JP2018173417A - Ball rotation amount measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball rotation amount measurement system with which it is possible to measure the rotation amount of a ball with high accuracy.SOLUTION: A ball rotation amount measurement system 1 comprises a magnetic sensor 2, fixed to a ball, for measuring terrestrial magnetism in at least one axial direction; and a computation unit 3 for computing the rotation amount of the ball using the terrestrial magnetism data acquired in multiplicity chronologically by the magnetic sensor 2. The computation unit 3 includes a differential data calculation unit 31 for calculating differential data that is a difference between two terrestrial magnetism data chronologically adjacent to each other and obtaining a large number of differential data chronologically, a differential waveform calculation unit 32 for finding a differential waveform that is a waveform of temporal change of the large number of differential data; and a rotation amount calculation unit 33 for calculating the rotation amount of the ball on the basis of an intersection count that indicates the number of times the differential waveform interests a straight line having zero difference in a prescribed period.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball rotation amount measurement system that measures the rotation amount of a ball moving in the air.

  As a rotational speed measuring device for measuring the rotational speed of a ball moving in the air, a device using a magnetic sensor for measuring geomagnetism is disclosed in Patent Document 1. In this rotational speed measurement device, a magnetic sensor is fixed to the ball, and the rotational speed of the ball moving in the air is calculated by analyzing the frequency of the detection data of this magnetic sensor using a technique such as FFT (Fast Fourier Transform). doing.

JP, 2014-160025, A

However, the rotational speed calculation method of Patent Document 1, that is, the calculation method by analyzing the frequency of the magnetic sensor has the following problems.
The ball to be measured according to the present invention may be a ball for various competitions such as baseball and golf. For example, when considering baseball, the ball speed may exceed 150 km / hr. In this case, the time from the pitcher's hand to reach the catcher is an extremely short time of less than 0.5 seconds. In such a case, even if the acquisition interval of the geomagnetic data for measuring the rotational speed is acquired as a very short interval of about 2 milliseconds, the number of data that can be acquired is only about 200.

  Patent Document 1 describes a technique for calculating a rotation speed by frequency analysis using FFT analysis. However, when FFT analysis is performed with such a number of data, the resolution becomes rough and high accuracy is obtained. There is a problem that can not be. In particular, depending on the pitcher, there may be a very high rotational speed, and in this case, the influence of this decrease in accuracy becomes significant. In the first place, frequency analysis such as FFT has a problem that RAM is consumed much.

  In order to solve the above problem, it is also conceivable to implement a method of counting the frequency by counting the number of times that the magnetic sensor output intersects a straight line where the output becomes zero. However, the measured geomagnetic data may be offset due to the influence of the magnetic field around the magnetic sensor or the like. That is, even if geomagnetism is not actually acting in the sensing direction, the output of the magnetic sensor may deviate from zero. In such a case, it is difficult to calculate the frequency of the sine wave by counting the zero cross points where the above-described sine wave intersects the straight line of output zero unless the offset amount, which is the deviation amount, is sufficiently smaller than the amplitude. It becomes.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a ball rotation amount measuring system capable of measuring a ball rotation amount with high accuracy.

One aspect of the present invention is a ball rotation amount measurement system for measuring a rotation amount of a ball moving in the air,
A magnetic sensor fixed to the ball and measuring geomagnetism in at least one axial direction;
An arithmetic unit that calculates the amount of rotation of the ball using geomagnetic data acquired in time series by the magnetic sensor,
With
The calculation unit calculates difference data that is a difference between two geomagnetic data adjacent in time series, and obtains a large number of the difference data in time series, a difference data calculation unit,
A differential waveform calculation unit for obtaining a differential waveform that is a waveform of a time change of a large number of the differential data;
A ball rotation amount measurement system comprising: a rotation amount calculation unit that calculates a rotation amount of the ball based on the number of times of intersection, which is the number of times the difference waveform intersects a straight line with a difference of zero in a predetermined period.

  In the ball rotation amount measurement system, the calculation unit includes the difference data calculation unit, the difference waveform calculation unit, and the rotation amount calculation unit. As a result, as will be described later, even when the ball rotates at a high speed, the amount of rotation of the ball can be accurately calculated.

