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US 4,320,320 AGranted
Coupled mode tuning fork type quartz crystal vibrator
AssigneeKabushiki Kaisha Suwa Seikosha
InventorsEishi Momosaki, Shigeru Kogure, Minoru Inoue
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AssigneeKabushiki Kaisha Suwa Seikosha
InventorsEishi Momosaki, Shigeru Kogure, Minoru Inoue
Estimating the term…
Cutting a quartz tuning fork crystal vibrator at a preferred angle and with a thickness which establishes a close coupled relationship between the flexural and torsional modes of vibration of the arms or tines produces a vibrator having a highly favorable cubic frequency temperature characteristic at predetermined frequencies. Weight added to the ends of the vibrating tines reduces the frequency of both flexural and torsional vibration, whereas weight added at nodal points in the flexural vibration primarily reduces only the torsional vibrational mode. Accordingly, a wide range of frequency adjustments is possible. Deviations from the desired crystal operating frequency due to manufacturing variances are adjustable by sequential weight modifications while the desirable cubic temperature characteristic is retained. High accuracy over a wide temperature range permits operation in oscillator circuits at relatively low frequencies and with attendant low power consumption. Close coupling between vibrational modes occurs when the difference between the flexural and torsional frequencies is .ltoreq.0.15 of the flexural frequency. The principles for dimensioning the crystal, and adjusting thickness and weight, are applicable to both fundamental and overtone frequencies.
A quartz tuning fork vibrator for a timekeeping device, said vibrator having at least two modes of vibration, said vibrator comprising quartz crystal formed in the shape of a tuning fork, said tuning fork including a base portion and arms extending therefrom, at least said arms having electrodes formed thereon, said quartz crystal having electrical X, mechanical Y, and optical Z axes, and said vibrator formed by cutting said quartz crystal at a selected cutting angle relative to said axes to form a quartz crystal plate, said quartz crystal plate having a selected thickness whereby the frequency difference between the first and second modes of vibration is no greater than 15% of said first mode of vibration, whereby a favorable frequency-temperature characteristic is provided.
A quartz crystal tuning fork vibrator having a first resonant frequency of vibration which changes with changes in ambient temperature, the relationship between said first resonant frequency and said temperature being approximated mathematically by a Taylor's expansion having a first order term with the coefficient .alpha., a second order term with the coefficient .beta., and a third order term with the coefficient .gamma., and said vibrator having at least a second frequency of vibration, and the frequency difference between said first resonant frequency and said second frequency of vibration is no greater than 15% of said first resonant frequency of vibration, said vibrator being produced from quartz crystal having an electrical X axis, a mechanical Y axis and an optical Z axis, said crystal vibrator being cut at a selected angle and a selected thickness such that said first coefficient .alpha. and second coefficient .beta. are approximately 0, whereby said frequency-temperature relationship has a cubic characteristic and said changes in resonant frequency with said changes in temperature are minimized over the working range of said vibrator.
A coupled tuning fork vibrator, said vibrator vibrating in first and second coupled modes, at least said first mode of vibration having a resonant frequency which changes with variations in ambient temperature, comprising:
A method for adjusting the vibrational rates of a tuning fork vibrator, said vibrator having first and second modes of vibration, said vibration mode differing in frequency and being coupled, at least said first vibration mode having at least one nodal point of vibrational displacement, comprising the steps of:
A quartz crystal vibrator for a timekeeping device, said vibrator having at least two modes of vibration, said vibrator having electrodes formed on at least a portion thereof, said vibrator being produced from quartz crystal having electrical X, mechanical Y, and optical Z axes by cutting said quartz crystal at a selected cutting angle relative to said axes to form a quartz crystal plate, said quartz crystal plate having a selected thickness whereby the frequency difference between the first and second mode of vibration is no greater than 15% of said first mode of vibration, said first mode of vibration having a cubic frequency-temperature characteristic, whereby a stable frequency source is provided.
Dependencies are inferred from the claim text.