Apparatus for branched scissor linkage and associated auxetic mechanisms

According to one embodiment, there is taught herein a family of “branched” variants of the traditional scissor mechanism, in which each stage is formed from more than two arms, joined at their midpoints by a branched rivet. In one embodiment arms in adjacent stages are joined at their endpoints with joints that allow for rotation in a single plane. Each resulting mechanism has one degree of freedom in its motion. It deploys from a compact, collapsed state to an extended state. One embodiment is a grasping member that is mechanically coupled to a scissor mechanism so that when scissor mechanism is collapsed the grasping member is open. Then, when the scissor mechanism is extended the grasping member becomes closed.

TECHNICAL FIELD

This disclosure relates generally to mechanical linkages and, more particularly, to scissor linkages and associated auxetic mechanisms.

BACKGROUND

The traditional scissor linkage as shown inFIGS.1A and1Bhas one degree of freedom in its motion: it deploys from a compact, collapsed state (FIG.1B) to an extended state (FIG.1A). The linkage consists of a number of stages, each stage consisting of two arms joined at their midpoints by a rivet that allows the arms to rotate against each other. Arms in adjacent stages are joined at their endpoints with joints that again allow for rotation.

Although these sorts of devices are in common use they are subject to certain disadvantages including, among others, that the traditional scissor linkage is weak against bending forces that act perpendicular to the plane in which the mechanism lies, although it is strong against forces within the plane. The usual fix to this weakness in the traditional scissor linkage (as used, for example, in electric and hydraulic scissor lifts) is to use two parallel scissor linkages, connected across at the hinge points, as shown inFIGS.3A and3B. This is effective in certain circumstances, although it introduces an asymmetry between the different directions: the horizontal direction in the plane of the scissor linkages acts differently from the horizontal direction perpendicular to the plane of the scissor linkages. For some use cases, e.g. a robotic arm, it may be useful to have the same level of stability in all orientations, which the branched linkages provide.

As such, what is needed is a scissor linkage that does not suffer from the disadvantages of the prior art.

Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.

SUMMARY OF THE INVENTION

According to an embodiment, there is taught herein a family of “branched” variants of the traditional scissor mechanism, in which each stage is formed from more than two arms, each joined preferably at their respective midpoints by a “branched” rivet. In one embodiment, arms in adjacent stages are joined at their endpoints with joints that allow for rotation. Each resulting mechanism has one degree of freedom in its motion. It deploys from a compact, collapsed state to an extended state.FIGS.2A to2Fshow examples with three (FIGS.2A and2B), four (FIGS.2C and2D) and six (FIGS.2E and2F) arms. The arms in the embodiment ofFIGS.2A,2C, and2Eare identical, so such a mechanism could be taken apart and reconfigured into another arrangement, only needing a different branched rivet part in order to affect the reconfiguration.

These designs have a number of potential advantages over the traditional scissor linkage. For example:(1) More independent interlinked parts are involved. Particularly for the versions with four or more arms per stage, this makes the mechanisms stronger and more stable in general.(2) With more arms at each end of the linkage, more motors can be used to move the mechanism, so greater force can be applied.(3) The traditional scissor linkage is weak against bending forces that act perpendicular to the plane in which the mechanism lies, although it is strong against forces within the plane. Various embodiments of the branched mechanisms disclosed herein are strong against forces from any direction.

According to another embodiment, there is provided a grasping or grabbing mechanism suitable for use with the scissor linkage disclosed herein. In one variation, the device consists of a syringe-like handle attached to a four-armed branched scissor linkage, which has a set of claws attached at the other end. This embodiment has a number of useful properties:(1) The mechanism is compact when retracted, but significantly extends the user's reach when extended.(2) Even when extended, the mechanism is strong against lateral forces in all directions. This allows it, for example, to support the weight of the grasped object no matter the orientation in which the device is held.(3) The claws approach an object from four directions as opposed to the two in most grabber tools, enhancing the ability of the device to securely grasp the object.(4) The grasping motion of the claws is a natural consequence of the action of the branched scissor mechanism, requiring no additional moving parts.

The foregoing has outlined in broad terms some of the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described hereinafter in detail, some specific embodiments of the instant invention. It should be understood, however, that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments or algorithms so described.

