Mobile apparatus, control device and control program

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus or the like which autonomously moves along a target path.

[0003] 2. Description of the Related Art

[0004] As robots have become more sophisticated in functionality, there are increasing opportunities for the robots to perform jobs or works such as carrying luggage or guiding human beings to their destinations, and the need for the robots to move while preventing contact with the human beings is increasing. In this relation, a technique to decrease the traveling speed of a robot based on a result of determination that the obstacle is a human being has been proposed (see Japanese Patent Application Laid-Open No. 2006-79325). Further, a technique to cause a robot to move along a path having a shortest moving distance to a target point among a plurality of paths for preventing contact with an obstacle has been proposed (see Proc. 2000 IEEE International Conference on Robotics and Automation (ICRA 2000) “RRT-Connect: An Efficient Approach to Single-Query Path Planning”).

[0005] When the traveling speed of the robot is decreased, however, the human beings around the robot may feel uncomfortable about the behavioral change of the robot. Thus, it is difficult for the robot to move while cooperating with the human beings surrounding it.

[0006] Further, it is unclear for the human beings how the robot sets its target path and, hence, how the robot will change its direction. There may be a case where, when the human being expects that the robot will shift its position to his/her right and thus moves to the left, the robot also moves to its right. This may rather increase the possibility that the human being and the robot come to contact with each other due to the behavioral change of the human being based on the false prediction. Thus, it is difficult for the robot to move while cooperating with the human beings surrounding it.

[0007] In view of the foregoing, an object of the present invention is to provide a mobile apparatus or the like capable of moving or acting while reliably preventing contact with an object such as a human being, by preventing the undesirable situation where the object inappropriately changes its behavior for the purposes of preventing contact with the mobile apparatus.

[0008] A mobile apparatus according to a first aspect of the present invention is a mobile apparatus that autonomously moves along a target path, wherein the mobile apparatus includes a control device, and the control device includes: a first processing element which recognizes states of a region where the mobile apparatus is passable, the mobile apparatus, and an object as states of an element space, a reference spatial element, and a first spatial element, respectively; a second processing element which, based on a recognition result of the first processing element, recognizes one of a plurality of expanded spatial elements arranged around the first spatial element that satisfies a requirement regarding a size in the element space as a third spatial element; and a third processing element which, based on recognition results of the first and second processing elements, sets a path that allows the reference spatial element to prevent contact with the first spatial element and the third spatial element in the element space as the target path.

[0009] According to the mobile apparatus of the first aspect of the present invention, the path that can prevent contact with the “third spatial element” satisfying a requirement regarding the size in the element space, among the plurality of expanded spatial elements arranged around the first spatial element, is set as the target path. As used herein, the “spatial element” in the element space refers to the “point” for which its position, velocity, acceleration and other states in the element space can be defined, the “line segment” for which its shape, length and other states in addition to the position and the like in the element space can be defined, the “region” for which its shape, area and other states in addition to the position and the like in the element space can be defined, and the like. Further, the expanded spatial elements arranged around the first spatial element have their sizes in the element space varying in accordance with the width of the clearance between the object, recognized as the first spatial element, and the boundary of the passable region where the mobile apparatus is capable of pass, recognized as the element space.

[0010] Accordingly, it is possible to cause the mobile apparatus to move in accordance with a consistent rule that is modified in response to the width of the clearance between the object and the boundary of the passable region. This allows the object such as a human being to predict the behavior of the mobile apparatus based on the position of the object with respect to the boundary of the passable region such as a wall surface of a passage way or the like. It is thus possible to encourage the object to make an appropriate behavior or behavioral change, based on the above prediction, for the purposes of preventing contact with the mobile apparatus, without causing the object to feel uncomfortable.

[0011] As used herein, that the component of the present invention “recognizes” the information means that the component performs every kind of information processing, such as searching a database for the information, reading the information from a storage device such as a memory, measuring, calculating and estimating the information based on the output signals of the sensors and the like, and storing the measured information and the like in a memory, which is necessary for the information to be prepared or ready for further information processing. Further, when a plurality of objects moves in an integrated manner, as in the case where an object is attached to another object, the objects may collectively be recognized as the first spatial element.

