Four-degree-of-freedom parallel manipulator for producing Schönflies motions

[0001] This is a continuation of International Patent Application No. PCT/CA2003/001695 filed Nov. 5, 2003, which claims benefit of U.S. Provisional Patent Application No. 60/424,393 filed on Nov. 6, 2002, now abandoned.

[0002] 1. Field of the Invention

[0003] The present invention relates to a manipulating device aiming at the production of four-degree-of-freedom displacements of a rigid body.

[0004] 2. Description of the Prior Art

[0005] Four-degree-of-freedom displacements were first studied by the German mathematician-mineralogist Arthur Moritz Schönflies (1853–1928), who found that these displacements have the algebraic structure of a group. For this reason, the set of such motions is known to geometers as the Schönflies subgroup of the group of rigid-body displacements. A familiar instance of Schönflies motions is found in the motions undergone by the tray of a waiter: the tray is free to move in all directions, but is prevented from tilting. The displacements comprise three independent translations and one rotation about an axis of fixed orientation with respect to a fixed base.

[0006] Schönflies motions are suitable for assembly tasks of the type occurring in the electronics industry. In these tasks, electronic chips having a flat geometry are picked up from a magazine, where they lie in a planar array. The chips are then placed on an electronic board in a planar array as well, the two planes involved being parallel but lying at different levels, the arrays thus having different orientations. These tasks require free translations in the three directions of space plus one free rotation about an axis of orientation fixed with respect to the plane of the magazine. The mechanism realizing these tasks must therefore exhibit a very large stiffness against rotations about two axes normal to the axis of rotation. These features motivate the name SCARA for this type of devices: Selective-Compliance Assembly Robot Arm.

[0007] Schönflies-motion generators, or SCARA systems, are not new. The Russian Patent SU921848 of Sep. 25, 1980 to Zharkov et al., discloses a redundant manipulating device that can be used for the generation of Schönflies motions, but through a serial layout of links and motors.

[0008] U.S. Pat. No. 4,610,598 issued on Sep. 9, 1986 to Hamada et al. discloses an industrial robot implementing Schönflies motions. The industrial robot has a kinematic chain of a serial manipulator, with the four axes of the Schönflies motions being actuated by motors traveling with the moving links. This mounting of the motors on the moving links imposes a high inertia load on the links, bringing about a low load-carrying capacity and a high flexibility of the structure. The high flexibility prevents high-speed operations because these operations induce structural resonance in flexible structures. As opposed to a serial layout, current industrial trends point at parallel arrays because they allow for a placement of the motors on a fixed base, thereby allowing for lighter, stiffer, and hence, faster structures.

[0009] A parallel array of serial chains producing individually Schönflies motions are found in U.S. Pat. No. 4,976,582 issued on Dec. 11, 1990, to Clavel, and in EP patent EP1084802 issued on Mar. 21, 2001, to Company et al., as well as in a number of similar devices appearing in the technical literature. The outcome of the patent to Company et al., like that to Clavel, is that the coordinated motion of various legs coupled to a common moving platform is lacking the rotation required in a Schönflies motion, because the rotations of the Schönflies motions of the individual legs are incompatible since their axes of rotation are nonparallel. In order to produce Schönflies motions of axis normal to all four motor axes, which are all parallel to a given plane, Company et al. resort to a planar linkage carrying the moving platform that hence undergoes Schönflies motions. Various embodiments of this invention have been reported in the Proceedings of the IEEE International Conference of Robotics and Automation in 2001, 2002, and 2003.

[0010] U.S. Pat. No. 6,095,011 issued on Aug. 1, 2000, and U.S. Pat. No. 6,301,988 issued on Oct. 16, 2001, both to Brogårdh, disclose devices intended to enhance Clavel's patent by having an axis of rotation normal to the coplanar axes of the Schönflies motions of the legs. However, none of these two inventions provides four degrees of freedom of the Schönflies type.

[0011] U.S. Pat. No. 6,336,374 issued on Jan. 8, 2002, to Brogårdh, discloses an improved version of his previous patents, providing for translations in three directions, as well as rotation around one of the axes. Here, the rotation is provided with a separate motor, installed on a first link of a manipulator with a long and intricate transmission between the motor and the rotating device. In a four-degree-of-freedom embodiment, two motors are installed on a base of the structure, and two are installed on a moving link. Thus, this embodiment represents a relatively complex, heavy and, consequently, slow device.

