JP2007178295A - Fall detection device and fall detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably detect a fall state by relatively simple analog circuit constitution. <P>SOLUTION: A fall detection device 10 is provided with: an acceleration sensor 11 constituted using a GMR element that is a magnetoresistive element and a magnet; a first low-pass filter 12 removing high-frequency components not less than a prescribed first frequency from an output signal of the acceleration sensor 11; a second low-pass filter 13 removing high-frequency components not less than a second frequency higher than the first frequency from the output signal of the acceleration sensor 11; a differential amplification circuit 14 amplifying the difference between the output signal of the first low-pass filter 12 and the output signal of the second low-pass filter 13; a full wave rectification circuit 15 for fully rectifying the output signal of the differential amplification circuit 14; and a comparison circuit 16 comparing the output signal of the full wave rectification circuit 15 with a threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fall detection device and a fall detection method, and more particularly to a fall detection device and a fall detection method for early detection of a fall state of an electronic device such as a hard disk drive.

  In recent years, the spread of hard disk drives has been remarkable, and it has been installed in various information devices from video recorders to portable music players as well as personal computers. Recently, a 1-inch hard disk drive with a capacity of 5 GB has also appeared, and the miniaturization and thinning of the hard disk drive is rapidly progressing. In the future, it is expected that a large number of mobile phones will be equipped with a hard disk drive. ing.

  As described above, when a hard disk drive is mounted on a portable device and frequently carried, it can be easily predicted that an accident in which the hard disk drive is dropped and broken will frequently occur. Since a large impact is fatal for a hard disk drive, means for avoiding the impact, such as detecting the fall state immediately and retracting the magnetic head, is necessary.

In order to solve such a problem, for example, the signal from the electrostatic acceleration sensor is analog-calculated by a circuit inside the sensor or an external circuit connected to the sensor, and the acceleration sensor in the triaxial direction (XYZ direction) is used. A method has been proposed in which a fall state is determined when a state in which all the acceleration values obtained are zero continues for a certain period of time (see Patent Document 1). A sensor device configured using a microcomputer has also been proposed (see Patent Document 2). This sensor device includes an acceleration sensor using a piezoelectric element, a signal processing circuit for amplifying an analog signal from the acceleration sensor and extracting a signal in a predetermined frequency band as an analog filter, and a signal from the acceleration sensor supplied via the signal processing circuit. And a microcomputer that has a digital filter function to reduce the sensitivity of the sensor in the vicinity of the resonance frequency and reduce the influence of resonance on the sensor output.
JP 2000-241442 A JP 2003-315356 A

  In the method described in Patent Document 1, since it is configured by only a simple analog circuit and the drop detection is performed based on a simple determination whether it is higher or lower than a certain threshold value, for example, drift occurs in the sensor output due to a temperature change or the like. If the sensor output fluctuates due to battery consumption, it may be erroneously determined to be in a fall state despite being in normal use in real life, and stable fall detection cannot be performed. There's a problem. Further, as many arithmetic circuits as the number of XYZ axes are required. In addition, the method described in Patent Document 2 has a problem that a filter function for selecting a frequency component is required when detecting a fall.

  Accordingly, an object of the present invention is to provide a fall detection device and a fall detection method capable of stably detecting a fall state with a relatively simple circuit configuration.

  An object of the present invention is to provide an acceleration sensor, a noise removal circuit for removing a frequency component lower than a first frequency included in an output signal of the acceleration sensor, and an output signal of the acceleration sensor from which the frequency component has been removed. And a comparison circuit that compares the threshold value with a threshold value.

  The noise removal circuit includes: a first low-pass filter that removes a frequency component equal to or higher than the first frequency from the output signal of the acceleration sensor; an output signal of the acceleration sensor; and an output signal of the first low-pass filter. Preferably, the comparator circuit includes a differential amplifier circuit that generates a differential signal, and the comparator circuit compares the differential signal with a threshold value.

