JPH08194535A - Position detection system - Google Patents

Abstract

PURPOSE: To provide a position detection system capable of eliminating errors by a sensor and the accumulation of the errors and obtaining highly accurate position information. CONSTITUTION: A moving distance sensor 2 for detecting distances of the movement of right and left respective wheels and a bearing sensor 4 for detecting an azimuth angle in the advancing direction of a vehicle are mounted on the vehicle, an angle obtained from the difference between the moving distances of the right and left wheels and the angle obtained from the azimuth angle change of the bearing sensor are used, large weighting is applied to the angle obtained from the bearing sensor when an angular velocity is large, the large weighting is applied to the angle obtained from the moving distance difference when the angular velocity is small and the advancing direction of the vehicle is highly accurately detected. Then, a present position is calculated from the advancing direction and the moving distance of the vehicle obtained from the moving distances of the right and left wheels. Further, a mark detector 3 for detecting a mark arranged on ground is mounted on the vehicle and the advancing direction and the present position are corrected at the time of detecting the mark.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for detecting the position of a moving vehicle such as a forklift that moves in a warehouse, and more particularly, to a position for obtaining highly accurate position information by eliminating an error or accumulation of the error by a sensor. It relates to a detection system.

[0002]

2. Description of the Related Art A track-less vehicle such as a forklift operated by a driver, a non-guided unmanned trolley, or a mobile robot is used to move a vehicle from a receiving place of a warehouse to a plurality of storage places by carrying a load on the vehicle. In this case, it is important for the warehouse location management to correctly identify the storage location of the package. For this purpose, a system for detecting the current position of the vehicle is required, and it is desired for this system to obtain highly accurate position information.

A method is known in which the traveling direction and the traveling distance of a moving vehicle are detected from the vehicle and the current position of the vehicle is obtained from the traveling direction and the traveling distance. Further, in order to eliminate the detection error caused by this method, a thing (known as a sign or marker) such as a reflective tape or a guide wire laid on the ground is known from the vehicle, and the current position of the vehicle is corrected. Methods are also known.

As a method of detecting the traveling direction of a vehicle, 1) a method of mounting a geomagnetic sensor on the vehicle to detect an azimuth angle and detecting the traveling direction from a change in the azimuth angle.

2) A method of mounting a rate gyro on a vehicle to detect an azimuth angle and detecting a traveling direction from a change in the azimuth angle.

3) A method of detecting the traveling direction from the turning angle of the steered wheels of the vehicle (Japanese Patent Publication No. 63-39923, etc.) 4) Moving distance sensors are attached to the left and right wheels of the vehicle, and the traveling direction is determined from the difference in these traveling distances. Method of detection
No. 23200) is known.

[0007]

However, each of the methods for detecting the traveling direction of the vehicle has a problem.

1) The accuracy of the geomagnetic sensor may deteriorate due to the disturbance of the geomagnetism due to the influence of metal structures inside and outside the warehouse.

2) The rate gyro has a large error in detecting an angle change when the angular velocity is small when the traveling direction changes, and there is a problem of drift due to noise at rest.

3) When the traveling direction changes at high speed, a centrifugal force causes a slip, which causes a deviation between the actual traveling direction and the turning angle of the steered wheels.

4) When the traveling direction changes at high speed, if either one of the left and right wheels or both wheels slip, a detection error occurs in both the moving distance and the traveling direction.

The correction of the current position of the vehicle by the marker detection is performed in a vehicle in which the movement is controlled by a guide device of a wireless type, a magnetic type, an optical type or the like, and the movement route is restricted to a fixed track or the like. Is effective, but is not always effective for vehicles that move without a track. That is, since the traveling direction of the vehicle is free, the traveling direction is not constant even at the position of the marker. Even if the current position is corrected by the marker detection, the traveling direction at that position cannot be corrected, and therefore errors in the traveling direction are accumulated. Therefore, an error in the traveling direction remains at the calculated current position.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a position detecting system which can obtain highly accurate position information by eliminating errors and accumulation of errors by a sensor.

[0014]

In order to achieve the above object, the present invention provides a position detection system for detecting the current position of a vehicle that has wheels on at least the left and right of the traveling direction and moves in a trackless manner. The vehicle has a moving distance sensor that detects the distance traveled by the wheels and an azimuth sensor that detects the azimuth angle of the vehicle's traveling direction. Using the obtained angle, the angle obtained from the direction sensor is greatly weighted when the angular velocity is high, and the angle obtained from the movement distance difference is greatly weighted when the angular velocity is small to detect the traveling direction of the vehicle with high accuracy. Sign detection that calculates the current position from the traveling direction and the moving distance of the vehicle calculated from the moving distance of the left and right wheels, and further detects the sign placed on the ground Was mounted on a vehicle, and corrects the traveling direction and current position upon detection of the label.

