ROBOT AND ROBOT ACTUATOR MODULE THEREFOR

BACKGROUND OF THE INVENTION

The present invention relates to an actuator module for inducing the relative motion of robot members joined in a robot joint, and a robot using the actuator module. In particular, the invention relates to an actuator module comprising a Ferguson epicyclic gear train, integral motor and integrated control means (brakes, encoders, sensors, etc.) .

Today's robots are designed with virtually no stan¬ dardization. This results in a costly technology which cannot rapidly adapt to emerging technologies and may be obsolete before it goes to production. Modularity would do much to reduce the level of cost and would reduce the threat of obsolescence, allowing rapid changeover in favor of improved module technology. The model of the personal computer can provide a benchmark for the benefits of modularity in another system architecture. While the original computers were dedicated mainframes, each designed separately with little compatibility from one generation to the next, the personal computer is now highly modular, layered, interfaced at each level, etc. in a nearly standardized format.

The pressing need is to develop a robot architecture which can rapidly evolve in the same fashion as is now feasible for personal computers. Existing drive systems usually include encoders, brakes, motors, drive trains and joint bearings, each provided with its own housing, mounting plates, wiring interfaces, etc. Before the present invention, no thought had been given to

aggressively integrating these multi-component systems into a combined whole to reduce weight, size and complexity and to increase scalability and adaptability. The architecture which results from modularity maximizes the number of physical parameters still available so that a designer has a full selection with which to design.

Of course, there are literally billions of systems which can be derived from the hundreds of design parameters available. Hence, a strategy for design must be developed which allows optimum results to occur in smaller, more addressable packages. This is the primary design argument in favor of modularity in robotics. Evolutionary changes in previous designs are presently made without having the capability to make dramatic changes which could provide substantial benefits.

Although the need for modularity and compactness has been recognized in the prior art, see, e.g., U.S. Patent Nos. 4,738,576 and 4,062,601, these proposed solutions retain such deficiencies as separately housed motors and unnecessary complexity.

The use of epicyclic gear trains is also known in the art. See, e.g., U.S. Patent Nos. 4,686,402;

4,492,510; and Nasa Publication JSC-09709 (June 1975). These devices are particularly suited for robotics because of their compactness (for the reduction ratios possible) , efficiency (and thus back-driveability) , durability and smooth operation. As with most gear trains, however, the use of an epicyclic gear train typically adds a relatively heavy structure to the robot joint assembly. The prior art, characterized by separately-housed, discrete components and long force paths, has not provided an adequate solution to this and other stumbling blocks facing the development of robot- drive technology. Finally, none of the proposed

solutions combine modularity and compactness with superior redundancy and stiffness characteristics.

SUMMARY OF THE INVENTION

The present invention provides an actuator module which can be easily integrated in a series of one, two and three degree-of-freedom ("DOF") structural robot modules (elbows, knuckles, wrists, shoulders, etc.) which can then be rapidly scaled and assembled into a full architecture of 3 to 12-DOF multilayered robot systems as might be found in multi-fingered hands, dual-arm robots, walking machines, micro-surgery devices and the like. The actuator modules of the present invention can be treated as separate entities which can be designed in- depth, provided with generic interfaces, classified in terms of scaling rules, etc. Once these packages exist in optimum units, they can then be integrated into a system which then will contain far fewer available design parameters and therefore becomes much more tractable to the designer. This versatility means that the designer will be able to consider a much broader range of options and would more likely take a top-down approach.

In addition to enhanced modularity, the invention offers many other advantages over existing robot actuators. Specifically, the actuator module of the present invention is one third to one-tenth lighter, three to five times smaller, three to ten times stiffer, with two to four times fewer interfaces, three times fewer bearings, and twice the redundancy.

These advantages are achieved through an actuator module featuring a Ferguson epicyclic gear train, motor and control means, with the motor and control means preferably being integrated with selected gear train

components. The actuator module may be of frameless construction, being adapted to mate with robot members designed to enclose the gear train and motor. Alterna¬ tively, the gear train may be integrated with the housing for the gear train and motor.

In a first embodiment of the invention, the gear train comprises a first base gear connected to a first robot member, a second base gear connected to a second robot member, a planet gear carrier, and a plurality of planet gears rotatably mounted in the planet gear carrier and adapted to mesh with both the first and second base gears, with the base gears and planet gear carrier all rotating about the same central axis. The base gears may be ring (internally-toothed) gears, wherein the planet gears rotate within the base gears, or sun (externally-toothed) gears, wherein the planet gears rotate outside the base gears.

In this first embodiment, a d.c. motor having a pair of permanent magnets is integrated with the gear train components, with an armature connected to the planet gear carrier and a plurality of magnets connected to one of the base gears. An alternative embodiment features an armature connected to one of the base gears and a plurality of magnets connected to the planet gear carrier.

The first and second base gears are formed with a different number of teeth. Because of this difference in the geometries of the two base gears, the rotation of the planet gears about the base gears' circumferences induces relative motion between the two base gears, i.e., one base gear rotates relative to the other. This phenomenon is known as Ferguson's paradox, and an epicyclic gear train utilizing this principle is referred to herein as a Ferguson epicyclic gear train. The resulting relative

rotation of the base gears represents a significant reduction in rotational speed from the rotational speed of the motor (and the rotational speed of the planet gear carrier) . The relative motion of the base gears is translated to the robot members and is adaptable to form a variety of robot joints, including elbow joints, joints for continuous rotational motion and joints for linear motion. The use of a Ferguson epicyclic gear train provides a much shorter force path than conventional epicyclic drives, resulting in greater stiffness and compactness.

