Technology for detecting density of furniture board by using acoustic principle

Abstract

This invention discloses a technology for detecting the density of furniture board materials using acoustic principles, belonging to the field of furniture board material testing technology. The technology includes an acoustic signal transmitting module, an acoustic signal receiving module, a signal preprocessing module, a density calculation module, an error correction module, a result output module, and a board material positioning module. These modules communicate bidirectionally via a hybrid embedded bus and employ a closed-loop collaborative control mode. The transmitting module emits a 1.2MHz-2.8MHz high-frequency narrow-pulse acoustic signal, which is focused onto the board material by a sound-gathering structure. The receiving module receives the signal penetrating the board material and converts it into an electrical signal. Finally, the output module displays and stores the detection results. This invention achieves non-contact, non-destructive, and high-precision detection with a detection error ≤ ±0.5 kg / m³. 3 With a testing efficiency of ≥120 pieces / hour, it is highly versatile, has good anti-interference capabilities, and is suitable for batch testing of various furniture boards.

Description

Technical Field

[0001] This invention belongs to the field of furniture board testing technology, specifically involving a technology for detecting the density of furniture boards using acoustic principles. It is mainly applied in the furniture production process to perform non-contact, high-precision, and rapid testing of the density of various furniture boards, such as wood-based panels, engineered wood panels (particleboard, MDF, etc.), and bamboo panels, providing reliable technical support for the quality control of furniture boards. Background Technology

[0002] The density of furniture boards is a core indicator determining the strength, stability, durability, and environmental performance of furniture products, directly affecting their lifespan and safety. Therefore, in the process of large-scale furniture production, accurate and efficient density testing of various furniture boards is a crucial step in ensuring product quality. Currently, existing furniture board density testing technologies in the industry are mainly divided into two categories: destructive testing and non-destructive testing. Both types of technologies have obvious defects and limitations, failing to meet the core requirements of modern furniture production for high precision, high efficiency, non-destructive testing, and strong versatility. Furthermore, they differ fundamentally from the core design of this technology and cannot achieve the testing results achievable by this technology. Existing destructive testing technologies, such as the sampling and weighing method, rely on a core principle of cutting standard-sized samples from the board material to be tested, measuring the sample's mass using a balance, measuring its volume using calipers, and then calculating the board's density using the mass-to-volume ratio. While this method theoretically possesses a certain level of accuracy, it suffers from numerous insurmountable drawbacks. It requires destructive sampling of the board material, rendering it unusable for production and resulting in significant waste of raw materials. Furthermore, the sampling, measurement, and calculation processes are cumbersome, leading to extremely low testing efficiency; testing a single board typically takes several minutes or even longer, making continuous online testing in mass production impossible. It is only suitable for small-batch laboratory sample testing and is unsuitable for large-scale furniture production scenarios, completely contradicting the design philosophy of this technology: non-contact, non-destructive, and rapid batch testing. Existing non-destructive testing technologies mainly include X-ray testing, traditional ultrasonic testing, and vibration testing. All of these technologies have significant shortcomings and do not employ the core technologies of this technology, such as high-frequency narrow-pulse acoustic design, improved correlation algorithms, and multi-factor coupling error correction. Their detection accuracy and efficiency are far lower than this technology. X-ray testing, in particular, uses X-rays and gamma rays to penetrate the board material and calculate its density based on the attenuation of the rays. While this method is relatively fast, the radiation is highly radioactive, posing a serious health hazard to operators. Furthermore, X-ray testing equipment is extremely expensive to manufacture and maintain, bulky, and requires specialized protective equipment, making it unsuitable for ordinary furniture manufacturers, especially small and medium-sized enterprises. Its detection accuracy is also significantly affected by the uniformity of the board material, making it impossible to accurately test different types of boards. This is completely different from the environmentally friendly, low-cost, and highly versatile design of this technology. Existing traditional ultrasonic testing methods are currently widely used non-destructive testing technologies, but their core design differs fundamentally from this technology, failing to achieve the same testing accuracy and stability. Existing traditional ultrasonic testing methods mostly use low-frequency ultrasonic signals, typically with transmission frequencies below 1MHz, unlike the 1.2MHz-2.8MHz high-frequency narrow pulse design of this technology. This results in severe acoustic signal diffusion, making precise signal focusing impossible, leading to a larger detection area that is easily affected by impurities and textures on the board surface, resulting in low detection accuracy. Furthermore, the transmitting module of existing traditional ultrasonic testing methods lacks an arc-shaped sound-focusing structure, failing to focus the acoustic signal on a specific area of ​​the board surface for testing. This results in low signal utilization, and the transmission power and frequency cannot be adaptively adjusted according to the board thickness, limiting its application to boards of fixed thickness and severely limiting its versatility. Their receiving modules use ordinary piezoelectric sensors without a double-layer copper mesh anti-interference shield, resulting in weak resistance to external electromagnetic interference and environmental noise. The signal-to-noise ratio is typically below 70dB, far lower than the 85dB or more of this technology, making the received signal susceptible to interference and leading to larger detection errors. Existing traditional ultrasonic testing methods have simple signal preprocessing modules. The filtering units often use first-order filter circuits instead of the second-order active bandpass filter circuits used in this technology, resulting in poor filtering performance and an inability to effectively remove interference signals. Filter attenuation is typically greater than 1dB, and the cutoff frequency cannot be adaptively matched to the transmission frequency, leading to significant interference components in the preprocessed signal. The amplification units use ordinary operational amplifiers instead of low-noise differential amplification structures, resulting in large input offset voltages and bias currents. The amplification factor cannot be adjusted in stages, and the common-mode rejection ratio is typically below 80dB, failing to effectively suppress common-mode interference and causing severe signal distortion after amplification. The A / D conversion units often use 8-bit or 12-bit analog-to-digital converters with conversion rates below 500kSps and conversion errors greater than ±0.1%, failing to achieve high-speed, high-precision acoustic signal conversion. This is significantly different from the 16-bit high-speed A / D conversion, conversion rate ≥1MSps, and conversion error ≤±0.01% design of this technology. Existing traditional ultrasonic testing methods calculate density using a simple linear fitting algorithm, relying solely on the linear relationship between ultrasonic signal propagation speed and density. This method does not employ the improved quadratic polynomial correlation algorithm used in this technology, nor does it incorporate material correction factors or thickness compensation mechanisms. Consequently, it fails to account for differences in the acoustic properties of different materials and cannot compensate for the impact of thickness variations on the test results, resulting in significant detection errors, typically ≥ ±2 kg / m³. 3 This is significantly higher than the ±0.5 kg / m² corrected by this technology. 3 The detection error is within a certain range. Furthermore, existing traditional ultrasonic testing methods lack a dedicated error correction module, making it impossible to correct for major error sources during the testing process, such as temperature, humidity, and surface flatness of the board, in real time. The test results are greatly affected by environmental factors and the surface condition of the board, resulting in extremely poor stability and an inability to achieve accurate detection. Existing vibration testing methods calculate board density by measuring the vibration frequency of the board. This method's principle is completely different from the acoustic penetration testing principle of this technology and has significant limitations. The accuracy of this method is greatly affected by the board's size, shape, and thickness, limiting its application to boards of fixed sizes and shapes. It has extremely poor versatility and cannot meet the testing needs of furniture boards of different sizes and materials, which is completely inconsistent with the design of this technology, which can adapt to various boards with lengths of 500mm-2000mm, widths of 300mm-1500mm, and thicknesses of 1mm-50mm. Furthermore, the vibration testing method has extremely low efficiency, typically requiring tens of seconds to test a single board, making continuous batch testing impossible. Its accuracy is also significantly affected by external vibration interference, making it unsuitable for stable operation in the complex environments of industrial production. Furthermore, existing non-destructive testing technologies often use a single bus for communication between modules. The hybrid bus structure combining CAN and SPI buses, which does not employ this technology, suffers from slow data transmission speeds, with communication rates typically below 1 Mbps and communication error rates exceeding 10%. -8 The current technology fails to achieve high-speed and stable data transmission between modules. Furthermore, the bus interface lacks overvoltage and overcurrent protection circuits and a bus diagnostic unit, making it susceptible to damage due to voltage or current abnormalities. Real-time monitoring of bus communication status is also impossible, hindering rapid troubleshooting and impacting the continuity of testing. Most existing testing technologies lack dedicated board positioning modules or rely solely on simple mechanical positioning, failing to combine mechanical and optical positioning as employed in this technology. This results in extremely low positioning accuracy, typically greater than 1mm, failing to ensure that the acoustic signal transmission and reception points correspond to the same testing area on the board, leading to significant deviations in test results. Moreover, the positioning process is cumbersome, requiring repeated manual adjustments by operators, further reducing testing efficiency.

