Abstract:
A robot, wherein the operating amounts of the first and second actuators are adjusted according to a torque necessary for maintaining a body member and an end member at specified angles in a mechanism in which the body member ( 361 ) and the end member ( 363 ) are rotatably connected to each other and first and second wires ( 366 ) connected to the end member are advanced and retreated by the first and second actuator ( 368 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application claims priority to Japanese Patent Application No. 2004-214343 filed on Jul. 22, 2004, the contents of which are hereby incorporated by reference into the present application. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a robot in which a distal side member is rotatably jointed to a body side member, and at least two wires are connected to the distal side member. The robot is adapted such that a wire is moved back and forth by an actuator to rotate the distal side member with respect to the body side member. 
   2. Description of the Related Art 
   In recent years, humanoid robots or animal-shaped robots have been developed actively. In such robots, the distal side member is rotatably jointed to the body side member via a joint. As a joint angle (the rotation angle of the distal side member with respect to the body side member) is adjusted, the robots walk, carry an object or operate an object. 
   Here, the term “body side member and distal side member” means, for example, “body part and head part”, “body part and upper-arm part”, “upper-arm part and forearm part”, “forearm part and palm part”, “palm part and finger part”, “body part and thigh part”, “thigh part and lower leg part”, “lower leg part and foot part”, etc. Here, the foot part means a member on the distal side of an ankle joint. 
   The robot has an actuator which actuates each joint. When an actuator is disposed in each joint, it is difficult to reduce the size and weight of the joint. Therefore, a technique for providing an actuator on the body side member and connecting a distal side member to the actuator with a wire has been developed. 
   In this technique, an end of a first wire is connected to a portion of the distal side member located in one side of a rotation center, and an end of a second wire is connected to a portion of the distal side member located in the other side of the rotation center. By pulling the first wire and loosening the second wire, the distal side member is rotated in a first direction. By loosening the first wire and pulling the second wire, the distal side member is rotated in a second direction. The operation of the joint can be adjusted by adjusting an operation amount of the actuator that moves the other end of the first wire back and forth, and an operation amount of the actuator that moves the other end of the second wire back and forth. 
   For example, a robot arm is disclosed in Japanese Patent Application Publication No. H04-300179. The robot arm has a plurality of joints and a plurality of wires which operate the group of joints. In the robot arm, the tension of each wire and the torque of each joint are adjusted by using actuators (referred to as a wire drive system in this publication). In this publication, a technique for adjusting the joint angle of each joint is not described. 
   BRIEF SUMMARY OF THE INVENTION 
   When the joint angle is adjusted with wires, wire stretching cannot be ignored. For example, when an external force to rotate the joint (hereinafter referred to as the load torque of a joint) is applied to the distal side member, the wires will stretch according to their tensions and consequently the wire stretching will change the joint angle. Therefore, when a particular joint angle is instructed, the deviation between the instructed joint angle and an actual joint angle will vary according to the load torque of a joint, as long as the operation amounts of the actuators are uniformly determined from the instructed joint angle. For this reason, in order to accurately adjust the joint angle to an instructed angle, it is necessary to calculate a modified instruction angle which is obtained by modifying the instruction angle depending on the deviation between the instruction angle and the actual angle, and to determine the operation amount of the actuator from the modified instruction angle. That is, it is necessary to feed back the deviation in the joint angle when determining the operation amount of the actuator. 
   In a case where the operation amount of the actuator is determined based upon the modified instruction angle, when the instruction angle is modified to a slight excess with respect to the magnitude of the deviation, it will be possible to rapidly reduce the deviation caused in the joint angle. On the other hand, when the instruction angle is modified too much with respect to the magnitude of the deviation, the actuator may operate excessively with respect to the deviation of the joint angle, and consequently the joint angle cannot be accurately adjusted to the instructed angle. Therefore, It is necessary to determine a rate (so-called a feedback gain) such that the instruction angle is modified with respect to the magnitude of a deviation on the basis of the mechanical structure of a joint or the operation needed for a joint. 
   While the robot operates, each joint acts in various ways. For example, in a bipedal robot, while one foot part makes contact with the ground, the other foot part moves forward as an idling leg. Also, when the other foot part makes contact with the ground, the first foot part moves forward as an idling leg. The bipedal robot walks by repeating these operations. Since each leg becomes a grounded leg or an idling leg, the load torque, for example, applied to an ankle joint changes every moment. When a large feedback gain is used to adjust the joint angle of the ankle joint, the joint angle can be accurately adjusted to an instructed angle while the ankle joint is an ankle joint on the grounded leg, but the joint angle may oscillate while the ankle joint is an ankle joint on the idling leg. In contrast, when a small feedback gain is used, the joint angle can be adjusted correctly while the ankle joint is an ankle joint on the idling leg, but a deviation in the joint angle will not be removed sufficiently while the ankle joint is an ankle joint on the idling leg. A large feed back gain should be selected if joint angle oscillation is permissible, or a small feed back gain should be selected if a degree of deviation in the joint angle is permissible. 
   At least two wires, i.e., a first wire which is pulled to change the joint angle in a first direction, and a second wire which is pulled to change the joint angle in a second direction, are used for a joint. Also, a torque is generated in the joint by the first wire and the second wire so as to resist a load torque of the joint. The tension in the first wire and the second wire varies according to the load torque of the joint. For example, when the load torque of the joint is a torque which rotates the joint in the first direction, the tension of the first wire becomes smaller than the tension of the second wire. However, when the load torque is a torque which changes the joint angle in the second direction, the tension of the first wire becomes larger than the tension of the second wire. 
   The relationship between the amount of change in the tension of a wire and the amount of change in the extension of the wire (the rigidity of the wire) is not constant, unlike an ideal elastic object.  FIG. 11  is a graph showing the relationship between the tension of a wire and the stretch thereof. In the graph in  FIG. 11 , the abscissa axis represents the tension of the wire and the ordinate axis represents the degree of wire stretching. The gradient of the graph represents rigidity, and a larger gradient represents a smaller rigidity. In a range where the tension is small, like range A in the figure, the rigidity is relatively low and is apt to change. In a range where the tension is large, like range B in the figure, the rigidity is relatively high and is stable. This mainly results from the structure of the wire in which a number of strands are twisted. 
   While the robot operates, the tension of the first wire and the tension of the second wire change every moment. This means that the rigidity of the first wire and the rigidity of the second wire change every moment. This change in the rigidity means that the relationship between the operation amount of the actuator which moves the other end of a wire back and forth and the amount of change in the joint angle caused by the operation amount is apt to change. When the rigidity of the wire is high and stable, for example, in a state where the tension of the wire is large, even when a change occurs in the tension of the Mire, the relationship between the operation amount of the actuator and the amount of change in the joint angle is stabilized. On the other hand, when the rigidity of the wire is low and unstable in a state where the tension of the wire is small, when a change occurs in the tension of the wire, the relationship between the operation amount of an actuator and the amount of change in the joint angle is apt to change. For this reason, even if the deviation of a joint angle is merely fed back to the operation amount of each actuator that moves a wire back and forth, the joint angle cannot be adjusted correctly. For example, if the joint angle is controlled using a large feedback gain, the joint angle may oscillate in a state where the tension of the wire is small. On the other hand, if a small feedback gain is used, deviation in the joint angle will not be sufficiently removed in a state where the tension of the wire is large. A large feed back gain should be selected if joint angle oscillation is permissible, or a small feed back gain should be selected if a degree of deviation in the joint angle is permissible. 
   The present invention solves the above problems. The present invention provides a technique for appropriately adding the deviation in a joint angle to the operation amounts of the actuators that move the wires back and forth, and makes it possible to accurately adjust the joint angle to an instructed angle. 
   A robot embodied by the present invention is provided with a body side member, a distal side member, a first wire, a first actuator, a second wire, a second actuator, a first controller, a second controller, and an adjustor. 
   The distal side member is rotatably jointed to the body side member. An end of the first wire is connected to a portion of the distal side member located in one side of a rotation center. The first wire is constructed to rotate the distal side member in a first direction when the first wire is pulled. The first actuator is constructed to move the other end of the first wire back and forth. An end of the second wire is connected to a portion of the distal side member located in the other side of the rotation center. The second wire is constructed to rotate the distal side member in a second direction when the second wire is pulled. The second actuator is constructed to move the other end of the second wire back and forth. 
   The first controller is constructed to instruct an operation amount to the first actuator. Here, the first controller calculates a first modified instruction angle by modifying an instructed rotation angle of the distal side member based upon a deviation between the instructed rotation angle and an actual rotation angle of the distal side member, and calculates the operation amount of the first actuator based upon the first modified instruction angle. The second controller is constructed to instruct an operation amount to the second actuator. Here, the second controller calculates a second modified instruction angle by modifying the instructed rotation angle of the distal side member based upon the deviation between the instructed rotation angle and the actual rotation angle of the distal side member, and calculates the operation amount of the second actuator based upon the second modified instruction angle. 
   The adjustor is constructed to adjust, in accordance with the torque required to maintain the rotation angle of the distal side member at the instructed rotation angle, the magnitude of the modification performed by the first controller and/or the second controller. 
