WO2009027979A2

WO2009027979A2 - Pressurized deformable actuating device and method thereof

Info

Publication number: WO2009027979A2
Application number: PCT/IL2008/001170
Authority: WO
Inventors: Alon Wolf
Original assignee: Technion Research & Development Foundation Ltd.
Priority date: 2007-08-31
Filing date: 2008-08-28
Publication date: 2009-03-05
Also published as: WO2009027979A3

Abstract

A deformable actuating device comprises at least one inflatable tube having an inlet for inflating a space within the tube by a pressurized fluid. The tube has a wall with sections of different elasticity along the tube so as to cause the tube to bend in a predetermined direction when inflated

Description

PRESSURIZED DEFORMABLE ACTUATING DEVICE AND METHOD THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to actuators. More particularly, the present invention relates to a pressurized deformable actuating device and method thereof.

BACKGROUND OF THE INVENTION

[0002] The design of an autonomous small mechanical device is often limited by the need for small-sized actuation devices that cover a large workspace (i.e., the space reachable by the actuation device), and for small energy sources that provide sufficient power. These factors often impose constraints on the design with respect to the size of the device, the forces it can apply, and the duration of the time during which it can work without being connected to a permanent energy source. These requirements are often ^' contradictory: a small motorized actuator may have a somewhat low output torque, cover a small workspace, but has low power requirements, while a motorized actuator that can generate a large amount of torque and covers a large workspace is often large in size and consumes a lot of power.

[0003] One solution that has been proposed is the inflatable bellows actuator. An inflatable actuator has a low weight due to the structural materials of which the actuator is constructed. An inflatable actuator is controlled by controlling the pressure of fluid (gas or liquid) in the actuator. The controllability of an inflatable actuator may be useful in carrying out delicate operations.

[0004] Inflatable bellows actuators have been proposed for use as artificial muscles. For example, inflatable actuators are described by Morin in U.S. patent no. 2642091, by Yarlott in U.S patent no. 3645173, and by Immega et al. in U.S. patent no. 4939982. By inflating the actuator and increasing the radial dimension of the actuator, the axial length contracts, imitating the action of a muscle. AU of these actuators are limited to contraction and relaxation in a single, axial dimension. [0005] Others have described actuators with motion in several degrees of freedom. Thomann et al. ("The design of a new type of micro robot for the intestinal inspection," in IROS 2002) describes a micro-actuator catheter driven by three flexible nickel bellows whose pressure is controlled separately. Recently, a new type of a bending pneumatic rubber actuator has been presented by Suzumori et al. ("A Bending Pneumatic Rubber Actuator Realizing Soft-bodied Manta Swimming Robot," IEEE International Conference on Robotics and Automation Roma, Italy, pp. 4975-4980, 2007). These actuators consist of several hollow sections. Inflating a section while other section remains deflated causes the actuator to bend in one direction or another. Actuators with two or more separately inflatable sections require a more complex inflation mechanism than an actuator with a single inflatable section. [0006] It is an object of the present a pressurized deformable actuating device with a single inflatable section that is capable of bending, generating a large amount of torque and covering a large workspace.

[0007] Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings.

SUMMARY OF THE INVENTION

[0008] There is thus provided, in accordance with some embodiments of the present invention, a deformable actuating device comprising at least one inflatable tube having an inlet for inflating a space within the tube by a pressurized fluid, the tube having a wall with different elasticity along the tube so as to cause the tube to bend in a predetermined direction when inflated.

[0009] Furthermore, in accordance with some embodiments of the present invention, the sections of the sections of different elasticity comprise materials of different elasticity. [0010] Furthermore, in accordance with some embodiments of the present invention, the sections of different elasticity vary in thickness from one another.

[0011] Furthermore, in accordance with some embodiments of the present invention, the sections of different elasticity comprise two sections of different elasticity.

[0012] Furthermore, in accordance with some embodiments of the present invention, said at least one inflatable tube comprises at least two inflatable tubes joined in such a manner that each of said at least two inflatable tubes is designed to bend in a predetermined direction when inflated, wherein the predetermined directions of at least two of said at least two inflatable tubes differ from one another.

[0013] Furthermore, in accordance with some embodiments of the present invention, said at least two inflatable tubes comprise three inflatable tubes.

[0014] Furthermore, in accordance with some embodiments of the present invention, the space is confined by the wall.

