Wheel drive vehicle and wheel contact sensing method of the same

Disclosed is a wheel drive vehicle including a main body having a rotatable arm and an arm driving unit for driving the arm, a wheel rotatably mounted to the arm, respectively, and a sensing unit for sensing a non-contact state of the wheel from a ground, wherein the sensing unit includes a spring, first and second sensors, and a controller.

TECHNICAL FIELD

The present invention relates to a wheel contact sensing method for sensing contact or non-contact of the wheel, and a wheel drive vehicle employing the same.

BACKGROUND ART

As high technologies are developed and advanced, various techniques are being applied to military fields. Especially, development of various sensors and computer hardware enables an unmanned combat system.

Developed countries have been concerned about development of military robots, especially, researches for an unmanned system in the field of national defense is undergoing in the United States in order to dispose unmanned vehicles in a future combat system. Active researches for the unmanned vehicles have been in progress even within the country and development of various unmanned systems is being conducted in the field of national defense.

Examining the course of technical development in the field of the unmanned system, unmanned vehicles may perform various missions, such as reconnaissance and attack, command and control, explosive detection/disposal and the like. Upon employing a wheel drive method in the unmanned vehicle, it is needed to detect (sense) whether or not the wheel contacts a ground in order for the unmanned vehicle to be unaffected by obstacles.

In general, a contact sensor (or pressure sensor) is attached between two objects to check contact or non-contact between the two objects. However, for example, if wheels of the unmanned vehicle occur severe friction at contact portions, the contact sensor may not be easy to be attached thereto.

Therefore, a new type of wheel contact sensing structure to be appropriate for the unmanned vehicle and a method thereof are required.

DISCLOSURE OF INVENTION

Technical Problem

Therefore, to address the above-mentioned problem, an aspect of the present disclosure is to provide a new type of wheel contact sensing structure and method, different from the related art, for detecting a wheel contact of a wheel drive vehicle.

Solution to Problem

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there are provided a wheel drive vehicle including a main body having a rotatable arm and an arm driving unit for driving the arm, a wheel rotatably mounted to the arm, respectively, and a sensing unit for sensing a non-contact state of the wheel from a ground, wherein the sensing unit includes a spring installed between the arm driving unit and the arm, and extended or compressed in response to a relative rotary motion of the arm with respect to an output shaft of the arm driving unit, first and second sensors configured to detect rotation drive information related to the arm with respect to the main body and attitude information related to the main body, and a controller configured to measure a reference length of the spring in the non-contact state based upon at least one of the rotation drive information related to the arm and the attitude information related to the main body, and detect the non-contact state of the wheel based upon the measured length of the spring and the reference length thereof, and a wheel contact sensing method applied thereto.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there are provided a wheel drive vehicle including a main body having a rotatable arm and an arm driving unit for driving the arm, a wheel rotatably mounted to the arm, respectively, and a sensing unit for sensing a non-contact state of the wheel from a ground, wherein the sensing unit includes a spring installed between the arm driving unit and the arm, and extended or compressed in response to a relative rotary motion of the arm with respect to an output shaft of the arm driving unit, first and second sensors configured to detect rotation drive information related to the arm with respect to the main body and attitude information related to the main body, and a controller configured to measure a reference angle of the arm in the non-contact state based upon at least one of the rotation drive information related to the arm and the attitude information related to the main body, and detect the non-contact state of the wheel based upon the measured angle of the arm and the reference angle thereof, and a wheel contact sensing method applied thereto.

A wheel driving unit for rotating the wheel may be provided in each wheel, and the controller may run the wheel driving unit to rotate the wheel in the non-contact state. In addition, the controller may detect a contact state of the wheel with respect to the ground based upon a velocity change of the wheel, generated in response to the wheel contacting the ground.

Advantageous Effects of Invention

The present disclosure provides a new type of wheel contact sensing structure and method, capable of detecting a non-contact state of a wheel using a state of a spring and detecting a contact state of the wheel using a change in a rotation (angular) velocity of the wheel.

