Lock for telescoping tubular support

A lock for a tubular telescoping support such as tripod leg includes a clamping lever for locking inner and outer members against telescoping displacement and load bearing portions interposed between the two members such that the locking force applied by the clamp is circumferentially distributed among the clamp and two load bearing portions to thereby prevent flattening of the inner tube under locking clamp force.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains generally to extendable supports and 
mechanisms for locking the same at arbitrarily extended positions, and is 
more particularly directed to a lock for a telescoping tubular leg, 
particularly for use in a tripod of the type used in photographic or 
cinematographic applications among others. 
2. Background of the Invention 
Tripod legs typically consist of a number of telescoping tubular sections 
of successively smaller cross section, each section being slidable within 
a larger section. Each section, except the smallest, is provided with a 
lock for locking together each connected pair of tubular sections against 
telescoping sliding movement so that the support or tripod may be fixed at 
any desired height within the limits of the extendable support. Existing 
tripod leg locks typically have included a camming lever mounted to the 
larger diameter tube section. The lever was pivotable into camming 
engagement with the inner, smaller diameter tube through an opening in the 
outer, larger diameter tube. These locks had the effect of applying 
localized force by the cam lever on one side of the inner tube, which was 
thus wedged against the opposite inner surface of the larger diameter 
tube. The locking force is thus applied at diametrically opposed points of 
the inner tube. If the inner tube is made of thin material, there is a 
possibility of deforming or flattening the inner tube. 
SUMMARY OF THE INVENTION 
The improved locking mechanism disclosed herein overcomes these and other 
shortcomings of the prior art by distributing the locking pressure exerted 
on the inner tube section of the extendable support over a greater area of 
the tube than has been previously possible, and more particularly by 
distributing the locking force among at least three circumferentially 
spaced areas of the inner tube to thereby prevent deformation or 
flattening of the inner tube, even if it is of relatively thin wall 
thickness or has an oval cross section. 
The lock comprises a window opening defined in the outer tube, load bearing 
means interposed between the inner and the outer tubes, the load bearing 
means being disposed circumferentially so as to define an axially 
extending recess diametrically opposed to the window opening, and lever 
means for applying radially inward locking force against the inner tube 
through the window opening, thereby to wedge the inner tube against the 
load bearing means on either side of the recess. 
Desirably the load bearing means and the lever by means of which the 
telescoping support is locked, are all approximately circumferentially 
equidistant from each other so as to balance the forces acting radially 
inwardly on the inner tube. 
In a presently preferred embodiment of the invention the load bearing means 
take the form of a generally cylindrical sleeve inserted coaxially between 
the inner and the outer tubes. The sleeve has a second window opening 
aligned with the aforementioned window opening in the outer tube. The 
sleeve may be split longitudinally or, in the alternative, may have a 
longitudinally extending wall portion of reduced thickness so as to define 
a recess diametrically opposed to the aligned windows. When the inner tube 
is wedged against the sleeve and into the recess, it finds no support at a 
point diametrically opposed to the designed window openings, and is thus 
supported by the sleeve portions of greater thickness adjacent to either 
side of this recess. By properly sizing and proportioning the sleeve 
insert, the locking forces can be distributed among three different points 
symmetrically disposed about the tube circumference. 
The lever means may comprise a camming lever pivotably mounted between the 
arms of a U-shaped band extending about the outer tube such that the 
center portion of the band is drawn against the window opening upon 
actuation of the camming lever, thereby to apply locking force to the 
inner tube through said window opening. The locking mechanism may be 
secured against rotation as well as axial translation relative to the 
outer tube by cooperation of the U-shaped band, the window opening, and 
the lever mechanism, so that no special fasteners or adhesives are 
required for assembly of the telescoping support.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the drawings generally and FIG. 1 in particular a lock 
mechanism 10 is affixed to the outer tube 1 within which is telescopically 
slidable an inner tube 2 of reduced diameter. The lock comprises a camming 
lever 19 provided with a cam element 14 mounted by means of a shaft 15 
between the arms of a U-shaped band 6 extending about the outer tube 1. A 
lever base 13 is positioned between the arms of the band 6 and also 
between the cam element 14 and the outer tube 1. 
Turning now to FIG. 2, the intermediate or bottom portion of the U-shaped 
band 6 overlies a first window opening 4 which may be rectangular in shape 
and is cut in the outer tube 1. A generally cylindrical sleeve insert 3 is 
coaxially interposed between the inner tube 2 and the outer tube 1. A 
second window opening 5 is cut in the sleeve insert 3, and is aligned with 
the first window opening 4 as best appreciated in FIG. 3. 
The camming lever 19 is provided with a cam element 14 which has portion of 
reduced radius 14a and portion of greater radius 14b. The band 6 is drawn 
against the window opening 4 when the camming lever is brought to its down 
or locked position shown in FIG. 2, in which the portion of greater radius 
14b acts against the concave surface 18 of the lever base 13. The band 6 
is released by moving the lever 19 approximately 90 degrees upwardly to an 
erect position in which the cam portion of smaller radius 14a moves into 
the cam recess 18 of the base 13. 
