Biased hinges

Abstract

A snap-hinge in which two hinge members are hinged together about a first hinge line. A resilient connecting link is joined at one end integrally to one of the hinge members at a second hinge line and is hinged at the other end to the other hinge member at a third hinge line. The connecting link is capable either of compression or .[.of expansion.]. .Iadd.deformation .Iaddend.as between its two ends, and tends to maintain the hinge members in a given angular relationship, and to return the hinge members to that relationship if they depart from it.

What I claim as my invention is:  .[.1. A snap-hinge comprising: 
       a first hinge member, 
       a second hinge member hinged to said first hinge member about a first hinge line, 
       a curved resilient connecting link of uniform cross-section joined at one end integrally to said first hinge member at a second hinge line and joined at the other end integrally to said second hinge member at a third hinge line, the resilient connecting link tending resiliently to maintain its two ends apart at a given spacing, said second hinge line being spaced at an invarible distance from said first hinge line, said third hinge line being spaced at an invariable distance from said first hinge line, the snap-hinge having a first position and a second position, in each of which stress in the connecting link is at a minimum, the snap-hinge being at rest in each of said positions, a small departure from either of which increases the stress in the connecting link, which tends to restore the snap-hinge to the respective position, the connecting link being capable of resilient expansion between its one end and its other end, the snap-hinge being adapted to articulate between said first-mentioned position and said second position in such a way that the connecting link is resiliently expanded in positions intermediate said first-mentioned position and said second position, the maximum expansion of said connecting link representing a state of unstable equilibrium for the snap-hinge, departure from which in either direction causes said connecting link to urge the snap-hinge further in that direction to return the snap-hinge to one of said positions..].  .[.2. A snap-hinge as claimed in claim 1, in which said second hinge line and said third hinge line are equidistant from said first hinge line..]. .[.3. A snap-hinge as claimed in claim 1, in which said first hinge member is integral with said second hinge member through a flexible web defining said first hinge line, in which said one end of said resilient connecting link is integral with said first hinge member through a flexible web defining said second hinge line, and in which said other end of said resilient connecting link is integral with said second hinge member through a flexible web defining said third hinge line..]. .[.4. A snap-hinge as claimed in claim 3, in which said first and second hinge members and said resilient connecting link are made of a thermoplastic material..]. .[.5. A snap-hinge as claimed in claim 4, in which said thermoplastic material is polypropylene..]. .Iadd. 6. A snap-hinge comprising: 
       a first hinge member, 
       a second hinge member hinged to said first hinge member about a first hinge line, 
       a curved resilient connecting link of uniform cross-section, the link being joined at one end integrally to said first hinge member at a second hinge line and joined at the other end integrally to said second hinge member at a third hinge line, the link being curved and said ends of substantially uniform cross-section intermediate its ends, the resilient connection link tending resiliently to maintain its two ends apart at a given spacing, said second hinge line being spaced at an invariable distance from said first hinge line, said third hinge line being spaced at an invariable distance from said first hinge line, the snap-hinge having a first position and a second position, in each of which stress in the connecting link is at a minimum, the snap-hinge being at rest in each of said positions, a small departure from either of which increases the stress in the connecting link, which tends to restore the snap-hinge to the respective position, the connecting link being capable of resilient deformation between its one end and its other end when the distance between the ends changes, the snap-hinge being adapted to articulate between said first-mentioned position and said second position in such a way that the connecting link is resiliently deformed in positions intermediate said first-mentioned position and said second position when the distance between the ends of the link changes, the maximum deformation of said connecting link representing a state of unstable equilibrium for the snap-hinge, departure from which in either direction causes said connecting link to urge the snap-hinge further in that direction to return the snap-hinge to one of said positions. .Iaddend. .Iadd. 7. A snap-hinge as claimed in claim 6, in which said first hinge member is integral with said second hinge member through a flexible web defining said first hinge line, in which said one end of said resilient connecting link is integral with said first hinge member through a flexible web defining said second hinge line, and in which said other end of said resilient connecting link is integral with said second hinge member through a flexible web defining said third hinge line. .Iaddend. .Iadd. 8. The snap-hinge as claimed in claim 6, wherein when said snap-hinge is in the rest position, the distance between the second hinge line and the third hinge line is less than the distance at which the maximum stress exists in the connecting link. .Iaddend..Iadd. 9. A snap-hinge as claimed in claim 8 wherein as the snap-hinge proceeds from the first position to the second, the distance between the second hinge line and the third hinge line increases, deforming said connecting link with said deformation continuing until a maximum point is reached, prior to reaching this maximum point the first hinged member is biased towards the first position, after exceeding this maximum point the distance between the second hinge line and the third hinge line decreases and the first hinge member is biased towards the second position, eventually realizing said position. .Iaddend. .Iadd. 10. A snap-hinge as claimed in claim 8, wherein as the snap-hinge proceeds from the second position to the first position, the distance between the second hinge line and the third hinge line increases, deforming said connecting link with said deformation continuing until a maximum point is reached, prior to reaching this maximum point the first hinge member is biased towards the second position, after exceeding the maximum point the distance between the second hinge line and the third hinge line decreases and the first hinge member is biased towards the first position, eventually realizing said position. .Iaddend. .Iadd. 11. A snap hinge as claimed in claim 6 wherein said resilient connecting link is curved throughout its entire length. .Iaddend..Iadd. 12. A snap hinge as claimed in claim 6 wherein said resilient connecting link is of uniform cross-section throughout its entire length. .Iaddend. .Iadd. 13. A snap-hinge as claimed in claim 6, in which said second hinge line and said third hinge line are equidistant from said first hinge line. .Iaddend..Iadd. 14. A snap-hinge as claimed in claim 7, in which said first and second hinge members and said resilient connecting link are made of a thermoplastic material. .Iaddend..Iadd. 15. A snap-hinge as claimed in claim 13, in which said thermoplastic material is polypropylene. .Iaddend.