Electrostatic Watch Motor Holding Force and Power Trade-off
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Solution Overview
Problem
Conventional electronic watches with electrostatic motors face challenges in maintaining hand position stability while reducing power consumption, as the holding force is insufficient when no drive signal is applied, leading to positional deviations due to impacts.
Innovation Solution
An electronic watch design incorporating an electrostatic motor with a rotor and fixed electrodes, where electret films are used to generate electrostatic forces to keep the hand stationary by maintaining the polarities of the fixed electrodes, reducing power consumption through selective execution of hand movement and stop modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If no drive signal is applied to the electrostatic motor to reduce power consumption, then power consumption is reduced, but the holding force becomes small and the hand position deviates due to impacts
Solution Approach 1:
The motor control circuit executes stop modes at periodic intervals rather than continuously, allowing the electrostatic motor to maintain hand position only when necessary. This periodic execution reduces cumulative power consumption while ensuring position stability is maintained at critical moments, resolving the contradiction between energy savings and position reliability.
Solution Approach 2:
The system changes the operational parameters of the electrostatic motor by switching between different stop modes (first stop mode with full holding force, second stop mode with reduced holding force). By dynamically adjusting the holding force parameter based on operational conditions, the system achieves both power consumption reduction and adequate position stability maintenance.
2Reliability
If the electrostatic motor maintains holding force to keep the hand stationary, then hand position stability is improved, but power consumption increases
Solution Approach 1:
Instead of maintaining continuous holding force, the system applies holding force periodically through intermittent stop modes. This approach maintains adequate hand position stability when needed while significantly reducing power consumption by allowing the motor to enter lower-power states between stop mode executions.
Solution Approach 2:
The system uses partial action by implementing two types of stop modes: a first stop mode with full holding force for critical position maintenance, and a second stop mode with reduced holding force for less critical periods. This partial application of holding force achieves adequate position stability while reducing overall power consumption compared to continuous full-strength holding.
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
The solution effectively keeps the hands stationary while minimizing power consumption by utilizing electrostatic forces to maintain the hand position, reducing positional deviations and energy usage.
Implementation Method 1
an electrostatic motor including a rotor in which a plurality of electret films are arranged in a rotational direction and a plurality of fixed electrodes arranged in the rotational direction at positions facing the rotor
Implementation Method 2
in the stop mode, the motor control circuit keeps the rotor stationary through electrostatic forces exerted on the electret films from the fixed electrodes with polarities of the fixed electrodes maintained
Data Source
AI summary
An electronic watch includes a power source, an electrostatic motor including a rotor in which a plurality of electret films are arranged in a rotational direction and a plurality of fixed electrodes arranged in the rotational direction at positions facing the rotor, a hand rotating in conjunction with the rotation of the rotor, and a motor control circuit controlling the electrostatic motor. The motor control circuit selectively executes a hand movement mode for rotating the hand and a stop mode for keeping the hand stationary. In the stop mode, the motor control circuit keeps the rotor stationary through electrostatic forces exerted on the electret films from the fixed electrodes with the polarities of the fixed electrodes maintained.