CN202230060U - Wood nondestructive testing system based on stress wave technology - Google Patents
Wood nondestructive testing system based on stress wave technology Download PDFInfo
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Abstract
The utility model relates to a wood nondestructive testing system based on a stress wave technology. The technical problem to be solved is as follows: the provided system needs to have the characteristics of high speed, strong anti-interference capability, higher detection precision, low detection cost and convenience for testing. The technical scheme is as follows: the wood nondestructive testing system based on the stress wave technology comprises a signal acquisition part, a signal processing part and a microcontroller which are electrically conducted in sequence, wherein the signal acquisition part comprises an acceleration sensor, a pulse hammer and a counter and the signal processing part is formed by connecting an impedance matching module for converting and processing 'starting' and 'stopping' of two stress wave pulse waveforms, a signal amplifying circuit module and a filter shaping circuit module in sequence; and the input end of the microcontroller part is communicated with the output end of the signal processing part so as to calculate the stress wave propagation time and the elastic modulus of the detected wood. A uA741 chip is adopted in the impedance matching module; and the acceleration sensor accesses into the chip after passing through a resistor.
Description
Technical field
The utility model relates to a kind of detection system, the nondestructive detection system in travel-time of especially measuring stress wave in timber.
Background technology
Timber is a kind of human the longest historical reproducible natural resources that use.Along with social progress, people are to the raising of producing, quality of life requires, and the demand of timber is increased gradually.Fully effectively utilizing timber resources, make it to produce maximum economy and society benefit, is various countries' forestry researcher common concern and the problem of constantly studying.Because artificial method is adopted in the detection of traditional timber mostly, even detect after must wood sample being destroyed, thereby these detection methods can not satisfy non-destructive fast detecting and the needs that continue to detect in the timber production.In recent years; The development of Along with computer technology and sensing technology; And the development of technology such as ultrasound wave, X-ray or gamma-rays, infrared ray, laser, microwave and stress wave; The Dynamic Non-Destruction Measurement of timberphysics, mechanical property and defective has also risen to new level, and forms emerging, a comprehensive timber detection technique.
The elastic modulus of timber is an important parameter, and it has reflected the physics and the mechanical property of timber.Detect the quality that to come assessment material through the elastic modulus of measuring timber in order wood property to be carried out non-destructive.Therefore, how using the stress wave technology, through measuring the elastic modulus of timber, realize the assessment to the lumber quality situation, is our present problem.
Summary of the invention
The purpose of the utility model provides a kind of timber nondestructive detection system based on stress wave technology, with in real time, reliably, velocity of propagation and the modulus of elasticity of wood of calculated stress ripple in timber exactly, thereby judge whether timber inside exists defective; This system should have the characteristics that speed is fast, antijamming capability is strong, accuracy of detection is higher, and detects low, the convenient test of cost.
The technical scheme that the utility model provides is: the timber nondestructive detection system based on the stress wave technology comprises signals collecting, signal Processing and three parts of microcontroller of conducting in regular turn; Wherein the signal acquisition part branch comprises acceleration transducer, pulse hammer, counter; Signal processing is connected in sequence by impedance matching module, signal amplification circuit module, the filtering shaping circuit module of conversion process " initial " and " termination " two stress wave pulse waveforms; The input end of microcontroller part and the output terminal of signal processing are connected, with the elastic modulus of calculated stress wave propagation time and tested timber.
Described impedance matching module adopts the uA741 chip, and acceleration transducer is through inserting this chip behind the resistance.
Described signal amplification circuit module adopts the OP07 chip, and the output terminal of impedance matching module inserts the input end of this chip.
Described filtering shaping circuit module adopts the MAX7408 chip, and the output terminal of signal amplification circuit module inserts the input end of this chip.
Described microcontroller adopts the ATmega16 single-chip microcomputer.
Experimental result shows, the utility model is for flawless timber, through measure modulus of elasticity of wood that the stress wave propagation time conversion obtains near or equal the reference value that pertinent literature is announced; If the Spreading Velocity of Stress Wave of some timber is significantly less than the velocity of propagation in normal timber, the elastic modulus that obtains that converts departs from normal reference value, just can confirm that there is defective in these timber inside.
