Note: Descriptions are shown in the official language in which they were submitted.
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TILTER MECHANISM FOR A WINDOW BLIND
CROSS REFERENCE TO RELATED APPLICATION
This application is a non-provisional application related to a
provisional application filed June 4, 1996 and assigned Serial No.
60/018,941 and entitled Worm Gear Tilter Mechanism for a Window
Blind.
BACKGROUND OF THE INVENTION
Field of the Invention.
The present invention relates to the field of tilter mechanisms for
window blinds. In particular, the present invention relates to a spur gear
tilter mechanism that has a zinc die cast spur gear, a zinc die cast worm
drive gear and a plastic housing.
Description of the Art.
Window blinds such as Venetian blind structures typically have a
number of horizontal slats or vanes positioned parallel to one another
that are suspended by ladder tapes. The ladder tapes are coupled to a tilt
rod so that when the tilt rod is rotated, the slats of the Venetian blind
rotate about their longitudinal axis. Rotation of the slats provides light
control because the slats can be rotated from a fully open position to a fully
closed position.
A tilter mechanism is coupled to the tilt rod to rotate the tilt rod
which provides rotational control of the slats. Typically this tilter
mechanism is a spur gear that is annularly or concentrically positioned on
the tilt rod and is rotated or driven by a mating worm gear. The worm
gear is generally rotated or driven by either a wand or a cord attached to a
drum or pulley operatively connected to the worm gear. It is conceivable
that other methods exist to drive the spur gear.
Examples of cord driven tilter mechanisms described in the prior art
are: U.S. patent 2,388,000 to Larson that discloses a worm gear coupled to a
spring loaded pulley so that only a single cord is necessary to operate the
shade; U.S. patent 2,855,991 to Loucony that discloses a drum having a
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slidable guide grommet mounted in a slot adjacent the drum that slides
along the drum as the cords are wound around or unwound from the
drum to prevent the cords from becoming displaced and jamming; U.S.
patent 3,357,270 that discloses a pulley in which the cylindrical surface of
5 the pulley is provided with two recesses of different dimension as viewed
in the axial direction of the pulley to provide for very good fit of the cord
into the pulley and for easy positioning of the cord onto the pulley; and
U.K. patent 1,132,985 which discloses a guard that covers the pulley so as
to prevent a cord extending around the pulley from being inadvertently
10 separated therefrom.
Wand driven tilter mechanisms generally have a wand coupled
through a simple linkage positioned on an end of the worm gear that
causes the worm gear to rotate when the wand is rotated. This type of
system is well known in the art, being used for both Venetian blinds and
vertical blinds.
Cord driven mechanisms are often made from stamped steel. The
cord drum is a union of two symmetric pieces spot welded together.
When lifting a heavy shade, these two pieces may separate causing failure
of the part. The stamped steel mechanism is also costly. While the steel
itself may be no more expensive than plastic, the assembly and welding of
the pieces is very time consuming. Die cast zinc worms and spur gears
usually have flashing at the mold line. This flashing is very sharp and
may destroy plastic that it contacts. However, the advantage of the die cast
zinc gears is that they have stronger teeth and will not break during use.
Therefore, it is an objective of the present invention to provide a
spur gear tilt mechanism that has a plastic housing and die cast zinc spur
gears that overcome the shortcomings in the prior art. It is another
objective of the present invention to have a plastic housing that is easy to
assemble. It is a further objective of this invention to have a one-piece
unitary cord drum that is easily positioned into the drive mechanism.
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SUMMARY OF THE INVENTION
The above-discussed objects and other advantages of the present
invention will become clear in this summary of the invention and the
description of the invention that follows. The present invention is a tilt
mechanism that is preferably cord driven. A unique feature of the
invention is the use of a die cast zinc spur gear and a die cast zinc worm
drive gear that are operably housed in a plastic housing. The housing of
the preferred embodiment is made of two plastic parts joined together.
One part optionally houses a cord drum and the other part houses the spur
gear and the worm gear.