[0012] Several U.S. patents, namely, U.S. Pat. No. 4,437,635 issued on Mar. 20, 1984, to Pham; U.S. Pat. No. 5,746,093 issued on May 5, 1998, to Poglitsch; U.S. Pat. No. 5,397,323 issued on Mar. 14, 1995, to Taylor et al.; U.S. Pat. No. 5,419,674 issued on May 30, 1995 to Chang; U.S. Pat. No. 4,782,726 issued on Nov. 8, 1988 to Ryder et al.; and U.S. Pat. No. 5,931,832 issued on Aug. 3, 1999, to Jensen, disclose a variety of devices, all based on two serial parallelogram linkages, moving in the same plane, thus providing planar two-degree-of-freedom motion. Some of the foregoing inventions provide also additional motion of a base with the help of an additional motor. None of these inventions provides four-degree-of-freedom motions of the Schönflies type.

[0013] U.S. Pat. No. 5,536,135 of Jul. 16, 1996 to Robertson discloses a serial device with two orthogonal parallelogram-arrays, but only with two drives, thus allowing for two-degree-of-freedom translations with constant orientation of a tool.

[0014] Two four-degree-of-freedom parallel mechanisms, by Rolland, are described in Vol. 67, pp. 831–844 of ASME Journal Dynamic Systems and Control Division, of 1999. These two devices provide Schönflies motions. In one of these mechanisms, dubbed Kanuk, the author suggests to use four linear motors driving lower ends of links along rails. The second mechanism, dubbed Manta, uses three linear motors also driving the lower ends of links along the rails, and a fourth rotation motor installed on one of the links. These two devices thus need a very large space for installation and motion of the legs, providing at the same time a rather small workspace.

[0015] Finally, 50 parallel mechanisms capable of generating Schönflies motions were disclosed by Yang et al. in “Structure Synthesis of a 4-dof (3-translation and 1-rotation) Parallel Robot Mechanisms Based on the Units of Single-Opened-Chain”, Proceedings of the ASME 2001 Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2001/DAC-21151, Pittsburgh, Pa., U.S.A. Some of the mechanisms disclosed have legs with a single parallelogram, and the other mechanisms have a configuration without any parallelograms.

[0016] It is therefore an aim of the present invention to provide a new manipulating device capable of producing Schönflies, or SCARA, motions.

[0017] It is another aim of the present invention to provide a new manipulating device in which motors driving links thereof are fixed to a base so that moving parts can be lighter, thereby allowing for higher velocities and accelerations of an end-effector, a moving platform undergoing Schönflies motions.

[0018] It is yet another aim of the present invention to provide a new manipulating device in which four independent motions are produced by motors resting on a base thereof, the motions being transmitted from the motors to an end-effector of the device by at least two legs.

[0019] It is a further aim of the present invention to provide a new manipulating device which is capable of producing the motions of SCARA systems with a simple, fully-parallel structure that allows for high operational speeds in order to maximize production throughput.

[0020] It is an additional aim of the present invention to provide a new manipulating device that is capable of producing the motions of SCARA systems with a relatively simple parallel structure including as few as two legs, thereby reducing a likelihood of link-interference.

[0021] It is another aim of the present invention to provide a device which can be used in the electronics industry and in any other application where high-speed pick-and-place operations are needed, such as in packaging and bottling, the device producing translations in three directions and rotation about an axis of fixed direction.

[0022] It is a further aim of the present invention to provide a new manipulating device with four degrees of freedom which can be used in the design of virtual-axis machine tools upon mounting of a workpiece on a rotating table, common in the industry, to provide a fifth degree of freedom.

