaging state from being released. 
   That is, according to the aspect of the invention, even if the strong external force acts on the regulating wall member ( 94 ), the engaging state can be prevented from being released without enlarging the spring constant of the elastic unit ( 96   d ) to increase the holding force. 
   Therefore, even if the strong external force acts on the regulating wall member ( 94 ), the regulating wall member ( 94 ) can be prevented from moving without deteriorating the workability of the position changing operation of the regulating wall member ( 94 ). 
   According to a second aspect of the invention, the sheet feed tray further comprising a second engagement member which is disposed on the regulating wall member and includes a second regulating wall member side engagement portion, the second regulating wall member engaging with a second tray side engagement portion disposed on the placing tray, wherein an elastic deformation portion which is elastically deformable and constitutes the elastic unit is provided in at least a part of the second engagement member, wherein the second regulating wall member side engagement portion is pushed onto the second tray side engagement portion by a reaction force of an elastic force of the elastic unit in pushing the first regulating wall member side engagement portion to the first tray side engagement portion, and wherein, when the releasing operation unit is operated, the first regulating wall member side engagement portion is displaced in a direction to increase the deformation of the elastic unit and releases the engaging state between the first tray side engagement portion and the first regulating wall member side engagement portion. 
   At this time, the second regulating wall member side engagement portion ( 96   b ) is pushed onto the second tray side engagement portion ( 91   b ) by the reaction force of the elastic force for the elastic unit ( 96   d ) to push the first regulating wall member side engagement portion ( 96   a ) onto the first tray side engagement portion ( 91   a ). Therefore, even if the engaging state between the first regulating wall member side engagement portion ( 96   a ) and the first tray side engagement portion ( 91   a ) is released so as to change the position of the regulating wall member ( 94 ), only the force for holding the engaging state between the second regulating wall member side engagement portion ( 96   b ) and the second tray side engagement portion ( 91   b ) (that is, the elastic force generated in the elastic unit ( 96   d )) is increased. However, the engaging state between the second regulating wall member side engagement portion ( 96   b ) and the second tray side engagement portion ( 91   b ) is not released. 
   Therefore, if the second ray side engagement portion ( 91   b ) is disposed at a position corresponding to a standard size such as A4 or A5 determined by the Japanese Industrial Standards (JIS) or the like, tactile sensation can be given to the user when the regulating wall member ( 94 ) is positioned at the position corresponding to the standard size. As a result, the regulating wall member ( 94 ) can be easily displaced to a desired position without confirming the position of the regulating wall member ( 94 ) with graduations. 
   According to a third aspect of the invention, the sheet feed tray further comprising an elastic deformation regulating operation unit which is disposed on an upper face side of the regulating wall member and operates the elastic deformation regulating unit. 
   As a result, the elastic deformation regulating operation unit ( 102 ) can be operated from the upper face side of the regulating wall member ( 94 ). Accordingly, an operability of the elastic operation unit ( 102 ) can be improved. 
   According to a fourth aspect of the invention, the regulating wall member includes a recess portion which is recessed from the upper face side toward the lower end side thereof, and the releasing operation unit and the elastic deformation regulating operation unit are formed on the bottom portion of the recess portion. 
   As a result, the releasing operation unit ( 97 ) and the elastic deformation regulating operation unit ( 102 ) can be prevented from protruding from the upper face (or the upper end face) of the regulating wall member ( 94 ). It is also possible to prevent the image forming apparatus having the sheet feed tray of the invention from being large-sized. 
   According to a fifth aspect of the invention, the sheet feed tray further comprising a moving portion which is movable integrally with the elastic deformation regulating operation unit, wherein one of the moving portion and the regulating wall member includes an engagement projection which engages with an engagement recess portion formed on another one of the moving portion and the regulating wall member. 
   As a result, when the elastic deformation regulating operation unit ( 102 ) is operated, the engagement recess ( 94   d ) and the engagement projection ( 103   a ) engage with each other so that they can give tactile sensation to the user. Therefore, the user can be easily notified whether or not the engaging state between the first regulating wall member side engagement portion ( 96   a ) and the first tray side engagement portion ( 91   a ) is locked (or held). Accordingly, the operability of the elastic deformation regulating operation unit ( 102 ) can be improved. 