The worm gear is supported in the housing by a bushing on a gear
axle. The bushing creates a self-lubricating interface to protect the plastic
housing from wear associated with any flash on the die cast zinc drive
gear.
The spur gear has a bore, with the bore having a hexagonal shape so
as to matingly engage the similarly configured cross-section of the tilt rod.
This bore could be of any shape as long as it intimately engages in driving
relationship with the tilt rod for unitary rotation therewith. The outer
dimension of the spur gear has gear teeth and two outer axle members.
These axle members do not have bushings, but because they are supported
by the tilt rod, will not cause nearly as much wear on the plastic housing as
would the worm gear without a bushing. The spur gear also rotates
through fewer revolutions and sometimes through less than a full
revolution.
In the cord driven arrangement, the cord drum housing
substantially encapsulates the cord drum which in combination with an
operating cord serves as a driver for the mechanism. The cord drum
housing has appropriate openings provided at its base or bottom through
which the two depending ends of the cord pass. The cord drum itself is a
hollow cylindrical body of plastic that has a hexagonal annular opening
that fits around the extended axle of the worm gear. A catch is provided
within the hexagonal annular opening to rele~ hly hold the cord drum to
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the worm gear. The extended axle of the worm gear has a hexagonal cross
section and a detent located inwardly from its end. The catch releasably
mates with the detent and secures the drum to the axle. To remove the
cord drum, the catch can be released so that the cord drum can be slid off
the axle.
The assembly of the two plastic housing parts is very easy because
the two parts are joined in a plane extending perpendicular to the axis of
rotation of the worm gear and in a cross-cut configuration instead of a
longitudinal cut. Thus all the gears and bushings can be easily positioned
and held in place. Once in place, the two parts can be joined without fear
of tipping the part and having the gears fall out. This joining line is in the
opposite direction of most assemblies of this nature. Having only two
plastic parts to join together with mechanical fasteners or other joining
means is very easy and therefore not labor intensive. Because there are
only six parts to be joined (excluding the cord drum), assembly of the parts
is not time consuming, especially in comparison to a stamped metal cord
driven spur gear tilt mechanism.
It is conceivable that many elements of this invention can apply to a
wand driven mechanism, in particular the cross-cut part line of the two
plastic parts and the use of the die cast zinc gears in the plastic housing.
The details of the present invention, both as to its construction and
operation, can best be understood by reference to the accompanying
drawings, in which like numerals refer to like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure lA is a top, front isometric view of the tilter mechanism of
the present invention.
Figure lB is a bottom, rear isometric view of the tilter mechanism
of the present invention.
Figure 2 is an exploded isometric of the tilter mechanism of the
present invention.
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Figure 3 is a top plan of the worm gear of the tilter mechanism of
the present invention.
Figure 4 is a view taken along line 4-4 of Figure 3.
Figure 5 is a view taken along line 5-5 of Figure 3.
Figure 6 is a top, front isometric of the cord drum with portions
removed for clarity.
Figure 7 is a bottom, rear isometric of the cord drum.
Figure 8 is an enlarged section taken along line 8-8 of Figure 6.
Figure 9 is an isometric view of the cord wrap.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The tilter mechanism 10 of the present invention is utilized to
reversibly rotate a tilt rod (not shown) which is conventionally found in
various types of coverings for architectural openings. The tilt rod, as is
well known in the art, is operatively connected to a plurality of parallel
slats or vanes so as to pivot the slats or vanes about their longitudinal axes
upon rotative movement of the tilt rod.
Referring initially to Figures lA and lB, the tilter mechanism 10 of
the present invention has a cord housing portion 12, a gear housing
portion 14 releasably connected to the cord housing portion and a
positioning flange 16. The positioning flange 16 is triangular in shape and
reinforced with a brace 18. The cord housing portion 12 substantially
encapsulates a cord drum 20 about which an operating cord 21 is wrapped.
