JP2014025702A - Fatigue testing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fatigue testing machine capable of performing a fatigue and endurance test in a wide acceleration region.SOLUTION: A deformation waveform generation unit 52 includes an interval change unit 61 and a frequency shift unit 62, and outputs a control deformation waveform. The deformation waveform generation unit 52 allows the interval change unit 61 or the frequency shift unit 62 to change a target acceleration waveform that has been input from a target waveform generator 46 in order to attain the maximum and minimum accelerations of a target acceleration waveform based on an actual vibration waveform input from the target waveform generator 46 within a range where deformation does not exceed the deformation limit of a vibration table 34 of a fatigue testing machine.

Description

  The present invention relates to a fatigue testing machine that performs a fatigue / durability test on a specimen.

  In a fatigue testing machine, for example, the vibration (seismic acceleration) given to the structure due to an actual earthquake and the vibration given to the part during driving of the automobile are reproduced, and the earthquake resistance of the structure and the durability of the part are reproduced. Fatigue / endurance tests are conducted to verify the above. In the fatigue / endurance test using such a fatigue tester, the vibration to be reproduced is preset as a target waveform. Then, the test force of a random waveform is loaded on the specimen by driving the load actuator, the deformation amount of the specimen by the random waveform is detected, and the transfer function is calculated based on the difference between the random waveform and the detected response waveform. ing. The drive signal corresponding to the target waveform given to the load actuator is generated by multiplying the target waveform by the inverse transfer function (see Patent Document 1).

  After the drive signal is determined, iteration (repetitive correction) is performed to correct the waveform of the drive signal from the difference between the response waveform when the load actuator is driven based on this drive signal and the target waveform. . Then, the correction of the waveform of the drive signal based on the difference between the response waveform and the target waveform is continuously executed even during the test.

  In addition, the accelerometer measurement values are measured so that the physical displacement (displacement) of the shaking table that can achieve the target acceleration can be obtained by placing the accelerometer on the specimen and the shaking table on which the specimen is placed. There is known a fatigue testing machine that performs vibration control to operate a load actuator by using (see Patent Document 2). In such a fatigue testing machine, when an accelerometer is provided on the specimen, the acceleration waveform generated by the movement of the shaking table due to the vibration of the load actuator is subjected to the displacement of the shaking table itself. Since the acceleration waveforms due to vibration overlap, the waveform reproducibility (coherence) of the response waveform measured by the accelerometer becomes lower as the target acceleration frequency becomes higher. For this reason, in the fatigue testing machine of Patent Document 2, the reproducibility of the target acceleration waveform is improved by identifying the transfer function (frequency transfer function) for each frequency region having a different waveform reproducibility.

  In this way, in the fatigue testing machine, vibration control is performed to convert the physical movement amount (displacement amount) of the shaking table to obtain the target acceleration and operate the load actuator. For example, when excitation control is performed using the measurement value of an accelerometer arranged on a shaking table, the target acceleration waveform is integrated twice and the target displacement waveform converted to the displacement target value is applied to the load actuator. By using the signal, the target acceleration waveform is reproduced.

Registered Utility Model No. 3119610 JP 2011-169866 A

FIG. 5 is a diagram illustrating a target acceleration waveform and a displacement waveform. FIG. 5A is a diagram showing an example of the target acceleration waveform based on the actual vibration waveform, and FIG. 5B is a diagram in which the acceleration is displaced by integrating the target acceleration waveform of FIG. 5A twice. It is the converted displacement waveform. In FIG. 5A, the vertical axis represents acceleration (m / s ² ) and the horizontal axis represents time (s). Moreover, in FIG.5 (b), a vertical axis | shaft is displacement (mm) and a horizontal axis is time (s).

  By the way, there is a physical limit to the amount of displacement of the load actuator and the amount of displacement of the shaking table that moves during vibration by driving the load actuator. For this reason, even if the shaking table is moved with the maximum applied amplitude, the target acceleration may not be realized. When the target acceleration waveform shown in FIG. 5A is integrated twice as it is, it is converted into a displacement of about plus or minus 60 mm as shown in FIG. 5B. Here, for example, if the limit jerk of the fatigue tester or the shaking table is plus or minus 25 mm, a displacement waveform exceeding plus or minus 25 mm cannot be loaded, so the target acceleration waveform in FIG. 5A cannot be reproduced. .

  On the contrary, depending on the target acceleration waveform to be reproduced, the amount of displacement converted into the displacement waveform may become so small that the control of the load actuator becomes difficult.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fatigue testing machine capable of performing a fatigue / endurance test in a wide acceleration range.

