Patent Publication Number: US-2019184548-A1

Title: Robot arm design for high force delivery

Description:
FIELD OF THE INVENTION 
     The general field of this invention is construction of robotic arm required to deliver force through an end effector attached at or near one of its ends. More specifically, this invention teaches a novel way of constructing a robot arm that is carrying payload or delivering force at the first of its extremity and supported by a joint at the second extremity. This joint at the second extremity, transfers reaction force and bending moment that arise out of delivering force at the end effector, to the predecessor arm or to the ground. Thus, in order to support force at the end effector, the robot arm in question, its predecessor arm or arms, and all the joints across each of the robot arms are required to be progressively stronger, thus making the overall robot bulky. This is the traditional design approach for robot arms in prior art. However frequently the robot end effectors are required to deliver the force against a static or quasi static structure. Such examples are robots doing spot welding of an automotive chassis. Here the robot is applying spot welding force against automotive chassis, which itself is riding on a conveyor frame. Another example is a robot establishing a charging connection to an electric vehicle, where the robot end effector needs to deliver insertion or contact force to establish sufficient forces across the contactor interface while sliding the contacts together. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1 : Typical robot arm prevalent in prior art: Isometric view. 
         FIG. 2 : Typical robot arm prevalent in prior art: Side view. 
         FIG. 3 : Floating robot arm realized using rotational motion, showing significantly reduced joint force: Deployed position. 
         FIG. 4 : Floating robot arm in retracted position. 
         FIG. 5 : Floating robot arm realized using linear motion: Deployed position, side view. 
         FIG. 6 : Floating robot arm realized using linear motion: Deployed position, isometric view. 
         FIG. 7 : Floating robot arm realized using linear motion: Retracted position, isometric view. 
         FIG. 8 : Floating robot arm realized using linear motion: Retracted position, isometric view. 
         FIG. 9 : Floating robot arm realized using rotational motion in deployed position, and leveraging support from workpiece frame. 
         FIG. 10 : Floating robot arm realized using rotational motion in deployed position, and leveraging support from workpiece frame. 
         FIG. 11 : Floating robot arm realized using rotational motion in deployed position, and leveraging support from workpiece frame, showing vibration isolation capabilities of floating robot arm design. 
         FIG. 12 : Application example of innovation presented in this patent for EV charging from bottom of the EV.
     Error! Application example of innovation presented in this patent for EV charging from   Reference side or front of the EV.   source   not   found.:   
         FIG. 13 : Application example of innovation presented in this patent for EV charging from side or front of the EV. 
     
    
    
     PRIOR ART RELATED TO THE INVENTION 
     A traditional robot arm design prevalent in prior art is picturized in  FIG. 1 . Although specific robot arms may differ in design,  FIG. 1  essentially captures the basic design elements on all such designs. In particular this innovation focuses on the arm  4 . On one end of this arm, an end effector  5  is attached. This end effector is required to support force  6  demanded by the function the robot is carrying out. On the other end, the arm  4  is connected to a series of kinematic linkages represented by arm  3 , swivel base  2 , which is finally mounted to a stable base  1 . The joint between arm  4  and arm  3  is actuated by a motor  8  and gears  7 A,  7 B. The side view of the same arm is shown in  FIG. 2 . The motor  8  and gearbox  7 A,  7 B moves arm  4  relative to its predecessor arm  3 . The motor&#39;s holding torque and joint bearings transmit the reaction force and bending moment required to support force  6  of magnitude F imposed on end effector to the predecessor arm  3 . The holding force  10  at the joint of arms  3  and  4  is equal to F, but in opposite direction. The bending moment  11  at the joint of arms  3  and  4  is F·D, where D is the moment arm of force F, as viewed from the joint of arms  3  and  4 . This force  10  and bending moment  11  are borne by arm  3  and subsequently transmitted to the support  1 . In order to perform this task, the actuation mechanism comprising of motor  8  and gearbox  7 A &amp;  7 B as well as the arm  3 , base  2 , and the support  1  need to be appropriately strong. Within the range of hardware implementation and specific application needs, a real robot may look slightly different, but it will still follow the basic force and bending moment transmission structure. Such traditional design is appropriate in many cases where the robot does not have a readily available ground or a rigid frame to which it can lean against. Hence the traditional robots must be designed with enough strength and may become bulky. 
     DETAILED DESCRIPTION OF THE INVENTION 
     This patent teaches a novel method wherein a robot arm design can take advantage of a nearby rigid structure to significantly reduce the strength requirements of the entire robot. In essence—if designed correctly, a robot arm can lean on the nearby rigid structure and directly transmit the end-effector force to this rigid structure and effectively reduce the strength requirements of the robot. A convenient rigid structure to lean on may not always be available. However if available, this patent teaches a design philosophy to take advantage of it and effectively extract many advantages such as lighter compact design, immunity from vibration. 
