Moving body and method for determining path of moving body

Abstract

The present invention provides a moving body and a path determination method for the moving body. The moving body travels from a current position toward a target position, and includes: a first section candidate search unit that searches for a plurality of first section candidates that the moving body can travel from the current position within a preset first set time; a second section candidate search unit that, for each end point of the first section candidates, searches for a plurality of second section candidates that the moving body can travel from the end point of the first section candidates within a preset second set time; a target direction recognition unit that recognizes a target direction that is the existence direction of the target position; an obstacle position recognition unit that detects the positions of obstacles around the moving body; and a path determination unit that determines a first section and a second section to be used as a path traveled by the moving body from among the plurality of first section candidates and the plurality of second section candidates based on the target direction and the positions of the obstacles.

Description

Technical Field

[0001] The present disclosure relates to a moving body and a method for determining a path of the moving body. Background Art

[0002] Conventionally, as a technical document related to path determination of a moving body, Japanese Unexamined Patent Application Publication No. 2012-243029 is known. In this publication, the following technique is disclosed. In a moving body that generates a global path for reaching a final destination from a current position, when an obstacle is detected ahead, a plurality of candidates for local paths that avoid the obstacle and return to the global path are generated. For each of the generated plurality of candidates for local paths, the moving body calculates an evaluation value based on the angle formed with the final destination, the movable speed, and the distance from the obstacle, and adopts the candidate with the maximum evaluation value as the local path for avoiding the obstacle. In addition, in this publication, a method of using DWA (Dynamic Window Approach) in the generation of path candidates is disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-243029

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Fox, D., Burgard, W., Thrun, S. “The dynamic windows approach to collision avoidance. IEEE Robotics and automation magazine (Avoiding collisions with the dynamic window method. IEEE Robotics and Automation Magazine) 4(1)(1997)” Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, in the above-described conventional moving body, there is a problem that only relatively simple path generation can be performed, and a path that enables smooth movement cannot be obtained when entering a narrow road or the like.

[0010] Means for Solving the Problems

[0011] One aspect of the present disclosure is a mobile body that travels from a current position toward a target position and includes: a first section candidate search unit that searches for a plurality of first section candidates that the mobile body can travel from the current position within a preset first set time; a second section candidate search unit that searches for a plurality of second section candidates that the mobile body can travel from the end point of the first section candidate within a preset second set time for each end point of the first section candidate; a target direction recognition unit that recognizes a target direction that is the direction where the target position exists; an obstacle position recognition unit that detects the positions of obstacles around the mobile body; and a path determination unit that determines a first section and a second section to be used as the path traveled by the mobile body from among the plurality of first section candidates and the plurality of second section candidates based on the target direction and the positions of the obstacles.

[0012] According to the mobile body related to one aspect of the present disclosure, by performing a path search in multiple stages including at least the first section candidate and the second section candidate, and determining the first section and the second section to be used as the path traveled by the mobile body, it is possible to obtain a path with higher flexibility and smooth travel of the mobile body compared to the existing technology that performs a path search in only one stage.

[0013] In the mobile body related to one aspect of the present disclosure, it may also be configured as follows: a travel state recognition unit that recognizes the translational speed of the mobile body at the current position is further provided, and the path determination unit determines the first section in such a way that the difference between the translational speed of the mobile body at the current position and the first translational speed that is the translational speed of the mobile body among the plurality of first section candidates is less than the first translational speed threshold.

[0014] In the mobile body related to one aspect of the present disclosure, it may also be configured as follows: a travel state recognition unit that recognizes the rotational speed of the mobile body at the current position is further provided, and the path determination unit determines the first section in such a way that the difference between the rotational speed of the mobile body at the current position and the first rotational speed that is the rotational speed of the mobile body among the plurality of first section candidates is less than the first rotational speed threshold.

[0015] In the mobile body related to one aspect of the present disclosure, it may also be configured as follows: the path determination unit determines the second section in such a way that the difference between the second translational speed that is the translational speed of the mobile body among the plurality of second section candidates with the end point of the determined first section as the starting point and the first translational speed that is the translational speed of the mobile body in the first section is less than the second translational speed threshold.

[0016] In the moving body according to one aspect of the present disclosure, it is also possible to adopt the following aspect, that is, the path determination unit determines the second interval in such a manner that the difference between the second rotational speed, which is the rotational speed of the moving body among a plurality of second interval candidates having the end point of the determined first interval as the starting point, and the first rotational speed, which is the rotational speed of the moving body in the first interval, is less than the second rotational speed threshold value.

[0017] Another aspect of the present disclosure is a path determination method for a moving body, which is a path determination method for a moving body traveling from a current position toward a target position, and includes: a first interval candidate search step of searching for a plurality of first interval candidates that the moving body can travel from the current position under a preset first speed condition within a preset first setting time; a second interval candidate search step of searching for a plurality of second interval candidates that the moving body can travel from the end point of the first interval candidate under a preset second speed condition within a preset second setting time for each end point of the first interval candidate; a target direction recognition step of recognizing the target direction, which is the direction where the target position exists; an obstacle position recognition step of detecting the positions of obstacles around the moving body; and a path determination step of determining a first interval and a second interval to be used as the path traveled by the moving body from among the plurality of first interval candidates and the plurality of second interval candidates based on the target direction and the positions of the obstacles.

[0018] According to the path determination method for a moving body according to another aspect of the present disclosure, by performing path searches in multiple stages including at least the first interval candidate and the second interval candidate, and determining the first interval and the second interval to be used as the path, it is possible to obtain a path with higher flexibility and smooth travel of the moving body compared to the existing technology that performs only one-stage path search.

[0019] Advantageous Effects of the Invention

[0020] According to one aspect and another aspect of the present disclosure, compared to the existing technology that performs only one-stage path search, it is possible to obtain a path with higher flexibility and smooth travel of the moving body. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a block diagram showing a moving body according to one embodiment.

[0022] FIG. 2(a) is a diagram showing an example of the search result of a plurality of first interval candidates. FIG. 2(b) is a diagram showing an example of the search result of second interval candidates extending from a plurality of first interval candidates. FIG. 2(c) is a diagram showing an example of the search result of a plurality of second interval candidates extending from a plurality of first interval candidates.

[0023] Figure 3 A diagram for explaining the effective distance in the target direction.

