Patent Grant
8181744
The present invention relates to lifeline systems and, particularly, to self-retracting lifeline systems and braking systems therefore.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosures of all references cited herein are incorporated by reference.
Many devices have been developed in an attempt to prevent or minimize injury to a worker falling from a substantial height. For example, a number of devices (known alternatively as self-retracting lifelines, self-retracting lanyards, fall arrest blocks, etc.) have been developed that limit a worker's free fall distance to a specified distance and limit fall arresting forces to a specified value.
In general, most currently available self retracting lifeline safety devices or systems include a number of common components. Typically, a housing or cover provides enclosure/protection for the internally housed components. The housing includes attached thereto a connector for anchoring the self-retracting lifeline to either the user or to a fixed anchor point. The connector must be capable of withstanding forces required to stop a falling body of a given mass in a given distance.
A drum or spool around which a lifeline is coiled or spooled rotates within the housing. The drum is typically under adequate rotational tension to reel up excess extended lifeline without hindering the mobility of the user. Like the anchor connector and the other operative components of the retractable lifeline safety device, the drum is formed to withstand forces necessary to stop a falling body of a given mass in a given distance. The lanyard or lifeline is attached at one end thereof to the drum to allow the drum to reel in excess lifeline. The lifeline is attached at the other end thereof to either the user or to an anchorage point, whichever is not already attached to the housing.
Self-retracting lifeline systems also include a braking mechanism which locks (that is, prevents rotation of) the drum assembly of the self-retracting lifeline upon indication that a fall is occurring. For example, when the safety line (for example, rope, cable or web) being pulled from the self-retracting lifeline system causes the drum assembly to rotate above a certain angular velocity, a brake mechanism can cause the drum assembly to suddenly lock.
Many currently available braking systems for self-retracing lanyard systems actuate upon the drum assembly reaching a predetermined angular velocity. The rotational velocity of the drum assembly is proportional to the linear velocity of the safety line. In the case of a self-retracting lanyard braking system which actuates at a predetermined or threshold angular velocity (such as that disclosed in U.S. Pat. No. 5,771,993), a pawl is typically attached to the drum assembly at a pawl pivot that is spaced from the center of gravity of pawl. The pawl can pivot relative to the drum assembly about the pawl pivot. A pawl spring applies a force tending to keep the pawl retracted against a pawl stop on the drum assembly. When the pawl is retracted, it cannot strike an abutment as the drum assembly rotates. As the drum assembly rotates, the center of mass of the pawl tends to follow a straight path tangent to the drum assembly, but the pawl is prevented from pivoting outward by the force of the pawl spring. If, however, the drum rotates at a sufficient velocity, the centripetal force required to keep the pawl against the pawl stop will exceed the force supplied by the pawl spring. At that point, the pawl rotates about the pawl pivot to a radially outwardly extended position wherein the pawl abuts an abutment (for example, on the housing) and brings the drum assembly (and the safety line) to a halt.
In designing a velocity actuated brake, the desired maximum or threshold safety line velocity (and a corresponding angular velocity of the drum assembly) must be defined. For example, the velocity or speed of a fast walk can be used. From the maximum safety line velocity, the maximum or threshold angular or rotational velocity of the drum assembly is determined. The centripetal force that must be supplied by the pawl spring is then determined from the mass of the pawl.
Braking systems based upon angular acceleration are, for example, commonly used in connection with automobile seatbelt restraints. Currently available acceleration braking systems typically include a system of low strength, complexly interacting parts and have not been widely accepted in the fall protection arts.
Although a number of braking mechanisms have been developed for use in connection with self-retracting lifeline and other systems, such mechanisms are often complex (for example, requiring a significant number of interconnected and often complexly operating components), relatively high in cost and insufficiently rugged.
It is thus desirable to develop systems, devices and methods that reduce or eliminate the above and other problems associated with currently available self-retracting lifeline systems.