   According to a sixth aspect of the invention, the sheet feed tray further comprising: an arm-shaped member which is extended from a rotation center set in the regulating wall member and constitutes the first engagement member, the first regulating wall member side engagement portion being provided at a leading end side thereof; a leaf spring member which is extended from the first engagement member and constitutes the elastic member, the second regulating wall member side engagement portion being provided at a leading end side thereof; and an operation arm portion which is extended from the rotation center in a direction to intersect a longitudinal direction of the first engagement member and is rotatable integrally with the first engagement member, the releasing operation unit being disposed at a leading end side thereof. 
   According to a seventh aspect of the invention, the elastic deformation regulating unit regulates the rotation of the first engagement member and regulates the deformation of the elastic unit. 
   According to an eighth aspect of the invention, the elastic deformation regulating unit includes a stopper which moves in association with the operation of the elastic deformation regulating operation unit, and the rotation of the first engagement member is regulated by contacting the first engagement member with the stopper. 
   According to a ninth aspect of the invention, the stopper is displaced substantially in parallel with the longitudinal direction of the first engagement member in association with the operation of the elastic deformation regulating operation unit. 
   According to a tenth aspect of the invention, the regulating wall member constitutes at least a part of an outer peripheral wall of the placing tray, and the regulating wall member is arranged on a rear end side of the placing portion. The aspect of the invention can be effectively applied to the sheet feed tray for the image forming apparatus, because it is highly probable that the regulating wall member ( 94 ) impinges directly against the wall or the like near the portion where the image forming apparatus is disposed. 
   Incidentally, the parenthesized reference numerals of the aforementioned individual means present only the corresponding relations to the specific means to be described in the aspect. However, the invention should not be limited to the specific means designated by the parenthesized numerals. 
   &lt;Illustrative Aspects&gt; 
   In an illustrative aspect, which will be described with reference to the accompanying drawings, a sheet feed tray for an image forming apparatus is applied to an electrophotographic image forming apparatus (laser printer). 
   1. Exterior Structure of Laser Printer 
     FIG. 1  is a perspective view showing the exterior of a laser printer  1  according to the aspect of the invention taken from a rear side thereof. This laser printer  1  is disposed such that an upper side of the drawing is directed to an upper side of a direction of gravity. The laser printer  1  is usually used with a far side of the drawing being a front side. 
   A casing  3  of the laser printer  1  is formed into a substantially box shape (or a substantially stereoscopic shape) A discharge tray  5  for placing a recording medium, which is discharged from the casing  3  after being subjected to printing, is provided on an upper face side of the casing  3 . The recording medium may be a sheet such as a paper sheet or OHP sheet. 
   The discharge tray  5  is configured to have a slope face  5   a  which slopes down from the upper face of the casing  3  toward the rear side. On the rear end side of the slope face  5   a , there is formed a discharge port  7  (as referred to  FIG. 2 ), from which the recording medium is discharged. 
   An upper cover  9  is so formed in a substantially C-shape as to enclose the discharge tray  5  (or the slope face  5   a ) of the casing  3 . The upper cover  9  has a line switch  1   a  for switching the laser printer  1  to be connected with a network and to be disconnected from the network, and a job cancel switch  1   b  for ending (or interrupting) printing forcibly. 
   2. Internal Configuration of Laser Printer 
     FIG. 2  is a sectional side view of the laser printer  1 . An image forming unit  10  forms an image on the recording medium. A feeder unit  20  constitutes a portion of a conveying unit for feeding the recording medium to the image forming unit  10 . 
   A first discharge chute  30  and a second discharge chute  40  constitute a guide member for causing the recording medium having formed with the image at the image forming unit  10  to make a U-turn of about 180 degrees in a conveying direction thereof so as to guide the recording medium into the discharge port  7  that is formed above a fixing unit  80 . 
   A forward/backward switching mechanism  50  constitutes a discharge roller reversing mechanism for reversing the conveying direction of the recording medium, which is conveyed from the image forming unit  10 , and for conveying the recording medium reversed in the conveying direction toward the image forming unit  10 . These devices  10 ,  20 ,  30 ,  40 ,  50  and so on are housed in the casing  3 . 
   2.1 Image Forming Unit 
   The image forming unit  10  includes a scanner unit  60 , a process cartridge  70  and a fixing unit  80 . 
   2.1.1. Scanner Unit 
   The scanner unit  60  is disposed in the upper portion of the casing  3  for forming an electrostatic latent image on the surface of a photo sensitive drum  71 . Specifically, this scanner unit  60  includes a laser light source, a polygon mirror, an fθ lens and reflecting mirrors. 
