JP2016049921A - Wheel driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wheel driving device enabling multiple rotation of a pivot shaft without any difficulty of motor wiring, eliminating the necessity of initializing a pivot shaft angle, and having improved road surface ground-contact property.SOLUTION: The wheel driving device includes a casing, a first rotary shaft, a first motor, a second rotary shaft, a second motor, a pivot part disposed coaxially to the first rotary shaft and the second rotary shaft and rotatable relative to the casing and the first rotary shaft and the second rotary shaft, an absolute value encoder capable of detecting the rotational angle of the pivot part, a first wheel and a second wheel rotatable around a horizontal axis at a position offset from the pivot shaft, a transmission part for transmitting rotation from the first rotary shaft to the first wheel and transmitting rotation from the second rotary shaft to the second wheel, and a suspension part for enabling the first wheel and the second wheel to vertically move with respect to a road surface and pressing the first wheel and the second wheel toward the road surface.SELECTED DRAWING: Figure 2A

Description

  The present invention relates to a wheel drive device for moving a wheel mobile robot in all directions. In particular, the present invention relates to a wheel drive device in which a turning shaft is capable of multiple rotations, initialization of the turning shaft is unnecessary, and road surface grounding property is improved.

  Conventionally, in a robot that moves with wheels in all directions, there is a method using a special wheel in which free rollers such as an omni wheel or a mecanum wheel are arranged on the circumference. Since these wheels use a large number of free rollers, the cost is high, and there is a problem that vibration occurs during rotation or the road surface is damaged.

  On the other hand, a method of moving in all directions with wheels using ordinary rubber tires has been devised (see, for example, Patent Document 1). It is possible to change the direction of the wheel in any direction by turning a pair of drive wheels around the steering axis, but since there is no offset between the drive axis and the steering axis, it can move instantaneously in the lateral direction. I need time for that.

  On the other hand, there is known an active single wheel caster having a wheel traveling drive shaft that is offset from the steering drive shaft so as to be instantaneously movable in the lateral direction (see, for example, Patent Document 2). . However, there is a problem that the utilization ratio of the steering drive motor is less than that of the wheel drive motor, which is not efficient. Some of these problems have been improved in efficiency by differential driving (see, for example, Patent Documents 3 and 4), but it is difficult to lower the floor to prevent the steering shaft and wheels from interfering with each other. There was a problem.

  One having two drive wheels offset from a free-turning swivel axis (active twin-wheel caster) has also been proposed (see, for example, Patent Document 2). The efficiency of the motor is improved compared to the active single wheel caster, and if it is divided into two wheels, interference between the steering shaft and the wheel can be avoided, but the two wheels from the steering shaft must be driven, the steering In order to be able to make multiple rotations of the shaft, the wiring of the travel motor has become a problem. On the other hand, a mechanism is shown in which a motor is installed at the upper part by arranging a rotating shaft on the same axis (see, for example, Patent Document 5).

Japanese Patent No. 3055250 Japanese Patent No. 3560403 Japanese Patent No. 5228156 Japanese Patent No. 5376347 Japanese Patent No. 4147581

  However, it is necessary to initialize the angle of the steering shaft, and there is a problem that it is difficult to move in all directions if there is even unevenness on the road surface.

  Therefore, an object of the present invention is to provide a wheel drive device that can rotate a turning shaft without causing a problem of motor wiring, does not require initialization of the turning shaft angle, and has improved road surface grounding. .

  In order to achieve the above object, according to the present invention, a housing disposed substantially horizontally with respect to a road surface and a first rotatable relative to the housing about a pivot axis substantially perpendicular to the road surface. A rotating shaft, a first motor that is installed in the housing and rotationally drives the first rotating shaft, and is arranged coaxially with the first rotating shaft, the housing and the first rotation A second rotation shaft that is rotatable relative to the shaft; a second motor that is installed in the housing and that rotationally drives the second rotation shaft; the first rotation shaft and the second rotation; And a swivel unit disposed coaxially with the shaft and rotatable relative to the housing, the first rotation shaft, and the second rotation shaft, and a rotation angle of the swivel unit installed in the housing. Detectable absolute value encoder and rotatable around a horizontal axis at a position offset from the swivel axis A first wheel and a second wheel; and a transmission unit that transmits rotation from the first rotating shaft to the first wheel, and transmits rotation from the second rotating shaft to the second wheel; A wheel driving device comprising: a suspension unit that allows the first wheel and the second wheel to move in a direction substantially perpendicular to a road surface, and that presses the first wheel and the second wheel toward the road surface. Provided.