In one aspect, the present invention provides a lifeline system including a lifeline and a drum assembly around which the lifeline is coiled. The drum assembly is rotatable about a first axis in a first direction during extension of the lifeline and in a second direction, opposite of the first direction, during retraction of the lifeline. The lifeline system further includes a tensioning mechanism in operative connection with the drum assembly to impart a biasing force on the drum assembly to bias the drum assembly to rotate about the first axis in the second direction. The lifeline system further comprises a braking mechanism in operative connection with the drum assembly. The braking mechanism includes a catch that is rotatable relative to the drum assembly about a second axis that is not concentric with the first axis. The second axis is operatively connected to the first axis so that the second axis rotates about the first axis in the same direction as the drum assembly when the drum assembly is rotating about the first axis. A center of mass of the catch is located in the vicinity of the second axis. The catch rotates about the second axis in the second direction when the drum assembly is rotated in the first direction at at least a determined angular acceleration to cause an abutment section of the catch to abut an abutment member of the lifeline system (for example, by moving radially outward a sufficient amount) and stop the rotation of the drum assembly.
The system can further include a biasing mechanism to bias the catch to rotate in the first direction about the second axis (or equivalently, to bias the catch against rotating in the second direction). In several embodiments, the biasing force of the biasing mechanism is balanced against rotational inertia of the catch so that catch rotates in the second direction only when the lifeline is extended at an accelerating rate corresponding to the determined angular acceleration of the drum assembly. The biasing mechanism can, for example, include a spring mechanism attached at one end to the drum assembly and attached at another end to the catch. The spring mechanism can for example, include a torsion spring, an extension spring, a compression spring or a spring clip.
The first axis can, for example, be defined by or correspond to the axis of a shaft passing generally through the center of the drum assembly. In several embodiments, the shaft passes through a slot formed in the catch.
The catch can, for example, be rotatable about the second axis relative to the drum assembly about an extending member extending from the drum assembly. The extending member can define the second axis.
The drum assembly can further include at least one abutment element to limit rotation of the catch in the first direction and to limit rotation of the catch in the second direction. In several embodiments in which the catch includes a slot therein, the slot of the catch is arced or curved and contact or abutment of edges of the slot with the shaft limits rotation of the catch in the first direction and limits rotation of the catch in the second direction
The center of mass of the catch can, for example, be located in the vicinity of or generally upon the second axis.
In another aspect, the present invention provides a braking mechanism for use in a lifeline system. The lifeline system includes a lifeline and a drum assembly around which the lifeline is coiled. The drum assembly is rotatable about a shaft defining a first axis in a first direction during extension of the lifeline and in a second direction, opposite of the first direction, during retraction of the lifeline. The lifeline system further includes an abutment member. The braking mechanism includes a catch including a slot through which the shaft can pass, an element defining a second axis about which the catch is rotatable relative to the drum that is not concentric with the first axis, and at least one abutment section to abut an abutment member of the lifeline system and stop the rotation of the drum assembly. The second axis is operatively connected to the shaft so that the second axis rotates about the first axis in the same direction as the drum assembly when the drum assembly is rotating about the first axis. A center of mass of the catch is located in the vicinity of the second axis. The center of mass of the catch can, for example, be located generally (or exactly) upon the second axis. The abutment section of the catch abuts the abutment member of the lifeline upon rotation of the catch about the second axis in the second direction. The catch rotates about the second axis in the second direction when the drum assembly is rotated in the first direction at at least a determined angular acceleration
In a further aspect, the present invention provides a lifeline system including a lifeline; a shaft having a first axis, a hub connected to the shaft to rotate with the shaft and an abutment member. The lifeline is coiled around the hub. The hub is rotatable with the shaft in a first direction during extension of the lifeline and in a second direction, opposite of the first direction, during retraction of the lifeline. The lifeline system further includes a tensioning mechanism in operative connection with shaft to impart a biasing force on the shaft to bias the shaft to rotate about the first axis in the second direction. The lifeline system also includes a braking mechanism in operative connection with the shaft. The braking mechanism includes a catch that is rotatable about a second axis that is not concentric with the first axis defined by the shaft. The second axis is operatively connected to the shaft so that the second axis rotates about the first axis in the same direction as the drum assembly when the drum assembly is rotating about the first axis. A center of mass of the catch is located in the vicinity of the second axis. The catch rotates about the second axis in the second direction when the shaft is rotated in the first direction at at least a determined angular acceleration to cause an abutment section of the catch to move radially outward (relative to the shaft/first axis) a sufficient amount to abut the abutment member of the lifeline system and stop the rotation of the shaft. A center of mass of the catch is preferably located in the vicinity of or generally upon the second axis.