   The laser beam, which is emitted from the laser light source and based on image data, is deflected by the polygon mirror and passed through the fθ lens. The optical path is then folded back and bent downward by the reflecting mirror so that the surface of the photosensitive drum  71  is irradiated with the laser beam to form the electrostatic latent image. 
   2.1.2. Process Cartridge 
   The process cartridge  70  is removably arranged in the casing  3  on the lower side of the scanner unit  60 . This process cartridge  70  includes the photosensitive drum  71 , a charger  72 , a transfer roller  73  and a developing cartridge  74 . 
   The photosensitive drum  71  acts as an image carrying unit for carrying the image to be transferred to the recording medium. The photosensitive drum  71  includes a cylindrical drum body  71   a  and a drum shaft  71   b . An outermost layer of the cylindrical drum body is made of a positively chargeable photosensitive layer such as polycarbonate. The drum shaft  71   b  extends axially and longitudinally in the drum body  71   a  for supporting the drum body  71   a  rotatably. 
   The charger  72  acts as a charging unit for charting the surface of the photosensitive drum  71 . The charger  72  is so arranged obliquely above the rear side of the photosensitive drum  71  as to confront the photosensitive drum  71  across a predetermined spacing such that it does not contact with the photosensitive drum  71 . The charger  72  may be a scorotron type charger for charging the surface of the photosensitive drum  71  substantially uniformly with a positive charge by making use of corona discharge. 
   The transfer roller  73  is arranged to confront the photosensitive drum  71  and to rotate in association with the photosensitive drum  71 . This transfer roller  73  acts as a transfer unit for transferring the toner having adhered to the surface of the photosensitive drum  71  to a printing surface of the recording medium by causing a charge (i.e., negative charge), which is opposed to the charge at the photosensitive drum  71 , to act on the recording medium from the side opposite to the printing face. 
   The developing cartridge  74  includes a toner housing chamber  74   a  housing the toner, a toner feed roller  74   b  for feeding the toner to the photosensitive drum  71  and a developing roller  74   c.    
   The toner, which is housed in the toner housing chamber  74   a , is fed toward the developing roller  74   c  by the rotation of the toner feed roller  74   b . The toner, which is fed toward the developing roller  74   c , is carried on the surface of the developing roller  74   c . After regulated to a predetermined constant (or uniform) thickness, the toner is fed to the surface of the photosensitive drum  71 , which is exposed to light by the scanner unit  70 . 
   2.1.3. Fixing Unit 
   The fixing unit  80  is arranged on the down stream side of the photosensitive drum  71  in the conveying direction of the recording medium. The fixing unit  80  fixes the toner, transferred to the recording medium, by heating and melting it. Specifically, the fixing unit  80  includes a heating roller  81 , which is arranged on the printing face side of the recording medium for heating the toner, and a pressure roller  82 , which is arranged on the opposite side of the heating roller  81  across the recording medium for pushing the recording medium toward the heating roller  81 . 
   The heating roller  81  includes a metal tube, a surface of which is coated with a fluorine resin, and a halogen lamp disposed in the metal tube for heating. On the other hand, the pressure roller  82  is configured by coating a metallic roller shaft coated with a roller made of a rubber material. 
   In the above-described image forming unit  10 , an image is formed on the recording medium in the following manner. 
   Specifically, the photosensitive drum  71  is uniformly and positively charged by the charger  72 , as it rotates, and is exposed to the laser beam, which is irradiated from and scanned at a high speed by the scanner unit  70 . As a result, the electrostatic latent image corresponding to the image to be formed on the recording medium is formed on the surface of the photosensitive drum  71 . 
   When the toner, which is carried on the developing roller  74   c  and positively charged, is brought to face and contact with the photosensitive drum  71  by the rotation of the developing roller  74   c , the toner is fed to the electrostatic latent image formed on the surface of the photosensitive drum  71 , namely, to such an exposed portion in the uniformly positively charged surface of the photosensitive drum  71  as has been exposed to the laser beam to lower its potential. As a result, the toner image by the reversal phenomenon is carried on the surface of the photosensitive drum  71 . 
   The toner image carried on the surface of the photosensitive drum  71  is transferred to the recording medium by the transfer bias applied to the transfer roller  73 . Then, the recording medium having the toner image transferred is conveyed to and heated by the fixing unit  80  so that the toner transferred as the toner image is fixed on the recording medium. Accordingly, the image formation is completed. 
