Multi-degree-of-freedom length measuring instrument based on LVDT displacement sensor and curved surface measuring method of multi-degree-of-freedom length measuring instrument

Abstract

The invention provides a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor and a curved surface measuring method, and belongs to the field of precision measurement. The device is composed of a base, a measuring seat driven by a linear motor, a sliding objective table, a tailstock and a measuring head assembly, a fixed measuring head and an LVDT measuring head are arranged on the tailstock / measuring seat respectively, and displacement is fed back in real time in combination with a grating ruler. The computer integrally controls the motor rotor, the Y / Z axis of the objective table and the sensor through a single-chip microcomputer to construct a closed-loop system. The method is characterized in that LVDT non-contact monitoring and grating ruler data are fused, multi-point continuous measurement can be completed through single-time feeding, dynamic posture adjustment is conducted through the displacement change rate, and rapid positioning of curved surface inflection points is achieved. The method breaks through the limitation of traditional multiple clamping and manual point searching, the measurement efficiency of the complex curved surface is remarkably improved, the method is suitable for precision machining detection, and an efficient solution is provided for automatic measurement of the curved surface contour.

Description

Technical Field

[0001] The present invention relates to a novel multi-degree-of-freedom length measuring device, and particularly relates to the field of length measuring instruments. Background Art

[0002] As a precision geometric quantity measuring device, the core function of a length measuring instrument is to perform high-precision measurement on the size of a workpiece through a contact probe. In the prior art, a mechanical probe is usually used in cooperation with a stage to achieve measurement. The typical working process is as follows: manually adjust the position of the workpiece, then the probe contacts, read the mechanical scale or grating data, and finally repeat multiple times to obtain the coordinates of key points. This measurement method has low measurement efficiency. Each repeated measurement requires a large movement of the measurement seat, and traditional length measuring instruments have problems such as low efficiency, rapid accuracy decay, and high dependence on manual operation in the measurement of complex curved surfaces. Therefore, there is still room for improvement in the measurement efficiency of current length measuring instruments. Summary of the Invention

[0003] (1) Technical Problems to be Solved

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the main object of the present invention is to provide a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor and its curved surface measurement method, which solves the problems that the existing length measuring instrument requires the measurement personnel to feed the measurement length multiple times when measuring the length and a large number of measurements are required to find the inflection points of the curved surface.

[0005] Another object is to propose a new inflection point finding method for quickly finding inflection points in curved surface measurement.

[0006] (2) Technical Solutions

[0007] To solve the above technical problems, the present invention provides a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor and its curved surface measurement method, which is particularly suitable for the rapid and high-precision measurement of special-shaped end-face workpieces such as arc surfaces and spherical surfaces. Through the rebound and displacement measurement of the LVDT sensor probe, the telescopic measurement of the probe during measurement can be realized, and multiple measurements can be carried out more quickly and the inflection points of the arc surface can be found quickly, with higher measurement efficiency.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor, the device includes a base, a measurement seat, a stage, a tailstock, a fixed probe, an LVDT displacement sensor probe, a grating scale reading head, a grating scale, a slide rail, a computer host and a processing circuit single-chip microcomputer;

[0009] Among them, the measurement seat is fixed on the moving part of the linear motor of the base; the carrier table is placed on the base to form a sliding fit; the tailstock is fixed at one end of the base away from the measurement seat; the fixed probe and the probe of the LVDT displacement sensor are respectively fixed on the tailstock and the measurement seat; the grating scale reading head is fixed on one side of the measurement seat; the grating scale cooperates with the grating scale reading head; the slide rail is fixed on the base and slides with the measurement seat; the computer host is used to write control software programs and store measurement data, and realizes electrical connection with the linear motor moving part, the grating scale reading head, the LVDT sensor probe, and the carrier table through the processing circuit single-chip microcomputer, so as to realize motion control.

[0010] Preferably, the driving mechanism of the carrier table includes a Z-axis driving mechanism and a Y driving mechanism; the Z-axis transmission mechanism drives the lead screw to rotate by a stepping motor-driven gear reduction transmission device, driving the lead screw nut and the carrier table side plate fixed to the nut fixing seat to move along the Z axis; the Y-axis driving mechanism drives the lead screw to rotate by a stepping motor-driven gear reducer, so that the carrier table top plate fixed on the nut fixing seat moves along the Y axis; the rib plate is connected between the carrier table top plate and the side plate to reduce the vibration amplitude during the movement.

[0011] Preferably, the processing circuit single-chip microcomputer has the following built-in function modules: a displacement closed-loop control module based on the grating scale and the grating scale reading head; a real-time data acquisition module based on the signal of the LVDT displacement sensor probe; an inflection point positioning algorithm module that automatically triggers the Y / Z-axis linkage of the carrier table according to the displacement change rate.

