Flexible shaft arrangement

[0001] The invention is in the field of mechanical engineering, in particular mechanics, and relates to the transfer of torques and movements via flexible shafts. Flexible shaft drives are known from different fields of the art, with them varying greatly with respect to the torques to be transferred and the speeds. Shaft arrangements are, for example, known from the field of flexibly usable machine tools which run at relatively low speeds and should transfer high torques, whereas shafts are known from dental engineering which rotate at extremely high speeds and transfer lower torques.

[0002] Different problems result in the operation of such shafts, in particular as a consequence of the vibration behavior. Small asymmetries at certain points of a shaft arrangement and/or at certain speeds can result in knocking movements with corresponding unpleasant noise developments and in mechanically high strains due to friction between the shaft and its guidance.

[0003] Different proposals have become known on how to be able to reduce such knocking movements, for example from German patent No. 350682, in which the kinking of a sleeve of a flexible shaft at points is proposed to narrow the inner contour of the sleeve sectionally and thus to enforce a direct and clearance-free contact of the shaft in these regions, which is associated with a certain friction, but may result in a clearance-free guidance of the shaft and thus in the prevention of knocking movements.

[0004] DE 103 24 717 A1 discloses a ductile drive cable in which a core is surrounded by a circle of leads, with the leads having different cross-sections and an asymmetrical arrangement thereby arising within a jacket.

[0005] In accordance with JP 61 062614 A, a core is provided within a sleeve and in a jacket with the latter, with the sleeve and the jacket each extending in the same sense and coaxially to one another in changing arcs.

[0006] It is known from the laying-open publication DE 195 41 549 A1 to deform a sleeve, in which the shaft runs, selectively inwardly radially toward the shaft to fix the shaft sufficiently in the interior of the sleeve. It is moreover mentioned there that corresponding deformations can be offset helically section-wise. Squeezing, arching and compressing the sleeve is spoken of there.

[0007] It is the underlying object of the present invention with respect to the prior art to provide a shaft arrangement which allows an operation of the shaft at high speeds with low friction and in so doing ensures that a minimum service life of the shaft arrangement can be guaranteed and that vibrations of the shaft can be reliably prevented. In this respect, the solution should in particular be able to be used with long and very thin shafts. Damage to or deformation of the shaft itself within the shaft arrangement must be able to be precluded.

[0008] The object is achieved in accordance with the invention by the features of claim 1.

[0009] In contrast to the known prior art, in accordance with the invention, a ductile shaft, a sleeve surrounding it and a jacket surrounding the sleeve and the shaft are provided for the shaft arrangement. The shaft should be able to rotate freely within the jacket, whereas the jacket is usually stationary.

[0010] Provision is made to achieve the object that the sleeve extends in arcuate form at least sectionally within the jacket. This means that the sleeve has a different spacing from a center axis, a longitudinal axis or a an axis of symmetry along the length of the jacket in some regions than in other regions or, in other words, differs sectionally along the length of the jacket, in particular in arcs, from the longitudinal axis, the axis of symmetry or the center line of the jacket, said axis not necessarily having to extend straight.

[0011] It is hereby achieved that the shaft which is arranged with clearance within the sleeve and which is rotatable relative thereto, contacts the inner wall of the sleeve section-wise inside the sleeve due to its inherent stiffness. A point-wise fixing of the shaft in a sliding friction relationship at the inner wall of the sleeve thereby results. Any vibrations of the shaft which occur are thus damped with minimal friction.

[0012] This solution has the advantage that the inner contour of the sleeve can remain very largely unchanged in cross-section so that the shaft has the necessary space for the rotation within the sleeve, for example in the form of a cylindrical inner space when the sleeve has a circular cross-section and a hollow-cylindrical shape. The arcuate shape of the sleeve has to be sufficiently pronounced for this purpose, which is, however, easy to effect in the individual application.