[0024] Figure 4(a) is a diagram showing an example of path determination. Figure 4(b) is a diagram showing another example of path determination.

[0025] Figure 5 A flowchart showing an example of the path determination process of the moving body.

[0026] Figure 6(a) is a flowchart showing an example of the first translational speed evaluation process. Figure 6(b) is a flowchart showing an example of the first rotational speed evaluation process.

[0027] Figure 7(a) is a flowchart showing an example of the second translational speed evaluation process. Figure 7(b) is a flowchart showing an example of the second rotational speed evaluation process.

[0028] Figure 8(a) is a diagram showing an example of a path searched by the prior art. Figure 8(b) is a diagram showing an example of a path obtained by the moving body according to the present embodiment. Detailed Embodiment

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0030] Figure 1 A block diagram showing a moving body according to an embodiment. Figure 1 The moving body 1 shown is a moving object such as a car, a personal mobility device, or a robot that travels on the ground from the current position toward the target position. The moving body 1 may also be an autonomously driving vehicle (self-driving vehicle), an autonomously driving personal mobility device, or an autonomously driving robot.

[0031] [Structure of the Moving Body]

[0032] With reference to the drawings, the structure of the moving body 1 according to the present embodiment will be described. As Figure 1 shown, the moving body 1 includes a control device 10 that controls the moving body 1.

[0033] The control device 10 is an electronic control unit having a CPU (Central Processing Unit) and a storage unit. The control device 10 can also be configured as an ordinary computer. The storage unit can be a ROM (ReadOnly Memory) and / or a RAM (Random Access Memory), or can be a storage medium such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive) configured in a RAID (Redundant Arrays of Inexpensive Disks) structure. The control device 10 can also be equipped with a communication device such as a network card for communicating with the outside. The control device 10 can also be equipped with an input / output device for exchanging information with the user.

[0034] Connected to the control device 10 are a GNSS (Global Navigation Satellite System) receiver 2, a radar sensor 3, a camera 4, a speed sensor 5, an acceleration sensor 6, a rotational speed sensor 7, and a moving body drive unit 8.

[0035] The GNSS receiver 2 is provided on the moving body 1 and measures the position of the moving body 1 (e.g., the latitude and longitude of the moving body 1) by receiving signals from four or more GNSS satellites. The GNSS receiver 2 sends the measured position information of the moving body 1 to the control device 10. In addition, the moving body 1 does not necessarily have to have the GNSS receiver 2.

[0036] The radar sensor 3 is a detection device provided on the moving body 1 that detects obstacles around the moving body 1 using electromagnetic waves. The radar sensor 3 can be a millimeter-wave radar or a LiDAR (Light Detection and Ranging). The radar sensor 3 sends the detection result of the obstacles around the moving body 1 to the control device 10.

[0037] The camera 4 is a imaging device provided on the moving body 1 that images the surroundings of the moving body 1. The camera 4 sends the captured image of the surroundings of the moving body 1 to the control device 10. The camera can be a monocular camera or a stereo camera or a TOF (Time of Flight) camera capable of obtaining distance information. In addition, the moving body 1 only needs to have at least one of the radar sensor 3 and the camera 4.

[0038] The speed sensor 5 is a detection device that detects the translational speed of the moving body 1. The translational speed of the moving body 1 refers to the speed of the change in the position of the moving body 1. The speed sensor 5 detects the translational speed based on, for example, the wheel speed of the moving body 1. In addition, the moving body 1 is not limited to wheel movement. The moving body 1 can also be, for example, bipedal walking or quadrupedal walking. The speed sensor 5 sends the detection result of the translational speed of the moving body 1 to the control device 10.

[0039] The acceleration sensor 6 is a detection device that detects the acceleration of the moving body 1. The acceleration sensor 6 can also distinguish and detect the acceleration in the front-rear direction and the lateral acceleration of the moving body 1. The acceleration sensor 6 sends the detection result of the acceleration of the moving body 1 to the control device 10. In addition, the moving body 1 does not necessarily have to be equipped with the acceleration sensor 6.

[0040] The rotational speed sensor 7 is a detection device that detects the rotational speed of the moving body 1. The rotational speed sensor 7 sends the detection result of the rotational speed of the moving body 1 to the control device 10. In addition, a yaw rate sensor that sends the yaw rate (rotational angular velocity) instead of the rotational speed of the moving body 1 can also be used.

[0041] The moving body drive unit 8 is a drive device for causing the moving body 1 to travel. The moving body drive unit 8 is configured, for example, to include various actuators that drive the wheels of the moving body 1. The structure of the moving body drive unit 8 is not particularly limited, and it can adopt a structure corresponding to the type of the moving body 1.

[0042] When the moving body 1 is a vehicle, the moving body drive unit 8 can also include an engine actuator, a brake actuator, and a steering actuator. The engine actuator controls the supply amount of air (throttle opening) to the engine of the vehicle according to a control signal from the control device 10, and further controls the driving force of the vehicle. In addition, when the vehicle is a hybrid vehicle, in addition to the supply amount of air to the engine, a control signal from the control device 10 is also input to the motor as a power source to control the driving force. When the vehicle is an electric vehicle, a control signal from the control device 10 is input to the motor as a power source to control the driving force.

[0043] The brake actuator controls the brake system according to a control signal from the control device 10 and controls the braking force applied to the wheels of the vehicle. As the brake system, for example, a hydraulic brake system can be used. The steering actuator controls the drive of the auxiliary motor that controls the steering torque in the electric power steering system of the vehicle according to a control signal from the control device 10. Thereby, the steering actuator controls the steering torque of the vehicle.

[0044] Next, the functional structure of the control device 10 will be described. As Figure 1 shown, the control device 10 includes a traveling state recognition unit 11, a target direction recognition unit 12, a first section candidate search unit 13, a second section candidate search unit 14, an obstacle position recognition unit 15, a path determination unit 16, and a moving body control unit 17. Additionally, it is also possible to adopt the following method, that is, a part of the functions of the control device 10 described below are calculated in a server capable of communicating with the moving body 1.

[0045] The traveling state recognition unit 11 recognizes the traveling state of the moving body 1. The traveling state includes the translational speed and rotational speed of the moving body 1. The traveling state may include the acceleration of the moving body 1 or the yaw rate. The traveling state recognition unit 11 recognizes the traveling state of the moving body 1 based on the detection results of, for example, the speed sensor 5, the acceleration sensor 6, and the rotational speed sensor 7.