[0012] A mobile apparatus according to a second aspect of the present invention is characterized in that, in the mobile apparatus of the first aspect of the present invention, the second processing element regards a plurality of regions of same shape and same area arranged at an equal distance from the first spatial element as the plurality of expanded spatial elements, and regards an overlapping area of each of the plurality of regions with the element space as the size of the expanded spatial element, for recognition of the third spatial element.

[0013] According to the mobile apparatus of the second aspect of the present invention, it is possible to cause the mobile apparatus to move in accordance with a consistent rule that is modified in response to the width of the clearance between the object and the boundary of the passable region, which is represented by the size of the overlapping area of each of the regions, recognized as the expanded spatial elements arranged around the first spatial element, with the element space.

[0014] A mobile apparatus according to a third aspect of the present invention is characterized in that, in the mobile apparatus of the first aspect of the present invention, the second processing element regards a plurality of line segments of same shape extending from the first spatial element in different directions as the plurality of expanded spatial elements, and regards a length of a part of each of the plurality of line segments continuing from the first spatial element to a boundary of the element space as the size of the expanded spatial element, for recognition of the third spatial element.

[0015] According to the mobile apparatus of the third aspect of the present invention, it is possible to cause the mobile apparatus to move in accordance with a consistent rule that is modified in response to the width of the clearance between the object and the boundary of the passable region, which is represented by the length of the part of each of the line segments, recognized as the expanded spatial elements extending from the first spatial element, that continues from the first spatial element to the boundary of the element space.

[0016] A mobile apparatus according to a fourth aspect of the present invention is characterized in that, in the mobile apparatus of the first aspect of the present invention, the second processing element recognizes one of the plurality of expanded spatial elements that satisfies the requirement that its size in the element space is the smallest or not greater than a threshold value as the third spatial element.

[0017] According to the mobile apparatus of the fourth aspect of the present invention, a target path is set in the region where the clearance between the object and the boundary of the passable region is wide by avoiding the region where the clearance is narrow. It is thus possible to cause the mobile apparatus to move in accordance with a consistent rule that the mobile apparatus moves to the region having the wider clearance between the object and the boundary of the passable region. This allows the object such as a human being to predict that the mobile apparatus will move to the region where the clearance between the object and the boundary of the passable region is wider. It is thus possible to encourage the object to make an appropriate behavior or behavioral change, based on the above prediction, for the purposes of preventing contact with the mobile apparatus, without causing the object to feel uncomfortable.

[0018] A mobile apparatus according to a fifth aspect of the present invention is characterized in that, in the mobile apparatus of the first aspect of the present invention, the first processing element recognizes behavioral states of the mobile apparatus and the object as behavioral states of the reference spatial element and the first spatial element, respectively, in the element space, the second processing element, based on a recognition result of the first processing element, recognizes the first spatial element expanded intermittently or continuously in accordance with the behavioral states in the element space a second spatial element, and the third processing element, based on recognition results of the first and second processing elements, sets a path that allows the reference spatial element to prevent contact with the third spatial element and with the second spatial element incorporating the first spatial element in the element space as the target path.

[0019] According to the mobile apparatus of the fifth aspect of the present invention, the first spatial element expanded based on the behavioral states of the reference and first spatial elements in the element space is recognized as the second spatial element. The behavioral state of each spatial element is defined by a part or all of the position, velocity, acceleration and the like that change over time. Thus, the second spatial element is recognized as a spatial element having a size or spatiality greater than that of the first spatial element. Further, a path that allows the reference spatial element to prevent contact with the second spatial element is set as the target path of the mobile apparatus. Thus, compared to the case where the target path that allows the reference spatial element to prevent contact with the first spatial element or other spatial element smaller than the second spatial element is set, a more appropriate target path can be set from the standpoint of more reliably preventing the mobile apparatus from contacting the object in consideration of the behavioral state of the object.

[0020] A mobile apparatus according to a sixth aspect of the present invention is characterized in that, in the mobile apparatus of the fifth aspect of the present invention, the second processing element determines whether there is a possibility of contact between the reference spatial element and the first spatial element in the element space based on the recognition result of the first processing element, and the third processing element newly sets the target path on the condition that the second processing element determines that there is the possibility of contact.

