Patent Application
20240383549
This application is a Paris Convention application which claims the benefit of Japanese Patent Application No. 2023-080855 filed on May 16, 2023. The contents of the above application is all incorporated by reference as if fully set forth herein in its entirety.
The present disclosure relates to a traveling device including omnidirectional wheels.
Traveling devices that are equipped with omnidirectional wheels such as mecanum wheels or omni wheels and are movable in all directions have been known. Such a traveling device includes a traveling device main body, a plurality of omnidirectional wheels (typically four wheels) provided on the traveling device main body, drive devices that independently drive omnidirectional wheels, and a control device that controls the drive devices. By independently controlling the drive of each omnidirectional wheel, the traveling device can be moved in any direction such as front, back, left, right, or diagonal direction, or in various other ways, such as turning.
When a travel floor surface (namely, floor surface on which a traveling device travels) is uneven, some of the plurality of omnidirectional wheels may be separated from the travel floor surface, which may cause the traveling device to travel in an unexpected direction, making the traveling unstable. For this problem, the following is proposed. Omnidirectional wheels are provided on the traveling device body via a suspension, thereby allowing the omnidirectional wheels to be moved up and down relative to the traveling device main body. The omnidirectional wheels thus follow the unevenness of the travel floor surface, allowing all omnidirectional wheels to always maintain contact with the travel floor surface (for example, Patent Literature (hereinafter, referred to as PTL) 1).
In addition, omnidirectional wheels have a more complex structure than regular wheels, so there is a limit to their maximum load carrying capacity. For this problem, a traveling device is known that includes swivel casters in addition to mecanum wheels with a suspension (PTL 2). Such a device is configured as follows. When there is no cargo on the loading platform (no load) or for transporting a light cargo, the traveling device main body is supported only by the mecanum wheels, and for transporting relatively a heavy cargo, the weight of the cargo causes the suspension to contract, allowing the swivel casters to touch the ground. In this case, the traveling device main body is supported by swivel casters in addition to the mecanum wheels, thereby preventing the application of excessive loads to the mecanum wheels.
Furthermore, it is conceivable to provide the traveling device with a sensor such as a light detection and ranging (Lidar) sensor to control the autonomous travel while obtaining the situation around the traveling device. The traveling device compares information on the map and obstacles given in advance with information on obstacles and the like around the traveling device detected and measured by the sensor, and autonomously travels along a predetermined route while obtaining the position of the own vehicle.
In the traveling devices described in PLTs 1 and 2, the amount of contraction of each suspension changes depending on the presence or absence of a cargo to be transported or the weight of the cargo, thereby changing the vehicle height. In addition, when the loads acting on respective suspensions differ from each other (becomes uneven) due to cargo or the like, the posture of the traveling device main body may be tilted. When the posture of the traveling device main body is tilted, the weight balance of the traveling device may become lost and traveling may become unstable. In addition, when the traveling device main body is provided with a sensor for autonomous travel, the following may occur: when the vehicle height or posture of the traveling device changes, the height or measurement axis of the sensor installed in the traveling device main body changes, causing errors in the measurement results regarding obstacles and the like around the traveling device.
An object of the present disclosure is to provide a traveling device including omnidirectional wheels with suspensions. The traveling device is capable of always maintaining the vehicle height and posture of the traveling device main body in a constant state without tilting the traveling device main body with respect to a travel floor surface.
In order to achieve the above object, the traveling device according to the present disclosure includes: a placing part on which a cargo is to be placed; and an omnidirectional wheel that is provided on the placing part via a suspension to be vertically movable relative to the placing part. The traveling device further comprises three or more swivel casters, the three or more swivel casters being fixed to a lower section of the traveling device so as to define a plane, and when the traveling device is on a flat floor surface, the three or more swivel casters are always in contact with the floor surface, and frictional force of the omnidirectional wheel against the floor surface is greater than or equal to force required for traveling drive by the omnidirectional wheel.
The traveling device of the present disclosure further includes a sensor that measures a situation around the traveling device.
In addition, in the traveling device of the present disclosure, the three or more swivel casters are provided at positions surrounding a center of gravity of the traveling device in plan view.
In addition, in the traveling device of the present disclosure, the suspension includes a support member that rotatably supports the omnidirectional wheel, a coupling mechanism that couples the support member to the traveling device in a movable manner relative to the traveling device, and an urging member that urges the support member in a direction away from the traveling device.
