Patent Description:
Platform elevators are becoming increasingly common for transport people or goods between floors in private homes or in minor buildings. A platform elevator is disclosed in <CIT> and comprises an elongated threaded screw which is arranged vertical in an elevator shaft in a building and a corresponding drive nut arranged on the screw. An elevator platform is supported on the drive nut and an electric motor is arranged to rotate the nut such that the nut and the elevator are moved along the screw. Typically, the threaded screw is provided in separate threaded sections that are joined to each other when installing the platform elevator in the building. The threaded sections may thereby be joined together by a male/female screw joint formed in the ends of two consecutive threaded sections.

A general problem associated therewith is that a play may occur between the ends of the threads of two consecutive threaded sections. The play may be caused by over-turning or under-turning one of the threaded sections at the assembly of the threaded screw. When the upper screw section is overturned, its thread end will form a cutting edge that the drive nut meets when it moves upwards. The upper screw section may also be under-turned, and that can cause wear to drive nut as well. However, the predominant problem relating to drive nuts for elevator platforms relates to overturned upper screw sections and will therefore this problem will be mostly discussed below. When the drive nut runs over the uneven interface where the two threaded screw sections meet, the thread of the drive nut may hit the end of the thread of the consecutive screw section. The impact may cause unpleasant noise and chocks to the platform with resulting discomfort of the passengers.

<FIG> show in cross-section a prior-art drive nut <NUM> that runs over an interface 30c between the screw sections 30a and 30b of a threaded screw. <FIG> shows schematically the impact between the thread 18a of the inner thread of the drive nut <NUM> and the thread of the second screw section 30b in the interface 30c of the screw sections 30a, 30b. To solve this impact problem, the lower thread flank of the drive nut in <CIT> has been provided with a sloping profile which facilitates running up onto the end the thread 30b of the consecutive screw section. <FIG> schematically illustrate this. The design of drive nut of <CIT> has shown effective in reducing adverse effects when the drive nut runs over an interface between two screw sections. However, there is still a need for improvement in drive nuts for platform elevators.

Further technology related to platform elevators is shown in <CIT>, which discloses a drive nut <NUM>. The underlying problem that the drive nut <NUM> aims to solve are to eliminate vibrations that are caused when the drive nut runs up and down the threaded screw <NUM>. To solve this problem, attempts were made to provide widening ends of the drive nut <NUM>. However, at the time <CIT> it was not known that the vibrations were caused by the fact that the thread flanks of the screw and the nut come into engagement before the crest of the screw thread touches the bottom of the nut thread. This mechanism was discovered later and now the threads of conventional drive nuts and screws are mutually configured such that the crest of the screw thread touches the bottom of the nut thread before the thread flanks of screw and nut come into engagement.

Thus, it is an object of the present disclosure to provide an improved drive nut for a platform elevator.

In detail, it is an object of the present disclosure to provide a drive nut for a platform elevator which allows for smooth passing across an interface between two consecutive screw sections.

According to one aspect of the present invention at least one of these objects are met by a method of adapting a platform elevator drive nut to a threaded screw of a platform elevator according to appended claim <NUM>.

In practice, the decreasing width of the nut thread lower flank results in a small contact area between the nut thread lower flank and an edged formed interface of the threads of two consecutive screw segments of the threaded screw as the nut thread lower flank enters the screw thread of the consecutive screw segment. This facilitates smooth cutting of the underside of lower thread flank against the edge-formed interface and adapts the shape of the thread lower flank to the interface between the screw segments. This, in turn result in smooth entering, with no or little noise and chocks, of the nut thread lower flank onto the screw thread of the consecutive screw segment.

The pitch of the drive nut inner thread of a platform elevator is preferably relatively high. The general problem associated with the play between the ends of the threads of two consecutive threaded sections is believed to increase as the thread pitch is increased. In platform elevators, it is preferred to design the threads such that a high vertical elevator speed is achieved at a low rotational speed of the drive nut. Therefore, the pitch of the drive nut inner thread is preferably relatively high, such as <NUM> to <NUM>.

The drive nut and the screw of a platform elevator may comprise more than one thread each. The general problem associated with the play between the ends of the threads of two consecutive threaded sections is believed to increase as the number of threads are increased. For safety reasons, the drive nut and the threaded screw preferably comprise more than one thread each, such as five, six, seven or eight threads.

