WO2003054411A1

WO2003054411A1 - Brake for linear movements of rods

Info

Publication number: WO2003054411A1
Application number: PCT/CA2002/001890
Authority: WO
Inventors: Pierre Laforest; Joey Larouche
Original assignee: Gestion Laforest Inc.
Priority date: 2001-12-13
Filing date: 2002-12-09
Publication date: 2003-07-03
Also published as: AU2002347163A1

Abstract

The linear brake defines a longitudinal axis (A) and comprises a tubular housing (12) for axial engagement about a post (P) and a radially deformable tubular friction sleeve (22) for axial engagement along the post, the friction sleeve located radially spacedly within an inner wall of the housing. The linear brake also comprises an annular axially convergent ball channel defined between the housing inner wall and the friction sleeve and a number of balls (38) disposed in an annular row within the ball channel, the balls being axially movable between a non-braking position in which they apply little or no radial pressure against the friction sleeve for allowing the friction sleeve to freely slide along the post; and a braking position in which the balls are wedged between the housing inner wall and the friction sleeve and apply significant radial pressure against the friction sleeve to forcibly radially inwardly deform the friction sleeve for the friction sleeve to apply friction-borne radial pressure against the post for hindering movement of the linear brake along the post. The linear brake further comprises a number of axially extending, peripherally spaced grooves (24) provided on the friction sleeve, each the ball being seated in a corresponding one of the grooves, an actuator (40) continuously biasing the balls towards the braking position and a counter-actuator attached to the housing and which selectively moves the balls into the non-braking position against the action of the actuator.

Description

BRAKE FOR LINEAR MOVEMENTS OF RODS

CROSS-REFERENCE DATA

5

The present application claims conventional priority of provisional patent application No. 60/339,344 filed on December 13, 2001 in the United States.

FIELD OF THE INVENTION

10

The present invention relates to braking systems, and more particularly to a linear brake.

BACKGROUND OF THE INVENTION

15

Linear brakes are used on a variety of applications, often as auxiliary or emergency braking systems, although their uses are not limited to such applications. Such linear brakes are usually attached to an element which is movable along a fixed structure. For example, such a movable element could be an elevator within the fixed structure 20 which is the elevator shaft structure. However, conventional linear brakes are often inefficient, or may be designed to brake only small loads (in other applications than elevator-related applications), or may cause uneven load repartitions within the brake structure resulting in important stresses thereon.

25 SUMMARY OF THE INVENTION

The present invention relates to a linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having 30 an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; an annular axially convergent ball channel defined between said housing inner wall and said friction sleeve; a number of balls disposed in an annular row within said ball channel, said balls being axially movable between a non-braking position in which they are positioned away from a smaller section of said ball channel and in which they apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at a smaller section of said ball channel and in which they are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post for hindering movement of said linear brake along the post; a number of axially extending, peripherally spaced grooves provided on said friction sleeve, each said ball being seated in a corresponding one of said grooves and being axially movable therealong between said non-braking and braking positions, each said ball applying radial pressure in a non-punctual, peripherally distributed fashion against a groove surface of said friction sleeve when said balls are in said braking position; an actuator continuously biasing said balls towards said braking position; and a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator.

In one embodiment, said actuator is a biasing member carried by said housing and continuously biasing said balls towards said braking position. In one embodiment, said housing inner wall comprises an annular, axially tapered wall portion with said ball channel being formed between said axially tapered wall portion and an axially straight portion of said friction sleeve.

In one embodiment, the linear brakefurther comprises: additional balls disposed in a number of annular rows axially spaced-apart between one another and axially spaced from the first mentioned said row of balls; a number of additional annular axially convergent ball channels defined between said housing inner wall and said friction sleeve, with all said ball channels being convergent in the same axial direction; wherein each said row of balls is disposed within a corresponding ball channel and is movable therein between a non-braking position in which said balls are positioned away from smaller sections of said corresponding ball channels and in which said balls apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at smaller sections of said corresponding ball channels and in which said balls are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post for hindering movement of said linear brake along the post.

