Abstract:
A casing is provided for a reflection measurement device emitting a scanning beam and receiving an echo beam caused by reflection of the scanning beam at an object, and detecting a distance to the object in response to the received echo beam. The casing has a window for conducting a beam, and a protective member being transparent to the beam and covering the window from an inside. A predetermined range through which the beam passes is provided in the window. An interval between a lower edge of the beam pass range and a lower edge of the window is greater than an interval between opposing edges of the beam pass range and the window which differ from the lower edges thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a casing for a reflection measurement device such as a device for measuring the distance to a reflective object by using a light beam or a radar device using a laser beam.  
           [0003]    2. Description of the Related Art  
           [0004]    A typical on-vehicle reflection measurement device emits a forward laser beam from the subject vehicle, and controls the forward laser beam to scan a prescribed area outside the subject vehicle. In the case where an object exists in the prescribed area, the forward laser beam encounters the object before being at least partially reflected thereby. Generally, a portion of the reflection-resultant laser beam returns to the measurement device as an echo laser beam. The measurement device converts the echo laser beam into an electric echo signal. The measurement device processes the electric echo signal into data for recognizing or detecting the object.  
           [0005]    Such an on-vehicle reflection measurement device can be used in an apparatus for alarming when an obstacle (for example, a preceding vehicle) to the subject vehicle is detected. Also, the measurement device can be used in an apparatus for controlling the speed of the subject vehicle to maintain the distance to a preceding vehicle in a safe range.  
           [0006]    The on-vehicle reflection measurement device is provided with a casing for housing members and parts of the device. The casing has an outlet window via which the forward laser beam is propagated. The casing also has an inlet window via which a return laser beam (an echo laser beam) enters the device. Plate-like protective covers transparent to laser beams extend over the inlet and outlet windows, respectively. The protective covers are supported by inner surfaces of the walls of the casing. The protective covers prevent pebbles and raindrops from entering the casing.  
           [0007]    The upwardly-facing surface of the walls of the casing which defines the lower side of the outlet window is exposed to the atmosphere. Rainwater tends to be collected on this wall surface. When the forward laser beam meets the collected rainwater and passes therethrough, it is scattered and partially absorbed thereby. As a result, the power of the forward laser beam reaching an object, and also the power of a return laser beam coming from the object are reduced. The power reduction causes a decrease in the detectable distance to an object.  
           [0008]    Japanese patent application publication number 11-38122 discloses a casing for a reflection measurement device. The casing in Japanese application 11-38122 has drain grooves to enable rainwater to escape from the lower side of an outlet window. During the manufacture of the casing, a special processing step is required to make the drain grooves.  
           [0009]    Japanese utility model application publication number 4-54746 discloses an on-vehicle laser radar device. The laser radar device in Japanese application 4-54746 includes a cylindrical hood provided on a front of a laser radar head. The hood covers a laser emitting section and a laser receiving section. During the travel of the subject vehicle, wind coming from the front thereof acts as a dynamical pressure in the hood. Under a rainy condition, the dynamical pressure directs raindrops toward the sides of the hood, thereby preventing them from meeting the front surface of the laser radar head.  
           [0010]    Japanese utility model application publication number 5-14961 discloses an inter-vehicle distance measurement device using a laser beam. The measurement device in Japanese application 5-14961 has a front surface covered with a lens. A wiper is provided to clean a surface of the lens. Cleaning liquid can be injected from a nozzle toward the lens surface. A dirt sensor acts to detect dirt on the lens surface. The injection of cleaning liquid from the nozzle and the drive of the wiper are controlled in response to the output signal of the dirt sensor.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of this invention to provide a casing for a reflection measurement device which can be manufactured without a special processing step, and which can prevent rainwater from being considerably collected in the lower edge of an outlet window.  
           [0012]    A first aspect of this invention provides a casing for a reflection measurement device emitting a scanning beam and receiving an echo beam caused by reflection of the scanning beam at an object, and detecting a distance to the object in response to the received echo beam. The casing comprises a window for conducting a beam; and a protective member being transparent to the beam and covering the window from an inside. A predetermined range through which the beam passes is provided in the window, and an interval between a lower edge of the beam pass range and a lower edge of the window is greater than an interval between opposing edges of the beam pass range and the window which differ from the lower edges thereof.  