When the drive nut and the threaded screw comprise a relatively high pitch and multiple threads, a high thread lead is safely obtained. The lead for a screw thread is the axial travel for a single revolution. In platform elevators, it is preferred to design the threads such that a high vertical elevator speed is achieved at a low rotational speed of the drive nut. Thus, a high thread lead is preferred. The pitch may be <NUM> to <NUM>.

The portion of the nut thread lower flank that has a decreasing, e.g. continuously decreasing, width may extend along approximately <NUM>/<NUM> to <NUM>/<NUM>, such as <NUM>/<NUM> to <NUM>/<NUM>, of the circumference of the drive nut. If the portion is too short, the wear of the underside of the nut thread lower flank against the irregularity may not be sufficiently smooth. If the portion is too long, the load bearing capability of the drive nut may be unnecessarily weakened.

If the drive nut and the threaded screw comprise five, six, seven or eight threads, the portion of the nut thread lower flank that has a decreasing width may extend along approximately <NUM>/<NUM> to <NUM>/<NUM>, such as <NUM>/<NUM> to <NUM>/<NUM>, of the circumference of the drive nut. If the drive nut and the threaded screw comprise six or seven threads, the portion of the nut thread lower flank that has a continuously decreasing width may extend along approximately <NUM>/<NUM> to <NUM>/<NUM> of the circumference of the drive nut.

In one embodiment, the drive nut and the threaded screw comprise six threads and the pitch is <NUM>, thus the lead is <NUM>. In this embodiment, the portion of the nut thread lower flank that has a (e.g. continuously) decreasing width may extend along approximately <NUM>/<NUM> of the circumference of the drive nut.

The drive nut may be manufactured from a metal material which has a hardness lower than the hardness of the threaded screw in order to further facilitate a controlled wear of the underside of the nut thread lower flank against the irregularity.

The drive nut may have a hardness of <NUM> - <NUM> HB. The threaded screw may have a hardness higher than <NUM> HB, such as <NUM> - <NUM> HB.

The outer thread of the threaded screw and the inner thread of the drive nut may be corresponding trapezoidal threads, mutually configured such that when the outer thread of the threaded screw engages the inner thread of the drive nut, the screw thread crest touches the nut thread bottom before the upper and lower nut thread flanks and the upper and lower screw flanks touches each other. Thereby the vibrations that are caused when the drive nut runs up and down the threaded screw may be eliminated.

The drive nut may comprise an upper conical portion that widens in direction from a nut center axis towards the upper nut end, and the width of the nut thread lower flank may decrease within the upper conical portion, in direction from the lower nut end towards the upper nut end. The provision of the conical portion may be advantageous for achieving the decreasing width of the nut thread lower flank. The conical portion may be achieved by a machining process that is available at relatively low cost.

As is to be apprehended, the conical portion needs only be made in the threads of the drive nut, not the goods that radially surrounds the threads.

The decreasing width of the nut thread lower flank may be achieved by other measures than by forming a conical portion. For example, the drive nut may comprise an upper portion within which the width of the inner thread decreases in direction from the lower nut end towards the upper nut end. The width of the inner thread may continuously decrease from a nominal width to a reduced width at the upper nut end, the reduced width may be zero.

The present disclosure further relates to an arrangement of a drive nut as described above and a threaded screw for a platform elevator, wherein the threaded screw comprises an outer thread having a screw thread bottom, a screw thread upper flank, a screw thread lower flank and a screw thread crest. In addition, the present disclosure relates to a platform elevator comprising a drive nut and a threaded screw as described above. Such an arrangement and such a platform elevator ensure a controlled wear of the nut thread against an irregularity formed between adjacent screw sections.

In a further aspect, the present disclosure relates to a method of adapting a platform elevator drive nut as described above a threaded screw of a platform elevator as described above. The method comprises operating the platform elevator such that the drive nut passes an interface between adjacent sections of the threaded screw of the platform elevator. The method may comprise operating the platform elevator such that the drive nut passes the interface at least two times. Typically, no more than four passages are required for adapting the platform drive nut, i.e. finalising the method. In a further aspect, the present disclosure related to a similar use of the drive nut. Typically, the drive nut of such a method and such a use has a hardness of <NUM> - <NUM> HB whereas the threaded screw has a hardness of <NUM> - <NUM> HB.