In a first embodiment of the invention illustrated in FIGS. 1-3, the lock 
includes a pressure plate 8 which has a concavely shaped inner surface 
conforming to the outer surface of the inner tube 2. The pressure plate 8 
fits within the aligned first and second window openings 4, 5, and has a 
radially protruding interlock portion 9 which closely fits into an opening 
7 in the band 6 so as to lock the band against rotation about the outer 
tube 1 since the pressure plate 8 is fixed against such rotation within 
the aligned window openings 4, 5. The sleeve 3 is likewise held against 
the rotation within tube 2 by the pressure plate 8 which is fixed within 
the window opening 4 of the outer tube 1. 
The lever base 13 is provided with an interlock portion 17 extending 
radially inwardly into tube 2 through an opening 16 defined therein to 
similarly hold the base piece 13 against displacement along the surface of 
tube 2. The base 13 is further held against separation from the outer tube 
by the overlying cam lever, which in turn is retained by the U-shaped band 
6. The entire lock assembly is thus held in place by cooperation of the 
various elements, thereby facilitating and speeding up the assembly of 
such locks. 
The sleeve insert 3 is of generally cylindrical shape, and may have a 
collar abutting against the end rim of the outer tube 1 as seen in FIG. 2, 
thereby holding the collar against sliding movement into the outer tube 1. 
The sleeve 3 has an axially extending wall portion of reduced thickness 
disposed diametrically opposite the pressure plate 8 as shown in FIGS. 2 
and 3. The reduced wall thickness defines a longitudinal recess 12 in the 
inner surface of the sleeve 3. The sleeve is further split longitudinally 
by slot 11 which extends down the middle of the recess 12. 
When the lever 19 is pivoted to its locked position shown in FIG. 2, the 
cam portion 14b of increased radius is urged against concave camming 
surface 18 of the base 13, thereby drawing the curved intermediate portion 
of the band 6 upwardly in FIG. 3. Ihe pressure plate 8 is thus urged 
radially inwardly against the inner tube 2, wedging the inner tube towards 
the longitudinal recess 12, which extends the full length of the sleeve 3. 
The inner tube does not find support at a point diametrically opposite the 
pressure plate 8 due to the recess defined by the sleeve 3. Instead the 
inner tube is supported by the thicker wall portions of the sleeve 3 on 
either side of the recess 12. The locking forces are thus distributed 
circumferentially among three areas approximately equidistant, as 
suggested by the inwardly pointing arrows in FIG. 3. By so distributing 
the locking forces, the tendency to flatten the inner tube 2 by 
diametrically opposed locking forces conventionally applied in existing 
locks is avoided. 
FIGS. 4 and 5 illustrate an alternate embodiment of the invention wherein 
the lever base 13 and the pressure plate 8 of FIGS. 2 and 3 have been 
eliminated. The cam element 14 of the camming lever has a camming surface 
32 curved to conform to the surface of outer tube 1, as best appreciated 
in FIG. 5, and acts directly against the outer tube rather than against an 
intermediate base element. The intermediate portion of the U-shaped band 6 
has been indented radially to define a clamping portion 31 disposed within 
the aligned window openings 4 and 5 in contact with the inner tube 2. When 
the band 6 is drawn upwardly in FIG. 5 by actuation of the camming lever, 
the clamping portion 31 applies direct radially inward locking force 
against the inner tube 2, urging the same towards the diametrically 
opposed longitudinal recess 12 defined by the sleeve insert 3, such that a 
distribution of the locking forces takes place as described in connection 
with the embodiment of FIGS. 2 and 3. 
The lock in either of the illustrated embodiments further includes a detent 
sleeve 21 coaxially affixed to the inner tube 2 near its end by means of a 
radially inwardly extending portion 24 fitted into an opening 23 defined 
in the inner tube 2. The band 21 may, however, be affixed to the tube 2 by 
any other convenient means. The detent 21 limits the telescoping extension 
of the outer and inner tubes so as to prevent separation of the 
telescoping sections 1 and 2. If such separation is attempted, the detent 
sleeve 21 abuts against the inner end of the sleeve insert 3, thereby 
preventing further separation of the tube sections. Ihe sleeve 3 is 
interlocked to the outer tube 2 by the pressure plate 8, which is disposed 
within the aligned window openings 4 and 5. Yet other means of securing 
the sleeve 3 to the outer tube 2 may be employed. 
The camming lever 19 is desirably provided with a stop 20 which limits 
downward pivoting movement of the camming lever by abutting against the 
base 13 when the portion 14b of extended radius of the cam element 14 is 
correctly aligned with the base 13 for maximum locking force on the band 
6. A similar stop element is provided in the alternate embodiment of FIGS. 
4 and 5, but acts directly against the outer tube section 1. 
While particular embodiments of the invention have been described and 
illustrated for purposes of clarity it will be understood that many 
changes, modifications and substitutions to the invention may be made by 
those possessed of ordinary skill in the art. The scope of the invention 
is therefore limited only by the following claims: