HAND GEAR TRAIN WITH THREE DEGREES OF FREEDOM

Abstract: A remotely operated hand gear train for the orientation of an end effector mounted at one end of a hand gear train, comprising an external housing (39) adapted to be mounted onto a robot arm. The housing defines a first axis A₁. A first housing (41) is rotatably mounted within the external housing for movement about the first axis A₁. The first housing defines therein a second axis A₂ which is substantially perpendicular to the first axis A₁. A second housing (71) is rotatably mounted in the first housing for rotation about the second axis A₂. The second housing defines therein an axis A₃ which is normal to axis A₂ and radially spaced from axis A₁. A third housing (101) is rotatably mounted in the second housing for rotation about axis A₃. The third housing has a gear rack (109) circumferentially disposed about the end thereof. Separate drive systems are provided for effecting the rotation of the different housings about their respective axes and relatively to one another.

Description: The invention is directed generally to industrial manipulators, and more particularly, to a robotic wrist for use in industrial manipulators. The improved wrist of this invention takes the form of an end effector mounted at the end of a robotic arm, and provides three degrees of freedom. The introduction of robotics into the manufacturing facility has resulted in a demand for a variety of robotic components, such as end effectors which are gripper like devices which manipulate tools or components in the manufacturing process and wrists which can offer any number of degrees of freedom or levels of compliance. The specific application of the end effector to a given manufacturing process can require a multi-jointed, complex wrist design which also provides several degrees of freedom. The dexterity of the end effector and the industrial manipulator is reflected in directional movement capabilities which are indicated as degrees of freedom. It is an objective in the design and construction of industrial manipulators to mimic limited aspects of various human hand capabilities in order to improve the positional accuracy of industrial manipulators in a variety of tasks. Accordingly, an end effector of a robotic arm must be able to reach workpieces and tools. This requires a combination of an arm and a wrist subassembly, plus an end effector. The robot's sphere of influence is based upon the volume into which the robot's arm can deliver the wrist subassembly. A variety of geometric configurations have been studied and tried and their relative kinematic capabilities appraised. Such configurations include cartesian coordinates, cylindrical coordinates, polar coordinates and revolute coordinates. Evidently each of these configurations offers a different shape to its sphere of influence, the total volume of which depends upon arm link lengths. For different applications, different configurations may be appropriate. For example, a revolute arm might be best for reaching into a tub, while a cylindrical arm might be best suited to a straight thrust between the dies of a punch press. In every case however, the arm carries a wrist assembly to orient its end effector as demanded by workpiece placement. Commonly, the wrist provides three articulations that offer motions labeled pitch, yaw and roll. It should be noted that any of the arm coordinate systems requires three articulations to deliver the wrist assembly anywhere in this sphere of influence. It then requires three more articulations in the wrist for universal orientation of the end effector. Quite often, robots are able to cope with job assignments without employing a full set of six articulations. This arises out of some symmetry in either the workpiece or the workpiece layout. For example, to move a bowling ball around in the sphere of influence requires only three articulations, because a ball is always oriented, irrespective of a gripper's orientation. More frequently, parts have one axis of symmetry, i.e. cylindrical, and this allows the robot arm to degenerate to five articulations. In practice, five articulations are quite often adequate when the workpiece is arranged to reduce part manipulation needs. This happens, for example, when the beds of machine tools are all located parallel to one axis of a cartesian coordinate robot or on a radius of base rotation for cylindrical, polar or revolute robot arms. It may be argued that this compromising of the number of articulations is begging the question of robots versusspecial purpose automation. The robot should be the universal solution, readily transferred to other applications. In this vein, reference should be made to the elegance of computer control of robot arms. Given a six articulation arm of any confuguration, soft ware can permit a program to be generated in cartesian coordinates irrespective of the choice of articulations. Indeed, the software can be powerful enough to think only in tool coordinates. That is, the programmer concerns himself with the tool on the end of the robot arm, He can think in terms of the tool's frame of reference and computer subroutines automatically make the various articulations move so as to accomplish the desired tool manipulation. A drive mechanism of the desired form is known from the European Patent EP 0 0054 763. The reference discloses a gear train, that uses in addition to gear members belts for driving communications with respect to two axis. This is a disadvantage that can influence in positioning of the end effector. Since belts may be demaged, a loss of production time must be accounted for, when the gear train is used in a robotic system for production. The problem of the invention is to create the compact gear train with three degrees of freedom that does not contain any belts. The invention in its broad form comprises a remotely operated hand gear train for the orientation of an end effector mounted at one end thereof comprising: an external housing adapted to be mounted onto a robot arm, defining a first axis A1; a first housing rotatably mounted within said external housing for rotation about said first axis A1 defining therein a second axis A2, which is substantially perpendicular to said first axis A1; a second housing rotatably mounted within the first housing for rotation about the second axis A2, said second housing defining therein a third axis A3 which is normal to the second axis A2 and radially spaced from the first axis A1; a third housing rotatably mounted in said second housing for rotation about the third axis A3, said third housing having a third housing gear rack