   2.2. First Discharge Chute  30  and Second Discharge Chute  40   
   The first discharge chute  30  is a guide unit, which is arranged downstream of the fixing unit  80  in the conveying direction of the recording medium as shown in  FIG. 2  and turns the conveying direction of the recording medium formed with an image at the image forming unit  10  by about 90 degrees and guides the recording medium to the second discharge chute  40 . 
   The second discharge chute  40  is a guide unit, which is arranged on the upper cover  9  while having a predetermined clearance  40   a  from the first discharge chute  30  and which turns the recording medium turned by about 90 degrees in the conveying direction by the first discharge chute  30  further by about 90 degrees and guides the recording medium to the discharge port  7 . 
   The clearance  40   a  between the first discharge chute  30  and the second discharge chute  40  forms part of a conveying passage (i.e., a conveying path indicated by a thick double-dotted line), in which the conveying direction is reversed by the forward/backward switching mechanism  50 . In  FIG. 2 , a conveying path, which is indicated by a thick single-dotted line, indicates the conveying passage of the recording medium to be conveyed by the feeder unit  20 . 
   2.3. Feeder Unit 
   The feeder unit  20  includes a sheet feed tray  90  housed in the lowest position of the casing  3 , a sheet feed roller  22  disposed in a printer body portion above the front end portion of the sheet feed tray  90  for conveying the recording medium to the image forming unit  10 , and a separating roller  23  and a separating pad  24  for separating the recording medium being conveyed by the sheet feed roller  22  one at a time. The recording medium, which is placed on the sheet feed tray  90 , is caused to make a U-turn on the front side in the casing  3  and is conveyed to the image forming unit  10  arranged at a substantially central portion in the casing  3 . 
   In the conveying path of the recording medium from the sheet feed tray  90  to the image forming unit  10 , a paper dust removing roller  25  for removing paper dust or the like having stuck to image forming face (or the printing face) of the recording medium is arranged on the outer side of a crest of the substantially U-turned portion. An opposed roller  26  for pushing the recording medium to be conveyed onto the paper dust removing roller  25  is arranged on the inner side of that crest. 
   At the entrance of the image forming unit  10  in the conveying path from the sheet feed tray  90  to the image forming unit  10 , moreover, there is arranged a resister roller  27 , which is composed of a pair of rollers for regulating the conveying state of the recording medium by applying a conveying resistance to the recording medium. 
   2.4. Sheet Feed Tray 
     FIG. 3  is a perspective view of the upper face side of the sheet feed tray  90 .  FIG. 4  is an exploded perspective view of the sheet feed tray  90 .  FIG. 5  and  FIG. 6  are lower face views of a regulating wall member  94 .  FIG. 7  and  FIG. 8  are enlarged views of a lock mechanism  95 .  FIG. 9  is a sectional view taken along line IX-IX of  FIG. 7 . 
   As shown in  FIG. 3 , the sheet feed tray  90  includes a placing tray  92  having a placing portion  91  for placing the recording medium and the regulating wall member  94  having a wall portion  93  for contacting with the end portion of the recording medium thereby to regulate the position of the recording medium. 
   The regulating wall member  94  is assembled with the rear end side of the placing tray  92  so that it may be displaced back and forth with respect to the placing tray  92 . The regulating wall member  94  constitutes part of the outer peripheral wall of the placing tray  92  formed in a substantially rectangular shape. This displacement of the regulating wall member  94  is regulated by the lock mechanism  95  shown in  FIG. 5  and  FIG. 6 . 
   As shown in  FIG. 7 , the lock mechanism  95  includes a first tray side engagement portion  91   a  and a second tray side engagement portion  91   b  disposed on the bottom portion (or the placing portion  91 ) of the placing tray  92  and an engagement member  96  assembled with the regulating wall member  94  and adapted to be moved integrally with the regulating wall member  94  with respect to the placing tray  92 . The engagement member  96  includes a first regulating wall member engagement portion  96   a  for engaging with the first tray side engagement portion  91   a  and a second regulating wall member side engagement portion  96   b  for engaging with the second tray side engagement portion  91   b.    
   The first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  are formed into projections and depressions having saw-tooth shapes to mesh with each other, as shown in  FIG. 8 . The second regulating wall member side engagement portion  96   b  is formed into a projection having a shape of a substantially isosceles triangle. The second tray side engagement portion  91   b  are formed into such a recess as to fit the projection having the isosceles triangle shape of the second regulating wall member side engagement portion  96   b.    