[0003] Existing detection technologies often employ simple output modules with limited digital display capabilities, lacking the high-definition industrial-grade LCD displays found in this technology. These modules cannot display real-time information such as density values, errors, and environmental parameters, resulting in low display accuracy and inability to adapt to harsh industrial environments with varying light levels. Data storage capacity is typically less than 4GB, insufficient for storing large amounts of data, and lacks support for high-speed USB export, making data traceability and analysis extremely inconvenient. Furthermore, the absence of audible and visual alarms prevents timely alerts to operators of defective materials, impacting quality control efficiency. Simultaneously, existing acoustic transmitters often utilize ordinary piezoelectric ceramic materials with low piezoelectric constants and electromechanical coupling coefficients, resulting in short lifespans (typically less than 5000 hours). The lack of heat dissipation structures leads to significant temperature increases during operation, causing unstable transmission frequencies and affecting detection accuracy. Finally, the acoustic sensors lack gold-plated receiving surfaces and flexible connection designs, resulting in low receiving sensitivity, severe signal attenuation, and susceptibility to external vibrations, further reducing detection stability. In summary, existing technologies for detecting the density of furniture boards suffer from numerous drawbacks, including low accuracy, large errors, weak anti-interference capabilities, poor versatility, low efficiency, inability to conduct destructive testing in batches, poor environmental friendliness, high cost, and poor stability. Furthermore, none of these technologies utilize the core design of this new technology, failing to meet the demands of modern furniture production for high-precision, high-efficiency, non-destructive, versatile, environmentally friendly, low-cost, and reliable detection of board density. Therefore, there is an urgent need to develop a technology that utilizes acoustic principles to detect the density of furniture boards, overcoming all the shortcomings of existing technologies. Through novel module design, algorithm design, and structural design, this technology can achieve accurate, rapid, non-destructive, and batch detection of furniture board density. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing furniture board density testing technologies, such as low detection accuracy, large errors, weak anti-interference ability, poor versatility, low detection efficiency, and the inability to apply destructive testing in batches. This invention provides a technology for detecting furniture board density using acoustic principles, achieving non-contact, high-precision, rapid, and environmentally friendly detection of furniture board density. This improves detection accuracy and efficiency, reduces detection costs, enhances the versatility and anti-interference ability of the detection technology, meets the needs of batch testing in furniture production, and provides reliable support for furniture board quality control.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a technology for detecting the density of furniture board using acoustic principles, including an acoustic signal transmitting module, an acoustic signal receiving module, a signal preprocessing module, a density calculation module, an error correction module, and a result output module. Each module is connected bidirectionally via an embedded bus and adopts a closed-loop collaborative control mode to achieve non-contact, high-precision detection of furniture board density. The acoustic signal transmission module uses a high-frequency narrow-pulse acoustic transmitter. The transmission frequency is continuously adjustable within the range of 1.2MHz-2.8MHz, the transmission pulse width is set to 80ns-150ns, and the transmission power can be adaptively adjusted between 0.8W-3.2W according to the thickness of the board. The transmitting end is equipped with an arc-shaped sound focusing structure with a sound focusing angle of 35°-55°, which can focus the acoustic signal on a designated area of ​​the board detection surface. The diameter of the focusing point is controlled within 0.3mm-0.8mm to avoid detection errors caused by signal diffusion. The acoustic signal receiving module uses a high-sensitivity piezoelectric acoustic sensor with a receiving frequency response range of 0.8MHz-3.2MHz, a signal-to-noise ratio of ≥85dB, and a sampling frequency of 10MHz-20MHz. The receiving end is equipped with an anti-interference shield, which adopts a double-layer copper mesh structure with a mesh diameter of 0.1mm-0.2mm. This effectively shields against external electromagnetic interference and environmental noise. The vertical distance between the sensor and the detection surface of the board is fixed at 5mm-12mm, and the distance can be adjusted in steps through a micro-adjustment mechanism with an adjustment accuracy of 0.1mm. The signal preprocessing module includes a filtering unit, an amplification unit, a shaping unit, and an A / D conversion unit. The filtering unit uses a second-order active bandpass filter circuit, and the cutoff frequency can be adaptively matched according to the transmission frequency. The filter attenuation is ≤0.5dB. The amplification unit uses a low-noise operational amplifier, and the amplification factor can be adjusted in stages between 100x and 1000x with an adjustment step size of 50x. The shaping unit uses a Schmitt trigger to shape the irregular received signal into a standard square wave signal. The A / D conversion unit uses a 16-bit high-speed analog-to-digital converter with a conversion rate ≥1MSps and a conversion error ≤±0.01%, ensuring that the preprocessed signal meets the accuracy requirements for density calculation. The density calculation module is based on an improved acoustic propagation speed and density correlation algorithm, combined with the plate thickness compensation coefficient, to achieve accurate density calculation; The error correction module uses a multi-factor coupled correction algorithm to correct errors caused by temperature, humidity and surface flatness of the board in real time. The result output module adopts an integrated design of digital display and data storage, which can display the detection density value, detection error and detection time in real time, and can export the detection data via USB interface. The storage capacity is ≥16GB and the data storage format is CSV, which facilitates subsequent data traceability and analysis.

[0006] Furthermore, the high-frequency narrow-pulse acoustic transmitter of the acoustic signal transmission module is made of aluminum nitride (AlN) piezoelectric ceramic material, with a piezoelectric constant d33≥350pC / N, an electromechanical coupling coefficient kp≥0.65, an operating temperature range of -10℃-60℃, and a service life of ≥10000 hours; The transmitter's drive circuit adopts a constant current drive mode, with a drive current range of 10mA-50mA and a drive voltage range of 5V-24V. The rise time of the drive signal is ≤10ns and the fall time is ≤10ns, which can effectively ensure the stability and narrow pulse characteristics of the transmitted signal. The arc-shaped sound-gathering structure is made of polytetrafluoroethylene (PTFE) material with a thickness of 2mm-5mm. The inner surface of the sound-gathering structure is polished, with a surface roughness Ra≤0.1μm, which can reduce the reflection loss of acoustic signals on the surface of the sound-gathering structure and achieve a sound-gathering efficiency ≥90%. The sound-focusing structure and the transmitter are connected by ultrasonic welding with a welding strength of ≥5MPa. A sealing gasket is installed at the weld joint. The sealing gasket is made of silicone rubber material with a thickness of 0.5mm-1mm to prevent dust and moisture from entering the transmitter and affecting the transmission performance. The transmitter's mounting base is made of aluminum alloy and has heat dissipation grooves. The width of the grooves is 1mm-2mm, the depth is 3mm-5mm, and the spacing is 5mm-8mm. This effectively reduces the temperature of the transmitter during operation, keeping it below 40℃ to prevent excessive temperature from affecting the stability of the transmission frequency.

[0007] Furthermore, the high-sensitivity piezoelectric acoustic sensor of the acoustic signal receiving module is made of lead zirconate titanate (PZT) piezoelectric ceramic material, with a piezoelectric constant d31≥-180pC / N, electromechanical coupling coefficient kt≥0.55, receiving sensitivity≥100mV / Pa, and frequency stability≤±0.1% / ℃; The receiving surface of the sensor is gold-plated with a thickness of 0.1μm-0.2μm, which can improve the reception efficiency of acoustic signals and reduce signal attenuation. An insulating layer is provided between the double copper meshes of the anti-interference shielding cover. The insulating layer is made of polyimide material and has a thickness of 0.1mm-0.2mm. This can prevent the formation of eddy currents between the double copper meshes, which would affect the shielding effect. The shielding cover and the sensor are connected by an elastic connection. The elastic connector is made of polyurethane foam material with a hardness of Shore A30-A50, which can reduce the impact of external vibration on the sensor and the vibration attenuation is ≥20dB. The micro-adjustment mechanism adopts ball screw drive with a lead of 0.2mm-0.5mm, an adjustment range of 5mm-12mm, and an adjustment accuracy of 0.1mm. The drive motor of the adjustment mechanism adopts a micro stepper motor with a step angle of 1.8° and a speed range of 10r / min-50r / min. The motor drive circuit adopts microstepping drive mode with a microstepping factor of 8-32 times, which can achieve smoothness and high precision in the adjustment process. The sensor's posture remains unchanged during the adjustment process, ensuring the consistency of the received signal.

[0008] Furthermore, the transfer function of the second-order active bandpass filter circuit in the filtering unit of the signal preprocessing module is:

[0009] Where K is the gain of the filter circuit, and its value ranges from 0.8 to 1.2. The center angular frequency of the filter circuit. , Where is the transmission frequency of the acoustic signal, and Q is the quality factor, with a value ranging from 5 to 15. The Q value can be adaptively adjusted according to the change of transmission frequency to ensure the filtering effect. The low-noise operational amplifier of the amplification unit has an input offset voltage ≤10μV, an input bias current ≤1nA, an output voltage swing of 0V-20V, and a bandwidth ≥10MHz. The amplification circuit adopts a differential amplification structure, which can effectively suppress common-mode interference with a common-mode rejection ratio ≥100dB. The Schmitt trigger of the shaping unit has a threshold voltage adjustable between 0.5V and 5V, and a hysteresis voltage ≤0.1V. It can shape the preprocessed sinusoidal acoustic signal into a standard square wave signal with a duty cycle of 45%-55%, a rise time ≤5ns, and a fall time ≤5ns. The 16-bit high-speed analog-to-digital converter of the A / D conversion unit has a reference voltage of 2.5V±0.01V and a conversion time of ≤1μs. It adopts a pipelined conversion structure, which can realize real-time sampling and conversion of acoustic signals. The converted digital signal is transmitted to the density calculation module through the SPI interface with a transmission rate of ≥10Mbps.

[0010] Furthermore, the improved acoustic propagation speed and density correlation algorithm of the density calculation module, based on the intrinsic correlation between the acoustic characteristics and density of furniture boards, and combined with board thickness compensation, breaks through the linear fitting limitations of existing algorithms, and adopts a combination of quadratic polynomial fitting and correction factors. The specific calculation process is as follows: The first step involves collecting the propagation time t of the acoustic signal in the furniture board through the acoustic signal transmitting and receiving modules, and simultaneously collecting the actual thickness h of the board through the thickness detection unit. The thickness detection unit uses a laser rangefinder sensor with a ranging accuracy of 0.01mm and a ranging range of 1mm-50mm. The second step is to calculate the propagation speed v of the acoustic signal in the board material. The calculation formula is:

[0011] Where h is the actual thickness of the board (unit: m), t is the acoustic signal propagation time (unit: s), and v is the propagation speed (unit: m / s). The third step is to introduce a material correction factor λ for the board material. λ is adaptively adjusted according to the material type of the furniture board. The value of λ for wood-based boards is 0.85-0.95, the value of λ for engineered wood-based boards (particleboard, MDF) is 0.90-1.00, and the value of λ for bamboo-based boards is 0.88-0.98. The fourth step is to calculate the density ρ of the sheet material using the improved correlation formula. The improved correlation formula is as follows:

[0012] Where a, b, and c are fitting coefficients, a = -0.0002 ± 0.00001, b = 0.35 ± 0.01, and c = -120 ± 5. This is the propagation speed deviation value. , ρ is the standard propagation speed of the material (unit: m / s), and ρ is the density of the material (unit: kg / m³). The fifth step is to perform preliminary smoothing on the calculated density values ​​using a moving average filtering algorithm with a filter window size of 5-10. This reduces the impact of random errors on the density calculation results. The smoothed density values ​​are the preliminary detection results.

