Patent Description:
Nuts that are configured to be moved manually or driven along an external screw thread extending in a longitudinal direction are especially advantageous in combination with a strut used by safety and rescue workers. In the description below, the use of such a nut will also be explained in great detail in relation to such a strut. The skilled person will however acknowledge that such nuts may have many other applications, especially in industry, such as for hydraulic cylinders comprising a lock nut for mechanically fixation of the cylinder.

Struts comprise an elongate member extending in an axial direction to define a spacer. Oftentimes, struts comprise an outer post and an inner post that are extendable relative to each other in a longitudinal direction to thereby allow safety and rescue workers to set a desired length for the strut. For many applications, it is desired that the length of the strut may be adjusted during use, e.g. for following a deliberate or unexpected movement of the load, which may be related to either an extension or a retraction of the inner post relative to the outer post.

Struts are used for many applications, and in particular for shoring applications. In this respect, shoring is defined as providing a temporary support to an instable load, for example to secure a risky situation and provide safety and rescue workers, such as firemen, the safest possible working conditions obtainable at that time. Such shoring applications may be very diverse, such as providing support against structural collapse of e.g. a building, trench shoring to prevent collapse of earth surrounding a trench, and providing vehicle stabilization, in particular after a crash.

There is an ongoing need to improve the working conditions of safety and rescue workers, in particular in view of safety, but also in view of user comfort and occupational health. Safety risks when dealing with unstable loads are especially related to changing conditions, such as the initial placement of the strut to support a still unstable load and the final removal of said strut. However, also during use the conditions may change, for example if the load moves, which may be unexpected in case of instable load situations.

Prior art struts often comprise a nut that may be moved manually along an external screw thread extending in a longitudinal direction of an inner post of the extendable strut. Once the nut is moved along the screw thread and brought into abutting contact with the outer post, the nut secures the inner post against retracting into the outer post. For this reason, such a nut is also referred to as a securing nut. Manually moving the nut however requires the safety and rescue worker that is manually driving the nut to be physically present near the strut, at an arms length away from the nut, which is often very dangerous due to the unstable load conditions and initial unsecured situation. In view of the extreme risks that may be involved with manually screwing the nut, safety and rescue workers sometimes try to make use of made up "tools", such as a trying to push the nut with a rod or trying to screw the nut by moving a strap that is wrapped around the nut.

Ideally, safety and rescue workers would have the opportunity to remotely drive the nut along the external screw thread of the inner post of the extendable strut to allow them to control the nut from a safe distance. However, such a remote control of the nut is preferably provided without sacrificing the possibility to easily move the same nut manually. After all, some unstable situations simply cannot be stabilized without a safety and rescue worker first physically arranging the strut by being physically present in a high risk area near or even below the unstable load, for example in case the strut is to be arranged for providing support against structural collapse of e.g. a building. In such situations, a manual operation of the nut may be preferred, because it is the fastest way to move the nut along the screw thread and obtain a secure situation as fast as possible.

United States patent application <CIT> is considered the closest prior art, and discloses a strut extender mechanism. Relative to this document, at least the characterizing features of claim <NUM> are novel.

The German patent application <CIT> and the international patent applications <CIT> and <CIT> are acknowledged as further prior art.

An objective of the present invention is to provide a nut, that is improved relative to the prior art and wherein at least one of the above stated problems is obviated or alleviated.

Said objective is achieved with the kit-of-parts according to claim <NUM> of the present invention, said kit-of-parts comprising:.

characterized in that the transmission is further configured to selectively form a coupling between the housing and the rotatable member in the manual mode wherein the nut is manually rotated relative to the external screw thread, the coupling causing the rotatable member and the housing to jointly rotate relative to the external screw thread, thereby moving the nut in the longitudinal direction along the external screw thread.

The nut of the kit-of-parts according to the invention thus allows a safety and rescue worker to screw the nut both in a drive mode and in a manual mode. In a driven mode, the safety and rescue worker may be remote at a safe distance, while the optional manual mode also allows the safety and rescue worker to secure the nut as soon as possible in specific situations, as described above.