           [0013]    A second aspect of this invention provides a casing for a reflection measurement device emitting a scanning beam and receiving an echo beam caused by reflection of the scanning beam at an object, and detecting a distance to the object in response to the received echo beam. The casing comprises a window for conducting a beam; and a protective member being transparent to the beam and covering the window from an inside. A predetermined range through which the beam passes is provided in the window, and an area of a zone between a lower edge of the beam pass range and a lower edge of the window is greater than an area of a zone between opposing edges of the beam pass range and the window which differ from the lower edges thereof.  
           [0014]    A third aspect of this invention is based on the first aspect thereof, and provides a casing further comprising a casing member defining the window, and a resilient member provided between the casing member and the protective member and non-projecting into the window.  
           [0015]    A fourth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the lower edge of the window inclines at a predetermined angle relative to the lower edge of the beam pass range.  
           [0016]    A fifth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the window has a pentagonal shape with a downwardly-projecting lower side.  
           [0017]    A sixth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the lower edge of the window tapers as viewed in a direction perpendicular to a plane of the window. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a perspective view of a first prior-art casing for a reflection measurement device.  
         [0019]    [0019]FIG. 2 is a perspective view of a second prior-art casing for a reflection measurement device.  
         [0020]    [0020]FIG. 3 is a diagram of a reflection measurement device provided with a casing according to a first embodiment of this invention.  
         [0021]    [0021]FIG. 4 is a perspective view of the casing in FIG. 3.  
         [0022]    [0022]FIG. 5 is a front view of the casing in FIGS. 3 and 4.  
         [0023]    [0023]FIG. 6 is a front view of an outlet window in FIGS.  3 - 5 .  
         [0024]    [0024]FIG. 7 is a sectional view of the outlet window which is taken along the line A-A in FIG. 5.  
         [0025]    [0025]FIG. 8 is a front view of a casing for a reflection measurement device according to a second embodiment of this invention.  
         [0026]    [0026]FIG. 9 is a front view of an outlet window in a casing for a reflection measurement device according to a third embodiment of this invention.  
         [0027]    [0027]FIG. 10 is a front view of an outlet window in a casing for a reflection measurement device according to a fourth embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    Prior-art casings for reflection measurement devices will be explained below for a better understanding of this invention.  
         [0029]    [0029]FIG. 1 shows a first prior-art casing  202  for a reflection measurement device. A front panel of the casing  202  has an outlet window  204  via which a forward laser beam is propagated. The front panel of the casing  202  also has an inlet window  205  via which a return laser beam (an echo laser beam) enters the device.  
         [0030]    Plate-like protective covers  208  transparent to laser beams extend over the outlet and inlet windows  204  and  205 , respectively. The protective covers  208  are supported by inner surfaces of the walls of the front casing panel. The protective covers  208  prevent pebbles and raindrops from entering the casing  202  via the outlet and inlet windows  204  and  205 .  
         [0031]    The walls of the front casing panel have surfaces defining the outlet window  204 . The protective cover  208  for the outlet window  204  contacts with and extends along the inner surfaces of the walls of the front casing panel. Accordingly, the upwardly-facing surface of the walls of the front casing panel which defines the lower side of the outlet window  204  is exposed to the atmosphere. The upwardly-facing surface of the walls has a width  212  equal to the thickness of the walls. In the outlet window  204 , there is a corner  216  between the upwardly-facing surface of the walls and a surface of the related protective cover  208 . The corner  216  extends along the inner edge of the upwardly-facing surface of the walls.  
         [0032]    Rainwater  214  tends to be collected in the corner  216  in the outlet window  204 . When the forward laser beam meets the collected rainwater  214  and passes therethrough, it is scattered and partially absorbed thereby. As a result, the power of the forward laser beam reaching an object, and also the power of a return laser beam coming from the object are reduced. The power reduction causes a decrease in the detectable distance to an object.  
         [0033]    [0033]FIG. 2 shows a second prior-art casing  302  for a reflection measurement device which is disclosed in Japanese patent application publication number 11-38122. A front panel of the casing  302  has an outlet window via which a forward laser beam is propagated. The walls of the front panel of the casing  302  have drain grooves  320  extending downward from the upwardly-facing surface of the walls of the front casing panel which defines the lower side of the outlet window. The drain grooves  320  enable rainwater to escape from the lower side of the outlet window. During the manufacture of the casing  302 , a special processing step is required to make the drain grooves  320 .  