BEST MODE FOR CARRYING OUT THE INVENTION

Description will now be given in detail of a wheel drive vehicle and a wheel contact sensing method of the same according to an embodiment, with reference to the accompanying drawings.

FIG. 1is a perspective view of a wheel drive vehicle in accordance with one exemplary embodiment, andFIG. 2is a side view of the wheel drive vehicle shown inFIG. 1.

A wheel drive vehicle in accordance with one exemplary embodiment may include a main body110having an arm120, and a wheel130rotatably connected to the arm120.

Both side surfaces of the main body110is shown having a plurality of arms120rotatably connected thereto. This exemplary embodiment illustrates that total six arms120are connected to the both side surfaces by three for each surface. However, the number of arms120may differ according to designs thereof.

The wheels130may be rotatably connected to the arms120, respectively. Namely, one end of the arm120is rotatably connected to the main body110and another end of the arm120is rotatably connected to the wheel130.

The main body110may be provided with arm driving units121for rotating the arms120, respectively. A wheel driving unit145(seeFIG. 4) for rotating the corresponding wheel130may be installed within each wheel130. The arm driving unit121and the wheel driving unit145may be implemented in the form of a driving motor, and be controllable to be independently operable.

As the arms120are rotated with respect to the main body110, the main body110may be moved up and down, which allows the wheel drive vehicle to pass over obstacles.

FIG. 2exemplarily shows that the main body110passes over an obstacle responsive to the rotation of the arms120.

A topography detector installed in the main body110may estimate a height of an obstacle, a distance up to the obstacle and the like. Referring toFIG. 2, in order to pass over an obstacle perpendicularly protruded at the front, a rotation operation is performed to lift the arms120mounted at the front of the main body110.

Here, considering sensing errors or the like, the front arms120may be listed higher than the estimated height of the obstacle derived from the measurements of the topography detector, and the main body110may be allowed to be moved forward by the estimated distance.

Afterwards, the front arms120may be taken down in a direction that the obstacle is located so as to render the front wheels130come in contact with the obstacle. When the front wheels130contact the obstacle, the next sequence of arm attitude control may be performed for overcoming the obstacle.

Thus, detecting whether or not the wheels130are in a contact state with the ground is an important part in control of traveling of the wheel drive vehicle. Hereinafter, description will be given in detail of a structure of a sensing unit for sensing contact or non-contact of the wheel130and a sensing method thereof, which are applied to the present disclosure.

FIG. 3is a view showing a structure of the sensing unit in accordance with the one exemplary embodiment, andFIG. 4is a block diagram of the sensing unit.

Hereinafter, description will be made based upon one of the plurality of arms120, but the structure of the sensing unit for sensing the wheel contact can be implemented in each arm, accordingly, whether the wheel is in the contact state or non-contact state can be sensed in each arm.

Referring toFIGS. 3 and 4, the sensing unit may include a spring141installed between the arm driving unit121of the main body110and the arm120, a first sensor142for detecting rotation information related to the arm driving unit121, a second sensor143for detecting attitude information related to the main body110, and a controller144for detecting a non-contact state of the wheel130based upon those information detected by the first and second sensors142and143and the spring141.

The arm120may be rotated by the arm driving unit121or by a contact force responsive to the wheel130contacting the exterior (for example, a ground). Describing this specification, the rotation of the arm120by the arm driving unit121may be referred to as ‘arm rotation drive’ and the rotation of the arm120by the wheel contact force may be referred to as ‘arm rotary motion’.

The spring141may have one end secured with an output shaft of the arm driving unit121and another end secured with the arm120so as to be extended or compressed responsive to the rotary motion of the arm120. The spring141may be implemented as a type of coil spring, gas spring, torsion bar or the like, for example. This exemplary embodiment shows the spring141is implemented as a type of coil spring.