   In this robot, the operation of the first actuator and the second actuator is adjusted so that the actual rotation angle of the distal side member may become the instructed rotation angle. The operation amounts of the first actuator and the second actuator are calculated by the first controller and the second controller, respectively. The first controller and the second controller calculate the operation amount of the first actuator and the operation amount of the second actuator on the basis of the modified instruction angle which is obtained by modifying an instructed rotation angle for the distal side member depending on the deviation between the instructed rotation angle and an actual rotation angle of the distal side member. Accordingly, the deviation between the instructed rotation angle and the actual rotation angle is added to the operation amount of the first actuator and the operation amount of the second actuator. The first actuator and the second actuator operate in a direction such that the deviation in the actual rotation angle of the distal side member is removed. 
   The load torque, which is applied to the distal side member and changes the actual rotation angle of the distal side member, varies according to the operation of the robot. For this reason, a torque required to maintain the actual rotation angle of the distal side member at an instructed rotation angle also varies according to the operation of the robot. When the load torque is large, the first wire and the second wire may extend or retract substantially, and a large deviation in the actual rotation angle of the distal side member may result. In such a case, it is preferable that the first actuator and the second actuator perform larger operation with respect to the caused deviation. On the other hand, when the load torque is small, the first wire and the second wire merely expand or contract slightly, and a large deviation in the actual rotation angle of the distal side member does not result. In such a case, when the first actuator and the second actuator perform large operation with respect to the caused deviation, they may, for example, cause the distal side member to vibrate. 
   In this robot, the magnitude of the instructed rotation angle modification performed by the first controller or the second controller is adjusted according to the magnitude of the torque required to maintain the actual rotation angle of the distal side member at the instructed rotation angle. That is, the magnitude of the instructed rotation angle modification performed by the first controller or the second controller changes according to the magnitude of the load torque. Accordingly, for example, when the load torque is large, the operation amount of the first actuator or the operation amount of the second actuator can be more substantially increased with respect to the deviation between the instructed rotation angle and the actual rotation angle. On the other hand, when the load torque is small, the operation amount of the first actuator or the operation amount of the second actuator can be partly reduced with respect to a deviation between the instructed rotation angle and the actual rotation angle. 
   According to this robot, a deviation in the rotation angle of the distal side member can be more appropriately utilized to modify the operation amount of the first actuator and the operation amount of the second actuator. The actual rotation angle of the distal side member can be correctly adjusted to the instructed rotation angle. 
   In the aforementioned robot, it is preferable that the robot further comprises a storage device for storing an expected value of the torque required to maintain the actual rotation angle of the distal side member at the instructed rotation angle. 
   A torque required to maintain the actual rotation angle of the distal side member at the instructed rotation angle can be estimated in advance on the basis of the expected operation of the robot. The first controller and the second controller can more accurately adjust the magnitude of the instructed rotation angle modification if the required torque is estimated in advance, based upon the expected operation. 
   Another robot embodied by the present invention is provided with a body side member, a distal side member, a first wire, a first actuator, a second wire, a second actuator, a first controller, a second controller, and an adjustor. 
   The distal side member is rotatably jointed to the body side member. An end of the first wire is connected to a portion of the distal side member located in one side of a rotation center. The first wire is constructed to rotate the distal side member in a first direction when the first wire is pulled. The first actuator is constructed to move the other end of the first wire back and forth. An end of the second wire is connected to a portion of the distal side member located in the other side of the rotation center. The second wire is constructed to rotate the distal side member in a second direction when the second wire is pulled. The second actuator is constructed to move the other end of the second wire back and forth. 
   The first controller is constructed to instruct an operation amount to the first actuator. Here, the first controller calculates a first modified instruction angle by modifying an instructed rotation angle of the distal side member based upon the deviation between the instruction rotation angle and an actual rotation angle of the distal side member, and it calculates the operation amount of the first actuator based upon the first modified instruction angle. The second controller is constructed to instruct an operation amount to the second actuator. Here, the second controller calculates a second modified instruction angle by modifying the instructed rotation angle of the distal side member based upon the deviation between the instructed rotation angle and the actual rotation angle of the distal side member, and calculates the operation amount of the second actuator based upon the second modified instruction angle. 
   The adjustor is constructed such that it will adjust the magnitude of modification performed by the second controller so it is larger than the magnitude of modification performed by the second controller when the tension of the first wire is larger than the tension of the second wire. When the tension of the second wire is larger than the tension of the first wire, the adjuster will adjust the magnitude of modification performed by the second controller so it is larger than the magnitude of modification performed by the first controller 
   In this robot, the deviation in the actual rotation angle of the distal side member will be added to the operation amount of the first actuator and the operation amount to the second actuator, and the first actuator and the second actuator operate in a direction in which the deviation in the actual rotation angle of the distal side member is removed. 
   Depending upon the operation of the robot, the tension of the first wire and the tension of the second wire varies, and consequently their rigidity also varies. In many cases, it is necessary to assign different tensions to each wire in order to maintain a distal side member at the instructed rotation angle while a lord torque is applied. At this time, although the rigidity of one wire is high and stable, the rigidity of the other wire is low and unstable. 
   In this robot, the magnitude of the modification of the first controller and the magnitude of the modification of the second controller can be modified on the basis of the tension of the first wire and the second wire, respectively. Accordingly, for an actuator which moves a wire with a larger tension, the deviation in the rotation angle of the distal side member can be added to the operation amount of the actuator such that it has a substantial effect. Conversely, for the other actuator which moves the other wire, whose tension is smaller, the deviation in the rotation angle of the distal side member can be added to the operation amount such that it has only a slight effect. 
   In this robot, when a deviation in the actual rotation angle of the distal side member occurs, the actuator which moves the wire whose tension is larger can be operated to a substantial degree with respect to the deviation. Further, the other actuator which moves the other wire whose tension is smaller can be operated to a slight degree with respect to the deviation. Accordingly, the deviation of the actual rotation angle of the distal side member can be removed rapidly, and the distal side member can be prevented from vibration. 
   According to this robot, a deviation in the actual rotation angle of the distal side member can be more appropriately added to the operation amount of the first actuator and the operation amount of the second actuator. The actual rotation angle of the distal side member can be correctly adjusted to the instructed rotation angle. 
   It is preferable that the adjustor is constructed such that the magnitude of modification performed by either the first controller or the second controller is set to zero. That is, even when a deviation in the actual rotation angle of the distal side member occurs, the actuator which moves the wire whose tension is smaller is not operated. 
   Since the wire whose tension is small has a low rigidity, the wire itself is apt to stretch or contract. The actual rotation angle of the distal side member can be adjusted by moving only the wire whose tension is larger with the actuator, and consequently the other wire whose tension is smaller stretches or contracts passively. In this robot, the actuator, which is unstable in terms of the relationship between the operation amount and the amount of change in the actual rotation angle of the distal side member, is not operated unnecessarily. 
   It is also preferable that the adjustor is constructed such that it will adjust the magnitude of modification performed by the first controller to be proportional to the tension of the first wire, and will adjust the magnitude of modification performed by the second controller to be proportional to the tension of the second wire. 
   It becomes possible to more appropriately adjust the operation amount of each actuator with respect to the deviation in the actual rotation angle of the distal side member so that it corresponds to the magnitude of the tension of each wire. 
   In the aforementioned robot, it is preferable that the robot further comprises a storage device for storing an expected value of the tension of the first wire and/or the second wire. 
   The tension of the first wire or the second wire can be estimated in advance on the basis of the expected operation of the robot. If the tension of the first wire or the tension of the second wire, estimated from the expected operation of the robot, is stored in advance, the first controller and the second controller can more accurately adjust the magnitude of the modification by which the instructed rotation angle is modified. 
   It is also preferable that the robot further comprises a sensor for measuring the tension of the first wire and/or the second wire. 
   Accordingly, the first controller and the second controller can more accurately adjust the magnitude of the modification by which the instructed rotation angle is modified on the basis of the actual tension of each wire. Even when an unexpected external force acts on the robot, it becomes possible to correctly adjust the actual rotation angle of the distal side member to the instructed rotation angle. 
   According to the present invention, it is possible to provide a technique for appropriately adding the deviation in a joint angle to the operation amount of an actuator which moves a wire back and forth, and to accurately adjust the joint angle to the instructed rotation angle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the basic configuration of each joint of a robot of an embodiment 
       FIG. 2  shows a major configuration of the controller of the embodiment 1. 
       FIG. 3  shows a major configuration of the controller of the embodiment 2. 
       FIG. 4  is a front view of both legs of the robot of the embodiment. 
       FIG. 5  is a side view of a left leg of the robot of the embodiment 
       FIG. 6  shows the structure of an ankle joint of the robot of the embodiments. 
       FIG. 7  shows the configuration of an actuator of the robot of the embodiments. 
       FIG. 8  shows the configuration of the controller of the robot of the embodiment 1. 
       FIG. 9  is a view illustrating a force relating to the ankle joint. 
       FIG. 10  shows the configuration of the embodiment 2. 
       FIG. 11  shows the relationship between the stretch and tension of a wire. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Features of Embodiment 1 
     FIG. 1  is a view schematically showing the configuration of a joint part of a robot. As shown in  FIG. 1 , the robot has a body side member  361 , a distal side member  363 , and a joint  362  which rotatably joints the distal side member  363  to the body side member. The distal side member  363  is adapted to be rotatable around an X axis with respect to the body side member  361 . 
