(1) Field of the Invention
The present invention relates to a method of controlling a movement of a mobile robot, and in particular to a method of controlling a movement of a mobile robot which moves along with a target to accompany.
(2) Description of the Related Art
Conventionally, there have been introduced various technologies relating to an accompanying method for a mobile robot represented by an automatic cart, an automatic moving vehicle and the like, to follow an accompanied target.
For example, there has been introduced an accompanying method for performing an accompanying behavior by calculating a relative distance and relative velocity between a mobile robot and a leading accompanied target using a wireless device such as an ultrasonic sensor and a wired device such as a lead wire, and by moving the mobile robot to have the relative distance and relative velocity within a predetermined range (e.g. refer to Japanese Laid-Open Patent Applications No. 6-274223, No. 6-105938, and No. 2003-92749).
The conventional mobile robot is described with reference to
As shown in
Here, a measurement method by the measurement apparatus 11b for measuring a relative positional relationship between the mobile robot 11 and the accompanied target 10 is described. In Japanese Laid-Open Patent Application No. 6-274223, the measurement apparatus 11b measures a distance to the accompanied target 10 by transmitting and receiving ultrasonic waves and radio waves to/from a transmitting/receiving apparatus attached to the accompanied target 10.
Also, in Japanese Laid-Open Patent Application No. 6-105938, the measurement apparatus 11b measures a distance and a direction to the accompanied target 10 in accordance with a direction of the lead wire connected to the accompanied target 10, and the like.
Further, in Japanese Laid-Open Patent Application No. 2003-92749, the measurement apparatus 11b measures the direction of the accompanied target 10 by detecting a direction of radio waves transmitted from a portable radio wave transmitter equipped to the accompanied target 10.
In the methods described above, the accompanying movement of the mobile robot 11 to follow the accompanied target 10 is controlled as shown in
Furthermore, Japanese Laid-Open Patent Application No. 10-172099 discloses a technology relating to a control of an automatic moving vehicle which moves along a moving path of an accompanied target (a leading vehicle).
An example of the case where the control method of the automatic moving vehicle is applied to the mobile robot is described with reference to
As shown in
As shown in
However, in the case where the conventional technology is applied to the mobile robot, there are following problems.
In other words, in the conventional technology, the accompanying behavior is performed so as to follow the current accompanied target or its moving path. Accordingly, the mobile robot results in following behind the accompanied target. Therefore, when the accompanied target suddenly stops, there is a possibility that a collision with the accompanied target is caused because of a delay of braking by the robot.
Additionally, in the case where the accompanied target is a person, in order to check an accompanying condition of the mobile robot positioned behind the person, the checking must be done by turning around a neck or a body so that the checking requires efforts in labor and time. Also, there is a possibility that an accident is caused by forward-carelessness of the person by turning the back.
The aforementioned problems of the conventional technology are described with references to
For example, as shown in
Further, as shown in
An object of the present invention is to solve the aforementioned problems and to provide a method of controlling a movement of a mobile robot for realizing safe and appropriate accompanying behavior to follow a target to accompany.
A method of controlling a movement of a mobile robot according to the present invention includes: detecting at least a position and a direction of an accompanied target; and controlling the movement of the mobile robot, based on the detected position of the accompanied target, so that the mobile robot moves along a path that is directed toward the same direction as a moving direction of the accompanied target and is parallel to the moving direction.
According to this structure, the mobile robot moves together with the accompanied target. Therefore, even in the case where the accompanied target suddenly stops, the mobile robot does not collide with the accompanied target. Also, since the mobile robot moves together with the accompanied target, in the case where the accompanied target is a person, the person can always check the presence of the mobile robot from the atmosphere. Consequently, a collision between the person and an obstacle on his/her moving direction caused by paying attention to check the mobile robot is no longer caused. Therefore, a safe and appropriate accompanying behavior to follow the accompanied target can be realized.
