Patent Publication Number: US-9846435-B2

Title: Obstacle sensing module and cleaning robot including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 13/911,525 filed on Jun. 6, 2013, which claims the priority benefit of Korean Patent Application No. 10-2012-0061059, filed on Jun. 7, 2012 in the Korean. Intellectual Property Office, and Korean Patent Application No. 10-2013-0061815, filed on May 30, 2013 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments relate to an obstacle sensing module capable of sensing an obstacle present therearound, and a cleaning robot including the same. 
     2. Description of the Related Art 
     Generally, an obstacle sensor irradiates light, ultrasonic waves or the like, and detects light or ultrasonic waves returned after being reflected from obstacles in the form of detect signals. Based on time differences, phase differences or intensity differences among the detect signals, the obstacle sensor discriminates whether or not there is an obstacle and the distance from the sensor to the obstacle. The obstacle sensor may discriminate the distance from the sensor to the obstacle, based on reflection angles of the reflected light or ultrasonic waves. 
     Recently, an obstacle sensing method employing a point light source has been proposed. However, when a point light source is employed, a plurality of light emitters should be installed, and there may be a non-sensible zone in spite of installation of such plural light emitters. When the point light source is rotatable to solve the above-mentioned problems, a separate servo mechanism is needed. Furthermore, a certain scanning time is required. For this reason, there may be degradation in efficiency. 
     SUMMARY 
     In an aspect of one of more embodiments, there is provided an obstacle sensing module capable of sensing an obstacle present therearound through formation of uniform planar light using a wide-angle lens, and a cleaning robot including the same. 
     In an aspect of one or more embodiments, there is provided a cleaning robot which includes a body, a driver to drive the body, an obstacle sensing module to sense an obstacle present around the body, and a control unit to control the driver, based on sensed results of the obstacle sensing module, wherein the obstacle sensing module includes at least one light emitter including a light source, a wide-angle lens to refract or reflect light incident from the light source to diffuse the incident light in the form of planar light, and a light source driver to drive the light source to emit light, and a light receiver including a reflection mirror to reflect reflection light reflected by the obstacle to generate reflection light, an optical lens spaced from the reflection mirror by a predetermined distance, to allow the reflection light to pass through the optical lens, an image sensor to receive the reflection light emerging from the optical lens and to generate an image signal from the reflection light emerging from the optical lens, and an image processing circuit to receive the image signal, and to convert the received image signal into an image signal in the form of a digital image signal. 
     The obstacle sensing module may further include an obstacle sensing controller to generate optical control signals to control turn-on/off of the light source, and to generate obstacle sensing information, based on the digital image signal. 
     The control unit may generate a drive control signal, based on the obstacle sensing information. 
     The control unit may generate optical control signals to control turn-on/off of the light source, may generate obstacle sensing information, based on the digital image signal, or may generate a drive control signal, based on the obstacle sensing information. 
     The obstacle sensing information may include at least one of a distance from the body to the obstacle, a position of the obstacle, a height of the obstacle, a shape of the obstacle, and a fall point. 
     The optical control signal to control turn-off of the light source may be generated when the cleaning robot is lifted from a floor. 
     The optical control signal to control turn-on of the light source may be generated when the cleaning robot starts to travel, and the optical control signal to control turn-off of the light source may be generated when the cleaning robot completes traveling. 
     In an aspect of one or more embodiments, there is provided a cleaning robot which includes a body, a driver to drive the body, an obstacle sensing module to sense an obstacle present around the body, and a control unit to control the driver, based on sensed results of the obstacle sensing module, wherein the obstacle sensing module includes at least one light emitter including a light source, and a wide-angle lens to diffuse light incident from the light source in the form of planar light, and a light receiver including an image sensor to receive reflection light reflected by the obstacle and to generate an image signal from the reflected received line light. 
     In an aspect of one or more embodiments, there is provided an obstacle sensing module installed in a cleaning robot which includes at least one light emitter including a light source, a wide-angle lens to refract or reflect light incident from the light source to diffuse the incident light in the form of planar light, and a light source driver to drive the light source to emit light, and a light receiver including a reflection mirror to reflect reflection light reflected by an obstacle to generate reflection light, an optical lens spaced from the reflection mirror by a predetermined distance, to allow the reflection light to pass through the optical lens, an image sensor to receive the reflection light emerging from the optical lens to generate an image signal from the reflection light emerging from the optical lens, and an image processing circuit to receive the image signal, and to convert the received image signal into an image signal in the form of a digital image signal. 
     The light emitter may further include a slit disposed in front of the wide-angle lens, to adjust a thickness of the planar light. 
     The optical lens may be arranged between the reflection mirror and the image sensor, and the light emitter may be arranged in front of the image sensor. 
     The at least one light emitter may include a plurality of light emitters disposed at different positions on the cleaning robot and being arranged at a same level from a floor. 
     The plurality of light emitters may diffuse planar light in a simultaneous manner or in a sequential manner. 
     The plurality of light emitters may include first to third light emitters disposed on the cleaning robot. The light receiver may be disposed at a front side of the cleaning robot. The first light emitter may be arranged in front of the light receiver. The second light emitter may be spaced from the first light emitter in a left direction by a predetermined distance. The third light emitter may be spaced from the first light emitter in a right direction by a predetermined distance. 
     The plurality of light emitters may include first to fourth light emitters disposed on the cleaning robot. The light receiver may be disposed at a front side of the cleaning robot. The first and second light emitters may be spaced from the light receiver in a left direction by a predetermined distance. The third and fourth light emitters may be spaced from the light receiver in a right direction by a predetermined distance. 
     The reflection mirror may be a conical reflection mirror arranged such that an apex of the conical reflection mirror faces the image sensor. 
     The reflection mirror may have a conical structure formed with a conical surface having a side surface portion extending from a bottom surface of the conical structure to a predetermined height and having a concave shape, and a side surface portion extending from the predetermined height to an apex of the conical structure and having a convex shape. 
     A filter may be coated over a surface of the optical sensor, a surface of the reflection mirror, or a surface of the optical lens, to allow light having a wavelength of the planar light to pass through the optical lens. 
     The obstacle sensing module may further include an obstacle sensing controller to generate optical control signals to control turn-on/off of the light source, and to generate obstacle sensing information, based on the digital image signal. 
     The obstacle sensing information may include at least one of a distance from the body to the obstacle, a position of the obstacle, a height of the obstacle, a shape of the obstacle, and a fall point. 
     In an aspect of one or more embodiments, there is provided a wide-angle lens formed of a transparent material to allow light incident from a light source to pass therethrough. The wide-angle lens includes a first diffusion surface to refract the light incident from the light source to diffuse the incident light within the wide-angle lens, a second diffusion surface to refract or reflect the light refracted by the first diffusion surface to generate planar light, and a holding recess formed at a surface opposite to the first diffusion surface, to hold the light source received therein. 
     The wide-angle lens may further include a third diffusion surface to refract the light refracted by the first diffusion surface or the light reflected by the second diffusion surface to generate planar light. 
     The second diffusion surface may be formed at one surface of the second wide-angle lens, to have a U or V-shaped concave structure. 
     The second diffusion surface may include a first surface formed at a central portion of the second diffusion surface, to extend perpendicularly in a forward direction in the form of a flat surface, and second surfaces having a curved shape and forming a predetermined angle with regard to the first surface. The first surface may refract the light reflected by the first diffusion surface to generate planar light. The second surfaces may reflect, toward the third diffusion surfaces, the light reflected by the first diffusion surface. 
     A diffusion range of the planar light may be adjusted in accordance with the predetermined angle or a curvature of the curved shape. 
     The second diffusion surface may be formed with wave patterns each having a tapered ridge. 
     The second diffusion surface may be formed at one surface of the wide-angle lens and has a concave conical shape. The holding recess may have a central axis aligned with a central axis of the second diffusion surface. 
     The second diffusion surface or the third diffusion surface may have a convex shape to reduce a thickness of the planar light. 
     The at least one light emitter may include a plurality of light emitters disposed at different positions on the cleaning robot or at different levels from a floor. 
     The at least one light emitter may include a plurality of light emitters disposed at a same position on the cleaning robot and at different levels from a floor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a concept view of a cleaning robot including an obstacle sensing module according to an exemplary embodiment; 
         FIG. 2A  is a block diagram illustrating a control configuration of the cleaning robot which includes an obstacle sensing module according to an exemplary embodiment; 
         FIG. 2B  is a perspective view of the cleaning robot including the obstacle sensing module according to an exemplary embodiment; 
         FIG. 2C  is a rear view of the cleaning robot including the obstacle sensing module according to an exemplary embodiment; 
         FIG. 2D  is a perspective view illustrating the obstacle sensing module according to an exemplary embodiment; 
         FIG. 3A  is a block diagram of a control configuration of the obstacle sensing module according to an exemplary embodiment; 
         FIG. 3B  is a view illustrating an example in which the obstacle sensing module generate planar light in accordance with an exemplary embodiment; 
         FIG. 3C  is a view illustrating an example in which the obstacle sensing module generate planar light in accordance with an exemplary embodiment; 
         FIG. 4A  is a view illustrating an outer configuration of the obstacle sensing module according to an exemplary embodiment; 
         FIG. 4B  is a view illustrating a view range of the cleaning robot when two light emitters included in the obstacle sensing module are mounted at different positions in accordance with exemplary an embodiment; 
         FIG. 4C  is a view illustrating a view range of the cleaning robot when the obstacle sensing module includes three light emitters in accordance with an exemplary embodiment; 
         FIG. 4D  is a view illustrating a view range of the cleaning robot when the obstacle sensing module includes four light emitters in accordance with an exemplary embodiment; 
         FIG. 5A  is a view illustrating a light receiver included in the obstacle sensing module in accordance with an exemplary embodiment and an image acquired by the light receiver; 
         FIG. 5B  is a view illustrating a first example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror; 
         FIG. 5C  is a view illustrating a second example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror; 
         FIG. 5D  is a view illustrating a third example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror; 
         FIG. 5E  is a view illustrating a fourth example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror; 
         FIG. 5F  is a view illustrating a fifth example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror; 
         FIG. 6A  is a view illustrating another example of the light receiver of the obstacle sensing module according to exemplary an embodiment; 
         FIG. 6B  is a view corresponding to a region A of  FIG. 6A ; 
         FIG. 6C  is a cross-sectional view taken along the line B-B′ of  FIG. 6A ; 
         FIG. 6D  is a view illustrating a view range of the cleaning robot including the example of the light receiver according to the exemplary embodiment of  FIG. 6A ; 
         FIG. 6E  is a graph explaining determination of a distance to an obstacle by the cleaning robot which includes another example of the light receiver of the obstacle sensing module according to an exemplary embodiment; 
         FIG. 7A  is a view illustrating a first example of a wide-angle lens included in the obstacle sensing module in accordance with exemplary an embodiment; 
         FIG. 7B  is a view illustrating diffusion of planar light emerging from the first example of the wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 7C  is a view illustrating a state in which the first wide-angle lens according to an exemplary embodiment is installed at the obstacle sensing module; 
         FIG. 7D  is a view illustrating a second wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 7E  is a view illustrating diffusion of planar light emerging from the second wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 7F  is a view illustrating a third wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 7G  is a view illustrating diffusion of planar light emerging from the third wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 8A  is an exploded perspective view illustrating a fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 8B  is a perspective view illustrating the fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 8C  is a view illustrating diffusion of planar light emerging from the fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment; 
         FIG. 8D  is a view illustrating a state in which the fourth wide-angle lens according to an exemplary embodiment is installed at the obstacle sensing module; 
         FIG. 9A  is a view illustrating a slit capable of adjusting the thickness of planar light when one of the first to third wide-angle lenses is employed, in accordance with an exemplary embodiment; 
         FIG. 9B  is a view illustrating a slit capable of adjusting the thickness of planar light when the fourth wide-angle lens is employed, in accordance with an exemplary embodiment; 
         FIG. 10A  is a view illustrating obstacle sensing results obtained when the size of the slit in the obstacle sensing module is large in accordance with an embodiment; 
         FIG. 10B  is a view illustrating obstacle sensing results obtained when the size of the slit in the obstacle sensing module is small in accordance with an exemplary embodiment; 
         FIG. 11  is a schematic view illustrating a relation between each constituent element of the obstacle sensing module and an obstacle for obstacle distance calculation according to an exemplary embodiment; 
         FIG. 12A  is a plan view of the obstacle sensing module according to an exemplary embodiment and obstacles; 
         FIG. 12B  is an elevation view of the obstacle sensing module according to an exemplary embodiment and the obstacles; 
         FIG. 12C  is a view of images received by the image sensor of the obstacle sensing module according to an exemplary embodiment; 
         FIG. 13A  is a plan view of a plurality of light emitters which are included in the obstacle sensing module while being installed at positions having different levels in accordance with an exemplary embodiment, and an obstacle; 
         FIG. 13B  is an elevation view of the light emitters which are included in the obstacle sensing module while being installed at positions having different levels in accordance with an exemplary embodiment, and the obstacle; 
         FIG. 13C  is a view of planar light received by the image sensor in the form of an image after being irradiated from each of the plural light emitters included in the obstacle sensing module while being installed at different levels and reflected by the obstacle in accordance with an exemplary embodiment; 
         FIG. 14  is a plan view of a plurality of light emitters which are included in the obstacle sensing module while being installed at different positions in accordance with an exemplary embodiment, and an obstacle; 
         FIG. 15A  is an elevation view illustrating an arrangement in which the second wide-angle lens is vertically arranged to allow the obstacle sensing module to sense a fall point in accordance with an exemplary embodiment; 
         FIG. 15B  is an elevation view illustrating an arrangement in which the fourth wide-angle lens is vertically arranged to allow the obstacle sensing module to sense a fall point in accordance with an exemplary embodiment; 
         FIG. 16A  is a view of a state in which the obstacle sensing module irradiates planar light when there is no fall point in accordance with an exemplary embodiment; 
         FIG. 16B  is a view illustrating an image of planar light received by the image sensor after being reflected from the floor when there is no fall point in accordance with an exemplary embodiment; 
         FIG. 17A  is a view of a state in which the obstacle sensing module irradiates planar light when there is a fall point in accordance with an exemplary embodiment; and 
         FIG. 17B  is a view illustrating an image of planar light received by the image sensor after being reflected from the floor when there is a fall point in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. 
