BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a bi-directional clutch, and,
more particularly, to a clutch having internal gears to provide a mechanical advantage.
The clutch is particularly useful for operating a window dressing such as a roller
Description of the Prior Art
Roller shades are often used as window dressing and provide
both a practical and an aesthetic function. Typically, a roller shade includes a
tubular mandrel and a decorative panel wound on the mandrel. The mandrel can be
selectively rotated by a user either in one direction or the other causing the panel
to be either raised or lowered, depending on how it is wound on the mandrel. The
roller shade is provided at its two ends with mounting means so that it can be mounted
on a window frame or other similar location, using suitable brackets. Normally,
one end of the roller shade is a simple rotatable coupling that allows the roller
shade to rotate with respect to the bracket. The other end is provided with a bi-directional
clutch that provides a mechanical advantage during the operation of the roller shade.
Bi-directional clutch mechanisms of this type are disclosed in U. S. Patent Nos.
, incorporated herein by reference. These references disclose clutch mechanisms
in which the mechanical advantage is developed between a large pulley and a small
shaft. One or more springs are also provided as a means for locking the mandrel
to prevent undesirable rotation. Other clutch mechanisms are also known which are
based on frictional braking. U. S. Patents Nos.
also disclose bi- directional clutches useable for roller shades.
Recently there has been an increased need for roller shades
having larger sizes and/or weights which in turn require stronger clutch mechanisms
with a larger mechanical advantage, normally requiring more space. However, in the
existing roller blinds, since mechanical advantage is dependent on the relative
diameters of a pulley and a small shaft, and since the shaft has already been minimized,
the mechanical advantage can be increased by increasing the size of the pulley.
However, this is not a practical solution because space is too limited to accommodate
a larger pulley, and in addition, a larger pulley may not be aesthetically unacceptable.
In addition, a stronger clutch mechanism requires more
springs for locking the roller blind to prevent its undesirable rotation. However,
more springs complicate the structure of the clutch mechanism, and increase the
force required to operate the same.
OBJECTIVES AND SUMMARY OF THE INVENTION
Accordingly, it is abroad objective of the present invention
to provide an improved bi-directional clutch particularly suited for roller shades
and other window dressings.
It is a further objective to reduce the number of springs
required and thereby reduce the inherent friction associated with the operation
of the bidirectional multi-spring clutch.
It is still a further objective to locate the gear box
between the user interface (for example, a cord or a bead chain) and the wrap springs
of the clutch to permit the use of less force in releasing the wrap spring of the
clutch to yield a user interface with a smother performance.
Yet another objective is to provide a clutch mechanism
that can provide a larger mechanical advantage then previous clutch mechanisms but
without a corresponding increase in size.
According to the present invention there is provided a
clutch for operating a window dressing as defined in claim 1. Additional, alternative
or preferred features are defined in the dependent claims.
Embodiments of the invention may include features of a
related aspect providing a clutch, particularly useful for operating a window dressing,
that includes an input member arranged to be activated by a user for operating the
window dressing; an output member coupled to the window dressing, antirotational
means adapted to prevent the output member from rotation in response to a rotational
torque from the window dressing, and a gear box coupled to the input member and
adapted to transmit a rotational motion at a mechanical advantage to the output
member in response to the activation of said input member. The input member may
include an elongated element such as a cord, a string, a chain, etc., arranged for
pulling by the user. The gear box includes a gear pulley coupled to the elongated
member and arranged to rotate in response to the pulling of the elongated element.
The gear box includes a stationary gear, a stationary drum
attached to the stationary gear, a rotating member mounted coaxially on the drum
and a planetary gear arranged between the gear pulley and the stationary gear to
transfer rotation to the rotating member.
The antirotational means is associated with the stationary
drum and the rotating member and it includes spring coils adapted to selectively
form an interference fit with the stationary drum, thereby preventing undesirable
rotation of the rotation member.
Embodiments of the invention may include features of another
aspect, in which the clutch is provided for operating a window dressing mounted
on a stationary structure, and includes an end member adapted for mounting the window
dressing to the stationary structure. The end member receives a cord adapted for
manipulation by a user to operate the window dressing. The end member includes a
gear box adapted to translate a movement of the cord into a rotation at a preselected
mechanical advantage. An output member is adapted to couple the rotation to the
window dressing. In addition, an antirotational member is coupled to the output
member to prevent undesirable rotation.
Further objectives, features and advantages of the invention
will become apparent upon consideration of the following detailed description of
preferred, but nonetheless illustrative embodiments, when considered in conjunction
with the following drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE DRAWINGS
- Fig. 1 shows an exploded orthogonal view of a bi-directional clutch mechanism
constructed in accordance with this invention and that can incorporated into a roller
- Fig. 2 shows an exploded orthogonal view of the mechanism of Fig. 1 taken from
a different angle;
- Fig. 3 shows an orthogonal view of an assembled bi-directional clutch mechanism
in accordance with this invention; and
- Fig. 4 shows a cross-sectional view taken along lines 4-4 in Fig. 3.
