A zero-adjustable linear variable differential transformer and an adjusting method thereof

Abstract

The application belongs to the technical field of sensors, and discloses a linear variable differential transformer with adjustable zero and a method for adjusting the same. A coil frame of the transformer is movably sleeved on an inner tube frame, and a cylindrical shell is arranged outside the coil frame. Left and right end covers are respectively arranged at two ends of the cylindrical shell. An assembly composed of an iron core and a connecting rod is arranged inside the inner tube frame. The right end cover is rotatable relative to the cylindrical shell, and rotation of the right end cover can drive the coil frame to move axially on the inner tube frame. Through design of a differential screw mechanism, displacement reduction effect generated by threads with different pitches and same rotation directions is utilized to achieve micron-level or even sub-micron-level zero adjustment precision, which is 500 to 1000 times higher than millimeter-level adjustment precision of the prior art. A pure mechanical adjustment mechanism is adopted, and no additional electronic components are needed, so that circuit complexity and potential failure points introduced by electronic zero adjustment methods are avoided, and system reliability is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology and relates to a differential transformer, specifically a zero-position adjustable linear variable differential transformer and its adjustment method. Background Technology

[0002] A linear variable differential transformer (LVDT) is a displacement sensor based on the principle of electromagnetic induction. It measures the axial displacement of the iron core by generating an alternating magnetic field through the excitation of a primary coil and outputting a differential voltage signal from a secondary coil. LVDTs offer advantages such as non-contact measurement, high sensitivity, good linearity, and repeatability, and are widely used in aerospace, precision machine tools, hydraulic control, and other fields requiring high accuracy in displacement measurement.

[0003] In practical applications, due to manufacturing tolerances, assembly errors, and installation stress, the mechanical zero point (the position of the iron core at its geometric center) of the LVDT often does not coincide with the electrical zero point (the position where the differential output voltage is zero), resulting in zero-point deviation. This zero-point deviation directly affects the measurement accuracy, and is particularly prominent in high-precision displacement detection applications.

[0004] In existing technologies, zero-point compensation in LVDTs primarily relies on electronic zeroing via subsequent signal processing circuitry. This method electronically corrects zero-point deviation by adding a compensation circuit at the output. However, electronic zeroing introduces additional electronic components and conditioning circuitry, increasing system complexity and potential failure points. Furthermore, the compensation range is limited by circuit design, making it difficult to effectively compensate for larger zero-point deviations. Moreover, electronic zeroing cannot eliminate the inherent mismatch between mechanical and electrical zero points; zero-point drift persists after temperature changes or prolonged use.

[0005] Another common method is to achieve zero-point calibration through mechanical adjustment. For example, adjusting shims can be added to the sensor mounting flange, or the relative position of the core and coil can be changed by fine-tuning the overall sensor mounting position. While this method can eliminate zero-point deviation mechanically, the adjustment accuracy is limited by the shim thickness or the resolution of the mounting adjustment mechanism, typically achieving only millimeter-level or even lower precision. For applications requiring micrometer-level zero-point calibration, this method is clearly insufficient. Furthermore, the mechanical adjustment process requires repeated disassembly, testing, and reinstallation, making it cumbersome and time-consuming, especially inconvenient in field environments.

[0006] Some technical solutions attempt to incorporate adjustment mechanisms within the sensor. For example, threaded connections can be used to adjust the position of coil or core assemblies. However, these solutions typically employ a single thread structure, and their adjustment accuracy is directly limited by the thread pitch. The pitch of conventional threads is generally in the range of 0.5 to 1.0 millimeters. Even with fine-pitch threads, the displacement per revolution remains in the millimeter range, making it difficult to achieve micrometer-level or even sub-micrometer-level precision adjustments.

[0007] Therefore, a technical solution is needed that can achieve high-precision zero-position adjustment, is easy to operate, has a compact structure, and is highly reliable, in order to meet the zero-position correction requirements of high-precision LVDT in practical applications. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a zero-position adjustable linear variable differential transformer and its adjustment method, which achieves ultra-high precision and stepless adjustment of the electrical zero position through an innovative differential thread structure.

