DE102011104026B4 - Flexible fluid drive for producing a nearly exact bidirectional screw movement and associated method - Google Patents

Abstract

The present invention is intended to provide a miniaturizable compliant fluid drive and associated method which succeed in a simple manner and with minimal effort to produce a nearly exact bi-directional screw movement of the coupling surface fluid-drive active element. According to the invention, the screw movement opposite to the output rotation of the coupling surface fluid drive active element is realized with a cavity element having fluid drive from reversibly deformable, elastically extensible material by changing the pressure load within the cavity element. Such fluid drives are used in robotics, preferably for the manipulation and handling of sensitive objects or in medical technology, preferably for the positioning and holding of sensors.

Description

The invention relates to a resilient fluid drive for producing a nearly exact bidirectional screw movement (rotational movement about an axis with simultaneous translational movement along this axis in both directions) and an associated method for use in robotics, preferably for the manipulation and handling of sensitive objects or in the Medical technology, preferably for positioning and holding sensors.

The vast majority of compliant fluid drives are cavity structures. They consist of a highly stretchable, elastically deformable material (preferably elastomers that allow strains up to 1000%). Due to the resilience of the material used, from which these cavity structures are made, the surrounding structural parts are stretched or deformed with a growing pressure or vacuum load of the cavity. This results in a movement of the coupling point (s) or surface (s) between the fluid drive and active element.

Fluid drives of this type are known from the prior art, which consist in their simplest structure of a monolithic compliant unit. Due to their advantageous properties, of which especially the simple construction and large realizable ranges of motion are emphasized, these fluid drives find an application in both the macro and in the microtechnology.

Besides these, there are hybrid assemblies composed of a combination of such compliant fluid drives with rigid bodies. As a result, disadvantageous properties of the simply constructed resilient fluid drives, such as low mechanical strength and the susceptibility to vibration u. a. at the expense of complexity, serviceability and weight. Since the assembly costs for hybrid structures are generally much higher, they can only be miniaturized within certain limits. The advantages of resilient fluid drives with a simple structure, such. As freedom from play and friction, are no longer given in many cases. In addition, the design of the coupling points / surface (s) between yielding and rigid elements should be taken into account.

With both fluid drive types, monolithic units and hybrid structures, various movements can be realized. These range from simple rotations, swiveling or bending movements over translational movements to complex spatial movement paths. The deformation behavior achieved can be stable, monotone or with reversal of direction, as well as unstable, with breakdown or with a bifurcation. In addition, it may be a (continuous) or multi-level (discontinuous) movement in detail.

With the previously known monolithic or hybrid structures, simple movements (rotation or translation or pivoting or bending) can be easily realized. To generate superimposed (combined) spatial movements, such. As screw movements, so far only a few bodies are known (eg. DE 195 00 368 A1 . EP 0 437 792 A1 . WO 9739861 A1 . US 4,815,782 A ). However, the disadvantage here is the complex, material-side and / or structure-combined structure or the expense associated with the use of multiple cavities for the control.

From the US 5,090,297A are known monolithic fluid drives of elastomer, which have a tubular, spiral shape. In the inner, fluid-fillable chamber are reinforcing ribs that allow axial rotation but prevent or minimize radial bulge and axial expansion for the purpose of pure rotation generation. The application of negative pressure is not intended, since this leads to the buckling of the reinforcing ribs and to the collapse of the entire structure and can only be prevented by an expanded hybrid structure (expansion around an at least axially rigid component).

Furthermore, from the US 5,992,900 A a monolithic tubular fluidic rotary joint) of metallic material having a circumferential spiral groove or grooves similar to a bellows. The drive generates a material-related small screw movement in the axial direction at a positive internal pressure. Application of negative pressure is not intended and disadvantageous because increasing the curvature would cause the notch stresses to increase rapidly and lead to failure of the component.

In addition, fluid drives are known which have a tortuous structure. However, these are either hybrid and thus not monolithic, z. B. rubber and inelastically embedded threads ( DE 199 10 196 A1 ), Their output twist z. B. by biasing individual parts is achieved ( EP 0 236 764 A1 ), or they are designed for a one-time function or use, wherein the output twist through plastic deformation of the material can be achieved ( US 5,033,270 A1 . US 5,842,657 A ).

In addition, in the US 3,613,455 A described a pressure transducer, are used in the metal pipes of constant wall thickness, whose outer shape by forming processes, such. Rolling, in the final shape (eg helically wound) is realized. The resulting structures are also plastically deformed and not free of residual stress. This and the low elastic strain range of the metallic structures lead to a disadvantageous low degree of mobility.

