Transport vehicle

Abstract

To provide a carrier vehicle capable of suppressing the deviation between a current steering command angle and a steering angle of a wheel based on the current steering command angle. [Solution] In the transport vehicle 1, a steering correction coefficient Kθ corresponding to a steering command angle θα is acquired, the steering correction coefficient Kθ being based on the cylinder length L for steering the wheel 4a to that steering command angle θα, and a proportional solenoid valve command value Ed is calculated using the steering command angle θα and the acquired steering correction coefficient Kθ. Here, the steering correction coefficient Kθ is a coefficient based on the cylinder length L for steering the wheel 4a to that steering command angle θα, so by using this steering correction coefficient Kθ, it is possible to calculate the proportional solenoid valve command value Ed for setting the length of the hydraulic cylinder 4c to that steering command angle θα. This makes it possible to suppress the deviation between the steering command angle θα and the actual steering angle θN of the wheel 4a steered based on that steering command angle θα.

Description

[Technical Field]

[0001] The present invention relates to a transport vehicle. [Background technology]

[0002] Patent Document 1 discloses a vehicle 1 that adjusts its horizontal orientation (i.e., steers) by rotating the front wheels 3a using a steering device 4. Specifically, the steering device 4 is provided with a hydraulic cylinder that is connected to the front wheels 3a by a joint mechanism, and by changing the amount of hydraulic oil supplied to the hydraulic cylinder in accordance with the steering angle input from a handlebar 13, the hydraulic cylinder expands and contracts, and in accordance with this expansion and contraction, the front wheels 3a are rotated in the horizontal direction and steered. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-80144 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when steering the front wheels 3a, the extension and contraction of the linear hydraulic cylinder is converted into the rotation of the front wheels 3a. That is, while the hydraulic cylinder extends and contracts at a substantially constant speed (i.e., changes according to a linear function), the front wheels 3a rotate according to a sine function or cosine function. Therefore, there may be a time lag between the steering angle input from the steering wheel 13 and the front wheels 3a actually pointing in that direction. If this time lag is large, the vehicle 1 may travel in a position that deviates from the traveling course intended by the operator operating the steering wheel 13, requiring position correction, which reduces the traveling efficiency of the vehicle 1.

[0005] Furthermore, for example, when vehicle 1 is traveling on a narrow, curved road, if vehicle 1 deviates from the course of travel that the operator envisions on the road, as described above, vehicle 1 will approach the roadside of the road, and this approach to the roadside will be erroneously detected as an abnormality, causing the speed of vehicle 1 to decrease. This also poses the problem of reduced traveling efficiency of vehicle 1.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a transport vehicle that can suppress the deviation between a steering command angle and the steering angle of the wheels based on that steering command angle. [Means for solving the problem]

[0007] In order to achieve this object, the transport vehicle of the present invention comprises a wheel, a rotary shaft supporting the wheel so that it can rotate in a horizontal direction, a cylinder connected to the rotary shaft and rotating the rotary shaft in a horizontal direction, a command angle acquisition means for acquiring a steering command angle which is a target steering angle of the wheel, a command value calculation means for calculating a command value to extend or retract the cylinder based on the steering command angle acquired by the command angle acquisition means, and a steering means for extending or retracting the cylinder based on the command value calculated by the command value calculation means to rotate the rotary shaft to steer the wheel, and further comprises steering correction coefficient acquisition means for acquiring a steering correction coefficient corresponding to the steering command angle acquired by the command angle acquisition means, the steering correction coefficient being a coefficient based on the length of the cylinder for setting the wheel to that steering command angle, and the command value calculation means calculates the command value using the steering command angle acquired by the command angle acquisition means and the steering correction coefficient acquired by the steering correction coefficient acquisition means. [Effects of the Invention]

[0008] According to the transport vehicle of claim 1, the transport vehicle includes a wheel, a rotating shaft that supports the wheel so that it can rotate horizontally, and a cylinder that is connected to the rotating shaft and rotates the rotating shaft horizontally, and a command value to extend or contract the cylinder is calculated based on the acquired steering command angle that is the target steering angle of the wheel, and the wheel is steered by rotating the rotating shaft by extending or contracting the cylinder based on the command value, and further a steering correction coefficient is acquired that is a coefficient based on the length of the cylinder for setting the wheel to that steering command angle, according to the acquired steering command angle, and the command value is calculated using the acquired steering command angle and steering correction coefficient.

[0009] Since the steering correction coefficient is a coefficient based on the cylinder length required to achieve the acquired steering command angle, the use of this steering correction coefficient makes it possible to calculate a command value for the cylinder length required to achieve that steering command angle, thereby reducing the deviation between the steering command angle and the steering angle of the actual wheels steered based on that steering command angle.

[0010] According to the transport vehicle of claim 2, in addition to the effect achieved by the transport vehicle of claim 1, the steering correction coefficient is set according to the amount of change in the cylinder length when the steering command angle is changed by a predetermined angle. Here, in steering the wheels, the linear extension and contraction of the cylinder is converted into the rotation of the wheel about the rotation shaft, so the relationship between the steering command angle and the cylinder length corresponding to that steering command angle is not always constant, and there are a mixture of steering command angles that require a large change in the cylinder length and steering command angles that require a small change in the cylinder length.

[0011] Therefore, by setting the steering correction coefficient according to the amount of change in the cylinder length when the steering command angle is changed by a predetermined angle, the cylinder length can be set to appropriately steer the wheels to the steering command angle for any steering command angle, which has the effect of further suppressing the deviation between the steering command angle and the steering angle of the wheels.

[0012] According to the transport vehicle of claim 3, in addition to the effect achieved by the transport vehicle of claim 1, the steering correction coefficient is acquired from a calculation function that inputs the steering command angle, so that the steering correction coefficient according to the steering command angle can be easily acquired. Furthermore, since the calculation function is configured as a cubic function, the calculation function can more accurately represent the relationship between the steering command angle and the steering correction coefficient. As a result, an appropriate steering correction coefficient can be acquired according to the steering command angle, so that there is an effect that the deviation between the steering command angle and the steering angle of the actual wheels can be suitably suppressed.

