JPH0524544A - Steering mechanism using noncircular gear - Google Patents

Abstract

PURPOSE:To provide a steering mechanism which can set the turning center at an arbitrary point and reduce the turning radius. CONSTITUTION:The left and right front wheels 11 and 12 of car base 10 are connected each other through a pair of noncircular gears 23, 24, worm gear mechanisms 21, 22, and a pair of noncircular gears 25, 26. These pairs of noncircular gears 23, 24, and 25, 26 consist of the elliptical gears having each elliptical pitch curve. In steering, a steering motor 19 is driven according to the steering angle, and the revolution is transmitted to each pair of left and right noncircular gears 23, 24; 25, 26 through a belt pulley mechanism 20 and worm gear mechanisms 21 and 22. Accordingly, the left and right front wheels 11 and 12 are steered by the angle determined by each pair of gears 23, 24; 25, 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering mechanism used in a vehicle such as a four-wheeled vehicle that steers a plurality of wheels at the same time, and more particularly to a so-called wheel type mobile robot such as an automatic guided vehicle or an autonomous vehicle. The present invention relates to a steering mechanism suitable for.

[0002]

2. Description of the Related Art Many automated guided vehicles for transporting parts and products have been introduced into factory automation lines. Such an automatic guided vehicle is usually a wheel-type mobile robot that moves by wheels. By the way, a carrier vehicle used in such a factory is required to have a small turning radius, that is, a minimum turning radius for the purpose of use. For example, if the turning center is located inside the plane of the traveling vehicle so that the vehicle can turn on the spot, the traveling vehicle becomes extremely manoeuvrable. Therefore,
It is desirable that such a carrier be provided with a steering mechanism that can set the turning center at an arbitrary position. For this reason, in the case of the wheel type mobile robot as described above, it is often a three-wheel type in which only one wheel is a steering wheel. With the three-wheel type, the steering mechanism can be made extremely simple while having high turning performance.

However, the three-wheel type transport vehicle is more disadvantageous than the four-wheel type in terms of load capacity and running stability. Therefore, it is desirable that the transport vehicle is of a four-wheel type or more. In such a four-wheel system, it is necessary to steer at least two wheels. Moreover, in order to make a smooth turn, it is necessary to nonlinearly control the steering angle between the inner wheel and the outer wheel according to the turning radius. Therefore, conventionally, in the case of a four-wheeled transport vehicle, each wheel to be steered is provided with an independent steering device, and each wheel is provided with a steering function. A link mechanism is used to connect the two, and the steering angle of each wheel is approximately controlled.

[0004]

However, in order to give each wheel an independent steering function, a plurality of steering drive devices such as motors are required, and the drive system becomes complicated. is there. On the other hand, in the case where the steering angle of a plurality of wheels is controlled by the link mechanism, the steering drive device may be only the drive system for moving the link, but the error becomes large when the steering angle is increased, and the link mechanism itself has a large error. There is a problem that it is difficult to reduce the turning radius due to restrictions.

The present invention has been made in view of the above circumstances, and an object thereof is to be able to appropriately steer a plurality of steered wheels with a simple mechanism, whereby the turning center can be arbitrarily set. To obtain a steering mechanism that can be applied to points.

[0006]

In order to achieve this object, in the present invention, each steering wheel is connected by a steering angle transmission mechanism, and a pitch curve approximate to an elliptic system curve is provided in the steering angle transmission mechanism. The non-circular gear pair which it has is made to interpose.

[0007]

First, n steering wheels s ₁ , s ₂ , ..., S _j , ..., S _n as shown in FIG. 6 are not steered 2
A dolly 1 of arbitrary shape provided with fixed wheels f ₁ and f _2.
think of. The fixed wheels f ₁ and f ₂ drive the carriage 1 for traveling. Then, a coordinate system in which the straight traveling direction of the carriage 1 is the y axis and the axles of the fixed wheels f ₁ and f ₂ are the x axes is determined. When steering is performed on all wheels without using fixed wheels as in a four-wheel steering vehicle, an arbitrary axis orthogonal to the y axis is defined as the x axis. On the coordinates thus determined, the relationship between the steering angles of the respective steered wheels s ₁ , s ₂ , ..., S _n when the carriage 1 turns around an arbitrary point on the x-axis including the inside of the plane is shown. Ask. Assume a virtual two-wheeled vehicle having a fixed wheel f ₀ at a point O _f0 and a steering wheel s ₀ having a steering turning center at the point O ₀ as shown by a broken line in FIG. And all of the steering wheel _{s 1, s 2, ...,} s n shall be steered based on the turning center of the virtual two-wheeled vehicle. For simplicity, the caster angle of the steered wheels is zero. Here, if the steering angle of the steered wheels in the region of y ≧ 0 is positive in the clockwise direction and the counterclockwise direction is positive in the steered wheels in y <0, y <0.
Then, by inverting the sign of y, it can be handled as in the case of y> 0. Therefore, in the following, it is assumed that y ≧ 0.

