WO2008001323A2

WO2008001323A2 - Umbrella rib

Info

Publication number: WO2008001323A2
Application number: PCT/IB2007/052515
Authority: WO
Inventors: Chaim Simcha Amsel
Original assignee: Chaim Simcha Amsel
Priority date: 2006-06-28
Filing date: 2007-06-28
Publication date: 2008-01-03
Also published as: WO2008001323A3; IL176604A0

Abstract

An umbrella rib (1) is disclosed, comprising a body having a proximal end (Ia), a distal end (1b), and a most distant fulcrum (1c) at a location there between, which is the most distant point on the rib supported to the umbrella stick. The rib is characterized by a directional bending unit (2; 6) constituting a member of the rib body in some mid portion between the distal end and the most distant fulcrum. The directional bending unit is configured to allow bending a rib portion (4) in a first direction (CW) respective to a linearity axis (7) of the rib (1), in response to a small shaping force interacting with the rib through a tensioning canopy fabric, and to prevent bending of said rib's portion (4) in a direction (CCW) opposite to the first even by forces to a substantial extent greater than the shaping force.

Description

UMBRELLA RIB

FIELD OF THE INVENTION

This invention relates to the field of umbrella ribs fabricated from polymeric materials.

BACKGROUND OF THE INVENTION

Umbrella ribs function in a folding construction supporting the umbrella fabric. Under normal operation conditions the forces acting on umbrella canopy fabric increase toward peak values when the canopy becomes fully deployed, and when wind gusts tend to overturn the canopy. These forces are transmitted from the canopy fabric to the canopy ribs, and may act on the ribs in opposite directions depending on the direction of the wind. The ribs thus have to be strong enough to withstand forces which may act on them from anyone of two main opposite directions.

In addition to their strength requirements, the shape of umbrella ribs should change between a substantially straight contour when the umbrella is folded, and a curved one, when the canopy is fully deployed. The straight design is aimed to allow the folded ribs lay parallel to the stick of the umbrella when the umbrella is folded, and the curved design provides for the typical mushroom-like shape taken by canopies of opened umbrellas

(sometimes termed also "bell-shape"). Umbrella ribs thus should further be sufficiently elastic so as to take the typical shape when the umbrella is opened and return to linearity when the umbrella is folded.

As far as the elasticity properties more easily allow the formation of a mushroom-like canopy by curving the ribs (which happen to be when the rib material is more flexible or less resistant) , the umbrella becomes less resistant to wind gusts tending to invert the mushroom shape and to deform the shape of the ribs. Vice versa, in case the rib is made stiffer and less elastic, it may not allow full deployment of the canopy by conventional deployment forces and/or may not take the customary curved shape of umbrellas.

It is therefore may be well understood that the ribs' elasticity should obey certain limitations and that in order to have them withstanding intense wind gusts, the ribs should have certain resistance, which in turn increases their resistance to forces transmitted to the ribs for bending them to take the mushroom-like curvature .

In this regard it should be noticed that the main curvature of a rib in a mushroom-like canopy is located remotely from the umbrella's stick, in some mid portion of the rib nearer to the free end of the rib. Under such conditions the forces exerted on the ribs by a tensioning canopy fabric tending to bend the ribs for taking the customary mushroom-like shape, have certain lever advantage versus the force acting to deploy the canopy. This is because the resistance of the rib to its bending enjoys a lever arm being the average distance between the bending site and the rib pivoting axis. Since the bending site is close to the free end of the rib, the lever arm's length equals almost to the entire rib's length. On the other hand, the force acting to deploy the canopy enjoys significantly shorter lever arm being the distance between the rib's pivoting axis and a rib support site

(which is the site from which the rib is bridged to the stick e.g. by a strut), which is normally shorter than the distance from said bending site to the pivoting axis.

Accordingly, the force for complying with tensioning the umbrella increases as the rib support site is designed closer to the rib's pivoting axis.

The need in providing increased tensioning force becomes more difficult to comply with when dealing with strutless umbrellas .

