Patent Application
20190276286
This specification relates generally to pulley systems and, more specifically, to safety mechanisms to address lifting cord failure in pulley systems.
Pulleys are used to lift an object attached to a cord (e.g., a cable, rope, wire, chain, string, or other cord) by translating a downward force applied to one end of the cord to an upward force on the object attached to the other end of the cord. If the lifting portion of the cord happens to be severed or released while lifting the object, a conventional pulley, with no built-in safety system, will allow the object to fall. This type of cord failure can not only cause damage to the object, but also harm those close to the object when it falls.
Disclosed are pulley systems featuring safety mechanisms that address lifting cord failure. Among other advantages, embodiments feature a mechanical locking mechanism for a pulley that automatically locks a cord when failure occurs on either end of the cord.
In general, a first aspect features a pulley system for lifting a load using a cord. The pulley system includes a first stage and a second stage mechanically coupled to the first stage at a pivot point, the first and second stages being independently rotatable about a stage axis passing through the pivot point. The pulley system also includes a first pulley attached to the first stage and the second stage at the pivot point, the first pulley being rotatable about a first pulley axis coinciding with the stage axis. Additionally, the pulley system includes a second pulley attached to the second stage, the second pulley being rotatable about a second pulley axis parallel to but displaced from the stage axis. The pulley system also includes a third pulley attached to the second stage, the third pulley being rotatable about a third pulley axis parallel to but displaced from the stage axis and the second pulley axis. The pulley system further includes a pair of braking elements attached to the first stage, a first of the braking elements being positioned between the first and second pulleys and a second of the braking elements being positioned between the first and third pulleys. With respect to the pulley system, an even tension on the cord aligns the first stage and the second stage in a neutral arrangement in which both braking elements are disengaged from the cord, and an uneven tension on the cord rotates the first stage with respect to the second stage about the stage axis so that the first braking element engages the cord at the second pulley or the second braking element engages the cord at the third pulley.
Implementations of the electronic display can include one or more of the following features and/or one or more features of other aspects. For example, the pulley system can also include a pair of guide elements attached to the first stage defining a channel for the cord. The first, second, and third pulleys and the pair of guide elements can define a path for the cord in a plane perpendicular to the stage axis extending from the channel to the second pulley, from the second pulley to the first pulley, from the first pulley to the third pulley, and from the third pulley to the channel. The pulley system can also include a guide element attached to the second stage and positioned in the channel defined by the pair of guide elements. The pair of guide elements attached to the first stage and the guide element attached to the second stage can be cylindrically-shaped guide elements, each having a corresponding cylinder axis parallel to the first pulley axis. The cord path of the pulley system can extend on either side of the guide element attached to the second stage.
In some implementations, the first stage includes a suspension point for fastening to a suspension cable. The suspension point, stage axis, and channel defined by the pair of guide elements can lie along a common line. The common line can be in a vertical direction when the pulley system is suspended from the suspension point.
In addition, the first and second pulley axes can define a horizontal line when the pulley system is suspended from the suspension point.
In other implementations, the second and third pulleys can have the same diameter. The first pulley can also have the same diameter as the second and third pulleys.
Additionally, the braking elements can each include teeth arranged to engage the cord when the corresponding braking element engages the cord.
The pulley system can also include a rope, a cable, a chain, a wire, or a string.
In
Pulley system 100 is suspended from a suspension point 160, to which a suspension cable can be attached and anchored to a stable structure. Under the force of gravity, pulley system 100 hangs from the stable structure, as shown in
First stage 110 and second stages 120a and 120b each extend primarily in the X-Y plane and have a height that extends in the Z-direction, having parallel front and rear surfaces. More generally, provided the stage surfaces do not hinder their relative motion (described below), the surfaces need not be parallel to one another.
Each of the pulleys 112, 122, and 132 rotate both clockwise and counter-clockwise about a corresponding axis 114, 124, and 134, respectively. Axes 114, 124, and 134 extend in the Z-direction and are all parallel to one another. From the front to the back of pulley system 100, axis 114 passes through second stage 120a, pulley 112, first stage 110, and second stage 120b. Similarity, axes 124 and 134 pass through second stage 120a, pulleys 122 and 132, respectively, as well as through second stage 120b.
Axis 114 serves as a fulcrum for the pulley system. While the position of first stage 110 remains mostly fixed within the X-Y plane, second stages 120a and 120b can rotate together about axis 114. Pulley 112 is rotatably attached to first stage 110 and second stages 120a and 120b at axis 114. Pulleys 122 and 132 are rotatably attached to second stages 120a and 120b at axes 124 and 134.
Pulley system 100 is used to raise or lower a load using cord 130, which loops partially around pulleys 122 and 132, and loops completely around pulley 112. Because cord 130 loops completely around pulley 112, at the lowest point of pulley 112, with regard to the Y-direction, two portions of cord 130 are adjacent to one another. The portion of cord 130 below the cord's contact with guiding element 140a is referred to as the left hanging portion of cord 130, while the portion below the cord's contact with guiding element 140b is referred to as the right hanging portion of cord 130.
First stage 110 includes guiding elements 140a and 140b. These elements define a channel through which the two hanging portions of cord 130 are threaded. In this embodiment, guiding elements 140a and 140b are cylindrical components that extend in the Z-direction from the front surface of first stage 110. In other embodiments, guiding elements 140a and 140b can have different geometries, so long as they are able to provide a channel for cord 130. For example, guiding elements 140a and 140b can be either solid or hollow or rotatably attached to first stage 110 at two separate axes.
