Implementation method for rapid response of laser power detection

Abstract

The invention discloses a technical scheme of a laser power detection rapid response realization method, and the method comprises the steps: describing a laser-induced thermal voltage time response characteristic curve through employing a Bessel function when laser-induced thermal voltage is measured through employing a thermopile temperature difference sensing principle based on a plane heat conduction process; and predicting a thermal voltage steady-state value in advance and converting the thermal voltage steady-state value into a laser power value. Differential calculation is used, the starting time of a thermoelectric signal caused by laser input does not need to be preset, the rising edge and the falling edge of a sensing signal can be automatically and continuously detected in an unattended mode, the convenience and operability of laser power detection are greatly improved, the thermal voltage steady-state value can be obtained through calculation only by accurately collecting 4-6 pieces of thermal voltage data, and the detection accuracy is improved. Therefore, the thermoelectric response time is shortened from conventional 9s to 4s, the steady-state time is shortened from 30s to 6s, and the error of the steady-state value is less than 2%.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor signal acquisition and analysis, and particularly to a method for realizing fast response of laser power detection. Background Art

[0002] In the field of high-power laser processing, the key of a laser power detection device is a detector, which can monitor the working laser power in real time.

[0003] A thermoelectric laser probe utilizes the thermoelectric effect: when irradiated by a laser, an absorber absorbs the laser heat and generates a voltage due to the thermoelectric effect. The laser power can be inferred according to the measured voltage value. Compared with the traditional photoelectric type, the thermoelectric detector can measure a higher laser power.

[0004] However, since the thermoelectric detector is based on the heat conduction process, slow response has always been its shortcoming. It takes 30 s from the application of laser to generate a thermal voltage until the thermal voltage reaches a steady state, and the corresponding response time is 8 s. At the same time, laser safety puts forward higher requirements for the response time of the thermoelectric detector.

[0005] Currently, there are two solutions to shorten the response time: one is to use a substrate with a high thermal conductivity, but this will result in a smaller temperature difference, thereby reducing the sensitivity of the detector. The other solution is to predict the steady-state value of the signal in advance from the perspective of signal processing.

[0006] A method for realizing fast response of a thermopile detector announced by the State Intellectual Property Office of China (application number 201510749757.5, publication number CN105424200, application date November 4, 2015) includes the following steps: determining the rising law function of the output voltage of the thermopile detector; irradiating the thermopile detector with a laser of stable power, testing the output voltage of the thermopile detector, and recording the rising curve; performing exponential fitting on the rising curve part of the output voltage of the thermopile detector to obtain the time constant; processing the real-time output voltage of the thermopile detector to obtain the fast response voltage of the thermopile detector. This implementation method calculates the steady-state value of the thermal voltage using the response characteristic function of the thermopile detector, and it is the only method currently using a signal processing solution to improve the response speed of the thermopile detector.

[0007] However, the accuracy of this method depends on the definition of the zero point time. If the zero point time is not defined and real-time calculation is directly carried out, an excessively large calculated value (close to 43 mV) will appear at the rising edge, unreasonably deviating from the measured value. Then it gradually falls back, and the correct steady-state value will also be obtained at 6 s. Although the steady-state time is short and the steady-state value is correct, the same as this method, the data at the initial moment is unreasonably large, and the entire calculation requires prior fitting to obtain the characteristic time, which makes the entire thermal voltage test and calculation inconvenient, and the correct response time cannot be obtained. Therefore, this method is not convenient to use. Summary of the Invention

[0008] The object of the present invention is to provide a technical solution for an implementation method of rapid response of laser power detection in view of the deficiencies of the prior art. The differential calculation result of this implementation method is independent of the definition of the zero point of time. Loading laser on the thermopile probe at any time does not affect the calculation of the steady-state value of the thermal voltage by this method. When in use, it is not necessary to fit the response curve of the probe by the least square method in advance to obtain the characteristic time, but to calculate the characteristic time during the process of real-time data acquisition and use it for the calculation of the steady-state value of the thermal voltage. At the same time, this method can be used to detect the rising edge and falling edge of the sensing signal automatically and continuously without human intervention, greatly improving the convenience and operability of laser power detection. Only 4 to 6 thermal voltage data need to be accurately collected to calculate the steady-state value of the thermal voltage, so that the thermoelectric response time is shortened from the conventional 9 s to 4 s, the steady-state time is shortened from 30 s to 6 s, and the error of the steady-state value is less than 2%.

