Patent Publication Number: US-2020278424-A1

Title: Distance measuring sensor

Description:
TECHNICAL FIELD 
     The present invention relates to a distance measurement sensor, and more specifically, to a distance measurement sensor with improved light emitting efficiency and light receiving efficiency. 
     BACKGROUND ART 
     A sensor which measures distance using light may be generally implemented by selecting one among a triangulation method and a method of calculating a return time of reflected light (TOF measurement method). 
     A sensor using the TOF measurement method may include a light emitting unit (a device for providing light) and a light receiving unit (a device for receiving light). A time of light taken for being emitted from the light emitting unit, being radiated to and reflected by an object, and reaching the light receiving unit may be calculated. The distance measurement sensor using the TOF measurement method can be miniaturized and applied to various electronic devices. 
     However, in the case of the distance measurement sensor using the TOF measurement method, the risk of error related to distance measurement can be very high due to the neighboring arrangement of the light emitting unit and the light receiving unit. If the probability of light, radiated from the light emitting unit, of being reflected by the object and entering again the light emitting unit is lowered, the error related to the distance measurement can be significantly reduced. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a distance measurement sensor provided with a light emitting lens which forms unaligned multiple optical axes. 
     Another object of the present invention is to provide a distance measurement sensor provided with a light guide for collecting incident light and transferring the collected light to a light receiving unit. 
     The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and unmentioned other technical problems may be clearly understood by those skilled in the art from the following descriptions. 
     Technical Solution 
     To accomplish the above objects, according to one aspect of the present invention, there is provided a distance measurement sensor comprising: a housing including a first hollow unit formed to be opened toward the top at one end, and a second hollow unit formed to be opened toward the top at the other end; a sensor package disposed in the housing and located under the first hollow unit; a light guide disposed in the housing and located between the second hollow unit and the sensor package to transfer light entering the second hollow unit to the sensor package; and a lens unit located in at least one among the first hollow unit and the second hollow unit, in which the sensor package includes: a light emitting unit for providing light toward the first hollow unit; and a light receiving unit spaced apart from the light emitting unit and located between the light emitting unit and the second hollow unit to receive light from the light guide, and the lens unit includes at least one among a light emitting lens located in the first hollow unit above the light emitting unit to slantingly face the light emitting unit, and a light receiving lens located in the second hollow unit above the light guide to slantingly face the top of the housing. 
     Advantageous Effects 
     A distance measurement sensor according to an embodiment of the present invention may be provided with a light emitting lens which forms unaligned multiple optical axes. 
     A distance measurement sensor according to an embodiment of the present invention may be provided with a light guide for collecting incident light and transferring the collected light to a light receiving unit. 
     The effects of the present invention are not limited to the effects mentioned above, and it should be understood that all the effects that can be inferred from the configuration of the present invention disclosed in the detailed description or the claims of the present invention are included. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are views showing a distance measurement sensor according to an embodiment of the present invention. 
         FIGS. 3 to 6  are views showing several embodiments of a light emitting lens and a sensor package of a distance measurement sensor according to an embodiment of the present invention. 
         FIGS. 7 to 9  are views showing various embodiments of a light emitting lens. 
         FIGS. 10 and 11  are views showing a distance measurement sensor according to another embodiment of the present invention. 
         FIG. 12  is a view showing a light guide seen from the top according to an embodiment of the present invention; and 
         FIGS. 13 to 16  are views showing diverse combinations of a light receiving lens and a light guide of the present invention. 
         FIG. 17  is a view showing the cross-section of light traveling inside the light guide shown in  FIG. 16 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be implemented in various different forms and accordingly is not limited to the embodiments described here. In addition, the parts unrelated to the description are omitted from drawings to clearly describe the present invention, and like elements are denoted by like reference numerals throughout the specification. 
     Throughout the specification, when an element is “connected to (link to, in contact with, coupled to)” another element, it includes a case of “indirectly connecting” the elements with intervention of another element therebetween, as well as a case of “directly connecting” the elements. In addition, when an element “includes” a constitutional element, it means further including another constitutional element, not excluding another constitutional element, as far as an opposed description is not specially specified. 
     The terms used herein are only to describe particular embodiments, not intended to limit the present invention. Singular expressions are intended to include plural expressions as well, unless the context clearly indicates otherwise. It should be understood that the terms “include”, “have” and the like used herein are to specify presence of features, integers, steps, operations, elements, components or a combination of these stated in the specification, but do not preclude the possibility of presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations of these. 
     Referring to  FIG. 1 , a distance measurement sensor  100  according to an embodiment of the present invention is observed. The distance measurement sensor  100  may include a housing  200 . The housing  200  may include a housing body  210 . The housing body  210  may form a skeleton of the distance measurement sensor  100 . The housing body  210  may have a shape elongated in one direction. For example, the housing body  210  may have a shape elongated in the Y-axis direction. The length direction of the housing body  210  may be parallel to the Y-axis direction. 
     The housing body  210  may form a space for accommodating the parts of the distance measurement sensor  100 . For example, a first hollow unit  220  (see  FIG. 2 ) may be formed at an end of the housing body  210 . 
     The distance measurement sensor  100  may include a light emitting lens  400  and a coupling plate  600 . The light emitting lens  400  and the coupling plate  600  may be located at an end of the housing body  210 . The light emitting lens  400  may be accommodated in the first hollow unit  220  (see  FIG. 2 ) of the housing body  210 . The coupling plate  600  may be coupled to the light emitting lens  400 . The coupling plate  600  may support the light emitting lens  400 . The coupling plate  600  may be seated on the housing body  210 . The light emitting lens  400  may be referred to as a “first lens”. The light emitting lens  400  may be referred to as a “light emitting lens”. 
     A second hollow unit  230  may be formed at the other end of the housing body  210 . A light emitting element located inside the housing body  210  may provide light to the light emitting lens  400 . Light passing through the light emitting lens  400  may reach and be reflected by a measurement object. The light reflected by the measurement object may enter inside the housing body  210  through the second hollow unit  230 . Measurement of distance (or position) to the measurement object may be performed by analyzing the emitted light and the reflected light. For example, the distance to the measurement object may be measured by calculating a time of light emitted from the distance measurement sensor  100 , which is taken to enter and be reflected by the measurement object and reach the distance measurement sensor  100 . The distance measurement sensor  100  may measure the distance to the measurement object by using a time of flight (TOF) method. 
     The distance measurement sensor  100  may be installed and used in a device and/or a facility. For example, the distance measurement sensor  100  may be installed in a robot cleaner, a process facility, a car, a gate, or the like. The housing body  210  may form a portion protruding toward one side. For example, the housing body  210  may form a protrusion protruding in the X-axis direction. The protrusions formed in the housing body  210  may facilitate the distance measurement sensor  100  to be installed in a device and/or a facility. 