Elastic deformable resilient fluid actuators for producing a nearly exact bidirectional screw movement, in which the advantages of both embodiments of the known resilient fluid drives (simple monolithic units and hybrid structures) are combined with each other, are not known from the prior art.

The invention is therefore based on the object to overcome the disadvantages of the prior art and to provide a miniaturizable flexible fluid drive and an associated method with which it succeeds in a simple manner and minimal effort, a nearly accurate bidirectional screw movement of the coupling surface fluid drive - active element to create.

According to the invention the object is achieved with the features of the first and the ninth patent claim.

Advantageous embodiments of the flexible fluid drive according to the invention are specified in the subclaims.

With the fluid drive according to the invention a superimposed movement of the coupling surface fluid drive active element can be realized in the form of a nearly exact bidirectional screw movement by an internal pressure load change. The maximum realizable range of motion is limited by the geometric shape of a reversibly deformable, elastically extensible cavity element comprehensive fluid drive, which is designed monolithically according to the invention, and its material properties.

The detailed description and advantages of the invention will become apparent from the following description part, in which the invention with reference to the accompanying drawings is explained in more detail. It shows:

1 - A first embodiment of a compliant fluid drive according to the invention in the initial state (cavity without pressure load) in four views

2 - The extrusion path for the shell structure of the first embodiment

• A – Teilbewegung 1: normierte Verschiebung in z-Richtung u_zP/h sowie Teilbewegung 2: den Winkel der Rückdrehung φ_R
• B – Überlagerung der beiden Teilbewegungen 1 und 2

3 A graphical representation of the relationship between the cavity pressure load (p) and the individual partial movements of a characteristic point (P) on the coupling surface for the first embodiment:

• A - partial movement 1: normalized displacement in the z-direction and _{z P} / h and partial movement 2: the angle of the reverse rotation φ _R
• B - superposition of the two partial movements 1 and 2

4 - Different cross sections of the fluid drive according to the invention

5 - A second embodiment of the fluid drive according to the invention

6 - A third preferred embodiment of the fluid drive according to the invention

A first embodiment of the flexible fluid drive according to the invention is shown in FIG 1 represented in the cylindrical coordinate system. The fluid drive ( 1 ) comprises at least one cavity element ( 2 ), which is open at its lower end. The fluid drive ( 2 ) is at this lower end to a bracket ( 4 ) clamped or fastened. The upper end of the cavity element ( 2 ) is covered by a lid ( 3 ), which the coupling surface ( 6 ) between fluid drive and active element comprises, closed. The cavity element ( 2 ) of the fluid drive ( 1 ) is monolithic and has a spiral-like twisted shell structure ( 5 ). The shell structure ( 5 ) corresponds to the geometry produced by extrusion of the cross-section (shown in section AA) along an extrusion path (exemplified in FIG 2 represented) arises. The monolithic running fluid drive is due to production in the basic or initial state in a mechanically de-energized state and is thus free of plastic deformation. The cylindrical cross-section comprises in this embodiment, three curves (but at least 2) with the same radius R _K and constant wall thickness d _K , which regularly over the circumference of the cross section of the cavity element ( 2 ) are distributed. The curvatures are connected to one another by tangentially adjoining indentations, which in each case also have the same radius R _E and a constant wall thickness d _E. The external dimensions of the fluid drive ( 1 ) Are above the height h and the outer radius R _a limited. The height h is made up of the thickness of the lid d _D , the height of the Holder h _Ha and the height of the shell structure h _M together. The height of the cavity element h _Ho accordingly corresponds to the sum of the height of the holder h _Ha and the height of the jacket structure h _M.

A preferred extrusion path of the shell structure ( 5 ) to reduce during stress in material stress and strain maxima in the area of the holder ( 4 ) and at the transition to the lid ( 3 ) is in 2 in the cylindrical coordinate system for a constant outer radius R _{A of} the fluid drive ( 1 ). The extrusion path consists of 3 sections, which merge into one another tangentially. The first and last sections of the extrusion path (between points 0 and A and B and E) have a constant radius R _Ex . The middle part of the extrusion path is characterized by a constant pitch angle α. With the extrusion path, the height of the shell structure h _M and the output rotation of the fluid drive φ _A can be determined.