     The arrangement: The basic concept of innovative design to reduce the joint forces and strength requirements of robotic systems is presented in its deployed form is presented  FIG. 3 . In  FIG. 4  the robot arm is shown in its retracted from. The arm  4  is split into two parts arm  4 A and arm  4 B. The arm  3  is modified to the shape  3 A. Arm  4 A and  4 B are free to rotate with respect to its predecessor arm  3 A. The end effector  5  is carried by the new arm  4 B. The original motor  8  and gearbox  7 A &amp;  7 B, which was originally designed to move  4  with respect to  3 A, is now modified to motor  13  and gearbox  12 A &amp;  12 B designed to move  4 A with respect to  4 B, with both  4 A and  4 B free to rotate with respect to  3 . 
     The operation: As an immediate consequence the bending moment transmitted to arm  3 A is reduced to zero. The arm  4 A+ 4 B starts in its home position shown in  FIG. 4 . As the  4 A and  4 B are made to move with respect to each other,  4 A first starts rotating counterclockwise while  4 B continues resting against extension if  3 A. Once  4 A reaches a stiff structure,  4 B and end effector  5  start their motion which is essentially same as the motion of the original arm  4 , eventually leading end effector  5  to its same original interaction point with the workpiece. Motor  13  and gearbox  12 A+ 12 B continue to exert torque until the desired force F is created at the interface between end effector  5  and workpiece. 
     Advantages: The force analysis of the arm  4  reveals that most of the required reaction force is derived from interaction between  4 A and the stiff structure  1 —it leans against. This force is F·D/(D−d), where d is the moment arm of the end effector force when viewed from the contact point between  4 A and the stiff structure  1 . Consequently, the remainder of the reaction force, is supported by arm  3 A through its joint with  4 A and  4 B. This force is merely F·d/(D−d). As can be visualized from  FIG. 3 , d can be made to approach zero or at least can be made significantly smaller than D. When d is made to approach zero, the force across  4 A and  1  will approach the end effector force F, and the force across  3 A and ( 4   a + 4 B) will approach zero. This—near zero force transmittal to arm  3 A and the inherent fact described earlier that there is no bending moment transmitted to  3 A, will allow for lighter and compact design for  3 A and  2 . 
     Three variants of this basic arrangement are shown in  FIG. 9 ,  FIG. 10  and  FIG. 11 . Each of those variations offer more specific advantages.  FIG. 9  shows that if a suitable extension of the workpiece  50  is available, then  4 A can be advantageously made to lean against that extension. This may be the case when a spot welding robot is welding an automobile frame which itself is being carried on a conveyer. Then the lean-against point could be other suitable part of the frame or part of the conveyer.  FIG. 10  shows that the force exerted at end effector  5  can be oriented differently as long as a suitable manner of leaning is chosen for  4 A. Furthermore, as shown in  FIG. 11 , if the base  2  is mounted on suitable roller bearings  52 , this arrangement can isolate the relative vibrations ( 60 ) between robot mount  1  and the workpiece  50 . 
     Variations: The arrangement presented in  FIG. 3  is an example of using a revolute pair to move the end arms  4 A+ 4 B in order to deliver end effector force. However the principle presented in this invention can also equally apply for other types of joints. For example,  FIG. 5 ,  FIG. 6 ,  FIG. 7  and  FIG. 8  show how the same concept can be used when a prismatic joint is used to deliver force  28  at the end effector  21 . The end effector  21 , the stoppers  22  are integral part of first half ( 20 ) of a prismatic pair. The prismatic pair is comprised of elements  20  (first half) and  23  (second half) sliding with respect to each other. The sliding is actuated by a suitable gearing (rack and pinion shown as example here) and a motor, collectively labeled as  25 . Another pair of stopper  24 , are integral part of  23 . The prismatic pair  20 - 23  is carried by the modified version  3 B or original link  3  using another prismatic pair formed by the interface of  20  and  3 B. Part  20  is free to move linearly with  3 B except its motion is arrested when the stoppers  22  press against  3 B. Part  23  is free to move linearly with respect to  3 B, except its motion is arrested when the stoppers  24  press against  3 B. 