In one embodiment, each row of balls is axially carried by an annular ball- carrying element between said braking and non-braking positions, with a first and a second ball-carrying elements being defined at a first and a second extremity, respectively, of said ball-carrying elements which are axially successively disposed.

In one embodiment, each said row of balls is further sandwiched between a pair of successive annular ball-carrying elements.

In one embodiment, said counter-actuator comprises said first ball-carrying element and a selectively powered reciprocating member for selectively moving said first ball-carrying element between a first and a second positions corresponding to said braking and non-braking positions of said balls, with said selectively powered reciprocating member forcing said balls into said non-braking position against the action of said actuator when it is in said first position. In one embodiment, said actuator is a coil spring engaging said housing and acting on said second ball-carrying element.

In one embodiment, all except either one of said first and second ball- carrying elements are crown rings comprising a number of openings each provided with a corresponding ball therein. In one embodiment, each said crown ring comprises ball positioning means to independently position each said ball within its corresponding ball channel in a substantially equally operative way.

In one embodiment, said ball positioning means comprises ball positioning springs carried by said crown rings within said openings.

In one embodiment, said openings are crenels. In one embodiment, said friction sleeve comprises a number of axially- extending slots therein for promoting radial deformation of said friction sleeve.

In one embodiment, the linear brake further comprises ball positioning means to independently position each said ball within said ball channel in a substantially equally operative way, said ball positioning means being defined by the inherent resiliency of said grooved friction sleeve whereby said balls will be independently positioned within said ball channel by a resilient biasing action of said grooved friction sleeve.

The present invention also relates to a linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; a number of annular axially successive ball channels defined between said housing inner wall and said friction sleeve, with each said ball channel being axially convergent in a same direction as the other said ball channels; a number of rows of balls each axially disposed within a corresponding said ball channel and axially movable therein, each row of balls being sandwiched between and axially carried by a pair of annular ball-carrying elements, said balls being commonly axially movable between a non-braking position in which said balls are positioned away from smaller sections of said corresponding ball channels and in which said balls apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at smaller sections of said corresponding ball channels and in which said balls are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post to hinder movement of said linear brake along the post; an actuator attached to said housing and continuously biasing said balls towards said braking position through the instrumentality of said ball-carrying elements; and - a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator through the instrumentality of said ball-carrying elements.

In one embodiment, a first and a second ball-carrying elements are defined at a first and a second extremity, respectively, of said axially spaced-apart ball-carrying elements, wherein said actuator acts on said first ball carrying element to continuously bias said balls towards said braking position.

In one embodiment, a first and a second ball-carrying elements being defined at a first and a second extremity, respectively, of said axially spaced-apart ball- carrying elements, wherein said counter-actuator comprises said first ball-carrying element and a selectively powered reciprocating member capable of selectively moving said first ball-carrying element between a first and a second position corresponding to said braking and non-braking positions of said balls, with said selectively powered reciprocating member forcing said balls into said non-braking position against the action of said actuator when it is in said first position. The present invention further relates to a linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; an annular axially convergent ball channel defined between said housing inner wall and said friction sleeve; a number of balls disposed within said ball channel, said balls being axially movable between a non-braking position in which they are positioned away from a smaller section of said ball channel and in which they apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at a smaller section of said ball channel and in which they are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post to hinder movement of said linear brake along the post; ball positioning means to independently position each said ball within said ball channel in a substantially equally operative way; an actuator attached to said housing and continuously biasing said balls towards said braking position; and - a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator.