  As described above, according to the above aspect, it is possible to provide a ball rotation amount measuring system capable of measuring the rotation amount of the ball with high accuracy.

1 is a conceptual diagram of a ball rotation amount measurement system in Embodiment 1. FIG. The diagram which shows the time change of the geomagnetic data in Embodiment 1. FIG. The diagram which shows the difference waveform in Embodiment 1. FIG. The diagram which shows the inflection point vicinity of the time change of geomagnetic data in Embodiment 1. FIG. The diagram which shows the zero crossing point vicinity of a difference waveform in Embodiment 1. FIG. FIG. 3 is a perspective explanatory view of the magnetic sensor in the first embodiment. The conceptual diagram of the ball rotation amount measuring system in Embodiment 2. FIG. The conceptual diagram of the ball | bowl rotation amount measuring system in Embodiment 3. FIG. Explanatory drawing of the calculation method of the attitude | position change amount in Embodiment 3. FIG.

  In the ball rotation amount measuring system, the rotation amount of the ball calculated by the calculation unit can be, for example, the number of rotations of the ball per unit time, a change in the posture of the ball between two predetermined time points, or the like.

  The ball rotation amount measurement system can be, for example, a system that measures the rotation amount of a ball thrown by a baseball pitcher. In this case, for example, the number of rotations of the ball per unit time, that is, the rotation speed can be measured. Alternatively, for example, the rotation amount of the ball from the time when the pitcher releases the ball to the time when the catcher catches the ball can be measured. In the former case, the unit time is the predetermined period, and in the latter case, the period from the time when the pitcher releases the ball to the time when the catcher catches the ball is the predetermined period.

  The rotation amount calculation unit may be configured to calculate the rotation speed of the ball based on the number of crossings per unit time. In this case, the number of rotations of the ball per unit time, that is, the rotation speed can be accurately measured.

  The magnetic sensor is configured to measure the geomagnetism in a plurality of axial directions different from each other, and the difference data calculation unit uses the geomagnetic data having the largest amplitude among the geomagnetic data in the plurality of axial directions. It is preferable that the difference data is calculated. In this case, it can be suppressed that only geomagnetic data having a small amplitude can be obtained depending on the rotation direction of the ball with respect to the direction of geomagnetism. As a result, the amount of rotation of the ball can be measured with higher accuracy.

  The magnetic sensor is preferably configured to measure the geomagnetism in three axial directions orthogonal to each other. In this case, when the ball rotates in an arbitrary rotation direction, geomagnetic data having a large amplitude can be obtained in any one of the three axial directions. As a result, an accurate amount of rotation of the ball can be measured regardless of the direction of rotation of the ball.

The calculation unit includes a vector calculation unit that calculates a geomagnetic vector based on three axial geomagnetic data obtained by the magnetic sensor, and the ball between a start time and an end time of the air movement of the ball. A posture change amount calculation unit for obtaining the posture change amount of
The posture change amount calculation unit includes a start vector that is the geomagnetic vector obtained by the vector calculation unit at the start time and an end vector that is the geomagnetic vector obtained by the vector calculation unit at the end time. Based on the above, it is possible to calculate the posture change amount of the ball.
In this case, the rotation angle of the ball from the start time to the end time can be calculated. The posture change amount calculation unit is particularly useful, for example, when the number of intersections is less than two times from the start point to the end point, or when the rotation speed is low in accordance with it.

  Further, an acceleration sensor fixed to the ball and measuring an acceleration in at least one axis direction, and a start time and an end time of the air movement of the ball are detected based on acceleration data acquired by the acceleration sensor, respectively. It is preferable to further include a detection unit and an end detection unit. In this case, the start time and end time of the ball movement in the air can be easily obtained.

  The acceleration sensor is preferably configured to measure accelerations in a plurality of different axial directions. In this case, when acceleration acts on the ball in an arbitrary direction, it is easy to acquire sufficiently large acceleration data. As a result, it is easy to accurately detect the start point and the end point in the start detector and the end detector, respectively.

  The acceleration sensor is preferably configured to measure the acceleration in three axial directions orthogonal to each other. In this case, when acceleration is applied to the ball in any direction, it is easy to obtain sufficiently large acceleration data in any one of the three axial directions. As a result, it is easy to accurately grasp the start point and the end point regardless of the direction of acceleration acting on the ball.

