Patent Publication Number: US-9905013-B2

Title: Speed calculating device and speed calculating method, and collision determination device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2012/072362 filed Sep. 3, 2012, the contents of all of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a speed calculating device, a speed calculating method, and a collision determination device which calculate the speed of an object around a moving body. 
     BACKGROUND ART 
     A technique has been known which calculates a distance to an object around a moving body and the speed of the object on the basis of image information in order to control the moving body. For example, Japanese Unexamined Patent Application Publication No. 2010-146494 discloses a device which switches a detection algorithm for short distance and a detection algorithm for long distance to detect an object in front of a vehicle, on the basis of whether the distance to the object is less than a threshold value. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2010-146494 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the device calculates the speed of the object, using different algorithms in a situation in which the distance to the object is slightly less than the threshold value and a situation in which the distance to the object is slightly greater than the threshold value. Therefore, when there is a large difference in the calculation result of the speed of the object, the moving body is not smoothly controlled and the operator of the moving body feels discomfort. 
     An object of the invention is to provide a speed calculating device, a speed calculating method, and a collision determination device which can accurately calculate the speed of an object around a moving body such that the operator of a moving body does not feel discomfort. 
     Solution to Problem 
     According to an aspect of the invention, there is provided a speed calculating device that calculates a speed of an object around a moving body. The speed calculating device includes: an image detection unit that captures an image of the surroundings of the moving body and detects the object from the captured image; and a speed calculation unit that calculates the speed of the object, using a moving body speed indicating the speed of the moving body and an image speed, which indicates the speed of the object and is calculated from the image, at a ratio corresponding to a distance from the moving body to the object. The speed calculation unit calculates the speed of the object using the moving body speed and the image speed such that the ratio of the moving body speed increases as the distance to the object increases and the ratio of the image speed increases as the distance to the object decreases. 
     According to this structure, the speed of the object is calculated using the moving body speed and the image speed at a ratio corresponding to the distance to the object. Therefore, it is possible to accurately calculate the speed of a distant object and the speed of a near object according to a change in the distance to the object. As the distance to the object increases, the accuracy of the image speed is reduced. Therefore, in particular, the ratio of the moving body speed increases in order to calculate the speed of the distant object and the ratio of the image speed increases in order to calculate the speed of the near object. As a result, it is possible to accurately calculate the speed of the object. 
     The speed calculating device may further include a radar detection unit that detects the object using a radar wave. When the object is not detected by the radar detection unit, but is detected by the image detection unit, the speed calculation unit may calculate the speed of the object, using the moving body speed and the image speed. According to this structure, the detection result obtained by the radar wave and the detection result obtained by the image can be appropriately used according to the detection situation of the object to calculate the speed of the object. 
     The speed calculating device may further include a composite target generation unit that generates a composite target of the object using a detection result obtained by the radar detection unit and a detection result obtained by the image detection unit. When the radar detection unit does not detect the object after the composite target is generated, the speed calculation unit may calculate the speed of the object, using the moving body speed and the image speed. According to this structure, the composite target and the detection result obtained by the image can be appropriately used according to the detection situation of the radar detection unit to calculate the speed of the object. 
     The speed calculating device may further include a radar detection unit that detects the object using a radar wave. When the object is present outside a detection range of the radar detection unit and is present in a detection range of the image detection unit, the speed calculation unit may calculate the speed of the object, using the moving body speed and the image speed. According to this structure, the detection result obtained by the radar wave and the detection result obtained by the image can be appropriately used according to the position of the object to calculate the speed of the object. 
     The speed calculating device may further include a stationary state determination unit that determines whether the object is stationary in a traveling direction of the moving body. When it is determined that the object is stationary, the speed calculation unit may calculate the speed of the object using the moving body speed and the image speed. According to this structure, it is possible to accurately calculate the speed of the object using the moving body speed. 