[0009] To solve the above technical problems, the present invention adopts the following technical solutions:

[0010] An implementation method for rapid response of laser power detection, characterized in that: when measuring the thermal voltage induced by laser using the thermopile temperature difference sensing principle based on the plane heat conduction process, the time response characteristic curve of the thermal voltage induced by laser is described by the Bessel function, and its steady-state value of the thermal voltage is predicted in advance and then converted into a laser power value; this implementation method only needs to accurately collect 4 to 6 thermal voltage data to calculate the steady-state value of the thermal voltage, so that the thermoelectric response time is shortened from the conventional 9 s to 4 s, the steady-state time is shortened from 30 s to 6 s, and the error of the steady-state value is less than 2%.

[0011] Further, the time response characteristic curve of the thermal voltage induced by laser is described by the Bessel function, and its steady-state value of the thermal voltage is predicted in advance and then converted into the steady-state value of the thermal voltage, which specifically includes the following steps:

[0012] S1. Connect the voltage measuring device to the output end of the thermopile and detect the thermal voltage in real time;

[0013] S2. Use the differential method to calculate the steady-state value of the thermal voltage in real time during the detection process;

[0014] S3. Apply laser to the thermopile-based laser power probe at any time during real-time detection. The voltage measurement device measures the thermal voltage that gradually rises or falls over time output by the thermopile in real time, and calculates the expected steady-state value of the thermal voltage.

[0015] S4. Convert the expected steady-state value of the thermal voltage calculated in real time into the laser power value irradiated on the probe.

[0016] The differential calculation result of this implementation method is independent of the definition of the zero point of time. Applying laser to the thermopile probe at any time does not affect the calculation of the steady-state value of the thermal voltage by this method. When in use, it is not necessary to fit the response curve of the probe with the least squares method in advance to obtain the characteristic time. Instead, the characteristic time is calculated during the process of real-time data acquisition and used for the calculation of the steady-state value of the thermal voltage. At the same time, this method can be used for unattended automatic continuous detection of the rising edge and falling edge of the sensing signal, greatly improving the convenience and operability of laser power detection.

[0017] Further, the thermal voltage time response characteristic curve follows the second-order Bessel function of the heat conduction equation, and the corresponding thermal voltage function is:

[0018]

[0019] where U(t) is the thermoelectric potential, p is the laser power incident on the center of the thermopile probe, t is the time, J n0 (r) is the nth-order Bessel function, B n is an integral function independent of time (n = 1, 2), τ is the exponential characteristic time, and τ1 < τ2.

[0020] Further, the sampling frequency of real-time detecting the thermal voltage in step S1 is greater than 1 / τ1, and equation (1) is modified to:

[0021]

[0022] Further, the difference method in step S2 is specifically:

[0023] At time t k , the measured voltage value The steady-state value of the thermal voltage is:

[0024]

[0025] where the difference δU(t k+N ) = U(t k+N ) - U(t k+N-1 ), δU(t k ) = U(t k ) - U(t k-1 ), δt = t k+N - t k+N-1。

[0027] Furthermore, applying laser to the laser power probe based on the thermopile at any moment in step S3 does not affect the calculation of the steady-state value of the thermal voltage, and the differential calculation result has nothing to do with the definition of the zero point of time.

[0028] Furthermore, the conversion of the expected steady-state value of the thermal voltage in step S4 to the laser power value irradiated on the probe is based on the proportional relationship between the laser heat source power and the thermal voltage.

[0029] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0030] The present invention only needs to accurately collect 4 to 6 thermal voltage data to calculate the steady-state value of the thermal voltage, thereby shortening the thermoelectric response time from the conventional 9 s to 4 s, the steady-state time from 30 s to 6 s, and the error of the steady-state value is less than 2%.

