Abstract:
The present invention provides a robot apparatus is capable of moving autonomously, flexibly responding to a motion of conforming to an external moving subject that may typically be the user of the robot apparatus and conforming to the motion of the moving subject, and also capable of modifying the conforming relationship with the moving subject. The robot apparatus is capable of moving autonomously, and comprises an input section that inputs an image or sound of an external moving subject, a plurality of motion generating sections that generate a plurality different motions in response to the image or sound input by way of the input section, conforming to the motion of the external moving subject, a motion expressing section that integrally expresses one or more than one motions out of the plurality of motions generated by the plurality of motion generating sections, and a control section that controls the number of motions integrated by the motion expressing section and the ratio of the motions to be integrated.

Description:
CROSS REFERENCES TO THE RELATED APPLICATIONS 
   The present invention contains subject matter related to Japanese Patent Application JP 2004-168785 filed in the Japanese Patent Office on Jun. 7, 2004, the entire contents of which being incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a robot apparatus capable of moving autonomously and a method of controlling the motion thereof. More particularly, the present invention relates to a robot apparatus capable of moving autonomously, conforming to a motion of an external moving subject that may typically be as a user of the robot apparatus and also to a method of controlling the motion thereof. 
   2. Description of the Related Art 
   A mechanical apparatus that is electrically or magnetically driven to move and act like a man (living thing) is called a “robot”. In Japan, robots became popular in the late 1960s but many of them are industrial robots such as manipulators and carrier robots designed to realize unmanned automated production lines in factories. 
   Recently, developments of utility robots that can operate as men&#39;s partners to support human activities in various different scenes in living environments of human being are under way. Unlike industrial robots, such utility robots are provided with the ability of learning by themselves a number of techniques necessary to adapt themselves to different people with different personalities in various scenes of living environments of human being and also to various environments. For example, “pet type” robots designed by imitating the physical mechanism and motions of tetrapodal animals such as dogs and cats and “humanoid” robots designed by imitating the physical mechanism and motions of men who are creatures of erect bipedalism are being put to practical use. Unlike industrial robots, such robot apparatus can move in various different ways because of their entertaining capabilities and hence they are also sometimes referred to as entertainment robots. 
   One of the most important themes in the technological development of such entertainment robots is the necessity of pursuing a scheme that can keep the user away from being bored. However, since boringness to men has not been elucidated yet, it is obviously difficult to prepare a scheme that can keep the user away from being bored. Therefore, techniques for preparing many schemes for attracting the user&#39;s interest are being devised and employed currently. 
   Schemes for making a robot apparatus to move, conforming to the voice and the motion of the user have been proposed (see, inter alia, Patent Document 1: Japanese Patent Application Laid-Open No. 2001-246174 and Non-Patent Document 1: Masato Ito, Jun Tani, “On-line Imitative Interaction with a Humanoid Robot Using a Mirror Neuron Model”, IEEE International Conference on Robotics and Automation (2004, in press). 
   SUMMARY OF THE INVENTION 
   With the technique described in the above-cited Patent Document 1, it is possible to draw the user into a conversation with a pseudo-listener, or a robot apparatus, by containing in the robot apparatus a mechanism for a scheme for generating a drawing (conforming) phenomenon such as a nodding motion, a winking motion or a gesturing motion in response to a sounded voice of the user. However, the conforming scheme described in the Patent Document 1 does not provide a flexible learning ability and hence gives rise to a problem that it is difficult for the robot apparatus to flexibly interact with the user in various different ways. Additionally, since the conforming pattern of the scheme contained in the robot apparatus in advance is not adapted to be modified, the behavior of the robot apparatus gradually becomes boring to the user as it interacts with the latter. 
   With the technique described in the above-cited Non-Patent Document 1, on the other hand, a robot apparatus can learn a conforming scheme by means of a recurrent type neural network (RNN) that is provided with a parametric bias. In other words, it can build a motion model by learning joint angle time series data that are obtained by mimicking motion, conforming to a motion of the user by using the RNN after the learning. However, the robot apparatus can only built a basic conforming relationship by means of the above-cited Non-Patent Document 1 and hence it is difficult for the robot apparatus to deal with a complex conforming relationship. Additionally, since it is not possible for the robot apparatus to modify the conforming relationship established by using the RNN. The robot apparatus can become gradually boring to the user as it interacts with the latter. 
   In view of the above identified circumstances, it is therefore desirable to provide a robot apparatus capable of moving autonomously, flexibly responding to a motion of conforming to an external moving subject that may typically be a user of the robot and conforming to the motion of the moving subject, and also capable of modifying the conforming relationship with the moving subject and also a method of controlling the motion thereof. 