   The robot has a first wire  366   a  an end of which is connected to a connection point  372   a  of the distal side member  363  located in one side of a rotation center (x in the figure), and a second wire  366   b  an end of which is connected to a connection point  372   b  of the distal side member  363  located in the other side of the rotation center. By pulling the first wire  366   a  and loosening the second wire  366   b , the distal side member  363  rotates in an A direction in the figure. By loosening the first wire  366   a  and pulling the second wire  366   b , the distal side member  363  rotates in a B direction in the figure. 
   The robot has a first actuator  368   a  which moves the other end of the first wire  366   a  back and forth, and a second actuator  368   b  which moves the other end of the second wire  366   b  back and forth. When the first actuator  368   a  moves the other end of the first wire  366   a  back and forth, and the second actuator  368   b  moves the other end of the second wire  366   b  back and forth, the robot can change the angle of the distal side member  363  with respect to the body side member  361 . Hereinafter, the angle of the distal side member  363  with respect to the body side member  361  is referred to as the joint angle of the joint  362 . 
   The robot has an encoder  472  disposed in the vicinity of the joint  362 . The encoder  472  is a sensor which detects an actual joint angle θmx of the joint  362 . Hereinafter, the actual joint angle of the joint is often referred to as an actual angle. 
   The robot has a controller  400  which controls an operation amount of the first actuator  368   a  and an operation amount of the second actuator  368   b . The controller  400  controls the operation amounts of the actuators  368   a  and  368   b  to thereby control the joint angle of the joint  362 . 
     FIG. 2  shows the configuration of the controller  400 . The controller  400  has major features of the controller  200  provided to the robot  10  of the embodiment 1 as described below. The controller  400  has a data storage device  402  as shown in  FIG. 2 . The data storage device  402  stores data required to operate the robot. The data storage device  402  stores joint angle data and load torque data, for example. 
   The joint angle data is data which describes a joint angle (instructed angle) of each joint when the robot actuates each joint to make a predetermined operation thereof over time. The joint angle data is prepared in advance by an operator of the robot, etc., and is taught in advance to the robot. The controller  400  controls the operation amount of actuators so that the joint angle of each joint will become an angle instructed by the joint angle data. Hereinafter, a joint angle described in the joint angle data is often referred to as an instructed angle. 
   The load torque data is data which describes a load torque of each joint which is expected when the robot actuates each joint to make a predetermined operation thereof over time. The load torque of a joint is an external torque applied from the outside, and is a torque to change a joint angle. That is, the load torque does not include a torque applied by wires. 
   The controller  400  has a differentiator  412 , a proportional integral derivative control (PID control) circuit  414 , a gain circuit  416 , an adder  418 , and a converter  434 . The differentiator  412 , the PID control circuit  414 , the gain circuit  416 , and the adder  418  are connected in series, and the data storage device  402  and the converter  434  are connected to each other by the series circuits. The gain circuit  416  is directly connected even to the data storage device  402 . The adder  418  is directly connected even to the data storage device  402 . The encoder  472  is connected to the differentiator  412 . 
   The differentiator  412  inputs an instructed angle θtx of the joint  362  from the data storage device  402 , inputs an actual angle θmx of the joint  362  from the encoder  472 , and outputs a deviation angle (θtx−θmx) therebetween. The deviation angle (θtx−θmx) represents an error between the instructed angle θtx and the actual angle θmx, and shows an angle required to modify the actual angle of the joint  362  to the instructed angle. 
   The PID control circuit  414  inputs the deviation angle (θtx−θmx) from the differentiator  412 , and outputs a modified deviation angle Δθx which is obtained by increasing and decreasing the deviation angle. If the magnitude (absolute value) |θtx−θmx| of the deviation angle is large, the PID control circuit  414  will output a modified deviation angle Δθx which is modified so that the deviation angle may be increased. The PID control circuit  414  cumulatively calculates the deviation angle, and outputs a modified deviation angle Δθx which is modified so that a larger cumulative value of the deviation angle may result in a further increased deviation angle. Further, the PID control circuit  414  calculates the change rate of the deviation angle, and outputs a modified deviation angle Δθx which is modified so that a smaller change rate of the deviation angle may result in a further increased deviation angle. In addition, increasing the deviation angle means that the (plus/minus) sign of the deviation angle (θtx−θmx) is kept unchanged, while the absolute value thereof is modified so that it may become large. A general-purpose PID control circuit, etc. can be used as the PID control circuit  414 . 
   The gain circuit  416  inputs the modified deviation angle Δθx from the PID control circuit  414 , inputs a load torque θtx of the joint  362  from the data storage device  202 , and outputs an amplified deviation angle Gx·Δθx. This coefficient Gx is a coefficient for amplifying the modified deviation angle Δθx. The gain circuit  416  will set a larger amplification coefficient Gx as the input load torque Etx is larger. The gain circuit  416  multiplies the input modified deviation angle Δθx by the set amplification coefficient Gx. 
   The adder  418  inputs the instructed angle θtx of the joint  362  from the data storage device  402 , inputs the amplified deviation angle Gx·Δθx from the gain circuit  416 , and outputs a modified instruction angle (θtx+Gx·Δθx). The adder  418  obtains the modified instruction angle (θtx+Gx·Δθx) by adding the instructed angle θtx to the amplified deviation angle Gx·Δθx. The modified instruction angle (θtx+Gx·Δθx) outputted by the adder  418  is an angle that has been modified from the instructed angle θtx with respect to the deviation between the instructed angle θtx and the actual angle θtm concerning the joint  362 . Here, as the load torque of the joint  362  is larger, the magnitude of the modification will be larger. 
   The converter  434  inputs the modified instruction angle from the adder  414 , and calculates a modified effective length La 2  for the first wire  366   a  and a modified effective length Lb 2  for the second wire  366   b  form the modified instruction angle. The effective length of a wire is the length of a wire projected from an actuator. If the effective lengths of the first wire  366   a  and the second wire  366   b  are adjusted to the modified effective length La 2  and Lb 2  calculated from the modified instruction angle, respectively, the joint angle of the joint  362  will be adjusted to the modified instruction angle. 
   As shown in  FIG. 2 , the controller  400  has a first driver  451  which controls the first actuator  368   a , and a second driver  452  which controls the second actuator  368   b . The first driver  451  and the second driver  452  are connected to the converter  434 . The first actuator  368   a  is connected to the first driver  451 . The second actuator  368   b  is connected to the second driver  452 . 
   The first driver  451  inputs the modified effective length La 2  for the first wire  366   a  calculated by the converter  434 , and calculates an operation amount of the first actuator  368   a  on the basis of the input modified effective length La 2 . And then, the first driver  451  operates the first actuator  368   a  by the calculated operation amount. The first driver  451  stores a reference relationship between an operation amount of the first actuator  368   a  and a length by which the first wire  366   a  is moved back and forth by the operation amount (or, a distance by which the other end of the first wire  366   a  moves back and forth). The first driver  451  calculates the operation amount of the first actuator  368   a  on the basis of the modified effective length La 2  and the stored reference relationship. 
   The second driver  452  stores a reference relationship between an operation amount of the second actuator  368   b , and a length by which the second wire  366   b  is moved back and forth by the operation amount (or, a distance by which the other end of the second wire  366   b  moves back and forth). The second driver  452  inputs the modified effective length Lb 2  for the second wire  366   b  calculated by the converter  434 , and calculates an operation amount of the second actuator  368   b  from the input modified effective length Lb 2 . And then, the second driver  452  operates the second actuator  368   b  by the calculated operation amount. 
   As described above, the controller  400  can calculate the modified instruction angle (θtx+Gx·Δθx) by modifying the instructed angle θtx of the joint  362  based upon the deviation between the instructed angle θtx and the actual angle θmx of the joint  362 , and can calculate the modified effective lengths La 2 , Lb 2  for the wires  366   a ,  366   b  based upon the modified instruction angle (θtx+Gx·Δθx). Then, the controller  400  can calculate the operation amount of the first actuator  368   a  from the modified effective length La 2 , and can calculate the operation amount of the second actuator  368   b  from the modified effective length Lb 2 . Accordingly, the operation amounts of the actuators  368   a ,  368   b  is calculated with respect to the deviation in the joint angle of the joint  362 . In the controller  400 , when the deviation in the joint angle of the joint  362  occurs, the operation amount of the first actuator  368   a  and the second actuator  368   b  are calculated so that the deviation will be removed. 
   In the controller  400 , when the instructed angle of the joint  362  is modified by the deviation between the instructed angle and the actual angle, the magnitude of the modification is adjusted by the PID control circuit  414  and the gain circuit  416 . Particularly, the magnitude of the modification is adjusted by the gain circuit  416  so that a larger load torque of the joint  362  may result in a larger magnitude of the instruction angle modification. As a result, when the load torque of the joint  362  is larger, the operation amount of the first actuator  368   a  or the second actuator  368   b  will be adjusted to be larger with respect to the deviation in the joint angle of the joint  362 . 
   While the robot operates, the joint  362  acts in various ways. For example, there is a case where the joint  362  operates to support the total weight of the robot, and there is also a case where the joint  362  operate to support only the weight of the distal side member  363 . The load torque of the joint  362  varies according to the operation of the robot. When the load torque applied to the joint  362  is large, the first wire  366   a  and the second wire  366   b  will stretch or contract substantially, and a large deviation in the joint angle of the joint  362  may result. When the load torque of the joint  362  is larger, the controller  400  modifies the instructed angle more substantially with respect to the magnitude of the deviation. Therefore, when the load torque of the joint  362  is larger, the first actuator  368   a  and the second actuator  368   b  perform larger operation so that the deviation is removed. Therefore, the deviation in the joint angle of the joint  362  will be removed rapidly, and the joint angle is accurately adjusted to the instruction angle. 