  The magnetic sensor is preferably a magneto-impedance sensor. In this case, the amount of rotation of the ball can be measured more accurately. That is, since the magneto-impedance sensor (hereinafter also referred to as “MI sensor”) is excellent in detection sensitivity and responsiveness, it can accurately detect geomagnetism and can extremely shorten the measurement interval. Therefore, even when the ball is rotating at high speed, the amount of rotation of the ball can be measured more accurately.

(Embodiment 1)
An embodiment of a ball rotation amount measurement system will be described with reference to FIGS.
The ball rotation amount measurement system 1 is a system that measures the rotation amount of a ball moving in the air.
As shown in FIG. 1, the ball rotation amount measurement system 1 includes a magnetic sensor 2 and a calculation unit 3. The magnetic sensor 2 is fixed to the ball and measures at least uniaxial geomagnetism. The computing unit 3 computes the amount of rotation of the ball using the geomagnetic data acquired in time series by the magnetic sensor 2. The calculation unit 3 includes a difference data calculation unit 31, a difference waveform calculation unit 32, and a rotation amount calculation unit 33.

  The difference data calculation unit 31 calculates difference data that is a difference between two adjacent geomagnetic data m (n) in time series, and obtains a large number of difference data Δm (n) in time series. Here, m (n) means the geomagnetic data acquired nth in time series. Also, Δm (n) is defined by Δm (n) = m (n) −m (n−1).

The difference waveform calculation unit 32 obtains a difference waveform Lb (see FIG. 3), which is a time-change waveform of a large number of difference data Δm (n).
The rotation amount calculation unit 33 calculates the rotation amount of the ball based on the number of intersections, which is the number of times that the difference waveform Lb intersects the straight line Lc with zero difference in a predetermined period. Note that the straight line Lc with zero difference means a straight line along the time axis when Δm (n) = 0 in the graph of time change of the difference data Δm (n) shown in FIG.

  Moreover, the graph of the time change La of the geomagnetic data m (n) is shown in FIG. In FIG. 2, each of a large number of dots shown on the graph represents the local magnetic data m (n). Similarly, in FIG. 3, each of a large number of dots shown on the graph represents each difference data Δm (n).

  In the present embodiment, the rotation amount calculation unit 33 is configured to calculate the rotation speed of the ball based on the number of crossings per unit time. That is, half of the number of crossings per unit time substantially matches the frequency of the time change La of the geomagnetic data. Therefore, half of the number of crossings per unit time is regarded as the time change frequency of the geomagnetic data, and the rotation speed of the ball is calculated. For example, when the number of crossings in 0.3 seconds is 27, the time change frequency of the geomagnetic data is regarded as 45 Hz, and the rotation speed of the ball is calculated as 45 rotations / second.

  Further, the magnetic sensor 2 is configured to measure a plurality of different geomagnetic fields in the axial direction. And the difference data calculation part 31 calculates difference data using the geomagnetism data with the largest amplitude among the geomagnetism data about a plurality of axial directions.

  In the present embodiment, the magnetic sensor 2 is configured to measure geomagnetism in three axial directions orthogonal to each other. Then, the difference data is calculated using the geomagnetism data having the largest amplitude among the triaxial geomagnetism data. In the present embodiment, unless otherwise indicated, the geomagnetic data means geomagnetic data having the largest amplitude among the geomagnetic data in the three axial directions. Further, the difference data means difference data calculated using the geomagnetic data unless otherwise indicated.

  As shown in FIG. 6, the magnetic sensor 2 includes three sensor elements 2x, 2y, and 2z that are arranged with their respective sensitivity directions oriented in three axial directions (X direction, Y direction, and Z direction) orthogonal to each other. It is arranged on the substrate 20. Each sensor element 2x, 2y, 2z consists of a magneto-impedance sensor element.

  Each sensor element 2x, 2y, 2z includes a base portion 21 made of a non-magnetic material, an amorphous wire 22 fixed to the base portion 21, and a detection coil 23 wound around the amorphous wire 22. Based on the strength of the geomagnetism in each axial direction detected by each sensor element 2x, 2y, 2z, the magnetic sensor 2 has geomagnetic data in the X-axis direction, geomagnetic data in the Y-axis direction, and geomagnetic data in the Z-axis direction. , Can be detected respectively.

