WO2013105849A1

WO2013105849A1 - Actuated hexapod platform

Info

Publication number: WO2013105849A1
Application number: PCT/NL2012/050903
Authority: WO
Inventors: Hubertus Cornelius Antonius Dirkx; Ruud VAN DER AALST
Original assignee: Wittyworx Llp
Priority date: 2012-01-10
Filing date: 2012-12-19
Publication date: 2013-07-18

Abstract

A piezoelectric actuated hexapod design (100) usable as inner work for a robot in the personal robotics domain, enabling quiet actuation, compact design, beneficial force transmission ratios, low-cost and beneficial actuation dynamics. Piezoelectric actuators (16) are used in combination with sets of crank pushrod mechanisms (13), wherein each pushrod is connected to a wheel segment (15). These wheel segments are placed in a triangular orientation, resulting in a compact design. Position measurements can be performed at wheel segments.

Description

Actuated Hexapod Platform

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The present invention is in the technical field of mechanically actuated devices.

More particularly, the present invention is in the technical field of actuation of personal robotics. The definition of personal robotics as used herein is that Personal Robots are domestic service robots that educate, entertain and/or assist in the home environment and/or provide social interaction. More particularly, the present invention is in the technical field of actuated hexapod devices as robotic inner work.

The widely known hexapod platforms make use of pushrods that change in length to enable a certain motion of an upper platform, e.g. they make use of kinds of linear actuators. This results in limited optimization possibilities regarding obtainable dynamics, e.g. actuator choice, and required compactness. These designs are not regarded usable for the personal robotics domain, missing the required dynamic performance like high accelerations, being too expensive or excessive in size.

Less common is the use of a crankshaft to drive each pushrod of a hexapod. These designs require either large actuators or a combination of an actuator with a gearbox to supply the required torque. This results in increased volume requirements, increased costs and the introduction of noise and play.

DE202009001366U by Elliptec Resonant Actuator AG describes a micromanipulator needle, positioning device for use in micro assembly, which has piezoelectric actuators controlled independently of each other, provided for moving a body and comprising coupling units arranged between driven units and body. However, shortcomings are identified in the arrangement of DE202009001366U. The proposed setup design is not compact, limiting the possible use in miniaturization. This, for instance, makes it unsuitable to use as an inner work in personal robotics. Furthermore, the proposed setup design is not beneficial for the transferred force or torque ratio. Lastly, the proposed setup design is targeted for precise and fast positioning instead of application in the personal robotics domain.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved hexapod design. It is a further object of the invention to provide a hexapod design that allows efficient miniaturization. It is a further object of the invention to provide a hexapod design that can efficiently be used in the actuation of personal robots. It is a further object of the invention to provide a

mechanically actuated device including an improved actuating mechanism. It is a further object of the invention to provide a personal robot including an improved actuating mechanism.

Thereto according to the present invention is provided a compact piezoelectrically actuated hexapod design usable as inner work for a robot in the personal robotics domain. With triangular orientated crank pushrod mechanisms, driven by piezo actuators, it enables the possibihty for compact design, quiet actuation, beneficial force transmission ratios, low-cost and beneficial actuation dynamics. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further elucidated by means of non-limiting examples referring to the drawings, in which

Fig. 1 is a crank pushrod mechanism assembly (13);

Fig. 2 is an actuator assembly (150);

Fig. 3 is a set of two actuator assemblies; Fig. 4 is a top view of an actuated hexapod platform excluding the upper body (11);

Fig. 5 is a perspective view of an actuated hexapod platform excluding frame;

Fig. 6 is a bottom perspective view of an actuated hexapod platform excluding frame;

Fig. 7 is a side view of an actuated hexapod platform excluding frame;

Fig. 8 is a side view of an actuated hexapod platform (100);

Fig. 9 is a perspective view of an actuated hexapod platform (100);

Fig. 10 is a bottom perspective view of an actuated hexapod platform (100);

Fig. 11 is a front view of a personal robot;

Fig. 12 is a front view of an actuated hexapod platform (110) with horizontal rotational stroke limitation;

Fig. 13 is a perspective view of an actuated hexapod platform (110) with horizontal rotational stroke limitation;

Fig. 14 is a bottom perspective view of an actuated hexapod platform (110) with horizontal rotational stroke limitation;

Fig. 15 is a front view of an actuated hexapod platform (120) with metal spring gravity compensator; and

Fig. 16 is a front view of an actuated hexapod platform (130) whereby the flexible body functions as gravity compensator. DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1 to Fig. 10 an actuated hexapod platform 100 (or hexapod for short) according to the invention is shown. The hexapod 100 has an upper body 11 connected at three joint positions 12 to six crank pushrod mechanisms 13. In this example the upper body 11 is a upper disc. At each side of the upper body 11 an end stop 10 is positioned, attached to body 9. Body 9 is attached to a frame 17. Each of the crank pushrod mechanisms 13 comprises a pushrod 14, only stiff along the longitudinal direction, at the upper end connected to a joint position 12 at the upper body 11 and at the lower end connected with a joint 18 to a wheel segment 15.