In strutless umbrellas the rib support site is very close to the rib's pivoting axis. This is because in strutless umbrellas the rib support site is located at the proximal end of the rib, near the longitudinal axis of the umbrella. Furthermore, in strutless umbrellas there is a certain motivation to shorten the distance between the support site and the rib's axis as much as possible since in such umbrellas said distance has a significant impact on the diameter of the umbrella when folded.

U.S. 5,638,846 discloses ribs for strutless umbrellas, the ribs tapered towards their free ends are aimed at providing for a mushroom-like canopy shape. The resulting increased elasticity of the ribs which provides for a mushroom-like shape of the canopy may be considered a drawback when dealing with winds tending to overturn the canopy . The need in having the ribs resistant against wind gusts tending to overturn the canopy, without sacrificing their responsiveness to a tensioning force aimed at bringing the deploying canopy to its customary curved shape, is thus acknowledged.

SUMMARY OF THE INVENTION

In a first broad aspect the present invention relates to an umbrella rib, comprising a body having a proximal end, a distal end (this part of the rib will be referred to also "the free end of the rib"), and a most distant fulcrum at a location there between in which the rib is to be supported to a stick of the umbrella (the most distant fulcrum is a point in the rib most closest to the free end, in which the rib gets a support from the stick. In strutless umbrellas this point is normally also the pivot point of the rib. In umbrellas having struts, this point will be the most distant joint point between the rib and any other constructional element bridging it to the stick) ; the rib is characterized by a directional bending unit constituting a member of the rib body between the distal end and the most distant fulcrum configured to allow bending a rib portion at the distal end in a first direction in response to a small shaping force interacting with the rib through a tensioning canopy fabric, and to prevent bending of said rib's portion in a direction opposite to the first even by forces to a substantial extent greater than the shaping force .

The directionality of a bending unit according to the invention may be tested in laboratory conditions, independently of the umbrella. This can be made by providing a naked rib containing the bending unit, fixing the rib's proximal end and its most distant fulcrum to a stationary table (or any other stationary construction) , and, with the rib laying substantially linearly, applying a measurable force on the ribs free end in one of two opposite directions thereby displacing the free end of the rib a predetermined distance from the rib's linearity axis. If due to the directional bending unit the force to be applied to the rib in a direction analogues to the direction of the canopy shaping force is substantially smaller than the force to be applied to the rib for achieving a similar displacement in the opposite direction, then the tested directional bending unit characterizes a rib according to the present invention.

Such directional bending unit may be advantageous in defending against wind gusts tending to overturn the canopy, without requiring increased forces for deploying and/or maintaining the canopy fully deployed in a mushroom-like shape.

In the context oh this invention the term "shaping force" relates to a force directed at providing the umbrella with a canopy having a mushroom-like shape.

In the context oh this invention the term "mushroom-like shape" means a shape in which a rain (or sun) protective fabric of a deployed canopy is lowering more sharply near the canopy circumference than in adjacent more inner canopy areas .

In the context of this invention the term "shape-breaking force" refers to a force tending to overturn a deployed canopy . According to a first preferred embodiment the directional bending unit comprises a joint in which a first and a second separate pieces of rib's material are hinged together, the first piece is or connected to a rib member bearing an inner portion of the canopy fabric, the second piece is or connected to a rib member bearing a peripheral portion of the canopy fabric, the joint is configured to allow the second separate piece to pivot freely or against a biasing force within a predetermined angular section thus allowing the peripheral portion of the canopy fabric to pivot restrictedly between a substantial alignment with the inner portion of the canopy fabric and between a predetermined angular relation with the inner portion thereby imitating a mushroom-like canopy shape.

In order to restrict the second piece from pivoting beyond said angular section, the directional bending unit may comprise stopper members which block further rotation of the second piece upon reaching any of two axis lines defining the angular section.

