Patent ID: 12204048

DETAILED DESCRIPTION

Example Use

A collision avoidance apparatus for an autonomous vehicle according to one or more embodiments of the present invention used in one example situation will now be described. The collision avoidance apparatus for the autonomous vehicle uses a radar sensor to avoid collision of, for example, an automated guided vehicles (AGV) with an object such as an obstacle.

The collision avoidance apparatus for the autonomous vehicle obtains a reflected power level based on a signal from the radar sensor. In response to the obtained reflected power level higher than or equal to a predetermined value, the apparatus defines an area (travel-restricted area) adjacent to the object. In this area, the vehicle is restricted from traveling. For example, a metal wall having a relatively high level of reflected power is present, and another object having a relatively low level of reflected power is located in front of the metal wall. The other object having the relatively low level of reflected power may be difficult to detect. The collision avoidance apparatus for the autonomous vehicle according to one or more embodiments of the present invention defines the travel-restricted area adjacent to the metal wall to include the position of the other object. The vehicle is controlled not to enter the travel-restricted area, and can thus avoid the other object having the relatively low level of reflected power.

Embodiments

(Structure of Vehicle)

FIG.1is a schematic block diagram of a vehicle1in an embodiment. The vehicle1in the present embodiment mainly includes a radar sensor11, a controller12, a travel controller13, and a drive14. The vehicle1can travel autonomously and is, for example, an AGV. The vehicle1is an example autonomous vehicle.

The radar sensor11uses, for example, millimeter wave radar. The radar sensor11in the present embodiment may use FMCW radar. However, the radar sensor11may use another detection method (e.g., pulse radar). In response to the presence of an object such as an obstacle around the vehicle1, the controller12processes a signal output from the radar sensor11to detect the distance and the direction from the vehicle1to the object. The controller12may calculate the position (e.g., three-dimensional coordinates) of the object based on the distance and the direction to the object. The controller12outputs information about the object to the travel controller13. The travel controller13then controls the drive14to avoid the object.

(Structure of Radar Sensor)

FIG.2is a schematic diagram of the radar sensor11. The radar sensor11includes a synthesizer101, a transmitting antenna102, a receiving antenna103, and a mixer104. The synthesizer101generates a chirp. A chirp is a signal with the frequency that increases or decreases with time. The transmitting antenna102transmits a radar wave (radio wave) in accordance with the chirp. The travel direction or the illumination direction of the radar wave may be defined to align with, for example, the straight-traveling direction of the vehicle1. The receiving antenna103receives a reflected wave resulting from the radar wave transmitted from the transmitting antenna102being reflected from an object. Multiple receiving antennas103may be included. To detect the position of the object three dimensionally, the radar sensor11in the present embodiment may include multiple receiving antennas103staggered horizontally and multiple receiving antennas103staggered vertically. The mixer104generates an intermediate frequency signal by combining the chirp generated by the synthesizer101and the signal of the reflected wave received by the receiving antenna103. The intermediate frequency signal is output to the controller12. The radar sensor11may output, to the controller12, information for calculating the distance to the object, the direction to the object, and the reflected power level of the reflected wave from the object, for example. The radar sensor11may include a filter to remove unintended signal components from the output from the mixer104and an analog-digital converter.

(Structure of Controller)

The controller12will now be described. The controller12is a computer for performing object detection and includes, for example, a processor and a memory. The processor is, for example, a central processing unit (CPU) or a digital signal processor (DSP). The memory is, for example, a random access memory (RAM), a read-only memory (ROM), an erasable programmable ROM (EPROM), a hard disk drive (HDD), or a removable medium. The memory is a computer-readable recording medium to store various programs and other information items. The programs stored in the memory are executed by the processor to control the components. This allows the controller12to perform functions achieving predetermined purposes. The controller12may include multiple computers.