A pulse encoder may be used as the moving distance sensor and a rate gyro may be used as the azimuth sensor.

In order to detect the traveling direction from the above sign, a sign consisting of alternating parallel straight lines is arranged on the floor of the warehouse,
The sign detectors are installed on the left and right of the traveling direction of the vehicle and detect the signs when they come on the signs respectively.The distance between the two detectors, the distance between the straight lines, and one of the sign detectors is one straight line. The vehicle's approach angle is calculated from the distance traveled by the vehicle from when the other sign detector detects another straight line, and the advancing direction is calculated from this approach angle and the direction of the straight line registered in advance. Good.

[0017]

With the above structure, the traveling direction of the vehicle is a compromise between the angle obtained from the moving distance sensor and the angle obtained from the azimuth sensor with weighting. The azimuth sensor has a characteristic that the detection error increases when the angular velocity is low,
On the other hand, since the moving distance sensor has a characteristic that the detection error increases when the angular velocity is large, weighting is given according to the angular velocity, and the better the characteristic of each sensor becomes, the heavier the traveling direction of the vehicle becomes. The detection error is eliminated. Therefore, highly accurate position information can be obtained.

Further, when the sign is detected, not only the current position but also the traveling direction is corrected, so that the current position can be detected without error even in a vehicle with no track.

Each sensor can be simplified by using the pulse encoder and the rate gyro.

Since the traveling direction is obtained from the approach angle of the vehicle to the sign and the direction of the sign itself, the sign can be arranged in any position and in any direction, and the sign detector can be simply constructed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the forklift 10 is designed to be operated by a driver on a cab. The forklift 10 is for carrying luggage from a cargo receiving location of a warehouse to a plurality of storage locations.

The front wheels 1 of the forklift 10 are provided symmetrically in the traveling direction, and the width between the left and right wheels is H. Each front wheel 1 is provided with a pulse encoder 2a that outputs a pulse at a constant distance as a moving distance sensor 2 that detects the distance traveled by the front wheel from its rotation.
Optical switches 3a are attached to both sides of the vehicle body of the forklift 10 toward the floor. The optical switch 3a is a detector (marker detector) 3 for detecting a marker on the floor of the warehouse. The width between the left and right detectors is h. The forklift has an azimuth sensor 4 for detecting an azimuth angle in the traveling direction.
A rate gyro 4a is mounted as the. The rate gyro 4a is not limited to the position shown in the figure and may be placed anywhere. The vehicle-mounted control device 5 is placed at a position where the driver's cab of the forklift 10 can be directly viewed and operated.

The on-vehicle control device, as shown in FIG.
A counter 21 that counts the detection pulses of the pulse encoder 2a, a DI 22 that determines whether a marker is detected from the output level of the optical switch 3a, a SIO 23 that receives the azimuth output of the rate gyro 4a, and the arithmetic processing of the present invention. And a wireless device 25 for wirelessly transmitting the position information and the like obtained by the operation. The arithmetic device 24 also serves as a correction device that performs a correction process.

On the ground, there are provided a base station 26 which receives position information and the like from the wireless device 25, and a processing device (in-warehouse location management device) 27 which performs processing for location management in the warehouse based on the position information. Has been.

An example of a warehouse in which this forklift is used is shown in FIG. The floor has a rectangular shape, and a vertical passage 31 and a horizontal passage 32 are provided. A plurality of receiving locations and storage locations are provided along the passages 31 and 32.
The forklift position is represented by XY coordinates with the horizontal direction as the X axis and the vertical direction as the Y axis. On the floor of the warehouse,
Origin 33 of XY coordinates, angle correction point 34 whose angle is registered in advance, X-axis correction point 35 whose X coordinate is registered in advance
Also, markers having different shapes are arranged at respective points at different positions of the Y-axis correction point 36 in which the Y coordinate is registered in advance. The marker is formed by stretching a reflective tape that reflects light on the optical switch on the floor surface. Each coordinate and angle is registered in the correction device in the arithmetic device 24.

As shown in FIG. 4, the marker at the angle correction point 34 separates two parallel straight lines 41, 42 shorter than the detector interval h along the direction corresponding to the registered angle by a distance D in the perpendicular direction. Are staggered, and the straight line 41,
42 is formed of a reflective tape. The positional relationship between the marker and the forklift 10 is such that when the forklift 10 passes, the left and right optical switches 3a, 3a do not operate simultaneously.

As shown in FIG. 5, the marker at the Y-axis correction point 36 is a straight line 5 orthogonal to the Y-axis and longer than the detector interval h.
It is 1. The positional relationship between the marker and the forklift 10 is such that when the forklift 10 passes, the left and right optical switches 3a, 3a operate simultaneously. The tape width and the tape length are determined so that the left and right optical switches 3a, 3a always operate at the same time. The markers at the origin 33 and the X-axis correction point 35 also conform to the Y-axis correction point 36.