     When the distance to the object is equal to or greater than an upper limit, the speed calculation unit may calculate the speed of the object using the moving body speed and the image speed such that the ratio of the moving body speed is 1 and the ratio of the image speed is 0. According to this structure, it is possible to accurately calculate the speed of a distant object using only the moving body speed. 
     When the distance to the object is equal to or less than a lower limit, the speed calculation unit may calculate the speed of the object using the moving body speed and the image speed such that the ratio of the moving body speed is 0 and the ratio of the image speed is 1. According to this structure, it is possible to accurately calculate the speed of a near object using only the image speed. 
     According to another aspect of the invention, there is provided a collision determination device including: the above-mentioned speed calculating device; and a collision determination unit that determines a collision with the object on the basis of the speed of the object calculated by the speed calculating device. According to this structure, it is possible to determine a collision with the object on the basis of the speeds of a near object and a distant object which are accurately calculated according to a change in the distance to the object. 
     The speed calculating device may capture the image of the front side of the moving body, detect the object from the captured image, and calculate the speed of the object in front of the moving body. 
     The speed calculating device may capture an image in the traveling direction of the moving body, detect the object from the captured image, and calculate the speed of the object in the traveling direction of the moving body. 
     The moving body may be a vehicle or other moving bodies, such as a ship, an airplane, and a flying object. 
     According to still another aspect of the invention, there is provided a speed calculating method that calculates a speed of an object around a moving body. The speed calculating method includes: capturing an image of the surroundings of the moving body and detecting the object from the captured image; and calculating the speed of the object, using a moving body speed indicating the speed of the moving body and an image speed, which indicates the speed of the object and is calculated from the image, such that the ratio of the moving body speed increases as the distance to the object increases and the ratio of the image speed increases as the distance to the object decreases. According to this structure, it is possible to accurately calculate the speeds of the near and distant objects according to a change in the distance to the object. 
     Advantageous Effects of Invention 
     According to the invention, it is possible to provide a speed calculating device, a speed calculating method, and a collision determination device which can accurately calculate the speed of an object around a vehicle such that the operator of a moving body does not feel discomfort. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating the structure of a collision determination device according to a first embodiment of the invention. 
         FIG. 2  is a flowchart illustrating the operation of the collision determination device. 
         FIG. 3  is a diagram illustrating an example of a distance coefficient map. 
         FIG. 4  is a diagram illustrating the comparison between the calculation result of a collision time based on an image speed and the calculation result of a collision time based on a vehicle speed and the image speed. 
         FIG. 5  is a block diagram illustrating the structure of a collision determination device according to a second embodiment of the invention. 
         FIG. 6  is a diagram illustrating the detection ranges of a stereo camera and a radar. 
         FIG. 7  is a flowchart illustrating the operation of the collision determination device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same components are denoted by the same reference numerals and the description thereof will not be repeated. 
     A speed calculating device, a speed calculating method, and a collision determination device according to embodiments of the invention will be described below. The speed calculating device and the speed calculating method calculate the speed of an object around a moving body. The collision determination device determines a collision with the object on the basis of the speed of the object calculated by the speed calculating device. 
     Hereinafter, an embodiment will be described in which the moving body is a vehicle and the collision determination device determines a collision with an object on the basis of the speed of the object calculated by the speed calculating device that calculates the speed of the object around the vehicle, particularly, in front of the vehicle. However, the moving body is not limited to the vehicle and may be, for example, a ship, an airplane, or a flying object. In addition, the position where the speed of the object is calculated by the speed calculating device is not limited to the front side of the moving body and the speed calculating device may calculate the speed of the object in the traveling direction of the moving body. The collision determination device may determine a collision with the object on the basis of the speed of the object. 
     The collision determination device according to a first embodiment of the invention will be described with reference to  FIGS. 1 to 4 . 
     The collision determination device is provided in the vehicle and determines a collision between the vehicle and the object using an image sensor. The collision determination device also functions as a speed calculating device which calculates the speed of the object using the image sensor. The object includes a moving body and a stationary body and is an obstacle which prevents the traveling of the vehicle, such as, a vehicle in front, an oncoming vehicle, a bicycle, a pedestrian, a parked vehicle, or a guardrail. 