InFIG. 3, θs denotes an initially mounted angle of the arm120to the output shaft of the arm driving unit121. The first sensor142may sense (or detect) an angle of the arm120being rotated from the initially mounted angle upon rotation of the arm driving unit121, namely, an output shaft rotation angle of the arm driving unit121. The first sensor142may be implemented as an angular sensor (for example, a resolver of an arm driving motor) of the arm driving unit121.

The second sensor143may detect attitude information related to the main body110, especially, a pitch angle that the main body110forms with respect to the ground. The pitch angle may be generated as the main body110is inclined from the ground when the arms120are rotated. The second sensor143may be implemented as an attitude sensor mounted to the main body110.

The controller144may detect a reference length L of the spring141in a non-contact state from at least one of the rotation information related to the arm driving unit121and the attitude information, and detect a non-contact state of the wheel130based upon the measured length of the spring141and the detected reference length L.

Meanwhile, in addition to this method, the controller140may alternatively detect the reference angle Φ, which the spring has, in the non-contact state from at least one of the rotation information related to the arm driving unit121and the attitude information, and detect the non-contact state of the wheel130based upon a rotary motion angle and the reference angle Φ of the arm120.

That is, the controller140may detect the non-contact state of the wheel130based upon the reference length L of the spring141and the length measured upon the spring141being transformed, or based upon the reference angle Φ of the arm120and the rotation angle measured upon the arm120being rotated.

The controller140may employ one of the two methods or combination of the two methods.

The following equations express the method of detecting the reference angle Φ and the reference length L based uponFIG. 3.

In those equations, W denotes a weight of the arm120and the wheel130, and lSdenotes a distance between a rotation center of the arm120and the center of gravity between the arm120and the wheel130.

θSdenotes an initially mounted angle of the arm120with respect to the output shaft of the arm driving unit121, and θPdenotes a rotation angle of a mounting surface D of the output shaft of the arm driving unit121with respect to a horizontal surface S horizontal with the ground. Here, θPmay be generated by a pitch angle of the main body110in response to inclination of the main body110or generated as the arm120is rotated with respect to the main body110.

Kr denotes a rotation spring constant, Wldenotes a weight applied to a mounted point of a linear spring by Wr, and Kldenotes a linear spring constant.

Referring to the above equations, the reference angle Φ and the reference length L may be decided based upon the weight of the arm120and the wheel130, a physical property of the spring141and the like. In addition, it can be found that the weight Wr deciding the reference angle Φ and the reference length L may differ due to θP. Also, the weight Wrcan be decided by the pitch angle of the main body110and the rotation angle of the arm driving unit121.

The first and second sensors142and143of the sensing unit may sense the rotation angle of the arm driving unit121and the pitch angle of the main body110, respectively, so as to allow the controller144to detect the reference angle Φ or the reference length L.

FIG. 5is a flowchart showing a wheel contact sensing method in accordance with one exemplary embodiment.

First, the first and second sensors142and143may detect rotation information related to the arm driving unit121and attitude information related to the main body110, respectively (S10). The controller144may measure a reference length L of the spring141or a reference angle Φ of the arm120according to those equations (S20).

Those processes may be performed in real time during traveling of the wheel drive vehicle. The controller144may compare the measured length of the spring141, which is changed in shape upon rotation of the arm120, with the reference length L thereof, or compare an angle measured with respect to the rotary motion of the arm120with the reference angle Φ (S30).

When the measurement value is within an error range of the reference length L or the reference angle Φ, the controller144may consider it as the wheel130being in a non-contact state (S40).

In the meantime, in order to detect that the wheel130in the non-contact state is changed to a contact state with the ground, the controller144runs the wheel driving unit145for rotating the wheel130(S50). Here, the wheel driving unit145may rotate the wheel130with power as less as being able to rotate the wheel130.

When the wheel130in the non-contact state is turned to the contact state with the ground, a angular velocity (rotational velocity) of the wheel130may change. Thus, when the change in the angular velocity of the wheel130is generated (S60), the controller144may recognize it as the wheel130being in contact state (S70).