Now, assuming that the steering angle of the virtual steering wheel s ₀ placed at the point O ₀ (0, y ₀ ) is θ ₀ , the point O _j (x _j , y _j )
Let θ _{j be} the steering angle of the actual steered wheel s _j placed at. Then, when it is made dimensionless by using ξ = x / y ₀ (1) η = y / y ₀ (2), the positional relationship between both wheels s ₀ and s _j is shown in FIG. 7. When the truck 1 turns at a low speed, both wheels s ₀ , s _j are prevented so that the tires do not skid during turning.
In order to have the same turning center, the following relations must be satisfied. cot θ ₀ −η _j cot θ _j = ξ _j (3) As a special case, η _j = 1, that is, steering wheels s ₀ , s
_{If the} line segment connecting the turning centers of _j is parallel to the axle of the fixed wheel, Equation 3 is equivalent to the equation called Ackermann-Junt's equation.

Now, in order to control the steering angle, consider a pair of non-circular gears whose two axes are parallel and whose distance between the axes is constant.
As shown in FIG. 8, the pitch curve of the non-circular gear (driver) on the driving side is r ₀ (φ ₀ ) in polar coordinates, and the pitch curve of the non-circular gear (follower) on the driven side is r _j (φ _j). ),
Letting the distance between both axes be d _j , the relationship of r ₀ + r _j = d _j r ₀ · dφ ₀ = r _j · dφ _j (4) holds between the pitch curves. Therefore, the pitch curve is r ₀ = {(dφ _j / dφ ₀ ) / (1 + dφ _j / dφ ₀ )} d _j (5) r _j = {1 / (1 + dφ _j / dφ ₀ )} d _j ( 6) given by.

Next, a pitch curve satisfying the relationship of Expression 3 is obtained as a rotation condition between the driver and the follower. Differentiating Equation 3 by θ ₀ , dθ _j / dθ ₀ = 1 / {m−n cos (2θ ₀ −β ₀ )} (7) or dθ _j / dθ ₀ = m−n cos (2θ _j −β _j )… (8). Here ^{_{m = (ξ j 2 + η}} j 2 +1) / 2η j ... (9) n = {(ξ j 2 + η j 2 +1) 2 + 4ξ j 2} 1/2 / 2η j ... (10) β 0 = tan ^-1 {2ξ _j / (ξ _j ² + η _j ² -1)} (11) β _j = tan ^-1 { ² η _j ξ _j / (ξ _j ² −η _j ² +1)}… (12) is there. Equations 7 and 8 are the virtual steering wheel s ₀ and the actual steering wheel s _j.
And shows the turning angle ratio. Therefore, ν ₀ and ν _j are set to arbitrary positive numbers and φ ₀ = (2θ ₀ −β ₀ ) / ν ₀ φ _j = (2θ _j −β _j ) / ν _j (13) Rewriting 8, dφ _j / dφ ₀ = (ν ₀ / ν _j ) / {m−n cos (ν ₀ φ ₀ )} = (ν ₀ / ν _j ) {m−n cos (ν _j φ _j ). } (14) Substituting Equation 14 into Equations 5 and 6 to obtain the pitch curve, r ₀ = ι ₀ / {1-ε ₀ cos (ν ₀ φ ₀ )} (15) r _j = ι _j / {1-ε _j cos (ν _j φ _j )} (16) where ι ₀ = {(ν ₀ / ν _j ) / (ν ₀ / ν _j + m)} d _j ι _j = {(ν _j / ν ₀ ) / (Ν _j / ν ₀ + m)} d _j (17) ε ₀ = n / (ν ₀ / ν _j + m) ε _j = n / (ν _j / ν ₀ + m) (18) It can be seen that the pitch curves of Equations 15 and 16 match what is called the ν _i leaf elliptic pitch curve. Here, ι _i and ε _i respectively represent 1/2 of the diameter and the eccentricity.