Moreover, the drive mode may allow for a variety of additional applications, such as an (auto-)follow mode, either for extending the strut or for retracting the strut. If a load moves away from a strut, it may be desired to have the strut automatically extend ("Auto Follow Extend"), especially to make sure that the strut stays in contact and cannot accidentally move away. In other situations, for example for a controlled lowering of an instable load, it may be desired that the strut can automatically retract ("Auto Follow Retract") to maintain contact while lowering the load.

Preferred embodiments are the subject of the dependent claims.

These individual aspects, and in particular the aspects and features described in the attached dependent claims, may be an invention in its own right that is related to a different problem relative to the prior art.

In the following description preferred embodiments of the present invention are further elucidated with reference to the drawing, in which:.

One of many potential applications of struts <NUM> is shown in the shoring situation of <FIG>, wherein a crash has happened and a tank truck <NUM> has come to rest on top of a passenger car <NUM>. In order to safely approach the passenger car <NUM> for giving first aid to any passengers inside the passenger car <NUM>, the safety and rescue worker <NUM> first has to stabilize the unstable load <NUM> defined by the tank truck <NUM>. In this specific situation, the safety and rescue worker <NUM> applies two struts <NUM>, wherein the right strut <NUM> is being actuated by a controllable actuator <NUM> comprising an hydraulic pump <NUM> that is configured to pump hydraulic fluid via the hydraulic line <NUM> and thereby extend the right strut <NUM>. The left strut <NUM> comprises a drive <NUM> that is connected via a control wire <NUM> to a control unit <NUM> having a power pack <NUM>. The functionality of this left strut <NUM> will be discussed in greater detail below.

Strut <NUM> is shown in <FIG> and <FIG>, and comprises an outer post <NUM> and an inner post <NUM> that are extendable relative to each other in a longitudinal direction L (indicated in <FIG> and <FIG>) and that are rotationally locked relative to each other. The rotational lock may be provided by a keyway <NUM> and associated key <NUM> (<FIG>). A first end <NUM> of the strut <NUM> may comprise a connector half <NUM> that is configured to mechanically interlock with a geometrically identical connector half <NUM> of another strut <NUM>. Both the connector half <NUM> at the first end <NUM> and the opposite end <NUM> of the strut <NUM> may define a coupler <NUM> that allow both ends <NUM>, <NUM> to be coupled to an accessory <NUM>, such as end plates <NUM> (<FIG>).

A nut <NUM> is configured to be moved manually or driven along an external screw thread <NUM> extending in the longitudinal direction L. For the strut <NUM> shown in <FIG> and <FIG>, the nut <NUM> forms a mating engagement with the external screw thread <NUM> of the inner post <NUM> and is configured to be moved manually or driven along the external screw thread <NUM> extending in the longitudinal direction L to selectively secure the inner post <NUM> relative to the outer post <NUM>. If the nut <NUM> is moved into abutting contact with the outer post <NUM> or with an optional sensing arrangement <NUM> associated with the outer post <NUM>, the inner post <NUM> is secured relative to the outer post <NUM> to prevent the inner post <NUM> to move into, i.e. retract relative to, the outer post <NUM>. The nut <NUM> is therefore a securing nut.

The nut <NUM>, which is now explained in greater detail with reference to <FIG>, comprises a housing <NUM> and a rotatable member <NUM> that is rotatably arranged in the housing <NUM>. The rotatable member <NUM> comprises an internal screw thread <NUM> that is configured to form a mating engagement with the external screw thread <NUM> of the inner post <NUM>. A transmission <NUM> is arranged in the housing <NUM> and the transmission <NUM> comprises an input shaft <NUM> that is connectable to a drive <NUM>. The transmission <NUM> is configured to selectively:.