According to some preferred embodiments the directional bending unit comprises a biasing spring configured to maintain a biasing force for returning and holding the second piece aligned with the first piece whenever the shaping force transmitted to the rib through the canopy fabric is absent or is insufficient to overcome the biasing force. Thus, when folding the umbrella, the biasing force will align the rib so as to keep it with the canopy fabric attached to, substantially parallel to and juxtapose the umbrella stick. The spring, e.g. a leaf spring, may be an integral part of any of the two pieces. When the rib is made of plastic, the spring can be made of and cast with the same plastic piece forming one of the first and second rib pieces.

According to other preferred embodiments the rib and at least certain members of its directional bending unit are made of a single piece of material. In these embodiments the directional bending unit comprises (i) a weakened rib region having a reduced resistance against the shaping force, the reduced resistance is measured in comparison with the resistance non weakened rib regions have against a similar force; and (ii) a directional stopper configured to increase the force required for bending the free end of the rib in a shape-breaking direction, the force is measure in comparison with the shaping force required for bending the rib to form a mushroom-like canopy shape .

According to some preferred embodiments, both the rib and its directional bending unit are formed as a single piece of material cast altogether from a polymeric substance.

By providing the rib with a weakened portion (according to some embodiments) or a hinge joint (according to other embodiments) of the directional bending unit of the present invention, a mushroom-like canopy shape is achievable with much less tension in the fully deployed canopy fabric comparing to the tension of the fully deployed canopy fabric of most conventional umbrellas.

The design of the canopy fabric may be changed however as a matter of designer preferences, so if one so wishes he may design the shape and dimensions of the canopy fabric so as to be in some preferred tension greater than needed for just taking the mushroom-like shape. In yet additional broad aspect the invention relates to umbrellas comprising canopy ribs of the type having a directional bending unit located in some mid portion between a free end of the rib and a most distant fulcrum of the rib, as described above and as will be explained in detail by the accompanying description and Figs.

The invention further relates to a method for providing umbrellas with a mushroom-like canopy shape, the method comprising providing an umbrella with a plurality of ribs each having a directional bending unit located in some mid portion between a free end of the rib and a most distant fulcrum of the rib.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be further explained by the accompanying Figures. These figures intend to exemplify some embodiments of the invention. In no manner should these Figures be interpreted as a renunciation of the broadest eligible scope of protection claimable by this invention based on it textual and/or graphical description.

Brief Description of the Figures

Fig. 1 illustrates a general isometric view of an entire umbrella rib according to one of the invention embodiments .

Fig. 2A illustrates an isometric view concentrating on the directional bending unit of the rib embodiment of

Fig. 1, in its bent state useful for imitating a mushroom-like canopy shape. Fig. 2B illustrates an isometric view concentrating on the directional bending unit of the rib embodiment of Fig. 1, in its non bent (straight) state.

Fig. 2C illustrates a side view of the directional bending unit shown by Fig. 4.

Fig. 3 illustrates a side view of an entire umbrella rib according to additional exemplified embodiment of the invention. The rib is shown in its neutral linear state.

Fig. 4 illustrates an isometric view concentrating on the directional bending unit of the rib embodiment of Fig. 3.

Fig. 4A illustrates a side view of the directional bending unit shown by Fig. 4.

Fig. 4B illustrates a side view of the directional bending unit of Fig. 4 when a shape breaking force is in action, tending to bend the distal part of the rib out of shape .

Fig. 4C illustrates a side view of the directional bending unit of Fig. 4 when a shaping force is in action, bending the distal part of the rib to provide the umbrella with a mushroom-like shape.

Figs. 5A-5B illustrate in respective side views two states of an umbrella rib having a directional bending unit according to yet further exemplifying embodiment of the invention.

Figs. 6A - 6C illustrate in isometrics umbrellas with different mushroom-like canopy shapes imitated using ribs according to the present invention. DETAILED DESCRIPTION OF THE FIGs.

