JP2020020683A - Obstacle detection device, and obstacle detection method - Google Patents

Abstract

To easily detect an obstacle in a short range region.SOLUTION: An obstacle detection device includes a short range obstacle detection unit. The short range obstacle detection unit includes: a sound reverberation termination time calculation unit for calculating a sound reverberation termination time; and a standard deviation calculation unit for calculating a standard deviation of the sound reverberation termination time; and a determination unit for determining whether or not an obstacle exists in a short range region. The reverberation termination time calculation unit calculates a sound reverberation termination time T2. A standard deviation calculation unit calculates a standard deviation of the sound reverberation termination time T2 for each calculation time of the sound reverberation termination time T2. The determination unit determines the presence/absence of an obstacle in the short range region whether or not the standard deviation exceeds a threshold.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an obstacle detection device and an obstacle detection method for detecting an obstacle.

  An obstacle detection device that detects an obstacle using ultrasonic waves includes an ultrasonic sensor and a control unit that detects an obstacle from the detection result of the ultrasonic sensor. The ultrasonic sensor includes a piezoelectric vibrator, a transmitting unit that transmits a ultrasonic wave from the piezoelectric vibrator by outputting a drive signal to the piezoelectric vibrator, and a receiving unit that detects a reception signal generated in the piezoelectric vibrator by a reflected wave. , Is provided. The control unit determines the presence or absence of an obstacle and calculates the distance to the obstacle from the time from transmission of the ultrasonic wave to reception of the reflected wave.

  When ultrasonic waves are transmitted from the ultrasonic sensor, reverberation occurs in the piezoelectric vibrator. The reverberation continues even after the output of the drive signal from the transmission unit stops. When an obstacle is present near the ultrasonic sensor, there is a possibility that a received signal generated by reverberation and a received signal generated by a reflected wave may be combined. Then, the reverberation and the reflected wave cannot be distinguished, and an obstacle may not be detected.

  In the obstacle detection device described in Patent Document 1, a reference reverberation time is set, and it is determined whether the reverberation time is longer than the reference reverberation time. When an obstacle exists near the ultrasonic sensor, the reverberation time becomes longer due to the influence of the reflected wave. Therefore, if the reverberation time is longer than the reference reverberation time, it can be determined that an obstacle exists near the ultrasonic sensor.

JP 2016-31354 A

  By the way, due to the influence of tolerances and the like, the reverberation time varies even for ultrasonic sensors of the same product. Therefore, in the obstacle detection device described in Patent Literature 1, it is necessary to set an individual reference reverberation time for each ultrasonic sensor, which is troublesome.

  An object of the present invention is to provide an obstacle detection device and an obstacle detection method that can easily detect an obstacle in a short distance area.

  An obstacle detection device that solves the above problem transmits an ultrasonic wave, an ultrasonic sensor that receives a reflected wave reflected by the obstacle, and a control unit that detects an obstacle from a detection result of the ultrasonic sensor, An obstacle detection device comprising: a drive command unit that sends a drive command to the ultrasonic sensor; andthe reflected wave by the ultrasonic sensor until the reverberation due to the transmission of the ultrasonic wave stops. If the area to be received is a short-distance area, a short-distance obstacle detection unit that detects an obstacle in the short-distance area is provided, and the short-distance obstacle detection unit operates until the reverberation of the ultrasonic sensor stops. A reverberation end time calculating unit that calculates a reverberation end time that is a time of, and an average value of the reverberation end time each time the reverberation end time is calculated, and a standard deviation calculation that calculates a standard deviation of the reverberation end time. Part and said And a determination unit that the obstacle exists in the short range when the quasi deviation exceeds a threshold value.