[0021] According to the mobile apparatus of the sixth aspect of the present invention, the first spatial element is recognized as a spatial element having the size or spatiality smaller than that of the second spatial element in the element space, and the requirement for setting a new target path is that the reference spatial element may possibly contact the first spatial element. Accordingly, compared to the case where the requirement for setting a new target path is that the reference spatial element may possibly contact the second spatial element or other spatial element greater in size than the first spatial element, the frequency of change of the target path, and hence, the frequency of behavioral change of the mobile apparatus such as a change of direction is restricted low. This reduces the possibility that the behavioral change of the mobile apparatus would induce the behavioral change of the object, thereby rather increasing the possibility of contact therebetween.

[0022] A control device according to a seventh aspect of the present invention is a device for controlling an operation of a mobile apparatus autonomously moving along a target path, wherein the device includes: a first processing element which recognizes states of a region where the mobile apparatus is passable, the mobile apparatus, and an object as states of an element space, a first spatial element, and a first spatial element, respectively; a second processing element which, based on a recognition result of the first processing element, recognizes one of a plurality of expanded spatial elements arranged around the first spatial element that satisfies a requirement regarding a size in the element space as a third spatial element; and a third processing element which, based on recognition results of the first and second processing elements, sets a path that allows the reference spatial element to prevent contact with the first spatial element and the third spatial element in the element space as the target path.

[0023] According to the control device of the seventh aspect of the present invention, it is possible to cause the mobile apparatus to move in accordance with a consistent rule that is modified in response to the width of the clearance between the object and the boundary of the passable region.

[0024] A program according to an eighth aspect of the present invention is characterized in that it causes a computer mounted on a mobile apparatus that autonomously moves along a target path to function as the control device of the seventh invention.

[0025] According to the program of the eighth aspect of the present invention, it is possible to cause the computer mounted on the mobile apparatus to function as the device that controls the behavior of the mobile apparatus so that it moves in accordance with a consistent rule that is modified in response to the width of the clearance between the object and the boundary of the passable region.

[0036] Embodiments of a mobile apparatus and others of the present invention will now be described with reference to the drawings.

[0037] A robot 1 as a mobile apparatus includes: a body (trunk of the body) P₀, a head P₁ provided on top of the body P₀, left and right arms P₂ extended from the respective left and right sides of an upper part of the body P₀, a hand P₄ provided at an end of each of the arms P₂, left and right legs P₃ extended downward from a lower part of the body P₀, and a foot P₅ provided at an end of each of the legs P₃. The robot 1 is capable of bending and stretching the arms P₂ and the legs P₃ at a plurality of joint portions corresponding to the joints of a human being, such as shoulder, elbow, carpal, hip, knee, and ankle joints, by the force transmitted from an actuator M (see FIG. 2), as disclosed in Japanese Re-Publications of PCT International Publications Nos. 03/090978 and 03/090979. The robot 1 can autonomously move with the left and right legs P₃ (or the feet P₅) repeatedly taking off and landing on the floor. The height of the head P₁ may be adjusted through adjustment of the tilt angle of the body P₀ with respect to the vertical direction. The head P₁ is mounted with a pair of head cameras (CCD cameras) C₁ arranged side by side to face forward of the robot 1. The body P₀ is mounted with a waist camera (infrared camera) C₂ in front at the lower part. The robot 1 is mounted with various sensors S (see FIG. 2) which include a gyro sensor that outputs a signal responsive to the acceleration of the body P₀, a rotary encoder that outputs a signal responsive to the joint angle of each joint, and a 6-axis force sensor that outputs a signal responsive to the floor reaction force acting on the legs P₃.

[0038] The robot 1 includes a control device 10 which controls operations of the arms P₂, legs P₃ and others. The control device 10 is configured with an ECU or computer (constructed by CPU, ROM, RAM, I/O and others) serving as hardware and a “control program” of the present invention serving as software. While the control program may be prestored in a memory of the computer, it may be distributed or broadcast to the computer via a network or an artificial satellite by a server in response to a request signal transmitted from the robot 1 to the server, and then stored in the memory.

[0039] The control device 10 shown in FIG. 2 includes a first processing element 11, a second processing element 12, and a third processing element 13.