Fig. 1 illustrates a general isometric view of an entire umbrella rib (1) according to one of the invention embodiments. The rib, comprising a body having a proximal end (Ia), a distal end (Ib), and a most distant fulcrum

(Ic) at a location there between, which is the most distant point on the rib supported to the umbrella stick.

In the illustrated embodiment the point (Ic) is a protrusion through which the rib is to be hinged to a rib nesting member connected to the top of the umbrella stick. The invented rib is characterized by a directional bending unit (2; 6) constituting a member of the rib body in some mid portion between the distal end (Ib) and the most distant fulcrum (Ic) . The directional bending unit (2; 6) is configured to allow bending a rib portion (4) in a first direction (CW) respective to a linearity axis (7) of the rib (1), in response to a small shaping force interacting with the rib through a tensioning canopy fabric (not illustrated) , and to prevent bending of said rib's portion (4) in a direction (CCW) opposite to the first even by forces to a substantial extent greater than the shaping force.

According to this embodiment the directional bending unit (2) comprises a joint (6) in the area of which a first

(3) and a second (4) separate pieces of rib's material are hinged together by means of a pin (5) passing through apertures made in each of the pieces in the joint area, the first piece (3) is (or alternatively may be connected to) a rib member bearing an inner portion of the canopy fabric (not illustrated), the second piece (4) is (or alternatively may be connected to) a rib member bearing a peripheral portion of the canopy fabric (not illustrated), the joint (6) is configured to allow the second separate piece (4) to pivot against a biasing force (and according to other embodiments freely) within a predetermined angular section (A) thus allowing the peripheral portion of the canopy fabric (which is connected to and supported by the second separate piece

(4)) to pivot restrictedly between a substantial alignment with the inner portion of the canopy fabric when the second piece (4) overlaps the longitudinal rib axis (7), and between a predetermined angular relation with the inner portion of the canopy fabric, as indicated by the angular section represented by the arrow (A) , thereby imitating a mushroom-like canopy shape when the first and the second pieces (3) and (4) are forced by a tensioning canopy fabric (not illustrated in this Fig.) to take the illustrated angled shape.

The rib in the illustrated embodiment is preferably fabricated by casting a plastic material, (the pin (5) can be made of metal in case a designer so prefer) . Due to the directional bending unit (2) the entire rib length can be made rigid, e.g. by providing it with an I-shape profile for reducing its elasticity and for strengthening, while still having bending ability.

Fig. 2A illustrates a close-up isometric view concentrating in the directional bending unit (2) of the rib embodiment of Fig. 1, illustrated in its bent state. In this embodiment the directional bending unit (2) is a joint (6) between a first (3) and a second (4) separate pieces of rib's material. The hinge between the pieces comprises a pin (5) (not shown in this Fig.), passing through apertures (5a) made in each of the pieces in the joint area. The first piece (3) is (or alternatively may be connected to) a rib member bearing an inner portion of the canopy fabric (not illustrated) , and the second piece (4) is (or alternatively may be connected to) a rib member bearing a peripheral portion of the canopy fabric

(not illustrated), the joint (6) is configured to allow the second separate piece (4) to pivot against a biasing force (and according to other embodiments freely) within a predetermined angular section (A) thus allowing the peripheral portion of the canopy fabric (which is connected to and supported by the second separate piece

(4)) to pivot restrictedly between a substantial alignment with the inner portion of the canopy fabric when the second piece (4) overlaps the longitudinal rib axis (7), and between a predetermined angular relation with the inner portion of the canopy fabric, as indicated by the angular section arrow (A) , thereby allowing for imitating a mushroom-like canopy shape.

In the illustrated embodiment the biasing force is produced by a leaf spring (13), which is a piece of elastic material protruding from the bottom part (21) of the second piece (4) . As can be appreciated, rotating the second piece (4) clockwise, away from the longitudinal axis (7) about the hinge pin (5), will cause the leaf spring (13) to become tensed since it cannot follow the rotation, being blocked on its free end (22) by the bottom part (18) of the rib piece (3) . The force required for bending the rib by rotating the second piece (3) clockwise is negligibly increased by this leaf spring arrangement, since the spring may be engineered to produce the minimum force required for just returning the rib to its straightness in the absence of other forces, which is quite small.