Next, the operation of the embodiment will be described.

First, a method for obtaining the current position will be described.

From the left and right movement distance sensors, the movement distances ΔLr and ΔLi for each time can be obtained.

From this, the moving distance ΔL of the forklift per unit time is obtained. That is, the moving distance ΔL of the vehicle per hour is obtained from the intermediate value of the moving distances of the left and right wheels.

ΔL = (ΔLr + ΔLi) / 2 (1) Further, the angular change amount Δφe per hour in the traveling direction of the forklift is obtained from the difference between the moving distances of the left and right wheels over time and the width H between the left and right wheels.

Δφe = (ΔLr−ΔLi) / H (2) On the other hand, from the amount of change in the azimuth angle output of the rate gyro over time, the amount of angle change Δφg in the traveling direction of the forklift truck can be obtained.

When the angular velocity when the forklift bends is small, the angular variation Δφg obtained from the rate gyro has a larger error as the angular velocity approaches the detection limit (about 0 ° / s). On the contrary, the angle change amount Δφe obtained from the difference in the moving distance between the left and right wheels has a small error because the influence of the slip due to the centrifugal force is small. On the other hand, when the angular velocity is large, the amount of angular change Δ
Since φe is greatly affected by the slip due to the centrifugal force, the error becomes large, and conversely, the angle change amount Δφg obtained from the rate gyro is more accurate than when the angular velocity is small.

Therefore, the angle change amount Δφ for two times
Using e and Δφg and the coefficient W that changes depending on the angular velocity, the change amount Δφ in the traveling direction per time is obtained. That is, positive weights W and 1-W smaller than 1 given in accordance with the angular velocity when the traveling direction of the vehicle changes are respectively multiplied, and both are added to obtain the traveling direction change amount Δφ per hour.

Δφ = WΔφg + (1−W) Δφe 0 <W <1 (3) The amount of change Δφ in the traveling direction obtained in this manner is true to the amount of change in the traveling direction of the actual forklift regardless of the magnitude of the angular velocity. Will be represented in.

The calculation of the current position is performed at each time when the traveling direction change amount Δφ and the movement distance ΔL are obtained.
First, the position variation per unit time for that time is calculated using the integrated angle φ obtained by integrating the moving direction change amount Δφ, the moving distance ΔL, and the moving direction change amount Δφ up to that time.
The integrated angle φ represents the current traveling direction. The position variation is calculated separately for the X and Y components ΔX and ΔY.

When Δφ ≠ 0,

[0040]

[Equation 1]

When Δφ = 0, ΔX = ΔLcosφ ΔY = ΔLsinφ (5) Therefore, the current position (X _n , Y _n ) is expressed by the formula (4) or the formula (5) and the position ( X _n-1 , Y _n-1 )
Can be expressed as follows.

X _n = X _n-1 + ΔX Y _n = Y _n-1 + ΔY (6) Next, a method of correcting the current position and the traveling direction will be described.

When starting the operation of the forklift, the driver stops the forklift on the origin 33 and sends an origin confirmation signal to the vehicle controller 5. As a result, the origin in the warehouse is registered in the arithmetic unit 24 and the current position is cleared to the origin. Thereafter, as the forklift moves, errors in the current position and the traveling direction are accumulated, but the angle correction points 34,
The correction is performed at the X-axis correction point 35 and the Y-axis correction point 36, respectively.

At the angle correction point 34, as shown in FIG. 4, the reflection tapes are installed at a distance D so that the right optical switch 3a operates first. When the forklift passes, the moving distance d from the actuation of the right optical switch 3a to the actuation of the left optical switch 3a, and the optical switch 3
From the distance h between a and 3a, the approach angle φi when passing is obtained. That is, when D ≠ h,

[0045]

[Equation 2]

From this approach angle φi and the registered angle φ ₀ registered at the angle correction point 34, the traveling direction is corrected to φ ₀ + φi.

At the X-axis correction point 35 and the Y-axis correction point 36, when the left and right optical switches 3a, 3a are simultaneously operated, the X coordinate or Y coordinate of the current position is corrected to the registered coordinate.

Next, the flow of operation when operating the forklift 10 will be described with reference to FIG.

First, as the initial setting, the origin is set,
The origin in the warehouse and the origin of calculation (XY coordinates) are matched, correction points are set, and the coordinates and angles of each correction point are registered in advance.

After that, the forklift is moved according to the work. The calculation of the current position is continued until the optical switch is activated. The obtained current position is used as the wireless device 2 at any time.
5, sent to the processing device 27 via the base station 26.