   According to the present invention, there is provided a robot apparatus capable of moving autonomously, the robot apparatus comprising: an input means for inputting an image or sound of an external moving subject; a plurality of motion generating means for generating a plurality different motions in response to the image or sound input by way of the input means, conforming to the motion of the external moving subject; a motion expressing means for integrally expressing one or more than one motions out of the plurality of motions generated by the plurality of motion generating means; and a control means for controlling the number of motions integrated by the motion expressing means and the ratio of the motions to be integrated. 
   A robot apparatus according to the invention may further comprise a plurality of modulation means for modulating the respective motions generated by the plurality of motion generating means. In this instance, the control means controls the modulation processes of the plurality of modulation means. 
   According to the present invention, there is also provided a method of controlling the motion of a robot apparatus capable of moving autonomously, the method comprising: an input step of inputting an image or sound of an external moving subject: a plurality of motion generating steps of generating a plurality different motions in response to the image or sound input in the input step, conforming to the motion of the external moving subject; a motion expressing step of integrally expressing one or more than one motions out of the plurality of motions generated in the plurality of motion generating steps; and a control step of controlling the number of motions integrated in the motion expressing step and the ratio of the motions to be integrated. 
   Thus, since a robot apparatus according to the invention comprises a plurality of motion generating means for generating a plurality of different motions, conforming to the motion of an external moving subject, who may typically be the user of the robot apparatus, so as to integrally express one or more than one motions out of the plurality of generated motions, it can deal with a complex conforming relationship when moving in response to the motion of the external moving subject, conforming to the motion of the latter. Additionally, since a robot apparatus according to the invention modulates the respective motions generated by the plurality of motion generating means and controls the number of motions integrated by the motion expressing means and the ratio of the motions to be integrated, it can realize a motion that is less boring to the external moving subject, who may typically be the user of the robot apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic perspective view of an embodiment of robot apparatus according to the invention, illustrating its appearance; 
       FIG. 2  is a schematic illustration of the functional units of the embodiment of robot apparatus of  FIG. 1 ; 
       FIG. 3  is a schematic block diagram of the control unit of the embodiment of robot apparatus of  FIG. 1 ; 
       FIG. 4  is a schematic block diagram of the embodiment of robot apparatus of  FIG. 1 , illustrating the functional blocks and the control method thereof; 
       FIG. 5A  is a schematic illustration of a movement region that the embodiment of robot apparatus of  FIG. 1  extracts from an image and a block region surrounding the movement region; and 
       FIG. 5B  is a schematic illustration of projection of the central point of the block region of  FIG. 5A  on an axis passing through the central point of the image and tilted by an arbitrarily selected angle to extract the rhythm. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate a preferred embodiment of the invention. This embodiment is a biped type robot apparatus provided with affect models formed by modeling affects such as instinct and emotion. The robot apparatus is a utility robot that supports human activities in various different scenes of daily life in a domestic environment or some other environment. It is also an entertainment robot that can do basic motions that are specific to human being. In the following, the configuration of the robot apparatus will be described first and then the method of controlling the motions of the robot apparatus will be described in detail. 
   (1) Configuration of Robot Apparatus 
   Firstly, the configuration of the robot apparatus of this embodiment will be described. As shown in  FIG. 1 , the robot apparatus  1  of this embodiment comprises a trunk unit  2 , a head unit  3  linked to a predetermined position of the trunk unit  2 , left and right arm units  4 R/L and left and right leg units  5 R/L, the arm units  4 R/L and the leg units  5 R/L also being linked to the trunk unit  3 . (R and L are prefixes respectively denoting right and left throughout this letter of specification.) 
     FIG. 2  schematically illustrates the degree of freedom of each of the joints of the robot apparatus  1 . The neck joint that supports the head unit  3  has three degrees of freedom realized by a neck joint yaw axis  101 , a neck joint pitch axis  102  and a neck joint roll axis  103 . 
   Each of the arm units  4 R/L, or the upper limb units, has a shoulder joint pitch axis  107 , a shoulder joint roll axis  108 , an upper arm yaw axis  109 , an elbow joint pitch axis  110 , a forearm yaw axis  111 , a wrist joint pitch axis  112 , a wrist joint roll axis  113  and a hand section  114 . The hand section  114  is in fact a multi-joint multi-degree-of-freedom structure that includes a thumb and a plurality of fingers. However, since the motion of the hand section  114  contributes to and influences little the attitude control and the locomotion control of the robot apparatus  1 , it is assumed to have zero degrees of freedom in this letter of specification. Therefore, each of the arm units  4 R/L has seven degrees of freedom. 