  If an obstacle is present in the short distance area, the reverberation time becomes longer due to the influence of the reflected wave. Further, when the ultrasonic wave propagates in the air, the attenuation of the ultrasonic wave changes depending on the atomic weight in the air. As a result, when a reflected wave from an obstacle in a short distance area is received, the reverberation end time varies due to reflected waves having different attenuations. On the other hand, when no obstacle is present in the short distance area, the reflected wave has no effect on the reverberation end time, and the reverberation end time is less likely to vary than when no obstacle is present in the short distance area. Therefore, the standard deviation of the reverberation end time is larger when an obstacle is present in the short distance area than when no obstacle is present in the short distance area. The obstacle detection device can determine whether or not an obstacle exists in the short-distance region by determining whether or not the standard deviation exceeds a threshold.

  As described above, the variation in the reverberation end time is due to the propagation of the ultrasonic wave in the air. Therefore, the standard deviation of the reverberation end time is hardly affected by the individual difference of the ultrasonic sensors due to the tolerance, and when setting the threshold to the standard deviation, the same threshold may be set regardless of the individual difference of the ultrasonic sensors. For this reason, an obstacle in a short-distance area can be detected more easily than in a case where individual thresholds are set according to individual differences between ultrasonic sensors.

  The obstacle detection device may include an obstacle detection unit that detects an obstacle in a region farther from the ultrasonic sensor than the short distance region. If an obstacle exists in a region farther than the short distance region, the reflected wave will be received after the reverberation has subsided. Therefore, the obstacle detection unit can detect the obstacle based on the propagation speed of the ultrasonic wave in the air and the time required from transmission of the ultrasonic wave to reception of the reflected wave. In addition to obstacles in the short distance area, obstacles in an area farther than the short distance area can be detected, so that obstacles can be detected over a wide range.

  In the obstacle detection device, the standard deviation calculation unit may correct the standard deviation with the average value. According to this, it is possible to improve the detection accuracy of the obstacle in the short distance area.

  An obstacle detection method for solving the above-mentioned problem is an obstacle detection method of transmitting an ultrasonic wave and detecting an obstacle from a detection result of an ultrasonic sensor that receives a reflected wave reflected by the obstacle, A drive command is sent to the acoustic wave sensor, and a reverberation end time, which is a time until the reverberation of the ultrasonic sensor stops, is calculated.Every time the reverberation end time is calculated, an average value of the reverberation end time, and the reverberation Calculate the standard deviation of the end time, and if the region where the reflected wave is received by the ultrasonic sensor is a short distance region until the reverberation due to the transmission of the ultrasonic wave stops, if the standard deviation exceeds a threshold value. It is determined that an obstacle exists in the short distance area. According to this, an obstacle in a short distance area can be easily detected.

  According to the present invention, an obstacle in a short distance area can be easily detected.

FIG. 1 is a schematic side view of a forklift on which an obstacle detection device is mounted. FIG. 2 is a block diagram showing a configuration of a forklift. FIG. 2 is a block diagram illustrating a configuration of an obstacle detection device. The figure which shows the relationship between a drive signal, a reception signal, and a digital signal when an obstacle does not exist in a short distance area | region. FIG. 4 is a diagram illustrating a relationship among a drive signal, a reception signal, and a digital signal when an obstacle exists in a short-distance region. 9 is a flowchart illustrating a process performed by the obstacle detection device. The figure which shows the relationship between a temperature and a standard deviation, and the relationship between a temperature and a variation coefficient.

Hereinafter, an embodiment of an obstacle detection device and an obstacle detection method will be described.
As shown in FIG. 1, the forklift 10 includes a vehicle body 11, a cargo handling device 12 provided in front of the vehicle body 11, and a counterweight 13 provided behind the vehicle body 11. Note that the forklift 10 may be a forklift operated by a passenger or a forklift operated automatically.

  As shown in FIG. 2, the forklift 10 includes a main controller 17, a cargo handling mechanism 14 for operating the cargo handling device 12, a driving mechanism 15 for running the forklift 10, and a key switch for switching the forklift 10 between a start state and a stop state. And 16.

  The main controller 17 includes a CPU 18 and a memory 19. The memory 19 stores a program for operating the forklift 10 and the like. When the forklift 10 is activated by the key switch 16, the main controller 17 controls the drive mechanism 15 and the cargo handling mechanism 14 to cause the forklift 10 to perform the cargo handling operation and the traveling operation. On the other hand, when the forklift 10 is stopped by the key switch 16, the main controller 17 does not cause the forklift 10 to perform the cargo handling operation or the traveling operation.

