Free fall detection device

Fall detection device {FREE FALL DETECTION DEVICE}

1 is a functional block diagram of a fall detection device according to an embodiment of the present invention.

2A and 2B are diagrams showing an example of rotation determination processing;

Fig. 3 is a diagram showing an example of a rotation determination result;

It is a figure which shows the application range of the fall determination method.

5A, 5B and 5C are functional block diagrams of a fall detection device according to another embodiment of the present invention;

6A, 6B, and 6C are functional block diagrams of a fall detection device according to another embodiment of the present invention.

7A, 7B, 7C, 7D, and 7E are views for explaining the operation of the embodiment of FIG. 6C;

8A and 8B are functional block diagrams of a fall detection device according to another embodiment of the present invention.

9 is a view showing an embodiment of a portable device on which a fall detection device according to the present invention is mounted.

10A and 10B are diagrams showing a design support system for a fall detection device;

11A and 11B are diagrams showing an example of an interface of a fall detection device design support system;

<Explanation of symbols for main parts of the drawing>

1101 : Accelerometer

1102 : Fall judgment unit

1103, 1104: logic operation unit

1105 : Rotation judgment unit

1106 : Fall detection output terminal

1107 : switch part

1108 : selector

1109 : Matrix switch part

1110 : Angular velocity sensor

1111 : Center of gravity acceleration calculation unit

1112 : Center of gravity position, sensor position, moment of inertia information input unit

1113 : Geometry deformation information/detachable device information input unit

1114 : Angular velocity sensor connection part

1115 : Accelerometer connection part

1116 : Parameter setting terminal

1117 : Relational relationship determination unit

1203 : Removable parts

1204 : microcomputer

1205 : programming terminal

1209 : Host CPU

1210 : Acceleration output terminal

1211 : Acceleration sensor module

1701 : Filter characteristic adjustment unit

1702 : High-pass filter unit

1703 : Low-pass filter unit

1704 : arithmetic unit

1705 : comparison department

1706 : logic operation unit

1707 : Rotation judgment output unit

1708 : Acceleration input unit

1709, 1710: comparison decision value holding unit

1711 : power calculator

1905 : Accelerometer body

1906 : paper

1907 : weight

1908 : Piezo resistance element

<backgrounddocuments><p>[Patent Document 1] Japanese Patent Laid-Open No. 2000-241442</p></backgrounddocuments><backgroundart><p>The present invention relates to a fall detection device capable of detecting a fall accompanied by rotation. </p><p>As a device capable of improving the impact resistance by knowing in advance the end of the drop, there is a magnetic disk. In the magnetic disk, the impact resistance is greater in the retracted state in which the head moves to the retracted area and does not write or read data than in the state in which the head can write and read data on the disk. Therefore, by detecting the fall and moving the head to the retracted state before landing, the impact resistance of the magnetic disk against the fall can be improved.</p><p>As a prior art for realizing the above function using an acceleration sensor, the output of the acceleration sensor in the three axial directions (eg, mutually orthogonal x, y, and z axes) that is not in the same plane shape simultaneously becomes approximately 0, so that it is free. There is a technique for determining a fall (see, for example, Patent Document 1). </p></backgroundart><abstractproblem><p>In the prior art, when the device to be protected falls while rotating, the acceleration sensor detects the centrifugal force. For this reason, the acceleration sensor output of all axes does not become substantially 0 at the same time, and a fall cannot be detected.</p><p>The problem to be solved by the present invention is to provide a fall detection device capable of detecting a fall accompanied by rotation. </p></abstractproblem>