[0013] According to the transport vehicle of claim 4, in addition to the effect achieved by the transport vehicle of any one of claims 1 to 3, the load of the platform of the transport vehicle is acquired, and a load correction coefficient corresponding to the acquired load is acquired. Then, a command value is calculated using the acquired steering command angle, the acquired steering correction coefficient, and the acquired load correction coefficient.

[0014] Here, the road pressure of the wheels acts as a resistance to steering, but because the road pressure varies depending on the load on the loading platform, wheel steering is affected by the load on the loading platform. Therefore, by calculating a command value using a load correction coefficient according to the load on the loading platform, the speed at which the cylinder extends and retracts according to the command value can be set to take the load on the loading platform into account. This has the effect of effectively suppressing the deviation between the steering command angle and the steering angle of the wheels.

[0015] According to the transport vehicle of claim 5, in addition to the effect of the transport vehicle of claim 4, a load correction coefficient is acquired such that the greater the load, the greater the command value calculated by the command value calculation means. Here, the heavier the load on the loading platform, the higher the ground contact pressure of the wheels, and this high ground contact pressure becomes resistance to steering of the wheels. In this way, when the load on the loading platform is heavy, in order to bring the wheels to the steering command angle quickly, it is necessary to operate the cylinder to extend and retract more quickly.

[0016] Therefore, by obtaining a load correction coefficient that calculates a larger command value as the load on the loading platform increases, the cylinder can be operated to expand and contract more quickly as the load on the loading platform increases, which has the effect of quickly reducing the difference between the steering command angle and the actual steering angle of the wheels.

[0017] According to the transport vehicle of claim 6, in addition to the effect achieved by the transport vehicle of any one of claims 1 to 3, the cylinder is configured as a hydraulic cylinder, the temperature of the hydraulic oil that operates the hydraulic cylinder is acquired, and a temperature correction coefficient that is a coefficient according to the acquired temperature of the hydraulic oil is acquired. Then, a command value is calculated using the acquired steering command angle, the acquired steering correction coefficient, and the acquired temperature correction coefficient.

[0018] The viscosity of the hydraulic fluid acts as a resistance to the operation of the hydraulic cylinder. However, because the viscosity of the hydraulic fluid changes depending on the temperature of the hydraulic fluid, the steering of the wheels is affected by the speed at which the hydraulic cylinder extends or retracts, i.e., the temperature of the hydraulic fluid. Therefore, by calculating the command value using a temperature correction coefficient corresponding to the temperature of the hydraulic fluid, the speed at which the hydraulic cylinder extends or retracts according to the command value can be adjusted to take the temperature of the hydraulic fluid into account. This has the effect of effectively suppressing the deviation between the steering command angle and the steering angle of the wheels.

[0019] According to the transport vehicle of claim 7, in addition to the effect of the transport vehicle of claim 6, a temperature correction coefficient is acquired such that the lower the temperature of the hydraulic oil, the larger the command value calculated. Here, the lower the temperature of the hydraulic oil, the greater the viscosity of the hydraulic oil, and this high viscosity of the hydraulic oil creates resistance to the operation of the hydraulic cylinder, which also creates resistance to the steering of the wheels by the operation of the hydraulic cylinder. In this way, when the temperature of the hydraulic oil is low, in order to quickly bring the wheels to the steering command angle, it is necessary to operate the hydraulic cylinder to extend and retract more quickly.

[0020] Therefore, by obtaining a temperature correction coefficient that calculates a larger command value as the hydraulic oil temperature decreases, the hydraulic cylinder can be operated to expand and contract more quickly as the hydraulic oil temperature decreases, which has the effect of quickly reducing the difference between the steering command angle and the actual steering angle of the wheels. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2(a) is a side view of a transport vehicle according to an embodiment of the present invention, and FIG. 2(b) is a top view of the transport vehicle. [Figure 2] FIG. 1(a) is a diagram illustrating a traveling device, FIG. 1(b) is a diagram illustrating a proportional solenoid valve, and FIG. 1(c) is a diagram illustrating calculation of the length of a hydraulic cylinder corresponding to a steering command angle. [Figure 3] 10(a) is a table showing the cylinder length for each steering command angle, and FIG. 10(b) is a graph showing the relationship between the steering command angle and the steering correction coefficient. [Figure 4] 10A is a graph showing the relationship between the load on the loading platform and the load correction coefficient, and FIG. 10B is a graph showing the relationship between the temperature of the hydraulic oil and the temperature correction coefficient. [Figure 5] FIG. 4 is a block diagram illustrating calculation of a proportional solenoid valve command value. [Figure 6] FIG. 2 is a block diagram showing the electrical configuration of the transport vehicle. [Figure 7] 10 is a flowchart of a main process. [Figure 8] 10 is a flowchart of a command value calculation process. DETAILED DESCRIPTION OF THE INVENTION

[0022] A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. First, the configuration of a transport vehicle 1 in this embodiment will be described with reference to Fig. 1. Fig. 1(a) is a side view of the transport vehicle 1 in one embodiment of the present invention, and Fig. 1(b) is a top view of the transport vehicle 1. In Figs. 1(a) and 1(b), the left side of the page is the front side of the transport vehicle 1, and the right side of the page is the rear side of the transport vehicle 1. In Fig. 1(b), the upper side of the page is the right side of the transport vehicle 1, and the lower side of the page is the left side of the transport vehicle 1.

[0023] The transport vehicle 1 is a vehicle having a vehicle body 2, a loading platform 3, a traveling device 4, and a cab 5. The loading platform 3 is disposed on the vehicle body 2 and is a platform for loading transported objects. A plurality of traveling devices 4 are disposed below the loading platform 3 and are devices for driving the transport vehicle 1 in accordance with driving instructions from the cab 5. In this embodiment, the traveling devices 4 are disposed in six rows in the longitudinal direction of the transport vehicle 1, with two in each row.

[0024] Hereinafter, in the fore-and-aft direction of the transport vehicle 1, the front running device 4 will be referred to as the "first row running device 4," the rear running device 4 will be referred to as the "sixth row running device 4," and the running devices 4 between the "first row" and the "sixth row" will be referred to from the front end as the "second row running device 4," the "third row running device 4," the "fourth row running device 4," and the "fifth row running device 4," respectively.