[0009] The technical solution of the present invention is as follows: A zero-position adjustable linear variable differential transformer is disclosed, wherein the transformer's coil frame is movably mounted on an inner tube frame, and the coil frame is enclosed in a cylindrical shell, with a left end cover and a right end cover respectively mounted at both ends of the cylindrical shell. The transformer's core and connecting rod assembly are located inside the inner tube frame; wherein the right end cover is rotatable relative to the cylindrical shell, and the rotation of the right end cover can drive the coil frame to move axially on the inner tube frame.

[0010] Furthermore, the left end of the right end cover is connected to the right end of the coil frame, and a spring is provided between the left end of the coil frame and the left end cover.

[0011] Furthermore, a linear guide mechanism is provided outside the coil frame, which prevents the coil frame from rotating.

[0012] Furthermore, the right end cap is connected to the cylindrical outer shell by a threaded connection, and the left end of the right end cap is also connected to the right end of the coil frame by a threaded connection.

[0013] Furthermore, the pitch of the external thread that mates with the cylindrical outer shell on the right end cap is P2, and the pitch of the external thread that mates with the right end cap of the coil bobbin is P1, where P1 is greater than P2.

[0014] Furthermore, P2 is set between 0.8 times P2 and 0.95 times P1.

[0015] Furthermore, the right end face of the right end cover is a circular surface, and the circumference of the right end face of the right end cover is provided with uniform graduations, and the circumference of the right end cover is provided with anti-slip knurling.

[0016] Furthermore, it also includes an insulating screw, which is inserted radially from the outside of the cylindrical housing into the inside of the right end cover for unlocking and locking the position of the right end cover.

[0017] A method for adjusting a zero-position adjustable linear variable differential transformer, wherein the aforementioned zero-position adjustable linear variable differential transformer is adjusted to zero position: S1, fix the cylindrical outer shell and push the iron core to the mechanical zero position; S2, energize the zero-position adjustable linear variable differential transformer, detect the output of the zero-position adjustable linear variable differential transformer, and rotate the right end cover when the output signal is not zero; S3, the rotation of the right end cover is converted into a small axial displacement of the coil frame through the differential thread mechanism, and the adjustment stops when the output signal is zero; S4. Fix the position of the right end cover to complete the zero-position adjustment of the zero-position adjustable linear variable differential transformer.

[0018] The advantages of this invention are as follows: 1. By designing a differential thread mechanism, the displacement reduction effect generated by two threads with unequal pitches and the same direction of rotation is utilized to achieve zero-position adjustment accuracy at the micron or even sub-micron level. When the pitch P1 of the first thread pair is 1.0 mm and the pitch P2 of the second thread pair is 0.9 mm, the net displacement generated by rotating the end cover one revolution is only 0.1 mm. If the end cover circumference is set with 100 divisions, an adjustment accuracy of 1 micron can be achieved for each division, which is 500 to 1000 times higher than the millimeter-level adjustment accuracy of the existing technology.

[0019] 2. The system adopts a purely mechanical adjustment mechanism, which eliminates the need for additional electronic components. This avoids the circuit complexity and potential failure points introduced by electronic zeroing methods, significantly improving system reliability and reducing the failure rate by approximately 50%.

[0020] 3. The adjustment mechanism is integrated inside the sensor, while the operation interface is exposed. Adjustment can be completed on-site in any environment without disassembly or return to the factory. The adjustment time is reduced from several hours in the traditional method to several minutes, and the maintenance cost is significantly reduced.

[0021] 4. The structure is compact, and the adjustment mechanism does not occupy additional axial or radial space. The overall volume is reduced by about 30% compared with the solution that requires an external adjustment device. It is particularly suitable for short to medium stroke, small space and high precision displacement detection applications.

[0022] 5. Through the design of spring preload and locking mechanism, the zero position stability is good after adjustment. The zero position stability reaches ±2 micrometers in the temperature range of -40℃ to +85℃, the repeatability reaches ±1 micrometer, and the zero position residual voltage is reduced from ±10mV before adjustment to less than 1mV, with the accuracy improved by more than 10 times. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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.

[0024] Figure 1 This is a schematic cross-sectional view of the overall structure of the zero-position adjustable LVDT of the present invention.

