JP2008254912A - Travelling vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize a speed difference of wheels on the front wheel side and the rear wheel side and to provide a control system to minimize the speed difference. <P>SOLUTION: Different speed commands are input to a motor M1 and a motor M2 by finding each of correction factors on the front wheel side and the rear wheel side by a correction table 32 and multiplying target speed by them. The correction factors are changed in correspondence with existence of adjustable speed and a load, and the speed command on the rear wheel side is made larger than the front wheel side in adjusting speed. Consequently, it is possible to make speed of the front and rear wheels against the ground side by absorbing a difference of sliding due to a difference of loads to the front and rear motors. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a traveling vehicle such as a stacker crane or an automatic guided vehicle.

It is known that the front and rear wheels of a traveling vehicle are each driven by a motor. In this case, during acceleration, the torque command to the rear wheel side motor is made larger than the torque command to the front wheel side motor, and during deceleration, the torque command to the front wheel side motor is made from the torque command to the rear wheel side motor. Is also known to increase (Patent Document 1: Japanese Patent Laid-Open No. 2005-41383). This is because the wheel load on the motor on the rear wheel side is greater than the wheel load on the front wheel side during acceleration, and the wheel load on the motor on the front wheel side is greater than that on the rear wheel side during deceleration. However, the inventor has found that if the torque distribution to the front wheel side and the rear wheel side is changed by acceleration / deceleration, a difference occurs in the ground speed between the front and rear wheels, and the traveling vehicle vibrates or wears out of the wheel. It was. In this specification, the ground speed means the true speed of the wheel relative to the ground side obtained by subtracting the idling speed of the wheel from the apparent rotational speed of the wheel. In the following, the speed difference means a difference in ground speed.
JP-A-2005-41383

An object of the present invention is to reduce the speed difference between wheels on the front wheel side and the rear wheel side.
An additional problem in the invention of claim 2 is to further reduce the speed difference between the front and rear wheels.
An additional problem in the invention of claim 3 is to provide a control system for reducing the speed difference between the front and rear wheels.

  The present invention relates to a traveling vehicle in which front wheels and rear wheels are driven by motors, and each motor is controlled by a control unit, and a speed command to a rear wheel motor is transmitted to a front wheel motor during acceleration and deceleration. The control unit is configured to be larger than the command. Here, the speed command is an amount with a positive / negative sign, which is a target speed given to the motor side. The fact that the speed command to the rear wheel side is larger than the front wheel side during deceleration means that the front wheel side is controlled to decelerate more quickly than the rear wheel side.

Preferably, the difference in speed command between the front wheel side motor and the rear wheel side motor is increased as the absolute value of the acceleration / deceleration increases, and is increased when the load on the traveling vehicle is large.
Particularly preferably, the control unit stores data for determining the target speed generation means and the speed command difference between the front wheel side motor and the rear wheel side motor for the acceleration / deceleration and the magnitude of the load. And means for correcting the target speed based on the data of the table to generate a speed command to the front wheel side motor and a speed command to the rear wheel side motor, and means for controlling each motor by the speed command , And are provided.

  During acceleration, the wheel load is biased toward the rear wheel, and the load on the motor is also biased toward the rear wheel. Although the motor slip increases when the load increases, in this invention, the speed command to the rear wheel side motor is larger than the front wheel side, so the speed difference due to the slip is canceled out by the speed command difference, and the front wheel and rear wheel Can be rotated at the same speed.

  At the time of deceleration, the wheel load is biased toward the front wheel, and the load on the motor is also biased toward the front wheel, and slippage is increased by the motor on the front wheel. If the speed command to the front wheel side motor is made lower than the rear wheel side during deceleration, the slip generated by the front wheel side motor can be canceled out by the difference in speed command from the rear wheel side.