[0013] Furthermore, the multi-factor coupled correction algorithm of the error correction module, targeting the three main error sources of temperature, humidity, and surface flatness of the board, adopts a coupled correction model to achieve real-time and accurate error correction. The specific correction process is as follows: The first step involves collecting the ambient temperature T (unit: °C) using a temperature sensor. The temperature sensor's measurement range is -10 °C to 60 °C, and its measurement accuracy is ±0.1 °C. The second step involves collecting the ambient humidity H (unit: %RH) using a humidity sensor. The humidity sensor's measurement range is 20% to 90%RH, and its measurement accuracy is ±1%RH. The third step involves collecting the surface flatness deviation δ (unit: mm) of the board material using a laser flatness detection unit. The flatness detection accuracy is ±0.005 mm. The second step is to establish a temperature error correction factor. Humidity error correction factor and flatness error correction factor The calculation model uses the following formula to calculate the temperature error correction factor:

[0014] 25℃ is the standard testing temperature. When the temperature deviates from 25℃, it will be detected by... Correct the density value; The formula for calculating the humidity error correction factor is: ; 50%RH is the standard test humidity. When the humidity deviates from 50%RH, it is detected by... Correct the density value; The formula for calculating the flatness error correction factor is:

[0015] When there is a flatness deviation on the surface of the board, by Correct the density value; The third step involves establishing a multi-factor coupling correction formula to analyze the preliminary detection results obtained from the density calculation module. The coupling correction formula is as follows:

[0016] Where ρ is the corrected final density measurement value (unit: kg / m³). 3 The corrected detection error is ≤ ±0.5 kg / m 3 To ensure the accuracy of the test results; The fourth step involves the correction module collecting various environmental and material parameters in real time, performing an error correction calculation every 10ms to achieve dynamic tracking and correction of errors, adapting to changes in different testing environments and material conditions.

[0017] Furthermore, the result output module includes an LCD screen, a data storage unit, a USB interface, and an alarm unit; The LCD screen is a high-definition industrial-grade display with a screen size of 3.5 inches to 5 inches, a resolution of 800×480 pixels, and a brightness of up to 50 cd / m². 2 -300cd / m 2 The parameters can be adjusted between these ranges, and the system can display parameters such as the detected density value, detection error, detection time, ambient temperature, ambient humidity, and board thickness in real time, with a display accuracy of 0.1 kg / m². 3 The screen response time is ≤50ms, which can adapt to strong light and weak light scenarios in industrial testing environments; The data storage unit uses a Flash storage chip with a storage capacity of ≥16GB, which can store ≥100,000 sets of detection data. The data storage adopts a cyclic overwrite mode. When the storage capacity is full, the oldest detection data is automatically overwritten. At the same time, the data storage trigger conditions can be manually set, supporting single detection storage and continuous detection timed storage (the storage interval can be adjusted between 1s and 60s). The USB interface uses a USB 3.0 interface with a transmission rate of ≥5Gbps, supports hot-swapping, and can be directly connected to devices such as computers and printers to export test data for subsequent analysis and printing. It also supports firmware upgrades for the device via the USB interface. The alarm unit adopts an audible and visual alarm mode with a preset density acceptable range. When the detected density value exceeds the acceptable range, the alarm unit is automatically triggered. The audible alarm volume is ≥80dB, and the alarm frequency is 1kHz-2kHz. The visual alarm uses a red LED light with a flashing frequency of 1-2 times / second. At the same time, the alarm prompt information is displayed on the screen. The alarm status can be cleared by manually pressing a button, or it can be set to automatically clear when the next set of data is detected, which makes it convenient for operators to promptly detect unqualified boards.

[0018] Furthermore, it also includes a board positioning module, which uses a combination of mechanical and optical positioning to achieve precise positioning of furniture boards, ensuring that the emission point and reception point of the acoustic signal correspond to the same detection area of ​​the board. The mechanical positioning unit includes a positioning clamp and an adjustment platform. The positioning clamp adopts an adjustable structure to adapt to furniture boards of different sizes (length 500mm-2000mm, width 300mm-1500mm, thickness 1mm-50mm). The clamping force of the clamp can be adjusted between 50N-200N. The clamping surface is made of rubber material with a thickness of 1mm-2mm to prevent damage to the surface of the board during clamping. The adjustment platform adopts an XYZ three-axis adjustment structure. The adjustment range of the X and Y axes is 0mm-500mm with an adjustment accuracy of 0.1mm, and the adjustment range of the Z axis is 0mm-100mm with an adjustment accuracy of 0.1mm. It can realize precise adjustment of the board in the horizontal and vertical directions. The optical positioning unit includes two laser positioners, which are respectively installed on one side of the acoustic signal transmitting module and the receiving module. The laser positioners emit red lasers with a wavelength of 650nm and a laser spot diameter of 0.1mm-0.2mm. The laser beams of the two laser positioners coincide at the focal point of the board detection surface. The operator can quickly locate the detection area through the laser spot, with a positioning error ≤0.1mm. The positioning module is linked with each detection module. After the board is positioned, the system automatically triggers the acoustic signal transmission and reception to start density detection. After the detection is completed, the positioning fixture is automatically released, which facilitates the operator to change the board and improves the detection efficiency. The detection time for a single board is ≤3s.

[0019] Furthermore, the embedded bus adopts a hybrid bus structure combining CAN bus and SPI bus. The CAN bus is used for communication between the acoustic signal transmitting module, receiving module, and error correction module, with a communication rate of 1Mbps-5Mbps, a communication distance ≤100m, and a communication bit error rate ≤10%. -9 It enables high-speed and stable data transmission; the SPI bus is used for communication between the signal preprocessing module, density calculation module, and result output module, with a communication rate of 10Mbps-50Mbps, a communication distance ≤10m, and a communication bit error rate ≤10%. -10 It enables rapid transmission of real-time data; The bus interface adopts a differential interface design and is equipped with overvoltage and overcurrent protection circuits. The overvoltage protection threshold is 36V and the overcurrent protection threshold is 1A, which can prevent the bus interface from being damaged due to abnormal voltage or current. The system is also equipped with a bus diagnostic unit, which can detect the communication status of the bus in real time. When a bus communication abnormality is detected (such as open circuit, short circuit, or excessive bit error rate), the alarm unit is automatically triggered and the fault information is displayed in the result output module. The fault information includes the fault module, fault type and fault occurrence time, which makes it easy for operators to quickly troubleshoot the fault. Bus communication uses encrypted transmission with AES-128 encryption algorithm to prevent detection data from being tampered with or stolen, ensuring data security and confidentiality.

[0020] Furthermore, the detection process of this technology includes the following steps: Step 1: Device initialization. Connect the power supply. The system will automatically perform self-tests on each module. The self-test includes the transmission frequency and power of the acoustic signal transmitting module, the sensitivity and signal-to-noise ratio of the acoustic signal receiving module, the filtering and amplification effects of the signal preprocessing module, the algorithm operation status of the density calculation module, the sensor status of the error correction module, and the display and storage functions of the result output module. The self-test time is ≤5 seconds. After the self-test is passed, the system enters standby mode and the display shows "Standby Ready". If the self-test fails, the corresponding fault information will be displayed and an alarm will be triggered. Step 2, board positioning: Place the furniture board to be inspected on the adjustment platform of the positioning module, and clamp and fix the board with mechanical positioning fixtures. Adjust the XYZ three-axis adjustment platform so that the laser spot of the optical positioning unit coincides with the detection area of ​​the board. After positioning is completed, press the detection start button. Step 3: Environmental and board parameter acquisition. The temperature sensor, humidity sensor, and flatness detection unit of the error correction module acquire the temperature T, humidity H, and flatness deviation δ of the detection environment in real time. The thickness detection unit acquires the actual thickness h of the board. After the acquisition is completed, the parameters are transmitted to the density calculation module and the error correction module. Step 4, Acoustic signal transmission and reception: The acoustic signal transmission module adaptively adjusts the transmission power, frequency and pulse width according to the thickness of the board material to transmit high-frequency narrow pulse acoustic signals to the detection area of ​​the board material. After the acoustic signals penetrate the board material, they are received by the acoustic signal receiving module. The receiving module converts the acoustic signals into electrical signals and transmits them to the signal preprocessing module. Step 5, signal preprocessing: The signal preprocessing module filters, amplifies, shapes, and performs A / D conversion on the received electrical signal, removes interference signals, converts the analog signal into a digital signal, and transmits it to the density calculation module. Step 6, density calculation and error correction: The density calculation module calculates the propagation time t of the acoustic signal in the board material based on the preprocessed digital signal, calculates the propagation velocity v in combination with the board thickness h, and then calculates the preliminary density value using an improved correlation formula. The error correction module calculates various error correction factors based on the collected environmental and material parameters, and applies a multi-factor coupling correction formula to correct these errors. After correction, the final density detection value ρ is obtained; Step 7, Result Output and Storage: The result output module displays the final density detection value, detection error, detection time, and various acquisition parameters in real time, and stores the detection data in the data storage unit. If the detection value exceeds the preset qualified range, an audible and visual alarm is triggered. Step 8: Inspection complete. The operator presses the stop button, the positioning fixture automatically releases, the inspected board is removed, and the system returns to standby mode, waiting for the next inspection. If continuous testing is required, simply repeat steps 2-7. The detection accuracy of this technology is ≥99.5%, and the detection efficiency is ≥120 pieces / hour. It can adapt to the density testing of furniture boards of different materials and sizes. Moreover, the testing process is free of consumables and causes no damage to the boards.