According to a further aspect of the present disclosure at least one of the above objects are met by a drive nut <NUM> for moving a platform <NUM> of a platform elevator <NUM>, said platform elevator <NUM> comprising a platform <NUM> and a threaded screw <NUM>, <NUM> with an outer thread <NUM>, <NUM> having a screw thread bottom <NUM>, <NUM>; a screw thread upper flank <NUM>, <NUM>; a screw thread lower flank <NUM>, <NUM> and a screw thread crest <NUM>, <NUM>; wherein the drive nut <NUM> is configured to be turnably arranged on the threaded screw <NUM>, <NUM> and to support the platform <NUM>, wherein the drive nut <NUM> comprises:.

The provision of a conical portion is advantageous for achieving the decreasing width of the nut thread lower flank <NUM>. The conical portion may advantageously be achieved by available machining processes that are available at relatively low cost.

The axial extension of the conical portion <NUM>, in direction of the lower nut end <NUM>, may be limited by a lower conical limitation line <NUM> on the nut thread crest <NUM>. The length and inclination of the conical portion makes possible to control the narrowing angle of the nut thread lower flank <NUM> and its radial extension.

Typically, the width (wl) of the nut thread lower flank <NUM> decreases from a nominal thread flank width (wn) to an apex <NUM> between the nut lower flank edge <NUM> and the conical surface <NUM>. This facilitates further smooth entering of the nut thread lower flank onto the screw thread of the consecutive screw segment.

The width (wu) of the nut thread upper flank <NUM> may also decrease within the upper conical portion <NUM>, in direction from the lower nut end <NUM> towards the upper nut end <NUM>. Typically, the width (wu) of the nut thread upper flank <NUM> decreases from a nominal thread flank width to an apex between the nut upper flank edge <NUM> and the nut thread bottom <NUM>.

The apex of the nut thread upper flank <NUM> may be located before the apex <NUM> of the nut thread lower flank <NUM> in direction from the upper nut end <NUM> towards the lower nut end <NUM>. This allows for exposure of a portion of the nut thread upper flank <NUM>.

The drive nut <NUM> may comprise a lower conical portion <NUM> that widens in direction from a nut center axis (X) towards the lower nut end <NUM>, wherein, the width (wl) of the nut thread lower flank <NUM> decreases within the lower conical portion <NUM>, in direction from the upper nut end <NUM> towards the lower nut end <NUM>.

Typically, the drive nut <NUM> is manufactured from a metal material which has a hardness lower than the hardness of the threaded screw <NUM>. Typically, the hardness of the threaded screw is <NUM> - <NUM> HB, or <NUM> - <NUM> HB. The threaded screw may be manufactured of steel and, as an example, have a hardness of <NUM> HB. The drive nut <NUM> may have a hardness of <NUM> - <NUM> HB or <NUM> - <NUM> HB. The drive nut may be manufactured of brass and, as an example, have a hardness of <NUM> HB. The hardness difference facilitates the controlled wear of the nut thread lower flank against the edge like interface between the first and the second screw section. It thereby further improves adaptation of the drive nut to any interface between screw sections of the threaded screw.

The present disclosure also relates to an arrangement of a drive nut <NUM> as disclosed above and a threaded screw <NUM> for a platform elevator <NUM>, said threaded screw <NUM> comprising an outer thread <NUM> configured for mutual engagement with the inner thread <NUM> of the drive nut <NUM> and having:.

In the arrangement, both the width of the nut thread lower flank <NUM> and the width of the upper flank 75b of the second screw section 61b of the threaded screw <NUM> decreases. This results in an even smaller contact area between the nut thread lower flank <NUM> and the upper flank 75b the second screw section 61b of the threaded screw <NUM>. The result is a smoother entering of the nut thread lower flank <NUM> onto the upper flank 75b of the second screw section 61b of the threaded screw <NUM>. In addition, the controlled wear of the nut thread lower flank <NUM> is improved. Typically, as shown in a simplified, schematic manner in <FIG>, the width of the lower flank <NUM> decreases by an angle (α) and the width of the upper flank 75b of the first thread section 70b of the second screw section 61b decreases by an angle (β). The angles (α) and (β) should be different from each other. This is particular important when the second screw section 61b is overturned. Angle (α) and angle (β) will form a cutting angle (γ) that will wear down the nut flank in such way that the irregularities in the interface between screw sections adapt the nut. It is emphasized that <FIG> are schematic and merely provided to facilitate the understanding of the invention.

The drive nut for a platform elevator according to the present disclosure will now be described more fully hereinafter. The drive nut for a platform elevator according to the present disclosure may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those persons skilled in the art. Same reference numbers refer to same elements throughout the description. In the following, the drive nut for a platform elevator will be denominated "the drive nut".