     First, the structure of the collision determination device will be described with reference to  FIG. 1 .  FIG. 1  is a block diagram illustrating the structure of the collision determination device according to the first embodiment. As shown in  FIG. 1 , the collision determination device includes a speed sensor  11 , a stereo camera  12 , and an electronic control unit (ECU)  20 . 
     The speed sensor  11  detects the speed of the vehicle. For example, a wheel speed sensor is used as the speed sensor  11 . The speed sensor  11  supplies the detected vehicle speed (absolute speed) to the ECU  20 . 
     The stereo camera  12  functions as an image detection unit (image sensor) which captures the image of the front side of the vehicle and detects the object on the basis of the captured image. For example, a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor is used as the stereo camera  12 . The stereo camera  12  includes a plurality of cameras and is provided on the front surface of the vehicle or in the cabin of the vehicle. The stereo camera  12  supplies image detection information indicating the detection result of the object to the ECU  20 . In addition, a single camera may be used instead of the stereo camera  12 . 
     The ECU  20  includes an image target generation unit  21 , a stationary state determination unit  24 , a speed calculation unit  25 , and a collision determination unit  26 . The ECU  20  includes, for example, a CPU, a ROM, and a RAM as main components. The CPU executes a program to implement the functions of the image target generation unit  21 , the stationary state determination unit  24 , the speed calculation unit  25 , and the collision determination unit  26 . The ECU  20  may be a single unit or it may include a plurality of units. 
     The image target generation unit  21  generates an image target on the basis of the image detection information from the stereo camera  12 . The image target has target information related to the distance to the object and the lateral position of the object which are calculated from the coordinates of the vehicle as a reference point. 
     The target information of the image target is calculated by the principle of triangulation, on the basis of the deviation between the image detection information items of the left and right cameras forming the stereo camera  12 , or it is calculated on the basis of the detection size and position of, for example, a number plate of the vehicle in front. The distance to the object indicates the distance from the vehicle (stereo camera  12 ) to the object in the traveling direction of the vehicle. The lateral position of the object indicates the distance from the vehicle (stereo camera  12 ) to the object in a direction perpendicular to the traveling direction of the vehicle. The lateral position of the image target also includes the range of the object detected from the image in the lateral direction, that is, information about the width of the object. When the target information is calculated, for example, a process of averaging the calculated values may be performed in order to reduce a calculation error. 
     The image target generation unit  21  calculates an image speed (absolute speed) from the image detection information indicating the speed of the object. The image speed is calculated on the basis of the distance to the object and the vehicle speed, using the target information of the image target. The image speed is calculated on the basis of, for example, a change in the distance to the object in consecutive cycles. For example, the image speed is calculated by dividing the difference between the distance in a processing cycle i and the distance in a processing cycle i+1 by the interval of the processing cycle and reducing the vehicle speed from the divided value. When the image speed is calculated, for example, a process of averaging the calculated values in the consecutive processing cycles may be performed in order to reduce a calculation error. 
     The stationary state determination unit  24  determines whether the object in front of the vehicle is stationary on the basis of the image speed. The stationary state of the object means that the speed (absolute speed) of the object in the traveling direction of the vehicle is 0 or substantially 0. For example, a pedestrian who crosses in front of the vehicle is assumed as the object. 
     The speed calculation unit  25  calculates the speed (relative speed) of the object on the basis of the vehicle speed and the target information of the image target. The speed calculation unit  25  calculates the speed of the object, using the vehicle speed indicating the speed of the vehicle and the image speed indicating the speed of the object at a ratio corresponding to the distance to the object. The speed calculation unit  25  sets the ratio corresponding to the distance to the object such that the ratio of the vehicle speed increases as the distance to the object increases and the ratio of the image speed increases as the distance to the object decreases. In addition, the speed calculation unit  25  may calculate the speed of the object using the vehicle speed and the image speed only when the object in front of the vehicle is stationary. 