   On the other hand, when the load torque of the joint  362  is small, the first wire  366   a  and the second wire  366   b  will stretch or contract slightly, and therefore a large deviation in the joint angle of the joint  362  does not occur. As the load torque of the joint  362  is smaller, the controller  400  modifies the instructed angle more slightly with respect to the magnitude of the deviation. Therefore, neither the first actuator  368   a  nor the second actuator  368   b  operates excessively. This prevents the joint angle of the joint  362  from vibrating, for example. Since the deviation occurs slightly, the deviation can be removed rapidly and the joint angle is accurately adjusted to the instructed angle. 
   The controller  400  can appropriately add the deviation in the joint angle of the joint  362  to the operation amount of the first actuator  368   a  or the second actuator  368   b , thereby adjusting the joint angle of the joint  362  accurately to an instructed angle. 
   Features of Embodiment 2 
     FIG. 3  shows a controller  404 . The controller  404  has major features of the controller provided to the robot of the embodiment 2 as described below. The controller  404  can be used for controlling the operation amount of the first actuator  368   a  and the second actuator  368   b  shown in  FIG. 1  similarly to the controller  400 . The controller  404  can replace the controller  400  for controlling the robot shown in  FIG. 1 . 
   Hereinafter, although the controller  404  will be described, the same components as those of the controller  400  shown in  FIG. 1  are denoted by the same reference numerals, and the detailed description thereof is omitted so as to avoid repeated description. 
   As shown in  FIG. 3 , the controller  404  has the data storage device  402 . The data storage device  402  stores joint angle data and expected tension data The expected tension data is data which describes a tension expected to be generated in each wire when the robot actuates each joint to make a predetermined operation thereof over time. 
   The controller  404  has the differentiator  412 , the PID control circuit  414 , the adder  418 , a first converter  432 , and a second converter  434 . The first converter  432  is connected to the data storage device  402 . The differentiator  412 , the PID control circuit  414 , and the adder  418  are connected in series, and the data storage device  402  and the second converter  434  are connected to each other by the series circuits. 
   The adder  418  inputs an instructed angle Δθx of the joint  362  from the data storage device  402 , inputs a modified deviation angle Δθx from the PID control circuit  414 , and outputs a modified instruction angle (θtx+Δθx) obtained by adding the instructed angle θtx to the modified deviation angle Δθx. The modified instruction angle (θtx+Δθx) output by the adder  418  is an angle which is obtained by modifying the instructed angle θtx of the joint  362  according to the deviation between the instructed angle θtx and the actual angle θtx. 
   The first converter  432  and the second converter  434  are almost the same as the converter  434  in the controller  400 . Here, the first converter  432  inputs the instructed angle θtx of the joint  362  from the data storage device  402 , and calculates an expected effective length La 1  for the first wire  366   a  and an expected effective length Lb 1  for the second wire  366   b  from the instructed angle. The second converter  434  inputs the modified instruction angle (θtx+Δθx) from the adder  414 , and calculates a modified effective length La 2  for the first wire  366   a  and a modified effective length Lb 2  for the second wire  366   b  from the modified instruction angle. 
   The controller  404  has a first variable distributor  461  and a second variable distributor  462 . The first converter  432 , the second converter  434 , and the data storage device  402  are connected to the input part of the first variable distributor  461 . The first driver  451  is connected to the output part of the first variable distributor  461 . The first converter  432 , the second converter  434 , and the data storage device  402  are connected to the input part of the second variable distributor  462 . The second driver  452  is connected to the output part of the second variable distributor  462 . 
   The first variable distributor  461  inputs the expected effective length La 1  for the first wire  366   a  from the first converter  432 , inputs the modified effective length La 2  for the first wire  366   a  from the second converter  434 , and inputs an expected tension Ta of the first wire  366   a  from the data storage device  402 . And then, the first variable distributor  461  calculates a distributed effective length from the input expected effective length La 1  and modified effective length La 2 . The distributed effective length calculated by the first variable distributor  461  is a value between the expected effective length La 1  and the modified effective length La 2 . And, the distributed effective length is set to be near to the modified effective length La 2  as the tension of the first wire  366   a  is larger. The first variable distributor  461  input the expected tension Ta of the first wire  366   a  from the data storage device  202 , and calculates the distributed effective length expressed by the following equation.
 
(Distributed effective length)= La 1+( La 2− La 1)· k  
 
k in the above equation is 0 (zero)≦k≦1, and is a coefficient proportional to the tension of the first wire  366   a . The distributed effective length calculated by the first variable distributor  461  can be considered as a value which is modified by adding the deviation in the joint angle of the joint  362  to the expected effective length La 1  calculated from the instruction angle of the joint  362 . The magnitude of the modification becomes larger as the tension of the first wire  366   a  is larger, and especially, is proportional to the tension of the first wire  366   a . The second variable distributor  462  calculates the distributed effective length (Lb 1 +(Lb 2 −Lb 1 )·k) for the second wire  366   b  similarly to the first variable distributor  461 . In addition, the coefficient k which is used for calculation by the second variable distributor  462  is determined from the tension of the second wire  366   b , and differs from the coefficient k which is used for calculation by the first variable distributor  461 .
 
   The first driver  451  inputs the distributed effective length of the first wire  366   a  from the first variable distributor  461 , and calculates an operation amount of the first actuator  368   a  from the distributed effective length. The operation amount calculated from the distributed effective length can be considered as an operation amount calculated from an angle which is obtained by modifying an instructed angle of the joint  362  according to the deviation angle between the instructed angle and the actual angle. The magnitude of the modification of the instructed angle will be larger as the tension of the first wire  366   a  is larger. The second driver  452  calculates an operation amount of the second actuator  368   b  similarly to the first driver  451 . As a result, when the tension of the first wire  366   a  is larger than the tension of the second wire  366   b , the first driver  451  calculates the operation amount from an angle which is obtained by modifying the instructed angle more substantially than the second driver  452 . When the tension of the second wire  366   b  is larger than the tension of the first wire  366   a , the second driver  452  calculates the operation amount from an angle which is obtained by modifying the instructed angle more substantially than the first driver  451 . The first driver  451  and the second driver  452  operate the first actuator  368   a  and the second actuator  368   b  by the calculated operation amount, respectively. 
   The controller  404  calculates the expected effective length La 1  for the first wire  366   a  and the expected effective length Lb 1  for the second wire  366   b  from the instructed angle of the joint  362 . The expected effective lengths La 1  and Lb 1  are calculated without considering the deviation in the joint angle of the joint  362 . Further, the controller  404  calculates the modified effective length La 2  for the first wire  366   a  and the modified effective length Lb 2  for the second wire  366   b  from the modified instruction angle which is obtained by modifying the instructed angle of the joint  362  according to the deviation between the instructed angle and the actual angle. The modified effective lengths La 2  and Lb 2  are calculated with considering the deviation in the joint angle of the joint  362 . Then, the controller  404  calculates the distributed effective length for the first wire  366   a  from the expected effective length La 1  and modified effective length La 2  for the first wire  366   a . At this time, as the tension of the first wire  366   a  is larger, the distributed effective length will be near to the effective length La 2 . That is, as the tension of the first wire  366   a  is larger, the distributed effective length for the first wire  366   a  will be more substantially affected by the deviation in the joint  362 . The distributed effective length for the second wire  366   b  is calculated similarly to that for the first wire  366   a . As a result, in the first wire  366   a  and the second wire  366   b , the distributed effective length for the wire with a larger tension will be more substantially affected by the deviation in the joint angle the joint  362 . 
   In the controller  404 , the operation amounts of the first actuator  368   a  and the second actuator  368   b  are calculated from the distributed effective lengths for the first wire  366   a  and the second wire  366   b , respectively. As a result, when the tension of the first wire  366   a  is larger than the tension of the second wire  366   b , the operation amount of the first actuator  368   a  will be more substantially modified with respect to the deviation in the joint angle of the joint  362  than the operation amount of the second actuator  368   b . Conversely, when the tension of the second wire  366   b  is larger than the tension of the first wire  366   a , the operation amount of the second actuator  368   b  will be more substantially modified with respect to the deviation in the joint angle of the joint  362  than the operation amount of the first actuator  368   a.    
   As described previously, while the robot operates, the load torque applied to the joint  362  varies according to the operation of the robot. When the load torque is applied to the joint  362 , the tension of either the first wire  366   a  or the second wire  366   b  will increase, while the tension of the other one will decrease. As the load torque of the joint  362  varies every moment, the tensions of the first wire  366   a  and the tension the second wire  366   b  also vary every moment. Since the rigidities of the wires vary depending on the tension of the wire, the rigidity of the first wire  366   a  and the second wire  366   b  will vary every moment according to the operation of the robot. 