Further, in following description, any references to direction or positions or orientation are in relation to a horizontal surface, such as a horizontal ground surface.

<FIG> shows schematically a platform elevator <NUM>. The platform elevator <NUM> comprises a support structure <NUM> which may be installed in a building structure. The support structure <NUM> may be arranged to extend substantially vertically between a lower and upper level of a building that the elevator <NUM> is intended to serve. The support structure <NUM> comprises two substantially straight guide rails <NUM>, <NUM> that guide the elevator platform <NUM> during movement between the different levels. The guide rails <NUM>, <NUM> may preferably be secured in the building structure to provide the desired rigidity to the installation.

The elevator platform <NUM> may further comprise a substantially flat platform floor <NUM> for persons or goods and a platform support <NUM> that is extending in vertical direction from the platform floor between the two guide rails <NUM>, <NUM> of the support structure <NUM>.

The elevator platform <NUM> is movably arranged in vertical direction and the movement is generated by a vertically arranged threaded screw <NUM> arranged between the two guide rails <NUM>, <NUM> of the support structure <NUM>, a drive nut <NUM> with a corresponding inner thread is arranged on the threaded screw <NUM> such that the drive nut <NUM> bears on the lower surface of the platform support <NUM>.

The threaded screw <NUM> is shown in <FIG> and may comprise least a first and a second screw section 20a, 20b. Each screw section 20a, 20b is provided with an outer thread section 30a, 30b which, when the screw <NUM> is assembled, form the outer thread <NUM> of the screw <NUM> (see <FIG>).

<FIG> shows an enlarged view of the encircled area of <FIG>. Thus, the threaded screw <NUM> comprises an outer thread <NUM> which comprises a screw thread bottom <NUM>, a screw thread crest <NUM>, a screw thread upper flank <NUM> and a screw thread lower flank <NUM>.

The screw sections 20a, 20b are produced with high precision but it is almost impossible to achieve a perfect fit between the threads of adjacent screw sections. Even a small angular misalignment in the interface between adjacent screw sections will cause an irregularity in the threads which is illustrated in <FIG> where the interface 30c of the screws where adjacent sections meet is enlarged to more clearly illustrate the irregularity. Typically, the irregularity in the interface 30c is a leap in vertical direction between the end of the thread 30a of the first screw section 20a and the end of the thread 30b of the second screw section 20b. The leap may form a sharp cutting edge. The screw sections 20a, 20b could be joined together in different ways like for example a male-female configuration comprising a threaded section extending from the end surface of one screw section and a corresponding recess with internal threads formed in the end surface of the adjacent screw section.

Returning to <FIG>. A motor <NUM>, such as an electrical motor is arranged on the platform support <NUM> to rotate the nut <NUM> around the elongated screw <NUM> to move the elevator platform along the screw to the different levels. The electrical motor <NUM> rotates the drive nut <NUM> to move the elevator platform <NUM> along the screw and stops the rotation at the selected level. The elevator furthermore comprises a braking arrangement (not shown) that is intended to ensure that the elevator platform remains at the selected level even though the electrical motor is turned off.

The platform elevator <NUM> further comprises a number of different components such as for example user interface for the operator to start and select the desired level, control units, cables for powering the electrical motor etc. that are not illustrated in the schematic illustration but these components are well known within this technical field and not relevant for the present invention.

In the following, the drive nut <NUM> according to the present disclosures will be described in more detail.

<FIG> shows schematically an exemplary manufacturing process for achieving the drive nut <NUM> according to the present disclosure (excluding the embodiment of <FIG>).

Thus, in a first step a drive nut <NUM> precursor is provided. The drive nut precursor is a rotationally cylindrical drive nut with a single inner thread <NUM> that extends between opposite first and second nut ends <NUM>, <NUM>. Turning to <FIG>, the nut precursor <NUM> is subjected to a machining operation which forms a conical portion <NUM> that extends from the first nut end <NUM> towards the second nut end <NUM> and that widens outwards in direction from the second nut end <NUM> towards the first nut end <NUM>. By machining, a corresponding conical portion <NUM> is also made to extend from the second end <NUM> of the nut precursor. In <FIG>, the inner thread <NUM> has been omitted to elucidate the conical portion. Machining may be performed by turning. <FIG> shows the final drive nut <NUM>. Thus, during machining of the conical portions <NUM>, <NUM>, a portion of the thread <NUM> is removed which results in that the width the nut thread lower flank decreases within the upper conical portion <NUM>, and within the lower conical portion <NUM>.