  The invention according to claim 1 is a fatigue testing machine that drives a load actuator and applies acceleration to a specimen, and a displacement waveform obtained by converting a target acceleration waveform based on an actual vibration waveform into a displacement amount of the load actuator. An acceleration having an interval changing unit that changes an interval between time series data points obtained by discretizing the target acceleration waveform at the time of conversion to Control displacement waveform generating means for generating a displacement waveform based on the waveform, drive signal output means for outputting a drive signal for driving the load actuator based on the control displacement waveform generated by the control displacement waveform generating means, and the load Response signal detecting means for driving the actuator and detecting a response signal when acceleration is applied to the specimen.

  The invention according to claim 2 is the invention according to claim 1, further comprising a vibration table that vibrates by driving the load actuator, wherein the response signal detection means is an accelerometer disposed on the vibration table. .

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the control displacement waveform creating means is expected to be out of a predetermined displacement range in the time series data of the target acceleration waveform. A region extracting unit that extracts a region having data points, and the interval changing unit changes the interval between the time-series data points in the target acceleration waveform for the region extracted by the region extracting unit.

  According to a fourth aspect of the present invention, in the invention according to the third aspect, the control displacement waveform creating means changes the time series data points changed in the interval changing unit with respect to a region not extracted by the region extracting unit. A data point increasing / decreasing unit for adding or deleting data points in inverse proportion to the interval between them is further provided.

  According to a fifth aspect of the present invention, in the first aspect of the invention, a transfer function calculation for identifying a transfer function of a vibration system that vibrates by driving the load actuator, and a control system including the load actuator and the specimen. And the response signal detecting means is an accelerometer disposed at an arbitrary position of the specimen and the shaking table, and the control displacement waveform creating means is a target acceleration waveform based on an actual vibration waveform. Is further provided with a frequency shift unit that shifts the frequency component of the target acceleration waveform, and the accelerometer is disposed on the shaking table. The displacement changing unit generates a displacement waveform based on the acceleration waveform in which the interval between the time series data points is changed, and the accelerometer is disposed on the specimen. If you are produces a displacement waveform using an acceleration waveform frequency component is shifted by the frequency shifting unit, the transfer function calculated by the transfer function calculating unit.

  The invention according to claim 6 is a fatigue testing machine that drives a load actuator and applies acceleration to a specimen, and performs transfer function calculation for identifying a transfer function of a control system including the load actuator and the specimen. And a frequency shift unit that shifts a frequency component of the target acceleration waveform when the target acceleration waveform based on the actual vibration waveform is converted into a displacement waveform converted into a displacement amount of the load actuator, and the frequency shift unit An acceleration waveform whose frequency component is shifted by the control function, a control displacement waveform generating means for generating a displacement waveform using the transfer function calculated by the transfer function calculating means, and a control displacement waveform generated by the control displacement waveform generating means Drive signal output means for outputting a drive signal for driving the load actuator based on Characterized in that and a response signal detecting means for detecting a response signal when the applied acceleration in the specimen.

  According to a seventh aspect of the invention, in the invention of the sixth aspect, the response signal detecting means is an accelerometer disposed on the specimen.

  The invention according to an eighth aspect is the invention according to the sixth aspect or the seventh aspect, wherein the control displacement waveform creating means is expected to be out of a predetermined displacement amount range in the time series data of the target acceleration waveform. Before and after the region extracted by the region extraction unit after shifting the frequency component of the target acceleration waveform for the region extracted by the region extraction unit by the shift unit. And a waveform connecting unit for connecting to a region where the frequency component is not shifted.

  According to the first and second aspects of the present invention, there is provided an interval changing unit that changes an interval between time series data points obtained by discretizing the target acceleration waveform, and the time series data point is obtained by the interval changing unit. Control displacement waveform creation means for generating a displacement waveform based on the acceleration waveform with the interval between them being changed, so that in the displacement waveform obtained by integrating the target acceleration waveform twice as it is, the maximum added amplitude of the fatigue tester Even if there is a region that exceeds the displacement, or a displacement that is smaller than the minimum applied amplitude of the fatigue testing machine, by using the acceleration waveform in which the interval between the time series data points is changed, while maintaining the target acceleration, It is possible to generate a control displacement waveform in which the displacement is within the range of the excitation capability of the fatigue testing machine. Therefore, it is possible to perform a fatigue / endurance test in a wide acceleration range.

  According to the third aspect of the present invention, the control displacement waveform creating means has a region extraction unit that extracts a region having a data point that is expected to exceed a predetermined amount of displacement in the time series data of the target acceleration waveform. Therefore, from the viewpoint of reproducing the excitation time, a test more faithful to the actual vibration waveform can be performed.

