Abstract:
A tilt angle adjusting device has a shaft configured to be fixed to a bottom surface of a housing at least one end, and a moment transmission member connected to the shaft. The moment transmission member allows relative rotation between the shaft and the moment transmission member when a moment equal to or more than a predetermined value is applied about an axis of the shaft from the housing, and restricts the relative rotation when the moment is released. The moment transmission member includes a leg configured to be placed on a surface on which the housing is installed. The leg is provided with part of a bearing to support the shaft. The moment transmission member also includes a plate member to press an outer peripheral surface of the shaft. The plate member forms the rest of the bearing.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a tilt angle adjusting device and a projector equipped with the tilt angle adjusting device. More particularly, the present invention relates to a device for adjusting the orientation of a projector. 
   2. Description of the Related Art 
   A typical projector is equipped with a tilt angle adjusting device to adjust a longitudinal and a transverse inclination of the projector in accordance with various situations. Conventional tilt angle adjusting devices are generally classified into two types according to the tilt angle adjusting mechanism. In a tilt angle adjusting device of the first type, extending lengths of tilt feet arranged on the bottom of a housing are varied in order to incline the housing in a longitudinal and/or transverse direction. In a tilt angle adjusting device of the second type, a housing is tiltably mounted on a pedestal and tilted on the pedestal in order to incline the housing in a longitudinal and/or transverse direction. 
   Irrespective of which type of tilt angle adjusting device is used, a change in the longitudinal inclination of projector  100  causes a change in the projected angle of the centerline of image light in the vertical direction (referred to as a projection angle hereinafter), so that a displayed position of image  101  is moved up and down, as illustrated in  FIG. 1 . On the other hand, a change in the transverse inclination of projector  100  causes a change in the projected angle of the centerline of image light in the horizontal direction (referred to as an image angle hereinafter), so that image  101  is displayed such that the upper right or the upper left portion of the image is raised, as illustrated in  FIG. 2 . 
     FIGS. 3A to 3D  illustrate examples of projectors which are equipped with a tilt angle adjusting device according to the first type. Projectors  102  of  FIGS. 3A to 3D  are commonly equipped with at least one tilt foot  105  on bottom surface  104  of housing  103 . In projector  102  illustrated in  FIG. 3A , one tilt foot  105  is arranged in the front portion of bottom surface  104 , and two fixed legs  106  are arranged in the rear portion of bottom surface  104 . The term “fixed leg” used herein refers to a leg, the length of which cannot be adjusted, unlike tilt foot  105 . In projector  102  illustrated in  FIG. 3B , one tilt foot  105  is arranged in the front portion of bottom surface  104 , and one tilt foot  105  and one fixed leg  106  are arranged in the rear portion of bottom surface  104 . In projector  102  illustrated in  FIG. 3C , two tilt feet  105  are arranged in the front portion of bottom surface  104 , and one fixed leg  106  is arranged in the rear portion of bottom surface  104 . In projector  102  illustrated in  FIG. 3D , two tilt feet  105  are arranged in the front portion of bottom surface  104 , and two fixed legs  106  are arranged in the rear portion of bottom surface  104 . 
   In projector  102  illustrated in  FIG. 3A , tilt foot  105  can be lengthened or shortened to adjust the projection angle. In projector  102  illustrated in  FIG. 3B , front and rear tilt feet  105  can be lengthened or shortened to adjust the projection angle and the image angle independently of each other. In projectors  102  illustrated in  FIGS. 3C ,  3 D, two front tilt feet  105  can be lengthened or shortened to adjust both the projection angle and the image angle at one time. 
   Another example of the first type of a tilt angle adjusting device is described in the specification etc. of Japanese Patent Laid-open Publication No. 2001-42423 (Document 1). The tilt angle adjusting device described herein comprises a support leg pivotally arranged on the bottom surface of a housing of a projector; and a fixing mechanism for fixing the support leg at a desired angle. The fixing mechanism comprises an operating gear which rotates in association with pivotal movements of the support leg, and a rotating gear fixed to the housing. The operating gear usually meshes with the rotating gear. The operating gear, however, is released from engagement with the rotating gear when it slides in the horizontal direction. Specifically, as a release button is pushed, the operating gear slides in the horizontal direction away from the rotating gear to allow the operating gear to be released from engagement with the rotating gear, and to allow pivotal movement of the support leg. As the release button is released after the support leg has been pivotally moved to a desired angle, the operating gear slides in the opposite direction and comes into mesh with the rotating gear to lock the support leg. 