[0013] Provision is made that at least one spacer arrangement is provided at a part of the periphery between the inner contour of the jacket and the outer contour of the sleeve in at least one axially bounded section. In this respect, the jacket can extend substantially straight; this means that any arcs in which the jacket extends have substantially larger radii than the arcs which the sleeve describes within the jacket. Corresponding arc radii of the jacket can, for example, be at least 3 times, 5 times, 10 times or 50 times as large as the radii of the arc sections which are formed by the sleeve inside the jacket. As a rule, the sleeve is disposed with radial clearance within the jacket. This clearance is eliminated or at least reduced by the spacer device and the sleeve lies at the inner contour of the jacket on a side of the longitudinal axis eccentrically thereto. It is not necessary for this purpose that the corresponding spacer device does not extend in an azimuthal manner at the total periphery of the sleeve or of the jacket, but is rather only provided in a specific azimuthal peripheral section.

[0014] Provision is advantageously made that a plurality of spacer arrangements are provided spaced apart from one another along the length of the shaft arrangement. A wave-shape contour of the sleeve within the jacket is enforced by such an arrangement of the spacer device and can, for example, be meandering or of sinus wave shape.

[0015] Provision can moreover be made that directly mutually adjacent spacer arrangements are offset angle-wise with respect to one another azimuthally at the periphery of the shaft arrangement with respect to the shaft. A three-dimensional wave-shaped profile of the sleeve hereby results so that the shaft is fixed in a plurality of planes.

[0016] Provision can, for example, be made for this purpose that the spacer arrangements are arranged helically or circumferentially in the axial direction.

[0017] An advantageous realization of the invention provides that the spacer arrangement comprises at least one imprinting of the jacket radially inwardly or of the sleeve radially outwardly.

[0018] The material of the sleeve or of the jacket can be made so thin that imprints indent or bulge the respective contour, that is the inner contour of the jacket and/or the outer contour of the sleeve, such that an elevated portion is created by the imprinting which forms a corresponding spacer device.

[0019] Provision can be made in a particularly simple construction realization of the invention that the sleeve is made as a wound spiral. A simple type of manufacture of the sleeve is thus made possible and the cooling of the shaft within the sleeve is moreover facilitated by a free exchange of a coolant, for example a liquid, through the spiral within the jacket.

[0020] Such a spiral can advantageously comprise a flat material, for example in the form of a metal sheet or a plastic material. Provision can be made in this respect that the spacer arrangement is made as radially outwardly directed imprints of individual windings or groups of windings of the spiral. It is, however, also possible to use a round material and to provide it with corresponding imprints.

[0021] The advantage of such a construction comprises the fact that the material stretched before the winding of the spiral can be imprinted as such and that the corresponding imprints subsequently form the desired elevated portions on the winding of the spiral. This procedure facilitates the production, with the desired locations of the spacer devices/elevated portions being able to be predetermined by corresponding spacings of the imprints on the stretched spiral material. The imprints can in this respect in each case only be provided on individual winds of the windings or on mutually directly adjacent winds of the winding. In the forming of groups of imprints, the imprints of directly mutually adjacent windings of the spiral are disposed close to one another with respect to the periphery and the imprints of the respective next group can then be offset angle-wise with respect to the adjacent group.

[0022] Provision can, however, also be made that individual windings are imprinted at certain axial intervals from one another in a helically circumferential arrangement.

[0023] Provision can moreover advantageously be made that the imprints or groups of imprints are arranged equidistantly from one another with respect to the spiral material stretched before the winding. It can be ensured by a correspondingly calculated spacing of the imprints on the starting material of the spiral that the angle-wise offset of mutually following elevated portions/spacer devices will also be regular.

[0024] In addition to a flexible shaft arrangement in accordance with the above description, the invention also relates to a method for manufacturing such a shaft arrangement in which a spiral material is imprinted before the winding to a spiral forming the sleeve such that at least one elevated portion arises which is radially outwardly directed with respect to the sleeve.