       First Embodiment  
       [0034]    [0034]FIG. 3 shows a reflection measurement device  110  provided with a casing  102  according to a first embodiment of this invention. The casing  102  houses members and parts of the device  110 . The device  110  includes an optical system disposed in the casing  102 . The optical system has a laser diode  112 , a collimator lens  114 , a mirror  116 , a polygon mirror  118 , a condenser lens  120 , and a photodiode  122 .  
         [0035]    The laser diode  112  converts an electric signal into infrared laser light. The laser diode  112  emits the laser light toward the collimator lens  114 . The collimator lens  114  changes the laser light into a parallel laser beam directed toward the mirror  116 . The mirror  116  reflects the parallel laser beam toward the polygon mirror  118 . The polygon mirror  118  reflects the parallel laser beam. The reflection-resultant laser beam travels from the polygon mirror  118  as a forward laser beam (a scanning laser beam). The polygon mirror  118  is rotatable. As the polygon mirror  118  rotates, the direction of travel of the forward laser beam changes in a prescribed angular range. Thus, during the rotation of the polygon mirror  118 , a detection area corresponding to the prescribed angular range is scanned by the forward laser beam. The condenser lens  120  gathers a return laser beam (an echo laser beam) on the photodiode  122 . The photodiode  122  converts the return laser beam into an echo electric signal. The photodiode  122  outputs the echo electric signal.  
         [0036]    The device  110  includes a laser-diode driving section  124 , a polygon scanner motor  126 , a motor driving section  128 , a receiving circuit  130 , and a controlling section  132  which are disposed in the casing  102 .  
         [0037]    The laser-diode driving section  124  acts to drive the laser diode  112 . The polygon mirror  118  is rotated by the polygon scanner motor  126 . The motor driving section  128  acts to drive the polygon scanner motor  126 . Thus, the rotation of the polygon mirror  118  can be controlled via the motor driving section  128 . The receiving circuit  130  amplifies and wave-shapes the output signal of the photodiode  122 . The receiving circuit  130  outputs the resultant signal to the controlling section  132 . The controlling section  132  controls the laser-diode driving section  124  and the motor driving section  128 , thereby enabling the forward laser beam to scan the detection area. The controlling section  132  processes the output signal of the receiving circuit  130  to calculate, for example, the distance to an object (or an obstacle) in the detection area, and the position and relative speed of the object.  
         [0038]    The device  110  is mounted on a vehicle referred to as the subject vehicle (the present vehicle) hereafter. In general, the device  110  is located at the front surface of the body of the subject vehicle. The detection area which is scanned by the forward laser beam extends ahead of the subject vehicle. The device  110  emits the forward laser beam into the detection area.  
         [0039]    As shown in FIG. 4, the casing  102  has a shape of a rectangular parallelepiped or a shape of a box. The casing  102  is formed by, for example, shaping an aluminum plate. As shown in FIGS. 3, 4, and  5 , the casing  102  has a front panel formed with an outlet window  104  and an inlet window  105 . The forward laser beam coming from the polygon mirror  118  passes through the outlet window  104 . A return laser beam (an echo laser beam) passes through the inlet window  104  before reaching the condenser lens  120 . The outlet window  104  has a pentagonal shape with a downwardly-projecting lower side of a V configuration.  
         [0040]    With reference to FIG. 6, during the scanning of the detection area, the forward laser beam moves over a rectangular range (a rectangular region)  158  as viewed in a cross section of the outlet window  104 , that is, as viewed in a plane of the outlet window  104 . The rectangular range  158  is also referred to as the laser pass range  158 . The laser pass range  158  is smaller than the outlet window  104 , and is contained therein as viewed from the front. All the sides of the laser pass range  158  are separate from the edges  154  of the outlet window  104 . Specifically, the lower edge (the lower side)  190  of the laser pass range  158  is separate from a lowermost part or end  180  in the lower edge of the outlet window  104  at a predetermined relatively-large interval  160 . The upper edge (the upper side)  191  of the laser pass range  158  is separate from the upper edge  181  of the outlet window  104  at a predetermined interval  161 . The right-hand edge (the right-hand side)  192  of the laser pass range  158  is separate from the right-hand edge  182  of the outlet window  104  at a predetermined interval  162 . The left-hand edge (the left-hand side)  193  of the laser pass range  158  is separate from the left-hand edge  183  of the outlet window  104  at a predetermined interval  163 . The interval  160  between the lower edge  190  of the laser pass range  158  and the lowermost part or end  180  in the lower edge of the outlet window  104  is greater than the other intervals  161 ,  162 , and  163 . Preferably, the area of the zone between the lower edge  190  of the laser pass range  158  and the lower edge of the outlet window  104  is greater than the area of the zone between the upper edge  191  of the laser pass range  158  and the upper edge  181  of the outlet window  104 , the area between the right-hand edge  192  of the laser pass range  158  and the right-hand edge  182  of the outlet window  104 , and the area between the left-hand edge  193  of the laser pass range  158  and the left-hand edge  183  of the outlet window  104 .  
