EP0067161A1 - Height adjustable stairway with an elevator platform - Google Patents

Abstract

Escalier ajustable en hauteur pourvu de moyen de transport pour, entre autres, des personnes handicapees ou invalides. Le probleme qu'impliquent generalement de telles structures reside dans le fait qu'une plate-forme (15) destinee a soulever des invalides, par exemple dans un fauteuil roulant, doit etre deplacee dans un plan horizontal quelle que soit la hauteur a laquelle l'escalier ajustable a ete regle, en meme temps que l'escalier doit etre disponible en tant que tel pour les utilisateurs habituels Les principes fondamentaux de la solution resident dans une geometrie de parallelogramme dans laquelle les elements formant rampe (5) sont incorpores dans une structure de support qui comprend des guides cooperant avec des organes d'engagement sur la plate-forme elevatrice. L'utilisation essentielle d'un tel escalier reglable en hauteur se rapporte au trafic des passagers, en particulier a titre d'escalier d'acces aux avions dans les aeroports, et il peut egalement etre utilise pour la manipulation des bagages qui ne sont pas facilement portables.Height-adjustable staircase with means of transport for, among others, disabled and disabled people. The problem generally implied by such structures resides in the fact that a platform (15) intended for lifting invalids, for example in a wheelchair, must be moved in a horizontal plane whatever the height at which the adjustable staircase has been adjusted, at the same time that the staircase must be available as such for regular users The fundamental principles of the solution reside in a parallelogram geometry in which the elements forming a ramp (5) are incorporated in a support structure which includes guides cooperating with engagement members on the lifting platform. The essential use of such a height-adjustable staircase relates to passenger traffic, in particular as a staircase for access to aircraft in airports, and it can also be used for handling baggage which is not easily portable.

Description

"Height Adjustable Stairway with an Elevator Platform".

For many uses, for example at airports, there has for a long time been a need for a practicle solution to the problem of bringing handicapped and invalid persons, in particular wheel chair patients, from a lower level to a higher level, for example from the ground up to an airplane door. Hitherto no satisfactory solution to this problem has been proposed.

The problem is made complicated thereby that normally ther will be for such purposes a stairway for passengers and others who are able to ascend on their own, and such stairways are usually height adjustable in order to be adapted for example to the various airplane types using an airport. It has been a starting-point for the efforts in connection with the present invention, to try and find a combination solution including a height adjustable stairway and, besides, transport means for wheel chair users and other handicapped persons, or possibly for goods.

An example of a known and conventional height adjustable stairway, for example an airplane stairway, may be found in US Patent 2,362,170. This known design comprises a number of treads which are kept horizontal independent of changes in the angular adjustment of the supporting beams or stringers of the stairway, when the height regulation is varied. Moreover, there is provided an elevating device for the height adjustment so that the angle of the supporting beams is changed in relation to a horizontal frame. Finally, the known design is provided with hand rails on both sides of the stairway. The automatic horisontal positioning of the treads and also of an upper landing, is obtained with a parallelogram geometry in which two parallel supporting beams form the stairway stringers on each side and the treads are supported horizontally therebetween.

Further, there are transport means or transport tracks, known per se, which run at an inclination and which are adapted to keep a transport cage or car horizontally during elevation from a lower to an upper level. An example of such structure having a fixed angle of inclination or height difference may be found in published European Patent Appli cation 0012149. An example of such an inclined transport arrangement having two different angles of inclination, is shown in US Patent 3,312,307. The latter patent specification relates to an embodiment having two fixed angles of inclination , and a specific cam-like guide rail provides for keeping the transport car horizontally at the transition from one inclination angle to the other on the transport track. Finally, it may be mentioned that US Patent 3,592,294 shows an inclined transport arrangement for variable angle adjustment in which a manually operable screw device may serve to adapt the orientation of a transport cage or box depending upon the angular position of the transport arrangement. This manual adjustment apparently requires som work effort and would for example, when applied to airplane stairways, not be able to satisfy the need for a quick and automatic adjustment in the different situations of use.

Thus, more particularly this invention is directed to a height adjustable stairway comprising an upper landing and a number of treads being kept horizontal independently of changes in the angular position of the supporting beams or stringers of the stairway, when the height adjustment is varied, and elevating means for the height adjustment in order to change the angle of the supporting beams in relation to ahorizontal frame, as well as hand rails on both sides of the stairway.