     Hereinafter, embodiments will be described with reference to the accompanying drawings. 
       FIG. 1  is a concept view of a cleaning robot including an obstacle sensing module according to an exemplary embodiment. 
     As illustrated in  FIG. 1 , the cleaning robot according to an exemplary embodiment, which is designated by reference numeral ‘ 1 ”, is a device for automatically cleaning a region to be cleaned by sucking foreign matter such as dust from a floor of the cleaning region while autonomously traveling about the cleaning region without user control. The cleaning robot  1  senses an obstacle or a wall, which is located within a region to be cleaned, through various sensors or the like. Based on the sensed results, the cleaning robot  1  controls a travel path thereof and a cleaning operation thereof. 
     In particular, the cleaning robot  1  irradiates planar light while traveling in a room, and senses obstacles present in paths, along which the planar light is irradiated. “Planar light” means thin light beams advancing in various directions on the same plane after being emitting from a light source, as will be described later. 
     The cleaning robot  1  is equipped with an obstacle sensing module (not shown) and, as such, may sense a region therearound in omni-directions or a fan-shaped wide region. Based on sensed results of the obstacle sensing module, the cleaning robot  1  may determine the distance to an obstacle present in the region, the position of the obstacle, the height of the obstacle, the shape of the obstacle, and a fall point. Based on results of the determination, the cleaning robot  1  may determine an environment of the region to be cleaned, and may then execute a cleaning operation for the region. 
       FIG. 2A  is a block diagram illustrating a control configuration of the cleaning robot which includes an obstacle sensing module according to an exemplary embodiment.  FIG. 2B  is a perspective view of the cleaning robot including the obstacle sensing module according to an exemplary embodiment.  FIG. 2C  is a rear view of the cleaning robot including the obstacle sensing module according to an exemplary embodiment.  FIG. 2D  is a perspective view illustrating the obstacle sensing module according to an exemplary embodiment. 
     Referring to  FIGS. 2A to 2D , the cleaning robot  1  includes a body  20  to form an appearance of the cleaning robot  1 . The cleaning robot  1  also includes a cleaning unit to clean a space to be cleaned (hereinafter, referred to as a “cleaning space”), a travel unit  40  to move the cleaning robot  1 , an input/output unit  12  to receive operation commands for the cleaning robot  1 , and to display information as to operation of the cleaning robot  1 , a position detection unit  13  to detect a position of the cleaning robot  1  in the cleaning space, an obstacle sensing unit  14  to sense an obstacle disposed in the cleaning space, a lift sensing unit  15  to sense lifting of the cleaning robot  1  from a floor of the cleaning space, an operation sensing unit  16  to sense movement of the cleaning robot  1 , a driving unit  17  to drive the travel unit  40  and cleaning unit  30 , a storage unit  18  to store various data, a power supply unit  19  to supply power to the cleaning robot  1 , and a control unit  11  to control constituent elements of the cleaning robot  1 . 
     The cleaning unit  30  includes a main brush unit  31  to sweep dust present on a floor so as to guide the swept dust to a suction port, and side brush units  32   a  and  32   b  to clean an area adjacent to a wall and a corner area. 
     The main brush unit  31  may be mounted at an opening  33  formed at a bottom of the body  20 , to sweep dust accumulated on the floor, on which the body  20  is disposed. The opening  33  may be formed at a portion of the bottom of the body  20  biased from a central region of the body  20  in a rearward direction R. The opening  33  may function as a dust inlet into which dust is introduced. The main brush unit  31  may include a roller  31   a , and a main brush  31   b  stuck in an outer surface of the roller  31   a.    
     The roller  31   a  functions to rotate the main brush  31   b . As the roller  31   a  rotates, the main brush  31   b  sweeps dust accumulated on the floor such that the swept dust is guided to the dust inlet  33 . In this case, the roller  31   a  may be formed of a rigid steel body, and the main brush  31   b  may be made of various materials having elasticity. Of course, embodiments are not limited to such materials. 
     Although not shown, the cleaning unit  30  may include a fan unit (not shown) provided within the opening  33 , to generate suction force. The fan unit functions to move dust introduced into the dust inlet to a dust collector (not shown). 
     The travel unit  40  includes travel wheels  41  and  42  to move the body  20  in accordance with a travel control signal, and a caster  43  to enables the body  20  to enable the body  20  to maintain a stable posture while rotating in accordance with a travel direction of the cleaning robot  1 . 
     For example, two travel wheels  41  and  42  may be centrally arranged at opposite sides of the bottom of the body  20  in a symmetrical manner, respectively. The travel wheels  41  and  42  may perform movement operations including forward movement, backward movement, and rotation under the control of the drive circuit during a cleaning operation of the cleaning robot  1 . 
     The caster  43  may be installed at a front edge portion of the bottom of the body  20  when viewed on the basis of a travel direction. 
     The travel wheels  41  and  42 , and caster  43  may be configured into a single assembly detachably mounted to the body  20 . 
     The input/output unit  12  is provided at a top surface of the robot body  20 . The input/output unit  12  includes a plurality of operating buttons  81  to input operation commands for the cleaning robot  1  from the user, and a display panel  82  to display information as to operation of the cleaning robot, for example, information as to whether the cleaning robot  1  operates, information as to a travel mode, etc. Membrane switches may be employed as the operating buttons  81 . As the display panel  82 , a liquid crystal display (LCD) panel or a light emitting diode (LED) panel may be employed. 
     The position detection unit  13  may include a top camera module  70  to acquire a top image of the cleaning robot  1 , namely, an image of a ceiling in the cleaning space. 
     For example, when the cleaning robot  1  travels in a random direction under the condition that there is no predetermined path, along which the cleaning robot  1  travels, that is, when the cleaning robot  1  travels, using the obstacle sensing module, it may travel about a cleaning region, using an obstacle sensing module. In this case, the position detection unit  13  may photograph a top image of the cleaning robot  1 , using the top cameral module  70  to generate information as to a position of the cleaning robot  1 . 
     The obstacle sensing unit  14  includes an obstacle sensing module  100  to irradiate planar light in a forward or lateral direction of the cleaning robot  1 , and then to detect reflection light reflected from an obstacle, for obstacle detection. 
     Referring to  FIG. 2D , the obstacle sensing module  100  is mounted to the front side of the cleaning robot  1  when viewed in a travel direction of the cleaning robot  1 . Of course, when a plurality of obstacle sensing modules  100  is installed in the cleaning robot  1 , the mounting position thereof may further include a position different from the front side of the robot  1 . 
     The obstacle sensing module  100  will be described in detail below. 
     The lift sensing unit  15  may include a separation sensor module (not shown) to sense separation of the travel wheels  41  and  42 . In detail, when the cleaning robot  1  is separated from the floor of the cleaning space, the travel wheels  41  and  42  may be separated from original positions thereof. In this case, the separation sensing module senses separation of the travel wheels  41  and  42 . As will be described later, when lifting of the cleaning robot  1  is sensed by the lift sensing unit  15 , the cleaning robot  1  turns off a light source (not shown) included in the obstacle sensing module (not shown). 
     The operation sensing unit  16  may include an accelerometer (not shown), a gyro sensor, or the like, to sense translation and rotation of the cleaning unit  16 . The operation sensing unit  16  generates information as to travel of the cleaning robot  1 . A light source driver which is included in the obstacle sensing module operates based on the travel information. For example, when the light source driver which will be described later receives a travel signal from the operation sensing unit  16 , it may turn on the light source. On the other hand, when the light source driver receives a stop signal, it may turn off the light source. 
     The storage unit  18  may include a non-volatile memory (not shown) such as a magnetic disc or a solid state disc) to permanently store programs and control data to control operation of the cleaning robot  1 , and a volatile memory (not shown) such as a D-RAM or an S-RAM to store temporary data generated during control of operation of the cleaning robot  1 . 
     The power supply unit  19  includes a battery  50  to supply drive power to constituent elements of the cleaning robot  1 . 
     The battery  50  may be a rechargeable secondary battery. When the body  20  is coupled to a charger or a docking station (not shown) after completing a cleaning operation, the battery  50  may receive electric power from the docking station, to be charged. 
     The control unit  11  functions to control driving of the cleaning robot  1 , based on sensed results of the obstacle sensing module  100  in the cleaning robot  1 . For example, the control unit  11  may set a travel path, based on information as to a surrounding environment of the cleaning robot  1 , namely, obstacle sensing information, and may generate a drive control signal for control operations as to travel and cleaning operations of the cleaning robot  1 . 