The gear housing portion 14 has a spur gear section 22 and a drive or
worm gear section 24 which includes axially and oppositely extending axle
members 26. The gear housing portion 14 has slots 28 that rotatably
receive and support the axle members 26 and hold them in place. The gear
housing portion 14 has a cylindrical drive gear housing segrnent 30 that
includes a large cylindrical section 32 that surrounds the drive gear (Fig. 2)
and a small support section 34. The cord housing portion 12 and the gear
housing portion 14 are joined together in the preferred embodiment by
mechanical fasteners 35 such as screws. Of course any type of proper
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fastening means could be used to join the parts including adhesive,
ultrasonic bonding, male female plugs, and their equivalents.
Figure 2 shows an exploded view of the tilter mechanism 10. The
tilter mechanism is shown having the cord housing portion 12, the gear
housing portion 14 and the positioning flange 16 for securing the tilter
mechanism to the headrail of a covering for an architectural opening, such
as a window. The gear housing portion 14 is substantially cubically shaped
with the exception of the drive or worm gear housing segment 30 located
at its base. Gear housing portion 14 has a top wall 36 from which extends
the triangular shaped headrail locking flange 16. Also projecting from top
wall 36 is an angularly shaped female fastening boss 38 that will accept a
mechanical fastener. Gear housing portion 14 has two side walls 40 which
cooperate with the top wall in defining the spur gear section 22 of the
housing. The drive gear housing segment 30 occupies the lower portion of
housing 14 and has the two previously mentioned main parts, the large
cylindrical section 32 that encapsulates the helical teeth 42 of a worm gear
44 and the small cylindrical section 34 that supports a drive gear bushing
46 for a drive gear support axle 48. The drive gear 44 is preferably a worm
gear. Extending outwardly from the base of drive gear housing segment 30
is a base having two opposed female fastening recesses 49 and 49'.
As best seen in Figure 2, worm gear 44 is comprised of four distinct
sections, the worm gear helical teeth 42, the worm or drive gear support
axle 48, a worm gear active support axle 50, and a worm gear drive axle 52.
In the preferred embodiment worm gear drive axle 52 has an annular
detent 54 near its end, and is hexagonal in cross-section.
Worm gear 44 is preferably made of die cast zinc or some other
equally strong material such as cast steel. This choice of materials provides
a worm gear with sufficient teeth strength to overcome the weight load of
some Venetian blinds such as two-inch wood slat blinds which weigh
significantly more than equally sized metal or plastic slat blinds of the
same dimension. If the teeth are made of plastic, these teeth will often fail
when placed under a similar slat load. A negative aspect of using die cast
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metal for worm gear 44 is that flashing (not shown) may occur at the part
line of the die. This flashing can be very sharp and will cause an uneven
diameter of the support axles 48 and 50. The sharp flashing would cut into
any plastic housing supporting it, and the uneven diameter will cause
wobbling of the gear in use.
To circumvent this problem, a pair of annular bushings are slid
over the support axles 48 and 50. This pair of bushings includes drive gear
support bushing 46, and drive gear active support bushing 58. These
bushings are snugly fit over their respective support axles and provide an
even diameter for the axles and serve to free the axles from the die cast
zinc flashing problem. The bushings can be made of any suitable material.
The preferred material is Nylon, though other materials may be used such
as brass, copper or some other suitable plastic, provided that, it is
compatible with the material of the housing.
If the bushings are appropriately dimensioned, the flashing may
also assist in locating and holding the bushings on the respective support
axles.
Placement of worm gear 44 into the gear housing 14 first requires
that support axle bushing 46 is slid over worm gear support axle 48, then
active support axle bushing 58 is slid into position over worm gear active
support axle 50. With both bushings in place, worm gear 44 is slid into
drive gear housing segment 30. The properly positioned support axle
bushing 46 is then positioned into small cylindrical section 34 so that the
helical teeth 42 are seated in large cylindrical section 32. Once worm gear
44 is in place, a spur gear 60 can be positioned in place in the spur gear
section 22 of the housing 14 in mating engagement with the worm gear 44.
