Patent Application
20240328828
This application claims priority to foreign French patent application No. FR 2303184, filed on Mar. 31, 2023, the disclosure of which is incorporated by reference in its entirety.
The invention relates to the field of detection of proximity and of movement or of deformation for producing sensors. More particularly, the invention relates to a sensor of movement of a movable or deformable proof body coupled to an inductive flux. The scope of the invention can cover weighing devices with wide dynamic range applied for laboratories (1 mg to 200 g), people (1 g to 200 kg) or major works (1 kg to 200 tonnes).
In the field of measurement devices, sensitivity is a crucial parameter, notably in weighing devices or pressure sensors. The sensitivity of a measurement device represents its capacity to detect small variations in the measurement. The more sensitive the device is, the more able it is to accurately measure variations in the measured quantity. More particularly, in the case of weighing devices, an increased sensitivity makes it possible to measure smaller quantities and obtain more accurate results. That can be particularly important in fields such as pharmacology, laboratory research or the agri-food industry, in which accurate and reliable measurements are essential to ensure the quality and the safety of the products or of the scientific research results. Consequently, an adequate sensitivity is essential to guarantee the precision of the results and meet the quality standards currently in force.
In addition, the dynamic range is another important parameter in measurement devices generally, and in weighing or pressure measurement devices in particular. «Dynamic range» is understood to mean the interval comprising the values that are measurable by the measurement device, ranging from the smallest detectable measurement to the largest. A high dynamic range means that the device can measure very small quantities as well as very high quantities. More particularly, in the case of the weighing devices, a wider dynamic range can be particularly useful in the situations in which objects of different weights have to be weighed. For example, a balance with a wider dynamic range can be used to weigh small samples in a research laboratory, and to weigh greater quantities of raw materials in industry. By having a wider dynamic range, the users can obtain accurate and reliable results for a wide panoply of measurements, which is essential for many applications.
In this context, the analysis of the deformation of a proof body presents a solution that is suitable for measuring an applied weight or a force. This method uses an elastic proof body, which is a structural element designed to undergo a deformation in response to an applied force. The deformation provokes a variation of physical characteristics of the proof body which can be converted into electrical signals. For example, the relative deformation of a proof body comprising piezoresistive deformation gauges generates a relative variation of the resistance of the strain gauges. The measurement of this variation of the resistance, necessitates sticking the gauges onto the proof body and establishing a physical electrical connection between the proof body and an electronic circuit. The sensitivity to mechanical shocks and the connection system considerably reduce the robustness of the sensor because a part of the measurement electronics undergoes the mechanical forces applied during the measurement. In engineering, the robustness of a system is defined as the stability of the performance levels despite external conditions exhibiting wide variations that are likely to reduce the reliability of the system. In addition, the total or partial implementation of the measurement electronics on the proof body limits the dynamic range of the sensor to avoid damaging the measurement electronics.
Thus, the objective is to develop a measurement sensor on the basis of a deformable and/or movable proof body with a high sensitivity, a wide dynamic range while ensuring its mechanical and electronic robustness so making it possible to enhance the reliability and the lifetime of the sensor.
The international patent application WO98/19133 describes a dimensional checking device based on the local and selective generation and detection of ultrasounds. The solution is based on the coupling of the ultrasound field between the read head and the surface of the object being probed. The drawback of the solution described is that the measurement device exhibits a high temperature dependency of the order of 1700 ppm/° C. which necessitates a compensation of the drift in temperature of the measurement signal by means of a high-resolution temperature sensor.
The patent application DE10048435A1 describes an inductive sensor of lateral movement of a movable object with respect to a fixed object. The device detects the variations in translation by maintaining a fixed distance between a conductive surface and a circuit in coil form. Although it is effective for detecting the passage of objects, this configuration does not offer a great dynamic range in the direction at right angles to the plane of the detector, or a high resolution at right angles to the plane of the coil.
To mitigate the limitations of the existing solutions with respect to sensitivity, dynamic range and robustness, the invention proposes a sensor which exploits the variation of the relative magnetic permeability of an inductive impedance coupled directly or indirectly with a magnetic coupling element secured with a proof body. The invention is based on a variation of a frequency response of said inductive impedance in response to a pulsed stimulation and/or the variation of a measured amplitude in response to a voltage ramp signal. The invention allows a contactless measurement between the electronic signal processing circuit and the proof body which undergoes mechanical stresses. In addition, the device according to the invention exhibits a low dependency on temperature, which enhances its stability compared to the solutions of the prior art.
The subject of the invention is an inductive sensor comprising a fixed part and a movable part; the movable part comprising:
According to a particular aspect of the invention, the acquisition chain comprises an analogue-digital converter for converting the voltage at the terminals of the reception inductance into a first digital signal.
