Abstract:
A multi-actuator robotic device for performing knot-tying is provided herein. The device performs an automatic knot-tying to mimic human hand making a clove hitch knot using a sequence of coordinated string delivery and capturing actions and is particularly useful in the field of hop twining. In one example, the device uses four pneumatic actuators to perform nine coordinated knot-tying actions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Application claims priority from U.S. Provisional Application Ser. No. 61/567,498, filed Dec. 6, 2011, the contents of which are incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This disclosure relates generally to automated devices for knot-tying. The disclosure has particular utility as a robotic knot-tying device that is useful for tying knots on overhead trellis wires in hop twining, and will be described in connection with such utility, although other utilities are possible. 
     BACKGROUND OF THE INVENTION 
     Hop plant is a vigorous climbing herbaceous perennial, usually trained to grow up on strings in commercial production. The string is used to provide a connection between the ground and the overhead trellis wires for hop plants. The twining process comprises two primary tasks: to tie an end of the string in a knot on the trellis wire and to stake the other end of the string into the ground. Currently, the knot tying task in hop production fields is performed manually by skilled workers. 
     Trellis networks are usually 18 feet off the ground and twining is labor intensive. Motivated by shortage in skilled twinning worker supply and increasing labor costs, hop producers have a significant need for practical, reliable automated solutions to twining operation. There have been few developments in hop twining in recent history. For example, Gentry and Giannini, in U.S. Pat. No. 3,563,583, describe a knot-tying machine designed for providing a series of knots in selected spaced locations on a horizontal wire. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a device and method for automating the tying of a secure knot (as opposed to a slip knot) about a structure, e.g., a wire. More particularly, in one aspect, the present disclosure provides a knot-tying device for tying a secure knot around a structure with a string. The device includes a clip attached to the end of a clip support arm, the clip support arm being rotatably attached to a first actuator, wherein the clip support arm is curved to cross over the structure when rotated, and wherein the clip attaches to the end of the string. A motion arm is attached to a second actuator for rotating the clip support arm relative to the structure. A rod is attached to a third actuator for limiting motion of the string during rotation of the clip support arm by the motion arm. And, a hook is attached to a fourth actuator for retrieving the end of the string from the clip. Completing the device is a controller for controlling motion of the actuators. 
     In another aspect, the disclosure provides a method for tying a knot around a wire with a piece of string, using the aforesaid device. The method includes the step of activating the first actuator to move from an original clip support arm position and rotate the clip support arm about the wire; attaching the end of the string to the clip; using the first actuator to return the clip support arm to the original clip support arm position, thereby drawing the end of the string over the wire; activating the third actuator to extend the rod from an original rod position; activating the fourth actuator to extend the hook; activating the second actuator to rotate the clip support arm relative to the wire, wherein motion of the string is limited by the rod, thereby forming a loop; activating the first actuator to rotate the clip support arm around the wire; activating the fourth actuator to retract the hook, wherein the clip releases the end of the string which is then carried by the hook through the loop; and activating the first, second, and third actuators to return the rod to the original rod position and the clip support arm to the original clip support arm position. 
     Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic showing a trajectory plan for knot-tying in accordance with the present disclosure; 
         FIG. 2  is an illustration schematically showing one example of a knot-tying device in accordance with the present disclosure; 
         FIG. 3  is a schematic showing the operation of the pneumatic system of the knot-tying device shown in  FIG. 2 ; 
         FIGS. 4(   a )- 4 ( i ) are illustrations of different stages of the knot-tying device of  FIG. 2  during operation; and 
         FIG. 5  is a flow diagram illustrating the knot-tying method of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, various embodiments of the present disclosure. It is understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention. 
     One aspect of the present disclosure provides a knot-tying device useful, e.g. for tying knots on overhead trellis wires in hop twining. In an example of a device in accordance with the first aspect of the present disclosure, the device is constructed to perform a knot (clove-hitch) illustrated in  FIG. 1 . In this knotting process, a string is brought to start point A, proximate to wire  2 . Next, the string is brought over the wire, around the string, and over the wire again to form two loops. Finally, with the end of the string at end point B, tension is applied to the string to tighten the knot. This knotting method has been used successfully in hop production for decades. 
     In order to perform the knot according to the planned trajectory, the disclosure provides a multi-actuator pneumatic knotting device (see  FIGS. 2-4 ). As shown in  FIG. 2 , the exemplary device is designed to tie a clove hitch knot on a structure (wire  2 ), as demonstrated in  FIG. 1 . The device comprises a support structure in the form of base  1 ; two arms  51 ,  52  for holding the wire in place; a clip  4 ; a rod  61  driven by pneumatic cylinder  5 ; a clip support arm  3  driven by pneumatic cylinder  6 ; a motion arm  7  driven by pneumatic cylinder  8 ; and a hook  10  controlled by pneumatic cylinder  9 . 