In one embodiment, said ball positioning means comprises an annular ball carrying element having a number of ball positioning springs each corresponding to a said ball and each independently positioning said corresponding ball within said ball channel. In one embodiment, said friction sleeve is resilient and comprises a number of axially extending, peripherally spaced grooves provided on an outer surface thereof, each said ball being seated in a corresponding one of said grooves and being axially movable therealong between said non-braking and braking positions, each said ball consequently applying radial pressure in a substantially linear fashion against a groove surface of said friction sleeve when said balls are in said braking position, said ball positioning means being defined by the inherent resiliency of said grooved friction sleeve whereby said balls will be independently positioned within said ball channel by a resilient biasing action of said grooved friction sleeve.

DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

Figure 1 is a perspective view of the linear brake according to the present invention, operatively installed on a post P;

Figure 2 is a enlarged, partially cut-away perspective view of the linear brake of figure 1 , with the solenoid casing portion being removed;

Figure 3 is a transverse cross-sectional view of the linear brake as shown in figure 2 without the solenoid casing portion, with the ball assembly being in a non-braking position; Figure 3 A is similar to figure 3, but with the ball assembly being in a braking position;

Figure 4 is an enlarged perspective view of the friction sleeve of the linear brake;

Figure 5 is an end view of the friction sleeve of figure 4;

Figure 6 is an elevation of the linear brake of figure 1 , with the solenoid casing being shown in cross-section according to line 6-6 of figure 1 , with the solenoid casing being in a first position corresponding to the non-braking position of the ball assembly of figure 3; and

Figure 6A is a view similar to figure 6, but with the solenoid casing being in a second position corresponding to the braking position of the ball assembly of figure 3 A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figures 1, 2 and 3 show a linear brake 10 for use along a post P. Linear brake 10 defines a longitudinal axis A which is coaxial with post P, and comprises a tubular housing 12 for axial engagement about post P, and a tubular solenoid casing 14 which is also axially engaged about post P and which is linked to housing 12 in a manner described hereinafter.

Linear brake 10, in the embodiment shown in the drawings and explained hereinafter, is unidirectional. More specifically, in figure 3, if post P is motionless, linear brake 10 is destined to prevent motion downwardly along post P, which will be said to be the "braking direction" of linear brake 10. However, it is understood that an additional inverted linear brake 10 could be provided to allow selective braking in the opposite direction. Also, linear brake 10 could be motionless while post P would be moved within linear brake 10, without departing from the scope of the present invention. Thus, although in the following explanation linear brake 10 is considered as movable along post P, it is understood that this is a relative movement, and that post P could actually be the movable element while linear brake 10 would be motionless.

As shown in figures 2 and 3, housing 12 and defines first and second openings 18, 20 at both its extremities through which post P extends, with a low-friction bushing 15 being provided between housing 12 and post P at the housing first end 18. Housing 12 is made of steel and comprises a low-friction cap 21 which may be made of a different material such as nylon, and which is bolted to the housing main body, with second opening 20 being located within cap 21.

Housing 12 also comprises an inner wall 16, and defines an inner chamber 19 between the housing first and second ends 18, 20 and inner wall 16, with post P extending through the housing inner chamber 19. Inner wall 16 comprises a number of axially tapered annular wall portions 17. In the embodiment shown in the annexed drawings, tapered annular wall portions 17 are made from annular axially tapered rings made from a hard steel alloy, with rings 17 being fixedly attached to and being considered to be part of housing inner wall 16. Linear brake 10 further comprises a radially deformable tubular friction sleeve 22 for axial engagement along post P, friction sleeve 22 located radially spacedly within housing inner wall 16 inside the housing inner chamber 19. Friction sleeve is slightly movable within housing 12, as detailed hereinafter. As further shown in figures 4 and 5, friction sleeve 22 comprises a number of axially extending, peripherally equally spaced grooves 24 provided on its outer surface. Friction sleeve 22 defines first and second ends 22a, 22b and has a number of axially extending, peripherally spaced slots 26a, 26b therein, with a number of slots 26a (for example two slots as shown in the drawings) extending from first end 22a but short of second end 22b, and with a number of slots 26b (for example two slots as shown in the drawings) extending the full length of friction sleeve 22. Although the two full-length slots 26b effectively separate friction sleeve 22 into two distinct sleeve portions, friction sleeve 22, including both sleeve portions, will continue to be referred to as a single element, since both sleeve portions co-operate to act as a single, resiliently deformable sleeve element. It is understood that slots 26a, 26b are optional, and that a suitably deformable friction sleeve 22 devoid of any slots could be provided within an alternate embodiment of the present invention.