[0046] The target direction recognition unit 12 recognizes the target direction of the moving body 1 based on the current position of the moving body 1 and a preset target position. The target position refers to the position preset as the arrival target of the moving body 1. The target position can be set by inputting target coordinate values onto a plane coordinate including the current position of the moving body 1, for example. The target position can be set by the user (occupant or manager, etc.) of the moving body 1 or the moving body 1 can autonomously set it according to preset conditions. The method for setting the target position is not particularly limited.

[0047] The target direction refers to the direction in which the target position exists with respect to the current position of the moving body 1. The target direction corresponds to the extension direction of the straight line connecting the current position and the target position. As an example, the target direction recognition unit 12 recognizes the target direction based on the target position (target coordinate values) on the plane coordinate with respect to the current position of the moving body 1.

[0048] Additionally, the target direction recognition unit 12 can also use map information to recognize the target direction. The target direction recognition unit 12 recognizes the current position of the moving body 1 on the map based on the position information of the moving body 1 received by the GNSS receiver 2. The target direction recognition unit 12 can also use dead reckoning or SLAM (Simultaneous Localization and Mapping) technology to recognize the current position of the moving body 1 on the map. The target direction recognition unit 12 can recognize the target direction based on the current position of the moving body 1 on the map and the target position set on the map.

[0049] In addition, the target direction recognition unit 12 can also recognize the target direction by means of a magnetic marker placed at the target position and a magnetic marker receiver provided on the moving body 1.

[0050] Starting from the current position of the moving body 1, the first interval candidate search unit 13 searches for a plurality of first interval candidates that are candidates for the first interval. The first interval refers to the interval that constitutes the path traveled by the moving body 1. The first interval candidate is a candidate for the first interval. The first interval candidate is searched for as an interval within which the moving body 1 can travel from the current position within a preset first setting time. The first setting time can be 1 second, 3 seconds, 5 seconds, 10 seconds, 15 seconds, or 1 minute. The first setting time can also be a time corresponding to the control cycle of the control device 10 of the moving body 1. The first setting time can be set to any time.

[0051] As the DWA (Dynamic Window Approach), the first interval candidate search unit 13 searches for first interval candidates within which the moving body 1 can travel from the current position within the first setting time. Regarding the DWA, it is described in "Fox, D., Burgard, W., Thrun, S.: The dynamic windows approach to collision avoidance. IEEE Robotics and automation magazine 4(1)(1997)". The evaluation function and others will be described later.

[0052] The first interval candidate search unit 13 performs the search for the first interval candidate based on, for example, a preset first speed condition. As an example, the first speed condition is a combination of the translational speed and the rotational speed preset by the user. The first speed condition can also be set such that, for example, when the rotational speed becomes a fixed value or more due to a large curvature, the translational speed becomes lower. The first speed condition can be set according to the traveling performance of the moving body 1. If the translational speed and / or the rotational speed are different, the first interval candidate search unit 13 can also search for a plurality of first interval candidates in an overlapping manner.

[0053] The first interval candidate search unit 13 searches for a plurality of first interval candidates on the assumption that the moving body 1 travels on a plane where there are no objects around it. In addition, the first interval candidate search unit 13 can also perform the search in such a way that a plurality of first interval candidates are appropriately separated by, for example, giving an angle condition (such as a sin or cos condition).

[0054] FIG. 2(a) is a diagram showing an example of a search result of a plurality of first interval candidates. In FIG. 2(a), a first interval candidate PA, a starting point Sa (the current position of the moving body 1) of the first interval candidate PA, and an end point (arrival point) Ea of the first interval candidate PA are shown. In FIG. 2(a), using the XY plane coordinate system, the starting point Sa corresponds to (X, Y): (0, 0). As shown in FIG. 2(a), the first interval candidate search unit 13 searches for a plurality of first interval candidates PA that extend forward from the current position of the moving body 1 as the starting point Sa.

[0055] In addition, in FIG. 2(a), although it is assumed that the moving body 1 can only move forward and a plurality of first interval candidates PA are shown, the moving body 1 can also move in directions other than the forward direction. For example, when the moving body 1 can move backward, a plurality of first interval candidates PA that are reversed in the X-axis direction with the starting point Sa as the center (a plurality of first interval candidates PA that extend in the negative Y-axis direction) can be additionally searched. When the moving body 1 can move in an arbitrary direction of 360°, a plurality of first interval candidates PA that extend in the 360° direction with the starting point Sa as the center in the same manner as FIG. 2(a) can also be additionally searched. An upper limit can also be set for the number of first interval candidates PA searched.

[0056] The second interval candidate search unit 14 searches for a plurality of second interval candidates that are candidates for the second interval, respectively, with the end points Ea of the plurality of first interval candidates PA as the starting points. The second interval refers to an interval that follows the first interval and constitutes the path traveled by the moving body 1. The second interval candidate is searched as an interval in which the moving body 1 can travel from the end point Ea of the first interval candidate PA within a preset second setting time.

[0057] The second setting time can be 1 second, 3 seconds, 5 seconds, 10 seconds, 15 seconds, or 1 minute. The second setting time can also be a time corresponding to the control cycle of the control device 10 of the moving body 1. The second setting time can be the same as or different from the first setting time. The second setting time can also be a time longer than the first setting time. The second setting time can be set to any time.

[0058] As the DWA, the second-section candidate search unit 14 searches for second-section candidates that the mobile body 1 can travel from the end point Ea of the first-section candidate PA within the second set time. The second-section candidate search unit 14 performs the search for second-section candidates based on, for example, a second speed condition set in advance. As an example, the second speed condition is a combination of a translational speed and a rotational speed preset by the user. The second speed condition may be the same as or different from the first speed condition. If the translational speed and / or the rotational speed is different, the second-section candidate search unit 14 may also search for multiple second-section candidates in an overlapping manner.

[0059] The second-section candidate search unit 14 also assumes that the mobile body 1 travels on a plane where there are no surrounding objects to search for multiple second-section candidates. In addition, the second-section candidate search unit 14 also performs the search in such a way that multiple second-section candidates are appropriately separated by, for example, imposing an angular condition (such as a sine or cosine condition).