[0021] This invention provides a technology for detecting the density of furniture boards using acoustic principles, which has the following beneficial effects: This invention, based on acoustic principles, utilizes the collaborative work of an acoustic signal transmission module, an acoustic signal reception module, a signal preprocessing module, a density calculation module, an error correction module, a result output module, and a board positioning module. Employing a hybrid embedded bus communication and closed-loop collaborative control mode, and combining core technologies such as high-frequency narrow-pulse acoustic design, improved correlation algorithms, and multi-factor coupling error correction, it possesses numerous significant advantages compared to existing detection technologies. All these advantages correspond to the core design of the claims in this invention, accurately reflecting its innovation and practicality, completely avoiding the shortcomings of existing technologies, and fully meeting the diverse needs of modern furniture production for board density testing.

[0022] This invention boasts extremely high detection accuracy and minimal error, enabling precise detection of board density. This advantage is entirely based on the core design outlined in the claims, forming a stark contrast to existing technologies. The acoustic signal transmission module employs a 1.2MHz-2.8MHz high-frequency narrow-pulse acoustic transmitter with continuously adjustable transmission frequency and a pulse width controlled between 80ns and 150ns. This effectively reduces acoustic signal diffusion and improves signal focusing. Furthermore, the transmission power can be adaptively adjusted between 0.8W and 3.2W according to the board thickness, ensuring stable penetration of acoustic signals through boards of varying thicknesses. Simultaneously, the transmitting end features an arc-shaped focusing structure with a focusing angle of 35°-55° and a focal point diameter controlled between 0.3mm and 0.8mm. This allows for precise focusing of the acoustic signal onto a designated area of ​​the board's detection surface, further improving signal utilization and reducing detection errors caused by signal diffusion. The transmitting module is made of aluminum nitride (AlN) piezoelectric ceramic material with a piezoelectric constant d33≥350pC / N and an electromechanical coupling coefficient kp≥0.65, resulting in extremely high stability of the transmitted signal. In addition, the mounting base is equipped with heat dissipation slots, which can control the transmitter's operating temperature below 40℃, avoiding the impact of excessive temperature on the stability of the transmission frequency and ensuring the consistency of the transmitted signal.

[0023] The acoustic signal receiving module of this invention adopts a high-sensitivity piezoelectric acoustic sensor with a receiving frequency response range covering 0.8MHz-3.2MHz, which is precisely matched with the frequency range of the transmitting module. The signal-to-noise ratio is ≥85dB, which can effectively receive weak acoustic signals after penetrating the board and reduce the influence of environmental noise. The sampling frequency is set to 10MHz-20MHz, which can realize high-speed sampling of acoustic signals and ensure that subtle changes in the signal can be accurately captured. The receiving end is equipped with a double-layer copper mesh anti-interference shield with a mesh diameter of 0.1mm-0.2mm. A polyimide insulating layer is placed between the double copper mesh layers, which can effectively shield external electromagnetic interference and environmental noise, preventing interference signals from affecting the reception effect. The vertical distance between the sensor and the detection surface of the board can be adjusted in steps through a micro-adjustment mechanism driven by a ball screw, with an adjustment accuracy of 0.1mm. This ensures that the distance between the sensor and the detection surface of the board is always kept at the optimal state, improving the stability and consistency of the received signal. The receiving surface of the sensor is gold-plated with a gold plating layer thickness of 0.1μm-0.2μm, which can effectively improve the acoustic signal reception efficiency and reduce signal attenuation. The sensor and the shield are connected by a polyurethane foam elastic connection with vibration attenuation ≥20dB, which can reduce the impact of external vibration on the sensor and further improve the stability of the received signal.

[0024] The filtering unit of the signal preprocessing module of this invention adopts a second-order active bandpass filter circuit with a transfer function of Where K is 0.8-1.2, The Q value is 5-15, and the cutoff frequency can be adaptively matched according to the transmission frequency. The filter attenuation is ≤0.5dB, which can effectively remove external interference signals and retain useful acoustic signals. The amplification unit adopts a low-noise operational amplifier with an input offset voltage ≤10μV and an input bias current ≤1nA. It adopts a differential amplification structure with a common-mode rejection ratio ≥100dB, which can effectively suppress common-mode interference. The amplification factor can be adjusted in stages from 100x to 1000x with an adjustment step of 50x, and can adaptively adjust the amplification factor according to the strength of the received signal. The system ensures that the amplified signal is not distorted; the shaping unit uses a Schmitt trigger to shape irregular received signals into standard square wave signals with a duty cycle of 45%-55% and rise and fall times of ≤5ns, ensuring signal stability; the A / D conversion unit uses a 16-bit high-speed analog-to-digital converter with a conversion rate ≥1MSps, conversion error ≤±0.01%, and a reference voltage of 2.5V±0.01V, enabling high-speed and high-precision conversion of acoustic signals and providing an accurate signal basis for density calculation.

[0025] This invention achieves non-contact, non-destructive testing, effectively avoiding raw material waste and reducing testing costs. This advantage is unattainable by existing destructive testing technologies and is superior to some existing non-destructive testing technologies. This technology employs a detection method where acoustic signals penetrate the board material. Neither the acoustic signal transmitting nor receiving module directly contacts the board material, eliminating the need for destructive sampling and preventing any damage. The tested board material can continue to be used in production, effectively avoiding raw material waste and reducing production costs. Simultaneously, the non-contact testing method avoids surface wear and contamination, ensuring the production quality of the board material. Furthermore, the testing process requires no consumables, further reducing testing costs. This contrasts sharply with the raw material waste and high costs of existing destructive testing technologies and is also superior to some existing non-destructive testing technologies that require consumables.

[0026] This invention boasts extremely high testing efficiency, enabling continuous batch testing and fully meeting the demands of modern large-scale furniture production. This advantage is achieved through the collaborative design of the various modules outlined in the claims. The board positioning module of this technology combines mechanical and optical positioning. The mechanical positioning fixture is adaptable to boards of different sizes, with adjustable clamping force. The clamping surface is made of rubber to prevent damage to the board. The XYZ three-axis adjustment platform has an adjustment accuracy of 0.1mm. The optical positioning unit uses two red laser positioners with laser spot diameters of 0.1mm-0.2mm and a positioning error ≤0.1mm, enabling rapid and precise board positioning. After positioning, the system automatically triggers the testing process without manual intervention. This technology achieves a single board testing time of ≤3s and a testing efficiency of ≥120 boards / hour, far exceeding existing testing technologies. It also supports continuous batch testing. Operators only need to place and remove the boards to achieve fully automated testing, effectively reducing workload and improving production efficiency.

[0027] This invention boasts exceptional versatility, capable of detecting the density of furniture boards of varying materials and sizes, overcoming the limitations of existing testing technologies with poor versatility. The acoustic signal transmission power and frequency of this technology can be adaptively adjusted according to the board thickness, accommodating various boards with thicknesses ranging from 1mm to 50mm. The positioning fixture of the board positioning module can accommodate boards with lengths of 500mm to 2000mm and widths of 300mm to 1500mm, meeting the testing needs of furniture boards of different specifications. The density calculation module incorporates a material correction factor, which can adaptively adjust the correction factor based on the acoustic characteristics of different materials such as wood, artificial materials, and bamboo, ensuring the accuracy of test results for different materials. This enables precise testing of various furniture boards, with versatility far exceeding existing traditional ultrasonic and vibration testing methods. It eliminates the need for specialized testing equipment for boards of different materials and sizes, further reducing testing costs for enterprises.

[0028] This invention boasts strong anti-interference capabilities and excellent stability, enabling long-term stable operation in complex industrial production environments. This advantage is achieved through multiple anti-interference designs outlined in the claims. The acoustic signal receiving module is equipped with a double-layer copper mesh anti-interference shield, effectively shielding against external electromagnetic interference and environmental noise. The signal preprocessing module employs a differential amplification structure and a second-order active bandpass filter circuit, effectively suppressing common-mode interference and various external interference signals. An elastic connection is used between the acoustic sensor and the shield to reduce the impact of external vibrations. The transmitter is equipped with a heat dissipation vent to effectively control the operating temperature and ensure the stability of the transmission frequency. The modules utilize a hybrid bus structure combining CAN and SPI buses, with a CAN bus communication rate of 1Mbps-5Mbps, a communication distance ≤100m, and a bit error rate ≤10%. -9 The SPI bus communication rate is 10Mbps-50Mbps, the communication distance is ≤10m, and the bit error rate is ≤10%. -10 It can achieve high-speed and stable data transmission. The bus interface is equipped with overvoltage and overcurrent protection circuits. The overvoltage protection threshold is 36V and the overcurrent protection threshold is 1A, which can prevent the bus from being damaged due to abnormal voltage and current. The bus diagnostic unit can detect the communication status in real time, trigger an alarm and display fault information when abnormality occurs, which facilitates quick troubleshooting and ensures long-term stable operation of the equipment.

[0029] This invention is easy to operate, offers strong data traceability, and effectively improves the efficiency of quality control in furniture production. This technology adopts a fully automated testing design; operators only need to place the boards, position and start the process, and remove them after testing. They do not need to participate in complex testing procedures, making operation simple and convenient, requiring no professional testing technology training, thus lowering the barrier to entry for operators. The result output module uses a high-definition industrial-grade LCD display screen, with a screen size of 3.5 inches to 5 inches and a resolution of 800×480 pixels. The display brightness is adjustable, and it can display multiple parameters in real time, including the detected density value, detection error, detection time, ambient temperature, ambient humidity, and board thickness, with a display accuracy of 0.1 kg / m³. 3 It can adapt to various lighting scenarios in industrial testing environments; the data storage unit adopts Flash storage chips with a storage capacity of ≥16GB, which can store ≥100,000 sets of test data. It supports cyclic overwrite mode and timed storage, and can export test data at high speed via USB 3.0 interface with a transmission rate of ≥5Gbps, which facilitates the traceability, analysis and archiving of subsequent test data, and provides reliable data support for quality control in furniture production; the sound and light alarm unit can be automatically triggered when the test value exceeds the qualified range, with a sound volume of ≥80dB and a flashing red LED light, which makes it easy for operators to detect unqualified boards in time and improve the efficiency of quality control.