[0031] The differential calculation result of the present invention has nothing to do with the definition of the zero point of time. Applying laser to the thermopile probe at any moment does not affect the calculation of the steady-state value of the thermal voltage by this method. When in use, it is not necessary to fit the response curve of the probe by the least squares method in advance to obtain the characteristic time, but to calculate the characteristic time during the process of real-time data acquisition and use it for the calculation of the steady-state value of the thermal voltage. At the same time, this method can be used for unattended automatic continuous detection of the rising edge and falling edge of the sensing signal, greatly improving the convenience and operability of laser power detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below with reference to the accompanying drawings:

[0033] Figure 1 It is a fitting diagram of the thermal voltage response curve and the Bessel function in a method for realizing fast response of laser power detection according to the present invention;

[0034] Figure 2 It is a characteristic time diagram of real-time calculation of the thermal voltage response data of 30 W laser according to the present invention;

[0035] Figure 3 It is a calculation curve diagram of the thermal voltage response data of 30 W laser and the method of the present invention according to the present invention;

[0036] Figure 4 It is a calculation curve diagram of continuous multiple power thermal voltage response data and the method of the present invention according to the present invention;

[0037] Figure 5 It is a diagram for converting the steady-state value of the thermal voltage into the laser power value according to the present invention;

[0038] Figure 6 It is a flow chart for converting the steady-state value of the thermal voltage into the laser power value according to the present invention;

[0039] Figure 7 This is the flowchart of the sampling method in the present invention. Specific embodiments

[0040] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0041] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion.

[0043] The commonly used thermoelectric laser power detector measures the laser power by generating a thermal voltage at the low and high temperature ends of the thermopile based on the heat conduction mechanism. The general solution of the heat conduction equation is the Bessel function.

[0044] Generally, the first two orders are intercepted: where T(t) is the temperature at different times, p is the laser power incident on the center of the thermopile probe, t is the time, J n0 (r) is the nth-order Bessel function, B n is an integral function independent of time (n = 1, 2), τ is the characteristic time, and τ1 is much smaller than τ2. Since the thermal voltage of the Seebeck effect is proportional to the temperature difference between the high and low temperatures, the time response function of the thermal voltage can be written as

[0045] As Figure 6 shown, this is a method for realizing fast response of laser power detection in the present invention. When measuring the thermal voltage induced by a laser using the thermopile temperature difference sensing principle based on the planar heat conduction process, the Bessel function is used to describe the time response characteristic curve of the thermal voltage induced by the laser, and the steady-state value of the thermal voltage is predicted in advance and then converted into the laser power value; this implementation method only needs to accurately collect 4 to 6 thermal voltage data to calculate the steady-state value of the thermal voltage, thereby shortening the thermoelectric response time from the conventional 9 s to 4 s, the steady-state time from 30 s to 6 s, and the error of the steady-state value is less than 2%.

[0046] The thermal voltage time response characteristic curve follows the second-order Bessel function of the heat conduction equation, and the corresponding thermal voltage function is:

[0047]

[0048] where U(t) is the thermoelectric potential, p is the laser power incident on the center of the thermopile probe, t is the time, J n0 (r) is the Bessel function of the nth order, B n is an integral function independent of time (n = 1, 2), τ is the exponential characteristic time, and τ1 < τ2.

[0049] Using the Bessel function to describe the laser-induced thermal voltage time response characteristic curve, predicting its thermal voltage steady-state value in advance and then converting it into the laser power value specifically includes the following steps:

[0050] S1. Connect the voltage measuring device to the output end of the thermopile and detect the thermal voltage in real time;

[0051] When using an oscilloscope or a digital voltmeter with a relatively high sampling frequency, the sampling frequency for detecting the thermal voltage in real time can be much greater than 1 / τ1, and Equation (1) is modified as:

[0052]

[0053] As Figure 7 shown, the time interval for voltage acquisition is δt = t k -t k-1 = t k+N -t k+N-1 << τ2. And t k and t k+N are relatively far-apart moments. Assume that the laser is loaded at a certain moment before t k-1 , so the voltage change from t k-1 to t k can be written as:

[0054] δU(t k ) = bexp(-t k / τ)(1 - exp(-δt / τ2)) ≈ bδtexp(-t k / τ) / τ2 (3),

[0055] Similarly, the voltage change from t k+N-1 to t k+N can also be written as: δU(t k+N ) ≈ bδtexp(-t k+N / τ2) / τ2, so the characteristic time can be calculated during the data acquisition process:

[0056] τ2 = (t k+N -tk ) / ln(δU(t k ) / δU(t k+N )) (4),

[0057] S2. During the detection process, the differential method is used to calculate the steady-state value of the thermal voltage in real time;

[0058] As can be seen from formula (2), using time t k+N when, the steady-state value of the thermal voltage calculated by the thermal voltage is

[0059]

[0060] Substitute equations (3) and (4) into equation (5), and the steady-state value of the thermal voltage can be calculated using the thermally collected thermal voltage in real time:

[0061]

[0062] Among them, the difference δU(t k+N ) = U(t k+N ) - U(t k+N-1 ), δU(t k ) = U(t k ) - U(t k-1 ), δt = t k+N - t k+N-1 .