[0025] A manufacturing process of this type is, on the one hand, easy to carry out and, on the other hand, allows the precise predetermination of the corresponding spacer devices to ensure the optimized extent of the sleeve within the jacket for a problem-free operation of the shaft.

[0026] Finally, the invention also relates to a blood pump arrangement having a flexible shaft arrangement such as is described above in different embodiments. Such blood pump arrangements can, for example, be introduced in a minimally invasive process through a blood vessel into the body of a patient to assist or to replace heart activity. The shaft then represents the drive shaft of a pump rotor and rotates with speeds of typically more than 10,000 r.p.m. It is connected to a rotor of the pump, for example to a rigid shaft of the rotor or, with a hubless rotor, to one of its end faces. The shaft can also merge in one piece into a rotor shaft and can bear one or more impeller blades at its pump-side end. The sleeve and the jacket then end in front of the rotor.

[0037] FIG. 1 shows the shaft arrangement 1 in a schematic view with a motor drive which has an electric motor 2 as well as a motor shaft 3 and a coupling 4 by means of which the flexible shaft 5 is rotationally fixedly coupled to the motor 2. In addition, a jacket 6 of the shaft arrangement is shown which is fixed in the holder 7 at the motor side. A sleeve 8 which surrounds the shaft 5 is shown in the interior of the jacket.

[0038] A pump 9 having a pump rotor 10 which has impeller blades 11 is shown on the output side of the shaft arrangement. Such a pump can serve in medical engineering in the microinvasive sector, for example, for conveying blood in a blood vessel and forms a very fast-rotating axial flow pump.

[0039] The shaft arrangement in accordance with the invention solves the problem that the very fast-rotating shaft 5, i.e. rotating at more than ten thousand revolutions per minute, can be prone to knocking movements which can result in disturbing noise development and in some cases also to a point-wise increased wear so that the service life of the shaft arrangement is impaired.

[0040] The cross-section of the shaft arrangement in which the jacket 6 is shown at the outside will first be looked at for the solution of the problem. Said jacket can, for example, be made as a plastic jacket or also as a thin-walled metal jacket. The sleeve 8, which can likewise be made of metal or of plastic, is located within the jacket 6. Clearance is provided between the jacket 6 and the sleeve 8 since the sleeve 8 can optionally move with the shaft 6 within the jacket.

[0041] The shaft 5 comprises a plurality of braided strands 12, 13 to produce the corresponding flexibility. Clearance is likewise provided between the shaft 5 and the sleeve 8 to minimize the friction.

[0042] FIG. 3 shows a cross-section at a point of the shaft arrangement at which a spacer device is provided between the sleeve 8 and the jacket 6. The spacer device 14 is made as a radially outwardly directed elevated portion in the sleeve 8. The sleeve 8 is urged in cross-section in the direction of the arrow 15 within the inner contour of the jacket 6 by this elevated portion.

[0043] Since the elevated portion 14 is only provided in a closely bounded section of the shaft arrangement in the axial direction, as will be explained in more detail further below, this deflection of the sleeve 8 only takes place axially point-wise within the jacket 6 so that the sleeve 8 adopts a wave shape within the jacket 6. The elevated portion 14 can be produced, for example, by an imprint in the material of the sleeve 8 from the inside radially to the outside.

[0044] The shaft is formed, for example by twisting from thin threads/wires, with each individual strand element of the shaft having a diameter which is between half and twice the height of the elevated portion in the sleeve. A snagging of shaft elements with the irregularities/imprints of the sleeve is thus avoided.

[0045] It is also advantageous, for example, in a modification for avoiding the snagging of the shaft elements in the irregularities/imprints of the sleeve if the imprints are formed or are arranged in a different pitch around the sleeve than that in which the shaft elements of the shaft are wound so that no parallelism is present between the shaft elements and the irregularities/imprints.