[0023] Therefore, in accordance with the present invention, there is provided a manipulating device for producing Schönflies motions comprising a parallel array of at least two legs, each leg including an actuator unit having first and second ends and producing a pan-tilt motion, each leg also including a passive unit having first and second ends, the first end of the passive unit being coupled to the first end of the actuator unit such that the passive unit reacts to the pan-tilt motion, a base connected to the second end of each actuator unit, all second ends having a constant relative position with respect to one another, and a common end-effector connected to the second end of all passive units such that the common end-effector is provided with a Schönflies motion by the legs, the Schönflies motion being composed of three independent translations and one rotation about an axis of fixed orientation.

[0024] Further in accordance with the present invention, there is provided a manipulating device for imparting a four-degree-of-freedom motion to an end-effector, the four-degree-of-freedom motion being composed of three independent translations and one rotation about a first axis of fixed orientation, the manipulating device comprising a parallel array of at least two legs attached to the end-effector, each leg including an actuator unit serially coupled to a passive unit, each actuator and passive units including a turntable adapted to experience a rotation about a second axis parallel to the first axis, each actuator and passive units also including a swing member having a first end attached to the turntable and being adapted to experience a tilt motion so that a second end of the swing member is translated along a perimeter of an imaginary circle lying in a plane parallel to the second axis, and each actuator unit being provided with actuating means to provide the rotation of the turntable thereof and the tilt motion of the swing member thereof such as to produce an actuator motion, the actuator motion of each actuator unit causing a passive motion of the passive unit coupled thereto, the passive motion of the passive unit being composed of the rotation of the turntable thereof and the tilt motion of the swing member thereof, such that a combination of the actuator motion with the passive motion produces a leg motion for the corresponding leg, whereby a combination of the leg motions imparts the four-degree-of-freedom motion to the end-effector.

[0051] FIG. 1 illustrates a preferred embodiment of the present invention wherein a manipulating device A generally comprises two identical four-degree-of-freedom serial legs B arranged in a parallel array. Each leg B has a base 1 and all legs B share one common end-effector, namely moving platform 35. All bases 1 are fixed relatively to one another. It is also contemplated to have a manipulating device A having more than two legs B, as will be seen further below. In any case, each leg B comprises an actuator unit C serially connected to a passive unit D, each passive unit D being a non-actuated version of the actuator unit C. All legs B produce Schönflies displacements of identical directions. The direction of a set of Schönflies displacements is the direction of the axis of the unique rotation comprised therein. The intersection of all Schönflies displacements forms a Schönflies subgroup having a direction identical to the direction of the individual Schönflies displacements.

[0052] More specifically, the actuator unit C and the passive unit D of each leg B each produces a set of two-degree-of-freedom displacements: one pan motion, or rotation about an axis parallel to a line L fixed to the base 1 of the leg B, and one tilt motion, or translation along a circle lying in a plane parallel to L (see FIG. 2–3), both combining to produce a pan-tilt motion. While the axes of rotation of the two units C,D are both parallel to L, and hence, parallel to each other and to the axis of the rotation of the moving platform 35, the axes translate independently, keeping their orientations fixed. Moreover, the planes of the two circles make a dihedral angle of variable magnitude.

[0053] As shown in FIG. 4, each actuator unit C comprises the base 1 linked to a support frame 2. A rotating housing 8 is rotatable similarly to a turntable, thereby producing the pan motion, by being rotatively mounted on the support frame 2 and supported by thrust bearings housed in a thrust bearing housing 24. As shown in FIG. 2, each actuator unit C further includes a driving link 27 operatively connected to an active parallelogram linkage 30 via a coupler link 31, so that the active parallelogram linkage 30 can act as a tilt or swing member. Likewise, as shown in FIG. 1, each passive unit D comprises a base 32 mounted at the distal end of the active parallelogram linkage 30, a passive rotating housing 34 supported on the base 32 and also acting as a turntable with respect thereto, and a passive parallelogram linkage 33 linked to the rotating housing 34 and acting as a swing member. Each of the identical actuator units C is therefore coupled to its companion passive unit D, both units C,D being capable of tilt motion through the parallelogram linkages 30,33 and of pan motion through the rotating housings 8,34. The bases 32 of the two passive units D are kept horizontal by virtue of the active parallelogram linkages 30 of the actuator units C; their parallelogram linkages 33, in turn, keep horizontal the common platform 35, to which both passive parallelogram linkages 33 are coupled by means of pin joints.

