Patent Publication Number: US-2022221574-A1

Title: Camera and radar sensor system and error compensation method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Applications of No. 10-2021-0003243, filed on Jan. 11, 2021 and No. 10-2021-0055139, filed on Apr. 28, 2021 and the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The techniques set forth herein are related to a camera and radar sensor system and an error compensation method thereof. 
     2. Discussion of Related Art 
     Fatality rates of collision accidents occurring during high-speed driving of vehicles are high and such an accident may cause a chain collision accident leading to a big accident. Generally, forward collision accidents occur due to a failure to keep a sufficient distance between vehicles to avoid collision due to drivers&#39; carelessness or difficulties in securing a field of view that is caused by bad weather. In particular, a driver&#39;s limited visual ability and a response delay time required to recognize and decide a dangerous situation have a great influence on a chain collision accident of vehicles moving at high speeds. 
     Recently, technologies for fixing such a problem and providing safe driving conditions are being studied. 
     SUMMARY OF THE INVENTION 
     Driver warning devices of the related art include sensors divided and installed in various parts of a vehicle and a controller installed in an engine room. Therefore, when the sensors are installed, brackets for fixing the sensors for transmitting signals to the controller, a power cable for supplying power to the sensors, and a communication cable for providing a detected signal to the controller are needed. These factors may be largely influenced by electromagnetic waves generated in the engine room and electromagnetic waves introduced from the outside, and thus a serious error may occur in data transmission. 
     One of aspects of embodiments set forth herein is for solving the above-described problem of the related art. That is, embodiments are directed to providing a sensor system capable of minimizing external influences and generating fewer errors. 
     Embodiments are also directed to providing a sensor system capable of combining one of camera modules having different field-of-view (FOV) angles and/or different resolutions and one of radar modules of different detection ranges according to a user&#39;s selection. 
     An embodiment provides a camera and radar sensor system including a camera module and a radar module, wherein the camera module and the radar module are separately and detachably housed, and the camera and radar sensor system is mounted in a cabin of a vehicle. 
     The camera and radar sensor system of the embodiment is applicable to devices such as a driver warning device and an autonomous emergency braking (AEB) system. 
     According to an aspect of the embodiment, a data transceiving connector may be provided at positions corresponding to a camera housing for housing the camera module and a radar housing for housing the radar housing. 
     According to an aspect of the embodiment, the radar module may include a radar processor configured to calculate a position and movement information of an object from radio waves reflected from the object, the camera module may include a camera processor configured to calculate the position and movement information of the object from a captured image, and the camera processor may receive the position and movement information of the object that are calculated by the radar processor, and create and output a driver warning with respect to the object. 
     According to an aspect of the embodiment, the sensor system may be mounted on a windshield of the vehicle. 
     According to an aspect of the embodiment, the camera module may be one of a first camera module and a second camera module with different field-of-view (FOV) angles, and the radar module may be one of a first radar module and a second radar module with different detection ranges. 
     According to an aspect of the embodiment, the detection range of the first radar module may be less than 100 nm, and the detection range of the second radar module may be 100 nm or more. 
     According to an aspect of the embodiment, the first radar module may use radio waves of 79 GHz, and the second radar module may use radio waves of 77 GHz. 
     According to an aspect of the embodiment, the first radar module may be one of two-dimensional (2D) radar, three-dimensional (3D) radar, and four-dimensional (4D) radar, and the second radar module may be another one of the 2D radar, the 3D radar, and the 4D radar. 
     According to an aspect of the embodiment, the FOV angle of the first camera module may be less than 60 degrees, and the FOV angle of the second camera module may be 60 degrees or more. 
     According to an aspect of the embodiment, the first camera module may have a resolution of less than FHD (1920×1080), and the second camera module may have a resolution of FHD (1920×1080) or more. 
     According to an aspect of the embodiment, the radar module may include a transmitter configured to transmit radio waves, a receiver configured to receive radio waves reflected from an object, and a radar processor configured to control the transmitter to transmit the radio waves, and calculate at least one of a distance to the object and a speed of the object from the reflected radio waves. 
     According to an aspect of the embodiment, the radar module may further include a radar interface configured to output formed object information to at least one of an external warning device and the camera module. 