  An obstacle detection device 20 is mounted on the forklift 10. The obstacle detection device 20 includes an ultrasonic sensor 21 and a control ECU 30 that controls the ultrasonic sensor 21. The ultrasonic sensor 21 transmits an ultrasonic wave and receives a reflected wave of the transmitted ultrasonic wave. The control ECU 30 as a control unit is an electronic control unit including a CPU and a storage unit including a RAM, a ROM, and the like. Various programs for controlling the obstacle detection device 20 are stored in the storage unit. The control ECU 30 may include dedicated hardware for executing at least a part of various processes, for example, an application-specific integrated circuit (ASIC). The control ECU 30 may be configured as one or more processors operating according to a computer program, one or more dedicated hardware circuits such as an ASIC, or a circuit including a combination thereof. The processor includes a CPU and a memory such as a RAM and a ROM. The memory stores program codes or instructions configured to cause the CPU to execute processing. Memory, or computer readable media, includes anything that can be accessed by a general purpose or special purpose computer. The control ECU 30 is communicably connected to the main controller 17. In the present embodiment, the control ECU 30 is formed separately from the main controller 17, but may be integrated.

  As shown in FIG. 1, the ultrasonic sensor 21 is attached to the counterweight 13. The ultrasonic sensor 21 may be attached by providing a hole in the counterweight 13 and inserting the ultrasonic sensor 21 into the hole, or may be attached by screwing. The ultrasonic sensor 21 is attached so as to transmit an ultrasonic wave to the rear of the vehicle body 11. Therefore, the obstacle detected by the obstacle detection device 20 of the present embodiment is an obstacle existing behind the forklift 10.

  As shown in FIG. 3, the ultrasonic sensor 21 includes a piezoelectric vibrator 22, a transmission unit 23, a reception unit 24, and an A / D conversion unit 27. The ultrasonic sensor 21 is a transmission / reception-type ultrasonic sensor that uses one piezoelectric vibrator 22 for both transmission and reception. The transmission unit 23 outputs a drive signal to the piezoelectric vibrator 22. The transmission unit 23 includes, for example, a transmission unit that outputs a drive signal that is a burst signal, and a transformer that amplifies the drive signal. The piezoelectric vibrator 22 vibrates by receiving a drive signal and transmits ultrasonic waves. The piezoelectric vibrator 22 receives a transmitted reflected wave of the ultrasonic wave and vibrates to output a received signal based on the reflected wave. The receiving unit 24 detects a reception signal generated in the piezoelectric vibrator 22.

  The receiving unit 24 includes an amplifier circuit 25 that amplifies the received signal, and a detector 26 that outputs the received signal amplified by the amplifier circuit 25. The amplifier circuit 25 is configured by, for example, an operational amplifier. The detection unit 26 is an envelope detection unit that obtains an envelope from the reception signal amplified by the amplification circuit 25. The detector 26 outputs the envelope obtained from the received signal to the A / D converter 27.

  The A / D converter 27 converts an analog signal into a digital signal. The digital signal of the present embodiment is a binary signal that has been binarized to a high level or a low level. The A / D converter 27 outputs a high-level digital signal when an envelope whose reception level is equal to or higher than the lower threshold and lower than the upper threshold is input. The A / D converter 27 outputs a low-level digital signal when an envelope whose reception level is lower than the lower threshold and an envelope whose reception level is higher than the upper threshold are input. The A / D converter 27 includes, for example, a plurality of comparators.