The spur gear 60 has a substantially tubular cylindrical base 62
defining the oppositely directed stub axle members 26. Spur gear teeth 64
protrude substantially radially from the base 62 at an oblique angle to the
longitudinal axis of the spur gear. The spur gear has an inner passageway
66 which is hexagonal in shape. The hexagonal shape is preferred for
axially receiving a hexagonal tilt rod (not shown). If the outer shape of the
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tilt rod were something other than hexagonal, then the different shape
would be the preferred shape of the spur gear passageway 66. The axle
members 26 are axially notched to define flexible tabs 68 which can be bent
or crimped inwardly to grip the tilt rod which extends through the
passageway 66 to secure the tilt rod in the housing 14. Spur gear 60 is
preferably also made of die cast metal, preferably zinc. However, it is
advantageous that spur gear 60 be made of the same die cast material as
that of worm gear 44.
With worm gear 44 positioned in the drive or worm gear segment
30 of gear housing 14, spur gear 60 can be slid over the worm gear teeth 42
into the spur gear slots 28. Once the spur gear stub axles 26 are firmly
seated in the back of slots 28, cord drum housing portion 12 can be
positioned in place in abutting relationship with gear housing portion 14.
Cord drum housing portion 12 has a substantially hollow cylindrical
body 70 with a back plate 72 and an open bottom that is substantially closed
off with a bottom plate 76. The bottom plate 76 has an elongated
rectangular slot 78 extending axially along the right side as viewed from
the left in Fig. lA, and a relatively short rectangular slot 80 on the opposite
side. The relatively long slot extends the full length of the cord drum 20
when it is positioned in the cord drum housing portion 12, and the
relatively short slot is positioned approximately midway along the length
of the cord housing portion 12 so as to be positioned adjacent to the
innermost end of the cord drum 20 and so as to extend approximately half
way along the length of the cord drum. The slots are provided to receive
the depending ends of the operating cord 21 which is wound on the cord
drum 20. There is no front surface on the cylindrical body 70 so the front
remains open to receive the cord drum 20. Back plate 72 has a circular
opening that receives the worm gear active support axle 50 and the worm
gear drive axle 52. Spur gear active support bushing 58 rotatably fits into
the circular opening of back plate 72. Back plate 72 at its top has a back
plate fastening recess 82 which mates with the annular shape of female
fastening boss 38 on the top wall 36 of the gear housing 14. Extending from
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the back plate toward the gear housing are spur gear stub axle supports 84.
Spur gear stub axles 26 slide into a portion of the spur gear slots 28 that are
not occupied by the spur gear stub axle members 26. At the bottom corners
of the back plate 72 are lower back plate fastening recesses 86. The lower
back plate fastening recesses 86 are alignable with female fastening recesses
49 and 49'. A pair of elongated ribs 88 are formed along opposite sides of
the internal surface of the cylindrical body 70 and helps to confine the
control cord on the cord drum in a uniform wrapped manner as will be
apparent with the description that follows.
To couple the cord housing portion 12 to the gear housing portion
14, the circular opening in the back plate 72 is slid over the worm gear
drive axle 52, active support bushing 58 and worm gear active support axle
50. Once the support bushing 58 is properly positioned in the circular
opening in the back plate 72, the fastening recesses 82 and 86 are aligned
with the female fastening bosses or recesses 38, 49 and 49'. With cord
housing portion 12 and gear housing portion 14 in proper alignment and
with worm gear 44 and spur gear 60 properly positioned in operative
engagement with the bushings in place, mechanical fasteners 35 are passed
into the passageways defined by the alignment of the female fastening
holes and tightened into place. The preferred fastener is a screw, but
rivets, adhesive, ultrasonic bonding and other alternative methods may be
used. Once fasteners 90 are tightened, cord drum 20 angularly wrapped
with cord 21 can be slid into position over the worm gear drive axle 52 and
snapped into place. Cord 21 can then extend through the rectangular 78
and square slots 80 in the bottom plate 76 of the cord housing portion 12.