   In this aspect of the invention, of the projections and depressions of the saw-tooth shapes formed at the first tray side engagement portion  91   a , a number of projections are formed into a substantially right-angled triangular shape such that the inclination angle θ 1  of the rear side slopes is smaller than the inclination angle θ 2  of the front side slopes and that the first tray side engagement portion  91   a  forms the saw-tooth shape. The second tray side engagement portion  91   b  is discretely formed such that the wall portion  93  is fixed at a position to correspond to the sheet size such as the standard size of A4 or A5 determined by the standards such as the JIS. 
   As shown in  FIG. 4 , the first regulating wall member side engagement portion  96   a  is formed on the leading end side of a first arm  96   c  extending from the rotation center O 1  (or a pivot  99 ) set in the regulating wall member  94 . The second regulating wall member engagement portion  96   b  is formed on the leading end side of a second arm  96   d  of a leaf spring extending from the first arm  96   c.    
   A releasing operation unit  97  (which will be described later) is disposed at the leading end side of a third arm  96   e , which extends from the rotation center O 1  (or the pivot  99 ) in a direction substantially perpendicular to the longitudinal direction of the first arm  96   c  and which rotates integrally with the first arm  96   c.    
   As shown in  FIG. 3 , on the opposite side of the placing portion  91  across the wall portion  93 , there is arranged the releasing operation unit  97  for releasing the regulated state of the lock mechanism  95 . On the side closer to the placing portion  91  than the releasing operation unit  97  and on the opposite side of the placing portion  91  across the wall portion  93 , there is fixed and arranged on the regulating wall member  94  a pinch member  98  which has a pinch face  98   a  substantially normal to the operation direction (or forward and backward) of the releasing operation unit  97  and to the displacement direction (or forward and backward) of the regulating wall member  94 . 
   The regulating wall member  94  has a first recess  94   a , which is recessed from the upper end to the lower end side thereof. The releasing operation unit  97  and the pinch member  98  are disposed on the bottom portion  94   b  of the first recess  94   a , and the upper end of the releasing operation unit  97  and the upper end of the pinch member  98  are substantially flush, when viewed horizontally, with the bottom portion  94   b  of the first recess  94   a.    
   The bottom portion  94   b  of the first recess  94   a  is provided with a second recess  94   c , which is recessed in a box shape in the lower end side of the regulating wall member  94 . In this aspect, the pinch face  98   a  is formed by the side wall of the second recess  94   c  recessed in the substantially box shape. 
   The releasing operation unit  97  is operated back and forth on the sheet feed tray  90  by turning (or rocking) it slightly on the pivot  99  (as referred to  FIG. 4 ), which is turnably assembled with the regulating wall member  94 . In this aspect, the releasing operation unit  97 , the pivot  99 , a spring portion (as referred to  FIG. 4 ) and the first to third arms  96   c  to  96   e  are integrally molded of a resin. 
   The spring portion  100  is a leaf spring, which contacts at its leading end side with the inner wall of the regulating wall member  94  and causes the elastic force for returning the releasing operation unit  97  to the original position to act on the releasing operation unit  97 . 
   Moreover, the releasing operation unit  97  is disposed at a position displaced transversely (or in a horizontal direction) with respect to the pivot  99 . The second arm  96   d  is given such a spring property which has a lower rigidity than that of the first arm  96   c  and is easily deformed. The first arm  96   c  and the second arm  96   d  are displaced (or rocked) around the pivot  99  in response to the displacement (or the rocking motion) of the operated releasing operation unit  97  around the pivot  99 . 
   The first arm  96   c , i.e., the first regulating wall member side engagement portion  96   a  is pushed toward the first tray side engagement portion  91   a  by the force, which is generated on the root side (or at a portion A shown in  FIG. 7 ) when the second arm  96   d  of the leaf spring shape is elastically deformed in the direction of solid arrow in  FIG. 7 . This pushing action holds the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a.    
   On the other hand, a reaction force, which is generated on the root side (or at the portion A in  FIG. 7 ), acts on the second regulating wall member side engagement portion  96   b . Thus, the second regulating wall member side engagement portion  96   b  is pushed by the reaction force toward the second tray side engagement portion  91   b . Accordingly, the engaging state between the second regulating wall member side engagement portion  96   b  and the second tray side engagement portion  91   b  can be kept. 