[0054] Thus, the passive units D react to the motions of the actuator units C, the manipulating device A providing as a result a four-degree-of-freedom motion to the moving platform 35: three translations and one rotation about one axis of fixed orientation. The manipulating device A provides a manipulation system with a horizontal end-effector (the moving platform 35) having the motion capability of a SCARA leg, thereby giving such a motion to a gripper 36 installed on the moving platform 35 and grasping rigidly a workpiece or tool 37.

[0055] As can be seen in FIG. 5, a top view of the manipulating device A shows that the passive parallelogram linkages 33 are attached to the common moving platform 35 in a diametrically aligned fashion, thus characterizing this embodiment by parallel vertical mid-planes of the passive parallelogram linkages 33 of the two legs B.

[0056] Referring to FIG. 4, a layout of the transmission, with a sketch of a differential mechanism of an actuator unit C, will be described.

[0057] The rotating housing 8, enclosing the differential mechanism, rotates with respect to the base 1, where motors 28 and 29 are mounted. The pairs of motors 28 and 29 of both actuator units C can generally be installed at different levels. However, it is preferable to keep them at the same level in order to obtain a better load balance. In a preferred embodiment, the motors 28,29 are placed as shown in FIG. 4, which allows for all four motors of the device A to be fixed to the bases 1.

[0058] A driving torque from motor 28 is successively transmitted from a motor shaft 4 to a first gear 3 rigidly attached thereto, then to a second gear 10 meshed with gear 3, to a hollow shaft 11 rigidly attached to gear 10, and then to a bevel lower sun gear 20, rigidly attached to an opposite end of the hollow shaft 11. Similarly, a driving torque of motor 29 is successively transmitted from a motor shaft 21 to a first gear 22 rigidly attached thereto, then to a second gear 12 meshed with gear 22, to a central shaft 5 rigidly attached to gear 12, and then to a bevel upper sun gear 15 rigidly attached to an opposite end of the central shaft 5.

[0059] The torque from the bevel sun gears 15,20 is transmitted to bevel planet gears 17 and 17′ which are orthogonally meshed with both sun gears 15,20 to form a differential system, the planet gears 17,17′ being respectively fixed on first and second output shaft 18 and 19. The torque is then transmitted from each of the output shafts 18,19 to a respective one of the driving links 27 through one of the speed reducers 6,9. The two speed reducers 6,9 are of opposite hands, which allows for a balanced driving of the parallelogram linkage 30. This requires that one of the two speed reducers 6,9 include a speed reverser. Also, because of the differential system, a difference of rotation velocity between sun gears 15,20 creates a rotation of the axis of the planet gears 17,17′ around the central shaft 5, which causes the rotating housing 8 to rotate with respect to the base 1.

[0060] In order to add structural stability to these transmissions, ends of the motor shafts 4,21 are supported in the support frame 2 by support bearings 13. The hollow shaft 11 of the lower sun gear 20 passes through a bore in the support frame 2, the assembly hollow shaft 11—sun gear 20 being held in place by thrust bearings 16 for additional structural stability. The central shaft 5 passes through the hollow shaft 11 and is supported therein by lower and upper intermediate bearings 23,25. The central shaft 5 is also supported in the base 1 by a lower central bearing 26 and in the rotating housing 8 by an upper central bearing 14.

[0061] The above described arrangement makes it possible to transmit motion to both sun gears 15 and 20 from the lower part of each differential mechanism, thereby avoiding interference of the housings 8 of the two actuator units C when the manipulating device A is in motion.

[0062] The differential mechanism formed by the two sun gears 15,20 and the two planet gears 17,17′ is supported by: (a) the case of the rotating housing 8; (b) the support frame 2; and (c) planet supports 7. The planet supports 7 are fixed to the rotating housing 8 and restrain the relative displacement of the planet gears 17,17′ to a rotation about their axis of symmetry.

[0063] Let ω_A and ω_B denote the input velocities of the motors 28 and 29, respectively, the output velocity of planet gears 17,17′ around their axes being denoted by ω₁. Moreover, the rotation of the axes of the planet gears 17,17′ around the axis of the shaft 5 is denoted by ω₂ which is the angular velocity of the housing 8 and constitute the pan motion of the actuator unit C.

