Note: Descriptions are shown in the official language in which they were submitted.
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SCRE~ ADJUSIMENT ME~L~NISM WITh PRE-SEr BACKL~SH
BACXGROUND OF ~IE INVENTION
1. Field of the Invention
This invention relates to screw adjustment mechanisms for ink fountain
blades and the like, and more particularly to a screw adjustment
mechanism wherein tlle amount of looseness (thread backlash) between two
threadedly mated parts can be easily adjusted to a desired minimum.
2. Description of the Prior Art
Threaded shafts (screws) are much used to change the positional
relationship between two or more parts. Normally one of such parts is
longitudinally movable but held against rotation about a mating screw,
and hence is displaced axially of the screw and moved with respect to
the other part on turning of the screw. Unfortunately, the amount of
looseness of fit (thread backlash) that occurs between mating threaded
parts is unpredictable, with the result that the adjusted relationship
between the two parts can not be made as precise as is desi~able without
resort to expensive components.
But even expensive components are not a complete answer to the
problem. Wear and tear resulting from use of the screw adjustment
mechanism eventually results in a looseness of fit which makes precise
adjustment of the part impossible. The problem becomes acute when
differe~t metals are in contact, and particularly so when one of the metals
is a soft one like aluminum of which ink fountain blades are frequently
made.
Existing technology includes many ways of adjusting for thread
backlash where the threaded components act as an "in and out" adjustment
of a mechanism. A11 methods employed to date require an assembly procedure
which either requires extreme accuracy of the mating parts, or a
_ calibrating adjus~nent to be made after final assembly of the constituent
parts. /A11 existing methods of accomplishing the desired results ~re
. either too expensive or difficult to adjust to allow their use in a
U predictable manner when many such assemblies are re~uired. With the
increased use of computer control of adjusting mechanisms, the need for
reliable, ine~ sive n~ans of achieving innproved Fit in threaded
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mechanisms is rapidly exceeding the pr~cticality of the means of achieving
it.
Particular prior art inclu~1es p~tet1t nos. 9,000,695; 4,655,133;
1,275,34~; 2,583,640; 4,534,290; ~,581,994; 3,559,573; 3,730,090; and
4,058,058. Patent 4,000,695 (Perretta) shows an ink fountain blade
assembly wherein a screw 16 is used to adjust the matingly-threaded ink
fountain blade 13 with respect to the assembly frame. Patent 4,655,133
(O'Dea et al3 shows the use oE a spring 3~ about a screw 36 to compensate
yieldably for backlash. Showing similar arrangements are patent nos.
1,275,348 (Wood); 2,583,640 (Faeber); 4,534,290 (Schroder et al); and
4,581,994 (Wildman). Patent no. 3,559,573 (Hantscho) shows a
differential~y tl1readed screw 26 matingly engaging two threaded parts
20 and 22, but no backl~sh adjus~1ent mec11anism. Patent no. 3,730,090
(Lamberg) also shows a differential thread assembly, but no backlash
adjustment mechanism. Patent no. 4,058,058 (~lantscho) shows use of a
set screw 56 to hold a screw 4~ in place with respect to its mating
member, and use of a set screw 52 extending into a recess 54
to limit longitudinal movement of a blade 37.
SUMMARY OF ~-E INVENrION
A main object of the invention is to provide a screw adjusting
med1anism for ink fountain blade assemblies and the like, wherein the
backlash between parts threadedly mated, can be adjustably limited.
Another object of the invention is to provide such a screw adjustment
mechanism that allows easy adjustment of the amount of desired backlash
prior to final assembly of the mating threaded parts.
Another object of the invention is to provide such a screw adjusting
mechanism wherein the constituent parts can be inexpensive to manufacture.
Still another object of the invention is to provide such a screw
adjusting mechanism that permits assembly without complicated calibration.
Yet another object of the invention is to provide such a screw
adjustment mechanism that allows subsequent readjustment to compensate
_ for wear between the threaded parts.
Thqse objects of the invention are achieved through the use of a
spring between two bushings threadedly mated to a screw and locking the
bushings to one of two parts to be moved relative to each other on turning
I of the screw. The spring causes the bushings to be oppositely situated,
, th eadwise, i eir relationships to the screw, efore they are locked
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finnly in place Witll respect to the part ~o be adjusted and to each other.
Lost motion possibilities between the sc~ew and the part to be adjusted
are thus reduced if not eliminat~d.
~ feature of the invel1tioll is t:llat the tightness of the fit can be
increased or decreased by the prop~r selection of the size or constant
of a spring, or by the amount that the spring is tensioned.