     The collision determination unit  26  determines a collision with the object on the basis of the speed of the object calculated by the speed calculation unit  25 . The collision determination unit  26  determines the possibility of a collision with the object on the basis of whether a collision time obtained by dividing the distance to the object by the speed of the object is less than a predetermined threshold value. For example, the determination result of the collision possibility is used to notify the driver of information or to control the braking or steering of the vehicle to support collision avoidance. 
     Next, the operation of the collision determination device will be described with reference to  FIGS. 2 and 3 .  FIG. 2  is a flowchart illustrating the operation of the collision determination device. The collision determination device repeatedly performs the process shown in  FIG. 2  in a predetermined cycle. 
     The speed sensor  11  detects the vehicle speed (absolute speed) (Step S 11 ). When there is an object in the detection range of the stereo camera  12 , the image target generation unit  21  generates an image target (S 12 ). The image target generation unit  21  calculates the image speed (absolute speed) from the image detection information indicating the speed of the object (S 13 ). 
     The stationary state determination unit  24  determines whether the object in front of the vehicle is stationary on the basis of the image speed (S 14 ). This is because the accuracy of calculating the speed of the object on the basis of the vehicle speed can increase as the speed of the object in the traveling direction of the vehicle is reduced. However, the process in S 14  may be omitted. 
     When the process in S 14  is performed, the process in S 15  and the subsequent steps is performed if it is determined in S 14  that the object is stationary. If it is determined in S 14  that the object is not stationary, the process is not performed and ends. In addition, it may be determined whether the object is a pedestrian who crosses a road on the basis of image recognition or it may be determined whether the object is present at the position of a crosswalk on the basis of image recognition or map information, instead of determining whether the object is stationary. 
     The speed calculation unit  25  calculates a distance coefficient corresponding to the distance to the object, using the target information of the image target (S 15 ). The distance coefficient is a coefficient indicating the ratio (weighting) of the vehicle speed and the image speed used to calculate the speed of the object and is calculated using, for example, a distance coefficient map which will be described below. 
       FIG. 3  is a diagram illustrating an example of the distance coefficient map. As shown in  FIG. 3 , the distance coefficient map indicates the relationship between the distance to the object on the horizontal axis and the distance coefficient on the vertical axis. The lower limit T 1  and upper limit Tu of the distance are set on the distance coefficient map. For example, the distance coefficient indicates the ratio (0 to 1) of the vehicle speed when the sum of the ratio of the vehicle speed and the ratio of the image speed is 1. In this example, the distance coefficient is set to “0” when the distance to the object is equal to or less than the lower limit T 1 , is set to “1” when the distance is equal to or greater than the upper limit Tu, and is set to a value between “0” and “1” when the distance is between the lower limit T 1  and the upper limit Tu. In the example shown in  FIG. 3 , the distance coefficient is set so as to monotonically increase between the lower limit T 1  and the upper limit Tu. However, the distance coefficient may be set so as to increase in different manners. 
     Returning to  FIG. 2 , when the distance coefficient is calculated in S 15 , the speed calculation unit  25  calculates the speed (relative speed) V of the object on the basis of the distance coefficient (p), the vehicle speed (V 1 ), and the image speed (V 2 ) (S 16 ). The speed V of the object is calculated by the following expression:
 
 V=p ·(− V 1)+(1− p )·( V 2− V 1).  [Expression (1)]
 
     That is, the speed of the object is calculated using only the image speed when the distance to the object is equal to or less than the lower limit T 1  and is calculated using only the vehicle speed when the distance is equal to or greater than the upper limit Tu. When the distance to the object is between the lower limit T 1  and the upper limit Tu, the speed of the object is calculated using (with a larger weight) a higher ratio of the vehicle speed as the distance to the object increases and is calculated using (with a larger weight) a higher ratio of the image speed as the distance to the object decreases. 