<p>A fall detection apparatus according to the present invention includes a rotation determination unit configured to detect a fall accompanying rotation based on a waveform of the acceleration detected by the acceleration detection unit or an angular velocity detected by the angular velocity detection unit. </p><p>In addition, the fall detection apparatus according to the present invention includes a center-of-gravity acceleration calculation unit for calculating the center-of-gravity acceleration of the device to be protected by the acceleration detected by the acceleration detecting unit and the angular velocity detected by the angular velocity detecting unit. </p><p>&lt;Embodiment&gt;</p><p>1 is a functional block diagram of a fall detection device according to an embodiment of the present invention. First, the operation of the fall detection unit using the acceleration threshold will be described. It relates to the acceleration in each axial direction detected by the multi-axis acceleration sensor 1101 which is an acceleration detection unit that detects the acceleration in the three axial directions (x, y, z axes orthogonal to each other) that is not in the same plane shape, and the drop determination unit 1102 ), the threshold value determination processing is performed. When the threshold value determination result is logically multiplied by the logic operation unit 1103, when the acceleration of all axes becomes a value smaller than the threshold value, that is, when it becomes approximately 0, it is judged as a falling state, and the determination result from the fall detection output terminal 1106 to output Here, Atx, Aty, and Atz are acceleration thresholds for determining a fall in each axial direction, for example, set to values close to 0G such as 0.4G.</p><p>Further, in the present embodiment, the rotation determination unit 1105 performs rotation determination processing on the output from the multiaxial acceleration sensor 1101 . In the rotation determination unit 1105, rotation is determined from the characteristics of the acceleration waveform due to centrifugal force during falling accompanied by rotation. The rotation determination processing result is determined together with the above-described threshold determination result by the logic operation unit 1104 , and output to the drop detection output terminal 1106 . In addition, the threshold value determination result, that is, the fall determination result at the time of non-rotation, and the fall determination result at the time of rotation may be output separately, respectively, without going through the logic calculation part 1104.</p><p>An example at the time of rotation determination processing is shown to FIG. 2A, FIG. 2B. Fig. 2A shows a rotation determination unit for one axis. In this process, the new knowledge obtained by the present inventors is utilized that the acceleration waveform detected by the acceleration sensor installed in the fall protection target apparatus shows a waveform close|similar to a relatively smooth sinusoidal wave accompanying rotation during fall. In the case of a waveform close to a sine wave, as shown in Fig. 2B, the spectrum of the acceleration waveform shows a shape in which the high frequency component PH is smaller than that of the low frequency component PL. Therefore, the ratio of the power of the high frequency component and the low frequency component with the arbitrary frequency fc as a boundary can be used as an index. Specifically, in Fig. 2A, a high-pass filter unit 1702 and a low-pass filter unit 1703 for extracting a high-frequency component and a low-frequency component, respectively, from the acceleration value from the acceleration input unit 1708 with the frequency fc as a boundary. It is divided into high-frequency components and low-frequency components. Each of these components is converted into electric power values by the electric power calculating unit 1711, and the calculating unit 1704 performs calculation by dividing the power value of the high frequency component by the power value of the low frequency component. The calculation result is compared with the power ratio threshold held in the comparison determination value holding unit 1709 by the comparison unit 1705 . When the calculation result is smaller than the threshold value, that is, in the case of a waveform close to a sine wave, the output of the comparator 1705 becomes the logical value 1. Here, the boundary fc between the high frequency and the low frequency is set by the filter characteristic adjustment unit 1701 . On the other hand, the acceleration value from the acceleration input unit 1708 is converted into a total power value by the power calculating unit 1711 without passing through the filter unit. This total power value and the total power threshold held by the comparison determination value holding unit 1710 are compared by the comparison unit. As a result of the comparison, when the total power value is greater than the total power threshold value, the output of the comparator becomes a logical value 1. The logical product of the output values of these two comparison units is calculated by the logical operation unit 1706, and when both output values are logical 1, the result of the determination of logical product 1, i.e., a fall accompanying rotation, is the rotation determination output unit. (1707). In addition, the calculation of the total power value of the acceleration waveform is because, in the division by the calculating unit 1704, when both the denominator and the numerator are small values, the calculation result (quotient) of the same degree as the rotation state may be accidentally output. am. In addition, in the present embodiment, the mask is performed at the lower limit of the total power value, but by using a window comparator using the upper limit, it is possible to reduce malfunction due to the acceleration of the impulse shape and improve the determination accuracy.