[0064] The velocities ω₁ and ω₂ are known in the art to be related to those of the motors by

[0065] ${\omega }_1=\frac{1}{2}\left(K_B{\omega }_B-K_A{\omega }_A\right)\frac{N_S}{N_P}$ ${\omega }_2=\frac{1}{2}\left(K_A{\omega }_A+K_B{\omega }_B\right)$
where K_A is the reduction ratio of the gear train between motor 28 and the hollow shaft 11; K_B is the reduction ratio of the gear train between motor 29 and the central shaft 5; N_S is the number of teeth of the sun gears 15,20 and N_P is the number of teeth of the planet gears 17,17′. In general, K_A and K_B need not be equal. However, it is preferable that K_A=K_B in order to equally distribute the load between the two motors 28,29.

[0066] Furthermore, the rotation of planets 17 and 17′ is transmitted to the driving links 27 via the speed reducers 6,9. The driving links 27 then move the active parallelogram linkage 30 of FIG. 1 via the coupler link 31. The speed reducers 6,9 provide a high reduction ratio K_R between the outputs of the differential mechanism and the motion of the active parallelogram linkages 30. The speed reducers 6,9 also provide synchronization of the output rotations of the differential mechanism driving the parallelogram linkage 30. Moreover, the use of worm-gears as speed reducers 6,9 provides a self-locking capability to the manipulating device A, which is a desirable feature in the manipulation of heavy loads.

[0067] In operation, the driving links 27 therefore drive the active parallelogram linkage 30 located outside of the housing 8 with an angular velocity ω₁/K_R, constituting the tilt motion of the actuator unit C. The pan motion of the actuator unit C, as stated above, is denoted by ω₂ and constitutes the rotation of the axes of the planet gears 17,17′ around the axis of the shaft 5, which causes the housing 8, and the active parallelogram linkage 30 attached thereto, to rotate. The active parallelogram linkage 30 transfers this combined pan-tilt motion to the base 32 of the passive unit D linked therewith through pin joints. The structure of the parallelogram linkage 30 ensures that the base 32 of the corresponding passive unit D remains parallel to the base 1. The movement of the base 32 causes the pan motion of the passive rotating housing 34 and the tilt motion of the passive parallelogram linkage 33 which is attached to the common moving platform 35 with pin joints. Hence, the collaboration of the legs B causes the common platform 35 to remain parallel to the bases 1 by virtue of the passive parallelogram linkages 33 of all legs.

[0068] Now referring to FIG. 18, a layout of an alternative transmission to the one presented in FIG. 4 will now be described, where like elements are identified by like reference characters. The two motors 28,29 are fixed to the base 1 in a manner similar to that of the precedent embodiment, but the bevel gears 15,17,17′,20 forming the differential mechanism described in FIG. 4 are replaced by an epicyclic train of helicoidal gears 17,17′,20 combined with universal joints 46,47 that enable the transmission of force and motion from a vertical to a horizontal shaft.

[0069] In this embodiment, a driving torque from motor 28 is successively transmitted from a motor shaft 4 to a first gear 3 rigidly attached thereto, then to a second gear 10 meshed with gear 3, to a hollow shaft 11 rigidly attached to gear 10, to a sun gear 20 rigidly attached to the hollow shaft 11, and then to planet gears 17,17′ meshed with the sun gear 20. The planet gears 17, 17′, in turn, transmit the driving torque to output shafts 18,19 through universal joints 46,47. Similarly, a driving torque from motor 29 is successively transmitted from a motor shaft 21 to a first gear 22 rigidly attached thereto, then to a second gear 12 meshed with gear 22, to a central shaft 5 rigidly attached to gear 12, and then to the planet carrier 8 rigidly attached to the central shaft 5 and playing the role of the housing 8 shown in FIG. 4.

