ANCHORING A FIRST OBJECT IN A SECOND OBJECT

Abstract

A method of anchoring a first object in a second object is described. The first object extends along an axis between a proximal end and a distal end and has a circumferential surface. The circumferential surface comprises at least one helical protrusion of a thermoplastic material. For anchoring, the first object is brought in contact with the second object, and mechanical vibration is coupled into the first object from a proximally facing coupling-in face thereof so as to drive the first object into the second object in a manner that the vibration and pressing cause the first object to be subject to a helical movement relative to the second object and cause thermoplastic material of the first object to become flowable and to penetrate into structures of the second object to yield, after resolidification, a positive fit connection with the second object.

Claims

1.-47. (canceled)

48. A method of anchoring a first object in a second object, the method comprising: providing the first object, the first object extending along an axis between a proximal end and a distal end and having a circumferential surface extending around the axis, the circumferential surface comprising at least one helical protrusion of a first material; providing the second object; bringing the first object in contact with the second object; and coupling mechanical vibration into the first object from a proximally facing coupling-in face thereof, thereby causing the first object to be subject to a helical movement relative to the second object.

49. The method according to claim 48, wherein the first material is a thermoplastic material, and wherein the mechanical vibration is coupled into the first object to further cause thermoplastic material at least of the helical protrusion to become flowable and to penetrate into structures of the second object to yield, after re-solidification, a positive fit connection with the second object, wherein the circumferential surface consists of the thermoplastic material.

50. The method according to claim 48, wherein due to the mechanical vibration, the helical protrusion is caused to penetrate into material of the second object, whereby the helical protrusion and the mechanical vibration cause a groove in material of the second object, the groove extending helically around an opening in the second object, wherein the second object remains solid around the helical groove.

51. The method according to claim 48, wherein coupling the mechanical vibration into the first object comprises holding a coupling-out face of a vibrating sonotrode against the coupling-in face by a pressing force.

52. The method according to claim 51, wherein during coupling the mechanical vibration into the first object at least one of the following occurs the sonotrode is subject to longitudinal vibration; there is a purely axial coupling between the sonotrode and the first object, without any torque transmitted from the sonotrode onto the first object; the coupling-out face of the sonotrode is caused to hammer onto the coupling-in face of the first object so as to cause a slip-stick movement of the first object relative to the second object; or the coupling-out face of the sonotrode includes a guiding protrusion that engages into an opening in the coupling-in face.

53. The method according to claim 48, wherein the second object comprises a porous material that is brittle.

54. The method according to claim 48, wherein the second object is at least one of: a lightweight building element with a low density interlining layer sandwiched between a first and second building layer of higher density and strength than the interlining layer; and a hard foam.

55. The method according to claim 48, wherein the first object is a connector comprising a connecting structure.

56. The method according to claim 48, wherein the proximally facing coupling-in face of the first object is a proximal end face defining the proximal end.

57. The method according to claim 48, wherein coupling the mechanical vibration force into the first object causes the first object to advance into an opening in the second object to be anchored therein.

58. The method according to claim 57, comprising pre-making the opening in the second object prior to bringing the first object in contact with the second object, wherein a depth of the opening is smaller than an axial extension of the first object.

59. The method according to claim 57, wherein the first object has a proximal collar with proximal energy directing structures, and wherein the method comprises causing the proximal collar to be in physical contact with a mouth of the opening during coupling the mechanical vibration into the first object to cause thermoplastic material of the proximal collar to become flowable and to interpenetrate structures of the second object around the mouth.

60. The method according to claim 57, wherein the opening is cylindrical.

61. The method according to claim 48, wherein a lateral surface from which the at least one helical protrusion extends is cylindrical.

62. The method according to claim 48, wherein the first object has a proximal collar and an anchoring portion extending distally from the proximal collar, the at least one helical protrusion extending radially outwardly from the anchoring portion.

