JPH031685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling an automatic guided vehicle, and particularly to an automatic guided vehicle that travels by independently controlling left and right drive wheels.

A method for driving straight ahead, turning, etc. by controlling the drive speed of the left and right drive wheels independently (hereinafter referred to as power wheeled steering method, abbreviated as power wheeled steering method)
In automatic guided vehicles (PWS system), detection means detects left and right displacement from the specified travel route,
For example, when an optical sensor, a magnetic sensor, etc. detects that the actual traveling route has shifted to the left or right from the prescribed route, the drive wheel that is on the inside of the turn made to correct the traveling route, for example. When the actual travel route deviates to the left from the prescribed route, the drive speed of the right drive wheel is reduced in order to make a right turn. Then, when returning to the prescribed route, control is performed to accelerate the drive wheel on the inside of the turn and return to steady running on the prescribed route.

However, when a sensor with on/off output is used as the above-mentioned detection means, for example, when a reflective tape installed on a running road is optically detected with a sensor such as a phototransistor, the on/off output
If a pair of off-output sensors is used, it is possible to detect whether the actual driving route is on the specified route or whether it is off to the left or right. When traveling using the control method described above, there was a problem in that when the traveling speed was increased, it became impossible to return to the specified route due to the effect of steering delay, and the vehicle could not travel at a practical speed. Therefore, when using on/off output sensors, conventionally it has been necessary to use several or more sensors and arrange them in a row from side to side with respect to the running direction.

The purpose of the present invention is to improve the followability of a PWS type automatic guided vehicle using a pair of on/off output sensors as described above to a prescribed route, and to improve the ability of a PWS type automatic guided vehicle to follow a prescribed route. Regarding wheel drive speed: (1) Limit the deceleration of the drive wheel on the inside of a turn for route correction to a certain value.

(2) When it is detected that the drive wheel on the inside of the turn has returned to the specified path, the drive wheel on the inside of the turn is accelerated and at the same time the drive wheel on the outside is decelerated to quickly return to a straight line, and then both wheels are accelerated to maintain a steady state. Back to running.

It is characterized by the following control.

Hereinafter, the present invention will be explained based on drawings showing embodiments. FIG. 1 is a style diagram showing an automatic guided vehicle using the PWS system, and shows an example of a six-wheeled vehicle having driving wheels 2 and 3 on the left and right sides of the center of the vehicle body 1 and casters 4, 4, 4, 4 on the front and rear. The detection means is a sign (hereinafter referred to as a guide) installed on the driving road that indicates a specified driving route by sensors 5 and 6 with on/off output located on the lower surface of the front part of the vehicle in the direction of travel indicated by the arrow in the figure. It detects lane (referred to as lane) 7 and runs. FIG. 2 shows changes in the outputs S _L and S _R of the sensors 5 and 6 when the vehicle body 1 shifts to the left and right with respect to the guide lane 7. In the figure, the horizontal axis represents the left and right displacement of the vehicle body 1 with respect to the guide lane 7 at the mounting portion of the sensors 5 and 6;
The vertical axes are the output voltages S _L and S _R of the sensors 5 and 6. In this way, by the combination of ON and OFF of the outputs S _L and S _R of the sensors 5 and 6, it is detected whether the vehicle body 1 is on the guide lane 7 and whether it is displaced to the left or right, and the left and right drive wheels are Controls the drive speed of 2 and 3.