  According to the fourth aspect of the present invention, the control displacement waveform creating means sets data points in an area not extracted by the area extracting unit in inverse proportion to the interval between the time series data points changed in the interval changing unit. Since the data point increasing / decreasing unit to be added or deleted is provided, the interval between the data points of the entire acceleration waveform can be unified. As a result, the waveform data can be handled easily, and the subsequent generation of the control displacement waveform can be performed smoothly.

  According to the fifth aspect of the present invention, since the control displacement waveform creation means has the frequency shift section that shifts the frequency component of the target acceleration waveform, the response signal detection means is provided in the specimen. Even so, by using an acceleration waveform with a shifted frequency component and a periodic transfer function, it is possible to generate a controlled displacement waveform in which the displacement is within the range of the vibration testing machine's excitation capability while maintaining the target acceleration. Can do.

  According to the sixth and seventh aspects of the present invention, since the control displacement waveform creating means has the frequency shift unit that shifts the frequency component of the target acceleration waveform, the acceleration waveform and the period transmission in which the frequency component is shifted are included. By using the function, it is possible to generate a control displacement waveform in which the displacement is within the range of the excitation capability of the fatigue testing machine while maintaining the target acceleration. Therefore, it is possible to perform a fatigue / endurance test in a wide acceleration range.

  According to the eighth aspect of the present invention, the control displacement waveform creating means extracts a region that is expected to exceed a predetermined amount of displacement in the time series data of the target acceleration waveform, and the region extraction unit extracts the region. Since it has a waveform connection part that connects to the area where the frequency component was not shifted before and after the specified area, the joint of the area is prevented from becoming discontinuous, and the movement of the fatigue testing machine during the test Can be made smooth.

1 is a schematic diagram of a fatigue testing machine according to the present invention. 3 is a functional block diagram inside a control device 50. FIG. 6 is a waveform diagram showing a target acceleration waveform whose fundamental frequency has been changed by the interval changing unit 61 in the displacement waveform creating unit 52 and a control displacement waveform output from the displacement waveform creating unit 52. FIG. 6 is a graph for explaining frequency shift in a frequency shift unit 62; It is a wave form diagram which shows a target acceleration waveform and a control displacement waveform after integrating this target acceleration waveform twice.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a fatigue testing machine according to the present invention.

  This fatigue tester conducts a fatigue test by continuously applying a vibration load to the specimen 20 via a hydraulic actuator 31 that vibrates the vibration table 34. A random waveform generator 45 and a target waveform generator 46 are connected to the control device 50.

  The random waveform generator 45 outputs a PSD random waveform, which is a waveform having a constant value of PSD (Power Spectral Density) indicating a power spectrum value for each frequency, to the control device 50. The PSD random waveform is generated based on a synthesized arbitrary waveform including various frequency components previously stored in the random waveform generator 45 or an actual vibration waveform used for a target waveform selected as a model waveform. The The PSD random waveform is used to identify a transfer function of a control system including a hydraulic actuator 31 and a specimen 20 described later.

  The target waveform generator 46 generates a target waveform from a velocity waveform observed in an actual earthquake or a measurement signal collected by actual vehicle running when the specimen 38 is a vehicle part, and the signal is generated by the control device 50. Output to. This target waveform is used when generating a control displacement waveform in a displacement waveform creation unit 52 in the control device 50 described later.

  The control device 50 is configured by a computer or a sequencer that includes a storage device such as a ROM and a RAM and an arithmetic device, and controls the overall operation of the fatigue testing machine. A drive signal for the hydraulic actuator 31 is transmitted from the control device 50. The digital drive signal is converted into an analog signal by the D / A converter 41, amplified by the amplifier 35, and input to the servo valve of the hydraulic actuator 31. The displacement amount of the vibration table 34 is detected by the displacement meter 33, and the displacement detection signal is amplified by the amplifier 36, converted into a digital detection signal by the A / D converter 42, and then input to the control device 50.

  The vibration acting on the specimen 20 is an accelerometer 21 (shown in phantom lines in FIG. 1) disposed on the vibration table 34 on which the specimen 20 is placed, or the accelerometer 21 disposed on the specimen 20. The measured value is amplified by the amplifier 37 and converted into a digital signal by the A / D converter 43, and then input to the control device 50. The control device 50 calculates the difference between the drive signal given to the hydraulic actuator 31 and the detection signal (response signal) of the accelerometer 21, and feeds back data based on the difference to the servo valve of the hydraulic actuator 31. Excitation control of this fatigue tester is performed. In this fatigue testing machine, the accelerometer 21 is configured to be able to be moved to an arbitrary location on the vibration table 34 and the specimen 20 according to the content of the test to be performed.