Furthermore, in accordance with some embodiments of the present invention, the wall of the tube comprises an inner wall and outer wall and the space is confined by the inner wall and the outer wall.

[0015] .

[0016] Furthermore, in accordance with some embodiments of the present invention, at least one of said at least one inflatable tube comprises a conduit for conducting a fluid.

[0017] Furthermore, in accordance with some embodiments of the present invention, the wall comprises a sensor adapted to sense strain.

[0018] Furthermore, in accordance with some embodiments of the present invention, there is proceed an actuating method, the method comprising:

[0019] providing at least one inflatable tube having an inlet with a space within the tube, the tube having a wall with sections of different elasticity along the tube so as to cause the tube to bend in a predetermined direction when inflated; and

[0020] inflating the space within the tube by a pressurized fluid.

[0021] Furthermore, in accordance with some embodiments of the present invention, the method comprises using a pump in the step of inflating the space within the tube.

[0022] Furthermore, in accordance with some embodiments of the present invention, the method further comprises monitoring the shape of the deformable actuating device.

[0023] Furthermore, in accordance with some embodiments of the present invention, the step of providing at least one inflatable tube comprises providing at least two inflatable tubes joined in such a manner that each of said at least two inflatable tubes is designed to bend in a predetermined direction; and inflating the tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals.

[0025] Fig. 1 shows a pressurized deformable actuating device constructed of two materials, in accordance with embodiments of the present invention.

[0026] Fig. 2 shows a pressurized deformable actuating device constructed of a single material, in accordance with embodiments of the present invention.

[0027] Fig. 3 A shows a cross section of the actuator of Fig. 2 in an initial straight state. [0028] Fig. 3B shows a cross section of the actuator of Fig. 2, partially bent. [0029] Fig. 3C is a cross section of the actuator of Fig. 2, further bent.

[0030] Fig. 4 shows another arrangement of a pressurized deformable actuating device, in accordance with embodiments of the present invention.

[0031] Fig. 5 is a schematic diagram of a method of monitoring the state of a pressurized deformable actuating device in accordance with embodiments of the present invention.

[0032] Fig. 6A is a cross section of an inflatable device adapted to delivering fluids, in accordance with embodiments of the present invention.

[0033] Fig. 6B shows a section of the device of Fig. 6 A.

DETAILED DESCRIPTION OF EMBODIMENTS

[0034] A pressurized deformable actuating device in accordance with embodiments of the present invention includes an elongated tube that is sealed at one end. The elasticity of the wall of the tube varies along its perimeter. When pressurized fluid, such as a liquid or gas, is forced into the tube, the tube elongates. Due to the variation in the elasticity of the wall along the perimeter of the tube, one side of the tube may elongate more than another side. Therefore, applying pressure to the inside of the tube results in an elongated curved tube. The curvature of the tube is determined by the varying elasticity of the tube wall and the applied pressure.

[0035] Such a tube may serve, for example, as an actuator in a robotic system. By controlling the pressure applied to the inside of the actuator, the actuator may be manipulated to press, push, pull or contact various objects or surfaces in its vicinity.

[0036] Fig. 1 shows a pressurized deformable actuating device constructed of two materials, in accordance with some embodiments of the present invention. Bi-material pressurized deformable actuating device 10 is constructed in the form of a hollow cylindrical tube. The cross section of bi-material pressurized deformable actuating device 10 is circular, although the cross section could be constructed with any appropriate shape. The tube is divided lengthwise into sections, e.g. two sections, as in the embodiment shown in this figure (section 12 and section 14) that are bonded to each other. Each section is constructed of a material with different elastic properties. For example, the material of which section 12 is constructed may be more elastic than the material of which section 14 is constructed. In this case, pressurizing the hollow interior of bi-material pressurized deformable actuating device 10 may cause section 12 to elongate along the axis of the actuator more than section 14. Since section 12 and section 14 are bonded mechanically to move together, bi-material pressurized deformable actuating device 10 may bend in the direction of less elastic section 14. Bi- material pressurized deformable actuating device 10 thus acquires a curvature with less elastic section 14 on the concave side, and more elastic section 12 on the convex side.