       FIG. 2  is a cross-sectional view of the distance measurement sensor  100  of  FIG. 1  cut in the longitudinal direction (length direction). Referring to  FIG. 2 , the housing body  210  may have a shape elongated from one end toward the other end. The first hollow unit  220  may be formed at one end of the housing body  210 . The second hollow unit  230  may be formed at the other end of the housing body  210 . The first hollow unit  220  and the second hollow unit  230  may be located opposite to each other in the housing body  210 . The first hollow unit  220  and the second hollow unit  230  may be opened toward the top. 
     The distance measurement sensor  100  may include a substrate  250 . The substrate  250  may be installed in the housing body  210 . The substrate  250  may be connected to an external power source. The substrate  250  may communicate with an external device. For example, the substrate  250  may include a communication module. The substrate  250  may be electrically connected to the external device. For example, the substrate  250  may include a port connected to the external device. The substrate  250  may include a micro controller unit (MCU) for controlling various signals. For example, the MCU may control the strength (or intensity) and cycle of the light emitted from the light emitting unit  320 . 
     The distance measurement sensor  100  may include a sensor package  300 . The sensor package  300  may be electrically connected to the substrate  250 . The sensor package  300  may be mounted on the substrate  250 . The sensor package  300  may be located to be adjacent to one end of the housing body  210 . For example, a portion of the sensor package  300  may be located in the first hollow unit  220  of the housing body  210 . 
     The sensor package  300  may include a base  310 , a light emitting unit  320 , and a light receiving unit  330 . The light emitting unit  320  and the light receiving unit  330  may be mounted on the base  310 . The light emitting unit  320  may include, for example, a laser diode or an infrared diode. The sensor package  300  may be mounted on the substrate  250  through SMT or wire bonding. 
     The light emitting unit  320  may be located under the first hollow unit  220 . The light emitting unit  320  may provide light toward the top of the first hollow unit  220 . 
     The light receiving unit  330  may be spaced apart from the light emitting unit  320 . The light receiving unit  330  may be closer to the second hollow unit  230  than the light emitting unit  320 . The light receiving unit  330  and the light emitting unit  320  may be disposed in the length direction (Y-axis direction) of the housing body  210 . The light receiving unit  330  may be located between the light emitting unit  320  and the second hollow unit  230 . 
     The light emitting lens  400  may be accommodated in the first hollow unit  220 . The light emitting lens  400  may include an exterior surface. For example, the light emitting lens  400  may include a first lens surface  410 , a second lens surface  420 , and a body surface  430 . The first lens surface  410  may be referred to as an “incident surface”. The second lens surface  420  may be referred to as an “emission surface”. The body surface  430  may be referred to as a “lateral surface”. 
     The light emitting lens  400  may include a medium in which incident light may travel. For example, the light emitting lens  400  may include glass. The refractive index of the light emitting lens  400  including glass may be about 1.45 at room temperature. For example, the refractive index of the light emitting lens  400  may be 1.517 for light having a wavelength of 589.29 nm. 
     For example, the light emitting lens  400  may include polycarbonate (PC). The refractive index of the light emitting lens  400  using the PC as a material may be 1.584 for light having a wavelength of 587.6 nm. For example, the light emitting lens  400  may include polymethylmethacrylate (PMMA). The refractive index of the light emitting lens  400  including the PMMA may be about 1.5 at room temperature. For example, the refractive index of the light emitting lens  400  may be 1.502 for light having a wavelength of 436 nm. For example, the refractive index of the light emitting lens  400  may be 1.492 for light having a wavelength of 589 nm. 
     When the light emitting lens  400  includes PC and/or PMMA, manufacturing of the light emitting lens  400  may be easy. When the light emitting lens  400  includes PC and/or PMMA, miniaturization of the light emitting lens  400  may be easy. 
     The first lens surface  410  may face the light emitting unit  320 . For example, the first lens surface  410  may slantingly face the light emitting unit  320 . The light generated from the light emitting unit  320  may slantingly enter the first lens surface  410 . 
     The second lens surface  420  may be located on the opposite side of the first lens surface  410 . The second lens surface  420  may be spaced apart from the first lens surface  410 . The second lens surface  420  may face the exterior of the housing body  210 . The second lens surface  420  may form a curvature. The light passing through the first lens surface  410  may pass through the second lens surface  420  and proceed toward the outside. 
     The body surface  430  may be elongated from the first lens surface  410  and meet the second lens surface  420 . The body surface  430  may form a lateral surface of the light emitting lens  400 . The body surface  430  may have a partial shape of the lateral surface of a cylinder. The body surface  430  may be coupled to the coupling plate  600 . Alternatively, the coupling plate  600  may be integrally formed on the body surface  430  of the light emitting lens  400 . 
     The coupling plate  600  may be coupled to the light emitting lens  400 . The coupling plate  600  may have rigidity. The coupling plate  600  may have a shape of a plate. For example, the coupling plate  600  may have an opening. The light emitting lens  400  may be inserted in and coupled to the opening formed in the coupling plate  600 . The coupling plate  600  may be seated on the housing body  210 . 
     The distance measurement sensor  100  may include a light guide  500 . The light guide  500  may be located in the housing body  210 . The light guide  500  may have a shape elongated from the first hollow unit  220  toward the second hollow unit  230 . The length direction of the light guide  500  may be parallel to the length direction of the housing body  210 . 
     A portion of the light guide  500  may be located in the second hollow unit  230 . The light guide  500  may be disposed between the sensor package  300  and the second hollow unit  230 . For example, the light guide  500  may be disposed between the light receiving unit  330  and the second hollow unit  230 . 
     The light guide  500  may form an exterior surface. For example, the light guide  500  may include a first guide surface  510 , a second guide surface  520 , a third guide surface  530 , and a fourth guide surface  540 . 
     The light guide  500  may include a medium in which incident light may travel. For example, the light guide  500  may include quartz or PMMA. The characteristics related to the medium of the light guide  500  may be similar to the characteristics related to the medium of the light emitting lens  400 . 
     The first guide surface  510  may be referred to as an “incident surface”. At least a portion of the first guide surface  510  may be located in the second hollow unit  220 . At least a portion of the first guide surface  510  may face the top of the second hollow unit  220 . The first guide surface  510  may be referred to as a “top surface”. 
     The second guide surface  520  may be bent downward from the first guide surface  510  and elongated toward the first hollow unit  220 . The second guide surface  520  may be located in the second hollow unit  230 . The second guide surface  520  may form a slope with the first guide surface  510 . For example, an angle formed by the second guide surface  520  and the first guide surface  510  may be related to a critical angle. The critical angle may be related to total internal reflection of light traveling from the first guide surface  510  toward the second guide surface  520 . The second guide surface  520  may form a curved surface. 
     The third guide surface  530  may be located on the opposite side of the second guide surface  520 . The direction that the third guide surface  530  faces may be substantially opposite to the direction that the second guide surface  520  faces. The third guide surface  530  may be located at an end of the light guide  500 . On the contrary, the second guide surface  520  may be located at the other end of the light guide  500 . Light reaching the second guide surface  520  may travel toward the third guide surface  530 . The light traveling from the second guide surface  520  toward the third guide surface  530  may travel in the length direction of the light guide  500 . 
     The light traveling from the second guide surface  520  toward the third guide surface  530  may be collected while traveling toward the third guide surface  530 . For example, when at least a portion of the second guide surface  520  forms a curved surface, the second guide surface  520  may perform a function of a lens collecting light. The curved surface formed on the second guide surface  520  may be convex, for example, toward the outside of the second guide surface  520 . 
     The third guide surface  530  may form a slope with respect to the direction toward the second guide surface  520 . The third guide surface  530  may form a slope with respect to the first guide surface  510 . An angle formed by the third guide surface  530  with respect to the first guide surface  510  may be related to total internal reflection of light traveling from the second guide surface  520  toward the third guide surface  530 . 
     The fourth guide surface  540  may be bent downward from the third guide surface  530  and elongated toward the second hollow unit  230 . The fourth guide surface  540  may be located on the opposite side of the first guide surface  510 . The fourth guide surface  540  may form the bottom surface of the light guide  500 . The fourth guide surface  540  may be referred to as a “bottom surface”. The fourth guide surface  540  may be located on the top of the light receiving unit  330 . The fourth guide surface  540  may face the light receiving unit  330 . 
     The light totally internally reflected by the third guide surface  530  may travel toward the fourth guide surface  540 . The light traveling from the third guide surface  530  toward the fourth guide surface  540  may be collected while traveling toward the fourth guide surface  540 . For example, when at least a portion of the third guide surface  530  forms a curved surface, the third guide surface  530  may perform a function of a lens collecting light. For example, the curved surface formed on the third guide surface  530  may be convex toward the outside. For example, the shape of the third guide surface  530  may correspond to a partial shape of a cylinder. 
     A measurement object may be positioned on the top of the distance measurement sensor  100 . Part of the light emitted from the light emitting unit  320  may reach the measurement target by way of the first lens surface  410  and the second lens surface  420 . Part of the light reaching the measurement object may be reflected from the measurement object and enter the second hollow unit  230 . The light passing through the second hollow unit  230  may enter the first guide surface  510 . 
     The second hollow unit  230  may be located below the top of the housing body  210 . That is, the top side of the housing body  210  adjacent to the second hollow unit  230  may be formed to be further elongated upward from the second hollow unit  230 . Accordingly, the light reflected from the measurement object and entering the second hollow unit  230  may be less affected by disturbance light. 
     The light entering the first guide surface  510  may travel inside the light guide  500  and reach the second guide surface  520 . The light reaching the second guide surface  520  may travel toward the third guide surface  530  by total internal reflection of the second guide surface  520 . The light reaching the third guide surface  530  may travel toward the fourth guide surface  540  by the total internal reflection. The light reaching the fourth guide surface  540  may travel toward the outside of the light guide  500  and reach the light receiving unit  330 . 
     Remaining part of the light reaching the measurement object may be reflected from the measurement object and reach again the second lens surface  420  of the light emitting lens  400 . When the light entering the second lens surface  420  from the measurement object passes through the first lens surface  410  and reaches the light emitting unit  320 , distance measurement efficiency of the sensor package  300  may be lowered. 
       FIG. 3( a )  is a view showing a substrate  250 , a sensor package  300 , a light emitting lens  400 , and a coupling plate  600 .  FIG. 3( b )  is a view of  FIG. 3( a )  seen from the front. 
     The sensor package  300  may be mounted on the substrate  250 . The sensor package  300  may be located on the top surface of the substrate  250 . The light emitting unit  320  and the light receiving unit  330  may be located on the top surface of the base  310 . The light emitting unit  320  may provide light to the light emitting lens  400 . The light provided from the light emitting unit  320  may travel along the optical axis of the light emitting unit  320 . A first optical axis LX 1  may be the optical axis of the light emitting unit  320 . 
     The light emitting lens  400  may be located above the light emitting unit  320 . The first lens surface  410  of the light emitting lens  400  may slantingly face the light emitting unit  320 . The first lens surface  410  may be located under the coupling plate  600 . The optical axis of the first lens surface  410  may be referred to as a second optical axis LX 2 . The second optical axis LX 2  may be shifted from the first optical axis LX 1 . The second optical axis LX 2  may form an angle with the first optical axis LX 1 . The first lens surface  410  may be inclined downward in the direction from the light emitting unit  320  toward the light receiving unit  330 . The direction from the light emitting unit  320  toward the light receiving unit  330  may be parallel to the direction from the first hollow unit  220  (see  FIG. 2 ) toward the second hollow unit  230  (see  FIG. 2 ). The direction from the light receiving unit  330  toward the light emitting unit  320  may be parallel to the direction from the second hollow unit  230  (see  FIG. 2 ) toward the first hollow unit  220 . 
     The second lens surface  420  may be located above the first lens surface  410 . The second lens surface  420  may be located on the coupling plate  600 . The second lens surface  420  may be spaced apart from the first lens surface  410 . The second lens surface  420  may be convex toward the top. The third optical axis LX 3  may be the optical axis of the second lens surface  420 . The third optical axis LX 3  may be parallel to the first optical axis LX 1 . The third optical axis LX 3  may form an angle with the second optical axis LX 2 . 
     The light emitting lens  400  may form multiple optical axes. For example, the first lens surface  410  of the light emitting lens  400  may form the second optical axis LX 2 , and the second lens surface  420  may form the third optical axis LX 3 . The multiple optical axes of the light emitting lens  400  may be unaligned. For example, the second optical axis LX 2  may form an angle with the third optical axis LX 3 . 
     The body surface  430  may connect the first lens surface  410  and the second lens surface  420 . The body surface  430  may be longer toward the bottom as it approaches the light receiving unit  330 . The body surface  430  may be coupled to the coupling plate  600 . 
     The light starting from the light emitting unit  320  and entering the first lens surface  410  may be refracted by the first lens surface  410 . The light refracted by the first lens surface  410  may enter the second lens surface  420 . The light entering the second lens surface  420  from the first lens surface  410  may pass through the second lens surface  420  and reach the measurement object (not shown) located outside. The light reaching the measurement object (not shown) may be reflected and reach the second lens surface  420 . The light reaching the second lens surface  420  from the outside may travel toward the first lens surface  410 . Since the second optical axis LX 2  forms an angle with the third optical axis LX 3 , the light reflected from the measurement object (not shown) and directed toward the first lens surface  410  may be prevented from traveling toward the light emitting unit  320 . 
       FIG. 4( a )  is a view showing a substrate  250 , a sensor package  300 , a light emitting lens  400 , and a coupling plate  600 .  FIG. 4( b )  is a view of  FIG. 4( a )  seen from the front. 
     The light emitting lens  400  may be located above the light emitting unit  320 . The first lens surface  410  of the light emitting lens  400  may slantingly face the light emitting unit  320 . The first lens surface  410  may be inclined downward in the direction from the light receiving unit  330  toward the light emitting unit  320 . The second optical axis LX 2  may form an angle with the first optical axis LX 1 . 
     The second lens surface  420  may be convex toward the top. The third optical axis LX 3  of the second lens surface  420  may be parallel to the first optical axis LX 1  and form an angle with the second optical axis LX 2 . As the third optical axis LX 3  forms an angle with the second optical axis LX 2 , the light reflected from the top of the light emitting lens  400  may be prevented from passing through the first lens surface  410  and traveling toward the light emitting unit  320 . 