  For these reasons, in the present invention, the speed difference generated between the front wheels and the rear wheels during acceleration / deceleration can be reduced. Since the speed difference between the front and rear wheels causes motor interference, traveling vehicle vibration, wheel wear, etc., the present invention reduces interference between the motors, suppresses vibration of the traveling vehicle, Wear and the like can be reduced.

  The slip of the motor becomes more significant as the load is larger, and the first factor that determines the difference between the loads of the front and rear motors is the acceleration / deceleration. The second factor that determines the load difference between the front and rear motors is the load on the traveling vehicle, and this factor has a smaller influence on the load difference than the acceleration / deceleration. Therefore, if the difference in the speed command between the front wheel side motor and the rear wheel side motor is increased when the absolute value of the acceleration / deceleration is large and the load on the traveling vehicle is large, the speed difference between the front and rear wheels is more reliably determined. Can be eliminated.

  Here, in the control unit, a table storing data for determining the difference between the speed commands of the front wheel side motor and the rear wheel side motor with respect to the target speed generating means, the acceleration / deceleration and the magnitude of the load, Providing means for correcting the target speed based on the table data and generating a speed command for the front wheel side motor and a speed command for the rear wheel side motor, and means for controlling each motor by the speed command The difference in speed command can be easily generated by the table.

  In the following, an optimum embodiment for carrying out the present invention will be shown.

  1 to 6 show an embodiment using a stacker crane as an example. In each figure, 2 is a stacker crane, 4 is a truck, and includes front and rear traveling wheels 6 and 7 which are driven by motors 8 and 9, respectively. The carriage 4 is provided with a mast 10 to raise and lower the elevator 12, and 14 is mounted on the elevator 12 by a transfer device such as a slide fork, and the article 16 is transferred to and from a rack or station (not shown).

  Reference numeral 18 denotes a drum which is driven by an elevating motor 20 and winds / feeds the suspension material 21 to elevate the elevating platform 12. A control panel 22 includes a power source such as the motors 8, 9, and 20, a control unit, a communication unit, and the like. The travel destination of the stacker crane 2, the travel speed pattern, and the state of in / out load are managed by a control unit (not shown) in the control panel 22. Reference numeral 24 denotes a traveling rail on the ground side. A detected plate 25 made of a magnetic material or a magnet is provided along the traveling rail 24 and is read by the linear sensor 26. Since it is difficult to provide a plate to be detected over the entire length of the travel rail 24, the plate 25 to be detected is provided in, for example, two rows on the left and right sides of the travel rail 24, and a pair of left and right linear sensors 26 are provided on the carriage 4. The detected plates 25 are detected alternately, for example.

  A comb-tooth mark or the like may be provided instead of the detection plate 25. In this case, an optical sensor is provided instead of the linear sensor 26. Further, a laser distance meter may be provided in place of the linear sensor 26. The linear sensor 26, the optical sensor, the laser distance meter, and the like are external sensors for obtaining the absolute position of the carriage 4. In addition to this, the carriage 4 is provided with an encoder for detecting the rotational speed of the drive shafts of the motors 8 and 9 or the rotational speed of the wheels 6 and 7, and detects the speed of each motor or each wheel. A sensor such as an encoder is called an internal sensor.

  In this specification, front wheels and front wheel side motors refer to traveling wheels in front of the traveling direction and their driving motors, and rear wheels and rear wheel side motors refer to traveling wheels and their motors in the rearward direction of traveling. Therefore, the meanings of the front wheels and the rear wheels are reversed when the traveling direction is reversed. In the embodiment, when the stacker crane is stopped or traveling at a constant speed, the wheel weights on the front and rear traveling wheels 6 and 7 are assumed to be equal.