  As shown in FIG. 4, when a drive command is given to the ultrasonic sensor 21 from a drive command unit 31 to be described later, the transmission unit 23 outputs a drive signal D, and the ultrasonic sensor 21 transmits an ultrasonic wave. While the ultrasonic wave is being transmitted by the vibration of the piezoelectric vibrator 22, the reception signal R1 is also generated. Further, the vibration of the piezoelectric vibrator 22 continues even after the output of the drive signal D is stopped. This vibration is reverberation. Due to the effect of reverberation, the received signal R1 is generated even after the driving signal D is stopped, and the high-level digital signal D1 is output. The reception signal R1 generated by the transmission of the ultrasonic wave is also called a reverberation signal.

  When the ultrasonic wave hits the obstacle, the ultrasonic wave returns to the piezoelectric vibrator 22 as a reflected wave. When a reflected wave hits the piezoelectric vibrator 22, the piezoelectric vibrator 22 vibrates. Due to this vibration, a reception signal R2 is generated, and a high-level digital signal D2 is output.

  The ultrasonic sensor 21 described above is not a dedicated product having a limited use, but a general-purpose product having many uses. That is, the ultrasonic sensor 21 of the present embodiment is an off-the-shelf product not designed for use in the obstacle detection device 20.

  As shown in FIG. 3, the control ECU 30 includes a drive command unit 31 that outputs a drive command to the ultrasonic sensor 21. When the drive command section 31 outputs a drive command, the ultrasonic sensor 21 is driven. The drive command unit 31 periodically outputs a drive command when the forklift 10 is activated by the key switch 16. The drive command unit 31 is realized as one function of the control ECU 30, and the control ECU 30 can be regarded as having a function of outputting a drive command.

  The control ECU 30 detects a short-range obstacle detection unit 40 that detects a short-range obstacle from the detection result of the ultrasonic sensor 21, and detects an obstacle that is farther from the short-range region from the detection result of the ultrasonic sensor 21. And an obstacle detection unit 32 that performs the operation. The short-range obstacle detection unit 40 and the obstacle detection unit 32 are realized as one function of the control ECU 30, and the control ECU 30 can be regarded as having these obstacle detection functions.

  The short-distance region is a region where the reflected wave is received by the piezoelectric vibrator 22 until the reverberation stops when an obstacle is present in the region. In other words, it is a region where a received signal is generated by a combined wave of reverberation and reflected waves. The size of the short distance region changes depending on the characteristics of the piezoelectric vibrator 22 and the environment in which the ultrasonic sensor 21 is used.

  The area farther than the short distance area is an area where the reflected wave is received by the piezoelectric vibrator 22 after the reverberation has subsided when an obstacle exists in the area. When detecting an obstacle present behind the forklift 10 as in the present embodiment, an area farther than the short distance area is an area behind the short distance area.

  As shown in FIG. 4, the obstacle detection unit 32 detects an obstacle in an area farther than the short distance area from the digital signal output from the A / D conversion unit 27. The obstacle detection unit 32 calculates a time T1 from transmission of the ultrasonic wave by the ultrasonic sensor 21 to reception of a reflected wave from the obstacle. The time td at which the ultrasonic sensor 21 transmits the ultrasonic wave is the time at which the drive command unit 31 outputs the drive command. The time td may be the time when the high-level digital signal D1 rises. The time tr when the reflected wave is received is the time when the high-level digital signal D2 rises. The obstacle detection unit 32 transmits the ultrasonic wave from the ultrasonic sensor 21 to the time td at which the ultrasonic sensor 21 transmits the ultrasonic wave and the time tr at which the ultrasonic sensor 21 receives the reflected wave, It is calculated as the time T1 until the reflected wave is received.

  The obstacle detection unit 32 determines that an obstacle exists when the high-level digital signal D2 rises after the high-level digital signal D1 due to the output of the drive signal D falls. Further, the obstacle detection unit 32 calculates the distance from the ultrasonic sensor 21 to the obstacle based on the propagation speed of the ultrasonic wave in the air and the calculated time T1. The obstacle detection unit 32 outputs a detection result to the main controller 17. The obstacle detection by the obstacle detection unit 32 is continuously performed while the forklift 10 is in the activated state.