     In this case, the obstacle sensing information may include the distance from the body  20  to the sensed obstacle, the position of the obstacle, the height of the obstacle, the shape of the obstacle, a fall point, etc. The obstacle sensing information may be received from the obstacle sensing module  100  or may be directly generated from the control unit  11 . 
     Heretofore, the configuration of the cleaning robot  1  has been described. Hereinafter, the obstacle sensing module included in the cleaning robot will be described. 
       FIG. 3A  is a block diagram of a control configuration of the obstacle sensing module according to an exemplary embodiment. 
     Referring to  FIG. 3A , the obstacle sensing module  100  may include at least one light emitter  110  to diffuse light emitted from a light source  112  so as to emit planar light, a light receiver  120  to receive reflection light reflected from an obstacle so as to generate an electrical image signal, and an obstacle sensing controller  130 . 
     The light source  112  is included in the light emitter  110 . The light emitter  110  may further include a light source driver  113  to drive the light source  112 . 
     The light source  112  functions to emit light. The light source  112  may be a laser diode (LD), a light emitting diode (LED), or the like. Light emitted from the light source  112  may include invisible infrared light, visible light, etc. The light source  112  may generate light having the form of beams advancing in one direction. 
     The light source driver  113  may drive the light source  112  to emit light in accordance with a light control signal from the obstacle sensing controller  130 , and may feed back an intensity of irradiated light, using a photodiode (not shown) or the like. 
     The light receiver  120  may include an optical mechanism  121  to change a path of reflection light reflected from an obstacle, an optical sensor  123  to receive the path-changed reflection light and thus to generate an electrical image signal, and a signal processing circuit  124  to receive the electrical signal and then to convert the received signal into a digital signal. Of course, when the optical sensor  123  has a function to convert an electrical image signal into a digital signal, the light receiver  120  may dispense with the signal processing circuit  124 . 
     The optical mechanism  121  changes a path of reflection light reflected from an obstacle such that the reflection light is directed to the optical sensor  123  which will be described later. As the optical mechanism  121 , any one of a mirror, a lens, a total reflection prism, etc. which may change a path of light may be employed. 
     For example, when a mirror is employed as the optical mechanism  121 , the optical mechanism  121  again reflects reflection light reflected from an obstacle such that the reflection light is directed to the optical sensor. On the other hand, when a lens is employed as the optical mechanism  121 , the optical mechanism  121  refracts reflection light reflected from an obstacle such that the reflection light is directed to the optical sensor. In addition, when a total reflection prism is employed as the optical mechanism  121 , the optical mechanism  121  reflects or refracts reflection light reflected from an obstacle such that the reflection light is directed to the optical sensor. 
     A filter may be coated over a surface of the optical mechanism  121  or optical sensor  123  of the light receiver  120 , to allow light having a wavelength of planar light to pass through the optical mechanism  121 . In this case, light other than reflection light generated in accordance with reflection of planar light irradiated from the light emitter  110  by an obstacle may be removed. 
     The optical sensor  123  receives reflection light reflected from an obstacle, and thus generates an analog or digital signal. For example, as the optical sensor  123 , an image sensor may be employed. The image sensor may include a photodiode sensor to detect an amount of reflection light, a complementary metal oxide semiconductor (MOS) image sensor to acquire an image based on reflection light or a charge coupled device (CCD) image sensor. 
     Reflection light reflected from an obstacle after being emitted from the light emitter  110  is incident upon the optical sensor  123  via the optical mechanism  121 . The incident light is converted into an electrical image signal in the optical sensor  123 . 
     When an image sensor is employed as the optical sensor  123 , the light receiver  120  may further include an optical lens (not shown) arranged between the optical mechanism  121  and the optical sensor  123  while being spaced from the optical mechanism  121  by a predetermined distance, to allow reflection light to pass therethrough. In detail, the optical lens (not shown) condenses reflection light path-changed by the optical mechanism  121  so as to focus an image on the optical sensor  123 . The optical lens (not shown) may be a convex lens. 
     The image processing circuit  124  may convert an analog signal received from the optical sensor  123  into a digital signal, and may convert the format of the signal. The image processing circuit  124  may include an analog/digital (ND) converter (not shown) to convert an analog signal into a digital signal. 
     For example, when the above-described image sensor is employed as the optical sensor  123 , the image processing circuit  124  may convert the format of an image acquired by the image sensor such that the converted format matches a desired appliance. The image processing circuit  124  may convert the format of the image into a particular format such as JPEG or MPEG in accordance with characteristics and requirements of the appliance (for example, the cleaning robot). 
     The obstacle sensing controller  130  may generate optical control signals to control turn-on/off of the light source  112 , and may generate obstacle sensing information, based on an image signal applied to the obstacle sensing controller  130 . For example, the obstacle sensing information may include the distance from the body to the sensed obstacle, the position of the obstacle, the height of the obstacle, the shape of the obstacle, a fall point, etc. 
     The obstacle sensing controller  130  may execute modulation of frequency, duty ratio, and intensity, based on the intensity of light received from the photo detector (not shown), and may transmit a control signal according to the modulation to the light source driver  113 , for emission of light having a frequency, a duty ratio, and an intensity which are desired by the user. For example, the obstacle sensing controller  130  may control intensity of light through control such as pulse width modulation (PWM). 
     It is unnecessary for the obstacle sensing controller  130  to be a single module in which the obstacle sensing controller  130  is physically coupled with the light emitter  110  and light receiver  120 . Other devices, to which the obstacle sensing module  100  may be mounted, such as a central processing unit (CPU) or a multipoint control unit (MCU), may be employed as the obstacle sensing controller  130 . 
     The light source  112  of the obstacle sensing module  100  may generate planar light. Alternatively, the light emitter  110  may include a plurality of light sources  112  to generate planar light. 
     Hereinafter, a method of generating planar light in the obstacle sensing module  100  will be described. 
       FIG. 3B  is a view illustrating an example in which the obstacle sensing module generate planar light in accordance with an exemplary embodiment.  FIG. 3C  is a view illustrating an example in which the obstacle sensing module generate planar light in accordance with an exemplary embodiment. 
     Referring to  FIG. 3B  associated with the case in which the light emitter  110  includes a single light source  112  to generate planar light, the obstacle sensing module  100  may generate fan-shaped planar light by reflecting light irradiated from the light source  112  by a mirror or refracting the light through a lens. For example, the light emitter  110  may generate fan-shaped planar light, using a conical mirror to reflect incident light so as to widely diffuse the light or a wide-angle lens to refract incident light so as to widely diffuse the light. 
     On the other hand, referring to  FIG. 3C  associated with the case in which the light emitter  110  includes a plurality of light sources  112  to generate planar light, the light sources  112  are densely arranged at the front side of the cleaning robot  1  such that a plurality of beams irradiated from the light sources  112  overlap with one another, to form planar light. 
     Hereinafter, generation of fan-shaped or semicircular planar light from the obstacle sensing module  100  through refraction of light irradiated from the light source  112  using a wide-angle lens, as shown in  FIG. 3B , will be described. 
       FIG. 4A  is a view illustrating an outer configuration of the obstacle sensing module according to an exemplary embodiment. 
     When one light emitter  110  and one light receiver  120  is integrally formed, they may be disposed on a stand  100   b . In this case, the light emitter  110  may be in front of the light receiver  120 . The light emitter  110  may be disposed within a light emitter housing  100   a . The light receiver  120  may be coupled to a pillar  100   c  to support the light receiver  120  by a coupling member  100   e.    
     Of course, the configuration illustrated in  FIG. 4A  is an example of the obstacle sensing module  100 , and is not limited to that of  FIG. 4A . That is, the light emitter  110  may be disposed beneath the stand  100   b , and the light receiver  120  may be disposed above the stand  100   b . Alternatively, the light emitter  110  and light receiver  120  may be disposed at the same position. 
     Of course, when the obstacle sensing module  100  is mounted to the robot  1 , it is important to reduce the size of the obstacle sensing module  100  as much as possible. It may be possible to reduce the height of the obstacle sensing module  100  by arranging the light emitter  110  ahead of the light receiver  120 . In this case, the light receiver  120  may be arranged at a level higher than that of the light emitter  110 . Accordingly, even when the light emitter  110  is arranged ahead of the light receiver  120 , reflection light reflected from an obstacle may be completely transmitted to the light receiver  120  without being shielded by the light emitter  110 . 
     Although the obstacle sensing module includes an integrated structure of one light emitter and one light receiver in the illustrated case, the light emitter and light receiver may be separate from each other. Alternatively, the obstacle sensing module may include a plurality of light emitter or a plurality of light receiver. In other words, the light emitter and light receiver may be arranged at different positions such that they may be independently of each other. 
       FIG. 4B  is a view illustrating a view range of the cleaning robot when two light emitters included in the obstacle sensing module are mounted at different positions in accordance with an exemplary embodiment. 
     Referring to  FIG. 4B , the obstacle sensing module  100  may include two light emitters  110   a  and  110   b  disposed at different positions, and one light receiver  120 . 
     The two light emitters  110   a  and  110   b  may have different installation positions on the cleaning robot  1  or different levels from the floor. 
     In this case, it may be possible to sense obstacles arranged at various levels by arranging the plural light emitters  110   a  and  110   b  at different levels or arranging the plural light emitters  110   a  and  110   b  to be inclined. When the light emitters  110   a  and  110   b  and the light receiver  120  are arranged at different positions without being vertically aligned, it may be possible to sense obstacles arranged at various levels without increasing the height of the obstacle sensing module  100 . 
       FIG. 4C  is a view illustrating a view range of the cleaning robot when the obstacle sensing module includes three light emitters in accordance with an exemplary embodiment. 
     Referring to  FIG. 4C , the obstacle sensing module  100  may include three light emitters  110   a ,  110   b , and  110   c  arranged at different positions on the cleaning robot  1 . When three light emitters  110   a ,  110   b , and  110   c  capable of diffusing planar light of 120° are employed, it may be possible to obtain the same effect as that of the case in which a single light emitter capable of diffusing planar light of 220° is employed. 
     In this case, the first light emitter  110   a  may be installed ahead of the light receiver installed at the front side of the robot  1  while being arranged to forwardly diffuse planar light. The second light emitter  110   b  is installed to be spaced from the first light emitter  110   a  in a left direction by a predetermined distance while being arranged to diffuse planar light in a direction forming a predetermined angle from the front side of the robot  1 . On the other hand, the third light emitter  110   c  is installed to be spaced from the first light emitter  110   a  in a right direction by a predetermined distance while being arranged to diffuse planar light in a direction forming a predetermined angle from the front side of the robot  1 . 
     In this case, the planar light diffusion zones of the first light emitter  110   a , second light emitter  110   b , and third light emitter  110   c  may partially overlap with one another. In addition, the first light emitter  110   a , second light emitter  110   b , and third light emitter  110   c  may be arranged to minimize a dead zone that may not be sensed by the robot  1 , taking into consideration the positional characteristics of the first light emitter  110   a , second light emitter  110   b , and third light emitter  110   c.    
       FIG. 4D  is a view illustrating a view range of the cleaning robot when the obstacle sensing module includes four light emitters in accordance with an exemplary embodiment. 
     Referring to  FIG. 4D , four light emitters  110   a ,  110   b ,  110   c , and  110   d  arranged at different positions on the robot  1  are illustrated. When four light emitters  110   a ,  110   b ,  110   c , and  110   d  capable of diffusing planar light of 120° are employed, it may be possible to diffuse planar light over a wider zone than that of the case in which a single light emitter capable of diffusing planar light of 220° is employed. 