[0012] Preferably, the contact end surface of the measuring rod of the LVDT displacement sensor probe and the fixed probe is a spherical structure.

[0013] Preferably, the LVDT sensor probe uses a linear variable differential transformer (LVDT) to replace the traditional mechanical probe, and the measuring rod measures displacement non-contact through the principle of electromagnetic induction, avoiding the accuracy attenuation caused by mechanical wear.

[0014] Preferably, the LVDT sensor probe and the fixed probe of the tailstock are installed strictly coaxially to ensure that the measurement direction coincides with the axis of the workpiece and eliminate the cosine error.

[0015] Preferably, in order to achieve the purpose of quickly measuring the inflection point of the arc surface, the main technical solution of the present invention is:

[0016] S1. Initial calibration: Fix the standard gauge on the carrier table top plate, adjust the LVDT sensor probe and the fixed probe to be coaxial, and record the zero voltage value V of the LVDT through the computer host ref; Drive the measuring seat to move along the X-axis, and calibrate the displacement conversion coefficient k of the LVDT sensor probe through the grating ruler and the reading head;

[0017] S2. Coarse positioning of the workpiece: Install the workpiece with the arc surface to be measured on the top plate of the carrier table, start the Y-axis driving mechanism of the carrier table, and move the workpiece along the Y-axis to the measurement area between the LVDT sensor probe and the fixed probe; Start the Z-axis driving mechanism of the carrier table, and adjust the height of the workpiece so that the vertex of the arc surface is initially aligned with the probe axis;

[0018] S3. Automatic inflection point measurement:

[0019] 1. Control the measuring seat to move along the X-axis at a constant speed, and synchronously execute:

[0020] a. Continuously collect displacement signals through the LVDT sensor probe, and calculate the real-time displacement value according to the formula

[0021] ΔL = k(V out -V ref )

[0022] b. Record the absolute position coordinates of the measuring seat through the grating ruler;

[0023] c. Calculate the displacement change rate When (preset threshold), it is determined that the arc surface inflection point area is entered;

[0024] 2. Trigger the Y / Z-axis linkage fine-tuning mode of the carrier table:

[0025] a. According to the gradient direction, control the carrier table to step along the Y-axis or Z-axis until approaches zero, and lock the inflection point coordinates;

[0026] b. Repeat the above process to obtain at least three inflection point coordinates;

[0027] S4. Data fitting and output: Based on the inflection point coordinates, fit the arc surface curve equation by the least square method, calculate the radius of curvature or diameter: Output the measurement result and confidence evaluation (judged according to the inflection point coordinate dispersion).

[0028] Preferably, the grating ruler provides the absolute position of the measuring seat, the LVDT sensor collects displacement details in real time, and outputs a high-precision composite signal through the data fusion algorithm of the controller; Dynamically control the Y / Z-axis fine-tuning of the carrier table based on the displacement change rate to achieve automatic locking of the arc surface inflection point. Description of the Drawings

[0029] Figure 1 is the overall schematic diagram of a new type of multi-degree-of-freedom length measuring device and its measuring method of the present application;

[0030] Figure 2 Schematic diagram of the stage for a novel multi-degree-of-freedom length measuring device and its measuring method of the present application;

[0031] Figure 3 Schematic diagram of the base for a novel multi-degree-of-freedom length measuring device and its measuring method of the present application;

[0032] Figure 4 Schematic diagram of the LVDT sensor probe for a novel multi-degree-of-freedom length measuring device and its measuring method of the present application;

[0033] Figure 5 Schematic diagram of the working principle of the measuring device for a novel multi-degree-of-freedom length measuring device and its measuring method of the present application;

[0034] Figure 6 Schematic diagram of the measuring method principle for a novel multi-degree-of-freedom length measuring device and its measuring method of the present application; Detailed implementation manners

[0035] In the present invention, unless otherwise clearly defined and limited, terms such as "installed", "connected", "connected to", "fixed" and the like shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium; it may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0036] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium.

[0037] In order to better understand the above technical solutions, the exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and the scope of the present invention can be completely conveyed to those skilled in the art.

[0038] A multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor and its curved surface measurement method proposed in an embodiment of the present invention. The LVDT sensor probe and the tailstock probe are coaxially installed. The grating ruler provides the absolute position of the measuring seat. The LVDT sensor collects displacement details in real time, and a high-precision composite signal is output through the data fusion algorithm of the controller. The fine adjustment of the Y / Z axis of the stage is dynamically controlled based on the displacement change rate to achieve automatic locking of the inflection point of the arc surface.