The controller12performs object detection using the signal output from the radar sensor11. The object detection includes calculating the distance and the direction from the vehicle1to the object.FIG.3is a diagram of the controller12showing its example functional components. The controller12includes, as its functional components, a transmission-reception unit201, a processor202, a determiner203, a generator204, and an output unit205. The transmission-reception unit201, the processor202, the determiner203, the generator204, and the output unit205are functional components implemented by, for example, the processor executing various programs stored in the memory.

The transmission-reception unit201controls transmission and reception of the radar wave by the radar sensor11. The transmission-reception unit201causes the synthesizer101to output a chirp and obtains an intermediate frequency signal from the mixer104. The processor202performs object detection based on, for example, the intermediate frequency signal. The processor202calculates the distance and the direction to the object based on the signal from the transmission-reception unit201. The processor202calculates the reflected power level of the reflected wave based on the signal from the transmission-reception unit201. The reflected power level may be, for example, received electric power or received signal intensity. Any known technique may be used for the calculation.

The determiner203determines, based on the reflected power level of the reflected wave, whether a travel-restricted area is to be defined. The travel-restricted area may be defined as an area in which the vehicle1is restricted from traveling. The travel-restricted area may be defined as an area in which an object is difficult to detect. For example, the determiner203determines whether the reflected wave from a detected object has a reflected power level higher than or equal to a predetermined value. In response to the reflected power level being higher than or equal to the predetermined value, the determiner203determines that the travel-restricted area is to be defined. The predetermined value is a threshold for the reflected power level to determine an area in which an object is difficult to detect. For another object located adjacent to a detected object, the predetermined value is, for example, the reflected power level at which the other object is undetectable. The predetermined value may be obtained by, for example, experiment or simulation. The predetermined value may have some margin. More specifically, the predetermined value may be lower than the reflected power level at which the other object is undetectable.

The generator204generates information about the travel-restricted area. The information about the travel-restricted area includes, for example, information about the coordinates indicating the outer edge of the travel-restricted area. The generator204determines the travel-restricted area for the object based on the reflected power level and the information stored in the memory. To determine the travel-restricted area, the peak value of the reflected power level is used, for example. The travel-restricted area can be determined based on a travel-restricted distance from the position (point) at which an object is detected. The travel-restricted distance is the maximum distance from the object within which the vehicle1is restricted from traveling. The travel-restricted distance corresponds to the distance from the object to the outer edge of the travel-restricted area. The information about the travel-restricted distance corresponding to the reflected power level may be determined by experiment or simulation and stored in the memory. The travel-restricted distance is defined to reflect the separation resolution and the detection error of the radar. The area in which another object is difficult to detect changes depending on the separation resolution and the detection error of the radar. The travel-restricted distance is thus defined for the travel-restricted area to include the area in which another object is difficult to detect. The separation resolution and the detection error of the radar sensor11may be obtained based on, for example, the specifications of the radar sensor11.

FIG.4is a diagram describing the travel-restricted distance and the travel-restricted area in the embodiment.FIG.4illustrates a metal wall40in front of the vehicle1, and a metal rod50near the metal wall40between the vehicle1and the metal wall40. In the example shown inFIG.4, the straight-traveling direction of the vehicle1is orthogonal to the surface of the metal wall40. The direction of the radar wave is thus orthogonal to the surface of the metal wall40. In this case, the metal wall40corresponds to an object that reflects a wave with a relatively high level of reflected power. The metal rod50corresponds to another object that reflects a wave with a relatively low level of reflected power. The dashed line60inFIG.4shows the outer edge of the radar coverage (monitoring area A1). The arrows61inFIG.4each indicate the travel-restricted distance for a corresponding position62on the metal wall40. The radar sensor11receives the reflected wave from each position62on the metal wall40. The metal wall40is thus detected as a point cloud. The dot-and-dash lines63inFIG.4each indicate the outer edge of the travel-restricted area for a corresponding position62on the metal wall40.