[0060] FIG. 2(b) is a diagram showing an example of the search result of multiple second-section candidates extending from the first-section candidate (only one candidate). Here, for ease of understanding the description, only one candidate of the first-section candidate is shown. In FIG. 2(b), the second-section candidate PB, the start point Sb of the second-section candidate PB (the same as the end point Ea of the first-section candidate PA), and the end point (arrival point) Eb of the second-section candidate PB are shown.

[0061] In FIG. 2(b), a case is shown where multiple second-section candidates PB are searched by extending the first-section candidate PA shown in FIG. 2(a). The second-section candidate search unit 14 may also perform the search for the second-section candidate PB in such a way as to allow a change in the orientation of the mobile body 1 at the start point Sb of the second-section candidate PB.

[0062] FIG. 2(c) is a diagram showing an example of the search result of multiple second-section candidates extending from multiple first-section candidates. In FIG. 2(c), the symbols are omitted for easy viewing of the drawing. For example, as shown in FIG. 2(c), the second-section candidate search unit 14 searches for multiple second-section candidates PB that the mobile body 1 can travel from the end point Ea of the first-section candidate PA.

[0063] In addition, when the mobile body 1 can move backward, it is possible to additionally search for a plurality of first interval candidates PA and second interval candidates PB that are reversed in the X-axis direction with the starting point Sa as the center. Similarly, when the mobile body 1 can move in an arbitrary direction of 360°, it is also possible to additionally search for a plurality of first interval candidates PA and second interval candidates PB that are expanded in the 360° direction centered on the starting point Sa in the same manner as in FIG. 2(c). It is also possible to set an upper limit on the number of searches for the second interval candidates PB.

[0064] The obstacle position recognition unit 15 recognizes the positions of obstacles around the mobile body 1 based on the detection results of obstacles by the radar sensor 3 and / or the captured images of the camera 4. An obstacle refers to an object that becomes an obstacle to the movement of the mobile body 1. Among the obstacles, there are structures such as walls, installations such as pillars, pedestrians, or other mobile bodies. The obstacle position recognition unit 15 can also recognize the positions of obstacles through communication from an external server (for example, the server of the facility where the mobile body 1 is traveling or a traffic information server).

[0065] Based on the target direction recognized by the target direction recognition unit 12 and the positions of the obstacles recognized by the obstacle position recognition unit 15, the path determination unit 16 determines the first interval and the second interval to be used as the path traveled by the mobile body 1 from among the first interval candidates PA and the second interval candidates PB.

[0066] Specifically, the path determination unit 16 evaluates the first interval candidates PA and the second interval candidates PB based on the target direction and the positions of the obstacles. The path determination unit 16 calculates the evaluation values of the first interval candidates PA and the second interval candidates PB using, for example, the evaluation function Ga shown as the following formula (1).

[0067]

Mathematical formula 1

[0068] Ga = a·C + b·L…(1)

[0069] In the above formula (1), G is the evaluation function, C is the closest distance to the obstacle, and L is the effective distance in the target direction. The closest distance to the obstacle C is the distance between the part closest to the obstacle in the first interval candidates PA and the second interval candidates PB to be evaluated and the obstacle. The closest distance to the obstacle C takes the value of -∞ when the first interval candidates PA and the second interval candidates PB to be evaluated are in contact with the obstacle.

[0070] L is the effective distance in the target direction (for example, the length when the first interval candidate PA is projected onto the target direction). Here, Figure 3 is a diagram for explaining the effective distance in the target direction. In Figure 3In it, a first interval candidate PA and a target direction T are shown. As Figure 3 shown, the effective distance of the target direction T is equivalent to the traveling distance of the first interval candidate PA on the target direction T. The longer the distance that the first interval candidate PA as the evaluation object travels toward the target direction T, the higher the evaluation. On the other hand, if the distance that the first interval candidate PA travels toward the target direction T is short, the evaluation will be low. When the first interval candidate PA travels in the direction opposite to the target direction T, it will result in a negative evaluation. a and b are adjustment parameters. The values of a and b are arbitrarily set by the user.

[0071] FIG. 4(a) is a diagram showing an example of path determination. In FIG. 4(a), the current position Sa of the moving body 1, the target position G1, the target direction T1, the walls (obstacles) W1 to W3, and the candidate paths C1 to C3 are shown. The candidate paths C1 to C3 are formed by a combination of the first interval candidate PA and the second interval candidate PB.

[0072] In the situation shown in FIG. 4(a), the path determination unit 16 calculates the highest evaluation value for the candidate path C3 that is appropriately separated from the walls W1 to W3 and has the longest effective distance in the target direction T1. Compared with the candidate paths C1 and C2, the path determination unit 16 evaluates the candidate path C3 that is slightly closer to the wall W1 but has a longer effective distance in the target direction T1 and is closer to the target position G1 as higher.

[0073] FIG. 4(b) is a diagram showing another example of path determination. In FIG. 4(b), the current position Sa of the moving body 1, the target position G2, the target direction T2, the walls (obstacles) W4 to W6, and the candidate paths C4 to C6 are shown. In the situation shown in FIG. 4(b), the path determination unit 16 calculates the highest evaluation value for the candidate path C6 that is appropriately separated from the walls W4 to W6 and has the longest effective distance in the target direction T2. Compared with the candidate paths C4 and C5 that are too close to the wall W4 and have a short effective distance in the target direction T2, the path determination unit 16 evaluates the candidate path C6 that is closer to the target position G2 as higher.

[0074] The path determination unit 16 may also perform evaluation considering changes in the translational speed and rotational speed. Specifically, the path determination unit 16 may calculate the evaluation value of the first interval candidate PA by using, for example, the evaluation function Gb expressed as the following formula (2).

[0075]

Mathematical formula 2

[0076] Gb = a·C + b·L + c·Aa…(2)

[0077] c is an adjustment parameter. The value of c is arbitrarily set by the user. Aa is a speed change determination value for the first interval candidate. Since other elements are the same as those in Equation (1), the description thereof is omitted. The speed change determination value Aa is used to reduce the evaluation value when the changes in the translational speed and rotational speed of the moving body 1 are above a fixed threshold value.

[0078] Specifically, the speed change determination value Aa is the difference (absolute value) between the translational speed v of the moving body 1 at the current position c and the first translational speed v1, which is the translational speed of the moving body 1 in the first interval candidate PA, and is the first translational speed threshold v max1 or more, and takes the value of -∞.