     According to an aspect of the embodiment, the camera module may include an imaging unit configured to capture an image of a moving direction of the vehicle, a camera processor configured to calculate whether there is an object, a speed of the object, and a distance to the object from the image captured by the imaging unit, and a camera interface configured to output information about whether there is an object, the speed of the object, and the distance to the object that are calculated by the camera processor. 
     An embodiment provides an error compensation method of a camera module and a radar module, the error compensation method including: (a) calculating the sum of an angle of deviation of a center axis of the camera module and an angle of deviation of a center axis of the radar module after assembling the camera module and the radar module, (b) calculating an angle of deviation of one of the camera module and the radar module after mounting the camera module and the radar module in a vehicle, and (c) calculating an angle of deviation of the other camera module or radar module by subtracting the angle of deviation of the one of the camera module and the radar module from the sum of the angles of deviation. 
     According to an aspect of the embodiment, (a) may include (a1) forming a reference center axis connecting a center of an integrated target, which includes a camera target of a camera module and a radar target of a radar module, and a center of an assembly of the camera module and the radar module, and (a2) calculating an angle between a camera center axis viewed from the camera module and a radar center axis viewed from the radar module. 
     According to an aspect of the embodiment, (b) may include (b1) calculating an ideal angle from distances between central points on the camera module and the radar module and centers of a camera target and a radar target and distances from the central points on the camera module and the radar module to the camera module or the radar module, (b2) calculating an angle of a center axis that is beyond the ideal angle when viewed from one of the camera module and the radar module, and (b3) calculating a difference between the ideal angle and an angle formed by a center axis viewed from one of the camera module and the radar module to calculate an angle of deviation of the one of the camera module and the radar module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing an overview of a sensor system according to an embodiment; 
         FIG. 2A  is a front view of a camera module, and  FIG. 2B  is a side view of the camera module; 
         FIG. 3  is a diagram showing an overview of a radar module; 
         FIG. 4  is a block diagram of a state in which the camera module and the radar module are combined with each other; 
         FIG. 5  is a flowchart of an overview of an error compensation method according to an embodiment; 
         FIG. 6  is a diagram illustrating an overview of calculating an offset angle between a center axis of the camera module and a center axis of the radar module; 
         FIG. 7A  is a diagram illustrating a case in which both a measured angle of deviation θc 1  and an angle of deviation θ r1  are values with a positive sign, and  FIG. 7B  is a diagram illustrating a case in which both the measured angle of deviation θc 1  and the angle of deviation θ r1  are values with opposite signs; 
         FIG. 8  is a diagram illustrating a case in which a deviation corresponding to an angle of installation occurs to both a center axis of the camera module and a center axis of the radar module when the camera module and the radar module are installed; and 
         FIGS. 9 and 10  are diagrams for describing an error compensation process. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a sensor system  10  according to the present embodiment will be described with reference to the accompanying drawings.  FIG. 1  is a perspective view showing an overview of a sensor system  10  according to an embodiment.  FIG. 2A  is a diagram illustrating one side of a camera module  100 .  FIG. 2B  is a diagram illustrating another side of the camera module  100 .  FIG. 3  is a diagram illustrating one side of a radar module  200 . 
     Referring to  FIGS. 1 to 3 , the sensor system  10  according to the present embodiment includes the camera module  100  and the radar module  200 . The camera module  100  is housed in a camera housing H 1 , and the radar module  200  is housed in a radar housing H 2  different than the camera housing H 1 . The camera module  100  and the radar module  200 , which are housed separately from each other, may be combined with each other to form the sensor system  10 . 
     An imaging unit  110  of the camera module  100  captures an image of a moving direction of a vehicle and provides the captured image to a camera processor  120  (see  FIG. 4 ). In the radar module  200 , a radar transmitter  210  (see  FIG. 4 ) transmits radio waves through a radio wave transceiving surface  240  facing the moving direction of the vehicle, and a receiver  220  (see  FIG. 4 ) receives radio waves reflected from an object. 
     In embodiments illustrated in  FIGS. 2B and 3 , a coupling member Il is located on a side surface of the camera module  100 , and a coupling member  12  is located on a side surface of the radar module  200  corresponding to the side surface of the camera module  100 . In the illustrated embodiments, the coupling member  12  of the radar module  200  is a protruding portion, and the coupling member It of the camera module  100  is an insertion portion into which the protruding portion is inserted. According to an embodiment not shown herein, a coupling member of a radar module is an insertion portion and a coupling member of a camera module is a protruding portion inserted into the insertion portion. 