What is novel and specific to a height adjustable stairway according to the invention for obtaining a combined solution as discussed above, mainly consists therein that a rail element on each side of the stairway forms an upper supporting beam for tread elements and runs parallel to a lower supporting beam of equal length, that the upper and the lower supporting beams each at their lower portion has a pivot point which is fixed in relation to the horizontal frame and of which at least one pivot point is located on an upright support which is rigidly connected to the frame, and being at their upper portion pivoted to a support member incorporated in the upper landing, that the line connecting the lower pivot points of the supporting beams is parallel to the connecting line between their upper pivot points, that there are provided for each tread, carrying elements pivotably supported at points on the lower and the upper supporting beams, respective lying on a straight line parallel to the above connecting line that the treads are arranged at the lower end of the carrying elements and beneath the lower supporting beam, and that an elevator platform is adapted to be moved up and down along the stairway by the cooperation between engagement members in the form of rollers on the platform, and guides on the upper and lower supporting beams, respectively, the spacing between the engagement members being equal to the mutual distance between the pivot points for the tread carrying elements, and that there is provided drive means for the movement of the elevator platform.

With this solution there is obtained a simple, inexpensive and practical, but above all a combined structure which is favourable to the users and which in a very advantageous way utilizes the various structural elements which must be incorporated into such a height adjustable stairway, in order to provide a transport arrangement in the form of an elevator platform which in the first place is intended to solve the problems for wheel chair patients and other invalids, but which may also be used for the transport of goods, either in the form of common packages, for example passenger luggage, food Containers, litter boxes and cleaning equipment,orpossibly in the form of trolleys, carriages or the like, which it is difficult to drive up a common stairway.

The invention shall be explained more closely in the following with reference to the drawings, in which: Fig. 1 shows a first embodiment of the invention where the height adjustable stairway is mounted on a movable undercarriage which may be towed by a tractor or the like in similarity with a trailer, Fig. 2 shows in part and at a larger scale a vertical section through the hand rail structure with supporting beams for the stairway as shown in Figure 1, and a carrying member for the elevator platform. Fig. 3 shows another embodiment in which the stairway is mounted on a movable, electrically driven undercarriage, and in which the stairway structure proper is somewhat modified in relation to the one in Figure 1, Fig. 4 shows in par an at a larger scale a horizontal Section through the side wall structure in the stairway of Figure 3, and Figs. 5 and 6 shows two modified embodiments with a middle landing in the stairway, particularly intended for large total heights. The undercarriage for the stairway in Figure 1 comprises a horizontal frame 1 provided with steerable front wheels la and rear wheels lb as well as a towing rod 2. On the undercarriage frame 1 there is, moreover, provided elevating means having a driving aggregate 3 and a lifting cylinder 4 which may be hydraulically operated or may consist of mechanically or possibly electrically driven components. The elevating assembly 3, 4 supports the upper end of the actual stairway structure by means of a supporting point under the upper fixed landing 16 the level of which above the ground may be adjusted as desired up to a certain maximum height. During such height adjustment the angular position of the stairway will be changed in relation to the frame 1.

The load-bearing structure of the stairway comprises a lower supporting beam 6 and an upper supporting beam 5, of which the latter beam is simultaneously a hand rail which is usually necessary in such stairways. The hand rail ele-ments are accordingly here utilized as a part of the loadbearing structure and, besides, have a specific function in connection with an elevator platform 15 to be discussed below. The lower end of supporting beam 6 is connected to the frame 1 at a point 9, whereas the upper end of lower supporting beam 6 is connected to the lower part of an upper supporting member 25 which forms a part of the upper landing 16. The upper supporting beam 5 is at its lower end connected at a point 8 on top of a support 24 which is rigidly joined to the rear end of frame 1. At the upper end supporting beam 5 is connected to support member 25 at a point 10 on the top of this member. This sapport member is parallel to the support 24 so that there is established a parallelogram geometry in which also the tread elements of the stairway are incorporated. In Figure 1 these tread elements comprise supporting rods 7 being mounted vertically between pivot points 12 and 13 at the upper supporting beam 5 and the lower supporting beam 6, respectively, the actual tread 7a projecting at a right angle from rods 7 underneath the lower supporting beam 6 . It is an advantage to let the supporting rods 7 on either side of the stairway, run continuously underneath the stairway so that there is formed a U-shaped supporting structure for each tread 7a. This also contributes to an increased stability of the whole stairway structure. Since the mutual distance between the pivot points 12 and 13 is equal to the distance between the connecting points of the supporting beams to the support 24 and the supporting member 25, respectively, a change in the angular position of the stairway when the height is adjusted, will involve a parallel movement of all treads and also of the upper landing 16 so that the treads and the landing floor automatically will be kept in a horizontal position irrespective of the level to which the stairway is adjusted.