[0040] The first processing element 11 accesses an environmental database 112 via a radio system to recognize the region through which the robot 1 can travel or pass as an element space QS. The environmental database 112 manages data indicating the shape, area and others of the region where the robot 1 is passable. It is noted that the environmental database 112 may be mounted on the robot 1 as a part of the control device 10. Further, the first processing element 11 recognizes the robot 1 and its behavioral states, such as its position, velocity and the like, as a reference spatial element Q₁ and its behavioral states in the element space QS, based on the output signals of the sensors S and the like. Furthermore, the first processing element 11 recognizes the object 2 and its behavioral states, such as its position, velocity and the like, as a first spatial element Q₂ and its behavioral states in the element space QS, based on the images of the surroundings of the robot 1 picked up by either or both of the head cameras C₁ and the waist camera C₂.

[0041] The second processing element 12 recognizes the first spatial element Q₂ expanded intermittently or continuously based on the recognition result of the first processing element 11 as a second spatial element EQ₂. Further, the second processing element 12 recognizes one of a plurality of expanded spatial elements Q_3i (i=1, 2, . . . ) arranged around the first spatial element Q₂ that satisfies a requirement regarding the size in the element space QS as a third spatial element Q₃₊, based on the recognition result of the first processing element 11.

[0042] The third processing element 13 sets a path that allows the reference spatial element Q₁ to prevent contact with the first spatial element Q₂, the second spatial element EQ₂ and the third spatial element Q₃₊ in the element space QS as a target path R_k of the robot 1 in the real space or in the passable region, based on the recognition results of the first processing element 11 and the second processing element 12.

[0043] Now, the functions of the robot having the above-described configuration will be described. The situation as shown in FIG. 4 is assumed in which the robot 1 and an object (human being) 2 are moving, while facing each other, in a corridor (passable region) delimited by the left and right walls. In this case, the robot 1 is walking or running along the target path R_k indicated by a dashed line in FIG. 5, for example. The target path R_k is preset in the initial state (k=0), and updated whenever necessary by the third processing element 13, as will be described later.

[0044] Firstly, the first processing element 11 carries out “first processing” (S010 in FIG. 3). Specifically, the first processing element 11 accesses the environmental database 112 via a radio system to recognize the region where the robot 1 can pass as the element space QS (S012 in FIG. 3). In this manner, the element space QS in accordance with the shapes of the corridor and fixed structures as shown e.g. in FIG. 4, and having the shape and area as shown e.g. in FIG. 5, is recognized.

[0045] Further, the first processing element 11 recognizes the robot 1 and its behavioral states, such as its position, velocity and the like, in the global coordinate system as the reference spatial element Q₁ and its behavioral states in the element space QS, based on the output signals of the sensors S and the like (S014 in FIG. 3). The position of the robot 1 is measured based on the signals representing the latitude and longitude obtained by its GPS function, or the signals representing the acceleration of the robot 1 sequentially output from the gyro sensor. The velocity of the robot 1 may be measured based on the positions of the robot 1 measured in time series, the output signals from the gyro sensor, or the output signals from the rotary encoder responsive to the joint angles of the legs P₃, and the inverse dynamics model. In this manner, the robot 1 and its position and velocity are recognized as the reference spatial element (small circular region) Q_i, the first position (center of the small circular region) p₁ the first velocity v₁, respectively, in the element space QS as shown e.g. in FIG. 5.

[0046] Furthermore, the first processing element 11 recognizes the object 2 and its behavioral states, such as its position, velocity and the like, as the first spatial element Q₂ and its behavioral states in the element space QS, based on the images of the surroundings of the robot 1 picked up by either or both of the head cameras C₁ and the waist camera C₂ (S016 in FIG. 3). Since the position of the object 2 in the robot coordinate system measured based on the images obtained by the head cameras C₁ and/or the waist camera C₂ corresponds to the relative position of the object 2 with respect to the robot 1, it is converted to the position in the global coordinate system based on the position of the robot 1 in the global coordinate system. In this manner, the object 2 and its position and velocity in the global coordinate system are recognized as the first spatial element (circular region) Q₂, the second position P₂ and the second velocity v₂, respectively, in the element space QS as shown e.g. in FIG. 5.