In both the drive mode and the manual mode, the rotatable member <NUM> rotates relative to the external screw thread <NUM>, thereby longitudinally displacing the housing <NUM> of the nut <NUM> along the external screw thread <NUM>. The nut <NUM> according to the invention thus allows a safety and rescue worker <NUM> to screw the nut <NUM> both in a drive mode and in a manual mode. In the drive mode, the safety and rescue worker <NUM> may be remote at a safe distance (<FIG>), while the optional manual mode also allows the safety and rescue worker <NUM> to secure the nut <NUM> very fast in specific situations. After all, due to the coupling being formed between the housing <NUM> and the rotatable member <NUM> in the manual mode, the rotatable member <NUM> and housing <NUM> will jointly rotate relative to the external screw thread <NUM> when a user, i.e. a safety and rescue worker <NUM>, manually rotates the nut <NUM> along the external screw thread <NUM>. In this respect it is mentioned that the coupling formed between the housing <NUM> and the rotatable member <NUM> in the manual mode may act as a slip coupling. The skilled person will acknowledge that some slip may be acceptable, as long as the level of slip is small enough to allow the housing <NUM> and the rotatable member <NUM> of the nut <NUM> to be jointly manually rotated relative to the external screw thread <NUM>. Ideally, an absence of slip in the coupling allows for a lossless transfer of the manual rotation of the nut <NUM> into a longitudinal displacement of the nut <NUM> along the external screw thread <NUM>. A grease fitting <NUM> allow grease to be arranged in the housing <NUM> for lubrication of the rotatable member <NUM> relative to the housing <NUM>.

In the drive mode, the housing <NUM> is rotationally locked relative to the external screw thread <NUM>. This is preferably automatically caused by the drive <NUM> being arranged on the nut <NUM>, as will be explained in greater detail below with reference to <FIG>.

The transmission <NUM> may be irreversible to thereby form the coupling between the housing <NUM> and the rotatable member <NUM> in the manual mode wherein the nut <NUM> is manually rotated relative to the external screw thread <NUM>. For example, the transmission <NUM> may comprise a self-braking gear, and more preferably a self-locking gear. A self-locking gear is a gear wherein driving an input will cause an output to be driven, but wherein driving the output will not cause the input to be driven. Hence, a transmission comprising a self-locking gear will be an irreversible transmission. A self-braking gear is interpreted as a self-locking gear that may have some slip, but wherein the level of slip is small enough to allow the housing <NUM> and the rotatable member <NUM> of the nut <NUM> to be jointly manually rotated relative to the external screw thread <NUM>. Due to the irreversible behaviour of the transmission <NUM>, i.e. the self-braking or self-locking nature thereof, there is no need to manually activate a lock in order to rotationally lock the rotatable member <NUM> relative to the housing <NUM>. Since there is no need for such a lock, the design of the nut <NUM> may be simplified, and more importantly, it reduces the number of actions a safety and rescue worker <NUM> has to take during high risk situations. The irreversible transmission <NUM> automatically adapts to the way of driving, i.e. manually or via a drive <NUM>, and thereby improves safety and provides user comfort.

Self-braking properties may be obtained if the coupling between the housing <NUM> and the rotatable member <NUM> in the manual mode is provided by a gear ratio of the transmission <NUM> being larger than <NUM>:<NUM>.

In the shown embodiment, the transmission <NUM> comprises a worm drive <NUM>, wherein a worm <NUM> is rotatably arranged in said housing <NUM>, and a worm wheel <NUM> is arranged at an outer circumference <NUM> of the rotatable member <NUM>. A worm drive <NUM> is an embodiment of a self-braking gear, and more preferably a self-locking gear. If the worm wheel <NUM> cannot drive the worm <NUM> at all, it is called self-locking or irreversible. Whether a worm drive <NUM> is self-locking depends on the lead angle, the pressure angle, and the coefficient of friction. It is however conceivable that for some configurations a minimal slip will occur, in which case there is no complete locking. Some slip may be acceptable, as long as the level of slip is small enough to allow the housing <NUM> and the rotatable member <NUM> of the nut <NUM> to be jointly manually rotated relative to the external screw thread <NUM>.