   The trunk unit  2  has a trunk pitch axis  104 , a trunk roll axis  105  and a trunk yaw axis  106  and hens has three degrees of freedom 
   Each of the leg units  5 R/L, or the lower limb units, has a hip joint yaw axis  115 , a hip joint pitch axis  116 , a hip joint roll axis  117 , a knee joint pitch axis  118 , an ankle joint pitch axis  119 , an ankle joint roll axis  120  and a foot section  121 . In this letter of specification, the intersection of the hip joint pitch axis  116  and the hip joint roll axis  117  is defined as the hip joint position of the robot apparatus  1 . The foot section is in fact a multi-joint multi-degree-of-freedom structure that includes a sole. However, the foot section  121  is assumed to have zero degrees of freedom in this letter of specification. Therefore, each of the leg units  5 R/L has six degrees of freedom. 
   To summarize, the robot apparatus  1  has a total of 3+7×2+3+6×2=32 degrees of freedom as a whole. However, robot apparatus  1  for entertainment are not necessarily limited to 32 degrees of freedom. It may be needless to say that the degrees of freedom and hence the number of joints can be increased or decreased appropriately depending on the restrictive conditions and the requirements of the specification to be met for designing and preparing a robot apparatus. 
   Each of the degrees of freedom of the robot apparatus  1  is realized by means of an actuator. In view of the requirements to be met by a robot apparatus  1  including that it should not have an excessively expanded appearance and should approximate the natural profile of man and that it should be controlled reliably for its attitude although it is an unstable structure designed for erect bipedalism, each actuator is preferably compact and lightweight. 
     FIG. 3  schematically shows the control system of the robot apparatus of  1 . As shown in  FIG. 3 , the control system comprises a thinking control module  200  that controls the emotional judgment and the sentimental expression that dynamically respond to the user-related input and a movement control module  300  that controls the concerted movement of the whole body of the robot apparatus  1  that is driven to move by actuators  350 . 
   The thinking control module  200  includes a CPU (central processing unit)  211  that executes arithmetic processing operations relating to the emotional judgment and the sentimental expression, a RAM (random access memory)  212 , a ROM (read only memory)  213  and an external memory device (which may include a hard disc drive)  214 . It is a stand-alone type information processing device that can process various pieces of information in a self-conclusive manner in the module itself. 
   The thinking control module  200  decides the current emotion and the current will of the robot apparatus  1  according to the external stimuli including the image data input from an image input device  251  and sound data input from a sound input device  252 . The image input device  251  typically comprises a pair of left and right CCD (charge coupled device) cameras, while the sound input device  252  typically comprises a plurality of microphones. The thinking control module  200  can output a sound by way of a sound output device  253  that typically comprises a speaker. 
   The thinking control module  200  issues a command to the movement control module  300  for carrying out a motion or behavior sequence according to the decision made by the robot apparatus  1  by moving the four limes. 
   On the other hand, the movement control module  300  comprises a CPU  311  for controlling the concerted movement of the entire body of the robot apparatus  1 , a RAM  312 , a ROM  313  and an external memory device (which may include a hard disc drive)  314 . It is a stand-alone type information processing device that can process various pieces of information in a self-conclusive manner in the module itself. The external memory device  314  can accumulate walking patterns, ZMP trajectories and other behavior plans computationally determined on an offline basis. The expression of a ZMP, or a zero moment point, refers to a point on the floor where the moment is reduced to nil by the reaction force of the floor when the robot apparatus  1  is walking and a ZMP trajectory refers to a trajectory along which the ZMP moves in a locomotive period of the robot apparatus  1 , for example. The concept of ZMP and application of stability determining norms of locomotion robots are described in Miomir Vukobratovic “LEGGED LOCOMOTION ROBOTS” (Ichiro Kato “Locomotion Robots and Artificial Legs” (Nikkan Kogyo Shinbun-sha). 
   The movement control module  300  is connected to various devices of the robot apparatus  1  including the actuators  350  for realizing the degrees of freedom of the joints of the robot apparatus  1  that are distributed in the whole body of the robot apparatus  1  as illustrated in  FIG. 2 , an attitude sensor  351  for observing the attitude and the inclination of the trunk unit  2 , landing verification sensors  352 ,  353  for detecting the takeoff and the touchdown of the left and right soles and power source control device  354  for managing the power source of the robot apparatus  1  that may typically be a battery by way a bus interface (I/F)  301 . The attitude sensor  351  is typically formed by combining an acceleration sensor and a gyro sensor, whereas the landing verification sensors  352 ,  353  are typically formed by using proximity sensors or micro-switches. 
