JP2010071916A - Drop detection device, magnetic disk drive, and mobile electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drop detection device for preventing drop of an acceleration sensor from not being sensed, suppressing malfunction and achieving compactness and cost reduction by solving problems of characteristic irregularities of the acceleration sensor, and to provide a magnetic disk drive provided with it and a mobile electronic device. <P>SOLUTION: The drop detection device includes: obtaining absolute values of acceleration change amounts in each of three-axes directions; determining whether they satisfy a condition indicating values between first thresholds Ax1_min and second thresholds Ax1_mid higher than the first thresholds; determining whether the absolute values of the acceleration change amounts satisfy a condition reaching third thresholds Ax1_max higher than the second thresholds after satisfying the condition; and regarding them as drop start when the absolute values of the acceleration change amounts are lower than fourth thresholds Ax2 lower than the third thresholds Ax1_max after further satisfying the condition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fall detection device that detects the fall of a device based on acceleration, a magnetic disk device including the fall detection device, and a portable electronic device.

Conventionally, patent document 1 is disclosed as an apparatus which detects the fall of an apparatus.
FIG. 1 shows how the output of the acceleration sensor in the Z-axis direction of Patent Document 1 changes from 1 to almost 0. In Patent Document 1, an arithmetic circuit that calculates the magnitude of acceleration from an output signal of an acceleration sensor, a comparison circuit that compares whether or not the magnitude of acceleration is a value close to 0, and the acceleration are almost zero. Whether or not a state in which all the accelerations in the (X-axis, Y-axis, Z-axis) are substantially zero continues for the reference duration. For example, it is determined whether or not the magnetic disk device is free-falling.

As described above, the determination circuit determines that “fall” is obtained when the output of all three axes becomes approximately 0 for the reference time or more.
Japanese Patent No. 3441668

  However, in the fall detection method shown in the above-mentioned Patent Document 1, the state where the output of the three-axis acceleration sensor is almost zero must correspond to the zero-gravity state of each axis. An acceleration sensor whose output is always 0 in a state is necessary.

  However, since the acceleration sensor has manufacturing variations and variations in characteristics due to changes in temperature and changes with time, the following problems occur in the above-described determination method.

  (1) If the variation in characteristics of the acceleration sensor exceeds a certain threshold value, the fall determination becomes impossible.

  (2) If the threshold value is set to a large value in consideration of variations in the characteristics of the acceleration sensor, malfunctions such as erroneous determination of “falling” even though the vehicle is not falling will increase.

  (3) The variation in the characteristics of the acceleration sensor can be calibrated (corrected) by several methods. For this reason, a correction circuit is separately required, which is a factor that hinders downsizing and cost reduction.

  Therefore, an object of the present invention is to eliminate the problem of variation in the characteristics of the acceleration sensor to prevent the drop detection from becoming impossible, to suppress a malfunction, and to achieve a small and low cost drop detection device, and a magnetic device equipped with the fall detection device. To provide a disk device and a portable electronic device.

In order to solve the above problems, the present invention is configured as follows.
(1) A fall detection device that detects fall based on an output signal of an acceleration sensor,
Acceleration detecting means for obtaining a detection value corresponding to acceleration in three orthogonal directions;
For each of the three axis directions, the amount of change in acceleration with the passage of time of the detected value is obtained, and the absolute value of the amount of change in acceleration is determined from the first threshold value (Ax1_min) and the first threshold value. First condition determination means for determining whether or not a condition for taking a value between the high second threshold value (Ax1_mid) is satisfied;
After satisfying the first condition, a second condition determination is made to determine whether or not a condition for the absolute value of the acceleration change amount to reach a third threshold value (Ax1_max) equal to or greater than a second threshold value is satisfied. Means,
Third condition determining means for determining whether or not the absolute value of the acceleration change amount satisfies a condition that is lower than a fourth threshold value Ax2 lower than a third threshold value Ax1_max after satisfying the second condition. When,
When at least one of the three axial directions satisfies the third condition, it is determined whether or not the vehicle is in a falling state based on a difference value between detection values in different axial directions of the three axial directions. And a falling state determination means to perform.