[0064] S3. At any moment during the real-time detection, a laser is applied to the laser power probe based on the thermopile, and the voltage measuring device measures the thermal voltage that gradually rises or falls with time output by the thermopile in real time, and calculates the expected steady-state value of the thermal voltage;

[0065] Applying a laser to the laser power probe based on the thermopile at any moment does not affect the calculation of the steady-state value of the thermal voltage, and the differential calculation result has nothing to do with the definition of the zero point of time.

[0066] S4. Convert the expected steady-state value of the thermal voltage calculated in real time into the laser power value irradiated on the probe.

[0067] The conversion of the expected steady-state value of the thermal voltage into the laser power value irradiated on the probe is based on the proportional relationship between the laser heat source power and the thermal voltage.

[0068] The differential calculation result of this implementation method has nothing to do with the definition of the zero point of time. Applying a laser to the thermopile probe at any moment does not affect the calculation of the steady-state value of the thermal voltage by this method. When using it, there is no need to fit the response curve of the probe with the least squares method in advance to obtain the characteristic time. Instead, the characteristic time is calculated during the process of real-time data acquisition and used for the calculation of the steady-state value of the thermal voltage. At the same time, this method can be used for unattended automatic continuous detection of the rising edge and falling edge of the sensing signal, greatly improving the convenience and operability of laser power detection.

[0069] Example 1

[0070] This example includes the theoretical basis of the present invention - the fitting of the Bessel function to the thermal voltage response curve. This fitting does not need to be included in the subsequent use of this method, and is only for illustrating the reliability of this method.

[0071] As Figure 1 shown, the square dots are the thermal voltage response curves of 30 W loaded on the thermopile detector.

[0072] The laser loading time is at 30 s.

[0073] The round dots are the fitting curves, with 30 s as the time zero point (Note: When using this method to measure the steady-state value of the thermal voltage in real time, it is not necessary to know the time zero point).

[0074] The final fitting curve is U(t) = 2.5×(1 - e -t / 6.9 ) + 4.6×(1 - e -t / 0.45 ). This curve includes two exponential responses, with characteristic times of 6.9 s and 0.45 s respectively.

[0075] Therefore, the theoretical function used in actual calculation of the steady-state value of the thermal voltage by this method is U(t) = 4.6 + 2.5×(1 - e -t / 6.9 ).

[0076] Figure 1 The dotted line of the actual response curve in [] is the deviation between the fitting curve and the actual response curve, and it can be seen that the maximum deviation is about 1%. The above fitting shows that the theoretical basis of this method is reliable.

[0077] When actually measuring the steady-state value of the thermal voltage, use equations (4) and (5) to calculate the characteristic time and the steady-state value of the thermal voltage in real time. Figure 2 is the characteristic time calculated during the process of real-time measurement and calculation of the steady-state value of the thermal voltage. It can be seen that the characteristic time calculated in real time changes consistently within 5 s before and after the laser loading, and a stable value of 6.85 s can be obtained at the 6th s, which is consistent with the 6.9 s of the fitting curve. This proves the feasibility of calculating the characteristic time in real time by this method.

[0078] Figure 3 is the comparison of the sampling data under the condition of 30 W laser loading and the results of two calculation schemes.

[0079] The laser is loaded at 30 s. It can be seen that at the 36th s, the calculation result of this method has obtained the steady-state value of the thermal voltage, and the deviation is less than 2%. Therefore, the steady-state time is 6 s.

[0080] On the other hand, 90% of the steady-state value of the thermal voltage is obtained at 34.3 s, so the response time is 4.3 s.

[0081] The original sampled data respectively take 9 s and 30 s to reach 90% of the steady-state value.