   The thinking control module  200  and the movement control module  300  are built on a common platform and connected to each other by way of bus interfaces  201 ,  301 . 
   The movement control module  300  controls the concerted movement of the whole body of the robot apparatus  1  that is produced by the actuators  350  to express a motion directed from the thinking control module  200 . More specifically, the CPU  311  takes out a motion that corresponds to the behavior specified by the thinking control module  200  from the external memory device  314  or internally generates a motion pattern. Then, the CPU  311  defines the movement of each of the feet, the ZMP trajectory, the movement of the trunk, that of each of the upper limbs, the horizontal position and the height of the waist and so on according to the specified motion pattern and transfers the command values for realizing the motion as indicated by the definitions to the respective actuators  350 . 
   Additionally, the CPU  311  can adaptively control the concerted movement of the whole body of the robot apparatus  1  by detecting the attitude and the inclination of the trunk unit  2  of the robot apparatus  1  according to the output signal of the attitude sensor  351  and, at the same time, if each of the leg units  5 R/L is in an idle state or in a standing state according to the output signal of the corresponding landing verification sensor  352  or  353 . 
   Still additionally, the CPU  311  controls the attitude and the movement of the robot apparatus  1  so as to make the ZMP position to be constantly directed toward the center of the ZMP stability region. 
   The movement control module  300  is adapted to feedback the extent to which the behavior of the robot apparatus  1  is expressed according to the will decided by the thinking control module  200  and hence the status of the processing operation of itself to the thinking control module  200 . 
   In this way, the robot apparatus  1  can judge the situation of itself and its surroundings and behave autonomously according to the control program. 
   (2) Motion Control Method of Robot Apparatus 
   Now, the method of controlling the motions of the above-described robot apparatus  1  will be described below. 
   As pointed out above, it is important to pursue a scheme that can keep the user away from being bored for an entertainment robot such as the above-described robot apparatus  1 . The inventors of the present invention thought that it is effective to repeat
     (i) making the motion of the user and that of the robot apparatus conform to (to be drawn into) each other and   (ii) deforming (modulating) the conforming relationship by means of an appropriate method
 
for a scheme that can keep the user away from being bored and invented a method of controlling the motions of a robot apparatus  1  within such a framework. Now, imagine a scene where the user and the robot apparatus  1  dance with each other as an example of interaction between them.
   

   The method is aimed to build a conforming relationship between the motion of the user and that of the robot apparatus  1  firstly on a rhythm level in (i) above. As a technique for achieving the aim, the robot apparatus  1  is made to extract the rhythm of the motion of the user as time series waveform information (one-dimensional time series data), which will be described in greater detail hereinafter, and learn a recurrent type neural network (RNN) on a real time basis, using the time series waveform information. Then, the robot apparatus  1  predicts time series waveform information, using the RNN it has learnt, and moves its body with the rhythm. The aimed conforming relationship has been built if the rhythm of the user and that of the robot apparatus  1  conform to each other at this time. It is possible for the robot apparatus  1  to adapt itself to various conforming (drawing) relationships by utilizing the RNN learning ability by means of this technique. 
   Then, the conforming relationship built in (i) is modified by means of an appropriate technique in (ii). However, if the modulation technique is simple, the user may easily understand it and gradually become bored. Therefore, it is necessary to make the modulation technique complex to a certain extent. However, it is difficult to realize a complex modulation technique simply on the basis of the above-described conforming relationship on the rhythm level. 
   Therefore, in this embodiment, a number of conforming relationships including the above-described one that is established on a rhythm level are defined and then the defined conforming relationships are modified. As an example, let us define three conforming relationship layers (modules) below. The first module deals with the simplest conforming relationship that is much simpler than the above-described one. More specifically, it is adapted to build a conforming relationship on a predefined rule that the robot apparatus  1  moves its body randomly when it detects a motion on the part of the user. The second module is adapted to build a conforming relationship on a rhythm level by means of the above-described RNN. The third module is adapted to build a complex conforming relationship that is more complex than the above-described conforming relationship and according to which the robot apparatus  1  uses the movement of a part of its body (e.g., the trajectory of the center of the head, one of the hands or one of the feet) as time series data and mimics the motion of the user in a state where the robot apparatus  1  can establish correspondence between its body and its movement. 