   The specification etc. of Japanese Patent Laid-open Publication No. 2004-109359 (Document 2) describes a projector which has a tilt angle adjusting device of the second type. The projector described herein is provided with a hemispherical protrusion on the bottom surface of the housing of the projector. A pedestal on which the projector is mounted has a top surface provided with a hole into which the protrusion is fitted. Thus, as the projector is placed on the pedestal such that the protrusion is fitted into the hole, the projector can be inclined to the front, back, right, and left on the pedestal, as well as rotated in the horizontal direction. 
   Although the tilt angle adjusting device illustrated in  FIG. 3A  can adjust the projection angle, it cannot adjust the image angle, and although the tilt angle adjusting device illustrated in  FIG. 3B  can adjust both the projection angle and image angle, it cannot adjust them at one time. Therefore, either the projection angle or the image angle must be adjusted first, then followed by the adjustment of the other. Although the tilt angle adjusting mechanisms illustrated in  FIGS. 3C ,  3 D can adjust the projection angle and image angle at one time, they cannot adjust them independently of each other (i.e., individually). Further, to adjust the angles, any of the tilt angle adjusting devices illustrated in  FIGS. 3A-3D  must be lifted up to raise the tilt foot (feet), resulting in complicated and burdensome adjustment work. 
   The projector described in Document 1 involves complicated and burdensome work for adjustments, because the release button must be pushed each time the angle is adjusted. Further, the housing must be lifted up to raise the support leg to adjust the angle, similar to the tilt angle adjusting devices illustrated in  FIGS. 3A-3D . 
   In the projector described in Document 2, the orientation of the housing is only maintained by the frictional resistance of the surface of the protrusion with the periphery of the hole. As such, the orientation can vary with only small force applied to the housing. Further, if the housing is inclined at an excessive angle, the frictional resistance of the surface of the protrusion with the periphery of the hole may not be sufficient to maintain the orientation of the housing. Even if the orientation is maintained, the orientation of the housing is liable to vary with any slight force. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a tilt angle adjusting device which is capable of adjusting the orientation of a projector with highly simple operations and of ensuring that the adjusted orientation is maintained. It is another object of the present invention to provide a projector equipped with the tilt angle adjusting device. 
   A tilt angle adjusting device comprises a shaft configured to be fixed to a bottom surface of a housing at at least one end, and a moment transmission member connected to the shaft. The moment transmission member allows relative rotation between the shaft and the moment transmission member when a moment equal to or more than a predetermined value is applied about an axis of the shaft from the housing, and restricts the relative rotation when the moment is released. 
   According to one aspect of the present invention, the moment transmission member includes a leg configured to be placed on a surface on which the housing is installed. The leg is provided with part of a bearing to support the shaft. The moment transmission member also includes a plate member to press an outer peripheral surface of the shaft. The plate member forms the rest of the bearing. 
   As force is applied toward the bottom surface at one side of the top surface of the housing in a width direction, rotation moment is caused about the shaft which serves as a center of rotation. On the other hand, since the outer peripheral surface of the shaft is pressed against the bearing formed on the leg, a frictional resistance is caused between the outer peripheral surface of the shaft and the surface of the bearing. Therefore, as the rotation moment exceeds the frictional resistance, the shaft rotates, causing a pivotal movement of the housing fixed to the shaft. On the other hand, when no external force is applied to the top surface of the housing, or when external force is applied to the housing that only generates rotation moment that is smaller than the frictional resistance, the shaft will not rotate, so that no pivotal movement of the housing will occur. 
   According to another aspect of the present invention, the moment transmission member includes a first disk provided with a plurality of teeth on one side, a second disk provided with a plurality of teeth on a surface opposite to the first disk, the teeth of the second disk meshing with the teeth of the first disk, a resilient member to press the second disk against the first disk, and a leg configured to be placed on a surface on which the housing is installed, the leg being fixed to the first disk. The shaft extends through the first disk, the second disk, and the resilient member, and is configured to restrict rotation of the second disk about an axis of the shaft. The first disk, the second disk, and the resilient member are configured such that when a moment equal to or more than a predetermined value is applied to the shaft, the second disk is moved in an axial direction of the shaft against the resilient member, to disengage the teeth of the first disk from the teeth of the second disk. 
   As force is applied downward from the top surface of the housing, rotating moment is caused about the shaft that is fixed to the housing. Only when this rotating moment is equal to or larger than a predetermined value, the locking state of the shaft, which is caused by the engagement of the first disk with the second disk, is released to permit the housing to pivot. Further, since the first disk is engaged with the second disk by the mesh of the teeth formed on opposite surfaces of the disks, the housing pivots by an angle corresponding to one tooth in a stepwise manner. 
