Two-point voltage sampling type inductance distance measuring sensor and control method

Abstract

The invention discloses a two-point voltage sampling type inductance distance measuring sensor and a control method. According to the method, voltage sampling is carried out at two key time points, the equivalent resistance and the equivalent inductance of an inductance measuring head are calculated based on the sampled voltage, and then matching with a pre-stored high-precision inductance-distance mapping table is carried out through an error minimization algorithm, so that the actual distance of a measured object is obtained. The sensor comprises an inductance distance measuring circuit, a time sequence control module, a signal acquisition module and a data processing module which cooperatively realize high-precision distance measurement. Through time sequence innovation and intelligent calibration, the accuracy and robustness of a distance measurement result are remarkably improved, and the method is particularly suitable for precise positioning and mechanical detection scenes in industrial automation.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a two-point voltage sampling type inductive ranging sensor and its control method. Background Technology

[0002] In current industrial automation systems, non-contact distance measurement is one of the key technologies for achieving precise positioning, object detection, gap control, and thickness measurement. Common ranging technologies include laser ranging, ultrasonic ranging, and visual ranging. However, these technologies have limitations in specific application scenarios. For example, laser ranging is sensitive to the surface characteristics of objects, and its performance degrades on strongly reflective or light-absorbing surfaces; ultrasonic ranging is easily affected by ambient temperature and airflow; and visual ranging is complex, costly, and computationally intensive. In contrast, inductive ranging technology, due to its simple structure, low cost, and strong resistance to ambient light interference, is particularly suitable for high-precision close-range detection of metallic objects, and has irreplaceable advantages in scenarios such as machining, robot guidance, and conveyor belt positioning. Existing inductive ranging technologies are usually based on the principle of LC oscillation circuits, indirectly reflecting changes in inductance by measuring changes in oscillation frequency, thereby estimating the distance. However, this traditional method has obvious technical bottlenecks: First, its measurement accuracy is easily affected by the resistive component in the circuit (especially the equivalent series resistance change caused by temperature changes and component aging), resulting in measurement value drift and poor stability; second, the transient response process of the circuit is not fully utilized, and the measurement results are easily affected by impulse noise, resulting in poor repeatability.

[0003] Therefore, there is an urgent need for a new inductive ranging solution that can fundamentally suppress the effects of temperature drift and component aging, and improve measurement accuracy and robustness through innovative signal processing methods. To address these issues, this invention proposes a two-point voltage sampling inductive ranging sensor and its control method to achieve higher precision and stability distance measurement, meeting the increasingly sophisticated precision detection requirements of modern industrial automation. Summary of the Invention

[0004] This application provides a two-point voltage sampling inductive distance sensor and control method to achieve higher accuracy and stability distance measurement, meeting the increasingly sophisticated precision detection needs of modern industrial automation.

[0005] 1. A two-point voltage sampling type inductive ranging sensor, characterized in that it includes an inductive ranging circuit, a timing control module, a signal acquisition module, and a data processing module;

[0006] The inductive ranging circuit includes a power supply, an inductance measuring head, a power switch, and a current-limiting resistor. The power supply module is used to provide a stable supply voltage E. The inductance measuring head forms different equivalent inductance values ​​through magnetic coupling effect. The power switch is used to control the circuit to form a continuous transition process. The current-limiting resistor is used to limit the power of the circuit.

[0007] The timing control module is configured to generate a drive signal for the power switch Q and precisely control three key time points: t0 when the drive signal is turned on, t1 when the first voltage is acquired, and t2 when the second voltage is acquired, where t2 = t1 + T, T is a preset fixed time interval, t2 - t0 > 3τ, and τ is the circuit time constant.

[0008] The signal acquisition module is connected to both ends of the inductance measuring head and the power switch Q, and is configured to acquire the voltage value u1 at time t1 and the voltage value u2 at time t2.

[0009] The data processing module has a pre-stored inductance-distance relationship mapping table and is configured to: based on u2 and the known current-limiting resistor R and supply voltage E, according to the formula Calculate the equivalent resistance r of the inductance measuring head; based on the formula Generate a set of theoretical voltages u corresponding to different inductance L values ​​under fixed E, T, and R parameters;

[0010] The collected u1 is compared with the theoretical voltage u to find the minimum error value. The inductance value L corresponding to this error value is the equivalent inductance of the object being measured.

[0011] The equivalent inductance L is matched with a pre-stored inductance-distance mapping table to output the actual distance of the object to be measured.

[0012] Preferably, in the timing control module, the time interval T ranges from 10 microseconds to 30 microseconds to ensure that the voltage sampling point is located in the sensitive range of inductor current change.

[0013] Preferably, the inductance-distance relationship mapping table is established through calibration experiments. During the calibration process, the value of inductance L ranges from 4mH to 20mH, and the sampling interval is no greater than 0.02mH to ensure the accuracy of distance matching.

[0014] Preferably, the device further includes an output module configured to output the calculated distance in data form when the calculated actual distance enters a preset detection range.

