Abstract:
The present invention relates to a manipulator having distributed mechanism for maximizing the performance of the manipulator. The manipulator is comprised of a first link; a second link; a joint for rotatably joining the first link and the second link each other; a connector having a first movable node at one end and a second movable node at the other end; a driver for providing power to linearly move the first movable node and the second movable node; and a guide for guiding the first movable node and the second movable node linearly. 
     The first movable node is connected to the first link and is capable of linearly moving and rotating with respect to the first link. The second movable node is connected to the second link and is capable of linearly moving and rotating with respect to the second link.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2009-0022316, filed on Mar. 16, 2009, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to the actuation mechanism of manipulator for maximizing performance such as velocity and force by moving the forcing-points which produce torque. 
         [0004]    2. Background Art 
         [0005]    Robots are being used over a variety of industrial areas. In addition to industrial robots, a remotely-controlled robot with multipurpose and a humanoid robot which has as high degree of freedom (hereinafter, referred to as “DOF”) as being capable of conducting various work in lieu of human is in demand and the research and development thereof are actively conducted recently. 
         [0006]    In order to embody the various motion of a robot, a manipulator called a multi-joint arm including a plurality of articulated links joined together and actuators are commonly used. The actuators transform the energy into actual movement of the manipulator. 
         [0007]    Redundant actuation mechanism is the mechanism with lower DOF than the number of actuators. While more difficult to control, larger and heavier than non-redundant mechanism, the redundant actuation mechanism is advantageous in several aspects such as avoidance of kinematical singularity, overcoming limit of velocity and input velocity, lessening impact force in contacting outer environment and avoidance of obstacle. The above-mentioned characteristics can be achieved by obtaining optimal solution from the given application purpose and environment. 
         [0008]    As prior researches regarding to the redundant actuation mechanism, there are “Performance Analysis and Optimal Actuator Sizing for Anthropomorphic Robot Modules with Redundant Actuation” (The Korean Society of Mechanical Engineer, Vol. 19, No 1, pp. 181-192, 1995) which shows the performance improvement of a redundant actuation mechanism by comparing with a non-redundant actuation mechanism in terms of maximum load capacity, maximum velocity and maximum acceleration at an end-operator and “Operational quality analysis of parallel manipulators with actuation redundancy” (IEEE International Conference on Robotics and Automation, pp. 2651-2656, 1997) regarding the performance improvement of a manipulator by redundant actuation. 
         [0009]    As further prior research regarding to distribution actuation mechanism, there are “A five-bar finger mechanism involving redundant actuators: Analysis and its applications” (IEEE Transactions on Robotics and Automation, Vol. 15, No. 6, pp. 1001-1010, 1999) regarding the effect to the working performance by the location of actuators and the number of used actuators in force distribution, “Load Distribution using Weighted Pseudoinverse Matrix in Redundant Actuation” (The Korean Society of Mechanical Engineer, 2002) regarding the force-distribution-method of a redundant actuation system by use of pseudoinverse matrix in 5-axis finger mechanism of the redundant actuation, and “Torque Distribution Control of 3RRR Redundant Parallel Robot” (Korean Journal of Precision Engineering and Manufacturing, Vol. 25, No. 2, pp. 72-79, 2008) regarding lowering maximum actuating torque by effectively distributing actuation input. 
       SUMMARY OF THE DISCLOSURE 
       [0010]    Many links and joints used for embodying redundant actuation mechanism make the structure more complex, larger and heavier than the other types of mechanism. As a result, the redundant actuation mechanism has low output in spite of its big size. 
         [0011]    The mechanism for optimizing the location of actuator has not been properly developed. Further, the working performance of the manipulator can be improved by distributing force (or torque) with structurally redundant actuation and by moving the location of the actuator (or the forcing-points). However, the mechanism reflecting these characteristic has not been developed as yet. 
         [0012]    The object of the present invention is to overcome the problem by maximizing the performance of a manipulator with simultaneously applying the conventional redundant actuation mechanism and distributed actuation mechanism. 
         [0013]    To accomplish this object, in one aspect, there is provided a manipulator with distributed actuation mechanism, the manipulator comprising: a first link; a second link; a joint for rotatably joining the first link and the second link; a connector having a movable node at one end and a fixed node at the other end, the movable node being provided in the first link and capable of linearly moving and rotating with respect to the first link, and the fixed node being provided in the second link and capable of rotating with respect to the second link; a actuator for providing power to linearly move the movable node; and a guide connected to the actuator for linearly guiding the movable node. 
