Transport vehicle

Abstract

To provide a transport vehicle that can monitor driving stability with a simple configuration. [Solution] The transport vehicle 1 includes a first calculation unit 21 that calculates a first acceleration of the vehicle body based on the rotational position of the motor 4 that drives the wheels 6, a second calculation unit 22 that calculates a second acceleration of the vehicle body based on measurement data from a position and attitude measurement sensor 3 mounted on the vehicle body, a determination unit 23 that determines whether the difference vector between the first acceleration vector and the second acceleration vector exceeds a predetermined threshold, and an abnormality output unit 24 that outputs a message indicating that an abnormality has been detected when it is determined that the difference vector exceeds a predetermined threshold.

Description

[Technical Field]

[0001] This invention relates to an autonomous transport vehicle. [Background technology]

[0002] Patent Document 1 below discloses an automated guided vehicle (AGV) that travels unmanned on the floor of a factory or the like. This AGV drives its four drive wheels with four drive motors and turns based on the difference in rotational speed between the left and right drive wheels. The rotational speed of each drive wheel is determined by the steering angle detected by a steering sensor. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-52323 [Overview of the project] [Problems that the invention aims to solve]

[0004] The automated guided vehicle (AGV) described in Patent Document 1 uses the steering angle detected by a steering sensor and the rotational speed of each drive wheel to determine if a slip has occurred when any of the four drive wheels are operating at a rotational speed exceeding a predetermined value. However, AGVs that do not control turning motion with a steering angle do not have a steering sensor in the first place. In such AGVs, it is not possible to detect slip using the method described in Patent Document 1, so there is room for improvement.

[0005] Therefore, the present invention aims to provide a transport vehicle that can monitor the stability of its movement with a simple configuration. [Means for solving the problem]

[0006] A transport vehicle according to one aspect of the present invention includes: a first calculation unit that calculates a first acceleration of the vehicle body based on the rotational position of a motor that drives the wheels; a second calculation unit that calculates a second acceleration of the vehicle body based on measurement data from a position and attitude measuring sensor mounted on the vehicle body; a determination unit that determines whether the difference vector between the first acceleration vector and the second acceleration vector exceeds a predetermined threshold; and an abnormality output unit that outputs a message indicating that an abnormality has been detected when it is determined that the difference vector exceeds a predetermined threshold.

[0007] According to this embodiment, if the difference vector between the first acceleration vector calculated based on the rotational position of the motor driving the wheels and the second acceleration vector calculated based on the measurement data of the position and attitude measurement sensor mounted on the vehicle body exceeds a predetermined threshold, an abnormality can be detected and output. This makes it possible to output an abnormality in the driving state when it is determined that there is a discrepancy between the planned driving path of the transport vehicle and the path that the transport vehicle 1 actually traveled.

[0008] In the above embodiment, the first calculation unit may calculate the vehicle speed based on the change in the rotational position of the motor, and calculate the first acceleration based on the calculated change in speed.

[0009] According to this embodiment, it becomes possible to calculate the first acceleration based on the change in speed calculated based on the change in the rotational position of the motor.

[0010] In the above embodiment, the second calculation unit may calculate the axial components of the measurement data in a coordinate system based on the vehicle body based on the measurement data of the position and attitude measurement sensor, and calculate the second acceleration based on the calculated axial components.

[0011] According to this embodiment, the second acceleration can be calculated by converting the measurement data from the position and attitude measurement sensor into the components of each axis of a coordinate system based on the vehicle body.

[0012] In the above aspect, a travel control unit may be further provided that stops the vehicle body when it is determined that the difference vector exceeds a predetermined threshold value.

[0013] According to this aspect, when an abnormality in the traveling state is detected, the vehicle body can be stopped, so that the safety of the vehicle body can be enhanced.

[0014] In the above aspect, the position and attitude measurement sensor may be an acceleration sensor, and the abnormality may be a slip.

[0015] According to this aspect, it becomes possible to accurately detect by the acceleration sensor that the vehicle body has slipped.

[0016] In the above aspect, the position and attitude measurement sensor may be a gyro sensor, and the abnormality may be a spin.