[0025] 1(b), each traveling device 4 is provided with wheels 4a, a rotating shaft 4b, and a hydraulic cylinder 4c. In this embodiment, two wheels 4a are arranged in the left and right direction for each traveling device 4. The rotating shaft 4b supports the wheels 4a so that they can rotate horizontally.

[0026] The hydraulic cylinder 4c is a cylinder connected to the rotating shaft 4b, and its overall length expands and contracts depending on the amount of hydraulic oil supplied. One end of the hydraulic cylinder 4c and the rotating shaft 4b are connected by a joint structure, and as the hydraulic cylinder 4c expands and contracts, the rotating shaft 4b rotates horizontally, changing the orientation of the wheels 4a. Hereinafter, the connection between one end of the hydraulic cylinder 4c and the rotating shaft 4b will be referred to as the "first connection part Cb" (see Figure 2(c)). Furthermore, changing the orientation of the wheels 4a in conjunction with the rotation of the rotating shaft 4b will be referred to as "steering the wheels 4a."

[0027] As shown in FIG. 1(b), the other end opposite one end of the hydraulic cylinders 4c of the traveling units 4 is connected to the vehicle body 2 by a joint structure. Specifically, the other ends of the hydraulic cylinders 4c of the traveling units 4 in the first, second, fifth, and sixth rows are connected near the side of the vehicle body 2, while the other ends of the hydraulic cylinders 4c of the traveling units 4 in the third and fourth rows are connected to the center of the vehicle body 2. Hereinafter, the connection part between the other ends of the hydraulic cylinders 4c and the vehicle body 2 will be referred to as the "second connection part Cc" (see FIG. 2(c)).

[0028] The number of travelling devices 4 provided on the transport vehicle 1 is not limited to 12 (6 rows in the front-rear direction x 2 rows in the left-right direction). For example, the number of travelling devices 4 provided may be 12 or more or 12 or less depending on the size of the loading platform 3 and the size and mass of the transported object transported by the transport vehicle 1.

[0029] The driver's cabs 5 are disposed at the front and rear ends of the transport vehicle 1, and are control rooms where an operator issues instructions to raise and lower the platform 3 and to drive and brake the traveling devices 4. A steering device 6 (see FIGS. 5 and 6) consisting of, for example, a handle is provided in the driver's cab 5, and a steering angle is input by an operator via the steering device 6. A steering command angle θα, which is a target steering angle for the wheels 4a of each traveling device 4, is calculated based on the steering angle input from the steering device 6. The wheels 4a of each traveling device 4 are steered by extending and retracting the hydraulic cylinders 4c of each traveling device 4 based on the calculated steering command angle θα.

[0030] Next, the traveling device 4 will be further described with reference to Figures 2(a) and (b). Figure 2(a) is a diagram illustrating the traveling device 4. In addition to the wheels 4a, the rotating shaft 4b, and the hydraulic cylinder 4c described above, the traveling device 4 is provided with a proportional solenoid valve 4d for supplying hydraulic oil to the hydraulic cylinder 4c.

[0031] Fig. 2(b) is a diagram illustrating the proportional solenoid valve 4d. As shown in Fig. 2(b), the hydraulic cylinder 4c is provided with a piston 4c1, a head side chamber 4c2, and a rod side chamber 4c3. The proportional solenoid valve 4d is a valve that controls the extension and contraction of the hydraulic cylinder 4c by controlling the amount of hydraulic oil supplied from a hydraulic oil tank Tk to the head side chamber 4c2 and the rod side chamber 4c3 by a hydraulic pump (not shown). Specifically, the proportional solenoid valve 4d is provided with Asol4d1 and Bsol4d2, each of which is configured to be excitable.

[0032] When Asol4d1 is excited, the hydraulic cylinder 4c extends. On the other hand, when Bsol4d2 is excited, the hydraulic cylinder 4c retracts. The greater the excitation current input to Asol4d1 and Bsol4d2, the greater the amount of hydraulic oil from the hydraulic oil tank Tk. When neither Asol4d1 nor Bsol4d2 is excited, the supply of hydraulic oil to the head side chamber 4c2 and the rod side chamber 4c3 and the discharge of hydraulic oil from the head side chamber 4c2 and the rod side chamber 4c3 are stopped, and the extension and contraction of the hydraulic cylinder 4c is stopped.

[0033] The excitation of Asol4d1 and Bsol4d2 and the magnitude of the excitation current input to Asol4d1 and Bsol4d2 are controlled by a proportional solenoid valve command value Ed input to the proportional solenoid valve 4d. The proportional solenoid valve command value Ed is a command value created based on the steering command angle θα.

[0034] Specifically, the proportional solenoid valve command value Ed is set with information regarding the excitation and excitation current of the proportional solenoid valve 4d that sets the cylinder length L, which is the length of the hydraulic cylinder 4c, to the length that causes the direction of the wheels 4a to match the steering command angle θα. Based on the input proportional solenoid valve command value Ed, the proportional solenoid valve 4d has either Asol4d1 or Bsol4d2 excited, or neither excited. The hydraulic cylinder 4c expands or contracts in response to the excitation of the proportional solenoid valve 4d, and this expansion or contraction rotates the rotary shaft 4b to which the hydraulic cylinder 4c is connected, thereby steering the wheels 4a.

[0035] Incidentally, when steering the wheels 4a, the extension and contraction of the linear hydraulic cylinder 4c is converted into the rotation of the rotary shaft 4b. That is, while the hydraulic cylinder 4c extends or contracts at a substantially constant speed (i.e., changes according to a linear function), the wheels 4a rotate according to a sine function or cosine function. Therefore, there may be a time lag between the steering angle input from the steering device 6 and the wheels 4a actually pointing in that direction. If this time lag is large, the transport vehicle 1 may travel in a position that deviates from the travel course expected by the operator operating the steering device 6, requiring position correction, which reduces the travel efficiency of the transport vehicle 1.

[0036] Furthermore, for example, when the transport vehicle 1 is traveling on a narrow, curved road, if the transport vehicle 1 deviates from the travel course assumed by the worker on the road, the transport vehicle 1 will approach the roadside of the road, and such approach to the roadside will be erroneously detected as an abnormality, causing the speed of the transport vehicle 1 to decrease. This also reduces the travel efficiency of the transport vehicle 1.