     In this case, a pair of light emitters, namely, the first light emitter  110   a  and second light emitter  110   b , are installed to be spaced from the light receiver  120  installed at the front side of the robot  1  in a left direction by a predetermined distance while being directed in different directions forming a predetermined angle therebetween. Another pair of light emitters, namely, the third light emitter  110   c  and fourth light emitter  110   d , are installed to be spaced from the light receiver  120  installed at the front side of the robot  1  in a right direction by a predetermined distance while being directed in different directions forming a predetermined angle therebetween. 
     In this case, the first light emitter  110   a  and second light emitter  110   b  may diffuse planar light in forward and left directions of the robot  1 , respectively. On the other hand, the third light emitter  110   c  and fourth light emitter  110   d  may diffuse planar light in forward and right directions of the robot  1 , respectively. In this case, the planar light diffusion zones of the first light emitter  110   a , second light emitter  110   b , third light emitter  110   c , and fourth light emitter  110   d  may partially overlap with one another. In addition, the first light emitter  110   a , second light emitter  110   b , third light emitter  110   c , and fourth light emitter  110   d  may be arranged to minimize a dead zone that may not be sensed by the robot  1 , taking into consideration the positional characteristics of the first light emitter  110   a , second light emitter  110   b , third light emitter  110   c , and fourth light emitter  110   d.    
     The obstacle sensing module  100  may sense obstacles present around the robot  1  by generating uniform planar light. 
     The robot  1  equipped with the obstacle sensing module  100  may achieve more effective cleaning and travel in accordance with sensing of obstacles present therearound and utilization of the sensed results in driving control. 
     Hereinafter, the light receiver will be described in detail. 
     For better understanding of the light receiver, the following description will be given in conjunction with the case in which, as the optical mechanism (“ 121 ” in  FIG. 3A ), a reflection mirror is employed to reflect, toward the optical sensor (“ 123 ” in  FIG. 3A ), reflection light reflected by an obstacle. 
     In addition, the light receiver will be described in conjunction with the case in which the light receiver employs an image sensor and the case in which the light receiver employs a photodiode. First, the light receiver which employs an image sensor will be described. 
       FIG. 5A  is a view illustrating a light receiver included in the obstacle sensing module in accordance with an exemplary embodiment and an image acquired by the light receiver. 
     As illustrated in  FIG. 5A (a), the light receiver which is designated by reference numeral “ 120   a ” includes a reflection mirror  121   a  to change a path of reflection light reflected from an obstacle such that the reflection light is directed to an image sensor  123   a , and an optical lens  122   b  to condense the reflection light path-changed by the reflection mirror  121   a . The light receiver further includes an image sensor  123   a  to receive the reflection light condensed by the optical lens  122   b.    
     As the reflection mirror  121   a , a conical mirror may be employed in order to change a path of reflection light incident upon the mirror in various directions toward the image sensor  123   a . The reflection mirror  121   a  may be arranged over the image sensor  123   a  while extending vertically downwardly such that an apex of the conical reflection mirror downwardly faces the image sensor  123   a . Alternatively, although not shown, the reflection mirror  121  may be a conical mirror arranged beneath the image sensor  123   a  while extending vertically upwardly such that an apex of the conical reflection mirror upwardly faces the image sensor  123   a . Of course, the shape of the reflection mirror  121   a  is not limited to the conical shape. 
     The reflection mirror  121   a  may be made of a metal such as aluminum or may be formed of a plastic body and chromium (Cr) plated over the plastic body in order to achieve an enhancement in reflectance of the surface of the reflection mirror  121   a  and, as such, may reflect reflection light reflected from an obstacle to the image sensor  123   a  without distortion. 
     When a conical mirror is employed as the reflection mirror  121   a , the image sensor  123   a  may acquire an image as illustrated in  FIG. 5A (b). In detail, at a central portion of an image acquired by the image sensor  123   a , there is no image associated with an obstacle due to blocking of reflection light by the body of the cleaning robot. The acquired image includes an image associated with the obstacle while being arranged in a range from a position spaced in a radial direction from the center of the acquired image. The image of an obstacle disposed at a position near to the body of the cleaning robot while being spaced from the floor of the cleaning space by a small height is arranged at a position near to the center of the acquired image. On the other hand, the image of an obstacle disposed at a position far from the body of the cleaning robot while being spaced from the floor of the cleaning space by a great height is arranged at a position near to the periphery of the acquired image. In other words, the image of an obstacle nearer to the cleaning robot is arranged at a position nearer to the center of the image acquired by the image sensor  123   a , whereas the image of an obstacle farther from the cleaning robot is arranged at a position farther from the center of the image acquired by the image sensor  123   a.    
     Hereinafter, various conical shapes of the reflection mirror  121   a  will be illustrated, and view ranges of the cleaning robot associated with respective conical shapes of the reflection mirror  121   a  and obstacle images acquired by the image sensor  123   a  in association with respective conical shapes of the reflection mirror  121   a  will be described. 
       FIG. 5B  is a view illustrating a first example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror. 
     Referring to  FIG. 5B , the reflection mirror which is designated by reference numeral “ 121   a - 1 ” has a general conical shape as illustrated in  FIG. 5B (a). 
     The cross-section of the reflection mirror  121   a - 1  taken along the line A-A′ of  FIG. 5B (a) has a triangular shape as illustrated in  FIG. 5B (b). 
     The cleaning robot  1  employing the reflection mirror  121   a - 1  having the above-described conical shape has a fan-shaped view range as illustrated in  FIG. 5B (c). In detail, the cleaning robot  1  may have a view angle of 100 to 150° in left and right directions with regard to the front side of the cleaning robot  1  where the light receiver  120   a  including the reflection mirror  121   a - 1  is disposed. In other words, the cleaning robot  1  may totally have a view angle of 200 to 300°. Since the body of the cleaning robot  1  blocks the field of view of the light receiver  121   a , it may be impossible to secure a view angle of 360°. The view angle of the cleaning robot  1  may be varied in accordance with the position of the light receiver  121   a . For example, when the light receiver  121   a  is provided to be protruded from the body of the cleaning robot  1 , a wide view angle may be secured. On the other hand, when the light receiver  121   a  is disposed inside the body of the cleaning robot  1 , the view angle may be narrowed. 
     In addition, the cleaning robot  1  may secure a predetermined view distance d. The view distance d of the cleaning robot  1  may be varied in accordance with the resolution of the image sensor  123   a , the material of the reflection mirror  121   a - 1 , and the shape of the reflection mirror  121   a - 1 , namely, the angle of side surface of the conical shape. 
     The image sensor  123   a  included in the cleaning robot  1  employing the reflection mirror  121   a - 1  may acquire a fan-shaped image as illustrated in  FIG. 5B (d). In detail, as illustrated in  FIG. 5B (d), it may be possible to acquire an image having a shape similar to that of the view range of the cleaning robot  1 . It may also be possible to acquire a bright obstacle image formed at a position corresponding to the position of an obstacle. For example, when an obstacle is disposed at a position slightly biased toward a left direction in front of the cleaning robot  1 , as illustrated in  FIG. 5B (c), the image sensor  123   a  may acquire an obstacle image OI having a bright arc shape at a position slightly biased toward a left direction in front of the cleaning robot  1 . As will be described later, based on the position of the acquired obstacle image OI, the cleaning robot  1  may determine presence of an obstacle O and the position of the obstacle O. 
       FIG. 5C  is a view illustrating a second example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror. 
     Referring to  FIG. 5C , the reflection mirror which is designated by reference numeral “ 121   a - 2 ” has a shape formed by vertically truncating a conical shape from a bottom of the conical shape (hereinafter, referred to as a vertically-truncated conical shape”), as illustrated in  FIG. 5C (a). 
     The cross-section of the reflection mirror  121   a - 2  taken along the line B-B′ of  FIG. 5C (a) has a right-angled triangular shape as illustrated in  FIG. 5C (b). 
     The cleaning robot  1  employing the reflection mirror  121   a - 2  having the vertically-truncated conical shape has a semicircular view range as illustrated in  FIG. 5C (c). 
     In detail, the cleaning robot  1  may have a view angle of 90° in left and right directions with regard to the front side of the cleaning robot  1  where the light receiver  120   a  is disposed. In other words, the cleaning robot  1  may totally have a view angle of 180°. This is because reflection light is only incident upon the side surface of the conical shape, and no reflection light is incident upon a rear surface of the reflection mirror  121   a - 2 . 
     In addition, the cleaning robot  1  may secure a predetermined view distance d. As described above, the view distance d of the cleaning robot  1  may be varied in accordance with the resolution of the image sensor  123   a , the material of the reflection mirror  121   a - 2 , and the shape of the reflection mirror  121   a - 2 , namely, the angle of side surface of the conical shape. 
     The image sensor  123   a  included in the cleaning robot  1  employing the reflection mirror  121   a - 2  may acquire a semicircular image as illustrated in  FIG. 5C (d). 
     In detail, as illustrated in  FIG. 5C (d), it may be possible to acquire an image having a shape similar to that of the view range of the cleaning robot  1 . It may also be possible to acquire a bright obstacle image formed at a position corresponding to the position of an obstacle. For example, when an obstacle is disposed at a position slightly biased toward a left direction in front of the cleaning robot  1 , as illustrated in  FIG. 5C (c), the image sensor  123   a  may acquire an obstacle image OI having a bright arc shape at a position slightly biased toward a left direction in front of the cleaning robot  1 . 
       FIG. 5D  is a view illustrating a third example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror. 
     Referring to  FIG. 5D , the reflection mirror which is designated by reference numeral “ 121   a - 3 ” has a shape formed by horizontally truncating a conical shape from a bottom of the conical shape (hereinafter, referred to as a horizontally-truncated conical shape”), as illustrated in  FIG. 5D (a). 
     The cross-section of the reflection mirror  121   a - 3  taken along the line C-C′ of  FIG. 5D (a) has a horizontally-truncated conical shape as illustrated in  FIG. 5D (b). 
     The cleaning robot  1  employing the reflection mirror  121   a - 3  having the horizontally-truncated conical shape has a cut donut-shaped view range as illustrated in  FIG. 5D (c). That is, a region very near to the cleaning robot  1  is not included in the view range of the cleaning robot  1 . 
     In detail, the cleaning robot  1  may have a view angle of 100 to 150° in left and right directions with regard to the front side of the cleaning robot  1  where the light receiver  120   a  is disposed. In other words, the cleaning robot  1  may totally have a view angle of 200 to 300°. Since the body of the cleaning robot  1  blocks the field of view of the light receiver  121   a , it may be impossible to secure a view angle of 360°. 
     In addition, the cleaning robot  1  may secure a predetermined view distance d. That is, the cleaning robot  1  has a view distance range between a view distance d1 corresponding to a length of the side surface of the conical shape and a view distance d2 corresponding to a length of the side surface of the cut portion of the conical shape. In other words, the cleaning robot  1  has a view range from to a first distance d1 to a second distance d2. This is because reflection light is incident upon the side surface of the reflection mirror  121   a - 3 , whereas no reflection light is incident upon a cut bottom surface of the reflection mirror  121   a - 3 . The view distance d of the cleaning robot  1  may be varied in accordance with the resolution of the image sensor  123   a , the material of the reflection mirror  121   a , and the shape of the reflection mirror  121   a - 3 , namely, the angle of side surface of the conical shape. 
     The image sensor  123   a  included in the cleaning robot  1  employing the reflection mirror  121   a - 3  may acquire a cut donut-shaped image as illustrated in  FIG. 5D (d). 