     Referring also to  FIGS. 4(   a )- 4 ( i ) clip  4  is used to carry the end  101  of string  100  to the start point of the knotting process. Pneumatic cylinder  6  controls the rotational motion of the clip support arm over the wire  2 . Rod  61  is driven by pneumatic cylinder  5  to limit the motion of the string as the clip support arm is moved by pneumatic cylinder  8  and motion arm  7 . The clip support arm  3  is u-shaped or c-shaped and oriented so that it may adequately carry the end  101  of the string  100  around wire  2  and around the string to form loops as it is moved by the actuation of motion arm  7 . In the exemplary device shown, pneumatic cylinder  6  is actually mounted to one end of the motion arm  7  and motion arm  7  moves by rotating about pivot  7 . 1 . Hook  10  is then used to pull the end  101  back through the loop  103  formed by the string through the motion of the clip support arm  3 . With the hook still attached to end  101 , tension may be applied to the other end of the string, either by a user or by another pneumatic device, to tighten the knot. 
     In order to perform these functions, the exemplary device includes other features, shown in the schematic of  FIG. 3 . Air compressor  11  provides compressed air to drive the pneumatic cylinders. Filter  12 , regulator  13  and lubricator  15  are used regulate the air compressor and ensure proper function. Pressure gauge  14  is used to monitor the air pressure applied to the device during operation.  FIG. 3  shows one example of how valving might be arranged to accomplish the objective of the disclosure. A two-position, three-way, directional control valve  16  is used to control moving of pneumatic cylinder  8 , which includes a spring  19 . 1  to force a normally closed position. Three three-position four-way directional control valves  17 . 1 - 17 . 3  are used for direction control of pneumatic cylinder  5 , pneumatic cylinder  6  and pneumatic cylinder  9 , respectively. Seven two-way throttle valves  18 . 1 - 18 . 7  are used for speed control of all cylinders. The device also includes muffler  23  for releasing compressed air and controller  21  for controlling the operation of the valves and thereby operating the device. 
     Another aspect of the present disclosure provides a method for automated knot-tying utilizing the device described above. This method is best described in relation to  FIGS. 4(   a )-( i ) and  5 . 
     A first step  150  involves activating the first actuator to move from an original clip support arm position and rotate the clip support arm about the wire. The next step  152  involves attaching the end of the string to the clip. Then, in step  154 , using the first actuator to return the clip support arm to the original clip support arm position, the end of the string is drawn over the wire. In step  156  the third actuator is activated to extend the rod from an original rod position. In step  158  the fourth actuator is activated to extend the hook. Then, in step  160 , the second actuator is activated to rotate the clip support arm relative to the wire, wherein motion of the string is limited by the rod, thereby forming a loop. The next step  162  involves activating the first actuator to rotate the clip support arm around the wire. Then, in step  164 , the fourth actuator is activated to retract the hook, wherein the clip releases the end of the string which is then carried by the hook through the loop. And, finally in step  166 , the first, second, and third actuators are activated to return the rod to the original rod position and the clip support arm to the original clip support arm position. The device is moved to the next location, step  168 , and the process is repeated. 
       FIG. 4(   a ) is the original position of the whole knotting process. In  FIG. 4(   b ), clip support arm  3  is driven over the wire, where clip  4  catches the end  101  of string  100 . In  FIG. 4(   c ), pneumatic cylinder  5  extends rod  61  to catch string  100  as the clip support arm is returned to its original position, drawing the string over wire  2 . In  FIG. 4(   d ), pneumatic cylinder  9  extends hook  10 . In  FIG. 4(   e ), pneumatic cylinder  8  and motion arm  7  rotates clip support arm  3  and moves it laterally to the right side of the figure. In  FIG. 4(   f ), clip support arm  3  crosses over the wire again to the other side with the end  101  of the string. In  FIG. 4(   g ), pneumatic cylinder  9  retracts and hook  10  catches the end  101  of string to go through the loop  103 , while clip  4  releases the end of string. In  FIG. 4(   h ), pneumatic cylinder  5  retracts, and the knot is achieved as tension is applied to string  100 . In  FIG. 4(   i ), pneumatic cylinder  8  rotates back, and all parts return to the original position. 
     It should be emphasized that the above-described embodiments of the present device and process are merely possible examples of implementations and merely set forth for a clear understanding of the principles of the disclosure. Many different embodiments of the disclosure described herein may be designed and/or fabricated without departing from the spirit and scope of the disclosure. For example, string  100  may encompass many different types of stranded or solid structures, including for example wire, cable, twine, etc. Also, the pneumatic cylinders may be replaced by electric motors including linear motors, or other actuators. All these and other such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Therefore the scope of the disclosure is not intended to be limited except as indicated in the appended claims.