[0037] Therefore, in this embodiment, in calculating the proportional solenoid valve command value Ed, a steering correction coefficient Kθ, which is a coefficient based on the length of the hydraulic cylinder 4c for setting the wheel 4a to the steering command angle θα (hereinafter, the length of the hydraulic cylinder 4c will be referred to as the "cylinder length L"), is used to suppress the deviation between the steering command angle θα and the actual steering angle θN, which is the angle of the actual wheel 4a in the horizontal direction (i.e., the steering angle). The steering correction coefficient Kθ will be explained using Figures 2(c) and 3.

[0038] 2(c) is a diagram for explaining the calculation of the cylinder length L corresponding to the steering command angle θα. When setting the steering correction coefficient Kθ, first, the cylinder length L corresponding to the steering command angle θα is calculated. When the steering command angle θα is set to 0 (rad) (i.e., the state of FIG. 2(c)), the distance between the second connection part Cc and the center Ca of the turning shaft 4b in the length direction of the vehicle body 2 (the horizontal direction on the plane of FIG. 2(c)) is Da, and the distance in the width direction of the vehicle body 2 (the vertical direction on the plane of FIG. 2(c)) is Db. Then, the distance Dd between the second connection part Cc and the center Ca is calculated using Equation 1.

[0039]

number

[0040] Next, if the fixed angle (the angle at the position where one end of the hydraulic cylinder 4c is connected to the rotating shaft 4b, which is the angle between the line connecting the first connection part Cb and the center Ca of the rotating shaft 4b and the width direction of the vehicle body 2) is θe, the angle θ between the line connecting the first connection part Cb and the center Ca of the rotating shaft 4b and the line connecting the center Ca and the second connection part Cc is calculated using Formula 2.

[0041]

number

[0042] If the distance between the first connection portion Cb and the center Ca of the rotation shaft 4b is Dc, the cylinder length L for achieving the steering command angle θα is calculated using Equation 3 according to the cosine theorem.

[0043]

number

[0044] The steering command angle θα in the above formula 3 is changed in increments of 1 degree from the minimum angle of -60 degrees to the maximum angle of -60 degrees, and the cylinder length L at that time is obtained. The steering command angle θα actually input to formula 3 is obtained by converting "degrees" into radians. Note that the minimum angle of the steering command angle θα is not limited to -60 degrees, and may be less than or equal to -60 degrees. Similarly, the maximum angle of the steering command angle θα is not limited to 60 degrees, and may be less than or equal to 60 degrees.

[0045] The cylinder length L for each steering command angle θα thus obtained is shown in FIG. 3(a).

[0046] FIG. 3(a) is a table showing the cylinder length L for each steering command angle θα. For each steering command angle θα, a differential length ΔL is calculated by subtracting the cylinder length L for the steering command angle θα that is one angle smaller than that by the cylinder length L for the next smaller steering command angle θα. For example, in FIG. 3(a), the cylinder length L is 411 mm when the steering command angle θα is 44 degrees, and the cylinder length L is 408 mm when the steering command angle θα is 43 degrees, so the differential length ΔL when the steering command angle θα is 44 degrees is 411 mm - 408 mm = 3 mm.

[0047] Next, the maximum value ΔLmax of the calculated differential length ΔL for each steering command angle θα is acquired, and a value ΔL / ΔLmax is calculated by dividing the differential length ΔL for each steering command angle θα by the maximum value ΔLmax. Then, a calculation function is calculated from a graph plotting the steering command angle θα and the value ΔL / ΔLmax corresponding to that steering command angle θα. In this embodiment, the calculation function is a cubic function, and is calculated by approximating the graph plotting the steering command angle θα and the value ΔL / ΔLmax corresponding to that steering command angle θα to a cubic function using a known method such as the least squares method.

[0048] By inputting the steering command angle θα into the calculated calculation function, a value ΔL / ΔLmax corresponding to the input steering command angle θα is output. This value ΔL / ΔLmax is a value based on the cylinder length L for setting the wheel 4a to that steering command angle θα, and this value is used as the steering correction coefficient Kθ. Figure 3(b) shows a graph of the steering correction coefficient Kθ when the steering command angle θα is input into the calculated calculation function.

[0049] Fig. 3(b) is a graph showing the relationship between the steering command angle θα and the steering correction coefficient Kθ. In the steering correction coefficient Kθ in Fig. 3(b), when the steering command angle θα is 20 degrees, the maximum value (local maximum value) of 1.0 for the steering correction coefficient Kθ is calculated. This indicates that when the steering command angle θα for the wheel 4a is set to 20 degrees, the cylinder length L is made the longest.

[0050] Setting of such a calculation function and calculation of the steering correction coefficient Kθ when a steering command angle θα changed in 1-degree increments from the minimum angle of -60 degrees to the maximum angle of 60 degrees is input to the calculation function are performed for each traveling unit 4, and the calculated steering correction coefficient Kθ for each traveling unit 4 and steering command angle θα is stored in the guided vehicle 1. Then, the proportional solenoid valve command value Ed for each traveling unit 4 is calculated using the stored steering correction coefficient Kθ.

[0051] The steering command angle θα for calculating the steering correction coefficient Kθ from the calculation function is not limited to one that changes in increments of 1 degree, but may change in increments of 1 degree or more, or may change in increments of 1 degree or less.

[0052] In this embodiment, a load correction coefficient KL and a temperature correction coefficient KT are provided as coefficients used in calculating the proportional solenoid valve command value Ed, in addition to the steering correction coefficient Kθ. These coefficients will be described with reference to FIG.

[0053] FIG. 4(a) is a graph showing the relationship between the load Ld of the loading platform 3 and the load correction coefficient KL. The contact pressure between the wheels 4a and the road surface varies depending on the magnitude of the load Ld of the loading platform 3, but when the load Ld is large and the contact pressure between the wheels 4a and the road surface is high, this high contact pressure creates a large resistance to steering of the wheels 4a. When the load Ld is large like this, in order to quickly bring the actual steering angle θN of the wheels 4a into the steering command angle θα, it is necessary to operate the hydraulic cylinder 4c more quickly (i.e., to increase the amount of hydraulic oil supplied to the hydraulic cylinder 4c per unit time = to increase the exciting current input to Asol4d1 or Bsol4d2 of the proportional solenoid valve 4d).