[0039] As Figure 1 shown, a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor, the device includes a base 1, a measuring seat 2, a stage 3, a tailstock 4, a fixed probe 5, an LVDT displacement sensor probe 6, a grating ruler reading head 7, a grating ruler 8, a slide rail 9, a computer host 10 and a processing circuit single-chip microcomputer 11;

[0040] Among them, the measuring seat 2 is fixed on the linear motor mover 1-1 of the base 1 to realize the movement of the X axis; the stage 3 is placed on the base 1 to form a sliding fit to realize the X-axis movement of the stage 3 to meet the measurement of longer measured objects; the tailstock 4 is fixed at one end of the base 1 away from the measuring seat 2; the fixed probe 5 and the LVDT displacement sensor probe 6 are respectively fixed on the tailstock 4 and the measuring seat 2 to form a coaxial installation to reduce the cosine error; the grating ruler reading head 7 is fixed on one side of the measuring seat 2; the grating ruler 8 cooperates with the grating ruler reading head 7 to record the absolute coordinates of the measuring seat 2; the slide rail 9 is fixed on the base 1 and slidably cooperates with the measuring seat 2; the computer host 10 is used to write control software programs and store measurement data, and realizes electrical connection with the linear motor mover 1-1, the grating ruler reading head 7, the LVDT sensor probe 6, and the stage 3 through the processing circuit single-chip microcomputer 11 to realize motion control.

[0041] As Figure 2 shown, the driving mechanism of the stage 3 includes a Z-axis driving mechanism 3-1 and a Y driving mechanism 3-2; the Z-axis transmission mechanism 3-1 is driven by a stepping motor 3-1-1 to drive a gear reduction transmission device 3-1-0 to drive a lead screw 3-1-4 to rotate, driving a lead screw nut 3-1-2 and a stage side plate 3-0 fixed to the nut fixing seat 3-1-1 to move along the Z axis; the Y-axis driving mechanism 3-2 is driven by a stepping motor 3-2-0 to drive a gear reducer 3-2-1 to drive a lead screw 3-2-2 to rotate, so that a stage top plate 3-3 fixed on a nut fixing seat 3-2-4 moves along the Y axis; a rib plate 3-4 is connected between the stage top plate and the side plate.

[0042] As Figure 4 shown, the contact end surface of the measuring rod 6-1 of the LVDT sensor probe 6 and the fixed probe 5 is a spherical surface structure.

[0043] As Figure 5 , Figure 6 shown, a rapid measurement method includes the following steps: First, perform initial calibration. Place the standard gauge block on the top plate of the stage, adjust the fixed probe and make one side of the gauge block closely adhere to the fixed probe, adjust the probe of the LVDT sensor to be coaxial with the fixed probe, and record the zero voltage; Drive the linear motor to move the measurement seat along the X-axis, make the probe of the LVDT displacement sensor contact the standard gauge block, record the absolute displacement of the measurement seat feedback by the grating scale and the voltage change of the LVDT, and calculate the displacement conversion coefficient; Subsequently, install the workpiece to be measured on the stage, adjust the stage and the fixed probe to make one end of the workpiece to be measured closely adhere to the fixed probe; The stage is driven by the stepping motor of the Y-axis drive mechanism to drive the gear reducer to drive the lead screw to rotate, so that the top plate of the stage moves along the Y-axis to move the workpiece to be measured to the measurement area between the probes. At the same time, the stepping motor of the Z-axis drive mechanism drives the lead screw lifting side plate through the gear reduction device to initially align the arc vertex with the probe axis; During measurement, control the measurement seat to move along the X-axis at a constant speed, synchronously collect the LVDT displacement signal and the absolute coordinates of the grating scale, and calculate the displacement change rate of the measuring rod of the LVDT displacement sensor in real time; When the displacement change rate exceeds the preset threshold, the measurement seat stops moving and triggers the Y / Z-axis linkage fine adjustment of the stage: Control the top plate of the stage to move along the Y-axis or Z-axis with a small step precisely driven by the lead screw nut according to the gradient direction until the displacement change rate approaches zero, lock the inflection point coordinates, and repeat to obtain at least three inflection points; Finally, based on the inflection point coordinates, calculate the radius of curvature by fitting the circular arc equation with the least squares method and evaluate the confidence level.