[0030] This invention is environmentally friendly and low-cost, suitable for all types of furniture manufacturers, especially small and medium-sized enterprises. This technology uses acoustic principles for detection, eliminating the need for radiation, chemical reagents, or any other polluting consumables. It produces no radioactive or chemical pollution, poses no harm to the health of operators, and is environmentally friendly, meeting the environmental protection requirements of modern industrial production. The modular structure of this technology is rationally designed, using conventional and low-cost materials. Its manufacturing cost is far lower than that of X-ray detection equipment and high-end ultrasonic detection equipment, and its maintenance cost is extremely low. The transmitter has a lifespan of ≥10,000 hours, and each module has a low failure rate and is easy to maintain, requiring no specialized maintenance personnel or complex maintenance equipment. This effectively reduces the investment and maintenance costs of testing equipment for enterprises, making it suitable for furniture manufacturers of all sizes, especially small and medium-sized enterprises with relatively weak financial and technical capabilities, and has broad application prospects.

[0031] The modules of this invention are scientifically and rationally designed, with strong synergy and stable and reliable overall performance. They can adapt to the complex environment of industrial production for a long time and have good scalability and upgradeability. The modules of this technology are connected bidirectionally via an embedded bus and adopt a closed-loop collaborative control mode. The modules work in a coordinated manner, enabling seamless connection of the detection process and further improving detection efficiency and stability. The bus communication of this technology uses AES-128 encryption to prevent tampering and theft of detection data, ensuring the security and confidentiality of the detection data. Simultaneously, the firmware of this technology can be upgraded via a USB interface, allowing for flexible upgrades of detection algorithms and equipment functions according to the needs of furniture production and technological developments. This extends the service life of the equipment, improves its applicability, and provides reliable technical support for the long-term development of enterprises. Attached Figure Description

[0032] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0033] Figure 1 This is a flowchart of the density testing process for wooden furniture boards according to the present invention; Figure 2 This is a flowchart of the density testing process for artificial furniture boards according to the present invention; Figure 3 This is a flowchart of the density testing process for bamboo furniture boards according to the present invention. Detailed Implementation

[0034] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] How to use: Equipment initialization operation: Upon powering on the equipment, the system automatically initiates self-test procedures for each module, focusing on the operational status of the acoustic signal transmitting module, acoustic signal receiving module, signal preprocessing module, density calculation module, error correction module, and result output module as described in claim 1. Simultaneously, it checks the board positioning module as described in claim 8 and the embedded bus communication status as described in claim 9. After self-test completion, the result output module displays a standby ready message. If a self-test fails, the corresponding faulty module name will be displayed for easy troubleshooting by the operator.

[0037] Board positioning operation: The operator places the furniture board to be tested on the adjustment platform of the board positioning module as described in claim 8, adjusts the positioning clamp to fix the board, adjusts the XYZ three-axis adjustment platform according to the board size, and aligns the board detection area with the focal point of the acoustic signal transmitting module and the receiving end of the acoustic signal receiving module as described in claim 1 through the laser spot of the optical positioning unit, ensuring that the transmitting point and the receiving point correspond to the same detection area. After positioning is completed, the adjustment platform is locked.

[0038] Preset detection parameters: By using the operation buttons of the result output module as described in claim 7, the material type of the board to be tested is preset, corresponding to the value range of the material correction factor λ as described in claim 5, without the need to manually input specific values; at the same time, the qualified density range of the board is preset for subsequent alarm judgment, and the preset parameters are automatically transmitted to the density calculation module and the error correction module.

[0039] Acoustic signal transmission adjustment operation: Based on the thickness of the material to be tested, the system automatically adjusts the transmission power, transmission frequency, and transmission pulse width of the acoustic signal transmission module described in claims 1 and 2 to ensure that the transmission power is within the range of 0.8W-3.2W and the transmission frequency is within the range of 1.2MHz-2.8MHz. The arc-shaped sound-focusing structure at the transmitting end automatically focuses the signal, and the diameter of the focal point is controlled within the specified range.

[0040] Receiver module debugging operation: Adjust the micro adjustment mechanism of the acoustic signal receiving module as described in claims 1 and 3 so that the vertical distance between the sensor and the detection surface of the board is within the range of 5mm-12mm, ensure that the anti-interference shield of the receiving end works normally, reduce external interference, and at the same time start the sampling function of the receiving module to ensure that the signal-to-noise ratio meets the requirement of ≥85dB.

[0041] Signal preprocessing and density detection operation: When the detection button is activated, the acoustic signal transmitting module described in claim 1 transmits an acoustic signal to the detection area of ​​the board material. After the signal penetrates the board material, it is received by the acoustic signal receiving module. The receiving module converts the acoustic signal into an electrical signal and transmits it to the signal preprocessing module described in claim 4. The preprocessing module sequentially performs filtering, amplification, shaping, and A / D conversion. The processed signal is then transmitted to the density calculation module.

[0042] Density calculation and error correction operation: The density calculation module of claim 5 calculates the preliminary density value based on the preprocessed signal, combined with the plate thickness and the preset material correction factor, through an improved correlation formula; at the same time, the error correction module of claim 6 collects the ambient temperature, humidity and plate surface flatness parameters, and corrects the preliminary density value through a multi-factor coupling correction formula to obtain the final test result.

[0043] Viewing and storing test results: The result output module described in claim 7 displays the final density detection value, detection error, and related parameters in real time. If the detection value exceeds the preset acceptable range, the audible and visual alarm unit is automatically triggered. Operators can view the test results, and the test data is automatically stored to the data storage unit. It supports export via USB interface in CSV format.

[0044] Continuous Testing and Equipment Shutdown: After a single board piece is tested, the clamps on the board positioning module automatically release, allowing the operator to remove the board. Repeating steps 2-8 enables continuous batch testing. After the testing is completed, turn off the equipment power, clean the surface impurities of the board positioning module and each testing module to ensure normal operation of the equipment next time, and back up the testing data.

[0045] This method is fully aligned with actual production practices, is easy to operate, and requires no expertise in complex technical principles or data calculations. All steps correspond to the relevant reference numerals and names in the claims, completely bypassing the operational procedures of existing testing technologies and ensuring efficient and accurate testing. Example:

[0046] Example 1: Density Testing of Wooden Furniture Boards This embodiment focuses on density testing of wood-based furniture boards, following the aforementioned method and steps throughout. All modules and operations strictly correspond to the relevant names and reference numerals in the claims. The specific implementation process is as follows: First, the equipment is initialized by turning on the main power. The system automatically starts the self-test process of each module, focusing on testing the working status of the acoustic signal transmitting module, acoustic signal receiving module, signal preprocessing module, density calculation module, error correction module, and result output module as described in claim 1. At the same time, the board positioning module as described in claim 8 and the embedded bus communication status as described in claim 9 are also tested to ensure that each module and bus can work normally. After the self-test is completed, the result output module as described in claim 7 displays a standby ready prompt and enters the test preparation state.

[0047] The board positioning operation is then performed. The operator places the wooden furniture board to be tested stably on the adjustment platform of the board positioning module described in claim 8. The positioning fixture is adjusted to firmly fix the board and prevent displacement during the testing process. According to the actual size of the wooden board, the XYZ three-axis adjustment platform of the board positioning module is adjusted. Through the laser spot of the optical positioning unit, the preset detection area of ​​the board is accurately aligned with the focusing point of the acoustic signal transmitting module and the receiving end of the acoustic signal receiving module described in claim 1, ensuring that the emission point and the receiving point of the acoustic signal correspond to the same detection area of ​​the board. After accurate positioning, the adjustment platform is locked to complete the board positioning.

[0048] Next, the detection parameters are preset. Using the operation buttons of the result output module described in claim 7, the material type of the board to be tested is preset to wood. The system automatically matches the corresponding value range of the material correction factor λ described in claim 5, without requiring the operator to manually input any values. At the same time, based on the conventional qualified standards for wooden furniture boards, the qualified range of board density is preset for subsequent judgment of test results. After the preset is completed, the relevant parameters are automatically transmitted to the density calculation module described in claim 5 and the error correction module described in claim 6 via the embedded bus to complete the parameter preset.

[0049] Then, the acoustic signal transmission adjustment operation is performed. The system automatically adjusts the transmission power, transmission frequency and transmission pulse width of the acoustic signal transmission module described in claims 1 and 2 according to the actual thickness of the wood board to be tested, so as to ensure that the transmission power, transmission frequency and pulse width are within the range specified in the claims. At the same time, the arc-shaped sound focusing structure of the acoustic signal transmission module automatically focuses the acoustic signal, so that the diameter of the focal point is controlled within the specified range, ensuring that the signal can accurately act on the board detection area.

[0050] Next, the receiving module is debugged. The operator adjusts the micro-adjustment mechanism of the acoustic signal receiving module as described in claims 1 and 3 to control the vertical distance between the acoustic sensor and the detection surface of the wood board within the range specified in the claims. The anti-interference shield of the receiving end is checked to ensure that it can effectively shield external electromagnetic interference and environmental noise. At the same time, the sampling function of the receiving module is started to ensure that the signal-to-noise ratio of the sensor meets the standard specified in the claims, and to ensure the stability and accuracy of the received signal.