Added benefits such as redundancy, stability and superior design flexibility may be achieved through a dual substantially symmetric gear train and motor system. In a second embodiment of the invention, the actuator module features a pair of outer base gears, a pair of inner base gears located axially between the outer base gears, and a pair of planet gear carriers substantially perpendicular to the central axis, with the outer base gears being connected to one robot member and the inner base gears being connected to the other robot member. The planet gears of each planet gear carrier mesh with one outer base gear and one inner base gear. In this embodiment, the actuator module also comprises a dual motor system, having two armatures and two sets of magnets. As in the unitary system, an armature is connected to each planet gear carrier and is disposed adjacent a plurality of magnets connected to one of the base gears. The actuator module thus comprises a dual symmetric system. Symmetry of two drive trains reduces torsional deformations and thus allows the use of much lighter bearings and structural elements within the actuator. The duality of this configuration enhances the reliability and design flexibility of the actuator module. Separate control means may be provided for each gear train/motor system and the two systems may be

adapted to operate independently, such as through the use of a dog-leg clutch assembly.

In other embodiments of the present invention, multiple epicyclic stages may be provided to accommodate greater gear reduction needs. In particular, each half of the dual gear train and motor system described in the second embodiment may be adapted to comprise two stages of epicyclic gearing, with two sets of inner and outer base gears, two sets of planet gears, and two planet gear carriers. A variety of drive means may be used in the present invention, including electric motors, hydraulic motors and pneumatic motors, with the of type of motor being selected according to the requirements of the particular application.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional view of the actuator module of the present invention featuring a single gear train/motor system mated with two robot members to form a robot joint for continuous rotation.

Figure 2 is side view of the Ferguson epicyclic gear train of the present invention.

Figure 3 is a cross-sectional view of the actuator module of the present invention featuring a dual gear train/motor system mated with two robot members to form an elbow joint.

Figure 4 is an isometric view of the actuator module of Figure 3.

Figure 5 is a cross-sectional view of the actuator module of the present invention featuring dual gear train/motor

system mated with two robot members to form a robot joint for continuous rotation.

Figure 6 is an isometric view of the actuator module of Figure 5.

Figure 7 is a cross-sectional view of the actuator module of the present invention featuring a dual gear train/motor system adapted to mate with two robot members in a ballscrew and sleeve configuration for inducing the linear motion of one robot member relative to the other.

Figure 8 is an isometric view of the actuator module of Figure 7.

Figure 9 is a side view of the ballscrew and sleeve configuration of Figures 7 and 8.

Figure 10 is a cross-sectional view of an actuator module featuring dual gear train/motor system and mated with two robot members to form an elbow joint, with each gear train/motor system comprising two stages of epicyclic gearing.

Figure 11 is an exploded side view of one half of the actuator module of Figure 10.

Figure 12 is an exploded isometric view of one half of the actuator module of Figure 10.

Figure 13 is a cross-sectional view of the actuator module of the present invention of sim ar configuration to the actuator module shown in Figure ::.

Figures 14a-f are 1-DOF robot elbow joints formed using actuator modules of the present invention.

Figures 15a-c are 2-DOF general actuated robot knuckle joints utilizing actuator modules of the present invention.

Figure 16a-c are 2-DOF robot knuckle joints with perpendicular axes utilizing actuator modules of the present invention.

Figure 17a and 17b are 2-DOF robot planar curve robot structures utilizing actuator modules of the present invention in parallel.

Figures 18a and 18b are 3-DOF serial planar robot structures utilizing actuator modules of the present invention.

Figures 19a and 19b are 3-DOF parallel planar robot structures utilizing actuator modules of the present invention.

Figures 20a-c are 3-DOF serial spherical robot shoulder joints utilizing actuator modules of the present invention.

Figure 21 is a general hybrid robot manipulator chain utilizing actuator modules of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the invention, actuator module 50, is shown in Figure 1 and comprises a Ferguson epicyclic gear train formed by first base gear 3 detachably connected to robot member 1, second base gear 5 detachably connected to robot member 2, and planet gear carrier 7 with a'plurality -of planet gears 14 rotatably mounted therein, with base gears 3 and 5 and planet gear

carrier 7 being horizontally disposed along a central rotational axis 13 and adapted to rotate about axis 13. Robot members 1 and 2 may be integrally connected to base gears 3 and 5, respectively, such as by forming the robot members and base gears as single components, or by welding, bolting or functionally equivalent connections. Bolted connections and other detachable connections are particularly useful for ease of assembly and interchange- ability. Alternatively, robot members 1 and 2 may be movably connected to base gears 3 and 5, respectively, such as through a hinge, screw, or ball-and-socket assembly.

Planet gear carrier 7 comprises an annular body forming a substantially cylindrical interior space.

Planet gears 14 carried by planet gear carrier 7 mesh with first base gear 3 and second base gear 5. A side view of the Ferguson epicyclic gear train of the present invention is shown in Figure 2. Not all of the planet gears 14 are shown in Figure 2 nor is planet gear carrier 7. As can be seen from Figure 2, each planet gear 14 comprises two sets of teeth, one set 14a for meshing with first base gear 3 and a second set 14b for meshing with second base gear 5. The teeth sets 14a and 14b of one planet gear 14 may be axially aligned as in planet gear 14' in Figure 2. The remainder of the planet gears 14, as illustrated by the planet gears 14" and 14'" in Figure 2, have teeth sets 14a and 14b which are offset a given distance, the offset distance being governed by the location of the planet gear 14 on the planet gear carrier 7 and the difference in the number of teeth of base gears 3 and 5.

As planet gear carrier 7 and planet gears 14 rotate about base gears 3 and 5, rotation of base gear 3 relative to base gear 5 is induced by the different in the number of teeth of base gears 3 and 5. This

phenomenon is known as Ferguson's paradox. Although the Ferguson epicyclic gear train of the present invention can operate with only one planet gear 14 mounted in planet gear carrier 7, the use of as many planet gears as space and the tooth requirements of Ferguson's paradox will permit proportionally increases drive train stiffness and load carrying capacity and distributes tooth wear and deformation.

