According to an embodiment, a coil spring includes a wire rod having an end and the other end. The wire rod of the coil spring includes, with regard to a section of the wire rod, a round section potion of an effective spring part, a square section portion in which the section is substantially square, and a taper portion. The square section portion includes an end turn part. A length of each side of the section of the square section portion is less than or equal to a square root of ½ multiplied by a diameter of the wire rod of the round section portion. In the taper portion, from the round section portion to the square section portion, the section changes from a round shape to substantially a square shape, and a sectional area is decreased.

A torsion spring used in a flexible display device includes a spring body having a first connection end configured to connect a reel of the flexible display device, and a second connection end configured to fix the torsion spring. An axial sectional area of the spring body near the first connection end is greater than an axial sectional area of the spring body away from the first connection end. When the reel rotates, the torsion force generated during the initial rotation of the reel is relatively large, and with the increase of the rotation turn number of the reel, the increase of the torsion force is relatively small.

A coil spring includes a wire rod and an elastic coat provided on the wire rod. The coil spring includes a coil section including a plurality of coil portions. The wire rod includes a round cross-sectional portion, a cross-section varying portion, and a rectangular cross-sectional portion along the longitudinal direction of the wire rod. The cross section of the rectangular cross-sectional portion is substantially square and has a first plane and a second plane. The first plane and the second plane oppose each other in the coil section. The elastic coat is provided on at least one of the first plane and the second plane. The elastic coat is continuous from the round cross-sectional portion to the cross-sectional variation portion and the rectangular cross-sectional portion.

A coil spring includes a wire rod and an elastic coat provided on the wire rod. The coil spring includes a coil section including a plurality of coil portions. The wire rod includes a round cross-sectional portion, a cross-section varying portion, and a rectangular cross-sectional portion along the longitudinal direction of the wire rod. The cross section of the rectangular cross-sectional portion is substantially square and has a first plane and a second plane. The first plane and the second plane oppose each other in the coil section. The elastic coat is provided on at least one of the first plane and the second plane. The elastic coat is continuous from the round cross-sectional portion to the cross-sectional variation portion and the rectangular cross-sectional portion.

According to one embodiment, a coil spring includes a wire rod with a first end and a second end. The wire rod includes a round section portion including a round first cross section perpendicular to a longitudinal direction of the wire rod, a quadrangle section portion including a quadrangle a second section perpendicular to the longitudinal direction, and a variable section portion formed between the round section portion and the quadrangle section portion of the wire rod. The cross section of the variable section portion varies from circular to quadrangle from the round section portion to the quadrangle section portion. The end turn part of the coil spring includes the quadrangle section portion. The width and thickness of the second cross-section are smaller than the diameter of the first cross-section. The area of the second cross section is smaller than the area of the square inscribed in the circle of diameter of the first cross section.

According to an embodiment, a coil spring includes a wire rod having an end and the other end. The wire rod of the coil spring includes, with regard to a section of the wire rod, a round section portion of an effective spring part, a square section portion in which the section is substantially square, and a taper portion. The square section portion includes an end turn part. A length of each side of the section of the square section portion is less than or equal to a square root of ½ multiplied by a diameter of the wire rod of the round section portion. In the taper portion, from the round section portion to the square section portion, the section changes from a round shape to substantially a square shape, and a sectional area is decreased.

A 3D printed additively manufactured (AM) elliptical bifurcating torsion flexure assembly system includes a base section; elliptical bifurcating torsion springs, each including a bifurcated legs section supported by the base; a bifurcated elliptical torsion spring section contiguous with the bifurcated legs section; and a single upper section contiguous with the elliptical torsion spring section. The single upper section includes a connection component, and the device material includes Hot Isostatic Pressing (HIP) heat-treated Ti6Al4V. The elliptical bifurcating torsion flexure assembly is printed as one part by a 3D additive manufacturing process, and the bifurcation maintains consistent balance while being torqued. The stiffness-spring rate of the device is at least partly controlled by varying cross-sectional shape and diameters by the 3D additive manufacturing printing.

According to one embodiment, a coil spring includes a wire rod with a first end and a second end. The wire rod includes a round section portion including a round first cross section perpendicular to a longitudinal direction of the wire rod, a quadrangle section portion including a quadrangle a second section perpendicular to the longitudinal direction, and a variable section portion formed between the round section portion and the quadrangle section portion of the wire rod. The cross section of the variable section portion varies from circular to quadrangle from the round section portion to the quadrangle section portion. The end turn part of the coil spring includes the quadrangle section portion. The width and thickness of the second cross-section are smaller than the diameter of the first cross-section. The area of the second cross section is smaller than the area of the square inscribed in the circle of diameter of the first cross section.

A 3D printed additively manufactured (AM) elliptical bifurcating torsion flexure assembly system includes a base section; elliptical bifurcating torsion springs, each including a bifurcated legs section supported by the base; a bifurcated elliptical torsion spring section contiguous with the bifurcated legs section; and a single upper section contiguous with the elliptical torsion spring section. The single upper section includes a connection component, and the device material includes Hot Isostatic Pressing (HIP) heat-treated Ti6Al4V. The elliptical bifurcating torsion flexure assembly is printed as one part by a 3D additive manufacturing process, and the bifurcation maintains consistent balance while being torqued. The stiffness-spring rate of the device is at least partly controlled by varying cross-sectional shape and diameters by the 3D additive manufacturing printing.

The invention relates to a one-piece balance spring comprising a single strip wound on itself between an inner coil and an outer coil, the strip having a geometry such that when the angle of contraction of the balance spring has a value of 360 degrees, there is a constant distance between each coil from the inner coil to the penultimate coil.