[0037] Fig. 2 shows a pressurized deformable actuating device constructed of a single material, in accordance with embodiments of the present invention. In this embodiment, the wall of pressurized deformable actuating device 16 may again be divided lengthwise into two sections, section 18 and section 20. However, in this case, both section 18 and section 20 are constructed of a single material. Section 18, however, is thicker than section 20. Therefore, given uniform material elastic properties in both sections, section 20 is more elastic than section 18. Pressurizing the hollow interior of pressurized deformable actuating device 16 causes section 20 to elongate more than section 18. As a result, pressurized deformable actuating device 16 maj' bend toward thicker section 18, acquiring a curvature with thicker section 18 on the concave side, and thinner section 20 on the convex side.

[0038] In an alternative embodiment of the present invention, the thickness or elastic properties of the wall of the pressurized deformable actuating device may vary continuously (and not discretely as shown in Fig. 2) along the perimeter of the pressurized deformable actuating device, or the wall may be divided into more than two sections. In another alternative embodiment of the present invention, the elastic properties of various parts of the actuator may be varied by applying varying degrees of thermal, electrical, chemical, or other physical stimuli to a section or sections of an actuator made from a material whose elastic properties are sensitive to changes in temperature, electrical current, chemical concentration, or other physical stimuli. In yet another alternative embodiment of the present invention, the walls of the actuator may be constructed with folds, projections, or other morphological features in such a manner that one side is more readily extendible than another. [0039] The elastic properties of the wall of a pressurized deformable actuating device may also vary along the length of the actuator. This may result in the pressurized deformable actuating device acquiring more complex shapes (for example, an "S" shape or helical shape) when inflated, with the direction and radius of curvature varying along the length of the actuator. [0040] Fig. 3 A shows a cross section of the actuator of Fig. 2 in an initial straight state. End 15 of pressurized deformable actuating device 16 is sealed, forming hollow chamber 13 along the central axis of pressurized deformable actuating device 16. At one end, the walls of the pressurized deformable actuating device 16 are widened to form inlet 11. Inlet 11 may be connected to a connection port of a source of compressed air, or another pressurized gas or fluid. The connection port to which inlet 11 is connected may be rotatable. Rotating the connection port then rotates pressurized deformable actuating device 16. In the state illustrated in Fig. 3 A, the pressure of the introduced fluid is equal to the ambient atmospheric pressure, and the elasticity of the actuator walls contracts pressurized deformable actuating device 16 to its deflated, unextended shape. In its unextended state, the walls of pressurized deformable actuating device 16 take the form of a cylinder with circular cross section and straight axis. [0041] Fig. 3B shows a cross section of the actuator of Fig. 2, partially bent. In this state, gas or fluid pressurized to a pressure somewhat greater than atmospheric pressure, is forced into hollow chamber 13 of pressurized deformable actuating device 16 through inlet 11. The pressurized fluid expands pressurized deformable actuating device 16. Due to the greater flexibility of the wall of section 20, the wall of section 20 stretches by a greater amount than the wall of section 18. Therefore, as pressurized deformable actuating device 16 expands, it begins to curve toward the direction of less flexible section 18, so that end 15 extends toward the bottom and left of Fig. 3B. Continued expansion of pressurized deformable actuating device 16 may cause end 15 to apply a force or move an object or surface placed in the path of end 15. The connection port to which inlet 11 is connected may be rotated while pressurized deformable actuating device 16 is pressurized to a given pressure. Such rotation may enable placement of end 15 anywhere within a workspace defined by the limits of the rotation of the connection port, and the form of pressurized deformable actuating device 16 at the given pressure. [0042] Fig. 3C is a cross section of the actuator of Fig. 2, further bεnt. In this state, gas or fluid that has been highly pressurized has been forced into the interior of pressurized deformable actuating device 16, expanding it to a larger volume. Again, due to the greater flexibility of the wall of section 20, the wall of section 20 has been stretched by a greater amount than the wall of section 18. Pressurized deformable actuating device 16 has curved by about 180°, so that end 15 extends back toward the connection port of inlet 11. End 15 may be made to apply a force to an object or surface placed at the extreme point reached by end 15.