According to a particular aspect of the invention, the acquisition chain comprises a computer configured to:
According to a particular aspect of the invention, the excitation signal is a square-wave pulse.
According to a particular aspect of the invention, the fixed part further comprises a capacitive element and a resistive element mounted in series with the emission inductance so as to produce an RLC circuit powered by the voltage generator.
According to a particular aspect of the invention, the acquisition chain comprises a computer configured to:
According to a particular aspect of the invention, the excitation signal is a voltage ramp.
According to a particular aspect of the invention, the acquisition chain comprises an amplifier circuit mounted upstream of the analogue-digital converter to amplify the voltage at the terminals of the reception inductance.
According to a particular aspect of the invention, the magnetic coupling element is an object made of a ferrite material in π form or in half-torus form or in rod form or in sheet form.
According to a particular aspect of the invention, the ferrite material is chosen such that the thermal sensitivity of the relative magnetic permeability of said material is less than 1%/° C.
According to a particular aspect of the invention, the emission inductance and the reception inductance are produced in coplanar metal tracks deposited on a printed circuit.
According to a particular aspect of the invention, each of the emission inductance and of the reception inductance is produced by a coil wound around a solid rod.
According to a particular aspect of the invention, the emission inductance is disposed alongside the reception inductance, or superposed on the reception inductance.
According to a particular aspect of the invention, the movable part comprises N magnetic coupling elements mechanically secured to the proof body that are aligned in a row, with N an integer strictly greater than 1; and in which the fixed part comprises N−1 intermediate magnetic coupling elements disposed between the emission inductance and the reception inductance.
Also a subject of the invention is a weight or pressure measurement device comprising an inductive sensor according to the invention.
Other features and advantages of the present invention will become more apparent on reading the following description in relation to the following attached drawings.
The movable part 2 comprises a proof body CE and a magnetic coupling element Fe mechanically secured to the proof body CE.
The proof body CE is a bridge or a plate orthogonal to the first direction Z. The proof body CE can be movable or elastically deformable in the first direction Z following the application of a force F in said first direction. The applied force F corresponds for example to the weight of a physical object resting on the proof body CE or to a pressure exerted on its top surface. In the case of a proof body CE that is movable by translation in the first direction Z, elastic means are attached to the proof body CE in order to replace it in its initial position in the absence of an applied force F.
The magnetic coupling element Fe is mechanically secured to the proof body CE so as to follow its movement or its deformation in the first direction Z. The magnetic coupling element Fe is an object produced in ferromagnetic material in π form or in half-torus form or in rod form or in sheet form. As an example, the ferromagnetic material is a ferrite produced in an alloy of Ni—Zn or Mn—Zn or Co—Ni—Zn.
Advantageously, the ferromagnetic material exhibits a thermal sensitivity of said relative magnetic permeability μr less than 1%/° C. Furthermore, the ferromagnetic material has a high bandwidth ranging up to 50 MHz.
Advantageously, apart from the sheet case, it is possible to wind metal turns around the magnetic coupling element Fe in order to improve the magnetic coupling capabilities of the magnetic coupling element Fe.
In the example illustrated, the magnetic coupling element Fe is in π form, comprises a base and two parallel protuberances which extend from said base in the first direction Z. The protuberances can be straight rods, or be of tapered form. The base is fixed onto a surface, preferably the bottom surface, of the proof body CE, and the protuberances extend orthogonally to said surface downwards.
The fixed part 1 comprises a voltage generator G1, a coil transformer 12 comprising an emission inductance L1 mounted in parallel with the generator G1 and a reception inductance L2, and an acquisition chain 11 connected to the reception inductance L2.
The generator G1 is configured to generate an excitation signal Vin in electrical pulse form and exhibits an output resistance Rs less than 0.5Ω. The fixed part 1 further comprises a capacitive element C1 mounted in series with the output resistance Rs and the emission inductance L1. The capacitive element C1, the output resistance Rs and the emission inductance L1 together form an RLC circuit excited by the electrical pulse Vin generated by the generator G1. The dimensioning of the capacitive element C1 and the emission inductance L1 is chosen so as to have a damping factor ζ less than 0.7 so as to obtain a damped oscillatory regime following the application of the electrical pulse Vin.
The reception inductance L2 is placed in proximity to the emission inductance L1 to allow a magnetic coupling between the two inductances and thus obtain an energy transformer 12 mode of operation. The axis of the emission inductance L1 and the axis of the reception inductance L2 are oriented in the first direction Z. Thus, the variations of the voltage at the terminals of the emission inductance L1 are reproduced at the terminals of the reception inductance L2. The initial state of the inductive sensor D1 corresponds to the absence of a force F on Z applied to the proof body CE. In the initial state of the sensor D1, the first protuberance of the magnetic coupling element Fe in π form is placed at a predetermined initial distance d=d0 with respect to the top end of the emission inductance L1.