It is preferred that the detecting further includes smoothing at least the detected position of the accompanied target. Also, the controlling may further include estimating a continuous region having a constant width in a direction vertical to the path of the accompanied target, based at least on the position of the accompanied target, and keeping the moving path of the mobile robot while the accompanied target moves within the continuous region. Additionally, the controlling may further include keeping the moving path of the mobile robot while the accompanied target moves within the continuous region and an angular between the moving direction of the accompanied target and the path of the accompanied target is within a predetermined range.
In the case where a precision of detecting the position and velocity of the accompanied target varies, the above structure can prevent the mobile robot from moving depending on the variations.
It is further preferred that the controlling also includes stopping the mobile robot in the case where the velocity of the accompanied target is 0 and the distance between the accompanied target and the mobile robot is within a predetermined distance.
Thus, instead of making the mobile robot stop when the accompanied target stops, the mobile robot is kept moving even when the accompanied target stops and is stopped when the mobile robot approaches the accompanied target. Therefore, even in the case where the accompanied target repeats stopping and moving, a delay of the mobile robot to follow the accompanied target is limited to the minimum.
It is further preferred that the controlling also includes stopping the mobile robot in the case where it is detected that the moving direction of the accompanied target changes to a direction approaching the mobile robot. Additionally, the controlling further includes re-starting the movement of the mobile robot in the case where it is judged that the accompanied target moves away from the stopped mobile robot.
Even in the case where the accompanied target makes a U-turn and passes in front of the mobile robot, a collision between the accompanied target and the mobile robot can be avoided.
It is further preferred that the controlling also includes causing the mobile robot to follow after the accompanied target in the case where an obstacle is detected in the moving direction of the mobile robot.
Since there is no obstacle after the accompanied target has passed, the mobile robot can avoid the obstacle.
It is further preferred that the controlling also includes controlling the movement of the mobile robot by making a distance between the accompanied target and the mobile robot shorter as a surrounding environment is more crowded.
The possibility of causing a collision with other objects is lower and safer as the mobile robot is closer to the accompanied target. Therefore, in the case where the surrounding environment is crowded, the movement of the mobile robot can be safely controlled by making the distance between the accompanied target and the mobile robot shorter.
It is further preferred that the controlling also includes determining a distance between the accompanied target and the mobile robot in proportion to the moving velocity of the accompanied target, and controlling the movement of the mobile robot in accordance with the distance.
In the case where the moving velocity of the accompanied target is slow, the probability of colliding with the accompanied target is low even when the mobile robot is moved closer to the accompanied target, so that there is no problem on making the distance shorter. However, the possibility of causing a collision between them is higher as the moving velocity of the accompanied target is higher. Therefore, by controlling the distance as described above, the probability of causing a collision can be lowered and a safe movement control of the mobile robot can be performed.
Note that, the present invention can be realized not only as a method of controlling the movement of the mobile robot including such characteristic steps, but also as a mobile robot having the characteristic steps included in the method of controlling the movement of the mobile robot as units, and as a program for causing a computer to execute the characteristic steps included in the method of controlling the movement of the mobile robot. Also, it is obvious to say that such program can be distributed through a recording medium such as a Compact Disc-Read Only Memory (CD-ROM), and a communication network such as the Internet.
According to the accompanying method of the present invention, even in the case where the accompanied target suddenly changes its moving velocity, an appropriate accompanying behavior to follow the accompanied target in accordance with an accompanied target and an environment can be performed while preventing a collision with the accompanied target.
As further information about technical background to this application, the disclosure of Japanese Patent Application No. 2004-334573 filed on Nov. 18, 2004 including specification, drawings and claims is incorporated herein by reference in its entirety.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:
Hereafter, embodiments of the present invention are described with reference to drawings. In the following embodiments, there is provided a mobile robot that is not to follow after a person as in the conventional technologies but to move along with a person. In other words, there is assumed a mobile robot which moves along with a person, while keeping an appropriate distance with the person so that its presence is recognized without bothering the user.