[0082] Therefore, using this method, the response time can be shortened from the original 9 s to 4 s, and the steady-state time can be shortened from 30 s to 6 s.

[0083] As a comparison, the calculation results of the method of the 41st Institute of China Electronics Technology Group Corporation (CN201510749757.5) are also shown in the figure. As mentioned above, this method depends on the definition of the zero point moment. If the zero point moment is not defined and real-time calculation is directly carried out, there will be an excessively large calculated value (close to 43 mV) at the rising edge, unreasonably deviating from the measured value. Then it gradually falls back, and the correct steady-state value will also be obtained at 6 s. Although the steady-state time is short and the steady-state value is correct, the data at the initial moment is unreasonably large, and the entire calculation requires prior fitting to obtain the characteristic time, which makes the entire thermal voltage test and calculation seem not very convenient, and the correct response time cannot be obtained.

[0084] Embodiment 2

[0085] This embodiment applies the calculation method to the thermal voltage response curve including multiple laser loading and unloading processes. For the unloading process, the theoretical function of the time response of its thermal voltage is Similarly, the steady-state values of the thermal voltage at different powers can be quickly obtained using equations (4) and (5). The calculation results are in Figure 4 it.

[0086] Figure 5 It is the laser power calculated using the relationship that the thermal voltage is proportional to the heat source power in the thermoelectric Seebeck principle. Therefore, after this method processes the steady-state value of the thermal voltage in real time, it can immediately calculate the laser power hitting the probe.

[0087] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms.

[0088] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements or modifications made based on the present invention to achieve substantially the same technical effects are all covered by the protection scope of the present invention.

Claims

1. A method for realizing rapid response of laser power detection, characterized in that: When measuring the laser-induced thermovoltage using the thermopile temperature difference sensing principle based on the planar heat conduction process, the Bessel function is used to describe the laser-induced thermovoltage time response characteristic curve, and its thermovoltage steady-state value is predicted in advance and converted into a laser power value.

2. The method for realizing rapid response of laser power detection according to claim 1, characterized in that: The method of using the Bessel function to describe the laser-induced thermovoltage time response characteristic curve and predicting the thermovoltage steady-state value in advance so as to convert it into a steady-state power value specifically includes the following steps: S1, connect the voltage measuring device to the output end of the thermopile to detect the thermovoltage in real time; S2. During the detection process, the differential method is used to calculate the steady-state value of the thermal voltage in real time; S3, applying laser to the laser power probe based on the thermopile at any time during the real-time detection, the voltage measuring device measuring in real time the thermal voltage output by the thermopile that gradually rises or falls over time, and calculating the expected steady-state value of the thermal voltage; S4. Convert the expected steady-state value of thermal voltage calculated in real time into the laser power value irradiated on the probe.

3. The method for realizing rapid response of laser power detection according to claim 2, characterized in that: The thermovoltage time response characteristic curve follows the second-order Bessel function of the heat conduction equation, and the corresponding thermovoltage function is: where U(t) is the thermoelectric potential, p is the laser power incident on the center of the thermopile probe, t is time, and J n0 (r) is the nth-order Bessel function, B n It is an integral function independent of time (n=1,2), τ is the exponential characteristic time, τ1<τ2.

4. The method for realizing rapid response of laser power detection according to claim 3, characterized in that: The sampling frequency of the real-time detection of the thermal voltage in step S1 is greater than 1 / τ1, and formula (1) is modified as follows:

5. The method for realizing rapid response of laser power detection according to claim 2, characterized in that: The difference method in step S2 is specifically: Time t k When the measured voltage value The steady-state value of the thermal voltage is: where the difference δU(t k+N ) = U(t k+N ) - U(t k+N-1 ), δU(t k ) = U(t k ) - U(t k-1 ) δt = t k+N - t k+N-1 .

6. The method for realizing rapid response of laser power detection according to claim 2, characterized in that: Applying laser to the laser power probe based on the thermopile at any time in step S3 does not affect the calculation of the steady-state value of the thermal voltage, and the difference calculation result is independent of the definition of the zero point of time.

7. The method for realizing rapid response of laser power detection according to claim 1, characterized in that: The expected steady-state value of the thermal voltage in step S4 is converted into the laser power value irradiated on the probe based on the positive proportional relationship between the laser heat source power and the thermal voltage.

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