According to the present disclosure, the three or more swivel casters fixed to the traveling device are always in contact with a travel floor surface, the posture of the traveling device with respect to the travel floor surface is maintained in a constant state.
Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
Placing part 21 is a loading platform on which cargo 22 to be carried by traveling device 1 is placed, and is provided in the front section of traveling device main body 2. In addition to the loading platform illustrated in
Lidar device 11 is provided at the upper section of traveling device main body 2 as an example of a sensor for detecting objects such as obstacles and the like around traveling device 1. Lidar device 11 measures the distance from Lidar device 11 to an object in the surroundings of traveling device 1 by emitting laser light 12 toward the surroundings and detecting the light reflected from the object. Providing Lidar device 11 on the upper section of traveling device main body 2 allows measurement of the distance to the object in the surroundings without being affected by cargo 22 placed on placing part 21. Traveling device 1 autonomously travels to the destination while obtaining the current position of traveling device 1 by comparing the distance to the object measured by Lidar device 11 to the map information of the traveling area stored in advance.
Spring 8 contracts due to the weight of traveling device 1. The initial lengths and spring constants of springs 8 are selected so that the three swivel casters 6 are in contact with a travel floor surface even in an unloaded state in which no cargo 22 is placed on placing part 21, and so that the frictional force between mecanum wheel 5 and the travel floor surface is greater than or equal to the force required for the traveling device 1 to travel.
Spring 8 will be described in detail. First, length H is defined as the length of spring 8 when the three swivel casters 6 are in contact with the travel floor surface, then, in order for the three swivel casters 6 to be in contact with the travel floor surface even in the unloaded state, the elastic force generated by springs 8 having length H is required to be less than or equal to the weight of traveling device 1 supported by springs 8.
On the other hand, in order for traveling device 1 that transports cargo 22 to travel by driving of mecanum wheels 5, predetermined frictional force is required between mecanum wheel 5 and the travel floor surface, and this frictional force is generated based on the force of spring 8 pressing mecanum wheel 5 against the travel floor surface. That is, the elastic force generated by springs 8 having length H is required to be greater than or equal to the elastic force required to generate the above-described predetermined frictional force. The above-described predetermined frictional force allows traveling device 1 having the total weight of its own and the cargo placed thereon to travel at a predetermined speed or acceleration.
In this manner, the initial length and spring constant of springs 8 are selected so that the elastic force generated by springs 8 having length H allows the three swivel casters to touch the ground and generates the frictional force necessary for and travel.
The three swivel casters 6 are provided on the undersurface surface of chassis 4. Swivel casters 6 are disposed in a triangular shape so as to surround the center of gravity G of the total of traveling device 1 and cargo 22 in plan view (
In the following, the operations and effects of traveling device 1 of the present embodiment will be described. In traveling device 1 of the present embodiment, the three swivel casters 6 are always in contact with a travel floor surface even in an unloaded state in which no cargo is placed. As a result, the height and posture of traveling device main body 2 are always constant, and even when the load on traveling device main body 2 is offset from the center during the transportation of the cargo, traveling device main body 2 does not tilt and the traveling becomes stable, thereby preventing errors from occurring in measurements by Lidar device 11. In addition, mecanum wheels 5 are provided on traveling device main body 2 via suspensions, and therefore, mecanum wheels 5 do not leave a travel floor surface even when the travel floor surface is uneven, thereby preventing traveling device 1 from making unexpected moves. When swivel caster 6 runs over unevenness on the travel floor surface, traveling device main body 2 may be temporarily tilted, but this inclination is temporary and returns to its original state once swivel caster 6 passes over the unevenness. This inclination is thus recognized as a temporary error in the measurement of distances to surrounding objects by Lidar device 11, and the autonomous traveling of traveling device 1 continues without any problem.
In the above examples, three swivel casters are provided to define a plane, but it is also possible to include four or more swivel casters. Further, the structure of the suspension that supports the mecanum wheel is not limited to the above example, and various structures may be adopted. Furthermore, although the above example has been described assuming that the omnidirectional wheel is a mecanum wheel; however, the same effect can naturally be obtained even when other types of omnidirectional wheels such as an omni wheel are used in place of the mecanum wheel.
The present disclosure is suitably utilized for traveling devices including omnidirectional wheels with suspensions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-080855 | May 2023 | JP | national |