     A connector  260  is provided on the protruding portion  12  of the radar module  200  to provide position and moving information of an object calculated by the radar module  200  to the camera module  100  or receive position and moving information of the object from the camera module  100 . Similarly, a connector (not shown) is located on the insertion portion of the camera module  100  to transmit or receive data, when connected to the connector  260 . As described below, object information, including a distance to an object, the size of the object, and speed information, which is formed by the radar module  200 , may be provided to the camera module  100  or an external warning device (not shown) through a radar interface  250 . 
     As another example, when a radar module and a camera module are combined with each other, camera module image processing information such as lane information may be provided to the radar module through a camera interface. Radar-camera data fusion may be implemented using a module coupling structure. 
     In an embodiment not shown herein, a radar interface and a camera interface transmit and receive information using a wireless communication protocol such as Bluetooth, ZigBee, or Wi-Fi. 
     Holes may be formed in the radar housing H 2  of the radar module  200 . Heat generated in a transmitter, a receiver, a radar interface, and a radar processor which are inner components may be dissipated through the holes. 
     Referring to  FIGS. 1 and 2A , the camera module  100  may include an imaging unit  110  configured to capture an image of an object and provide the image to the camera processor  120  (see  FIG. 4 ), and a hinge structure  170  provided on the camera housing H. In an embodiment, the camera module  100  further includes a lens hood that blocks stray light, which is generated when sunlight is reflected from a dashboard of a vehicle or a surface of the road, from coming into the imaging unit  110 . The lens hood prevents the quality of a captured image from deteriorating due to stray light coming into the imaging unit  110 . 
     In an embodiment, a side surface A of the hinge structure  170  may be a mounting surface A attached to a windshield of the vehicle. On the mounting surface A, an adhesive such as adhesive tape may be provided, and a suction plate formed of a material such as rubber may be provided although not shown. Thus, the radar module  200  may be fixed on the camera module  100  to be mounted in the vehicle at the same angle as the camera module  100  with respect to the windshield. 
     In the embodiments of  FIGS. 1 and 2A , the hinge structure  170  is illustrated as being provided on the camera module  100 , but in an embodiment not shown here, a hinge structure may be provided on a radar module and a camera module may be fixed on the radar module and mounted in a vehicle. 
       FIG. 4  is a block diagram illustrating a state in which the camera module  100  and the radar module  200  are combined with each other. Referring to  FIG. 4 , the radar module  200  includes a transmitter  210  configured to transmit radio waves under control of a radar processor  230 , a receiver  220  configured to receive radio waves reflected from an object (not shown), the radar processor  230  configured to control the transmitter  210 , form object information by calculating at least one of a distance to an object, the size of the object, and a speed of the object from the reflected radio waves, and a radar interface  250  configured to output the object information. In an embodiment, the radar interface  250  may receive object information detected by the camera module  100  and provide the object information to the radar processor  230 . 
     The radar module  200  may be classified as a first radar module or a second radar module according to a wavelength band of radio waves transmitted from the transmitter  210 . For example, the first radar module may transmit radio waves of 79 GHz band to detect an object within a short distance of less than 100 m. The second radar module may transmit radio waves of 77 GHz band to detect an object within a middle or long distance of  100  m or more. A user may select a radar module according to object detection characteristics of the first and second radar modules and his or her intention and use the selected radar module in combination with the camera module  100 . 
     As another example, the first radar module may be one of a two-dimensional (2D) radar for detecting an object on a plane, a three-dimensional (3D) radar for detecting an object in a space, and a four-dimensional (4D) radar for detecting not only an object but also a speed of the object, and the second radar module may be another one of the 2D, the 3D, and the 4D radar. 
     The radar processor  230  forms object information, including a distance to an object, a position of the object, the size of the object, a speed of the object, etc., from radio waves received by the receiver  220 . As described above, the radar processor  230  detects at least one of a plane including an object, a space, and the speed of the object in the space, and forms object information about a result of the detection. 
     The radar interface  250  receives the object information formed by the radar processor  230 . In an embodiment, the radar interface  250  may provide the object information to the camera interface  130  through the connector  260 . In another embodiment, the radar interface  250  receives object information, which is formed by the camera processor  120 , through the camera interface  130 . 