BRIEF DESCRIPTIGN OF T~ DRAWINGS
The above objects, advantages and features of the invention will
be apparent from a consideration of the following description of an
illustrative embodiment of the invention when taken together with the
accompanying drawings wherein:
Fig. 1 is a schematic sectional view of a screw adjustment mechanism
constructed according to the invention.
Fig. 2 is a pre-assembly, p~rtly exploded view of the mechanism of
Fig, 1.
DEr~ILED DESCRIPTION OF T~E INVENTION
Referring now to Fig. 1, a screw adjusting mechanism constructed
according to the invention is shown as including a threaded stainless
steel shaft 1 fitted with two threaded bronze bushings 3 and 5
respectively. The bushings are separated on the shaft 1 which mounts
there between a steel coil spring 7 that is compressed to approximately
one-half its free length. The bushings are snugly located in a hole 19
- in a longitudinally moveable part 9 which may be an aluminum alloy ink
fountain blade. Set screws 11 and 13 threaded in the part 9 engage the
bushings 3 and 5 respectively to hold the bushings against movement with
respect to part 9.
me screw adjusting mechanism of Fig. 1 would be adjusted for backlash
prior to final assembly. ~ss~mbly may be begun by first screwing bushing
5 on one end of the stainless steel shaft 1, then placing ~he coil
spring 7 on the shaft, and then threading on the shaft the bùshing 3.
_ m e bushing 3 will be screwed on shaft 1 to compress a desired amount
the coi~ spring 7 between it and the other bushing 5. Cbmpression of
the coil spring 7 causes it to exert axial forces on the bushings which
results in the right side tFig. 2) of the thread of bushings 5 resting
against the le~t side of the thread of the stainless steel shaft 1 at
point 17. It also results in the left side of the thread of bushing 3
esting against the right slde of the thread of the stainless steel
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shaft 1 at point 15. It will be evident that any looseness between either
of the bushings and the shaft is now caused by the coil spring 7 to be
taken in yielding engagement. It will also be evident that this yielding
el~gagement is op~ositc for tl1e two busl~ gs. It will be evident too that
axial forces urged by the compression spring and hence the forces acting
between the bushing and the shaft threads can be varied by choosing springs
of different sizes and constants, and by varying the location of the
bushings with respect ~o each other on the shaft.
Assembly of the screw adjustment mechanism is completed by inserting
the end of the steel shaft 1 with its bushings and coil spring fitted
in place into the opening 19 formed in the longitudinally movable part
9. The shaft is inserted to a depth which permits threaded
bushing 3 to fall adjacent set screw 11 and thre~ded bushing 5 to fall
adjacent set screw 13. With the coil sprin~ 7 continuing to keep the
bushings 3 and 5 in intimate contact with the shaft 1 at points 15
and 17, the set screws 3 and 5 are tightened to secure bushings 3 and
5 fixedly in place with respect to the longitudinally movable part 9.
In fixing the bushings with respect to the part, the looseness of bushings
with respect to the shaft 1 is also fixed. Basically, the entity of the
part 9 acting through the two bushings 3 and 5 is now in firm engagement
with each side of the thread on shaft 1, essentially eliminating any
looseness ~threaded backlash).
After assembly, the shaft 1 remains free to rotate srnoothly with
a minirnum of backlash relative to the mating part 9. Should it be or
become desirable to change the tightness of the fit, adjustment may be
- made by loosening either of the set screws 11 and 13 and turning the
shaft ~o advance it and the (now) loose bushing towards or away from the
still fixed bushing to increase or decrease spring 7 compression and
hence the axial forces acting on the threads. The loosened set screw
would thereafter be tightened. Of course, both set screws 11 and 13 may
be loosened to allow removal of the shaft 1, bushings 3 and 5, and spring
7, to enable external adjustment of the thread backlash.
It should be apparent that applicant has provided for the precise
_ adjustment of backlash between two mating threaded parts used in a
controlimechanism without requiring constituent parts that are costly
~ of manufacture. Furthermore that assembly can be made without
t cornplicated calibration. Moreover, applicant's invention allows subseqyent
readjustment of the tightness of fit in a simple uncomplicated manner.
It should also be observed that the relatively soft alu~inum alloy part
is effectively isolated from thread contact to effectively neutralize
it as a source of looseness of fit.
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It will be appreciated tllat tlle Eoregoing is to be considered as
illustrative only of the principles of the invention, and that while
certain novel features of the invention have been shown and described,
various omissions, substitutiol~s and changcs in the form and detail of
the mechanism illustrated and in their use and operation can be made by
those skilled in the art without de~rting from the spirit of the
invention.
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