Geometrical instruments – Straight-line light ray type – Rod or target
Patent
1983-06-27
1985-06-18
Little, Willis
Geometrical instruments
Straight-line light ray type
Rod or target
403109, G01C 1500
Patent
active
045233853
DESCRIPTION:
BRIEF SUMMARY
This invention concerns latches especially latches which lock by an over center action.
Although the latch is applicable to extending tripods, ladders, center firearms and the like, the latch will be described with particular reference to applications where the latch must exert a clamping action which can be applied and released frequently. One example of such an application is a surveyor's rod which consists of two or more mutually connected sliding calibrated sections which when extended for taking readings rely upon a clamping latch to lock the overlapping lengths of the rod sections in a reproducible position. Over the lifetime of the rod thousands of operations of the latch occur. No slip is permissable between the sections when latched closed and rod is in extended position.
Broadly the invention provides a latch of the over centre type adapted to mutually lock a first and second inter engaged, axially slidable members in an axially overlapping disposition by utilising a first pivot axis on the first member and a second parallel pivot axis on the second member characterised in that the latch straddles the two members, is connected to the first member by a pair of pin and slot connections at the first pivot axis, is adapted to engage fulcrum means at a second axis in the second member and extends from the zone of the two axes like a lever whereby the latch is tiltable between a release position wherein the members are slidable and a locked position where the distance between the two axes changes and in doing so locks the members together and a latch arrester holds the latch closed.
More particularly the invention provides a latch of the over center type adapted to mutually lock a first and second interengaged, axially slidable members in an axially overlapping disposition comprising:
(a) a pair of transversely disposed latch-supporting pivots extending from the first member along a first common transverse axis;
(b) a pair of latch fulcrum pivots extending from the second member along a second common transverse axis which is parallel to the first transverse axis;
(c) a latch arrester extending from the first member which constitutes with the other two pairs of pivots a triangular disposition of parts;
(d) a latch body having a face and a pair of sides which extend to or past the latch fulcrum pivots; each side having recess means to engage the associated fulcrum pivot and an elongated slot to engage the associated latch support pivot and at least one of the sides having an edge protrusion, which protrusion must be snapped past the latch arrester to complete the latch action, the arrangement being that for adjustment the first member together with the captive latch body is free to slide relative to the second member, but when the members reach a desired overlap position, the first recess means in each latch side engages the associated fulcrum pivot and the body becomes tiltable about the latter, like ends of the slots engage the latch-supporting pivots drawing the first member in a locking direction, the protrusion is snapped past the latch arrester which urges the first member together with the latch-support pivots further in the locking direction, such further movement being permitted by travel of the pivots in the slots and causing an over centre clamping action, such action being irreversible except by snapping the latch body past the protrusion.
Each pair of pivots may be constituted by a single pin the ends of which project from the sides of the rod so as to provide a pair of supports on a common axis. Thus the pins may be conveniently pressed in the holes drilled in the members. Conversely the latch has projections which engage recesses or dimples in the members. Such connections are cheap and convenient for application to a surveyor's rod where specific latching sites are required but when any overlap position is required instead, the second member has a longitudinal groove in each sidewall thereof and the latch has a pair of projections which slide in the grooves.
One embodiment of the inventio
REFERENCES:
patent: 1824023 (1931-09-01), Langsner
patent: 1971751 (1934-08-01), Keuffel
patent: 2909839 (1959-10-01), Miller
patent: 3120386 (1964-02-01), Janssen
patent: 4029279 (1977-06-01), Nakatani
Hunter Warwick A.
Robinson Allan F.
Little Willis
Napintas Pty. Ltd.
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