According to an embodiment, there is taught herein a family of “branched” variants of the traditional scissor mechanism, in which each stage is formed from three or more equal-length arms, joined at their midpoints by a “branched” rivet. Note that for purposes of the instant disclosure, the term branched rivet will be used to describe, in a first embodiment, a device that contains three or more radially projecting coplanar protrusions substantially equally spaced about its perimeter, although that spacing is not a requirement. In some embodiments, the protrusions will be threaded on their outer termini but that is not a requirement. In other cases, rather than protrusions, holes in the branched rivet will be provided instead, which holes might be internally threaded. Note, although various embodiments are designed so that each arm is mounted to the branched rivet at its midpoint, that is only one configuration that might be employed since, in some cases, mounting the arms other than at their midpoints would allow additional leverage to be applied. For example, a group of asymmetrically mounted arms could be arranged so that increased movement distance at one end could provide increased force at the other end. The offset rivet position could also be usefully employed in the middle of the linkage, to change the distance moved/force ratio as needed. That being said, for purposes of the instant disclosure when it is said that multiple equal length arms are mounted on the same branched rivet, it should be noted that the mounting could be symmetric (at the midpoint of each arm) or asymmetric (the mounting point of each arm is offset from the midpoint by the same amount so that each arm extends above/below the mounting point by the same amount).

In one embodiment, the branched rivet might have holes equally spaced about its perimeter but all must generally lie in the same plane. When threaded holes are provided, it is anticipated that a matching threaded bolt or similar structure will be used to attach the arms described below to the branched rivet. Note that, for purposes of the instant disclosure, when the branched rivet is said to have protrusions, that term should be understood to include both instances where the protrusions are integral to the device as well as instances where the there are holes into which bolts, rivets, etc., are removably or permanently inserted. It should also include instances where the protrusions are equally spaced around the perimeter of the device as well as when they are not.

In some variations the branched rivet might be made of metal but other variations are certainly possible (e.g., plastic for small embodiments) and well within the ability of one of ordinary skill in the art to devise.

As is generally indicated in the embodiments ofFIGS.2A-2F, the instant branched scissor linkages2A,2C, and2E generally comprise three or more arms205each of which are each rotatably mounted on one of the protrusions of the branched rivet210. As can be seen, in this particular embodiment each arm205is mounted at its midpoint to one of the protrusions of the branched rivet210and should be mounted so as to be freely rotatable about that protrusion with a single degree of freedom. In some embodiments, the protrusions of the branched rivet210might be surmounted by a nut (if the protrusion is threaded) or a cap215which serves to keep the arm205mounted on the branched rivet210. In some embodiments the branched rivet210will have a flat upper and lower surface.

In some embodiments, the instant branched scissor linkage will be comprised of two or more stages. In the embodiments ofFIGS.2A-2F, each example2A,2C, and2E is comprised of two identical stages, Stage1and Stage2assemblies, which are in mechanical communication with each other via rotatable joints. More particularly, the arms205in adjacent stages are joined at their endpoints with rotatable joints. Preferably the joints will be rotatable in a single plane. In the example ofFIG.2A, the upper terminus of each Stage2assembly arm205contains an orthogonally extending rod220which is sized to mate with a socket225on one of the lower terminus arms205of the Stage1assembly. As can be seen, this arrangement limits each mated arm to rotation is a single plane. Clearly, the exact means by which the arms in adjacent stages are hinged or otherwise rotatably joined together could take many forms and those of ordinary skill in the art will be able to readily devise alternatives to those presented herein. For purposes of instant disclosure, the hinging component225on lower end of an arm in the Stage1assembly will generally be referred to as an upper hinge component and the mating part220which is situated on the upper end of the an arm in the Stage2assembly will be referred to a lower hinge component. As described previously, the upper and lower hinge components must be designed to mate with each other and allow rotation in a single plane or with one degree of freedom.

Further, although it is preferred that the arms205in both stages be of the same length, that is not an absolute requirement. In some embodiments, the arm lengths of the arms in the Stage1assembly might be different from the lengths of the arms in Stage2. That being said, it is a requirement that the lengths of all of the arms in a stage must be the same length.

Each resulting mechanism inFIGS.2A-2Fhas one degree of freedom in the relative motion of each of the connected arms205, which means that it can readily deploy from a compact, collapsed state (FIGS.2B,2D, and2F) to an extended state (FIGS.2A,2C, and2E).FIGS.2A-2Fshow examples with three, four and six arms205in each stage. The arms205in each stage of the embodiments ofFIGS.2A,2C, and2Eare identical, so that a stage with, say, six arms (FIG.2E) could readily be disassembled and reconfigured into another arrangement, only needing a different branched rivet part210,220, or230in order to reconfigure the device, with larger branched rivet parts being preferably utilized in the three and four arm versions. Thus, the arms inFIGS.2E and2Fcould also be reconfigured to form the embodiments ofFIG.2Aor D, albeit with a smaller sized branched rivet part210/220than part230.