The actuator assembly 150 includes a crank pushrod mechanism

13 and a piezoelectric actuator 16. Each wheel segment 15 is actuated by a piezoelectric actuator 16 so as to rotate the wheel segment 15 around an axis of rotation 19. The wheel segment 15 can also be used for direct position measurement of the crank pushrod mechanism 13 as detailed below. The wheel segments 15 and actuators 16 are positioned and secured in frame 17. The actuators 16 are positioned and secured in a motor frame 25 of which an example is given in Fig.12 to Fig.14. The hexapod 100 has a central axis 117 extending through the center of the frame 17 and through the center of body 9. In the example, the central axis 117 forms a longitudinal axis of the hexapod 100. In the example, the central axis 117 is substantially vertical in use.

As can be seen in Fig. 4, the actuator assemblies 150 are positioned such that three sets 150A, 150B, 150C of two actuator assemblies are formed. In each set 150A, 150B, 150C of two actuator assemblies the axes of rotation 19 of both wheel segments 15 are substantially parallel. In this example, the axes of rotation of both wheel segments 15 of each set 150A, 150B, 150C are coaxial. This provides the advantage that the two wheel segments 15 of the set are positioned side by side, so as to occupy a limited amount of space. The axes of rotation 19 of the actuator assemblies 150 are substantially directed towards a central point between the six wheel segments 15. The axes of rotation 19 of the actuator assemblies 150 are substantially directed towards a center of the hexapod 100, here towards the central axis 117 of the hexapod 100. In this example, the axes of rotation 19 intersect at the center of the hexapod 100. Since the axes of rotation 19 point towards the center of the hexapod 100, the three sets 150A, 150B, 150C of two actuator assemblies are positioned in a triangular orientation. The wheel segments 15 each extend in a plane that is substantially parallel to a longitudinal side plane of a virtual beam having its longitudinal direction substantially vertical and having a triangular cross section in top plan view. It will be appreciated that the three sets 150A, 150B, 150C of two actuator assemblies 150 correspond to three sets of crank pushrod

mechanisms 13.

Still referring to Fig. 1 to Fig. 10, the upper body 11 is able to exhibit actuated motion in six degrees-of-freedom by means of actuation of the six actuator assemblies 150. Each piezoelectric actuator 16 is controlled independently of the other piezoelectric actuators 16. The piezoelectric actuator 16 is coupled by friction force to wheel segment 15 and actuates wheel segment 15 to rotate around the axis 19. The rotation of the wheel segment 15 around the axis 19 is then transferred by the pushrod 14 in to translation of the joint position 12 at the upper body 11. This way, two pushrod mechanisms 13 can control the position of one joint position 12 at the upper body 11. In the example the position of the joint position 12 at the upper body 11 is controlled by one set of pushrod mechanisms 13. The three joint positions 12 at the upper body 11 together determine the position of the upper body 11 in six degrees-of -freedom. To facilitate actuated motion of the upper body 11 in six degrees-of -freedom like this, the pushrods 14 are only stiff in longitudinal direction. The pushrods 14 can be connected to the upper body 11 and to the respective wheel segment 15 by a spherical joint to allow the required freedom of motion. In the example, the pushrods 14 are designed to be rotatable, e.g. by torsion, around their longitudinal direction, and the connections to the upper body 11 and the respective wheel segment 15 are hinged joints, which results in an equivalent of a spherical joint at each end. The vertical stroke of the upper body 11 is along central axis 117 limited by two end stops 10. The motion of the upper body 11 in the horizontal plane, i.e. perpendicular to axis 117, is limited by body 9. Both end stops 10 as well as body 9 facilitate a motion stop and absorb external forces, guiding them in to frame 17 by bypassing the forces exerted on one or more assemblies 150.

Referring to Fig. 15, if desired, the previous described actuated hexapod platform 100 allows to be extended by a gravity compensator 40. This gravity compensator 40 is attached to frame 17 at its lower end and upper body 11 at its upper end. It reflects a resilient body. The resilient body has a certain desirable stiffness, providing a spring function exerting upward forces upon upper body 11 to compensate for its weight and possibly the weight of bodies it carries, e.g. the robotic head 20. Many forms of realizations are possible, e.g. placing a helical spring as shown in Fig.15. Note that also a body 24 realized in a flexible resilient material, e.g. silicone, could act as the gravity compensator 40 as shown in Fig.16. The gravity compensator 40 is advantageous for system dynamics of the actuated hexapod platform 100, by compensating gravitational forces to overcome during motion.