circumferentially disposed about the end thereof; a first drive system for effecting the rotation of said first housing about said first axis A1 comprising gear means disposed about said first housing and gear drive means engaged therewith, a second drive system for effecting rotational movement of said second housing about said second axis A2, comprising first gear means, mounted rotatably around the first axis A1 with a first gear rack and a second gear rack disposed within said housing about one end of said axis A1, gear drive means engaged with said first gear rack, wherein said second housing includes gear means disposed concentrically about said second axis A2, and wherein said second gear rack is engaged therewith such that rotation is efffected by a said gear drive means; a third drive system for effecting rotational movement of said third housing about said third axis A3, comprising gear means rotatably mounted about the other end of said first axis A1 and having a first gear rack and a second gear rack, said third gear drive system engaged with said first gear rack, a drive shaft having a third gear rack at one end and a fourth gear rack to the other end rotatably mounted within said second housing about said second axis A2, said fourth gear rack being engaged with said first gear rack and said second gear rack being engaged with said housing gear rack; characterized by, that said gear means mouted at the second housing of the second drive system being located between said third gear rack and said fourth gear rack mounted on said drive shaft of said third drive system. It is an advantage of the invention to locate parts of the third degree of freedom inside the part that belongs to the second degree of freedom. Further, it saves space and allows a construction, where belts can be avoided. The movement of rotation is only transmitted be gear racks, so that the accuracy of positioning only depends on the tolerances of the construction and is independent on additional factors like the weekness or the resilience of the belts. A preferred embodiment described herein provides a remotely operated hand gear train for the orientation of an end effector mounted at one end of a hand gear train. The described arrangement comprises an external housing adapted to be mounted onto a robot arm. The housing defines a first axis A₁. A first housing is rotatably mounted within the external housing for movement about the first axis A₁. The first housing defines therein a second axis A₂ which is substantially perpendicular to the first axis A₁. A second housing is rotatably mounted in the first housing for rotation about the second axis A₂. The second housing defines therein an axis A₃ which is normal to axis A₂ and radially spaced from axis A₁. A third housing is rotatably mounted in the second housing for rotation about axis A₃. The third housing has a gear rack circumferentially disposed about the end thereof. A first drive system for effecting the rotation of the first housing about the first axis A₁ comprises gear means disposed about the first housing and gear drive means operatively associated therewith. A second drive system for effecting rotational movement of the second housing about the second axis A₂ comprises a first gear means with a first gear rack and a second gear rack concentrically disposed about one end of the first axis A₁ within the housing. Gear drive means are operatively associated with the first gear rack. The second housing includes gear means disposed thereabout and the second rack is operatively associated therewith such that rotation of the gear drive means is effected thereby. A third drive system for effecting rotational movement of the third housing about the third axis A₃ comprises gear means rotatably mounted about the other end of the first axis A₁. The third drive system includes a first gear rack and a second gear rack. A third gear drive means is operatively associated with the first gear rack and a drive shaft having a third gear rack at one end and a forth gear rack at the other end is rotatably mounted within the second housing about the second axis A₂. The gear means second rack is operatively associated with the gear rack and the second gear rack is operatively associated with the third housing gear rack. BRIEF DESCRIPTION OF THE DRAWINGS A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjuntion with the accompanying drawing in which: Figure 1 is a perspective view of an industrial manipulator incorporating the hand gear train according to this invention therewith; Figure 2 is a sectional view of the hand gear train of this invention illustrating the various axes of motion and the drive means by which this motion is effected; Figure 3 is a schematical representation of the hand gear train of this invention illustrating the gears and drive shafts associated with the A₁ axis; Figure 4 is a schematical representation of the hand gear train of this invention illustrating the gears and drive shafts associated with motion about the A₂ axis; and Figure 5 is a schematical representation of the hand gear train of this invention illustrating the gears and drive shafts which affect motion about the A₃ axis. DETAILED DESCRIPTION OF THE INVENTION A hand gear train generally indicated by the reference character 11, is shown in Figure 1 mounted at the end of an arm of a Unimate Series 2000 industrial robot generally indicated by the reference character 13. The hand gear train 11 provides three degrees of freedom as indicated by the axes designated A₁, A₂ and A₃. The Unimate Series 2000 robot 13 is but a single example of any one of a variety of robots onto which the hand gear train of this invention can be mounted. The robot 13 is designed for welding, adhesive or sealant deposition, machine loading, inspection and a variety of other material handling applications. The robot 13 is secured to a work area by means of base member 15 and includes an arm 17 mounted onto the base member 15. As can be seen from Figure 1, the hand gear train 11 is operably mounted on the free end of the arm 17 as at 19. Considering now Figures 2, 3, 4 and 5 the construction and operational capabilities of the hand gear train 11 are described with respect to the axes of motion incorporated therewith. More specifically, Figures 3, 4 and 5 are individually dedicated to axes A₁, A₂ and A₃, respectively while Figure 2 illustrates a sectional view of the hand gear train in which the cooperation of the various subsystems is shown in detail. As can be seen axes A₁ and A₃ are perpendicular to axis A₂ and are in a spaced relationship with respect to each other. The hand gear train