The stress wave timber nondestructive detection system that the utility model provides to the non-homogeneous and anisotropic characteristics of timber, uses highly sensitive sensor, can catch the faint stress wave signal of propagating in the timber fast; Simultaneously, use the filtering frequency selection network to suppress circuit and neighbourhood noise, improved the hardware system antijamming capability, improved the reliability of stress wave signal gatherer process.In addition, the utility model uses the running mean algorithm that the measurement data sequence is handled, and further reduces error, has improved precision and the reliability measured.
The utility model can confirm whether timber has inherent vice or timber to be tested is carried out grade classification; Not only have the characteristics of very high reliability, radiationless, convenient test, and can save cost, improve detection efficiency and precision; Not only can be applied in wood processing enterprise and carry out the product quality detection, also may be used on the health monitoring of ancient and well-known trees and ancient building wooden structures, have broad application prospects.
Description of drawings
Fig. 1 is a stress wave Method Of Time Measurement synoptic diagram.
Fig. 2 is the timber cross sectional representation when measuring the timber inherent vice.
Fig. 3 is each circuit module annexation figure of stress wave nondestructive detection system.
Fig. 4 is each the circuit connecting relation figure in the control module among Fig. 3.
Fig. 5 is the software flow pattern of stress wave nondestructive detection system.
Embodiment
In order to illustrate our method, introduce basic concepts earlier.
1, stress wave is meant the elastic medium stress application, causes elastic deformation, because the continuity of medium, elastic deformation produces elastic force, and elastic force causes elastic deformation.Thus, in the inner wave propagation form that forms of medium, be referred to as elastic stress wave again.
2, the elastic modulus of timber
EBe meant that timber receives the ability of recovering its original shape and structure when stress causes deformation.It can reflect the physics and the mechanical property of timber.When there was the stress wave propagation in timber inside, following equality was set up:
In the following formula,
VThe velocity of propagation of expression stress wave in timber,
ρThe density of expression timber.
3, Non-Destructive Testing (Non destructive Testing or Non destructive Evaluation are called for short NDT or NDE) claims that again non-destructive detects; Be meant that the different physical mechanicses that utilize material or chemical property are under the prerequisite of not destroying target object inside and surface structure and characteristic; Object correlation properties (like shape, displacement, stress, optical characteristics, fluid properties, mechanical property etc.) are carried out Test And Checkout, especially to the detection of various defectives.
4, slip (moving) average algorithm is meant a kind of simple smooth forecasting techniques, and its basic thought is: according to time series data, passing item by item, mean value when calculating the preface that comprises certain item number successively is with the method for reflection secular trend.Therefore; When seasonal effect in time series numerical value owing to receive the influence of cyclical swing and random fluctuation; Big rise and fall when being difficult for the development trend of the incident that demonstrates, uses moving average method can eliminate the influence of these factors; Demonstrate the developing direction and the trend (being Trendline) of incident, then according to the secular trend of Trendline analyses and prediction sequence.
In the utility model, the elastic modulus of timber
EBe an important parameter, it has reflected the physics and the mechanical property of timber, need compare the elastic mould value (canonical reference value) whether its elastic modulus size meets harmless timber for the quality testing of timber.For this reason, in real time, non-destructive ground detects and the quality of assessment lumber quality must at first be calculated its elastic modulus, but this parameter often can't directly obtain, can only measure indirectly.
We are known:
In the formula
VThe velocity of propagation of expression stress wave in timber, ρ representes the density of this material.Try to achieve
EKey be how to obtain
VFor a long time, measure relatively difficulty of the velocity of propagation of stress wave in timber.In order to address the above problem, we suppose that stress wave passes through length
LHomogeneous materials institute's time spent do
t, then
This just requires us accurately to measure stress wave
LTime of timber internal communication.
1, stress wave propagation Method Of Time Measurement
The main process of stress wave propagation time measurement is: the initiating terminal and the clearing end that two acceleration transducers are placed on tested timber respectively; Use pulse hammer to knock timber, produce and the conduction stress wave, when stress wave arrives " initial " end sensor; The detection system timer is started working; When it arrived " termination " end sensor, timer quit work, and preserved and corresponding display time.Microcontroller adopts the running mean algorithm that the measurement data sequence is handled, and calculates corresponding elastic modulus, and direct and canonical reference value compares, or supplies the user on PC, further to analyze and processing.