Referring now to the drawings, and more particularly to
Figs. 1 and 2, a clutch 10 constructed in accordance with this invention includes
an end member consisting of a protective guard 12 including an outer disk 14. The
outer disk 14 is adapted to couple to a bracket (not shown) used to mount a respective
window dressing to a structure (such as a window frame) in a conventional manner.
A lip 16 is disposed circumferentially around the disk 14 and is cut at one location
to form a mouth 18. Attached to an inner surface of the guard 12 is a cylindrical
drum20. Disposed at the distal axial end of this drum 20, adjacent to the inner
wall of guard 12, there is provided a toothed gear 22. The opposite or free end
of the drum 20 is provided with two semicircular extensions 24 separated by a slot
26. All the remaining elements of the clutch 10 are mounted telescopically on drum
20 as described in more detail below.
Next, the clutch has a gear pulley 30. Gear pulley 30 has
the shape of a ring with the outer surface being formed with a plurality of teeth
32 separated by depressions 34. The teeth 32 and depressions 34 are constructed
and arranged to entrain a beaded cord described below in conjunction with Fig. 3.
The inner surface of the gear pulley 30 has a plurality of gear teeth 36.
Next, the clutch 10 has a spring drive 40 formed of a ring-shaped
hub 42 and a tubular boss 44. The ring-shaped hub 42 has on its surface facing guard
12 two or more axles 46 (in Fig. 2 three such axles are shown). Each of the axle
supports a planetary gear 48. The intermediate gears are rotatably supported on
the axles 46. Each planetary gear 48 has outer teeth 48A.
The boss 44 has an inner diameter that is larger than the
diameter of drum 20 so that when the boss 44 is slipped over the drum 20, there
is an annular space therebetween. The clutch 10 has two identical coil springs 50A,
50B that are mounted between the drum 20 and the boss 44. Each of the springs 50A,
50B has an inner tang 52A, 52B and an outer tang 54A, 54B. These tangs extend radially
outwardly as shown. The coil springs are wound precisely with a diameter that is
preferably slightly smaller than the diameter of drum 20. Moreover, the coil springs
are preferably made of a high quality steel and preferably have a rectangular cross
section. As a result, the coils of the springs present an almost continuous inner
cylindrical surface that rests on, and forms an interference fit with, the outer
surface of drum 20. The coil springs 50A, 50B are mounted on the drum by squeezing
their respective inner and outer tangs together thereby causing the coils of the
springs to expand and slip over the drum 20. When the tangs are released, the springs
settle snugly over the drum 20.
Boss 44 is formed with slots 46,48. Slot 46 is defined
between two axial edges 46A, 46B. The angular dimension of these slots is slightly
larger than the angular separation between the tangs of one of the coils 50,52.
The front end of the boss 44 as seen in Fig. 1 is terminated with a circular hole
49. When the spring drive 40 is inserted over the drum 20, its hub 42 defines an
annular chamber with the outer disk 14. This annular chamber houses and protects
the gear pulley 30 and planetary gears 48.
Finally, a tubular housing 60 fits over the boss 44. The
tubular housing has a front end with a small axial hole 62. This hole 62 is sized
and shaped to receive the extensions 24 on drum 20.
The housing 60 has in its cylindrical surface 64 two axial
troughs or keys 66 and 68. The trough 66 is formed with two interior axial walls
66A, 66B and trough 68 is formed with two axial walls 68A,68B. The angular distance
between these walls is smaller than the angular spacing between the tangs of the
Typically, window dressings consist of a tubular member
supporting a decorative panel. The housing 60 is arranged and constructed so that
it can be mated with the tubular member (not shown) of a decorative panel. In this
manner the decorative panel is supported at least at one end by the clutch 10.
The clutch is assembled as follows. First, a cord 90 is
trained around the gear pulley 30. Preferably the cord 90 is formed with spherical
beads 92 or other protrusions that fit between the teeth 32. Alternatively, cord
90 may have a uniform cross section, in which case an alternative pulley design
can be implemented. Gear pulley 30 is positioned adjacent to disk 12, with the cord
90 extending through the mouth 18.