In another aspect, the present invention provides a braking mechanism for use in a lifeline system including a lifeline, a shaft having a first axis, and a hub connected to the shaft to rotate with the shaft. The lifeline is coiled around the hub. The hub is rotatable with the shaft in a first direction during extension of the lifeline and in a second direction, opposite of the first direction, during retraction of the lifeline. The lifeline system further includes an abutment member. The braking mechanism includes a catch including a slot through which the shaft can pass, an element having or defining a second axis about which the catch is rotatable that is not concentric with a first axis defined by the shaft. The element is operatively connected to the shaft so that the element rotates about the first axis in the same direction as the hub when the hub is rotating about the first axis. A center of mass of the catch is located in the vicinity of the second axis of the element. The catch further includes at least one abutment section in the vicinity of a perimeter of the catch. The catch rotates about the second axis in the second direction when the shaft is rotated in the first direction at at least a determined angular acceleration to cause the abutment section of the catch to move radially outward relative to the shaft a sufficient amount to abut the abutment member of the lifeline system and stop the rotation of the shaft. A center of mass of the catch can be located generally upon or coincide with the second axis.
In a further aspect, the present invention provides a method of providing a braking function in a lifeline system as described above. In that regard, the lifeline system includes lifeline and a drum assembly around which the lifeline is coiled. The drum assembly is rotatable about a first axis in a first direction during extension of the lifeline and in a second direction, opposite of the first direction, during retraction of the lifeline. A tensioning mechanism is in operative connection with the drum assembly to impart a biasing force on the drum assembly to bias the drum assembly to rotate about the first axis in the second direction. The lifeline system also include and an abutment member.
The method includes placing a braking mechanism in operative connection with the drum assembly of the lifeline system, wherein the braking mechanism include a catch that is rotatable relative to the drum assembly about a second axis that is not concentric with the first axis. The second axis is operatively connected to the first axis so that the second axis rotates about the first axis in the same direction as the drum assembly when the drum assembly is rotating about the first axis. A center of mass of the catch is located in the vicinity of the second axis. The catch rotates about the second axis in the second direction when the drum assembly is rotated in the first direction at at least a determined angular acceleration to cause an abutment section of the catch to move radially outward (relative to the first axis) a sufficient amount to abut an abutment member of the lifeline system and stop the rotation of the drum assembly.
The catch can be biased against rotating in the second direction. A biasing force applied to the catch can, for example, be balanced against rotational inertia of the catch so that catch rotates in the second direction only when the lifeline is extended at an accelerating rate corresponding to the determined angular acceleration of the drum assembly.
The method can further include providing at least one abutment element to limit rotation of the catch in the first direction and limit rotation of the catch in the second direction.
Thus, in several embodiments, the present invention provides acceleration-actuated stop, brake or catch devices, systems or methods for self retracting lifeline systems used for personal fall protection. Self-retracting lifeline systems of the present invention allow a user to move about freely by releasing or retracting a lifeline as needed. However, if the user were to fall, the stop, brake or catch devices or systems of the present invention lock the drum assembly of the self-retracting lifeline to reduce the fall distance. The braking devices, systems and/or methods of the present invention are significantly less complex, less costly and more rugged than brake mechanisms found on currently available self-retracting lifeline systems.