[0025] Figure 2 for Figure 1 Schematic diagram of the principle of the differential thread fine adjustment mechanism.

[0026] Among them, 1—cylindrical outer shell, 2—left end cover, 3—spring, 4—coil frame, 5—magnetic cover, 6—secondary coil, 7—primary coil, 8—inner tube frame, 9—iron core, 10—connecting rod, 11—right end cover, 12—insulating screw, 13—magnetic sheet, 14—adjusting shim. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0029] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0031] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] First embodiment: A zero-position adjustable linear variable differential transformer is provided, wherein the transformer coil frame 4 is movably mounted on the inner tube frame 8, the coil frame 4 is surrounded by a cylindrical shell 1, and the two ends of the cylindrical shell 1 are respectively equipped with a left end cover 2 and a right end cover 11. The transformer core 9 and the connecting rod 10 are arranged inside the inner tube frame 8; wherein, the right end cover 11 can rotate relative to the cylindrical shell 1, and the rotation of the right end cover 11 can drive the coil frame 4 to move axially on the inner tube frame 8.

[0033] The left end of the right end cover 11 is connected to the right end of the coil frame 4, and a spring 3 is provided between the left end of the coil frame 4 and the left end cover 2.

[0034] The coil frame 4 is provided with a linear guide mechanism, which prevents the coil frame 4 from rotating.

[0035] The right end cover 11 is connected to the cylindrical outer shell 1 by a threaded connection, and the left end of the right end cover 11 is also connected to the right end of the coil frame 4 by a threaded connection.

[0036] The pitch of the external thread that mates with the cylindrical outer shell 1 on the right end cover 11 is P2, and the pitch of the external thread that mates with the right end of the coil frame 4 on the right end is P1, where P1 is greater than P2.

[0037] P2 is set between 0.8 times P2 and 0.95 times P1.

[0038] The right end face of the right end cover 11 is a round surface. The circumference of the right end face of the right end cover 11 is evenly divided, and the circumference of the right end cover 11 is provided with anti-slip knurling.

[0039] It also includes an insulating screw 12, which is inserted radially from the outside of the cylindrical housing 1 into the right end cover 11 for unlocking and locking the position of the right end cover 11.

[0040] A method for adjusting a zero-position adjustable linear variable differential transformer, wherein the aforementioned zero-position adjustable linear variable differential transformer is adjusted to zero position: S1, fix the cylindrical outer shell and push the iron core to the mechanical zero position; S2, energize the zero-position adjustable linear variable differential transformer, detect the output of the zero-position adjustable linear variable differential transformer, and rotate the right end cover when the output signal is not zero; S3, the rotation of the right end cover is converted into a small axial displacement of the coil frame through the differential thread mechanism, and the adjustment stops when the output signal is zero; S4. Fix the position of the right end cover to complete the zero-position adjustment of the zero-position adjustable linear variable differential transformer.

[0041] Second embodiment: See Figure 1 This embodiment provides a zero-position adjustable linear variable differential transformer, including a cylindrical shell 1, a left end cover 2, a spring 3, a coil frame 4, an inner tube frame 8, an iron core 9, a connecting rod 10, a right end cover 11, and an insulating screw 12.

[0042] The coil frame 4 is axially movable and fitted onto the inner tube frame 8, with a fitting clearance of 0.05mm to 0.1mm between them. This ensures that the coil frame 4 can move freely along the axial direction while avoiding radial wobble caused by excessive clearance. A cylindrical outer shell 1 covers the coil frame 4, and the two ends of the outer shell 1 are respectively equipped with a left end cap 2 and a right end cap 11. The iron core 9 and the connecting rod 10 are connected by threads and fixed with fastening sealant to form an iron core assembly. This iron core assembly is set in the inner hole of the inner tube frame 8 and can move axially.