[0047] The shape and size of the reference spatial element Q₁ in the element space QS may be recognized by reading them from a memory (where the shape and size of the robot 1 are stored). The shape and size of the first spatial element Q₂ in the element space QS may be recognized, after the type of the object 2 is recognized based on the images of the surroundings of the robot 1 obtained by the head cameras C₁ and the like, by referring to the memory or database (where the types, shapes and sizes of the objects are associated with each other and stored or managed) based on the recognition result. Further, the position of the object 2 may be measured or recognized, when signals representing the latitude and longitude of the object 2 are received from a communication device or the like mounted on the object 2, based on these signals. Furthermore, the velocity of the object 2 may be measured as the change in position of the object 2 over time. While the element space QS may be defined as a flat surface or a curved surface on which a given point is specified by the latitude and longitude, it may be defined sequentially based on the shape of the floor surface around the robot 1, such as its tilt angle, presence/absence of steps or irregularities, recognized from the images obtained by the head cameras C₁ and the like.

[0048] In the case where a box, an instrument, or other object is moving with the robot 1 in an integrated manner, for example when the robot 1 is carrying the box with its arms P₂ or when the optional instrument is attached to the body P₀ to provide the robot 1 with an additional function, the shapes and sizes of the robot 1 and the object that are moving together may be recognized as the shape and size of the robot 1.

[0049] The region corresponding to the geometric characteristics (shape and size) of the object 2 and expanded in response to the geometric characteristics of the robot 1 is recognized as the first spatial element Q₂. Here, the Minkowski sum of the two regions having the geometric characteristics in the element space corresponding to the geometric characteristics of the robot 1 and the object 2 is recognized as the first spatial element Q₂. In the case where the robot 1 and the object 2 are defined as a first region q₁ of a circular shape having a radius r₁ and a second region q₂ of a circular shape having a radius r₂, respectively, as shown in FIG. 6(a), the Minkowski sum of these two regions, q₁+q₂, represented as a circular region as shown in FIG. 6(b), is recognized as the first spatial element Q₂. When the first region q₁ is moved around the second region q₂ in such a manner that the center of the first region q₁ follows the contour of the second region q₂, the sum of the second region q₂ and the ring-shaped region of the first region q₁ running off the edge of the second region q₂ corresponds to the Minkowski sum (=the circular region having the radius r₁+r₂). The shape and size of the first region q₁ are prestored in the memory in response to the size (or the shape and size) of the robot 1, and recognized by reading them from the memory. The second region q₂ is recognized as the region having the spatiality corresponding to the size (or the shape and size) of the object 2 recognized from the images obtained by the head cameras C₁ and the like. Alternatively, the second region q₂ as it is may be recognized as the first spatial element Q₂, or the second region q₂ expanded in accordance with the size or other geometric characteristics of the first region q₁ using a method other than the Minkowski sum may be recognized as the first spatial element Q₂.

[0050] The second processing element 12 carries out “second processing” (S020 in FIG. 3). Specifically, the second processing element 12 determines whether the first spatial element Q₂ satisfies a “first contact condition” regarding the movement cost from the reference spatial element Q₁ in the element space QS (S022 in FIG. 3).

[0051] The movement cost is evaluated by the second processing element 12 as a function of one or both of the required time for and the moving distance of the reference spatial element Q₁ until it comes into contact with the first spatial element Q₂ in the element space QS. Specifically, the distance in a straight line or the distance d along the target path (dashed line) R_k between the reference spatial element Q₁ and the first spatial element Q₂, the time t=(d/|{v₂−v₁|) required for the reference spatial element Q₁ to contact the first spatial element Q₂ with the reference spatial element Q₁ and the first spatial element Q₂ moving while maintaining the first velocity v₁ and the second velocity v₂, respectively, shown in FIG. 5, or an increasing function of one or both of the above-described distance d and the required time t, is evaluated as the movement cost. For example, the first contact condition that “the movement cost falls within the prescribed range of {0, ε_+(>0)}” is adopted.

[0052] Further, if the second processing element 12 determines that the first spatial element Q₂ satisfies the first contact condition (YES in S022 in FIG. 3), it determines whether the first spatial element Q₂ satisfies a “second contact condition” regarding the positional relationship with the target path R_k (S024 in FIG. 3).

