Cam Timepiece Mechanism With Negative-Stiffness Return Spring
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Solution Overview
Problem
Existing cam-operated clock mechanisms experience varying torque requirements due to the increasing resistance from the rocker arm and return spring, affecting energy consumption and measurement accuracy.
Innovation Solution
A clockwork mechanism with a specially shaped rocker return spring that maintains a zero or negative stiffness within a predetermined range of angular positions, ensuring a consistent torque application by compensating for the increasing lever arm during the rocker's movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional return spring with positive stiffness is used, then the rocker arm can be kept pressed against the cam, but the torque required to rotate the cam varies significantly, increasing energy consumption and affecting measurement accuracy
Solution Approach 1:
The patent applies parameter changes by modifying the stiffness characteristic of the return spring from conventional positive stiffness to negative stiffness. This fundamental parameter change allows the spring to exert a torque that compensates for the varying lever arm, thereby maintaining more constant torque requirements during cam rotation while still keeping the rocker arm pressed against the cam surface.
Solution Approach 2:
The patent converts the harmful effect of varying torque requirements into a benefit by using negative stiffness to actively compensate for the changing lever arm. The negative stiffness property, which would traditionally be considered undesirable, is harnessed to reduce energy consumption by counteracting the torque variation caused by the cam's spiral shape.
2Reliability
If a conventional return spring with positive stiffness is used, then the rocker arm can be kept pressed against the cam, but the variation in torque affects the regularity of oscillations and measurement accuracy
Solution Approach 1:
The patent applies parameter changes by modifying the stiffness characteristic of the return spring from conventional positive stiffness to negative stiffness. This fundamental parameter change allows the spring to exert a torque that compensates for the varying lever arm, thereby maintaining more constant torque requirements during cam rotation while still keeping the rocker arm pressed against the cam surface.
3Ease of operation
If the cam's spiral shape is used to achieve instantaneous indicator movement, then the indicator can jump to the correct position, but the lever arm increases causing torque variation
Solution Approach 1:
The patent converts the harmful effect of varying torque requirements into a benefit by using negative stiffness to actively compensate for the changing lever arm. The negative stiffness property, which would traditionally be considered undesirable, is harnessed to reduce energy consumption by counteracting the torque variation caused by the cam's spiral shape.
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
Reduces energy consumption and enhances the regularity of oscillations, improving the accuracy of timekeeping by maintaining a consistent torque throughout the cam's rotation.
Implementation Method 1
a return spring arranged to keep the cam follower pressed against the cam, the return spring being arranged to work in a predetermined range of winding angles
Implementation Method 2
the stiffness of the return spring is zero or negative in at least a part of the predetermined range
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The clockwork mechanism (1) according to the invention comprises a cam (4) that is intended to be driven in rotation, a cam follower (2) and a return spring (9) arranged so as to keep the cam follower (2) pressed against the cam (4), the return spring (9) being arranged so as to work within a predetermined range of winding angles during each rotation of the cam (4). The stiffness of the return spring (9) is zero or negative in at least part of the predetermined range.