  Moreover, as for the said wheel drive device, the said suspension part may consist of a spring.

  Moreover, as for the said wheel drive device, the said suspension part may consist of a spring and a damper.

  Moreover, in order to achieve the said objective, in this invention, the omnidirectional mobile trolley | bogie provided with two or more wheel drive apparatuses as described in any one of the above is provided.

  According to the wheel drive device of the present invention, it is possible to provide a wheel drive device in which the turning shaft can be rotated many times without causing a problem of motor wiring, initialization of the turning shaft angle is unnecessary, and road surface grounding property is improved. .

It is a conceptual diagram of a wheel drive device. It is a conceptual diagram of a wheel drive device. It is a figure of a wheel drive device. It is sectional drawing in the steering shaft of MADC. It is an enlarged view of the upper part. It is a figure which shows the external appearance of an omnidirectional mobile robot. It is a figure which shows the external appearance of an omnidirectional mobile robot. It is a figure which shows the external appearance of an omnidirectional mobile robot. It is a figure which shows the external appearance of an omnidirectional mobile robot. It is a system configuration diagram. It is a figure which shows a kinematic model.

  Embodiments of the present invention will be described below.

  1 and 2A and 2B show an example of a conceptual diagram of a wheel driving device according to an embodiment of the present invention.

[Outline of wheel drive unit]
The wheel drive device is disposed coaxially with the housing, the first rotating shaft that is rotatable relative to the housing, and the first rotating shaft around a pivot axis substantially perpendicular to the road surface. A second rotation shaft that is rotatable relative to the housing and the first rotation shaft, a first motor that drives the first rotation shaft, and a second motor that drives the second rotation shaft , The first rotation axis and the second rotation axis are arranged coaxially, and the casing, the first rotation axis and the swivel unit that can rotate relative to the second rotation axis, and the casing are installed, An absolute value encoder capable of detecting a rotation angle of the turning unit, a first wheel and a second wheel which are rotatable around a horizontal axis at a position offset from the turning shaft, and a first wheel from the first rotating shaft. A transmission unit for transmitting rotation to the wheel and transmitting rotation from the second rotating shaft to the second wheel; a first wheel and a second vehicle; Was movable in a direction substantially perpendicular to the road surface, and a suspension portion for pressing the first wheel and the second wheel in the direction of the road surface. In addition, the suspension part can have a spring and / or a damper.

[Details of wheel drive device]
(Multi-turn active twin-wheel caster mechanism)
An omnidirectional movement mechanism using an active twin-wheel caster mechanism is theoretically feasible, but there is a problem that multiple rotations are difficult due to restrictions on wiring to the drive unit when mounted. A method using a slip ring is also conceivable, but the cost is high and there is still concern about long-term reliability. Therefore, the present inventors have developed an active double-wheel caster mechanism (hereinafter referred to as MADC: Multirotatable ActiveDual-wheel Caster) that can mechanically perform multiple rotations. The outline is shown in FIG. 1 and FIG.

  FIG. 3 shows an example of a cross section of the steering axis of the MADC, and FIG. 4 shows an example of an enlarged upper part.

The transmission path from the motor to the right wheel is indicated by “A”, the transmission path from the motor to the left wheel is indicated by “B”, the upper part of the MADC is indicated by “C”, and the lower part is indicated by “D”. As shown in FIG. 3, the inner shaft (first rotating shaft, A), the outer shaft (second rotating shaft, B), the MADC lower portion (swivel unit, D), and the MADC upper portion, centered on the steering shaft. (Case, C) are arranged in this order. By supporting each part with a bearing, each can rotate relatively. Thus, the MADC is roughly divided into two parts, an upper part (housing) and a lower part (swivel part), the upper part is fixed to the mobile robot, and the lower part rotates relative to the upper part. Two motors are provided on the upper part of the MADC, and the rotation is transmitted to the left and right wheels via gears and pulleys. Furthermore, since the turning angle of the lower part with respect to the upper part is measured by a 10-bit absolute encoder, it is not necessary to initialize it at every start-up. In this embodiment, since the reduction ratio between the motor and the rotating shaft is 1/10 and the reduction ratio between the rotating shaft and the wheel is 1/3, each wheel axis ω _wL , ω _wR , turning axis The relationship between the angular velocities between ω and the motor shafts ω _mL and ω _mR is expressed by the following equation.