InFIG.4, the metal wall40has a relatively large radar cross-section (RCS) and easily reflects the radar wave. Thus, the reflected wave from the metal wall40is received by the radar sensor11with a relatively high level of reflected power. The metal rod50has a smaller RCS than the metal wall40. Thus, the reflected wave from the metal rod50is received with a lower level of reflected power. In response to the presence of an object with a large RCS in the monitoring area A1, the radar sensor11may fail to detect another object with a small RCS located near the object with the large RCS. In other words, the reflected wave from the other object with the small RCS may be less noticeable in the reflected wave from the object with the large RCS, causing the waves to be non-separable from each other. This may cause the metal rod50in front of the metal wall40to be undetectable. In this case, the reflected wave from the metal wall40has a reflected power level higher than or equal to a predetermined value. The determiner203thus determines that the travel-restricted area is to be defined adjacent to the metal wall40.

The generator204then defines a travel-restricted area adjacent to the metal wall40and generates information about the travel-restricted area. In the metal wall40shown inFIG.4, the reflected power level is the highest in front of the vehicle1and is lower at a longer distance from the front toward the left and right with a smaller incident angle of the radar wave onto the metal wall40. The reflected wave from the metal wall40having a lower level of reflected power allows easier detection of the reflected wave from another object. Thus, the travel-restricted distance for a position62on the metal wall40is the longest in front of the vehicle1and is shorter at a longer distance from the front toward the left and right. The travel-restricted distance for each position62on the metal wall40is associated with the reflected power level, the separation resolution (which may be the frequency band), and the detection error. The travel-restricted distance may thus be defined in accordance with the reflected power level, the separation resolution, and the detection error. The separation resolution and the detection error may be predetermined. Using these parameters, the relationship between the reflected power level and the travel-restricted distance may be predetermined. This allows the travel-restricted distance to be determined in accordance with the reflected power level. The area around each position62within the travel-restricted distance is defined as the travel-restricted area for the position62. In this case, multiple travel-restricted areas are defined for the metal wall40. The two-dot chain line B1inFIG.4may define the outer edge of a travel-restricted area A2for the entire metal wall40. The two-dot chain line B1indicates a tangent to the outer edge63of the travel-restricted area for each position62on the metal wall40. The two-dot chain line B1may not be a straight line.

FIG.5is a diagram describing a situation with no travel-restricted area being defined. For the vehicle1traveling diagonally to the metal wall40, a reflected wave from the metal wall40can have a lower level of reflected power than for the vehicle1traveling orthogonally to the surface of the metal wall40. In this case, the reflected wave from the metal rod50may be separable from the reflected wave from the metal wall40. The processor202can then detect the metal rod50in front of the metal wall40. In this case, the reflected power level is lower than the predetermined value. The determiner203thus determines that the travel-restricted area is not to be defined. The generator204thus generates no information about the travel-restricted area.

The output unit205then outputs information about the travel-restricted area to the travel controller13. The output information includes, for example, the coordinates of the outer edge of the travel-restricted area. The output unit205also outputs information about the detected object to the travel controller13. The information may include, for example, information about the distance and the direction from the vehicle1to the object calculated by the processor202.

(Structure of Travel Controller)

The travel controller13is a computer for controlling the travel of the vehicle1and includes, for example, a processor and a memory. The processor and the memory are the same as those in the controller12and thus are not described repeatedly. The controller12and the travel controller13may be implemented by a single computer.

The travel controller13generates a control command for controlling the autonomous travel of the vehicle1based on the operation plan input by the user and on the information output from the output unit205. The operation plan may be prestored in the memory. For example, the travel controller13generates a control command to cause the vehicle1to travel along a predetermined travel-permitted area in accordance with the operation plan while preventing obstacles from entering a predetermined area around the vehicle1and preventing the vehicle1from entering the travel-restricted area. The generated control command is transmitted to the drive14. To generate the control command for the autonomous travel of the vehicle1, any known method may be used.