[0054] Therefore, in this embodiment, a load correction coefficient KL corresponding to the load Ld of the platform 3 of the transporting vehicle 1 is acquired and used to calculate the proportional solenoid valve command value Ed. The load Ld of the platform 3 used to acquire the load correction coefficient KL is acquired from a load sensor 7 (see FIGS. 5 and 6) provided on the platform 3.

[0055] 4(a), the load Ld and the load correction coefficient KL corresponding to that load Ld have a linear relationship in which the larger the load Ld, the larger the load correction coefficient KL. The load correction coefficient KL for each load Ld is also set for each traveling device 4, similar to the steering correction coefficient Kθ described above, and is stored in the guided vehicle 1, and is used to calculate the proportional solenoid valve command value Ed.

[0056] The larger the load Ld, the larger the load correction coefficient KL that is used, and the calculated proportional solenoid valve command value Ed also becomes larger in proportion to the load Ld. Therefore, the larger the load Ld, the faster the hydraulic cylinder 4c can be operated to expand and contract, and the difference between the steering command angle θα and the actual steering angle θN of the wheels 4a can be reduced quickly.

[0057] Next, the temperature correction coefficient KT will be explained with reference to Figure 4(b). Figure 4(b) is a graph showing the relationship between the temperature T of the hydraulic oil and the temperature correction coefficient KT. The lower the temperature T of the hydraulic oil used to extend and retract the hydraulic cylinder 4c, the greater the viscosity of the hydraulic oil. This high viscosity of the hydraulic oil creates resistance to the extension and retraction of the hydraulic cylinder 4c, and also creates resistance to the steering of the wheels 4a caused by the extension and retraction of the hydraulic cylinder 4c. Thus, even when the temperature T of the hydraulic oil is low, it is necessary to operate the hydraulic cylinder 4c to extend and retract more quickly in order to quickly bring the wheels 4a to the steering command angle θα.

[0058] Therefore, in this embodiment, a temperature correction coefficient KT corresponding to the hydraulic oil temperature T is obtained and used to calculate the proportional solenoid valve command value Ed. The hydraulic oil temperature T used to obtain the temperature correction coefficient KT is obtained from a hydraulic oil temperature sensor 4e (see FIGS. 5 and 6) provided in a supply section of the proportional solenoid valve 4d into which hydraulic oil supplied from a hydraulic oil tank Tk by a hydraulic pump (not shown) flows in the proportional solenoid valve 4d of each traveling device 4.

[0059] As shown in FIG. 4(b), the hydraulic oil temperature T and the temperature correction coefficient KT corresponding to that temperature T have a linear relationship in which the lower the hydraulic oil temperature T is between a predetermined minimum temperature (10°C in this embodiment) and a predetermined maximum temperature (60°C in this embodiment), the larger the temperature correction coefficient KT becomes. The temperature correction coefficient KT is constant at a maximum value below the predetermined minimum temperature, and is constant at a minimum value above the predetermined maximum temperature. The temperature correction coefficient KT for each hydraulic oil temperature T is set for each traveling unit 4, like the steering correction coefficient Kθ and load correction coefficient KL, and is stored in the guided vehicle 1, and is used to calculate the proportional solenoid valve command value Ed.

[0060] As described above, the lower the temperature of the hydraulic oil, the larger the temperature correction coefficient KT is used, and the calculated proportional solenoid valve command value Ed increases in inverse proportion to the temperature of the hydraulic oil. Therefore, the lower the temperature of the hydraulic oil, the faster the hydraulic cylinder 4c can be operated to expand and contract, and the difference between the steering command angle θα and the actual steering angle θN of the wheels 4a can be reduced quickly.

[0061] Next, calculation of the proportional solenoid valve command value Ed using the steering correction coefficient Kθ, the load correction coefficient KL, and the temperature correction coefficient KT will be described with reference to Fig. 5. Fig. 5 is a block diagram for explaining calculation of the proportional solenoid valve command value Ed. In Fig. 5, one of the twelve traveling units 4 will be described, but since the proportional solenoid valve command value Ed is calculated for the other eleven traveling units 4 in the same way, description thereof will be omitted.

[0062] First, the actual steering angle θN of the wheel 4a is acquired from the steering angle sensor 4f provided on the traveling device 4. The steering angle sensor 4f is a sensor that acquires the actual steering angle θN of the wheel 4a. A steering command angle θα is calculated from the steering angle according to the operation of the steering device 6 described above. A known method is used to calculate the steering command angle θα from the steering angle, so a detailed description will be omitted. Then, a first difference value, which is a difference value between the acquired actual steering angle θN and the steering command angle θα, is calculated.

[0063] A steering correction coefficient Kθ corresponding to the calculated steering command angle θα is acquired, and a load correction coefficient KL corresponding to the load Ld detected by the load sensor 7 is acquired. The acquired steering correction coefficient Kθ, the load correction coefficient KL, the steering gain K1, and the first difference value are multiplied together to calculate a steering difference value Δθ. Note that the steering gain K1 is a coefficient that is set uniquely for each traveling device 4.

[0064] Next, the opening degree V is acquired from the proportional solenoid valve 4d of the traveling device 4. The opening degree V is a value based on the opening degree of a spool (not shown) in the proportional solenoid valve 4d. An opening degree difference value ΔV, which is the difference value between the acquired opening degree V and the steering difference value Δθ, is calculated.

[0065] Furthermore, the hydraulic oil temperature T is acquired from the hydraulic oil temperature sensor 4e provided in the traveling device 4, and a temperature correction coefficient KT corresponding to the acquired temperature T is acquired. Then, the proportional solenoid valve command value Ed is calculated by multiplying the calculated opening difference value ΔV, the temperature correction coefficient KT, and a differential gain K2. Note that the differential gain K2 is a coefficient that is set uniquely for each proportional solenoid valve 4d.

[0066] The calculated proportional solenoid valve command value Ed is input to the proportional solenoid valve 4d, causing the proportional solenoid valve 4d to operate. In accordance with the operation of the proportional solenoid valve 4d, hydraulic oil is supplied to the hydraulic cylinder 4c, causing the hydraulic cylinder 4c to expand and contract. The expansion and contraction of the hydraulic cylinder 4c is converted into rotation of the rotary shaft 4b, causing the wheels 4a to be steered.