The rib's bending is directional, since the directional bending unit (2) allows a portion of the rib, in this embodiment - the second piece (4), to deviate from the longitudinal axis (7) by bending in only one direction, i.e. downwardly, while preventing its deviation to the opposite, upwards, direction. The prevention is achieved by means of blocking protrusions (12) and (12a) formed in the first piece (3) at the joint region (6), and configured to stop counterclockwise rotation of the second piece (4) across the rib's longitudinal axis (7), by blocking the way for the surfaces (16a) and (17a) formed in the second piece (4) (this blocking state is depicted by Fig. 2B) .

The rotation of the second piece (4) of the rib is restricted also in the clockwise rotation direction so as not to exceed the angular section A allocated for the rib's bending. The restriction is achieved by inclined surfaces (11) (only one of which is visible in this Fig.) formed from both sides of the second piece (4) in the joint region (6). These inclined surfaces (11) engage and thus being blocked by the bottom surfaces of protrusions (12) and (12a) made in the first piece (3) .

The illustrated embodiment thus emphasizes that even though the rib body has an I-shaped profile which provides it with a substantial rigidity to its entire length, it may still be bent in the required direction for acquiring a customary shape of canopy, keeping yet a substantial strength against forces tending to overturn the canopy. The narrower portion of the I-shaped profile is formed by pairs of recesses (20) and (19) formed from both sides of the first and the second pieces (3) and (4), respectively .

The joint (6) is formed by forming in one of the pieces

(in the illustrated embodiment the first piece (3) ) a pair of recesses (23) (only one is visible in the Fig.) from both sides of a core portion (9), and by forming in the other piece (in the illustrated embodiment the second piece (4)) a pair of side protrusions (16) (17) with a gap

(8) in between matching the core portion (9) of the other piece. An aperture (5a) formed in each of the side protrusions (16) and (17), and respectively in the core portion (9), is configured to receive a hinging pin (5) (not illustrated in this Fig.) .

Other joint and/or hinging methods between the rib pieces may be used as well, without departing from the scope of the present invention. Engineering other blocking arrangements for use in the illustrated joint method, or for use in different types of joint methods which may be used, for defining the angular section in which the second piece of the rib is allowed to pivot, should not be considered as departing from the scope of the present invention .

An aperture (15) made in the narrow part of the I-shaped profile formed by the recesses (20) made in both rib's sides, exemplifies a useful connection point for stitching the canopy to the rib. A plurality of such aperture may be provided in different locations along the two pieces (3) and (4) to allow for a satisfactory connection between the canopy fabric and the ribs. Use of other connection methods between the canopy and the rib should not be considered as departing from the scope of the present invention.

Fig. 2B illustrates an isometric view concentrating on the directional bending unit (2) of the rib embodiment of

Fig. 1, in its non bent (straight) state. In the straight state of the rib the protrusions (12) and (12a) of the first piece (3) of the rib are contacted by respective surfaces (16a) and (17a) formed in the second piece (4) of the rib, such that the rib is in its straight state and further counterclockwise rotation of the second piece

(4) about the hinge pin (5) is blocked.

Fig. 2C illustrates a side view of the directional bending unit (2) shown by Fig. 2B. In this side view the leaf spring (13) protruding from the bottom part of the second piece (4) is more clearly seen in its inactive state which corresponds to the straight state of the rib. In the inactive state the end portion (22) of the leaf spring (13) does not press on the bottom part (18) of the first piece (3) , thus no biasing force is generated. Upon clockwise rotation of the second piece (4) about the hinge pin (5), the end portion (22) of the leaf spring