   When the rigidity of the wire varies, the relationship between the operation amount of the actuator which moves the wire and the amount of change in the joint angle caused by the operation amount also varies. In particular, when the tension of the wire is small, the rigidity of the wire is low and is apt to vary. A delay may occur in the change (so-called responsiveness) of the joint angle with respect to the operation of the actuator, if the operation amount of the actuator is modified substantially with respect to the deviation in the joint angle. As a result, the joint angle may be vibrating. On the other hand, when the tension of the wire is large, the rigidity of the wire is high and stable. The deviation in the joint angle can be rapidly removed by modifying the operation amount of the actuator substantially with respect to the deviation. The joint angle can now be accurately adjusted to an instructed angle. 
   When the controller  404  calculates the operation amount of the first actuator  368   a  and the operation amount of the second actuator  368   b , the controller  404  adds the deviation in the joint angle more largely to the operation amount of the actuator which moves the wire, whose tension is larger, than to the operation amount of the other actuator, whose tension is smaller. When the deviation in the joint angle of the joint  362  occurs, the controller  404  operates the actuator for the wire with a larger tension substantially with respect to the deviation, while it operates the other actuator for the other wire with a smaller tension slightly with respect to the deviation. That is, the controller  404  causes a wire which is high and stable in rigidity to be moved substantially with respect to the deviation, and causes a wire which is low and unstable in rigidity to be moved slightly with respect to the deviation. Accordingly, the deviation in the joint angle of the joint  362  can be rapidly removed, and the joint angle can be prevented from vibrating. 
   The controller  404  can appropriately add the deviation caused in the joint angle of the joint  362  to the operation amounts of the first actuator  368   a  and the second actuator  368   b , thereby adjusting the joint angle of the joint  362  accurately to the instructed angle. 
   Embodiment 1 
   An embodiment of the present invention will be described with reference to the drawings. The present embodiment applies the technique of the present invention to a humanoid robot. 
     FIG. 4  is a front view of a lower body of a robot  10 .  FIG. 5  is a side view of the lower body of the robot  10 .  FIG. 6  is a view showing the structure of an ankle joint  FIG. 7  is a view showing the configuration of an actuator. Although not shown, the robot  10  additionally has a head part, an upper body, an upper arm, a lower arm, etc. 
   In the present embodiment, an anteroposterior direction (traveling direction of the robot  10 ) of a foot part is defined as an X-axis, a horizontal direction is defined as a Y axis, and a direction in which a lower leg part or a body extends is defined as a Z axis. The axes are orthogonal to each other. 
   As shown in  FIG. 4 , the robot  10  in the present embodiment has right and left legs  12 . The shape of the right and left legs  12  is mirror-symmetrical. The leg  12  is mainly composed of a thigh part  14 , a lower leg (shin) part  16 , and a foot part  18 . The thigh part  14  and the body part  20  are jointed by a hip joint  22 . The thigh part  14  and the lower leg part  16  are jointed by a knee joint  24 . The lower leg part  16  and the foot part  18  are jointed by an ankle joint  26 . 
   With reference to  FIGS. 4 ,  5 , and  6 , the hip joint  22 , the knee joint  24 , and the ankle joint  26  will be described in order. First, the hip joint  22  will be described. A disk  36  which rotates around the Z axis is attached to a plate-like pelvic part  28  via a bearing  34  (refer to  FIG. 5 ). A pair of right and left disks  36  are provided. A shaft  30  extending from the pelvic part  28  side toward the thigh part  14  (extending in the Z axis direction) is fixed to the center of each disk  36 . The shaft  30  rotates around the Z axis with respect to the pelvic part  28 . 
   An upper end of the thigh part  14  is connected to a lower end of a shaft  30  via a universal joint  32 . The universal joint  32  permits the thigh part  14  to rotate around the X axis and around the Y axis with respect to the shaft  30 . 
   The hip joint  22  has the shaft  30  which can rotate around the Z axis with respect to the pelvic part  28 , and the universal joint  32  which permits the thigh part  14  to rotate around the X axis and around the Y axis with respect to the shaft  30 , and constitutes a triaxial joint which is rotatable around each of the X, Y, and Z axes. 
   Next, the knee joint  24  will be described. Two parallel flanges  40  extend downward at a lower end of each thigh part  14 . Two parallel flanges  44  extend upward at an upper end of a shaft  42  constituting each lower leg part  16 . The knee joint  24  has a shaft  46  which extends in the Y axis direction through these flanges  40  and  44 . The knee joint  24  permits the lower leg part  16  to rotate around the Y axis with respect to the thigh part  14 . 
   Next, the ankle joint  26  will be described. Since  FIG. 6  shows the simplified structure of the ankle joint  26 , the shape or dimension of the angle joint does not necessarily coincide with an actual shape or actual dimension. Two parallel flanges  58  extend downward at a lower part of the shaft  42  of each lower leg part  16 . Two parallel flanges  60  extend upward at the top face of the foot part  18 . The flanges  58  of the lower leg part  16  and the flanges  60  of the foot part  18  are jointed by a cross tip universal coupling  62  to constitute a universal joint. The ankle joint  26  permits the foot part  18  to rotate around the X axis and around the Y axis with respect to the lower leg part  24 . That is, the ankle joint  26  is a biaxial joint which has the degree of freedom for each of the X and Y axes. 
   Each joint of the robot  10  is driven using a wire (The rotation of a hip joint around the Z axis excluded. Only this rotation is directly rotated by a motor without using a wire). Each wire has an end connected to a distal side member, and the other end connected to an actuator. The actuator moves each wire back and forth with respect to the distal side member. 
   As shown in  FIGS. 4 and 5 , the robot  10  has, for example, a wire  50   a  and an actuator  52   a  which moves the wire  50   a  back and forth, a wire  50   b  and an actuator  52   b  which moves the wire  50   b  back and forth, a wire  50   c  and an actuator  52   c  which moves the wire  50   c  back and forth, etc. These control mainly the operation of the hip joint  22 . As shown in  FIGS. 4 and 5 , the robot  10  has a wire  66   a  and an actuator  68   a  which moves the wire  66   a  back and forth, a wire  66   b  and an actuator  68   b  which moves the wire  66   b  back and forth, a wire  66   c  and an actuator  68   c  which moves the wire  66   c  back and forth, a wire  66   d  and an actuator  68   d  which moves the wire  66   d  back and forth, etc. These mainly control the operation of the knee joint  24  or the ankle joint  26 . 
   The wires used for the robot  10  have the relationship between tension and stretch as previously described with reference to  FIG. 11 . That is, the rigidity of each wire changes depending on a caused tension. Particularly, the rigidity is low in a state where a small tension is caused, and as the tension changes, the rigidity is also apt to change. 
   With reference to  FIG. 6 , the wires  66   a ,  66   b , and  66   c  which drive the ankle joint  26  will be described. Wire termination guides  70   a ,  70   b , and  70   c  are fixed to the foot part  18 . Each of the wire termination guides  70   a ,  70   b , and  70   c  is circular arc-shaped, the central axis of each circular arc extends in the Y axis direction, and the surface of the circular arc has a predetermined width (distance extending along the Y axis). The wire termination guide  70   a  is on X axis, and is disposed further ahead than the ankle joint  26  in the X axis direction. The circular arc surface of the wire termination guide  70   a  faces the front direction of the X axis. The wire termination guides  70   b  and  70   c  are located further behind than the ankle joint  26  in the X axis direction. The wire termination guide  70   b  is located outside the ankle joint  26 , and the wire termination guide  70   c  is located inside the ankle joint  26 . The circular arc surface of the wire termination guide  70   b ,  70   c  faces the rear direction of the X axis. 
   Lower ends of the three wires  66   a ,  66   b , and  66   c  are fixed to wire connection points  72   a ,  72   b , and  72   c , respectively, of the lower ends of the wire termination guides  70   a ,  70   b , and  70   c  (the wire connection point  72   c  is shown in  FIG. 4 ). The other end of each of the wires  66   a ,  66   b , and  66   c  extends toward the knee joint  24 . The wire termination guides  70   a ,  70   b , and  70   c  prevent the wires  66   a ,  66   b , and  66   c  from being sharply bent with a small radius of curvature. 
   By the above configuration, by loosening the wires  66   b  and  66   c  in the same way while the wire  66   a  is pulled toward the knee joint  24 , the foot part  18  rotates in one direction around the Y axis of the ankle joint  26 , and the tiptoe side (the left in the X axis direction of  FIG. 6 ) of the foot part  18  operates to rise. Otherwise, by pulling the wires  66   b  and  66   c  toward the knee joint  24  in the same way while the wire  66   a  is loosened, the foot part  18  rotates in the other direction around the Y axis of the ankle joint  26 , and the heel side (the right in the X axis direction of  FIG. 6 ) of the foot part  18  operates to rise. 
   Further, by loosening the wire  66   c  while the wire  66   b  is pulled toward the knee joint  24 , the foot part  18  rotates in one direction around the X axis of the ankle joint  26 , and the outside (the right in the Y axis direction of  FIG. 6 ) of the foot part  18  operates to rise. By pulling the wire  66   c  toward the knee joint  24  while the wire  66   b  is loosened, the foot part  18  rotates in the other direction around the X axis of the ankle joint  26 , and the inside (the left in the Y axis direction of  FIG. 6 ) of the foot part  18  operates to rise. 
   By combining the above operations, the joint angle of the ankle joint  26  around the X axis and the joint angle of the ankle joint around the Y axis can be independently adjusted by moving the three wires  66   a ,  66   b , and  66   c  back and forth. In addition, the positions of the wire connection points  72   a ,  72   b , and  72   c  are not limited to those in the present embodiment. 