For example at airports it may often be necessary to have a relatively closed covering of the stairway, and in Figure

1 it is indicated at 14 how a side plate may extend over a the substantial part of or the whole height of rail and supporting structure so that there is formed a more or less complete side wall on each side of the stairway. These side plates may suitably be attached at points 14a on each tread as well as at a point 14b on the frame and at a point 14c on the landing 16, and are thereby incorporated into the parallelogram system together with the supporting beams. Moreover, the side or cover plates 14 on each side may be connected to each other by means of an underneath plate which will cover the treads 7a completely against observation, wind, etc. from underneath the stairway. With such a U-shaped cross-section of the cover plate structure 14 this will also contribute to the strength and rigidity of the complete stairway.

The stairway structure discussed above is designed particularly with the object of moving an elevator platform 15 from the bottom position shown, to an upper position 23 as indicated with dotted lines, and vice versa. On each side the platform 15 includes a vertical carrying member 26 which in similarity with the supporting member 25 for the upper fixed landing 16, is a main component in the platform structure. As shown in more detail in Figure 2 each carrying member 26 is provided with engagement members at the upper and lower parts, in the form of rollers 17 and 18, respectively, which are in engagement with guides 29 and 49, respectively, formed as open profiles of which the supporting beams 5 and 6 may consist. The elevator platform 15 may thereby be moved upwards by means of the supporting beams 5 and 6 on each side and above the stairway treads 7a by parallel displacement so that the platform 15 is all the time moved with a horizontal floor from the lower position shown to the upper position indicated at 23. In order to perform this elevating movement there may be provided for example a motor driven chain traction as indicated at 21 and 22 at the lower and upper ends, respectively, as shown in Figure 1. This chain traction may be located within the profile which constitutes the lower supporting beam 6. In Figure 2 the chain itself is indicated at 27. On the upper side of the upper supporting beam 5 there is according to Figure 2, shown a hand rail 28 to be used by those who ascend or descend the stairway on their own feet.

The elevator platform 15 is provided with a movable plate or ramp 19 which is moved on a guide member 20 and which in its rest position may be pushed underneath the floor of the platform 15 and which may also be raised into a vertical position as a rear wall of the platform.

In its upper position 23 the elevator platform is adapted to be exactly aligned with the upper fixed landing 16 so that for example wheel chair patients may easily roll from the elevator platform to the fixed landing and into an airplane or the like to which the adjustable stairway here described, provides for admittance.

The embodiment shown, in Figures 3 and 4 is in principle based upon the same main features as the embodiment of Figures 1 and 2. What is different is in the first place the undercarriage which has the form of a self-contained vehicle which may for example be electrically driven with a battery box 31 and a driver's seat 30. This driving module for the vehicle is rigidly joined to a horizontal frame 51 and, besides, has steerable front wheels as well as rear wheels as in the embodiment of Figure 1. Corresponding elevating means is also shown in Figure 3.

In addition to the structure of the height adjustable stairway in Figure 3 as shown with full lines and in detail, the stairway is also shown therein in a lower position 39 and in an upper position 40, by means of broken lines.

The main components of the stairway structure here in similarity to the one in Figure 1, also comprise, an upper supporting beam 45 and a lower supporting beam 46 which are both at the upper end connected to a supporting member 55 which has pivot points 60 and 61 and which constitute a main part of the upper fixed landing 66.