<FIG> shows an enlarged cross-sectional view of a drive nut <NUM> after a machining process as described under <FIG>. The drive nut <NUM> comprises an upper nut end <NUM>, and a lower nut end <NUM>. The drive nut <NUM> further comprises a single inner thread <NUM>, which comprises a nut thread bottom <NUM>, a nut thread crest <NUM>, a nut thread upper flank <NUM> and a nut thread lower flank <NUM>. The inner thread <NUM> has nominal flank width (nw) which is measured from the nut thread bottom <NUM> to the nut thread crest <NUM>. The nominal flank width of the nut may be the maximum flank width of the nut, both with regards to the upper flank <NUM> and to the lower flank <NUM>. The drive nut <NUM> may have outer axial grooves (not shown).

According to the present disclosure, the drive nut <NUM> comprises an upper conical portion <NUM> that widens outwards in direction from a nut center axis (X) towards the upper nut end <NUM>. In axial direction, towards the second end <NUM> of the drive nut, the upper conical portion <NUM> is limited by a lower conical limitation line <NUM>. The conical limitation line <NUM> is convex, i.e. it protrudes towards the center of the drive nut. Further according to the present disclosure, the width (wl) of the nut thread lower flank <NUM> decreases within the upper conical portion <NUM> of the drive nut <NUM>, in direction from the lower nut end <NUM> towards the upper nut end <NUM>. Thus, a portion of the nut thread lower flank <NUM> in the vicinity of the upper nut end <NUM> has a continuously decreasing width (wl).

The portion of the nut thread lower flank <NUM> with decreasing flank width (wl) has a lower flank edge <NUM>. The lower flank edge <NUM> extends between the nut thread lower flank <NUM> with decreasing width (wl) and an upper conical surface <NUM>. The upper conical surface <NUM> forms part of the conical portion <NUM>, and extends between the lower flank edge <NUM> and the first nut end <NUM>.

In <FIG>, the width (wl) of the nut thread lower flank <NUM> with decreasing width may be determined as the distance between the nut thread bottom <NUM> and the nut lower flank edge <NUM>.

<FIG> shows a further enlarged cross-sectional view of the drive nut <NUM> after a machining process as described under <FIG>. However, to elucidate further features, <FIG> is cut in an angle different from <FIG>. Thus, in <FIG> is illustrated that the width (wl) of the nut thread lower flank <NUM> decreases from nominal flank width (wn) of the nut thread <NUM> to an apex <NUM>, i.e. a point, between the nut thread bottom <NUM>, the lower flank edge <NUM> and the upper conical surface <NUM>. By varying the length and angle of the conical portion <NUM> it is possible to control the length of the nut thread lower flank <NUM> with decreasing flank width (wl). It is also possible to control how much the flank width (wl) decreases per length unit of the thread <NUM>.

<FIG> also shows that the width of the nut thread upper flank <NUM> (wu) decreases within the upper conical portion <NUM> of the drive nut <NUM>, in direction from the lower nut end <NUM> towards the upper nut end <NUM>. Also the width (wu) of the nut thread upper flank <NUM> may decrease from nominal flank width (wn) of the nut thread <NUM> to an apex, i.e. a point, between the nut thread bottom <NUM>, the upper flank edge <NUM> and a conical surface <NUM> that extends from the upper flank edge <NUM> in direction of the second nut end <NUM>. This apex is not shown in <FIG>.

A conical portion <NUM> may also extend from the lower end <NUM> of the drive nut <NUM>. Within the conical portion <NUM>, the nut lower thread flank <NUM> has the same configuration as described above with reference to the conical portion <NUM> in the upper nut end <NUM>.

The advantage of the drive nut <NUM> according to the present disclosure will in the following be described with reference to <FIG>. These figures are simplified functional figures with straightened thread for easier understanding of the function and effect of drive nut according to the present disclosure.

<FIG> show, in a view from above, a situation in which the portion of the nut thread lower flank <NUM> with decreasing width (wl) enters the interface 30c between the thread section 30a and 30b of a first and second screw section 20a, 20b as shown in <FIG>. In the <FIG> only the interface 30c and the second thread section 30b is visible. Thanks to decreasing width of the nut thread lower flank <NUM>, only a small portion of the nut thread lower flank <NUM> and the interface 30c will be in contact during entering of the nut thread lower flank <NUM> onto the second thread portion 30b. This will result in less resistance and higher surface pressure and thus in cutting wear of the nut thread lower flank <NUM> when it moves over a screw section interface where the upper screw section is overturned.