     The body surface  430  may be elongated upward from the first lens surface  410  and connected to the second lens surface  420 . The body surface  430  may be longer downward in the direction from the light receiving unit  330  toward the light emitting unit  320 . 
       FIG. 5( a )  is a view showing a substrate  250 , a sensor package  300 , a light emitting lens  400 , and a coupling plate  600 .  FIG. 5( b )  is a view of  FIG. 5( a )  seen from the front. 
     The light emitting lens  400  may be located above the light emitting unit  320 . The first lens surface  410  of the light emitting lens  400  may slantingly face the light emitting unit  320 . The first lens surface  410  may be inclined downward in the direction from the light emitting unit  320  toward the light receiving unit  330 . The second optical axis LX 2  may form an angle with the first optical axis LX 1 . 
     The second lens surface  420  may be inclined with respect to the sensor package  300 . For example, the plane formed by the outer circumference of the second lens surface  420  may be inclined downward in the direction from the light emitting unit  320  toward the light receiving unit  330 . The second lens surface  420  may be convex toward the outside. The third optical axis LX 3  of the second lens surface  420  may form an angle with the first optical axis LX 1  of the light emitting unit  320 . The third optical axis LX 3  may form an angle with the second optical axis LX 2 . 
     For example, the third optical axis LX 3  may be located between the first optical axis LX 1  and the second optical axis LX 2 . An angle (acute angle) formed by the first optical axis LX 1  and the second optical axis LX 2  may be referred to as a first angle. An angle (acute angle) formed by the first optical axis LX 1  and the third optical axis LX 3  may be referred to as a third angle. An angle (acute angle) formed by the second optical axis LX 2  and the third optical axis LX 3  may be referred to as a second angle. The first angle may be the sum of the second angle and the third angle. 
     As the third optical axis LX 3  forms an angle with the first optical axis LX 1  and the second optical axis LX 2 , respectively, the light reflected from the top of the light emitting lens  400  may be prevented from passing through the second lens surface  420  and the first lens surface  410  and traveling toward the light emitting unit  320 . 
       FIG. 6( a )  is a view showing a substrate  250 , a sensor package  300 , a light emitting lens  400 , and a coupling plate  600 , and for convenience of explanation, it may be expressed to delete the housing  200  (refer to  FIG. 2 ).  FIG. 6( b )  is a view of  FIG. 6( a )  seen from the front. 
     The light emitting lens  400  may be located above the light emitting unit  320 . The first lens surface  410  of the light emitting lens  400  may slantingly face the light emitting unit  320 . The first lens surface  410  may be inclined downward in the direction from the light receiving unit  330  toward the light emitting unit  320 . The second optical axis LX 2  may form an angle with the first optical axis LX 1 . 
     The second lens surface  420  may be inclined with respect to the sensor package  300 . For example, the plane formed by the outer circumference of the second lens surface  420  may be inclined upward in the direction from the light receiving unit  330  toward the light emitting unit  320 . The second lens surface  420  may be convex toward the outside. 
     An angle (acute angle) formed by the first optical axis LX 1  and the second optical axis LX 2  may be referred to as a first angle. An angle (acute angle) formed by the first optical axis LX 1  and the third optical axis LX 3  may be referred to as a third angle. An angle (acute angle) formed by the second optical axis LX 2  and the third optical axis LX 3  may be referred to as a second angle. The first optical axis LX 1  may be located between the second optical axis LX 2  and the third optical axis LX 3 . The second angle may be the sum of the first angle and the third angle. 
     As the second optical axis LX 2  and the third optical axis LX 3  form an angle with respect to the first optical axis LX 1 , respectively, the light reflected from the top of the light emitting lens  400  may be prevented from passing through the second lens surface  420  and the first lens surface  410  and traveling toward the light emitting unit  320 . 
       FIG. 7( a )  is a view showing a light emitting lens  400  and a coupling plate  600 .  FIG. 7( b )  is a view of the light emitting lens  400  and the coupling plate  600  of  FIG. 7( a )  seen from the front. 
     The first lens surface  410  may include a first incident surface  411  and a second incident surface  413 . The first incident surface  411  may form an angle with the second incident surface  413 . The first incident surface  411  and the second incident surface  413  may increase downward in the direction toward the boundary of the first incident surface  411  and the second incident surface  413 . 
     The first incident surface  411  may be inclined downward in the direction from the light emitting unit  320  (see  FIG. 2 ) toward the light receiving unit  330  (see  FIG. 2 ). The second incident surface  413  may be inclined downward in the direction from the light receiving unit  330  (see  FIG. 2 ) toward the light emitting unit  320  (see  FIG. 2 ). 
     At least one among the first incident surface  411  and the second incident surface  413  may slantingly face the light emitting unit  320  (see  FIG. 2 ). For example, the first incident surface  411  may slantingly face the light emitting unit  320  (see  FIG. 2 ). The light generated from the light emitting unit  320  (refer to  FIG. 2 ) may be refracted by the first incident surface  411  in the direction from the first incident surface  411  toward the second incident surface  413 , and reach the second lens surface  420 . 
     The light reaching the second lens surface  420  may pass through the second lens surface  420 , and reach the measurement object (not shown) through the second lens surface  420 . The light reaching the measurement object (not shown) may be reflected from the measurement object (not shown) and reach the second lens surface  420 . The light reaching the second lens surface  420  may travel toward the first lens surface  410 . The light traveling from the second lens surface  420  toward the first lens surface  410  may be divided into light traveling from the second lens surface  420  toward the first incident surface  411  and light traveling from the second lens surface  420  toward the second incident surface  413 . 
     The light traveling from the second lens surface  420  toward the second incident surface  413  may be refracted by the second incident surface  413 . Input of the light refracted by the second incident surface  413  into the light emitting unit  320  (see  FIG. 2 ) may be suppressed by the geometric structure of the first lens surface  410 . 
     The light traveling from the second lens surface  420  toward the second incident surface  413  may be totally internally reflected by the second incident surface  413 . A large portion of the light totally internally reflected by the second incident surface  413  may be totally internally reflected by the first incident surface  411  and directed toward the second lens surface  420 . That is, input of the light totally internally reflected by the second incident surface  413  into the light emitting unit  320  (see  FIG. 2 ) may be suppressed by the geometric structure of the first lens surface  410 . 
     The light traveling from the second lens surface  420  toward the first incident surface  411  may be refracted or totally internally reflected by the first incident surface  413 . For example, a large portion of the light totally internally reflected by the first incident surface  411  may be totally internally reflected by the second incident surface  413  and directed toward the second lens surface  420 . Accordingly, input of the light traveling from the second lens surface  420  toward the first incident surface  411  into the light emitting unit  320  (see  FIG. 2 ) may be suppressed by the geometric structure of the first lens surface  410 . 
       FIG. 8( a )  is a view showing a light emitting lens  400  and a coupling plate  600 .  FIG. 8( b )  is a view of the light emitting lens  400  and the coupling plate  600  of  FIG. 8( a )  seen from the front. 
     The first lens surface  410  may be inclined downward in the direction from the light emitting unit  320  (see  FIG. 2 ) toward the light receiving unit  330  (see  FIG. 2 ). The first lens surface  410  may have a shape elongated downward in the direction toward the positive Y axis. The positive Y-axis direction may be a direction from the light emitting unit  320  (see  FIG. 2 ) toward the light receiving unit  330  (see  FIG. 2 ). 
     The second lens surface  420  may have a shape protruding upward in the direction toward the positive Y axis. The second lens surface  420  may have a partial shape of the lateral surface of a cylinder having the X-axis direction as the length direction. 
