JP2007218717A - Inertial force sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inertial force sensor for reducing power consumption. <P>SOLUTION: The inertial force sensor comprises a vibrator 2; a drive circuit 4 for driving the vibrator 2; a monitor circuit 6 for monitoring the vibrating state of the vibrator 2; and a detection circuit 8 for detecting the distortion of the vibrator 2 caused by the Coriolis force. The drive circuit 4 controls voltage energized to the vibrator 2 so that the vibrator 2 vibrates with a fixed period and amplitude according to the vibrating state of the vibrator 2 by the monitoring circuit 6. Especially, the inertial force sensor has a voltage/current control means 22 for reducing the voltage added to the vibrator 2 in activation, as compared with that added to the vibrator 2 in a steady state, and increasing current added to the vibrator 2 in activation, as compared with that added to the vibrator 2 at steady state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inertial force sensor used in various electronic devices.

  Hereinafter, a conventional inertial force sensor will be described.

  As an inertial force sensor, an angular velocity sensor can be cited. This angular velocity sensor senses a transducer, a drive circuit for vibrating the transducer, and distortion generated in the transducer due to Coriolis force (inertial force). And a power supply circuit for supplying power to the driving circuit and the sensing circuit.

  There are various types of vibrators such as a tuning fork shape, H shape, T shape, and sound piece shape. The vibrator is vibrated to electrically generate distortion caused by the Coriolis force. Is used to calculate the angular velocity.

  Such an angular velocity sensor is mounted, for example, as a component constituting a camera shake prevention function of a digital camera or the like.

As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.
JP 2002-243451 A

  In general, since a digital camera or the like is operated by driving a battery, the usable time is shortened if the power consumption of the battery is increased. Therefore, in order to save battery power consumption and use it for a long time, when not in use, the power supply to the main function is set to the minimum and the power supply to other additional functions is cut off. Has been.

  However, the inertial force sensor that constitutes the camera shake prevention function constantly supplies power to the vibrator, thus hindering power saving of battery power consumption. This is because, when the energization to the vibrator is cut off and the energization is started again, the vibrator that has stopped vibrating due to the interruption of the energization will be activated even if the energization is started again and the vibrator vibrates. It takes time for the vibration of the to become stable. That is, since the inertial force cannot be accurately detected until the vibration of the vibrator becomes stable, it is necessary to always energize the vibrator from the drive circuit.

  In particular, the voltage for energizing the vibrator needs to be larger at the time of starting until the vibration is stabilized after the vibration of the vibrator is started than when the vibrator is oscillating stably. is there. Therefore, it is necessary to set the voltage for energizing the vibrator to the maximum value (voltage required at startup) necessary to vibrate the vibrator, resulting in a problem of increased power consumption. It was.

  The present invention solves the above-described problems, and an object thereof is to provide an inertial force sensor with reduced power consumption.

  In order to achieve the above object, the present invention particularly reduces the voltage applied to the vibrator at the time of startup than the voltage applied to the vibrator at the time of steady state and the current at the time of startup than the current applied to the vibrator at the time of steady state. In this configuration, voltage current control means for increasing the current applied to the vibrator is provided.

  With the above configuration, the voltage applied to the vibrator during steady operation is smaller than the voltage applied to the vibrator during startup, so the voltage for energizing the vibrator is the maximum value required for vibrating the vibrator (when starting up) It is not necessary to always set the required voltage) to reduce power consumption.

  In particular, the current applied to the vibrator at startup is greater than the current applied to the vibrator during steady state, so the voltage waveform rises and falls sharply and the maximum value required to vibrate the vibrator is set. The time that can be secured becomes longer, and the startup efficiency can be improved. In addition, since the energized current is large with respect to the voltage waveform at the time of activation, the phase is hardly delayed and the vibration efficiency of the vibrator can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 is a block diagram of an inertial force sensor according to an embodiment of the present invention, FIG. 2 is a characteristic waveform diagram at points A to C in FIG. 1, and FIG. 3 is a constant waveform at point C with respect to the characteristic waveform at point B in FIG. It is a characteristic waveform diagram at the time of normal and startup.

  In FIG. 1, an inertial force sensor according to an embodiment of the present invention includes a vibrator 2, a drive circuit 4 that vibrates the vibrator 2, a monitor circuit 6 that monitors the vibration state of the vibrator 2, and an inertia. A sensing circuit 8 that senses distortion of the vibrator 2 caused by force (Coriolis force), and a power supply circuit (not shown) for supplying power to the drive circuit 4 and the sensing circuit 8 are provided.

  The vibrator 2 includes a drive electrode 10, a sensing electrode 12, and a monitor electrode 14 having a multilayer structure formed by sandwiching a piezoelectric thin film made of PZT with electrodes made of a metal conductor such as Ag or Au on a tuning fork-shaped silicon substrate. Formed. The shape of the silicon substrate may be an H shape, a T shape, a sound piece shape, or the like.

  The drive circuit 4 includes an AGC circuit 16 that controls the voltage, a BPF circuit 18, and an amplification circuit 20 that amplifies the voltage for energizing the drive electrode 10, and depends on the vibration state of the vibrator 2 by the monitor circuit 6. If the amplitude value of the vibrator 2 is monitored to be small, the voltage for energizing the vibrator 2 via the AGC circuit 16 is increased. If the amplitude value of the vibrator 2 is monitored to be large, the AGC circuit 16 is The voltage for energizing the vibrator 2 is controlled so that the voltage for energizing the vibrator 2 is reduced and the vibration of the vibrator 2 vibrates with a constant period and amplitude.

  The sensing circuit 8 is a circuit that senses distortion of the vibrator 2 due to inertial force and processes a sensing signal electrically output from the sensing electrode 12, and is configured by a differential amplifier circuit, a synchronous detection circuit, and the like. Yes.

  In particular, the inertial force sensor described above is more resistant to vibration at the start-up (when the power is turned on, etc.) than the voltage applied to the vibrator 2 at steady state (when the vibrator 2 vibrates in a stable state). The voltage applied to the vibrator 2 is reduced when the vibrator 2 is oscillating in a stable state, and is activated more than the current applied to the vibrator 2 at a steady state (when the vibrator 2 is oscillating in a stable state). Voltage / current control means 22 is provided to increase the current applied to the vibrator 2 when the vibrator 2 vibrates in an unstable state (eg, when the power is turned on).

  The voltage / current control means 22 includes a DC conversion circuit 24, a comparison circuit 26, and a memory unit 28, and an amplitude value (including a calculated value calculated from the amplitude value) of the vibrator 2 monitored by the monitor circuit 6. The amplitude value of the vibrator 2 at the normal time (including the calculated value calculated from the amplitude value) or the amplitude value of the vibrator 2 at the startup (including the calculated value calculated from the amplitude value) stored in the memory unit 28 in advance. Compared to the above, the vibration timing of the vibrator 2 is determined, and the voltage and current applied to the vibrator 2 are controlled according to the vibration timing.

  Specifically, it is as shown in FIG.

  2A is a characteristic waveform diagram of the DC conversion value converted by the DC conversion circuit at point A in FIG. 1, and FIG. 2B is a vibration of the vibrator output from the monitor circuit at point B in FIG. (C) is a characteristic waveform diagram showing the amplitude of the voltage of the drive circuit for vibrating the vibrator at point C in FIG. As shown in FIG. 2C, the voltage / current control means 22 secures a voltage necessary for starting the vibrator 2 and performs predetermined energization when the vibrator 2 is started. In the method, the predetermined energization necessary for the steady state is performed by lowering the voltage from the voltage necessary for starting. As shown in FIG. 2B, the DC conversion value DC-converted by the DC conversion circuit 24 is stored in the memory unit 28 as shown in FIG. 2A according to the characteristic waveform indicating the vibration of the vibrator 2. The comparison circuit 26 compares the predetermined reference value (amplitude value of the vibrator 2 at a steady state or the amplitude value of the vibrator 2 at the time of activation) stored in advance, so that the vibration timing of the vibrator 2 is activated. It is judged whether it is time or steady time.

  Further, the amplifier circuit 20 of the drive circuit 4 is provided with two phase compensation capacitors having different capacitance values, and when a voltage is applied to the vibrator 2 in a steady state, the phase compensation capacitor having the smaller capacitance value is energized to start. When a voltage is sometimes applied to the vibrator 2, switching means is provided for energizing the phase compensation capacitor having the larger capacitance value.

  In general, the wideband and high gain amplifier circuit 20 is used with feedback, but if the phase of the amplifier circuit 20 exceeds 180 degrees, the feedback circuit oscillates because it is positively fed back. Therefore, in order to maintain an appropriate gain frequency characteristic, a phase compensation capacitor is used to control the phase to prevent oscillation and perform stable operation. Since the voltage needs to be increased when the vibrator 2 is started up, when amplifying by the amplifier circuit 20, the phase compensation capacitor having a large capacitance value is energized to stably operate the amplifier circuit 20, so that the vibrator 2 is steady. In some cases, the voltage is reduced to suppress power consumption. Therefore, when the voltage is amplified by the amplifier circuit 20, the amplifier circuit 20 can be stably operated by supplying current to a phase compensation capacitor having a small capacitance value.

  3A is a characteristic waveform diagram showing the vibration (amplitude) of the vibrator output from the monitor circuit at the point B in FIG. 1, and FIG. 3B is a graph showing the steady-state voltage of the drive circuit at the point C in FIG. FIG. 3C is a characteristic waveform diagram showing the amplitude of the starting voltage of the drive circuit at the point C in FIG. As shown in FIGS. 3 (b) and 3 (c), the amplitude of the voltage is a rectangular wave at the time of startup, and a sine wave at the time of steady state. In particular, as shown in FIG. With respect to the voltage rectangular wave, the phase is likely to be delayed if the energized current is small, and the phase is difficult to be delayed if the energized current is large.

  As shown in FIGS. 4A and 4B, the influence of this phase delay causes a shift in the resonance frequency, and the vibrator 2 does not vibrate at the resonance frequency with the best vibration efficiency. That is, since the startup time is prolonged or the sensitivity at startup is reduced, it is advantageous that the current at startup is large in order to suppress the phase delay. However, if it is larger than necessary, it simply leads to an increase in power consumption.

  With the above configuration, the voltage applied to the vibrator 2 during steady state (when the vibrator 2 vibrates in a stable state) vibrates in an unstable state when the vibrator 2 is activated (eg when the power is turned on). Therefore, the voltage for energizing the vibrator 2 is always set to the maximum value required for vibrating the vibrator 2 (the voltage required at startup). Power consumption can be reduced without the need for setting. In particular, since the current to be added to the vibrator 2 at the time of startup is larger than the current to be added to the vibrator 2 at the steady state, it is necessary to make the rise and fall of the voltage waveform steep and to vibrate the vibrator 2. The time for which the maximum value can be secured becomes longer, and the startup efficiency can be improved. In addition, since the energized current is large with respect to the voltage waveform at the time of activation, the phase is hardly delayed and the vibration efficiency of the vibrator can be improved.

  The amplifier circuit 20 is provided with two phase compensation capacitors having different capacitance values. When a voltage is applied to the vibrator 2 in a steady state, the phase compensation capacitor having the smaller capacitance value is energized, and to the vibrator 2 at startup. When applying the voltage, since the switching means for energizing the phase compensation capacitor having the larger capacitance value is provided, the amplifier circuit 20 can be stably operated. In particular, when the vibrator 2 is in a steady state, the voltage is reduced to suppress power consumption. In this case, the phase compensation capacitor having the smaller capacitance value is energized, so that the voltage can be accurately increased and decreased. The amplifier circuit 20 can be stably operated.

  Further, the voltage / current control means 22 includes the amplitude value (including the calculated value calculated from the amplitude value) of the vibrator 2 monitored by the monitor circuit 6 and the amplitude value (amplitude) of the vibrator 2 stored in a steady state in advance. In addition, the vibration time of the vibrator 2 is judged and added to the vibrator 2 in comparison with the amplitude value of the vibrator 2 at the time of activation (including the computed value calculated from the amplitude value). Therefore, the voltage applied to the vibrator 2 can be controlled by accurately determining whether the vibration timing is the start time or the steady time.

  In the embodiment of the present invention, the drive circuit 4 and the monitor circuit 6 are provided with a sleep mode means for applying a voltage without applying a voltage to the sensing circuit 8, and the voltage applied to the vibrator 2 in a steady state is provided. Alternatively, a configuration may be provided in which the voltage applied to the vibrator 2 is reduced during the sleep mode. Thereby, power consumption can be further suppressed. Further, the return from the sleep mode to the steady state is the same as that at the time of activation in the embodiment of the present invention. The difference is whether the startup is at power-on or in sleep mode.

  As described above, the inertial force sensor of the present invention can reduce power consumption and can be applied to various devices.

The block diagram of the inertial force sensor in one embodiment of this invention Characteristic waveform diagram at points A to C in FIG. Characteristic waveform diagram at the time of steady and starting at point C with respect to the characteristic waveform at point B in FIG. Characteristic waveform diagram showing phase lag and resonance frequency deviation

Explanation of symbols

2 vibrator 4 drive circuit 6 monitor circuit 8 sensing circuit 10 drive electrode 12 sense electrode 14 monitor electrode 16 AGC circuit 18 BPF circuit 20 amplifier circuit 22 voltage current control means 24 DC conversion circuit 26 comparison circuit 28 memory unit

Claims (4)

A vibrator, a drive circuit that vibrates the vibrator by applying voltage and current to the vibrator, a monitor circuit that monitors the vibration state of the vibrator, and senses distortion of the vibrator due to inertial force And the drive circuit oscillates the vibrator according to the voltage and current applied to the vibrator and changes the amplitude value of the vibrator.
Voltage / current control that reduces the voltage applied to the vibrator at startup than the voltage applied to the vibrator at steady state and increases the current applied to the vibrator at startup than the current applied to the vibrator at steady state Inertial force sensor provided with means. The drive circuit includes an amplifier circuit, and the amplifier circuit is provided with two phase compensation capacitors having different capacitance values. When voltage is applied to the vibrator in a steady state, the phase compensation capacitor having the smaller capacitance value is used. The inertial force sensor according to claim 1, further comprising a switching unit that energizes the phase compensation capacitor having a larger capacitance value when energizing and applying a voltage to the vibrator at the time of activation. The voltage / current control means compares the amplitude value of the vibrator monitored by the monitor circuit with the amplitude value of the vibrator at steady state or the amplitude value of the vibrator at startup stored in advance, The inertial force sensor according to claim 1, wherein the inertial force sensor is configured to determine a vibration timing of the vibrator and to control a voltage and a current applied to the vibrator. The sensing circuit is provided with sleep mode means for applying voltage to the driving circuit and the monitor circuit without applying voltage, and is applied to the vibrator in the sleep mode rather than the voltage to be applied to the vibrator during steady state. The inertial force sensor according to claim 1, wherein the voltage is reduced.

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