63. The method according to claim 48, wherein the distal end of the first object has distal energy directing structures of the thermoplastic material, and wherein coupling the mechanical vibration into the first object causes material of the distal energy directing structures to become flowable and to interpenetrate structures of the second object at the distal end of the first object.

64. The method according to claim 48, comprising at least one of coupling a pressing force on the first object relative to the second object while the mechanical vibration is coupled into the first object, wherein the pressing force is exerted onto the first object until the proximal end of the first object is flush with a proximally facing surface of the second object; or providing an inner connector element with a circumferential connector element surface and a proximally facing support face at a periphery of the circumferential connector element surface, wherein the first object is sleeve-shaped and equipped to enclose the circumferential connector element surface, the method further comprising positioning the inner connector element relative to the second object, wherein during coupling the mechanical vibration and the pressing force into the first object, a face of the first object is pressed against the support face of the inner connector element to cause thermoplastic material of the first object to liquefy at the interface to the support face, and to be directed radially outwardly into structures of the second object.

65. The method according to claim 48, wherein the mechanical vibration is coupled into the first object by a sonotrode, and wherein the sonotrode has a flat distal end without any guiding features engaging into structures of the first object.

66. A connector of a thermoplastic material suitable to be used as the first object in a method according to claim 48, the connector extending along an axis between a proximal end and a distal end and having a circumferential surface extending around the axis, the connector comprising a proximally facing coupling-in face equipped for a sonotrode to couple mechanical vibration into the connector, wherein the circumferential surface comprises at least two helical protrusions of the thermoplastic material.

67. The connector according to claim 66, wherein each helical protrusion has at least one of the following a same helix angle, the helix angle being between 40° and 80°; or extends around a portion of the circumferential surface but does not encompass the entire circumferential surface.

68. The connector according to claim 66, comprising a proximal collar, wherein the proximal collar preferably comprises energy directing structures.

69. The connector according to claim 66, wherein the connector is sleeve-shaped.

70. The connector according to claim 66, wherein the distal end forms a circular edge; and the circular edge is interrupted so as to form a plurality of teeth.

71. The connector according to claim 66, comprising a body of a non-liquefiable material, wherein the body of the non-liquefiable material forms an inner portion and is circumferentially enclosed by a thermoplastic portion comprising the protrusions, wherein the body has at least one of an accessible fastening structure for a further object to be fastened to the connector; or an engagement structure into which thermoplastic material of the thermoplastic portion engages to secure the thermoplastic portion to the body of non-liquefiable material in a positive-fit manner with respect to axial directions.

72. The connector according to claim 66, comprising at least 3 or at least 4 of the helical protrusions.

73. The connector according to claim 66, wherein at least one of the helical protrusions has an aspect ratio of at least 1; has a width that is constant as a function of a distance to a first object axis or increases as a function of the distance to the first object axis; has a portion with a radial height (h) of which increases as a function of an axial distance from the distal end; has a portion with a cross section area of which increases as a function of an axial distance from the distal end; has a first radial height, and wherein another one of the helical protrusions has a second radial height, and wherein the first radial height is different from the second radial height; distally ends at a first end position, and wherein at least another one of the helical protrusions distally ends at a second end position, and wherein the first end position is proximal of the second end position; is one of a plurality of helical protrusions that are arranged at a distance from each other; or is one of a plurality of helical protrusions that are spaced from each other around the periphery by a distance of 360°/n, wherein n is the number of the helical protrusions.