An important modification of the embodiment in Figure 3 compared to the embodiment first discussed with reference to Figure 1, consists therein that the supporting beams 45 and 46 at their lower ends are connected to a vertical support 54 having pivot points 34 and 35 being displaced a distance inwardly from the lower ends of the supporting beams. This does not change anything in the parallelogram principle, but means that the lower end of the lower supporting beam 46 is moved downwardly towards the ground when the height of the stairway is adjusted up, so that wheels 36 mounted at the bottom of supporting beams 46 may be brought in engagement with the ground and thereby give an additional support for the stairway, possibly as an advantageous relief of load on the rear wheels of the vehicle. In the maximum level position as shown at 40, and with the relative dimensions as in Figure 3, the rear wheels actually will be lifted from the ground if they are not provided with springs, as the wheels 36 will support the rear part of the whole vehicle with a relative position of the ground or base as indicated with broken lines at 41. The corresponding dot-and-dash indication of the lower part of the stairway with the elevator platform shows that the entering level in such an embodiment may be very low. In the lower position 39 of the stairway (normal driving position) on the other hand the elevator platform and the lowermost or rearmost portions of the stairway structure are sufficiently raised above the ground in order that driving may take place without obstruction.

O.V.Pi Another modification which appears from Figure 3 and is shown more in detail in Figure 4, consists therein that the tread elements 37 are here built- as a sheet metal structure Thus, the side members or carrying elements for these treads are formed as bent profiles- 32 consisting of plate parts 32a and 32b lying in somewhat different planes as shown more in detail in Figure 4. It is thereby possible for neighbour tread elements to overlap and be in engagement with each other with the possibility of mutual displacement during height adjustment of the stairway. The carrying elements 32 may together with the actual tread 33 have the form of an integrated plate structure having a U-shaped cross-section. Pivot points for such a tread element is shown at 32 and 63 on the upper supporting beam 45 and the lower supporting beam 46, respectively. The upper edge of the carrying elements 32 is shown with an inclination, which has been done for purely esthetic reasons.

The tread element coinciding with support 54 may have pivot points coinciding with the connecting points 34 and 35 for the supporting beams on support 54. In Figure 3 this relates to tread element number 3 from below.

In similarity to the embodiment of Figure 1 the one in Figure 3 may also be provided with additional coverage of the tread structure, which is shown in the form of a cover plate 38 which here mainly serves to cover the underside of the tread. The plate structure 32, 32a, 22b of the tread elements proper makes it more or less superfluous here to have a complete side coverage by means of the cover plate 38. Cover plate 38 is connected to the treads as indicated at 38a and to the upper landing 66 at point 38b. In this way the cover plate 38 participates in the angular and parallel displacement when the whole stairway is adjusted as to level, and the cover plate 38 may also here have a strengthening or stiffening effect in the structure.

As may have appeared from the above the invention provides an advantageous combination in which the load-bearing rail structure outwardly serves the suspension of the tread elements and inwardly is adapted to guide the elevator platform so that the double function of the height adjustable stairway is made possible by simple means and maximum utilization of the structural elements from which the stairway is assembled.

It shall be emphasized that the vertical orientation of the supports, supporting members and carrying elements for the treads, which is found in both the embodiments shown, is not strictly necessary. It is clear that a completely corresponding parallel movement of the various parts is also possible on the basis of an inclined position of the supports, support members and carrying elements. In certain situations such an inclined orientation may be an advantage, namely in the case of very steep stairways. Another possible and obvious modification may consist therein that the undercarriage or frame 1 or 51, respectively, is provided with feet or the like in all four corners, in particular adjacent the front wheels, which may serve to relieve the wheels from their load more or less completely when the stairway shall be used. This is particularly of interest when stairway structures for heavy loads are concerned. The wheels 36 in Figure 3 represent means of this type.

Finally, it is obvious that the drive means for the elevator platform may be based upon other principles than a chain drive. Possible conventional means may be screw arrangements, sprocket drive and others. A completely corresponding design of an adjustable stairway may also be thought of for uses in which the same cannot suitably be mounted on a horizontal frame or a movable undercarriage, for example as a gangway belonging to a ship, whereby the upper landing must be fixedly attached to the ship's hull as a foundation. Similar situations may also be found in connection with building structures or the like where there is a need for an adjustable stairway with an elevator platform as described above. In this case the necessary elevating means may possibly consist of a winch with a steel wire which is attached to the lower and here movable end of the stairway.