The preferred embodiment shown in the Figures comprises a sensing arrangement <NUM> that will now be discussed in detail with reference to <FIG>. Such a sensing arrangement <NUM> may provide many advantages when it is applied in association with a drive <NUM>. For example, using the sensing arrangement <NUM>, the drive mode may allow for a variety of additional applications, such as an (auto-)follow mode, either for extending the strut <NUM> or for retracting the strut <NUM>. If a load <NUM> moves away from a strut <NUM>, it may be desired to have the strut automatically extend ("Auto Follow Extend"), especially to make sure that the strut <NUM> stays in contact and cannot accidentally move away. In other situations, for example for a controlled lowering of an instable load <NUM>, it may be desired that the strut <NUM> can automatically retract ("Auto Follow Retract") to maintain contact while lowering the load <NUM>. Despite the advantages offered by a sensing arrangement <NUM>, it is explicitly mentioned that such a drive <NUM>, that will be described with reference to <FIG> later, may also be used in absence of such a sensing arrangement <NUM>.

The sensing arrangement <NUM> is configured to provide at least one of a parameter indicative for a relative longitudinal displacement between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>, and a parameter indicative for a magnitude of a compressive force between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>. An abutment sensor <NUM>, that is preferably comprised by the drive <NUM> discussed below, is configured to detect the parameter of the sensing arrangement <NUM>. Such an abutment sensor <NUM> may already be considered to measure a load or displacement in the most basic form, considering that it measures the absence or presence of a load or contact. However, according to a preferred embodiment, the sensing arrangement <NUM> is configured to not only provide a parameter indicative for a relative longitudinal displacement or a compressive force between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>, but the sensing arrangement <NUM> is moreover configured to provide a parameter indicative for a magnitude of such a displacement or compressive force.

In the preferred embodiment shown in the Figures, the sensing arrangement <NUM> comprises an inner ring <NUM> and an outer ring <NUM>, wherein one of the inner ring <NUM> and the outer ring <NUM> is connected to the outer post <NUM>, and the other of the inner ring <NUM> and the outer ring <NUM> defines the abutment <NUM> that is associated with the outer post <NUM>. In the shown embodiment, the outer ring <NUM> is associated with the outer post <NUM>, and the inner ring <NUM> is longitudinally moveable relative to the outer ring <NUM> and defines the abutment <NUM> that is associated with the outer post <NUM>. When nut <NUM> is screwed along the external screw thread <NUM> towards sensing arrangement <NUM> (<FIG>), it will come into abutting contact with this abutment <NUM> (<FIG>).

A guide <NUM> is configured to restrict a relative rotation between the inner ring <NUM> and the outer ring <NUM> and allow them to slide relative to each other in the longitudinal direction L over a predetermined sliding distance. The shown guide <NUM> comprises a guide slot <NUM> that is arranged in the outer ring <NUM>. A protrusion <NUM> that is arranged on the inner ring <NUM> extends in this guide slot <NUM>. A pretensioner <NUM> is configured to urge the inner ring <NUM> and the outer ring <NUM> away from each other. This pretensioner <NUM> may comprise a plurality of springs <NUM>. When nut <NUM> is screwed even further towards the outer post <NUM> after initial abutting contact with the abutment <NUM> (<FIG>), the outer ring <NUM> and inner ring <NUM> will move towards each other, against the force executed by pretensioner <NUM>. The springs <NUM> will compress, and protrusions <NUM> will slide in their associated slots <NUM>, which may provide a visual indication to safety and rescue workers <NUM> that the nut <NUM> is in a secure abutting contact with the outer post <NUM>, more in particular with the abutment <NUM> associated with the outer post <NUM>. The position of the protrusion <NUM> in guide slot <NUM> thus provides a visual parameter indicative for the magnitude of the compressive load between the outer post <NUM> and the securing nut <NUM>, or for the magnitude of the relative longitudinal displacement between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>.