[0043] Several pressurized deformable tubes may be joined to achieve a greater range of motion. Fig. 4 shows an arrangement of a pressurized deformable actuating device, in accordance with embodiments of the present invention, that includes several such tubes joined together. In the embodiment shown in Fig. 4, actuator 40 includes three individual pressurized deformable actuating tubes 16a, 16b, and 16c, bundled in a trefoil arrangement. The stiffer, more rigid segment of each individual pressurized deformable actuating device faces outward from the center of the bundle. Each individual pressurized deformable actuating tube of actuator bundle 40 maybe pressurized separately, or several in combination may by pressurized to varying degrees. Pressurizing a single pressurized deformable actuating tube of actuator bundle 40 may cause that actuator to bend outward from the center of the bundle, as indicated by the arrows in Fig. 4. In this example, the bending directions, or bending planes, of individual pressurized deformable actuating tubes 16a, 16b, and 16c are oriented approximately 120° apart from each other. The bending of a single pressurized deformable actuating tube may cause entire actuator bundle 40 to bend with it.

[0044] Two pressurized deformable actuating tubes of actuator bundle 40 may be simultaneously pressurized to an approximately equal degree. Simultaneous pressurization may cause actuator bundle 40 to bend in a direction midway between the bending directions of the individual pressurized deformable actuating tubes. For example, simultaneously pressurizing pressurized deformable actuating tubes 16a and 16b may cause actuator bundle 40 to bend toward the left hand side of Fig. 4. Pressurizing each individual pressurized deformable actuating tube to a different pressure may cause actuator bundle 40 to bend in a different direction. In this manner, varying the pressure applied to each individual pressurized deformable actuating tube of actuator bundle 40 in a controlled manner. Such controlled application of pressure may enable controlled manipulation of actuator bundle 40 to cover a wider workspace than would be possible for a single pressurized deformable actuating tube.

[0045] In order to properly control the shape of a pressurized deformable actuating device, it is advantageous to monitor it. Fig. 5 is a schematic diagram of a method of monitoring the state of a pressurized deformable actuating device in accordance with embodiments of the present invention. Pump 24 pumps pressurized fluid into pressurized deformable actuating device 16 through inlet 11. The pressure of the pressurized fluid may be controlled by means of adjusting pump 24. The pressurized fluid may cause pressurized deformable actuating device 16 to inflate, extend, and bend.

Background surface 22 is marked with a visible coordinate grid. Camera 30 is positioned and aimed such that pressurized deformable actuating device 16 is positioned between camera 30 and background surface 22. An image acquired by camera 30, then, shows pressurized deformable actuating device 16 against background surface 22. The shape of pressurized deformable actuating device 16 may then be ascertained with regard to the coordinate grid of background surface 22. Alternatively, the position and orientation of front surface 15 or any other portion of pressurized deformable actuating device 16 may be ascertained. The information thus obtained may be utilized by a control system of a robotic system that incorporates pressurized deformable actuating device 16. The obtaining of shape, position, and orientation information may provide feedback to the control system with regard to the status and performance of pressurized deformable actuating device 16.

[00461 Alternatively, pump 24 may be adjusted to achieve a sequence of values of the pressure of the pressurized air, while images of pressurized deformable actuating device 16 against background surface 22 are acquired concurrently. In this manner, the dependence of the shape of pressurized deformable actuating device 16 on the pressure of the pressurized air may be determined empirically. The determined dependence may provide calibration information that allows the shape of pressurized deformable actuating device 16 to be predicted as a function of the applied air pressure.

[0047] Alternatively, the performance, or current shape, position, or orientation, of a pressurized deformable actuating device may be monitored by means of one or more sensors that are incorporated within the actuator itself. For example, one or more sensors may be incorporated into the walls of a pressurized deformable actuating device. The sensors may be capable of generating signals that indicate the local strain of a section of an actuator wall. For example, one or more piezoelectric sensors constructed of polyvinylidene fluoride (PVDF) may be affixed to a segment of a wall such as to indicate the elongation of that segment. Analysis of the signals generated by the sensors may determine the current shape of the pressurized deformable actuating device. Such analysis of strain sensor output may continue to accurately indicate the current shape of the pressurized deformable actuating device even if the elastic properties of the walls are altered. The results of the analysis may be provided as feedback to a control sj'stem controlling the pressurized deformable actuating device.