Figures 2 and 3 also show that linear brake 10 comprises a number of spacer elements or ball-carrying elements in the form of crown rings 28 (for example five crown rings as shown in the drawings) which are co-axially installed within housing 12 and around friction sleeve 22, and which each define a number of peripherally equally spaced crenels 30 between peripherally equally spaced merlons 32. Crowns rings 28 are axially stacked on one another, resting on the merlons 32 of the underlying crown ring 28. A hollow opening 34 is provided under each crenel 30, wherein a ball positioning spring 36 is seated. A ball 38 is disposed within each crenel 30, over a corresponding ball positioning spring 36 and under the overlying crown ring 28. Consequently, balls 38 are disposed in substantially coplanar rows in each of the crown rings 28, with each row being located between friction sleeve 22 and a corresponding one of the tapered annular wall portions 17.

An axially convergent ball channel is defined between each tapered wall portion 17 and sleeve 22, wherein the balls 38 are movable between a non-braking position shown in figure 3, in which they are positioned away from a smaller section of the convergent ball channel and in which they apply insignificant radial pressure against friction sleeve 22 for allowing fiiction sleeve 22 to freely slide along post P; and a braking position shown in figure 3 A, in which balls 38 are positioned at the above-mentioned smaller section of the ball channel and in which they are wedged between housing inner wall portions 17 and friction sleeve 22 and apply significant radial pressure against friction sleeve 22 to forcibly radially inwardly deform friction sleeve 22.

As balls 38 slide against their tapered wall portion 17 from their non- braking position towards their braking position, they gradually apply radial pressure against friction sleeve 22 due to the inclination of tapered wall portions 17. Friction sleeve 22 is consequently pressed against post P and applies friction-borne radial pressure against post P to hinder movement of linear brake 10 along post P. It is understood that by properly calibrating the friction-borne radial pressure which can be applied by sleeve 22 on post P, this movement hindrance can result in linear brake 10 entirely stopping its translation movement along post P. Thus, in most applications, the movement hindrance will in fact be a complete braking action. An actuator in the form of a main actuator spring 40, compressed between the lowermost crown ring 28 and a peripheral shoulder 42 in the housing cap 21, continuously biases balls 38 towards their braking position. Indeed, by continuously applying axially-oriented pressure on the lowermost crown ring 28, this lowermost crown ring 28 and all the other stacked crown rings 28 will be biased axially towards the housing first opening 18. Consequently, each crown ring 28, with the help of positioning springs 36, will in turn bias balls 38 towards their braking position, as further described hereinafter. A counter-actuator in the form of a selectively controlled flanged push ring 44 selectively moves balls 38 into their non-braking position against the action of actuator spring 40. Push ring 44 is located in the inner chamber 19 of housing 12 near the housing first end 18, thus opposite actuator spring 40. Push ring 44 is axially movable within the inner chamber 19 of housing 12, and engages the balls 38 of the topmost crown ring 28.

By pushing atop the topmost balls 38 with push ring 44, an axially oriented displacement of all stacked crown rings 28 towards the housing second end 20 occurs. Thus, all balls

38 are moved into their non-braking position by push ring 44 when the latter is moved accordingly into its first limit position shown in figure 3. However, as push ring is moved towards its second limit position shown in figure 3 A, balls 38 may move towards their braking position.