     The radar interface  250  may provide object information formed by the radar processor  230  to the camera interface  130  using a wireless communication protocol such as Bluetooth, ZigBee or Wi-Fi, and the camera interface  130  may provide an object interface formed by the camera processor  120  to the radar interface  250  using a wireless communication protocol such as Bluetooth, ZigBee or Wi-Fi. 
     In another embodiment, the radar module  200  may be used as standalone. When the radar module  200  is used as standalone, the radar interface  250  may transmit object information to or receive object information from an external warning device  300 . The object information may be transmitted and received through wired communication using the connector  260  illustrated in  FIG. 3  or a separate connector (not shown). As another example, the radar interface  250  and the external warning device  300  may transmit and receive object information using the wireless communication protocol described above. 
     The camera module  100  includes the imaging unit  110  configured to form an image, the camera processor  120  configured to form object information by calculating as to whether there is an object, a speed of the object, and a distance to the object from an image captured by the imaging unit  110 , and the camera interface unit  130  configured to output the object information, including whether there is an object, the speed of the object, and the distance to the object, calculated by the camera processor  120 . 
     In an embodiment, the imaging unit  110  may include at least one of a CMOS image sensor and a CCD sensor. The imaging unit  110  may include a lens unit (not shown) for performing optical processing such as concentrating light and/or spreading light into a spectrum. The imaging unit  110  photographs a moving direction of a vehicle, forms an image consisting of several frames per unit time, and provides the image to the camera processor  120 . 
     The camera module  100  may be classified as a first camera module or a second camera module according to a field-of-view (FOV) angle at which photographing of the imaging unit  110  is performed. For example, the first camera module may be a narrow-angle camera module with an FOV angle of less than 60 degrees and may be capable of capturing an image of an object located remotely from the camera module  100 . The second camera module may be a wide-angle camera module with an FOV angle of 60 degrees or more and may be capable of capturing an image of an object located within a shorter distance than the first camera module. As another example, the first camera module and the second camera module may form images of different resolutions. For example, the first camera module may have a resolution of less than FHD (1920×1080), and the second camera module may have a resolution of greater than or equal to FHD (1920×1080). 
     A user may select a camera module according to object detection characteristics of the first and second camera modules and his or her intention and use the selected camera module in combination with the radar module  200 . 
     The camera processor  120  may receive object information provided by the radar module  200  from the camera interface  130  and form object information by adding thereto information about whether there is an object, a speed of the object, a distance to the object, and the like from images captured and provided by the imaging unit  110 . In another embodiment, the camera processor  120  may receive object information provided by the camera module  100  from the camera interface  130  and form object information by adding thereto object information about whether there is an object, a speed of the object, a distance to the object, and the like from radio waves received by the receiver  220 . 
     For example, the radar module  200  may be superior to the camera module  100  in terms of object detection characteristics in a bad weather environment, e.g., fog, heavy snowfall, or heavy rain, when there is no illumination, and the camera module  100  may be superior to the radar module  200  in terms of object recognition and traverse position detection for detecting whether an object is currently driving in a current lane or is driving in an adjacent lane. Accordingly, the camera module  100  may use both object information generated from an image provided by the imaging unit  110  and object information provided by the radar module  200  to achieve a higher level of object detection and recognition characteristics than when the camera module  100  is used alone. For example, even when a calculated distance to an object decreases sharply in a bad weather environment, a user may be provided with a warning about collision to prevent collision. 
     Object information formed by the camera processor  120  is provided to the camera interface  130 . The camera interface  130  may provide the object information to the external warning device  300 , and the external warning device  300  may provide a user with a warning on the basis of the object information provided. For example, the camera interface  130  and the external warning device  300  transmit and receive object information through wired communication using a separate connector (not shown) and/or a wireless communication protocol such as Bluetooth, ZigBee, or Wi-Fi. 
     Object information formed by the radar processor  230  is provided to the radar interface  250 . The radar interface  250  may provide the object information to the external warning device  300 , and the external warning device  300  may provide a user with a warning on the basis of the object information. For example, the radar interface  250  and the external warning device  300  transmit and receive object information through wired communication using a separate connector (not shown) and/or a wireless communication protocol such as Bluetooth, ZigBee, or Wi-Fi. 
     In an embodiment not shown here, the camera module  100  and/or the radar module  200  may be used as standalone. When the camera module  100  and the radar module  200  are used as standalone, the camera interface  130  and the radar interface  250  may transmit object information to or receive object information from the external warning device  300 . The object information may be transmitted and received through wired communication using a separate connector (not shown). As another example, the camera interface  130  and the external warning device  300  and/or the radar interface  250  and the external warning device  300  may transmit and receive object information using the wireless communication protocol described above. 