   Modulations of two different levels as listed below may be conceivable to realize the modulation technique aimed at in (ii) under the above defined circumstances.
     (a) modulation in each of the modules and   (b) modulation among the modules   

   Of the above-listed two techniques, (a) represents a technique of designing a modulability for the input/output relationship in each of the modules that is different from the ordinary relationship. While any of various different techniques may be used, a simple technique of assigning a random noise to the output data (RNN output value) at a predetermined ratio will be used in this embodiment. 
   On the other hand, (b) represents a technique of designing an inter-module modulability. For example, the strongest conforming state in the above-described instance is a state where all the three modules show a conforming relationship. If the conforming relationship of an arbitrarily selected module is released and hence the function of the module is turned non-influential on the actuators, a conforming state that is weaker by a step appears and the entire system comes to appear to the user as if it has been modulated. Thus, it is possible to flexibly provide a modulability to the system on a level different from the level of (a) by controlling the conforming state among the modules. 
   In practice, it is desirable to control the extent of modulation in (ii) according to the reaction of the user, which will be described in greater detail hereinafter. 
     FIG. 4  illustrates the functional blocks of the robot apparatus  1  designed to realize the above-described motion control method. As shown in  FIG. 4 , the robot apparatus  1  possesses modules I through III, which correspond respectively to the above-described first through third modules. The modulators  21 ,  36 ,  44  that are arranged respectively in the modules I through III are modulation blocks in the respective modules, while module controller  50  is a block for controlling inter-module modulations. 
   A camera image input device  10  corresponds to the image input device  251  of  FIG. 3  and is adapted to supply a user image to movement detector  11 , rhythm extractor  12  and body part detector/transformer  13  per unit time. 
   The movement detector  11  computes the difference between the image supplied from the camera image input device  10  and the immediately preceding image and extracts a moving region on the basis of the subtraction image. Then, if the area of the moving region is greater than a predetermined value, the movement detector  11  judges that it detects a movement of the user and supplies an ON signal to a fundamental reaction rule base  20  of the module I. Otherwise, the movement detector  11  supplies an OFF signal to the fundamental reaction rule base  20 . 
   The rhythm extractor  12  extracts a moving region like the movement detector  11  and determines a rectangle, which is referred to as block region (BR), surrounding the moving region as shown in  FIG. 5A . Then, the rhythm extractor  12  extracts the rhythm of the movement of the user from the locus of the central point of the BR at each time point as waveform information. More specifically, as shown in  FIG. 5B , it projects the central point of the BR on an axis L that passes the center of the image with an arbitrarily selected angle of inclination at each time point and transforms the projected central point into waveform information that is defined in terms of the axis L and a time base. The rhythm extractor  12  supplies time series waveform information of every predetermined time period to a data buffer  30  of the module II. 
   The body part detector/transformer  13  determines the positions of the head and the left and right hands, for example, by using basic template matching or color histogram information that is well known in the technological field of image processing and transforms the positional information into joint angle control information of the robot apparatus  1  itself by means of inverse kinematics (see, inter alia, the above-cited Non-Patent Document 1). Then, the body part detector/transformer  13  supplied the joint angle control information of every predetermined time period to a data buffer  40  of the module III. 
   The module I is a module for building a simple conforming relationship on a predefined rule that the robot apparatus  1  moves its body randomly when it detects a motion on the part of the user and comprises a fundamental reaction rule base  20  and a modulator  21 . 
   A motion to be expressed when an ON signal is supplied from the movement detector  11  and a motion to be expressed when an OFF signal is supplied from the movement detector  11  are designed in the fundamental reaction rule base  20  in advance by a programmer. When an ON signal is supplied, the fundamental reaction rule base  20  typically supplies the ID of each of the two arms and an output value w_out 1  that indicates the joint angle vector of the arm in order to cause the two arms to swing back and forth at a given angular speed within a given range. When, on the other hand, an OFF signal is supplied, the fundamental reaction rule base  20  stops supplying them. 
   The modulator  21  randomly modulates the output value that is supplied to body controller  51  according to the control signal from the module controller  50 . For example, if the robot apparatus  1  swings the two arms back and forth at a given angular speed within a given range, the modulator  21  applies a random noise to the angular speed and the range. The random noise may show fluctuations of 1/f that are known to be pleasant to men (see “The Science of Fluctuations 1-9”, edited under the supervision of Toshimitsu Musha, Morikita Shuppan). 