(13) will contact and press on the bottom surface (18) of the first piece (3), thus biasing the second piece (4) with a small force resisting the rotation. The rotation of the second piece clockwise is limited by the inclined surface (11) formed in the side protrusion (16), which upon reaching the bottom surface of the protrusion (12) made in the first piece (3) will be blocked, leaving the bending angle of the second piece respective to the first piece as predefined for the specific umbrella for making the customary mushroom-like shape. Fig. 3 illustrates a side view of an entire umbrella rib (10) according to additional exemplified embodiment of the invention. According to this embodiment the rib

(10) and its directional bending unit (32) are preferably made both of a single piece of material. The other main parts of the illustrated rib are a rib lever (31), a rib hinge (33), a rib proximal part (34) and a rib distal part (35) .

A close up isometric view of the directional bending unit (32) is shown by Fig. 4.

The directional bending unit (32) comprises (i) a weakened rib region (36) having a reduced resistance against the shaping force (i.e. the force exerted on the rib by the canopy fabric in the direction (CW) useful for bending the rib for taking a mushroom-like shape) , the reduced resistance is measured in comparison with the resistance non weakened rib regions such as (37) and (38) have against a similar force (e.g. due to an I-shape profile or to a thicker profile) ; and (ii) a directional stopper (39) configured to increase the force required for bending the free end of the rib (including the rib's distal part (35) ) in a shape-breaking direction (CCW) , the force is measure in comparison with the shaping force required for bending the rib to form a mushroom-like canopy shape. The directional stopper (39) comprises an accordion-like bridge (39a) having at least one wave-like portion bridging between the neighboring ends (41) and

(42) of the proximal rib part (34) and of the distal rib part (35), respectively. The accordion-like bridge is located opposite the bottom surface of the weakened rib region (36) . The weakening of this rib region may be achieved e.g. by providing the rib with a thinner profile than the profile of most of its body, as exemplified by the illustrated embodiment. The directional stopper (39) is further comprising at least on stopping bar (39b) and

(39c) , formed as downward protrusions projecting from the bottom surface of the weakened region (36) . In this

Figure the rib is in a neutral state, with no bending forces acting on it. In this situation the rib takes its pre-fabricated state, namely is substantially linear with both its parts (34) and (35) lay along the same longitudinal axis.

Fig. 4A illustrates a side view of the directional bending unit shown by Fig. 4. It is observable in this Fig. that the stopping bars (39a) and (39b) are projecting each into a U-shaped section of the accordion- like bridge (39) , and are closer to a proximal wall of the U shape (which is closer to the proximal part (34) of the rib) than to the distal wall of the U shape (which is closer to the distal part (35) of the rib) . It is further observable in this Fig. that a U shape (39d) of the accordion-like bridge (39) which is connected to the distal part (35) of the rib is wider than a U shape (39e) of the accordion-like bridge (39) which is connected to the proximal part (34) of the rib. This design results as follows:

As shown by the following Fig. 4B the stopping bars (39a) and (39b) make contact with the proximal walls (39f) (39g) of the U shapes immediately (after a small negligible tolerance) when the accordion-like bridge (39) starts to extend due to a shape breaking force acting on the distal rib part in the CCW direction. This contact between the stopping bars and the walls of the U shapes dramatically increases the resistance of the directional bending unit to the bending force in the CCW direction.

Fig. 4C illustrates the state of the directional bending unit when a shaping force is acting on the distal part of the rib in the CW direction. In this situation the accordion-like bridge becomes compressed with the U shapes narrowing and with their proximal walls moving away from the stopping bars (39a) and (39b) . The rib thus can take its customary shape for obtaining a mushroom- like canopy. Further bending of the rib in the CW direction is blocked either when the stopping bars (39a) and (39b) make contact with the distal walls of the U shapes or when the tops of the U shapes make contact with and stopped by the bottom surface of the weakened rib region (36) .

Immediately after withdrawal of any bending forces, the directional bending unit will return from its deformed state to its pre-fabricated state with the rib linear as illustrated by Fig. 4. It is thus appreciated that the accordion-like bridge (39) functions also as a biasing spring. It is further appreciable that according to the embodiment illustrated by Figs. 4 -4C both the rib and its directional bending unit may be formed as a single piece of material cast altogether from a polymeric substance .