Next, the short distance obstacle detection unit 40 will be described together with an obstacle detection method.
As shown in FIG. 3, the short-range obstacle detection unit 40 includes a reverberation end time calculation unit 41 that calculates a reverberation end time, a standard deviation calculation unit 42 that calculates a standard deviation of the reverberation end time, A determination unit 43 that determines whether an obstacle exists.

  As shown in FIG. 4, the reverberation end time calculation unit 41 calculates a reverberation end time T2. The reverberation end time T2 is a time from a predetermined measurement start time ts to a reverberation end time te. In the present embodiment, the measurement start time ts is the time td at which the drive command was output. Note that the measurement start time ts may be the rising time of the high-level digital signal D1 generated when the drive signal D is output. The reverberation end time te is a fall time of the high-level digital signal D1. In the present embodiment, the reverberation end time T2 is the same as the time at which the high-level digital signal D1 is output.

  The standard deviation calculator 42 calculates the standard deviation of the reverberation end time T2 every time the reverberation end time T2 is calculated. Further, the standard deviation calculation unit 42 calculates the average value of the reverberation end time every time the reverberation end time T2 is calculated. The standard deviation calculation unit 42 calculates the variation coefficient by correcting the standard deviation of the reverberation end time T2 with the average value of the reverberation end time T2. Specifically, the standard deviation calculator 42 obtains a coefficient of variation by dividing the standard deviation by the average value.

  Here, as shown in FIG. 5, when an obstacle exists in the short distance area, the variation of the reverberation end time T2 becomes large. If an obstacle exists in the short distance area, a reflected wave will be received during reverberation, and vibration due to the reflected wave will occur in addition to vibration due to the reverberation. The received signal R1 is a composite wave of the received signal due to the reverberation and the received signal due to the reflected wave, so that the reverberation time becomes longer. For example, in FIG. 4, since no obstacle exists in the short-distance region, the reception signal R1 includes waves due to reverberation for three cycles continuing after the driving signal D is stopped. On the other hand, in FIG. 5, due to the vibration due to the reflected wave in addition to the vibration due to the reverberation, the received signal R1 includes a reverberation wave for five periods continuing after the driving signal D is stopped, and the reverberation end time T2 is long. Has become. In the present embodiment, the reception signal R1 has a sine wave shape, but the shape of the reception signal R1 may vary depending on the type of the ultrasonic sensor 21 and the surrounding environment. Therefore, the reception signal R1 is not limited to the sine wave shape but may be another shape such as a pulse shape.

  Further, when the ultrasonic wave propagates in the air, the attenuation of the ultrasonic wave changes depending on the atomic weight in the air. For this reason, when a reflected wave from an obstacle in a short distance region is received, the reverberation end time T2 varies due to reflected waves having different attenuation amounts. On the other hand, when the obstacle does not exist in the short-range area, the reflected wave has no effect on the reverberation end time T2, and the reverberation end time T2 varies more than when no obstacle exists in the short-range area. Hateful. For this reason, when an obstacle is present in the short distance area, the standard deviation of the reverberation end time T2 has a larger value than when no obstacle is present in the short distance area.

The determination unit 43 determines whether or not an obstacle exists in the short-distance region by performing the processing illustrated in FIG.
As shown in FIG. 6, in step S1, the determination unit 43 determines whether the variation coefficient exceeds a threshold. As described above, the standard deviation of the reverberation end time T2 is larger when an obstacle is present in the short distance area than when no obstacle is present in the short distance area.

  Further, the reverberation end time T2 changes depending on the temperature characteristics of the members constituting the ultrasonic sensor 21. In addition, ultrasonic waves have a temperature dependence on the amount of attenuation when propagating in air. Therefore, the standard deviation of the reverberation end time T2 changes depending on the environmental temperature.

  For example, as shown in FIG. 7, when the conditions other than the environmental temperature are the same, the standard deviation of the reverberation end time T2 is calculated when the environmental temperature is −40 ° and when the environmental temperature is + 20 °. When the environmental temperature is −40 °, the standard deviation of the reverberation end time T2 is larger.