[0053] For example, assuming the case where the second contact condition that “there is an intersection point or a contact point with the target path R_k” has been adopted, in the situation shown in FIG. 5, the first sec-end-spatial element Q₂ intersects the target path R_k of the robot 1, and thus, it is determined that the second contact condition is satisfied. Alternatively, the following may be adopted as the second contact condition: “that the accumulation or integration along a part or a whole of the shortest distance to the first spatial element Q₂ or the target path R_k thereof is not greater than a predetermined value”, “that there is an intersection point or a contact point between the tangent line of the target path R_k at the first position p₁ (extending in the traveling direction of the reference spatial element Q₁) and the first spatial element Q₂”, or the like.

[0054] If the second processing element 12 determines that the first spatial element Q₂ satisfies the second contact condition in addition to the first contact condition (YES in S024 in FIG. 3), it recognizes the first spatial element Q₂ expanded based on the recognition result of the first processing element 11 as an a second spatial element EQ₂ (S026 in FIG. 3). For example, when the first spatial element Q₂ shown on the left in FIG. 7(a) is continuously enlarged in the direction corresponding to the relative velocity (vector), v₂−v₁, of the second velocity v₂ with respect to the first velocity v₁, the resultant, approximately straight band-shaped region shown on the right in FIG. 7(a) is recognized as the second spatial element EQ₂. How much the first spatial element Q₂ is to be enlarged is set in accordance with the following expression (1), based on the second velocity v₂ of the first spatial element, the second position P₂ (or the relative second position P₂−P₁ with respect to the first position p₁), and the relative velocity v₂−v₁.
(Enlarged Amount)=|P₂∥V₂|/|v₂−v₁|  (1)

[0055] Alternatively, when the first spatial element Q₂ shown on the left in FIG. 7(b) is continuously enlarged so as to turn around in accordance with the relative velocity v₂−v₁, the resultant, bent band-shaped region shown on the right in FIG. 7(b) is recognized as the second spatial element EQ₂. In the above-described situation shown in FIG. 5, the second spatial element EQ₂ as shown in FIG. 8(b) is recognized. Still alternatively, the first spatial element Q₂ shown on the left in FIG. 7(c) may be intermittently enlarged in the direction corresponding to the relative velocity v₂−v₁, and the resultant, discrete spatial elements shown on the right in FIG. 7(c) may be recognized as the second spatial element EQ₂. The second processing element 12 further recognizes one of a plurality of expanded spatial elements Q_3i (i=1, 2, . . . ) arranged around the first spatial element Q₂ that satisfies a requirement regarding the size in the element space QS as a third spatial element Q₃₊, based on the recognition result of the first processing element 11 (S028 in FIG. 3).

[0056] For example, as shown in FIG. 8(a), four circular regions circumscribing the first spatial element Q₂ in front and back and left and right, with the advancing direction of the first spatial element Q₂ as the front, are set as the expanded spatial elements Q₃₁ to Q₃₄. Of these four expanded spatial elements Q₃₁ to Q₃₄, the expanded spatial element Q₃₂ in which the overlapping region with the element space QS (see the shaded portion in FIG. 8(a)) is the smallest in area is recognized as the third spatial element Q₃₊. The area is measured according to the Monte Carlo method, for example. That is, dots are arranged at random in the element space QS, and the number of dots included in the respective expanded spatial elements (regions) Q₃₁ to Q₃₄ is counted, and the counted numbers are measured as the areas of the respective regions.

[0057] Alternatively, as shown in FIG. 9(a), eight line segments extending frontward, backward, leftward, rightward, and diagonally from the first spatial element Q₂, with the advancing direction of the first spatial element Q₂ as the front, may be set as the expanded spatial elements Q₃₁ to Q₃₈. Of these eight expanded spatial elements Q₃₁ to Q₃₈, the expanded spatial element Q₃₃ whose part continuing from the second space element Q₂ to the boundary of the element space QS (see the bold line portion in FIG. 9(a)) is the shortest may be recognized as the third spatial element Q₃₊.