Push ring 44 axially carries friction sleeve 22 along post P. Indeed, friction sleeve is carried either by housing second end 20 or by push ring 44, depending on the direction in which housing 12 moves along post P. The position of push ring 44 can be controlled in any suitable manner. In the embodiment shown in the drawings, and more particularly in figures 1, 2, 3 and 6, the position of push ring 44 is controlled by means of a selectively powered reciprocating member 46 which will move between a first and a second position corresponding to the braking and non-braking positions of said balls, respectively. The selectively powered reciprocating member 46 comprises solenoid casing 14 which is bored to be axially movable relative to housing 12 along four guide rods 50 which engage housing 12 at their first threaded end, and which are bolted to a stop plate 52 at their second threaded end. Thus, solenoid casing 14 is movable between housing 12 and stop plate 52. Solenoid casing 14 comprises a central bore at 53 wherein post P extends. Solenoid casing 14 also comprises an annular inner chamber 55 enclosing a magnetic coil 54 which is selectively fed with electric current. For example, magnetic coil 54 can be linked to the local electric grid with a suitable electric wire (not shown). Rods 48 which abut against push ring 44 are fixed to solenoid casing 14. Four springs 56, each provided about a corresponding guide rod 50, continuously bias solenoid casing 14 towards its second position in which it is spaced-apart from housing 12. In use, according to whether electrical current is fed to magnetic coil 54, or not, reciprocating member 46 will move between its first and second limit positions shown in figures 6 and 6A. More specifically, upon electric current being fed to magnetic coil 54, magnetic attraction will occur between the steel housing 12 and coil 54. Thus, when electric current is fed to magnetic coil 54, it is attracted to housing 12 and consequently carries solenoid housing 14 into its first limit position shown in figure 6 wherein rods 48 force push ring 44 to move balls 38, through the instrumentality of crown rings 28, into their non-braking position. In this non-braking position of balls 38, linear brake 10 is free to axially move along post P, with friction sleeve 22 applying insignificant radial pressure on post P to allow this axial movement. However, if the electrical current fed to magnetic coil 54 is interrupted, solenoid casing 14 ceases to apply axial pressure against push ring 44. Actuator spring 40 consequently stops to be countered and forces crown rings 28 axially towards the housing first end 18, consequently carrying balls 38 towards their braking position with the help of positioning springs 36. Springs 56 will help prevent eventual hindrance against this displacement by the weight of solenoid casing 14, by forcing solenoid casing 14 towards its second limit position.

More particularly, the braking action will occur as actuator spring 40 moves balls 38 at least slightly towards their braking position, until balls 38 become at least slightly wedged between tapered wall portions 17 and friction sleeve 22. Consequently, a slight radial pressure will be applied by balls 38 on sleeve 22 and by sleeve 22 on post P. This will result in a slight frictional engagement between sleeve 22 and housing 12, with sleeve 22 slightly moving relative to housing 12 as a result of this frictional engagement if an attempt to move linear brake 10 in its braking direction (i.e. downwardly in figures 3 and 3 A, relative to post P) is made. This relative movement of sleeve 22 and housing 12 will result in the wedged balls 38 rolling between sleeve 22 and tapered wall portions 17 towards their braking position, thus becoming more wedged therebetween. This will increase the pressure applied by balls 38 on sleeve 22 and by sleeve 22 on post P, and consequently the frictional engagement of sleeve 22 on post P will also increase. Thus, as soon as balls 38 become at least slightly wedged between tapered wall portions 17 and friction sleeve 22, the system will force balls 38 to spontaneously gradually wedge themselves into their respective ball channels, to eventually effectively reach their braking position and prevent housing 12 from moving relative to post P (or at least to significantly hinder movement of housing 12 relative to post P). Thus, the braking pressure applied by balls 38 on sleeve 22 and by sleeve 22 on post P is not necessarily proportional to the force of the actuator spring 40, since balls 38, once they become slightly wedged within their ball channels, are likely to automatically move towards their wedged braking position. In the embodiment of the linear brake shown in the drawings, this braking motion occurs within a fraction of a turn from the small balls 38, and consequently the gradual wedging of balls 38 within their ball channels will effectively appear almost instantaneous for an onlooker. The purpose of the ball positioning springs 36 is to independently position each ball 38 in a substantially equally operative way within its corresponding convergent ball channel. More particularly, each positioning spring 36 biases its corresponding ball 38 towards and against the lower surface of the overlying crown ring 28, with the balls 38 of the topmost crown ring 28 being biased against the surface of push ring 44. Thus, all balls 38 are positioned at a same position relative to their corresponding ball channels before they are biased away from their non-braking position, which ensures that all balls 38 will in fact act substantially concurrently to apply radial pressure on sleeve 22 when balls 38 are moved towards their braking position. This is advantageous since, when used to brake important loads, linear brake 10 will be submitted to important stresses. Having these stresses divided substantially equally among all balls 38 will help to provide an efficient linear brake 10, and one that is less prone to being damaged or broken.