         [0041]    It should be noted that the interval  160  may be greater than at least one of the other intervals  161 ,  162 , and  163 .  
         [0042]    As shown in FIG. 7, a plate-like protective cover  108  disposed in the casing  102  extends over the outlet window  104 . In other words, the protective member  108  covers the outlet window  104  from inside. The protective cover  108  is connected to and supported by the casing  102 . The protective cover  108  is parallel to the front panel of the casing  102 . The protective cover  108  is located near the front panel of the casing  102 . The protective cover  108  is transparent to the forward laser beam. The protective cover  108  includes a glass plate or a resin plate. A ring-shaped resilient member or a rubber ring  156  is airtightly (fluid-tightly or liquid-tightly) provided between the protective cover  108  and the front panel of the casing  102 . The rubber ring  156  serves as a sealing member for preventing sands and raindrops from entering the casing  102 . The walls of the front panel of the casing  102  have surfaces defining the edges  154  of the outlet window  104 . These surfaces  154  are tapered so that the cross section of the outlet window  104  continuously increases as viewed in the outward direction (the forward direction) which is perpendicular to a plane of the outlet window  104 . The rubber ring  156  does not project into the outlet window  104 .  
         [0043]    It is preferable that the size of the edges  154  of the outlet window  104  is relatively small, and the area of an exposed portion of the protective cover  108  is relatively small. In this case, stray light, pebbles, and raindrops can be effectively prevented from adversely affecting the device  110 .  
         [0044]    Since the outlet window  104  has a pentagonal shape with a downwardly-projecting lower side, rainwater is guided toward the lowermost part  180  of the lower edge of the outlet window  104 . As shown in FIG. 6, even in the case where rainwater  214  is collected in the lowermost part  180  of the lower edge of the outlet window  104 , the collected rainwater  214  does not reach the laser pass range  158  since the lower edge  190  of the laser pass range  158  is separate from the lowermost part  180  in the lower edge of the outlet window  104  at the relatively-large interval  160 . The tapered edges  154  of the outlet window  104  facilitate the flow of the rainwater  214  out of the outlet window  104 . Accordingly, the forward laser beam is prevented from meeting the collected rainwater  214 . Thus, it is possible to prevent the occurrence of the scatter and absorption of the forward laser beam by the collected rainwater which would cause a reduction of the power of the forward laser beam and a decrease in the detectable distance to an object. In addition, even under a rainy condition, the device  110  can accurately detect an object in the detection area.  
         [0045]    As previously mentioned, the rubber ring  156  is airtightly (fluid-tightly or liquid-tightly) provided between the protective cover  108  and the front panel of the casing  102 . The rubber ring  156  prevents sands and raindrops from entering the casing  102 . Since the rubber ring  156  does not project into the outlet window  104 , a recess can be formed among the rubber ring  156 , the protective cover  108 , and the front panel of the casing  102  (see FIG. 7). Even in the case where rainwater  158  is collected into this recess, the collected rainwater  214  does not reach the laser pass range  158  (see FIG. 7).  
         [0046]    Preferably, the cross-sectional area of the inlet window  105  is large enough to prevent a return laser beam (an echo laser beam) from being scattered and absorbed by rainwater collected in the lower edge of the inlet window  105 .  
       Second Embodiment  
       [0047]    [0047]FIG. 8 shows a casing  102 A according to a second embodiment of this invention. The casing  102 A is similar to the casing  102  (see FIGS.  3 - 7 ) except for design changes mentioned hereafter. The casing  102 A has an inlet window  105 A instead of the inlet window  105  (see FIGS.  3 - 5 ).  