Planet gear carrier 7 is connected to motor rotor 9, which may be a pancake armature disk and may be formed integrally with planet gear carrier 7 as a single component or may be securably fastened to planet gear carrier 7 for ease of assembly or manufacture as where different materials are needed for each component.

In this embodiment, base gears 3 and 5 are shown as ring (internally-toothed) gears. First base gear 3 is connected to central shaft 18, central shaft 18 being disposed in the space formed by planet gear carrier 7 and aligned with central rotational axis 13. Second base gear 5 is connected to motor stator 11 by means of motor stator arm 23, motor stator arm 23 preferably being connected to second base gear 5, rotatably connected to central shaft 18 and detachably connected to robot member 2. Second base gear 5 may be formed with motor stator arm 23 as a single component or these may be formed as separate components and securably fastened together for ease of assembly. Motor stator 11 comprises a set of opposing permanent rare earth magnets mounted in motor stator arm 23, each set being made up of one or more magnets. Motor stator 11 may be configured to receive motor rotor 9 in a space formed within motor stator 11. In this fashion, an electric motor is formed. In operation, the electromechanical force generated by the motor causes motor rotor 9, and thus planet gear carrier 7, to rotate about central rotational axis 13. As planet

gear carrier 7 rotates, the planet gears 14 rotatably mounted therein rotate both about their own individual axes and about the inner circumference of first base gear 3 and second base gear 5, i.e., about central rotational axis 13.

The actuator module of the present invention may also be used with other types of motors, including but not limited to hydraulic and pneumatic motors, depending upon desired performance characteristics or other constraints.

Because first base gear 3 is formed with a different number of teeth than second base gear 5, the rotation of planet gear carrier 7 within base gears 3 and 5 induces first base gear 3 to rotate about axis 13 in a direction relative to second base gear 5, this being the phenomenon of Ferguson's paradox. This relative motion is transmitted to the robot members 1 and 2 by virtue of the connection of robot member 1 with first base gear 3 and the connection of robot member 2 with second base gear 5.

Also shown in Figure 1 are brakes 16 and position sensors 17, which allow for the control of the relative motion of the drive train components. Potentiometers, tachometers, resolvers, hall effect sensors, torque meters and other measuring and sensing devices be integrated into the actuator module to improve the control characters. Needle bearings 21 and tapered roller bearings 15 provide for enhanced stiffness and reduced friction.

Actuator module 100, as shown in Figure 3, features a dual substantially symmetric gear train/motor system mated with a first robot member 1 and second robot member 2 to form an elbow joint, a one degree-of-freedom joint wherein the axis of rotation of the gear train and motor

components has a range of about 270° about centerline axis of the attached robot members 1 and 2. This configuration is also shown in Figure 4.

Actuator module 200, as shown in Figure 5, features a dual substantially symmetric gear train/motor system mated with a first robot member 1 and second robot member 2 to form a robot joint wherein the gear train and motor components rotate about the centerlines of the attached robot members 1 and 2. This configuration, also shown in Figure 6, essentially doubles the gear train/motor system shown in Figure 1. In a similar fashion, actuator module 100 could be reduced to a single system configuration. While the configurations of actuator module 200 shown in Figures 5 and 6 describe a single DOF joint, with the robot member centerlines being aligned with the axis of rotation of the actuator module, actuator module 200 may also be adapted to form a continuously rotatable elbow joint, as shown in Figure 14c, with the robot member centerlines being perpendicular to the actuator module's axis of rotation.

Actuator module 300, as shown in Figure 7, features a dual substantially symmetric gear train/motor system mated with a first robot member 1 and second robot member 2 in a ballscrew and sleeve assembly for inducing the linear motion of robot member 2 relative to robot member 1. As with actuator models 100 and 200, actuator model 300 could also be formed as a single system configuration. The use of this actuator module with a ballscrew and sleeve assembly is shown in Figure 8 and the assembly itself is shown in more detail in Figure 9.

The components of actuator modules 100, 200 and 300 shown in Figures 3, 5, and 7 are essentially the same, thus allowing the use of a common numbering system for all three figures. Each of actuator modules 100, 200 and

300 comprises a Ferguson epicyclic gear train formed by an outer base gear pair comprising first outer base gear 3 and second outer base gear 4, an inner base gear pair comprising first inner base gear 5 and second inner base gear 6, and planet gear carriers 7 and 8 with a plurality of planet gears 14 rotatably mounted therein, with the base gears and planet gear carriers being substantially perpendicular to a central rotational axis 13 and adapted to rotate about this axis. Planet gear carriers 7 and 8 comprise annular bodies forming substantially cylindrical interior spaces. The planet gears 14 of first planet gear carrier 7 mesh with first outer base gear 3 and first inner base gear 5, as shown in Figure 2. Likewise, planet gears 14 of second planet gear carrier 8 mesh with second outer base gear 4 and second inner base gear 6.

Base gears 3, 4, 5 and 6 comprise sun (externally- toothed) gears in Figures 1 and 6 and ring (internally- toothed) gears in Figure 4. Outer base gears 3 and 4 are connected to robot member 1. This connection may be made by fastening outer base gears 3 and 4 directly to robot member 1 with a bolt circle or the like.

In actuator models 100 and 300, inner base gears 5 and 6 are connected to a central shaft 18, central shaft 18 being aligned with central rotational axis 13. Inner base gears 5 and 6 may be formed with central shaft 18 as a single component or splined to central shaft 18 for assembly purposes. Integrated with central shaft 18 is motor stator arm 23.

In actuator module 200, inner base gears 5 and 6 are connected to motor stators 11 and 12 by means of magnet stator arm 23, motor stator arm 23 being connected to both inner base gears 5 and 6 and motor stators 11 and 12. Inner base gears 5 and 6 may be formed with motor stator arm 23 as an integral component or may be formed

as separate components and securably fastened together for ease of assembly.