   The housing is inclined to the left or right just by pushing the top surface of the housing with force equal to or larger than a predetermined value, consequently the image angle is adjusted. When the operator stops pushing the top surface of the housing, the housing is automatically locked and the image angle is securely maintained. 
   A projector according to the present invention includes the tilt angle adjusting device described above. 
   The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an explanatory diagram illustrating the adjustment of a projection angle; 
       FIG. 2  is an explanatory diagram illustrating the adjustment of an image angle; 
       FIGS. 3A to 3D  are perspective views of tilt angle adjusting devices according to prior arts; 
       FIG. 4  is a perspective view illustrating an embodiment of a tilt angle adjusting device equipped in a projector according to the present invention; 
       FIG. 5  is a cross-sectional view of the tilt angle adjusting device illustrated in  FIG. 4 ; 
       FIG. 6  is an exploded perspective view illustrating a method for mounting the tilt angle adjusting mechanism to a projector; 
       FIG. 7  is a schematic rear view illustrating an embodiment of a projector according to the present invention; 
       FIG. 8  is a partially enlarged cross-sectional view illustrating a modification to the tilt angle adjusting device illustrated in  FIG. 4 ; 
       FIG. 9  is an enlarged cross-sectional view illustrating another modification to the tilt angle adjusting device illustrated in  FIG. 4 ; 
       FIG. 10  is a perspective view illustrating another embodiment of a tilt angle adjusting device equipped in a projector according to the present invention; 
       FIG. 11  is an exploded perspective view of the tilt angle adjusting device illustrated in  FIG. 10 ; 
       FIG. 12  is a partially enlarged cross-sectional view illustrating the structure of the tilt angle adjusting device illustrated in  FIG. 10 ; and 
       FIG. 13  is a partially enlarged diagram for illustrating forces acting between the teeth of a first disk and teeth of a second disk. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first embodiment of a projector according to the present invention will be described. As illustrated in  FIGS. 4 and 5 , tilt angle adjusting device  1  has leg  10 , shaft  11 , and clamp plate  12 . Leg  10  has an elongate shape. Bottom surface  20  is substantially flat, and top surface  21  gradually approaches bottom surface  20  from the center of top surface  21  towards the both ends. Thus, leg  10  is tapered narrowing down in a longitudinal direction. Semi-arc shaped bearing  22  is formed at the longitudinal center of top surface  21  of leg  10 . Shaft  11  includes a round-bar shaft section  23 , and plate-shaped brackets  24  arranged at both axial ends of shaft section  23 . Semi-arc recess  25  which covers shaft section  23  of shaft  11  is formed at the center of clamp plate  12 . Flanges  26  are formed integrally with recess  25  on both ends thereof. 
   As clearly illustrated in  FIG. 5 , a radially lower half of shaft section  23  of shaft  11  is fitted in bearing  22  of leg  10 . The remaining radially upper half of shaft section  23  that is fitted in bearing  22  of leg  10  is covered with recess  25  of clamp plate  12 . Flanges  26  of clamp plate  12  are fixed to top surface  21  of leg  10  with screws. Recess  25  has a slightly smaller radius of curvature than shaft section  23 . Therefore, the inner surface of recess  25  is pressed against the outer peripheral surface of shaft section  23  with a pressure equal to or higher than a predetermined value. As a result, frictional resistance F 1  is caused between the contact surfaces. 
   As illustrated in  FIG. 6 , tilt angle adjusting device  1  provided with the foregoing structure is mounted in a rear portion (opposite to the plane on which a projection lens is arranged) of housing bottom surface  30  of projector  2 . Specifically, housing bottom surface  30  is provided in its rear portion with mount area  33  which forms a recess on housing  32 , with stages  34  to fix brackets  24  of shaft  11 , formed in front and at the back of mount area  33 . Brackets  24  are fixed to corresponding stages  34  with screws, not shown. In other words, leg  10  is coupled with housing  32  pivotally about shaft  11  which serves as an axis of rotation. Tilt foot  35  is provided in the front portion of the bottom surface  30  of housing, to move the front side of housing  32  in an up/down direction to adjust the projection angle (launching angle). Tilt foot  35 , which is arranged on the axis of shaft  11 , is similar to the conventional tilt foot in structure. Detailed description of tilt foot  35  is omitted. 