(Formula 1)

(Formula 2)

  Since the upper part of the MADC to which the motor / encoder main body is fixed does not rotate, the routing of the wiring, which is one of the problems of the active twin-wheel caster mechanism, is eliminated, and the lower part of the MADC can be rotated many times.

(Omnidirectional robot)
An omnidirectional mobile robot provided with two MADCs as wheel portions will be described. The external appearance is shown in FIGS. 5A to 5D, and an example of the entire system configuration is shown in FIG.

(Kinematics of omnidirectional mobile robot)
A kinematic model of the omnidirectional mobile robot is shown in FIG. Here, the space in which the mobile robot moves is assumed to be on a horizontal plane, and the coordinate system viewed from above the robot is set as shown in FIG. A vector representing the position and orientation of the robot as viewed from the absolute coordinate system ΣA is P = [P _x , P _y , φ] ^T. Further, the number of the left wheel part as viewed from the robot is 1, the right number is 2, the position vector viewed from the origin of ΣA of each wheel part is p _i , the direction (angle) of the wheel part body is θ _i , The wheel interval is b, the wheel radius is r, the offset between the wheel shaft and the steering shaft is l, the angular velocity of the wheel is (ω _iL , ω _iR ), and the distance between the steering shaft of the wheel portion and the center of the robot is L. However, i = 1 and 2.

Assuming that the wheels rotate without slipping on the road, the speed of the robot
From the following equation, the following inverse kinematic equation for obtaining the wheel angular velocity U = [ω _1L , ω _1R , ω _2L , ω _2R ] ^T holds.

(Formula 3)

  However, the following relationship is satisfied, and R (θ) is a rotation transformation matrix.

(Formula 4)

(Formula 5)

(Formula 6)

  Thus, the movement of the robot in any direction can be realized by the two active twin wheel casters.

(Running experiment)
It was confirmed by running experiments that the omnidirectional mobile robot can actually move to any position and posture. This is shown in FIGS. It moved to the right of the photograph in FIGS. 5A to 5B, and further moved upward in the photograph in FIGS. 5B to 5C. Furthermore, in the position of FIG. 5C, the turning motion could be performed as shown in FIG. 5D.

(Effect of embodiment)
The wheel drive device according to the present embodiment uses an active caster that is not a special wheel to generate an instantaneous driving force in an arbitrary direction, and an active double-wheel caster capable of multi-rotation that is not restricted by wiring. Can be provided. Moreover, the wheel drive device according to the present embodiment can be applied to an omnidirectional mobile robot.

  That is, according to the wheel drive device according to the present embodiment, an omnidirectional moving mechanism using ordinary wheels can be realized, an active twin-wheel caster mechanism capable of multiple rotations can be realized, and an omnidirectional mobile robot can be realized. According to a running experiment in the robot according to the present embodiment, it was confirmed that it was possible to actually generate a speed instantaneously in an arbitrary direction.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

Claims (4)

A housing disposed substantially horizontally with respect to the road surface;
A first rotation axis rotatable around the pivot axis substantially perpendicular to the road surface relative to the housing;
A first motor that is installed in the housing and rotationally drives the first rotating shaft;
A second rotating shaft that is arranged coaxially with the first rotating shaft and is rotatable relative to the housing and the first rotating shaft;
A second motor that is installed in the housing and rotationally drives the second rotating shaft;
A swivel unit disposed coaxially with the first rotation shaft and the second rotation shaft and rotatable relative to the housing and the first rotation shaft and the second rotation shaft;
An absolute value encoder installed in the housing and capable of detecting the rotation angle of the swivel unit;
A first wheel and a second wheel rotatable around a horizontal axis at a position offset from the pivot axis;
A transmission unit for transmitting rotation from the first rotating shaft to the first wheel and transmitting rotation from the second rotating shaft to the second wheel;
A wheel drive device comprising: a suspension unit that allows the first wheel and the second wheel to move in a direction substantially perpendicular to the road surface, and that presses the first wheel and the second wheel in the direction of the road surface.   The wheel driving device according to claim 1, wherein the suspension portion is made of a spring.   The wheel drive device according to claim 1, wherein the suspension portion includes a spring and a damper.   An omnidirectional mobile trolley comprising two or more wheel drive devices according to any one of claims 1 to 3.