   The next module II is a module for building a conforming relationship on a rhythm level by means of an RNN as described above and comprises a data buffer  30 , an RNN controller  31 , an RNN  32 , a transformer  33 , a direct-coupling reaction rule base  34 , an adder  35  and a modulator  36 . 
   The data buffer  30  holds the time series waveform information of a given time period supplied from the rhythm extractor  12 . The data buffer  30  has a queue structure and discards any data that are older than a predetermined time period. 
   When time series waveform information of a given time period is held in the data buffer  30 , the RNN controller  31  transmits a prediction mode signal to the RNN  32 , which RNN  32  by turn computes the prediction accuracy error in the time period, using the time series waveform information of the time period. Then, the transformer  33  transforms the predicted time series waveform information into a motion of the robot apparatus  1  itself. For example, the transformer  33  supplies the ID of each of the two arms and an output value w_RNN 2  that indicates the joint angle vector of the arm to the adder  35  in order to cause the two arms to express a motion of swinging back and forth at an angular speed and in a range corresponding to the time series waveform information. 
   If the value of the predicted accuracy error is not lower than a threshold value, the RNN controller  31  transmits a learning mode signal and has the RNN  32  learn the time series waveform information (see, inter alia, the above-cited Non-Patent Document 1). While the RNN  32  is learning, the direct-coupling reaction rule base  34  transforms the time series waveform information supplied from the rhythm extractor  12  into a motion of the robot apparatus  1  itself. For example, the direct-coupling reaction rule base  34  supplies the ID of each of the two arms and an output value w_Rule 2  that indicates the joint angle vector of the arms to the adder  35  in order to cause the two arms to express a motion of swinging back and forth at an angular speed and in a range corresponding to the time series waveform information. Note that the body part or body parts to be moved by the above-described output value W_RNN 2  may or may not differ from the body part or body parts to be moved by the output value w_Rule 2 . Then, the adder  35  determines the linear sum of the output value W_RNN 2  and the output value w_Rule 2  by means of formula (1) below.
 
 W _out2=α1· w _RNN2+β1· w _Rule2  (1)
 
Then, the adder  35  supplies the obtained output value W_out 2  to the body controller  51 . Note that the parameters α 1 , β 1  may be made to change so as to cause the component of the output value w_Rule 2  decrease and the component of the output value W_RNN 2  increase with time as the learning of the RNN  32  progresses and the prediction accuracy error is reduced for the purpose of making the motion goes on smoothly.
 
   If, on the other hand, the value of the predicted accuracy error is not higher than a threshold value, the adder  35  supplies the above-described output value W_RNN 2  as output value W_out 2  to the body controller  51  without suing the output value w_Rule 2 . As a result, the robot apparatus  1  actively outputs a motion on the basis of its own internal structure so that its mimicking operation becomes stabilized. However, it may alternatively be so arranged that the adder  35  determines the output value W_out 2  by means of the above formula (1) if the value of the predicted accuracy error is not higher than the threshold value. Then, it may be so arranged that the adder  35  changes the parameters α 1 , β 1  so as to cause the component of the output value w_Rule 2  decrease and the component of the output value W_RNN 2  increase with time. 
   The modulator  36  randomly modulates the output value supplied to the body controller  51  according to the control signal from the module controller  50 . The modulator  36  applies a random noise to the parameters α 1 , β 1  of the above-described adder  35  or to the output values w_RNN 2 , w_Rule 2 . 
   Finally, the module III is a module adapted to build a complex conforming relationship of establishing correspondence between its body and its movement and mimicking the motion of the user and comprises a data buffer  40 , an RNN controller  41 , an RNN  42 , an adder  43  and a modulator  44 . 
   The data buffer  40  holds the joint angle control information of a given time period supplied from the body part detector/transformer  13 . The data buffer  40  has a queue structure and discards any data that are older than a predetermined time period. 
   When the joint angle control information of a given time period is held in the data buffer  40 , the RNN controller  41  transmits a prediction mode signal to the RNN  42 , which RNN  42  by turn computes the prediction accuracy error in the time period, using the joint angle control information of the time period. 
   If the value of the predicted accuracy error is not lower than a threshold value, the RNN controller  41  transmits a learning mode signal and has the RNN  42  learn the joint angle control information (see, inter alia, the above-cited Non-Patent Document 1). Then, the adder  43  determines the linear sum of the output value w_RNN 3  and the output value w_Rule 3  supplied from the body part detector/transformer  13  by means of formula (2) below.