  In the present embodiment, in order to suppress the influence of the standard deviation due to the environmental temperature, the standard deviation is corrected by the average value, and the variation coefficient is calculated. The variation coefficient indicates the magnitude of variation relative to the average value. The variation coefficient is larger when an obstacle is present in the short distance area than when no obstacle is present in the short distance area. As shown in FIG. 7, the variation coefficient has little variation due to the influence of the environmental temperature. By using the variation coefficient, erroneous determination of the presence or absence of an obstacle due to the influence of the environmental temperature can be suppressed.

  The threshold value is set based on this value obtained by measuring the coefficient of variation calculated when an obstacle is present in the short-distance area by experiment or simulation. For example, the threshold is set to a value slightly smaller than a variation coefficient expected to be calculated when an obstacle is present in the short distance area.

  As shown in FIG. 6, when the determination result in step S1 is affirmative, the determination unit 43 determines in step S2 that an obstacle exists in the short distance area, and ends the process. On the other hand, when the determination result of step S1 is negative, the determination unit 43 performs the process of step S3.

  In step S3, the determination unit 43 determines whether the number of times of calculation of the reverberation end time T2 exceeds a predetermined number. That is, it is determined whether the standard deviation of the reverberation end time T2 and the population of the average value of the reverberation end time T2 exceed a predetermined number. When the determination result of step S3 is negative, the determination unit 43 performs the process of step S1. If the number of times the standard deviation of the reverberation end time T2 is calculated is only one, the standard deviation of the reverberation end time T2 may be accidentally reduced in spite of the presence of an obstacle in a short distance area. . For this reason, by performing determination until the number of times of calculation of the reverberation end time T2 exceeds a predetermined number, it is possible to accurately detect the presence or absence of an obstacle in a short-distance region. The predetermined number of times is set to the number of times that it is expected that a variation in the reverberation end time T2 will be obtained. For example, the predetermined number is set to 10 to 20 times.

  If the determination result in step S3 is affirmative, the determination unit 43 determines in step S4 that there is no obstacle in the short distance area, and ends the processing. Upon completion of the processing, the short-range obstacle detection unit 40 outputs the presence or absence of an obstacle to the main controller 17. In the present embodiment, the process by the short-range obstacle detection unit 40 is performed once when the stop state of the forklift 10 is switched to the start state by the key switch 16. This is because when the forklift 10 is switched from the stopped state to the activated state by the key switch 16, it is most difficult to detect an obstacle in the short distance area. When the forklift 10 is in the activated state, the obstacle detection unit 32 can detect an obstacle in an area farther than the short distance area. Therefore, when the forklift 10 is in the activated state, the obstacle detection unit 32 can detect an obstacle before the obstacle enters the short distance area due to the movement of the forklift 10.

  On the other hand, if the forklift 10 is switched from the stopped state to the activated state and an obstacle exists in the short distance area, the obstacle cannot be detected by the obstacle detection unit 32. That is, it is necessary for the short-range obstacle detection unit 40 to detect an obstacle existing in the short-range area when the forklift 10 is switched from the stopped state to the activated state. Therefore, the determination as to whether or not an obstacle exists in the short-distance area is performed only once when the stop state of the forklift 10 is switched to the start state by the key switch 16.

  The main controller 17 recognizes the presence or absence of an obstacle and the position of the obstacle from the detection results of the obstacle detection unit 32 and the short-range obstacle detection unit 40. The main controller 17 performs notification that the obstacle is close, limits the speed, and the like, according to the relative position between the obstacle and the forklift 10.

The operation of the embodiment will be described.
The short-range obstacle detection unit 40 detects an obstacle in a short-range region from the standard deviation of the reverberation end time T2. The ultrasonic sensor 21 may have a difference in reverberation time when transmitting an ultrasonic wave due to an individual difference due to tolerance, and a difference occurs in the absolute value of the reverberation end time T2 even if the ultrasonic wave is transmitted under the same condition. There are cases. If an attempt is made to detect an obstacle in a short distance region from the absolute value of the reverberation end time T2, it is necessary to set a threshold value of the reverberation end time T2 in accordance with the individual difference of the ultrasonic sensor 21.

