Hairspring, balance with hairspring, timepiece movement, and timepiece
There is provided a hairspring including a main body portion that extends around a central axis along an Archimedes curve; an outer end curve portion that extends along a circumferential direction around the central axis on an outer side in a radial direction from the main body portion; and a reformed portion including a first bent portion that connects the main body portion and the outer end curve portion to each other and is bent outward in the radial direction from a tangent line of the Archimedes curve in a first connection portion with the main body portion, and a second bent portion bent inward in the radial direction from the outer end curve portion in a second connection portion with the outer end curve portion, and in which at least one is curved of the first bent portion and the second bent portion.
1. A hairspring comprising:
a main body portion wound around a central axis along an Archimedes curve, wherein the main body portion has an inner end and an outer end thereof, and the inner end is attached to the central axis;
an outer end curve portion that arcuately extends along a circumferential direction around the central axis outside the main body portion, wherein the outer end curve portion has a first end and a second end thereof; and
a reformed portion connecting the outer end of the main body portion and the first end of the outer end curve portion, wherein the reformed portion has a first connection portion connected to the outer end of the main body and is bent radially outward from the outer end of the main body portion in a direction at a first angle from a line tangential to the Archimedes curve at the outer end of the main body portion, and a second connection portion connected to the first end of the outer end curve portion and is bent radially inward in a direction at a second angle from a line tangential to the outer end curved portion at the second end of the outer end curved portion wherein
the main body portion has a time diameter D that falls in a range of 3.5 mm≤D≤5.5 mm,
the outer end curve portion has a radius R that falls in range of 0.25 mm≤R−(D/2)≤0.65 mm, and
the reformed portion circumferentially extends over an angle θ, which falls in a range of 10°≤θ≤35°, at the center axis between both ends of the reformed portion.
2. The hairspring according to claim 1 , wherein at least one of the first or second connection portion of the reformed portion is arcuately formed with a certain curvature.
3. The hairspring according to claim 1 , wherein both the first and second connection portions are arcuately formed.
4. The hairspring according to claim 3 , wherein the first connection portion and the second connection portion are connected to each other.
5. A balance with a hairspring comprising:
the hairspring according to claim 1 ;
a balance staff fixed to an inner end portion of the hairspring; and
a balance wheel fixed to the balance staff.
6. A timepiece movement comprising the balance with a hairspring according to claim 5 .
7. A timepiece comprising the timepiece movement according to claim 6 .