       FIG. 5E  is a view illustrating a fourth example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror. 
     Referring to  FIG. 5E , the reflection mirror which is designated by reference numeral “ 121   a - 4 ” has a conical shape having a convex side surface (hereinafter, referred to as a convex conical shape”), as illustrated in  FIG. 5E (a). 
     The cross-section of the reflection mirror  121   a - 4  taken along the line D-D′ of  FIG. 5E (a) has a convex conical shape as illustrated in  FIG. 5E (b). 
     The cleaning robot  1  employing the reflection mirror  121   a - 4  having the convex conical shape has a fan-shaped view range as illustrated in  FIG. 5E (c). In detail, the cleaning robot  1  may have a view angle of 100 to 150° in left and right directions with regard to the front side of the cleaning robot  1  where the light receiver  120   a  including the reflection mirror  121   a - 4  is disposed. In other words, the cleaning robot  1  may totally have a view angle of 200 to 300°. Since the body of the cleaning robot  1  blocks the field of view of the light receiver  121   a , it may be impossible to secure a view angle of 360°. 
     In addition, the cleaning robot  1  may secure a predetermined view distance d. The view distance d of the reflection mirror  121   a - 4  having the above-described convex conical shape is long, as compared to the reflection mirror (“ 121   a - 1 ” in  FIG. 5B ) having the above-described general conical shape, as in the case of a convex mirror having a wider view range than a flat mirror. 
     The image sensor  123   a  included in the cleaning robot  1  employing the reflection mirror  121   a - 4  may acquire a fan-shaped image as illustrated in  FIG. 5E (d). Since the reflection mirror  121   a - 4  having the above-described convex conical shape has a wider view range than the reflection mirror (“ 121   a - 1 ” in  FIG. 5B ) having the above-described general conical shape, the image acquired by the convex conical reflection mirror  121   a - 4  may include obstacle information of a wider cleaning space than that of the image acquired by the general conical reflection mirror (“ 121   a - 1 ” in  FIG. 5B ). 
       FIG. 5F  is a view illustrating a fifth example of the reflection mirror included in an example of the light receiver of the obstacle sensing module according to an exemplary embodiment and an image acquired by the reflection mirror. 
     Referring to  FIG. 5F , the reflection mirror which is designated by reference numeral “ 121   a - 5 ” has a conical structure having a convex side surface portion extending from an apex of the conical structure to a predetermined height and a concave side surface portion extending from the predetermined height to a bottom of the conical structure, as illustrated in  FIG. 5F (a). 
     The cross-section of the reflection mirror  121   a - 5  taken along the line E-E′ of  FIG. 5F (a) has a convex conical shape as illustrated in  FIG. 5F (b). 
     As illustrated in  FIG. 5F (c), the cleaning robot  1  employing the reflection mirror  121   a - 5  may have a view angle of 200 to 300°. Since the body of the cleaning robot  1  blocks the field of view of the light receiver  121   a , it may be impossible to secure a view angle of 360°. 
     In addition, the cleaning robot  1  may secure a predetermined view distance d. 
     The image sensor  123   a  included in the cleaning robot  1  employing the reflection mirror  121   a - 5  may acquire a fan-shaped image as illustrated in  FIG. 5F (d) 
     Heretofore, examples of the light receiver employing the image sensor have been described. Hereinafter, examples of the light receiver employing the photodiode will be described. 
       FIG. 6A  is a view illustrating another example of the light receiver of the obstacle sensing module according to an exemplary embodiment.  FIG. 6B  is a view corresponding to a region A of  FIG. 6A .  FIG. 6C  is a cross-sectional view taken along the line B-B′ of  FIG. 6A .  FIG. 6D  is a view illustrating a view range of the cleaning robot including the example of the light receiver according to the embodiment of  FIG. 6A . 
     Referring to  FIGS. 6A to 6D , the light receiver  120  includes a reflection mirror  121   b  to change a path of reflection light reflected from an obstacle, a plurality of shields  122   b  to divide the reflection mirror  121   b  into a plurality of reflection regions  121   b - 1 ,  121   b - 2 ,  121   b - 3 ,  121   b - 4 , and  121   b - 5 , and a plurality of photodiodes  123   b  provided to respectively correspond to the reflection regions  121   b - 1 ,  121   b - 2 ,  121   b - 3 ,  121   b - 4 , and  121   b - 5  divided by the shields  122   b.    
     As the reflection mirror  121   b , a conical mirror may be employed in order to change a path of reflection light incident upon the mirror in various directions toward the image sensor  123   a .  FIGS. 6A to 6D  illustrate conical mirrors as the reflection mirror  121   b . However, the reflection mirror  121   b  is not limited to the illustrated cases. The reflection mirror  121   b  may have various shapes as illustrated in  FIGS. 5B to 5F . 
     The shields  122   b  divide the reflection mirror  121   b  into a plurality of reflection regions. In addition, the cleaning robot  1  has a field of view v 123   b  divided into a plurality of view field regions v 120   b - 1 , v 120   b - 2 , v 120   b - 3 , v 120   b - 4 , and v 120   b - 5 . Each shield  122   b  blocks reflection light incident upon reflection regions which do not correspond to a corresponding one of the view field regions. For example, the shields  122   b  corresponding to the first view field region v 120   b - 1  allow reflection light reflected from an obstacle O in the first view filed portion v 120   b - 1  to be incident upon the first reflection region  121   b - 1  of  FIG. 6A  while preventing reflection light reflected in the second to fifth view field regions v 120   b - 2  to v 120   b - 5  from being incident upon the first reflection region  121   b - 1 . 
     Each shield  122   b  may have a trapezoidal shape such that it may correspond to the side surface of the reflection mirror  121   b , as illustrated in  FIG. 6B . Each shield  122   b  may employ a material capable of effectively absorbing light in order to shield reflection light incident from view field regions other than the corresponding view field region. 
     A plurality of photodiodes  123   b - 1 ,  123   b - 2 ,  123   b - 3 ,  123   b - 4 , and  123   b - 5  are provided to correspond to respective reflection regions  121   b - 1 ,  121   b - 2 ,  121   b - 3 ,  121   b - 4 , and  121   b - 5 . The photodiodes  123   b - 1 ,  123   b - 2 ,  123   b - 3 ,  123   b - 4 , and  123   b - 5  detect reflection light reflected from respective reflection regions  121   b - 1 ,  121   b - 2 ,  121   b - 3 ,  121   b - 4 , and  121   b - 5 . For example, the first photodiode  123   b - 1  detects an amount of reflection light path-changed by a first reflection region  121   b - 1  of the reflection mirror  121   b  after being reflected by an obstacle disposed in the first view field region v 120   b - 1 . 
     Hereinafter, determination of a direction of an obstacle by the cleaning robot  1  will be described. The cleaning robot  1  may determine a direction of an obstacle, based on one of the photodiodes  123   b  which has detected reflection light. 
     For example, as illustrated in  FIG. 6D , the cleaning robot  1  emits planar light, and the planar light is then reflected by an obstacle O disposed in the first view field region v 120 - 1 . The reflection light reflected by the obstacle O is incident upon the reflection mirror  121   b  of the light receiver  120   b.    
     In this case, the reflection light is not only incident upon the first reflection region  121   b - 1  corresponding to the first view field region v 120   b - 1 , but also incident upon the second reflection region  121   b - 2  to fifth reflection region  121   b - 5 . However, the reflection light incident upon the second reflection region  121   b - 2  to fifth reflection region  121   b - 5  is blocked by the shields  122   b  corresponding to the first reflection region  121   b - 1 . Accordingly, only the reflection light incident upon the first reflection region  121   b - 1  is reflected from the reflection mirror  121   b , and is then incident upon the first photodiode  123   b - 1 . As a result, the reflection light reflected by the obstacle O disposed in the first view field region v 120 - 1  is detected only by the first photodiode  123   b - 1 . 
     When the first photodiode  123   b - 1  detects reflection light, the cleaning robot  1  may determine that an obstacle O is present in the first view field region v 120   b - 1 . 
     Hereinafter, determination of a distance to an obstacle by the cleaning robot  1  will be described. The distance to the obstacle is determined, based on an amount of light detected by the photodiode  123   b  of the cleaning robot  1 . 
       FIG. 6E  is a graph explaining determination of a distance to an obstacle by the cleaning robot which includes another example of the light receiver of the obstacle sensing module according to an exemplary embodiment. 
     An output I of the photodiode  123   b  according to a distance d to an obstacle is illustrated in  FIG. 6E . In detail, when the obstacle distance d is shorter than a predetermined focal distance, the output I of the photodiode  123   b  is gradually increased in accordance with an increase in the obstacle distance d. On the other hand, when the obstacle distance d is longer than the predetermined focal distance, the output I of the photodiode  123   b  is gradually decreased in accordance with an increase in the obstacle distance d. 
     Such a phenomenon is caused by the characteristics of the obstacle sensing module which utilizes light. The light emitter emits light under the condition that the light is focused at a position spaced from the light emitter by a predetermined distance, in order to achieve an enhancement in the sensitivity to an obstacle disposed at a position spaced from the light emitter by the predetermined distance. In this case, the light receiver outputs a maximum output value in response to light reflected from the obstacle disposed at the position spaced from the light emitter by the predetermined distance. Accordingly, when the photodiode  123   b  outputs a maximum output value when the obstacle is disposed at a position spaced from the light emitter by a focal distance. When the obstacle is disposed at a position spaced from the light emitter by a distance shorter or longer than the focal distance, the output value of the photodiode  123   b  is reduced. By virtue of such characteristics of the obstacle sensing module utilizing light, it may be possible to ignore a shorter distance than the focal distance by arranging the photodiode  123   b  at a position spaced in a rearward direction from the foremost portion of the cleaning robot  1  by the focal distance. 
     The cleaning robot  1  may determine the distance d to the obstacle, based on the output I of the photodiode  123   b  according to the obstacle distance d as illustrated in  FIG. 6E . For example, when the output of the photodiode  123   b  has a first output value I1, the cleaning robot  1  may determine the obstacle distance to be a first distance d1. When the output of the photodiode  123   b  has a second output value I2, the cleaning robot  1  may determine the obstacle distance to be a second distance d2. On the other hand when the output of the photodiode  123   b  has a third output value I1, the cleaning robot  1  may determine the obstacle distance to be a third distance d3. 
     In brief, when the cleaning robot includes a light receiver employing a plurality of photodiodes, it may determine the direction of an obstacle, based on one of the photodiodes which has detected reflection light, and may determine the distance to the obstacle, based on an output value from the photodiode. 
     Heretofore, the light receiver of the obstacle sensing module has been described. 
     Hereinafter, the light emitter of the obstacle sensing module will be described. 
       FIG. 7A  is a view illustrating a first example of a wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 7B  is a view illustrating diffusion of planar light emerging from the first example of the wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment. 
     Referring to  FIGS. 7A and 7B , the first wide-angle lens which is designated by reference numeral “ 111   a ” may include a transparent member allowing light incident from a light source (not shown) thereupon to pass therethrough. 
     The first wide-angle lens  111   a  may include a first diffusion surface u1 to refract light incident from the light source so as to diffuse the incident light within the first wide-angle lens  111   a , a second diffusion surface u2 to refract the light refracted by the first diffusion surface u1 outwardly of the first wide-angle lens  111   a  so as to generate planar light, and a holding recess u4 formed at a surface opposite to the first diffusion surface u1, to hold the light source received therein. 