This is based on a proxemics that is a theory developed by an American cultural anthropologist, Edward T Hall. According to the proxemics, as shown in
Also, according to the proxemics, as shown in
However, in the case where the mobile robot moves in front of the person, it is so bothersome in a close distance and is difficult to take an action against the person in a far distance. In addition, in the case where the mobile robot moves behind the person, it makes worry the person whether or not the robot has been following, and is dangerous because the person is surprised when the mobile robot suddenly takes an action.
Therefore, taking the best accompanying position of the mobile robot in consideration, it is a side of a person and is also preferred to keep the personal distance. By controlling the mobile robot to move while keeping such position, a person can recognize the presence of the mobile robot without too much attention, and the mobile robot can take an action against the person when necessary. However, it is desired to change the distance between the person and the mobile robot depending on the use of the mobile robot. For example, the distance with the person may be set to have the intimate distance in case of the mobile robot which provides nursing care. Also, the distance may be set larger in case of the mobile robot which provides touring and the like.
As shown in
The measurement apparatus 2c and the measurement apparatus 2d detect a position on an absolute coordinate and a velocity respectively for the accompanied target 1 and the robot body 2a itself. By using, for example, a Global Positioning System (GPS) or an external sensor that is set outside the mobile robot 2 as the measurement apparatuses 2c and 2d, an absolute coordinate can be directly detected. Also, the measurement apparatus 2d may detect a position of the robot body 2a itself by detecting a dead reckoning and an external landmark 3 using a sensor placed in the mobile robot 2. Further, the measurement apparatus 2c can be a wireless device such as ultrasonic waves and a camera or a wired device such as a lead wire. Thus, an absolute matrix of the accompanied target 1 can be measured by detecting a relative position between the mobile robot 2 and the accompanied target 1 using such measurement apparatus 2c and combining with the measurement results obtained by the measurement apparatus 2d.
Next, an overview of controlling an accompanying movement by the mobile robot 2 is described. For example, as shown in
In order to calculate the accompanying path LR of the mobile robot 2, it is necessary to obtain the moving path LT of the accompanied target 1. In order to do so, the moving path shown on an absolute coordinate system can be calculated based on a position and velocity information obtained by detecting the position and the velocity information on the absolute coordinate system of the accompanied target 1.
For example, it is assumed that an arbitrary position vector Pa on a straight line on the path LR to be followed by the mobile robot 2 is described as the following equation (1).
Pa=Pk+A*Vg (1)
Here, it is assumed that Pk is an arbitrary position vector that is positioned in an arbitral distance K from a point on the moving path LT of the accompanied target 1, Vg is a unit vector in a velocity direction of the accompanied target 1, and A is an arbitrary constant. Accordingly, when the position vector of the accompanied target 1 is Pg, the position vector Pk is set so as to satisfy the following equation (2).
|Pk−(Pg+((Pk−Pg)−Vg)Vg)|=K (2)
Next, a control method of a moving velocity for realizing the path LR to be followed by the mobile robot 2 is described. As a velocity of the mobile robot 2, when Vr is a velocity for moving together along with the path LR to follow, ωr is an angular velocity, dθ is an angular difference between a direction of the mobile robot 2 and a direction of the path LR to follow, and dh is a distance between the mobile robot 2 and the path LR to follow, the mobile mechanisms 2b are controlled so that the velocity of the mobile robot 2 is a velocity shown in the following equation (3).
Vr=G1×|Vg|, ωr=−G2×dθ−G3×dh (3)
Here, G1, G2 and G3 are arbitrary gains, and, in particular, the value of G1 changes depending on a condition of the mobile robot 2.
In the above control equation, when the mobile robot 2 is distant away from the path LR to follow, the direction of the mobile robot 2 is corrected so as to return on the straight line that is the path LR. Therefore, the mobile robot 2 can keep following the path LR.
Note that, in addition to such accompanying method, the mobile robot 2 may follow the accompanied target 1 so as to keep, on the path LR to follow, a constant distance toward a moving direction of the accompanied target 1. Also,
For example, a target coordinate Pl of the mobile robot 2 which follows only the distance L behind the accompanied target 1 toward its moving direction is set to satisfy the following equation (4) in addition to the conditional expression of the position vector Pa shown in the equation (1).