  FIG. 2 is a functional block diagram inside the control device 50. FIG. 2 shows only the configuration necessary for executing the functions of this embodiment.

  The control device 50 includes a transfer function calculation unit 51, a displacement waveform creation unit 52, an iteration processing unit 53, a drive signal output unit 54 that outputs a control signal based on the displacement waveform to a servo valve in the hydraulic actuator 31, And a detection signal receiving unit 55 that receives detection signals of the displacement meter 33 and the accelerometer 21.

  The transfer function calculation unit 51 is a waveform such as a PSD random waveform input to the entire control system including the hydraulic actuator 31 and the specimen 20, and a response obtained when a load is applied to the specimen 20 based on the waveform. The transfer function of this control system is identified based on the ratio to the signal waveform (displacement detection waveform or acceleration detection waveform).

  The displacement waveform creation unit 52 includes an interval change unit 61 and a frequency shift unit 62, and functions as a control displacement waveform creation unit of the present invention that outputs a control displacement waveform. The displacement waveform creation unit 52 uses the interval change unit 61 or the frequency shift unit 62 to calculate the maximum / minimum acceleration of the target acceleration waveform based on the actual vibration waveform input from the target waveform generator 46, and the vibration table of the fatigue testing machine. The target acceleration waveform input from the target waveform generator 46 is changed in order not to exceed 34 displacement limits.

  The interval changing unit 61 changes the interval between time-series data points in the target acceleration waveform by changing the fundamental frequency of the entire acceleration waveform. Thereby, while maintaining the maximum / minimum acceleration of the target acceleration waveform based on the actual vibration waveform, the displacement width of the control displacement waveform generated based on the changed target acceleration waveform is changed to the vibration table 34 of the fatigue testing machine. It can be within the range of the displacement width. Further, the frequency shift unit 62 shifts the frequency of the target acceleration waveform to increase / decrease both or both of the maximum value and the minimum value of the displacement of the control displacement waveform generated based on the frequency. It is possible.

  The iteration processing unit 53 repeatedly corrects the drive signal of the hydraulic actuator 31 created based on the control displacement waveform generated by the displacement waveform creation unit 52 during the test execution so that the response waveform matches the target waveform. To do. Note that the target waveform that is the target of this iterative correction is the target acceleration waveform that has been changed by the interval changing unit 61 or the frequency shifting unit 62 when the displacement waveform creating unit 52 generates the control displacement waveform. . That is, the iteration processing unit 53 is configured such that the ratio or difference between the response acceleration waveform of the accelerometer 21 and the target acceleration waveform, or the ratio or difference of the control displacement waveform converted from the response displacement waveform of the displacement meter 33 and the target acceleration waveform. Based on the above, the drive signal of the hydraulic actuator 31 is repeatedly corrected.

  The drive signal after the iteration process is input to the drive signal output unit 54. The drive signal output unit 54 outputs the drive signal corrected by the iteration processing unit 53 as a control drive signal (differential drive signal) for the servo valve of the hydraulic actuator 31. The control drive signal is converted into an analog signal by the D / A converter 41, amplified by the amplifier 35, and applied to the servo valve. By driving the servo valve with such a control drive signal, the hydraulic actuator 31 is driven and a load is applied to the specimen 38.

  The displacement of the vibration table 34 at this time is detected by the displacement meter 33, and a response signal for this displacement is input to the detection signal receiving unit 55 via the amplifier 36 and the A / D converter 42. Further, the acceleration applied to the specimen 20 at this time is detected by the accelerometer 21, and a response signal for this acceleration is input to the detection signal receiving unit 55 via the amplifier 37 and the A / D converter 43. Then, the detection signal receiving unit 55 performs an iteration process on the response signal selected as the control amount for controlling the drive signal of the hydraulic actuator 31 from the response signal from the displacement meter 33 and the response signal from the accelerometer 21. Input to the unit 53.

  Next, the change of the target acceleration waveform in the displacement waveform creation unit 52, which is a feature of the present invention, will be described in more detail. First, the change of the target acceleration waveform in the interval changing unit 61 will be described.

FIG. 3A shows an acceleration waveform obtained by multiplying the time interval between time series data points of the target acceleration waveform shown in FIG. 5A by 1 / 2.5, and FIG. 3B shows the acceleration waveform. It is a wave form diagram which shows the control displacement waveform after integrating twice. In FIG. 3A, the vertical axis represents acceleration (m / s ² ), and the horizontal axis represents time (s). Moreover, in FIG.3 (b), the vertical axis | shaft has shown the displacement (mm) and the horizontal axis has shown time (s).