By changing the pressure inside the cavity element ( 2 ) of the fluid drive ( 1 ) there is a deformation of the cavity element ( 2 ) and thus the entire fluid drive ( 1 ). When the pressure increases, the output twist is turned back and the fluid drive ( 1 ) expands in the direction of the axis of rotation (z-axis). When pressure is reduced, the output rotation increases with simultaneous shortening of the fluid drive ( 1 ) in the direction of the axis of rotation. This relationship between changing cavity pressure load (p) and the two partial movements of the biaxial movement (screw movement) of a point P in the centroid of the coupling surface (on the lid) of the fluid drive is in 3A shown schematically. It should be noted that the theoretically achievable maximum reverse rotation angle φ _Rmax can reach the maximum initial twist angle φ _A. In the case of a negative pressure application, an increase in output torsion angle φ _A by the amount of the minimum achievable return angle | φ _Rmin | possible. 3B schematically shows the approximate achievable by the fluid drive screw movement. By optimizing the structural features of the fluid drive, the deviation, characterized by the 2ε-band, can be minimized by the ideal screw movement (middle dashed line). The desired ratio of rotational movement to translation movement along the axis of rotation, characterized by the pitch angle β of an idealized screw movement under varying pressure load, can be defined by the ratio of the wall thicknesses of the indentations and the curvatures d _E / d _K , the radii R _E , R _K , and R _Ex , set the number of curvatures n uniformly distributed over the cross section and the angles α and φ _A. The dimensions of the entire fluid drive are set with R _A and h.

With a growing cavity pressure load (p), the cavity structure inflates on the cover and on the circumferential flanks of the bends. 4 shows various possible embodiments of the cross section of the fluid drive. In 4A is a cross section with three curvatures of constant wall thickness d _K and constant radii R _K shown, which are arranged regularly over the entire circumference of the cross section of the cavity element. These curvatures are connected to one another by tangentially adjoining indentations which in each case also have the same radius R _E and a constant wall thickness d _E. For the in 4A illustrated embodiment also applies d = _K d _E.

4B shows a further preferred cross section of the fluid drive, the five bends, which also have constant wall thicknesses d _K and constant radii R _K and are arranged regularly over the entire circumference of the cross section of the cavity element (the fluid drive) comprises. Also in this embodiment, the indentations each have the same radii R _E and wall thicknesses d _E , with d _K = d _E.

A comparison of these two fluid drives results in a smaller pitch angle β in the fluid drive with n = 5 curvatures, since with increasing number of curvatures the surface of the lid increases and thus at the same pressure a greater force acts from the inside on the lid in the direction of the axis of rotation, which favors the translational movement ,

At the in 4C shown embodiment of a cross section of the fluid drive according to the invention, the radius of curvature R _K compared to that in 4B shown embodiment twice as large. The outer radius R _{A of} the fluid drive ( 1 ) is the same size as in the previously described examples. It has been shown that with the same output twisting, the achievable maximum return angle φ _Rmax is greater at a smaller ratio R _K / R _A.

The cross section in 4D is different from the one in 4B in that the ratio of the wall thicknesses of the indentation d _E and the curvatures d _{K is} greater than one, namely d _E / d _K = 3. The choice of the wall thickness ratio has a great influence on the stiffness of the fluid drive. As a result, the performance and the required working pressure can be influenced.

5 shows a spatial view of an embodiment of the fluid drive according to the invention with a in 4B shown Cross sectional area. Here, the extrusion path of the cross section of the cavity element runs at both ends of the shell structure perpendicular to the end faces.

An embodiment with infinitely small radius of curvature R _K and infinite large radius R _Ex is in 6 shown. This is suitable for applications in which a scoop blade-shaped design of the outer surfaces z. B. is important for the coupling between fluid drive and active element.

In order to avoid curling of the cover during deformation and to improve the stability of the structure, the rigidity of the cover can be influenced by varying the material thickness or compliance as well as by its geometric shape (concave arrangement). This can also be deviated from the monolithic design and z. B. a rigid lid can be fixed on the resilient cavity element.

When using a material with anisotropic compliance oriented on the extrusion path, this material property can be used to adjust the ratio of rotational movement to translation movement along the axis of rotation.

Another way to influence the performance and the required working pressure, can be realized by the introduction of other forms of energy from the outside. By way of example, by introducing heat energy, the fluid drive can be reduced in its rigidity. In addition, the desired ratio of rotational movement to translation movement along the axis of rotation due to a directed stiffening of the fluid drive by an external magnetic field that acts on the introduced during the manufacture of the fluid drive into the material magnetic nano- or microparticles can be adjusted.

In order to increase the range of functions or to produce qualitatively different motion-pressure characteristics, several fluid drives according to the invention can also be interconnected in parallel or preferably in series in the same or opposite direction. By way of example, by means of a serial interconnection of two counter-rotating fluid drives according to the invention, which were manufactured monolithically together, with different screw characteristics, a reversal movement of the entire system can be realized.