  The noise removal circuit further includes a second low-pass filter that removes a frequency component equal to or higher than a second frequency higher than the first frequency from the output signal of the acceleration sensor, and the differential amplifier circuit includes the first low-pass filter. It is preferable to generate a differential signal between the output signal of the first low-pass filter and the output signal of the second low-pass filter.

  The fall detection device of the present invention further includes a full-wave rectification circuit that full-wave rectifies the differential signal and outputs an absolute value of the differential signal, and the comparison circuit includes the absolute value of the differential signal, the threshold value, Are preferably compared.

  5. The fall detection device according to claim 2, wherein the first frequency is a frequency within a range of 0.1 Hz to 1.0 Hz. apparatus.

  6. The fall detection device according to claim 3, wherein the second frequency is a frequency within a range of 1 Hz to 10 Hz.

  The object of the present invention is also to remove a frequency component below a predetermined frequency from the output signal of the acceleration sensor, compare the output signal of the acceleration sensor from which the frequency component has been removed with a threshold value, and And a step of determining a fall state when the threshold value is exceeded.

  According to the present invention, the falling state can be stably detected with a relatively simple analog circuit configuration.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a circuit diagram showing a circuit configuration of a drop detection device according to a preferred embodiment of the present invention.

  As shown in FIG. 1, the drop detection device 10 includes an acceleration sensor 11 configured using a GMR (Giant Magnetic Resistance) element that is a magnetoresistive element and a magnet, and a predetermined frequency based on an output signal of the acceleration sensor 11. The first low-pass filter 12 that removes the above high-frequency components (hereinafter referred to as the first frequency), and a predetermined frequency higher than the first frequency from the output signal of the acceleration sensor 11 as in the first low-pass filter 12. A difference that amplifies the difference between the output signal of the second low-pass filter 13 and the output signal of the second low-pass filter 13 from the second low-pass filter 13 that removes the above high-frequency components (hereinafter referred to as the second frequency). Dynamic amplifier circuit 14, full wave rectifier circuit 15 for full wave rectification of the output signal of differential amplifier circuit 14, and comparison circuit for comparing the output signal of full wave rectifier circuit 15 with a threshold value 16.

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the acceleration sensor 11.

  As shown in FIG. 2, the acceleration sensor 11 includes a base plate 21, an elastic body 22 connected to the base plate, a weight 23 attached to the distal end side of the elastic body 22, a magnet 24 attached to the weight 23, And a magnetoresistive element 25 disposed immediately below the magnet 24. The elastic body 22 has a cantilever structure in which the base end side is connected, and the weight 23 receiving the acceleration can be displaced in three axial directions. Although the magnet 24 applies a bias magnetic field to the magnetoresistive element 25, the magnetic field generated from the magnet 24 also changes due to the displacement of the weight 23, so that the resistance value of the magnetoresistive element 25 is displaced. With the above configuration, acceleration can be detected.

The output signal of the acceleration sensor 11 is input to the first and second low-pass filters 12 and 13, respectively. The first low-pass filter 12 includes a resistor R ₁ and a capacitor C ₁ , and the first frequency that is a cutoff frequency is set within a range of 0.1 to 1.0 Hz. Second low-pass filter 13 is constituted by a resistor R ₂ and capacitor C _2, a second frequency is a cutoff frequency is set in the range of 1 to 10 Hz.

  The first low-pass filter 12 and the second low-pass filter 13 both remove high-frequency components of the sensor signal, but the first low-pass filter 12 passes a signal component that changes relatively slowly, The low-pass filter 13 is different in that it passes a signal component that changes relatively abruptly when it falls. That is, a signal obtained by passing through the first low-pass filter 12 is a very low-frequency noise component caused by a drift in the sensor output due to a temperature change or the like, a fluctuation in the sensor output due to battery consumption, and the like. The signal obtained by passing through the low-pass filter 13 is the output signal itself of the acceleration sensor 11 from which high-frequency noise has been removed. Note that the low frequency side of the first frequency range can be expanded to about 0.01 Hz to cope with lower frequency applications. Further, the high frequency side of the second frequency range can be expanded to about 100 Hz, and it is possible to cope with higher frequency applications.

The differential amplifier circuit 14 is mainly constituted by an operational amplifier OP _1. The differential amplifier circuit 14 calculates the difference between the output signals of the low-pass filters 12 and 13 and extracts a sudden change in the output signal of the acceleration sensor 11. By removing signal components that change relatively slowly from the sensor signal in this way, effects such as fluctuations in power supply voltage, changes in sensor characteristics over time, changes in ambient temperature, etc. can be removed, and sudden changes at the time of falling can be assured. Can be detected. The differential signal generated by the differential amplifier circuit 14 is input to the full-wave rectifier circuit 15.

The full-wave rectifier circuit 15 includes an operational amplifier OP ₂ , diodes D ₁ and D ₂ , an operational amplifier OP _{3 and the} like, and calculates an absolute value of the sensor output. When the acceleration sensor shown in FIG. 2 is used, it is unknown whether the direction of acceleration due to falling is positive or negative, so the fall state is determined using the absolute value of acceleration. There is a need to. Note that a low-pass filter may be provided in the full-wave rectifier circuit 15 to remove the influence of noise due to a very short impact. The output signal of the full wave rectification circuit 15 is input to the comparison circuit 16.

Comparison circuit 16 is constituted mainly of an operational amplifier OP _4, it compares the output signal of the full-wave rectifier circuit 15 with a predetermined threshold value. To one input terminal of the comparison circuit 16 the output signal of the full-wave rectifier circuit 15 is supplied, the threshold voltage V _s is supplied to the other input terminal. Thus, the comparison circuit 16 compares the output signal of the full-wave rectifier circuit 15 with the threshold value, and determines that the output signal of the full-wave rectifier circuit 15 is in the fall state when the output signal of the full-wave rectifier circuit 15 exceeds the threshold value.

FIG. 3 is a signal waveform diagram at each point in the fall detection apparatus 10, where the horizontal axis indicates time t and the vertical axis indicates the signal level. 3, signals _{S 1} output signal, the signal _{S 2} is the output signal of the first low-pass filter 12, the signal _{S 3} output signal of the second low-pass filter 13, the signal _{S 4} of the acceleration sensor 11 is a differential amplifier the output signal of the circuit 14, the signal S ₅ shows the output signal of the full-wave rectifier circuit 15, respectively. That is, the signals S _{1 to} S ₅ correspond to the signal levels at points P _{1 to} P ₅ in FIG.

As shown in FIG. 3, the output signal of the acceleration sensor 11 is rapidly increases at the timing t _1, which rapidly decreases at time t _2. This begins to fall fall detection device 10 in t _1, it indicates that the acceleration has suddenly increased and reaches the ground fall detection device 10 at the timing t _2, the acceleration is suddenly reduced It means that. The waveform of the signal S ₂ after the output signal S ₁ of the acceleration sensor 11 passes through the first low-pass filter 12 becomes a very gentle waveform as shown in FIG. the waveform of the signal S ₃ having passed through is approximately equal to the unfiltered signals S ₁ waveform. Then, the waveform of the differential signal S ₄ and the signal S ₂ and the signal S _3, large swings negative between t ₁ ~t ₃ As shown, the timing t ₃ after a larger deflection waveform on the positive side . The waveform of the signal S ₅ after the differential signal S ₄ full-wave rectifier has a waveform in which the waveform between t ₁ ~t ₃ is inverted to the positive side. By comparing the level of such signal S ₅ with a predetermined threshold value, it can be determined whether the falling state.

  FIG. 4 is a flowchart for explaining a fall detection procedure by the fall detection device 10.

  As shown in FIG. 4, calculation processing for drop detection by the drop detection device 10 includes a step of removing a high frequency component equal to or higher than the first frequency from the output signal of the acceleration sensor 11 (S 41), and an output of the acceleration sensor 11. A step (S42) of removing a high frequency component equal to or higher than the second frequency from the signal, and a difference between the signal from which the high frequency component equal to or higher than the first frequency is removed and the signal from which the high frequency component equal to or higher than the second frequency is removed. A step of obtaining a signal (S43), a step of calculating an absolute value of the difference signal (S44), a step of comparing the absolute value of the difference signal with a threshold value, and determining a fall state when the threshold value is exceeded (S45 to S47) ). Here, steps S41 to S43 are steps for removing a low frequency component having a frequency equal to or lower than a predetermined frequency from the output signal of the acceleration sensor 11, and after step S44, the output signal of the acceleration sensor from which the low frequency component has been removed is used as a threshold value. As a step of determining a fall state when the output signal exceeds a threshold value, it can be captured. The above-described drop detection device 10 performs the arithmetic processing as described above with an analog circuit, and can stably determine the fall state while having a relatively simple analog circuit configuration.

  FIG. 5 is a schematic diagram showing a configuration of the hard disk drive 100 incorporating the fall detection device 10.

  As shown in FIG. 5, a hard disk drive 100 includes a platter 101 that is a recording medium, a spindle motor 102 that rotationally drives the platter 101, and a magnetic head 103 that records data on the platter 101 or reproduces recorded data. An arm 104 that slides the magnetic head 103 on the platter 101, a voice coil motor 105 that drives the arm 104, a control unit 106 that controls each unit, and a fall detection device that detects the fall state of the hard disk drive 1 10. The actual control unit 16 and the fall detection device 17 are accommodated in the housing of the hard disk drive 10.

  When the hard disk drive 100 falls from a predetermined height at which it is damaged and the fall detection device 10 determines that the hard disk drive 100 is in a free fall state, the control unit 106 that receives this determination result (retraction signal) The coil motor 15 is operated to move the arm and the magnetic head 13 to the retreat area P indicated by a broken line in FIG.

  The control unit 106 is a general circuit required for controlling the entire hard disk drive 100, and includes, for example, a head amplifier, a read / write channel circuit, a hard disk controller, a CPU, and a memory. The control unit 7 is divided into an analog system and a digital system, and an analog circuit is used to control the spindle motor 102 and the arm 104. In order to detect the fall state at an early stage, stop the rotation of the disk so as not to damage the platter 101, and retract the magnetic head 103 to a predetermined retreat position, the determination result of the fall detection device 10 is converted to an analog type. Although it is necessary to immediately transmit it to the control circuit, since the fall detection device 10 is constituted by an analog circuit, the combination with these analog system control circuits is easy. That is, if the fall detection device 10 is configured with an analog circuit, it can be configured integrally with the actuator drive analog circuit of the hard disk drive, and there is no problem of transmission delay of the fall detection result. Further, in order to minimize the influence of noise, the analog circuit must be arranged as close to the actuator as possible, and there is a great restriction on the circuit arrangement in the hard disk drive 100, but the drop detection device 10 of this embodiment is compared. Since the circuit configuration is simple and small, there is no particular problem.

  As described above, according to the present embodiment, the fall state can be detected early and reliably by performing predetermined analog calculation processing on the output signal of the acceleration sensor. It is possible to protect sensitive electronic devices at an early stage. In particular, since the fall detection device of this embodiment is configured by an analog circuit, it can be easily incorporated into an analog circuit for driving an actuator of a hard disk drive, and the control circuit and the fall detection device can be configured integrally.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention, and these are also included in the scope of the present invention. Needless to say.

  For example, in the above embodiment, the absolute value of the sensor output is calculated using the full-wave rectifier circuit 15, but when the direction of acceleration applied to the drop detection device 10 is one direction, full-wave rectification is performed. The circuit 15 may be omitted.

  In the above embodiment, full-wave rectification is performed after obtaining the difference between the sensor signal from which the high-frequency component has been removed by the first low-pass filter 12 and the sensor signal from which the high-frequency component has been removed by the second low-pass filter. Although the circuit 15 calculates the absolute value of the difference signal, the order of the arithmetic processing may be reversed. That is, after obtaining the absolute value of the sensor signal from which the high-frequency component has been removed by the first low-pass filter 12 and the absolute value of the sensor signal from which the high-frequency component has been removed by the second low-pass filter 13, respectively, You may ask for it.

  In the above embodiment, the difference between the sensor signal from which the high-frequency component has been removed by the first low-pass filter 12 and the sensor signal from which the high-frequency component has been removed by the second low-pass filter is obtained. The low-pass filter may be omitted. That is, the difference between the sensor signal from which the high-frequency component has been removed by the first low-pass filter 12 and the output signal itself of the acceleration sensor 11 may be obtained.

It is a circuit diagram which shows the circuit structure of the fall detection apparatus which concerns on preferable embodiment of this invention. 2 is a schematic diagram illustrating an example of a configuration of an acceleration sensor 11. FIG. FIG. 4 is a signal waveform diagram at each point in the fall detection device 10. 4 is a flowchart for explaining a drop detection procedure by the drop detection device 10; 1 is a schematic diagram showing a configuration of a hard disk drive 100 that incorporates a fall detection device 10. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fall detection apparatus 11 Acceleration sensor 12 1st low pass filter 13 2nd low pass filter 14 Differential amplifier circuit 15 Full wave rectifier circuit 16 Comparison circuit 21 Base plate 22 Elastic body 23 Weight 24 Magnet 25 Magnetoresistance element OP ₁ Operational amplifier OP ₂ op OP ₃ op OP ₄ op _R 1 _{to R 12} resistor _C 1 -C ₅ capacitor _D 1, _{D 2} diode output signal _{S 2} output signal _{S 3} of the first low-pass filter 12 and the second low-pass _{S 1} acceleration sensor 11 the output signal _{V s} threshold voltage _{t 1} timing of the output signal _{S 5} full-wave rectifier circuit 15 of the output signal _{S 4} the differential amplifier circuit 14 of the filter 13 (falling start)
t ₂ timing (landing)
t ₃ timing

Claims (7)

  An acceleration sensor; a noise removal circuit that removes a frequency component lower than a first frequency included in the output signal of the acceleration sensor; and a comparison circuit that compares the output signal of the acceleration sensor from which the frequency component has been removed with a threshold value A fall detection device comprising:   The noise removal circuit includes: a first low-pass filter that removes a frequency component equal to or higher than the first frequency from the output signal of the acceleration sensor; an output signal of the acceleration sensor; and an output signal of the first low-pass filter. The drop detection device according to claim 1, further comprising a differential amplifier circuit that generates a difference signal, wherein the comparison circuit compares the difference signal with a threshold value.   The noise removal circuit further includes a second low-pass filter that removes a frequency component equal to or higher than a second frequency higher than the first frequency from the output signal of the acceleration sensor, and the differential amplifier circuit includes the first low-pass filter. The fall detection device according to claim 2, wherein a difference signal between an output signal of one low-pass filter and an output signal of the second low-pass filter is generated.   A full-wave rectifier circuit for full-wave rectifying the differential signal and outputting an absolute value of the differential signal; and the comparison circuit compares the absolute value of the differential signal with the threshold value. The fall detection device according to claim 2 or 3.   5. The fall detection device according to claim 2, wherein the first frequency is a frequency within a range from 0.1 Hz to 1.0 Hz.   The fall detection device according to any one of claims 3 to 5, wherein the second frequency is a frequency within a range of 1 Hz to 10 Hz. The step of removing a low frequency component below a predetermined frequency from the output signal of the acceleration sensor is compared with a threshold value of the output signal of the acceleration sensor from which the low frequency component has been removed, and the output signal exceeds the threshold value. And a step of determining a fall state.

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