[0046] FIG. 4 shows in a three-dimensional view a plurality of elevated portions 14, 14′, 15, 15′, 16, 16′, wherein the groups of elevated portions are each axially spaced apart from one another and are mutually displaced azimuthally angle-wise with respect to the longitudinal axis of the shaft arrangement. The position of the groups of elevated portions changes in helical form in the clockwise direction running from left to right. If the sleeve shown is imagined as located in an elongated jacket 6 (shown by dashed lines), the sleeve is displaced, as is shown in FIG. 4, with respect to the jacket axis in the region of the elevated portions 14, 14′ downwardly in the region of the elevated portions 15, 15′ to the rear into the plane of the drawing and upwardly in the region of the elevated portions 16, 16′.

[0047] A wave shape of the sleeve 8 thus results when the jacket is considered as stable in shape. This has the result that the shaft 5, which has the tendency due to its inherent stiffness to run straight without any external effect, contacts in each case the inner contour of the sleeve 8 in the region of the elevated portions. The shaft 5 is thus sufficiently fixed in order to damp a large part of the knocking movements via friction.

[0048] FIG. 5 shows in a three-dimensional representation only a sleeve 8 which is made as a spiral in the embodiment shown. The spiral has elevated portions 17, 17′, 17″ and 18, 18′, 18″ which are mutually offset axially and in the peripheral direction. In the example shown, the elevated portions are mutually displaced by 180 degrees at the periphery.

[0049] The manner is shown in FIG. 6 in which the shown spiral in a jacket 6 contacts its inner contour. It is shown that in the region 19, in which the imprints are provided below the center axis, the sleeve 8 is displaced upwardly in the direction of the arrow 20, whereas the sleeve is displaced downwardly in the direction of the arrow 22 in the region 21 due to the imprints located above the center axis there. The addressed wave shape of the sleeve 8 thus results.

[0050] In FIG. 7, the Figure is further completed in that a shaft 5 is also drawn in which is conducted within the circular contour of the sleeve. The sleeve 8 is shown in the wave shape already introduced in FIG. 6 and the shaft 5 contacts at least spot-wise the inner contour of the sleeve 8 under sliding friction conditions.

[0051] The invention can thus be used beneficially in the sector of medical engineering where very fast-rotating shafts are required within a hollow catheter in a body, for example. The hollow catheter can also take over the role of the jacket. The total shaft arrangement can, however, also be arranged within a hollow catheter.

[0052] A reduction in friction, in wear and in noise development takes place with a design of the shaft arrangement in accordance with the invention. This also has the result, for example, that a reduced torque is required to drive the shaft, which is in particular useful on use of complex sluices for leading through the shaft from the body exterior to the body interior.

[0053] FIG. 8 shows a scheme which is useful in the calculation of the spacings of the imprints in the starting material of the spiral. The strand material of the spiral is labeled by 23 in the Figure. In the upper region of FIG. 8, the strand is shown before the introduction of imprints; in the lower region after the introduction of the imprints. In this respect, the spacing of the imprints within an imprint group is labeled by Ap. This results from an approximation equation for the ellipse calculation, wherein the amount by which the length is changed by the imprinting is taken into account. The spacing Ap of two adjacent imprints results from the formula

[0054] $\mathrm{AP}\approx \left[\left(a+b\right)·\pi ·\left\{1+\frac{3{\lambda }^2}{10+\sqrt{4-3{\lambda }^2}}\right\}\right]+c,\mathrm{where}$ $\lambda =\frac{a-b}{a+b}$
is given. a designates the large semicircle, b the small semicircle of the ellipse which is given by the contour of a wind of the spiral observed in cross-section. The amount c results from the extension of the imprint spacing by the stretching of the material as a consequence of the imprint.

[0055] Provision can also be made that the parameter c±x is used instead of the parameter c to offset the imprints of adjacent winds at the periphery by a constant angle with respect to one another and thus to achieve the helical circumferential distribution of the imprinted points.