  On the other hand, when detecting an obstacle in a short distance region from the standard deviation of the reverberation end time T2, the obstacle is detected based on a variation in the reverberation end time T2. The variation of the reverberation end time T2 is caused by the propagation of the ultrasonic sensor 21 in the air. Therefore, when setting a threshold value for the standard deviation, an obstacle in a short distance area can be detected by setting the same threshold value regardless of the individual difference of the ultrasonic sensor 21.

  It is also conceivable to detect an obstacle in a short distance area from the standard deviation of the signal level of the received signal. In this case, it is necessary to calculate a signal level from an analog signal before A / D conversion. Then, it is necessary to output the signal level of the received signal to the ultrasonic sensor 21, which causes the ultrasonic sensor 21 to be complicated.

  When detecting an obstacle in a short distance region from a digital signal output from the ultrasonic sensor 21 as in the present embodiment, a general-purpose ultrasonic sensor can be used. Therefore, there is no need to use a dedicated ultrasonic sensor that is assumed to be used only for the obstacle detection device 20 of the present embodiment.

The effects of the embodiment will be described.
(1) The determination unit 43 determines whether an obstacle is present in a short distance area based on whether the standard deviation exceeds a threshold. Since the standard deviation does not depend on the individual difference between the ultrasonic sensors 21, the threshold value can be set without considering the individual difference between the ultrasonic sensors 21. Therefore, an obstacle in a short-distance region can be detected more easily than in a case where individual threshold values are set in consideration of individual differences of the ultrasonic sensors 21.

  (2) The short-range obstacle detection unit 40 also detects an obstacle in an area farther than the short-range area. Therefore, it is possible to detect an obstacle not only in the short distance area but also in an area farther than the short distance area, and it is possible to detect an obstacle over a wide range.

  (3) A coefficient of variation is calculated by correcting the standard deviation by an average value, and an obstacle is detected using the coefficient of variation. The coefficient of variation is less affected by the environmental temperature. For this reason, it is possible to improve the detection accuracy of the obstacle in the short distance area. A similar effect can be obtained by detecting the environmental temperature with a temperature sensor and deriving the threshold from a map indicating the correspondence between the environmental temperature and the threshold. However, in this case, the number of temperature sensors is increased, and it is necessary to create a map indicating the correspondence between the environmental temperature and the threshold. On the other hand, by using the variation coefficient, it is possible to suppress an increase in the number of temperature sensors, and it is not necessary to create a map. Therefore, an increase in manufacturing cost can be suppressed.

  (4) An obstacle in a short distance area can be detected using the general-purpose ultrasonic sensor 21. By adding the processing performed by the control ECU 30, an obstacle in a short distance area can be detected. Therefore, it is possible to detect an obstacle in a short-distance region while suppressing an increase in manufacturing cost as compared with a case where a member is added to the general-purpose ultrasonic sensor 21 or a case where a dedicated ultrasonic sensor is manufactured. .

The embodiment can be modified and implemented as follows. The embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
O An obstacle in a short distance area may be detected from a standard deviation not corrected by the average value. In this case, it is preferable to set the threshold value of the standard deviation in consideration of the temperature of the environment where the obstacle detection device 20 is used.

  Further, the threshold value may be changed according to the temperature. The determination unit 43 grasps the environmental temperature from the detection result of the temperature sensor provided in the forklift 10. The obstacle detection device 20 includes a map in which the environmental temperature is associated with a threshold, and a memory in which a relational expression between the environmental temperature and the threshold is stored. The determining unit 43 derives a threshold value from the environmental temperature, and determines the presence or absence of an obstacle based on whether the standard deviation exceeds the derived threshold value.

  The obstacle detection device 20 only needs to be able to detect the presence or absence of an obstacle in a short distance area, and does not need to detect an obstacle in an area farther than the short distance area. In this case, it is preferable that an obstacle located in a region farther than the short distance region is detected by a device different from the obstacle detection device 20.