The embodiment of gravity compensator 40 as shown in Fig. 15 offers to a certain extent protection of the inner mechanism, i.e. the actuator assemblies 150, against externally applied forces, hereby increasing the robustness of the mechanism. Different embodiments of such gravity compensator 40 e.g. rectangular cross section or non-constant diameter or pitch or leaf springs possibly in combination with the flexible outer body 24 provide different behavior and protection from external forces.

The hexapod described thus far is very well suited for

miniaturization. Hence, the hexapod can efficiently be used in a personal robot or toy, at dimensions commonly used for personal robots or toys, e.g. 50mm - 500mm in height. Due to the simple and compact design, the hexapod can also be used in applications requiring other dimensions.

Referring to Fig. 1 to Fig. 11, the upper body 11 is sufficiently wide, such as a diameter of about 25 to 100 mm, for carrying a broad range of objects, e.g. a robotic head 20 including several components like one or more displays 21, actuators, cameras 22, microphones 23 and other sensors. The upper body 11 is located at a sufficient distance from the ground to be able to present a body part connection, e.g. the neck height, of the body 24 of a small personal robot, such as about 60 to 250 mm off the ground. The pushrods 14 are sufficiently long to ensure significant range of all six degrees-of-freedom, such as about 20 to 90 mm in length. The wheel segments 15 have a radius that ensures a beneficial transmission ratio regarding force and motion of the piezoelectric actuator 16 upon the upper body 11, such as a diameter of about 25 to 60 mm. The positioning of the wheel segments 15 in de embodiment 17 is triangular orientated such that the hexapod design 10 is able to maintain minimal volume.

The body 9 is of sufficient length, such as 35 to 100 mm, to facilitate vertical stroke of upper body 11. Furthermore body 9 has a radius that facilitates sufficient strength to absorb high forces, such as a diameter of about 5 to 15 mm. The end stops 10 should be sized larger than the central hole in upper body 11.

The wheel segments 15 can be used for determining an angular position of the wheel segment 15. It is for instance possible to provide the wheel segment with an angular encoder. The wheel segment may e.g.

comprise an angular position indication that can be read by an associated detector as is known in the art.

The construction details of the invention as shown in Fig. 1 to Fig. 10 are that the upper body 11, pushrods 14 and frame 17 may be made of high-strength plastics or of any other sufficiently rigid and strong material such as metal, and the like. The wheel segments 15 are made of a material sufficiently stiff and temperature-stable to support the static spring load and driving forces as exhibited by the piezoelectric actuator 16. Therefore the wheel segments 15 may be made of fiber enhanced materials,

thermosetting plastics, metals, and the like. The body 9 as well as the end stops 10 are made of a material sufficiently strong to endorse high forces. The body 9 as well as the end stops 10 may be made of high-strength plastics or of any other sufficiently rigid and strong material such as metal, and the like. These bodies may be combined with materials introducing additional damping characteristics, such as rubber, and the like.

Another example of an embodiment of the invention is given in Figs. 12 to 14 showing hexapod 110. In this example, body 9 is divided into three separate bodies 9A, 9B and 9C with central axis 117A, 117B and 117C, respectively. Accordingly, upper body 11 has three holes. The advantage of this embodiment is that the horizontal rotation of upper body 11 around central axis 117 is limited by the bodies 9A, 9B, 9C, preventing the mechanism, i.e. the crank pushrod mechanisms 13, from being overstressed e.g. by external forces. It will be appreciated that bodies 9A, 9B and 9C, e.g. when embodied as tubes, can be used for cable feed through to connect electronics on both outer ends of the bodies, e.g. electronics that are located in the robotic head 20 and the frame 17.

As can be seen in Figs. 8-10 and Figs. 12-14 the shaped of the end stop 10 may vary. It will be appreciated that in general the shape of the end stops 10, on the side on which upper body 11 collides for that end stop 10, can be designed in such a way that upper body 11 is forced into a horizontal position when external forces are exerted upon the upper body 11. This provides the advantage that the contact area between upper body 11 and end stop 10 during collision smoothly increases, decreasing impact and locally applied collision forces.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. For instance: - In Fig.4 the two side-by-side wheel segments 15 of a set do not have to be in line with each other. Their axes of rotation can be offset with respect to each other along their side of the triangular orientation

(especially the inner wheels) without increasing the outer diameter of the frame or with remaining compactness.

- In Fig.4 the axis (axes) 19 of each set of actuator assemblies can be offset with regard to the center of the hexapod 100, so as not to intersect with the center of the hexapod.

- Fig.6 The pushrods 14 can have a different orientation and variation of joint positions 12 when connected to the upper body 11.