     The second lens surface  420  may be inclined downward in the first direction from the most protruding portion. For example, the second lens surface  420  may be inclined downward in the positive Y-axis direction from the most protruding portion. The second lens surface  420  may be inclined downward in the negative Y-axis direction from the most protruding portion. 
     The second lens surface  420  may be parallel to the horizontal surface in the second direction from the most protruding portion. For example, the second lens surface  420  may be parallel to the horizontal surface in the X-axis direction (positive direction and negative direction). 
     The shapes of the second lens surface  420  and the first lens surface  410  may suppress the light emitted from the light emitting unit  320  (see  FIG. 2 ), passing through the light emitting lens  400 , and reflected by the measurement target (not shown) not to pass through the light emitting lens  400  and travel toward the light emitting unit  320  (see  FIG. 2 ) again. 
       FIG. 9( a )  is a view showing a light emitting lens  400  and a coupling plate  600 .  FIG. 9( b )  is a view of the light emitting lens  400  and the coupling plate  600  of  FIG. 9( a )  seen from the front. 
     The configuration of the first lens surface  410  may be the same as that of the first lens surface  410  shown in  FIG. 8 . 
     The second lens surface  420  may have a shape protruding upward in the direction toward the positive X axis. The second lens surface  420  may have a partial shape of the lateral surface of a cylinder having the Y-axis direction as the length direction. 
     The second lens surface  420  may be inclined downward in the first direction from the most protruding portion. For example, the second lens surface  420  may be inclined downward in the positive X-axis direction from the most protruding portion. The second lens surface  420  may be inclined downward in the negative X-axis direction from the most protruding portion. 
     The second lens surface  420  may be parallel to the horizontal surface in the second direction from the most protruding portion. For example, the second lens surface  420  may be parallel to the horizontal surface toward the Y-axis direction (positive direction and negative direction). 
     The light emitted from the light emitting unit  320  (see  FIG. 2 ), passing through the light emitting lens  400 , and reflected by the measurement target (not shown) may be prevented from passing through the light emitting lens  400  and traveling toward the light emitting unit  320  (see  FIG. 2 ) again due to the shapes of the second lens surface  420  and the first lens surface  410 . 
     Referring to  FIGS. 1 to 9 , the lens surfaces  410  and  420  may mean at least one among the first lens surface  410  and the second lens surface  420 . The shape of the lens surfaces  410  and  420  may include a flat shape and/or a curved shape. For example, the lens surfaces  410  and  420  may include a spherical surface and/or an aspherical surface. For example, the lens surfaces  410  and  420  may include a conic surface and/or an asymmetric curved surface. 
     Referring to  FIG. 10 , a distance measurement sensor  100  according to another embodiment of the present invention may be observed. The distance measurement sensor  100  may include a housing  200 . The housing  200  shown in  FIG. 10  may have a structure similar to that of the housing  200  shown in  FIGS. 1 and 2 . For example, the housing  200  may include a housing body  210 . The housing body  210  may form a skeleton of the housing  200 . The housing body  210  may protect the parts installed inside the housing  200 . The housing body  210  may be formed of a material such as metal and/or synthetic resin. 
     The housing  200  may include a first hollow unit  220 . The first hollow unit  220  may be formed in the housing body  210 . The first hollow unit  220  may be adjacent to one end of the housing  200 . The first hollow unit  220  may be opened toward the top of the housing  200 . 
     The housing  200  may include a second hollow unit (not shown). The second hollow unit may be formed in the housing body  210 . The second hollow unit may be adjacent to the other end of the housing  200 . The first hollow unit may be opened toward the top of the housing  200 . 
     The housing  200  may include a coupling unit  280 . The coupling unit  280  may be coupled to the housing body  210 . The coupling unit  280  may be integrally formed with the housing body  210 . A coupling hole  290  may be formed in the coupling unit  280 . The coupling hole  290  may have a shape of a hole. The coupling hole  290  may be coupled to a bolt. The bolt passing through the coupling hole  290  may be coupled to an electronic device or the like. 
     The distance measurement sensor  100  may include a light receiving lens  800 . The light receiving lens  800  may be located in the housing  200 . The light receiving lens  800  may be located on the opposite side of the first hollow unit  220 . For example, the light receiving lens  800  may be located in the second hollow unit of the housing  200 . 
       FIG. 11  is a cross-sectional view showing the distance measurement sensor  100  shown in  FIG. 10 . For convenience of explanation, the coupling unit  280  shown in  FIG. 10  may not be shown in  FIG. 11 . 
     The housing  200  may form a first hollow unit  220 . The first hollow unit  220  may be adjacent to one end of the housing  200 . The housing  200  may form a second hollow unit  230 . The second hollow unit  230  may be adjacent to the other end of the housing  200 . The second hollow unit  230  may be opened toward the top. The second hollow unit  230  may provide a space in which the light receiving lens  800  is accommodated. 
     The distance measurement sensor  100  may include a light receiving panel  700 . The light receiving panel  700  may be transparent. For example, the light receiving panel  700  may transmit light. The light receiving panel  700  may be coupled or attached to the housing  200 . The light receiving panel  700  may be located in the second hollow unit  230 . For example, the light receiving panel  700  may be located above the second hollow unit  230 . The light receiving panel  700  may shield the second hollow unit  230 . 
     The light receiving lens  800  may be coupled to or installed in the housing  200 . The light receiving lens  800  may be located, for example, in the second hollow unit  230 . The light receiving lens  800  may be located under the light receiving panel  700 . The top surface of the light receiving lens  800  may form a slope. For example, the top surface of the light receiving lens  800  may form a slope facing upward in the direction toward the first hollow unit  220 . 
     The distance measurement sensor  100  may include a light guide  500 . The structural and/or optical properties of the light guide  500  shown in  FIG. 11  may be substantially the same as the structural and/or optical properties of the light guide  500  shown in  FIG. 2 . For example, the light guide  500  may include a second guide surface  520  and a third guide surface  530 . The second guide surface  520  may be adjacent to the light receiving lens  800 . The third guide surface  530  may be adjacent to the sensor package  300 . The light guide  500  may include an optical path unit  550 . The optical path unit  550  may mean the inside of the light guide  500 . 
     The light guide  500  may be located under the light receiving lens  800 . For example, at least a portion of the light guide  500  may be located under the light receiving lens  800 . The light guide  500  may have a shape elongated from the light receiving lens  800  toward the first hollow unit  220 . The light guide  500  may be coupled to the light receiving lens  800 . For example, the light guide  500  may be coupled to the bottom surface of the light receiving lens  800 . The light guide  500  may be integrally formed with the light receiving lens  800 . 
     In  FIG. 11 , the dash double dot line arrows may indicate optical paths. Among the optical paths, a main optical path  910  may be formed. The main optical path  910  may be a path of light, along which at least part of the light provided from the light receiving lens  800  is totally internally reflected from the second guide surface  520  and directed toward the third guide surface  530 . The main optical path  910  may be a path of light, along which at least part of the light directed toward the third guide surface  530  is totally internally reflected from the third guide surface  530  and directed toward the light receiving unit  330 . 
     The distance measurement sensor  100  may include a sensor package  300 . The structure and/or the characteristics of the sensor package  300  shown in  FIG. 11  may be substantially the same as the structure and/or the characteristics of the sensor package  300  shown in  FIG. 2 . At least a portion of the sensor package  300  may be located under the first hollow unit  220 . The sensor package  300  may include a base  310 . The base  310  may be coupled to or installed in the housing  200 . 
     The sensor package  300  may include a light emitting unit  320 . The light emitting unit  320  may be located on the top of the base  310 . The light emitting unit  320  may be electrically connected to the base  310 . The light emitting unit  320  may receive power from the base  310 . The light emitting unit  320  may be located under or on the bottom of the first hollow unit  220 . The light emitting unit  320  may provide light toward the first hollow unit  220 . For example, the light emitting unit  320  may provide light having a wavelength of a predetermined range. For example, the light emitting unit  320  may provide infrared light. For example, the light emitting unit  320  may include an infrared LED. 
     The sensor package  300  may include a light receiving unit  330 . The light receiving unit  330  may be disposed on the top surface of the base  310 . The light receiving unit  330  may be electrically connected to the base  310 . The light receiving unit  330  may face the light guide  500 . The light receiving unit  330  may receive light from the light guide  500 . The light receiving unit  330  may sense light. 
     Referring to  FIG. 12 , the width of the light guide  500  may decrease toward the light receiving unit  330 . In other words, the width of the light guide  500  may decrease from the second guide surface  520  (see  FIG. 11 ) toward the third guide surface  530  (see  FIG. 11 ). 
     The light guide  500  may receive light from the light receiving lens  800  (see  FIG. 11 ) and provide the light to the light receiving unit  330 . The size of the light receiving unit  330  may be smaller than that of the light receiving lens  800  (see  FIG. 11 ). Accordingly, the light guide  500  having a width decreasing toward the light receiving unit  330  may transmit light to the light receiving unit  330  more efficiently. In other words, the light guide  500  having a width decreasing toward the light receiving unit  330  may collect light efficiently. 
     Referring to  FIG. 13 , the distance measurement sensor  100  may be disposed or installed in an electronic device. For example, the distance measurement sensor  100  may be disposed or installed in the robot cleaner. A see-through window  930  of the robot cleaner may be located on the distance measurement sensor  100 . 
     The light provided from the light emitting unit  320  (see  FIG. 11 ) of the sensor package  300  may pass through the first hollow unit  220  and reach the see-through window  930 . The light provided from the light emitting unit  320  (see  FIG. 11 ) of the sensor package  300  may be indicated as dash double dot lines in  FIG. 13 . 
     Part of the light reaching the see-through window  930  may pass through the see-through window  930 . Other part of the light reaching the see-through window  930  may be reflected from the see-through window  930 . The light reflected from the see-through window  930  may be indicated as solid lines in  FIG. 13 . When the light reflected from the see-through window  930  is provided to the light receiving panel  700 , the light sensed by the light receiving unit  330  (see  FIG. 11 ) of the sensor package  300  may include noise. That is, when the light reflected from the see-through window  930  is provided to the light receiving panel  700 , malfunction of the sensor package  300  may occur. As the light receiving panel  700  is spaced apart from the first hollow unit  220  by a predetermined distance, input of the light reflected from the see-through window  930  into the light receiving panel  700  may be suppressed. 
     At least part of the light passing through the see-through window  930  may reach the object  920 . At least part of the light reaching the object  920  may be reflected from the object  920  and reach the see-through window  930 . At least part of the light reaching the see-through window  930  may pass through the see-through window  930  and reach the light receiving panel  700 . At least part of the light reaching the light receiving panel  700  may pass through the light receiving panel  700  and reach the light receiving lens  800 . At least part of the light reaching the light receiving lens  800  may pass through the light receiving lens  800  and proceed toward the light guide  500 . At least part of the light provided to the light guide  500  may be provided to the light receiving unit  330  (see  FIG. 11 ) of the sensor package  300 . 
     The sensor package  300  may measure a time (hereinafter, referred to as “flight time”) of the light provided from the light emitting unit  320  (see  FIG. 11 ), which is taken to reach the light receiving unit  330  (see  FIG. 11 ) after being reflected from the object  920 . The flight time may have a positive correlation with the distance between the distance measurement sensor  100  and the object  920 . For example, the flight time may be proportional to the distance between the distance measurement sensor  100  and the object  920 . The sensor package  300  may extract information on the distance between the distance measurement sensor  100  and the object  920  from the flight time. 
     The light receiving panel  700  and/or the light receiving lens  800  may selectively transmit light having a wavelength of a predetermined range. The light receiving panel  700  and/or the light receiving lens  800  may selectively transmit, for example, infrared light. For example, the light emitting unit  320  (see  FIG. 11 ) of the sensor package  300  may provide infrared light. In other words, the light used by the sensor package  300  to detect the object  920  is infrared light, and light having a wavelength different from that of the infrared light may be a noise from the aspect of the light receiving unit  330  (see  FIG. 11 ) of the sensor package  300 . If the light receiving panel  700  and/or the light receiving lens  800  does not transmit light other than the infrared light, the noise provided to the light receiving unit  330  (see  FIG. 11 ) of the sensor package  300  may be reduced. 
     Referring to  FIG. 14 , the light receiving lens  800  may include a top surface  810 . The top surface  810  of the light receiving lens  800  may face the light receiving panel  700 . The top surface  810  of the light receiving lens  800  may be convex toward the top. The top surface  810  of the light receiving lens  800  may include a spherical surface. 
     The light receiving lens  800  may perform a function of a convex lens. That is, the light passing through the light receiving lens  800  may be collected. The collected light may travel inside the light guide  500  and be provided to the light receiving unit  330 . The second guide surface  520  and the third guide surface  530  may be formed as a plane. In this case, the property of the light collected by the light receiving lens  800  may be preserved in the second guide surface  520  and the third guide surface  530 . That is, the light passing through the light receiving lens  800  may maintain the collected property even when the light passes through the second guide surface  520  and the third guide surface  530 . 
     Alternatively, the second guide surface  520  and the third guide surface  530  may be configured in a spherical or aspherical shape. In this case, the light receiving lens  800  may primarily collect the light transmitted from the light receiving panel  700 . The second guide surface  520  may secondarily collect the light transmitted from the light receiving lens  800 . The third guide surface  530  may thirdly collect light transmitted from the second guide surface  520 . 
     In this case, the light receiving lens  800 , the second guide surface  520 , and the third guide surface  530  may be formed or disposed to collect the light transmitted from the light receiving panel  700  on the light receiving unit  330 . 
     The second guide surface  520  and the third guide surface  530  like this may have various shapes in addition to the shape of the spherical or aspherical surface. In this case, the focus of the light transmitted from the light receiving panel  700  may be formed on the light receiving unit  330 . 
     As described above, the light receiving lens  800 , the second guide surface  520 , and the third guide surface  530  may be formed to focus the light transmitted from the light receiving panel  700  on the light receiving unit  330 . 
     In addition, the light receiving lens  800  of the distance measurement sensor  100  may be formed of an aspherical lens. Compared with the spherical lens, the aspherical lens may be different from the aspect of collection of light. The shapes of the second guide surface  520  and the third guide surface  530  may be diversely modified so that the focus of the light transferred from the light receiving panel  700  may be formed on the light receiving unit  330 . 
     Table 1 shows a result of simulating the embodiments according to the present invention and comparative example. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 First 
                 Second 
               
               
                   
                 example 
                 embodiment 
                 embodiment 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 10 Cm 
                 22 
                 37 
                 27 
               
               
                   
                 20 Cm 
                 5 
                 10 
                 10 
               
               
                   
                 30 Cm 
                 1 
                 2 
                 10 
               
               
                   
                 40 Cm 
                 3 
                 4 
                 9 
               
               
                   
                   
               
               
                   
                 (Based on two millions of light radiated from light emitting unit) 
               
            
           
         
       
     
     Table 1 shows experiment data measuring the number of light flowing in the light receiving unit  330 , when the number of light radiated from the light emitting unit  320  is two million, by using the distance measurement sensors  100  according to the first embodiment, the second embodiment, and the comparative example, respectively. 
     Table 1 shows the number of light guided to the light receiving unit  330  while the distance between the distance measurement sensor  100  and the object  920  (see  FIG. 13 ) is adjusted to 10 cm, 20 cm, 30 cm, and 40 cm, respectively. The number of light may mean the number of photons. 
     The distance measurement sensor  100  according to the comparative example may be a distance measurement sensor  100  without having a light guide  500 . The distance measurement sensor  100  according to the first embodiment is the distance measurement sensor  100  shown in  FIG. 13 . The distance measurement sensor  100  according to the second embodiment is the distance measurement sensor  100  shown in  FIG. 14 . 
     Referring to Table 1, the number of photons guided to the light receiving unit  330  of the distance measurement sensor  100  according to the first and second embodiments may be larger than the number of photons guided to the light receiving unit  330  of the distance measurement sensor  100  according to the comparative example. That is, the light receiving performance of the distance measurement sensor  100  according to the first and second embodiments may be superior to the light receiving performance of the distance measurement sensor  100  according to the comparative example. 
     In addition, when the distance from the distance measurement sensor  100  to the object  920  (refer  FIG. 13 ) exceeds 20 cm, the light receiving performance of the distance measurement sensor  100  according to the second embodiment may be superior to the light receiving performance of the distance measurement sensor  100  according to the comparative example and the first embodiment. 
       FIG. 15  is a view showing a distance measurement sensor  100  according to a third embodiment of the present invention. Referring to  FIG. 15 , the distance measurement sensor  100  according to the third embodiment may be different from the distance measurement sensor  100  according to the first embodiment (see  FIG. 13 ). For example, the light receiving lens  800  of the distance measurement sensor  100  according to the third embodiment may be formed as a cylindrical lens. 
     The cylindrical lens is a lens using a cylindrical surface parallel to the axis of a cylinder as a refractive surface. The light receiving lens  800  may collect light entering the cylindrical surface on a straight line parallel to the axis of the cylinder. That is, the light receiving lens  800  is configured to form a focal line. 
     A focal line of light passing through the light receiving lens  800  may be formed in the width direction of the light guide  500  by the light receiving lens  800  of  FIG. 15( a ) . The focal line of the light passing through the light receiving lens  800  may be formed in the length direction of the light guide  500  by the light receiving lens  800  of  FIG. 15( b ) . Like this, the focal line formed by the light receiving lens  800  may vary according to the arrangement and/or shape of the light receiving lens  800 . 
       FIG. 16  is a view showing a distance measurement sensor  100  according to a fourth embodiment of the present invention.  FIG. 17  is an exemplary view schematically showing the cross section of light at each point guided along a main optical path  910  in the distance measurement sensor  100  according to the fourth exemplary embodiment of the present invention. 
     Referring to  FIGS. 16 and 17 , the second guide surface  520  and the third guide surface  530  of the distance measurement sensor  100  according to the fourth embodiment may have a cylindrical shape. 
     Here, the light receiving lens  800  may be a light receiving lens  800  in which the top surface of the light receiving lens  800  is inclined upward in the direction toward the first hollow unit  220  as shown in in the first embodiment. The light receiving lens  800  may refract light and change the traveling direction of the light without collecting the light. 
     The second guide surface  520  and the third guide surface  530  may have a concave cylinder shape on the basis of the light traveling inside the light guide  500 . The size of the second guide surface  520  may be different from that of the third guide surface  530 . That is, when the width of the light guide  500  decreases from the second guide surface  520  toward the third guide surface  530 , the size of the second guide surface  520  may be different from the size of the third guide surface  530 . At this point, each focal line formed by the second guide surface  520  and the third guide surface  530  may be formed on the light receiving unit  330 . The focal lines formed by the second guide surface  520  and the third guide surface  530  may be perpendicular to each other on the light receiving unit  330 . Accordingly, the focus of the light successively reflected from the second guide surface  520  and the third guide surface  530  may be formed on the light receiving unit  330 . 
     In other words, the length of the focal line formed by the second guide surface  520  may gradually decrease after passing through the third guide surface  530 . Accordingly, the focus of light may be formed on the light receiving unit  330 . 
     Changes in the shape of light moving along the main optical path  910  will be described with reference to  FIG. 17 . The second guide surface  520  and the third guide surface  530  shown in  FIG. 17  may be shown in the shape of a reflector to conveniently explain total internal reflection. 
     The light traveling inside the light guide  500  may be refracted by the second guide surface  520  and the third guide surface  530 . The path through which the light travels inside the light guide  500  may be located on a plane. The Y length of the cross section of the light traveling inside the light guide  500  may mean the length of a portion located on a plane in the cross section of the light. The X length of the cross section of the light traveling inside the light guide  500  may mean the length of a portion perpendicular to the Y length in the cross section of the light. 
     On the main optical path  910  located between the light receiving lens  800  and the second guide surface  520 , the cross section of light at the first point P 1  may have a first X length x 1  and a first Y length y 1 . 
     On the main optical path  910  located between the second guide surface  520  and the third guide surface  530 , the cross section of light at the second point P 2  may have a second X length x 2  and a second Y length y 2 . The second Y length y 2  may be smaller than the first Y length y 1 . The first X length x 1  may not be different from the second X length x 2 . That is, the light reflected from the second guide surface  520  may be collected along the main optical path  910  only for the Y length. 
     On the main optical path  910  located between the third guide surface  530  and the light receiving unit  330 , the cross section of light at the third point P 3  have a third X length x 3  and a third Y length y 3 . At this point, the third X length x 3  may be smaller than the second X length x 2 . Here, the light reflected from the third guide surface  530  may be collected along the first light path only for the X length. 
     The third Y length y 3  may be smaller than the second Y length y 2 . The reason why the third Y length y 3  is smaller than the second Y length y 2  is that light is collected by the third guide surface  530 . 
     The X length and the Y length of the light guided from the third guide surface  530  to the light receiving unit  330  may be reduced, and the focus of the light may be formed on the light receiving unit  330 . 
     Referring to  FIG. 16  again, the distance measurement sensor  100  may follow equations (1) and (2) shown below. 
       0.8× f 1≤ d 1+ d 2≤1.2× f 1  Equation (1)
 