     When the speed of the object is calculated, the collision determination unit  26  divides the distance to the object by the speed of the object to calculate a collision time (S 17 ). Then, the collision determination unit  26  determines a collision with the object on the basis of whether the collision time is less than a predetermined threshold value (S 18 ). 
       FIG. 4  is a diagram illustrating the comparison between the calculation result of the collision time based on the image speed and the calculation result of the collision time based on the vehicle speed and the image speed. The collision time based on the image speed is calculated by dividing the distance to the object by the speed of the object corresponding to the image speed and the collision time based on the vehicle speed and the image speed is calculated by dividing the distance to the object by the speed of the object calculated on the basis of the vehicle speed and the image speed. In  FIG. 4 , the horizontal axis indicates the actually measured collision time and the vertical axis indicates the calculation result of the collision time. 
       FIG. 4  shows a variation in the calculation result of the collision time due to a variation in the distance to the object. A dashed line indicates the range V 1  of the variation in the calculation result based on the image speed and a solid line indicates the range V 2  of the variation in the calculation result based on the vehicle speed and the image speed. As shown in  FIG. 4 , the variation in the calculation result (V 2 ) based on the vehicle speed and the image speed is reduced to about half the variation in the calculation result (V 1 ) based on the image speed. Therefore, when the collision time is accurately calculated, it is possible to accurately determine the collision with the object. 
     As described above, according to the speed calculating device of the first embodiment, the speed of the object is calculated using the vehicle speed (moving body speed) and the image speed at a ratio corresponding to the distance to the object. Therefore, it is possible to accurately calculate the speeds of a near object and a distant object according to a change in the distance to the object. As the distance to the object increases, the accuracy of the image speed is reduced. Therefore, in particular, the ratio of the vehicle speed (moving body speed) increases in order to calculate the speed of the distant object and the ratio of the image speed increases in order to calculate the speed of the near object. As a result, it is possible to accurately calculate the speed of the object. 
     When it is determined that the object is stationary, the speed of the object is calculated using the vehicle speed (moving body speed) and the image speed. Therefore, the speed of the object may be accurately calculated using the vehicle speed (moving body speed). 
     According to the collision determination device of the embodiment of the invention, it is possible to determine a collision with the object on the basis of the speeds of a near object and a distant object which are accurately calculated according to a change in the distance to the object. 
     According to the speed calculating method of the embodiment of the invention, the speed of the object is calculated using the vehicle speed (moving body speed) and the image speed at a ratio corresponding to the distance to the object. Therefore, it is possible to accurately calculate the speeds of a near object and a distant object according to a change in the distance to the object. 
     Next, a collision determination device according to a second embodiment of the invention will be described with reference to  FIGS. 5 to 7 . In the second embodiment, the description of the same components as those in the first embodiment will not be repeated. 
     The collision determination device is provided in a vehicle and determines a collision between the vehicle and an object using a radar sensor and an image sensor. The collision determination device also functions as a speed calculating device which calculates the speed of the object using the radar sensor and the image sensor. 
     First, the structure of the collision determination device will be described with reference to  FIGS. 5 and 6 .  FIG. 5  is a block diagram illustrating the structure of the collision determination device according to the second embodiment. As shown in  FIG. 5 , the collision determination device includes a speed sensor  11 , a stereo camera  12 , an ECU  30 , and a radar  13 . The structure and function of the speed sensor  11  and the stereo camera  12  are the same as those in the first embodiment and thus the description thereof will not be repeated. 
     The radar  13  functions as a radar detection unit (radar sensor) which detects an object in front of the vehicle using radar waves, transmits radar waves (electromagnetic waves) to the front side of the vehicle, and receives radar waves reflected from the object. For example, a microwave radar, a millimeter-wave radar, an ultrasonic radar, or a laser radar is used as the radar  13 . The radar  13  supplies radar detection information indicating the detection result of the object to the ECU  30 . 