[0048] Alternatively, one or more position sensors may monitor the positions of one or more points of a pressurized deformable actuating device, thus providing performance feedback to a control system that controls the pressurized deformable actuating device. Alternatively, one or more accelerometers, gjτoscopes, or other motion sensors may monitor the motion of one or more parts of the pressurized deformable actuating device. [0049] The techniques described above for the construction of a pressurized deformable actuating device may be adapted to the construction of a fluid delivery device, such as a catheter. A fluid delivery device so constructed may extend and bend in a controlled manner by forcing pressurized fluid into an interior chamber. Fig. 6A is a cross section of an inflatable device adapted to delivering fluids, in accordance with embodiments of the present invention. Fig. 6B shows a section of the device of Fig. 6A. Fluid delivery device 50 includes a conduit in the form of central bore 55 that is shaped in the form of a cylinder that is open at both ends. Thus, fluid may be introduced to one end of central bore 55 and removed from the other, as indicated by arrow S. Central bore 55 is surrounded by a hollow chamber 56 with an annular cross section between inner and outer walls. At one end of hollow chamber 56, the space between the inner and outer walls is sealed by means of annular cap 58. The other end of hollow chamber 56 is at least partially open and connects to a source of pressurized fluid. Pressurized fluid may be forced into hollow chamber 56, as indicated by arrows P. Forcing pressurized fluid into hollow chamber 56 causes hollow chamber 56 to expand. The walls of hollow chamber 56 are constructed so that the perimeter of each the inner and outer wall may be divided lengthwise into two sections, section 52 and section 54, along two radii. Section 52 and section 54 are so constructed such that the elastic properties of section 52 and section 54 differ from one another. For example, sections 52 and 54 may be constructed of materials with different elastic material properties, or one section may be thicker than the other. Alternatively, the walls of hollow chamber 56 may be constructed such that the elastic properties of the walls vary in a continuous fashion along the perimeters of the walls. As a result of the differing construction of the two sections, one section may be more elastic than the other. Therefore, when pressurized fluid is forced into hollow chamber 56, sections 52 and 54 stretch by differing amounts. When sections 52 and 54 elongate by differing amounts, fluid delivery device 50 bends toward the side with the less elastic walls. In this manner, by increasing the pressure of the fluid in hollow chamber 56, fluid delivery device 50 may be made to extend and bend, allowing the delivery of fluid via central bore 55 to a desired location. [0050] Several individual fluid delivery devices may be joined together in order to achieve a greater range of motion. [0051] Thus, embodiments of the present invention provide an actuator or fluid delivery device that is controlled by means of pressurized fluid, which may extend and bend in a controlled manner.

[0052] It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope.

[0053] It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the present invention.

Claims

1. A deformable actuating device comprising at least one inflatable tube having an inlet for inflating a space within the tube by a pressurized fluid, the tube having a wall with sections of different elasticity along the tube so as to cause the tube to bend in a predetermined direction when inflated.

2. The device as claimed in claim 1, wherein the sections of different elasticity comprise materials of different elasticity.

3. The device as claimed in claim 1, wherein the sections of different elasticity differ in thickness from one another.

4. The device as claimed in claim 1, wherein the sections of different elasticity comprise two sections of different elasticity.

5. The device as claimed in claim 1, wherein said at least one inflatable tube comprises at least two inflatable tubes joined in such a manner that each of said at least two inflatable tubes is designed to bend in a predetermined direction when inflated, wherein the predetermined directions of at least two of said at least two inflatable tubes differ from one another.

6. The device as claimed in claim 5, wherein said at least two inflatable tubes comprise three inflatable tubes.

7. The device as claimed in claim 1, wherein the space is confined by the wall.

8. The device as claimed in claim 1, wherein the wall of the tube comprises an inner wall and outer wall and the space is confined bj' the inner wall and the outer wall.

9. The device as claimed in claim 1, wherein at least one of said at least one inflatable tube comprises a conduit for conducting a fluid.

10. The device as claimed in claim 1, wherein the wall comprises a sensor adapted to sense strain.

11. An actuating method, the method comprising: providing at least one inflatable tube having an inlet with a space within the tube, the tube having a wall with sections of different elasticity along the tube so as to cause the tube to bend in a predetermined direction when inflated; and inflating the space within the tube by a pressurized fluid.

12. The method as claimed in claim 11, comprising using a pump in the step of inflating the space within the tube.

13. The method as claimed in claim 11, further comprising monitoring the shape of the deformable actuating device.

14. The method as claimed in claim 11, wherein the step of providing at least one inflatable tube comprises providing at least two inflatable tubes joined in such a manner that each of said at least two inflatable tubes is designed to bend in a predetermined direction; and inflating the tubes.