  The detection of the obstacle in the short distance area may be performed periodically while the forklift 10 is in the activated state. In this case, every time it is determined whether or not an obstacle exists in the short distance area, the reverberation end time T2 and the number of times of calculation of the reverberation end time T2 are reset.

  The ultrasonic sensor 21 may be an ultrasonic sensor including a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator. Even in this case, the ultrasonic wave transmitted from the transmitting piezoelectric vibrator is received by the receiving piezoelectric vibrator, or the vibration of the transmitting piezoelectric vibrator is transmitted to the receiving piezoelectric vibrator. Reverberation occurs in the receiving piezoelectric vibrator. Even in this case, similarly to the embodiment, the obstacle in the short distance area can be detected by calculating the standard deviation from the reverberation end time of the receiving piezoelectric vibrator.

  The obstacle detection device 20 may be mounted on any device that needs to detect an obstacle, such as an automobile, an industrial vehicle such as a towing tractor, or a robot that moves autonomously.

  The obstacle detection device 20 may detect an obstacle existing in front of the forklift 10 or on the side of the forklift 10. In this case, the ultrasonic sensor 21 may be attached to the forklift 10 so that ultrasonic waves are emitted in a direction in which an obstacle is to be detected. Note that the obstacle detection device 20 may be one that detects an obstacle in any one of the front, rear, and side directions, or one that detects obstacles in a plurality of directions. You may.

  The A / D converter 27 outputs a low-level digital signal when an envelope whose reception level is equal to or higher than the lower threshold and lower than the upper threshold is input, and outputs a high-level signal otherwise. It may be something.

  The A / D converter 27 may not have the upper threshold set. That is, the A / D converter 27 outputs a high-level digital signal when an envelope whose reception level is equal to or higher than the lower threshold is input, and outputs a low-level digital signal otherwise. You may.

  Reference Signs List 20: Obstacle detection device, 21: Ultrasonic sensor, 30: Control ECU (control unit), 31: Drive command unit, 32: Obstacle detection unit, 40: Short-range obstacle detection unit, 41: Reverberation end time calculation Unit, 42: standard deviation calculating unit, 43: determining unit.

Claims (4)

An ultrasonic sensor that transmits an ultrasonic wave and receives a reflected wave reflected by an obstacle,
An obstacle detection device, comprising: a control unit that detects an obstacle from the detection result of the ultrasonic sensor.
The control unit includes:
A drive command unit that sends a drive command to the ultrasonic sensor,
Assuming that the area where the reflected wave is received by the ultrasonic sensor is a short distance area until the reverberation due to the transmission of the ultrasonic wave is settled, a short distance obstacle detection unit that detects an obstacle in the short distance area, Prepared,
The short-range obstacle detection unit,
A reverberation end time calculation unit that calculates a reverberation end time that is a time until the reverberation of the ultrasonic sensor stops,
An average value of the reverberation end time every time the reverberation end time is calculated, and a standard deviation calculating unit that calculates a standard deviation of the reverberation end time,
A determining unit that determines that an obstacle exists in the short-distance region when the standard deviation exceeds a threshold value.   The obstacle detection device according to claim 1, further comprising an obstacle detection unit that detects an obstacle in a region farther from the ultrasonic sensor than the short distance region.   The obstacle detection device according to claim 1, wherein the standard deviation calculation unit corrects the standard deviation with the average value. An obstacle detection method that transmits an ultrasonic wave and detects an obstacle from a detection result of an ultrasonic sensor that receives a reflected wave reflected by the obstacle,
Send a drive command to the ultrasonic sensor,
Calculate the reverberation end time, which is the time until the reverberation of the ultrasonic sensor stops,
Each time the reverberation end time is calculated, the average value of the reverberation end time, and calculate the standard deviation of the reverberation end time,
If an area where the reflected wave is received by the ultrasonic sensor before the reverberation due to the transmission of the ultrasonic wave is set to a short distance area, an obstacle exists in the short distance area when the standard deviation exceeds a threshold. Obstacle detection method to determine.