     For example, the first wide-angle lens  111   a  may include diffusion of planar light over an angle of 120°. In this case, the second diffusion surface u2 of the first wide-angle lens  111   a  may have a convex shape in order to thin planar light diffused in the first wide-angle lens  111   a.    
     Hereinafter, the path of light in the first wide-angle lens  111   a  will be described. First, light emitted from the light source is refracted by the first diffusion surface u1 of the first wide-angle lens  111   a . The refracted light is then diffused within the first wide-angle lens  111   a.    
     The light, which is diffused in various directions while passing through the first diffusion surface u1, is again diffused in various directions while passing through the second diffusion surface u2. That is, the light is converted into planar light. 
     The above-described first wide-angle lens  111   a  may have a shape illustrated in  FIG. 7A . Of course, the first wide-angle lens  111   a  is not limited to the illustrated shape. 
       FIG. 7C  is a view illustrating a state in which the first wide-angle lens according to an exemplary embodiment is installed at the obstacle sensing module. 
     Referring to  FIG. 7C , the light source  112  of the light emitter  110  emits light in a direction parallel to the floor. 
     The first wide-angle lens  111   a  may forwardly diffuse planar light generated in accordance with refraction or reflection of light emitted from the light source  112 . Such planar light may be irradiated in a direction parallel to the floor or in a direction inclined from the floor. 
     As a result, the obstacle sensing module may sense an obstacle disposed at a higher or lower level than that of an obstacle disposed on the floor. 
     The planar light may be reflected by an obstacle, and the reflected light may be again reflected after being transmitted to the reflection mirror  121 . 
     Reflection light reflected by the reflection mirror  121  may be transmitted to the optical sensor  123 . 
       FIG. 7D  is a view illustrating a second wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 7E  is a view illustrating diffusion of planar light emerging from the second wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment. 
     Referring to  FIGS. 7D and 7E , the second wide-angle lens which is designated by reference numeral “ 111   b ” may include a transparent member allowing light incident from a light source thereupon to pass therethrough. The light source is designated by reference numeral “ 112 ”. The second wide-angle lens  111   b  reflects or refracts light incident from the light source  112 , thereby generating planar light L1 and planar light L2. 
     The second wide-angle lens  111   b  may include a first diffusion surface u1 to refract light incident from the light source  112  so as to diffuse the incident light within the second wide-angle lens  111   b , a second diffusion surface u2 to refract the light refracted by the first diffusion surface u1 outwardly of the second wide-angle lens  111   b  or to reflect the light refracted by the first diffusion surface u1 toward the interior of the second wide-angle lens  111   b , third diffusion surfaces u3 to refract the light refracted by the first diffusion surface u1 or the light reflected by the second diffusion surface u2 so as to generate planar light, and a holding recess u4 formed at a surface opposite to the second diffusion surface u2, to hold the light source  112  received therein. 
     For example, the planar light may include first planar light L1 and second planar light L2. The first planar light L1 is generated as light refracted by the first diffusion surface u1 is again refracted by the second diffusion surface u2. On the other hand, the second planar light L2 is generated as the light refracted by the first diffusion surface u1 is reflected by the second diffusion surface u2. 
     The second diffusion surface u2 may generate the first planar light L1 and the second planar light L2 by refracting or reflecting light. 
     The second diffusion surface u2 may include a U or V-shaped concave structure formed at one surface of the second wide-angle lens  111   b.    
     The second diffusion surface u2 may include a first surface u20 formed at a central portion of the second diffusion surface u2, to extend perpendicularly to a forward direction in the form of a flat surface, and second surfaces u22 having a curved shape while forming a predetermined angle with regard to the first surface u20. 
     The first surface u20 may generate planar light by refracting light reflected by the first diffusion surface u1, whereas the second surfaces u22 may reflect, toward the third diffusion surfaces u3, the light reflected by the first diffusion surface u2. 
     The diffusion range of planar light may be adjusted in accordance with the predetermined angle or curvature of the second surfaces u22. 
     Alternatively, the second diffusion surface u2 or third diffusion surfaces u3 may have a convex shape to reduce the thickness of planar light, namely, to thin planar light. 
     The holding recess u4 may be centrally formed at the surface opposite to the second diffusion surface u2. In this case, the first diffusion surface u1 may be additionally formed at an inner surface of the holding recess u4, in the form of a concave structure. 
     Hereinafter, the path of light in the second wide-angle lens  111   b  will be described. First, light emitted from the light source  112  is refracted by the first diffusion surface u1 of the second wide-angle lens  111   b  while passing through the first diffusion surface u1. The refracted light is then diffused within the second wide-angle lens  111   b.    
     A part of the light diffused within the second wide-angle lens  111   b  is refracted while passing through the second diffusion surface u2 and, as such, may be emitted outwardly of the second wide-angle lens  111   b . This light is referred to as the first planar light L1. 
     When light passes through the second diffusion surface u2, it is refracted at a refraction angle greater than an incidence angle thereof because this case corresponds to the case in which light is incident from a high-density medium upon a low-density medium. In accordance with such refraction, the refracted light is diffused in various directions. 
     A part of the first planar light L1 is refracted two times in that it is incident upon the second wide-angle lens  111   b  while passing through the second diffusion surface u2 of the second wide-angle lens  111   b , and is then emitted outwardly of the second wide-angle lens  111   b  in the form of first planar light L1. In accordance with generation of such first planar light L1, the planar light emission zone of the light emitter  110  is widened. 
     The remaining part of the light diffused into the interior of the second wide-angle lens  111   b  may be reflected by the second diffusion surface u2 toward the interior of the second wide-angle lens  111   b.    
     That is, when light incident upon the second wide-angle lens  111   b  reaches a boundary surface of a material exhibiting a lower index of refraction than the second wide-angle lens  111   b , namely, the second diffusion surface u2, the light may be totally reflected because a total reflection phenomenon occurs at such a surface. 
     For occurrence of such a total reflection phenomenon, it may be necessary for the incidence angle of light to be equal to or greater than a critical angle. For the incidence angle of light equal to or greater than the critical angle, it may be necessary to adjust the index of refraction of the material and the shape of the second wide-angle lens  111   b.    
     Light reflected toward the interior of the second wide-angle lens  111   b  by the second diffusion surface u2 is refracted while passing through the third diffusion surface u3 and, as such, may be emitted outwardly of the second wide-angle lens  111   b . This light is referred to as the second planar light L2. 
     For example, planar light may be diffused in parallel to the floor over a predetermined angle with regard to a forward direction (an x-axis direction) of the second wide-angle lens  111   b.    
     The predetermined angle may be 110° with regard to the forward direction (x-axis direction) of the second wide-angle lens  111   b  in a left or right direction and, as such, planar light may be emitted in a state of being totally diffused over an angle of 220°. Of course, the predetermined angle is not limited to the illustrated angle. 
     Hereinafter, the following description will be given in conjunction with the case in which the sum of angles extending in left and right directions with regard to the forward direction (x-axis direction) of the second wide-angle lens  111   b  is 220°. 
       FIG. 7F  is a view illustrating a third wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 7G  is a view illustrating diffusion of planar light emerging from the third wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment. 
     Referring to  FIGS. 7F and 7G , the third wide-angle lens which is designated by reference numeral “ 111   c ” may include a transparent member allowing light incident from a light source (not shown) thereupon to pass therethrough. The third wide-angle lens  111   c  reflects or refracts light incident from the light source, thereby generating planar light L1 and planar light L2. 
     The third wide-angle lens  111   c  may include a first diffusion surface u1 to refract light incident from the light source so as to diffuse the incident light within the third wide-angle lens  111   c , a second diffusion surface u2 to refract the light refracted by the first diffusion surface u1 outwardly of the third wide-angle lens  111   c  or to reflect the light refracted by the first diffusion surface u1 toward the interior of the third wide-angle lens  111   c , third diffusion surfaces u3 to refract the light refracted by the first diffusion surface u1 or the light reflected by the second diffusion surface u2, to generate planar light, and a holding recess u4 formed at a surface opposite to the second diffusion surface u2, to hold the light source received therein. 
     The third wide-angle lens  111   c  is similar to the second wide-angle lens  111   b , except that the second diffusion surface u2 of the third wide-angle lens  111   c  is formed with wave patterns each having a tapered ridge. By virtue of such wave patterns, the third wide-angle lens  111   c  may achieve a widened diffusion range of planar light. 
       FIG. 8A  is an exploded perspective view illustrating a fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 8B  is a perspective view illustrating the fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 8C  is a view illustrating diffusion of planar light emerging from the fourth wide-angle lens included in the obstacle sensing module in accordance with an exemplary embodiment.  FIG. 8D  is a view illustrating a state in which the fourth wide-angle lens according to an exemplary embodiments installed at the obstacle sensing module. 
     Referring to  FIGS. 8A to 8D , the fourth wide-angle lens which is designated by reference numeral “ 111   d ” may generate planar light by reflecting light emitted from a light source. The light source is designated by reference numeral “ 112 ”. 
     The fourth wide-angle lens  111   d  may include a transparent member allowing light incident from the light source  112  thereupon to pass therethrough. The fourth wide-angle lens  111   d  reflects or refracts light incident from the light source  112 , thereby generating planar light. 
     The fourth wide-angle lens  111   d  may include a first diffusion surface u1 to refract light incident from the light source  112  so as to diffuse the incident light within the fourth wide-angle lens  111   d , a second diffusion surface u2 to reflect the light refracted by the first diffusion surface u1 toward the interior of the fourth wide-angle lens  111   d , a third diffusion surface u3 to refract the light reflected by the second diffusion surface u2 so as to generate planar light, and a holding recess u4 formed at a surface opposite to the second diffusion surface u2, to hold the light source received therein. 
     The second diffusion surface u2 may be formed at one surface of the fourth wide-angle lens  111   d  while having a concave conical shape. 
     The second diffusion surface u2 of the fourth wide-angle lens  111   d  may be a surface of the fourth wide-angle lens  111   d  forming a boundary to a medium having an index of refraction different from that of the fourth wide-angle lens  111   d.    
     For example, the medium may be air having an index of refraction corresponding to “1” or may be a material having a lower index of refraction than that of the fourth wide-angle lens  111   d.    
     The material may be formed to be coupled with the fourth-wide angle lens  111   d.    
     The third diffusion surface u3 may be a side surface of the fourth wide-angle lens  111   d , and may have a convex shape to reflect light reflected by the second diffusion surface u2 so as to further thin planar light. 
     The holding recess u4 may have a central axis aligned with the central axis of the second diffusion surface u2. The holding recess u4 may be centrally formed at a surface opposite to the second diffusion surface u2 in the form of a concave structure. Although the holding recess u4 is illustrated as being formed at the fourth wide-angle lens  111   d , it may be formed to be separate from the fourth wide-angle lens  111   d  so as to be coupled to the fourth wide-angle lens  111   d.    
     Hereinafter, the path of light in the fourth wide-angle lens  111   d  will be described. First, light emitted from the light source  112  is refracted by the first diffusion surface u1 of the fourth wide-angle lens  111   d  while passing through the first diffusion surface u1. The light emerging from the first diffusion surface u1 is then reflected by the second diffusion surface u2, and is then refracted while passing through the third diffusion surface u3 formed at the side surface of the fourth wide-angle lens  111   d . At this time, the light is converted into planar light while passing through the third diffusion surface u3 and, as such, may be irradiated in omni-directions of 360°. 