     The external warning device  300  (see  FIG. 4 ) may be a device that displays a warning to a driver of a vehicle according to a position and movement information of an object and may be a light-emitting device, a display device, a speaker that provides an audio warning to the user and the like. 
     A collision warning signal formed by the camera processor  120  is provided to the camera interface  130 . The camera interface  130  performs interfacing with the camera processor  120  and a warning device (not shown), which includes a light-emitting device and a display, to allow the warning device to provide a user with a warning according to a signal output from the camera processor  120 . 
     In the embodiments of  FIGS. 1 and 4 , a case in which the camera module  100  and the radar module  200  are operated while being combined with each other is illustrated. However, as described above, each of a camera module and a radar module may be operated as standalone to provide the external warning device  300  with object information formed by detecting an object so that a user may be provided with a warning. 
     According to the present embodiment, the camera module  100  and the radar module  200  may be separated from each other, and an object may be more exactly detected using different advantages of the camera module  100  and the radar module  200 . Furthermore, effects on a module due to noise generated in another module may be reduced. 
     An error compensation method of the camera module  100  and the radar module  200  of the present embodiment will be described with reference to  FIGS. 5 to 10  below.  FIG. 5  is a flowchart of an overview of an error compensation method according to a present embodiment. Referring to  FIG. 5 , the error compensation method according to the present embodiment includes (a) measuring an assembly error angle between a center axis of a camera module and a center axis of a radar module after the assembly of the camera module and the radar module (S 100 ), (b) measuring a mounting error angle of one of the camera module and the radar module after mounting the camera module and the radar module in the vehicle (S 200 ), and (c) compensating for a mounting error angle of the other camera or radar module on the basis of the assembly error angle and the mounting error angle of the one of the camera module and the radar module (S 300 ). 
       FIG. 6  is a diagram for describing measuring an assembly error angle between a central axis Ac of the camera module  100  and a center axis Ar of the radar module  200  (S 100 ). Referring to  FIG. 6 , a radar assembly error angle θ r1  between a center axis Ar of the radar module  200  and an ideal center axis ref_r of the radar module  200  and a radar assembly error angle θc 1  between a center axis Ac of the camera module  100  and an ideal center axis ref_c of the camera module  100  are measured. 
     Targets T include a camera target Tc and a radar target Tr. A distance between a center of the camera target Tc and a center of the radar target Tr is the same as a distance between a center of the camera module  100  and a center of the radar module  200 . Therefore, when a midpoint in the distance between the center of the camera target Tc and the center of the radar target Tr and a midpoint in the distance between the center of the camera module  100  and the center of the radar module  200  are connected, a reference axis ref between a target T and the sensor system  10  is formed. 
     When the reference axis ref is parallel translated to pass through the center of the radar module  200 , a radar reference axis ref_r is formed, and when the reference axis ref is parallel translated to pass through the center of the camera module  100 , a camera reference axis ref_c is formed. The camera reference axis ref_c refers to a center axis of a camera field of view when the camera module  100  is assembled with a housing H 1  without an error. Likewise, the radar reference axis ref_f refers to a center axis of a radar field of view when the radar module  200  is assembled with a housing H 2  without an error. 
     Although the camera module  100  and the radar module  200  are manufactured and assembled through precision processes, an actual center axis Ac of the camera module  100  may not coincide with the camera reference axis ref_c and an actual axis Ar of the radar module  200  may not coincide with the radar reference axis ref_r due to an assembly process error or electrical causes such as a signal mismatch as shown in  FIG. 6 . 
     A radar assembly error angle θ r1  between the radar reference axis ref_r and the actual center axis Ar of the radar module  200  and a camera assembly error angle θc 1  between the camera reference axis ref_c and the actual center axis Ac of the camera module  100  are measured. 
     An angle is measured with respect to a reference axis. In the embodiment illustrated herein, an angle of deviation θc 1  between the camera reference axis ref_c and the actual center axis Ac of the camera module  100  may have a positive value, and an angle of deviation θ r1  between the radar reference axis ref_r and the actual center axis Ar of the radar module  200  may have a negative value. In an embodiment, an offset angle Oo between the measured camera assembly error θc 1  and the radar assembly error angle θ r1  is calculated. 