2, the design proposal of timber stress wave nondestructive detection system
Comprise signals collecting, signal Processing and three parts of microcontroller of conducting in regular turn; Wherein the signal acquisition part branch comprises acceleration transducer, pulse hammer, counter; Two stress wave pulse waveforms of the main conversion process of signal processing " initial " and " termination ", its structure is connected in sequence by sensor, impedance matching module, signal amplification circuit module, filtering shaping circuit module; Main being responsible for of microcontroller part measured the stress wave propagation time, and calculates the elastic modulus of tested timber.
Impedance matching module:
Sensor obtains the terminal resistance that meets a 10K behind the signal, and the magnitude of voltage that makes sensor obtain is more stable, reduces the noise of environment for sensor.Then insert the uA741 chip; UA741 adopts voltage follower to connect method; UA741 is the wideband low noise operational amplifier; Have very high input impedance and very low output impedance, be highly suitable for the signal condition of sensor rear end, make the signal of sensor acquisition and afterwards carry out impedance matching, conditioning between the one-level processing of circuit.Signal processing formula:
; (
is the value of the input signal voltage V,
is the output signal voltage V value) Signal frequency variation: 20KHz following frequencies do not change; signal phase changes:
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
.
The signal amplification circuit module:
Input signal is through inserting the signal amplification circuit module behind the impedance matching circuit, the signal amplification circuit functions of modules is intended to that sensor is obtained feeble signal and carries out undistorted amplification, for back one stage signal processing circuits is prepared.The signal amplification circuit module adopts OP07 high precision low noise operational amplifier, can be under the low noise state, and amplification input signal without distortion.Signal processing formula:
; signal frequency changes: 200KHz following frequencies do not change; signal phase changes:
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
,
signal phase shift rate
.
The filtering shaping circuit module:
Insert the filtering shaping circuit module behind the input signal process signal amplification circuit module amplifying signal; The filtering shaping circuit functions of modules is intended to suppress the high frequency interference noise signal; Obtain the standard of the signal of certain frequency in the shock stress ripple as signal research and processing; Filtering shaping circuit adopts the MAX7408 chip; MAX7408 is five rank, low pass, elliptic function, SCF; Can with the signal of upper frequency, acquisition cuicuit be tested the signal of needed certain frequency by
.Signal Processing formula:
(signal cutoff frequency); (
is the external clock incoming frequency, and
is cutoff frequency) signal frequency changes:
frequency cutoff; Signal phase changes: the signal phase of
frequency 50uS that all delays time; The signal of
frequency is by there not being phase place ripple signal.
Microcontroller part (comprising control module and display module among Fig. 3):
The timber nondestructive detection system that the utility model provides uses the ATmega16 single-chip microcomputer of the Atmel AVR of company series as controller; ATmega16 is 8 AVR single-chip microcomputers of high-performance, low-power consumption; Interrupt receiving by stress wave signal through " initial " and " termination " signal that signal conditioning circuit triggered with two the exterior I NT0 of ATmega16 and INT1; And the time of transmission is carried out timing with 8 bit timing device Timer0 of an inherence; After counting finishes through the algorithm correction; Data presentation on the graphic lcd of LCD12864 band character library, is saved the data on the FLASH in the sheet simultaneously, and the chronometric data that resets after delaying time register repeats to receive signal and preserve data again.Meanwhile can also the data of obtaining be sent to PC or other embedded devices through serial ports UART with stored history among the FLASH.
The running mean algorithm:
(moving) average algorithm that slides is meant a kind of simple smooth forecasting techniques, and its basic thought is: pass item by item according to time series, mean value when calculating the preface that comprises certain item number successively is with the method for reflection secular trend.Therefore; When seasonal effect in time series numerical value owing to receive the influence of cyclical swing and random fluctuation; Big rise and fall when being difficult for the development trend of the incident that demonstrates, uses moving average method can eliminate the influence of these factors; Demonstrate the developing direction and the trend (being Trendline) of incident, then according to the secular trend of Trendline analyses and prediction sequence.Specifically describe as follows:
NIndividual measurement data
x 1,
x 2,
x N Regard a formation as, the length of formation is fixed as
NAdopt the method for first in first out, promptly whenever carry out once new sampling, put into tail of the queue to measurement result, and remove data of original head of the queue, in formation, have all the time like this
NThe data of individual " up-to-date ".Output valve through after the running mean algorithm Filtering Processing is:
In the following formula,
Expression the
nOutput valve after the individual measurement data process Filtering Processing,
x N-i The measurement data of Filtering Processing is not passed through in expression,
NThe item number of expression running mean.