housing which defines the several axes of motion and encloses the various drive means associated with the hand gear train includes a housing right half and a housing left half 31 and 33, respectively. A further portion of the housing provides a robot arm interface as at 35. A housing cover 37 is fixedly secured to the housing right half 31 in order to enclose the A₃ axis drive pinion which will be described in detail hereinafter. The several housing components 31, 33, 35 and 37 generally comprise an external housing collectively indicated by the reference character 39 and defining therein a first axis A₁ which is substantially perpendicular to the arm 19 of the robot to which the housing is attached. A first housing generally indicated by the reference character 41 is rotatably mounted within the external housing 39 for rotation about the first axis A₁. The housing 41 is mounted by means of bearing sets and for rotation within the housing 39. The housing 41 includes a geared portion 47 which cooperates with the geared portion 49 of the drive pinion 51. Rotational movement is imparted to the drive pinion 51 by a conventional drive take off from the robot schematically indicated at the reference character 53. The drive pinion 51 is supported within the housing 39 by several bearing sets indicated at 55. The first housing 41 defines therein the second axis A₂ which is substantially perpendicular to axis A₁. Thus, as the drive pinion rotates and drives the through gears 49 and 47 the first housing 41, the hand gear train rotates about axis A₁. Rotation can be effected in either direction and is typically limited to approximately 270° in order to avoid interference with the robot arm 19 by the hand gear train. The housing 41 includes a center shaft member 57 which extends through the right and left housing portions 31 and 33 of the external housing 39. In addition to providing rigidity to the first housing 41 the center shaft 57 also serves to prevent the spreading of the right and left housing halves 31 and 33 during gear train operation. As can be seen, each end of shaft 57 includes a cap portion 59 between which cap portion 59 and the housing portion 61 adjacent thereto are disposed thrust bearings 63. This configuration in which the shaft extends beyond the housing portions and includes bearings disposed between the external portion of the housing and the ends of each shaft tends to eliminate any problems previously encountered due to the spreading of the external housing 39. A second housing 71 is rotatably mounted within the first housing 41 for rotation about the second axis A₂ defined by the first housing 41. The second housing 71 defines therein a third axis A₃ which is normal to axis A₂ and in a spaced relationship with axis A₁. The second housing 71 has a hollow inner portion which is adapted to receive the drive means and third housing for rotation about axis A₃ which will be described hereinafter. The first housing portion 41 supports the second housing 71 therewithin by means of bearing sets 73 and 75. The portion of the housing 71 furthest from the center shaft 57 includes an extended housing portion as at 77 which is adapted to receive therein the third housing 101. The portion 77 of the second housing 71 is capable of 360° of rotation about axis A₂ due to drive motion imparted to the housing portion 71 by means of the gear 79 mounted for rotation about shaft 57 and the drive pinion 81. The drive pinion 81 is mounted in the external housing 39 by means of bearing sets 83. A geared face 85 of the drive pinion 81 is in communication with a first geared section 87 of the gear means 79. The gear 79 also has a second toothed portion at 87 which is in mechanical communication with the geared portion 89 of the second housing 71. Here again, proper bearing support is provided as at 91 for the gear member 79 to permit rotational movement with respect to the shaft 57 of the first housing 41. The third housing 101 is rotatably mounted within the second housing portion 77 for rotation about axis A₃ defined by the third housing portion 77. Typically, the third housing 101 would be adapted to receive at the outside face 103 thereof, an end effector or appropriate tool for use in a desired application. Such a tool could be fixedly attached to the face portion 103 of the third housing 101 or removably mounted thereon for tool selection in a robotic system. The third housing 101 is mounted for rotation within the second housing member 77 by means of bearings 105. A geared face 107 is disposed on the inside face 110 of the third housing 131. Rotational movement of the third housing 101 about the axis A₃ is effected by means of a drive system. The drive system consists of drive pinion 105 mounted in the external housing 41 of the gear hand train. The drive pinion 105 which is supported within the external housing 41 by means of bearings 107 includes a gear portion 109 which is in direct mechanical communication with geared shaft 111. The geared shaft 111 includes a first geared portion as at 113 which is in communication with the drive pinion 105 gear set 109 and a second geared portion at the other end thereof 113. The shaft 111 is rotatably mounted about the center shaft 57 of the first housing 41 and supported thereon by means of bearings 115. Additional bearings as at 116 are disposed between the outside portion of the geared shaft 111 and the inner portion of the external housing 41. The gear portion 118 of the shaft 111 is in communication with a center drive shaft 117 by means of geared portion 119 of the shaft 117. The shaft 117 is disposed along the second, axis A₂. At the end of the shaft 117 which extends away from the central shaft 57 is a gear portion 121 which is in communication with the gear portion 107 of the third housing 101. Accordingly as the drive pinion 105 rotates, shaft 111 concentrically mounted with the shaft 57 along axis A₁ is rotated. The rotation of shaft 111 effects the rotation of pinion 117 which is coaxial with axis A₂. The rotation of pinion 117 effects the rotation of the third housing portion 101 about axis A₃. What has been described is a remotely operated hand gear train which orients an end effector mounted at one end of three interconnected drive means and housings. The hand gear train has two sets of concentric shafts with individual shafts that engage at an angle of 90°. The third connected drive shaft is not a set of concentric shafts. The preferred embodiment has the axis of the two sets intersecting at a single point and permits the rotation of two axes relative to each other by the combined movement of the connected drive shafts.