     The ECU  30  includes an image target generation unit  21 , a stationary state determination unit  24 , a speed calculation unit  25 , a collision determination unit  26 , a radar target generation unit  22 , and a composite target generation unit  23 . The ECU  30  includes, for example, a CPU, a ROM, and a RAM as main components. The CPU executes a program to implement the functions of the image target generation unit  21 , the radar target generation unit  22 , the composite target generation unit  23 , the stationary state determination unit  24 , the speed calculation unit  35 , and the collision determination unit  36 . The structure and function of the image target generation unit  21  and the stationary state determination unit  24  are the same as those in the first embodiment and thus the description thereof will not be repeated. 
     The radar target generation unit  22  generates a radar target on the basis of the radar detection information from the radar  13 . The radar target has target information related to the distance to the object and the lateral position of the object which are calculated from the coordinates of the vehicle as a reference. 
     The target information of the radar target is calculated on the basis of the radar detection information from the radar  13 . The distance to the object indicates the distance from the vehicle (radar  13 ) to the object in the traveling direction of the vehicle and is calculated on the basis of the time from the transmission of the radar wave from the radar  13  to the reception of the radar wave reflected from the object. The lateral position of the object indicates the distance from the vehicle (radar  13 ) to the object in a direction perpendicular to the traveling direction of the vehicle and is calculated on the basis of the direction (angle) of the radar wave which is reflected from the objected and is then received. The lateral position of the radar target is information about the position of the object detected by the radar  13  and does not include information about the width of the object. 
       FIG. 6  is a diagram illustrating the detection ranges A 1  and A 2  of the radar  13  and the stereo camera  12 . As shown in  FIG. 6 , the detection range A 1  of the radar  13  is narrower than the detection range A 2  of the stereo camera  12 . Therefore, a region which can be detected only by the stereo camera  12  and is arranged outside the detection range A 1  of the radar  13  is present diagonally in front of the vehicle.  FIG. 6  shows a target which moves from the detection ranges A 1  and A 2  of the radar  13  and the stereo camera  12  to the detection range A 2  of the stereo camera  12 . 
     The radar  13  has low accuracy in the detection of the lateral position considering the width of the object and is not capable of detecting the width of the object. However, the radar  13  has high accuracy in the detection of the distance to the object. In contrast, the stereo camera  12  has low accuracy in the detection of the distance to the object but has high accuracy in the detection of the lateral position and width of the object. Therefore, the detection accuracy of an image speed which is calculated on the basis of the distance to the object in the target information of an image target is reduced as the distance to the object increases. 
     The composite target generation unit  23  generates a composite target of the object, using the target information of the radar target and the image target, that is, the detection results of the radar  13  and the stereo camera  12 . The composite target is generated by collating the two targets on the basis of the target information of the radar target and the image target. The two targets are collated with each other on the basis of the similarity between the target information items of the two targets, that is, the similarity between the distances to the object and the lateral positions. The composite target has target information related to the distance to the object and the lateral position (including the width) of the object. The target information of the composite target is based on the target information of the radar target and the image target and has higher accuracy than the target information of only the radar target or the target information of only the image target. 
     The speed calculation unit  35  calculates the speed (relative speed) of the object on the basis of a vehicle speed and the target information of the composite target, the radar target, or the image target. When the composite target is generated, the speed calculation unit  35  calculates the speed of the object on the basis of the target information of the composite target. In this case, the speed of the object is calculated by dividing the distance to the object in the target information of the composite target by the interval of the processing cycle. When only the radar target is generated, the speed calculation unit  35  may calculate the speed of the object on the basis of the target information of the radar target. In this case, the speed of the object is calculated by dividing the distance to the object in the target information of the radar target by the interval of the processing cycle. 
     When only the image target is generated, the speed calculation unit  35  calculates the speed of the object on the basis of the target information of the image target. In this case, the speed calculation unit  35  calculates the speed of the object, using the vehicle speed indicating the speed of the vehicle and the image speed indicating the speed of the object at a ratio corresponding to the distance to the object. 