Advantageously, in the initial state of the sensor D1, the second protuberance of the magnetic coupling element Fe in π form is placed at said predetermined distance d=d0 with respect to the top end of the reception inductance L2. This configuration offers the advantage of twice duplicating the dependency of the magnetic flux produced at the axial output of the emission inductance L1 with the variation of the distance d: a first dependency characteristic of the axial decay of the magnetic flux produced by the emission inductance L1 when the magnetic coupling element is moved away or brought closer and a second dependency which characterizes the transfer of the magnetic field from the magnetic coupling element to the reception inductance L2.
The emission inductance L1, the reception inductance L2 and the magnetic coupling element Fe together form an assembly called «inductive part» of the sensor D1. The «inductive part» has an equivalent inductance value Leq.
The response to an excitation by a square-wave pulse Vin of the circuit RsLeqC1 is a damped pseudo-periodic oscillation. The oscillatory response is also reproduced at the terminals of the reception inductance L2 by magnetic coupling. The resonance frequency f observed at the terminals of the reception inductance L2 is determined by the following expression:
With N the number of contiguous turns of the emission inductance L1, R the radius of the turns of the emission inductance L1, I the length of the contiguous turns of the emission inductance L1, μ0 the magnetic permeability of the vacuum and μr,eq the equivalent relative magnetic permeability of the inductive part as a function of the relative magnetic permeability μr of the magnetic coupling element and the distance d separating the magnetic coupling element Fe from the emission inductance L1.
Among the abovementioned parameters, the distance d is the only parameter that is variable following the application of a force F on the proof body CE. The application of the force F in the direction Z induces the translation or the deformation of the proof body CE in the direction Z. That induces a variation of the distance d separating the magnetic coupling element Fe from the emission inductance L1. That induces a variation of μr,eq, the equivalent relative magnetic permeability of the inductive part. That induces a variation of the resonance frequency of the voltage VL2 observed at the terminals of the reception inductance L2 in response to the square-wave electrical pulse Vin. This chain of dependency thus makes it possible to convert the amplitude of the applied force F into a measurable parameter, namely the variation of the resonance frequency f.
The acquisition chain 11 comprises an analogue-digital converter DAC for converting the voltage VL2 (analogue signal) at the terminals of the reception inductance L2 into a first digital signal Vdig. The first digital signal Vdig thus corresponds to a digitized oscillatory signal with a resonance frequency f equal to that of the voltage VL2. The analogue-digital converter DAC is characterized by a predetermined sampling frequency fDAC. The values of the capacitance C1 and of the emission inductance L1 are chosen so as to always have a resonance frequency F less than half the sampling frequency fDAC of the analogue-digital converter DAC. For example, the sampling frequency fDAC is equal to 12 MHz so the resonance frequency f is always less than 6 MHz when the sensor D1 is operating.
The acquisition chain 11 further comprises a computer ECU configured to:
The reference frequency f0 is measured beforehand in a calibration step corresponding to the following conditions: F=F0 and d=d0. The reference frequency f0 is then stored as digital datum in the memory of the computer ECU. In the calibration operation, it is possible to be based on a reference applied force F=F0 that is non-zero.
The sensor thus generates a signal Vout of measurement of the variation of the distance Δd following a movement or the deformation of the proof body CE. The measurement signal Vout corresponding to a measurement of the variation of the frequency Δf=f1−f0.
Advantageously, the ferromagnetic material of the magnetic coupling element Fe exhibits an initial relative magnetic permeability μr between 1 and 1500. That makes it possible to increase the effect of the variation of the distance separating the magnetic coupling element Fe on the variation of the equivalent inductance Leq with a range of variation of between 10% to 400% and more particularly around 50% to 150%.
Advantageously, the protuberances of the magnetic coupling element Fe have a diameter less than that of the inductances L1 and L2. Their profile can be tapered. Thus, the insertion of the protuberances of the magnetic coupling element Fe in each of the inductances L1 and L2 makes it possible to considerably increase the dynamic range of the sensor D1. In addition, that makes it possible to maximize the magnetic coupling between the inductances L1 and L2 and thus increase the sensitivity of the inductive sensor according to the invention.
In the solution according to the invention, the physical quantity that is variable following the application of a force is a separation distance. The fixed part 1 corresponds to the measurement electronic circuitry which is not implemented directly on the proof body CE. That makes it possible to avoid applying mechanical stresses on the measurement electronic circuitry when using the sensor D1. That makes it possible to avoid the degradation of the components and electrical connections and thus makes it possible to improve the robustness of the sensor D1 with respect to the prior art solutions.