First planet gear carrier 7 is connected to first motor rotor 9 and second planet gear carrier is connected to second motor rotor 10. Motor rotors 9 and 10 may be pancake armature disks and may be formed with planet gear carriers 7 and 8 as integral components or may be securably fastened to planet gear carriers 7 and 8 for ease of assembly or manufacture where different materials are needed for each component. Planet gear carriers 7 and 8 may include annular end plates 20 to form the outer mount for planet gears 14 for ease of assembly, as shown in Figure 1.

In actuator modules 100, 200 and 300, first motor stator 11 and second motor stator 12 each comprise a group of opposing permanent rare earth magnets mounted in motor stator arm 23 and are configured to receive motor rotors 9 and 10 in the spaces formed within each motor stator 11 and 12, respectively. In this fashion, dual motors are formed. In operation, the electromechanical force generated by the motor causes motor rotors 9 and 10, and thus planet gear carriers 7 and 8, to rotate about central rotational axis 13. Because the dual motors are driven in phase, planet gear carriers 7 and 8 rotate in the same direction. As planet gear carrier 7 rotates about central rotational axis 13, planet gears 14 rotatably mounted therein rotate both about their own individual axes and about the outer circumference

(actuator modules 100 and 300). or inner circumference (actuator module 200) of first outer base gear 3 and first inner base gear 5, i.e., about central rotational axis 13. Similarly, planet gears 14 of second planet gear carrier 8 rotate both about their own axes and about the circumferences of second outer base gear 4 and second

inner base gear 6 as second planet gear carrier 8 rotates about central rotational axis 13.

Actuator modules 100, 200 and 300 each feature a central shaft 18 aligned with central rotational axis 13. In actuator module 200, central shaft 18 serves to connect outer base gears 3 and 4. Planet gear carriers 7 and 8 rotate about central shaft 18 which is disposed in the interior spaces formed by planet gear carriers 7 and 8, with bearings 26 (actuator modules 100 and 300) and needle bearings 21 (actuator module 200) disposed between central shaft 18 and planet gear carriers 7 and 8. The bearings 26 and 21 at these locations, as well as the bearings 26 at the interface of planet gear carriers 7 and 8 and outer base gears 3 and 4 of actuator modules 100 and 300, can be relatively small as they undergo almost no twisting and because the structure is symmet¬ rical. The bearings 15 disposed at the interface of cen¬ tral shaft 18 and outer base gears 3 and 4 (actuator od- ules 100 and 300) and at the interface of the housing 22 and motor stator arm 23 (actuator module 200) are major support bearings for the mechanical structure and will need to resist complex radial and axial forces. Bearings 15 may also be used at the interface of other locations in actuator modules 100, 200 and 300 to reduce friction and to increase stiffness.

In each of modules 100, 200 and 300, because the outer base gears 3 and 4 are formed with a different number of teeth than inner base gears 5 and 6, the rotation of planet gear carriers 7 and 8 about or within base gears 3, 4, 5 and 6 induces the outer base gears 3 and 4 to rotate relative to inner base gears 5 and 6, this being the phenomenon of the Ferguson paradox. This relative motion is transmitted to robot members 1 and 2 by virtue of the connection of robot member 1 with outer base gears 3 and 4 and the connection of robot member 2

with inner base gears 5 and 6. In actuator modules 100 and 200, all of these connections are rigid while in actuator module 300, only robot member 1 is rigidly con¬ nected with base gears (namely, outer base gears 3 and 4) .

In the ballscrew and sleeve assembly of actuator module 300, robot member 1 is slidably disposed within robot member 2, with robot member 2 essentially forming a sleeve around robot member 1. Central shaft 18 of actuator module 300 comprises a hollow shaft with an interior being adapted to mesh with a ballscrew 25, with ballscrew 25 being securably fastened to robot member 2. (Central shaft 18 of actuator modules 50, 100, and 200 may also be hollow as shown in Figures 1, 2 and 4, to achieve weight savings.) As inner base gears 5 and 6 rotate relative to outer base gears 3 and 4, central shaft 18 rotates about ballscrew 25, thus advancing the actuator module 300 and robot member 1 linearly along central rotational axis 13 while robot member 2 remains stationary, being fixed to ballscrew 25. This configuration is shown in more detail' in Figure 8.

Brakes 16 may be located between outer base gear 3 and inner base gear 5 and between outer base gear 4 and inner base gear 6 to control their relative motion. Position sensors 17 such as encoders or resolvers may be located at the interfaces of selected gear train, motor and housing components to measure their relative motion.

Because certain parts of the actuator system (encoders, magnetic pads, armature, brake pads, etc.) should be kept relatively clean, seals along the shaft and at other volume interfaces may be required. Positive ventilation of a high pressure air supply may prove useful in some cases.

Actuator module 400, a variation of actuator module 100 having a two-stage Ferguson epicyclic gear train, is shown in Figure 10, with exploded views of the right half of this configuration given in Figures 11 and 12. This configuration provides an improvement over the relative parameters of speed reduction available, offering reduction ratios in the range of 100 to 1000 to 1. Two- stage versions of actuator modules 200 and 300, and their single system counterparts (e.g., actuator module 50), are also possible using similar configurations.

Referring to Figure 10, the first stage comprises an inner primary base gear pair connected to central shaft 18 and comprising first inner primary base gear 35 and second inner primary base gear 36, an outer primary base gear pair comprising first outer primary base gear 33 and second outer primary base gear 34, first primary planet carrier 7 and second primary planet gear carrier 8, each planet gear carrier 7 and 8 having a plurality of primary planet gears 14 rotatably mounted therein.

