ADJUSTABLE STAIRCASE

Abstract: A staircase having adjustable treads comprises two strings (11) which are rigidly connected to each other and between which a number of treads (16-19) are provided. Each tread is at its ends pivotally mounted on a bearing shaft (25-28) in the adjacent string and is connected to a link arm (29-32), the link arm being connected to an adjustable link means (33). The link means can be adjusted by means of an operating arm (20) in such a way that the treads are turned around their bearing shafts, maintaining the upper surfaces of the treads in parallel, so that the angle between the upper surfaces of the treads and the longitudinal direction of the strings is changed. The treads (16-19) can also be turned to a common plane, so that the treads form a substantially continuous, plain surface. By adjustment of the treads, the treads can be positioned substantially horizontally irrespective of the inclination of the strings to the ground plane, so that the staircase is comfortable to use. Alternatively, the treads can form a plain surface, so that the straircase can be used as a ramp, e.g. for transport vehicles or wheeled chairs.

Description: Adjustable staircase Technical Field The present invention is related to an adjustable staircase comprising two strings which are rigidly connec¬ ted to each other and which have at least two intermediate treads. At its ends each tread is pivotally mounted in the adjacent string. The staircase is intended to be used both as a staircase with a variable slope, in which case the treads always can be adjusted so that the upper surfaces are substantially horizontal, and as a ramp having a sub- stantially plain surface of transportation. Background Art Staircases having adjustable treads have been disclo¬ sed previously, e. g. in the US Patent Specifications 2 888 182 and 3 731 761. However, these previously known staircases have had a complicated construction, and it has not been possible to adjust the staircases to a ramp having a plain surface of transportation in an easy way. Therefo¬ re, the usefulness of these prior art staircases has been limited. Disclosure of Invention The main object of the invention is therefore to pro¬ vide a staircase in which the treads are pivoted in such a way that the staircase easily can be adapted to different angles of inclination and converted into a ramp having a substantially plain working surface, and which has a simple construction. This object has been achieved in accordance with the invention by giving the staircase the features set forth in the claims. Brief Description of Drawings The invention will now be described more in detail below with reference to the accompanying drawings, wherein: Fig. 1 is a view in perspective of one embodiment of a staircase according to the invention having four treads and an operating lever for adjusting the treads. Fig. 2 shows the same staircase as Fig. 1 with the treads adjusted to a ramp having a substantially plain sur¬ face of transportation. Fig. 3 is a longitudinal section through the staircase according to Fig. 1 with the operating device for adjusting the treads. Fig. 4 shows schematically an alternative embodiment of the staircase according to the invention in which the strings of the staircase consist of telescopic sections, so that the staircase can be telescoped when not in use. Best Mode for Carrying Out the Invention The staircase shown in Fig. 1 comprises two side strings 10 and 11 rigidly connected to each other by means of cross bars 12-15. The staircase has four treads 16-19, and the treads are at their ends pivotally mounted on shafts (not shown) in the adjacent strings. The treads 16-19 can be turned around their bearing shafts, maintain¬ ing the upper surfaces of the treads in parallel, so that the angle between the upper surfaces of the treads and the longitudinal direction of the strings is changed. This tur¬ ning movement is provided by means of an operating lever 20, as will be further explained below. The treads 16-19 are also adapted to be turned to a common plane that is substantially parallel with the plane of the strings. The treads have a width that is so adapted that the front edge of a following, generally higher tread in this position abuts upon the rear edge of the preceding tread, so that a continuous, substantially plain surface is formed by the treads, as clearly shown in Fig. 2. Fig. 3 shows a longitudinal section through the stair¬ case shown in Fig. 1. The treads 16-19 are formed of cut pieces of aluminium sections and have been provided with end elements 21-24 at one end for stiffening the treads. The bearing shafts 25-28 of the treads pass through these end elements and run substantially along the longitudinal centerlines of the treads. Each end element 21-24 is at its rear end provided with a projecting tab 29-32, and these tabs are pivotally connected to a link bar 33, e. g. by means of rivets or screws. The top tread 19 is rigidly con¬ nected to the operating lever 20, and a locking plate 20A is attached to the string 11 adjacent the operating lever. The locking plate is provided with a plurality of recesses 34-36, and a locking means (not shown) on the operating lever 20 can be positioned in any one of the recesses for locking the operating lever in a definite angle position. At the front edges of the treads 16-19 the end ele- ments are provided with notches 37-40 for engagement with the cross bars 12-15, when the staircase is converted to a ramp, so that the front edges of the treads in this posi¬ tion along their full length rest upon the cross bars. When the staircase is to be used, the strings 10 and 11 are so positioned that the desired inclination is obtai¬ ned. The treads are then adjusted by means of the operating lever 20. When steps are desired, the treads can be adjus¬ ted so that the upper surfaces of the treads are substan¬ tially horizontal, irrespective of the angle of inclination of the strings to the ground plane, so that the staircase will be comfortable to use. When a ramp is desired, the treads are adjusted so that they form a continuous, sub¬ stantially plain surface. In Fig. 4 an alternative embodiment of an adjustable staircase according to the invention is shown. This embodi¬ ment is different from the embodiment shown in Figs. 1-3 in that the strings 10 and 11 have been designed of telescopic sections of which only the sections 10A, 10B and 10C of the string 10 have been shown. However, instead of the link bar shown in Fig. 3 another link means 41 has to be used, e. g. a telescopic arm or any other means capable to take up the reduced distance between the treads 16-19, when the sec¬ tions 10A, 10B and 10C are telescoped, so that the telesco¬ ping of the sections is not restrained. The embodiment shown in Fig. 4 is primarily intended to be used as an entrance or exit stair or ramp on buses or railway waggons. Therefore, the staircase is at its upper end provided with a shaft 42 around which the staircase can be lifted up when not in use. While only two embodiments of the adjustable staircase according to the invention have been described above, it is evident that many modifications and variations are possible within the scope of the invention. E. g., the treads can be provided with end elements at both ends. In that case also a link bar can be provided on either side of the staircase. The treads can also be connected to the link bar by means of tabs provided on the link bar, or by means of separate link arms pivotally connected to the treads as well as to the link bar. The link bar may also be a threaded shaft, the shaft providing the adjustment of the treads when tur¬ ned. In that case the treads are connected to the shaft over threaded nuts or sleeves which are displaced on the shaft, when the shaft is turned. The operating means for adjusting the treads can also be designed in many different ways, e. g. as a wheel. Alternatively, the operating means may be a hydralically, pneumatically or electrically driven adjusting means. The operating means can also be adapted to actuate locking means, e. g. movable taps, which can engage in holes in the opposite string, so that the treads can be locked to the strings at both ends. Furthermore, it is not necessary that the treads are adapted to rest on the cross bars between the strings, when the staircase is converted to a ramp. Instead, the treads can be adapted to rest upon projections on the strings. The strings may also at both ends be provided with wedge-shaped shoulders pivotally mounted on the strings for forming adjustable support sur- faces for the side strings.