[0017] According to this aspect, it becomes possible to accurately detect by the gyro sensor that the vehicle body has spun.

Effect of the Invention

[0018] According to the present invention, it is possible to provide a carrier vehicle that can monitor the traveling stability with a simple configuration.

Brief Description of the Drawings

[0019] [Figure 1] It is a block diagram illustrating the configuration of a carrier vehicle according to an embodiment. [Figure 2] It is a schematic diagram for explaining a processing procedure when calculating the speed of the vehicle body. [Figure 3] It is a schematic diagram for explaining the correspondence relationship between the carrier vehicle coordinate system and the sensor coordinate system. [Figure 4] It is a diagram illustrating a conversion law between data in the sensor coordinate system and data in the carrier vehicle coordinate system. [Figure 5] It is a schematic diagram for explaining a difference vector between a vector of a first acceleration and a vector of a second acceleration. [Figure 6] This is a flowchart illustrating the operation of the transport vehicle according to the embodiment. [Modes for carrying out the invention]

[0020] A preferred embodiment of the present invention will be described with reference to the attached drawings. In each drawing, components denoted by the same reference numerals have the same or similar configuration.

[0021] Figure 1 is a diagram illustrating a part of the configuration of the transport vehicle 1 according to an embodiment. The transport vehicle 1 is an autonomously mobile device and may be, for example, a transport cart that carries luggage or the like on its body, or a transport robot that transports luggage or the like. In this embodiment, the case in which the transport vehicle 1 is a transport cart will be described as an example. The transport vehicle 1 can move in all 360 degrees automatically or manually.

[0022] As shown in Figure 1, the transport vehicle 1 is composed of, for example, a control unit 2, a position and attitude measurement sensor 3, a motor 4, an encoder 5, and wheels 6.

[0023] The control unit 2 includes, for example, a processor and memory, and performs various processes by executing programs stored in memory, thereby comprehensively controlling each part of the transport vehicle 1.

[0024] The position and attitude measurement sensor 3 is, for example, an inertial measurement unit (IMU) and includes an acceleration sensor 31 and a gyroscope sensor 32. The acceleration sensor 31 measures the acceleration of the transport vehicle 1, and the gyroscope sensor 32 measures the angular velocity of the transport vehicle 1. The position and attitude measurement sensor 3 may also be mounted inside a camera device (not shown) that monitors the surroundings of the transport vehicle 1.

[0025] A motor 4 and an encoder 5 are provided for each wheel 6. The wheels 6 are wheels that can move in all directions, and for example, omni-wheels can be used. The motor 4 is a servo motor and drives the wheels 6. The encoder 5 detects the rotational position of the wheel 6's axis (motor 4), etc.

[0026] As shown in Figure 1, the control unit 2 of the transport vehicle 1 has a functional configuration that includes, for example, a first calculation unit 21, a second calculation unit 22, a determination unit 23, an abnormality output unit 24, and a driving control unit 25.

[0027] The first calculation unit 21 calculates the speed of the transport vehicle 1 based on the rate of change per unit time of the detected value of the encoder 5, and calculates the first acceleration, which is the acceleration of the vehicle body, based on the rate of change per unit time of that speed.

[0028] Referring to Figure 2, an example of the processing procedure when the first calculation unit 21 calculates the vehicle speed based on the detected value of the encoder 5 will be described. Figure 2 is a schematic representation of a transport vehicle 1 equipped with four wheels 6a, 6b, 6c, and 6d.

[0029] Here, let the speed of wheel 6a be V1 [m / s], the speed of wheel 6b be V2 [m / s], the speed of wheel 6c be V3 [m / s], and the speed of wheel 6d be V4 [m / s].

[0030] Also, the velocity of the transport vehicle 1 in the x-direction is V x Let the velocity be [m / s], and the velocity of transport vehicle 1 in the y direction be V. y Let the speed be [m / s], and let the rotational speed of transport vehicle 1 be Vθ [rad / s].