The sensing arrangement <NUM> discussed above may provide many additional advantages when it is applied in association with a drive <NUM>. This drive <NUM>, and especially the advantageous cooperation of the drive <NUM> and the sensing arrangement <NUM>, will be elucidated in more detail with reference to <FIG>. The skilled person will however understand that such a drive <NUM> may also be used in absence of the sensing arrangement <NUM>, for example if it suffices to remotely drive the nut <NUM>, but more sophisticated options like (auto-)follow modes - as described below - are not required.

The nut <NUM> may be part of an assembly or a kit-of-parts that comprises the drive <NUM>, wherein the drive <NUM> comprises a drive housing <NUM> accommodating a drive motor <NUM>, and a connector <NUM> configured to connect the drive housing <NUM> with the nut <NUM> and thereby connect the drive motor <NUM> with the transmission <NUM>, more in particular with the input shaft <NUM> of the transmission <NUM>. The connector <NUM> comprises a groove <NUM> (<FIG>) in the drive housing <NUM> that may engage, i.e. slide over, a ridge <NUM> (<FIG>) that is arranged on the housing <NUM> of the nut <NUM>.

The drive <NUM> may be integrated in the housing <NUM> for very large (industrial) nuts. However, for the nut <NUM> that is used for securing a strut <NUM> that is the subject of the shown embodiment, the drive <NUM> is an external drive that is releasably connectable to the housing <NUM> of the nut <NUM>. In <FIG> and <FIG>, the nut <NUM> is in abutting contact with the sensing arrangement <NUM>, and the drive <NUM> is shown in dashed lines indicating where the drive <NUM> is located when it is connected to the housing <NUM> of the nut <NUM>. An external power source <NUM> is connectable to the drive <NUM> and configured to provide power for driving the drive motor <NUM>. A wired connection <NUM> of the drive <NUM> to the external power source <NUM>, and preferably also to the control unit <NUM>, is schematically shown in <FIG>. Alternatively, the control unit <NUM> may have a wireless connection with the drive <NUM>.

<FIG> show the drive <NUM> in two perspective views. Control buttons <NUM> with plus and minus signs may allow a safety and rescue worker <NUM> to manually control the drive <NUM>, for extension and retraction, respectively. A visual indicator <NUM>, such as a (not shown) display or indicator lights <NUM>, may indicate a status of the strut <NUM>, in particular of the drive <NUM> and/or of the sensing arrangement <NUM> of said strut <NUM>. <FIG> shows an output shaft <NUM> of drive <NUM> that is configured to engage the input shaft <NUM> of the transmission <NUM>. The engaged state is shown in <FIG>.

In the drive mode, the housing <NUM> of the nut <NUM> is rotationally locked relative to the outer post <NUM> to prevent a relative rotation between the housing <NUM> of the nut <NUM> and the outer post <NUM> and allow the rotatable member <NUM> to be rotated relative to the housing <NUM>. In a preferred embodiment, the drive <NUM> is configured to rotationally lock the housing <NUM> of the nut <NUM> relative to the outer post <NUM> when the drive <NUM> is connected to the housing <NUM> of the nut <NUM>. In <FIG>, a locking pin <NUM> that is pretensioned with a spring <NUM>, engages one of the locking recesses <NUM> arranged in the outer circumference <NUM> of the outer ring <NUM> of the sensing arrangement <NUM>. The drive <NUM> may thus be configured to rotationally lock the housing <NUM> of the nut <NUM> relative to the outer ring <NUM> that is connected to the outer post <NUM> when the drive <NUM> is connected to the housing <NUM> of the nut <NUM>.