(Pl−Pg)·Vg=L (4)
Further, in addition to the aforementioned velocity control, for example, the velocity Vr for the mobile robot 2 to move toward a translational direction may be controlled as shown in the following equation (5).
Vr=G1×|Vg|+G4×|Vg|×dL (5)
Here, G4 is an arbitrary gain.
However, the difference dL is a difference toward a moving direction of the accompanied target 1 from the control target position Pl, and the control target position can be maintained by accelerating or decelerating the velocity depending on the difference using the equation (5).
Summarizing the aforementioned method of controlling the accompanying movement, the mobile robot 2 controls its accompanying movement as shown in
Further, the mobile robot 2 controls its accompanying movement as shown in
Note that, while an example that the path LR to follow which is parallel to the moving path LT is positioned on the right side of the accompanied target 1 is explained in
By the way, the case of straight path is explained for the accompanying method shown in
For example, the mobile robot 2 calculates a smooth moving path LT by performing smoothing, for the position and velocity of the accompanied target 1 in the first to fourth conditions as shown in
Thus, the dispersed variation of the position and velocity of the accompanied target 1 is smoothed by correcting the variation of the positions and velocity of the accompanied target 1 measured by the measurement apparatus 2c so that a smooth movement of the mobile robot 2 can be achieved.
Further, as shown in
Other than the above, the mobile robot 2 re-calculates the path LR in accordance with the position and velocity of the accompanied target 1 (S8) in the following cases: where the accompanied target 1 is outside the continuous region 15 (NO in S2); and where the moving direction of the accompanied target 1 has rapidly changed (NO in S4).
Through this, the mobile robot 2 can follow the accompanied target 1 without showing unnatural behavior even in the case of dispersed variations. In other words, the mobile robot 2 does not sensitively respond to a change of an output value from a sensor.
Note that, a width of the continuous region 15 differs depending on a task performed by the mobile robot 2 on the accompanied target 1. Specifically, in the case where the robot provides nursing care, the distance has to be set to be smaller so that the robot can immediately help a person when the person falls. Also, in the case where the robot provides guiding and touring, the distance has to be set to be larger because it is important for the guiding robot not to collide with a person.
Next, it is explained about the case where the accompanied target 1 repeats stopping and moving.
In the accompanying method shown in
Such accompanying movement is sufficient enough in the case where the accompanied target 1 does not repeat stopping and moving. However, in the case where a path changes suddenly when the accompanied target 1 starts moving again, the mobile robot 2 needs to consume mobile capability so as to approach a newly generated path, causing further accompanying delay. Accordingly, when such stopping and moving are repeated, the delay is gradually increased. As the result, there is a possibility that the mobile robot 2 loses the accompanied target 1 from the sight.
Accordingly, as shown in
By controlling the mobile robot 2 in the aforementioned manner, the mobile robot 2 stops not at the current position but after reaching a predetermined range even in the case where the accompanied target 1 stops in a distant. As the result, even in the case where the accompanied target 1 repeats stopping and moving, the mobile robot 2 does not lose the accompanied target 1 from the sight because the moving loss of the mobile robot 2 does not accumulated so that the delay is minimized.
Next, the movement control of the mobile robot 2 in the case where the accompanied target 1 has suddenly changed the moving direction significantly is described.
In the accompanying method shown in
For example, as shown in
As shown in
According to such accompanying method, the path LR4 to follow for a change of the path to follow caused by the U-turn becomes very short compared to the path LR3 to follow in
The mobile robot 2 judges whether or not an inner product of the velocity VT of the accompanied target 1 and the velocity VR of the moving robot 2 satisfies the following equation (6) (S22).