       0.8× f 2≤ d 2≤1.2× f 2  Equation (2)
 
     f 1  may mean the focal length of the second guide surface  520 . f 2  may mean the focal length of the third guide surface  530 . d 1  may mean the distance from the second guide surface  520  to the third guide surface  530 . d 2  may mean the distance from the third guide surface  530  to the light receiving unit  330 . 
     The light reflected from the second guide surface  520  and the third guide surface  530  may be collected and form a focus on the light receiving unit  330 . Therefore, as the amount and density of light applied to the light receiving unit  330  increase, accuracy of the distance measurement sensor  100  may be enhanced. 
     Preferably, the distance measurement sensor  100  may follow equations (3) and (4) shown below. 
       0.9× f 1≤ d 1+ d 2≤1.1× f 1  Equation (3)
 
       0.9× f 2≤ d 2≤1.1× f 2  Equation (4)
 
     Furthermore, further preferably, the distance measurement sensor  100  may follow equations (5) and (6) shown below. 
         f 1= d 1+ d 2  Equation (5)
 
         f 2= d 2  Equation (6)
 
     As described above, the light reflected from the second guide surface  520  and the third guide surface  530  may be collected and form a focus on the light receiving unit  330 . Accordingly, the light collecting ability of the light guide  500  including the second guide surface  520  and the third guide surface  530  may be maximized, and accuracy of the distance measurement sensor  100  may be enhanced. 
     Table 2 shows a result of simulating the fourth embodiment according to the present invention and the comparative example. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Fourth 
               
               
                   
                 example 
                 embodiment 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 10 Cm 
                 22 
                 53 
               
               
                   
                 10 Cm 
                 5 
                 13 
               
               
                   
                 20 Cm 
                 1 
                 3 
               
               
                   
                 30 Cm 
                 3 
                 8 
               
               
                   
                   
               
               
                   
                 (Based on two millions of light radiated from light emitting unit) 
               
            
           
         
       
     
     Table 2 shows experiment data measuring the number of light flowing in the light receiving unit  330 , when the number of light radiated from the light emitting unit  320  is set to two million, by using the distance measurement sensors  100  according to the fourth embodiment and the comparative example, respectively. 
     The distance measurement sensor  100  according to the comparative example may not include a light guide  500 . The distance measurement sensor  100  according to the fourth embodiment may be the distance measurement sensor  100  shown in  FIG. 16 . 
     Referring to Table 2, when the distance from the distance measurement sensor  100  to the object  920  (see  FIG. 13 ) is 30 cm, the number of photons transferred to the light receiving unit  330  of the distance measurement sensor  100  according to the fourth embodiment may correspond to 300% of the number of photons transferred to the light receiving unit  330  of the distance measurement sensor  100  according to the comparative example. 
     When the distance from the distance measurement sensor  100  to the object  920  (see  FIG. 13 ) is 40 cm, the number of photons transferred to the light receiving unit  330  of the distance measurement sensor  100  according to the fourth embodiment may correspond to 266.7% of the number of photons transferred to the light receiving unit  330  of the distance measurement sensor  100  according to the comparative example. 
     As described above, compared with the distance measurement sensor  100  according to the comparative example, the distance measurement sensor  100  according to the fourth embodiment may have a relatively high distance measurement accuracy although the distance between the distance measurement sensor  100  and the object  920  (see  FIG. 13 ) is large. 
     Referring to  FIGS. 1 to 17 , the lens units  400  and  800  may mean at least one among the light emitting lens  400  and the light receiving lens  800 . The lens units  400  and  800  may be adjacent to the top of the housing  200 . The lens units  400  and  800  may be adjacent to one end and/or the other end of the housing  200 . The surface into which light enters, among the surface of the lens units  400  and  800 , may form a slope. 
     The description of the present invention described above is for exemplary purpose, and those skilled in the art may understand that the present invention may be easily modified in other specific forms without changing the spirit and essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative and not restrictive in all respects. For example, each constitutional element described as an individual form may be embodied to be distributed, and in the same manner, constitutional elements described as being distributed may also be embodied in an aggregated form. 
     The scope of the present invention is defined by the accompanying claims, and the meaning and scope of the claims and all changes and modifications derived from equivalent concepts thereof should be interpreted as being included in the scope of the present invention.