[0043] The core technical feature of this embodiment lies in the design of the differential thread fine-tuning mechanism. The right end cover 11 is rotatable relative to the cylindrical outer shell 1. The right end cover 11 and the coil frame 4 are connected by a threaded engagement to form a first threaded pair, and the right end cover 11 and the cylindrical outer shell 1 are connected by a threaded engagement to form a second threaded pair. Specifically, the end of the coil frame 4 closest to the right end cover 11 is machined with a first internal thread, and the inside of the right end cover 11 is correspondingly machined with a first external thread that mates with it, together forming the first threaded pair with a pitch of P1. The inner wall of the right end of the cylindrical outer shell 1 is machined with a second internal thread, and the outside of the right end cover 11 is correspondingly machined with a second external thread that mates with it, together forming the second threaded pair with a pitch of P2. The pitches of the two threads are unequal and the directions of rotation are the same; both are right-hand threads.

[0044] The left end face of the right end cover 11 is connected to the right end face of the coil frame 4 via a first threaded pair. A spring 3 is provided between the left end of the coil frame 4 and the left end cover 2. The spring 3 provides axial preload to the coil frame 4, eliminates the axial gap between the coil frame 4 and the inner tube frame 8, and ensures that the position of the coil frame 4 is stable and repeatable during adjustment.

[0045] The coil frame 4 is equipped with a linear guide mechanism, specifically a key and keyway mating structure. A guide key is machined axially on the outer wall of the inner tube frame 8, and a corresponding guide keyway is machined on the inner wall of the coil frame 4, with the guide key embedded in the guide keyway. This linear guide mechanism restricts the circumferential rotation of the coil frame 4, allowing it to move only axially and preventing it from rotating with the right end cover 11.

[0046] The right end face of the right end cover 11 is circular, with 100 graduation lines evenly distributed on the circumference. The central angle between two adjacent graduation lines is 3.6 degrees. The outer circumference of the right end cover 11 is machined with anti-slip knurling to facilitate the operator to rotate the right end cover 11 with their fingers or tools.

[0047] An insulating screw 12 is radially disposed on the cylindrical outer shell 1 and inserted radially from the outside of the outer shell 1, with the end of the screw contacting the outer circumferential surface of the right end cover 11. When adjustment is required, the insulating screw 12 is loosened, and the right end cover 11 can rotate freely; after adjustment, the insulating screw 12 is tightened, and the radial clamping force of the screw end on the right end cover 11 locks the relative position of the right end cover 11 and the cylindrical outer shell 1, preventing the position from loosening due to vibration or temperature changes after adjustment.

[0048] The main structural parameters in this embodiment are shown in the table below.

[0049]

[0050] In this embodiment, when the operator rotates the right end cover 11, because the pitches of the first and second threaded pairs are unequal and their directions of rotation are the same, the rotation of the right end cover 11 simultaneously drives the coil frame 4 to produce an axial displacement relative to the right end cover 11 itself, and also drives the right end cover 11 to produce an axial displacement relative to the fixed cylindrical outer shell 1. Since the coil frame 4 is restricted by the linear guide mechanism and cannot rotate, but can only move axially, the net displacement of the coil frame 4 relative to the fixed cylindrical outer shell 1 is the resultant of the above two displacements. This net displacement is much smaller than the displacement produced by a single threaded pair, thereby achieving micron-level or even submicron-level precision adjustment.

[0051] Third embodiment: See Figure 2 This embodiment, based on Embodiment 1, elaborates in detail the working principle of the differential thread fine-tuning mechanism.

[0052] The working principle of the differential thread fine-tuning mechanism is based on the displacement reduction effect generated by two threads with unequal pitch and the same direction of rotation. In the differential thread structure, the right end cover 11 is equivalent to the screw, the cylindrical outer shell 1 is equivalent to the fixed nut, and the coil frame 4 is equivalent to the movable nut.

[0053] Assume the operator rotates the right end cover 11 clockwise one full turn, i.e., 360 degrees. Due to the presence of the second threaded joint, the right end cover 11 moves axially to the right relative to the fixed cylindrical outer shell 1. Figure 1 The coil bobbin 4 moves a distance L2 to the right (from the center), which is equal to the pitch P2 of the second threaded pair, i.e., L2=P2. At the same time, due to the presence of the first threaded pair, the rotation of the right end cover 11 will push the coil bobbin 4 to move a distance L1 to the left relative to the right end cover 11 itself along the axial direction, which is equal to the pitch P1 of the first threaded pair, i.e., L1=P1.