From the above, it can be seen that there is a non-circular gear mechanism that satisfies the expression 3, and its pitch curve is an elliptic pitch curve. In other words, elliptical steering wheel s ₁ with a non-circular gear pair having a pitch curve, s _2, ..., be caused to perform the steering angle transfer between s _n, all steering wheels s _1, s _2, ..., s _n both will be steered based on the same turning center. Therefore, the carriage 1 also turns around the turning center. The turning center is commanded by the steering angle θ ₀ of the virtual steering wheel s ₀ . When considering changes in the camber angle due to the suspension of the steered wheels, the pitch curve of the non-circular gear is an approximate elliptic pitch curve obtained by modifying the elliptic pitch curve.

[0012]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows an embodiment of a steering mechanism according to the present invention, and is a schematic configuration diagram of a drive system of an autonomous vehicle equipped with the steering mechanism. As is clear from this figure, the bogie 10 of the autonomous vehicle includes two front wheels 11 and 12 that are steering wheels and two rear wheels 13 and 14 that are fixed wheels. Then, the rear wheels 13 and 14 are independently driven by the servomotors 15 and 16 via the speed reduction mechanisms 17 and 18, respectively, whereby the carriage 10 is made to travel. The servomotors 15 and 16 are controlled by a computer so that the outer wheel is driven at a higher speed than the inner wheel when turning.

The front wheels 11 and 12 receive the input from the steering motor 19 which is a steering input section, and decelerate the belt pulley mechanism 2.
0 and worm gear mechanisms 21 and 22 are transmitted to the two pairs of left and right elliptical gears 23, 24; 25, 26, and the driven gears 24, 26 are rotated to steer the gears. Therefore, the two front wheels 11, 12
The steering angle relationships of the are determined by their non-circular gear pairs. The number of leaves of the pitch curves of the elliptical gears 23 and 25 on the driving side and the elliptical gears 24 and 26 on the driven side can be arbitrarily determined, but if they are made equal, the pitch curves of the respective gears match and the Since the gear cutting can be performed by overlapping cutting, the elliptical gear can be easily processed. Further, when the number of leaves is 2, it is not necessary to increase or decrease the input / output of the elliptical gear pair, so that the mechanism can be simplified. Therefore, in this embodiment, each elliptical gear 2
The pitch curves of 3 to 26 are all bilobed.

In such a trolley 10, since it is bilaterally symmetric, when the position of the virtual steering wheel that minimizes the eccentricity of the elliptical gear is determined, as shown in FIG. Is a position on the center line of the trolley 10 separated from the midpoint N of the axles of the rear wheels 13 and 14 by a distance equal to the distance B ₀ between the midpoint N and the front wheels 11 and 12 which are the steered wheels. Then, the virtual steering wheel s ₀ has a steering angle θ _0.
When a command is given from the steering motor 19 so that the front wheels 11 and 12 are steered by θ ₁ and θ ₂ , respectively, their turning centers O coincide with each other. Therefore, the carriage 10 turns around the turning center O.

In this embodiment, the steering mechanism is simplified by directly connecting the steered wheels 11 and 12 to the elliptical gears 24 and 26, but four elliptical gears are required. Become. The elliptical gears 24, 26
It is theoretically possible to use two elliptical gears by meshing with each other and driving one of them. However, if such an attempt is made, the eccentricity of the elliptical gear increases, making gear cutting difficult and causing problems such as interference. In order to reduce the number of elliptical gears without causing such a problem, the steered wheels may be driven from the elliptic gears via pulleys or circular gears.

FIG. 3 shows such an embodiment. In the case of this embodiment, three elliptical gears 27 and 2 are used.
8 and 29 are meshed with each other, and a gear 28 at the center thereof is rotationally driven by an input from the steering input section. The elliptical gears 27 and 29 on both sides and the steered wheels 11 and 12 are connected by the belt pulley mechanisms 30 and 31, and the rotation of the elliptic gears 27 and 29 is transmitted to the steered wheels 11 and 12. There is. Also in the steering mechanism configured as described above, when the elliptical gear 28 on the drive side is rotated by the angle −θ ₀ , the steered wheels 11 and 12 are steered by the angles θ ₁ and θ ₂ , respectively.
Therefore, it is possible to obtain the same turning performance as that of the embodiment of FIG. Since each mechanism can be installed at any position on the carriage, the degree of freedom in its arrangement is increased.