The second stage comprises an outer secondary base gear pair connected to robot member 1 and comprising first outer secondary base gear 3 and second outer secondary base gear 4, an inner secondary base gear pair detachably connected to robot member 2 and comprising first inner secondary base gear 5 and second inner secondary base gear 6, first secondary planet gear carrier 37 and second secondary planet gear carrier 38, with each planet gear carrier 37 and 38 having a plurality of secondary planet gears 24 rotatably mounted therein. Inner secondary base gears 5 and 6 may be splined to central shaft 18 for assembly purposes. First secondary planet gear carrier 37 is connected to first outer primary base gear 33 and second secondary planet gear carrier 38 is connected to second outer primary base gear 34. Planet gear carriers 37 and 38 may include

annular end plates 20 to form the outer mount for planet gears 24 for ease of assembly. In the embodiment shown, primary base gears 33, 34, 35 and 36 are ring gears while secondary base gears 3, 4, 5 and 6 are sun gears.

The dual motors are integrated with the first stage gearing. First primary planet gear carrier 7 is connected with first motor rotor 9 and second primary planet gear carrier 8 is connected with second motor rotor 10, with motor rotors 9 and 10 being disposed between magnet groups 11 and 12, respectively. Magnet groups 11 and 12 are mounted on motor stator arm 23, which is integrally connected to or formed with inner primary base gears 35 and 36. Motor stator arm 23 may be formed as part of central shaft 18. Possible motors include d.c, brushless d.c, a.c, hydraulic, and pneumatic motors. As in the other embodiments depicted, actuator module 400 is also equipped with brakes 16, position sensors 17 such as encoders, tapered roller bearings 15, needle bearings 21 and seals 19.

As an electromechanical force is generated by the motors, the rotation of the first stage gearing is transmitted to the second stage gearing through secondary planet gear carriers 37 and 38, these being connected to outer primary base gears 33 and 34. The second stage, in turn, imparts relative motion to robot members l and 2. Because primary planet gears 14 must run at the relatively high speed of the motors, their mass must be kept as low as possible. Hence, they should be of small diameter to reduce their rotational inertia. Because they are near the low torque end of the motors, lower tooth loads are necessary, meaning that fewer primary planet gears 14 are needed for this stage, that they can be smaller, and that lighter bearings are possible here. This reduces their inertia relative to the drive responsiveness of the actuator as a unit.

The second stage gearing should be more robust in order to carry large torque loads associated with the robot joint. Stiffness may be enhanced here by using more secondary planet gears 24, thicker secondary base gears 3, 4, 5 and 6 without the high cost in drive inertia (because of the lower speeds involved here) .

Another embodiment of a single stage dual system actuator module of the present invention is illustrated in Figure 13 as actuator module 500. Actuator module 500 represents a variation of actuator module 100, suitable for the same applications and comprising similar components in a somewhat different configuration. Specifically, actuator module 500 comprises first outer base gear 3, second outer base gear 4, first inner base gear 5, second inner base gear 6, planet gear carriers 7 and 8, and a plurality of planet gears 14 rotatably mounted therein. In the configuration shown in Figure 13, the base gears 3, 4, 5 and 6 comprise sun gears which rotate within the planet gear carriers 7 and 8. Outer base gears 3 and 4 may be connected directly to robot member 1 and inner base gears 5 and 6 may be connected directly to robot member 2. Inner base gears 5 and 6 are also rigidly attached to central shaft 18, with guidance rings 46 disposed between inner base gears 5 and 6 and the brakes 16.

Brakes 16 are mounted on the central shaft 18 proximate planet gear carriers 7 and 8 for arresting the motion of planet gear carriers 7 and 8. Planet gear carriers 7 and 8 may be fitted with plates 16a for this purpose, as shown in Figure 13. In the embodiment shown, brakes 16 each comprise a permanent magnet. When no power is supplied to brakes 16, brakes 16 engage plates 16a by means of the permanent magnets, thus preventing planet gear carriers 7 and 8 from moving. Supplying power to the brakes 16 neutralizes the magnetization of

the permanent magnets, allowing planet gear carriers 7 and 8 to rotate. In this configuration, brakes 16 are typically not used during operation of the actuator module 500 and may be referred to as "fail-safe" or "parking" brakes. These brakes are engaged to lock the drive train when actuator module 500 is not in use and also when power to the actuator module is unexpeptedly cut off. During operation of actuator module 500, "braking" of the drive train is accomplished instead by reverse torquing of the motors.

Motor stators 9 and 10 are rigidly connected to motor stator arm 23. In the configuration shown in Figure 13, motor stators 9 and 10 comprise armatures. Motor stators 9 and 10 are operatively aligned with motor rotors 11 and 12, which comprise a plurality of permanent magnets in this configuration. Motor rotors 11 and 12 are rigidly connected to planet gear carriers 7 and 8. As in the other embodiments, the operation of the dual motors comprised of motor rotors 11 and 12 and motor stators 9 and 10 causes planet gear carriers 7 and 8 and the planet gears 14 mounted therein to rotate about base gears 3, 4, 5, and 6, thereby generating the relative motion of robot members 1 and 2. A side view of one-half of the Ferguson epicyclic gear train is shown in Figure 2.

The movement of planet gear carriers 7 and 8 is sensed by position sensors 17. Position sensors 17 are shielded from the magnetic field generated by motor stators 9 and 10 by magnetic shielding 40. In the configuration shown, position sensors 17 comprise resolver rotors 17a mounted on planet gear carriers 7 and 8 operatively aligned with resolver stators 17b mounted on motor stator arm 23. In order to determine the relative position of the planet gear carriers 7 and 8, an electric field is applied to resolver stators 17a. The

electric field is then measured at resolver rotors 17b. The resulting information is transmitted to an associated controller via resolver contact rings 44 mounted on planet gear carriers 7 and 8 and resolver brushes 43 mounted on motor stator arm 23.

Motor stator arm 23 forms a housing for the components of actuator module 500, with additional housing members 45 mounted on and extending from motor stator arm 23 to enclose the Ferguson epicyclic gear train. In order to dissipate heat from motor stators 9 and 10, motor stator arm 23 may be provided with fins as shown in Figure 13.