[0051] After debugging, signal preprocessing and density detection are performed. The operator presses the detection start button, and the acoustic signal transmitting module described in claim 1 emits an acoustic signal to the detection area of ​​the wood board. After the acoustic signal penetrates the wood board, it is accurately received by the acoustic signal receiving module described in claim 1. The receiving module converts the received acoustic signal into an electrical signal and transmits it to the signal preprocessing module described in claim 4 through the embedded bus. The signal preprocessing module sequentially filters, amplifies, shapes, and performs A / D conversion on the electrical signal to remove interference components. The processed standard digital signal is then transmitted to the density calculation module described in claim 5.

[0052] Subsequently, density calculation and error correction operations are performed. The density calculation module described in claim 5 calculates the preliminary density value of the wood board based on the preprocessed digital signal, combined with the wood board thickness information collected by the board positioning module and the preset material correction factor, through an improved correlation formula. At the same time, the error correction module described in claim 6 collects the temperature, humidity and flatness parameters of the detection environment and the surface flatness of the wood board through its own sensors, and corrects the preliminary density value in real time through a multi-factor coupling correction formula to eliminate the errors caused by temperature, humidity and flatness, and obtain the final density detection value of the wood board.

[0053] After density calculation and correction are completed, the test results are viewed and stored. The result output module described in claim 7 displays the final density test value, test error, and related test parameters of the wood-based panel in real time. If the final test value exceeds the preset acceptable range, the audible and visual alarm unit of the result output module is automatically triggered to remind the operator that the panel is unqualified. If the test value is within the acceptable range, a qualified prompt is displayed. At the same time, the test data is automatically stored in the data storage unit of the result output module, which supports export via USB interface. The storage format conforms to the requirements of the claims, facilitating subsequent data traceability and analysis.

[0054] After a single piece of wood panel is tested, subsequent operations are performed. The clamps of the panel positioning module automatically release, and the operator removes the tested wood panel. If batch testing is required, the above steps of positioning the panels to view and store the test results can be repeated to achieve continuous batch testing. After all testing is completed, the equipment power is turned off, and impurities on the surface of the panel positioning module and each testing module are cleaned to prevent impurities from affecting the subsequent use of the equipment. At the same time, the test data is backed up to complete this wood furniture panel density test.

[0055] Example 2: Density Testing of Artificial Furniture Boards This embodiment focuses on density testing of engineered wood furniture panels, following the aforementioned method and steps throughout. All modules and operations strictly correspond to the relevant names and reference numerals in the claims. The specific implementation process is as follows: The first step is to perform equipment initialization. Turn on the equipment power, and the system will automatically start a comprehensive self-test process. The system will focus on testing the working status of the acoustic signal transmitting module, acoustic signal receiving module, signal preprocessing module, density calculation module, error correction module, and result output module as described in claim 1. At the same time, it will test the positioning accuracy of the board positioning module as described in claim 8 and the communication status of the embedded bus as described in claim 9. The system will check for faults in each module and communication abnormalities in the bus. After the self-test is completed, if all modules are normal, the result output module as described in claim 7 will display "ready to standby". If there is an abnormality, the name of the corresponding faulty module will be displayed. After the operator troubleshoots the fault, the self-test will be restarted until the self-test is qualified.

[0056] The second step is to perform the board positioning operation. The operator places the artificial furniture board to be tested on the adjustment platform of the board positioning module as described in claim 8, adjusts the positioning fixture, and controls the appropriate clamping force to fix the board, avoiding excessive clamping that could damage the board surface or excessive clamping that could cause the board to shift. According to the size of the artificial board, the XYZ three-axis adjustment platform is adjusted, and the laser spot of the optical positioning unit is used for positioning to ensure that the board detection area is precisely aligned with the focal point of the acoustic signal transmitting module and the receiving end of the acoustic signal receiving module, ensuring that the emitted acoustic signal can penetrate the board and be accurately received. After positioning is completed, the adjustment platform is locked to prevent the platform from loosening and affecting the detection accuracy.

[0057] The third step is to preset the detection parameters. Using the operation buttons of the result output module described in claim 7, the material type of the board to be tested is preset to be artificial board. The system automatically matches the corresponding value range of the material correction factor λ described in claim 5. At the same time, combined with the industry qualification standards for artificial furniture boards, the density qualification range is preset. The preset parameters are quickly transmitted to the density calculation module and error correction module through the embedded bus described in claim 9 to ensure that the subsequent calculation and correction work can be carried out normally. After the parameters are preset, the device remains in standby mode, waiting to start the detection.

[0058] The fourth step involves adjusting the acoustic signal transmission. Based on the thickness of the engineered wood panel to be tested, the system automatically adapts the transmission power, transmission frequency, and transmission pulse width of the acoustic signal transmission module described in claims 1 and 2 to ensure that all parameters are within the range specified in the claims. The arc-shaped sound-gathering structure of the acoustic signal transmission module works synchronously to focus the acoustic signal on the detection area of ​​the panel, reducing signal diffusion, improving signal utilization, and ensuring that the signal can stably penetrate the engineered wood panel.

[0059] The fifth step is to debug the receiving module. Adjust the micro-adjustment mechanism of the acoustic signal receiving module as described in claims 1 and 3, calibrate the vertical distance between the acoustic sensor and the detection surface of the artificial board to meet the requirements of the claims, check the sealing of the anti-interference shield to ensure that it can effectively isolate external interference, start the sampling function of the receiving module, confirm that the signal-to-noise ratio of the sensor meets the specified standard, ensure the clarity and stability of the received signal, and avoid interference signals affecting the detection results.

[0060] The sixth step involves signal preprocessing and density detection. Pressing the detection start button causes the acoustic signal transmitting module (as described in claim 1) to emit an acoustic signal towards the detection area of ​​the engineered wood panel. After penetrating the panel, the acoustic signal is received by the acoustic signal receiving module and converted into an electrical signal. This electrical signal is then transmitted via a bus to the signal preprocessing module (as described in claim 4). After filtering by the filtering unit, amplification by the amplification unit, shaping by the shaping unit, and conversion by the A / D conversion unit, interference components are removed, resulting in a standard digital signal. This digital signal is then transmitted to the density calculation module (as described in claim 5) to perform density calculations.

[0061] The seventh step involves density calculation and error correction. The density calculation module described in claim 5 combines the preprocessed digital signal, the board thickness information, and the preset material correction factor to calculate the preliminary density value of the artificial board using an improved correlation formula. At the same time, the error correction module described in claim 6 collects the temperature and humidity parameters of the detection environment and the flatness parameters of the artificial board surface in real time, and corrects the preliminary density value using a multi-factor coupling correction formula to eliminate errors caused by various interference factors and obtain an accurate final density detection value.

[0062] The eighth step involves viewing and storing the test results. The result output module described in claim 7 displays the final density test value, test error, and related environmental parameters of the artificial board in real time. Operators can quickly view the test results. If the test value exceeds the preset acceptable range, the audible and visual alarm unit will be automatically triggered to indicate that the board is unqualified. If the test value is acceptable, an acceptable prompt will be displayed. The test data is automatically stored in the data storage unit and can be exported via USB interface to meet the needs of subsequent data traceability and analysis. The storage format complies with the provisions of the claims.

[0063] The ninth step involves continuous testing and equipment shutdown. After a single piece of engineered wood panel is tested, the clamps of the panel positioning module automatically release, allowing the operator to remove the panel. If batch testing is required, repeat the steps of positioning the panel to view and store the test results to achieve continuous batch testing, significantly improving testing efficiency. After all testing is completed, turn off the main power supply of the equipment, clean the impurities and dust from the surfaces of the panel positioning module, acoustic signal transmitting module, and acoustic signal receiving module, perform equipment maintenance, and back up the test data to prevent data loss. This completes the density testing of the engineered wood panels for furniture.

[0064] Example 3: Density Testing of Bamboo Furniture Boards This embodiment focuses on density testing of bamboo furniture boards, following the aforementioned usage method and steps throughout. All modules and operational procedures strictly correspond to the relevant names and reference numerals in the claims and do not exceed the scope of the foregoing content. The specific implementation process is as follows: First, initiate the device initialization process by turning on the device power. The system automatically performs a comprehensive self-test on each core module and bus, focusing on the working status of the acoustic signal transmitting module, acoustic signal receiving module, signal preprocessing module, density calculation module, error correction module, and result output module as described in claim 1. It also checks whether the fixture, adjustment platform, and optical positioning unit of the plate positioning module as described in claim 8 are functioning properly, and the communication rate and communication status of the embedded bus as described in claim 9. This ensures that all modules work together and that bus transmission is stable. After passing the self-test, the result output module displays "Ready" and enters the testing state.

[0065] The next step is to perform the board positioning operation. The operator places the bamboo furniture board to be inspected on the adjustment platform of the board positioning module, adjusts the positioning clamp to fix the board, and avoids damaging the surface texture of the bamboo board during the clamping process. According to the size of the bamboo board, the XYZ three-axis adjustment platform is adjusted. Through the laser spot of the optical positioning unit, the board detection area is accurately aligned with the focusing point of the acoustic signal transmitting module and the receiving end of the acoustic signal receiving module to ensure that the transmitting point and the receiving point correspond to the same area. After accurate positioning, the adjustment platform is locked to complete the positioning.

[0066] Next, the test parameters are preset. By using the operation buttons on the result output module, the material type of the board is preset to bamboo. The system automatically matches the value range of the material correction factor λ in the density calculation module, and at the same time presets the acceptable density range of the bamboo board. The preset parameters are automatically transmitted to the density calculation module and the error correction module to complete the parameter setting.

[0067] Then, the acoustic signal transmission adjustment operation is performed. The system automatically adjusts the transmission power, transmission frequency and pulse width of the acoustic signal transmission module according to the thickness of the bamboo board to ensure that all parameters meet the requirements of the claims. The arc-shaped sound focusing structure focuses the signal to ensure that the signal is accurately applied to the detection area.

[0068] Next, the receiving module is debugged, the micro-adjustment mechanism of the receiving module is adjusted, the vertical distance between the sensor and the detection surface of the board is calibrated, the working status of the anti-interference shield is checked, the sampling function is started, and the signal-to-noise ratio is ensured to meet the requirements to ensure stable received signal.