FIG. 4 shows an embodiment in which four-wheel steering is performed using such a steering mechanism.
In the case of the embodiment of FIG. 4 (a), three elliptical gears 27, 28, 29 are meshed with each other and the central gear 28 is operated by the input from the steering input section, as in the embodiment of FIG. It is designed to be rotated. Then, by the gears 27 and 29 on both sides, the front wheels 11 and 12 and the rear wheels 13,
14 are belt pulley mechanisms 30, 31 and 32,
It is designed to be steered via 33. In that case,
The belts on the front wheels 11 and 12 side are wound so as to be reversed. Therefore, the front wheels 11, 12 and the rear wheels 13, 1
The steering wheel 4 and the steering wheel 4 are steered in opposite directions. In addition, FIG.
In the case of the above embodiment, the front wheels 11 and 12 and the rear wheels 13 and 1 are
Elliptical gear pair 3 meshing with each other at position 4
4, 35; 36, 37; 38, 39; 40, 41 are provided, and elliptical gears 34, 36, 38, 40 on the drive side thereof are provided.
Are rotatably driven by the belt pulley mechanism 42. The belt of the belt pulley mechanism 42 is 8
It is wound in a V shape and is driven to travel by the drive sprocket 43 of the steering input section.
The front wheels 11, 12 and the rear wheels 13, 14 are directly connected to the driven elliptical gears 35, 37, 39, 41, respectively, and steered by them. According to such a steering mechanism for four-wheel steering, since all the steered wheels can be rotated by 360 ° or more, it is possible to turn on the spot by positioning the turning center at the center of the bogie.

In the above embodiment, the case of using the non-circular gear pair having the two-lobed elliptic pitch curve has been described, but the number of leaves of the elliptic pitch curve can be arbitrarily determined. When the number of leaves is 1, 2, 3
The pitch curves are shown in FIGS. 5 (a), 5 (b) and 5 (c), respectively.
As shown in. In some cases, the number of leaves of the drive-side gear and that of the driven-side gear may be different. Further, even if the pitch curve is not an accurate elliptic pitch curve, almost the same effect can be obtained as long as it is an approximation thereof. Therefore, the pitch curve may be modified to some extent according to the conditions of the suspension, the tire, and the like.

[0019]

As is apparent from the above description, according to the present invention, a plurality of steered wheels are steered through a pair of non-circular gears having a pitch curve similar to an elliptic pitch curve. Therefore, even when it is applied to a vehicle having four or more wheels, the turning center can be given to an arbitrary point of the vehicle. Therefore, the turning radius can be reduced, and turning on the spot can be performed, so that the turning ability can be remarkably enhanced.

[Brief description of drawings]

FIG. 1 shows an embodiment of a steering mechanism according to the present invention, and is a schematic configuration diagram of a drive system of an autonomous vehicle equipped with the steering mechanism.

FIG. 2 is an explanatory view of the operation of the steering mechanism.

FIG. 3 is a configuration diagram of a main part showing another embodiment of the steering mechanism according to the present invention.

FIG. 4 is a schematic configuration diagram showing a four-wheel steering mechanism to which a steering mechanism according to the present invention is applied.

FIG. 5 is a diagram showing a pitch curve of a non-circular gear used in the steering mechanism of the present invention.

FIG. 6 is an explanatory diagram of a coordinate system used to derive the pitch curve.

FIG. 7 is an explanatory diagram of a wheel position assumed in the process of obtaining the pitch curve.

FIG. 8 is an explanatory diagram that defines the specifications of the pitch curve.

[Explanation of symbols]

 10 bogie 11,12 front wheel (steering wheel) 13,14 rear wheel (fixed wheel) 19 steering motor (steering input section) 21,22 worm gear mechanism 23,24 elliptical gear pair 25,26 elliptic gear pair

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[Procedure amendment]

[Submission date] August 23, 1991

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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Claims (1)

Claim: What is claimed is: 1. A steering mechanism in which a steering angle transmission mechanism is provided between a plurality of steering wheels, and the steering wheels are respectively steered by an input from a steering input unit; A steering mechanism using non-circular gears, characterized in that a non-circular gear pair having a pitch curve similar to an elliptic curve is interposed in the transmission mechanism.