Leveller for ladders and other apparatus

{
  "publication_number": "US4770275A",
  "country": "US",
  "kind": "A",
  "title": "Leveller for ladders and other apparatus",
  "abstract": "A leveller for a ladder has a pair of sliding legs telescopically engagable in respective up-right tubes (which may constitute the stiles of the ladder or separate tubes to be fixed to the stile of a ladder), and a substantially uniform continuous flexible ligament such as a wire rope fixed to upper regions of the legs and extending between the tubes and engaging with a support guide means which is fixed relative to the ladder structure or relative to the other apparatus on which the levelling device is mounted. When loaded, the ladder transmits its load through the support guide means to tension the ligament but when the load is removed (for example by subsidence of the ground beneath one of the legs) tension is released from the ligament allowing it to slide over the support guide means to cause rapid readjustment of the relative vertical positions of the ladder to compensate for variations in ground level, whereby the ladder is maintained in its desired attitude.",
  "claims": [
    "1. A levelling apparatus for a structure comprising: (i) a substantially rigid, support guide means adapted to be fixed relative to the structure; (ii) an elongated flexible ligament arranged to extend along the support guide means and to be moveable therealong; (iii) two elongated leg guides; (iv) support legs displaceably mounted in the leg guides and connected to the ends of the elongated ligament such that corresponding displacement of the support legs occurs during adjustment for levelling purposes, and during normal use the load of the structure is transmitted through the support guide means to the elongated ligament which is under tension and transmits the load to the support legs; (v) the ligament being of substantially uniform continuous form along at least the portion arranged for engaging the support guide means whereby there is provided stepless adjustment of the legs and automatic adjustment to compensate for ground subsidence at one leg relative to the other and the improvement comprising (vi) the support guide means having an elongated ligament engagement surface over which the ligament moves during adjustment of the legs and against which the ligament frictionally engages when under constant load, a portion of said engagement surface intermediate the legs being arranged at a higher level than end portions of the support guide means located nearer the legs.",
    "2. A levelling apparatus as claimed in claim 1 and wherein the intermediate portion of the support guide means is a smoothly curved member.",
    "3. A levelling apparatus as claimed in claim 2 wherein the curved member is of shallow inverted \"V\" shape form with a groove extending thereover for accommodating the ligament.",
    "4. A levelling apparatus as claimed in claim 1 wherein the intermediate portion of the support guide means is adapted to be mounted on a lower rung of a ladder which is to be levelled by use of the apparatus.",
    "5. A levelling apparatus as claimed in claim 1, and wherein the end portions of the support guide means comprise smoothly curved guide elements fixed adjacent said legs for guiding the ligament through a turn of about 90°.",
    "6. A levelling device as claimed in claim 1, wherein guide means for the elongated element are provided between the co-operating support legs and the respective leg guides.",
    "7. A levelling device as claimed in claim 1 and wherein the intermediate portion of the support guide means has a grooved profile for accommodating the ligament, and a texturing of the grooved profile corresponding to a texturing of the ligament surface.",
    "8. A levelling device as claim in claim 1 wherein the elongated ligament comprises a wire rope.",
    "9. A levelling apparatus as claim in claim 1, and dimensioned and constructed such that the elongaged leg guides are adapted to be secured to the stiles of a ladder and the support guide means is adapted to be fixed to a rung of the ladder."
  ],
  "description_excerpt": "This invention relates to a levelling apparatus comprising adjustable support legs and in one particular form can be detachably mounted to a ladder to compensate for variations in the surface on which the support legs are to rest. In another form, the apparatus can be incorporated in a ladder.\n\nTo overcome problems arising from uneven terrain, ladders have been equipped with slidably adjustable telescopic legs which can be fixed in a selected position by a locking screw so as to compensate for differences in level between the two legs supporting the ladder. This arrangement, however, is cumbersome to use and difficult to adjust. Other previously published levelling devices are disclosed in the following patent specifications:\n\nDE.A. 2327053 (ZARGES) Dec. 12, 1974\n\nU.S. Pat. No. 2,289,499 (HUSTED) Jul. 14, 1942\n\nU.S. Pat. No. 1,551,395 (HUSTED) Aug. 25, 1925\n\nGB.A. 1369365 (STRUM) Oct. 9, 1974\n\nAU.B. 60183/73 (483196) TEST SOCIETE ANONYME D'ETUDES TECHNIQUES Mar. 13, 1975\n\nWith use of embodiments of the present invention, ladder legs can adjust rapidly for changes caused by subsidence or instability of the ground on which the ladder rests and this can take place safely with a user at the top of the ladder; furthermore, the invention permits adjustment of the ladder without the necessity of locking and unlocking the legs manually.\n\nAccording to the present invention, there is provided a levelling apparatus for a structure comprising:\n\n(i) substantially rigid, support guide means adapted to be fixed relative to the structure;",
  "cpc": [
    "E06C 7/44"
  ],
  "ipc": [
    "E06C 7/44"
  ],
  "inventors": [
    "Patrick Y. Williams"
  ],
  "filing_date": "1986-05-29",
  "publication_date": "1988-09-13",
  "grant_date": "1988-09-13",
  "priority_date": "1985-05-29",
  "application_number": "US-1894487-A",
  "family_id": "3771124",
  "cited_by_count": 42,
  "citations": [
    "US2289499A",
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  ]
}