74. The connector according to claim 66, comprising a tapered distal guiding portion without any helical protrusions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In the following, ways to carry out the invention and embodiments are described referring to drawings. The drawings are schematical. In the drawings, same reference numerals refer to same or analogous elements. The drawings show:

[0077] FIG. 1 a connector suitable as first object in a method as described in this text;

[0078] FIG. 2 a connector of the kind shown in FIG. 1 during an early stage of the anchoring process;

[0079] FIG. 3 phases of vibration cycles;

[0080] FIG. 4 the connector of FIG. 2 after the anchoring process;

[0081] FIGS. 5-8 further embodiments of connectors;

[0082] FIG. 9 a configuration with an inner connector element and an outer sleeve;

[0083] FIGS. 10 and 11 yet further embodiments of connectors;

[0084] FIG. 12 an even further embodiment of a connector;

[0085] FIG. 13 a schematic horizontal cross section of a connector having different protrusions;

[0086] FIG. 14 a curve schematically illustrating a possible dependence of a maximum aspect ratio on the helix angle; and

[0087] FIG. 15 the principle of using a laterally protruding feature of the first object to secure a third object to the second object.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0088] The first object 1 shown in FIG. 1 is overall sleeve-shaped with a body 11 of a thermoplastic material extending along an axis 10 between a proximal end face 15 and a distal end 14, here being a circular edge. In the depicted embodiment, the body is tube-like with an inner through opening (lumen) 16 extending axially through the entire body 11. The first object further has a plurality of (about ten) relatively steep helical protrusions 12 being ribs of the same thermoplastic material extending along the circumferential surface of the body 11. The body 11 has a proximal collar 13 and an anchoring portion 20 extending distally from the collar, the anchoring portion carrying the protrusions 12. The anchoring portion has a generally cylindrical lateral outer surface from which the protrusions extend. An outer diameter of the anchoring portion 20 is smaller than an outer diameter of the collar 13. In the depicted embodiment, the collar 13 has a radial extension that is larger than a radial extension of the protrusions 12. In alternative embodiments, the collar may have a radial extension that corresponds to the radial extension of the protrusions, see for example FIG. 6 described hereinafter.

[0089] FIG. 1 also illustrates that the protrusions may have the optional feature of forming a distal bevel 45, i.e. a distal end of the protrusions is not perpendicular to the axis but is at an angle to the plane perpendicular to the axis. The angle may for example be greater (i.e. the bevel 45 may be steeper) for comparably hard second objects material. The bevel prevents the distal end of the protrusions 12 from impeding a rotation of the first object relative to the second object when driven forward into the second object in the process described in this text. A bevel angle (angle to the plane perpendicular to the axis) may especially be between 10° and 70°.

[0090] For anchoring in a second object 2 of a low-strength brittle or elastic material, such as a brittle foam, optionally in a first step an opening 22 may be pre-drilled into the proximally facing surface 21 of the second object 2 into which the first object is to be driven for being anchored. A cross section of the opening 22 in this is smaller than an outer cross section of the first object 1, i.e., a radius of the opening 22 is smaller than an outer radius of the helical protrusions 12 and often also equal to or smaller than a radius of the circumferential first object surface from which the protrusions 12 extend outwardly.

[0091] In a next step, the first object 1 is positioned relative to the second object 2 with the distal end 14 or a region near to it being brought into contact with the second object, if applicable at the mouth of the opening 22. This is shown in FIG. 2. Then, a sonotrode 6 is used to couple mechanical vibration into the first object, via the proximal end face 15 by holding a distally facing coupling-out face 61 against the proximal end face 15. The sonotrode may especially be subject to ultrasonic vibrations, i.e. vibrations with a frequency of about 20 kHz or more.

[0092] In the depicted configuration, the sonotrode 6 has a guiding protrusion 66 engaging with a corresponding feature of the first object 1, here with the through opening 16.

[0093] In other embodiments (see for example FIG. 9 described hereinafter), the sonotrode does not have such guiding protrusion but has a distal outcoupling face that is essentially flat where it is in contact with the first object. Such configuration may especially be advantageous if the hole in the second object, in which the first object is anchored, is pre-made. A configuration with a flat sonotrode prevents situations in which the system is overdetermined (such overdetermination could lead to asymmetries and stress in the system after anchoring).