[0067] As described above, the steering correction coefficient Kθ corresponding to the steering command angle θα, which is based on the cylinder length L for setting the wheel 4a to the steering command angle θα, is acquired, and the proportional solenoid valve command value Ed is calculated using the steering command angle θα and the acquired steering correction coefficient Kθ.

[0068] Here, the steering correction coefficient Kθ is a coefficient based on the cylinder length L for setting the wheel 4a to the steering command angle θα, so by using this steering correction coefficient Kθ, it is possible to calculate the proportional solenoid valve command value Ed, which specifies the speed at which the hydraulic cylinder 4c is operated to aim for the length required to set the steering command angle θα. This makes it possible to suppress the deviation between the steering command angle θα and the actual steering angle θN of the wheel 4a steered based on the steering command angle θα.

[0069] The steering correction coefficient Kθ is set based on the difference ΔL in the cylinder length L when the steering command angle θα is changed by one degree. Here, when steering the wheels 4a, the linear extension and contraction of the hydraulic cylinder 4c is converted into rotation by the rotary shaft 4b. Therefore, the relationship between the steering command angle θα and the cylinder length L corresponding to that steering command angle θα is not always constant. Specifically, it is necessary to control the coexistence of steering command angles θα that require a large change in the cylinder length L in order to rotate the wheels 4a at a constant speed, and steering command angles θα that require a small change in the cylinder length L.

[0070] Therefore, by setting the steering correction coefficient Kθ according to the difference length ΔL of the cylinder length L when the steering command angle θα is changed in increments of 1 degree, the cylinder length L can be more appropriately set to set the wheel 4a to the steering command angle θα using the set steering correction coefficient Kθ. This makes it possible to more appropriately suppress the deviation between the steering command angle θα and the actual steering angle θN of the wheel 4a.

[0071] Furthermore, a calculation function is calculated in which the value ΔL / ΔLmax obtained by dividing the differential length ΔL for each steering command angle θα by the maximum value ΔLmax is approximated by a cubic function, and the steering correction coefficient Kθ is obtained by inputting the steering command angle θα into the calculation function. As a result, the steering correction coefficient Kθ can be obtained simply by inputting the steering command angle θα into the calculation function, so the steering correction coefficient Kθ can be easily obtained. Furthermore, since the calculation function is configured as a cubic function that approximates the relationship between the steering command angle θα and the value ΔL / ΔLmax, a more appropriate steering correction coefficient Kθ can be obtained for the input steering command angle θα.

[0072] Next, the electrical configuration of the transport vehicle 1 will be described with reference to Fig. 6. Fig. 6 is a block diagram showing the electrical configuration of the transport vehicle 1. The transport vehicle 1 is equipped with a CPU 10, a flash ROM 11, and a RAM 12, which are each connected to an input / output port 14 via a bus line 13. The input / output port 14 is further connected to the above-mentioned traveling device 4, steering device 6, and load sensor 7, respectively.

[0073] The CPU 10 is a computing device that controls each unit connected to the bus line 13 and the input / output port 14. The flash ROM 11 is a rewritable nonvolatile memory that stores a control program 11a, steering correction coefficient data 11b, load correction coefficient data 11c, and temperature correction coefficient data 11d. When the CPU 10 executes the control program 11a, a main process described later in FIG. 7 is executed.

[0074] The steering correction coefficient data 11b stores a steering correction coefficient Kθ corresponding to the traveling unit 4 and the steering command angle θα. Specifically, the steering correction coefficient data 11b stores the steering correction coefficient Kθ for each steering command angle θα obtained from the calculation function for each traveling unit 4, distinguished for each traveling unit 4. The load correction coefficient data 11c stores the load correction coefficient KL corresponding to the load Ld of the cargo bed 3, distinguished for each traveling unit 4. Furthermore, the temperature correction coefficient data 11d stores the temperature correction coefficient KT corresponding to the temperature T of the hydraulic oil, distinguished for each traveling unit 4.

[0075] The RAM 12 is a memory for rewritably storing various work data, flags, etc. when the CPU 10 executes the control program 11a, etc., and is provided with a command value memory 12a in which the proportional solenoid valve command value Ed described above is stored.

[0076] The traveling device 4 is provided with the proportional solenoid valve 4d, hydraulic oil temperature sensor 4e, and steering angle sensor 4f described above. The opening V described above in FIG. 5 is acquired from the proportional solenoid valve 4d, and the calculated proportional solenoid valve command value Ed is transmitted to the proportional solenoid valve 4d. The actual steering angle θN described above in FIG. 5 is acquired from the steering angle sensor 4f. In addition, the temperature T of the hydraulic oil supplied to the proportional solenoid valve 4d is acquired from the hydraulic oil temperature sensor 4e.

[0077] Next, the processing executed by the CPU 10 will be described with reference to Figures 7 and 8. Figure 7 is a flowchart of the main processing. The main processing is processing that is repeatedly executed after the power of the transport vehicle 1 is turned on. The main processing first sets a counter variable N to 1 (S1). Identification numbers from 1 to 12 are assigned to the 12 traveling devices 4, respectively, and the value of the counter variable N is used to indicate the identification number. Hereinafter, "the Nth traveling device" will mean "the traveling device whose identification number is the value of the counter variable N."

[0078] After the process of S1, a steering command angle θα of the Nth traveling device 4 is calculated based on the steering angle acquired from the steering device 6 (S2). Note that a known method is used to calculate the steering command angle θα from the steering angle acquired from the steering device 6 in the process of S2, so a detailed description will be omitted. After the process of S2, a command value calculation process (S3) is executed. The command value calculation process will now be described with reference to FIG. 8.

[0079] Fig. 8 is a flowchart of the command value calculation process. The command value calculation process is a process for calculating the proportional solenoid valve command value Ed based on the method described in the block diagram of Fig. 5. In the command value calculation process, first, the actual steering angle θN is acquired from the steering angle sensor 4f of the Nth traveling device 4 (S10). After the process of S10, a first difference value is calculated, which is the difference value between the steering command angle θα calculated in S2 of Fig. 7 and the actual steering angle θN acquired in the process of S10 (S11).