VT·VR<0 (6)
In the case where the equation (6) is satisfied (YES in S22), it indicates that the accompanied target 1 and the mobile robot 2 do not face the same direction, that is, the accompanied target has made a U-turn. Accordingly, the mobile robot 2 is stopped in order to avoid the collision between the accompanied target 1 and the mobile robot 2 (S24). Therein, only the direction of the mobile robot 2 is changed while stopping the mobile robot 2. In other words, in order to stop the mobile robot 2 and only change the direction, for example, the direction of the mobile robot 2 may be controlled so as to satisfy the judgment equation as shown in the following equation (7).
Fr·Vg<0 (7)
Here, Fr is a vector showing a direction of a robot. Vg is a unit vector in a velocity direction of the accompanied target 1 as described above.
Next, an inner product between a direction vector PTR of the accompanied target 1 and the velocity VT of the accompanied target 1 based on the mobile robot 2 is calculated (YES in S26). The mobile robot 2 then judges whether or not the inner product satisfies the following equation (8) (S26).
PTR·VT>0 (8)
In the case where the equation (8) is satisfied (YES in S26), it is indicated that the accompanied target 1 is leaving away from the mobile robot 2. Therefore, the mobile robot 2 is started moving again (S28).
The mobile robot 2 using the aforementioned accompanying method and having the structure does not collide with the accompanied target 1 by taking a sufficient difference between the path of the accompanied target 1 and the path to be followed by the mobile robot 2, even in the case where the accompanied target 1 suddenly stops in an ordinary condition.
Further, according to the mobile robot 2 of the present embodiment, as shown in
The structure of the mobile robot 22 according to the second embodiment of the present invention shown in
Here, as the detecting apparatus 2h which detects a condition of the environment around the accompanied target 1 and the mobile robot 22, for example, the detecting device 2h is functioned as an obstacle detecting sensor using an ultrasonic sensor, an ultraviolet sensor and the like so as to detect a closeness condition to the obstacle, and the position for the mobile robot 22 to follow may be changed in order to avoid the obstacle. Further, the congestion degree of the surrounding environment is detected by a camera, a laser-range sensor and the like, and the difference d is changed depending on the congestion degree so that the mobile robot 2 may not be an obstacle when the environment is crowded.
Also, using the detecting apparatus 2h as a device for detecting a condition of the accompanied target 1 in addition to the aforementioned functions, the positional relationship may be changed depending on the velocity of the accompanied target 1. In addition, in the case where the detecting apparatus 2h is a camera, a gesture of the accompanied target 1 is detected by the camera, and a visibility may be increased by positioning behind or side of the moving direction of the accompanied target 1 when the camera is about to recognize an accompanying condition.
Further,
Note that, the congestion degree herein may be the number of objects in a surrounding environment such as passers 53 in a predetermined range around the mobile robot 22, or may be defined by a ratio of an area dominated by the objects in the surrounding environment.
Further,
Thus, the probability of causing a collision is small even when the mobile robot 22 is approached the accompanied target 1 in the case where the moving velocity of the accompanied target 1 is small, so that there is no problem of making the difference shorter. However, the moving velocity of the accompanied target becomes higher as the probability of causing a collision between the mobile robot 22 and the accompanied target 1 is higher. Therefore, it is necessary to make the difference larger so as to avoid the collision between them.
As described above, according to the present invention, the mobile robot can follow the accompanied target at the best accompanying position in accordance with the surrounding environment. Therefore, for example, in the cases where an obstacle is flexibly avoided, where the difference is adjusted in accordance with the congestion degree of the environment, or where the accompanied target is a person, the accompanying behavior can be performed having a positional relationship in accordance with the person's preference and a demand. Accordingly, the best accompanying behavior can be realized in a state where the mobile robot is placed.
Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
According to the present invention, a collision between an accompanied target and a mobile robot can be prevented even in the case where the accompanied target suddenly changes the velocity. Also, an appropriate accompanying behavior to the accompanied target can be realized in accordance with a state of the accompanied target and an environment. Therefore, the present invention is applicable to an automatic cart and a transporting robot used at home, hotel, golf course, factory, airport and the like, to an automatic ride, a robot which provides a touring, a robot which provides nursing care and the like.
Number | Date | Country | Kind |
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2004-334573 | Nov 2004 | JP | national |