Fig. 5A illustrates a side view of a part of umbrella rib according to yet further exemplifying embodiment of the invention. The rib has a proximal part (44) and a distal part (45) . The most distal fulcrum of the rib (not shown in this Fig.) is to the left of the proximal part, just near before the proximal end of the rib (also not shown) . The rib has a directional bending unit (41) defined by at least one cut (42) forming a narrow slit across the rib profile followed by an aperture. In its pre-fabricated state the rib is linear with its two parts (44) and (45) lay along the same longitudinal line. The rib parts (44) and (45) have a T-shaped profile with the wide top of the T indicated by numeral (46) . In the directional bending unit, the T shaped profile is inverted (i.e. near the directional bending unit (41) the wide top of the T-shape leaves the top surfaces of the rib parts (44) and (45) and approaches the bottom of the bending unit) . It can be appreciated that trying to force bending of the distal rib part (45) in the CCW direction will result in closing the slits (42) . When the slits (42) become closed with their sides contacting one another, further bending of the rib will be stopped. Vise versa, when a shaping force will act on the distal rib part (45) in the CW direction as indicated in Fig. 5B, the slits (42) will tend to open, allowing the rib to bend and take its customary shape for a mushroom-like canopy appearance.

It should be noted that according to various embodiments of the invention, the directional bending unit may have some small tolerances allowing some limited movements of the rib parts before its main directionality attributes actually become expressed.

Figs. 6A - 6C illustrate in isometrics umbrellas with different mushroom-like canopy shapes imitated using ribs according to the present invention. In Fig. 6A an umbrella is shown having a mushroom-like canopy (50) wherein the directional bending units are located about the middle of the ribs. Accordingly, each rib is bent near its middle in the bending site (51) .

Fig. 6B illustrates an umbrella having two separate bending units in each rib, thus the canopy (52) has a mushroom-like shape with two bending sites (53a) and

(53b) in each rib, the locations of which correspond to the locations of the respective bending units along the rib .

Fig. 6B illustrates an umbrella having one bending unit in each rib, located near the free end of the rib, thus the canopy (54) has a mushroom-like shape with the bending site (55) near the distal end of the rib.

Although the umbrella is strutless, and the moment arm of forces acting near the rib distal end are very long, the bending units make it easy to comply with.

Claims

CLAIMS :

1. An umbrella rib, comprising a body having a proximal end, a distal end, and a most distant fulcrum at a location there between; the rib is characterized by a directional bending unit constituting a member of the rib body between the distal end and the most distant fulcrum configured to allow bending a rib portion at the distal end in a first direction in response to a small shaping force interacting with the rib through a tensioning canopy fabric, and to prevent bending of said rib's portion in a direction opposite to the first even by forces to a substantial extent greater than the shaping force.

2. The umbrella rib of claim 1, wherein the directional bending unit comprises a joint in which a first and a second separate pieces of the rib's body are hinged together.

3. The umbrella rib of claim 1, wherein both the rib and its directional bending unit constitute a single piece of material cast altogether from a polymeric substance .

4. An umbrella rib according to anyone of the preceding claims, further comprising a biasing spring for returning the rib to linearity when folding the canopy.

5. An umbrella rib according to anyone of the preceding claims, wherein the directional bending unit comprises a weakened rib region.

6. An umbrella rib according to anyone of the preceding claims, wherein the directional bending unit comprises an accordion-like bridge bridging between distal and proximal parts of the rib.

7. Umbrella comprising canopy ribs of the type having a directional bending unit located in some mid portion between a free end of the rib and a most distant fulcrum of the rib.

8. Method for providing umbrellas with a mushroom-like canopy shape, the method comprising providing an umbrella with a plurality of ribs each having a directional bending unit located in some mid portion between a free end of the rib and a most distant fulcrum of the rib.