  In this way, by observing the amount of change with time in the acceleration detection value in each axis direction, it was possible to discriminate between a simple impact not caused by a fall and the start of the fall, and it was assumed that the fall started After that, since it is determined whether or not the vehicle is falling based on the difference value between the detected values in the three axial directions, whether the detected value of the acceleration sensor is equivalent to 0G. Whether or not can be detected by the difference value. In other words, it is not necessary to obtain the absolute value of the combined vector of the outputs of the axes of the acceleration sensor, which is conventionally required, and no multiplier is required. As a result, the arithmetic processing program can be simplified and the arithmetic processing time can be shortened.

(2) The time from when the first condition is satisfied until the second condition is satisfied, or the time from when the second condition is satisfied until the third condition is satisfied is within a specified value. Fourth condition determining means for determining

  As a result, it is possible to further suppress an erroneous determination such that some change in acceleration other than the start of dropping, such as some impact, is erroneously regarded as a falling start state.

(3) Of the detected values in the three axial directions detected by the acceleration detecting means, the sum of the absolute values of the differences between the detected values in the different axial directions is set higher by a predetermined amount than the value obtained in the gravitational acceleration state. Means is provided for discriminating between a drop start and an impact depending on whether or not the threshold is exceeded.

  For example, when an impact is applied in the X-axis direction, the detected acceleration value ax in the X-axis direction fluctuates greatly, and the absolute value of the change amount may behave in the same manner as when dropped. Among the detected values in the three axial directions, the absolute values | ax−ay |, | ay−az |, | az−ax | of the differences between the detected values in the different axial directions are constant values (gravitational acceleration) About twice the value). Therefore, among the detected values in the three axial directions, the sum of the absolute values of the differences between the detected values in the different axial directions is set higher by a predetermined amount than the value obtained in the 1G (gravity acceleration) state. It is possible to distinguish between a simple impact and a fall.

(4) A magnetic disk device including the drop detection device, wherein the head for recording or reading data on the magnetic disk, and the head is retracted when the drop detection device determines that the device is falling. Head retracting means for retracting to the area.

  As a result, the magnetic disk device can be protected against dropping.

(5) A portable electronic device including the fall detection device and a device capable of handling an impact, and when the fall detection device determines that the device is falling, the impact countermeasure processing is performed on the device. Impact countermeasure processing means to be applied.

  Thereby, the device capable of handling the impact countermeasure is effectively controlled, and the safety of the portable electronic device is enhanced.

  According to the present invention, even if a steady error such as an offset is included in the output signal of the acceleration sensor, the fall determination can be performed. It is also possible to distinguish between simple impact and fall.

<< First Embodiment >>
FIG. 2 is a block diagram showing the configuration of the fall detection device according to the first embodiment. The fall detection device 100 includes an acceleration sensor 60 that detects acceleration and outputs an analog voltage signal corresponding to the acceleration, an A / D converter 72 that converts the output voltage of the acceleration sensor 60 into digital data, and an A / D converter 72. A control unit 74 is provided that performs drop detection based on the output data and outputs the detection result to the outside (host device). Here, the acceleration sensor 60 corresponds to “acceleration detecting means” according to the present invention.

  Even when the falling direction is uncertain, in order to detect the falling, the acceleration in the three-dimensional direction is detected, and the falling is detected based on the detected acceleration. The acceleration sensor 60 includes three acceleration sensors that detect accelerations in the X-axis direction, the Y-axis direction, and the Z-axis direction that are orthogonal to each other. The A / D converter 72 converts the output voltage of each acceleration sensor into digital data. These are output as detected values ax, ay, az of accelerations in the respective axial directions. The control unit 74 performs the fall determination by a process described later.

  As the acceleration sensor 60, various types of acceleration sensors such as a piezoelectric type, a piezoresistive type, and a capacitive type can be used.

  FIG. 3 shows an example of the elapsed time of the acceleration detection value and the acceleration change amount for the X axis among the axes of the acceleration sensor 60 before and after the start of dropping. Here, the vertical axis represents the acceleration detection value in decimal representing the maximum value of 1.65 V in 11 bits. The horizontal axis represents the elapsed time t [ms].

In the 1G state before time t0, that is, in the steady state where the drop has not yet started, the acceleration detection value maintains a predetermined value (about 450).
When the electronic device equipped with the acceleration sensor 60 starts to fall, the acceleration detection value indicated by the broken line in the figure decreases toward 0 and the absolute value of the acceleration change amount indicated by the solid line in the figure starts to increase. When the absolute value of the acceleration change amount is between the first threshold value Ax1_min and the second threshold value Ax1_mid (time t0), the first stage ST1 is entered.

Thereafter, when the absolute value of the acceleration change amount reaches the third threshold value (Ax1_max) (in this example, the relationship of Ax1_max = Ax1_mid) (time t1), the second stage ST2 is entered.
Thereafter, when the absolute value of the acceleration change amount falls below the fourth threshold value Ax2 lower than the third threshold value Ax1_max (time t2), the third stage ST3 is entered. This third stage is a stage regarded as a falling state.

  Note that the third threshold value Ax1_max may be equal to or greater than the second threshold value Ax1_mid, and is not limited to the third threshold value Ax1_max = the second threshold value Ax1_mid.

  In the example shown in FIG. 3, the acceleration detection value and the acceleration change amount change greatly due to a collision with the floor or the ground at time t3 thereafter, and the change due to the bounce is repeated several times.

  FIG. 4 is an example in which a value Axyz for determining a falling state and an impact is obtained based on the same acceleration detection value as that shown in FIG. This value Axyz is the sum of the absolute values of the differences between the detected acceleration values in two different axial directions among the detected values in the three axial directions, and is expressed by the following equation.

Axyz = | ax-ay | + | ay-az | + | az-ax |
Even if the electronic device on which the acceleration sensor is mounted does not fall, the value of Axyz increases if any impact is applied to the electronic device. At this time, the value of Axyz is often larger than the value in the 1G (gravity acceleration) state. Therefore, as shown in FIG. 4, the threshold value Ath is set higher by a predetermined amount than the Axyz value obtained in the 1G state, and if Axyz exceeds the threshold value Ath, it is considered that an impact has been applied instead of dropping.

  In FIG. 4, the value Axyz is obtained as a ¼ value in consideration of the possibility that the above Axyz may exceed the number of bits that can be calculated. That is, a value shifted to the lower side by 2 bits.

  5 to 7 are flowcharts showing a processing procedure in which the control unit 74 shown in FIG. 2 performs the fall detection based on the output value of the A / D converter 72. FIG. 5 shows the process in the first stage, FIG. 6 shows the process in the second stage, and FIG. 7 shows the process in the third stage.

  In the determination process in the first stage, as shown in FIG. 5, first, absolute values of the change amounts with time of Axyz and the detected acceleration values in the respective axial directions | ax0−ax2 |, | ay0−ay2 |, | az0. -Az2 | is calculated respectively. Further, the value of Axyz is obtained (S11). Here, ax0, ay0, and az0 are the current (most recent) detected acceleration values for the respective axial directions, and ax2, ay2, and az2 are the past two detected acceleration values for the respective axial directions. Since the period of reading and calculating the acceleration detection value is, for example, 6.5 ms, the absolute value of the difference between the acceleration detection values at a timing that is 13 ms apart is obtained every 6.5 ms.

  Then, it is confirmed that the Axyz is less than the threshold value Ath (S12). If Axyz is greater than or equal to Ath, it means that there has been a large acceleration change exceeding the acceleration change from the 1G state to the falling state, and it is assumed that there was a simple impact and the process returns to the top (S12 → S11). .

  If Axyz <Ath, it is determined whether or not the absolute value | ax0−ax2 | of the change in acceleration in the X-axis direction is within the range between the first threshold value Ax1_min and the second threshold value Ax1_mid. (S13). Further, it is determined whether or not the absolute value | ay0-ay2 | of the change in acceleration in the Y-axis direction is within the range between the first threshold value Ay1_min and the second threshold value Ay1_mid (S14). Further, it is determined whether or not the absolute value | ax0−ax2 | of acceleration change in the Z-axis direction is within the range between the third threshold value Az1_min and the second threshold value Az1_mid (S15).

  If all three axes do not satisfy this condition, the process returns to the top (S13 → S14 → S15 → S11).

  If the above condition is satisfied in the X-axis direction, the flag Fx1 is set assuming that the first stage ST1 has been reached (S13 → S16). If the above condition is satisfied in the Y-axis direction, the flag Fy1 is set assuming that the first stage ST1 has been reached (S14 → S17). Similarly, if the above condition is satisfied in the Z-axis direction, the flag Fz1 is set assuming that the first stage ST1 has been reached (S15 → S18).

  The determinations in steps S13, S14, and S15 correspond to the “first condition determination unit” according to the present invention. The processes in steps S11 to S15 are repeated until any one of the determinations in steps S13, S14, and S15 satisfies the above conditions.

  In the determination process in the first stage, as shown in FIG. 6, first, a timer is started (S20), and the absolute value of the change in acceleration in each axis direction | ax0-ax2 |, | ay0-ay2 |, | az0 -Az2 | is obtained (S21). However, this value may be obtained only for the axis that has entered the second stage.

  If the flag Fx1 is in the set state, that is, if it is in the second stage in the X-axis direction, whether or not | ax0−ax2 | is within the range between the third threshold value Ax1_max and the upper limit Ax1_max2. Is determined (S22 → S24). If this condition is satisfied, a flag Fx2 indicating that the second stage has been reached is set (S25).

  If the flag Fy1 is in the set state, that is, if the second stage is reached in the Y-axis direction, whether | ay0-ay2 | is within the range between the third threshold value Ay1_max and the upper limit Ay1_max2. (S23 → S26). If this condition is satisfied, a flag Fy2 indicating that the second stage has been reached is set (S27).

  Similarly, if the flag Fz1 is in the set state, that is, if it is in the second stage in the Z-axis direction, is | az0−az2 | within the range between the third threshold value Az1_max and the upper limit Az1_max2? It is determined whether or not (S28). If this condition is satisfied, a flag Fz2 indicating that the second stage has been reached is set (S29).

  As described above, by setting the upper limits Ax1_max2, Ay1_max2, and Az1_max2, it is possible to prevent erroneous determination due to the influence of noise and impact. That is, when | ax0-ax2 |, | ay0-ay2 |, and | az0-az2 | appear to change suddenly due to noise or impact, these values exceed Ax1_max2, Ay1_max2, Az1_max2, and thus (the probability of exceeding is high). Therefore, it is possible to suppress erroneous determination that regards such noise and impact as a fall start state.

  The determinations in steps S24, S26, and S28 correspond to the “second condition determination unit” according to the present invention. If the conditions shown in steps S24, S26, and S28 are not satisfied even after a predetermined time has elapsed, the process returns to the top of FIG. 5 (S30 → S11). This step S30 corresponds to the “fourth condition determining means” according to the present invention.

  In the determination process in the third stage, as shown in FIG. 7, a timer is first started (S31), and the absolute value of the amount of change in acceleration in each axis direction | ax0-ax2 |, | ay0-ay2 |, | az0 -Az2 | is obtained (S32). However, this value may be obtained only for the axis that has entered the third stage.

  If the flag Fx2 is in the set state, that is, if it is in the third stage in the X-axis direction, it is determined whether or not | ax0−ax2 | has fallen below the fourth threshold value Ax2 (S33 → S35). If this condition is satisfied, it is regarded that the third stage has been reached, that is, it is regarded that the fall has started, and then the fall determination is performed (S38).

  If the flag Fy2 is in the set state, that is, if the third stage is reached in the Y-axis direction, it is determined whether or not | ay0−ay2 | has fallen below the fourth threshold value Ay2 (S34 → S36). If this condition is satisfied, it is considered that the fall has started, and the fall determination is performed (S38).

  Similarly, if the flag Fz2 is in the set state, that is, if it is in the third stage in the Z-axis direction, it is determined whether or not | az0−az2 | has fallen below the fourth threshold value Az2 (S37). ). If this condition is satisfied, it is considered that the fall has started, and the fall determination is performed (S38).

  The determinations in steps S35, S36, and S37 correspond to the “third condition determination unit” according to the present invention. If the conditions shown in steps S35, S36, and S37 are not satisfied even after a predetermined time has elapsed, the process returns to the top of FIG. 5 (S39 → S11). This step S39 corresponds to the “fourth condition determining means” according to the present invention.

  In the example described above, the first, second, third, and fourth threshold values are individually determined for each of the X axis, the Y axis, and the Z axis. If the characteristics are uniform and the first, second, third, and fourth threshold values for each axis are approximate, the first and second axes are common to the X, Y, and Z axes, respectively. -You may define the 3rd and 4th threshold value.

  FIG. 8 shows an example of the passage of time of the output voltages Vx, Vy, Vz and detected values az, ay, az of the respective axes of the acceleration sensor 60 before and after the start of dropping. Here, the relationship between the vertical axis and the horizontal axis is the same as in FIGS.

  As shown in FIG. 8, in the 1G state, that is, in the steady state where the drop has not yet started, the detected value (voltage) of each axis of the acceleration sensor 60 maintains a predetermined value. If it is in a falling state (0G) at a certain time, the detected value (voltage) of each axis of the acceleration sensor 60 maintains a value corresponding to 0G. Thereafter, the output of each axis of the acceleration sensor 60 greatly fluctuates by colliding with the floor or the ground.

  FIG. 9 is a flowchart showing the processing procedure of step S38 (decision of falling). The processing shown in FIG. 9 corresponds to the “falling state determination means” according to the present invention.

  In the figure, ax is a detection value of an acceleration sensor that detects acceleration in the x-axis direction (A / D converted value of the output voltage of the acceleration sensor), ay is a detection value of an acceleration sensor that detects acceleration in the y-axis direction, and similarly az is a detection value of an acceleration sensor that detects acceleration in the z-axis direction.

First, a timer is started (S41), and detection values ax, ay, and az of the acceleration sensor 60 are read (S42).
Next, the absolute value dxy of the difference of ax with respect to ay is obtained on the basis of ay, and the absolute value dzy of the difference of az with respect to ay is obtained (S43). Subsequently, it is determined whether or not the absolute values dxy and dzy of the two difference values are within a range of δxy ± α and a range of δzy ± α, which will be described later (S44, S45).

If dxy and dzy are stable as shown in FIG. 8, steps S44 and S45 are both “Yes”, and the processing of steps S42 to S46 is performed until this state reaches a predetermined duration T. Is repeated (S46 → S42 →...).
When the timer value reaches T, a falling state signal is output (S47).

The detected value (ax, ay, az) by the acceleration sensor has a relationship of (gx + δx, gy + δy, gz + δz) with respect to the actual acceleration (gx, gy, gz). Here, δ is the output variation in the weightless state inherent to the sensor element. That is,
(Ax, ay, az) = (gx + δx, gy + δy, gz + δz)
It is represented by

  Even in the weightless state (gx = gy = gz = 0), the sensor output is (δx, δy, δz). Therefore, if these are larger than the threshold value, they are not regarded as falling even in the weightless state. Or, a correction circuit for making them zero is required.

In the first embodiment, | ax-ay |, | az-ay |
| Δx−δy | −α <| ax−ay | <| δx−δy | + α (α> 0)
And | δz−δy | −α <| az−ay | <| δz−δy | + α
When the state is maintained for a predetermined duration or longer, it is determined that the vehicle is falling. Therefore, in the weightless state, the above determination values are theoretically | δx−δy | and | δz−δy |, respectively.

  This | δx−δy | is δxy in FIG. 9, and | δz−δy | is δzy in FIG.

  The output value (δx, δy, δz) of each axis at 0G of the acceleration sensor can be obtained in advance with the acceleration detection axis kept horizontal for each acceleration sensor of each axis, and based on that value The above | δx−δy | and | δz−δy | may be determined in advance.

Conventionally, in order to obtain the acceleration in the falling direction, the square root of the square sum of the acceleration detection values of the X, Y, and Z axes has been calculated. For this reason, it is necessary to obtain the square root of the sum of squares of each of (ax0-ax2), (ay0-ay2), and (az0-az2) when obtaining the amount of change with time of acceleration. In contrast, in the present application, the fall determination can be performed only by obtaining the change amount (| ax0-ax2 |, | ay0-ay2 |, | az0-az2 |) of the acceleration detection value of each axis. This eliminates the need for multiplication and root sign operations, improving the processing speed and simplifying the circuit.
<< Second Embodiment >>
FIG. 10 is a block diagram showing the configuration of a magnetic disk device such as a hard disk drive device. Here, the read / write circuit 202 uses the head 201 to read or write data written on a track on the magnetic disk. The control circuit 200 performs data read / write control via the read / write circuit 202 and communicates this read / write data with the host device via the interface 205. The control circuit 200 controls the spindle motor 204 and controls the voice coil motor 203. The configuration of the drop detection device 100 is as shown in the first to fourth embodiments. Further, the control circuit 200 reads the fall detection signal from the fall detection device 100, and controls the voice coil motor 203 to retract the head 201 to the retract area when it is falling. As a result, for example, when a portable device on which a hard disk device is mounted is dropped, the head is retreated from the magnetic disk area to the retraction area until the portable device collides with the floor or the ground. Damage due to contact with the recording surface can be prevented.

<< Third Embodiment >>
FIG. 11 is a block diagram showing the configuration of a portable electronic device such as a notebook computer or a music / video playback device with a built-in hard disk drive device. Here, the configuration of the fall detection device 100 is as shown in the first and second embodiments. The device 301 is a device that needs to be protected from an impact caused by a collision at the time of dropping, and is a device capable of handling the impact for that purpose. For example, a hard disk drive device. The control circuit 300 controls the device 301 based on the output signal of the fall detection device 100. For example, when a falling state signal is received from the fall detection device 100, the device 301 is controlled in preparation for an impact when dropped.

It is a figure which shows a mode that the output of the acceleration sensor of patent document 1 changes from 1 to substantially zero. It is a block diagram which shows the structure of the fall detection apparatus which concerns on 1st Embodiment. It is a figure which shows the example of the time passage of the detected value of the X-axis of the acceleration sensor 60 before and after the fall start. It is a figure which shows the example of the time passage of the value Axyz for determining a falling state and an impact based on the same acceleration detection value as what was shown in FIG. 3 is a flowchart showing the contents of processing in a first stage performed by the control unit 74 shown in FIG. 2 based on an output value of an A / D converter 72. 3 is a flowchart showing the content of processing in a second stage performed by the control unit 74 shown in FIG. 2 based on the output value of the A / D converter 72. 3 is a flowchart showing the contents of processing in a third stage performed by the control unit 74 shown in FIG. 2 based on an output value of an A / D converter 72. It is a figure which shows the example of the time passage of the detected value of each axis | shaft of the acceleration sensor 60 before and after the fall start. 3 is a flowchart illustrating a processing procedure in which a control unit 74 illustrated in FIG. 2 determines a falling state based on an output value of an A / D converter 72. It is a block diagram which shows the structure of magnetic disk apparatuses, such as a hard disk drive apparatus, based on 2nd Embodiment. It is a block diagram which shows the structure of portable electronic devices, such as a notebook personal computer incorporating a hard disk drive device, and a music and video reproduction device, according to the third embodiment.

Explanation of symbols

60 ... acceleration sensor 72 ... A / D converter 74 ... control unit 100 ... fall detection device 205 ... interface ax ... detected value of acceleration in the X-axis direction ay ... detected value of acceleration in the Y-axis direction az ... acceleration of acceleration in the Z-axis direction Detected value

Claims (5)

A fall detection device that performs fall detection based on an output signal of an acceleration sensor,
Acceleration detecting means for obtaining a detection value according to acceleration in three axial directions orthogonal to each other;
For each of the three axis directions, an acceleration change amount with the passage of time of the detected value is obtained, and an absolute value of the acceleration change amount is a first threshold value and a second value higher than the first threshold value. First condition determination means for determining whether or not a condition for taking a value between the threshold value and
Second condition determination means for determining whether or not a condition that an absolute value of the acceleration change amount reaches a third threshold value equal to or greater than a second threshold value after satisfying the first condition;
Third condition determining means for determining whether or not a condition that an absolute value of the acceleration change amount falls below a fourth threshold value lower than a third threshold value is satisfied after satisfying the second condition;
When at least one of the three axial directions satisfies the third condition, it is determined whether or not the vehicle is in a falling state based on a difference value between detection values in different axial directions of the three axial directions. A fall detection device comprising: a falling state determination means to perform.   It is determined that the time until the second condition is satisfied after the first condition is satisfied, or the time until the third condition is satisfied after the second condition is satisfied is within a specified value. The fall detection device according to claim 1 provided with the 4th condition judging means.   A threshold value in which the sum of absolute values of differences between detected values in different axial directions among the detected values in three axial directions detected by the acceleration detecting means is set higher by a predetermined amount than the value obtained in the gravitational acceleration state The drop detection device according to claim 1 or 2, further comprising means for discriminating between a drop start and an impact depending on whether or not the difference is exceeded.   A drop detection device according to any one of claims 1 to 3, a head for recording or reading data on a magnetic disk, and when the drop detection device determines that the device is in the falling state, the head is retracted. A magnetic disk apparatus comprising a head retracting means for retracting the head.   A portable electronic device comprising the drop detection device according to any one of claims 1 to 3 and a device capable of handling an impact, and when the fall detection device determines that the device is falling, the device A portable electronic device comprising impact countermeasure processing means for performing impact countermeasure processing.

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