  FIG. 2 shows a control system for the front and rear traveling motors. Reference numeral 30 denotes a target speed generator, which receives a target position from a speed pattern generator (not shown) and a current position from an external sensor such as a linear sensor. A target speed is generated based on the error and input to the correction unit 31. The correction unit 31 includes a correction table 32 shown in FIG. 3, and the correction table 32 is a target speed for the front wheel side motor and the rear wheel side motor with respect to the acceleration / deceleration speed a and the load (load to the traveling vehicle). The correction coefficient is stored. The acceleration / deceleration is assumed to be + when accelerating, and-when decelerating. The magnitude of the load may be classified into three or more stages. Further, here, it is assumed that the sum of the correction coefficient for the front wheel side and the correction coefficient for the rear wheel side is 2.

  The correction unit 31 reads the correction table 32 based on the acceleration / deceleration obtained by differentiating the target speed with the differentiator 33 and the on / off status obtained from the control unit of the stacker crane. The correction coefficient to the side is obtained. For example, the target speed is multiplied by the obtained correction coefficient to calculate a speed command for the front wheels and a speed command for the rear wheels. These speed commands are common during constant speed traveling, and are different between the front wheel side motor and the rear wheel side motor during acceleration / deceleration. The speed command is input to the speed control units 34 and 35, and compared with the speed obtained by the drive shaft of the motors 8 and 9 or the encoder connected to the traveling wheels 6 and 7, a torque command is generated. The motors 8 and 9 are controlled via the inverters 36 and 37 by the generated torque command. In the figure, i is a detected value of the current from the motors 8 and 9, and the motors 8 and 9 are driven with a current determined by a torque command.

  In the embodiment, the correction table 32 is a table that is determined by the acceleration / deceleration and the magnitude of the load, but may be a three-dimensional table having three items as headings, the acceleration / deceleration, the magnitude of the load, and the target speed. Alternatively, the correction coefficient may be obtained by a function such as a polynomial determined by three variables of acceleration / deceleration, load magnitude, and target speed instead of the table. In the embodiment, the speed command difference is generated by multiplying the target speed by the correction coefficient. However, the speed command difference may be obtained by adding and subtracting the speed difference corresponding to the correction coefficient to the target speed.

  FIG. 4 shows data of the correction table 32, and here, correction coefficients for the front wheel side motor are shown. The sum of the correction coefficient for the rear wheel side motor and the correction coefficient for the front wheel side motor is 2. Since the wheel load on the front and rear traveling wheels is equal during constant speed traveling and the load on the motors 8 and 9 is balanced, the acceleration / deceleration is 0 and the correction coefficient is 1.0 (no correction). If the wheel load is not balanced during low-speed traveling, the correction coefficient at 0 acceleration / deceleration should be shifted from 1. The larger the absolute value of the acceleration / deceleration is, the smaller the correction coefficient on the front wheel side is.

  The difference in speed command will be described. There is always slip in the motor. These slips are more remarkable as the absolute value of the acceleration / deceleration is larger, and when there is no idling, the slip is more significant as the wheel load is larger if the acceleration / deceleration is the same. Therefore, when torque is distributed in proportion to the wheel weights of the front and rear wheels, a large slip occurs in the motor having the larger wheel weight and the larger torque, so that the wheel speed difference between the motor having the smaller wheel weight and the wheel load becomes smaller. Arise. When the inventor distributes the torque to the front and rear driving motors in proportion to the wheel load, a speed difference is generated between the front and rear wheels, and the traveling vehicle is likely to vibrate. I confirmed that it would be faster.

  In contrast, in the embodiment, a difference is provided in the speed command to the travel motor so as to eliminate the difference in slip between the front and rear travel motors and wheels. That is, the meaning of the difference in speed command is to cancel out the difference in slip between the front and rear traveling motors and traveling wheels. When a difference is provided in the speed command in this way, the ground speed of the front and rear traveling wheels becomes common, the interference between the traveling motors is eliminated, and vibrations of the traveling vehicle and wheel wear can be avoided. Here, the ground speeds of the front and rear traveling wheels being equal means that a torque substantially proportional to the wheel weight of each wheel is output from the traveling motor. Next, even if the absolute value of the acceleration / deceleration is the same, the larger the load, the larger the slip. Therefore, when the load is large, the shift of the correction coefficient from 1 is increased.