  In this embodiment, both the magnetic sensor 2 and the calculation unit 3 are built in the ball. Further, the ball rotation amount measuring system 1 has a geomagnetic data memory 11 for storing a large number of geomagnetic data acquired by the magnetic sensor 2. The memory 11 is also built in the ball. Further, the ball rotation amount measuring system 1 includes an output unit 12 that outputs the rotation amount of the ball calculated by the calculation unit 3. In the present embodiment, the output unit 12 is a display unit that visually displays the measurement result. That is, the rotation speed of the ball is displayed on the display unit that is the output unit 12. The output unit 12 may be attached to the ball or may be provided separately from the ball. When the output unit 12 is separate from the ball, the calculation unit 3 mounted on the ball transmits the calculation result to the output unit 12 by wireless communication.

The operation of the ball rotation amount measurement system 1 of the present embodiment will be described assuming that the rotation speed of a ball thrown by a baseball pitcher toward a catcher is measured.
The ball thrown by the pitcher usually moves in the air while rotating. For example, when a professional baseball pitcher throws a straight ball (straight), there may be a high-speed rotation of 40 to 50 rotations / second.

  While the ball moves in the air, the magnetic sensor 2 sequentially detects geomagnetism. The detected geomagnetism is stored in the memory 11 as a large number of geomagnetic data m (n) in time series. Here, as described above, the magnetic sensor 2 measures the geomagnetism in three axial directions orthogonal to each other. And the geomagnetism data with the largest amplitude is used among the geomagnetism data in the triaxial directions.

  In addition, the detection of geomagnetism by the magnetic sensor 2 is detected at a frequency of 250 times / second or more, for example. That is, the measurement interval is set to 4 msec or less, for example. More specifically, in the present embodiment, the frequency is detected 500 times / second, that is, the acquisition interval of the geomagnetic data m (n) is 2 milliseconds.

  The magnetic sensor 2 is fixed to a ball that moves in the air while rotating. Therefore, as long as the rotation axis of the ball does not coincide with the direction of geomagnetism, the geomagnetic data m (n) obtained by the magnetic sensor 2 fluctuates periodically. FIG. 2 shows the time change La of the geomagnetic data m (n). Here, if there is no influence other than geomagnetism on the output value of the magnetic sensor 2, the time variation La of the geomagnetic data has equal amplitudes on the plus side and the minus side around the straight line Ld of the output zero along the time axis. It becomes a substantially sine wave such that Then, it is conceivable to calculate the number of rotations of the ball per unit time from the frequency of the substantially sine wave.

  Actually, however, the time change La of the geomagnetic data output from the magnetic sensor 2 is zero as shown in FIG. 2 due to the influence of the peripheral magnetic field other than the geomagnetism generated from the electronic components around the magnetic sensor 2. The waveform may be offset from the straight line Ld to the plus side or the minus side.

  Furthermore, as described above, the detection interval of terrestrial magnetism by the magnetic sensor 2 is extremely short, for example, 4 msec or less, but has a limit. As a result, the number of data that can be detected is limited, and the accuracy of the rotational speed measurement is reduced.

  Therefore, the calculation unit 3 obtains a large number of difference data Δm (n) based on the large number of geomagnetic data m (n) without using the geomagnetic data m (n) as it is. Specifically, for example, as shown in FIG. 4, when there is geomagnetic data m (k−2), m (k−1), and m (k) continuous in time series, the difference is based on these data. Data Δm (k−1) and Δm (k) are obtained. Here, Δm (k−1) = m (k−1) −m (k−2) and Δm (k) = m (k) −m (k−1). As described above, the difference data calculation unit 31 calculates difference data that is a difference between two geomagnetic data adjacent in time series to obtain a large number of difference data Δm (n) in time series.

  And these many difference data (DELTA) m (n) also fluctuates in a time series. The difference waveform calculation unit 32 acquires a difference waveform Lb that is a waveform of the difference data Δm (n) with time. As shown in FIG. 3, the difference waveform Lb draws a substantially sine wave around a straight line Lc with zero difference. Since the difference data Δm (n) is the difference between two time-series adjacent geomagnetic data, the difference data obtained at the timing of the peak of the peak and the peak of the valley in the time change La of the geomagnetic data is zero. . However, the acquisition interval of the difference data Δm (n) is the same as the acquisition interval of the geomagnetic data m (n) and cannot be shortened to the limit. Therefore, there is a timing when the difference data Δm (n) itself becomes zero. It does not visit periodically.

  However, as shown in FIG. 3, the differential waveform Lb draws a substantially sine wave around the straight line Lc with zero difference, and therefore always intersects the straight line Lc periodically. That is, as shown in FIGS. 4 and 5, two difference data Δm (k−1) and Δm (k) adjacent in time series among a plurality of difference data in the vicinity of the inflection point of the time change La of the geomagnetic data. ), Either one is positive and the other is negative. This state is not affected even if the temporal change La of the geomagnetic data is offset due to the influence of the magnetic field from the components around the magnetic sensor 2 or the like.

As a result, the difference waveform Lb surely intersects the straight line Lc with zero difference in the portion of the time zone near the inflection point of the time change La of the geomagnetic data (the portion shown in FIG. 5). Therefore, as shown in FIG. 3, the zero cross point P0 can be reliably obtained substantially periodically. Therefore, the number of zero cross points P0 per unit time, that is, the number of crossings per unit time can be obtained reliably.
Based on the number of intersections, the rotation amount calculation unit 33 of the calculation unit 3 calculates the rotation number of the ball per unit time, that is, the rotation speed.
Then, the calculated rotation speed of the ball is displayed on the output unit 12.

  As described above, the ball rotation amount measurement system 1 can accurately calculate the ball rotation amount even when the ball rotates at a high speed. In particular, in the present embodiment, the rotation amount calculation unit 33 calculates the rotation speed of the ball based on the number of crossings per unit time. Thereby, the rotation speed of the ball per unit time, that is, the rotation speed can be accurately measured.

  Further, the magnetic sensor 2 measures the geomagnetism in three axial directions orthogonal to each other, and the differential data calculation unit 31 uses the geomagnetic data having the largest amplitude among the geomagnetic data in the three axial directions to obtain differential data. Is calculated. Thereby, when the ball rotates in an arbitrary rotation direction, geomagnetic data having a large amplitude can be obtained in any one of the three axial directions. As a result, an accurate amount of rotation of the ball can be measured regardless of the direction of rotation of the ball with respect to the direction of geomagnetism.

  Further, since the magnetic sensor 2 is composed of an MI sensor, the amount of rotation of the ball can be measured more accurately. That is, since the MI sensor is excellent in detection sensitivity and responsiveness, it can accurately detect geomagnetism and can be detected with high accuracy even if the measurement interval is shortened compared to other magnetic sensors. Therefore, even when the ball is rotating at a high speed, it is possible to accurately measure the amount of rotation of the ball.

  As described above, according to the above aspect, it is possible to provide a ball rotation amount measuring system capable of measuring the rotation amount of the ball with high accuracy.

(Embodiment 2)
As shown in FIG. 7, the ball rotation amount measurement system 1 of the present embodiment includes an acceleration sensor 4, a start detection unit 51, and an end detection unit 52.
The acceleration sensor 4 is fixed to the ball and measures acceleration in at least one axial direction. The start detection unit 51 and the end detection unit 52 detect the start time and the end time of the air movement of the ball based on the acceleration data acquired by the acceleration sensor 4.

  The acceleration sensor 4 is configured to measure accelerations in three axial directions orthogonal to each other. Then, as shown below, the axial direction in which the amount of change in acceleration or acceleration per unit time is the largest at the time point determined immediately before the start time of the ball in the air and the time point determined immediately after the end time point. Use the data.

  When the ball starts moving in the air, a large impact is applied to the ball from the fingertip of the pitcher. And after leaving the pitcher's fingertip, the force acting on the ball is basically only air resistance, which is sufficiently smaller than the impact force applied from the pitcher's fingertip, and the amount of change is also small. Therefore, the point in time when the ball starts to move in the air can be grasped as the point in time when the acceleration greater than a certain threshold is detected immediately before the state where the acceleration detected by the acceleration sensor 4 is small.

  When the ball finishes moving in the air, for example, the ball collides with a catcher's mitt, a batter's bat, or the ground, and a large impact is applied to the ball. The impact applied to the ball can be measured as a large acceleration. This acceleration is detected by the acceleration sensor 4, and the end detection unit 52 determines the end time based on this detection signal.

  Accordingly, the ball rotation amount measurement system 1 grasps that the ball is moving in the air between the start time point detected by the start detection unit 51 and the end time point detected by the end detection unit 52. be able to. Therefore, the amount of rotation of the ball can be measured only during this period. That is, based on the geomagnetic data acquired during this time, the calculation unit 3 calculates the amount of rotation (rotation speed) of the ball.

The calculation of the rotation amount of the ball can be performed by the method shown in the first embodiment.
Other configurations are the same as those of the first embodiment. Of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-described embodiments represent the same components as those in the above-described embodiments unless otherwise indicated.

  In addition, when the acceleration sensor 4 is provided at a position greatly deviated from the center of gravity of the ball, the centrifugal force accompanying the rotation acts on the acceleration sensor 4. That is, even during the movement of the ball in the air, the acceleration sensor 4 detects the acceleration caused by the centrifugal force. Further, when the output value of the acceleration sensor 4 is offset, that is, when the output is deviated from zero even though the acceleration is not actually acting, the acceleration sensor 4 is not less than a certain level during the air movement of the ball. Will be output. Assuming such a situation, the start detection unit 51 and the end detection unit 52 may make a determination based on the amount of change in acceleration as follows.

  That is, when the ball starts to move in the air, a large impact is applied to the ball from the fingertip of the pitcher, and the impact force (acceleration) varies. Therefore, immediately before the state in which the variation in the detection value by the acceleration sensor 4 is small (hereinafter referred to as the low variation state), the time when the state in which the acceleration variation is large (hereinafter referred to as the high variation state) is detected The start time of movement can be grasped. Here, a state in which the amount of change in acceleration per unit time is equal to or greater than a certain threshold value can be a high fluctuation state, and a state in which the amount of change is less than the threshold value can be a low fluctuation state.

  Further, the impact force varies when the ball is finished moving in the air. That is, the acceleration varies. This change in acceleration is detected by the acceleration sensor 4, and the end detection unit 52 determines the end point based on this detection signal. That is, in the time zone including the time when the ball is moving in the air and before and after that, a high fluctuation state occurs first, then a low fluctuation state continues, and then a high fluctuation state occurs again. Therefore, the time point when the first high fluctuation state is switched to the low fluctuation state can be regarded as the start time point, and the time point when the low fluctuation state is switched to the subsequent high fluctuation state can be regarded as the end time point. Note that a method for determining the start point and the end point based on the amount of change in acceleration is described in detail in JP-A-2017-26427.

  Thereby, even when the acceleration sensor 4 is provided at a position greatly deviated from the center of gravity of the ball or when the output value of the acceleration sensor 4 is offset, the start time point and the end time point are not affected by these. Can be grasped.

As described above, in the present embodiment, the acceleration sensor 4 can be used to easily detect the start time and end time of the ball movement in the air.
In addition, the same effects as those of the first embodiment are obtained.

(Embodiment 3)
In the present embodiment, as shown in FIG. 8, the calculation unit 3 further includes a vector calculation unit 34 and an attitude change amount calculation unit 35 described below.
The vector calculation unit 34 calculates a geomagnetic vector based on the three axial geomagnetic data obtained by the magnetic sensor 2.
The posture change amount calculation unit 35 obtains the posture change amount of the ball from the start time to the end time of the air movement of the ball.

  The posture change amount calculation unit 35 includes a start time vector Ms that is a geomagnetic vector obtained by the vector calculation unit 34 at the start time and an end time vector Me that is a geomagnetic vector obtained by the vector calculation unit 34 at the end time. Based on this, the change in the posture of the ball is calculated.

  The start time vector Ms can be, for example, a geomagnetic vector based on the geomagnetic data acquired immediately after the start time is determined. Further, the end vector Me can be, for example, a geomagnetic vector based on the geomagnetic data acquired immediately before the end time is determined.

Specifically, the posture change amount calculation unit 35 calculates the posture change amount of the ball by the following method, for example.
That is, as shown in FIG. 9, the geomagnetic vector data detected by the triaxial geomagnetic sensor fixed to the ball is represented as geomagnetic vectors Ms, Mm, Me in the triaxial orthogonal coordinate system 10 fixed to the ball. Can be caught. Then, in this three-axis orthogonal coordinate system 10, the rotation axis K of the ball is obtained, and the change in the posture of the ball is calculated based on the relationship between the start vector Ms and the end vector Me around the rotation axis K. . Note that the X-axis, Y-axis, and Z-axis directions in the three-axis orthogonal coordinate system 10 shown in FIG. 9 need to match the X-axis, Y-axis, and Z-axis directions in the magnetic sensor 2 shown in FIG. ,Not particularly.

  When the geomagnetic vectors Ms, Mm, and Me at three different time points are drawn in the three-axis orthogonal coordinate system 10, for example, FIG. Of these three different time points, the first time point is the start time point of the air movement of the ball, and the last time point is the end time point of the air movement of the ball. That is, the three geomagnetic vectors Ms, Mm, and Me include a start time vector Ms and an end time vector Me. The other geomagnetic vector Mm is a geomagnetic vector at an intermediate time point between the start time point and the end time point. A plurality of the geomagnetic vectors Mm may be acquired, but here, a description will be given assuming that one.

  The end points Es, Em, and Ee of these three geomagnetic vectors Ms, Mm, and Me exist on the circumference of one trajectory circle Q drawn on one data plane S in the three-axis orthogonal coordinate system 10. . An axis that is orthogonal to the data plane S and that passes through the center C of the locus circle Q is the rotation axis K in the three-axis orthogonal coordinate system 10. That is, the geomagnetic vector rotates around the rotation axis K, and this rotation axis K becomes the rotation axis of the ball.

  Then, an angle θ formed by a straight line connecting the center C of the locus circle Q and the end point Es of the start time vector Ms and a straight line connecting the center C of the locus circle Q and the end point Ee of the end time vector Me is obtained. This angle θ is the rotation angle of the ball between the start time and the end time. That is, the rotation angle θ of the ball can be calculated as the amount of change in the posture of the ball. Note that details of an example of the above-described method for calculating the angle θ are disclosed in International Publication No. WO2007 / 099599.

The ball rotation amount measurement system 1 of the present embodiment can be used as follows, for example.
That is, it is conceivable to use the posture change amount calculation unit 35 when the amount of rotation of the ball during the air movement is extremely small.

  That is, if there are a plurality of the above-mentioned number of crossings between the start time and the end time, at least the rotation amount of the ball from the start time to the end time is calculated by the rotation amount calculation unit shown in the first embodiment. Can be sought. However, if the number of crossings is less than 2 between the start time and the end time, it can be determined that the ball is hardly rotating (less than half rotation), but more than the rotation amount. Cannot be calculated. For example, when a knuckle ball or a fork ball is thrown, it is assumed that the ball hardly rotates during the air movement of the ball. Even in such a case, it may be desired to investigate how much the ball is not rotating. In such a case, it is useful to use the posture change amount calculation unit 35 described in the present embodiment.

Furthermore, the ball rotation amount measurement system 1 of the present embodiment can be used as follows.
As described above, if the number of crossings is two or more between the start time and the end time, the rotation amount calculation unit 33 can calculate the rotation amount of the ball. However, for example, information such as 0.8 rotation and 1.3 rotation cannot be obtained. Such information may also be useful when measuring the knuckle balls or fork balls described above. Therefore, it is conceivable to use the rotation amount calculation unit 33 and the posture change amount calculation unit 35 in combination.

  Therefore, in this embodiment, as shown in FIG. 8, the calculation unit 3 integrates the calculation result by the rotation amount calculation unit 33 and the calculation result by the posture change amount calculation unit 35 to calculate the rotation amount of the ball. It is possible to have an integrated calculation unit 36 for calculating.

  That is, when the rotation amount calculation unit 33 calculates the rotation amount of the ball as one rotation and the posture change amount calculation unit 35 calculates the ball posture change amount (rotation angle θ) as 90 °, the integration is performed. The calculation unit 36 calculates 1.25 rotations as the amount of rotation of the ball from the start time to the end time.

  In addition, when the rotation amount of the ball obtained by the rotation amount calculation unit 33 is a sufficiently high rotation, the calculation unit 3 may be configured to determine that the posture change amount calculation unit 35 is not used. . When the amount of rotation of the ball from the start time to the end time is, for example, 10 rotations or more, it is assumed that detailed information such as a change in the posture (rotation angle) of the ball is unnecessary, and the posture change amount calculation unit 35 is used. You can also avoid it.

Thus, in this embodiment, even when the amount of rotation of the ball is very small, it is possible to measure the change in the posture of the ball. On the other hand, when the rotation speed of the ball is high, the same calculation as in the first embodiment can be performed, and the rotation amount of the ball can be calculated with high accuracy.
In addition, the same effects as those of the first embodiment are obtained.

  In the case where the number of crossings is two or more between the start point and the end point as described above, the posture is measured when measuring the fine information such as 0.8 rotation and 1.3 rotation as the ball rotation amount. A method that does not use the change amount calculation unit 35 is also conceivable. That is, it is also possible to estimate the rotation speed from the time interval of the zero cross point P0 (see FIG. 3) obtained by the rotation amount calculation unit 33. That is, in the ball rotation amount measuring system, not only the number of crossings but also the time of zero crossing is recorded together. At the same time, the start time and end time are recorded. For example, when the number of crossings is two, the amount of rotation of the ball, for example, 0.8 rotations based on the time difference between the first and second zero crosses and the time difference between the start time and the end time Can be requested.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the invention. For example, the embodiments can be appropriately combined with each other, for example, the embodiment 2 and the embodiment 3 can be combined. In addition, the start time and end time of the air movement of the ball are not limited to the method using the acceleration sensor as shown in the second embodiment, but can be obtained by other methods.

  Note that the ability to accurately measure the amount of rotation of a ball moving in the air as described above is useful from the following viewpoints when, for example, the above-mentioned baseball pitch is a measurement target. That is, it is conceivable to use a method of examining the relationship between the amount of rotation of the ball and the quality of the pitch, or evaluating the quality of the pitch by the amount of rotation of the ball. In the case of a straight ball, it is said that the higher the rotation speed is, the more the straight ball is stretched. However, the relationship can be examined quantitatively or the quality of the straight ball can be evaluated by the rotation speed. Alternatively, it is conceivable to examine or evaluate the relationship between the rotational speed of a changing sphere such as a curve or a chute and how the orbit changes. In addition, as in Embodiment 3 described above, the quality of these ball types can be evaluated by measuring the amount of rotation (rotation angle) of a low-rotation ball such as a knuckle ball or fork ball.

  Moreover, in the said embodiment, although the form which measures the rotation amount of the ball thrown by the baseball pitcher was demonstrated, the use of the ball rotation amount measuring system of this invention is not restricted to this. For example, tennis serve or the amount of rotation of a ball in a stroke can be measured. Further, the ball rotation amount measuring system can be used not only for baseball and tennis but also for other ball games such as softball, golf, table tennis, volleyball and soccer.

DESCRIPTION OF SYMBOLS 1 Ball rotation amount measurement system 2 Magnetic sensor 3 Operation part 31 Difference data calculation part 32 Difference waveform calculation part 33 Rotation amount calculation part Lb Difference waveform

Claims (1)

A ball rotation amount measuring system for measuring the amount of rotation of a ball moving in the air,
A magnetic sensor fixed to the ball and measuring geomagnetism in at least one axial direction;
An arithmetic unit that calculates the amount of rotation of the ball using geomagnetic data acquired in time series by the magnetic sensor,
With
The calculation unit calculates difference data that is a difference between two geomagnetic data adjacent in time series, and obtains a large number of the difference data in time series, a difference data calculation unit,
A differential waveform calculation unit for obtaining a differential waveform that is a waveform of a time change of a large number of the differential data;
A ball rotation amount measurement system, comprising: a rotation amount calculation unit that calculates the rotation amount of the ball based on the number of intersections, which is the number of times the difference waveform intersects a straight line with no difference in a predetermined period.

Images