These designs have a number of potential advantages over the traditional scissor linkage. Among them are:(1) More independent interlinked parts are involved. Particularly for the versions with four or more arms per stage, this makes the mechanisms stronger and more stable in general.(2) With more arms at each end of the linkage, more motors can be used to move the mechanism, so greater force can be applied.(3) The traditional scissor linkage is weak against bending forces that act perpendicular to the plane in which the mechanism lies, although it is strong against forces within the plane. Various embodiments of the branched mechanisms disclosed herein are strong against forces from any direction.

In addition to the branched scissor linkages, also taught herein are methods to join them together to make larger structures. One relevant comparison in existing work is with the Hoberman sphere. In the Hoberman sphere, traditional scissor linkages come together at a “node”, similar to the configurations shown inFIGS.4A and4B. In this embodiment three scissor linkages with arms405are rotatably joined415at their respective mid points. Each leg is further rotatably joined at one end to either a triangular upper node420or a triangular lower node422, preferably the triangular nodes will have three equal length sides. Each rotatable connection only allows rotation in a single plane, or a single dimension. The net effect that this has is that if one of the three linkages extends, it forces the two triangular connector parts together, which forces the other two linkages to extend. Thus, the entire system has one degree of freedom.

A similar method of connection also works for branched scissor linkages as shown inFIGS.5A-5B. Here, two four-armed branched scissor linkages520and530(e.g., as shown inFIGS.2C and2D) meet at two triangular connectors510and515. Note that when one of the linkages520/530extends, it forces the two triangular connectors510/515toward each other which, in turn, forces the other linkage to also extend. These two branched scissor linkages520/530are connected in the same way as the linkages in the larger structure inFIGS.8A and8B: they are situated at approximately right angles to each other. By altering the angle of the triangular connectors, incident to both branched scissor linkages, the angle between the linkages can be altered.

Although obviously three-dimensional, the mechanism inFIGS.4A and4Bacts in a region close to the horizontal plane through the midpoints of the arms of the scissors. If the mechanism is built outwards with more nodes connecting to more scissor linkages, this plane continues outwards. In the Hoberman sphere, the plane is bent around to form a sphere, but still, the mechanism acts in a region close to a two-dimensional surface. In contrast, the branched scissor mechanism can continue outwards in a truly three-dimensional manner:(1) Four three-armed branched scissor linkages can meet at a node, joined by four triangular connectors620as shown inFIGS.6A and6B. The four three-armed linkages are arranged around the node610as the vertices of a regular tetrahedron.(2) Similarly, six four-armed linkages can be joined by eight triangular connectors, with the linkages being arranged around the node as the vertices of a regular octahedron, by continuing the pattern inFIGS.5A and5B.(3) Eight three-armed linkages can be joined by six square connectors, the linkages arranged around the node as the vertices of a cube. SeeFIGS.7A and7B.(4) Twenty three-armed linkages can be joined by twelve pentagonal connectors.(5) Twelve five-armed linkages can be joined by twenty triangular connectors.

The above lists some of the most regular kinds of connections. Similar arrangements should be possible where the branched scissor linkages are connected together at arbitrary irregular polyhedral nodes.

By connecting together branched scissor linkages at nodes, larger auxetic structure can be built:FIGS.8A and8Bshow part of a cubic lattice built from four-armed branched scissor linkages, connected at nodes as in example (2) above. Any number of stages of the four-armed linkage can be used on each “edge” element between nodes, and the entire structure can be built outwards to make as much of the cubic lattice as is desired.Using three-armed branched scissor linkages connected as in (1) above, an auxetic structure based on the molecular structure of diamond can be built. In this case, an odd number of stages is required between nodes.Using three-armed branched scissor linkages connected as in (3) above, an auxetic structure based on the body centered cubic lattice can be built. Again, an odd number of stages is required between nodes.

Similar linkages connected to each other at arbitrary angles could be used to make arbitrary space graphs, not just the regular lattices displayed as examples herein.