- Fig.1 The eccentricity of the pushrods can be chosen to fit the transmission ratio.

- Fig.5 The diameter of the upper body 11 can be chosen to fit the transmission ratio for tilt.

- The type of actuator used in the present invention is not limited to piezoelectric actuators, e.g. electromagnetic actuators could be used.

- The end stops 10 could be integrated into other parts, e.g. into the robotic head 20, to limit the vertical and/or horizontal stroke of upper body 11.

- In Figures 12 to 14 the number of bodies (here three, i.e. 9A, 9B, 9C) providing the horizontal rotational end stroke of upper body 11 around central axis 17, and holding the vertical end stops 10, can be varied, e.g. with two or more bodies.

- The gravity compensator 40 as shown in Figure 15, can be placed elsewhere, e.g. it can be attached inside the robotic head 20, between the robotic head 20 inner shell and the upper end stop 10.

However, other modifications, variations, and alternatives are also possible. The specifications, drawings and examples are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. The advantages of the present invention include, without limitation, compact design with optimal actuator force transmission, no need for gearboxes, quiet motion, robust friction coupling, advantageous system and actuation dynamics, i.e. high accelerations in a very precise manner, low-cost and high robustness against external forces.

More in general, the present invention is a hexapod design, with piezoelectric actuated crank pushrod mechanisms installed in a triangular orientation, usable as inner work for a robot in the personal robotics domain.

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. An actuator assembly for a hexapod, comprising three sets of two wheel segments, each wheel segment being rotatable around a respective rotation axis, wherein the rotation axes of the two wheel segments of each set are substantially parallel and substantially directed towards a central point between the six wheel segments.

2. An actuator assembly according to claim 1, wherein the rotation axes of the two wheel segments of each set are coaxial.

3. An actuator assembly according to claim 1 or 2, wherein the rotation axes of the six wheel segments intersect in the central point between the six wheel segments.

4. An actuator assembly according to any one of claims 1-3 further comprising six actuators, such as piezoelectric actuators, each actuator being associated with a respective wheel segment for displacing said wheel segment in rotation around the associated axis of rotation.

5. An actuator assembly according to claim 4, wherein each actuator acts on an outer radius of the associated wheel segment.

6. An actuator according to claim 4 or 5, further including a frame, wherein the actuators are mounted to the frame and the wheel segments are rotatably connected to the frame.

7. An actuator assembly according to any one of claims 1-6, wherein each of the wheel segments is arranged for determining an angular position of that wheel segment.

8. A hexapod including an actuator assembly according to any one of claims 1-7, further comprising an upper body and six pushrods, wherein each pushrod is connected at a first end to the upper body, and each connected at an opposite, second, end to a respective one of the six wheel segments.

9. A hexapod according to claim 8, wherein the stroke of the mechanism is limited by the upper body and/or at least one vertically positioned body.

10. A hexapod according to claim 9, whereby the horizontal rotational stoke is limited by two or more vertically positioned bodies.

11. A hexapod according to claim 9 or 10 wherein at least one vertically positioned body is used for cable feed through.

12. A hexapod according to any one of claims 8-11, comprising one or more end stops arranged for absorbing external forces so as to bypass external forces exerted on the pushrods when the maximum stroke is reached

13. A hexapod according to claim 12 wherein one or more end stops are arranged to guide a body during collision when an end of stroke is reached, hereby optimizing absorption of externally applied forces.

14. A hexapod according to any one of claims 8 - 13, comprising a gravitation compensator, in the form of a resilient body, between the upper body and the frame.

15. A hexapod according to claim 14 wherein the resilient body is arranged to provide shielding for the inner mechanisms.

16. An actuated hexapod design driven by crank pushrod mechanisms whereby each crank is part of a wheel segment and these wheel segments are placed in sets of two, side by side, in a triangular orientation.

17. A hexapod according to any one of claims 8-16 wherein the actuation forces are applied at the outer radius of the wheel segments.

18. A hexapod according to any one of claims 8-17 wherein the wheel segments are used for position measurements.

19. A hexapod according to any one of claims 8-18 wherein external forces are absorbed by one or more end stops bypassing the forces exerted on the pushrods when the maximum stroke is reached.

20. A hexapod according to any one of claims 8-19 in combination with the use of piezo actuators.

21. A personal robot including a hexapod according to any one of claims 8-20.

22. A personal robot according to claim 21, wherein the personal robot comprises a head, e.g. including one or more of a camera, a display, a speaker, a microphone, and a tactile input device, the head being mounted to the upper body.

23. A personal robot according to claim 21 or 22, wherein the personal robot comprises a body being mounted to the frame of the actuator

assembly.

24. A toy including a hexapod according to any one of claims 8-20.