Analog Timepiece Stepper Motor With Stable Sweep Seconds
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Solution Overview
Problem
Conventional analog electronic timepieces lack shock resistance and have high manufacturing costs due to the use of two stepping motors without detent torque, and the sweep drive mechanism lacks stability in angular velocity.
Innovation Solution
A stepping motor with a rotor formed of a permanent magnet and a monolithic plate-shaped yoke, where detent torque is reduced using coils during sweep drive, and angular velocity control is implemented to achieve stable step and sweep motion seconds hands, with a single stepping motor replacing the need for two.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two stepping motors without detent torque are used for step drive and sweep drive, then step motion and sweep motion can be achieved, but shock resistance deteriorates and manufacturing cost increases
Solution Approach 1:
The patent combines step drive and sweep drive functionalities into a single stepping motor by providing two independent coils (first coil and second coil) that can independently control the rotor's motion. The stator includes two separate coil assemblies that can be energized independently to achieve either step-by-step motion or continuous sweep motion, eliminating the need for two separate motors and improving shock resistance while reducing manufacturing cost.
2Adaptability or versatility
If two stepping motors without detent torque are used for step drive and sweep drive, then step motion and sweep motion can be achieved, but manufacturing cost increases
Solution Approach 1:
The patent combines step drive and sweep drive functionalities into a single stepping motor by providing two independent coils (first coil and second coil) that can independently control the rotor's motion. The stator includes two separate coil assemblies that can be energized independently to achieve either step-by-step motion or continuous sweep motion, eliminating the need for two separate motors and improving shock resistance while reducing manufacturing cost.
3Ease of operation
If sweep drive is executed by continuous pulse open control, then sweep motion can be achieved, but angular velocity stability deteriorates
Solution Approach 1:
The patent employs feedback control for sweep drive by detecting the rotor's angular velocity and position, then adjusting the pulse width of the drive signal to the second coil based on the detected values. This closed-loop control ensures that the rotor maintains a constant angular velocity of 2π radians/second, improving angular velocity stability while keeping the sweep drive control simple and effective.
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
Enables stable step and sweep motion seconds hands with reduced manufacturing costs and improved shock resistance by using a single stepping motor with detent torque reduction and angular velocity control.
Implementation Method 1
a rotor formed of a permanent magnet with two poles and a stator including a monolithic plate-shaped yoke having a rotor hole that the rotor enters, the yoke being magnetically coupled to the rotor, and a coil fixed to the yoke
Data Source
AI summary
A sweep motion second function is added to an analog electronic timepiece. Angular velocity control of a stepping motor for a seconds hand in which a rotor is provided is executed. A stepping motor model calculates an equation of motion and a circuit equation regarding the stepping motor in real time. Sweep drive is executed with a sweep drive pulse width generated through performing a proportional integral of the difference between angular velocity set to π (radians/second) and angular velocity of the stepping motor model. Correction of the load torque is executed using the rotor angle at the zero crossing of a back electromotive voltage generated across a coil of the stepping motor and the calculated angular velocity. A DC current is applied to coils disposed at bridges of a yoke and the detent torque of the stepping motor is reduced. Time lag is corrected using a GPS time signal.