First, a case will be described in which the conventional control method described above is used. Figures 3a and 3b are diagrams showing speed changes of the left and right drive wheels 2 and 3 when the vehicle body 1 is displaced to the left with respect to the guide lane 7 using the conventional control method; An example of left and right displacement of the vehicle body 1 from the guide lane 7 detected by the sensor is shown, the horizontal axis is time, and the vertical axis is the left and right displacement detected by the sensors 5 and 6. Figure b shows the drive speeds V _L and V _R of the left and right drive wheels 2 and 3 at that time,
Similarly, the horizontal axis is time, and the vertical axis is driving speeds V _L and _VR . While driving with both the left and right drive wheels 2 and 3 driven at a steady speed V _O , at time t ₁ , when the sensors 5 and 6 detect that the drive wheel 3 is displaced to the left from the guide lane 7, the drive speed of the right drive wheel 3 is changed. V _R is decelerated by deceleration rate −α ₁ . When the sensors 5 and 6 detect that the vehicle has returned to the guide lane 7 at time _t2 , the drive speed of the drive wheel 3 changes.
_VR is accelerated at an acceleration rate α ₂ and returns to running at the steady speed _VO at time t ₃ .

FIG. 4 shows an example of the movement of the vehicle body 1 obtained by simulation when such a control method is used. In the figure, the distance between left and right drive wheels 2 and 3 is 400.
mm, the distance from the center of vehicle body 1 to the center of sensors 5 and 6 is 300 mm, steady speed V _O is 50 m/min, deceleration rate -α ₁ is -833 mm/S ² , acceleration rate α ₂ is 833 mm/S ² In this case, the traveling locus of the center point of the vehicle body 1 from a state where the vehicle body 1 is traveling at a steady speed V _O and inclined by 0.1 rod with respect to the guide lane 7 is shown.
The horizontal axis is the traveling distance (unit: mm), and the vertical axis is the left and right displacement of the center point of the vehicle body 1 (unit: mm). After detecting that it has returned to guide lane 7, the vehicle body 1
until it goes straight, that is, at time t ₂ in Figure 3.
Since the time from t3 to _t3 is long, there is a delay in returning to the straight-ahead state, and vibrations to the left and right are not attenuated and instead increase, making it impossible to drive. In order to be able to travel, for example, the steady speed V _O must be reduced to 20 m/min (per hour).
1.2 km), which is not practical.

Next, a case will be described in which the control method according to the present invention is used. FIGS. 5a and 5b are diagrams showing speed changes of the left and right drive wheels 2 and 3 when the vehicle body 1 is displaced to the left with respect to the guide lane 7 using the control method of the present invention. Figures a and b correspond to Figure 3 a and b, respectively.
The horizontal axis is time, the vertical axis a is the left and right displacement detected by the sensor, and b is the drive speed V _L , _VR . time
When the sensors 5 and 6 detect the displacement to the left from the guide lane 7 at t ₁ , in the first step shown by 11 in the figure, the drive speed V _L of the left drive wheel 2 is changed to the steady speed.
While maintaining V _O , the drive speed V _R of the right drive wheel 3 is decelerated at a deceleration rate -α ₁ . When V _R is decelerated to a predetermined speed V ₁ at time t ₂ , the drive speed V L of the left drive wheel 2 is reduced to V _O , and the drive speed of the right drive wheel 2 is reduced to V _O in the second stage shown at 12 in the figure. The driving speed V _R of the wheels 3 is maintained at V ₁ respectively.
At time _t3 , when the sensors 5 and 6 detect that the vehicle has returned to the guide lane 7, the drive speed V R of the right drive wheel 3 is accelerated at an acceleration rate α2, and at the same time, the drive speed V _R of the right drive wheel 3 is accelerated at an acceleration rate _α2 . Drive speed V _L of drive wheel 2
is decelerated by a deceleration rate of −α ₃ . At time _t4 , the drive speeds V _L and V _R of the left and right drive wheels 2 and 3 become equal, and the vehicle body 1
When the vehicle is running straight, in the fourth step shown by 14 in the figure, the drive speeds V L and V R of the left and right drive wheels 2 and 3 are simultaneously accelerated at an acceleration rate α ₄ , and at time t 3 the drive speeds V _L and V _R are accelerated to a steady speed V _O at time t ₃ . Return to running.