[0070] Let ω_A and ω_B denote the input angular velocities of motors 28 and 29, respectively, the common output velocity of the planet gears 17,17′ being given by

[0071] ${\omega }_{17}=\frac{N_3\times N_{20}}{N_{10}\times N_{17}}{\omega }_A-\left(1+\frac{N_{20}}{N_{17}}\right)\frac{N_{22}}{N_{12}}{\omega }_B$
while the angular velocity ω₂ of the pan motion, identical to the rotation of the planet-carrier 8, is

[0072] ${\omega }_2=-\frac{N_{22}}{N_{12}}{\omega }_B$

[0073] The angular velocity ω₁ producing the tilt motion is the horizontal component ω₁₇−ω₂ of the common angular velocity of output shafts 18,19, that is,

[0074] ${\omega }_1={\omega }_{17}-{\omega }_2=\frac{N_3\times N_{20}}{N_{10}\times N_{17}}{\omega }_A-\frac{N_{20}\times N_{22}}{N_{12}\times N_{17}}{\omega }_B$

[0075] If, in particular, N₂₂/N₁₂=N₃/N₁₀, then

[0076] ${\omega }_1=\frac{N_3\times N_{20}}{N_{10}\times N_{17}}\left({\omega }_A-{\omega }_B\right)$

[0077] A number of alternative embodiments of the manipulating device A are possible, including, but not limited to, the embodiments described herein below, with like elements being identified by like reference characters.

[0078] Referring to FIGS. 6–7, a second embodiment according to the present invention is shown. This embodiment, like the first embodiment described, uses horizontal positioning of the base 32 of each active parallelograms 30. However, the attachment of the passive parallelogram linkages 33 to the common moving platform 35 is such that the mid-planes of the passive parallelogram linkages 33 are orthogonal, as can be best seen in the orientation of the passive units D illustrated in FIG. 7.

[0079] Referring to FIGS. 10–11, a third embodiment in accordance with the present invention is shown, where the attachment points of each of the active parallelogram linkages 30 with both the housing 8 and the base 32 of the passive unit D are vertically aligned. This has the consequence of having vertically aligned pin joints between each of the bases 32 and the respective active parallelogram linkage 30. This geometry presents the advantage of eliminating the driving links 27 while still keeping the symmetry of the housing 8 of each actuator unit C. Nevertheless, a reversing output gear train for one side of the active parallelogram linkages 30 is still required in this embodiment. Similarly to the first embodiment, this embodiment is characterized by parallel mid-planes of the passive parallelograms 33, as can be best seen in FIG. 11.

[0080] Referring to FIGS. 12–13, a fourth embodiment in accordance with the present invention is shown, also using vertical alignment of the attachment points of each of the active parallelogram linkages 30 with the respective housing 8 and base 32. However, in one of the passive units D, the passive rotating housing 34 is replaced by a universal joint 45 and a vertical link 43 and the passive parallelogram linkage 33 is replaced by a passive single link 44 connected to the universal joint 45, producing a kinematic equivalent to the passive unit D of the previous embodiments. In this embodiment, the mid-planes of the passive parallelogram linkage 33 and the passive single link 44 are also parallel, as can be best seen in FIG. 13.

[0081] Referring to FIGS. 14–15, a fifth embodiment in accordance with the present invention is shown, also using vertical alignment of the attachment points of each of the active parallelogram linkages 30 with the respective housing 8 and base 32. As can be best seen in FIG. 15, this embodiment is characterized by mid-planes of the passive parallelogram linkages 33 that are parallel but farther apart than in the previous embodiments having parallel mid-planes. This embodiment can provide higher mobility and a larger workspace by virtue of a larger spacing between mid-planes, which reduces a likelihood of interference between the linkages of the two legs.

[0082] Referring to FIGS. 19–20, a sixth embodiment in accordance with the present invention has four legs B instead of two. This embodiment can also accommodate the variety of link layouts presented in the first five embodiments. Other variations include three-legged arrays, with a combination of one- and two-motor driving units.