(Structure of Drive)

The drive14causes the vehicle1to travel based on the control command generated by the travel controller13. The drive14includes, for example, a motor, an inverter, a brake, and steering for driving the wheels of the vehicle1. These components are driven in accordance with the control command to allow the autonomous travel of the vehicle1.

(Operation of Controller12)

FIG.6is a flowchart showing a control sequence performed by the controller12in the embodiment. The processing in the flowchart is repeatedly performed by the controller12at predetermined time intervals. The vehicle1operates in accordance with the operation plan prestored in the memory.

In step S101, the transmission-reception unit201transmits and receives a radar wave. In step S102, the processor202performs object detection. More specifically, the processor202calculates the position (distance and direction) and the reflected power level of the object based on the output from the radar sensor11. In step S103, the processor202determines whether an object has been detected through the object detection. In response to an affirmative determination result in step S103, the processing advances to step S104. In response to a negative determination result in step S103, the processing advances to step S108. In step S108, the output unit205outputs, to the travel controller13, information indicating no object detected.

In step S104, the determiner203determines whether the reflected wave from the detected object has a reflected power level higher than or equal to a predetermined value. In other words, the determiner203determines whether a travel-restricted area is to be defined. In response to an affirmative determination result in step S104, the processing advances to step S105. In response to a negative determination result in step S104, the processing advances to step S107.

In step S105, the generator204generates information about the travel-restricted area. The generator204obtains, based on the reflected power level and information stored in the memory (e.g., information about the travel-restricted distance corresponding to the reflected power level), the travel-restricted distance from the position having the reflected power level detected. The generator204then determines the travel-restricted distance from each position having the reflected power level higher than or equal to the predetermined value. The generator204thus determines the travel-restricted area for each position. The generator204may determine a travel-restricted area for the entire object based on the travel-restricted distance for each position.

In step S106, the output unit205outputs the information about the travel-restricted area to the travel controller13. In step S107, the output unit205outputs the information about the object to the travel controller13.

Upon receiving a signal from the controller12, the travel controller13controls the travel of the vehicle1based on the signal. In response to the travel controller13obtaining information about the object, or in other words, in response to information about the object being output in step S107, the travel controller13changes the movement direction of the vehicle1or decelerates or stops the vehicle1to avoid contact with the object. In response to the travel controller13obtaining information about the travel-restricted area, or in other words, in response to information about the travel-restricted area being output in step S106, the travel controller13changes the movement direction of the vehicle1or decelerates or stops the vehicle1to prevent the entry of the vehicle1into the travel-restricted area. For an overlap between the travel-permitted area and the travel-restricted area, for example, the travel-permitted area may be smaller by the area of overlap, and the vehicle1may travel along the smaller travel-permitted area. In response to no object being detected, or in other words, in response to information indicating no object detected being output in step S108, the vehicle1is controlled in accordance with the operation plan.

Advantages of Embodiments

In the apparatus described above, the radar sensor11can detect an object located in the vertical direction, as well as in the horizontal direction. This structure allows avoiding collision with, for example, an obstacle located in a three-dimensional space. The apparatus defines a travel-restricted area based on the reflected power level of a reflected wave from a detected object. For example, an object having a high level of reflected power is present, and another object having a low level of reflected power is located near the object. The apparatus allows the vehicle1to avoid colliding with the other object that may be difficult to detect. The apparatus can have the existing hardware configuration and thus can reduce cost.

Modifications

FIG.7is a schematic block diagram of the vehicle1in a modification. The vehicle1in the present modification includes multiple radar sensors11having different directions of radar waves. The components specific to the present modification are described below without describing the components that are the same as those in the above embodiments.

An object that easily reflects a radar wave, such as the metal wall40, as described inFIGS.4and5can reflect a radar wave with a relatively low level of reflected power when the radar wave is diagonally incident on the wall surface. The metal rod50near the metal wall40is then detectable. In this case, the position of the metal rod50is not to be included in the travel-restricted area. The travel controller13may simply control the vehicle1to avoid the detected metal rod50while traveling.