[0058] Still alternatively, from the standpoint that the robot 1 will pass through either side of the object 2, the expanded spatial elements Q_3i may be set only on the sides of the object 2 in its advancing direction; that is, only the expanded spatial elements Q₃₂ and Q₃₄ in FIG. 8(a), or only the expanded spatial elements Q₃₃ and Q₃₇ in FIG. 9(a), may be set. The size of each expanded spatial element Q_3i (diameter in the case of the circular region, length in the case of the line segment) is set as appropriate from the standpoint of preventing contact between the robot 1 and the object 2. Further, the size of each expanded spatial element Q_3i may be set in a variable manner in accordance with the magnitude of velocity of the object 2 or the like. The expanded spatial element Q_3i may take a variety of shapes besides the circular shape or the line segment, which may be a fan shape, rectangular shape, trapezoidal shape, or the like. Furthermore, the plurality of expanded spatial elements Q_3i may differ in shape and/or size from each other.

[0059] Of the plurality of expanded spatial elements Q_3i, the one satisfying the requirement that its size is not greater than a threshold value, instead of the requirement that it is the smallest in size, may be recognized as the third spatial element Q₃₊.

[0060] If it is determined that the first or second contact condition is not satisfied (NO in S022 and S024 in FIG. 3), it is determined whether the robot 1 terminates its movement (S040 in FIG. 3), as will be described later.

[0061] Further, the third processing element 13 carries out “third processing” (S030 in FIG. 3). Specifically, the third processing element 13 sets a path that allows the reference spatial element Q₁ to prevent contact with the first spatial element Q₂ and the third spatial element Q₃₊ in the element space QS, based on the recognition results of the first processing element 11 and the second processing element 12 (S032 in FIG. 3). This path is set as a target path R_k+1 of the robot 1 in the real space or the passable region (S034 in FIG. 3). In this manner, the path R_k+1 preventing contact with the second spatial element EQ₂ and the third spatial element Q₃₊, as shown by the dashed line in FIG. 8(b) or FIG. 9(b) for example, is set as a new target path for the robot 1.

[0062] The current supplied to the actuators M is adjusted to cause the robot 1 to move along the latest target path R_k+1, for control of the operation of the robot 1. This causes the robot 1 to change the traveling direction slightly to the right and continue to move so as to pass through the left side of the object 2, as shown in FIG. 10.

[0063] It is then determined by the control device 10 whether the robot 1 terminates its movement (S040 in FIG. 3). For example, it is determined whether the distance |p_d−p₁| between the first position p₁ and the target position p_d of the reference spatial element Q₁ in the element space QS has become not greater than a threshold value .delta.. If the result of determination is negative (NO in S040 in FIG. 3), the first through third processing as described above are carried out repeatedly. If the result of determination is positive (YES in S040 in FIG. 3), the series of processing is completed.

[0064] According to the robot 1 exerting the above-described functions, a path that can prevent contact with the third spatial element Q₃₊ that satisfies the requirement regarding the size in the element space QS, among the plurality of expanded spatial elements Q_3i arranged around the first spatial element Q₂ (see FIGS. 8(a) and 9(a)), is set as the target path R_k+1. The sizes of the expanded spatial elements Q_3i arranged around the first spatial element Q₂ in the element space QS vary according to the width of the clearance between the object 2 recognized as the first spatial element Q₂ and the boundary of the passable region recognized as the element space QS (see FIGS. 4 and 5).

[0065] Accordingly, it is possible to cause the robot 1 to move in accordance with a consistent rule that is modified in response to the width of the clearance between the object 2 and the boundary of the passable region. For example, it is possible to cause the robot 1 to move in accordance with the consistent rule that it moves to the region where the clearance between the object 2 and the boundary of the passable region is wider (see FIGS. 5, 8(b) and 9(b)). This allows the object 2 such as a human being to predict that the robot 1 will move to the region where the clearance between the object 2 and the boundary of the passable region is wider. Consequently, it is possible to encourage the object 2 to make an appropriate behavior or behavioral change such as slightly moving the body to the right from the state as shown in FIG. 4 based on the above prediction, for the purposes of preventing contact with the robot 1, without causing the object 2 to feel uncomfortable.