[0054] Since the coil frame 4 is restricted from rotating by the linear guide key on the inner tube frame 8 and can only move axially, the net displacement ΔL of the coil frame 4 relative to the fixed cylindrical outer shell 1 is the resultant of the two displacements mentioned above.

[0055] Since the pitch P1 of the first threaded pair is greater than the pitch P2 of the second threaded pair, and the two values ​​are very close, the net displacement ΔL is much smaller than the displacement P1 or P2 produced by a single threaded pair, thus achieving a displacement reduction effect.

[0056] In this embodiment, the pitch P1 of the first threaded pair is 1.0 mm, the pitch P2 of the second threaded pair is 0.9 mm, and the net displacement ΔL generated by rotating the right end cover 11 one revolution is only 0.1 mm. If 100 graduation lines are evenly distributed on the circumference of the right end cover 11, then for each graduation, i.e., a rotation of 3.6 degrees, the axial displacement of the coil frame 4 relative to the cylindrical outer shell 1 is 0.1 mm ÷ 100 = 0.001 mm, or 1 micrometer. This means that by rotating the graduation lines of the right end cover 11, a displacement adjustment accuracy of 1 micrometer can be achieved.

[0057] The ratio of the pitch P2 of the second threaded pair to the pitch P1 of the first threaded pair directly affects the adjustment accuracy and ease of operation. When the P2 / P1 ratio is closer to 1, the pitch difference ΔP = P1 - P2 is smaller, the net displacement per revolution is smaller, and the adjustment accuracy is higher. However, more revolutions are required to achieve a larger adjustment, reducing ease of operation. Conversely, when the P2 / P1 ratio is further away from 1, the pitch difference ΔP is larger, the adjustment accuracy decreases, but the ease of operation improves.

[0058] Through theoretical analysis and practical testing, it was found that when the pitch P2 of the second threaded pair is within the range of 0.8P1 to 0.95P1, a good balance can be achieved between adjustment accuracy and operational convenience. Specifically, when P2 = 0.8P1, the pitch difference ΔP = 0.2P1, the adjustment accuracy is at a medium level, but the operation is relatively fast; when P2 = 0.9P1, the pitch difference ΔP = 0.1P1, the adjustment accuracy is relatively high, and the operation speed is moderate; when P2 = 0.95P1, the pitch difference ΔP = 0.05P1, the adjustment accuracy is extremely high, but the operation is relatively slow.

[0059] The effects of different pitch parameters on adjustment performance are shown in Table 2.

[0060]

[0061] As shown in Table 2, by selecting an appropriate pitch ratio, a balance can be struck between adjustment accuracy and operational convenience according to actual application requirements. For applications requiring extremely high precision, a parameter combination of P2=0.95P1 can be selected to achieve a single indexing displacement of 0.5 micrometers; for applications requiring a balance between accuracy and efficiency, a parameter combination of P2=0.9P1 can be selected to achieve a single indexing displacement of 1 micrometer.

[0062] Theoretically, by further reducing the pitch difference ΔP, for example, by choosing P2 = 0.98P1, sub-micron level adjustment accuracy can be achieved. However, this would significantly reduce operational convenience and impose higher requirements on thread machining and assembly accuracy. Therefore, in practical applications, P2 in the range of 0.8P1 to 0.95P1 is the optimal choice.

[0063] This embodiment improves the millimeter-level adjustment accuracy of ordinary threads to the micrometer-level or even submicrometer-level through a differential thread fine-tuning mechanism. The adjustment accuracy is 500 to 1000 times higher than that of the prior art, and no additional electronic components or complex mechanical structures are required, resulting in high system reliability.

[0064] Fourth embodiment: This embodiment, based on Embodiments 2 and 3, adds the internal structure of the linear variable differential transformer and details the zero-position adjustment method.

[0065] See Figure 1 A primary coil 7 and two secondary coils 6 are wound on the coil frame 4. The primary coil 7 is wound in the middle of the coil frame 4, with 500 turns and a wire diameter of 0.2 mm. The two secondary coils 6 are wound on the left and right sides of the primary coil 7, respectively, symmetrically arranged about the primary coil 7, with each secondary coil having 250 turns and a wire diameter of 0.15 mm. The primary coil 7 and the secondary coils 6 are insulated with a fiberglass layer with a thickness of 0.1 mm.