     In its retracted form, the mechanism is shown in  FIG. 7  and  FIG. 8 . In this configuration, the prismatic joint  20 − 23  is pulled together such that stops  22  and  24  press against the arm  3 B. When actuator  25  is actuated to move  20  and  23  away from each other,  23  first moves downward till it hits the stiff base  1 , while  20  with its tabs  22 , continues to rest against  3 B. When actuator  25  continues to separate  20  and  23 , the part  20  starts is upward motion till the end effector  21  encounters the desired force against workpiece. As an immediate consequence, the prismatic pair  2 − 3 A transmits zero force to  3 A when direction of force  28  is aligned with the degree of freedom of  20 − 3 A pair. It&#39;s apparent from  FIG. 5 ,  FIG. 6 ,  FIG. 7  and  FIG. 8  that degree of freedom of  20 − 3 A pair can be made to align or “almost” align with the force  28 , and either eliminate or substantially reduce the force transmitted to  3 B, instead bulk of the force  28  is borne by the reaction  29  at the interface between  23  and  1 . 
     The Summary: The core concept of the invention presented here is to split a robot arm into a pair of linkages that are actuated with respect to each other, but are otherwise floating in a carrier. Since the linkage pair is floating within its carrier, it transmits zero or negligible force to the carrier. The force at the end effector acts on one member of the linkage pair into which the robot arm is split into, and is directly transmitted to the second member of the pair, which in turn leans against and transfers this force to a suitably chosen rigid structure. In the rendition shown in  FIG. 3 , the floating pair is  4 A− 4 B that is floating in the carrier  3 A. In the rendition shown in  FIG. 5 , the floating pair is  20 − 23  that is floating in the carrier  3 B. It should be noted that in both of the embodiments presented here the floating linkage pair is restricted to float along a single degree of freedom and completely eliminative any force or torque transmittal only along the floating degree of freedom. For example, in  FIG. 3 , the pair  4 A− 4 B is only rotationally floating along the axis of revolute pair between  3 A and the linkage pair  4 A+ 4 B. Similarly, in  FIG. 5 , the pair  20 − 23  is only linearly floating along the axis of prismatic pair between  3 B and the linkage  20 . Although this could be more commonly encountered situation, the floating need not be restricted to a single degree of freedom. 
     The floating linkage pair takes care of force or torque along those directions that are floating. Along the remaining directions, forces and torques can still be transmitted to the rest of the robot. However, by proper arrangement of dimensions of the linkage pair, designers can eliminate or significantly reduce the magnitude of such force or torque transmitted to the rest of the robot structure. For example, in the  FIG. 3 , the floating linkage  4 A+ 4 B is capable of transmitting a force to  3 A. However by adjusting the dimension d, one can significantly reduce or in some cases completely eliminate the transmitted force. Likewise, in the arrangement presented in  FIG. 5 , the floating linkage  20 + 23  is capable of transmitting a bending moment (torque) as well as force in one direction to  3 B. However by angularly aligning the direction of prismatic pair  3 B− 20  with force  28 , one can significantly reduce or in some cases completely eliminate the transmitted force. Also by arranging the geometry of  20  and  23  in such a way that the two forces  28  and  29  are aligned, one can eliminate or substantially reduce the bending moments transmitted to  3 B. 
     It should be noted that there are several more dimensional as well as joint configuration variations may arise from customization of this basic concept presented in this invention, and all of those should be treated as different embodiments of this invention. 
     Application Example: With the rebirth of electric vehicles (EVs), the problem of charging of EVs without human intervention has become a critical element in successful deployment of EVs. There are two possible technologies that can be used to charge an EV without human intervention. One is an inductive charging and another is conductive charging. In order to alleviate range anxiety, EV are evolving in the direction of bigger and bigger batteries. Since an inductive charger cannot deliver electrical energy at higher rate, the conductive charging is the technology of choice. In this approach, the charging energy is delivered to EV by a robot. Using its articulation, the robot compensates for parking misalignments associated with each time the EV is parked on the charging spot. Having compensated for the misalignments, the robot arm then pushes one half of a charging connector against its counterpart attached to the EV. Specific points to note in this case are (i) the robot arm is expected to deliver a particular predetermined force to the mating two halves of the charging connector, (ii) the EV is stationary at the time the robot is attempting to establish a charging connection, (iii) the charging robot needs to be placed at or near the location an EV will be parked, and consequently needs to be a compact device that consumers or parking lot operators can accept in their home garage or public charging sport respectively. If such a charging robot is compact it will also not come in the way of cars driving in and around the concerned charging spot. These key requirements of an EV charging robot make it a perfect application for innovation presented in this patent.  FIG. 12  shows how the arrangement originally shown in  FIG. 3  can be used for an EV charging robot.  FIG. 13  also shows an embodiment of this invention in which a pusher pin or a pull pin  4 A leans on an EV either to extract a charging plug out or to push a charging plug in. 
     What is presented in this patent application are only few representative embodiments of the core innovation. There are countless situations where this innovation can be applied. Any variant embodiments of this innovation are anticipated by this disclosure and hence are to be considered as part of this patent.