As in the other configurations, actuator module 500 is equipped with a number of bearings. The principal bearings 15 are mounted between inner base gear 5 and outer base gear 3 and between inner base gear 6 and outer base gear 4 and are held in place by lock nut 41 and lock washer 41a. Additional bearings 26 are provided at other locations as shown in Figure 13. Brakes 16 and inner base gears 5 and 6 may be held in place on central shaft 18 through the use of keys 42.

TIMKEN tapered roller bearings (Nos. LL 13049 and LL 13010) may be used for bearings 15 while SKF THINLINE ^™ or KAYDON ball (Nos. KB 020 ARO and KB 055 ARO) bearings may be used for bearings 26. Preferred position sensors 17 include AMERICAN ELECTRONICS 70 PX-1 resolvers and INLAND large bore annular resolvers AEI Model 64PX1.

ELECTROID permanent magnet safety brakes (No. CPMF SD-19) have been found suitable for brakes 16. MARTIN SPROCKET epicyclic gear sets may be used for the Ferguson epicyclic gear train for the present invention, with base gears having 60 and 58 teeth used in connection with planet gears having 12 teeth each, yielding a gear reduction ratio of 30:1. In a preferred embodiment.

twelve equally spaced planet gears 14 have been used for each planet gear carrier. For the motor, an INLAND rare earth ceramic brushless d.c. electric motor may be used (Model Nos. RBE 4501 A00 or 6201 A00) .

The use of superconducting materials may require forced circulation of a cooling medium such as liquid nitrogen. This may also be desirable where rare earth materials or pure copper is used to enhance the magnetic field strength.

Carbon fiber may be used wherever possible to reduce weight. Gears may be made of metal teeth on a ring attached to a carbon fiber disk structure which might then be attached to a metal shaft.

A generalized mechanical architecture will require a system controller of sufficient generality and adaptability to absorb control software which matches the mechanical structure. This system controller must interface with the distributed electronic control packages associated with each actuator module. Each actuator module will be supported by a local (distributed) electronic package with data reduction and local decision-making capability. It must absorb a broad range of signals from the actuator module encoders by means of wiring, fiber optics, light transmission, or radio waves. The electronic package may be built as two independent units normally controlling half of the actuator module but capable of controlling both sides of the actuator if one side of the electronic package fails. Full duality of both the electronic and mechanical components of the actuator modules is desirable to enhance reliability and safety. This can be achieved by using two encoders, two brakes, two armatures, two drive trains, and multiple transducers for current, temperature, strain, and the like.

It will be necessary to design an encoder subsystem to fit between the outer and inner base gears. Otherwise the encoder would be an add-on, reducing the symmetry and compactness of the unit. Preferred encoders include tachometers, resolvers, potentiometers, hall effect sensors, optical encoders, and electrical contact encoders.

Control in the small would require a secondary input between the motor armature and the planet gear carrier. There should be enough space to put a small subsystem (motor and bearings) to control very small motions at that point. It would be carried on that system of robot members as a subsystem.

A particularly simple, strong and light structural interface between the actuator module and the robot members is a bolt circle built into the robot member and attached to the base gear structure. Other quick disconnect interfaces are feasible. In addition, each module should provide for standardized control signal interfaces to a neighboring electronic control module package.

As previously noted, the actuator modules of the present invention, including single system modules such as actuator module 50, dual system, single stage modules such as actuator modules 100, 200, 300 and 500, and dual system, dual stage modules such as actuator module 400, may be used as building blocks for a variety of robot architectures. Although for most applications these three types of modules, as exemplified by actuator modules 50, 100 and 400, are interchangeable, only certain embodiments will be referred to for discussion purposes.

Actuator modules 100, 200 and 300 (and also 400 and 500) may be used to drive all possible 1-DOF joints (6) which may be called "elbows". The possible variations are represented in Figures 14a-f, showing the use of actuator modules 100, 200 and 300 to induce the relative motion of robot members 1 and 2. In the configuration shown in Figure 14a, actuator module 100 is contained in the volume of robot member 1 while robot member 2 forms a yoke on the outside of robot member 1. It forms a compact, simple assembly allowing up to 270° of rotation.

In the configuration of Figure 14b, actuator module 200 is divided into separate halves (actuator module 50) and placed in each branch of a yoke. The result is a compact simple assembly, providing 270° of rotation and being somewhat more rugged than the configuration of Figure 14a.

In the configuration of Figure 14c, actuator module 200 is incorporated in overlapping robot members, which allows the continuous rotation of two robot members as in the elbow shown, in the base robot in a forearm, or as the last driver before the robot end-plate. This configuration is not as rugged as those of Figures 14a and 14b for the same weight, but is relatively compact for exceptional dexterity.

Figure 14d is a prism (linear) joint. Here, actuator module 300 drives a slider joint by means of a built-in ballscrew.

In the configuration of Figure 14e, actuator module 300 acts as an inverted slider crank mechanism in the same fashion as hydraulic pistons are used. This system provides about 140° of rotation. It is very stiff in the direction of rotation and can be used to resist large forces (as in backhoes or heavy lifting systems) . These

systems could be doubly actuated but it would be difficult since the ballscrew is largely non-back- driveable.

Figure 14f is actuator module 300 with a four-bar mechanical amplifier, which amplifies the output of the actuator to make 270° of joint rotation possible. The system can be made very stiff but at the penalty of more bearings and robot members (more weight) and therefore it is less compact.

Actuator modules 100 and 300 may be used to drive 2- DOF actuated "knuckles". Knuckles combine the relative motion of three neighboring robot members in series. The three examples shown in Figures 15a-c are general, preserving all the robot member parameters (3) between the joint centerlines. The three examples shown in Figures 15a-c demonstrate three isometric physical configurations where the revolute joints are perpendicular to each other. Because the axes intersect at 90° in the configurations of Figures 15a-c, there are no geometric design parameters.