It is understood that the ball positioning springs 36 will indeed act as noted above to position all balls within their respective ball channels in a substantially equally operative way as long as actuator spring 40 and the solenoid-activated push ring are not stronger than the sum of the forces of all positioning springs 36.

One advantageous aspect of linear brake 10 relies on the axially extending, peripherally spaced grooves 24 provided on friction sleeve 22. Indeed, grooves 24 have a radius of curvature which is substantially the same as that of balls 38. Consequently, since each ball 38 is seated in a corresponding one of grooves 24, in addition to being guided in its axial displacement between its non-braking and braking positions, each ball 38 applies radial pressure according to a non-punctual, peripherally distributed pressure line against a groove surface of friction sleeve 22 when ball 38 is in its braking position. This is much better than the punctual pressure that a ball would apply on a smooth sleeve devoid of any grooves. Grooves 24 thus allow a pressure application by each ball 38 which is distributed along a pressure line instead of a punctual pressure application. This linear pressure distribution becomes very advantageous when linear brake 10 is used to brake important loads.

It is understood that when balls 38 are in a non-braking position, they may be applying either no pressure or an insignificant radial pressure against friction sleeve 22.

In the present specification, the expression "insignificant radial pressure" includes no radial pressure at all or small radial pressures which are insufficient to at least slow the movement of sleeve 22 relative to post P. "Significant radial pressure" applied by balls 38 against friction sleeve 22 means that enough friction-borne radial pressure will be applied by sleeve 22 against post P to hinder the movement of sleeve 22 relative to post P, so that braking occurs as detailed hereinabove. According to one embodiment of the invention, crown rings 28 comprise openings which, instead of being crenels, are slots which surround balls 38. More generally, any suitable ball carrying element can be installed between each row of balls or circumscribing each row of balls 38. This ball-carrying element could alternately be, for example, a simple ring-shaped member which axially carries the rows of balls along post P between their braking and non-braking positions.

It is noted that push ring 44, which acts as a counter-actuator in combination with the selectively powered reciprocating member 46, is also a ball-carrying element since it carries the topmost row of balls 38 towards their non-braking position. Similarly, the lowermost row of balls 38 is carried by the lowermost crown ring 28. According to one embodiment, the ball positioning means would not be related to ball positioning springs 36, but to the inherent resiliency of friction sleeve 22. More particularly, in such an embodiment, no ball positioning springs would be provided, and the position of balls 38 within their respective balls channels during the braking operation would be adjusted by the grooved friction sleeve 22 which would be made in a suitably resilient material. Thus, if balls 38 become eventually differently positioned relative to their respective ball channels, the resiliency of the grooved sleeve 22 would allow the grooved sleeve 22 to yieldingly deform to accommodate balls 38 within its grooves 24 until all balls 38 or a sufficient number of balls 38 become wedged within their respective ball channels to effectively accomplish the desired braking action in a substantially equally operative way. Thus, as the first balls reach their braking position without the other balls having reached this breaking position, they would nest themselves within the sleeve grooves 24 to allow the other balls to move towards a wedged braking position within their respective ball channels.