   Next, the wires which control the operation of the knee joint  24  will be described. The operation of the knee joint  24  is adjusted using the wires  66   a ,  66   b ,  66   c , and  66   d . As shown in  FIG. 6 , three pulleys  64   a ,  64   b , and  64   c  are arranged alternately with the two flanges  44  at an upper portion of the shaft  42  of the lower leg part  16 . The three pulleys  64   a ,  64   b , and  64   c  are supported so as to be rotatable around a shaft  46  which passes through the flanges  44  in the Y axis direction. The wires  66   a ,  66   b , and  66   c  are wound around the pulleys  64   a ,  64   b , and  64   c , respectively. The wires  66   a ,  66   b , and  66   c  are separated from the pulleys on the front side of the pulleys  64   a ,  64   b , and  64   c . Further, as shown well in  FIGS. 4 and 5 , the wire  66   d  is fixed by the flanges  44  around the rear side of the X axis of the knee joint  24 . 
   By the above configuration, by loosening the wire  66   d  while the three wires  66   a ,  66   b , and  66   c  are pulled in the same way toward the thigh part  14 , the knee joint  24  rotates in one direction around the Y axis, and the knee joint  24  operates to extend. By pulling the wire  66   d  toward the thigh part  14  while the three wires  66   a ,  66   b , and  66   c  are loosened in the same way, the knee joint  24  rotates in the other direction around the Y axis, and the knee joint  24  operates to bend. When the three wires  66   a ,  66   b , and  66   c  are made to simultaneously move back and forth at the same speed, the knee joint  24  can be rotated without rotating the ankle joint  26 . 
   As shown in  FIGS. 4 and 5 , the actuators  68   a ,  68   b ,  68   c , and  68   d  which move the wires  66   a ,  66   b ,  66   c , and  66   d  back and forth are disposed in the thigh part  14 . In the robot  10 , even an actuator for adjusting the rotation angle of the ankle joint  26  as well as the knee joint  24  is disposed in the thigh part  14 . Accordingly, the distal side of a leg  12  is configured lightly, and the moment of inertia around the hip joint  22  is suppressed low. The robot  10  can operate the lower leg  12  with a small torque. 
   Next, the wires which control the operation of the hip joint  22  will be described. As shown in  FIGS. 4 and 5 , ends of the wires  50   a ,  50   b , and  50   c  which drive the hip joint  22  are also fixed to lower ends  49   a ,  49   b , and  49   c  of the wire termination guides  48   a ,  48   b , and  48   c . The rotation angle of the hip joint  22  around the X axis and the rotation angle of the hip joint around the Y axis can be independently adjusted by moving wires  50   a ,  50   b , and  50   c  back and forth, respectively. Further, the disk  36  which is rotatable in the pelvic part  28  is rotated around the Z axis by a motor  38 . The motor  38  is fixed to the pelvic part  28 . The rotation angle of the hip joint  22  around the Z axis is adjusted by the motor  38 . 
   With reference to  FIG. 7 , actuators which move the wires back and forth will be described.  FIG. 7  shows the actuator  68   a  which moves the wire  66   a  back and forth. The actuator  68   a  has a pair of flanges  102  and  106 , and three guide rods  108 ,  110 , and  112  which connect them together. A feed screw  120  is disposed between the pair of flanges  102  and  106 . The feed screw  120  is supported to be rotatable, but not to be movable in its axial direction. A movable plate  104  is threadedly engaged with the feed screw  120 . The movable plate  104  has the structure of being guided by the guide rods  108 ,  110 , and  112 . An end of the wire  66   a  is fixed to the movable plate  104 . The actuator  68   a  has a motor  114 . The motor  114  is connected to the feed screw  120  via a gear  116  and a gear  118 . 
   When the motor  114  rotates, the feed screw  120  rotates. When the feed screw  120  rotates, the movable plate  104  slides along the guide rods and the wire  66   a  is pulled in or fed out. The rotational amount of the motor  114  is proportional to an amount by which a connecting end of the wire  66   a  connected to the movable plate  104  moves back and forth. The motor  114  is connected to a first driver  251  described in the latter section, and the operation of the motor  114  is adjusted by the first driver  251 . 
   In the robot  10  the actuators  48   b ,  48   c ,  68   a ,  68   b ,  68   c , and  68   d  which move the other wires  50   b ,  50   c ,  66   a ,  66   b ,  66   c , and  66   d  back and forth have the same structure as shown in  FIG. 7 . In addition, the actuators which move the wires back and forth are not limited to this type. 
   Next, the controller which controls the operation of the robot  10  will be described. The body part of the robot  10  (whose illustration is omitted) is provided with a controller which controls the operation of the actuators  48   b ,  48   c ,  68   a ,  68   b ,  68   c , and  68   d , etc. Hereinafter, taking the ankle joint  26  as an example, a method in which the controller controls the operation of the actuators  68   a ,  68   b , and  68   c  which operate the ankle joint  26  will be described. 
     FIG. 8  shows the configuration of a portion of a controller  200  included in the robot  10 .  FIG. 8  shows mainly a portion of the controller  200  for controlling the operation of the actuators  68   a ,  68   b , and  68   c . The portion of the controller  200  shown in  FIG. 8  controls the operation of the actuators  68   a ,  68   b , and  68   c  arranged in one of the right and left legs  12 . The controller  200  further includes a set of components shown in  FIG. 8  in order to control the operation of the actuators  68   a ,  68   b , and  68   c  arranged in the another leg  12 . 
   As shown in  FIG. 8 , the controller  200  has the data storage device  202 . The data storage device  202  stores joint angle data, load torque data, expected tension data, etc., for example. 
   The joint angle data is data which describes a joint angle (instructed angle) of each joint, when the robot  10  actuates each joint to make a predetermined operation thereof over time. For example, the joint angle data describes time-series data which describe an instructed angle θtx of the ankle joint  26  around the X axis, and time-series data which describe an instructed angle θty of the ankle joint around the Y axis. 
   The load torque data is data which describes a load torque expected to be applied thereto when the robot actuates each joint to make a predetermined operation thereof over time. The load torque data describes the load torque of each joint in its rotative direction over time. The load torque data describes, for example, an expected load torque Etx of the ankle joint  26  around the X axis and an expected load torque Ety of the ankle joint around the Y axis over time. 
   The expected tension data is data which describes a tension expected to be generated in each wire when the robot  10  actuates each joint to make a predetermined operation thereof over time. For example, as for the ankle joint  26 , the expected tension data describes the expected value of the tension Ta caused in the wire  66   a , the expected value of the tension Tb caused in the wire  66   b , and the expected value of the tension Tc caused in the wire  66   c  over time. 
   Referring to  FIG. 9 , taking the ankle joint  26  as example, a load torque applied to the ankle joint  26 , and tensions to be caused in the wires  66   a ,  66   b  and  66   c  will be described.  FIG. 9(   a ) shows a state where the foot part  18  is located in the air.  FIG. 9(   b ) shows a state where the foot part  18  makes contact with a ground surface H. It is assumed that the instructed angles (θtx, θty) concerning the ankle joint  26  are equal to each other in a point of time shown in  FIG. 9(   a ), and a point of time shown in  FIG. 9(   b ). 
   In the state where the foot part  18  is located in the air as shown in  FIG. 9(   a ), for example, the gravity Wt of the foot part  18 , etc. acts on the foot part  18 . The gravity Wt tends to rotate the ankle joint  26  around the Y axis. Such an external torque (except for torques caused by the wires  66   a ,  66   b , and  66   c ) which tends to change the joint angle of the ankle joint  26  around the Y axis is referred to as the load torque of the ankle joint  26  around the Y axis. In this state, when the load torque of the ankle joint  26  around the Y axis and the torques applied to the ankle joint  26  around the Y axis caused by the tensions Ta, Tb, and Tc of the wires  86   a ,  86   b , and  86   c  are balanced with each other in a state where the joint angle of the ankle joint  26  around the Y axis is the instructed angle θty, the joint angle of the ankle joint  26  around the Y axis is maintained at the instructed angle θty. 
   In the state where the foot part  18  makes contact with the ground surface H as shown in  FIG. 9(   b ), for example, the gravity Wt of the foot part  18 , a reaction force F of the foot part  18  from the ground surface H, etc. act on the foot part  18 . The gravity Wt and reaction force F tend to rotate the ankle joint  26  around the Y axis. When the load torque of the ankle joint  26  around the Y axis caused by the gravity W, the reaction force F, etc. and the torques applied to the ankle joint  26  around the Y axis caused by the tensions Ta, Tb, and Tc of the wires  86   a ,  86   b , and  86   c  are balanced with each other in a state where the joint angle of the ankle joint  26  around the Y axis is the instructed angle θty, the joint angle of the ankle joint  26  around the Y axis is maintained at the instructed angle θty. 
   As apparent from comparison between  FIGS. 9(   a ) and  9 ( b ), even when the instructed angles (θtx, θty) of the ankle joint  26  are equal to each other, the load torque of the ankle-joint  26  around the Y axis changes every moment following the operation of the robot. As the load torque changes every moment, the tension Ta, Tb, and Tc of the wires  66   a ,  66   b , and  66   c  also need to change every moment. This is not limited to the ankle joint  26 , but is similarly applied to about each of the other joints. 