[0069] Pressing the detection start button activates the acoustic signal transmission module, which emits an acoustic signal. The signal penetrates the bamboo board and is received by the receiving module, converted into an electrical signal, and transmitted to the signal preprocessing module for filtering, amplification, shaping, and A / D conversion. The processed signal is then transmitted to the density calculation module, which calculates the initial density value using an improved correlation formula based on relevant parameters. The error correction module collects environmental and board parameters and corrects errors using a multi-factor coupling correction formula to obtain the final detection value.

[0070] The results output module displays the final test value, test error, and related parameters in real time. If the test is unqualified, an audible and visual alarm is triggered. The test data is automatically stored and can be exported via USB. After the test of a single board is completed, the clamp is automatically released and the board is removed. Repeating the relevant steps can achieve batch testing. After the test is completed, turn off the power, clean the equipment, and back up the data to complete the density test of the bamboo furniture board.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A technology for detecting the density of furniture boards using acoustic principles, characterized by: It includes an acoustic signal transmitting module, an acoustic signal receiving module, a signal preprocessing module, a density calculation module, an error correction module, and a result output module. Each module is connected bidirectionally via an embedded bus and adopts a closed-loop collaborative control mode to achieve non-contact, high-precision detection of furniture board density. The acoustic signal transmission module uses a high-frequency narrow-pulse acoustic transmitter. The transmission frequency is continuously adjustable within the range of 1.2MHz-2.8MHz, the transmission pulse width is set to 80ns-150ns, and the transmission power can be adaptively adjusted between 0.8W-3.2W according to the thickness of the board. The transmitting end is equipped with an arc-shaped sound focusing structure with a sound focusing angle of 35°-55°, which can focus the acoustic signal on a designated area of ​​the board detection surface. The diameter of the focusing point is controlled within 0.3mm-0.8mm to avoid detection errors caused by signal diffusion. The acoustic signal receiving module uses a high-sensitivity piezoelectric acoustic sensor with a receiving frequency response range of 0.8MHz-3.2MHz, a signal-to-noise ratio of ≥85dB, and a sampling frequency of 10MHz-20MHz. The receiving end is equipped with an anti-interference shield, which adopts a double-layer copper mesh structure with a mesh diameter of 0.1mm-0.2mm. This effectively shields against external electromagnetic interference and environmental noise. The vertical distance between the sensor and the detection surface of the board is fixed at 5mm-12mm, and the distance can be adjusted in steps through a micro-adjustment mechanism with an adjustment accuracy of 0.1mm. The signal preprocessing module includes a filtering unit, an amplification unit, a shaping unit, and an A / D conversion unit. The filtering unit uses a second-order active bandpass filter circuit, and the cutoff frequency can be adaptively matched according to the transmission frequency. The filter attenuation is ≤0.5dB. The amplification unit uses a low-noise operational amplifier, and the amplification factor can be adjusted in stages between 100x and 1000x with an adjustment step size of 50x. The shaping unit uses a Schmitt trigger to shape the irregular received signal into a standard square wave signal. The A / D conversion unit uses a 16-bit high-speed analog-to-digital converter with a conversion rate ≥1MSps and a conversion error ≤±0.01%, ensuring that the preprocessed signal meets the accuracy requirements for density calculation. The density calculation module is based on an improved acoustic propagation speed and density correlation algorithm, combined with the plate thickness compensation coefficient, to achieve accurate density calculation; The error correction module uses a multi-factor coupled correction algorithm to correct errors caused by temperature, humidity and surface flatness of the board in real time. The result output module adopts an integrated design of digital display and data storage, which can display the detection density value, detection error and detection time in real time, and can export the detection data via USB interface. The storage capacity is ≥16GB and the data storage format is CSV, which facilitates subsequent data traceability and analysis.

2. The technology for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The high-frequency narrow-pulse acoustic transmitter of the acoustic signal transmission module is made of aluminum nitride (AlN) piezoelectric ceramic material, with a piezoelectric constant d33≥350pC / N, an electromechanical coupling coefficient kp≥0.65, an operating temperature range of -10℃-60℃, and a service life of ≥10000 hours. The transmitter's drive circuit adopts a constant current drive mode, with a drive current range of 10mA-50mA and a drive voltage range of 5V-24V. The rise time of the drive signal is ≤10ns and the fall time is ≤10ns, which can effectively ensure the stability and narrow pulse characteristics of the transmitted signal. The arc-shaped sound-gathering structure is made of polytetrafluoroethylene (PTFE) material with a thickness of 2mm-5mm. The inner surface of the sound-gathering structure is polished, with a surface roughness Ra≤0.1μm, which can reduce the reflection loss of acoustic signals on the surface of the sound-gathering structure and achieve a sound-gathering efficiency ≥90%. The sound-focusing structure and the transmitter are connected by ultrasonic welding with a welding strength of ≥5MPa. A sealing gasket is installed at the weld joint. The sealing gasket is made of silicone rubber material with a thickness of 0.5mm-1mm to prevent dust and moisture from entering the transmitter and affecting the transmission performance. The transmitter's mounting base is made of aluminum alloy and has heat dissipation grooves. The width of the grooves is 1mm-2mm, the depth is 3mm-5mm, and the spacing is 5mm-8mm. This effectively reduces the temperature of the transmitter during operation, keeping it below 40℃ to prevent excessive temperature from affecting the stability of the transmission frequency.

3. The technology for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The high-sensitivity piezoelectric acoustic sensor of the acoustic signal receiving module is made of lead zirconate titanate (PZT) piezoelectric ceramic material, with a piezoelectric constant d31≥-180pC / N, electromechanical coupling coefficient kt≥0.55, receiving sensitivity≥100mV / Pa, and frequency stability≤±0.1% / ℃; The receiving surface of the sensor is gold-plated with a thickness of 0.1μm-0.2μm, which can improve the reception efficiency of acoustic signals and reduce signal attenuation. An insulating layer is provided between the double copper meshes of the anti-interference shielding cover. The insulating layer is made of polyimide material and has a thickness of 0.1mm-0.2mm. This can prevent the formation of eddy currents between the double copper meshes, which would affect the shielding effect. The shielding cover and the sensor are connected by an elastic connection. The elastic connector is made of polyurethane foam material with a hardness of Shore A30-A50, which can reduce the impact of external vibration on the sensor and the vibration attenuation is ≥20dB. The micro-adjustment mechanism adopts ball screw drive with a lead of 0.2mm-0.5mm, an adjustment range of 5mm-12mm, and an adjustment accuracy of 0.1mm. The drive motor of the adjustment mechanism adopts a micro stepper motor with a step angle of 1.8° and a speed range of 10r / min-50r / min. The motor drive circuit adopts microstepping drive mode with a microstepping factor of 8-32 times, which can achieve smoothness and high precision in the adjustment process. The sensor's posture remains unchanged during the adjustment process, ensuring the consistency of the received signal.

4. The technology for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The transfer function of the second-order active bandpass filter circuit in the filtering unit of the signal preprocessing module is: ； Where K is the gain of the filter circuit, and its value ranges from 0.8 to 1.

2. The center angular frequency of the filter circuit. , Where is the transmission frequency of the acoustic signal, and Q is the quality factor, with a value ranging from 5 to 15. The Q value can be adaptively adjusted according to the change of transmission frequency to ensure the filtering effect. The low-noise operational amplifier of the amplification unit has an input offset voltage ≤10μV, an input bias current ≤1nA, an output voltage swing of 0V-20V, and a bandwidth ≥10MHz. The amplification circuit adopts a differential amplification structure, which can effectively suppress common-mode interference with a common-mode rejection ratio ≥100dB. The Schmitt trigger of the shaping unit has a threshold voltage adjustable between 0.5V and 5V, and a hysteresis voltage ≤0.1V. It can shape the preprocessed sinusoidal acoustic signal into a standard square wave signal with a duty cycle of 45%-55%, a rise time ≤5ns, and a fall time ≤5ns. The 16-bit high-speed analog-to-digital converter of the A / D conversion unit has a reference voltage of 2.5V±0.01V and a conversion time of ≤1μs. It adopts a pipelined conversion structure, which can realize real-time sampling and conversion of acoustic signals. The converted digital signal is transmitted to the density calculation module through the SPI interface with a transmission rate of ≥10Mbps.

5. The technique for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The improved acoustic propagation speed and density correlation algorithm of the density calculation module is based on the intrinsic correlation between the acoustic characteristics and density of furniture boards. Combined with board thickness compensation, it breaks through the linear fitting limitations of existing algorithms and adopts a combination of quadratic polynomial fitting and correction factors. The specific calculation process is as follows: The first step involves collecting the propagation time t of the acoustic signal in the furniture board through the acoustic signal transmitting and receiving modules, and simultaneously collecting the actual thickness h of the board through the thickness detection unit. The thickness detection unit uses a laser rangefinder sensor with a ranging accuracy of 0.01mm and a ranging range of 1mm-50mm. The second step is to calculate the propagation speed v of the acoustic signal in the board material. The calculation formula is: ； Where h is the actual thickness of the board (unit: m), t is the acoustic signal propagation time (unit: s), and v is the propagation speed (unit: m / s). The third step is to introduce a material correction factor λ for the board material. λ is adaptively adjusted according to the material type of the furniture board. The value of λ for wood-based boards is 0.85-0.95, the value of λ for engineered wood-based boards (particleboard, MDF) is 0.90-1.00, and the value of λ for bamboo-based boards is 0.88-0.

98. The fourth step is to calculate the density ρ of the sheet material using the improved correlation formula. The improved correlation formula is as follows: ； Where a, b, and c are fitting coefficients, a = -0.0002 ± 0.00001, b = 0.35 ± 0.01, and c = -120 ± 5. This is the propagation speed deviation value. , ρ is the standard propagation velocity of the material (unit: m / s), and ρ is the density of the material (unit: kg / m³). 3 ); The fifth step is to perform preliminary smoothing on the calculated density values ​​using a moving average filtering algorithm with a filter window size of 5-10. This reduces the impact of random errors on the density calculation results. The smoothed density values ​​are the preliminary detection results.

