A mechanical timepiece has a power source comprised of a mainspring for undergoing rewinding movement to generate a rotational force. A front train wheel undergoes rotation in accordance with a rotational force generated during rewinding movement of the mainspring. An escapement/speed-control device controls rotation of the front train wheel. The escapement/speed-control device has a balance with a hairspring for undergoing alternately repeating rotational movement in left and right directions. An escape wheel and pinion undergoes rotation in accordance with rotation of the front train wheel. A pallet fork controls rotation of the escape wheel and pinion in accordance with rotational movement of the balance. A switch mechanism outputs an ON signal when a rotation angle of the balance reaches a predetermined threshold angle or greater, outputs an OFF signal when the rotation angle of the balance does not exceed the predetermined threshold angle. A rotation angle control mechanism supresses rotation of the balance when the switch mechanism outputs an ON signal.
The anti-trip device is for a detent escapement mounted on a wristwatch. It includes a finger fixed to the arm of the balance, two columns between which the finger can pass, said columns being secured to the balance bridge, and a locking arm fixed to the outer coil of the balance spring, said locking arm being able to be inserted between said columns and said finger to prevent the balance from rotating beyond an angle exceeding its normal operating angle. The locking arm is a clamp hooked onto the outer coil of the balance spring.
The collet is formed by a metal band (10) whose inner contour (11) delimits the recesses (11a, 11b, 11c) for driving the collet onto a balance staff (2) and whose outer contour (12) includes a function point (4) between the collet and the balance spring (9) located at the end of an arm (14) at a distance R from the centre 0 of the staff (2) greater than that of any other point (6, 8, 13, 15, 17) of the outer contour (12). It is characterised in that the inner contour (11) includes a discrete number of points of contact (1, 3, 5, 7) with the staff (2) distributed along identical or different angular apertures .alpha. and in that width "I" of the band (10) varies such that the compression forces of the contact points (1, 3, 5, 7) on the staff (2) do not substantially alter the distance R after driving in, leading to a friction torque allowing angular orientation of the collet on the staff (2) and not introducing any unbalance.