As indicated above, the position of the protrusion <NUM> in guide slot <NUM> may provide a visual parameter indicative for the relative longitudinal displacement or of the compressive force between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>. In a preferred embodiment, the kit-of-parts forming strut <NUM> comprises an abutment sensor <NUM> that is configured to detect if the nut <NUM> that is arranged on the external thread <NUM> of the inner post <NUM> abuts against the abutment <NUM> that is associated with the outer post <NUM>. In a simple embodiment, the drive <NUM> may be powered with a constant current to thereby force the nut <NUM> to be screwed tighter as soon as an extension of the strut <NUM> provides a gap <NUM> between the nut <NUM> and the abutment <NUM>. However, using the abutment sensor <NUM> in its most basic embodiment, the drive <NUM> may only drive the nut <NUM> for screwing it towards the abutment <NUM> as soon as the gap <NUM> occurs. In this basic embodiment of the abutment sensor <NUM>, it may only detect contact, and the absence thereof indicates the presence of the gap <NUM>.

The kit-of-parts may further comprise a controller <NUM> configured to control the drive <NUM> to selectively drive the transmission <NUM> and thereby move the nut <NUM> in the longitudinal direction L along the external screw thread <NUM>. Controller <NUM> may be arranged in the control unit <NUM>, or alternatively in the drive housing <NUM>. The controller <NUM> may be configured to control the drive <NUM> in dependence of a signal received from the abutment sensor <NUM>.

In a preferred embodiment, the controller <NUM> is configured to control the drive <NUM> in dependence of at least one of a sensor signal obtained from the abutment sensor <NUM>, and the parameter provided by the sensing arrangement <NUM>. This provides very advantageous options, such as auto follow modes that may greatly improve safety of the working conditions for the safety and rescue workers <NUM>.

In an "Auto Follow Extend" mode, the controller <NUM> is configured to move the nut <NUM> in the longitudinal direction L along the external screw thread <NUM> towards the outer post <NUM> when the inner post <NUM> extends relative to the outer post <NUM> to thereby reinstate a secure connection between the inner post <NUM> and the outer post <NUM>. Thus, when the strut <NUM> extends, the controller actively drives the nut <NUM> to close any gap <NUM> as soon as possible. When controller <NUM> is used in conjunction with the sensing arrangement <NUM>, the gap <NUM> may even be pro-actively prevented, resulting in an even further improved securing of the strut <NUM>. After all, the controller <NUM> may already receive information from the sensing arrangement <NUM> that the nut <NUM> is moving away from the outer post <NUM>, even before the nut <NUM> loses physical contact with the abutment <NUM> on the outer ring <NUM>. After all, the pretensioner <NUM> will cause the abutment <NUM> to maintain in abutting contact with the nut <NUM> as long as the protrusion <NUM> is free to move in guide slot <NUM> of the guide <NUM>. Similar to the position of the protrusion <NUM> in guide slot <NUM> providing a visual indication of the magnitude of the compressive load between the outer post <NUM> and the securing nut <NUM>, or of the magnitude of the relative longitudinal displacement between the outer post <NUM> and the securing nut <NUM> that is arranged on the threaded inner post <NUM>, this magnitude may also be sensed with the abutment sensor <NUM>.

Although many alternatives for such an abutment sensor <NUM> capable of determining the magnitude of the compressive load between the outer post <NUM> and the securing nut <NUM>, or of the magnitude of the relative longitudinal displacement between the outer post <NUM> and the securing nut <NUM> may be easily designed by the skilled person, one practical embodiment is shown in <FIG>. The lever <NUM>, that is pivotable relative to pivot <NUM>, may abut against an edge <NUM> of the outer ring <NUM> of the sensing arrangement <NUM>. Thus, when then nut <NUM> abuts against abutment <NUM>, the outer ring <NUM> is displaced. The edge <NUM> of outer ring <NUM> is arranged opposite the abutment <NUM>. When the outer ring <NUM> displaces, the edge <NUM> moves the lever <NUM>. A tension spring <NUM> is configured to pull the lever <NUM> towards the outer ring <NUM>, so that it stays in contact with the edge <NUM> thereof. When the lever <NUM> rotates relative to pivot <NUM>, a tooth rack <NUM> may drive a pinion <NUM> that rotates a sensor <NUM>, such as a potentiometer. In this way, the abutment sensor <NUM> may obtain detailed information on any movement of the nut <NUM> relative to the outer post <NUM>.

