Piezoelectric vibration angular velocity meter and camera using the same

• US RE42,923 E1
• Filed: 05/26/2006
• Issued: 11/15/2011
• Est. Priority Date: 08/31/1994
• Status: Expired due to Term

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Fujii, Toru, Sango, Yoshinori, Hattori, Tetsuo
• Primary Examiner(s): Perkey; W. B.
• Application Number:
  US11/441,460
• Time in Patent Office: 1,999 Days
• Field of Search: 396/53, 735/040.4, 7350412-50416, 310/317, 310/366, 331/173
• US Class Current: 396/53
• CPC Class Codes: G01C 19/5649 Signal processing

Abstract

When a power switch is turned on, first and second analog switches are turned on while a third analog switch is turned off. Accordingly, at the time of starting, a forced excitation driving circuit supplies to a vibrator an oscillation output pulse which is substantially at the resonance frequency of the vibrator, thereby forcibly driving the vibrator in an excitation manner. Thereafter, when the vibrator substantially attains its stationary state and thereby the charged voltage of a capacitor reaches a threshold value of an inverter, the first and second analog switches are turned off while the third analog switch is turned on. Accordingly, the output of a self-excitation circuit is supplied to the electrode of the vibrator so as to vibrate the vibrator in a self-excitation manner.

Claims

1. An angular velocity meter comprising:

a vibrator and

a self-excitation driving circuit for driving said vibrator in a self-excitation manner,

said self-excitation driving circuit comprising;

a converting means for converting a first sine wave voltage indicative of a state of vibration of said vibrator into a square wave voltage which becomes a first predetermined level when said first square sine wave voltage is greater than a predetermined reference level while becoming a second predetermined level when said first square sine wave voltage is smaller than said predetermined reference level;

a filter for filtering a second sine wave voltage, which has a frequency identical to a frequency of said first sine wave voltage, from said square wave voltage; and

a phase shifter for adjusting a phase of said second sine wave voltage, which has been filtered by said filter, such that an amplitude of vibration of said vibrator is substantially maximized.

2. A meter according to claim 1, further comprising a current/voltage converter which receives one input signal from said vibrator as an electric current signal and converts said electric current signal into a voltage signal, said converting means converting an output of said current/voltage converter, as said first sine wave voltage, into said square wave voltage.

3. A meter according to claim 1, further comprising a means for receiving one input signal from said vibrator as a voltage signal, said converting means converting said voltage signal, as said first sine wave voltage, into said square wave voltage.

4. A meter according to claim 1, wherein said converting means includes a zero-cross comparator.

5. A meter according to claim 4, wherein said converting means further includes an attenuator for attenuating an output of said zero-cross comparator.

6. A meter according to claim 5, wherein said attenuator comprises a potential dividing circuit including a variable resistor.

7. A meter according to claim 1, wherein said vibrator comprises:

a first piezoelectric crystal layer;

at least three electrodes formed on an upper surface of said first piezoelectric crystal layer; and

an electrode formed on a lower surface of said first piezoelectric crystal layer.

8. A camera comprising the meter according to claim 1.

9. A self-excitation circuit for driving a vibrator in a self-excitation manner,

said self-excitation circuit comprising:

a converting means for converting a first sine wave voltage indicative of a state of vibration of said vibrator into a square wave voltage which becomes a first predetermined level when said first square sine wave voltage is greater than a predetermined reference level while becoming a second predetermined level when said first square sine wave voltage is smaller than said predetermined reference level;

a filter for filtering a second sine wave voltage, which has a frequency identical to a frequency of said first sine wave voltage, from said square wave voltage; and

a phase shifter for adjusting a phase of said second sine wave voltage, which has been filtered by said filter, such that an amplitude of vibration of said vibrator is substantially maximized.

10. A self-excitation circuit according to claim 9, wherein said converting means includes a zero-cross comparator.