The wheel contact sensing structure and method may have the following effects.

In general, a method of checking the contact of the wheel using a slip ratio, as a relation between the angular velocity of the wheel and the velocity of a vehicle, may be used as the wheel contact sensing method. However, if the location of the wheel is controlled by driving the arm in a stopped state of the vehicle, the method may be difficult in use because the location of the vehicle may change upon generating the velocity of the wheel (i.e., rotating the wheel) in the stopped state of the vehicle.

Consequently, the above problem has been overcome by sensing the non-contact state of the wheel130using the change in the length of the spring141or the change in the angle thereof in consideration of the attitude of the vehicle and the rotation angle of the arm120, applying minimum power only to the detected wheel130, and determining the contact using the change in the angular velocity of the wheel130when being contacted by the ground.

FIG. 6is a graph showing measurements of an arm resolver angle (arm rotation angle) and a wheel angular velocity (wheel rotational velocity) during driving of the vehicle shown inFIG. 2.

If the front arm120is lifted above the ground for passing over an obstacle, the spring141(rotation spring) installed at the front arm120is drawn down in a direction toward the ground (i.e., − direction), which is caused due to the gravity by the attitude of the main body110and the angle of the arm120. During this process, the controller144detects that the wheel130is in the non-contact state. For reference, in this experimental example, the spring141has been implemented as a rotatable type, for example, a torsion bar, a torsion spring and the like.

Upon detecting the non-contact state of the wheel130, the controller144may apply a command to the wheel driving unit145to rotate the wheel130, and the wheel130may be rotated with the minimum power.

Afterwards, when a contact between the wheel130and the ground is detected as the front arm120is moved down, the angular velocity of the wheel130may change. The graph exemplarily shows that the wheel130is in a stopped state after being rotated. Here, the rotation spring141may have a rotation angle in an opposite direction (i.e., + direction) to the ground.

Also, if the arm120is rotated in the opposite direction to the ground for changing the attitude of the vehicle, the rotation spring141may have a rotation angle in a minus direction (i.e., − direction). When the rotation angle of the rotation spring141is within the range of the reference angle Φ, the controller144may detect the non-contact state of the wheel130and run the wheel driving unit145.

As such,FIG. 6shows the changes in the angle of the spring141and the angular velocity of the wheel130in case where the wheel130is sequentially changed in the order of non-contact state-contact state-non-contact state with respect to the ground.

FIG. 7is a view showing a wheel contact sensing method in accordance with another exemplary embodiment.

This exemplary embodiment shows an operation of a sensing unit in a state, which may occur due to measurement errors of the sensors upon driving the wheel drive vehicle in front of an obstacle.

A case may occur in which a height of an obstacle is erroneously measured due to the measurement error of the sensors or unevenness of the ground. In this case, at the step in which the wheel130runs by an estimated distance in a state of the front arm120being lifted, the front wheel130contacts the obstacle.

Here, a force generated by the contact between the wheel130and the obstacle may apply in a lengthwise direction of the arm120, so a change in the length of the spring141may rarely occur. Here, the velocity of the wheel130being rotated may change.

Using these characteristics, the controller144may detect a sensing accuracy with respect to the height of the obstacle, namely, whether or not the height of the obstacle has been accurately estimated. That is, if the contact between the wheel130and the obstacle is detected (sensed) prior to reaching the estimated distance, the controller144may determine there is a problem in the step of listing the front arm120, namely, estimating the height of the obstacle. Accordingly, the wheel contact sensing can be supported in various directions as well as the ground, thereby determining an error in the control procedure.

The foregoing description has been given of the wheel drive vehicle and the wheel contact sensing method thereof with reference to the accompanying drawings. However, the present disclosure may be modified in various manners within the scope of the present disclosure without being limited to the embodiments and drawings disclosed in the specification.

INDUSTRIAL APPLICABILITY

The wheel drive vehicle and the wheel contact sensing method thereof may be industrially applicable.