[0066] Magnetic conductive sheets 13 are glued to the front and rear end caps of the coil frame 4, respectively. Insulating sheets are glued to the magnetic conductive sheets 13. The magnetic conductive sheets 13 and the insulating sheets together serve to close the magnetic circuit and provide electrical insulation. A magnetic cover 5 is fitted outside the coil assembly. The magnetic cover 5 is a cylindrical structure made of permalloy and is used to shield external magnetic field interference and improve the sensor's anti-interference capability.

[0067] The iron core 9 is a cylindrical structure with a length of 30mm and an outer diameter of 8mm, made of permalloy. The iron core 9 is threadedly connected to the connecting rod 10, which extends outside the cylindrical outer shell 1 for connection to the object being measured. The iron core 9 can move freely axially within the inner hole of the inner tube frame 8. When the object being measured is displaced, the connecting rod 10 drives the iron core 9 to move axially within the inner hole of the inner tube frame 8, changing the relative position of the iron core 9 with the primary coil 7 and the secondary coil 6, thereby changing the output voltage difference between the two secondary coils 6 and realizing the conversion of displacement into a voltage signal.

[0068] The working principle of a linear variable differential transformer is as follows: An AC excitation voltage is applied to the primary coil 7, which generates an alternating magnetic field. This magnetic field is coupled to the two secondary coils 6 through the iron core 9, inducing voltages in each secondary coil 6. When the iron core 9 is in the center position, the voltages induced in the two secondary coils 6 are equal in magnitude but opposite in phase, and the differential output voltage is zero; this position is called the electrical zero position. When the iron core 9 deviates from the center position, the voltages induced in the two secondary coils 6 are not equal, the differential output voltage is not zero, and the output voltage is proportional to the displacement of the iron core 9.

[0069] In practical applications, due to the influence of manufacturing tolerances, assembly errors, and installation stress, the mechanical zero position (geometric center position) of the iron core 9 often does not coincide with the electrical zero position (the position where the differential output voltage is zero), resulting in zero position deviation. In this embodiment, a differential thread fine-tuning mechanism is used to adjust the axial position of the coil frame 4 relative to the fixed cylindrical outer shell 1 and the iron core 9, thereby changing the relative position of the coil assembly and the iron core 9 and achieving precise adjustment of the electrical zero position.

[0070] The zero-point adjustment method includes the following steps: Step S1: Fix the cylindrical outer shell 1 and push the iron core 9 to the mechanical zero position. Specifically, install the sensor on the fixing fixture, ensuring that the cylindrical outer shell 1 cannot move, and then push the iron core 9 to the center position of the inner hole of the inner tube frame 8 through the connecting rod 10. This position is the mechanical zero position.

[0071] Step S2: Apply an excitation signal to the sensor and monitor the output signal. Specifically, apply an AC excitation voltage of 5V and 5kHz to the primary coil 7, and use a high-precision voltmeter to monitor the differential output voltage of the two secondary coils 6.

[0072] Step S3: When the output signal deviates from zero, rotate the right end cover 11. If the monitored differential output voltage is not zero, for example, +8mV, it indicates that the electrical zero point and the mechanical zero point do not coincide and adjustment is required. Loosen the insulating screw 12 and rotate the anti-slip knurling on the right end cover 11 with your fingers or a tool. Each rotation of 10 graduations corresponds to a 10-micrometer axial displacement of the coil frame 4 relative to the cylindrical outer shell 1. The rotation of the right end cover 11 is converted into a small axial displacement of the coil frame 4 through the differential thread mechanism, changing the relative center position of the coil assembly and the iron core 9.

[0073] Step S4: When the output signal reaches the preset zero-position threshold, stop rotating the right end cover 11. During the adjustment process, continuously monitor the differential output voltage. When the absolute value of the output voltage is less than 1mV, it is considered that the electrical zero position has been adjusted to the correct position, and stop rotating the right end cover 11.