The present invention is characterized by a number of advantages. These result on the one hand from the geometry of the fluid drive and on the other hand from the flexibility of the material used (reversible deformability). It can be realized with a single elementary, monolithic fluid drive with only one cavity a nearly exact bidirectional screw movement of the coupling surface with changing internal cavity pressure load. The fluid drive is well miniaturized due to its simple structure and can be z. B. with a mold in one step, without further assembly steps are necessary. At constant ratios of the geometric parameters (such as the radii), the qualitative motion and deformation behavior remains unchanged during miniaturization. Another advantage is that the output twist φ _{A of} the shell structure of the fluid drive is already introduced during production and does not have to be generated by a pre-stress by means of forming process or the like. The structure is thus in a mechanically de-energized state.

LIST OF REFERENCE NUMBERS

1

fluid drive

2

cavity element

3

Cover (with coupling surface)

4

bracket

5

shell structure

6

Coupling surface between fluid drive and active element

n

Number of bends

R _K

Radius of curvatures

d _K

Wall thickness of the bends

R _egg

Radius of the indentations

d _E

Wall thickness of the indentations

R _A

Outer radius of the fluid drive

R _ex

Radius of the first and last section of the extrusion path

H

Height of the fluid drive

d _D

Thickness of the lid

^h Ha

Height of the bracket

h _Ho

Height of the cavity element

_hm

Height of the shell structure

α

Pitch angle of the second section of the extrusion path

β

Slope angle of the idealized screw movement under increasing cavity pressure load

φ _A

Output twist of the shell structure

φ _R

Return angle of the shell structure of the fluid drive (opposite direction to the output rotation)

φ _Rmax

maximum achievable return angle

φ _Rmin

minimum achievable return angle

p

Cavity pressure load

P

Point on the lid of the fluid drive (in the centroid of the coupling surface)

Claims (10)

Flexible fluid drive for producing a nearly exact bidirectional screw movement, comprising a cavity element ( 2 ) made of reversibly deformable, elastically extensible material (preferably elastomer), which at its first end face to a holder ( 4 ) is attached and at the opposite second end face with a lid ( 3 ) is characterized in that the fluid drive ( 1 ) is miniaturizable and the cavity element ( 2 ) a monolithic spiral-wound jacket structure produced by extrusion ( 5 ) whose cross-sectional area is bounded alternately from outside and from inside by at least two outwardly directed positive curvatures and tangentially adjoining indentations with negative curvature, wherein the cavity element ( 2 ) is in the initial state without mechanical bias. Compliant fluid drive according to claim 1, characterized in that the central axis of the helically wound jacket structure ( 5 ) is perpendicular to the center of the cross section and the spiral is rounded at both ends so that they perpendicular to the end faces of the cavity element ( 2 ). Compliant fluid drive according to one of claims 1 or 2, characterized in that the bends regularly over the circumference of the cross section of the cavity element ( 2 ) are arranged. Compliant fluid drive according to one of claims 1 to 3, characterized in that the radii R _K and wall thicknesses d _{K of} the bends and the radii R _E and wall thicknesses d _{E of} the indentations are each equal to each other and the wall thicknesses of the curvatures d _K and the indentation d _{E are the} same size. Compliant fluid drive according to claim 4, characterized in that the ratio of the radii (R _K / R _E ) and the ratio of the wall thicknesses of the curvatures and the indentations (d _K / d _E ) is not equal to one. Resilient fluid drive according to claim 4, characterized in that the radii of the curvatures R _{K are} very small and / or the radii of the first and third sections of an extrusion path R _{Ex are} very large. Compliant fluid drive according to one of claims 1 to 6, characterized in that the resilience of the cavity element material is variable by external energy supply and / or the material of the cavity element has an isotropic or anisotropic compliance. Resilient fluid drive according to one of claims 1 to 7, characterized in that the cover has active or passive functional surfaces or elements and is designed so that its curvature is negligible with pressure increase in the cavity element. A method for producing a nearly exact bidirectional screw movement with a flexible fluid drive according to one of claims 5 to 8, characterized in that the almost exact bidirectional screw movement by means of changing the internal pressure in the reversibly deformable, elastically extensible cavity element ( 2 ) is realized, wherein the ratio between rotational and translational movement along the axis of rotation on the ratio of wall thickness d _E to the wall thickness d _K , the radii R _K , R _W and R _Ex , the number of bends n, the angle α and φ _A as well as the material properties of the cavity element ( 2 ) is adjustable. Use of a plurality of combined resilient fluid drives according to one of claims 1 to 8 for the generation of highly complex movements for medical technology and / or robotics.

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