   When the tension of each of the wires  66   a ,  66   b , and  66   c  changes, each of the wire  66   a ,  66   b , and  66   c  will stretch according to the tension change. As each of the wires  66   a ,  66   b , and  66   c  stretches, the joint angle of the ankle joint  26  changes even when the actuator  68   a ,  68   b , or  68   c  which moves each wire back and forth does not operate. In other words, it is necessary to calculate the operation amount of each of the actuators  68   a ,  68   b , and  68   c  in consideration of the extension of each of the wires  66   a ,  66   b , and  66   c.    
   The robot  10  previously grasps the load torque of each joint which changes every moment following its own operation, and the tension of each wire which changes every moment following its own operation. 
   As shown in  FIG. 8 , the controller  200  has a first converter  232 . The first converter  232  inputs the instructed angles (θtx, θty) of the ankle joint  26  around the X and Y axes, and calculates and outputs expected effective lengths La 1 , Lb 1 , and Lc 1  for the wires  66   a ,  66   b , and  66   c , respectively. The first converter  232  corresponds to the first converter  432  shown in  FIG. 3 . The first converter  232  calculates the effective length for each wire similarly to the first converter  432  shown in  FIG. 3 . When the effective length for each wire is adjusted by the expected effective lengths La 1 , Lb 1 , and Lc 1  calculated from the instructed angles (θtx, θty), the joint angles of the ankle joint  26  around the X and Y axes will be adjusted to the instructed angles (θtx, θty). 
   The controller  200  has a second converter  234 . The second converter  234  itself is the same as the first converter  232 . 
   The controller  200  has a first differentiator  212 , a first proportional integral derivative control (PID control) circuit  214 , a first gain circuit  216 , and a first adder  218 . The first differentiator  212 , the first PID control circuit  214 , the first gain circuit  216 , and the first adder  218  are connected in series, and the series circuit connects the data storage device  202  with the second converter  234 . 
   The controller  200  has a second differentiator  222 , a second proportional integral derivative control (PID control) circuit  224 , a second gain circuit  226 , and a second adder  228 . The second differentiator  222 , the second PID control circuit  224 , the first gain circuit  226 , and the first adder  228  are connected in series, and the series circuit connects the data storage device  202  with the second converter  234 . The first differentiator  212  and the second differentiator  222  are the same as each other. Similarly, the first PID control circuit  214  and the second PID control circuit  224  are the same as each other, the first gain circuit  216  and the second gain circuit  226  are the same as each other, the first adder  218  and the second adder  228  are the same as each other. 
   As shown in  FIG. 8 , the first gain circuit  216  and the second gain circuit  226  are directly connected even to a data storage device  216 . The first adder  218  and the second adder  228  are directly connected even to the data storage device  216 . 
   The controller  200  has a first encoder  272  which detects an actual joint angle (actual angle) θmx of the ankle joint  26  around the X axis, and a second encoder  274  θmy which detects an actual joint angle (actual angle) θmx of the ankle joint  26  around the Y axis. The first encoder  272  is connected to the first differentiator  212 . The second encoder  274  is connected to the second differentiator  222 . Although not shown in  FIGS. 4 ,  5 , and  6 , the first encoder  272  and the second encoder  274  are disposed in the vicinity of the ankle joint  26 . A set of the first encoder  272  and the second encoder  274  are disposed in each of the right and left legs  12 . 
   The first differentiator  212  inputs an instructed angle θtx of the ankle joint  26  around the X axis from the data storage device  202 , and inputs an actual angle θmx of the ankle joint  26  from the first encoder  272 , and outputs a deviation angle (θtx−θmx) therebetween. 
   The first PD control circuit  214  inputs the deviation angle (θtx−θmx) from the first differentiator  212 , and outputs a modified deviation angle Δθx which is modified by increasing and decreasing the deviation angle. The first PID control circuit  214  calculates the modified deviation angle Δθx in a way similar to the PID control circuit  414  shown in  FIG. 2 . 
   The first gain circuit  216  inputs the modified deviation angle Δθx from the first PID control circuit  214 , inputs a load torque Etx of the ankle joint  26  from the data storage device  202 , and outputs an amplified deviation angle Gx·Δθx. This coefficient Gx is a coefficient for amplifying the modified deviation angle Δθ. The first gain circuit  216  calculates the amplified deviation angle Gx·Δθx in a way similar to the gain circuit  416  described in Feature  1 . 
   The first adder  218  inputs the instructed angle θtx of the ankle joint  26  from the data storage device  202 , inputs the amplified deviation angle Gx·Δθx from the first gain circuit  216 , and outputs a modified instruction angle (θtx+Gx·Δθx) obtained by adding the instructed angle θtx to the amplified deviation angle Gx·Δθx. The modified instruction angle (θtx+Gx·Δθx) output by the first adder  218  is an angle which is obtained by modifying the instructed angle θtx of the ankle joint  26  around the Y axis according to the deviation between the instructed angle θtx and the actual angle θtm. The magnitude of the modification is adjusted so that a larger load torque Etx of the ankle joint  26  around Y axis may result in a larger magnitude of modification. 
   The second differentiator  222 , the second PID control circuit  224 , the second gain circuit  226 , and the second adder  228  perform the same processing as that in the ankle joint  26  around the Y axis. The second adder  228  outputs the modified instruction angle (θty+Gy·Δθy) of the ankle joint  26  around the Y axis. 
   The second converter  234  inputs the modified instruction angles (θtx+Gx·Δθx, θty+Gy·Δθy) of the ankle joint  26  around the X and Y axes from the first adder  218  and the second adder  228 , and calculates and outputs expected effective lengths La 2 , Lb 2 , and Lc 2  for the wires  66   a ,  66   b , and  66   c , respectively. When the effective length for each wire is adjusted by the expected effective lengths La 2  Lb 2 , and Lc 2  calculated from the instructed angles (θtx, θty), the joint angles of the ankle joint  26  around the X and Y axes will be adjusted to the modified instruction angles (θtx+Gx·Δθx, θty+Gy·Δθy). 
   The controller  200  has a first driver  251  which controls the operation of the actuator  68   a , a second driver  252  which controls the operation of the actuator  68   b , and a third driver  253  which controls the operation of the actuator  68   c.    
   The controller  200  has a first selector  241 , a second selector  242 , and a third selector  243 . The first selector  241  is interposed in a circuit which connects the first converter  232  and the second converter  234  to the first driver  251 . The second selector  242  is interposed in a circuit which connects the first converter  232  and the second converter  234  to the second driver  252 . The third selector  243  is interposed in a circuit which connects the first converter  232  and the second converter  234  to the third driver  253 . The first selector  241  is constructed to selectively connect one of the first converter  232  and the second converter  234  to the first driver  251 . The second selector  242  is constructed to selectively connect one of the first converter  232  and the second driver  252  to the second driver  252 . The third selector  243  is constructed to selectively connect one of the first converter  232  and the second converter  234  to the third driver  253 . 
   The controller  200  has a first switching unit  261 , a second switching unit  262 , and a third switching unit  263 . The first switching unit  261  is connected to the first selector  241 . The second switching unit  262  is connected to the second selector  242 . The third switching unit  263  is connected to the third selector  243 . Further, the first switching unit  261 , the second switching unit  262 , and the third switching unit  263  are connected even to the data storage device  202 . 
   The first switching unit  261  inputs an expected tension Ta of the wire  66   a  from the data storage device  202 , and switches the first selector  241  on the basis of the value of the expected tension Ta of the wire  66   a . When the expected tension Ta of the wire  66   a  is smaller than a predetermined value, the first switching unit  261  switches the first selector  241  so as to connect the first converter  232  to the first driver  251 . Further, when the expected tension Ta of the wire  66   a  is larger than a predetermined value, the first switching unit  261  switches the first selector  241  so as to connect the second converter  234  to the first driver  251 . Accordingly, when the tension of the wire  66   a  is small, the expected effective length La 1  is input to the first driver  251  from the first converter  232 . And, when the tension of the wire  66   a  is large, the modified effective length La 2  is input to the first driver  251  from the second converter  234 . 
   Similarly, the second switching unit  262  switches the second selector  242  on the basis of the expected tension Tb of the wire  66   b . That is, when the tension of the wire  66   b  is small, the expected effective length Lb 1  is input to the second driver  252  from the first converter  232 . And, when the tension of the wire  66   b  is large, the modified effective length Lb 2  is input to the second driver  252  from the second converter  234 . Similarly, the third switching unit  263  switches the third selector  243  on the basis of the value of the expected tension. To of the wire  66   c . That is, when the tension of the wire  66   c  is small, the expected effective length Lc 1  is input to the third driver  253  from the first converter  232 . And, when the tension of the wire  66   c  is large, the modified effective length Lc 2  is input to the third driver  253  from the second converter  234 . 
   The first driver  251  calculates an operation amount of the actuator  68   a  on the basis of the inputted one of the expected effective length La 1  and modified effective length La 2  for the wire  66   a , and operates the actuator  68   a  by the calculated operation amount. The first driver  251  stores a reference relationship between a rotation angle of the motor  114  of the actuator  68   a  and a length by which the wire  66   a  is moved back and forth by the operation of the actuator. The first driver  251  calculates the operation amount of the actuator  68   a  on the basis of the input effective length for the wire  66   a  and a stored reference relationship. 
   Similarly, the second driver  252  calculates an operation amount of the actuator  68   b , and operates the actuator  68   b  by the calculated operation amount. The third driver  253  calculates an operation amount of the actuator  68   c , and operates the actuator  68  by the calculated operation amount. 