[0074] Step S5: Lock the relative position of the right end cover 11 and the cylindrical outer shell 1. Tighten the insulating screw 12 to lock the relative position of the right end cover 11 and the cylindrical outer shell 1 through the radial clamping force of the screw end on the right end cover 11, preventing the position from loosening due to vibration or temperature changes after adjustment.

[0075] In this embodiment, the zero-position residual voltage of the sensor before adjustment was ±10mV, corresponding to a displacement error of approximately ±50 micrometers. After adjustment using the above method, the zero-position residual voltage was reduced to less than 1mV, and the corresponding displacement error was less than 5 micrometers, improving the zero-position accuracy by more than 10 times. After adjustment, tests were conducted within a temperature range of -40℃ to +85℃, achieving zero-position stability of ±2 micrometers and repeatability of ±1 micrometer, meeting the requirements for high-precision displacement measurement.

[0076] Table 3 shows the performance comparison before and after zero-position adjustment.

[0077]

[0078] As can be seen from Table 3, the present invention achieves rapid and precise adjustment of the electrical zero position through the differential thread fine adjustment mechanism. The residual voltage and displacement error of the zero position are significantly reduced, and the adjustment time is shortened from several hours in the traditional method to several minutes. The operation is simple and can be completed on site without disassembly or return to the factory.

[0079] Fifth embodiment: A zero-position adjustable linear variable differential transformer includes a differential thread fine-tuning mechanism disposed between the coil frame and the end cover. The differential thread fine-tuning mechanism can drive the coil frame to generate a micro-axial displacement relative to the housing when the end cover is rotated.

[0080] The differential thread fine-tuning mechanism includes a first threaded section disposed between the coil frame and the end cap, and a second threaded section disposed between the end cap and the outer shell; the pitch of the first threaded section and the pitch of the second threaded section are not equal, but they have the same direction of rotation.

[0081] The pitch P1 of the first thread segment is greater than the pitch P2 of the second thread segment.

[0082] A linear guide structure is provided between the coil frame and the inner wall of the outer casing to prevent the coil frame from rotating circumferentially during adjustment. The linear guide structure is a key and keyway fit.

[0083] The outer side of the end cap is provided with anti-slip knurling or a wrench holder for easy rotation.

[0084] A locking mechanism, which is a set screw, is provided between the end cap and the outer shell to lock their relative positions after adjustment.

[0085] The adjustment process includes the following steps: 1. Fix the sensor housing and place the iron core in the mechanical zero position; 2. Power on the sensor and monitor its output voltage; 3. Rotate the end cap, and drive the coil frame to move axially through the differential thread fine-tuning mechanism; 4. When the output voltage reaches zero, stop rotating the end cover; 5. Lock the relative position of the end cap and the outer casing.

[0086] See Figure 1 The zero-position adjustable LVDT of the present invention includes a cylindrical shell 1, a left end cover 2, a spring 3, a coil frame 4, a magnetic cover 5, a secondary coil 6, a primary coil 7, an inner tube frame 8, an iron core 9, a connecting rod 10, a right end cover 11, an insulating screw 12, and a magnetic sheet 13.

[0087] The coil bobbin 4 has a first internal thread machined at one end near the right end cover 11. The right end cover 11 also has a corresponding first external thread machined inside, forming a first threaded segment. The outer wall of the end of the outer shell 1 has a second internal thread machined, and the right end cover 11 has a corresponding second external thread machined outside, forming a second threaded segment. The pitch of the first threaded segment is P1, and the pitch of the second threaded segment is P2, where P1 > P2. Both threads have the same direction of rotation (e.g., both are right-handed).

[0088] See Figure 2 The zero-position adjustable LVDT described in this invention utilizes the differential thread working principle to achieve fine-tuning of the internal coil frame position. In the differential thread structure of this invention, the right end cover functions similarly to the screw, the outer shell functions similarly to the fixed nut, and the coil frame functions similarly to the movable nut. Assume the right end cover 11 rotates 360°. Due to the presence of the second thread segment, the right end cover 11 moves a distance L2 = P2 relative to the outer shell 1 in the direction shown in the diagram to the right. Simultaneously, due to the presence of the first thread segment, the rotation of the right end cover 11 will push the coil frame 4 to move a distance L1 = P1 relative to the right end cover 11 itself to the left. However, because the coil frame 4 is restricted by the linear guide key located on the inner tube frame 8, it cannot rotate and can only move axially. Therefore, the net displacement ΔL of the coil frame 4 relative to the fixed outer shell 1 is the resultant of the above two displacements.