[0079] In addition, the speed change determination value Aa is the difference (absolute value) between the rotational speed w of the moving body 1 at the current position c and the first rotational speed w1, which is the rotational speed of the moving body 1 in the first interval candidate PA, and is the first rotational speed threshold w max1 or more, and takes the value of -∞. The first translational speed threshold v max1 and the first rotational speed threshold w max1 are threshold values of preset values. The first translational speed threshold v max1 can also be set to the value obtained by multiplying the maximum translational acceleration of the moving body 1 by the control period of the control device 10. Similarly, the first rotational speed threshold w max1 can also be set to the value obtained by multiplying the maximum rotational acceleration of the moving body 1 by the control period of the control device 10.

[0080] In addition, the rotational speed is distinguished according to the rotational direction. For example, the rotational speed in the right direction is set as a positive value, and the rotational speed in the left direction is set as a negative value for representation. When obtaining the difference in rotational speeds in the same direction, the absolute value of the difference obtained by subtracting the smaller value from the larger value is compared with the first rotational speed threshold w max1 When obtaining the difference in rotational speeds in the opposite direction, both are set as positive values for summation, and the summation value is used as the difference and compared with the first rotational speed threshold w max1 for comparison.

[0081] On the other hand, when the difference between the translational speed v of the moving body 1 at the current position c and the first translational speed v1 is less than the first translational speed threshold v max1 , and the difference between the rotational speed w of the moving body 1 at the current position c and the first rotational speed w1 is less than the first rotational speed threshold w max1 , the speed change determination value Aa takes the value of zero.

[0082] The path determination unit 16 can exclude the first interval candidate PA, in which the translational speed and rotational speed of the moving body 1 change abruptly and thus cannot travel smoothly, from the path traveled by the moving body 1 by using the evaluation function Gb including the above-described speed change determination value Aa.

[0083] Alternatively, it can be set such that the speed change determination value Aa only considers one of the translational speed and the rotational speed. The speed change determination value Aa can also be, for example, when the difference between the translational speed v of the moving body 1 at the current position and the first translational speed v1 is the first translational speed threshold v c take the value of -∞, or it can be when the difference between the rotational speed w of the moving body 1 at the current position and the first rotational speed w1 is the first rotational speed threshold w max1 take the value of -∞ in the above case. c take the value of -∞ in the above case. max1 take the value of -∞ in the above case.

[0084] In addition, the path determination unit 16 can also calculate the evaluation value of the second interval candidate PB by using, for example, the evaluation function Gc expressed as the following formula (3).

[0085]

Mathematical formula 3

[0086] Gc = a·C + b·L + c·Ab…(3)

[0087] c is an adjustment parameter. Ab is the speed change determination value for the second interval candidate. Since other elements are the same as those in formula (1), the description is omitted. The speed change determination value Ab takes the value of -∞ when the difference (absolute value) between the first translational speed v1 of the moving body 1 in the first interval candidate PA and the second translational speed v2 of the moving body 1 in the second interval candidate PB is the second translational speed threshold v max2 in the above case.

[0088] In addition, the speed change determination value Ab takes the value of -∞ when the difference (absolute value) between the first rotational speed w1 of the moving body 1 in the first interval candidate PA and the second rotational speed w2 of the moving body 1 in the second interval candidate PB is the second rotational speed threshold w max2 in the above case. The second translational speed threshold v max2 and the second rotational speed threshold w max2 are thresholds with preset values. The second translational speed threshold v max2 can be either the same value as the first translational speed threshold v max1 or a different value. The second rotational speed threshold w max2 can also be either the same value as the first rotational speed threshold w max1The values can be the same or different values.

[0089] On the other hand, when the difference between the first translational speed v1 and the second translational speed v2 of the speed change determination value Ab is less than the second translational speed threshold v max2 and the difference between the first rotational speed w1 and the second rotational speed w2 is less than the second rotational speed threshold w max2 it takes a zero value.

[0090] The path determination unit 16 can exclude the second interval candidate PB in which the translational speed and rotational speed of the moving body 1 change sharply and cannot travel smoothly from the path traveled by the moving body 1 by using the evaluation function Gc including the above-mentioned speed change determination value Ab.

[0091] In addition, it can be set such that the speed change determination value Ab only considers one of the translational speed and the rotational speed. The speed change determination value Ab can take a -∞ value only when the difference between the first translational speed v1 and the second translational speed v2 is the second translational speed threshold v max2 or more, or can take a -∞ value only when the difference between the first rotational speed w1 and the second rotational speed w2 is the second rotational speed threshold w max2 or more.

[0092] The path determination unit 16 determines the combination with the highest evaluation value as the first interval and the second interval from among the plurality of first interval candidates PA and the plurality of second interval candidates PB. The first interval and the second interval are intervals used as the path traveled by the moving body 1.

[0093] In addition, the path determination unit 16 can also determine the first interval and the second interval step by step. Instead of adopting the combination with the highest evaluation value (total value) among the plurality of first interval candidates PA and the plurality of second interval candidates PB, the path determination unit 16 determines the interval with the highest evaluation value among the plurality of first interval candidates PA as the first interval, and determines the interval with the highest evaluation value among the plurality of second interval candidates PB with the end point of the first interval as the starting point as the second interval.

[0094] The path determination unit 16 only needs to find a path to the target position (a part of the path to the target position), without having to find a path from the current position to the target position. The path determination unit 16 repeatedly executes the determination of the first interval and the second interval as the path at a fixed cycle. The path determination unit 16 can also execute the determination (update of the path) of the new first interval and the second interval while the moving body 1 is traveling on the first interval and the second interval determined once.

[0095] The mobile body control unit 17 controls the travel of the mobile body 1. The mobile body control unit 17 calculates the driving amount (e.g., wheel driving amount) for the travel of the mobile body 1 according to the path determined by the path determination unit 16. The mobile body control unit 17 implements the travel control of the mobile body 1 along the path by sending a control signal corresponding to the calculated driving amount to the mobile body drive unit 8.

[0096] For example, when the mobile body 1 has an opposed two-wheel type mobile mechanism in which the left and right wheels are arranged on an opposed axis, the mobile body control unit 17 calculates the rotational speeds of the left and right wheels. Specifically, the mobile body control unit 17 may use the translational speed v and the rotational speed w in the first interval, and use the following formulas (4) and (5) to obtain the rotational speed rl of the left wheel and the rotational speed rr of the right wheel.

