Watch Balance Bearing Geometry for Stable Friction Torque
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Solution Overview
Problem
Conventional shock-absorbing bearings in watch movements experience variations in frictional torque due to changes in orientation relative to gravity, leading to inconsistencies in the amplitude of oscillation and speed, particularly affecting the balance wheel.
Innovation Solution
A mobile system with pyramidal-shaped cavities and pivots is employed, where the contact angles between the pivots and bearings are optimized to minimize frictional torque variations by ensuring the lever arm of the friction force remains consistent regardless of the orientation relative to gravity, using the equation cotαh + cotαb ≥ 4 cos(πN, where N is the number of faces of the pyramids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional shock-absorbing bearings with rounded pivot ends are used, then the pivots can absorb shocks without breaking, but the frictional torque varies significantly with orientation relative to gravity
Solution Approach 1:
The patent applies curvature by using a spherical pivot head that rotates within a spherical cavity. This spherical geometry ensures that the contact point between pivot and cavity always lies on the equatorial circle of the sphere, maintaining a constant lever arm distance from the rotation axis regardless of the bearing's orientation relative to gravity. This eliminates the friction torque variations that occur with rounded pivot ends in conventional bearings.
2Loss of energy
If the pivot end is rounded to reduce friction, then the friction force is applied to the axis of rotation, but the lever arm becomes zero only in specific orientations, causing friction torque variations
Solution Approach 1:
The spherical pivot and cavity configuration creates an equipotential condition where the lever arm distance remains constant for all orientations. The spherical geometry ensures that gravity's effect on the friction torque is neutralized, as the contact point's perpendicular distance to the rotation axis remains invariant regardless of the bearing's angular position, thereby maintaining consistent energy loss characteristics.
3Reliability
If a spring-mounted bearing is used to pre-constrain the pivot in the cavity, then the lever arm can be kept almost zero in all directions, but the spring adds weight and increases friction
Solution Approach 1:
The patent extracts and eliminates the spring component from the bearing structure. Instead of using a spring-mounted bearing to pre-constrain the pivot, the invention uses a simple spherical pivot head that fits into a spherical cavity. This extraction of the spring mechanism removes the added weight and structural complexity while maintaining the desired lever arm stability through the spherical geometry alone.
4Loss of energy
If the cavity base is made with precise surface finish to ensure proper pivot contact, then the friction can be reduced, but it is difficult to access the base for polishing
Solution Approach 1:
The spherical cavity geometry provides self-aligning contact surfaces that are inherently more accessible for manufacturing and finishing operations. The curved spherical surface allows for uniform contact distribution and is more easily polished and finished compared to the flat, hard-to-reach base of conventional pyramidal cavities. The spherical shape ensures proper contact without requiring extremely precise flat surface finishing in difficult-to-access locations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces friction torque variations, ensuring consistent operation of the balance wheel by maintaining nearly constant frictional torque across different orientations, thereby stabilizing the oscillation amplitude and speed.
Implementation Method 1
The chaton 3 is held against the bottom of a bearing block 5 by a damping spring 6 arranged to exert an axial force on the upper part of the counter-pivot stone 4
Implementation Method 2
the frictional torque on the axis due to the weight of the object varies depending on the object's orientation relative to gravity
Data Source
Figure 1~3
Figure 4~6
Figure 7~11
AI summary
Rotating moving part system (10) of a watch movement, the system (10) comprising a rotating part, for example a balance wheel (13), a first and a second bearing (18, 20), in particular shock absorbers, for a first and a second pivot (15, 17) of the axis (16) of the rotating part, the part having a center of mass (G) at a position on its axis (16), the first bearing (18, 20) having a counter-pivot (22) comprising a main body having a pyramidal cavity (19) configured to receive the first pivot (17) of the axis (16) of the rotating part, the cavity having at least three faces giving its pyramidal shape, the first pivot (17) being able to cooperate with the cavity (19) of the counter-pivot (22) in order to be able to rotate in the cavity (19), at least one contact zone (29) between the first pivot (17) and a face (24) being generated, the normal to the one or more contact zones (29) forming a contact angle (ah) relative to the plane perpendicular to the axis (16) of the pivot (17),characterized in that the contact angle (ah) is less than 45°, preferably less than or equal to 30°, or even less than or equal to arctan(1/2).