  In the interval changing unit 61, if the time interval between the time series data points of the target acceleration waveform is shortened, the maximum amplitude of the displacement waveform is reduced while securing the peak value of the acceleration, and conversely the time series data points of the target acceleration waveform. When the time interval between them is lengthened, the maximum amplitude of the displacement waveform is increased while securing the peak value of acceleration for the following reason. All acceleration waveforms a (t) can be expanded into discrete Fourier series using cos and sin functions as shown in the following equation (1).

F ₀ in this equation (1) is a fundamental frequency. The displacement waveform d _i (t) for realizing the acceleration of the acceleration waveform can be expressed by the following formula (2) obtained by integrating the formula (1) twice.

Mean in the equation (2) is an average value of the waveform. Further, in the interval changing unit 61 of the present invention, performing the process of changing the interval between the time series data points of the acceleration waveform is the same as changing the fundamental frequency f ₀ in the equation (1). That is, changing the interval between the time-series data points is, in other words, changing the sampling period T (f ₀ = 1 / T) of the time-series data afterwards. Then, the acceleration waveform a ′ (t) in which the interval between the time series data points is changed in the interval changing unit 61 can be expressed as the following equation (3).

In the interval changing unit 61 of the present invention, when the process for reducing the interval between time series data points of the waveform shown in FIG. Thus, the waveform shown in FIG. If the waveform in FIG. 5A is a (t) and the waveform in FIG. 3A is a ′ (t), f ′ _{0 in} this equation (3) is the fundamental frequency f _{0 in} equation (1). It is a larger value and can be expressed as f ′ ₀ = f ₀ × 2.5. Expression (3) is obtained by changing the fundamental frequency f ₀ of Expression (1) to f ′ ₀ without changing the Fourier coefficients a _n and b _n representing the amplitude. Thus, shortening the time interval between the time series data points of the target acceleration waveform, as can be seen by comparing FIG. 3A and FIG. 5A, the acceleration waveform a (t) and the acceleration waveform a. The result is the same as increasing the fundamental frequency f ₀ without changing the amplitude of '(t). A control displacement waveform d ′ (t) obtained by integrating this acceleration waveform a ′ (t) twice can be expressed as the following equation (4).

Equation (3) when _f'0 is greater than _{f 0} of the formula (1) is, cos displacement waveform d'(t), each component of the sin, 1 / (n · 2πf' 0) 2 become possible Thus, the amplitude of the displacement waveform d ′ (t) becomes smaller as a whole compared to the displacement waveform d (t). Therefore, the waveform of FIG. 3B, which is a displacement waveform obtained by integrating the expression obtained by expanding the discrete Fourier series of the acceleration waveform of FIG. 3A twice, has a displacement amplitude as compared with the waveform of FIG. It is small.

  As described above, when the time interval between the time series data points of the target acceleration waveform is shortened by the interval changing unit 61, the fundamental frequency increases, and as a result, the amplitude of the displacement waveform decreases. Therefore, when a displacement waveform is created from time-series data of the acceleration waveform as it is, even if there is an acceleration that cannot be realized due to a lack of physical movement (displacement) of the vibration table 34, the fatigue test of the present invention. The machine can achieve the target acceleration with a small amount of displacement.

Further, by increasing the time interval between the time series data points of the target acceleration waveform, if _f'0 of formula (3) is smaller than f ₀ of the formula (1) is the displacement waveform d (t) In comparison, the amplitude of the displacement waveform d ′ (t) increases as a whole. Thus, if the time interval between the time series data points of the target acceleration waveform is lengthened (decreasing the fundamental frequency), the displacement width can be increased while maintaining each acceleration peak value of the target acceleration waveform. The target acceleration, which is difficult to control the vibration of the shaking table 34 because the displacement amount is too small, can be stably controlled by increasing the amplitude.

  In this embodiment, the interval changing unit 61 performs the process of changing the time interval between the data points of the time series data of the target acceleration waveform. However, in place of the time series data processing in the interval changing unit 61. The control acceleration waveform in which the amplitude of the displacement waveform is changed may be created by expanding the discrete acceleration series of the target acceleration waveform and changing the value of the fundamental frequency of the expression obtained by expanding the discrete Fourier series.