If the sensors 5 and 6 detect that the drive speed V _R of the right drive wheel 3 has returned to the guide lane ₇ during the execution of the first stage in FIG. As shown in Figure 6 a and b, the drive speed V _R of the right drive wheel 3 is immediately accelerated at an acceleration rate α ₂ , and at the same time the drive speed of the left drive wheel 2 is increased.
It is sufficient to proceed to the third stage in which V _L is decelerated at a deceleration rate of −α ₃ . Furthermore, during the execution of the third or _fourth stage in FIG. For example, if a displacement is detected to the left of the guide lane 7, then the position is temporarily returned to the guide lane 7, and immediately after that, at time _t3 , a new displacement is detected to the right. Then, as shown in Fig. 8a and b, the drive speed V _L of the drive wheel on the inside of the new turn, that is, the left drive wheel 2, is set to V at a deceleration rate of -α ₁ or -α ₃ or a separately set value. slow down to ₁ ,
At the same time, after accelerating the drive speed V _R of the outer drive wheel, that is, the right drive wheel 3, to the steady speed V _O at an acceleration rate α ₂ or a separately set value, the left and right drive wheels 2 and 3 are driven at time t ₁ . It is sufficient to proceed to the second stage in which the velocities V _L and V _R are maintained respectively. Similarly to FIG. 5, in FIGS. 6 to 8, the horizontal axis represents time, and the vertical axis represents the horizontal displacement detected by the sensor at a and the driving speeds V _L and V _R at b.

In addition, in the control method of the present invention described above, the deceleration rate −α ₁ in the first stage and the acceleration rate α ₂ in the third stage
It is practically convenient to set the absolute values to be equal. Further, in order to quickly return the vehicle to the straight-ahead state in the third stage, it is desirable to set the absolute values of the acceleration rate α ₂ and the deceleration rate −α ₃ to be equal. On the other hand, in the fourth stage, the vehicle body 1 has returned to the straight-ahead state, so the acceleration rate α ₄ does not need to be as large as the acceleration rate α ₂ in the third stage, and it is better to set it to a smaller value than the acceleration rate α ₂ . Acceleration becomes smoother.

The value of the speed V ₁ is determined based on the radius of the curved portion of the travel path, etc. The distance between the left and right drive wheels is Tr
Then, the turning radius R of the center point of the vehicle body 1 when there is a difference between the driving speeds V _L and V _R is R = |Tr/2・V _L +V _R /V _L −V _R | However, V _L ≠ V _R Therefore, the minimum turning radius Ro of the vehicle body 1 was determined to be smaller than the radius r of the curved portion of the traveling path, and the above equation was modified.

V _R = R - Tr / 2 / R + Tr / 2 · V _L , V _R = V ₁ , V _L = V _O , R = R _O , V ₁ = R _O - Tr / 2 / R _O + Tr / 2 · V All you have to do is find the speed V ₁ from _O and set it. Also, the set value of V ₁ does not always have to be constant, but you can change the set value for straight sections and curved sections of the road, or for low-speed sections, etc. There is no problem.

Further, in the above description, the case where the vehicle body 1 is displaced to the left with respect to the guide lane 7 has been mainly explained, but the same is true when the vehicle body 1 is displaced to the right, only that the driving wheels that accelerate or decelerate are swapped left and right. Furthermore, the traveling direction of the vehicle body 1 indicated by the arrow in FIG. This is applicable as long as the detection means can detect the presence or absence and direction of displacement from the guide lane 7 to the left and right in the running direction. Therefore, the guide lane 7 is not limited to a sign placed on the road surface, but may be a sign placed above the road or a light beam propagating through the air. Also, sensor 5,
The mounting position of 6 is not limited to the lower surface of the vehicle body 1 either. Further, the vehicle body 1 is not limited to a six-wheeled vehicle as shown in FIG. 1, but can also be applied to a vehicle in which the number of casters 4 is increased or decreased.