</p><p>An example of the rotation determination result is shown in FIG. The waveform 1801 is the acceleration value, and the waveform 1802 is the result of determining the rotation during falling, that is, the output of the rotation determination output unit 1707 in Fig. 2A. The top part Rot of the waveform 1802 is in a state in which rotation is detected during free fall, and the bottom part (Not Rot) is in a non-detection state. At the time of fall 1803 accompanied by rotation, in which the waveform of the acceleration exhibits a substantially sinusoidal shape, the state portion in which the rotation of the waveform 1802 is detected almost coincides. In addition, it is not limited to the case where the acceleration waveform has a substantially sinusoidal shape, and the rotation determination processing shown in Figs. 2A and 2B can be applied as long as it is a relatively smooth and repetitive waveform with few high-frequency components.</p><p>Here, the rotation determination processings 1 to 3 in each axial direction in Fig. 1 are not limited to those shown in Figs. 2A and 2B, and various determination processing are possible, and the processing does not necessarily have to be the same. This is because, depending on the mass distribution of the device to be protected, the main moment of inertia values in each axial direction are generally not the same, and thus the characteristics of the acceleration waveforms in each axial direction are different. Therefore, it is preferable to determine the contents of the rotation determination processing (1 to 3) by simulation of rotational motion based on the mass distribution of the device to be protected, or actual measurement by an experimental apparatus simulating the mass distribution. Note that the principal moment of inertia is a diagonalized moment of inertia tensor that is a tensor of two layers. In the following description, the moment of inertia refers to the main moment of inertia.</p><p>The application range of the fall determination method is shown in FIG. The method of detecting when the detection acceleration becomes less than or equal to the overall axis threshold is applied when the rotation at the time of falling of the device to be protected is low speed, and the rotation detection during falling by the rotation determination processing is performed when the rotation at the time of falling is high. apply In the case of rotating at an intermediate speed, the judgment results of the two methods are appropriately weighted and then comprehensively judged.</p><p>5A to 5C are functional block diagrams of a fall detection device according to another embodiment of the present invention, showing an embodiment in which the rotation determination processing is asymmetrically performed for each axis or can be switched. </p><p>Fig. 5A is an embodiment in which the rotation determining unit 1105 is formed only along one axis, for example, the x-axis. In general, if the rotation determination axis is limited to only one axis, it is difficult to determine the characteristics of rotation from the change in acceleration when stable rotation occurs around that axis. However, in general, the value of the main moment of inertia is not the same in each axial direction. In particular, it is known that rotational motion around an axis having an intermediate moment of inertia has large fluctuations and is unstable. can be reduced to just one. In Fig. 5A, the x-axis is selected as the detection axis. In this case, if the main moments of inertia around the x, y, and z axes are Ix, Iy, and Iz, respectively, then Iy &gt; Ix &gt; Iz or Iz &gt; Ix &gt; Iy. By making only one rotation determination processing part, the circuit scale of a fall detection apparatus, manufacturing cost, power consumption, and an adjustment point can be reduced.</p><p>Further, in the embodiment of Fig. 5A, preferably, the acceleration sensor is provided so that the acceleration detection axis used for the rotation determination processing deviates from the direction of the main axis of inertia. Thereby, the fluctuation|variation of a rotational motion becomes large, and detection precision improves. In addition, depending on the rotational state that may occur, the rotation processing determination unit may be provided for two or more acceleration detection axes, but for detection axes smaller than the total number of axes.</p><p>Fig. 5B is an embodiment in which the switch unit 1107 and the selector unit 1108 enable selection of an axis used for rotation determination processing. According to the present embodiment, it is possible to relieve the restrictions on the mounting direction of the fall detection device including the acceleration sensor in the device to be protected. The selection of the axis by the switch unit 1107 and the selector unit 1108 is performed when the protection target device is designed. In addition, a parameter setting terminal 1116 is provided for changing a parameter setting value in the rotation determination unit, for example, fc in FIG. 2A, a threshold value, and the like. In embodiments other than this embodiment, although description is omitted, a parameter setting terminal may be provided.</p><p>Fig. 5C shows an embodiment in which the axes used for the rotation determination processing are switched in the case where all three axes are used for the rotation determination processing. In this embodiment, by using the matrix switch unit 1109, the connection between the detection axes x, y, and z and the rotation determination units 1, 2, 3 can be arbitrarily changed. According to the present embodiment, while all three axes are subjected to rotation determination processing, it is possible to relieve the restrictions on the mounting direction of the fall detection device including the acceleration sensor in the device to be protected. The number of axes used for the rotation determination process is not necessarily the same as the total number of acceleration detection axes. Further, for example, only the rotation determination unit 1 performs waveform determination requiring a circuit scale, and the rotation determination units 2 and 3 make simple processing that does not require a circuit scale, for example, a rotating plate requiring a circuit scale. The number of positive and negative poles and the number of acceleration detection axes may be different from each other. Further, the relative relationship determining unit 1117 may be used to increase the precision of rotation determination by using the relative relationship between the characteristic amounts of rotational motion extracted by the multi-axis rotation determination unit. Examples of the criterion for determining the relative relationship include whether the relative value of the center frequency of the acceleration waveform obtained on each axis falls within a predetermined ratio, or whether the maximum amplitude of the time-domain acceleration waveform falls within the predetermined amplitude on all axes during the fall period. cognition, and the like. In addition, the relative relationship determining unit is not limited to the embodiment shown in Fig. 5C, and may be applied to other configurations using a plurality of rotation determining units. Further, the relative relationship determining unit 1117 may be included in the rotation determination processing unit 1105 to interconnect the plurality of axis rotation determination processing units 1105 .</p><p>6A to 6C are functional block diagrams of a fall detection apparatus according to another embodiment of the present invention, showing an embodiment in which an acceleration sensor and an angular velocity sensor (gyro) serving as an angular velocity detection unit are used together. </p><p>6A is an embodiment in which a 3-axis acceleration sensor 1101 and a 1-axis angular velocity sensor 1110 are used together. The rotation determination unit 1105 determines the fall accompanying the rotation from the characteristics of the angular velocity signal waveform detected by the angular velocity sensor 1110 . In addition, similarly to the embodiment of Fig. 3A, it is preferable to select an axis having a large fluctuation in rotational motion as the detection axis of the angular velocity sensor 1110. As shown in Figs. Alternatively, the angular velocity detection axis may be provided so as to deviate from the stable direction of the main axis of inertia.</p><p>6B is an embodiment in which the 3-axis acceleration sensor 1101 and the 3-axis angular velocity sensor 1110 are used together. In the embodiment of FIG. 6B, the rotation determination unit inputs the acceleration signal output from the acceleration sensor 1101 via the acceleration sensor connection unit 1115, and rotates in combination with the angular velocity signal output from the angular velocity sensor 1110. The accompanying fall is judged. In addition, since the angular velocity sensor connection part 1114 is detachable, when there is no angular velocity sensor, only the acceleration signal output by the acceleration sensor through the acceleration sensor connection part 1115 may be used for rotation determination processing. In addition, the number of axes of the angular velocity sensor is not limited to three axes. In addition, the angular velocity sensor may be mounted in the same package or module as the acceleration sensor, or may be mounted in a separate package or module.</p><p>6C is an embodiment having a center-of-gravity acceleration calculator 1111 for detecting a fall by calculating the acceleration at the center of gravity of the device to be protected by using the acceleration signal from the acceleration sensor and the angular velocity signal from the angular rate sensor. . The operation of this embodiment will be described using Figs. 7A to 7E.</p><p>The coordinate system shown in Figs. 7A and 7B, the angular velocity around the axis (ω)<sb>a</sb>, ω<sb>b</sb>, ω<sb>c</sb>) and the position vector (r) from the center of gravity (GC) to the accelerometer position.<sb>a</sb>, r<sb>b</sb>, r<sb>c</sb>), when the device to be protected is in a falling state and there is no action of an external force, the fall can be determined by the following Equation 1 is established. where D<sb>a</sb>, D<sb>b</sb>, D<sb>c</sb>are the acceleration values by the acceleration sensors in the a, b, and c-axis directions, respectively. </p><p><maths num="1"><df><img file="KR20060111368A_D0001.tif" /></df></maths></p><p>The center of gravity position, sensor position, and moment of inertia information input unit 1112 shown in FIG. 7C provides information necessary for the calculation of Equation 1 above. In addition, in practice, it is desirable to consider the error due to air resistance or the precision of the sensor to be used. In addition, when the shape of the device to be protected is asymmetrical, the coordinate transformation is appropriately performed in consideration of the inclination of the main axis of inertia. According to this embodiment, since the acceleration at the position of the center of gravity of the device to be protected can be known, the sensor may be installed at a position away from the vicinity of the center of gravity of the device to be protected. Therefore, in addition to the relaxation of the sensor mounting position, as shown in FIG. 7C , it is applicable even when the center of gravity GC is outside the device to be protected. In addition, if the geometric shape deformation information/detachable device information input unit 1113 of FIG. 6C is used, information on a shape change that may cause a change in the position of the center of gravity in the device to be protected can be obtained. Therefore, as shown in FIG. 7D , a fall can be determined in consideration of the change in the position of the center of gravity when the flip-type portable terminal is folded. Also, when the position of the center of gravity changes, the position vector from the center of gravity to the sensor in Equation 1 changes. As another example of bringing about a change in the position of the center of gravity, as shown in FIG. 7E , there is the mounting of the removable part 1203 . Removable parts include, in addition to parts for adding functions, an external battery pack having a capacity different from that of the built-in battery. Even when the position of the center of gravity changes due to the mounting of the same part (1202), the position of the center of gravity is corrected using the information input from the geometric shape deformation information/removable device information input unit 1113 . The angular velocity described in the present embodiment is not limited to the angular velocity value obtained from the angular velocity sensor, and an angular velocity value calculated by a plurality of acceleration sensors arranged in a specific geometric shape may be used.</p><p>8A and 8B are functional block diagrams of a fall detection device according to another embodiment of the present invention. </p><p>Fig. 8A is an embodiment in which a microcomputer 1204 is used for determination of a fall. By a program in the microcomputer 1204, the fall determination processing in each of the above-described embodiments, for example, a non-rotational time of detecting a free fall when the acceleration in the three axial directions not on the same plane becomes approximately 0 at the same time. A fall detection process and a rotation determination process for detecting rotation during free fall are performed. It is not always necessary to use the total number of axes of each sensor for the determination of rotation. In addition, in the case of using the angular velocity sensor 1110 in addition to the multi-axis acceleration sensor 1101, as in the configuration shown in FIG. 6C, the fall determination is performed by Equation 1 to obtain the motion of the center of gravity of the device to be protected. also be From the programming terminal 1205, it is possible to input at least one of a program for determining a fall or a setting parameter. It is assumed that this program includes at least one of a part for judging rotation based on the characteristics of an acceleration waveform due to centrifugal force during falling, or a part for judging a fall according to Equation (1). Further, a portion 1206 surrounded by a broken line, a portion 1207 surrounded by a dotted line, and a portion 1208 surrounded by a dashed-dotted line indicate a portion to be modularized or one chip, respectively.</p><p>Fig. 8B shows an embodiment in which the fall determination is made by the host CPU 1209 in the protection target device. In the figure, a portion surrounded by a dashed-dotted line is one-modularized or one-chip-ized as the acceleration sensor module 1211 . The program related to the fall determination in the host CPU 1209, similarly to FIG. 8A, is a fall determination by a combination of a non-rotating drop detection and a rotation determination processing, or Equation 1 for obtaining the motion of the center of gravity of the device to be protected fall judgment is performed. The data acquired by the host CPU includes only the 3-axis acceleration output output from the acceleration output terminal 1210, or the acceleration output of 2 axes or less, and the threshold value determined within the sensor module output from the fall detection output terminal 1106 A combination of the fall detection output at the time of rotation may be sufficient. When the host CPU acquires the 3-axis acceleration and determines the non-rotational drop by threshold determination, in Fig. 8B, the acceleration sensor module 1211 includes a fall determination unit 1102, a logic operation unit 1103, It may consist of the acceleration sensor 1101 and the acceleration output terminal 1210 without including the fall detection output terminal 1106 . Moreover, you may use together an angular velocity sensor. In addition, the function of the host CPU mentioned above may be combined with the CPU which performs control/management of the mounted device of a protection target apparatus, etc.</p><p>9 shows an embodiment of a portable device on which a fall detection device according to the present invention is mounted. The portable device 1901 that is the device subject to fall protection is, for example, a mobile phone or the like. The portable device 1901 is equipped with a magnetic disk device 1903 . In addition, a package or module including the acceleration sensor body 1905 is installed at a mounting position 1902 in the portable device. In the present embodiment, due to restrictions on the layout of various parts in the portable device, the mounting position 1902 of the acceleration sensor is away from the center of gravity 1904 of the portable device 1901 . The acceleration sensor body 1905 is a semiconductor sensor manufactured by a MEMS (Micro Electro Mechanical System) process, as an enlarged view shows. In the acceleration sensor body 1905 , a weight 1907 is supported by a beam 1906 . By detecting the deformation of the beam 1906 due to the acceleration by the piezo-resistive element 1908 formed in the acceleration sensor body, it is possible to detect the acceleration in three axes. When a fall is detected by the acceleration sensor, a magnetic disk head retreat command signal 1909 is transmitted to the magnetic disk device 1903 from the sensor module or sensor package or peripheral circuits thereof. Thereby, since the head is in a retracted state before the portable device 1901 lands, the impact resistance at the time of a fall is improved. In this embodiment, a semiconductor acceleration sensor manufactured by microfabricating a semiconductor substrate by a MEMS process is used, but various other sensors may be applied.</p><p>10A and 10B show a design support system of a fall detection device. In the design of the drop detection device, in addition to the sensor mounting position in the device, many requirements such as the type of sensor, the installation direction, and the number of axes to be used are required. Therefore, by providing the program supporting the design task of a fall detection apparatus as software attached to a sensor, independent package software, or freeware (freeware), a fall detection apparatus with high detection precision and reliability can be designed.</p><p>Fig. 10A shows an example of a fall detection device design support system using a dedicated program. As the input data 1301, mass distribution and layout constraint data of the device to be protected are used. In creating the mass distribution, CAD data composed of a material and a shape may be directly read, and specific gravity data for each material may be added and created internally. The layout constraint data is data such as a place where a sensor can be installed, a range on the board, and an installation direction. Based on the data on these devices to be protected, the design option 1305 and the trade-off information 1306 indicated by the user, the drop sensor design program 1302 determines the design of the fall detection device. Support. The user may be configured to perform a simple operation in the form of, for example, answering a question from the user console 1304 . Options and trade-offs may be specified in a format other than the console, using a file or the like. The output data 1303 includes at least one of a recommended installation position of a sensor, a recommended installation direction, an axis of a sensor to be used, a setting parameter, a rotation detection routine, the number of recommended sensors, and detection performance. </p><p>10B is an example of use of the layout constraint data 1301. Reference numeral 1401 denotes the device to be protected, reference numeral 1402 denotes the projection of the center of gravity position onto the sensor installation plane, and reference numeral 1403 denotes the design value contour. The design value contour 1403 is, for example, a distribution of the maximum acceleration when an initial condition of rotation in various directions at an arbitrary initial number of rotations is given and the object is dropped. At this time, it is ideally appropriate to install the sensor at the center of gravity projection position 1402 , but since there is a layout constraint 1404 , it is difficult to install. Therefore, only from the viewpoint that the distance from the center of gravity is the shortest, the installation point 1405 and the installation point 1406 can be cited as installation position candidates. Referring to the design value contour 1403, the installation point 1405 is judged to be appropriate. In addition, assuming that the second candidate point is taken as an example, from the design value contour 1403 , an appropriate position is not the installation point 1406 but a point near the installation point 1405 . In the design support of the fall detection, such an operation|movement is performed under the instruction|indication of a user as needed.</p><p>11A and 11B show an example of an interface of a fall detection device design support system. </p><p>11A shows a display representation of the console (FIG. 10A, reference numeral 1304) as a setting interface for design options (FIG. 10A, reference numeral 1305). In the display display 1501, the type of sensor to be used is designated. For example, whether it is only the acceleration sensor or whether it is used in combination with other sensors, such as an angular velocity sensor, etc. is designated. Display indication 1502 designates the code number of the sensor. These may automatically narrow down candidates as the design progresses. The designation of the number of sensor use axes in the display display 1503 can also be automatically reduced. In the designation of the desired detection sensitivity of the display display 1504, in addition to the designation of high/low, etc., it may be represented by a determination rate, a detectable fall distance, or the like. The display display 1505 is a performance priority designation, which designates which performance value should be prioritized for design. The designation of the HDD evacuation time in the display display 1506 specifies the time from when the magnetic disk to be used receives the evacuation signal to actually entering the evacuation state. These may be designated by the code number of the magnetic disk. The display indication 1507 is the designation of the drop height to be detectable. In general, the higher the fall detection height, the longer it takes to determine the fall, so that the accuracy of the fall detection can be improved. The designation of the HDD access duty in the display indication 1508 designates the frequency at which the magnetic disk is used. For example, when the data rate required by the application used in the protection target device is low, the ratio of the magnetic disk operating time to the operating time of the protection target device decreases. Therefore, even if the erroneous determination rate of a fall (misdecision determining that a state other than a fall is a fall) is increased, there is little adverse effect. In general, since the state in which the false determination rate is high is a state in which the detection rate of a true drop is also high, it is possible to increase the detection sensitivity of the fall and improve the protective performance of the magnetic disk by increasing the false determination rate within the allowable range. . </p><p>Fig. 11B shows an example of trade-off information (Fig. 10A, reference numeral 1306). In the drop sensor design program, design work is promoted by mainly performing notification 1601, inquiry 1602, trade-off designation 1603, analysis result display 1604, and the like, and taking an interface with the user.</p><p>As mentioned above, although the embodiment of this invention was described, it is not limited to the said embodiment, and various modifications are possible within the scope of the technical idea of this invention. </p>

<p>According to the present invention, even when the device to be protected falls while rotating, the fall of the device can be detected from the detected acceleration or angular velocity. </p><p>Further, according to the present invention, by calculating the acceleration of the center of gravity that is not affected by rotation, it is possible to accurately detect the fall of the device to be protected even when the device to be protected is rotating.</p>