   The tilt angle can be adjusted in the following manner for projector  2  of the structure as described above. As illustrated in  FIG. 7 , as force F 2  is applied downward at one of the sides of top surface  36  of housing  32  in a width direction (longitudinal direction of leg  10 ), rotation moment M 1  is caused about shaft section  23  of shaft  11 . On the other hand, frictional resistance F 1  is caused between the surfaces of bearing  22  and recess  25  and the outer peripheral surface of shaft section  23  of shaft  11 . Therefore, as rotation moment M 1  is applied, reaction moment M 2  is caused. When rotation moment M 1  becomes larger than reaction moment M 2 , housing  32  pivots about fixed leg  35  which serves as a fulcrum ( FIG. 6 ) in the direction in which rotation moment M 1  is applied (in the counter-clockwise direction in  FIG. 7 ). In other words, while the relationship M 1 ≦M 2  is being established housing  32  is locked, and pivots only when the relationship M 1 &gt;M 2  is satisfied. Thus, housing  32  is inclined to the left or right only by pushing upper surface  36  of housing  32  of projector  2  installed on a table or a desk, and the image angle of a projected image is accordingly adjusted. Further, when the pressing force is released at top surface  36 , housing  32  is automatically locked to hold the image angle. 
   Next, a modification to the above-described tilt angle adjusting device will be described with reference to  FIG. 8 . In the tilt angle adjusting device illustrated in  FIG. 8 , shaft section  23  has an axially central portion arranged between bearing  22  of leg  10  and recess  25  of clamp plate  12 . The central portion has a smaller diameter than the remaining portion of shaft section  23 . Bearing  22  and recess  25  have arcuate surfaces which are able to be in close contact with the narrowed central portion of shaft section  23 . With this structure, displacement of leg  10  in the axial direction of shaft  11  is restricted. Further, a force is constantly maintained on bearing  22  of leg  10  to ensure that bearing  22  is kept in contact with the narrowest portion of shaft section  23 . Even if any external force acts on leg  10  to displace it temporarily in the axial direction of shaft  11 , leg  10  will immediately return to the original position. 
   Another modification of the tilt angle adjusting device will be described with reference to  FIG. 9 . In the tilt angle adjusting device illustrated in  FIG. 9 , clamp plate  12  is overlaid with a second clamp plate (auxiliary clamp plate  40 ), and both plates are fastened together to leg  10  with common screws  41 ,  42 . As clamp plate  12  suffers from deformation and/or creep due to aging and so on, frictional resistance may be reduced between the surface of recess  25  and the outer peripheral surface of shaft section  23  of shaft  11 , which may lower the capability to maintain the orientation of the housing, not shown. Clamp plate  12  is overlaid with auxiliary clamp plate  40 , which does not have a surface in contact with shaft section  23 , to prevent creep in clamp plate  12 . Thus, the reduction in the capability to maintain the orientation of the housing, which may result from a reduction in frictional resistance, can be avoided. It should be noted that creep is a common phenomenon with resin, and therefore, if clamp plate  12  is made of resin, this makes auxiliary clamp  40  particularly effective. Auxiliary clamp plate  40  is preferably formed of metal which is less likely to suffer from creep than resin. If auxiliary clamp plate  40  has a proper resiliency, it can usually press clamp plate  12  to shaft section  23  effectively as well as prevent creep. 
   Leg  10 , shaft  11 , clamp plate  12 , and brackets  24  which are of the above-mentioned structure may be entirely or partially made of resin or metal material. These components can be manufactured by an appropriate process such as molding, die casting, pressing, and the like. 
   A second embodiment of a projector according to the present invention will be described next. The projector of the second embodiment differs from the first embodiment only in the structure of the tilt angle adjusting device. Therefore, the following description will be focused on the structure of the tilt angle adjusting device, and description of the projector itself will be omitted. 
   As illustrated in  FIGS. 10 and 11 , tilt angle adjusting device  50  comprises leg  51 , shaft  52 , first disk  53 , second disk  54 , resilient member  55 , spacer  56 , brackets  57 ,  58 , and positioning member  59 . 
   Leg  51  has an elongated shape, with semi-arcuate bearing  61  formed on the top surface in the central portion of leg  51  in the longitudinal direction (hereinafter referred to as central top surface  60 ). Semi-arcuate recess  62 , into which first disk  53  is fitted, is formed on leg  51  on the back surface of the central portion in the longitudinal direction. 
   Circular hole  64  is formed through the center of first disk  53  through which shaft  52  extends. A large number of teeth  82  ( FIG. 13 ) are formed along the circumferential direction on the back surface of first disk  53 . Fixed pieces  66 , provided with throughholes  65 , are disposed on the front surface of first disk  53  and extend in the axial direction of shaft  52 . First disk  53  is fixed to leg  51  by screws (not shown) which extend through throughholes  65  of fixed piece  66  into screw holes  67  formed on central top surface  60  of leg  51 . First disk  53  is thus integrated with leg  51 . 
