Abstract:
A robot includes an arm including a plurality of joints, arm members that form the arm, each arm member supporting a load, actuators that drive the joints and that are supported by the arm members, a load sensor embedded in at least one of the arm members to measure the load applied to the at least one of the arm members, a controller that controls movements of the actuators on the basis of a result of the measurement performed by the load sensor, and a wire hole through which a sensor line extend from a space inside the at least one of the arm members to a space inside the arm, the sensor line connecting the load sensor to the controller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to under 35 U.S.C. §119 Japanese Patent Application No. 2009-161513, filed Jul. 8, 2009. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a robot having a force control function. 
     2. Description of the Related Art 
     Operations for assembling industrial products, such as automobiles and home appliances, have been performed manually, and automation of such an operation has been demanded. The operations that are generally manually performed include an operation of fitting a plurality of components to each other, a force-following operation (for example, an operation of pressing a component against another component at a certain force), etc., which require relatively delicate movements. In the case where a robot is caused to perform such operations in place of a human worker, it is necessary to accurately control a force (hereinafter referred to as an external force) applied by the robot to the components (workpieces) handled by the robot. 
     Japanese Patent No. 3383614 (Japanese Unexamined Patent Application Publication No. 2001-38673) discloses an example of a method for controlling a force applied by a robot. In this method, a contact sensor, such as a pressure-sensitive sensor, is attached to a surface of an arm of a robot. The external force applied to the arm is measured by the sensor, and a driving unit (actuator) of each joint of the robot is controlled on the basis of the result of the measurement. In addition, Japanese Unexamined Patent Application Publication No. 2008-307634 discloses a technique in which a six-axis force sensor is attached to a wrist of a robot. A force and a moment applied to a workpiece at a hand of the robot are determined, and a drive amount of each driving unit is controlled on the basis of the determined force and moment. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a robot includes an arm including a plurality of joints; arm members that form the arm, each arm member supporting a load; actuators that drive the joints and that are supported by the arm members; a load sensor embedded in at least one of the arm members to measure the load applied to the at least one of the arm members; a controller that controls movements of the actuators on the basis of a result of the measurement performed by the load sensor; and a wire hole through which a sensor line extends from a space inside the at least one of the arm members to a space inside the arm, the sensor line connecting the load sensor to the controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in further detail with reference to the accompanying drawings wherein: 
         FIG. 1  is a diagram illustrating the detailed structure of a distal end section of a robot; 
         FIG. 2  is a schematic front view of the robot; and 
         FIG. 3  is a sectional view of  FIG. 1  taken along line III-III. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be described with reference to the drawings. 
     As illustrated in  FIG. 2 , a robot (arm)  9  according to the present embodiment includes a base  1 , arm members  2  to  7 , a flange portion  8 , actuators (joints)  11  to  17 , and a controller  20 . An articulated arm is formed by the base  1 , the arm members  2  to  7 , and the actuators (joints)  11  to  17 . 
     The base  1  is fixed to the floor (or to a fixed plane, such as the ceiling) with anchor bolts (not shown). 
     The arm members  2  to  7  are structural support members supporting a load of robot  9  and what robot  9  is holding formed of a cast metal or the like, and are arranged in series in that order from the base  1 . 
     The actuator (joint)  11  is interposed between the base  1  and the arm member  2  and is capable of rotating the base  1  and the arm member  2  in the directions shown by the arrow  11 A. The actuators  12  to  16  are disposed at the connecting sections between the arm members  2  to  7 . The actuator  17  is mounted in the arm member  7  at a distal end thereof. 
     Each of the actuators  11  to  17  includes a servo motor, reduction gears, and a brake, and the operation of each of the actuators  11  to  17  is controlled in accordance with a signal from a controller  20 . 
     More specifically, the arm member  2  and the arm members  3  to  7  supported by the arm member  2  can be turned in the directions shown by the arrow  11 A by the driving operation performed by the actuator  11 . The arm member  3  and the arm members  4  to  7  supported by the arm member  3  can be turned in the directions shown by the arrow  12 A by the driving operation performed by the actuator  12 . The arm member  4  and the arm members  5  to  7  supported by the arm member  4  can be turned in the directions shown by the arrow  13 A by the driving operation performed by the actuator  13 . The arm member  5  and the arm members  6  and  7  supported by the arm member  5  can be turned in the directions shown by the arrow  14 A by the driving operation performed by the actuator  14 . The arm member  6  and the arm member  7  supported by the arm member  6  can be turned in the directions shown by the arrow  15 A by the driving operation performed by the actuator  15 . The arm member  7  is turned in the directions shown by the arrow  16 A by the driving operation performed by the actuator  16 . 
     The flange portion  8  can be turned in the directions shown by the arrow  17 A by the driving operation performed by the actuator  17 . The rotation axes of the actuators  11  to  17  that are adjacent to each other extend perpendicular to each other. 