<FIG> show the situation illustrated in <FIG> in a side view. Here, a further advantage of the drive nut according to the present disclosure becomes apparent. Namely, during engagement between the nut thread lower flank <NUM> and the step formed interface 30c, the nut thread lower flank <NUM> is subjected to wear from the interface 30c. The wear results in that the nut thread lower flank <NUM>, in merely a few passes, is worn down to an extent at which the nut thread lower flank <NUM> is adapted to the step of the interface 30c of the threaded screw. This makes possible to rapidly adapt the drive nut for smooth running with regards to any individual overturned or under-turned interface between the threaded screw sections.

<FIG> show a threaded screw <NUM> according to an aspect of the present disclosure. The threaded screw <NUM> may be used together with the drive nut <NUM> according to the first aspect of the present disclosure.

Turning to <FIG>, the threaded screw <NUM> comprises at least a first and a second screw section 61a, 61b. The first screw section 61a has a first end 62a and second end 63a. The first screw section 61a further has an outer thread section 70a which extends between the first and second screw end 62a, 63a. The thread section 70a has a first thread end portion 71a at the first end 62a of the screw section 61a and a second thread end portion 72a at the second end 63a of the screw section 61a.

The second screw section 61b has a first end 62b and second end 63b. The second screw section 61b further has an outer thread section 70b which extends between the first and second screw end 62b, 63b. The thread section 70b has a first thread end portion 71b at the first end 62b of the screw section 61b and a second thread end portion 72b at the second end 63b of the screw section 61b.

The thread sections 70a and 70b have respectively a thread bottom 74a, 74b, a thread upper flank 75a, 75b, a thread lower flank 76a, 76b and a thread crest 77a, 77b.

The first and the second screw sections 61a, 61b are inter-connectable. A first end 62b of the second screw section 61b may be connected to a second end 63a of the first screw section 61a and form a threaded screw <NUM> (not shown in <FIG>).

<FIG> shows a section of a threaded screw <NUM> that is formed by interconnection of the first and second screw section 61a and 61b. The screw <NUM> has an outer thread <NUM> with a thread bottom <NUM> an upper thread flank <NUM>, a lower thread flank <NUM> and a thread crest <NUM>. In <FIG>, the lower thread flank <NUM> is not visible, due to the perspective, however it is indicated by a dashed arrow.

Returning to <FIG>. According to the present disclosure, the first end portion 71b of the thread section 70b of the second screw section 61b is beveled, i.e. it comprises a bevel 73b. Further according to the present disclosure, the second end portion 72a of the thread section 70a of the first screw section 61a is beveled, i.e. it comprises a bevel 73a.

<FIG> shows an enlarged view of the first end 62b of the second screw section 61b. Thus, the first end portion 71b of the thread section 70b of the second screw section 61b is beveled such that the width of the upper thread flank 75b of the second screw section 61b narrows in radial direction towards the first end 62b of the second screw section 61b. <FIG> shows in detail how the width (wsu) of the upper thread flank 75b of the second screw section narrows. Returning to <FIG>, the bevel 73b may extend in axial direction between the upper thread flank 75b and an abutment surface 80b of threaded section 70b. The abutment surface 80b is configured to bear against a corresponding abutment surface of the first screw section (not shown). The width (wsu) of the upper thread flank 75b may terminate at an apex <NUM>, i.e.a point, between the bevel 73b, the upper flank 75b, the abutment surface 80b and the thread bottom 74b of the threaded section 70b. Beveling may be achieved by common machining processes, such as grinding or turning.

Turning to <FIG> which further shows that when the first and the second screw sections 61a, 61b assembled into a threaded screw <NUM>, the end of the bevel 73b of the second screw section 61b extends across the upper flank 75a of the first screw section 61a and terminates into the apex <NUM> at the screw thread bottom 74b. However, it is appreciated that the apex <NUM> need not to be at the thread bottom 74b. <FIG> also shows the bevel 73a and the narrowing upper thread flank 75a of the first screw section 61a. As apparent, the width of the upper flank thread flank 75a narrows in radial direction towards second end 63a of the first screw section 61a. It is appreciated that the thread flanks of the first and second screw section 61a, 61b do not need to be beveled.