     Meanwhile, the principle of reflection of light from the second diffusion surface u2 of the fourth wide-angle lens  111   d  is on the basis of the principle of total reflection. 
     That is, when light incident upon the fourth wide-angle lens  111   d  reaches a boundary surface of a material exhibiting a lower index of refraction than the fourth wide-angle lens  111   d , namely, the second diffusion surface u2, the light may be totally reflected because a total reflection phenomenon occurs at the surface. 
     For occurrence of such a total reflection phenomenon, it may be necessary for the incidence angle of light to be equal to or greater than a critical angle. For the incidence angle of light equal to or greater than the critical angle, it may be necessary to adjust the index of refraction of the material and the height and radius of the second diffusion surface u2 which has a conical shape. 
     Snell&#39;s law is applied to the principle of reflection of light at the side surface of the fourth wide-angle lens  111   d.    
     Referring to  FIG. 6D , the light source  112  of the light emitter  110  emits light in a direction perpendicular to the floor. 
     The fourth wide-angle lens  111   d  may diffuse, in omni-directions, planar light generated in accordance with reflection of light emitted from the light source  112 . Such planar light may be irradiated in a direction parallel to the floor or in a direction inclined from the floor. 
     As a result, the obstacle sensing module may sense an obstacle disposed at a higher or lower level than that of an obstacle disposed on the floor. 
     The planar light may be reflected by an obstacle, and the reflected light may be again reflected after being transmitted to the reflection mirror  121 . 
     When reflection light LR again reflected by the reflection mirror  121  is incident upon the optical lens  122 , it is refracted by the optical lens  122  while passing through the optical lens  122 . The light emerging from the optical lens  122  may be transmitted to the optical sensor  123 . 
       FIG. 9A  is a view illustrating a slit capable of adjusting the thickness of planar light when one of the first to third wide-angle lenses is employed, in accordance with an exemplary embodiment.  FIG. 9B  is a view illustrating a slit capable of adjusting the thickness of planar light when the fourth wide-angle lens is employed, in accordance with an exemplary embodiment. 
     Referring to  FIG. 9A , at least one slit  114  having a narrow vertical gap may be arranged in front of the first, second, or third wide-angle lens  111   a ,  111   b , or  111   c . As planar light irradiated from the first, second, or third wide-angle lens  111   a ,  111   b , or  111   c  passes through the slit  114 , thinner planar light parallel to the floor may be formed. It may be possible to generate planar light having a desired thickness by adjusting the size of the gap formed at the slit  114 , namely, “k”. 
     Referring to  FIG. 9B , at least one slit  114  having a narrow vertical gap may be arranged in front of the fourth wide-angle lens  111   d . As planar light irradiated from the fourth wide-angle lens  111   d  passes through the slit  114 , thinner planar light parallel to the floor may be formed. It may be possible to generate planar light having a desired thickness by adjusting the size k of the gap formed at the slit  114 . 
       FIG. 10A  is a view illustrating obstacle sensing results obtained when the size of the slit in the obstacle sensing module is large in accordance with an exemplary embodiment.  FIG. 10B  is a view illustrating obstacle sensing results obtained when the size of the slit in the obstacle sensing module is small in accordance with an exemplary embodiment. 
     Referring to  FIG. 10A , obstacle sensing results of the obstacle sensing module  100  when the size k of the gap of the slit  114  is large. In this case, it may be seen that light emitted from the light emitter  110  is thick. On the other hand, Referring to  FIG. 10B , obstacle sensing results of the obstacle sensing module  100  when the size k of the gap of the slit  114  is small. In this case, it may be seen that light emitted from the light emitter  110  is thin. 
       FIG. 11  is a schematic view illustrating a relation between each constituent element of the obstacle sensing module and an obstacle for obstacle distance calculation according to an exemplary embodiment. 
     The angle formed between incident light and reflection light in the case in which planar light irradiated from the light emitter  110  is reflected from an obstacle, namely, an angle θ i , may be expressed by the following Expression 1: 
     
       
         
           
             
               
                 
                   
                     
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       FIG. 12A  is a plan view of the obstacle sensing module according to an exemplary embodiment and obstacles.  FIG. 12B  is an elevation view of the obstacle sensing module according to an exemplary embodiment and the obstacles.  FIG. 12C  is a view of images received by the image sensor of the obstacle sensing module according to an exemplary embodiment. 
     The following description is applied to each of the cases in which the first to fourth wide-angle lenses  111   a  to  111   d  are employed, respectively. 
     Referring to  FIG. 12A , there are an x-axis extending in a forward direction of the obstacle sensing module  100  while being parallel to the floor, and a y-axis perpendicular to the x-axis. A first zone, which may be sensed by the obstacle sensing module, is present on a plane established by the x-axis and y-axis. 
     The first zone may be similar to a zone defined by an arc AB defined in a circle having a radius R by two radial lines OA and OB respectively extending from a center O of the circle to two points A and B on the circle while having a central angle AOB of θ. In this case, the radius R may be a far distance. 
     When the second wide-angle lens  111   b  is employed, “θ” may be 220°. When the fourth wide-angle lens  111   d  is employed, “θ” may have an increased value. The angle θ is not limited to the above-described value, and may have other values. 
     In the first zone, there are a first obstacle  5  and a second obstacle  6  disposed at positions spaced by different distances and different angles from the origin O, respectively. Obstacles present in the first zone are not limited to the first obstacle  5  and second obstacle  5 . One or more obstacles may be present in the first zone. The following description will be given in conjunction with the case in which there are two obstacles, namely, the first and second obstacles  5  and  6 , in the first zone. 
     The first obstacle  5  is disposed within an angular range extending in a counter-clockwise direction with respect to the x-axis between an angle 1β and an angle 1α while being spaced from the origin O by a distance g1. The second obstacle  6  is disposed within an angular range extending in a clockwise direction with respect to the x-axis between an angle 2α and an angle 2β while being spaced from the origin O by a distance g2. 
     Here, “1α” is an angle between the x-axis and an end point 1a of the first obstacle  5  spaced from the x-axis by a maximum distance, whereas “1β” is an angle between the x-axis and an end point 1b of the first obstacle  5  spaced from the x-axis by a minimum distance. 
     “2α” is an angle between the x-axis and an end point 2a of the second obstacle  5  spaced from the x-axis by a minimum distance, whereas “2β” is an angle between the x-axis and an end point 2b of the second obstacle  5  spaced from the x-axis by a maximum distance. 
     Referring to  FIG. 12B , it may be seen that planar light irradiated from the light emitter  110  travels in the forward direction of the light emitter  110 , and is then transmitted to the light receiver  120  after being reflected by obstacles spaced from the obstacle sensing module  100  by different distances. 
     The following description will be given in conjunction with the case in which the reflection mirror  121  is a conical mirror. 
     When an obstacle is nearer to the obstacle sensing module  100 , reflection light reflected from the obstacle reaches a point nearer to the apex of the reflection mirror  121 . When reflection light reflected from the obstacle reaches a point nearer to the apex of the reflection mirror  121 , reflection light emerging from the optical lens  122  is written in the optical sensor  123  at a location nearer to the center of the optical sensor  123 . 
     That is, when the obstacle is nearer to the obstacle sensing module  100 , reflection light is written in the optical sensor  123  at a location nearer to the center of the optical sensor  123 . 
     Referring to  FIG. 12C , images of the first and second obstacles  5  and  6  written on the optical sensor  123  may be seen. Reflection light reflected from each obstacle after being irradiated from the light emitter  110  is written in the optical sensor  123  in the form of an image after being reflected by the reflection mirror  121  and passing through the optical lens  122 . 
     The first obstacle  5  is written within a angular range extending in a left direction with respect to an x-axis between an angle 1β and an angle 1α while being spaced from an origin O′ by a distance g1′. That is, the first obstacle  5  is written in the optical sensor  123  in the form of a figure similar to an arc  5 ′ defined in a circle having a radius g1′ by two radial lines O′1a′ and O′1b′ respectively extending from a center O′ of the circle to two points 1a′ and 1b′ on the circle. 
     The second obstacle  6  is written within a angular range extending in a right direction with respect to the x-axis between an angle 2a and an angle 2β while being spaced from the origin O′ by a distance g2′. That is, the second obstacle  6  is written in the optical sensor  123  in the form of a figure similar to an arc  6 ′ defined in a circle having a radius g2′ by two radial lines O′2a′ and O′2b′ respectively extending from the center O′ of the circle to two points 2a′ and 2b′ on the circle. 
     Electrical image signals converted by the optical sensor  123  are converted into digital image signals by the image processing circuit  124 . The digital image signals are transmitted to the obstacle sensing controller (not shown) or control unit (not shown). 
     The obstacle sensing controller or control unit analyzes images, based on the digital image signals, into which the images have been converted, to determine distances from the obstacle sensing module  100  to respective obstacles  5  and  6 , and positions of the obstacles  5  and  6 . 
       FIG. 13A  is a plan view of a plurality of light emitters which are included in the obstacle sensing module while being installed at positions having different levels in accordance with an exemplary embodiment, and an obstacle.  FIG. 13B  is an elevation view of the light emitters which are included in the obstacle sensing module while being installed at positions having different levels in accordance with an exemplary embodiment, and the obstacle.  FIG. 13C  is a view of planar light received by the image sensor in the form of an image after being irradiated from each of the plural light emitters included in the obstacle sensing module while being installed at different levels and reflected by the obstacle in accordance with an exemplary embodiment. 
     The following description is applied to each of the cases in which the first to fourth wide-angle lenses  111   a  to  111   d  are employed, respectively. 
     Referring to  FIG. 13A , there is a first zone as described with reference to  FIG. 10A . An obstacle  2  is present in the first zone. One or more obstacles may be present in the first zone. The following description will be given in conjunction with the case in which there is one obstacle in the first zone. 
     The obstacle sensing module (not shown) includes three light emitters  110   a ,  110   b , and  110   c , and one light receiver  120 . The three light emitters  110   a ,  110   b , and  110   c  irradiate planar light at different levels from the floor, respectively. Planar light irradiated from each of the three light emitters  110   a ,  110   b , and  110   c  may rectilinearly travel in parallel to the floor or may rectilinearly travel while being inclined from the floor. The three light emitters  110   a ,  110   b , and  110   c  may be disposed at the same position on the cleaning robot  1 , or may be disposed at different positions on the cleaning robot  1 , respectively. 
     For example, the light emitters  110   a ,  110   b , and  110   c  illustrated in  FIG. 13A  are disposed at the same position on the cleaning robot  1 , and irradiate planar light at different levels from the floor, respectively. 
     Of course, the number of light emitters  110  is not limited to the above-described number. The number of light emitters  110  may be one or more. In addition, there is no limitation on the positions of the plural light emitters  110   a ,  110   b , and  110   c  on the cleaning robot  1 . 
     The light receiver  120  may receive reflection light beams respectively reflected from the obstacle  2  after being irradiated from the plural light emitters  110   a ,  110   b , and  110   c  in a simultaneous manner or in a sequential manner. 
     Referring to  FIG. 13B , it may be seen that planar light irradiated from each of the three light emitters  110   a ,  110   b , and  110   c  travels rectilinearly in a forward direction of the corresponding  110   a ,  110   b , or  110   c , and is then transmitted to the light receiver  120  after being reflected by the obstacle  2 . 
     The following description will be given in conjunction with the case in which the reflection mirror  121  is a conical mirror. 