[0080] After the process of S11, a steering correction coefficient Kθ corresponding to the steering command angle θα calculated in S2 of Fig. 7 for the Nth traveling device 4 is obtained from the steering correction coefficient data 11b (S12). After the process of S12, a load Ld of the platform 3 is obtained from the load sensor 7 (S13), and a load correction coefficient KL corresponding to the load Ld obtained in the process of S13 for the Nth traveling device 4 is obtained from the load correction coefficient data 11c (S14).

[0081] After processing S14, a steering differential value Δθ is calculated by multiplying the first differential value calculated in processing S11 by the steering correction coefficient Kθ obtained in processing S12, the load correction coefficient KL obtained in processing S14, and the steering gain K1 set specifically for the Nth traveling device 4 (S15).

[0082] After the processing of S15, the opening V is obtained from the proportional solenoid valve 4d in the Nth traveling device 4 (S16). After the processing of S16, an opening difference value ΔV is calculated, which is the difference between the steering difference value Δθ calculated in the processing of S15 and the obtained opening V (S17). After the processing of S17, the hydraulic oil temperature T is obtained from the hydraulic oil temperature sensor 4e in the Nth traveling device 4 (S18), and a temperature correction coefficient KT corresponding to the hydraulic oil temperature T in the Nth traveling device 4 obtained in the processing of S18 is obtained from the temperature correction coefficient data 11d (S19).

[0083] After the process of S19, the proportional solenoid valve command value Ed is calculated by multiplying the opening difference value ΔV calculated in the process of S17 by the temperature correction coefficient KT acquired in the process of S19 and the differential gain K2 set uniquely for each proportional solenoid valve 4d, and the calculated value is stored in the command value memory 12a (S20). After the process of S20, the command value calculation process ends.

[0084] Returning to Fig. 7, after the command value calculation process in S3, the proportional solenoid valve command value Ed in the command value memory 12a is sent to the proportional solenoid valve 4d in the Nth traveling unit 4 (S4). This operates the proportional solenoid valve 4d and hydraulic cylinder 4c of the Nth traveling unit 4 to rotate the rotary shaft 4b and steer the wheels 4a.

[0085] After the processing of S4, the counter variable N is incremented by 1 (S5), and it is confirmed whether the counter variable N is greater than the number of traveling units 4 (S6). If it is confirmed in the processing of S6 that the counter variable N is equal to or less than the number of traveling units 4 (S6: No), the processing from S2 onwards is repeated. On the other hand, if it is confirmed in the processing of S6 that the counter variable N is greater than the number of traveling units 4 (S6: Yes), other processing of the transport vehicle 1 is executed (S7), and the processing from S1 onwards is repeated.

[0086] The present invention has been described above based on an embodiment, but the present invention is not limited to the above-described embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope of the invention.

[0087] In the above embodiment, the differential length ΔL of the cylinder length L (see FIG. 3A) is used as is in setting the steering correction coefficient Kθ, but this is not limiting. For example, the steering correction coefficient Kθ may be calculated from a value obtained by adding, subtracting, multiplying, or dividing the differential length ΔL for each steering command angle θα by a predetermined coefficient. In this case, the magnitude of the predetermined coefficient may be changed according to the steering command angle θα, and the differential length ΔL may be weighted according to the steering command angle θα before being used in calculating the steering correction coefficient Kθ.

[0088] Furthermore, in the above embodiment, the steering correction coefficient Kθ is set based on the differential length ΔL, but the amount of change used to set the steering correction coefficient Kθ is not limited to the differential length ΔL. For example, for each steering command angle θα, a divided value may be calculated by dividing the cylinder length L at that steering command angle θα by the cylinder length L at the next smaller steering command angle θα, and the steering correction coefficient Kθ may be set using the calculated divided value.

[0089] In the above embodiment, the steering correction coefficient Kθ is obtained from a calculation function formed by a cubic function, but this is not limited to this. The calculation function may be formed by other functions such as a linear function, a quadratic function, an exponential function, or a logarithmic function. Furthermore, the steering correction coefficient Kθ is not limited to being obtained from a calculation function. For example, a value ΔL / ΔLmax corresponding to the steering command angle θα expected to be calculated in the process of S3 in Fig. 7 may be calculated in advance and stored in the steering correction coefficient data 11b.

[0090] In the above embodiment, in Fig. 4(a), the relationship between the load correction coefficient KL and the load Ld of the loading platform 3 is linear, but the relationship between the load correction coefficient KL and the load Ld is not limited to being linear. For example, the relationship between the load correction coefficient KL and the load Ld of the loading platform 3 may be nonlinear, such as a curve or a step. Furthermore, the load correction coefficient KL is set to a larger value as the load Ld increases, but the present invention is not limited to this. For example, the load correction coefficient KL may be a constant value regardless of the load Ld, or the load correction coefficient KL may be a smaller value as the load Ld increases.

[0091] 4(b), the relationship between the temperature correction coefficient KT and the temperature T of the hydraulic oil is linear, but this is not limited thereto, and the relationship between the temperature correction coefficient KT and the temperature T may be nonlinear, such as a curve or a step. Also, the temperature correction coefficient KT is set to a larger value as the temperature T decreases, but this is not limited thereto, and the temperature correction coefficient KT may be a constant value regardless of the temperature T, or the temperature correction coefficient KT may be set to a larger value as the temperature T increases.

[0092] In the above embodiment, the hydraulic oil temperature sensor 4e is provided in the hydraulic oil supply portion of the proportional solenoid valve 4d of each traveling device 4, but this is not limited to this. For example, the hydraulic oil temperature sensor 4e may be provided in the discharge portion that discharges the hydraulic oil in the proportional solenoid valve 4d of each traveling device 4. Furthermore, the hydraulic oil temperature sensor 4e may be provided in the hydraulic oil tank Tk (see FIG. 2(b)) in which the hydraulic oil is stored.