  In this embodiment, the time interval between the data points is changed with respect to the entire time series data of the target acceleration waveform, but the time series data of the target acceleration waveform input from the target waveform generator 46 is used as it is. An area having data points that are expected to be outside the predetermined displacement amount range is extracted from the displacement waveform obtained by integrating the times, and the interval changing unit 61 changes the time interval between the data points only in the area. Also good. Here, the range of the predetermined amount of displacement varies depending on the vibration capacity inherent to the fatigue tester (the displacement limit of the hydraulic actuator 31), and the drive of the hydraulic actuator 31 is controlled in the fatigue tester in this embodiment. This corresponds to a range of displacement that is larger than the minimum amplitude of the shaking table 34 and smaller than the maximum amplitude. In addition, as a member that moves in conjunction with the displacement of the hydraulic actuator 31, for example, in the case of a fatigue testing machine in which a platen that repeatedly applies a pressing load to the specimen is provided, the range of the predetermined displacement amount is: The displacement range is larger than the minimum movement width of the platen that can be realized by controlling the drive of the hydraulic actuator 31 and smaller than the maximum movement width.

  In this case, the displacement waveform creation unit 52 is provided with a region extraction unit that extracts a region that is expected to exceed a predetermined amount of displacement in the time-series data of the target acceleration waveform as a functional configuration so that the region extraction is executed. You can do it. For example, if there is a data point in the displacement waveform obtained by integrating the time-series data of the target acceleration waveform input from the target waveform generator 46 twice as it is, the displacement amount exceeds the maximum added amplitude of the vibration table 34, the data A region including the points is cut out from the time-series data of the target acceleration waveform, and the interval changing unit 61 changes the time interval between the data points only in the region.

  Further, when the time interval between data points is changed only for the region extracted from the time series data of the target acceleration waveform, the time interval between the data points is different in the entire time series data. For this reason, when the time interval between data points is shortened in the other regions by shortening the time interval between data points in the extracted region, the interval between data points in the region other than the extracted region Data points that are deficient at intervals corresponding to the period of a region with a small are complemented from nearby data points. On the other hand, when the time interval between the data points in the extracted region becomes longer due to a longer time interval between the data points, the time between the data points in the region other than the extracted region becomes shorter. Data points are deleted at intervals according to the period of the long interval. Thus, by unifying the intervals between the data points of the entire time series data, the acceleration waveform can be handled easily in the subsequent processing.

  Note that such data point increase / decrease processing includes a data point increase / decrease unit that adds or deletes data points in inverse proportion to the interval between the time-series data points changed in the interval change unit 61 in the displacement waveform creation unit 52. A functional configuration may be provided and executed. For example, if the time interval between data points is shortened only in the region extracted from the time series data of the target acceleration waveform, the time interval in the region where the time interval between data points is shortened in other regions. At the same time, the missing data points are complemented with values from nearby data points.

  Next, the change of the target acceleration waveform in the frequency shift unit 62 will be described. When the accelerometer 21 is disposed on the vibration table 34 as shown by a solid line in FIG. 1, the input acceleration on the actuator side when moving the vibration table 34 and the response acceleration on the accelerometer side are 1 There is a one-to-one correspondence. In such a case, it is only necessary to obtain the displacement waveform from the acceleration waveform based on the conventional idea that the displacement is a two-time acceleration integration, and to control the fatigue testing machine. However, when the accelerometer 21 is disposed on the specimen 20 as shown by a solid line in FIG. 1, it is necessary to create a control displacement waveform in consideration of the free vibration of the specimen 20.

  Therefore, when the accelerometer 21 is disposed on the specimen 20, first, the fatigue testing machine is driven by a PSD random waveform or the like, and the relationship (frequency transfer function) for each acceleration frequency with respect to the obtained response displacement. Thereafter, a control displacement waveform for realizing a target acceleration waveform is calculated using a frequency transfer function of a control system including the hydraulic actuator 31 and the specimen 20. In this embodiment, a PSD random waveform is input from the random waveform generator 45 and the frequency transfer function is calculated by the transfer function calculation unit 51.

  When the target acceleration waveform a (t) represented by the above equation (1) is converted into a control displacement waveform dt (t) using a frequency transfer function, it can be expressed as the following equation (5).

In the above-described formula (3), the basic frequency f ₀ is increased or decreased to obtain the target acceleration waveform a ′ (t) in which the time interval between the time series data points is changed. 2 shifts the frequency component of the target acceleration waveform using positive integers i and j as shown in the following equation (6).

nf ₀ is the frequency of the nth harmonic, but in this equation (6), n moves from i to N-1-j. When the target acceleration waveform a _s ′ (t) whose frequency is shifted using the positive integers i and j is converted into a control displacement waveform using a frequency transfer function, it can be expressed as the following equation (7).