 
 W _out3=α2· w _RNN3+β2· w _Rule3  (2)
 
Then, the adder  43  supplies the obtained output value W_out 3  to the body controller  51 . Note that the parameters α 2 , β 2  may be made to change so as to cause the component of the output value w_Rule 3  decrease and the component of the output value w_RNN 3  increase with time as the learning of the RNN  42  progresses and the prediction accuracy error is reduced for the purpose of making the motion goes on smoothly.
 
   If, on the other hand, the value of the predicted accuracy error is not higher than a threshold value, the adder  43  supplies the above-described output value w_RNN 3  as output value W_out 3  to the body controller  51  without using the output value w_Rule 3 . As a result, the robot apparatus  1  actively outputs a motion on the basis of its own internal structure so that its mimicking operation becomes stabilized. However, it may alternatively be so arranged that the adder  43  determines the output value W_out 3  by means of the above formula (2) if the value of the predicted accuracy error is not higher than the threshold value. Then, it may be so arranged that the adder  43  changes the parameters α 2 , β 2  so as to cause the component of the output value w_Rule 3  decrease and the component of the output value w_RNN 3  increase with time. 
   The modulator  44  randomly modulates the output value supplied to the body controller  51  according to the control signal from the module controller  50 . The modulator  44  applies a random noise to the parameters α 2 , β 2  of the above-described adder  43  or to the output values w_RNN 3 , w_Rule 3 . 
   As described above, the body controller  51  integrates the output values W_out 1 , W_out 2  and W_out 3  supplied respectively from the modules I through III and transforms them into an instruction for driving the actuators  52 . When integrating the output values W_out 1 , W_out 2  and W_out 3 , the body controller  51  may superpose the output values one on the other or determines the linear sum of the three output values in a manner as described above. 
   Thus, the robot apparatus  1  of this embodiment has the modules I through III for building respective conforming relationships that are different from each other and integrates their outputs to drive the actuators  52  so that it can handle a complex conforming relationship when it moves, conforming to the motion of the user. 
   Additionally, since the modules II, III respectively compute the linear sum of the output value W_RNN 2  obtained as a result of a learning session of the RNN  32  and the output value w_Rule 2  obtained without any learning session and the linear sum of the output value w_RNN 3  obtained as a result of a learning session of the RNN  42  and the output value w_Rule  3  obtained without any learning session, it is possible to make the expressed motion proceed smoothly. More specifically, the component of the output value w_Rule 2  is made to increase and the component of the output value W_RNN 2  is made to decrease in the initial stages of the learning session of the RNN  32  in order to make it possible to relatively stably express the motion without interrupting the motion but conversely the component of the output value W_RNN 2  is made to increase and the component of the output value w_Rule 2  is made to decrease as the learning progresses in order to gradually stabilize the motion. Similarly, the component of the output value w_Rule 3  is made to increase and the component of the output value w_RNN 3  is made to decrease in the initial stages of the learning session of the RNN  42  in order to make it possible to relatively stably express the motion without interrupting the motion but conversely the component of the output value w_RNN 3  is made to increase and the component of the output value w_Rule 3  is made to decrease as the learning progresses in order to gradually stabilize the motion. However, it is not necessary to use such an increasing/decreasing technique and the parameters can be freely modified for the modulations. 
   While three modules are used to build conforming relationships in the above-described embodiment, the number of modules is by no means limited to three and a number of modules other than three may be used for the purpose of the present invention. Additionally, while rule bases and RNNs are used for describing conforming (drawing) relationships of input/output data in the above embodiment, some other known technique such as the use of oscillator models or ordinary neural networks may alternatively be used for the purpose of the present invention. 
   Since the robot apparatus  1  of this embodiment is adapted to use three modules I through III, it can build complex conforming relationships and the conforming relationship of each module can be modulated. However, the modulation technique that is complete within each of the modules is simple and hence can be understood easily by the user. Then, the user may become bored gradually. 
   Therefore, not only the conforming relationship of each of the modules is modulated but also a technique of inter-module modulation of conforming relationships is adopted in this embodiment. The module controller  50  is responsible for such inter-module modulations of conforming relationships. Particularly, the module controller  50  of this embodiment controls the extent of inter-module modulation according to the reaction of the user such as “irritated”, “neutral”, “bored” or “comfortable” or some other state of affect on the part of the user. 