Claims: A remotely operated hand gear train (11) for the orientation of an end effector mounted at one end of a robot arm (19) comprising: an external housing (39) adapted to be mounted onto the robot arm (13), defining a first axis (A1), a first housing (41) rotatably mounted within said external housing (39) for rotation about said first axis (A1) defining therein a second axis (A2), which is substantially perpendicular to said first axis (A1), a second housing (71) rotatably mounted within the first housing (41) for rotation about the second axis (A2), said second housing (71) defining therein a third axis (A3) which is normal to the second axis (A2) and radially spaced from the first axis (A1), a third housing (101) rotatably mounted in said second housing (71 )for rotation about the third axis (A3), said third housing (101) having a third housing gear rack (107) circumferentially disposed about the end thereof, a first drive system (51,53) for effecting the rotation of said first housing (41) about said first axis (A1), comprising gear means (47) disposed about said first housing (41) and gear drive means (49) engaged therewith, a second drive system (81) for effecting rotational movement of said second housing (71) about said second axis (A2), comprising first gear means (79), mounted rotatably around the first axis (A1) with a first gear rack (87) and a second gear rack (88) disposed within said housing (71) about one end of said axis (A1), gear drive means (85) engaged with said first gear rack (87), wherein said second housing (71) includes gear means (89) disposed concentrically about said second axis (A2), and wherein said second gear rack (88) is engaged therewith such that rotation is effected by said gear drive means (85), a third drive system (105) for effecting rotational movement of said third housing (101) about said third axis (A3), comprising gear means (111) rotatably mounted about the other end of said first axis (A1) and having a first gear rack (113) and a second gear rack (118), said third drive system (105) engaged with said first gear rack (113), a drive shaft (117) having a third gear rack (121) at one end and a forth gear rack (119) at the other end rotatably mounted within said second housing (71) about said second axis (A2), said fourth gear rack (119) being engaged with said first gear rack (113) and said second gear rack (121) being engaged with said third housing gear rack (107), characterized by that said gear means (89) mounted at the second housing (71) of the second drive system is located between said third gear rack (113) and said forth gear rack (119) mounted on said drive shaft (117) of said third drive system. A remotely operated hand gear train according to claim 1, wherein said first housing (41) is mounted on a center shaft (57) for rotation about said first axis (A1) within said external housing (39), with said center shaft (57) extending beyond said external housing (39) and being mounted by means of bearing sets (63) positioned in an external portion of the external housing (39) covered by cap portion. A remotely operated hand gear train according to claim 1, wherein said second housing (71) is supported within said first housing (41) by means of bearing sets (73,75) and comprises an extended housing portion (77) which is adapted to receive therein said third housing (101), said extended housing portion (77) being rotatable by means of said first gear means (79,87) of the second drive system which meshes with said gear drive means (85) of the second drive system. A remotely operated hand gear train according to claim 1, wherein said housing gear rack (107) meshes with said third gear rack (121) of said drive shaft (117) which is disposed along the second axis (A2), with the opposite side of said drive shaft (117) engaging gear means (111) of the third drive system concentrically mounted with said center shaft (57) along the first axis (A1), said gear means (111) of the third drive system being directly engaged with a drive pinion of said third drive system (105). A remotely operated hand gear train for orientation of an end effector according to claims 1 to 4, wherein said hand gear train is combined with arm means of a robot for positioning said end effector within a work envelope of said robot.

Inventors: COLIMITRA, THOMAS ANDREW
Applicants: UNIMATION INC.
Application year: 1986
Main classification: B25J17
IPC codes: B25J17, F16H1, B23Q5