[0093] In the above embodiment, the proportional solenoid valve command value Ed is calculated using the steering correction coefficient Kθ, the load correction coefficient KL, and the temperature correction coefficient KT, but this is not limiting. For example, the proportional solenoid valve command value Ed may be calculated using the steering correction coefficient Kθ but without using the load correction coefficient KL and the temperature correction coefficient KT. Furthermore, the proportional solenoid valve command value Ed may be calculated using the steering correction coefficient Kθ and the load correction coefficient KL but without using the temperature correction coefficient KT, or the proportional solenoid valve command value Ed may be calculated using the steering correction coefficient Kθ and the temperature correction coefficient KT but without using the load correction coefficient KL.

[0094] In the above embodiment, the steering correction coefficient Kθ, the load correction coefficient KL, and the temperature correction coefficient KT are obtained for each traveling unit 4, but this is not limiting. For example, the steering correction coefficient Kθ, the load correction coefficient KL, and the temperature correction coefficient KT that are common to all traveling units 4 may be obtained, and the proportional solenoid valve command value Ed for each traveling unit 4 may be calculated using these obtained coefficients.

[0095] Alternatively, "groups" of traveling units 4 may be formed according to the manner in which the traveling units 4 are connected to the vehicle body 2, such as the traveling units 4 in the first, second, fifth, and sixth rows and the traveling units 4 in the third and fourth rows in FIG. 1(b), or the type of traveling unit 4, and a steering correction coefficient Kθ, a load correction coefficient KL, and a temperature correction coefficient KT may be obtained for each formed group, and the proportional solenoid valve command value Ed for the traveling units 4 belonging to that group may be calculated using these coefficients obtained for each group.

[0096] In the above embodiment, the hydraulic cylinder 4c is used as an example of the cylinder connected to the rotary shaft 4b, but this is not limiting and other types of cylinders, such as an electric cylinder, may also be used. When using other types of cylinders, for example, instead of parameters for operating the hydraulic cylinder 4c, such as the opening V in Fig. 5, parameters for operating that cylinder may be used to calculate a command value for operating that cylinder instead of the proportional solenoid valve command value Ed.

[0097] In the above embodiment, the steering device 6 is configured as a handle operated by an operator, but is not limited to this. The steering device 6 may be configured as another operator such as a lever. Also, the steering device 6 may be configured as a device that receives a steering angle transmitted from a remote location such as a monitoring room that monitors the travel of the transport vehicle 1, or may be configured as a device that calculates a steering angle for moving the transport vehicle 1 to the destination based on the detected situation of obstacles and the like around the transport vehicle 1.

[0098] In the above embodiment, a guided vehicle 1 was used as an example of a vehicle, but this is not necessarily limited to this, and the present invention may be applied to other vehicles such as unmanned guided vehicles, unit carriers, automobiles, etc. [Explanation of symbols]

[0099] 1 transport vehicle 3 Cargo bed 4a wheels 4b Rotating shaft 4c Hydraulic cylinder (cylinder) 7 Load sensor (part of the load acquisition means) 4e Hydraulic oil temperature sensor (part of hydraulic oil temperature acquisition means) Ed Proportional solenoid valve command value (command value) Kθ steering correction coefficient KL load correction factor KT temperature correction coefficient L Cylinder length (cylinder length) T Hydraulic oil temperature θα Steering command angle S2 Command angle acquisition means S4 Steering means S12 Steering correction coefficient acquisition means S13 Part of load acquisition means S14 Load correction coefficient acquisition means S18 Part of hydraulic oil temperature acquisition means S19 Temperature correction coefficient acquisition means S20 Command value calculation means

Claims

1. Wheels and a rotation shaft that supports the wheel so that the wheel can rotate horizontally; a cylinder connected to the rotation shaft and rotating the rotation shaft in a horizontal direction; a command angle acquisition means for acquiring a steering command angle that is a target steering angle of the wheel; a command value calculation means for calculating a command value for extending or retracting the cylinder based on the steering command angle acquired by the command angle acquisition means; a steering means for rotating the rotary shaft by extending and retracting the cylinder based on a command value calculated by the command value calculation means, thereby steering the wheels, a steering correction coefficient acquisition means for acquiring a steering correction coefficient according to the steering command angle acquired by the command angle acquisition means, the steering correction coefficient being a coefficient based on the length of the cylinder for setting the wheels to the steering command angle; The guided vehicle is characterized in that the command value calculation means calculates the command value using the steering command angle acquired by the command angle acquisition means and the steering correction coefficient acquired by the steering correction coefficient acquisition means.

2. 2. The transport vehicle according to claim 1, wherein the steering correction coefficient is set in accordance with the amount of change in the length of the cylinder when the steering command angle is changed by a predetermined angle.

3. 2. The transport vehicle according to claim 1, wherein the steering correction coefficient is obtained from a calculation function that uses the steering command angle as an input, and the calculation function is formed of a cubic function.

4. The transport vehicle has a loading platform, a load acquisition means for acquiring the load of the loading platform; a load correction coefficient acquisition means for acquiring a load correction coefficient that is a coefficient according to the load acquired by the load acquisition means; 4. The transport vehicle according to claim 1, wherein the command value calculation means calculates the command value using the steering command angle acquired by the command angle acquisition means, the steering correction coefficient acquired by the steering correction coefficient acquisition means, and the load correction coefficient acquired by the load correction coefficient acquisition means.

5. 5. The transport vehicle according to claim 4, wherein the load correction coefficient acquisition means acquires the load correction coefficient such that the larger the load, the larger the command value calculated by the command value calculation means.

6. The cylinder is a hydraulic cylinder that expands and contracts according to the amount of hydraulic oil supplied, a hydraulic oil temperature acquisition means for acquiring the temperature of the hydraulic oil that operates the hydraulic cylinder; a temperature correction coefficient acquisition means for acquiring a temperature correction coefficient that is a coefficient according to the temperature of the hydraulic oil acquired by the hydraulic oil temperature acquisition means; 4. A transport vehicle according to claim 1, wherein the command value calculation means calculates the command value using the steering command angle acquired by the command angle acquisition means, the steering correction coefficient acquired by the steering correction coefficient acquisition means, and the temperature correction coefficient acquired by the temperature correction coefficient acquisition means.

7. 7. The transport vehicle according to claim 6, wherein the temperature correction coefficient acquisition means acquires the temperature correction coefficient such that the lower the temperature of the hydraulic oil, the larger the command value calculated by the command value calculation means.

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