[0031] Furthermore, let D[m] be the diameter of each wheel 6a, 6b, 6c, and 6d, and let d[m] be the distance from the center O of the vehicle body to each wheel 6a, 6b, 6c, and 6d.

[0032] In this example, the change amount of the detection value of the encoder 5 per 20 [ms] is set as Et [rpm], and the change amount Et is updated every 20 [ms]. Also, the detection value of the encoder 5 until each of the wheels 6a, 6b, 6c, 6d makes one rotation is set as Er [rpm].

[0033] Under the above conditions, the first calculation unit 21 calculates the rotational speed R n (n: 1 to 4) [rpm] of each axis of each of the wheels 6a, 6b, 6c, 6d by the following formula (1).

[0034] R n =(Et / Er) × (60000 / 20) … (1)

[0035] Subsequently, the first calculation unit 21 calculates the speed V n (n: 1 to 4) [m / s] of each of the wheels 6a, 6b, 6c, 6d by the following formula (2). Here, π in formula (2) is the ratio of the circumference of a circle to its diameter, and Gp is the gear ratio of the reduction gear.

[0036] V n =(π / 60) × (D / Gp) × R n … (2)

[0037] Subsequently, the first calculation unit 21 calculates the speed V x [m / s] in the x - direction of the carrier vehicle 1, the speed V y [m / s] in the y - direction of the carrier vehicle 1, and the rotational speed Vθ [rad / s] of the carrier vehicle 1 by the following formula (3).

Equation

[0038] The speed V x [m / s] in the x - direction of the carrier vehicle 1 calculated by the above formula (3) and the speed V y [m / s] in the y - direction of the carrier vehicle 1 are substituted into the following formula (4) to calculate the absolute value V [m / s] of the speed of the carrier vehicle 1. This absolute value V [m / s] of the speed of the carrier vehicle 1 is the speed of the vehicle body. Note that this speed is the speed at the center O of the vehicle body.

number

[0039] The first calculation unit 21 adjusts the first acceleration of the vehicle body according to the mounting position of the position and attitude measurement sensor 3 attached to the vehicle body when calculating the first acceleration of the vehicle body based on the vehicle body speed. This is because if the mounting position of the position and attitude measurement sensor 3 is offset from the center O of the vehicle body, centripetal acceleration is generated in the position and attitude measurement sensor 3 due to the rotational speed Vθ of the transport vehicle 1. In this case, it is preferable to decompose the centripetal acceleration into an acceleration component in the x direction and an acceleration component in the y direction, and adjust the first acceleration by adding or subtracting these components to the x and y components of the first acceleration, respectively.

[0040] Returning to the explanation of Figure 1, the second calculation unit 22 calculates the axial components of acceleration in the transport vehicle coordinate system based on the transport vehicle 1, based on the measured values ​​of the position and attitude measurement sensor 3, and calculates the second acceleration of the vehicle body based on the calculated axial components.

[0041] Here, referring to Figure 3, we will explain an example of the correspondence between the transport vehicle coordinate system 1C, which is based on the transport vehicle 1, and the sensor coordinate system 3C, which is based on the position and orientation measurement sensor 3.

[0042] The transport vehicle coordinate system 1C is such that, for example, the X-axis is provided in the front-to-back direction of the transport vehicle 1, the Y-axis is provided in the left-to-right direction of the transport vehicle 1, and the Z-axis is provided in the up-to-down direction of the transport vehicle 1. The transport vehicle 1 rotates with the Z-axis as the axis of rotation θ.

[0043] The sensor coordinate system 3C is configured such that, for example, the Z-axis is provided in the front-to-back direction of the transport vehicle 1, the X-axis is provided in the left-to-right direction of the transport vehicle 1, and the Y-axis is provided in the up-to-down direction of the transport vehicle 1. The position and orientation measurement sensor 3 rotates around the Y-axis as its axis of rotation.

[0044] When the two coordinate systems have the correspondence shown in Figure 3, the second calculation unit 22 converts the measurement data of the position and orientation measurement sensor 3 in the sensor coordinate system 3C into data in the transport vehicle coordinate system 1C based on the conversion rules shown in Figure 4. This data conversion will be explained below for each axis.