Other suitable ball positioning means could also be envisioned, be it positioning springs, other resilient positioning elements such as rubber pads, a resilient friction sleeve, or any other suitable ball positioning means.

In one embodiment, the actuator allowing the balls to move from their non- braking position to their braking position, upon the counter actuator being selectively moved accordingly, is gravity. Indeed, for example, it is envisioned that if linear brake 10 is disposed vertically in the opposite direction than the one shown in figure 3, i.e. with the push-ring 44 being located at the lower end of housing 12, the actuator spring 44 may not be necessary to actuate the braking action of linear brake 10. In such a situation, if linear brake 10 is moving upwardly relative to post P, and upon push-ring 44 being moved downwardly, the balls, under their own weight, could engage their respective ball channels sufficiently to actuate the braking mechanism as described hereinabove. Any further modification to the present invention which does not deviate from the scope thereof, is considered to be included therein.

Claims

I CLAIM:

1. A linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; - an annular axially convergent ball channel defined between said housing inner wall and said friction sleeve; a number of balls disposed in an annular row within said ball channel, said balls being axially movable between a non-braking position in which they are positioned away from a smaller section of said ball channel and in which they apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at a smaller section of said ball channel and in which they are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post for hindering movement of said linear brake along the post; a number of axially extending, peripherally spaced grooves provided on said friction sleeve, each said ball being seated in a corresponding one of said grooves and being axially movable therealong between said non-braking and braking positions, each said ball applying radial pressure in a non-punctual, peripherally distributed fashion against a groove surface of said friction sleeve when said balls are in said braking position; an actuator continuously biasing said balls towards said braking position; and a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator.

2. A linear brake as defined in claim 1, wherein said actuator is a biasing member carried by said housing and continuously biasing said balls towards said braking position.

3. A linear brake as defined in claim 2, wherein said housing inner wall comprises an annular, axially tapered wall portion with said ball channel being formed between said axially tapered wall portion and an axially straight portion of said friction sleeve.

4. A linear brake as defined in claim 2, further comprising: additional balls disposed in a number of annular rows axially spaced-apart between one another and axially spaced from the first mentioned said row of balls; a number of additional annular axially convergent ball channels defined between said housing inner wall and said friction sleeve, with all said ball channels being convergent in the same axial direction; wherein each said row of balls is disposed within a corresponding ball channel and is movable therein between a non-braking position in which said balls are positioned away from smaller sections of said corresponding ball channels and in which said balls apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at smaller sections of said corresponding ball channels and in which said balls are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post for hindering movement of said linear brake along the post.

5. A linear brake as defined in claim 4, wherein each row of balls is axially carried by an annular ball-carrying element between said braking and non-braking positions, with a first and a second ball-carrying elements being defined at a first and a second extremity, respectively, of said ball-carrying elements which are axially successively disposed.

6. A linear brake as defined in claim 5, wherein each said row of balls is further sandwiched between a pair of successive annular ball-carrying elements.

7. A linear brake as defined in claim 6, wherein said counter-actuator comprises said first ball-carrying element and a selectively powered reciprocating member for selectively moving said first ball-carrying element between a first and a second positions corresponding to said braking and non-braking positions of said balls, with said selectively powered reciprocating member forcing said balls into said non-braking position against the action of said actuator when it is in said first position.

8. A linear brake as defined in claim 7, wherein said actuator is a coil spring engaging said housing and acting on said second ball-carrying element.

9. A linear brake as defined in claim 6, wherein all except either one of said first and second ball-carrying elements are crown rings comprising a number of openings each provided with a corresponding ball therein.

10. A linear brake as defined in claim 9, wherein each said crown ring comprises ball positioning means to independently position each said ball within its corresponding ball channel in a substantially equally operative way.

11. A linear brake as defined in claim 10, wherein said ball positioning means comprises ball positioning springs carried by said crown rings within said openings.