FIG. 4 is a diagram for explaining the relationship between the frequency shift and the amplitude in the target acceleration waveform in this embodiment. In this figure, cos component of the desired acceleration waveform magnitude of _{(a n cos (n · 2πf} 0 t of formula (1)), _a n cos of formula (6) ((n-i + j) · 2πf 0 t)) The distribution of a _n representing the height (amplitude) from the order 8 (a _{0 to} a ₈ ) is plotted, with the vertical axis representing amplitude and the horizontal axis representing n. Further, in this figure, the distribution of previous a _n performing frequency shift by a black circle, by showing the distribution of a _n after performing the frequency shift by white circles, the distribution change of the frequency shift before and after a _n Is shown. FIG. 4A shows the case where j = 2, and FIG. 4B shows the case where i = 2.

  Of the positive integers i and j in the above formulas (6) and (7), i is for shifting the frequency to the low frequency side, and j is for shifting the frequency to the high frequency side. In this embodiment, in the above formulas (6) and (7), j is empty (0) when a value is assigned to i, and i is empty when a value is assigned to j. (0). That is, in this embodiment, a positive integer can be input to either i or j.

state when the j = 2, as shown in FIG. 4 (a), when focusing on a ₀ of the black dots of nine (N = 9), a 0 _is the magnitude of the vertical axis does not change Thus, the position is shifted from the position of the horizontal axis n = 0 to the position of n = 2 (white circle). That is, the size of a ₀ is replaced with the magnitude of a _2. For even a ₁ ~a _8, as in the case of a _0, while the magnitude of the vertical axis does not change, shifted by 2 to the right direction in the drawing for the location of the horizontal axis. In this frequency shift of j = 2, the frequencies of the seventh and eighth harmonics are lost.

On the other hand, in the case of i = 2, as shown in FIG. 4 (b), when focusing on a ₈ out of black dots nine (N = 9), a _8, the size of the vertical axis does not change In the state, the position is shifted from the position of the horizontal axis n = 8 to the position of n = 6 (white circle). That is, the size of a ₈ replaces the size of a _6. For even a ₀ ~a _7, as in the case of a _8, the magnitude of the vertical axis direction in a state that does not change the position of the horizontal axis about to be shifted by 2 to the left direction in the drawing. In the frequency shift of i = 2, the frequencies of the 0th and 1st harmonics are lost.

By shifting the frequency of the target acceleration waveform in this way, the maximum value of the control displacement waveform d _ts ′ (t) (see Expression (7)) is decreased or the minimum value while the peak value of the acceleration waveform is maintained. Can be increased. That is, in the displacement waveform calculated using the target acceleration waveform input from the target waveform generator 46 and the frequency transfer function, if there is a displacement exceeding the maximum added amplitude of the shaking table 34, the frequency of the target acceleration waveform is set. When the shift is made higher, the maximum value of the control displacement waveform is reduced, and the target acceleration can be reproduced as a displacement equal to or less than the maximum applied amplitude of the vibration table 34. In addition, in the displacement waveform calculated using the target acceleration waveform input from the target waveform generator 46 and the frequency transfer function, when there is a displacement smaller than the minimum added amplitude of the vibration table 34, the frequency of the target acceleration waveform is set. When the shift is shifted to the lower side, the minimum value of the control displacement waveform is increased, and the target acceleration can be reproduced as a displacement greater than or equal to the minimum added amplitude of the vibration table 34.

  In the frequency shift of the target acceleration waveform using Expression (6) in the frequency shift unit 62, the frequency component whose order is less than i or greater than Nj is missing from the target acceleration waveform. However, in the normal target acceleration waveform, the components in the low frequency region and the high frequency region are almost negligible. Therefore, even if the frequency component having an order less than i or greater than Nj is missing from the target acceleration waveform, It does not affect the acceleration reproduction in the fatigue test.

  In this embodiment, the frequency shift in the frequency shift unit 62 is performed for the entire target acceleration waveform. However, the time-series data of the displacement waveform represented by the equation (5) and the movement limit of the shaking table 34 From the relationship, it is also possible to cut out the data of the region where the displacement amplitude is assumed to be insufficient from the time-series data of the target acceleration waveform, and to shift the frequency only in the cut region. Note that if the joint between the frequency-shifted region and the time-series data in other regions becomes discontinuous, the actuator may move unnecessarily. For this reason, an overlap region is provided at the joint between the frequency-shifted region and other regions, and the time-series data of the region where the frequency shift is performed in the overlap region and the time-series of other regions By averaging the data, the discontinuity of the joints is eliminated. Such a series of processing relating to region connection may be executed by providing the displacement waveform creation unit 52 with a region connection unit as a functional configuration.

  As described above, in this fatigue testing machine, the vibration control for operating the hydraulic actuator 31 is performed within the movable range of the vibration table 34 so that the target acceleration desired to be reproduced in the test can be realized.