[0094] The coupling between the sonotrode 6 and the first object 1 may, especially if the second object material is substantially not elastic but for example brittle, such that retracting movements (movements into proximal directions) of the sonotrode are not coupled into the first object 1. Rather, the sonotrode ‘hammers’ onto the proximal end face 15. FIG. 3 schematically illustrates the deflection A of the vibrating sonotrode as a function of time t. FIG. 3 illustrates that only forward movements (forward part 74 of the vibration cycle; solid line) are coupled into the first object, whereas backward movements (retraction part of the vibration cycle 75; dashed line) are not coupled into the first object. By applying a slight pressing force on the sonotrode—this pressing force may for example, depending on the chosen configuration, be the just the weight of the apparatus by which the vibration is applied and which comprises the sonotrode—the sonotrode is caused to move up during the backward movement parts of the cycle. This results in driving of the first object into the second object by hammering. The first object in these embodiments is thus subject to a slip-stick kind of movement relative to the second object. Due to the helical, protrusions 12, the driving into the second object causes a rotational movement 40 also. In contrast to prior art approaches, however, this rotational movement is not caused by any angular momentum applied actively by any tool but just results from the combined effect of the effect of the longitudinal vibration of the sonotrode and the helical protrusions.

[0095] The helical shape of the protrusions couples rotation and axial translation. Optimizing of the helix angle (this may optionally pertain to any embodiment) may consider the criterion that the steeper the helix angle, the easier the implementation of the “hammering” effect. Thus, for high resistance material, the helix angle may need to be chosen to be steeper than for materials offering less resistance.

[0096] FIG. 4 illustrates the situation after the anchoring process for the example of an embodiment in which the second object has substantial rigidity, for example by being of a brittle material of the kind mentioned hereinbefore. In such embodiments, the motion of the first object subject to the vibrations causes substantial friction at the interface between the first and second objects. As a consequence, thermoplastic material of the protrusions and, depending on the depth of the opening 22 in relation to the anchoring depth, also at the distal end 14 of the first object 1, during the process was made flowable (flow portion 8) and has interpenetrated structures of the second object to yield, after re-solidification, a positive fit connection between the first and second objects that in addition to the anchoring by the helical protrusions contributes to the stability of the connection.

[0097] FIG. 5 shows a variant of a first object 1 (connector). Compared to the first object 1 of FIG. 1, the first object 1 of FIG. 5 has a different ratio between length and radial extension.

[0098] Also, independently therefrom, the proximal collar is provided with a rib structure 17. The ribs of the rib structure 17 has energy directing properties and thus serve to cause additional liquefaction when the proximal collar gets into contact with material of the second object while being subject to the mechanical vibration. This yields an additional anchoring effect at the mouth of the opening in the second object, independent of whether an opening 22 is pre-drilled into it or not. Especially, configurations with an energy directing structure of the collar as the rib structure 17 shown in FIG. 5 are suited for second objects with a hard layer constituting the proximal surface. For example, the second object may be a lightweight building element in which the comparably weak and brittle or elastic material is sandwiched between hard, thin and dense building layers, wherein the collar with the energy directing structure is anchored relative to a first, proximal building layer in which the mouth of the opening for the first object is present.

[0099] FIG. 5 also shows the definition of the helix angle α used in this text. The embodiment of FIG. 5 has a helix angle of about α=50°.The helix angle can be chosen depending on the composition of the second object and of the specific requirements and can be chosen independently of the other properties, especially independent of the presence of a collar with energy directing structures. The helix angle can especially vary between steep (about 80° and relatively flat (down to about 40° or even to 350 or 30° or 20°).

[0100] FIG. 6 shows a further embodiment of a first object 1. Compared to the embodiment of FIG. 5, the embodiment does not have a collar. Instead, the distal end is provided with a plurality of teeth 18.