   When the releasing operation unit  97  is operated, the first arm  96   c  is rotationally displaced in the direction of a broken arrow in  FIG. 7  and the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  is released. At this time, the first arm  96   c  is rotationally displaced to approach the second arm  96   d , which is indicated by the broken arrow in  FIG. 7 . Thus, the elastic displacement amount of the second arm  96   d  increases according to the rotational displacement of the first arm  96   c.    
   As a result, the force to arise on the root side (or at the portion A of  FIG. 7 ) of the second arm  96   d  increases. Thus, the engaging state between the second regulating wall member side engagement portion  96   b  and the second tray side engagement portion  91   b  is held even if the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  is released. 
   A stopper  101  constitutes an elastic deformation regulating unit for regulating the elastic deformation of the second arm  96   d  by regulating the rotational displacement of the first arm  96   c . The stopper  101  is arranged between the side face  96   f  of the first arm  96   c  on the side of the second tray side engagement portion  91   b  and a wall face  92   a  formed on the placing tray  92  and extending substantially in parallel with the side face  96   f . The stopper  101  can move in parallel with the direction substantially parallel to the longitudinal direction of the first arm  96   c.    
   A stopper operation unit  102  is an elastic deformation regulating operation unit for moving the stopper  101  in parallel. The stopper operation unit  102  is disposed on the upper face side of the regulating wall member  94  and on the bottom portion  94   b  of the first recess  94   a , as shown in  FIG. 3 . 
   A moving portion  103 , which can move integrally with the stopper  101 , is disposed on the lower face side of the stopper operation unit  102 , as shown in  FIG. 5  and  FIG. 6 . On one of the moving portion  103  and the regulating wall member  94  the moving portion  103  in this aspect, there is formed an engagement projection  103   a , which engages with an engagement recess  94   d  disposed on the other (the regulating wall member  94 ). 
   As shown in  FIG. 9 , the first arm  96   c  is formed into a sectional shape having substantially two H components juxtaposed to enhance the bending rigidity. As a result, the warping deformation of the first arm  96   c  is vanishingly small and is smaller than that of the second arm  96   d.    
   The stopper  101  is formed into a substantially C-shaped (or substantially U-shaped) sectional shape having a longitudinally extending groove portion. A projection  91   c  having the second tray side engagement portion  91   b  is fitted in the groove portion. 
   3. Operations of Laser Printer (Sheet Feed Tray  90 ) 
   In this aspect of the invention, with the leading end side of the second arm  96   d  being elastically deformed and warped toward the first arm  96   c , the first tray side engagement portion  91   a  and the second tray side engagement portion  91   b  engage with the first regulating wall member side engagement portion  96   a  and the second regulating wall member side engagement portion  96   b , respectively. By at least the engagement (or mesh) between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a , the displacement of the regulating wall member  94  relative to the placing tray  92  is regulated. 
   When the operating force, which is indicated by the solid arrow in  FIG. 7 , acts on the releasing operation unit  97 , the releasing operation unit  97  is slightly turned (or rocked) leftward on the pivot  99  (or the rotation center O 1 ). Thus, the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  is released, and the second arm  96   d  is deformed to increase its warping deformation. 
   When the operating force indicated by the black arrow in  FIG. 7  is caused to act on the releasing operation unit  97  thereby to release the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a , the regulating wall member  94  can be displaced (or slid) back and forth with respect to the placing tray  92 , while the second regulating wall member side engagement portion  96   b  being pushed to contact with the second tray side engagement portion  91   b.    
   That is, when the operating force indicated by the black arrow in  FIG. 7  is caused to act on the releasing operation unit  97 , the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  is released, whereas the second arm  96   d  is forced to rotate leftward on the pivot  99 . At the same time, the projection, which has a substantially isosceles triangle shape and is disposed at the leading end of the second tray side engagement portion  91   b , is fitted in the recess forming the second regulating wall member side engagement portion  96   b . Accordingly, the second arm  96   d  is warped while being forced to turn leftward to an extent corresponding to the operation (or displacement) of the releasing operation unit  97 . 
   Therefore, even if the releasing operation unit  97  is operated to release the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a , the engaging state between the second tray side engagement portion  91   b  and the second regulating wall member side engagement portion  96   b  is not released. 
   However, as described hereinbefore, the projection forming the second tray side engagement portion  91   b  is formed into the substantially isosceles triangle shape, and the recess to form the second regulating wall member side engagement portion  96   b  is also formed into the isosceles triangle shape. When the forward/backward force acts on the first tray side engagement portion  91   a , the projection constituting the second regulating wall member side engagement portion  96   b  is so displaced toward the first arm  96   c  as to ride on the slope face of the recess formed in the second regulating wall member side engagement portion  96   b.    