     When the level, at which planar light is reflected from the obstacle  2 , is nearer to the floor, the reflection light reflected from the obstacle  2  reaches a point nearer to the apex of the reflection mirror  121 . When reflection light reflected from the obstacle  1  reaches a point nearer to the apex of the reflection mirror  121 , reflection light emerging from the optical lens  122  is written in the optical sensor  123  at a location nearer to the center of the optical sensor  123 . That is, when the level, at which planar light is reflected from an obstacle, is nearer to the floor, reflection light is written in the optical sensor  123  at a location nearer to the center of the optical sensor  123 . 
     Referring to  FIG. 13C , images of the obstacle  2  written on the optical sensor  123  may be seen. Reflection light reflected from the obstacle  2  after being irradiated from each of the light emitters  110   a ,  110   b , and  110   c  is written in the optical sensor  123  in the form of an image after being reflected by the reflection mirror  121  and passing through the optical lens  122 . 
     When there is a plurality of light emitters, for example, the light emitters  110   a ,  110   b , and  110   c , one of the light emitters  110   a ,  110   b , and  110   c  may be set as a reference light emitter. The reference light emitter may set the distance between the obstacle sensing module  100  and the obstacle. The following description will be given in conjunction with the case in which the second light emitter  110   b  is set as the reference light emitter. 
     Planar light irradiated from the second light emitter  110   b  is reflected at a level  2   e  of the obstacle  2 . Based on the planar light irradiated from the second light emitter  110   b , the obstacle  2  is written within a angular range extending in a counter-clockwise direction with respect to an x-axis between an angle 1β and an angle 1α while being spaced from an origin O′ by a distance g1′. That is, the obstacle  2  is written in the optical sensor  123  in the form of a figure similar to an arc  2 ′ defined in a circle having a radius g1′ by two radial lines O′1a′ and O′1b′ respectively extending from a center O′ of the circle to two points 1a′ and 1b′ on the circle. 
     Planar light irradiated from the first light emitter  110   a  is reflected at a level  1   e  of the obstacle  2 . Planar light irradiated from the first light emitter  110   a  is written in the optical sensor  123  at a location spaced from the center O′ by a greater distance than the distance g1′ in the form of a figure similar to an arc  4 ′. 
     Planar light irradiated from the third light emitter  110   c  is reflected at a level  3   e  of the obstacle  2 . Planar light irradiated from the third light emitter  110   c  is written in the optical sensor  123  at a location spaced from the center O′ by a smaller distance than the distance g1′ in the form of a figure similar to an arc  3 ′. 
     Electrical image signals converted by the optical sensor  123  are converted into digital image signals by the image processing circuit  124 . The digital image signals are transmitted to the obstacle sensing controller (not shown) or control unit (not shown). 
     The obstacle sensing controller or control unit analyzes images, based on the digital image signals, into which the images have been converted, to determine the distance between the obstacle sensing module  100  and the obstacle, the position of the obstacle, the height of the obstacle, and the shape of the obstacle. 
     The obstacle sensing controller or control unit may determine the height of the obstacle  2 , based on the three arcs  2 ′,  3 ′, and  4 ′ written in the optical sensor  123 , and the levels  1   e ,  2   e , and  3   e  of the three light emitters  110   a ,  110   b , and  110   c  installed in the obstacle sensing module  100 . 
       FIG. 14  is a plan view of a plurality of light emitters which are included in the obstacle sensing module while being installed at different positions in accordance with an exemplary embodiment, and an obstacle. 
     Referring to  FIG. 14 , a plurality of light emitters, for example, light emitters  110   a ,  110   b , and  110   c , may be installed at different positions on the cleaning robot  1 . 
     For example, the second light emitter  110   b  and the light receiver  120  may be installed at the same position at the front side of the cleaning robot  1 . The first light emitter  110   a  may be installed at a left side of the second light emitter  110   b , whereas the third light emitter  110   c  may be installed at a right side of the second light emitter  110   b.    
     The obstacle sensing controller (not shown) or the control unit (not shown) may determine the distance between the obstacle sensing module (not shown) and the obstacle, the position of the obstacle, the height of the obstacle, and the shape of the obstacle in a similar manner to that of the above-described case in which the plural light emitters  110   a ,  110   b , and  110   c , are installed at the same position. 
     When the plural light emitters  110   a ,  110   b , and  110   c  are installed at different positions, the sensing zone of the obstacle sensing module  100  may be widened. 
       FIG. 15A  is an elevation view illustrating an arrangement in which the second wide-angle lens is vertically arranged to allow the obstacle sensing module to sense a fall point in accordance with an exemplary embodiment.  FIG. 15B  is an elevation view illustrating an arrangement in which the fourth wide-angle lens is vertically arranged to allow the obstacle sensing module to sense a fall point in accordance with an exemplary embodiment. 
     Referring to  FIG. 15A , the second wide-angle lens  110   b  is vertically arranged. For example, the second wide-angle lens  110   b  is vertically elongated from the floor. In accordance with such an arrangement, planar light irradiated from the second wide-angle lens  110   b  is emitted in a forward direction in an x-z plane. 
     The light emitter  110  may be equipped with a slit (not shown). The slit may enable irradiation of thin planar light. 
     Referring to  FIG. 15B , the fourth wide-angle lens  110   d  is vertically arranged. For example, the fourth wide-angle lens  110   d  extends vertically from the floor. In accordance with such an arrangement, planar light irradiated from the fourth wide-angle lens  110   d  is emitted in an x-z plane. 
     The light emitter  110  may be equipped with a slit (not shown). The slit may enable irradiation of thin planar light. 
       FIG. 16A  is a view of a state in which the obstacle sensing module irradiates planar light when there is no fall point in accordance with an exemplary embodiment.  FIG. 16B  is a view illustrating an image of planar light received by the image sensor after being reflected from the floor when there is no fall point in accordance with an exemplary embodiment. 
     Referring to  FIG. 16A , the obstacle sensing module  100  of the cleaning robot  1  is installed within the cleaning robot  1 . In order to determine a fall point, the obstacle sensing module  100  may include one of the first to fourth wide-angle lenses (not shown). The wide-angle lens is vertically inclined. 
     Of course, the obstacle sensing module  100  is not limited to the above-described configuration. The obstacle sensing module  100  may have various configurations, so long as it emits light in a forward direction in an x-z plane. 
     Planar light irradiated from the obstacle sensing module  100  may advance toward the floor in a forward direction of the obstacle sensing module  100 . The floor is designated by reference numeral “ 9 ”. Planar light irradiated from the obstacle sensing module  100  may reach a region on the floor  9  between a point P disposed near the front side of the cleaning robot  1  and a point Q disposed far from the front side of the cleaning robot  1 . In this case, the light reaching region of the floor  9  in front of the obstacle sensing module  100  may be a region extending in a forward direction while having a line shape. 
     Planar light advancing toward the floor  9  is reflected from the floor  9 , and is then transmitted to the obstacle sensing module  100 . 
       FIG. 16B  illustrates an image of reflection light reflected from the floor  9  and written in the optical sensor  123 . Since light is emitted from the light emitter (not shown) in a forward direction in the x-z plane, reflection light is written in the optical sensor  123  in the form of a line extending in a direction far from a center O′. 
     Here, the near point P′ means a floor point P disposed just in front of the cleaning robot (not shown), whereas the fart point Q′ means a farthest floor point Q which may be sensed by the cleaning robot (not shown). 
     The obstacle sensing controller or control unit analyzes images, based on the digital image signals, into which the images have been converted, to determine whether there is a fall point in front of the obstacle sensing module  100 . From the images written in the optical sensor  123 , the obstacle sensing controller or control unit recognizes reflection light continuously reflected between a nearest point and a farthest point in front of the obstacle sensing module  100 , to determine whether there is a fall point. 
     For example, the obstacle sensing controller or control unit may recognize that there is reflection light continuously reflected between the near point P′ and the far point Q′ in front of the cleaning robot, based on images written in the image sensor. In addition, the obstacle sensing controller or control unit may determine the distance from the cleaning robot to the farthest point Q, and may determine that there is no fall point in a floor region extending to the farthest point Q. 
       FIG. 17A  is a view of a state in which the obstacle sensing module irradiates planar light when there is a fall point in accordance with an exemplary embodiment.  FIG. 17B  is a view illustrating an image of planar light received by the image sensor after being reflected from the floor when there is a fall point in accordance with an exemplary embodiment. 
     Referring to  FIG. 17A , the obstacle sensing module  100  of the cleaning robot  1  is installed within the cleaning robot  1 . In order to determine a fall point, the obstacle sensing module  100  may include one of the first to fourth wide-angle lenses (not shown). The wide-angle lens is vertically inclined. Of course, the obstacle sensing module  100  is not limited to the above-described configuration. The obstacle sensing module  100  may have various configurations, so long as it emits light in a forward direction in an x-z plane. 
     Planar light irradiated from the obstacle sensing module  100  may advance toward the floor in a forward direction of the obstacle sensing module  100 . The floor is designated by reference numeral “ 9 ”. Planar light irradiated from the obstacle sensing module  100  may reach a region on the floor  9  between a point P disposed near the front side of the cleaning robot  1  and a fall point S disposed far from the front side of the cleaning robot  1 . In this case, the light reaching region of the floor  9  in front of the obstacle sensing module  100  may be a region extending in a forward direction while having a line shape. 
     Planar light advancing toward the floor  9  is reflected from the floor  9 , and is then transmitted to the obstacle sensing module  100 . 
       FIG. 17B  illustrates an image of reflection light reflected from the floor  9  and written in the optical sensor  123 . Since light is emitted from the light emitter (not shown) in a forward direction in the x-z plane, reflection light is written in the optical sensor  123  in the form of a line extending in a direction far from a center O′. 
     Referring to  FIG. 17B , the image written in the optical sensor  123  may have a line shape extending between points P′ and S′. Here, the point P′ refers to a nearest point P of the floor  9  disposed in front of the cleaning robot (not shown), whereas the point S′ refers to a fall point S disposed in front of the cleaning robot (not shown). 
     The obstacle sensing controller or control unit analyzes images, based on the digital image signals, into which the images have been converted, to determine whether there is a fall point in front of the obstacle sensing module  100 . 
     From the images written in the optical sensor  123 , the obstacle sensing controller or control unit recognizes reflection light continuously reflected between a nearest point and a farthest point in front of the obstacle sensing module  100 , to determine whether there is a fall point. 
     For example, the obstacle sensing controller or control unit may recognize that there is reflection light continuously reflected between the near point P′ and the fart point S′ in front of the cleaning robot, based on images written in the image sensor. In addition, the obstacle sensing controller or control unit may determine the distance from the cleaning robot to the far point S, and may determine that there is a fall point at the far point S. 
     In addition, the obstacle sensing controller or control unit may calculate the distance between the cleaning robot (not shown) and the fall point. 
     As apparent from the above description, it may be possible to generate uniform planar light, using an obstacle sensing module according to an exemplary embodiment, and thus to achieve an enhancement in obstacle sensing accuracy. Using planar light, it may be possible to sense obstacles present around the obstacle sensing module. Accordingly, it may be unnecessary to mount a plurality of sensors or a separate servo mechanism. In this regard, enhanced efficiency in terms of economy and structure may be achieved. 
     The cleaning robot, which is equipped with the obstacle sensing module, may accurately sense obstacles present therearound and, as such, may efficiently travel. 
     The cleaning robot, which is equipped with the obstacle sensing module, may efficiently control the obstacle sensing module in accordance with the state of the cleaning robot. 
     Although a few exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.