[0045] The second calculation unit 22 converts the acceleration data of the Z axis in the sensor coordinate system 3C into acceleration data of the X axis in the transport vehicle coordinate system 1C. This acceleration data of the Z axis in the sensor coordinate system 3C is the acceleration component in the longitudinal direction of the transport vehicle 1 measured by the acceleration sensor 31.

[0046] The second calculation unit 22 inverts the sign of the acceleration data of the X axis in the sensor coordinate system 3C and converts it into acceleration data of the Y axis in the transport vehicle coordinate system 1C. This acceleration data of the X axis in the sensor coordinate system 3C is the lateral acceleration component of the transport vehicle 1 measured by the acceleration sensor 31.

[0047] The second calculation unit 22 inverts the sign of the Y-axis angular velocity data in the sensor coordinate system 3C and converts it into Z-axis angular velocity data in the transport vehicle coordinate system 1C. This Y-axis angular velocity data in the sensor coordinate system 3C is the angular velocity component due to rotation of the transport vehicle 1 with the vertical direction as the axis of rotation θ, as measured by the gyro sensor 32.

[0048] The second calculation unit 22 calculates the second acceleration of the vehicle body based on the acceleration data and angular velocity data converted to the transport vehicle coordinate system 1C. For example, the second calculation unit 22 calculates the second acceleration of the vehicle body by combining the angular velocity components of each axis converted to the transport vehicle coordinate system 1C.

[0049] Let's return to the explanation of Figure 1. The determination unit 23 determines whether the difference vector between the first acceleration vector and the second acceleration vector exceeds a predetermined threshold. Refer to Figure 5 for an explanation of the difference vector.

[0050] The first acceleration vector a is an acceleration vector calculated based on the detected value of the encoder 5. This first acceleration vector a represents the planned travel path of the transport vehicle 1.

[0051] On the other hand, the second acceleration vector b is an acceleration vector calculated based on the measurements of the position and attitude measurement sensor 3. This second acceleration vector b represents the actual path traveled by the transport vehicle 1.

[0052] Therefore, if there is a discrepancy between the first acceleration vector a and the second acceleration vector b, it is highly likely that the transport vehicle 1 is slipping or spinning and traveling along a different path than the one intended.

[0053] Therefore, the determination unit 23 calculates the difference vector c between the first acceleration vector a and the second acceleration vector b, and if the absolute value of the calculated difference vector c exceeds a predetermined threshold, the determination unit 23 determines that an abnormality has occurred in the movement of the transport vehicle 1.

[0054] Returning to the explanation of Figure 1, the abnormality output unit 24 outputs a signal to the control unit 2, the driving control unit 25, etc., indicating that an abnormality has been detected when it is determined that the difference vector c exceeds a predetermined threshold. Upon receiving the signal, the control unit 2 may output an audio or sound from the speaker to notify that an abnormality has been detected, or it may notify that an abnormality has been detected by lighting or flashing an indicator light, or it may display an abnormality detection message on the display.

[0055] If the driving control unit 25 determines that the difference exceeds a predetermined threshold, it stops the motor 4 and stops the transport vehicle 1.

[0056] Next, with reference to Figure 6, an example of the operation of the transport vehicle 1 according to the embodiment will be described.

[0057] First, the first calculation unit 21 calculates the vehicle speed based on the rate of change per unit time of the detected value of the encoder 5, and then calculates the first acceleration of the vehicle based on the rate of change per unit time of that speed (step S101).

[0058] Next, the second calculation unit 22 calculates the axial components of acceleration in the transport vehicle coordinate system 1C based on the measured values ​​of the position and attitude measurement sensor 3, and calculates the second acceleration of the vehicle body based on the calculated axial components (step S102).

[0059] Next, the determination unit 23 calculates the difference vector between the first acceleration vector and the second acceleration vector (step S103).

[0060] Next, the determination unit 23 determines whether the difference vector calculated in step S103 exceeds a predetermined threshold (step S104). If this determination is NO (step S104; NO), the process returns to step S101.