   The second arm  96   d  has a relatively elastically deformable structure. Thus, if the regulating wall member  94  is displaced back and forth while the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  being released, the engaging state between the second tray side engagement portion  91   b  and the second regulating wall member side engagement portion  96   b  is easily released. 
   Accordingly, the engagement between the second tray side engagement portion  91   b  and the second regulating wall member side engagement portion  96   b  hardly exerts influences to regulate the displacement of the regulating wall member  94 . Rather, by bringing the second tray side engagement portion  91   b  and the second regulating wall member side engagement portion  96   b  into engagement, a proper tactile sensation can be given to the user at a position corresponding to the standard size when the regulating wall member  94  is to be displaced. Thus, the regulating wall member  94  can be easily displaced to a desired position without confirming the position of the regulating wall member  94  with a scale or the like. 
   In this aspect of the invention, the first tray side engagement portion  91   a  is formed into the saw-tooth shape by forming a number of projections into such a substantially right-angled triangular shape as to have slopes on the rear side. When the external force from the rear side toward the front side acts on the engagement member  96  (or the first regulating wall member side engagement portion  96   a ), the projections formed on the first regulating wall member side engagement portion  96   a  are so displaced toward the second arm  96   d  as to rise on the slopes formed on the first tray side engagement portion  91   a.    
   Although the first arm  96   c  is harder to elastically deform than the second arm  96   d , the first arm  96   c  may be warped toward the second arm  96   d  thereby to displace the engaging state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  when a relatively strong force acts from the rear side toward the front side on the engagement member  96  (or the first regulating wall member side engagement portion  96   a ). 
   The first tray side engagement portion  91   a  is formed of the projections of such a substantially right-angled triangular shape as to have slopes on the rear side. Thus, even if the force acts from the front side toward the rear side on the engagement member  96  (or the first regulating wall member side engagement portion  96   a ), contrary to the above case, the force to displace the projections formed in the second regulating wall member engagement portion  96   b  toward the second arm  96   d  is weaker than that of the case, in which the external force acts from the rear side toward the front side on the regulating wall member  94 . 
   Therefore, even if the external force from the front side toward the rear side acts on the engagement member  96  (or the first regulating wall member side engagement portion  96   a ), the engagement state between the first tray side engagement portion  91   a  and the first regulating wall member side engagement portion  96   a  is usually not released. Thus, the regulating wall member  94  is not displaced. 
   If the external force to act on the regulating wall member  94  is high, the releasing force may exceed the holding force to release the engaging state. In such a case, the regulating wall member  94  may move unintentionally. 
   However, in this aspect, the stopper operation unit  102  is operated to move the stopper  101  in parallel, as shown in  FIG. 10A  and  FIG. 11A . Thus, the projection  96   g  projecting from the side face  96   f  of the first arm  96   c  toward the wall face  92   a  can be brought into contact with the stopper  101  thereby to prevent the first arm  96   c  from being rotationally displaced toward the second arm  96   d . Therefore, it is possible to prevent the second arm  96   d  from being warped and deformed to an extent that the engaging state between the first regulating wall member side engagement portion  96   a  and the first tray side engagement portion  91   a  is released. 
   Incidentally,  FIG. 10B  and  FIG. 11B  are diagrams showing the state, in which the projection  96   g  and the stopper  101  are spaced to leave the first arm  96   c  and the second arm  96   d  unregulated. 
   Therefore, even if a strong external force acts on the regulating wall member  94 , it is possible to prevent the engaging state from being released between the first regulating wall member side engagement portion  96   a  and the first tray side engagement portion  91   a . Moreover, the engaging state can be prevented from being released without enlarging the holding force by increasing the spring constant of the second arm  96   d.    
   Since the spring constant of the coil spring need not be enlarged to raise the holding force, the releasing operation unit  97  need not be operated (or pushed) by a strong operating force when the position of the regulating wall member  94  is to be changed. When a strong external force is applied to the regulating wall member  94 , it is possible to prevent the regulating wall member  94  from moving while preventing the deterioration of the workability of the position changing operation. 
   In this aspect of the invention, the stopper operation unit  102  is disposed on the upper face side of the regulating wall member  94 . Thus, the stopper operation unit  102  can be operated from the upper face side of the regulating wall member  94  thereby to improve the operability of the stopper operation unit  102 . 
