Abstract:
A novel linkage actuator. A frame mounts a screw and a motor driving the screw in a controlled fashion. Rotating the screw moves a ball nut engaged to the screw in a linear fashion, along with a carrier connected to the ball nut. An output link is pivotally connected to another part of the same frame. A transfer link is pivotally connected to the carrier on its first end and pivotally connected to the output link on its second end. In this arrangement, turning the screw causes the output link to pivot.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims the benefit of an earlier-filed provisional application under 37 C.F.R. section 1.53(c). The earlier application was assigned Ser. No. 62/205,992. It was filed on Aug. 17, 2015 and listed the same inventor. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable 
       MICROFICHE APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention pertains to the field of mechanical actuators. 
         [0006]    2. Description of the Related Art 
         [0007]    It is often a goal in the field of mechanical design to carefully control the rotational motion, velocity, and acceleration of one linkage with respect to another. The present invention provides a novel actuator that allows such control. 
       BRIEF SUMMARY OF THE PRESENT INVENTION 
       [0008]    The present invention comprises a novel linkage actuator. A frame mounts a screw and a motor driving the screw in a controlled fashion. Rotating the screw moves a ball nut engaged to the screw in a linear fashion, along with a carrier connected to the ball nut. An output link is pivotally connected to another part of the same frame. A transfer link is pivotally connected to the carrier on its first end and pivotally connected to the output link on its second end. In this arrangement, turning the screw causes the output link to pivot. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]      FIG. 1  is a side elevation view, showing the novel linkage actuator in a first position. 
           [0010]      FIG. 2  is a side elevation view, showing the novel linkage actuator in a second position. 
           [0011]      FIG. 3  is a block diagram depicting an exemplary control system used to control the angular position of the output link. 
           [0012]      FIG. 4  is a block diagram, depicting an exemplary control system used to control the torque applied to the output link. 
       
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
       [0013]      2  actuator 
         [0014]      10  frame 
         [0015]      12  output link 
         [0016]      14  screw 
         [0017]      16  motor 
         [0018]      18  transfer link 
         [0019]      20  trunnion 
         [0020]      22  pivot pin 
         [0021]      24  pivot pin 
         [0022]      26  load cell 
         [0023]      28  encoder 
         [0024]      30  linear bearing 
         [0025]      32  bearing way 
         [0026]      34  ballnut 
         [0027]      36  carrier 
         [0028]      38  controller 
         [0029]      40  encoder/torque sensor 
         [0030]      41  input block 
         [0031]      42  summation block 
         [0032]      44  summation block 
         [0033]      46  control function 
         [0034]      48  conversion function 
         [0035]      50  numerical differentiator 
         [0036]      52  low pass filter 
         [0037]      54  input block 
         [0038]      56  summation block 
         [0039]      58  summation block 
         [0040]      60  control function 
         [0041]      62  control function 
         [0042]      64  numerical differentiator 
         [0043]      66  low pass filter 
         [0044]      68  numerical differentiator 
         [0045]      70  low pass filter 
         [0046]      72  control function 
         [0047]      74  hardware-based low pass filter 
         [0048]      76  moving averager 
         [0049]      78  low pass filter 
         [0050]      80  numerical differentiator 
         [0051]      82  low pass filter 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0052]      FIG. 1  depicts actuator  2  in a first position. Frame  10  mounts the other components. It will typically be anchored to something—such as one link of a multi-link moving system. Output link  12  moves under the control of the actuator. Screw  14  is rotationally mounted in frame  10 . It is free to rotate but otherwise constrained. Ballnut  34  is driven to the left and right in the view as screw  14  turns. The ballnut and screw are preferably a close-tolerance assembly so that precisely controlled rotation of screw  14  produces precisely controlled linear motion of ballnut  34 . This type of assembly is familiar to those skilled in the field of linear motion control. 
         [0053]    Carrier  36  is connected to ballnut  34  and moves therewith. Linear bearing  30  is attached to carrier  36  and slides along bearing way  32 . Motor  16  is attached to frame  10 . It drives screw  14 . Transfer link  18  divides into a fork proximate carrier  36  and pivotally attaches to carrier  36  via two trunnions  20  (one on either side of the carrier). The opposite end of transfer link  18  pivotally connects to output link  12  at pivot pin  22 . Load cell  26  is also included in the transfer link. Load cell  26  is configured to accurately measure the linear load (tension or compression) in transfer link  18 . 
         [0054]    Output link  12  pivots about pivot pin  24 , which is secured to frame  10 . The output link may assume any desired shape. Only a portion of this link is shown but it may be quite long. 