Regular bearing grease can be added to the gear housing portion 14
in an amount to fill 1/4 to 1/2 of the helical teeth on the worm gear. This
grease lubricates the gears and provides for smoother operation of the tilt
mechanism 10.
Cord drum 20 is illustrated in more detail in Figures 6, 7 and 8 and
can be seen to have a substantially cylindrical body 92 having an outer
diameter that is smaller than the inner diameter of the hollow cylindrical
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body 70. The body 92 has a hole 94 aligned with a notch formed at opposite
ends to facilitate attachment of the control cord 21 as will be described
hereafter. Cord drum 20 has an inner sleeve 96 that fits over the worm
gear drive axle 52. Rather than using solid material between the body 92
and the inner sleeve 96, a plurality of radial ribs 98 extend between the
body 92 and the inner sleeve 96. The ribs reduce the amount of material
used to manufacture the drum without jeopardizing the strength of the
drum. The ribs run the full length of the sleeve. A flexible catch arm 100
is provided in the wall of the inner sleeve 96 of the drum 20. The catch
arm has an enlarged head 102 that mates with the detent 54 on the worm
gear drive axle 52. Once the enlarged head 102 is caught in the detent 54,
the cord drum 20 is held in place and cannot be moved until catch arm 100
is released. A relatively large disc 104 forms the end wall of the cord drum
20. The disc defines a lip or annular flange 106 which help to confine the
control cord 21 in a helically wrapped condition on the body 70 of the cord
drum.
Control cord 21 is captured on the drum 20 by passing the cord
inwardly through the hole 94 and along the space or passageway between
the body 92 and the sleeve 96 before pulling the cord out through the
notch 95 at the opposite end of the drum. The cord is then wound
counterclockwise around the outer diameter of the cord drum body 92 (as
viewed from the end of the drum having flange 106) with each wrap
getting closer to the flange end of the drum. The end of the cord extending
through hole 94 is extended through the relatively long rectangular slot 78
and the end of the cord depending from the drum after being wrapped
around the drum is extended through the relatively short slot 80. The
ends of the cord then depend from housing portion 20 where they are
positioned for manipulation by an operator of the system. The relatively
long rectangular slot 78 allows the cord to accumulate in a helical pattern
on the body 92 as the drum is rotated while the relatively short rectangular
slot 80 encourages the cord to wrap on the drum at an angle which
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discourages the cord from overlapping itself thereby permitting a smooth
and dependable one-layer helical wrap of the cord on the drum.
The housing portions of the tilt mechanism 10 are advantageously
made from acetal though any number of suitable plastics may be used
5 including polyvinylchloride, Ultem, nylon, glass filled melamine, high
density polyethylene, polypropylene, polyester, epoxy, alone or with any
suitable filler.
It will be appreciated that the method and sequence of assembly
described above is only a preferred method and any other method may be
10 suitable. It is important to note, that the preferred embodiment of the
tilter mechanism 10 is designed for use with a Venetian blind, but could be
used with any window blind that requires a tilt mechanism such as a
vertical blind.
A person of ordinary skill in the art would be able to understand
how to mount the tilter mechanism into the headrail of a Venetian blind.
The tilt rod of the Venetian blind would pass through the passageway 66 of
the spur gear as described previously. Once the tilt rod is in position, the
unit would be snapped into a hole found on the base of a Venetian blind
headrail. Flange 16 would then be captured under the back rim of the
headrail and the cord would be drawn through the headrail hole to
depend therefrom along the slats of the blind.
While the preferred embodiment of the invention discloses the use
of a cord drum to drive the worm gear, an operating wand could be used to
drive the worm gear with modifications which would be apparent to those
skilled in the art.
While the particular worm gear as herein shown and described in
detail is fully capable of attaining the above-described objects of the
invention, it is to be understood that it is the presently preferred
embodiment of the present invention and is thus representative of the
subject matter which is broadly contemplated by the present invention,
that the scope of the present invention fully encompasses other
embodiments which may become apparent to those skilled in the art, and
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that the scope of the present invention is accordingly to be limited by
nothing other than the appended claims.