[0061] If the determination in step S104 above determines that the difference vector exceeds a predetermined threshold (step S104; YES), the abnormality output unit 24 outputs a signal indicating that an abnormality has been detected (step S105).

[0062] Next, the travel control unit 25 stops the motor 4 and stops the transport vehicle 1 (step S106).

[0063] As described above, according to the transport vehicle 1 in the embodiment, if the difference vector c between the first acceleration vector a, calculated based on the rotational position of the motor 4 that drives the wheels 6, and the second acceleration vector b, calculated based on the measurement data of the position and attitude measurement sensor 3 mounted on the vehicle body, exceeds a predetermined threshold, an abnormality can be detected and output. This makes it possible to output an abnormality in the driving state when it is determined that there is a discrepancy between the planned driving path of the transport vehicle 1 and the path that the transport vehicle 1 actually traveled.

[0064] Therefore, according to the transport vehicle 1 in this embodiment, it is possible to monitor the stability of driving with a simple configuration without having to provide a steering sensor.

[0065] [Differentiation] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The elements of the embodiments, as well as their arrangement, shape, and size, are not limited to those exemplified and can be modified as appropriate. Furthermore, the order of the processing steps described above can be arbitrarily changed or executed in parallel, as long as no inconsistencies arise in the processing content.

[0066] For example, in the embodiment described above, when it is determined that the difference vector between the first acceleration vector and the second acceleration vector exceeds a predetermined threshold, the travel control unit 25 stops the motor 4 and stops the transport vehicle 1, but the embodiment is not limited to this.

[0067] For example, if it is determined that the difference vector exceeds a predetermined threshold, the travel control unit 25 may control the travel of the transport vehicle 1 to estimate its own position and return to its original position. Self-position estimation can be performed using, for example, a self-position estimation method such as odometry.

[0068] Furthermore, in the above-described embodiment, the transport vehicle 1 is equipped with an acceleration sensor 31 and a gyro sensor 32, but it may be equipped with only one of them. In this case, the second acceleration of the vehicle body is calculated based on the measurement data of either the acceleration sensor 31 or the gyro sensor 32. Using the acceleration sensor 31 makes it easier to detect when the vehicle body slips, and using the gyro sensor 32 makes it easier to detect when the vehicle body spins. [Explanation of Symbols]

[0069] 1... Transport vehicle, 1C... Transport vehicle coordinate system, 2... Control unit, 3... Position and orientation measurement sensor, 3C... Sensor coordinate system, 4... Motor, 5... Encoder, 6... Wheel, 21... First calculation unit, 22... Second calculation unit, 23... Judgment unit, 24... Anomaly output unit, 25... Driving control unit, 31... Acceleration sensor, 32... Gyro sensor, a... First acceleration vector, b... Second acceleration vector, c... Difference vector

Claims

1. A first calculation unit calculates the first acceleration of the vehicle body based on the rotational position of the motor that drives the wheels, A second calculation unit calculates the second acceleration of the vehicle body based on the measurement data of a position and attitude measurement sensor mounted on the vehicle body, A determination unit that determines whether the difference vector between the first acceleration vector and the second acceleration vector exceeds a predetermined threshold, An abnormality output unit outputs a message indicating that an abnormality has been detected when it is determined that the difference vector exceeds a predetermined threshold. A transport vehicle equipped with the following features.

2. The first calculation unit calculates the vehicle speed based on the change in the rotational position of the motor, and calculates the first acceleration based on the calculated change in speed. The transport vehicle according to claim 1.

3. The second calculation unit calculates the axial components of the measurement data in a coordinate system based on the vehicle body, based on the measurement data of the position and attitude measurement sensor, and calculates the second acceleration based on the calculated axial components. The transport vehicle according to claim 1.

4. The vehicle further includes a driving control unit that stops the vehicle body when it is determined that the difference vector exceeds a predetermined threshold. The transport vehicle according to claim 1.

5. The position and orientation measurement sensor is an acceleration sensor, and the abnormality is slippage. The transport vehicle according to claim 1.

6. The position and orientation measurement sensor is a gyro sensor, and the abnormality is spin. The transport vehicle according to claim 1.

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