According to another embodiment, there is provided the extendable grasping tool1000, various aspects of which are illustrated inFIGS.9A-9BthroughFIG.13. In this embodiment, the device is made from rigid components of the sort shown inFIGS.10and11, resulting in the arrangement (shown in both retracted and extended form) inFIGS.9A and9B.

The arm and branched rivet parts are used to build a branched scissor linkage of a desired length—in this examples three stages1040were used. Then four claws1005were attached to the end of the branched scissor linkage. In this example a claws clips rigidly onto each arm part (seeFIGS.10A and10B). Alternatively, a single solid part could be made consisting of an arm that ends in a claw. The claw may be designed differently to better grasp particular kinds of objects. For example, the claw may use a softer material or be designed with ripples, increasing its flexibility so as to provide a gentler grip. Alternatively, serrated teeth could be added to grip softer materials more firmly. The example claw is designed so that the four claws1005close shut when the branched scissor linkage is fully extended. The design could be altered so that the four claws1050enclose a sealed volume at full extension which could be used, as a specific example, for capturing e.g. insects or delicate sea creatures without harming them.

At the opposite end of the branched scissor linkage1000from the claws1005, the linkage is extended using four half-arms1050and another branched rivet1055(seeFIG.12). In this example, the half-arms1050are shorter than the standard arm parts which was done so that they do not collide with the syringe-like parts1010and1030discussed below.

Finally, two branched rivet parts have been incorporated into the two syringe-like parts1010and1030as indicated in the figures. The part that loosely corresponds to the barrel of a syringe is component1010, which includes two rings1012and1014that, in this embodiment, are sized to accommodate a user's fingers. Note, though, that those of ordinary skill in the art will be able to devise alternative forms of this embodiment that are much larger if needed. Between the two rings1012and1014is a channel1011sized to slideably accommodate shaft1032.

Continuing with the embodiment ofFIGS.9-13, the part of device1000that operates in a fashion analogous to that of a plunger of a syringe is the component1030. At its upper terminus is a ring1033which, in this embodiment, is sized to accommodate a user's thumb. As discussed previously, at the lower terminus of the component shaft1032is a branched rivet1034.

Note that in this particular embodiment each component of the device1000has four protrusions arranged as in a branched rivet at its respective terminus: the arms1010attach to these protrusions at their respective termini1013and1034. The thumb syringe part1030is threaded through a hole1011in the fingers syringe part1010, allowing the two components to slide against each other. In this particular variation, the geometry of the instant example1000does not allow components1010and1030to easily come apart since the four protrusions1034on the component1030do not fit through the hole1011in the fingers syringe part1010.

Those of ordinary skill in the art will understand that the grasping device can readily be modified in a number of ways, including, for example, the following variations:(1) A different branching number could be used, e.g., three arms in each stage could result in a lighter mechanism. However, increasing the number of arms in each stage results in a more robust mechanism that will be capable of resisting larger forces.(2) A different number of stages of arms in the mechanism could be used. Increasing the number of stages increases the reach of the extended device without significantly increasing the size of the retracted mechanism, although this approach also increases potential “slop” in the mechanism due to the increased number of parts.

Instead of activating the mechanism (and other branched scissor mechanisms) by hand, the syringe parts may be replaced with a linear motor, linear springs, pulleys or other method to pull the two branched rivets together and apart. Alternatively, rotational motors or torsion springs may be applied at hinges, either where two arms meet, where an arm meets a half-arm, or where an arm or half-arm meets a branched rivet. These methods allow the mechanisms to be built at any scale, not only near the scale of a human hand.

The half-arms described here are useful for other devices based on the branched scissor mechanisms. In particular, with the configuration shown inFIG.12, an object can be attached to the branched rivet connected to the half-arms. Such an object does not block the motion of the mechanism, and is carried along with the extension and retraction of the mechanism.

For purposes of the instant disclosure, the term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a range having an upper limit or no upper limit, depending on the variable being defined). For example, “at least 1” means 1 or more than 1 The term “at most” followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). For example, “at most 4” means 4 or less than 4, and “at most 40%” means 40% or less than 40%. Terms of approximation (e.g., “about”, “substantially”, “approximately”, etc.) should be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise. Absent a specific definition and absent ordinary and customary usage in the associated art, such terms should be interpreted to be ±10% of the base value.

Still further, additional aspects of the instant invention may be found in one or more appendices attached hereto and/or filed herewith, the disclosures of which are incorporated herein by reference as if fully set out at this point.