[0101] FIG. 7 depicts, from another angle, an embodiment with both, a collar with energy directing structures (rib structure 17) as the embodiment of FIG. 5 and with a distal end having a toothed crown as the embodiment of FIG. 6. The teeth 18 form an inner conical surface 19 and are, due to their shape, overall energy directing. The teeth have the function of penetrating into the material of the second object 2. Especially, the energy directing properties ensures anchoring of the distal end of the connector in for example harder and/or more dense material of the second object at a the bottom of the opening (if applicable) and/or for example in a harder layer of the second object. Such harder layer may for example be a distal building layer of the second object if the second object is a lightweight building element sandwiching a (low strength, for example brittle or elastic) interlining layer between a proximal and a distal building layer.

[0102] FIG. 8 shows the option of providing the first object (especially connector) with a body 31 of a non-liquefiable material. For example, such body may be a metallic insert with an inner thread 32 or other fastening structure. The body may have engagement structures 33 for the material of the thermoplastic portion of the first object to engage so that the thermoplastic portion and the non-liquefiable portion are secured to each other in a positive-fit manner. In the shown embodiment, the engagement structures 33 comprise circumferential grooves into which thermoplastic material of the thermoplastic portion engages.

[0103] More in general, the body 31 of non-liquefiable material may constitute an inner portion of the first object, and be circumferentially enclosed by the thermoplastic portion, as is shown in FIG. 8.

[0104] In FIG. 8, the height h (or depth) and width w of the protrusions 12 are also illustrated. Generally, and independently of whether or not the first object has a body of non-liquefiable material, the aspect ratio h/w of the protrusions 12 may depend on material parameters. In many embodiments, the aspect ratio is at least 1, for example 1.5 or more. Embodiments of first objects are possible in which the aspect ratio is even much higher, for example at least 3 or even 5 or more, whereby the helical protrusions 12 have more a character of being wings than ribs, see also FIGS. 10 and 11 described hereinbelow.

[0105] Also the cross section of the protrusion may be optimized depending on the requirements. In many embodiments, however, the cross section is different from a cross section of a thread ridge, which is often approximately triangular with the width continuously decreasing towards radially-outward. The cross section of the protrusion 12 of the embodiment of FIG. 8 (and similarly of FIGS. 1, 5 and 6 and of other embodiments) is approximately rectangular, with the width w slightly increasing towards radially-outward. More in general, in at least one radial range (region), the width of the protrusion may be constant or even increase as a function of the distance to the axis 10.

[0106] FIG. 9 shows a further variant in which the body of the non-liquefiable material is an initially separate part, namely an inner connector element 51 with the inner thread 32. The thermoplastic portion is then provided as an initially separate thermoplastic sleeve 52 enclosing the connector element 51. For the process, firstly the connector element is positioned in a suitably prepared opening in the second object 2, in a manner that it is supported towards distally. For example, as shown in FIG. 9, the connector element may rest against a stable layer, such as a distal building layer 23 of the second object.

[0107] The inner connector element 51 has a proximally facing support face, formed by a circumferential outward bulge 53. During the process, once the distal end face of the sleeve 52 reaches the support face, the distal end face is pressed against the support face, whereby material is liquefied at the interface between the support face and the distal end face, and is caused to flow radially outward with to penetrate into structures of the second object, as for example also described in Swiss patent application 00871/18.

[0108] This effect of a support face of an initially separate connector element may especially assist the anchoring process towards its end. Thus, it is possible that the distal end of the thermoplastic sleeve initially is not in contact with the support face, and the process is essentially as described hereinbefore referring to FIGS. 2-4 during this initial phase. Only towards the end of the process, in the configuration of FIG. 9, does the distal end face of the connector reach the support face, whereby the mentioned additional effect is achieved.

[0109] Alternatively, it would be possible to insert the connector element and the thermoplastic sleeve with the distal end face of the sleeve in contact with the support face, and without the connector element being supported by a particularly stable layer of the second object. Then, the connector element 51 and the thermoplastic sleeve 52 are pressed further into the second object together, with some mechanical resistance encountered by the connector element 51, whereby the relative force between the distal end face of the thermoplastic sleeve and the support face is generated.