In an "Auto Follow Retract" mode, the controller <NUM> is configured to move the nut <NUM> a distance in the longitudinal direction L along the external screw thread <NUM> away from the outer post <NUM> to allow the inner post <NUM> to securely retract said distance into the outer post <NUM> before a secure connection between the inner post <NUM> and the outer post <NUM> is reinstated. As described above, the controller <NUM> may already receive information from the sensing arrangement <NUM> that the nut <NUM> is moving relative to the outer post <NUM> within the range provided by the guide <NUM>. In the Auto Follow Retract", the nut <NUM> may be screwed away from the outer post <NUM>, while still maintaining an abutting contact with the outer ring <NUM> of the sensing arrangement <NUM>.

It is noted here that the sensing arrangement <NUM> may even be used for applying a generic "Auto Follow" mode that is not limited to a pre-selection for either one of the above mentioned "Auto Follow Extend" mode and "Auto Follow Retract" mode, but actually allows these "Extend" and "Retract" modes to be combined. This greatly improves the safety conditions of safety and rescue workers <NUM>, because it is not always clear in what direction (associated with "Extend" or "Retract") an unstable load <NUM> may move. Such a generic "Auto Follow" mode is possible if the controller <NUM> controls the drive <NUM> to have the protrusion <NUM> free from both ends of the guide slot <NUM>. In this case, the sensing arrangement <NUM> will be able to inform the controller <NUM> related to either an extension or a retraction of the strut <NUM>. Ideally, the controller <NUM> controls the drive <NUM> to maintain the protrusion <NUM> about halfway the free stroke allowed by the guide <NUM>.

Claim 1:
Kit-of- parts, comprising:
an outer post (<NUM>) and an inner post (<NUM>) that are rotationally locked and extendable relative to each other in a longitudinal direction (L), wherein the inner post (<NUM>) comprises an external screw thread (<NUM>) extending in the longitudinal direction (L);
a nut (<NUM>) configured to form a mating engagement with the external screw thread (<NUM>) of the inner post (<NUM>) and be driven along the external screw thread (<NUM>) to selectively secure the inner post (<NUM>) relative to the outer post (<NUM>) in a drive mode; and
a drive (<NUM>), comprising a drive housing (<NUM>) accommodating a drive motor (<NUM>), and a connector (<NUM>) configured to connect the drive housing (<NUM>) with the nut (<NUM>) and thereby connect the drive motor (<NUM>) with a transmission (<NUM>),
wherein the nut (<NUM>) comprises:
a housing (<NUM>);
a rotatable member (<NUM>) that is rotatably arranged in the housing (<NUM>), wherein said rotatable member (<NUM>) comprises an internal screw thread (<NUM>) that is configured to form a mating engagement with the external screw thread (<NUM>) of the inner post (<NUM>);
the transmission (<NUM>) arranged in the housing (<NUM>) and comprising an input shaft (<NUM>) that is connectable to the drive (<NUM>), wherein said transmission (<NUM>) is configured to selectively rotate the rotatable member (<NUM>) relative to the housing (<NUM>) in the drive mode wherein the transmission (<NUM>) is driven by the drive (<NUM>), thereby also rotating the rotatable member (<NUM>) relative to the external screw thread (<NUM>) and moving the nut (<NUM>) in the longitudinal direction (L) along the external screw thread (<NUM>),
wherein the nut (<NUM>) is further configured to be moved manually along the external screw thread (<NUM>) extending in the longitudinal direction (L) in a manual mode,
characterized in that the transmission (<NUM>) is further configured to selectively form a coupling between the housing (<NUM>) and the rotatable member (<NUM>) in the manual mode wherein the nut (<NUM>) is manually rotated relative to the external screw thread (<NUM>), the coupling causing the rotatable member (<NUM>) and the housing (<NUM>) to jointly rotate relative to the external screw thread (<NUM>), thereby moving the nut (<NUM>) in the longitudinal direction (L) along the external screw thread (<NUM>).