[0066] Further, the first spatial element Q₂ expanded based on the behavioral states of the reference spatial element Q₁ and the first spatial element Q₂ in the element space QS is recognized as the second spatial element EQ₂ (see FIGS. 7(a) to (c)). The behavioral state of the first spatial element Q₂ is specified according to a part or all of the position, velocity, acceleration and the like that change over time. This allows the second spatial element EQ₂ to be recognized as a spatial element greater in size or spatiality than the first spatial element Q₂.

[0067] Furthermore, the target path R_k+1 that allows the reference spatial element Q₁ to prevent contact with the second spatial element EQ₂ is set (see FIGS. 8(b) and 9(b)). Thus, compared to the case where the target path that can prevent the reference spatial element Q₁ from contacting the first spatial element Q₂ or other spatial element smaller than the second spatial element EQ₂ is set, a more appropriate target path R_k+1 is set from the standpoint of more reliably preventing the robot 1 from contacting the object 2 in consideration of the behavioral state of the object 2.

[0068] In the element space QS, the first spatial element Q₂ is recognized as the spatial element smaller in size or spatiality than the second spatial element EQ₂, and the requirement for setting a new target path R_k+1 is that there is a possibility that the reference spatial element Q₁ may contact the first spatial element Q₂ (see S022, S024 and S030 in FIG. 3). Therefore, compared to the case where the requirement for setting a new target path R_k+1 is that there is a possibility that the reference spatial element Q₁ may contact the second spatial element EQ₂ or other spatial element having the size greater than that of the first spatial element Q₂, the frequency of change of the target path R_k, and hence, the frequency of behavioral change of the robot 1 such as a change of direction, is restricted low. This reduces the possibility that the behavioral change of the robot 1 would induce the behavioral change of the object 2, which would rather increase the possibility of contact therebetween.

[0069] Further, the shape and size of the first spatial element Q₂ in the element space QS may be recognized by referring to the database or the like. This prevents the undesirable situation where the object 2 is recognized as the first spatial element Q₂ having spatiality in the element space too large in view of its actual size due to the limitation of measurement accuracy of the size (or the shape and size) of the object 2 by the head cameras C₁ and the like. The frequency of change of the target path R_k and the frequency of change of the traveling direction of the robot 1 accompanying the change of the path are restricted low. In other words, the undesirable situation where the target path R_k of the robot 1 is changed frequently due to the limitation of recognition accuracy of the geometric characteristics of the object 2 through the head cameras C₁ and the like, is prevented. In the case where the lower limit of the prescribed range regarding the movement cost is set to a positive value instead of “0”, the first contact condition is not satisfied if the movement cost is less than the lower limit, and the target path R_k is not changed (see S022 in FIG. 3). This prevents the traveling direction of the robot 1 from being changed in the state where the behavioral change of the robot 1 may induce the behavioral change of the object 2 because the object 2 is near the robot 1, thereby rather increasing the possibility of contact therebetween.

[0070] Furthermore, the Minkowski sum q₁+q₂ of the two regions corresponding to the geometric characteristics of the robot 1 and the object 2, respectively, is recognized as the first spatial element Q₂ (see FIGS. 6(a) and (b)). Thus, the sizes and shapes of the robot 1 and the object 2 are collectively reflected to the size and shape of the first spatial element Q₂ in the element space. This enables simple representation of the reference spatial element Q₁ as a point or a small region in the element space QS, and facilitates determination of presence/absence of the first spatial element Q₂ that may contact the reference spatial element Q₁, with the determination accuracy improved or maintained.

[0071] It is noted that the above-described control method may be applied to any apparatus having a mobile function, such as a robot that moves with the operations of more than two legs, a wheeled mobile robot (automobile) and the like, besides the robot that moves with the operations of the pair of left and right legs P₃ as in the robot 1.

[0072] While the expanded spatial element Q_3i satisfying the requirement that the size in the element space QS is the smallest or not greater than a threshold value has been recognized as the third spatial element Q₃₊ in the above embodiment (see FIGS. 8(a) and (b), and 9(a) and (b)), as another embodiment, the expanded spatial element Q_3i satisfying the requirement that the size in the element space QS is the largest or exceeding a threshold value may be recognized as the third spatial element Q₃₊.