         [0014]    A manipulator with distributed actuation mechanism according to another embodiment of the invention comprises a first link; a second link; a joint for rotatably joining the first link and the second link; a connector having a first movable node at one end and a second movable node at the other end, the first movable node being provided in the first link and capable of linearly moving and rotating with respect to the first link, the second node being provided to the second link and capable of linearly moving and rotating with respect to the second link; actuators for providing power to linearly move the first movable node and the second movable node; guides connected to the actuators for guiding the first movable node and the second movable node linearly. 
         [0015]    Preferably, the connector may be hydraulic or pneumatic operating device. 
         [0016]    In a preferred embodiment, the actuators are provided in both of the first link and the second link, and the guides are provided in both of the first link and the second link. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  shows a manipulator embodying distributed actuation mechanism with one actuator; 
           [0019]      FIG. 2  shows a manipulator embodying distributed actuation mechanism with two actuators; 
           [0020]      FIG. 3  shows notations for numerical analysis of the distributed actuation mechanism; 
           [0021]      FIG. 4  shows a manipulator embodying distributed actuation mechanism with three links; and 
           [0022]      FIG. 5  shows an example of hydraulic manipulator employing the distributed actuation mechanism of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Various features of the invention will be apparent by reference to the following description of various embodiments with reference to the drawings. 
         [0024]      FIG. 1  shows a manipulator of the distributed actuation mechanism with one actuator. 
         [0025]    The manipulator basically comprises a first link  10 , a second link  20 , a joint  120 , a connector  100 , an actuator  12 , and a guide  14 . 
         [0026]    The first link  10  and the second link  20  are rotatably joined together at the joint  120 . The connector  100  has a movable node  16  at one end and a fixed node  27  at the other end. The movable node  16  is provided in the first link  10  so as to be capable of linearly moving along the first link  10  and rotating with respect to the first link  10 . The fixed node  27  is provided in the second link  20  so as to be capable of rotating with respect to the second link  20 . 
         [0027]    The actuator  12  is provided to move the movable node  16 . Any device is available as the actuator  12  if it can move the movable node  16  linearly. 
         [0028]    An actuator including linear ultrasonic motor, voice-coil motor, hydraulic motor or pneumatic motor is available for the distributed actuation mechanism if it can linearly move the forcing-point. 
         [0029]    The movable node  16  is joined at the guide  14 . The guide  14  is connected to the actuator  12  to transmit the power and/or torque of the actuator  12  to the movable node  16 . That is, the guide  14  serves to guide the linear movement of the movable node  16 . 
         [0030]    The actuator  12  and the guide  14  are provided in the first link  10 . 
         [0031]    When the actuator  12  operates to pull the movable node  16  toward the actuator  12 , the second link  20  moves toward the first link  10  by the force to applied to the connector  100 . As a result, the angle between the first link  10  and the second link  20  decreases. 
         [0032]      FIG. 2  shows a manipulator of the distributed actuation mechanism with two actuators. In this embodiment, the first link and the second link are referred to as new reference numerals for distinguishing this embodiment from the embodiment shown in  FIG. 1 . 
         [0033]    The first link  30  and the second link  40  are rotatably joined together at the joint  120 . The connector  100  has the first movable node  36  at one end and the second movable node  46  at the other end. The first movable node  36  is provided in the first link  30  so as to be capable of linearly moving along the first link  30  and rotating with respect to the first link  30 . The second movable node  46  is provided in the second link  40  so as to be capable of linearly moving along the second link  40  and rotating with respect to the second link  40 . 
         [0034]    Actuators  32  and  42  are provided to move the first movable node  36  and the second movable node  46  respectively. Any actuator is available if it can move the movable nodes linearly. 
         [0035]    The first movable node  36  is joined at the guide  34  and the second movable node  46  is joined at the guide  44 . The guides  34 ,  44  are connected to the actuators  32 ,  42 , respectively so as to transmit the power and/or torque of the actuator to the movable nodes. That is, the guides serve to guide the linear movement of the movable nodes. 
         [0036]    The actuator  32  and the guide  34  are provided in the first link  30 . The actuator  42  and the guide  44  are provided in the second link  40 . 
         [0037]    As described with reference to  FIGS. 1 and 2 , the feature of the present invention is to move the forcing-point (the movable node) along the link by using one or two actuators per a link of a manipulator. With this distribution of the forcing-point, the optimization for torque of the joint is accomplished. 
         [0038]    The method to distribute forcing-point in operation of the embodiment of the present invention as illustrated in  FIG. 2  is to move the ends of the connector linearly along the guide by using the actuator. If the actuators are provided in the first link and the second link and if the actuators are provided to move the ends of the connector, the forcing-point producing torque varies in accordance with the position of the movable node. 
         [0039]      FIG. 3  shows notations for numerical analysis of the distributed actuation mechanism. When the thrusting forces are given by F 1  and F 2 , the torque at each joint is described as follows: 
         [0000]    
       