   The releasing operation unit  97  and the stopper operation unit  102  are disposed on the bottom portion of the first recess  94   a . Thus, the releasing operation unit  97  and the stopper operation unit  102  can be prevented from protruding from the upper face (or the top end face) of the regulating wall member  94 . Therefore, it is possible to prevent the vertical size of the regulating wall member  94  from being enlarged, thereby to prevent the sheet feed tray  90 , i.e., the laser printer  1  from being large-sized. 
   Moreover, the moving portion  103  has the engagement projection  103   a , and the regulating wall member  94  has the engagement recess  94   d  to engage with the engagement projection  103   a . Therefore, the engagement recess  94   d  and the engagement projection  103   a  can engage with each other thereby to give the user tactile sensation when the stopper operation unit  102  is operated. 
   Therefore, the user can easily notice whether or not the engaging state between the first regulating wall member side engagement portion  96   a  and the first tray side engagement portion  91   a  has been locked (or held), as shown in  FIG. 5  and  FIG. 6 . Accordingly, operability of the stopper operation unit  102  can be improved. 
   Incidentally,  FIG. 5  shows the state, in which the engaging state between the first regulating wall member side engagement portion  96   a  and the first tray side engagement portion  91   a  is locked.  FIG. 6  shows the state, in which the engaging state between the first regulating wall member side engagement portion  96   a  and the first tray side engagement portion  91   a  is released. 
   In the sheet feed tray  90 , the regulating wall member  94  forms part of the outer peripheral wall of the placing tray  92 , and the regulating wall member  94  is arranged on the rear end side of the placing portion  91 , as shown in  FIG. 4 . Therefore, it is possible that the regulating wall member  94  directly impinges against the wall or the like near the portion where the laser printer  1  is arranged. 
   Therefore, it is especially effective that the sheet feed tray  90  is applied to the sheet feed tray of the laser printer  1 , in which the regulating wall member  94  constitutes a portion of the outer peripheral wall of the placing tray  92  and is arranged on the rear end side of the placing portion  91 . 
   Incidentally, the first arm  96   c  corresponds to a first engagement member. The second arm  96   d  corresponds to a second engagement member, an elastic unit and an elastic deformation portion. The stopper operation unit  102  corresponds to an elastic deformation regulating operation unit. 
   Moreover, the third arm  96   e  corresponds to an operation arm portion. The stopper  101  corresponds to an elastic deformation regulating unit. The stopper operation unit  102  corresponds to elastic deformation regulating operation unit. 
   (Other Aspects) 
   In the aforementioned aspect, the sheet feed tray is applied to the laser printer. However, the application of the invention should not be limited thereto but can also be applied an image forming apparatus such as a copying machine. 
   In the aforementioned aspect, the regulating wall member  94  forms part of the outer peripheral wall of the placing tray  92 . However, the invention should not be limited thereto but can also be applied to a sheet feed tray, which is provided with the regulating wall member  94  separately of the outer peripheral wall of the placing tray  92 . 
   In the aforementioned aspect, the bottom portion of the first recess  94   a  is provided with the releasing operation unit  97  and the pinch member  98 , but the invention should not be limited thereto. 
   In the aforementioned aspect, the pinch face  98   a  is substantially normal to the displacing direction of the regulating wall member  94 , but the invention should not be limited thereto. 
   Moreover, the lock mechanism  95  should not be limited to one in the aforementioned aspect. For example, the second regulating wall member side engagement portion  96   b  and the second tray side engagement portion  91   b  may be eliminated. 
   In the aforementioned aspect, the second arm  96   d  is formed into a leaf spring shape to constitute an elastic unit and an elastic deformation portion. However, the invention should not be limited thereto, but may apply an elastic unit such as a coil spring, a torsion spring or rubber. 
   In the aforementioned aspect, the engagement recess  94   d  and the engagement projection  103   a  is provided to establish tactile sensation when the stopper operation unit  102  is operated, but the invention should not be limited thereto. 
   In the aforementioned aspect, the elastic deformation of the second arm  96   d  (or the elastic unit) is regulated by regulating the rotation stroke of the first arm  96   c . However, the invention should not be limited thereto, but the elastic deformation of the second arm  96   d  may also be directly regulated. 
   In the aforementioned aspect, the stopper  101  can be moved in a direction substantially parallel to the longitudinal direction of the first arm  96   c , but the invention should not be limited thereto.