The advantage of a screw with screw sections with beveled thread flanks in the ends together with a drive nut according first aspect of the present disclosure will be described with reference to <FIG>. It is again emphasized that <FIG> are schematic and merely provided to facilitate the understanding of the invention. Thus, in the arrangement shown in <FIG> the width of the screw thread upper flank 75b and the width of the nut thread lower flank <NUM> decreases continuously. This results in that only a very small portion of the screw thread upper flank 75b and the nut thread lower flank <NUM> will be in contact as the nut thread lower flank <NUM> enters onto the upper screw flank 75b. This results in less resistance and higher surface pressure between the nut thread lower flank <NUM> and screw thread upper flank 75b. As a consequence, the nut thread lower flank is subjected to cutting wear when it moves over the screw section interface. Cutting wear is predominantly achieved when upper screw section is overturned and the drive nut moves upwards. <FIG> shows the situation illustrated in <FIG> in a side view and illustrates the wear of the nut lower flank <NUM>.

Preferably, the angle (α) of the nut thread lower flank <NUM> and the angle (β) of the upper screw flank 75b, as seen from above, are different from each other. A cutting angle (γ) is defined in the contact between the nut thread lower flank <NUM> and the upper screw flank <NUM>. The cutting angle equals the angle (β) minus angle (α) of the upper screw flank 75b. It is important that angle (α) and angle (β) are different in order to achieve the cutting angle (γ). It is emphasized that angle (α), (β) and (γ) are schematic and merely provided to facilitate the understanding of the invention.

It is appreciated that, the outer thread <NUM> of the threaded screw <NUM> and the inner thread <NUM> of the drive nut <NUM> may be corresponding trapezoidal threads, mutually configured such that when the outer thread <NUM> of the threaded screw <NUM> engages the inner thread <NUM> of the drive nut <NUM> the thread crest <NUM> of the threaded screw touches the nut thread bottom <NUM> before the upper and lower nut thread flanks <NUM>, <NUM> and the upper and lower flanks <NUM>, <NUM> of the threaded screw touches each other. It is further appreciated that the drive nut <NUM> and the threaded screw <NUM> have been described with merely one thread each. However, it is appreciated, the drive nut <NUM> and the screw <NUM> may comprise more than one thread each. For example, seven threads each.

It is further appreciated that the threaded screw <NUM> may comprise more than two screw sections 61a, 61b.

<FIG> shows an example of an actual realisation of a platform elevator drive nut <NUM>. The drive nut <NUM> of <FIG> comprises multiple threads, i.e. more than one thread. The thread of the drive nut (and the cooperating screw sections) is thus not a single-start thread but a multi-start thread. More precisely, the drive nut illustrated in <FIG> comprises six threads.

At the lower nut end <NUM> there is shown a flange structure that protrudes radially and axially. The flange structure is connected to other components of the platform elevator and is not discussed in further detail in the present disclosure.

The threads <NUM> of the drive nut <NUM> of <FIG> are similar to the single tread <NUM> of the drive nut illustrated in <FIG> and <FIG>. That is to say, the drive nut of <FIG> also comprises an upper conical portion <NUM> (and a lower conical portion <NUM>) that widens outwards in direction from a nut center axis towards the upper nut end <NUM>. In axial direction, towards the second end <NUM> of the drive nut, the upper conical portion <NUM> is limited by a lower conical limitation line <NUM>. The width (wl), i.e. radial extension, of the nut thread lower flank <NUM> decreases within the upper conical portion <NUM> of the drive nut <NUM> of <FIG>, in direction from the lower nut end <NUM> towards the upper nut end <NUM>. Thus, a portion of the nut thread lower flank <NUM> in the vicinity of the upper nut end <NUM> has a continuously decreasing width (wl).

As a result, there is a small contact area and a high surface pressure between the nut thread lower flank <NUM> and the above-described irregularity between adjacent sections 20a, 20b; 61a, 61b of the threaded screw <NUM>; <NUM>, such that controlled wear of the underside of the nut thread lower flank <NUM> against the irregularity is facilitated as has been described above.

<FIG> shows another example of an actual realisation of a platform elevator drive nut <NUM>. The drive nut of <FIG> differs from the drive nut of <FIG> only in how the decreasing width (wl) of the nut thread lower flank <NUM> is accomplished.