In the case of very long and high stairways, for example for operation with certain modern and very big airplane types , it will be necessary to have a landing at the middle portion of the stairway, and this has been provided for by means of the modified embodiments as shown in Figures 5 and 6 of the drawings. In Figure 5 the complete stairway in fact consists of two stairways, i.e. in the first place a fixed stairway 100 which is mounted on a movable undercarriage or frame

101, in which an upright support 124 is rigidly joined to the frame 101 and carries the upper end of the fixed stairway 100, which at the upper end is provided with a fixed landing

102. The height adjustable stairway therefore here constitutes a direct continuation of the fixed stairway 100. Supporting beams 105 and 106 for the height adjustable part of the stairway have lower pivot points 108 and 109 on support 124 and upper pivot points 110 and 111 on a supporting member 125 which is incorporated in the upper height adjustable landing. The height adjustable stairway has tread elements 107 and otherwise is designed completely in accordance with the stairway of Figure 1. For lifting the elevator platform 115 in Figure 5 the stringers of the fixed stairway 100 are provided with guides as described in connection with the embodiments discussed above. For moving the elevator platform 115 without problems across the middle landing 102 these may be provided with respective cooperating auxiliary guide elements 177a and 177b, respectively, on either side.

In the modified embodiment of Figure 6 there is in similarity to the embodiments of Figures 1 and 3, provided straight supporting beams 205 and 206 so that the angular position and thereby the height, is adjustable over the whole length as one piece. A middle landing 207a has been obtained here by designing one of the treads with a significantly enlarged depth, for example corresponding to two or three times the normal tread dimension or depth, the subsequent treads above, for example tread 207b, being correspondingly lowered by extension of the carrying elements 207' downwardly underneath thelower supporting beam 206. As a consequence of the change in relative level between the treads below and above the middle landing 207a, with respect to the upper supporting beam 205., it may be an advantage to provide an additional and somewhat raised hand rail element 205' at the lower part of this stairway. As indicated at the upper position of the elevator platform 215, it will, moreover, in this embodiment be suitable to have a front plate or ramp 219 which may be lowered in order to make it easy to move from the elevator platform to the upper landing 216. Such a orward lowerable ramp on the elevator platform may also be useful in the other embodiments shown.

In all the embodiments shown it is possible for the elevator platform with associated guides and drive means to be manufactured more or less as an auxiliary equipment intended to mounted on a height adjustable stairway with tread and arrangements etc. based upon a parallelogram geometry as described.

Claims

PATENT CLAIMS: 1. Height adjustable stairway comprising an upper landing and a number of treads (7a, 33) which are maintained horizontal independently of changes in the angular position of supporting beams or stringers of the stairway when the height adjustment is varied, and elevating means (3, 4) for the height adjustment so that the angle of the supporting beams in relation to a horizontal frame (1,51,101,201) is changed, and hand rails on both sides of the stairway, characterized in that a rail element (5,45,105,205) at either side of the stairway constitutes an upper supporting beam for tread elements (7, 7a, 37,107,207,207') and runs parallel to a portion supporting beam (6,46,106,206) of equal length, that the upper and the lower supporting beams at their lower part each has a pivot point (8 ,9, 34 ,35,108,109,208,209) which is fixed with respect to the horizontal frame (1,51,101,201) and of which at least one pivot point (8,9,34,35,108,109, 208,209) is located on an upright support (24,54,124,224) which is rigidly joined to the frame, and at their upper portions are pivoted (10,60,110,210 resp. 11,61,111,211) on a supporting member (25,55,125,225) which is incorporated in the upper landing, that the connecting line between the lower pivot points of the supporting beams is parallel to theconnecting line through their upper pivot points, and that for each tread there are provided carrying elements (7, 32a-b) connected to the lower and upper support beams, respectively, at points (13 resp. 12, 63 resp. 62) which lie on a straight line parallel to said connecting lines, that the treads (7a, 33) are provided at the lower end of the carrying elements (7, 32a-b) and underneath the lower supporting beam (6,46,106,206), and that an elevator platform (15,115,215) is adapted to be moved up and down on the stairway by having engagement members in the form of rollers (17,18) on the platform in cooperation with guides (29,49) on the upper and lower supporting beams (5,6,105,106,205,206), respectively, the spacing between the engagement members (17,18) being equal to the mutual distance between the connecting or pivot points (12,13) of the tread carrying elements (7), and that there is provided drive means (21,22) for the movement of the elevator platform (15)

. characterized in that said connecting lines and said straight line through the pivot points of the carrying elements

(7, 32a-b) are all vertical.