When the optical switch is activated, the coordinates and angles registered in the origin setting and the correction point setting, the current position,
Comparing with the traveling direction, the one closest to the current position and within a certain range is selected and correction is performed.

1) Origin The current position is corrected to the origin coordinates input in the initial setting (origin reset).

2) XY correction point The X coordinate of the current position is corrected to the registered coordinate (X axis reset) or the Y coordinate of the current position is corrected to the registered coordinate (Y
Axis reset).

3) Angle correction point The moving distance d is measured, the approach angle φi is calculated by the equation (7), and the registered angle φ ₀ is added to obtain the traveling direction (angle calculation correction).

By repeating the above, each time the forklift passes the marker, the current position and the traveling direction are corrected, and the accumulated error is eliminated.

In the above embodiment, the pulse encoder for detecting the moving distance from the rotation of the wheel is used. However, the same result can be obtained by using the optical non-contact displacement sensor as the moving distance sensor. In addition, in order to obtain the angle change amount, the turning angle of the steered wheels may be used instead of the difference in the moving distance between the left and right wheels. Also, for correction, a marker with a reflective tape was detected with an optical switch, but a magnetic tape with a magnetic sensor,
Alternatively, the guide wire may be detected by an antenna.

The present invention can be applied not only to a forklift operated by a driver but also to an unguided unmanned trolley and a mobile robot.

[0058]

The present invention exhibits the following excellent effects.

(1) Since the angle is detected by two independent detecting means whose accuracy changes diametrically oppositely depending on the angular velocity and the weights of the two are distributed according to the angular velocity, the traveling direction with high accuracy regardless of the magnitude of the angular velocity. Information can be obtained, and thus highly accurate position information can be obtained.

(2) Since it is possible to correct not only the current position but also the traveling direction when a sign is detected, it is possible to effectively correct even a vehicle moving without a track.

[Brief description of drawings]

FIG. 1 is a perspective view of a forklift truck showing an embodiment of the present invention.

FIG. 2 is a block diagram of a position detection system of the present invention.

FIG. 3 is a plan view of a floor of a warehouse in which markers according to the present invention are arranged.

FIG. 4 is a plan view near an angle correction point on the floor of the warehouse in FIG.

5 is a plan view near the Y-axis correction point on the floor of the warehouse in FIG. 3;

FIG. 6 is a flowchart for calculating a current position according to the present invention.

[Explanation of symbols]

 1 front wheels (left and right wheels) 2 moving distance sensor 3 detector (marker detector) 4 direction sensor 5 vehicle-mounted control device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location // G01C 19/00 Z 9402-2F (72) Inventor Hisanori Nakai 5 Hidakacho, Hitachi City, Ibaraki Prefecture 1-1-1, Hitachi Cable Co., Ltd. Hidaka Plant (72) Inventor Toshiaki Inuma 7-2, Toyo, Koto-ku, Tokyo In-house Hitachi Logistics Co., Ltd. (72) Hiroki Adachi 7 Toyo, Koto-ku, Tokyo 2-18 No. 18 Hitachi Transport System, Ltd. (72) Inventor Kiyoshi Ono 7-21-18 Toyo, Koto-ku, Tokyo Within Hitachi Transport Service Co., Ltd.

Claims (3)

[Claims] 1. A position detection system for detecting a current position of a vehicle which has wheels at least on the left and right of a traveling direction and moves without a track, and a moving distance sensor for detecting a distance traveled by each of the left and right wheels and a vehicle. An azimuth sensor that detects the azimuth angle in the traveling direction is mounted on the vehicle, and the angle obtained from the difference in the moving distance between the left and right wheels and the angle obtained from the change in the azimuth angle of the azimuth sensor are used. The moving angle of the vehicle is detected with high accuracy by highly weighting the angle obtained from the difference in the moving distance when the angular velocity is small, and the moving direction of the vehicle obtained from this moving direction and the moving distance of the left and right wheels. The current position is calculated from this, and a sign detector that detects the sign placed on the ground is installed in the vehicle. A position detection system characterized by correcting the current position. 2. The position detecting system according to claim 1, wherein a pulse encoder is used for the moving distance sensor, and a rate gyro is used for the direction sensor. 3. A sign consisting of alternating parallel straight lines is arranged on the floor of the warehouse to detect the direction of travel from the sign, and the sign detectors are attached to the left and right of the direction of travel of the vehicle and come to the respective signs. And the distance between the two detectors, the distance between the straight lines, and the detection of one straight line from one of the label detectors to the detection of another straight line by the other. The position detection system according to claim 1 or 2, wherein an approach angle of the vehicle is calculated from a moving distance of the vehicle, and a traveling direction is obtained from the approach angle and a direction of a straight line registered in advance.