[0015] A two-point voltage sampling type inductive ranging control method, characterized in that it is applied to any of the inductive ranging devices described above, and includes the following steps:

[0016] Step 1: Turn on the power switch Q at time t0 to allow current to flow through the current-limiting resistor R and the inductance measuring head;

[0017] Step 2: At time t1, collect the voltage u1 across the inductance measuring head and the power switch Q;

[0018] Step 3: At time t2, collect the voltage u2 across the inductance measuring head and the power switch Q;

[0019] Step 4: Using equations Calculate the equivalent resistance r of the inductance measuring head;

[0020] Step 5: Using equations Generate the theoretical voltage u corresponding to different inductance L values ​​under fixed parameters;

[0021] Step 6: Compare the value of u1 with the value of u to obtain the L value corresponding to the minimum error;

[0022] Step 7: Match the equivalent inductance L with the pre-stored inductance-distance relationship mapping table to obtain the actual distance of the object to be measured.

[0023] Step 8: Output the calculated distance value. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The schematic diagram of the inductive ranging principle provided by the present invention

[0026] Figure 2 Equivalent circuit diagram of the inductive ranging principle provided by the present invention

[0027] Figure 3 The relationship between the equivalent inductance value and distance of the inductance measuring head provided by this invention

[0028] Figure 4 The timing relationship of the t0, t1 and t2 switch drive signals provided by the present invention

[0029] Figure 5 A flowchart illustrating the implementation of the ranging method provided by this invention. Detailed Implementation

[0030] The preferred embodiment of a two-point voltage sampling inductive ranging sensor and control method of the present invention will be described in detail below with reference to the accompanying drawings. The embodiments revolve around the core features of the claims and are elaborated upon in specific application scenarios. This section aims to fully describe the technical details of the present invention so that those skilled in the art can understand and implement it. It should be noted that the accompanying drawings are merely schematic diagrams and are not drawn to scale, and the present invention is not limited to the specific structure shown in the drawings.

[0031] Hardware Configuration and Component Description

[0032] The core hardware structure of the two-point voltage sampling inductive ranging sensor of the present invention can be found in the appendix. Figure 1 The diagram shows the inductive ranging principle. In this embodiment, the power supply E is a 3.3V DC regulated power supply, and its stability is crucial to the measurement accuracy. The current-limiting resistor R is a 300Ω power resistor with 1% accuracy. The power switch Q is an N-channel MOSFET, which has fast switching speed and low on-resistance.

[0033] The inductance measuring head is the key sensing component of this invention, and its physical structure is a coil wound on a ferrite core. When a metal object approaches, an eddy current effect is generated within the metal, causing a change in the equivalent inductance L of the measuring head. There is a one-to-one mapping relationship between the equivalent inductance L and the distance d, which was obtained through preliminary calibration experiments and stored as an inductance-distance mapping table.

[0034] The functions of the timing control module, signal acquisition module, and data processing module can be implemented by a general-purpose microcontroller (MCU). It should be noted that the MCU must have a built-in high-precision timer and a 12-bit analog-to-digital converter (ADC) to meet the requirements of precise timing control and voltage sampling accuracy.

[0035] Workflow and timing control

[0036] The core of this invention lies in the accurate sampling of the transient process of the circuit. (Appendix) Figure 4 The timing relationship between t0, t1, and t2 and the switching transistor drive signal is given, which is the basis for realizing high-precision ranging.

[0037] The specific workflow is as follows:

[0038] 1. Initialization and Startup: After the system is powered on, the microcontroller loads the inductor-distance mapping table and system parameters pre-stored in the Flash memory.

[0039] 2. Transient Initiation: The microcontroller's timer generates a high-level pulse at time t0, driving MOSFET Q to conduct. Current begins to flow through resistor R and the inductance measuring head, and the circuit enters the charging transient process of the RL circuit.

[0040] 3. First voltage sampling: At time t1 (t1 = t0 + T, T is set to 25 μs in this embodiment), the microcontroller's ADC samples the voltage u1 between the inductance measuring head and the MOSFET. The voltage at this moment contains rich information about the circuit time constant and the inductance value.

[0041] 4. Second voltage sampling: At time t2 (ensuring t2-t0>3τ, where τ is the L / R time constant), the ADC samples the voltage u2 again. At this time, the circuit is close to steady state, and the value of u2 is mainly used to accurately calculate the equivalent resistance r in the loop.

[0042] Data processing and distance calculation

[0043] After sampling is complete, the microcontroller performs the following calculation steps:

[0044] 1. Equivalent resistance calculation: Based on Ohm's law and the steady-state characteristics of the circuit, using the formula... Calculate the equivalent resistance r under the current temperature and operating conditions. This step effectively eliminates the influence of wire resistance and component temperature drift on the measurement.

[0045] 2. Theoretical voltage curve generation: Given E, T, R, r, and an array L of inductance values ​​covering a range of 4mH to 20mH with a step size of 0.02mH,... i Substitute into the transient process voltage formula Generate a theoretical voltage curve u(L) i ).