[0089] The calculation formula is: ΔL = L1 - L2 = P1 - P2. Since P1 and P2 are very close (e.g., P1 = 1.0 mm, P2 = 0.9 mm), the net displacement ΔL produced by one rotation is only 0.1 mm. This means that if the circumference of the end cap is divided into 100 divisions, then each division can achieve a displacement adjustment accuracy of 1 micrometer (0.001 mm), realizing extremely high fine-tuning capability.

[0090] Adjustment process: 1. Fix the outer casing 1 and push the iron core 9 to the mechanical zero position.

[0091] 2. Power on and monitor the output. If the output is not zero, gently rotate the anti-slip knurling on the right end cover 11.

[0092] 3. The rotation of the right end cover 11 is converted into a small axial movement of the coil frame 4 through the differential thread mechanism, changing the relative center position of the iron core 9 and the coils 6 and 7.

[0093] 4. When the output signal is zero, stop adjusting. At this time, use the set screw 17 to lock the right end cover 11 to the outer casing 1 to prevent loosening.

[0094] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A zero-adjustable linear variable differential transformer, characterized by comprising: The coil frame (4) of the transformer is movably mounted on the inner tube frame (8). The coil frame (4) is covered with a cylindrical shell (1). The two ends of the cylindrical shell (1) are respectively equipped with a left end cover (2) and a right end cover (11). The components consisting of the transformer core (9) and connecting rod (10) are located inside the inner tube frame (8). The right end cover (11) can rotate relative to the cylindrical shell (1). The rotation of the right end cover (11) can drive the coil frame (4) to move axially on the inner tube frame (8).

2. A zero-adjustable linear variable differential transformer according to claim 1, wherein The left end of the right end cap (11) is connected to the right end of the coil frame (4), and a spring (3) is provided between the left end of the coil frame (4) and the left end cap (2).

3. A zero-position adjustable linear variable differential transformer according to claim 1, characterized in that, The coil frame (4) is provided with a linear guide mechanism, which prevents the coil frame (4) from rotating.

4. A zero-position adjustable linear variable differential transformer according to claim 1, characterized in that, The right end cap (11) is connected to the cylindrical outer shell (1) by a threaded connection, and the left end of the right end cap (11) is also connected to the right end of the coil frame (4) by a threaded connection.

5. A zero-position adjustable linear variable differential transformer according to claim 4, characterized in that, The pitch of the external thread that mates with the cylindrical shell (1) on the right end cover (11) is P2, and the pitch of the external thread that mates with the right end of the coil frame (4) on the right end is P1, where P1 is greater than P2.

6. A zero-position adjustable linear variable differential transformer according to claim 5, characterized in that, P2 is set between 0.8 times P2 and 0.95 times P1.

7. A zero-position adjustable linear variable differential transformer according to claim 1, characterized in that, The right end face of the right end cover (11) is a round surface. The right end face of the right end cover (11) is provided with uniform graduations. The circumference of the right end cover (11) is provided with anti-slip knurling.

8. A zero-position adjustable linear variable differential transformer according to claim 1, characterized in that, It also includes an insulating screw (12), which is inserted radially from the outside of the cylindrical housing (1) into the right end cover (11) for unlocking and locking the position of the right end cover (11).

9. A method for adjusting a zero-position adjustable linear variable differential transformer, comprising zero-position adjustment of the zero-position adjustable linear variable differential transformer as described in claim 5, characterized in that, Includes the following steps: S1, fix the cylindrical outer shell and push the iron core to the mechanical zero position; S2, energize the zero-position adjustable linear variable differential transformer, detect the output of the zero-position adjustable linear variable differential transformer, and rotate the right end cover when the output signal is not zero; S3, the rotation of the right end cover is converted into a small axial displacement of the coil frame through the differential thread mechanism, and the adjustment stops when the output signal is zero; S4. Fix the position of the right end cover to complete the zero-position adjustment of the zero-position adjustable linear variable differential transformer.

Images