   Second disk  54 , which has substantially the same shape as first disk  53 , is provided with a large number of teeth  70  on the surface which is opposite to the back surface of first disk  53 . Teeth  70  mesh with teeth  82  formed on the back surface of first disk  53 . Hole  71  is formed on second disk  54  through which shaft  52  is inserted. Hole  71  is not circular but polygonal. 
   Shaft  52  does not have a uniform cross section in the axial direction. A portion of shaft  52  that is inserted into hole  64  of first disk  53  has a circular cross section, similar to hole  64 , and a portion that is inserted into hole  71  of second disk  54  has a polygonal cross section, similar to hole  71 . Therefore, shaft  52  can rotate about the axis independently of first disk  53 , but cannot rotate independently of second disk  54 . It means that when either shaft  52  or second disk  54  rotates, the other ( 52  or  54 ) also rotates in the same direction. However, second disk  54  can be independently displaced in the axial direction of shaft  52 . 
   One end of shaft  52  extends through second disk  54 , annular resilient member  55 , and spacer  56 . Bracket  58  is fixed to the end. Specifically, as illustrated in  FIG. 12 , resilient member  55  and spacer  56  are sandwiched between the back surface of second disk  54  and bracket  58 , such that second disk  54  is usually pressed against first disk  53  by the resilient force of resilient member  55 . The other end of shaft  52  extends through first disk  53 , and is supported from below by bearing  61  formed on central top surface  60  of leg  51 . Bracket  57  is fixed to the end. 
   Referring again to  FIG. 11 , positioning member  59  is fastened to central top surface  60  of leg  51  by common screws (not shown) which also fix fixed pieces  66  of first disk  53  to central top surface  60  of leg  51 . Protrusion  80  which is substantially triangular in shape is formed at the center of positioning member  59  by having it pressed into this shape. Positioning member  59  and bracket  57  are positioned such that protrusion  80  of positioning member  59  fits in a groove (not shown) formed in bracket  57  only when bracket  57  is parallel with leg  51 . 
   The tilt angle adjusting device having the above-mentioned structure is fixed to the housing of a projector (not shown) by screws (not shown) which extend through screw holes  81  formed in brackets  57 ,  58  arranged on both ends of shaft  52 , and which extends into the back surface of the housing of the projector. Therefore, the housing is coupled with leg  51  pivottaly about shaft  52  which serves as an axis of rotation. As a result, similar to the embodiment illustrated in  FIG. 7 , as force is applied downward at one of the sides of the top surface of the housing in a width direction (longitudinal direction of leg  51 ), rotation moment is caused about shaft  52 . Assume that the force applied to the housing is F 10 , the force with which resilient member  55  presses second disk  54  against first disk  53  is F 11 , and the combined force acting on the surface of teeth  57  of second disk  54  that engages with teeth  82  of first disk  53  is F 12 . The relationship between these forces is illustrated in  FIG. 13 . Thus, as F 12  becomes larger than F 11 , second disk  54  is displaced in the axial direction of shaft  52  (to the left in  FIG. 12 ) against the resilient force of resilient member  55 . Teeth  57  of second disk  54  is released from engagement with teeth  82  of first disk  53 , to cause second disk  54  and shaft  52  to rotate by an angle corresponding to one tooth. As a result, the housing also pivots by an angle corresponding to one tooth in the direction in which the rotation moment is caused. In the foregoing manner, tilt angle adjusting device  50  can rotate the housing to the left or to the right to adjust the image angle in a stepwise manner. 
   Further, when bracket  57  is positioned parallel with leg  51  while the housing of the projector is rotated to the left or to the right, protrusion  80  of positioning member  59  fits into the groove of bracket  57 . This fitting motion produces a clicking sound and tactile feedback to the hand of an operator who is applying force to the housing. As such, the operator can easily and securely know the horizontal orientation of the housing. The force required to disengage protrusion  80  of positioning member  59  fitted in the groove of bracket  57  from that groove may be smaller than the force required to release the engagement of teeth  82  of first disk  53  from teeth  57  of second disk  54 . 
   Additionally, a stopper may be provided between the surface of first disk  53  and recess  62  into which first disk  53  is fitted, in order to limit displacements of first disk  53  in the axial direction of shaft  52 . Preferably, a notch may be formed in recess  62  in order to avoid interference of the stopper with recess  62 . Further, a stopper may be provided between spacer  56  and bracket  58 , in order to avoid excessive displacements of second disk  54  in the axial direction of shaft  52 . 
   While certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims.