Micro rotational inertia measuring method capable of directly tracing source

Abstract

The invention discloses a tiny rotational inertia measuring method capable of directly tracing to the source. The method comprises the following steps: installing a measured object on a tray of a measuring device; the computer controls the signal source to generate a voltage signal with adjustable frequency and amplitude, and the voltage signal is amplified by the power amplifier to excite the torsion platform to work; meanwhile, the angle measured by the circular grating is used as a feedback quantity to carry out closed-loop control on the torsional pendulum table; a laser interferometer and a diffraction grating are adopted to form an angular acceleration measuring unit, and the angular acceleration a is calculated by measuring the torsional pendulum angle and frequency; acquiring a time-domain output signal U of the torque sensor, and calculating a torque amplitude M corresponding to the time-domain output signal U in combination with the sensitivity of the torque sensor; and the rotational inertia J of the measured object is calculated through a rigid body rotation dynamic formula. According to the method, the problems that the micro rotational inertia is difficult to measure, the value cannot be traced, and high-accuracy measurement is difficult to realize are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of moment of inertia measurement, and in particular relates to a method for measuring tiny moment of inertia that can be directly traced. Background Art

[0002] The moment of inertia is a physical quantity that characterizes the inertia of a rotating object. It is an important engineering technical parameter for studying, designing, and controlling the motion laws of rotating objects. Therefore, measuring the moment of inertia of an object has important practical significance.

[0003] The demand for measuring tiny moments of inertia is becoming increasingly prominent. For example, inertial instruments such as three-floating gyro accelerometers and three-floating gyroscopes have high precision and a large dynamic measurement range. They are suitable for various launch vehicles and other spacecraft with high anti-interference requirements. They are the core working instruments of the inertial navigation platform system and are developing towards the goal of miniaturization. The float is a key component in the three-floating inertial instrument. It generally weighs 30g to 300g, has a tiny moment of inertia, and accurate measurement of its moment of inertia is crucial to achieve high-precision inertial navigation.

[0004] Traditional methods for measuring the moment of inertia are mainly divided into two categories: the torsion bar (or worm spring) pendulum method and the hanging wire pendulum method. Both methods calculate the moment of inertia of the object being measured by measuring the period of the pendulum. Based on the moments of inertia measured by the above two methods, the measurement accuracy of the torsion bar (or worm spring) pendulum method is higher than that of the hanging wire pendulum method, up to 0.1%, but it is limited by the stiffness of the torsion bar and is more suitable for measuring moments of inertia with higher values. In addition, the traceability is poor, and the accuracy of the reference value of the standard sample directly affects the accuracy of the measurement result. The reference value of the standard sample is obtained by theoretical calculation, not by measurement, so the measurement result cannot be effectively traced. Summary of the invention

[0005] The technical solution of the present invention is to overcome the shortcomings of the prior art and provide a method for measuring a tiny moment of inertia that can be directly traced, aiming to solve the problems that tiny moments of inertia are difficult to measure, their values ​​cannot be traced, and high-precision measurements are difficult to achieve.

[0006] In order to solve the above technical problems, the present invention discloses a method for measuring a small moment of inertia that can be directly traced, comprising:

[0007] Mount the object to be measured on the tray of the measuring device;

[0008] The computer controls the signal source to generate a voltage signal with adjustable frequency and amplitude, which is amplified by the power amplifier to stimulate the torsion pendulum to work; at the same time, the angle measured by the circular grating is used as the feedback quantity to perform closed-loop control on the torsion pendulum;

[0009] The angular acceleration measurement unit is composed of a laser interferometer and a diffraction grating. The angular acceleration a is calculated by measuring the torsion angle and frequency.

[0010] The time domain output signal U of the torque sensor is collected, and the torque amplitude M corresponding to the time domain output signal U is calculated based on the sensitivity of the torque sensor;

[0011] The moment of inertia J of the object being measured is calculated using the rigid body rotational dynamics formula: J = M / a.

[0012] The above-mentioned directly traceable method for measuring tiny moments of inertia also includes: constructing a measuring device; wherein the measuring device includes: a torsion pendulum stage, an air bearing, a circular grating, a torque sensor, a diffraction grating, a laser interferometer, a tray, a power amplifier, a feedback controller and a signal source; wherein the tray is mounted on the torsion pendulum stage through an air bearing; a circular grating is mounted on the air bearing; a torque sensor is mounted between the air bearing and the tray; a diffraction grating is mounted on the side of the tray; a laser interferometer is arranged on the side of the diffraction grating, and the light beam generated by the laser interferometer shines on the diffraction grating; the signal source, the power amplifier and the feedback controller are connected in sequence and placed on the side of the torsion pendulum stage.

[0013] In the above-mentioned directly traceable method for measuring minute moments of inertia, the torsion pendulum stage comprises: a base, a magnetic yoke, a magnetic core, a moving coil, an exciting coil and a torsion pendulum shaft;

[0014] The magnetic yoke, the magnetic conductive core and the excitation coil constitute an excitation unit; wherein the magnetic yoke and the magnetic conductive core are fixed on the base, and the magnetic yoke is located outside the magnetic conductive core; the excitation coil is wound on the magnetic conductive core;

[0015] The moving coil is inserted into the gap between the magnetic yoke and the magnetic conductive core; wherein the magnetic conductive core is located inside the moving coil and the magnetic yoke is located outside the moving coil;

[0016] One end of the torsion pendulum shaft is connected to the moving coil, and the other end is connected to the tray through a torque sensor; the torsion pendulum shaft and the moving coil constitute a torsion pendulum motion unit; under the guidance of the air bearing, the moving coil rotates in the magnetic yoke and the magnetic core, and drives the torsion pendulum shaft to rotate, thereby driving the tray to rotate.

[0017] In the above-mentioned directly traceable method for measuring small moments of inertia, the sensitivity of the torque sensor is traceable to a superior torque measurement standard.

[0018] In the above-mentioned directly traceable method for measuring small moments of inertia, the angular acceleration a is measured by the angle Taking the second-order derivative with respect to time t yields:

[0019] The present invention has the following advantages:

[0020] (1) The present invention discloses a method for measuring minute moments of inertia that can be directly traced. The result of the moment of inertia is directly derived from the torque and angular acceleration, and there is no intermediate value (such as the stiffness coefficient of the torsion bar, etc.). The value can be traced back to the standard values ​​of torque, angle and time. Compared with the prior art, the present invention does not require a moment of inertia standard component to achieve accurate measurement of the moment of inertia.

[0021] (2) The present invention discloses a method for measuring minute moments of inertia that can be directly traced. Under the premise of ensuring accuracy, the lower limit of the moment of inertia measurement in the prior art is reduced from 0.1 kg·m 2 Reduced to 1kg·mm 2 , reduced by 5 orders of magnitude.

[0022] (3) The present invention discloses a method for measuring tiny moments of inertia that can be directly traced. For products with smaller moments of inertia, the oscillation frequency during measurement is higher. Therefore, unlike other existing methods, the oscillation frequency decreases as the moment of inertia decreases. The measurement time of the present invention is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of a measuring device in an embodiment of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a torsion swing table in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] One of the core ideas of the present invention is to provide a method for measuring tiny moments of inertia that can be directly traced, and the moment of inertia value can be traced to torque, length and time. The moment of inertia measurement process does not require the reference value of a standard sample as an intermediate calculation parameter, and the measurement accuracy is improved to 0.05%, thereby overcoming the shortcomings of tiny moments of inertia that are difficult to measure, the value cannot be traced, and it is difficult to achieve high-accuracy measurement.

[0027] In this embodiment, the directly traceable small moment of inertia measurement method is based on Figure 1The measuring device shown is implemented. The measuring device includes: a torsion pendulum stage 1, an air bearing 2, a circular grating 3, a torque sensor 4, a diffraction grating 5, a laser interferometer 6, a tray 7, a power amplifier 9, a feedback controller 10 and a signal source 11. Among them, the tray 7 is installed on the torsion pendulum stage 1 through the air bearing 2, and the air bearing 2 is used to reduce the friction of the system; the circular grating 3 is installed on the air bearing 2; the torque sensor 4 is installed between the air bearing 2 and the tray 7; the diffraction grating 5 is installed on the side of the tray 7; the laser interferometer 6 is set on the side of the diffraction grating 5, and the light beam generated by the laser interferometer 6 shines on the diffraction grating 5; the signal source 11, the power amplifier 9 and the feedback controller 10 are connected in sequence and placed at an appropriate position on the side of the torsion pendulum stage 1.

[0028] Further, such as Figure 2 As shown, in this embodiment, the torsion pendulum stage 1 specifically includes: a base 12, a yoke 13, a permeable core 14, a moving coil 15, an excitation coil 16 and a torsion pendulum shaft 17. The yoke 13, the permeable core 14 and the excitation coil 16 constitute an excitation unit; the yoke 13 and the permeable core 14 are fixed on the base 12, and the yoke 13 is located outside the permeable core 14; the excitation coil 16 is wound on the permeable core 14. The moving coil 15 is inserted into the gap between the yoke 13 and the permeable core 14; the permeable core 14 is located inside the moving coil 15, and the yoke 13 is located outside the moving coil 15. One end of the torsion pendulum shaft 17 is connected to the moving coil 15, and the other end is connected to the tray 7 through the torque sensor 4; the torsion pendulum shaft 17 and the moving coil 15 constitute a torsion pendulum motion unit; under the guidance of the air bearing 2, the moving coil 15 rotates in the magnetic yoke 13 and the magnetic core 14, and drives the torsion pendulum shaft 17 to rotate, thereby driving the rotation of the tray 7. While playing a guiding role, the air bearing 2 also reduces the motion damping. The torque sensor 4 is used to measure the torque value finally output to the tray, and the object to be measured is installed and fixed on the tray.

[0029] It should be noted that the function of the torsion pendulum stage 1 is to provide a power source for the object to be measured to perform torsion pendulum motion. Any device that can produce low-distortion sinusoidal torsion pendulum motion can be used, including but not limited to motor mechanisms, electromagnetic excitation mechanisms, etc. The torque sensor can be directly traced back to the superior torque measurement standard; the angular acceleration can be traced back to the superior measurement standards of geometric quantity (angle) and time frequency by parameters.

[0030] In this embodiment, the implementation process of the directly traceable small moment of inertia measurement method based on the above-mentioned measurement device is as follows:

[0031] Step 1: Mount the object 8 to be measured on the tray 7 of the measuring device.

[0032] Step 2, the computer controls the signal source 11 to generate a voltage signal with adjustable frequency and amplitude, which is amplified by the power amplifier 9 to excite the torsion pendulum 1 to work; at the same time, the angle measured by the circular grating 3 is used as a feedback quantity to perform closed-loop control on the torsion pendulum 1 to ensure the rotation accuracy of the torsion pendulum 1.

[0033] Step 3, using laser interferometer 6 and diffraction grating 5 to form an angular acceleration measurement unit, by measuring the torsion angle and frequency, the angular acceleration a is calculated, so that the angular acceleration can be traced back to the geometry (angle) and time quantity. Taking the second-order derivative with respect to time t yields:

[0034] Step 4, collect the time domain output signal U of the torque sensor 4, and calculate the torque amplitude M corresponding to the time domain output signal U in combination with the sensitivity of the torque sensor 4. The sensitivity of the torque sensor 4 can be traced back to the superior torque measurement standard.

[0035] Step 5, calculate the moment of inertia J of the object 8 to be measured using the rigid body rotational dynamics formula: J=M / a.

[0036] Based on the above embodiment, a specific example is described below.

[0037] (1) An electromagnetic excitation oscillating stage based on an air-floating shaft system is used. The object to be measured is mounted on a tray. A computer controls the signal source to generate a voltage signal with adjustable frequency and amplitude, which is amplified by a power amplifier to excite the oscillating stage. The circular grating measures the angle as feedback to perform closed-loop control of the oscillating stage and ensure the rotation accuracy of the oscillating stage.

[0038] The mass of the measured object with a small moment of inertia is generally small. Here is an example of a float of a three-float inertia instrument. The mass of the float of the three-float inertia instrument is 30g~100g, and the moment of inertia is about (1.5~5)kg·mm 2 , the recommended amplitude and frequency of the torsion pendulum excitation are given in Table 1:

[0039]

[0040] Table 1. Schematic diagram of the recommended amplitude and frequency of the torsion pendulum excitation

[0041] It can be seen that for the same object under test, the higher the excitation frequency and the larger the torsion pendulum amplitude, the greater the torque value generated. When the moment of inertia is small, it is advisable to select a higher excitation frequency or a larger torsion pendulum amplitude. The specific selection should be based on the capacity of the torsion pendulum to ensure a better output waveform. The minimum output torque in the example in Table 1 is 31.0mN·m. The current measurement lower limit of the national torque standard device is 1mN·m, which can ensure accurate traceability.

[0042] (2) The torque sensor is installed close to the tray, and the time domain output signal U of the torque sensor is collected. The calibrated torque sensor sensitivity is substituted to obtain the corresponding torque amplitude M.

[0043] (3) A laser interferometer and a diffraction grating are used to form an angular acceleration measurement unit. The angular acceleration a is calculated by measuring the torsion angle and frequency, and the angular acceleration is traced back to the laser wavelength and frequency through angle and time.

[0044] (4) The moment of inertia J of the object being measured is calculated using the moment of inertia calculation formula: J = M / a.

[0045] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0046] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for measuring small moments of inertia that can be directly traced, characterized in that: include: Mounting the object to be measured (8) on a tray (7) of the measuring device; A computer-controlled signal source (11) generates a voltage signal with adjustable frequency and amplitude, which is amplified by a power amplifier (9) to excite the torsion pendulum (1) to work; at the same time, the angle measured by the circular grating (3) is used as a feedback quantity to perform closed-loop control on the torsion pendulum (1); A laser interferometer (6) and a diffraction grating (5) are used to form an angular acceleration measurement unit, and the angular acceleration a is calculated by measuring the torsion angle and frequency; Collecting a time domain output signal U of the torque sensor (4), and calculating a torque amplitude M corresponding to the time domain output signal U in combination with the sensitivity of the torque sensor (4); The moment of inertia J of the object (8) being measured is calculated by using the rigid body rotational dynamics formula: J = M / a.

2. The directly traceable method for measuring small moments of inertia according to claim 1, characterized in that: Also includes: A measuring device is constructed; wherein the measuring device comprises: a torsion pendulum table (1), an air bearing (2), a circular grating (3), a torque sensor (4), a diffraction grating (5), a laser interferometer (6), a tray (7), a power amplifier (9), a feedback controller (10) and a signal source (11); wherein the tray (7) is mounted on the torsion pendulum table (1) via the air bearing (2); the circular grating (3) is mounted on the air bearing (2); the torque sensor (4) is mounted between the air bearing (2) and the tray (7); the diffraction grating (5) is mounted on the side of the tray (7); the laser interferometer (6) is arranged on the side of the diffraction grating (5), and the light beam generated by the laser interferometer (6) shines on the diffraction grating (5); the signal source (11), the feedback controller (10) and the power amplifier (9) are connected in sequence and placed on the side of the torsion pendulum table (1).

3. The directly traceable method for measuring small moments of inertia according to claim 2, characterized in that: A torsion pendulum table (1) comprises: a base (12), a magnetic yoke (13), a magnetic permeable core (14), a moving coil (15), an excitation coil (16) and a torsion pendulum shaft (17); The magnetic yoke (13), the magnetic permeable core (14) and the excitation coil (16) form an excitation unit; wherein the magnetic yoke (13) and the magnetic permeable core (14) are fixed on the base (12), and the magnetic yoke (13) is located outside the magnetic permeable core (14); the excitation coil (16) is wound on the magnetic permeable core (14); The moving coil (15) is inserted into the gap between the magnetic yoke (13) and the magnetic conductive core (14); wherein the magnetic conductive core (14) is located inside the moving coil (15) and the magnetic yoke (13) is located outside the moving coil (15); One end of the torsion pendulum shaft (17) is connected to the moving coil (15), and the other end is connected to the tray (7) through the torque sensor (4); wherein the torsion pendulum shaft (17) and the moving coil (15) form a torsion pendulum motion unit; under the guidance of the air bearing (2), the moving coil (15) rotates in the magnetic yoke (13) and the magnetic conductive core (14), and drives the torsion pendulum shaft (17) to rotate, thereby driving the tray (7) to rotate.

4. The directly traceable method for measuring small moments of inertia according to claim 1, characterized in that: The sensitivity of the torque sensor (4) is traceable to a superior torque measurement standard.

5. The directly traceable method for measuring small moments of inertia according to claim 1, characterized in that: Angular acceleration a is calculated by the angle Taking the second-order derivative with respect to time t yields:

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