12. A linear brake as defined in claim 9, wherein said openings are crenels.

13. A linear brake as defined in claim 2, wherein said friction sleeve comprises a number of axial ly-extending slots therein for promoting radial deformation of said friction sleeve.

14. A linear brake as defined in claim 2, further comprising ball positioning means to independently position each said ball within said ball channel in a substantially equally operative way, said ball positioning means being defined by the inherent resiliency of said grooved friction sleeve whereby said balls will be independently positioned within said ball channel by a resilient biasing action of said grooved friction sleeve.

15. A linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; - a number of annular axially successive ball channels defined between said housing inner wall and said friction sleeve, with each said ball channel being axially convergent in a same direction as the other said ball channels; a number of rows of balls each axially disposed within a corresponding said ball channel and axially movable therein, each row of balls being sandwiched between and axially carried by a pair of annular ball-carrying elements, said balls being commonly axially movable between a non-braking position in which said balls are positioned away from smaller sections of said corresponding ball channels and in which said balls apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at smaller sections of said corresponding ball channels and in which said balls are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post to hinder movement of said linear brake along the post; - an actuator attached to said housing and continuously biasing said balls towards said braking position through the instrumentality of said ball-carrying elements; and a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator through the instrumentality of said ball-carrying elements.

16. A linear brake as defined in claim 15, with a first and a second ball- carrying elements being defined at a first and a second extremity, respectively, of said axially spaced-apart ball-carrying elements, wherein said actuator acts on said first ball carrying element to continuously bias said balls towards said braking position.

17. A linear brake as defined in claim 15, with a first and a second ball- carrying elements being defined at a first and a second extremity, respectively, of said axially spaced-apart ball-carrying elements, wherein said counter-actuator comprises said first ball-carrying element and a selectively powered reciprocating member capable of selectively moving said first ball-carrying element between a first and a second position corresponding to said braking and non-braking positions of said balls, with said selectively powered reciprocating member forcing said balls into said non-braking position against the action of said actuator when it is in said first position.

18. A linear brake for use along a post, said linear brake defining a longitudinal axis and comprising: a tubular housing for axial engagement about the post, said housing having an inner wall; a radially deformable tubular friction sleeve for axial engagement along the post, said friction sleeve located radially spacedly within said housing inner wall; an annular axially convergent ball channel defined between said housing inner wall and said friction sleeve; a number of balls disposed within said ball channel, said balls being axially movable between a non-braking position in which they are positioned away from a smaller section of said ball channel and in which they apply insignificant radial pressure against said friction sleeve for allowing said friction sleeve to freely slide along said post; and a braking position in which said balls are positioned at a smaller section of said ball channel and in which they are wedged between said housing inner wall and said friction sleeve and apply significant radial pressure against said friction sleeve to forcibly radially inwardly deform said friction sleeve for said friction sleeve to apply friction-borne radial pressure against the post to hinder movement of said linear brake along the post; ball positioning means to independently position each said ball within said ball channel in a substantially equally operative way; an actuator attached to said housing and continuously biasing said balls towards said braking position; and - a counter-actuator attached to said housing and which selectively moves said balls into said non-braking position against the action of said actuator.

19. A linear brake as defined in claim 18, wherein said ball positioning means comprises an annular ball carrying element having a number of ball positioning springs each corresponding to a said ball and each independently positioning said corresponding ball within said ball channel.

20. A linear brake as defined in claim 18, wherein said friction sleeve is resilient and comprises a number of axially extending, peripherally spaced grooves provided on an outer surface thereof, each said ball being seated in a corresponding one of said grooves and being axially movable therealong between said non-braking and braking positions, each said ball consequently applying radial pressure in a substantially linear fashion against a groove surface of said friction sleeve when said balls are in said braking position, said ball positioning means being defined by the inherent resiliency of said grooved friction sleeve whereby said balls will be independently positioned within said ball channel by a resilient biasing action of said grooved friction sleeve.