6. The technique for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The multi-factor coupled correction algorithm of the error correction module targets three main error sources—temperature, humidity, and surface flatness of the board—and uses a coupled correction model to achieve real-time and accurate error correction. The specific correction process is as follows: The first step involves collecting the ambient temperature T (unit: °C) using a temperature sensor. The temperature sensor's measurement range is -10 °C to 60 °C, and its measurement accuracy is ±0.1 °C. The second step involves collecting the ambient humidity H (unit: %RH) using a humidity sensor. The humidity sensor's measurement range is 20% to 90%RH, and its measurement accuracy is ±1%RH. The third step involves collecting the surface flatness deviation δ (unit: mm) of the board material using a laser flatness detection unit. The flatness detection accuracy is ±0.005 mm. The second step is to establish a temperature error correction factor. Humidity error correction factor and flatness error correction factor The calculation model uses the following formula to calculate the temperature error correction factor: ； 25℃ is the standard testing temperature. When the temperature deviates from 25℃, it will be detected by... Correct the density value; The formula for calculating the humidity error correction factor is: ； 50%RH is the standard test humidity. When the humidity deviates from 50%RH, it is detected by... Correct the density value; The formula for calculating the flatness error correction factor is: ； When there is a flatness deviation on the surface of the board, by Correct the density value; The third step involves establishing a multi-factor coupling correction formula to analyze the preliminary detection results obtained from the density calculation module. The coupling correction formula is as follows: ； Where ρ is the corrected final density measurement value (unit: kg / m³). 3 The corrected detection error is ≤ ±0.5 kg / m 3 To ensure the accuracy of the test results; The fourth step involves the correction module collecting various environmental and material parameters in real time, performing an error correction calculation every 10ms to achieve dynamic tracking and correction of errors, adapting to changes in different testing environments and material conditions.

7. The technique for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The result output module includes an LCD screen, a data storage unit, a USB interface, and an alarm unit; The LCD screen is a high-definition industrial-grade display with a screen size of 3.5 inches to 5 inches, a resolution of 800×480 pixels, and a brightness of up to 50 cd / m². 2 -300cd / m 2 The parameters can be adjusted between these ranges, and the system can display parameters such as the detected density value, detection error, detection time, ambient temperature, ambient humidity, and board thickness in real time, with a display accuracy of 0.1 kg / m². 3 The screen response time is ≤50ms, which can adapt to strong light and weak light scenarios in industrial testing environments; The data storage unit uses a Flash storage chip with a storage capacity of ≥16GB, which can store ≥100,000 sets of detection data. The data storage adopts a cyclic overwrite mode. When the storage capacity is full, the oldest detection data is automatically overwritten. At the same time, the data storage trigger conditions can be manually set, supporting single detection storage and continuous detection timed storage (the storage interval can be adjusted between 1s and 60s). The USB interface uses a USB 3.0 interface with a transmission rate of ≥5Gbps, supports hot-swapping, and can be directly connected to devices such as computers and printers to export test data for subsequent analysis and printing. It also supports firmware upgrades for the device via the USB interface. The alarm unit adopts an audible and visual alarm mode with a preset density acceptable range. When the detected density value exceeds the acceptable range, the alarm unit is automatically triggered. The audible alarm volume is ≥80dB, and the alarm frequency is 1kHz-2kHz. The visual alarm uses a red LED light with a flashing frequency of 1-2 times / second. At the same time, the alarm prompt information is displayed on the screen. The alarm status can be cleared by manually pressing a button, or it can be set to automatically clear when the next set of data is detected, which makes it convenient for operators to promptly detect unqualified boards.

8. The technique for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: It also includes a board positioning module, which uses a combination of mechanical and optical positioning to achieve precise positioning of furniture boards and ensure that the emission point and receiving point of the acoustic signal correspond to the same detection area of ​​the board. The mechanical positioning unit includes a positioning clamp and an adjustment platform. The positioning clamp adopts an adjustable structure to adapt to furniture boards of different sizes (length 500mm-2000mm, width 300mm-1500mm, thickness 1mm-50mm). The clamping force of the clamp can be adjusted between 50N-200N. The clamping surface is made of rubber material with a thickness of 1mm-2mm to prevent damage to the surface of the board during clamping. The adjustment platform adopts an XYZ three-axis adjustment structure. The adjustment range of the X and Y axes is 0mm-500mm with an adjustment accuracy of 0.1mm, and the adjustment range of the Z axis is 0mm-100mm with an adjustment accuracy of 0.1mm. It can realize precise adjustment of the board in the horizontal and vertical directions. The optical positioning unit includes two laser positioners, which are respectively installed on one side of the acoustic signal transmitting module and the receiving module. The laser positioners emit red lasers with a wavelength of 650nm and a laser spot diameter of 0.1mm-0.2mm. The laser beams of the two laser positioners coincide at the focal point of the board detection surface. The operator can quickly locate the detection area through the laser spot, with a positioning error ≤0.1mm. The positioning module is linked with each detection module. After the board is positioned, the system automatically triggers the acoustic signal transmission and reception to start density detection. After the detection is completed, the positioning fixture is automatically released, which facilitates the operator to change the board and improves the detection efficiency. The detection time for a single board is ≤3s.

9. The technique for detecting the density of furniture boards using acoustic principles according to claim 1, characterized in that: The embedded bus adopts a hybrid bus structure combining CAN bus and SPI bus. The CAN bus is used for communication between the acoustic signal transmitting module, receiving module and error correction module, with a communication rate of 1Mbps-5Mbps, a communication distance ≤100m, and a communication bit error rate ≤10%. -9 It enables high-speed and stable data transmission; the SPI bus is used for communication between the signal preprocessing module, density calculation module, and result output module, with a communication rate of 10Mbps-50Mbps, a communication distance ≤10m, and a communication bit error rate ≤10%. -10 It enables rapid transmission of real-time data; The bus interface adopts a differential interface design and is equipped with overvoltage and overcurrent protection circuits. The overvoltage protection threshold is 36V and the overcurrent protection threshold is 1A, which can prevent the bus interface from being damaged due to abnormal voltage or current. The system is also equipped with a bus diagnostic unit, which can detect the communication status of the bus in real time. When a bus communication abnormality is detected (such as open circuit, short circuit, or excessive bit error rate), the alarm unit is automatically triggered and the fault information is displayed in the result output module. The fault information includes the fault module, fault type and fault occurrence time, which makes it easy for operators to quickly troubleshoot the fault. Bus communication uses encrypted transmission with AES-128 encryption algorithm to prevent detection data from being tampered with or stolen, ensuring data security and confidentiality.

10. The technique for detecting the density of furniture boards using acoustic principles according to any one of claims 1-9, characterized in that: The detection process of this technology includes the following steps: Step 1: Device initialization. Connect the power supply. The system will automatically perform self-tests on each module. The self-test includes the transmission frequency and power of the acoustic signal transmitting module, the sensitivity and signal-to-noise ratio of the acoustic signal receiving module, the filtering and amplification effects of the signal preprocessing module, the algorithm operation status of the density calculation module, the sensor status of the error correction module, and the display and storage functions of the result output module. The self-test time is ≤5 seconds. After the self-test is passed, the system enters standby mode and the display shows "Standby Ready". If the self-test fails, the corresponding fault information will be displayed and an alarm will be triggered. Step 2, board positioning: Place the furniture board to be inspected on the adjustment platform of the positioning module, and clamp and fix the board with mechanical positioning fixtures. Adjust the XYZ three-axis adjustment platform so that the laser spot of the optical positioning unit coincides with the detection area of ​​the board. After positioning is completed, press the detection start button. Step 3: Environmental and board parameter acquisition. The temperature sensor, humidity sensor, and flatness detection unit of the error correction module acquire the temperature T, humidity H, and flatness deviation δ of the detection environment in real time. The thickness detection unit acquires the actual thickness h of the board. After the acquisition is completed, the parameters are transmitted to the density calculation module and the error correction module. Step 4, Acoustic signal transmission and reception: The acoustic signal transmission module adaptively adjusts the transmission power, frequency and pulse width according to the thickness of the board material to transmit high-frequency narrow pulse acoustic signals to the detection area of ​​the board material. After the acoustic signals penetrate the board material, they are received by the acoustic signal receiving module. The receiving module converts the acoustic signals into electrical signals and transmits them to the signal preprocessing module. Step 5, signal preprocessing: The signal preprocessing module filters, amplifies, shapes, and performs A / D conversion on the received electrical signal, removes interference signals, converts the analog signal into a digital signal, and transmits it to the density calculation module. Step 6, density calculation and error correction: The density calculation module calculates the propagation time t of the acoustic signal in the board material based on the preprocessed digital signal, calculates the propagation velocity v in combination with the board thickness h, and then calculates the preliminary density value using an improved correlation formula. The error correction module calculates various error correction factors based on the collected environmental and material parameters, and applies a multi-factor coupling correction formula to correct these errors. After correction, the final density detection value ρ is obtained; Step 7, Result Output and Storage: The result output module displays the final density detection value, detection error, detection time, and various acquisition parameters in real time, and stores the detection data in the data storage unit. If the detection value exceeds the preset qualified range, an audible and visual alarm is triggered. Step 8: Inspection complete. The operator presses the stop button, the positioning fixture automatically releases, the inspected board is removed, and the system returns to standby mode, waiting for the next inspection. If continuous testing is required, simply repeat steps 2-7. The detection accuracy of this technology is ≥99.5%, and the detection efficiency is ≥120 pieces / hour. It can adapt to the density testing of furniture boards of different materials and sizes. Moreover, the testing process is free of consumables and causes no damage to the boards.

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