         [0055]    Encoder  28  provides information regarding the relative and absolute rotational position of screw  14 . A linear encoder may be included for the position of carrier  36 . This information, along with the information from load cell  26 , is preferably sent to controller  38 . Controller  38 , which may include a processor running software, uses this information to control the motion of the actuator. 
         [0056]    In studying  FIG. 1 , those skilled in the art will realize that actuating motor  16  causes screw  14  to turn. Carrier  36  will then be moved in a linear fashion. This motion will pivot both transfer link  18  and output link  12 .  FIG. 2  shows the relative position of these components after screw  14  has been driven through several revolutions. The motion of output link  12  is dependent upon the lengths L 1  and L 2 . 
         [0057]    Looking again at  FIG. 1 , the reader will note that controller  38  is provided to control the operation of the inventive actuator  2 . It is generally desirable to control the angular position of output link  12  and the torque applied to output link  12 . One can directly measure the angular position and torque. Alternatively, one can measure other values that may be used to determine the output link&#39;s angular position and the torque applied to it. In the example of  FIG. 1 , the angular position of motor  16  is fed to controller  38  by encoder  28 . A mathematical function relates the angular position of the motor to the angular position of the output link, so the motor&#39;s position may be converted to the output link&#39;s position. 
         [0058]    Similarly, load cell  26  is configured to measure the linear force applied by transfer link  18 . A second mathematical function relates the linear force applied by transfer link  18  to the torque applied to output link  12 , so the linear force may be converted to the output torque. 
         [0059]    It is also possible to measure these values directly. In  FIG. 2 , encoder/torque sensor  40  has been installed proximate pivot pin  24 . This component directly measures the angular position of the joint and the torque applied across the joint. In some applications it is advantageous to use a direct sensor since it can eliminate backlash and other sensing errors. 
         [0060]    The inventive actuator provides the potential for a wide variety of non-linear motion transfers between the screw drive and the pivoting output link. For example, the actuator can provide an initial fast pivoting of the output link with relatively low available torque output followed by a slow pivoting final range of motion with a relatively high output torque. 
         [0061]      FIGS. 3 and 4  provide some information regarding exemplary control systems that could be used to control the motion of the inventive actuator. Many different approaches could be taken to controlling the device. In the exemplary approach of  FIGS. 3 and 4 , the goal is to control the angular position of output link  12  and the torque applied to output link  12 . The only driving device is motor  16 . 
         [0062]      FIG. 3  shows a representative control system used to drive the angular position of the actuator output link. Function block  41  specifies the desired angular position of the output link (“theta”) and the desired angular velocity of the output link. The output of motor  16  is measured by encoder  28  (“theta motor”). Conversion function  48  is used to convert the motor&#39;s angular position to the angular position of the output link (“theta actuator”). As will be realized by those skilled in the art, it is straightforward to create a mathematical function relating the position of the output link to the angular position of the motor—since the motion of these two components is hard-linked together. “Theta actuator” is fed directly into summation block  42 . In addition, another branch of the same signal is passed through numerical differentiator  50  to obtain the first derivative. This value is then passed through low pass filter  52  and into summation block  44 . 
         [0063]    A first error signal is produced by summation block  42  and a second error signal is produced by summation block  44 . These two error signals are combined in control function block  46 . The result is the control function (u1(t)) which is used to drive motor  16 . 
         [0064]      FIG. 4  shows an exemplary system used to control the torque applied to the output link. In this example, the angular position of the motor is used as one monitored value and the torque applied to the actuator is used as the other. One can directly measure the actuator torque (such as by using the torque sensor  40  in  FIG. 2 ) or one can derive this value from load cell  26  or possible even from motor current. 
         [0065]    In the example of  FIG. 4 , the desired output link torque is specified in input block  54 . This value is fed into summation block  56 . In addition, the same value is fed forward via control function  62 . Control function  60  feeds into summation block  58 . The output of summation block  58  is the control function (u2(t)) used to drive motor  16 . 
         [0066]    The resulting angular position of the motor is again used as a measured output. This value is fed into numerical differentiator  64 . Then into low pass filter  66 , then into numerical differentiator  68 , then into low pass filter  70 , then to control function  72 , and finally to summation block  58 . 
         [0067]    The measured output torque for the actuator is fed to hardware-based low pass filter  74 , then to moving average  76 , then to low pass filter  78 . From low pass filter  78  the signal is split. The first branch feeds into summation block  56 . The second branch feeds into numerical differentiator  80 , then to low pass filter  82 , and then to control function  60 . 
         [0068]    Those skilled in the art will realize that many other variations are possible within the scope of the present invention. Thus, the scope should properly be fixed by the following claims rather than any particular example provided.