Segmented Cam Mechanism for Chronograph Fraction Display
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Solution Overview
Problem
Existing devices for displaying fractions of a second in chronograph mechanisms face challenges due to geometric complexity, manufacturing precision, and inertia issues, particularly at higher frequencies, leading to degraded performance and dimensional tolerance problems.
Innovation Solution
A counting device with a simplified cam geometry, featuring a first cam with regularly distributed recesses and a second cam with asymmetrical teeth, allowing precise positioning of a pawl to cooperate with either cam, enabling efficient counting and display of time fractions without excessive complexity or inertia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single spiral cam with multiple arms and steps is used to display fractions of a second, then the display precision is improved, but the geometric complexity and manufacturing precision requirements increase significantly
Solution Approach 1:
The patent divides the single complex spiral cam into two separate simpler cams: a first cam with regularly distributed recesses and a second cam with asymmetrical teeth. This segmentation reduces the geometric complexity of each individual cam while maintaining the overall display precision through their coordinated interaction with the pawl.
2Measurement precision
If a single spiral cam with multiple arms and steps is used to display fractions of a second, then the display precision is improved, but the manufacturing and assembly precision requirements increase significantly
Solution Approach 1:
By segmenting the cam function into two separate cams with simpler geometries, the manufacturing precision requirements for each cam are reduced. The first cam requires only regularly distributed recesses, while the second cam requires asymmetrical teeth, both of which are easier to manufacture with standard tolerances compared to the complex multi-armed spiral cam.
3Measurement precision
If a single spiral cam with multiple arms and steps is used to display fractions of a second, then the display precision is improved, but the inertia increases which degrades chronometric performance at high frequencies
Solution Approach 1:
Segmenting the cam system into two lighter, simpler cams reduces the total moving mass and moment of inertia compared to a single heavy spiral cam with multiple arms. This reduction in inertia allows the system to respond more quickly and accurately at higher oscillator frequencies (5 Hz and above), maintaining chronometric performance.
4Ease of operation
If a lever feeler is designed to cooperate with a cam by contact, then the display of fractions of a second is enabled, but the device complexity and dimensional tolerance requirements increase
Solution Approach 1:
The patent uses a single lever feeler with a pawl that cooperates with two segmented cams instead of requiring separate levers for each cam. This approach maintains the display functionality while reducing device complexity compared to previous designs that required multiple levers and felters.
5Measurement precision
If a cam with tightly distributed features is used to display fractions of a second, then the display precision is improved, but the external diameter becomes excessively large compared to available volume
Solution Approach 1:
By dividing the cam function into two separate cams with fewer features each, the patent reduces the external diameter required. The first cam with regularly distributed recesses and the second cam with asymmetrical teeth can be arranged in a compact configuration that fits within the available volume while maintaining the precision needed for fraction-of-a-second display.
Data Source
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AI summary
A device (100) for counting a number of fractions of a unit of time or a number of fractions of a unit of displacement of a movable part (1; 6; A2), the device comprising: - a first cam (1) having a first surface (10); - a second stop surface (20); - a movable support (4) elastically returned by a spring (R4); - a movable pawl (3) mounted on the support (4) and elastically returned by a spring (R3) towards the first surface, the pawl (3) being arranged so as to cooperate with one or the other of the first and second surfaces (10, 20) depending on the position of the support (4); and - a control system (80) arranged so as to maintain, in a first non-counting state of the control system, the support in a first position and to allow, in a second counting state of the control system, the movement of the support.