The present invention, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.
As used herein and in the appended claims, the singular forms “a,” “an”, and “the” include plural references unless the content clearly dictates otherwise. Thus, for example, reference to “a connector” includes a plurality of such connectors and equivalents thereof known to those skilled in the art, and so forth, and reference to “the connector” is a reference to one or more such connectors and equivalents thereof known to those skilled in the art, and so forth.
A hub or drum assembly 100 includes a first hub flange or plate 110, a hub or drum 120 around which lifeline web 40 is coiled, a web sleeve 130 (see, for example,
As common with self-retracting lifelines, tension can be applied to drum assembly 100 to retract lifeline web 40 after extension thereof. In that regard, shaft 70 can be rotationally locked to hub or drum assembly 100 via hub plate 110 (which can also act as a catch or braking base as described below) by a shaft pin 74 which engages slots 111 in hub plate 110. A power spring assembly 160 can include a conventional coiled strap of spring steel (not illustrated in detail in
Self-retracting lifeline system 10 also includes a braking mechanism indicated generally by reference 165 in
The center of mass of catch 190 is located in the vicinity of or generally at the axis about which it pivots or rotates on catch pivot 170. Preferably, the axis of catch pivot 170 is located at or as close as possible to the center of mass of catch 190. Catch 190 will thus maintain its position relative to catch base 110 when hub assembly 100 is rotating at a constant angular velocity as when lifeline web 40 is being pulled out of self-retracting lifeline 10 at a constant rate. That is, catch 190 and hub plate/catch base 110 will rotate as a unit and centrifugal force will not cause catch 190 to rotate (about catch pivot 170) relative to hub plate/catch base 110. However, if hub assembly 100 experiences a clockwise angular acceleration (as is the case when lifeline web 40 is being pulled out of self-retracting lifeline 10 at an increasing rate) sufficiently high for the rotational inertia of catch 190 to overcome the force of catch spring 200, catch 190 will rotate about catch pivot 170 in a second direction (counterclockwise in the illustrated embodiment) relative to hub plate/catch base 110. This condition is illustrated in
Analogous to the behavior of a mass having a linear velocity, a rotating mass will tend to keep rotating at a constant rotational velocity unless acted upon by some external torque according to the equation T=I×α, where I is the rotational moment of inertia of the mass and α is its rotational acceleration.
In a familiar example, one could be standing on a merry-go-round holding a bicycle wheel by its axle with the axis in a vertical orientation. Assume the axle bearings are frictionless and the initial rotational velocities of the wheel and the merry-go-round are zero. Also assume that one of the spokes of the bicycle wheel happens to be pointing due north. If the merry-go-round were to begin rotationally accelerating clockwise to some new rotational velocity, the bicycle wheel would be observed to begin rotating counter-clockwise relative to the person holding it but the spoke would still be pointing due north. The wheel would be translating in a circular path but it would not be rotating. The bicycle wheel is “left behind” rotationally because it is maintaining its initial zero rotational velocity. If the person holding the bicycle wheel grabbed the rim of the wheel, it would provide the torque needed to bring the wheel “up to speed” to match the rotational velocity of the merry-go-round.
The axle of the wheel need not be collinear with the merry-go-round axis, but only parallel thereto. If the wheel is perfectly balanced with its center of mass at the center of the axle, the rotational velocity of the merry-go-round will not produce any torque (from centripetal forces) to act on the wheel.
In the case of catch 190, the center of mass of catch 190 is in the vicinity of or at the center of catch pivot 170. Thus, catch 190 will not tend to rotate relative to the hub assembly 100 as a result of centripetal forces, regardless of the rotational velocity of hub assembly 100.