       FIG. 7  is a diagram illustrating calculating an offset angle Oo according to an embodiment. As shown in  FIGS. 7A and 7B , the offset angle Oo corresponds to an angle between an actual center axis Ac of the camera module  100  and an actual center axis Ar of the radar module  200  when the actual center axis Ac of the camera module  100  and the actual center axis Ar of the radar module  200  are aligned with respect to a reference axis ref.  FIG. 7A  illustrates a case in which both a measured camera assembly error angle θc 1  and a measured radar assembly error angle θ r1  are values with a positive sign, and the offset angle Oo may be calculated to be an absolute value of the difference between the camera assembly error angle θc 1  and the radar assembly error angle θr 1 . 
       FIG. 7B  illustrates a case in which the measured camera assembly error angle θc 1  and the measured radar assembly error angle θ r1  are values with different signs. 
     An offset angle θo formed by the camera assembly error angle Oc  1  and the radar assembly error angle θ r1  with different signs is as shown in  FIG. 7B  and may be calculated to be an absolute value of the difference between these angles. 
     The offset angle θo formed by the radar assembly error angle θ r1  and the camera assembly error angle θc 1  may be calculated by {circle around (1)} of Equation 1 below, and the radar assembly error angle θr 1 , and the camera assembly error angle θc 1 , and the offset angle θo, which are obtained during an assembly process, may be stored and used to compensate for an axis after a mounting process. 
       [Equation 1] 
       θ o=|θc−θr|   {circle around (1)}
 
       FIG. 8  is a diagram illustrating a case in which a variation corresponding to an angle of installation occurs to both a center axis of a camera module and a center axis of a radar module when the camera module and the radar module are installed. Referring to  FIG. 8 , the camera module  100  and the radar module  200  are mounted and used in a vehicle. During the mounting of the camera module  100  and the radar module  200 , the camera module  100  and the radar module  200  may deviate by the same angle from a center axis of the vehicle. However, the offset angle θo calculated as described above is maintained constant even after the mounting of the camera module  100  and the radar module  200 . 
       FIG. 9  is a diagram for describing an error compensation process. Referring to  FIG. 9 , a reference axis ref is an axis connecting a center of a radar target Tr and a center of a sensor system  10  and may coincide with or be parallel with a center axis of a vehicle. An ideal radar reference axis ref_r i  is an axis formed by parallel translating the reference axis ref to pass through a center of the radar module  200 . 
     An actual radar reference ref_r is a reference axis of the radar module  200  formed when the sensor system  10  according to the present embodiment is mounted. In an ideal state, the actual radar reference axis ref_r coincides with the ideal radar reference axis ref_r i . However, a mounting error angle θr 2  between the actual radar reference axis ref_r and the ideal radar reference axis ref_r i  is formed due to a mounting error angle formed by the mounting process and an assembly error angle θ r1  (see  FIG. 6 ) formed during an assembly process. When the center axis of the vehicle and the reference axis ref_coincide with each other due to no error during the mounting process, the mounting error angle θr 2  includes only a component of the assembly error angle θ r1  (see  FIG. 6 ). 
     After mounting the sensor system  10 , the mounting error angle θr 2  between the actual radar reference axis ref_r and the ideal radar reference axis ref_r i  is compensated for. The mounting error angle θr 2  is an angle measured counterclockwise from the ideal radar reference axis ref_r i  and has a negative value. Accordingly, a mounting error may be compensated for by adding the mounting error angle θr 2  to an angle (θt,r) at which the target Tr is viewed. 
     When the error is compensated for, an angle at which the target Tr is viewed from the radar module  200  is (θi,r). In this case, (θi,r) may be calculated by Equation 2 below based on a distance Rr between the center of the radar module  200  and the center of the target Tr and a distance dr between the center of the radar module  200  and the center of the sensor system  10 . 
     
       
         
           
             
               
                 
                   
                     θ 
                     
                       i 
                       , 
                       r 
                     
                   
                   = 
                   
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         dr 
                         Rr 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     
       15 
     
     When the mounting error angle θr 2  is not compensated for, the angle at which the target Tr is viewed from the radar module  200  is measured to be (θt,r) with respect to the actual radar reference axis ref_r. However, by compensating for the mounting error angle θr 2 , the angle θt,r at which the target Tr is detected by the radar module  200  is compensated for by θr 2  and thus is calculated to be (θt,r+θr 2 ) that coincides with the angle (θi,r) at which the target Tr is viewed from the ideal radar reference axis ref_r 1 . By performing compensation as described above, both the axis error θ r1  (see  FIG. 6 ) generated during the assembly process and the mounting error angle θr 2  formed due to the mounting process may be compensated for. 