Claims: Claims 1. Adjustable staircase, comprising two strings (10,11) which are rigidly connected to each other and which have at least two intermediate treads (16-19), each tread being pivotally mounted at its ends around a bearing shaft (25-28) in the adjacent string and each tread (16-19) being connected to at least one link arm (29-32), the link arm being connected to a link means (33) arranged to be adjus¬ ted in such a way that the treads (16-19) by means of the link arms (29-32) are turned around their bearing shafts (25-28), maintaining the upper surfaces of the treads in parallel, so that the angle between the upper surfaces of the treads (16-19) and the longitudinal direction of the strings (10,11) is changed, characterized in that the treads (16-19) are adapted to be turned to a common plane which is substantially parallel with the plane of the strings (10,11), and in that the treads (16-19) have such a width that the upper surfaces of the treads abut upon each other, when the treads are turned to the common plane, so that a substantially continuous, plain surface is formed by the treads. 2. Staircase according to claim 1, characterized in that the treads (16-19) are adapted to rest with their front edges on projections on the strings (10,11), when the treads are positioned in the common plane of the treads. 3. Staircase according to claim 2, characterized in that the strings (10,11) are connected by means of a plurality of cross bars (12-15), one cross bar being provided at each tread in such a way that the front edge of the tread (16-19) rests upon the cross bar, when the tread is posi- tioned in the common plane of the treads. 4. Staircase according to claim 3, in which the treads (16-19) consist of a section of light metal, characterized in that at least one end of each tread (16-19) is provided with an end element (21-24), the rear edge of which is OMP designed with a downward projecting tab (29-32), the tab being pivotally connected to the link means (33) and form¬ ing the link arm. 5. Staircase according to claim 4, characterized in that the end elements (21-24) at the front edges of the treads (16-19) are provided with notches (37-40) engaging with the cross bars (12-15), when the treads are positioned in the plane common to the treads, so that the front edges of the treads in this position along their full length rest upon the cross bars. 6. Staircase according to claim 1, characterized in that the link arms are pivotally connected to the treads (16-19) as well as to the link means (33). 7. Staircase according to any of the preceding claims, cha- racterized in that the link means (33) is provided with an operating lever (20) attached to a tread (19) in the stair¬ case and adapted to engage with a recess (35) in a locking plate (20A) provided with a plurality of recesses (34-36), the locking plate being provided adjacent the operating lever (20) along its path of movement for adjustment and retainment of the treads (16-19) in different angle posi¬ tion in relation to the longitudinal direction of the strings (10,11). 8. Staircase according to claim 1, characterized in that the strings (10,11) consist of telescopic sections (10A,10B,10C) , the link means (41) being linked between the sections in such a way that the link means does not retain telescoping of the sections. 9. Staircase according to claim 1, characterized in that the bearing shafts (25-28) of the treads (16-19) run sub¬ stantially along the longitudinal centerlines of the treads. 10. Staircase according to claim 1, characterized in that the strings (10,11) at their both ends are provided with wedge-shaped shoulders pivotally mounted on the strings for forming adjustable support surfaces for the strings.

Inventors: NYMAN AOKE, NYMAN, AOKE
Applicants: NYMAN AOKE, NYMAN, AOKE
Application year: 1984
Main classification: E04F11
IPC codes: E04F11