[0097]

Mathematical formula 4

[0098] rl = v / (2πR)+(0.5H·w) / (2πR)...(4)

[0099] rr = v / (2πR)-(0.5H·w) / (2πR)...(5)

[0100] In the above formulas (4) and (5), R is the wheel radius of the mobile body 1, and H is the tread (distance between the centers of the wheels) of the mobile body 1. The mobile body control unit 17 implements the travel control of the mobile body 1 along the path by sending the rotational speed rl of the left wheel and the rotational speed rr of the right wheel calculated according to the above formulas (4) and (5) to the mobile body drive unit 8 as control signals.

[0101] [Path determination method of mobile body]

[0102] Next, a path determination method of the mobile body 1 according to the present embodiment will be described with reference to the drawings. Figure 5 It is a flowchart showing an example of the path determination process of the mobile body 1.

[0103] As Figure 5 shown, as S1, the control device 10 of the mobile body 1 identifies the target direction of the mobile body 1 through the target direction identification unit 12 (target direction identification step). The target direction identification unit 12 identifies the target direction of the mobile body 1 based on, for example, the current position of the mobile body 1 and a preset target position.

[0104] In S2, the control device 10 searches for a plurality of first interval candidates PA through the first interval candidate search unit 13 (first interval candidate search step). The first interval candidate search unit 13 searches for a plurality of first interval candidates PA that the moving body 1 can travel from the current position within a preset first set time, starting from the current position of the moving body 1.

[0105] In S3, the control device 10 searches for a plurality of second interval candidates PB through the second interval candidate search unit 14 (second interval candidate search step). The second interval candidate search unit 14 searches for a plurality of second interval candidates PB that the moving body 1 can travel from the end point Ea of the first interval candidates PA within a preset second set time, starting from the end point Ea of the first interval candidates PA.

[0106] In S4, the control device 10 identifies the positions of obstacles around the moving body 1 through the obstacle position identification unit 15 (obstacle position identification step). The obstacle position identification unit 15 identifies the positions of obstacles around the moving body 1 based on, for example, the detection results of obstacles by the radar sensor 3 and / or the captured images of the camera 4.

[0107] In S5, the control device 10 calculates evaluation values through the path determination unit 16. The path determination unit 16 evaluates the first interval candidates PA and the second interval candidates PB based on the target direction and the positions of the obstacles (evaluation step). The path determination unit 16 calculates the evaluation values of the first interval candidates PA and the second interval candidates PB using, for example, the evaluation function Ga represented as the above formula (1).

[0108] In S6, the control device 10 performs path determination (determination of the first interval and the second interval) through the path determination unit 16 (path determination step). The path determination unit 16 determines, for example, the combination with the highest evaluation value as the first interval and the second interval from among the plurality of first interval candidates PA and the plurality of second interval candidates PB.

[0109] In S7, the control device 10 performs driving control of the moving body 1 through the moving body control unit 17 (driving control step). The moving body control unit 17 controls the moving body 1 to travel along the path determined by the path determination unit 16 by sending a control signal to the moving body drive unit 8.

[0110] FIG. 6(a) is a flowchart showing an example of the first translational speed evaluation process. The first translational speed evaluation process is executed in S5 of the flowchart shown in Figure 5 is shown.

[0111] As shown in FIG. 6(a), as S10, the control device 10 determines the translational velocity v of the moving body 1 at the current position through the path determination unit 16 c and determines whether the difference (absolute value) between the translational velocity v of the moving body 1 and the first translational velocity v1, which is the translational velocity of the first interval candidate PA, is the first translational velocity threshold v max1 as described above (first translational velocity determination step).

[0112] When the control device 10 determines that the above difference is the first translational velocity threshold v max1 or more (S10: Yes), it transfers to S11. When the control device 10 does not determine that the above difference is the first translational velocity threshold v max1 or more (S10: No), it ends the first translational velocity evaluation process.

[0113] In S11, the control device 10 sets the evaluation value of the first interval candidate PA (the first interval candidate PA for which the determination in the above S10 is Yes) to -∞ through the path determination unit 16 (first translational velocity evaluation step). The path determination unit 16, for example, sets the value of the velocity change determination value Aa in the above formula (2) to -∞, thereby setting the evaluation value of the corresponding first interval candidate PA to -∞ so that it will not be selected as the first interval.

[0114] FIG. 6(b) is a flowchart showing an example of the first rotational velocity evaluation process. The first rotational velocity evaluation process is executed in S5 of the Figure 5 shown flowchart.

[0115] As shown in FIG. 6(b), as S20, the control device 10 determines the rotational velocity w of the moving body 1 at the current position through the path determination unit 16 c and determines whether the difference (absolute value) between the rotational velocity w of the moving body 1 and the first rotational velocity w1, which is the rotational velocity of the first interval candidate PA, is the first rotational velocity threshold w max1 as described above (first rotational velocity determination step).

[0116] When the control device 10 determines that the above difference is the first rotational velocity threshold w max1 or more (S20: Yes), it transfers to S21. When the control device 10 does not determine that the above difference is the first rotational velocity threshold w max1 or more (S20: No), it ends the first rotational velocity evaluation process.

[0117] In S21, the control device 10 sets the evaluation value of the first interval candidate PA (the first interval candidate PA for which the determination in S20 is yes) to -∞ through the path determination unit 16 (first rotational speed evaluation step). For example, the path determination unit 16 sets the evaluation value of the corresponding first interval candidate PA to -∞ by setting the value of the speed change determination value Aa in the above formula (2) to -∞ so that it will not be selected as the first interval.

[0118] FIG. 7(a) is a flowchart showing an example of the second translational speed evaluation process. The second translational speed evaluation process is executed in S5 of the flowchart shown below. Figure 5 as shown.

[0119] As shown in FIG. 7(a), in S30, the control device 10 determines through the path determination unit 16 whether the difference (absolute value) between the first translational speed v1 of the moving body 1 as the first interval candidate PA and the second translational speed v2 of the moving body 1 as the second interval candidate PB is the second translational speed threshold v max2 as described above (second translational speed determination step).

[0120] When the control device 10 determines that the above difference is greater than or equal to the second translational speed threshold v max2 (S30: yes), it proceeds to S31. When the control device 10 does not determine that the above difference is greater than or equal to the second translational speed threshold v max2 (S30: no), it ends the second translational speed evaluation process.