       FIG. 10  is a diagram for describing an error compensation process. Referring to  FIG. 10 , a reference axis ref is an axis connecting a center of a camera target Tc and a center of a sensor system  10  and may coincide with or be parallel with a center axis of a vehicle. An ideal camera reference axis ref_ct is an axis formed by parallel translating the reference axis ref to pass through a center of the camera module  100 . 
     An actual radar reference ref_r is a reference axis of the camera module  100  formed when the sensor system  10  according to the present embodiment is mounted. In an ideal state, the actual camera reference axis ref_c coincides with the ideal camera reference axis ref_c i . However, a mounting error angle θc 2  between the actual camera reference axis ref_c and the ideal camera reference axis ref_c 1  is formed due to a mounting error angle formed by the mounting process and an assembly error angle θc 1  (see  FIG. 6 ) formed during an assembly process. When the center axis of the vehicle and the reference axis ref coincide with each other due to no error occurring during the mounting process, the mounting error angle θc 2  includes only a component of the assembly error angle θc 1  (see  FIG. 6 ). 
     After the mounting of the sensor system  10 , the mounting error angle θc 2  between the actual camera reference axis ref_c and the ideal camera reference axis ref_c i  is an angle measured counterclockwise from the deal camera reference axis ref_c i  and has a positive value. Thus, a mounting error may be compensated for by adding the mounting error angle θc 2  to an angle (θt,c) at which a target is viewed from the actual camera reference axis ref_c, and (θi,c)=(θt,c)+θc 2 . 
     In addition, when an error occurs during the mounting of the sensor system  10  in the vehicle, both the camera module  100  and the radar module  200  are misaligned by the same angle. Therefore, assembly error angles generated during the assembly process are maintained constant after the mounting process. Accordingly, an error angle may be compensated for by {circle around (1)} of Equation 3 below using a mounting error angle of the radar module  200 , a camera assembly error angle θc 1  measured and stored during the assembly process, and the radar assembly error angle θ r1  without measuring a mounting error angle of the camera module  100 . 
       [Equation 3] 
       θ i,c =θ x,c +θ r2  =θ t,c +θ c1 −θ r1 +θ r2    {circle around (1)}
 
     In an embodiment, an offset angle θo (see Equation 1) formed by assembly error angles of the camera module  100  and the radar module  200  may be stored and used to compensate for an error angle of the camera module  100  by achieving the same result as of Equation 3 above even when mounting is performed. For example, when a driver&#39;s vehicle equipped with the camera module  100  and the radar module  200  is traveling in the first lane and a vehicle is traveling in an opposite direction across the centerline, it may be identified that the vehicle traveling in the opposite direction is approaching while traveling the wrong way in the same lane as the driver&#39;s vehicle when an error angle is not calculated or inaccurately calculated, thereby generating a wrong warning and resulting in a big accident. 
     However, according to the error compensation method of the present embodiment, errors generated during manufacturing and assembling processes and an error generated when the camera module  100  and the radar module  200  are mounted in a vehicle may be more accurately compensated for, thereby more exactly identifying an object. 
     As described above, the error angle Or 2  includes both the error angle θ r1  due to an axis error generated during the assembling process and an error angle generated due to the mounting process. As described above, during the compensation for of the error angle Or 2 , both the error angle θ r1  due to an axis error generated during the assembling of the radar module  200  and an error angle generated due to the mounting process may be compensated for, values of axis errors generated during the assembly process may be stored, and both an error when a camera module is mounted and a manufacturing error of the camera module may be fixed on the basis of the values. 
     According to the present embodiment, a camera module and a radar module are installed in a cabin of a vehicle to reduce effects when installed outside the vehicle and reduce a data transmission length, thereby increasing a data transmission and reception rates and a transmission speed. 
     Although the embodiments illustrated in the drawings have been described above to help understand the present disclosure, these embodiments are only examples and it will be apparent to those of ordinary skill in the art that various modifications may be made and other equivalent embodiments are derivable from the embodiments. Therefore, the scope of the present disclosure should be defined by the appended claims.