     The flange portion  8  is provided with a jig (not shown), and various types of end effectors can be detachably attached to the flange portion  8  with the jig. 
     The robot  9  (controller  20 ) performs various operations, such as a fitting operation, a force-following operation, and a pressing operation, by controlling the movements of the actuators  11  to  17  and the end effectors (not shown) that are attached to the flange portion  8 . Detailed explanations of force control performed in the above-described operations will be omitted here. 
     The actuators  11  to  17  are provided with hollow holes at the central sections of the actuators  11  to  17  around the rotation axes corresponding to the turning directions  11 A to  17 A, respectively. A harness  19  in which wires connected to the actuators  11  to  17  and the end effectors are bound together extends through the hollow holes. The harness  19  extends from the base  1  to the outside of the robot  9 , and is connected to the controller  20  and a power supply (not shown). 
     As illustrated in  FIG. 1 , sensors (load sensors)  21  and  22  are respectively embedded in the arm member  7  provided at the distal end of the robot  9  and the arm member  6  that supports the arm member  7 . 
     The sensors  21  and  22  are strain sensors capable of measuring the amount of strain, and are configured to measure the amounts of distortion of the arm members  6  and  7 . 
     More specifically, as illustrated in  FIG. 3 , the sensors  21  are disposed in sensor-receiving holes  21 A provided in a cylindrical portion  7 A of the arm member  7 . The cylindrical portion  7 A has a cylindrical shape and is arranged to support the actuator  17 . Three sensors  21  are disposed at three positions in the cross section of the cylindrical portion  7 A such that the sensors  21  are arranged along the circumferential direction (along the circumference centered on the rotation axis of the actuator  17 ) with constant intervals therebetween. 
     The controller  20  calculates forces Fx, Fy, and Fz in the respective directions (Fx, Fy, and Fz are orthogonal to each other) on the basis of the amounts of deformation at the three positions measured by the three sensors  21 . 
     Although no sectional view is shown, the sensors  22  are disposed in three sensor-receiving holes, which are provided in a cylindrical portion of the arm member  6  that supports the actuator  16 . Three sensors  22  are disposed at three positions along the circumferential direction with constant intervals therebetween. 
     The sensor-receiving holes  21 A, in which the sensors  21  are disposed, communicate with wire holes  21 B for receiving wires at the side of the sensor-receiving holes  21 A closer to the proximal end of the robot  9 . Wires (hereinafter referred to as sensor lines) extend from the sensors  21  to spaces inside the arm member  7  at positions closer to the proximal end of the robot  9  than the actuator  17 . 
     In addition, amplifiers  10  that correspond to the sensor lines and that amplify signals supplied from the corresponding sensor lines are disposed in the spaces inside the arm member  7  at positions closer to the proximal end of the robot  9  than the actuator  17 . Wires that extend from the amplifiers  10  are connected to the harness  19 . 
     Similarly, the sensor-receiving holes in which the sensors  22  are disposed communicate with wire holes for receiving wires at the side of the sensor-receiving holes closer to the proximal end of the robot  9 , and sensor lines extend from the sensors  22  to spaces inside the arm member  6  at positions closer to the proximal end of the robot  9  than the actuator  16 . In addition, amplifiers  10  that amplify signals supplied from the corresponding sensor lines are disposed in the spaces inside the arm member  6 , and wires that extend from the amplifiers  10  are connected to the harness  19 . 
     The robot according to the present embodiment is structured as described above. Therefore, the amounts of deflection (strain) generated in the arm member  7  at the cylindrical portion  7 A that supports the actuator  17  can be measured by the three sensors  21  arranged along the periphery of the actuator  17  with constant intervals therebetween, and the forces supported by the arm member  7  can be accurately detected on the basis of the measured amounts of deflection (strain). 
     In addition, the sensor lines extend from the sensors  21  through the wire holes  21 B formed in the arm member  7  to the spaces closer to the proximal end of the robot  9  than the actuator  17 . Since the sensor lines are supported by the arm member  7 , even when the robot  9  is moved, excessive deformation can be suppressed and external forces can be reliably detected. 
     Although an embodiment is described above, the robot according to the present invention is not limited to the above-described embodiment and various modifications are possible within the scope of the present invention. 
     For example, in the above-described embodiment, three load sensors are arranged with constant intervals therebetween along the circumference centered on the rotation axis of the corresponding actuator. However, the number and arrangement of the sensors are not limited to those described in the embodiment. 
     In addition, in the above-described embodiment, the load sensors are attached to two of the arm members that are positioned near the distal end of the robot  9 . However, the structure may also be such that load sensors are attached to only one of the arm members. Alternatively, the load sensors may be attached to all of the arm members (including the base). 
     It is as the case may be desirable as load sensors with an acceleration sensor of a crystal piezo-electric method. Because the sensor is buried, the response speed can be improved further.