FIG. 9 shows an example of the movement of the vehicle body 1 determined by simulation using the control method according to the present invention shown in FIGS. 5 to 8. The same figure as in Figure 4 shows the guide lane 7 while the vehicle body 1 is running at a steady speed _VO .
It shows the traveling trajectory of the center point of the vehicle body 1 from a state where it is tilted 0.1 rad against mm). In Figure 9, the distance between the left and right drive wheels 2 and 3 is 400 mm, and the distance from the center of the vehicle body 1 to the center of sensors 5 and 6 is the same as in Figure 4.
300mm, and the steady speed V _O is 50m/min. In addition, the minimum turning radius R _O of vehicle body 1 is 800 mm, and the speed is
V ₁ was set to 30 m/min. Acceleration rate and deceleration rate −α ₁ ,
α ₂ , −α ₃ , α ₄ are −833 mm/S, 833 mm/S, respectively,
-833mm/S, 417mm/S. In the control method according to the present invention, in order for the vehicle body 1 to quickly return to the straight-ahead state after returning to the guide lane 7,
Compared to FIG. 4 where the conventional control method was used under the same conditions, the ability to follow the guide lane 7 is clearly improved, and the effect is remarkable. Even if the inclination of the vehicle body 1 with respect to the guide lane 7 becomes larger, it is possible to run. For example, even if the vehicle body 1 is inclined by 0.5 rad, the vibrations to the left and right will be attenuated and almost disappear after driving about 2 m.

As described above, in the control method according to the present invention, time t ₃
When the left and right drive wheels return to guide lane 7, the speed difference between the left and right drive wheels does not exceed a certain value V _O −V ₁ , and the drive wheels on the low speed side are accelerated and the drive wheels on the high speed side are accelerated to return to the straight-ahead state. Since this is done by decelerating the drive wheels, the return to the straight-ahead state is extremely quick. Therefore, we have significantly improved the ability of PWS-type automated guided vehicles to follow the specified travel route by using a pair of on/off output sensors.
This allows the vehicle to travel at practical speeds.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a PWS type six-wheeled automatic guided vehicle, Figure 2 is an explanatory diagram showing the output of the sensor when it is displaced left and right with respect to the specified route, and Figure 3 a, b.
is an explanatory diagram showing a speed diagram according to a conventional control method,
FIG. 4 is an explanatory diagram showing a traveling locus of the center of the vehicle body in the control method of FIG. 3; FIGS. FIG. 9 is an explanatory diagram showing a travel locus centered on the vehicle body according to the present invention. 1...Automated guided vehicle, 2...Left drive wheel, 3...
Right drive wheel, 4...caster, 5, 6...sensor, 7...guide lane.

Claims (1)

[Claims] 1 An automated guided vehicle that is equipped with a detection means for detecting the presence or absence and direction of displacement to the left or right from a prescribed travel route, and that travels and steers by independently controlling the left and right drive wheels based on the output of the detection means. In the control method, when the detecting means detects that the actual traveling route is displaced to the left or right from the prescribed route while the left and right drive wheels are driven at a steady speed, the traveling route is corrected. The drive speed of the first drive wheel on the inside of the turn is decelerated to a predetermined first speed at a first deceleration rate, and the drive speed of the other second drive wheel is reduced to the above-mentioned steady speed. a first stage of maintaining the driving speed of the first driving wheel at the first speed and a second stage of maintaining the driving speed of the second driving wheel at a steady speed; and the detecting means. When it is detected that the drive speed of the first drive wheel has returned to the prescribed path, the drive speed of the first drive wheel is accelerated at a second acceleration rate, and at the same time, the drive speed of the second drive wheel is reduced at a third deceleration rate. A third wheel that reduces speed to equalize the driving speed of the first driving wheel and the second driving wheel.
and a fourth step of simultaneously accelerating the drive speeds of the first drive wheel and the second drive wheel to the steady speed at a fourth acceleration rate, the detection output from the detection means and the current control 1. A control method for an automatic guided vehicle, characterized in that the automatic guided vehicle returns to running at a steady speed by transitioning to a predetermined control step in combination with a control step.