[0110] In order for the connector element to be held stably relative to the thermoplastic sleeve after the anchoring process, the connector element 51 and/or the thermoplastic sleeve may comprise axial retention structures, such as a circumferential rib 55 of the connector element. During the process, due to absorbed vibration energy, thermoplastic material of the sleeve in a vicinity of such retention structure becomes flowable to embed it after re-solidification.

[0111] For stability of the connector element relative to the thermoplastic sleeve with respect to rotations, according to a first possibility the connector element and the sleeve comprise an axially running rib-groove connection. Then, during insertion, when the sleeve rotates due to the helical protrusions 12, the connector is subject to a same rotation as the sleeve. According to a second possibility, the sleeve is allowed to rotate relative to the connector during insertion, and is only rotationally secured relative thereto towards the end of the process by the support face, formed by the outward bulge 53, having retention structures that are not rotationally symmetrical, liquefied thermoplastic material of the sleeve interpenetrating the retention structures to form, with the retention structures, after re-solidification, a positive fit connection with respect to rotational movements.

[0112] The embodiment of a first object (for example connector) shown in FIG. 10 compared to the embodiment of FIG. 1 has protrusions 12 with a higher aspect ratio and with a smaller helix angle—i.e., the protrusions are more pronounced, wing-like ribs with less steep helix. Compared to the embodiment of FIG. 1 the first object of FIG. 10 is suitable for softer and/or less strong second object material.

[0113] FIG. 10 illustrates a further being an optional feature of any embodiment of the invention. In contrast to threads according to the prior art, the protrusions do not form a sawtooth (or similar) cross section but are arranged at a distance d from each other, so that the valleys between the protrusions have a flat ground (i.e. a ground following the surface of a circular cylinder). Thereby, it is ensured that a substantial volume of foam is between the protrusions. It has been found that especially in brittle second object material this may be an important property. For pullout stability, the axial distance a (related to the distance d via the helix angle) may be an interesting parameter also.

[0114] In embodiments, for brittle second object materials lower limits for the distance are 2.5 mm or 3.5 mm, with 2.8 mm-6.5 mm being often ideal; for the axial distance a, a lower limit may be 3 mm or 4 mm.

[0115] The embodiment of FIG. 11 has protrusions 12 with an even higher aspect ratio. The body 11 is accordingly thinner compared to the previously described embodiments.

[0116] Also, independently of this, the body is not tube-shaped but rather pin-shaped.

[0117] Further, the distal end 14 is not an edge but forms a tip. Generally, first objects ending in a tip or other structure are an alternative to connectors forming a punching edge. Especially, if the first object is to be used in a method without pre-drilling, the first object in many embodiments has a distal edge or tip, with tips being an option especially for thinner bodies 11. In embodiments that involve pre-drilling of the opening, the shape of the distal end may be chosen freely if not liquefaction/interpenetration at the distal end is desired, and may be optimized in terms of liquefaction/anchoring at the distal end if such anchoring by interpenetration is desired.

[0118] The embodiment of FIG. 11 may especially be suited for anchoring in softer foam, whereas for more brittle second objects, first object shapes with less high protrusions are often preferred.

[0119] The embodiment of FIG. 12 has, compared to the embodiment of FIG. 1, the following features: [0120] The first object does not have a proximal collar. In the shown embodiment, the protrusions 12.1, 12.2 extend to the proximal end. In variants (also without the proximal collar), the protrusions could extend only to a position at a distance from the proximal end, the first object could have a collar, or a configuration of the kind shown in FIG. 5 or a configuration of the kind shown in FIG. 6 (at the respective proximal ends of the first object 1) could be present. [0121] The protrusions do not extend to the distal end. Rather, the body 11 has a distal portion that is free of protrusions, which portion serves for guiding the first object relative to the second object when the first object is introduced in the opening in the second object and during penetration further thereinto under the effect of the vibrations. In FIG. 12, this distal guiding portion 41 is slightly tapered, this being an optional feature. [0122] The first object 1 has two kinds of protrusions 12.1, 12.2 of different heights and consequently, given an approximately same widths, of different aspect ratios. [0123] The first object has protrusions that extend to towards distally to different extents. I.e. some of the protrusions 12.2 extend further towards distally than other protrusions 12.1. In the embodiment of FIG. 12, the higher protrusions 12.1 extend less far than the less high protrusions 12.2. [0124] The first object has protrusions 12.1 that do not have a uniform height but that have a distal portion 42 tapering off towards distally.