     The collision determination unit  36  determines a collision with the object on the basis of the speed of the object calculated by the speed calculation unit  35 . The collision determination unit  36  determines the possibility of a collision with the object on the basis of whether a collision time obtained by dividing the distance to the object by the speed of the object is less than a predetermined threshold value. For example, the determination result of the possibility of the collision is used to notify the driver of information or to control the braking or steering of the vehicle. 
     Next, the operation of the collision determination device will be described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating the operation of the collision determination device. The collision determination device repeatedly performs the process shown in  FIG. 7  in a predetermined cycle. 
     First, the speed sensor  11  detects the speed of the vehicle (vehicle speed) (Step S 21 ). The radar target generation unit  22  generates the radar target when the object is present in the detection range of the radar  13  (S 22 ). The image target generation unit  21  generates the image target when the object is present in the detection range of the stereo camera  12  (S 23 ). The composite target generation unit  23  generates the composite target when the radar target and the image target are collated with each other (S 24 ). 
     The speed calculation unit  35  determines whether the composite target has been generated, that is, whether the object has been detected by both the sensors  12  and  13  (S 25 ). 
     When it is determined that the composite target has been generated, the speed calculation unit  35  calculates the speed of the object on the basis of the composite target (S 26 ). That is, the speed calculation unit  35  calculates the speed of the object on the basis of the distance to the object in the target information of the composite target. Then, the collision determination unit  36  divides the distance to the object by the speed of the object to calculate the collision time, on the basis of the target information of the composite target (S 27 ). 
     On the other hand, when it is determined in S 25  that the composite target has not been generated, the ECU  30  generates the composite target and determines whether only the image target has been generated (S 28 ). That is, the ECU  30  determines whether the object is detected only by the stereo camera  12  in the current processing cycle after it is detected by the radar  13  and the stereo camera  12  in the previous processing cycle. 
     For example, this corresponds to a case in which the pedestrian who crosses in front of the vehicle that is traveling deviates from the detection range of the radar  13  or a case in which the object has not been detected (lost) by the radar  13  for any reason. In this case, as the distance to the object increases, the calculation accuracy of the speed of the object based on image detection information is reduced. 
     When it is determined in S 28  that only the image target has been generated, the image target generation unit  21  calculates the image speed (absolute speed) from the image detection information indicating the speed of the object (S 29 ). The stationary state determination unit  24  determines whether the object is stationary on the basis of the vehicle speed and the image speed (S 30 ). However, the process in S 30  may be omitted. 
     When the process in S 30  is performed, the process in S 31  and the subsequent steps is performed if it is determined in S 30  that the object is stationary, and is not performed and ends if it is determined in S 30  that the object is not stationary. When it is not determined in S 28  that only the image target has been generated, the process ends. 
     As described with reference to  FIG. 3 , the speed calculation unit  35  calculates a distance coefficient corresponding to the distance to the object, using the target information of the image target (S 31 ). The speed calculation unit  35  calculates the speed (relative speed) of the object on the basis of the distance coefficient, the vehicle speed, and the image speed, using the above-mentioned Expression (1) (S 32 ). 
     When the speed of the object is calculated, the collision determination unit  36  divides the distance to the object by the speed of the object to calculate the collision time, on the basis of the target information of the image target (S 33 ). When the collision time is calculated in S 27  or S 33 , the collision determination unit  36  determines a collision with the object on the basis of the collision time (S 34 ). 
     As described above, the speed calculating device according to the second embodiment calculates the speed of the object, using the vehicle speed (moving body speed) and the image speed when the radar  13  does not detect the object after the composite target is generated. Therefore, the composite target and the detection result obtained by the image can be appropriately used according to the detection situation of the radar  13  to calculate the speed of the object. 