Figure 15a is two revolute joints in series. In this configuration, an open chain of robot members 1, 2 and 3 is joined by two revolute joints (actuator module 100) whose centerlines are located relative to each other by three robot member parameters. A common condition in robots is to have the two centerlines parallel (only one robot member parameter remains) . In this case, if robot member 1 is fixed, it is possible to use a point in robot member 3 to track an arbitrary planar curve.

Figure 15b shows the use of one revolute and one prism in series. This results in a common pair combining a revolute (actuator module 100) and a slider (actuator module 300) in a series, especially if the joint

centerlines intersect at 90° which reduces the number of robot member parameters for design to zero.

Figure 15c is two prisms in series. It is possible to use an actuator module (actuator module 300) to provide linear motion between robot members 1 and 2 and robot members 2 and 3. When the angles between the joints is 90°, Cardan coupling between offset rotating shafts results. This is frequently used as an x-y support structure in gantry robots. Extending this to three joints creates the common x-y-z system as used in the IBM robot. If all three axes intersect, the number of design parameters has been reduced to zero.

Figure 16a is a 2-DOF gimbal in rotation. When the two serial revolute joint centerlines intersect at 90°, the result is a special geometry frequently found in robots. If the first joint uses two actuator module 200 halves (actuator module 50) in a yoke (robot member 1) and the second joint uses two actuator module 200 halves in an inner box structure (robot member 2) , the result is a 2-DOF gimbal structure. The joint rotations between robot members 2 and 3 generally cannot exceed 140°.

Figure 16b is a knuckle joint with an external frame. This configuration features four actuator module 200 halves in an external box frame (robot member 2) , each pair (on intersecting centerlines at 90°) driving an internal yoke on robot members 1 and 3. The operating joint rotations cannot exceed 140°. This system structure can be made compact .and exceptionally rigid and isometric. Each degree-of-freedom could be driven in- parallel by an actuator module model 300 if drive stiffness is a priority.

Figure 16c is an interior cross knuckle joint, com¬ prising four actuator modules 100 attached to external

yokes 1 and 3 driving an internal cross-member 2 (at 90° similar to a universal joint found on vehicle drive shafts) with a rotation cone of action approaching 270°. This system is exceptionally compact but not as rugged as the elbow joints of Figures 14a-f.

The actuator modules of the present invention may be used to create a rugged parallel structure robot which can follow an arbitrary planar curve. This 2-DOF parallel planar motion, depicted in Figures 17a and b, is achieved by using actuators near the base joints of the system in order to reduce the moving mass of the system.

Figure 17a is a 2-DOF crank-operated planar curve structure. This parallel structure uses rotational inputs and combines two sets of robot members to track the same point in order to form a parallel structure. Each set of robot members comprises a fixed robot member 1, a lower robot member 2 and an upper robot member 3, with actuator modules 100 being located at the joint formed by robot members 1 and 2 and the joint formed by robot members 2 and 3. Actuator modules 100 are employed at the latter location for antagonism or force level rotation control. This parallel structure is normally more rugged and involves less moving mass than the elementary serial structure. For example, upper robot members 3 experience forces primarily along their center lines (two force members) which they can easily resist with small mass content.

Figure 17b is a 2-DOF slider-operated planar curve structure, a parallel structure using translational inputs. This configuration comprises two serial systems such as those shown in Figure 15b combined to trace the same planar curve, a parallel structure having an actuator module 300 joining members 1 and 2 in each side of the structure. This type of structure is exception-

ally sti f relative to forces acting on the tracing point.

Figures 18a and 18b are 3-DOF serial planar structures based upon the present invention. The relative motion provided by a plane joint (Figure 14f) is the same as the three degrees-of-freedom which result when two flat surfaces move relative to each other (two in translation and one in rotation) . This type of motion is achieved in the configurations of Figures 18a and b and 19a and b.

Figure 18a is a 3-DOF planar serial structure based upon three revolute joints in series. In this configuration, four robot members 1 are joined by three rotary joints with parallel centerlines, each driven by actuator module 100.

Figure 18b is a one revolute and two linear (prisma- tic) joints. Here, four robot members 1 are joined by two linear joints (actuator module 300) whose centerlines intersect the rotary joint centerline at 90° _r with the rotary joint being driven by actuator module 100.

Figures 19a and b are 3-DOF parallel planar structures based upon the present invention. Figure 19a is a 3-DOF parallel planar structure with crank inputs (rotary actuators) . This configuration features a rigid triangle 5 with each apex driven by a separate rotary crank (actuator module 100) through a connecting binary robot "legs" 1, 2 and 3. This is the ideal totally parallel planar mechanical structure. Note that all joint axes must be parallel to provide planar motion. Because all the actuators are on the fixed base, very little mass is moving in this system. Only the cranks experience significant bending deflections. The rest of the system is remarkably rigid against normal planar

forces. The concept of "bracing" in the form of extra supporting structures (usually lightweight and used only on demand) can be used to stiffen an otherwise weak serial structure. The concept can be best understood in terms of parallel structures where it can be thought of as a part of an integrated and balanced design. Here, leg 4 (depicted by a dotted line) may be added to allow a full time utilization of an extra input driver system (in-parallel) for improved force control. Control software then can use any three legs or all four if necessary to provide a significant improvement on the systems tracking capability under force disturbances.

Figure 19b is a 3-DOF parallel planar structure with slider inputs (linear actuators) . In this case, the rotary actuation system of Figure 19a is replaced by three linear actuators (actuator module 300) . This forms a completely parallel planar 3-DOF robot system which is exceptionally rugged. Again, an extra leg (in-parallel) can be added for improved force control.

Figures 20a-c are 3-DOF serial spherical shoulder joints, based on the present invention. The simplest spherical motion is provided by a ball-and-socket joint. But this type of joint cannot be driven directly.

Figures 20a-c show how to create spherical motion by using the actuator modules of the present invention.