[0125] These features are independent of each other and do not need to be combined. For example the first object may have protrusions of different heights (or more generally: of different cross sections/envelopes) without the feature of different extensions towards distally and/or without the distal guiding portion 41. Or the first object may have protrusions the cross section of which increases as a function of the distance to the distal end with or without there being different kinds of protrusions and with or without the distal guiding portion. Etc.

[0126] Further optional features, that can be combined with any one or any combination of the above features, include [0127] A surface roughening of the protrusions, for example towards their distal ends. Such surface roughening may be beneficial in having an energy directing effect so as to enhance liquefaction of a flow portion of the material of the protrusions, which flow portion may subsequently penetrate into structures of the second object to yield, after re-solidification a positive-fit connection, which enhances the anchoring strength and especially secures the anchored first object against rotation relative to the second object. [0128] A variation of an other property of the protrusions different from their height as a function of the position along the helix, for example it thickness. More in general, the cross section area of at least one protrusion may increase as a function of a distance to the distal end.

[0129] FIG. 13 schematically illustrates the principle of the first object having large height protrusions 12.1 as well as small height protrusions 12.2, similar to the embodiment of FIG. 12. The large height protrusions 12.1 have the advantage of ensuring secure anchoring even in very brittle second object material. The volume of material between large height protrusions 12.1, which material prevents any undesired slipping rotation of the first object relative to the second object, is high. This is illustrated in FIG. 13 by the distance d.sub.1 between the large height protrusions 12.1. Because the large height protrusions 12.1 may have a high aspect ratio, they may, however, have a higher tendency to be subject to material failure, for example during the anchoring process when the material tends to be warmer than room temperature due to the energy absorbed. The small-height protrusions 12.2, being more dense by being at a smaller distance d.sub.2 relative to each other and to the large height protrusions add to the stability of the first object by yielding additional stability against undesired movement of the body 11 relative to the protrusions 12.1, 12.2.

[0130] The aspect ratio of the protrusions will generally depend on the first and especially second object materials. It may also depend on the helix angle. Especially, for high helix angles the aspect ratio may be higher than for smaller helix angle, because for a higher helix angle the load on the protrusions relative to the body is higher both, during insertion and also in response to axial loads thereafter. FIG. 14 illustrates this principle by illustrating a possible maximum aspect ratio h/w as a function of the helix angle α. As becomes clear from the figure, the maximum aspect ratio increases as a function of the helix angle α

[0131] FIG. 15 yet illustrates two optional features that are independent of each other and that can be combined with any other features described referring to the previous embodiment.

[0132] Firstly, the second object 2 comprises a comparably dimensionally stable proximal outer building layer 24 distally of which a for example more brittle interlining layer 25 is arranged. For example, the second object may be a lightweight building element of the herein described kind.

[0133] Secondly, the proximal collar 13 of the first object is used as a kind of head for securing a third, further object 81 to the second object.

[0134] In this kind of connections between the second object and a further object by the first object (being a connector), the first object serves as a kind of fixation element directly fixing the third object to the second object. This approach is an option in any embodiment, independent of the structure of the anchoring portion, which goes into the opening. In many embodiments, the requirement is that the first object has, proximally of the anchoring portion, a laterally protruding feature, such as the collar 13.