   The known techniques that have been proposed to date in order to detect the state of affect of a user include one using the facial expression and/or information on the pitch and the power of the voice of the user (see “J. R. Movellan and M. S. Bartlett, “The Next Generation of Automatic Facial Expression Measurement”, In; P. Ekman (eds) “What the Face Reveals”, Oxford University Press, 2003”). For the purpose of simplicity, assume here that a technique of having the user speak out words expressing states of affect and inputting them by way of a microphone voice input device  53  so as to be recognized by a voice recognizer  54  is used to classify the states of affect of the user into the above-listed four categories. In actuality, words that agree with “irritated”, those that agree with “bored” and those that agree with “comfortable” are prepared as dictionary and words that do not agree with any of them are judged to be “neutral. 
   If the state of affect of the user is “irritated”, the module controller  50  judges that the conforming relationship with the user is not sufficient yet and strengthens the conforming relationship by increasing the number of modules to be used for conforming outputs. For example, if the number of modules is two when the state of affect of the user is “neutral”, the module controller  50  increases the number of modules to three and builds a strengthened conforming relationship when the state of affect of the user is detected to be “irritated”. It is possible for the module controller  50  to transmit a control signal to each of the modules so as to increase the learning parameters that are defined in the learning algorithm of the RNNs by a given value. It will be appreciated that the module I that does not have any learning parameter is left unmodified. 
   If the state of affect of the user is “neutral”, the module controller  50  judges that the current conforming relationship is not bad and transmits a control signal to the modulators  21 ,  36 ,  44  at every given time period so as to modulate the conforming relationship by fluctuations without remarkably modulating the relationship. Modulation by fluctuations is not clearly perceived by the user but it is introduced as a steady state because fluctuations can relax the human mind. 
   If the state of affect of the user is “bored”, the module controller  50  judges that the user is bored by the current conforming relationship and modulates the conforming relationship depending on the extent of being bored on the part of the user. More specifically, if “bored” is detected consecutively for more than a predetermined number of times, the module controller  50  modulates the conforming relationship to a large extent. However, if otherwise, the module controller  50  modulates the conforming relationship only to a limited extent. When the conforming relationship is to be modulated to a large extent, the module controller  50  changes the configuration of the modules in addition to that it transmits a command for a random modulation to the modulators  21 ,  36 ,  44  of the modules. Techniques that can be used for changing the configuration include a technique of changing the configuration entirely randomly, a technique of randomly selecting a module out of the currently operating modules and excluding it from the conforming relationship, a technique of randomly selecting a module out of the modules that are currently not operating and adding it to the conforming relationship and a technique of adding a hierarchically high module to or excluding a hierarchically high module from the current conforming relationship provided that hierarchy is defined for the existing modules. For example, if hierarchy is defined for the modules I, II, III so as to restrict their motions in the listed order and the modules I and II are currently operating, the module II can be excluded and the module III can be added. When the body controller  51  computes the linear sum of the output values supplied from the modules I through III, it is possible to change the ratio of the output values of the modules by modifying the parameters that are used for the linear sum without increasing or decreasing the number of modules. When, on the other hand, the conforming relationship is to be modulated to a small extent, the module controller  50  transmits a command for a random modulation to the modulators  21 ,  36 ,  44  of the modules without changing the configuration of each of the modules. 
   If, finally, the state of affect of the user is “comfortable”, the module controller  50  judges that the current conforming relationship is good to the user. Therefore, it does not modulate the conforming relationship and allows the current motion to continue. 
   As described above, the robot apparatus  1  of this embodiment is adapted to modulate the conforming relationship not only within each of the modules but also on an inter-module basis depending on the state of affect of the user such as “irritated”, “neutral”, “bored” or “comfortable” so that it is possible to realize a motion that is less boring to the user. 
   The present invention is by no means limited to the above-described embodiment, which can be modified and altered without departing from the spirit and scope of the present invention. 
   For instance, while the modules I through III of this embodiment are adapted to generate respective motions that conform to the motion of the user but differ from each other in response to the image input to the robot apparatus  1  by way of the camera image input device  10  in the above description, they may be so adapted as to generate respective motions that differ from each other in response not to the image but to the sound input to the robot apparatus  1 . Alternatively, they may be so adapted to generate respective motions in response to the combination of the image and the sound. If they generate respective motions conforming to the motion of the user in response to the sound input from the user, they may be so adapted as to extract the rhythm or the like of the motion of the user from the clapping sound and/or the stamping sound of the user and generate respective motions in response to the extracted rhythm. 
   While the robot apparatus  1  of the above embodiment interacts with the user (human being) in the above description, the object of interaction of the robot apparatus  1  is not limited to the user. It may be some other robot apparatus that can operate like the robot apparatus  1  or some other moving subject. 
   It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.