The radar sensors11having different directions of radar waves can cause the radar waves to be incident on the same object at different angles. The reflected waves from the same object may have different levels of reflected power for different radar sensors11. Thus, different travel-restricted areas may be defined for different radar sensors11for the same object. The radar sensors11in the present modification each detect the same object (points) to produce a signal. From the signals output from the radar sensors11, a signal of the reflected wave having the lowest level of reflected power is selected. Based on the selected signal, the travel-restricted area is defined for the object.

The processing performed in this case will now be described with reference toFIG.6. In step S101, the transmission-reception unit201transmits and receives a radar wave for each radar sensor11. In step S102, the processor202calculates the position (distance and direction) and the reflected power level of an object based on the output from each radar sensor11. In step S103, the processor202determines whether an object has been detected through the object detection. The determination result may be affirmative in response to any of the radar sensors11detecting an object.

In step S104, the determiner203determines whether the reflected waves from the object detected by the radar sensors11have reflected power levels all higher than or equal to a predetermined value. In step S105, the generator204selects, from signals output from the radar sensors11, a signal of the reflected wave having the lowest level of reflected power. Based on the selected signal, the generator204generates information about the travel-restricted area for the object.

In step S106, the output unit205outputs the information about the travel-restricted area to the travel controller13. In step S107, the output unit205outputs the information about the object to the travel controller13. In step S108, the output unit205outputs, to the travel controller13, information indicating no object detected.

A minimum travel-restricted area is thus defined based on a signal of a reflected wave having the lowest level of reflected power. The reflected waves detected for the same object may, for example, include reflected waves having reflected power levels higher than or equal to the predetermined value and reflected waves having reflected power levels lower than the predetermined value. In this case, the travel-restricted area may not be defined.

With the minimum travel-restricted area being defined, the vehicle1can have a maximum travel-permitted area with a minimum chance of collision with objects. The vehicle1is also less likely to decelerate or stop unintendedly.

<Others>

The above embodiments describe exemplary structures according to one or more aspects of the present invention. The present invention is not limited to the specific embodiments described above, but may be modified variously within the scope of the technical ideas of the invention.

For example, the vehicle is an AGV in the above embodiments. In some embodiments, the technique may be used for an autonomous vehicle for purposes other than transportation. The controller12in the above embodiments is included in the vehicle1. In some embodiments, the controller12may be at least partially located outside the vehicle1.

The travel-restricted distance in the above embodiments is longer for a reflected wave from an object having a higher level of reflected power. In some embodiments, the travel-restricted distance may be constant for a reflected power level higher than or equal to a predetermined value. In this case, the travel-restricted distance may be defined to accommodate the highest level of reflected power, for example.

The generator204in the above embodiments generates information about the travel-restricted area in accordance with the reflected power level of the reflected wave from an object. In some embodiments, the information may indicate that a virtual object is located at the outer edge (e.g., the two-dot chain line B1inFIG.4) of the travel-restricted area. In this case, the travel controller13generates a control command to avoid the virtual object.

APPENDIX 1

(1) A collision avoidance apparatus for an autonomous vehicle including at least one radar sensor11for transmitting a radar wave and receiving a reflected wave from an object, the apparatus comprising:a processor202configured to obtain, from a signal received by the at least one radar sensor11, information about a position of the object and information about a reflected power level of the reflected wave;a generator204configured to generate, in response to the reflected power level being higher than or equal to a predetermined value, information about a travel-restricted area, the travel-restricted area being an area adjacent to the object and in which the autonomous vehicle is restricted from traveling; andan output unit205configured to output the information about the travel-restricted area.

REFERENCE SIGNS LIST

1vehicle11radar sensor12controller13travel controller14drive102transmitting antenna103receiving antenna201transmission-reception unit202processor203determiner204generator205output unit