When drum assembly 100 accelerates rotationally clockwise, catch 190 will also accelerate rotationally because the force of catch spring 200 is sufficient to provide the torque required to keep catch 190 in abutting contact with abutment element 117. However, if the rotational acceleration of drum assembly 100 is great enough, the torque supplied by the catch spring 200 will not be sufficient to prevent catch 190 from being “left behind” and moving/rotating to an extended, locking position as illustrated in
In
When catch 190 is rotated counterclockwise about catch pivot 170 and relative to hub plate/catch base 110, an abutment section, stop section or corner 195 of catch 190 extends radially outward beyond the periphery of hub plate/catch base 110, because catch pivot 170 is not concentric with shaft 70.
In several embodiments, the biasing force exerted by catch spring 200 is balanced against the rotational inertia of catch 190 as described above so that catch 190 “actuates” only when lifeline web 40 is being pulled from self-retracting lanyard 10 at an accelerating rate corresponding, for example, to the beginning of a fall. For example, catch 190 and catch spring 200 can be readily designed (using engineering principles known to those skilled in the art) to actuate when lifeline web 40 is being pulled out at a certain determined (maximum or threshold) acceleration (for example, ½ or ¾ times the acceleration of gravity). From the maximum linear acceleration of lifeline web 40, the corresponding maximum drum rotational or angular acceleration is determined. The rotational moment of inertia of catch 90 determines the maximum torque that must be supplied by the catch spring 200. For linear/angular accelerations below the threshold accelerations or when the user is extending the web at a constant rate, such as when walking, catch 190 will not actuate and hub assembly 100 will turn freely.
Self-retracting lifeline 10a can, for example, be connected via a connector 30a to some fixed object or anchor point. A distal end 44a of lifeline or lifeline web 40a can, for example, be connected to a harness 400 worn by the user 5 (see
Hub or drum assembly 100a of system 10A includes a first hub flange or plate 110a, a hub or drum 120a around which lifeline web 40a is coiled, a second hub flange 140a, and connectors such as screws 150a (which are oriented in the opposite direction as screws 150 of system 10). When assembled, hub plate 110a, hub 120a, hub flange 140a, and screws 150a form hub or drum assembly 100a which rotates with shaft 70a. Drum 120a is of decreased diameter and increased width as compared to drum 120 to accommodate a webbing that is approximately 25 mm wide (as compared to drum 120a, which is designed for use with webbing that is approximately 17 mm wide). A loop end 42a of the lifeline is positioned within a passage 123a formed within hub 120a around shaft 70a to anchor loop end 42a securely within drum assembly 100a. Loop end 42a extends through a slot 121a formed in hub 120a and a portion of lifeline web 40a is coiled around hub 120a, leaving a free end 44a which extends from housing 20. Lifeline web 40a can also include an energy absorbing portion or section 46a in which, for example, a length of lifeline web 40a is folded back on itself and sewn or stitched as know in the fall protection arts. In the case of a fall, the stitching of the energy absorbing portion 46a tears to absorb energy.
Shaft 70a is rotationally locked to hub plate 110 via a catch or braking base 112a (formed, for example, from a metal such as cast stainless steel) that is connected to hub plate 110a by screws 150a. In that regard, braking base 112a includes a passage 113a formed therein through which shaft 70a passes and a radially inward projecting member 114a which engages a radially outward portion of slot 76a in hub plate 110. Tension is applied to drum assembly 100a to retract lifeline 40a after extension thereof via a power spring assembly 160a including coiled strap of spring steel 162a inside a plastic housing formed by housing members 168a. A radially outward end 163a of spring steel strap can be anchored to frame 60a. A radially inward end 163a′ can engage a radially inward, narrow portion of slot 76a in shaft 70a. One housing member 168a of power spring assembly 160 can, for example, be rotationally locked to frame 60 by a projecting member or stud 164a on housing member 168a which engages a abutment member 64a in frame 60a. As described above, lifeline web 40a is anchored to and coiled around hub 120a of drum assembly 100a. At assembly, power spring 162a is “wound up” to provide torque to shaft 70a and thus to drum assembly 100a. The torque applied to shaft 70a pre-tensions lifeline web 40 and causes lifeline web 40 to coil up or retract around hub 120a after it has been uncoiled therefrom as described above in connection with self-retracting lanyard system 10.