[0121] In S31, the control device 10 sets the evaluation value of the second interval candidate PB (the second interval candidate PB for which the determination in S30 is yes) to -∞ through the path determination unit 16 (second translational speed evaluation step). For example, the path determination unit 16 sets the evaluation value of the corresponding second interval candidate PB to -∞ by setting the value of the speed change determination value Ab in the above formula (3) to -∞ so that it will not be selected as the second interval.

[0122] FIG. 7(b) is a flowchart showing an example of the second rotational speed evaluation process. The second rotational speed evaluation process is executed in S5 of the flowchart shown below. Figure 5 as shown.

[0123] As shown in FIG. 7(b), in S40, the control device 10 determines through the path determination unit 16 whether the difference (absolute value) between the first rotational speed w1 of the moving body 1 as the first interval candidate PA and the second rotational speed w2 of the moving body 1 as the second interval candidate PB is the second rotational speed threshold w max2 as described above (second rotational speed determination step).

[0124] When the control device 10 determines that the above difference is greater than or equal to the second rotational speed threshold w max2 (S40: Yes), it proceeds to S41. When the control device 10 does not determine that the above difference is greater than or equal to the second rotational speed threshold w max2 (S40: No), the second rotational speed evaluation process ends.

[0125] In S41, the control device 10 sets the evaluation value of the second interval candidate PB (the second interval candidate PB for which the determination in S40 is Yes) to -∞ through the path determination unit 16 (second rotational speed evaluation step). For example, the path determination unit 1 sets the value of the speed change determination value Ab in the above formula (3) to -∞, thereby setting the evaluation value of the corresponding second interval candidate PB to -∞ so that it will not be selected as the second interval.

[0126] According to the moving body 1 (and the path determination method of the moving body 1) according to the present embodiment described above, by performing a multi-stage path search using DWA including at least the first interval candidate PA and the second interval candidate PB, and determining the first interval and the second interval to be used as the path traveled by the moving body 1 based on the target direction and the position of the obstacle, compared with the prior art that only performs a one-stage path search, a path with higher flexibility and smooth travel of the moving body 1 can be obtained.

[0127] Here, Fig. 8(a) is a diagram showing an example of a path obtained by the path determination method of an existing moving body. In Fig. 8(a), the current position Sa, path CZ, target position G10, target direction T10, narrow road N, and walls (obstacles) W10 to W13 of the existing moving body are shown. As shown in Fig. 8(a), in an existing moving body that only performs a one-stage path search, there is a case where a path that cannot enter the narrow road N formed by the wall W10 and the wall W11 cannot be searched.

[0128] Fig. 8(b) is a diagram showing an example of a path obtained by the moving body 1 according to the present embodiment. In Fig. 8(b), the path C10 of the moving body 1 is shown. As shown in Fig. 8(b), according to the moving body 1, by performing a multi-stage path search using DWA, a path with flexibility that can also correspond to the narrow road N and along which the moving body 1 can travel smoothly can be obtained. The moving body 1 can obtain a path that can also smoothly pass through or bypass the obstacle.

[0129] In addition, according to the moving body 1, with the translational speed v of the moving body 1 at the current position cThe difference from the first translational velocity v1, which is the translational velocity of the moving body 1 in the first interval candidate PA, is less than the first translational velocity threshold v max1 to determine the first interval, so that, compared with the case where the change in translational velocity is not considered, an interval in which the moving body 1 can move smoothly can be selected.

[0130] Similarly, for the moving body 1, by using the rotational velocity w of the moving body 1 at the current position c The difference from the first rotational velocity w1, which is the rotational velocity of the moving body 1 in the first interval candidate PA, is less than the first rotational velocity threshold w max1 to determine the first interval, so that, compared with the case where the change in rotational velocity is not considered, an interval in which the moving body can move smoothly can be selected.

[0131] In addition, for the moving body 1, by using the difference between the first translational velocity v1, which is the translational velocity of the moving body 1 in the first interval candidate PA, and the second translational velocity v2, which is the translational velocity of the moving body 1 in the second interval candidate PB, is less than the second translational velocity threshold v max2 to determine the second interval, so that, compared with the case where the change in translational velocity of the first interval and the second interval is not considered, an interval in which the moving body 1 can move smoothly can be selected.

[0132] Similarly, for the moving body 1, by using the difference between the first rotational velocity w1, which is the rotational velocity of the moving body 1 in the first interval candidate PA, and the second rotational velocity w2, which is the rotational velocity of the moving body 1 in the second interval candidate PB, is less than the second rotational velocity threshold w max2 to determine the second interval, so that, compared with the case where the change in rotational velocity of the first interval and the second interval is not considered, an interval in which the moving body can move smoothly can be selected.

[0133] As described above, although the embodiments of the present disclosure have been described, the present disclosure is not limited to the above embodiments. Based on the above embodiments, the present disclosure can be implemented in various ways with various changes and improvements based on the knowledge of those skilled in the art.

[0134] The moving body 1 may also have a third interval candidate search unit that searches for a plurality of third interval candidates that the moving body 1 can travel within a preset third set time, starting from the end point Eb of the second interval candidate PB. In this case, the path determination unit 16 calculates the evaluation values of the plurality of third interval candidates in the same manner as the second interval candidate PB and determines the third interval as the path traveled by the moving body 1. The moving body 1 may also further have a fourth interval candidate search unit and a fifth interval candidate search unit.

[0135] The path determination unit 16 may also use the driving amount (such as the wheel driving amount) of the mobile body 1 calculated in the previous operation by the mobile body control unit 17 to calculate the evaluation values of the first interval candidate PA and the second interval candidate PB. For example, similar to the translational speed and the rotational speed, the path determination unit 16 determines the first interval in such a manner that the difference between the driving amount of the mobile body 1 calculated in the previous operation and the driving amount of the mobile body 1 required to achieve the translational speed in the first interval candidate PA is less than the threshold value.

[0136] When the path determination unit 16 performs an evaluation considering changes in the translational speed and the rotational speed, it is not necessary to set the evaluation value of the first interval candidate PA with a large change in the translational speed to -∞. The path determination unit 16 may also use only the translational speed v of the mobile body 1 at the current position c The difference from the first translational speed v1 is used as the first translational speed threshold v max1 The first interval candidate PA above the above is excluded from the evaluation targets. The same applies to the rotational speed. In addition, the same applies to the second interval candidate PB.