In the configuration of Figure 20a, three rotary joints are connected in series, with four robot members 1 being joined by rotary joints driven by actuator modules 100 whose centerlines all intersect at the center of a sphere. Because of the large twisting moments involved, this structure is difficult to make rugged. If the angle between the succeeding axes is 90°, the system results in a common wrist configuration.

Figure 20b is a 3-DOF compact shoulder (or wrist) joint. In this configuration, actuator module 200 is positioned on the base which drives a yoke (two actuator module 200 halves at 90° to the base centerline) which then holds actuator module 200 inside the yoke. This is a very compact and rugged serial shoulder. The same series of modules can be used as a lightweight wrist at the end of a robot. This configuration is subject to the constraint that all axes must intersect to provide spherical motion.

Figure 20c is a 3-DOF compact spherical shoulder with a central joint driven in parallel. This configuration comprises the shoulder joint of Figure 20b with the yoke joint driven in-parallel by actuator module 300. This makes a very rugged and stiff shoulder, although not as compact.

A completely parallel 3-DOF spherical structure may also be formed using the present invention. This configuration may be thought of as the planar system shown in Figure 18a wrapped on a sphere. If three sets of serial robot members are used to drive the same output robot member (robot member 4) , then a completely parallel shoulder module results where all the drivers (actuator module 100) can be located on the fixed robot member. A preloaded ball and socket can be maintained in the center of the sphere for load-carrying capacity if desired. If all the fixed axes of the shoulder are concentric, a wrist is formed which can be driven through torque tubes along the centerline of the robot forearm.

The present invention may be utilized to provide a general mechanical architecture by combining a series of robot members with 1-DOF joints in-between. This means that the weight of most of the actuators is carried by the moving structure. All forces, errors, deformations.

etc. , are additive in a serial structure making it the least rugged and least precise of all possible architectures. To be general, each robot member will contain two joint centerlines (having an offset, a twist angle and a distance along the robot member, i.e., three parameters) . In most robots, the only variable is the offset between the joints when they are parallel or the twist angle is fixed at 90° when they intersect. The reason serial structures are used is that they provide a maximum level of dexterity, excellent obstacle avoidance, simplicity of force analysis and design, minimal intrusion into their work space, small footprint, compact stowage, etc.

A variety of architectures may be achieved driven by the actuator modules of the present invention, including Stewart platforms, dual arms, hands and walking machines. A six-legged Stewart platform may be constructed with each leg of the platform containing a actuator module 300 actuator as a driver. Each leg could be driven at the base by a revolute with an elbow joint along the leg and a ball-and-socket joint where the leg joins the platform. This device can be miniaturized to make a micromanipulator. A three-legged Stewart platform may be constructed, having each leg driven by two revolute joints at the base in a gimbal format and containing an elbow and spherical joint at the top where it joins the platform. Dual arms may be constructed such that the object is held by two 6-DOF serial robots to provide a dual or parallel structure with an excess of six inputs. A robot hand based on the present invention may be configured with essentially identical fingers (three or more) used to control an object at its finger tips. Each finger may be driven by two or more actuators in series depending on the level of force control desired. Walking machines composed of two or more identical serial legs

with various numbers of drivers may also be based on the present invention.

Hybrid structures based on the present invention may be formed by combining structural modules of one, two or three degrees-of-freedom in a larger system. This level of modularity allows for optimum design of the individual modules leaving the system design (with much fewer parameters) to a later stage in the development process. A dynamic model for a manipulator structure may be composed of a selection of parallel-driven modules (elbows, knuckles, wrists, shoulders, etc.) Once this level of modeling is achieved, the hybrid structure can be considered as a substructure of a parallel structure.

Examples of such hybrid structures include 7-DOF modular arms, gantry systems, 9-string manual controllers, and snake robots. A 7-DOF modular arm may be formed by a 3-DOF shoulder 1 and a 3-DOF wrist 2 separated by a 1-DOF elbow 3, as shown in Figure 21.

Gantry systems may be formed with the first 2-or 3-DOF as rather long linear joints to form the gantry. Suspended below this x-y platform is a 4- to 6-DOF arm. The combination allows coverage of a large work volume. A 9- string manual controller involves three modules attached to a handgrip at three points (in-parallel) , with each module constrained by three strings to form a tetrahedron. One embodiment of a snake robot involves 2- DOF serial knuckles combined in a series of multiple modules. Another embodiment involves a series of 3-DOF shoulders (the first is. parallel, the rest are serial) to form a system of four modules and a total of 14 DOF.

Several scales of input may be mixed to govern the total motion of a robot system. To be effective, the same number of inputs (six or more) must occur at each scale. The large motion might be thought to be at scale

1. The motion of dexterous fingers is at approximately a 10% scale relative to the scale of the human arm. Deformations are of the scale of 1%; hence, a set of inputs to match this would enhance precision and resolution. Finally, problems of electronic drift, temperature, etc., might be taken care of by a 0.1% scale of inputs. This would then comprise a 4-layered control system.

Where a stable reference base is required within a large work volume while performing quite delicate and precise small-scale tasks, then a large 6-DOF transporting arm may be combined with a lightweight precision manipulator, in series, to make what is called a "cherry picker". This scale combination allows a user to write, paint, and carve within a relatively large work volume without the need to move the shoulder.

Micromanipulators, comprising parallel 6-DOF small motion devices, may be attached to the end of the robot to provide a high resolution vernier motion system for enhanced precision and disturbance rejection.

For control-in-the-small, a series of small scale inputs (say at the 1% scale) may be distributed throughout the structure for a generalized capability for improved precision and disturbance rejection.

The foregoing description of the invention has been directed to a particular embodiment for purposes of explanation and illustration. It will be apparent, however, to those skilled in this art that many modifications, additions and deletions may be made without departing from the essence of the invention. It is the applicant's intention in the following claims to cover all equivalent modifications and variation as fall within the scope of the invention.