[0083] Referring to FIGS. 23–24, a seventh embodiment in accordance with the present invention is characterized by the transfer of a second pin joint of the passive unit D to the attachment point of each leg B with the moving platform 35 in a pin-joint holder 53, thus enhancing the rotation capabilities of the device. The pan motion of the passive units D is provided by pin-joints 54 under the moving platform 35 and attached to the pin-joint holder 53. The actuator unit C and passive unit D are linked through a vertical intermediate coupler 52. Because of a smaller distance between pan axes of the passive units D, as compared with a corresponding distance in the previous embodiments, similar pan motions provided by the motors will produce larger angular displacements of the moving platform 35. The moving platform 35 in this embodiment can thus sweep a much greater angle of rotation, with smaller space needed for the pan motion of the units C,D, than with any of the first six embodiments described above. This transfer of the second pin joint can be applied to any other embodiment in order to enhance the rotation capabilities thereof.

[0084] Using the intermediate driving link 27 of FIG. 2 is one way to drive the active parallelogram linkages 30. Other types of transmissions can also be used, such as gear trains, belt pulleys, rack-and-pinions, etc. Examples of alternative transmissions systems are herein presented.

[0085] Referring to FIGS. 8–9, an alternative transmission in accordance with the present invention provide a pan-tilt motion to each active parallelogram linkage 30. The driving link 27 and coupler link 31 used in the transmission of the first embodiment (see FIGS. 2–3) are replaced by gear trains. It will be appreciated that, similarly to the transmission described in the first embodiment, one of the horizontal output rotations of the differential mechanism of an actuator unit C has to be reversed. One side of the output torque is therefore transferred from the differential mechanism to the active parallelogram linkage 30 through a reverse gear train as shown in FIG. 8 and the other through a direct gear train as shown in FIG. 9. The reverse gear train of FIG. 8 is composed of one output gear 38 meshed with two following gears 39. The direct gear train of FIG. 9 is composed of one output gear 40 meshed with two intermediate gears 40 which are each meshed with a following gear 42. The output gears 38,40 of both gear trains transmit the output torque from the differential mechanism, and the following gears 39,42 directly drive the active parallelogram linkage 30.

[0086] Referring to FIG. 22, an alternative transmission for the case where each leg B is driven by a single motor is shown. A driving torque from the motor (not shown) is successively transmitted from a central shaft 5 to a sun gear 20 rigidly attached thereto, then to a pair of planet gears 17,17′ meshed with sun gear 20, and to a pair of output shaft 18,19, each driven by one of the planet gears 17,17′ via a pair of universal joints 46,47 to transfer the torque from a vertical to an horizontal direction. Referring to FIG. 21, the torque is then transferred from each output shaft 18,19 to a corresponding output gear 49,49′. Each output gear 49,49′ is part of a train of helicoidal gears. Output gear 49, as shown in FIG. 21, is meshed with a pair of intermediate gears 50, each in turn being meshed with a following gear 51, and each following gear 51 being rigidly attached to an active linkage 48 playing the role of the active parallelogram linkage 30 of the previous embodiments. Although not shown, gear 49′ is meshed directly with a pair of following gears 51, in a manner similar to that of FIG. 8 where the output gear 38 is directly meshed with the gears 39. This allows to transmit angular velocities of identical directions to the linkages 48 of both sides of the transmission.

[0087] The present invention as described herein offers an extraordinary functional flexibility in its layout, with a large number of other possible embodiments depending on the tasks envisioned. Referring to FIGS. 16a–16b–16c, the active parallelogram linkage 30 of an actuator unit C can be set on the housing 8 with joint axes lying in: a) a horizontal plane; b) a vertical plane; c) an inclined plane making an angle α_p with the horizontal. Referring to FIGS. 17a–17b–17c, the passive parallelogram linkage 33 of a passive unit D can similarly be set on the housing 34 with joint axes lying in: a) a horizontal plane; b) a vertical plane; c) a plane making an angle α_d with the horizontal. In the manipulating device A all four parallelogram linkages 30,33 may have their own independent layout, thus allowing for n^k=3⁴=81 different embodiments, this number corresponding to that of permutations of distinct objects (3 arrangements of joint axes) and possible orderings (4 parallelogram linkages). Taking into account that the angles α_p and α_d may take any value in the range from 0° to 90°, the number of possible embodiments of the Schönflies-motion generator becomes almost unlimited. This characteristic provides a functional flexibility superior to the known prior art devices.

[0088] Another significant advantage of the present invention is that most of the wiring (control and power supply cables, sensor wires, etc.) ends on the base 1 in the area of installation of the motors 28,29, and need not be attached to the legs B, thus providing for a light structure.