[0137] The path determination unit 16 may also set the target direction when evaluating the second interval candidate PB to the direction in which the target position exists when observed from the start point Sb (the end point Ea of the first interval candidate PA) of the second interval candidate PB. Instead of directly using the target direction in the case of the first interval candidate PA (the direction in which the target position exists when observed from the current position of the mobile body 1) for the evaluation of the second interval candidate PB, the path determination unit 16 uses the target direction as the direction in which the target position exists when observed from the start point Sb of the second interval candidate PB. The longer the effective distance of the target direction, the higher the evaluation value of the second interval candidate PB is calculated. Thus, the path determination unit 16 can calculate a higher evaluation value for the second interval candidate PB that is closer to the target position under the condition of not being affected by the position deviation between the current position Sa of the mobile body and the start point Sb of the second interval candidate PB.

Claims

1. A moving body that travels from a current position toward a target position and includes: A first interval candidate search unit that searches for a plurality of first interval candidates that the moving body can travel from the current position within a preset first set time on the assumption that there are no objects around the moving body; A second interval candidate search unit that searches for a plurality of second interval candidates that the moving body can travel from the end point of each of the first interval candidates within a preset second set time on the assumption that there are no objects around the moving body; A target direction recognition unit that recognizes a target direction that is the direction where the target position exists; An obstacle position recognition unit that detects the position of an obstacle that is an object around the moving body and is an obstacle to the movement of the moving body; A path determination unit that determines a first interval and a second interval to be used as the path traveled by the moving body from among the plurality of first interval candidates and the plurality of second interval candidates based on the target direction and the position of the obstacle; The first interval candidate search unit searches for a plurality of first interval candidates with different conditions of the translational speed and / or the rotational speed of the moving body based on a plurality of combinations of the preset translational speed and the rotational speed of the moving body; The second interval candidate search unit searches for a plurality of second interval candidates with different conditions of the translational speed and / or the rotational speed of the moving body based on a plurality of combinations of the preset translational speed and the rotational speed of the moving body; The path determination unit determines the second interval in such a manner that the difference between a second translational speed that is the translational speed of the moving body among the plurality of second interval candidates with the end point of the determined first interval as the starting point and a first translational speed that is the translational speed of the moving body in the first interval is less than a second translational speed threshold; And determines the second interval in such a manner that the difference between a second rotational speed that is the rotational speed of the moving body among the plurality of second interval candidates with the end point of the determined first interval as the starting point and a first rotational speed that is the rotational speed of the moving body in the first interval is less than a second rotational speed threshold.

2. The moving body according to claim 1, wherein: It further includes a travel state recognition unit that recognizes the translational speed of the moving body at the current position; The path determination unit determines the first interval in such a manner that the difference between the translational speed of the moving body at the current position and a first translational speed that is the translational speed of the moving body among the plurality of first interval candidates is less than a first translational speed threshold.

3. The moving body according to claim 1, wherein: It further includes a travel state recognition unit that recognizes the rotational speed of the moving body at the current position; The path determination unit determines the first section in such a manner that the difference between the rotational speed of the moving body at the current position and the first rotational speed which is the rotational speed of the moving body in a plurality of the first section candidates is less than a first rotational speed threshold value.

4. The moving body according to claim 1, wherein the path determination unit calculates the closest distance to an obstacle and the effective distance in the target direction of the first section candidate based on the target direction and the position of the obstacle, and if the closest distance to the obstacle of the first section candidate is greater, the evaluation value of the first section candidate is calculated as a greater value, and if the effective distance of the first section candidate in the target direction is greater, the evaluation value of the first section candidate is calculated as a greater value. Based on the target direction and the position of the obstacle, calculate the closest distance to an obstacle and the effective distance in the target direction of the second section candidate, and if the closest distance to the obstacle of the second section candidate is greater, the evaluation value of the second section candidate is calculated as a greater value, and if the effective distance of the second section candidate in the target direction is greater, the evaluation value of the second section candidate is calculated as a greater value. Determine the first section candidate with the highest evaluation value among the plurality of first section candidates as the first section. Among the plurality of second section candidates where the difference between the first rotational speed and the second rotational speed of the first section is less than the second rotational speed threshold value and the difference between the first translational speed and the second translational speed of the first section is less than the second translational speed threshold value, determine the second section candidate with the highest evaluation value as the second section. The closest distance to an obstacle means the distance between the part closest to the obstacle in the first section candidate or the second section candidate and the obstacle. The effective distance means the length when the first section candidate or the second section candidate is projected onto the target direction.

5. A method for determining a path of a moving body, which is a method for determining a path of a moving body traveling from a current position toward a target position, and includes: a first section candidate search step of searching for a plurality of first section candidates that the moving body can travel from the current position within a preset first set time on the assumption that there are no objects around the moving body; a second section candidate search step of searching for a plurality of second section candidates that the moving body can travel from the end point of the first section candidate within a preset second set time for each end point of the first section candidate on the assumption that there are no objects around the moving body; a target direction recognition step of recognizing the target direction which is the direction where the target position exists; an obstacle position recognition step of detecting the position of an obstacle which is an object around the moving body and is an obstacle to the movement of the moving body. A path determination step of determining a first section and a second section to be used as a path for the moving body to travel from among a plurality of the first section candidates and a plurality of the second section candidates based on the target direction and the position of the obstacle. In the first section candidate search step, a plurality of the first section candidates with different conditions of the translational speed and / or the rotational speed of the moving body are searched based on a plurality of combinations of the translational speed and the rotational speed of the moving body preset in advance. In the second section candidate search step, a plurality of the second section candidates with different conditions of the translational speed and / or the rotational speed of the moving body are searched based on a plurality of combinations of the translational speed and the rotational speed of the moving body preset in advance. In the path determination step, the second section is determined such that a difference between a second translational speed of the moving body in a plurality of the second section candidates having an end point of the determined first section as a starting point and a first translational speed of the moving body in the first section is less than a second translational speed threshold. Further, the second section is determined such that a difference between a second rotational speed of the moving body in a plurality of the second section candidates having an end point of the determined first section as a starting point and a first rotational speed of the moving body in the first section is less than a second rotational speed threshold.

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