Like self-retracting lifeline system 10, self-retracting lifeline system 10a includes a braking mechanism. In that regard, a catch 190a (formed, for example, from a metal such as cast stainless steel) is pivotably or rotatably mounted (eccentric to the axis of shaft 70a) via a partially threaded member 180a which passes through a passage 192a formed in catch 190a to connect to brake or catch base 112a via a threaded passage 116a formed in catch base 112a. As described above in connection with catch 190, the axis of pivot member 180a (and passage 192a) preferably corresponds generally to the center of mass of catch 190a. The braking mechanism can also include a catch spring 200 having one end which engages a connector 117a in catch base 112a and another end which engages a connector 194a in catch 190a. The force exerted by the catch spring 200a is generally balanced against the rotational inertia of catch 190a so that catch 190a actuates (via centrifugal force) to effect braking only when lifeline web 40a is being pulled from self-retracting lifeline system 10a at an acceleration rate corresponding, for example, to the beginning of a fall.
As described above, shaft 70a is rotationally locked to the catch base 112a and thereby to drum assembly 100a.
The center of mass of catch 190a is located generally where it pivots or rotates on pivot member 180a. Catch 190a will thus maintain its position relative to hub assembly 100a, while hub assembly 100a is rotating at a constant angular velocity as when lifeline web 40a is being pulled out of self-retracting lifeline 10a at a constant rate. That is, catch 190a and catch base 112a/hub assembly 100a will rotate as a unit and centrifugal force will not cause catch 190a to rotate about pivot member 180a relative to catch base 112a/hub assembly 100a. However, if hub assembly 100a experiences a clockwise (in the orientation of
In
When catch 190a is rotated counterclockwise about pivot member 180a relative to hub assembly 100a, an abutment section, stop section or corner 195a of catch 190a extends radially outward (because catch pivot 180a is not concentric with shaft 70a).
As described in connection with self-retracting lifeline system 10, the biasing force exerted by catch spring 200a can be balanced against the rotational inertia of catch 190a so that catch 190a “actuates” only when lifeline web 40a is being pulled from self-retracting lanyard 10a at a predetermined accelerating rate corresponding, for example, to the beginning of a fall. For example, catch 190a and catch spring 200a can be readily designed (using engineering principles known to those skilled in the art) to actuate when lifeline web 40a is being pulled out at a certain determined acceleration (for example, ½ or ¾ times the acceleration of gravity). For lower accelerations or when the user is extending the web at a constant rate, such as when walking, catch 190a will not actuate and hub assembly 100a will turn freely.
In the above embodiments, the catch base is a component of or is attached to the drum assembly. However, one skilled in the art appreciates that the catch base (that is, that element to which the catch is rotatably attached about an axis other than the axis of the main shaft) can be separate from or not connected to the drum assembly. In that regard, the catch base can be a separate element or connected to a component of the lifeline system other than the drum assembly. The catch base can, for example, be independently connected to or locked to the shaft so that the shaft and catch base rotate together. The catch, rotatably connected to the catch base (about an axis eccentric from the axis of the shaft), can operate as described above to stop rotation of the shaft and, thereby, stop rotation of a lifeline hub (which can be part of a drum assembly) connected to the shaft.
Although the present invention has been described herein in connection with the representative example of a lifeline formed of a web material, the systems, devices and methods of the present invention will operate equally well with a cable, a rope, or other type of lifeline coiled or spooled on a hub or drum assembly. Moreover, the acceleration-based braking systems of the present invention can be used in connection with systems other than self-retracting lanyards.
The foregoing description and accompanying drawings set forth the preferred embodiments of the invention at the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope of the invention. The scope of the invention is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/031,336, filed Feb. 25, 2008, and U.S. Provisional Patent Application Ser. No. 61/045,808, filed Apr. 17, 2008, the disclosures of which are incorporated herein by reference.
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