         
           
             τ 
             = 
             
               
                 
                   
                     F 
                     1 
                   
                   
                     1 
                     + 
                     
                       μ 
                        
                       
                           
                       
                        
                       tan 
                        
                       
                           
                       
                        
                       
                         ψ 
                         1 
                       
                     
                   
                 
                  
                 
                   ( 
                   
                     
                       
                         x 
                         1 
                       
                        
                       tan 
                        
                       
                           
                       
                        
                       
                         ψ 
                         1 
                       
                     
                     + 
                     
                       h 
                       1 
                     
                   
                   ) 
                 
               
               + 
               
                 
                   
                     F 
                     2 
                   
                   
                     1 
                     + 
                     
                       μ 
                        
                       
                           
                       
                        
                       tan 
                        
                       
                           
                       
                        
                       
                         ψ 
                         2 
                       
                     
                   
                 
                  
                 
                   ( 
                   
                     
                       
                         x 
                         2 
                       
                        
                       tan 
                        
                       
                           
                       
                        
                       
                         ψ 
                         2 
                       
                     
                     + 
                     
                       h 
                       2 
                     
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where μ is the Coulomb friction coefficient, 
         [0000]    
       
         
           
             
               ψ 
               1 
             
             = 
             
               
                 tan 
                 
                   - 
                   1 
                 
               
               ( 
               
                 tan 
                  
                 
                     
                 
                  
                 θ 
                  
                 
                   
                     
                       
                         c 
                         2 
                       
                       - 
                       
                         
                           x 
                           1 
                           2 
                         
                          
                         
                           cos 
                           2 
                         
                          
                         θ 
                       
                     
                     
                       
                         c 
                         2 
                       
                       + 
                       
                         
                           x 
                           1 
                           2 
                         
                          
                         
                           sin 
                           2 
                         
                          
                         θ 
                       
                     
                   
                 
               
               ) 
             
           
         
       
       
         
           
             
               ψ 
               2 
             
             = 
             
               θ 
               - 
               
                 ψ 
                 1 
               
             
           
         
       
       
         
           
             
               x 
               2 
             
             = 
             
               
                 
                   - 
                   
                     x 
                     1 
                   
                 
                  
                 cos 
                  
                 
                     
                 
                  
                 θ 
               
               + 
               
                 
                   
                     
                       x 
                       1 
                       2 
                     
                      
                     
                       sin 
                       2 
                     
                      
                     θ 
                   
                   + 
                   
                     c 
                     2 
                   
                 
               
             
           
         
       