Next, the coil spring 50A, 50B are installed on the drum
20 the planetary gears 48 are installed on axles 46 and the spring drive is telescopically
positioned over the drum 20, with the planetary gears48 engaging the teeth 36 on
the gear pulley and gear 22. The spring drive 40 is positioned over the drum 20
and coil springs 50A, 50B so that the tangs of each coil are disposed in one of
the slots 46,48. For example, the tangs 52A, 54A of coil spring 50A can be positioned
in slot 48 while the tangs 52B, 54B of coil spring50B can be positioned in slot
46. The tangs maintain their angular separation as they are seated in these slots.
Next, the housing 60 is moved telescopically over the boss
44, with axial troughs 66,68 being positioned over slots 47,48. The troughs 66,68
are dimensioned angular so that each trough fits radially and angularly between
the tangs of one of the coil springs. As the housing 60 is being moved toward the
disk 14, the extensions 24 exit through hole 62. The separation between the two
extensions 24 is slightly larger than the diameter of the hole 62. As a result,
when the housing 60 reaches its final position over the boss 44, the extensions
26 extend outwardly of the hole 62. They flex slightly radially toward each other
and cooperate with the housing to hold all the clutch elements together as a single
assembly, as shown in Figs. 3 and 4.
The clutch 10 operates as follows. Normally, there are
no rotational forces or torques applied to the clutch and the tangs 52A, 54A, 52B,
54B are positioned in the slots 46,48, respectively, and are separated by troughs
66,68. The housing 60 is coupled to a window dressing (not shown). Any rotational
force on the window dressing causes a torque X to be applied to the housing 60 in
either a clockwise or counterclockwise direction, as shown in Fig. 4. If the torque
is in the clockwise direction, the housing 60 tries to move in response in the clockwise
direction. This movement causes the axial wall 66B of trough 66 to move clockwise
and apply a clockwise angular force on tang 52B. The coil spring 52 is wound in
such a manner that this force on tang 52B causes the coil spring to tighten around
drum 20. In this manner, the spring coil 52 resists the torque X. A similar resistance
force is generated between the axial wall68B and tang 54A of coil 50A. If the torque
X is applied in the counterclockwise direction, the axial wall 66A applies a similar
force on tang54B. Thus the coil springs 50A, 50B, the spring drive 40 and the housing
60 are constructed and arranged to form a counter-rotational locking means that
prevents the rotation of housing 60 from rotating in response to a torque applied
to the housing.
Pulling cord 90 causes the gear pulley 30 to turn around
the common axis of the clutch 10. As the gear pulley turns, it forces the planetary
gears to turn in a planetary motion around gear 22. This rotation forces the spring
drive 40. The speed of rotation of the housing 60 and the force applied to it (and
hence the mechanical advantage of the clutch) depends on the relative sizes of the
gear pulley 30 and planetary gears 48. Thus, the protection guard 12, the gear pulley
30 and the planetary gears 48 are arranged and constructed to transfer a rotational
motion in either direction to the spring drive 40 at a predetermined mechanical
advantage. Therefore, these elements cooperate to forma bidirectional gear box for
transferring rotational motion in either direction from the cord 90 to the spring
Referring again to Fig. 4, as the spring drive 40 starts
rotating in either direction, as indicated by arrow Y, one of the axial edges 46A,
46B comes into contact and applies a tangential force on one of the tangs 52B or
54B. This force causes the spring coil 50B to expand radially outward, thereby eliminating,
or at least reducing the interference fit between the spring coil 50B and the surface
of the drum 22. A similar action takes place in slot 47 to cause spring coil 50A
to expand. As a result, the spring drive 40 is free to rotate with respect to drum
22. As the spring drive 40 continues to rotate, one of the edges 46A, 46B comes
into contact (through respective tangs) with the walls of the troughs 66, N8. in
this manner the rotation of the spring drive 40 is transmitted to the housing 60.
Thus the counter-rotational locking means is disabled by the rotation of the spring
Importantly, because of the arrangement of the gears in
the gear box, the directions of rotation of the gear pulley and the housing 60 are
the same, and therefore the clutch is easier and more intuitive to operate.
The housing is used to support and rotate or otherwise
operate a standard window treatment.
The present invention provides several advantages over
the prior art. It provides a higher mechanical advantage without an increase in
size. It makes use of at least some of the components of a standard clutch to perform
multiple functions. It provides rotation of the input member (the gear pulley) and
the output member (the housing) in the same direction because the improved mechanical
advantage of the / clutch requires less spring coils then the prior art. Another
advantage is that because of the clutch mechanism, the friction exerted by the coil
spring is lower than in standard systems and, hence, require less force to raise
and lower the window dressing. Moreover, placing the gear box between the coil springs
and the pulley results in a device that operates more smoothly.
While the invention has been described with reference to
several particular embodiments, it is to be understood that these embodiments are
merely illustrative of the principles of the invention. Accordingly, the embodiments
described in particular should be considered as exemplary, not limiting, with respect
to the following claims. For example, the cord could be replaced by a chain, a rope,
a string, or any other similar elongated member known in the art. Similarly, the
antirotational means may be implemented using other means besides the coiled springs.