     When the object is not detected by the radar  13 , but is detected by the stereo camera  12 , the speed of the object may be calculated using the vehicle speed (moving body speed) and the image speed. Therefore, the detection result obtained by the radar waves and the detection result obtained by the image may be appropriately used according to the detection situation of the object to calculate the speed of the object. 
     When the radar  13  does not detect the object after the composite target is generated, the speed of the object is calculated, using the vehicle speed (moving body speed) and the image speed. Therefore, the composite target and the detection result obtained by the image may be appropriately used according to the detection situation of the radar  13  to calculate the speed of the object. 
     When the object is present outside the detection range of the radar  13  and is present in the detection range of the stereo camera  12 , the speed of the object is calculated using the vehicle speed (moving body speed) and the image speed. Therefore, the detection result obtained by the radar waves and the detection result obtained by the image may be appropriately used according to the position of the object to calculate the speed of the object. 
     When it is determined that the object is stationary, the speed of the object is calculated using the vehicle speed (moving body speed) and the image speed. Therefore, the speed of the object may be accurately calculated using the vehicle speed (moving body speed). 
     In the second embodiment, the case in which the composite target and the detection result obtained by the image are appropriately used according to the detection situation of the radar  13  to calculate the speed of the object has been described. However, this embodiment is similarly applied to a case in which the detection result obtained by the radar waves and the detection result obtained by the image are appropriately used according to the detection situation of the radar  13  to calculate the speed of the object. 
     The above-described embodiments are the preferred embodiments of the speed calculating device, the speed calculating method, and the collision determination device according to the invention. However, the speed calculating device, the speed calculating method, and the collision determination device according to the invention are not limited to these embodiments. The speed calculating device, the speed calculating method, and the collision determination device according to the invention may be modified without departing from the scope and spirit of the invention described in the claims or they may be applied to other techniques. 
     For example, in the above-described embodiments, the functions of the image target generation unit  21  are implemented by the ECU  20  or the functions of the image target generation unit  21  and the radar target generation unit  22  are implemented by the ECU  30 . However, the functions of the image target generation unit  21  may be implemented by a single ECU, for example, an ECU for an image sensor and the functions of the radar target generation unit  22  may be implemented by a single ECU, for example, an ECU for a radar sensor. 
     In the above-described embodiments, the speed of the object is calculated as the relative speed. However, the speed of the object may be calculated as an absolute speed. 
     The speed calculating device, the speed calculating method, and the collision determination device according to the embodiments of the invention have been described above. In the above-described embodiments, the collision determination device determines a collision with the object on the basis of the speed of the object calculated by the speed calculating device which calculates the speed of the object which is disposed around the vehicle, particularly, in front of the vehicle. 
     However, as described above, the moving body is not limited to the vehicle and may be, for example, a ship, an airplane, or a flying object. In the above-described embodiments, the speed calculating device calculates the speed of the object in front of the moving body. However, the invention is not limited thereto and the speed calculating device may calculate the speed of the object in the traveling direction of the moving body and the collision determination device may determine a collision with the object on the basis of the speed of the object. 
     For example, an image sensor (image detection unit) which captures the image of the front side of the moving body and detects an object from the captured image can be used to calculate the speed of the object in front of the moving body. In addition, at least two image sensors which capture the image of an object in front of the moving body and the image of an object on the rear side of the moving body and detect the objects from the captured images can be used to calculate the speed of the object in the traveling direction of the moving body. 
     REFERENCE SIGNS LIST 
     
         
         
           
               11 : SPEED SENSOR 
               12 : STEREO CAMERA 
               13 : RADAR 
               20 ,  30 : ECU 
               21 : IMAGE TARGET GENERATION UNIT 
               22 : RADAR TARGET GENERATION UNIT 
               23 : COMPOSITE TARGET GENERATION UNIT 
               24 : STATIONARY STATE DETERMINATION UNIT 
               25 ,  35 : SPEED CALCULATION UNIT 
               26 ,  36 : COLLISION DETERMINATION UNIT