3. Height adjustable stairway according to claim 1 or 2, characterized in that the carrying elements (7, 32a-b) for the treads are arranged outwardly of the supporting beams (5,6,45,46).

4. Height adjustable stairway according to claim 3, characterized in that the carrying elements (7, 32a-b) together with the actual treads (7a, 33) form a U-shaped structure which constitute the cross-section of the stairway proper at both sides and downwardly.

5. Height adjustable stairway according to any one of the preceding claims, characterized in that laterally and outwardly of the carrying elements (7,32,32a-b) there is provided a cover plate (14, 38) which is connected to each tread element at a point preferably adjacent the inner end of each tread, as well as on the frame and the upper landing (16,66).

6. Height adjustable stairway according to claim 5, characterized in that the cover plate (14,38) is continued underneath the treads so as to form a U-shaped cross-section of the cover plate structure.

7. Height adjustable stairway according to any one of the preceding claims, characterized in that the carrying elements (32, 32a-b) are plate shaped and overlap mutually so .that together they form a substantially continuous side wall below the upper supporting beam (45) on either side of the stairway.

8. Height adjustable stairway according to any one of the preceding claims, characterized by inwardly open guides

(29,39) at the upper (5) and lower (6) supporting beams, respectively, for cooperation with the engagement members (17,18) on the elevator platform (15).

9. Height adjustable stairway according to any one of the preceding claims, characterized in that said drive means for the elevator platform (15) comprise a chain drive (21,22) arranged in the lower supporting beams (6).

10. Height adjustable stairway according to any one of the preceding claims, characterized inthat the elevator platform (15) is provided with a ramp (19) which in its rest position may be pushed underneath the floor of the platform, which in one position of use may form a rear wall of the platform and which in another position of use may be lowered so as to form an entering ramp for the platform.

11. Height adjustable stairway according to any one of the preceding claims, characterized in that the pivot points (34, 35) for the supporting beams (45, 46) on the upright support (54) are displaced a distance inwardly from the lower ends of the supporting beams, so that these lower ends will move downwardly towards the ground when the height of the stairway is adjusted upwards, said pivot points (34,35) coinciding with the connecting or pivot points of a tread element on the supporting beams (45,46).

12. Height adjustable stairway according to claim 11, characterized in that a supporting wheel (36) is provided at the lower end of the lower supporting beam (46), said supporting wheel being adapted to engage the ground or base when the stairway is being adjusted up to a certain height.

13. Height adjustable stairway according to any one of claims 1-10, characterized in that the upright support (124) supports the upper end of a fixed stairway having an upper fixed landing, so that, the height adjustable stairway constitutes a continuation of this fixed stairway.

14. Height adjustable stairway according to any on of claims 1-12, characterized in that one of the treads (207a) at a middle portion of the stairway is designed with an enlarged depth so that there is formed a landing, and that the carrying elements (207') of the treads above this landing have a downward extension in order to provide for a correspondingly lowered position of these treads (207b).

15. Adjustable stairway comprising an upper landing being fixedly attached to a foundation, for example a building structure or a ship's hull, and having a number of treads which are maintained horizontal independently of changes in the angular position of the supporting beams or stringers of the stairway with varying angular adjustment, and elevating means for the height adjustment so that the angle of the

_Q?'PI supporting beams in relation to the horizontal piane is changed, as well as rails at both sides of the stairway, characterized in that a rail element on either side of the stairway constitutes an upper supporting beam for said element and runs parallel to a lower supporting beam of substantially equal length, that the lower and the upper supporting beams at their lower ends are connected to the lower and upper end, respectively, of an upright support, and are at their upper ends connected to the bottom and top, respectively, of a supporting member which is incorporated in a fixed landing and which is parallel to said support, that for each tread there are provided carrying elements connected to the lower and upper supporting beams, respectively, at points which lie on a straight line parallel to the support and the supporting member, that the treads are provided at the lower end of the carrying elements and below the lower supporting beam, and that an elevator platform is adapted to be moved up and down along the stairway by having engagement. members in the form of rollers on the platform in cooperation with guides on the. upper and lower supporting beams, respectively, the spacing between the engagement members being equal to the mutual distance between the connecting or pivot points of the tread carrying elements, and that there is provided drive means for the movement of the elevator platform.