The drive nut <NUM> of <FIG> comprises inner threads <NUM> of decreasing width, i.e. decreasing radial extension, in the vicinity of the upper nut end <NUM>. Thus, also the width (wl) of the nut thread lower flank <NUM> decreased in the vicinity of the upper nut end. In the example of <FIG>, the individual threads have been formed with a decreasing width. The nut thread crests <NUM> are aligned with the axial direction of the drive nut along the entire length of the drive nut, whereas the drive nut of <FIG> comprises a conical surface <NUM> as has been described with reference to <FIG>.

The inner threads <NUM> of decreasing width of <FIG> are provided without any conical portion being formed in the upper (or lower) nut end <NUM>. Instead of an upper conical portion <NUM>, the drive nut of <FIG> comprises an upper portion 58a, or upper adjusted portion 58a. By the term "adjusted" is meant that the inner threads <NUM> of the drive nut <NUM> that extend through the upper adjusted portion 58a (and lower adjusted portion 59a) are shaped such that the nut thread lower flank <NUM> has a decreasing width (wl), which results in a small contact area and a high surface pressure between the nut thread lower flank <NUM> and the above-described irregularity formed by an angular misalignment between adjacent screw sections.

The vertical lines <NUM>. 1a across the inner threads <NUM> of the drive nut of <FIG> mark the beginning of the decreasing width of the individual threads within the upper and lower adjusted portion 58a, 59a (or upper and lower portions 58a, 59a). In the example of <FIG>, the width (radial extension) of each inner thread <NUM> within the adjusted portions 58a, 59a continuously decreases to approximately one fifth nominal thread flank width (wn). Three thread starts are shown in <FIG>, see top drive nut surface.

As is indicated in <FIG>, each inner thread <NUM> has a nominal width (wn) at the proximal ends of the adjusted portions 58a, 59a and a decreased width (wl) at the distal ends of the adjusted portions 58a, 59a. Preferably, each inner thread <NUM> decreases to a zero width (not shown) at the distal ends of the adjusted portions 58a, 59a, see the embodiment of <FIG>. The proximal ends of the adjusted portions 58a, 59a are directed towards the axial center of the drive nut <NUM> whereas the distal ends of the adjusted portions 58a, 59a are directed towards the drive nut ends <NUM>, <NUM>.

Claim 1:
A method of adapting a platform elevator drive nut (<NUM>) to a threaded screw (<NUM>; <NUM>) of a platform elevator (<NUM>), the method comprising operating the platform elevator (<NUM>) such that the drive nut (<NUM>) passes an interface (30c) between adjacent sections (20a, 20b; 61a, 61b) of a threaded screw (<NUM>; <NUM>) of the platform elevator (<NUM>), wherein the drive nut (<NUM>) is adapted for moving a platform (<NUM>) of the platform elevator (<NUM>), said platform elevator (<NUM>) comprising a platform (<NUM>) and said threaded screw (<NUM>; <NUM>) comprising an outer thread (<NUM>; <NUM>) having a screw thread bottom (<NUM>; <NUM>), a screw thread upper flank (<NUM>; <NUM>), a screw thread lower flank (<NUM>; <NUM>) and a screw thread crest (<NUM>; <NUM>), wherein the drive nut (<NUM>) is configured to be turnably arranged on the threaded screw (<NUM>; <NUM>) and to support the platform (<NUM>), wherein the drive nut (<NUM>) comprises:
- an upper nut end (<NUM>) and an opposite lower nut end (<NUM>), and
- an inner thread (<NUM>) extending between the upper and lower nut ends (<NUM>, <NUM>) and configured to engage the outer thread (<NUM>; <NUM>) of the threaded screw (<NUM>; <NUM>), said at least one inner thread (<NUM>) having a nut thread bottom (<NUM>), a nut thread upper flank (<NUM>), a nut thread lower flank (<NUM>) and a nut thread crest (<NUM>), wherein
- the outer thread (<NUM>; <NUM>) of the threaded screw (<NUM>; <NUM>) and the inner thread (<NUM>) of the drive nut (<NUM>) are corresponding trapezoidal threads,
characterized in that
- in the vicinity of the upper nut end (<NUM>) the nut thread lower flank (<NUM>) has a decreasing width (wl), which results in a small contact area and a high surface pressure between the nut thread lower flank (<NUM>) and an irregularity formed by an angular misalignment between adjacent sections (20a, 20b; 61a, 61b) of the threaded screw (<NUM>; <NUM>), such that wear of the underside of the nut thread lower flank (<NUM>) against the irregularity is facilitated, whereby the shape of the nut thread lower flank (<NUM>) is adapted to the irregularity.