Two-Coil Stepper Motor Pulse Train for Smooth Watch Hands
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Solution Overview
Problem
Existing electronic watches with stepper motors for analog indication suffer from hand movement irregularities due to backlash and reduced holding torque, leading to poor appearance and potential malfunctions.
Innovation Solution
The electronic watch employs a drive pulse train with three drive pulses to rotate a two-coil stepper motor in increments of 360° per step, enhancing high-speed drive capabilities and increasing the gear speed reduction ratio to improve hand torque and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a two-step drive pulse configuration is used to rotate the rotor by 360°, then the holding torque of hands is increased, but the hands move in an awkward and unnatural manner with deceleration and vibration
Solution Approach 1:
The drive pulse train is divided into three distinct drive pulses (first, second, and third drive pulses) that sequentially excite different coil combinations. This segmentation allows the rotor to rotate through 360° in a controlled multi-step process, eliminating the deceleration and vibration issues of the two-step drive while maintaining high holding torque throughout the rotation.
Solution Approach 2:
The three drive pulses are applied in a periodic sequence with specific timing intervals. The first drive pulse excites the first coil, the second drive pulse excites the second coil, and the third drive pulse excites the first coil again, creating a periodic action pattern that ensures smooth continuous rotation without awkward movements.
2Ease of operation
If the time interval between drive pulses is reduced to avoid deceleration and vibration, then the movement becomes smoother, but the frequency of abnormal operation that reverses the rotor increases
Solution Approach 1:
The first drive pulse is applied in advance to excite the first coil before the rotor completes its rotation, preparing the magnetic field in advance. This preliminary action ensures that the magnetic field is ready to guide the rotor smoothly through its rotation without sudden reversals or abnormal operations, even when time intervals are reduced.
Solution Approach 2:
The drive pulse train is designed with feedback control where the application of each subsequent drive pulse is timed based on the rotor's position and the completion of the previous pulse's effect. This feedback mechanism prevents abnormal operations by ensuring that each pulse is applied at the optimal moment, maintaining reliability even at higher frequencies.
3Productivity
If the rotor is rotated by 360° through two-step drive, then the gear speed reduction ratio can be increased, but the rotation speed of the rotor is limited
Solution Approach 1:
The drive system is made dynamic by using three adjustable drive pulses instead of a fixed two-step configuration. The timing and duration of each pulse can be optimized to achieve both high rotation speeds and high gear reduction ratios simultaneously. The system adapts the pulse sequence to maintain optimal performance across different operating conditions, breaking the limitation of fixed two-step drives.
Solution Approach 2:
The invention changes the parameters of the drive system by introducing a third drive pulse and adjusting the timing intervals between pulses. This parameter change allows the system to achieve higher rotation speeds while maintaining the 360° rotation per step configuration, thereby increasing both the gear speed reduction ratio and the rotor rotation speed beyond the limitations of the two-step drive.
4Volume of moving object
If miniaturization of the stepper motor is prioritized, then the size is reduced, but the holding torque of the indicator wheel is reduced
Solution Approach 1:
The drive pulse parameters are optimized to maximize the holding torque output from the miniaturized motor. By adjusting the pulse width, amplitude, and timing of the three drive pulses, the system extracts maximum torque capability from the smaller motor, compensating for the reduced physical size through optimized electrical parameters.
Solution Approach 2:
The periodic application of three drive pulses creates a sustained magnetic field pattern that maintains high holding torque throughout the rotation cycle. This periodic action ensures that the rotor experiences consistent magnetic forces even in a miniaturized motor, preventing torque loss that would normally accompany size reduction.
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 solution enables smooth and high-speed movement of watch hands, reducing backlash-induced deviations and enhancing the watch's appearance and reliability by increasing the holding torque and impact resistance of the hands.
Implementation Method 1
a stator to be magnetized by a coil, and a rotor that is a disc-shaped rotary member magnetized into two poles
Data Source
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AI summary
Provided is an electronic watch including: a two-coil stepper motor (20) including: a magnetized rotor (21); a stator (22) including: first and second stator magnetic-pole portions, which are formed so as to oppose to each other through the rotor (21); and a third stator magnetic-pole portion, which is formed between the first stator magnetic-pole portion and the second stator magnetic-pole portion so as to face the rotor; a coil A to be magnetically coupled to the first stator magnetic-pole portion and the third stator magnetic-pole portion; and a coil B to be magnetically coupled to the second stator magnetic-pole portion and the third stator magnetic-pole portion; and a high-speed drive pulse generation circuit (4) configured to output a drive pulse for driving the rotor (21) to the coil A or the coil B, wherein the drive pulse includes a plurality of drive pulses, and wherein the rotor (21) is to be rotationally driven in increments of 360° due to a drive pulse train (SP10) formed of the plurality of drive pulses. With this configuration, the stepper motor (20) is rotationally driven in increments of 360° per step, to thereby move hands smoothly at high speed.