When practical application, because the user uses the dynamics of pulse hammer inhomogeneous, the bigger measurement data of deviation may appear once in a while.At this moment, we select to ignore this measurement data, skip running mean algorithm streamline, directly handle next measured value.
The equal outsourcing of all electronic devices and components that the utility model adopts obtains; The software that disposes in the stress wave nondestructive detection system can be write by the common software personnel, and the operational scheme of this software is by shown in Figure 5.
Embodiment 1 (see figure 1)
The first step is embedded into two screws in the tested wood sample 1, and initial sensor 4 links to each other with initial screw and pulse hammer 5, stops sensor 2 and links to each other with the terminal screw, and link to each other with detection system (i.e. signal processing 3 among the figure) through data cable.
Second step, open the detection system power switch, test environment is set.Comprise distance (distance between the screw) between timber kind, cycle tests number, cycle tests length (being the running mean item number), density of wood, the sensor etc.After the test environment setting finished, system carried out the test wait stage.
In the 3rd step, the tester uses pulse hammer to knock the initiating terminal screw, produces stress wave, makes it at timber internal communication (arrow is represented the direction of propagation among the figure).Initial sensor acquisition start signal, the detection trigger system picks up counting, and after the termination sensor received stress wave signal, the detection trigger system stopped timing, obtained stress wave thus in timber inner travel-time and speed.After follow-on test repeatedly (was determined by cycle tests length), system utilized the running mean algorithm to calculate the Spreading Velocity of Stress Wave of this wheel measurement, obtains the measured value of modulus of elasticity of wood thus.
Embodiment 2 (see figure 2)s
In order accurately to locate the timber inherent vice, need take multiple measurements wood sample from a plurality of directions, obtain the test result of different directions, to confirm the position and the defect level of timber inherent vice more accurately.Fig. 2 representes the xsect of tested timber, wherein
A, b, c, d, e, fRepresent six check points (3 initial sensors being installed, 3 termination sensors respectively) respectively, 7 expressions of figure middle body are inner rotten.The user detects from 9 directions successively, obtains different Spreading Velocity of Stress Wave and modulus of elasticity of wood, according to these measurement results, can confirm the size and the position of timber inherent vice more exactly.
Claims (5)
1. based on the timber nondestructive detection system of stress wave technology, comprise signals collecting, signal Processing and three parts of microcontroller of conducting in regular turn; Wherein the signal acquisition part branch comprises acceleration transducer, pulse hammer, counter; Signal processing is connected in sequence by impedance matching module, signal amplification circuit module, the filtering shaping circuit module of conversion process " initial " and " termination " two stress wave pulse waveforms; The input end of microcontroller part and the output terminal of signal processing are connected, with the elastic modulus of calculated stress wave propagation time and tested timber.
2. the timber nondestructive detection system based on the stress wave technology according to claim 1 is characterized in that described impedance matching module adopts the uA741 chip, and acceleration transducer is through inserting this chip behind the resistance.
3. the timber nondestructive detection system based on the stress wave technology according to claim 1 is characterized in that described signal amplification circuit module adopts the OP07 chip, and the output terminal of impedance matching module inserts the input end of this chip.
4. the timber nondestructive detection system based on the stress wave technology according to claim 1 is characterized in that described filtering shaping circuit module adopts the MAX7408 chip, and the output terminal of signal amplification circuit module inserts the input end of this chip.
5. according to claim 2 or 3 or 4 described timber nondestructive detection systems, it is characterized in that described microcontroller adopts the ATmega16 single-chip microcomputer based on the stress wave technology.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105181806A (en) * | 2015-08-05 | 2015-12-23 | 浙江农林大学 | Multichannel triggering based stress wave nondestructive testing data correction method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105181806A (en) * | 2015-08-05 | 2015-12-23 | 浙江农林大学 | Multichannel triggering based stress wave nondestructive testing data correction method |
| CN105181806B (en) * | 2015-08-05 | 2018-01-23 | 浙江农林大学 | Stress wave nondestructive testing data correcting method based on multichannel triggering |
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Granted publication date: 20120523 Termination date: 20120825 |