     
         [0040]    Where x 1  and x 2  are the distances of the movable nodes from the joint, c is the length of the connector, and θ=ψ 1 +ψ 2 , which is the joint angle. Note that if a joint angle θ is given, the variables ψ 1 , ψ 2 , and x 2  are uniquely determined by x 1 , which implies that the joint torque is the function of the joint angle θ and the position of the movable node x 1 . 
         [0041]    Many actuators are needed in the conventional manipulator with mechanism in order to distribute input torque. However, the manipulator of the present invention is capable of moving (or distributing) the forcing-points with lesser actuator(s) than the conventional manipulator. Further, it has advantage of miniaturization through eliminating additional links and joints. 
         [0042]    Further, because the torque of the joint is controllable in accordance with the position of the movable node although the actuator operates to output maximum power, the present invention has advantages of higher feasible range of power. 
         [0043]      FIG. 4  shows a manipulator embodying distributed actuation mechanism with three links. 
         [0044]    A first link  50 , a second link  60  and a third link  70  are used in this embodiment. 
         [0045]    The first link  50  and the second link  60  are rotatably joined together at the joint  121 . The first connector  101  has the first movable node  56  at one end and the second movable node  66  at the other end. The first movable node  56  is rotatably provided at the first link  50 . The second movable node  66  is rotatably provided at the second link  60 . 
         [0046]    Actuators  52  and  62  are provided to move the first movable node  56  and the second movable node  66 , respectively. Any actuator is available if it can move the movable nodes linearly. 
         [0047]    The first movable node  56  is connected to the guide  54 . The guide  54  is also connected to the actuator  52 . The guide  54  transmits the power and/or torque of the actuator  52  to the movable node  56  and also guides the linear movement of the movable node  56 . 
         [0048]    The second movable node  66  is connected to the guide  64 . The guide  64  is also connected to the actuator  62 . The guide  64  transmits the power and/or torque of the actuator  62  to the movable node  66  and also guides the linear movement of the second movable node  66 . 
         [0049]    The actuator  52  and the guide  54  are provided in the first link  50 . The actuator  62  and the guide  64  are provided in the second link  60 . 
         [0050]    The second link  60  and the third link  70  are rotatably joined together at the joint  122 . The second connector  102  has the third movable node  67  at one end and the fourth movable node  76  at the other end. The third movable node  67  is rotatably provided at the second link  60 . The fourth movable node  76  is rotatably provided at the third link  70 . 
         [0051]    Actuators  63  and  72  are provided to move the third movable node  67  and the fourth movable node  76 , respectively. Any actuator is available if it can move the each movable node linearly. 
         [0052]    The third movable node  67  is rotatably connected to the guide  65 . The guide  65  is also connected to the actuator  63 . The guide  65  transmits the power and/or torque of the actuator  63  to the third movable node  67  and also guides the linear movement of the third movable node  67 . 
         [0053]    The fourth movable node  76  is rotatably connected to the guide  74 . The guide  74  is also connected to the actuator  72 . The guide  74  transmits the power and/or torque of the actuator  72  to the fourth movable node  76  and also guides the linear movement of the fourth movable node  76 . 
         [0054]    The actuator  63  and the guide  65  are provided in the second link  60 . The actuator  72  and the guide  74  are provided in the third link  70 . 
         [0055]    As a result, two actuators, two guides and two movable nodes are provided in the second link  60 . 
         [0056]      FIG. 5  shows an example of hydraulic manipulator employing the distributed actuation mechanism of the present invention. 
         [0057]    The hydraulic manipulator employing the distributed actuation mechanism has high power. In the hydraulic manipulator, the connector is replaced by a hydraulic device  500 , and thus the available range of power increases further. As a result, it is possible to develop a small manipulator with high power. 
         [0058]    The both ends of the hydraulic device  500  include the first movable node  360  provided in the first link  300  and the second movable node  460  provided in the second link  400 . 
         [0059]    The two movable nodes  360 ,  460  are rotatably provided in the first and second links. 
         [0060]    The first link is rotatably joined to the base  700 . An end-operator  600  is provided in the end of the second link  400 . The end-operator means an apparatus connected the end of the manipulator, such as holder or welding device. 
         [0061]    While the present invention has been described with reference to particular illustration embodiments, it is to be understood that the invention should not be limited thereby. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope or spirit of the present invention.