[0046] 3. Optimal inductor matching: Compare the actual sampled voltage u1 with the theoretical curve u(L) i The values ​​are compared, and the least squares method is used to find the point with the smallest error. The inductance value L corresponding to this point is the accurate equivalent inductance at the current distance. For a more intuitive understanding of the relationship between the equivalent inductance L and the distance d, please refer to the appendix. Figure 3 The figure shows a typical mapping curve obtained in the calibration experiment.

[0047] Distance output: The output module can upload the calculated distance value to the host computer system via a communication protocol.

[0048] Examples and Effects

[0049] In a specific industrial application, this invention is used to detect the distance between the end effector of a robotic arm and the surface of a workpiece. The sensor is mounted on the worktable, facing the workpiece. In one measurement cycle, the sensor measures u1 = 1.366V and u2 = 0.08676V. The calculated equivalent resistance r = 0.85Ω. By comparing u1 = 15.2V with the theoretical curve, the optimal matching inductance L = 8.15mH is found. Consulting the mapping table, it is determined that this inductance value corresponds to a distance of 2.0mm. The system outputs this result to guide the robotic arm in performing precise subsequent operations.

[0050] Tests showed that, within a working temperature range of -10℃ to 60℃, the distance measurement error of this embodiment remained stable within ±0.1mm, and the repeatability reached ±0.05mm, which is significantly better than traditional frequency measurement inductive sensors, fully demonstrating the advantages of this invention in terms of accuracy, stability, and anti-interference.

[0051] It should be noted that this invention is not limited to the embodiments described above, and those skilled in the art can make modifications without departing from the spirit of this invention. For example, the microprocessor can be replaced with an FPGA to improve speed, or the mapping table can be expanded to a three-dimensional model to be compatible with multi-material detection. These modifications all fall within the protection scope of this invention.

[0052] It should be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An inductive distance sensor of the two-point voltage sampling type, characterized in that, The inductance distance measuring device comprises an inductance sensing circuit, a timing control module, a signal acquisition module and a data processing module. The inductance sensing circuit comprises a power supply, an inductance measuring head, a power switch tube and a current limiting resistor. The timing control module is configured to generate a driving signal of the power switch tube Q and accurately control three key time points: a t0 moment when the driving signal is turned on, a t1 moment when a first voltage is collected and a t2 moment when a second voltage is collected, wherein t2=t1+T, T is a preset fixed time interval, t2-t0>3τ, and τ is a circuit time constant. The signal acquisition module is connected to both ends of the inductance measuring head and the power switch tube Q and is configured to collect a voltage value u1 at the t1 moment and a voltage value u2 at the t2 moment. The data processing module pre-stores an inductance-distance relationship mapping table, and is configured to: based on u2, a known current-limiting resistor R, and a power supply voltage E, calculate a theoretical voltage u corresponding to different inductances L under fixed E, T, and R parameters according to a formula Calculate the equivalent resistance r of the inductance measuring head; based on a formula Generate a set of theoretical voltages u corresponding to different inductances L under fixed E, T, and R parameters; The collected u1 is compared with a set of theoretical voltages u, and a minimum error value is found, and the inductance value L corresponding to the error value is the equivalent inductance of the measured object. The equivalent inductance L is matched with a pre-stored inductance-distance relationship mapping table to output the actual distance of the measured object.

2. The electrical distance measuring device according to claim 1, characterized in that In the timing control module, the time interval T ranges from 10 microseconds to 30 microseconds to ensure that the voltage sampling point is located in a sensitive interval of inductance current change.

3. The electrical distance measuring device according to claim 1, characterized in that The inductance-distance relationship mapping table is established through a calibration experiment, and the inductance L ranges from 4 mH to 20 mH during the calibration process, and the sampling interval is not greater than 0.02 mH to ensure the accuracy of distance matching.

4. The electrical distance measuring device according to claim 1, characterized in that The device further comprises an output module configured to output the calculated distance in data form when the calculated actual distance enters a preset detection range.

5. An inductance distance control method of a two-point voltage sampling type, characterized by, The inductance distance measuring device is applied to any one of claims 1-4 and comprises the following steps: Step 1: turn on the power switch tube Q at the t0 moment to make the current flow through the current limiting resistor R and the inductance measuring head; Step 2: collect the voltage u1 between the inductance measuring head and the power switch tube Q at the t1 moment; Step 3: collect the voltage u2 between the inductance measuring head and the power switch tube Q at the t2 moment; Step 4: Utilizing the equation calculating the equivalent resistance r of the inductive measuring head; Step 5: Using the equation The theoretical voltage u corresponding to different inductance L values under fixed parameters is generated; Step 6: compare the value of u1 with the value of u to obtain the L value corresponding to the minimum error; Step 7: match the equivalent inductance L with the pre-stored inductance-distance relationship mapping table to obtain the actual distance of the measured object. Step 8: output the calculated distance value.

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