         [0048]    As shown in FIG. 8, the inlet window  105 A of the casing  102 A is similar in design to the outlet window  104 . Specifically, the inlet window  105 A has a pentagonal shape with a downwardly-projecting lower side of a V configuration.  
         [0049]    There is a rectangular range  258  in the inlet window  105 A. Return laser beams (each laser beams) reach the photodiode  122  through the condenser lens  120  (see FIG. 3) provided that they pass through positions in the rectangular range  258 . The rectangular range  258  is also referred to as the laser pass range  258 . The laser pass range  258  is smaller than the inlet window  105 A, and is contained therein as viewed from the front. All the sides of the laser pass range  258  are separate from the edges  254  of the inlet window  105 A. The interval between the lower edge of the laser pass range  258  and the lowermost part or end in the lower edge of the inlet window  105 A is greater than the interval between the upper edge of the laser pass range  258  and the upper edge of the inlet window  105 A, the interval between the right-hand edge of the laser pass range  258  and the right-hand edge of the inlet window  105 A, and the interval between the left-hand edge of the laser pass range  258  and the left-hand edge of the inlet window  105 A.  
         [0050]    This design of the inlet window  105 A effectively prevents stray light, pebbles, and raindrops from adversely affecting the related reflection measurement device. Even in the case where rainwater is collected in the lowermost part of the lower edge of the inlet window  105 A, the collected rainwater does not reach the laser pass range  258 . Accordingly, a return laser beam (an echo laser beam) to be received by the photodetector  122  (see FIG. 3) is prevented from meeting the collected rainwater. Thus, it is possible to prevent the occurrence of the scatter and absorption of the return laser beam by the collected rainwater which would cause a reduction of the power of the return laser beam and a decrease in the detectable distance to an object.  
       Third Embodiment  
       [0051]    [0051]FIG. 9 shows a casing  102 B according to a third embodiment of this invention. The casing  102 B is similar to the casing  102  (see FIGS.  3 - 7 ) except for design changes mentioned hereafter.  
         [0052]    As shown in FIG. 9, an outlet window  104 B of the casing  102 B has a trapezoidal shape with a lower side oblique relative to the horizontal direction. All the sides of the laser pass range  158  are separate from the edges  154 B of the outlet window  104 B. The lower edge of the outlet window  104 B inclines at a predetermined angle relative to the lower edge  190  of the laser pass range  158 . Since the lower edge of the outlet window  104 B inclines, rainwater  214 B can be smoothly guided therealong toward a lowermost part in the outlet window  104 B. This is effective in preventing the forward laser beam from meeting collected rainwater.  
         [0053]    The walls of the front panel of the casing  102 B have surfaces defining the edges  154 B of the outlet window  104 B. These surfaces  154 B are tapered so that the cross section of the outlet window  104 B continuously increases as viewed in the outward direction (the forward direction) which is perpendicular to a plane of the outlet window  104 B.  
       Fourth Embodiment  
       [0054]    [0054]FIG. 10 shows a casing  102 C according to a fourth embodiment of this invention. The casing  102 C is similar to the casing  102  (see FIGS.  3 - 7 ) except for design changes mentioned hereafter. The casing  102 C has an outlet window  104 C instead of the outlet window  104  (see FIGS.  3 - 5 ).  
         [0055]    As shown in FIG. 10, the outlet window  104 C of the casing  102 C has a rectangular shape. All the sides of the laser pass range  158  are separate from the edges  154 C of the outlet window  104 C. The interval between the lower edge  190  of the laser pass range  158  and the lower edge  180 C of the outlet window  104 C is greater than the interval between the upper edge  191  of the laser pass range  158  and the upper edge  181  of the outlet window  104 C, the interval between the right-hand edge of the laser pass range  158  and the right-hand edge of the outlet window  104 C, and the interval between the left-hand edge of the laser pass range  158  and the left- hand edge of the outlet window  104 C. Accordingly, the forward laser beam is prevented from meeting rainwater  214 C collected in the lower edge of the outlet window  104 C.  
         [0056]    The walls of the front panel of the casing  102 C have surfaces defining the edges  154 C of the outlet window  104 C. These surfaces  154 C are tapered so that the cross section of the outlet window  104 C continuously increases as viewed in the outward direction (the forward direction) which is perpendicular to a plane of the outlet window  104 C.