When the magnetic coupling element Fe approaches the ends of the inductances L1 and L2, the distance d decreases. That induces an increase of the equivalent relative magnetic permeability μr,eq of the inductive part which is reflected by an increase of the equivalent inductance Leq and at the same time a stronger magnetic coupling between the emission inductance L1 and the reception inductance L2. This effect is amplified if the magnetic losses in the magnetic coupling element Fe are low, which is the case of a ferrite in Π or half-torus form. Advantageously, the number of turns of the reception inductance L2 is greater, by preferably 2 to 5 times, than the number of turns of the emission inductance L1 so as to improve the sensitivity of the inductive sensor according to the invention.
Three results are then obtained simultaneously: a reduction of the measured resonance frequency Δf=f1−f0>0; an increase of the amplitude of the resonance peak because the magnetic coupling is improved; and an increase of the quality factor Q of the inductive part because the width of the resonance peak is reduced (BW1−BW0<0). Conversely, when the magnetic coupling element Fe moves away from the ends of the inductances L1 and L2, the distance d increases. That induces a reduction of the equivalent relative magnetic permeability μr,eq of the inductive part; which reduces the value of the equivalent inductance Leq and at the same time is reflected by a weaker magnetic coupling between the emission inductance L1 and the reception inductance L2. Three results are then obtained simultaneously: an increase of the measured resonance frequency Δf=f2−f0>0; a reduction of the amplitude of the resonance peak because the magnetic coupling is reduced; and a reduction of the quality factor Q of the inductive part because the width of the resonance peak is increased (BW2−BW0<0).
Thus, an inductive sensor D1 is obtained that has performance levels that are enhanced in terms of sensitivity, of dynamic range and of robustness. For example, the resonance frequency can vary by 50%, with a range of between, preferably, 2 and 6 MHz with a maximum travel of 3 mm in the first direction Z, preferably less than 1 mm. The frequency resolution is approximately 2.5 ppm (parts per million) with a measurement rate of 5 Hz, whereas the resolution in variation of the distance d is approximately 10 nm.
of between 2 and 11. The amplification circuit AMP has an input impedance RL greater than or equal to 105 times the residual resistance of the turns of the reception inductance L2.
The reference amplitude A0 is measured beforehand in a calibration step corresponding to the following conditions: F=F0 (with F0 possibly zero) and d=d0. The reference amplitude A0 is then stored as digital datum in the memory of the computer ECU.
The sensor thus generates a signal Vout of measurement of the variation of the distance Δd following a movement or the deformation of the proof body CE. The measurement signal Vout corresponds to a measurement of the variation of the amplitude ΔA=A1−A0.
The voltage plateau VL2 makes it possible to obtain a plurality of amplitude measurement points. The computer is thus configured to carry out an acquisition of several measurement points and then calculate an average to improve the resolution of the measurement.
Also, the fixed part 1 comprises N−1 (in the case illustrated, just one) intermediate magnetic coupling elements Fe1′ disposed between the emission inductance L1 and the reception inductance L2. Each intermediate magnetic coupling element Fei′ of rank i is intended to magnetically couple the magnetic coupling element Fei of the same rank i in the row of the movable part 2 to the next magnetic coupling element Fei+1. A cascaded magnetic coupling is thus produced.
The magnetic coupling elements Fei of the movable part 2 are separated by a distance d from the magnetic coupling elements Fei′ of the fixed part 1. Said distance is equal to the separation distance between magnetic coupling elements Fei of the movable part 2 and the inductances L1 and L2. That makes it possible to increase the dependency of the frequency and/or of the amplitude according to the variation of said separation distance d. More particularly, a dN dependency is obtained which considerably improves the sensitivity of the sensor.
In practice, the high losses in the magnetic coupling elements associated with this configuration cause the influence of the reception inductance L2 on the resonance frequency or the amplitude to be negligible by comparison to the cumulative effect of the magnetic permeability of the coupling elements as a function of the distance d on the equivalent magnetic permeability of the circuit. It is thus possible to achieve a configuration in which the introduction of a lateral magnetic insulation between the inductances L1 and L2 is strong through magnetic shielding. This means that the contribution of the lateral direct magnetic coupling between the inductances L1 and L2 is negligible compared to the effect of the magnetic coupling elements Fei and Fei′. The result thereof is that the contribution of the reception inductance L2 to the variations of the resonance frequency or the amplitude of the output signal Vout is negligible, above all if the number of turns of the reception inductance L2 is small, for example 2 to 5 times smaller, than the number of turns of the emission inductance L1.
Conversely, if the number of turns of the reception inductance L2 is great compared to that of the emission inductance L1, for example 2 to 5 times greater, and if the direct lateral magnetic insulation between L1 and L2 is great (through shielding), then the contribution of the reception inductance L2 to the variations of the resonance frequency or to the amplitude of the output signal Vout can become significant for small variations of d. That induces a significant increase of the range of variation of the frequency and/or of the amplitude of the output signal Vout
| Number | Date | Country | Kind |
|---|---|---|---|
| 2303184 | Mar 2023 | FR | national |