   With the configuration as described above, the controller  200  calculates the targeted expected effective lengths La 1 , Lb 1 , and Lc 1  for the wires  66   a ,  66   b , and  66   c  from the instructed angles of the ankle joint  26  around the X and Y axes. The expected effective lengths La 1 , Lb 1 , and Lc 1  are calculated without adding deviations caused in the joint angle of the ankle joint  26 . Further, the controller  200  calculates modified instruction angles around the X and Y axes, which are obtained by modifying the instructed angles of the ankle joint  26  on the basis of deviations between the instructed angles and actual angles, and calculates targeted modified effective lengths La 2 , Lb 2 , and Lc 2  for the wires  66   a ,  66   b , and  66   c  from the calculated modified instruction angles around the X and Y axes. The modified effective lengths La 2 , Lb 2 , and Lc 2  are calculated with deviations caused in the joint angle of the ankle joint  26  being added thereto. At this time, as the load torque of the ankle joint  26  is larger, the modified effective lengths are calculated with deviations being more largely added thereto. 
   In the controller  200 , when the tension of the wire  66   a  is small, the operation amount of the actuator  68   a  is calculated from the expected effective length La 1 . That is, when the tension of the wire  66   a  is small, the operation amount of the actuator  68   a  is calculated without respect to deviations caused in the joint angle of the ankle joint  26 . On the other hand, when the tension of the wire  66   a  is large, the operation amount of the actuator  68   a  is calculated from the modified effective length La 2 . That is, when the tension of the wire  66   a  is large, the operation amount of the actuator  68   a  is calculated with respect to the deviations caused in the joint angle of the ankle joint  26 . Each operation amounts of the other actuators  68   b ,  68   c  is calculated similarly to the above mentioned calculation. As a result, among the actuators  68   a ,  68   b , and  68   c , for only one (or some) of the actuators which moves a wire with a large tension, the operation amount thereof is calculated with respect to the deviations caused in the joint angle of the ankle joint  26 . Furthermore, as the load torque of the ankle joint  26  is larger, the deviations are modified so as to be larger than the actual value, and the operation amount of the actuator is calculated with respect to the modified deviations. 
   While the robot  10  operates, the load torque of the ankle joint  26  changes variously following the operation of the robot  10 , and consequently the tensions of the wires  66   a ,  66   b , and  66   c  also change variously therewith. Since the rigidity of the wires  66   a ,  66   b , and  66   c  change depending on the tensions of the wires  66   a ,  66   b , and  66   c , the rigidity of the wires  66   a ,  66   b , and  66   c  change every moment following the operation of the robot  10 . 
   When deviations are caused in the joint angle of the ankle joint  26 , the controller  200  operates, with respect to the deviation, actuators for wires whose tensions are larger, and operates, without respect to the deviation, actuators for wires whose tensions are smaller. That is, the controller  200  causes wires which are high and stable in rigidity to be moved in accordance with the deviations, and causes wires which are low and unstable in rigidity no to be moved in accordance with the deviations. At this time, for the actuators to be operated, they are operated more largely with respect to the deviation, as the load torque of the ankle joint  26  is larger. That is, the actuators made to move back and forth are operated more largely with respect to the deviations, as the load torque of the ankle joint  26  is larger and as the deviations caused in the joint angle of the ankle joint  26  are larger. Accordingly, the deviation caused in the joint angle of the ankle joint  26  can be rapidly removed, and the joint angle can be prevented from being vibrating. 
   The controller  200  can appropriately add the deviation caused in the joint angle of the ankle joint  26  to the operation amounts of the actuators  68   a ,  68   b , and  68   c , thereby adjusting the joint angle of the ankle joint  26  correctly to the instructed angle. 
   Although mainly the ankle joint  26  has been described hitherto, each of the other joints of the robot  10  performs the same processing operation. The robot  10  can continue to accurately control the joint angle of each joint, and can accurately perform an operation instructed by the joint angle data. 
   Even when the deviation in the joint angle occurs, the robot  10  is adapted such that a wire with a small tension is not operated selectively. Accordingly, the deviation in the joint angle can be more largely added to the operation amount of actuators which move wires back and forth (or, a feedback gain can be increased), even when some wires have small tensions. Accordingly, it becomes unnecessary to maintain the tension of all wires to be large. It is possible to reduce loads applied to the wires and the joints, and possible to reduce the power consumption of the actuators. 
   Embodiment 2 
   The robot  10  can also use a controller  300  shown in  FIG. 10  instead of the controller  200 . Hereinafter, the controller  300  will be described. Here, in order to avoid repeated description, points different from those of the controller  200  will mainly be described. 
   The controller  300  has a first variable distributor  311 , a second variable distributor  312 , and a third variable distributor  313 . The first variable distributor  311  is connected to the first converter  232 , the second converter  234 , and the first driver  251 . The second variable distributor  312  is connected to the first converter  232 , the second converter  234 , and the second driver  252 . The third variable distributor  313  is connected to the first converter  232 , the second converter  234 , and the second driver  253 . 
   The controller  300  has a tension sensor  321  which measures a tension caused in the wire  66   a , a second tension sensor  322  which measures a tension caused in the wire  66   b , and a third tension sensor  323  which measures a tension caused in the wire  66   c . The first tension sensor  321  is connected to the first variable distributor  311 , and outputs a measured value of the tension caused on the wire  66   a  to the first variable distributor  311 . The second tension sensor  322  is connected to the second variable distributor  312 , and outputs a measured value of the tension caused in the wire  66   b  to the second variable distributor  312 . The third tension sensor  323  is connected to the third variable distributor  313 , and outputs a measured value of the tension caused in the wire  66   c  to the third variable distributor  313 . 
   The first variable distributor  311  inputs the expected effective length La 1  outputted by the first converter  232 , and inputs the modified effective length La 2  outputted by the second converter  234 . And, the first variable distributor  311  calculates and outputs distributed effective lengths from the input expected effective length La 1  input and modified effective length La 2 . The first variable distributor  311  calculates the distributed effective length according to a calculating expression descried below.
 
(Distributed effective length)= La 1+( La 2− La 1)· k  
 
k of the above expression is a coefficient of 0 (zero)≦k≦1. The first variable distributor  311  sets the above coefficient k on the basis of the tension of the wire  66   a  inputted from the first tension sensor  321 . Especially, the coefficient k is set so as to be proportional to the input tension of the wire  66   a . Accordingly, as the tension of wire  66   a  is larger, the first variable distributor  311  outputs the distributed effective length which has a nearer value to the modified effective length La 2  output by the second converter  234 .
 
   Similarly to the first variable distributor  311 , the second variable distributor  312  calculates and outputs the distributed effective length for the wire  66   b , and the third variable distributor  313  calculates and outputs the distributed effective length for the wire  66   c.    
   The first driver  251  calculates an operation amount of the actuator  68   a  from the distributed effective length outputted by the first variable distributor  311 , and operates the actuator  68   a  by the calculated operation amount. The second driver  252  calculates an operation amount of the actuator  68   b  from the distributed effective length outputted by the second variable distributor  312 , and operates the actuator  68   b  by the calculated operation amount. The third driver  253  calculates an operation amount of the actuator  68   c  from the distributed effective length output by the third variable distributor  313 , and operates the actuator  68   c  by the calculated operation amount. 
   With the configuration as described above, the controller  300  calculates the operation amounts of the actuators  68   a ,  68   b , and  68   c  from the distributed effective lengths for the wires  66   a ,  66   b , and  68   c , respectively. For each of the wires  66   a ,  66   b , and  68   c , as the tension of a wire which is larger, the deviations caused in the joint angle of the ankle joint  26  will be added more largely to the operation amount of the actuator that moves the wire back and forth. 
   When deviations are caused in the joint angle of the ankle joint  26 , the controller  300  operates actuators for wires whose tensions are larger more largely with respect to the deviation, and operates actuators for wires whose tension are small slightly with respect to the deviation. That is, the controller  200  causes wires which are high and stable in rigidity to be moved more largely with respect to the deviations, and causes wires which are low and unstable in rigidity not to be moved much with respect to the deviation. Accordingly, the deviation caused in the joint angle of the ankle joint  26  can be rapidly removed, and the joint angle can be prevented from vibrating. 
   A robot using the controller  300  can appropriately add the deviation caused in the joint angle of the ankle joint  26  to the operation amounts of the actuators  68   a ,  68   b , and  68   c , thereby adjusting the joint angle of the ankle joint  26  accurately to the instructed angle. 
   Specific examples of embodiments of the present invention were described above, but these examples merely illustrate some possibilities of the invention and do not restrict the claims thereof. The art set forth in the claims includes various transformations and modifications of the specific examples explained above. 
   The wires are not limited to those made of metal. For example, wires (yams) may be made of polymeric fibers. 
   A robot may further include a device for calculating a load torque of each joint from stored joint angle data. The movement of a robot can be calculated from time-series data on the instructed angle concerning each joint described in the joint angle data. By calculating the movement of a robot, a load torque of each joint can be calculated. 
   Furthermore, the technical elements disclosed in the present specification or figures may be utilized independently or in various combinations, and are not limited to the combinations set forth in the claims at the time of filing of the application. Further, the purpose of the example illustrated by the present specification and drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical value and utility to the present invention.