Furthermore, guiding elements 140a and 140b are symmetric to one another about an axis of symmetry that extends in the Y-direction through axis 114. In other embodiments, guiding elements 140a and 140b can be asymmetric to one another about the axis of symmetry. In other embodiments, guiding elements 140a and 104b can be omitted from pulley system 100.
Second stage 120b includes guiding element 140c. Guiding element 140c ensures that the two hanging portions of cord 130 do not becoming intertwined with one another. This element can be identical in form and structure to guiding elements 140a and 140b.
First stage 110 also includes braking elements 150a and 150b, which engage and brake cord 130 when a differential force on the cord exceeds a certain threshold (described below). In this embodiment, braking elements 150a and 150b are cylindrical components that extend in the Z-direction from the front surface of first stage 110. In other embodiments, these elements can have a different geometry so long as the braking elements, when engaged, are able to prevent cord 130 from moving. For example, braking elements 150a and 150b can be either solid or hollow or have ridges (e.g., teeth) to better allow the element to grip cord 130. In some embodiments, pulley system 100 can include more than two braking elements.
In general, the components of pulley system 100 can be constructed of any material, or combination of materials, that have suitable mechanical properties and can be formed into the appropriate shapes. Generally, materials used should be sufficiently rigid to bear stresses associated with the use of the pulley system. For example, the components can be made of metal, plastic, wood, or a combination of these materials. Similarly, cord 130 can be any of a variety of suitable cords, such as a rope, a cable, a chain, a wire, or a string. As such, cords can be formed from metals, natural materials such as cotton, coir, hemp, henequen, jute, and sisal, as well as synthetic materials such as aramid, nylon, polyester, and polypropylene.
As illustrated in
When a differential tension is applied to cord 130, (i.e., when a different downward force is applied to the two ends of cord 130), the differential tension causes the cord to move and to rotate the pulleys about their respective axes. In addition, stages 120a and 120b rotate relative to stage 110 about axis 114. However, provided the differential tension does not exceed a certain threshold, cord 130 is free to move. Under these circumstances, a user can raise or lower a load using pulley system 100 by attaching the load to one end of the cord and then raising or lowering the load by applying an appropriate force to the other end of the cord.
The degree to which second stages 120a and 120b rotate relative to axis 114 depends on whether the difference in applied force is sufficient to cause either braking element 150a or 150b to contact cord 130. When cord 130 contacts either braking element, cord 130 is pinched between the braking element and its adjacent pulley, and second stages 120a and 120b can no longer rotate. Braking element 150a or 150b is said to be “engaged” when it makes contact with either pulley 122 or 132, respectively. The difference in forces required to engage braking element 150a or 150b is referred to as a threshold force of pulley system 100, or simply the threshold force.
In general, the threshold force can vary depending on the nature of the use of the pulley. Generally, the threshold force will be larger where larger loads are expected. For relatively modest loads, the the threshold force can be 50 N or less (e.g., 20 N or less, 10 N or less, 5 N or less). A larger threshold force is also possible (e.g., more than 50 N, such as 100 N or more, 1 kN or more, 2 kN or more, 5 kN or more, 10 kN or more).
As an example of when the difference in downward forces applied to the two ends of cord 130 is less than the threshold force, consider when the pulley system has a load attached to the right hanging portion of cord 130. The attached load results in a downward force on the right hanging portion, which corresponds to the weight of the attached load. At the left hanging portion, a downward force can be applied that is exactly equal to the weight of the load (e.g., by a user pulling downwards on the left hanging portion). In this example, the difference in forces applied to each end of cord 130 is zero. Therefore, cord 130 does not move, and the attached load remains stationary.
Not only can pulley system 100 allow an attached load to remain stationary while the difference in downward forces applied to the two ends of cord 130 is less than the threshold force, it can also allow the load to ascend. As an example, a load can be attached to the right hanging portion of cord 130. At the left hanging portion, a downward force can be applied that is greater than the weight of the load. While the difference between the forces on the right and left hanging portions is less than the threshold force, cord 130 is able to move as a result of unequal forces being applied to its ends. As a result of a greater force being applied to the left hanging portion compared to the force on the right hanging portion, the cord moves so as to allow the load to ascend.
In addition to allowing an attached load to ascend while difference in downward forces applied to the two ends of cord 130 is less than the threshold force, pulley system 100 can also allow the load to descend. For example, a load can be attached to the right hanging portion of cord 130. At the left hanging portion, a downward force can be applied that is less than the weight of the load. While the difference between the forces on the right and left hanging portions is less than the threshold force, cord 130 can move. As a result of a greater force being applied to the right hanging portion, when compared to the force on the left hanging portion, the cord moves so as to allow the load to descend.
When the difference in downward forces applied to the two ends of cord 130 is less than the threshold force, a weight attached to one of the hanging portions of pulley system 100 can be raised or lowered according to the force applied to the other hanging portion, which is also referred to as the “lifting portion”. In addition to allowing cord 130 to move while the difference in downward forces applied to the two ends of cord 130 is less than the threshold force, pulley system 100 can also transition to a braking configuration in which cord 130 is not able to move. Unequal forces on the hanging portions of cord 130 cause second stages 120a and 120b to rotate relative to axis 114. Second stages 120a and 120b are able to rotate through a certain arc before either pulley 122 or 132 makes contact with braking element 150a or 150b, respectively.
Although not shown in
In
A number of embodiments have been described. However, other implementations are also possible. For example, while the braking elements in pulley system 100 engage by pinching cord 130 between the braking element and a corresponding pulley, in other implementations, the braking elements can engage by contacting the pulley (e.g., in addition to or without contacting cord 130) and breaking the cord by preventing rotation of the pulley.
Other embodiments are in the following claims.