[0089] Referring to FIG. 25, a control system applicable to the embodiments having two legs B, each being driven by two motors, is shown. The main components of the control system are listed in Table 2. The control system includes digital hardware, and four servo-drives.

[0090] The digital hardware includes a central processor 1c, connected to the four servo-drives and sending control signals thereto according to the prescribed control algorithms for the manipulating device A. All other components of the digital hardware described in the following are in communication with the central processor 1c. A monitor 2c and a keyboard 4c are used for online programming and servicing of the device by the operator. Internal memory 5c is used for the functioning of the central processor 1c of the computer, and peripheral memory 6c, which may include a CD drive or any information-storage device, is used for uploading control programs according to the intended task. Finally, an input/output unit 3c is necessary for feedback from each leg B to the control system 1c in operation.

[0091] Each servo-drive includes a servo-control unit 7c,8c,9c,10c and a motor 28,29. The role of the servo-control unit 7c,8c,9c,10c is to interpret control signals from the central processor 1c and to implement them into the motion of the motors 28,29. Each actuator unit C of the manipulating device A contains two servo-drives, which produce output motions of the unit. These motions pass through gear trains as described in the embodiments above and move two legs B supporting the common moving platform 35.

[0092] A similar or equivalent control system can be used for alternative layouts, including embodiments having three or four legs.

[0093] The present invention can be used in a number of industries where high-speed pick-and-place operations are required, including, but not limited to, fabrication and packing of planar electronics components, packaging of various products, and bottling. The present invention can also be used in the design of virtual-axis machine tools by mounting a workpiece on a rotating table, commonly known in the art of machine tooling, to provide a second rotation which can become a fifth degree of freedom when combined with the Schönflies motions of the invention.

[0094] It will be appreciated that the present invention is not limited to the specific embodiments described herein, which are merely illustrative. For example, the third and the fourth embodiments can be readily transferred to embodiments characterized by orthogonal planes of motion of the passive parallelograms 33 or the passive parallelogram 33 and the passive single link 44. Other modifications and variations will be readily apparent to those skilled in the art. Accordingly, the scope of the invention is deemed to be in accordance with the claims as set forth below.

[0095]

TABLE 1
Main components of the active and passive units
No.	Description
A	Manipulating device
B	Leg
C	Actuator unit
D	Passive unit
1	Base
2	Support frame
3	Gear of motor shaft #4
4	Motor shaft of motor #28
5	Central shaft
6	Speed reducer with reverser
7	Planet support
8	Rotating housing or Planet carrier
9	Speed reducer
10	Gear of hollow shaft
11	Hollow shaft
12	Gear of central shaft
13	Support bearing
14	Upper central bearing
15	Upper sun gear
16	Thrust bearing
17, 17′	Planet gears
18	Output shaft
19	Output shaft
20	Lower sun gear
21	Motor shaft of motor #29
22	Gear of shaft #22
23	Lower intermediate bearing
24	Thrust bearing housing
25	Upper intermediate bearing
26	Lower central bearing
27	Driving link
28	Motor
29	Motor
30	Active parallelogram linkage
31	Coupler link
32	Base of passive unit
33	Passive parallelogram linkage
34	Passive rotating housing
35	Common moving platform
36	Gripper
37	Workpiece or tool
38	Output gear
39	Following gear of reversing gear train
40	Output gear
41	Intermediate gear of direct gear train
42	Following gear of direct gear train
43	Vertical link
44	Passive single link
45	Universal joint of vertical link #43
46	Universal joints
47	Universal joints
48	Lower active linkage
49, 49	Output gears
50	Intermediate gear
51	Following gear
52	Intermediate coupler
53	Pin-joint holder
54	Pin-joint

[0096]

TABLE 2
Main components of the control system
No.	Description
1c	Central processor
2c	Monitor
3c	Input/output unit
4c	Keyboard
5c	Internal memory
6c	Peripheral memory
7c	Servo-control unit of the first active module
8c	Servo-control unit of the first active module
9c	Servo-control unit of the second active module
10c	Servo-control unit of the second active module