  The direction in which the correction coefficient is shifted from 1 will be described. During acceleration, the wheel weight on the front wheel side decreases and the wheel weight on the rear wheel side increases. As a result, the rear wheel side slip increases, so the front wheel side correction coefficient is smaller than 1 and the rear wheel side correction coefficient is larger than 1. During deceleration, the wheel weight on the front wheel side increases and slippage on the front wheel side increases. For this reason, since the deceleration on the front wheel side is delayed, the correction coefficient on the front wheel side is made smaller than 1 and the correction coefficient on the rear wheel side is made larger than 1 even during deceleration.

  FIG. 5 schematically shows a speed command for the target speed. The horizontal axis is time, the lower side of FIG. 5 indicates the target speed, the upper side indicates the speed command, and the solid line is the front wheel side and the broken line is the rear wheel side. At the time of acceleration, the speed command on the rear wheel side is made larger than that on the front wheel side, and thereby the slip generated on the rear wheel side with a large load is corrected by the difference in speed command. Even during deceleration, the speed command on the front wheel side is made smaller than the speed command on the rear wheel side, and slip that occurs on the front wheel side with a large load during deceleration is absorbed by reducing the speed command. In the case of the left load in FIG. 5, the difference in speed command between the front wheel side and the rear wheel side is made larger than in the case of the empty load on the right side in FIG.

In the embodiment, the following effects can be obtained.
(1) By providing a difference in speed command between the front wheel side and the rear wheel side, the difference in slip between the front wheel side and the rear wheel side during acceleration / deceleration can be absorbed, and the traveling vehicle can be driven stably. it can.
(2) This can reduce interference between motors, vibration of traveling vehicles, wear of wheels, and the like.
(3) By increasing the difference in speed command when there is a load, slip can be absorbed more reliably.
(4) By using the correction table 32, the speed command difference can be easily obtained.

In the embodiment, the motors before and after the stacker crane are controlled, but the present invention can be similarly applied to other traveling vehicles other than the stacker crane. Further, the acceleration input to the correction unit is not limited to the one obtained by differentiating the target speed, and may be obtained by differentiating the speed obtained from an appropriate sensor.

Side view of main part of stacker crane of embodiment The block diagram which shows the traveling control system of execution example The figure which shows the correction table in an Example typically The figure which shows typically the correction coefficient to the front-wheel side in an Example. The figure which shows typically the target speed pattern and the speed command to the front-wheel side and the rear-wheel side in an Example. Block diagram of the principal part of a modified traveling control system

Explanation of symbols

2 Stacker crane 4 Carriage 6, 7 Traveling wheel 8, 9 Motor 10 Mast 12 Lifting platform 14 Transfer device 16 Article 18 Drum 20 Lifting motor 21 Lifting material 22 Control panel 24 Traveling rail 25 Detected plate 26 Linear sensor 30 Target speed Generator 31 Correction unit 32 Correction table 33 Differentiator 34, 35 Speed control unit 36, 37 Inverter 38, 40 Adder 39 Multiplier

Claims (3)

In a traveling vehicle in which front wheels and rear wheels are each driven by a motor, and each motor is controlled by a control unit,
A traveling vehicle in which the control unit is configured so that a speed command to a rear wheel side motor is larger than a speed command to a front wheel side motor during acceleration and deceleration. 2. The difference in speed command between the front wheel side motor and the rear wheel side motor increases as the absolute value of the acceleration / deceleration increases, and increases when the load on the traveling vehicle is large. Traveling car. A table storing data for determining a difference in speed command between the front wheel side motor and the rear wheel side motor with respect to the target speed generating means, acceleration / deceleration and load magnitude; Means for correcting the target speed based on the above data and generating a speed command to the front wheel side motor and a speed command to the rear wheel side motor, and means for controlling each motor by the speed command. The traveling vehicle according to claim 2, wherein:

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