  Further, in this fatigue testing machine, since the displacement waveform creating unit 52 includes the interval changing unit 61 and the frequency shifting unit 62, the target acceleration waveform is changed according to the arrangement position of the accelerometer 21, and the control displacement is changed. Waveforms can be created. For example, when the accelerometer 21 is disposed on the vibration table 34, the interval changing unit 61 changes the target acceleration waveform and generates a control displacement waveform, and the accelerometer 21 is disposed on the specimen 20. Sometimes, the frequency shift unit 62 may change the target acceleration waveform and generate the control displacement waveform.

20 Specimen 21 Accelerometer 31 Hydraulic Actuator 33 Displacement Meter 34 Shaking Table 35 Amplifier 36 Amplifier 37 Amplifier 41 D / A Converter 42 A / D Converter 43 A / D Converter 45 Random Waveform Generator 46 Target Waveform Generator 50 Control device 51 Reverse transfer function calculation unit 52 Displacement waveform creation unit 53 Iteration processing unit 54 Drive signal output unit 55 Detection signal reception unit 61 Interval change unit 62 Frequency shift unit

Claims (8)

A fatigue testing machine that drives a load actuator and applies acceleration to a specimen,
An interval changing unit for changing an interval between time-series data points obtained by discretizing the target acceleration waveform when converting the target acceleration waveform based on the actual vibration waveform into a displacement waveform converted into a displacement amount of the load actuator; Control displacement waveform creating means for generating a displacement waveform based on an acceleration waveform in which the interval between time-series data points is changed by the interval changing unit;
Drive signal output means for outputting a drive signal for driving the load actuator based on the control displacement waveform generated by the control displacement waveform creating means;
Response signal detecting means for driving the load actuator and detecting a response signal when acceleration is applied to the specimen;
A fatigue tester characterized by comprising: In the fatigue testing machine according to claim 1,
A vibration table that vibrates by driving the load actuator;
The fatigue tester, wherein the response signal detection means is an accelerometer disposed on the shaking table. In the fatigue testing machine according to claim 1 or 2,
The control displacement waveform creating means is
A region extraction unit for extracting a region having a data point that is expected to be out of a predetermined displacement range in the time-series data of the target acceleration waveform;
The interval changing unit is a fatigue testing machine that changes an interval between time-series data points in the target acceleration waveform for the region extracted by the region extracting unit. In the fatigue testing machine according to claim 3,
The control displacement waveform creating means is
A fatigue testing machine further comprising a data point increasing / decreasing unit that adds or deletes data points in inverse proportion to the interval between the time series data points changed in the interval changing unit for the region not extracted by the region extracting unit. In the fatigue testing machine according to claim 1,
A vibration table that vibrates by driving the load actuator;
A transfer function calculating means for identifying a transfer function of a control system including the load actuator and the specimen,
The response signal detection means is an accelerometer disposed at an arbitrary position of the specimen and the shaking table,
The control displacement waveform creating means is
A frequency shift unit that shifts a frequency component of the target acceleration waveform when the target acceleration waveform is converted into a displacement waveform converted into a displacement amount of the load actuator;
When the accelerometer is disposed on the shaking table, a displacement waveform is generated based on the acceleration waveform in which the interval between time-series data points is changed by the interval changing unit, and the accelerometer is A fatigue testing machine that generates a displacement waveform by using an acceleration waveform whose frequency component is shifted by the frequency shift unit and a transfer function calculated by the transfer function calculating means when arranged in a specimen. A fatigue testing machine that drives a load actuator and applies acceleration to a specimen,
A transfer function computing means for identifying a transfer function of a control system including the load actuator and the specimen;
A frequency shift unit that shifts a frequency component of the target acceleration waveform when the target acceleration waveform based on the actual vibration waveform is converted into a displacement waveform converted into a displacement amount of the load actuator; Control displacement waveform generating means for generating a displacement waveform using the acceleration waveform shifted by the transfer function and the transfer function calculated by the transfer function calculating means,
Drive signal output means for outputting a drive signal for driving the load actuator based on the control displacement waveform generated by the control displacement waveform creating means;
Response signal detecting means for driving the load actuator and detecting a response signal when acceleration is applied to the specimen;
A fatigue tester characterized by comprising: In the fatigue testing machine according to claim 6,
The response signal detecting means is a fatigue testing machine which is an accelerometer arranged on the specimen. In the fatigue testing machine according to claim 6 or 7,
The control displacement waveform creating means is
A region extraction unit that extracts a region that is expected to be outside the range of a predetermined amount of displacement in the time-series data of the target acceleration waveform;
After shifting the frequency component of the target acceleration waveform for the region extracted by the region extraction unit by the frequency shift unit, before and after the region extracted by the region extraction unit, A waveform connection for connecting
Fatigue testing machine equipped with.

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