[0044] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A multi-degree-of-freedom length measuring instrument based on LVDT displacement sensor, characterized in that: It comprises a base (1), a measuring base (2), a stage (3), a tailstock (4), a fixed probe (5), an LVDT displacement sensor probe (6), a grating ruler reading head (7), a grating ruler (8), a slide rail (9), a computer host (10) and a processing circuit single chip microcomputer (11); The measuring seat (2) is fixed on the linear motor mover (1-1) of the base (1); the stage (3) is placed on the base (1) to form a sliding fit; the tailstock (4) is fixed on one end of the base (1) away from the measuring seat (2); the fixed probe (5) and the LVDT displacement sensor probe (6) are respectively fixed on the tailstock (4) and the measuring seat (2); the grating ruler reading head (7) is fixed on one side of the measuring seat (2); the grating ruler (8) cooperates with the grating ruler reading head (7); the slide rail (9) is fixed on the base (1) to slide with the measuring seat (2); the computer host (10) is used to write control software programs and store measurement data, and realizes electrical connection with the linear motor mover (1-1), the grating ruler reading head (7), the LVDT sensor probe (6) and the stage (3) through the processing circuit single chip microcomputer (11) to realize motion control.

2. The multi-degree-of-freedom length measuring instrument based on LVDT displacement sensor according to claim 1, characterized in that: The driving mechanism of the worktable (3) comprises a Z-axis driving mechanism (3-1) and a Y-driving mechanism (3-2); the Z-axis transmission mechanism (3-1) is driven by a stepping motor (3-1-1) to drive a gear reduction transmission device (3-1-0) to drive a lead screw (3-1-4) to rotate, thereby driving a lead screw nut (3-1-2) and a worktable side plate (3-0) fixed to a nut fixing seat (3-1-3) to move along the Z-axis; the Y-axis driving mechanism (3-2) is driven by a stepping motor (3-2-0) to drive a gear reducer (3-2-1) to drive a lead screw (3-2-2) to rotate, thereby causing a worktable top plate (3-3) fixed to a nut fixing seat (3-2-4) to move along the Y-axis; a rib plate (3-4) is connected between the worktable top plate (3-3) and the side plate (3-0).

3. The multi-degree-of-freedom length measuring instrument based on LVDT displacement sensor according to claim 1, characterized in that: The processing circuit single chip computer (11) comprises a displacement closed-loop control module based on the grating ruler (8) and the grating ruler reading head (7); a real-time data acquisition module based on the signal of the LVDT displacement sensor probe (6); and an inflection point positioning algorithm module that automatically triggers the Y / Z axis linkage of the stage (3) according to the displacement change rate.

4. The multi-degree-of-freedom length measuring instrument based on LVDT displacement sensor according to claim 1, characterized in that: The contact end surfaces of the measuring rod (6-1) of the LVDT displacement sensor measuring head (6) and the fixed measuring head (5) are spherical structures.

5. A method for measuring a curved surface of a multi-degree-of-freedom length measuring instrument based on an LVDT displacement sensor according to any one of claims 1 to 4, characterized in that: The steps include: S1. Initial calibration: fix the standard gauge block on the top plate of the stage, adjust the LVDT sensor probe to be coaxial with the fixed probe, and record the LVDT zero-point voltage value through the computer host; drive the measuring seat to move along the X-axis, and calibrate the displacement conversion coefficient k of the LVDT sensor probe through the grating ruler and the reading head; S2, rough positioning of workpiece: install the arc surface workpiece to be measured on the top plate of the stage, start the Y-axis drive mechanism of the stage, move the workpiece along the Y-axis to the measuring area between the LVDT sensor probe and the fixed probe; start the Z-axis drive mechanism of the stage, adjust the height of the workpiece so that the vertex of the arc surface is initially aligned with the probe axis; S3, automatic measurement:

1. Control the measuring seat to move along the X-axis at a constant speed and execute synchronously: a. Continuously collect displacement signals through the LVDT sensor probe and calculate the real-time displacement value; b. Record the absolute position coordinates of the measuring seat through the grating ruler; c. Calculate the displacement change rate of the measuring rod in the LVDT displacement sensor probe. When the displacement change rate is greater than a preset threshold, it is determined that the arc surface inflection point area has been entered; 2. Trigger the stage Y / Z axis linkage fine adjustment mode: a. According to the gradient direction of the displacement change rate, control the stage to move step by step along the Y-axis or Z-axis until the displacement change rate approaches zero and locks the inflection point coordinates; b. Repeat the above process to obtain at least three inflection point coordinates; S4. Data fitting and output: Based on the inflection point coordinates, the arc curve equation is fitted by the least squares method to calculate the curvature radius or diameter: output the measurement results and confidence assessment (based on the discreteness of the inflection point coordinates).

6. The measuring method according to claim 5, characterized in that: The linkage fine-tuning mode described in step 3 adopts a PID control algorithm to dynamically adjust the step length of the stage movement according to the displacement change rate deviation value.

7. The measuring method according to claim 5, characterized in that: The confidence assessment described in step 4 is calculated using the following formula: Where: X is the confidence level, σ is the standard deviation of the inflection point coordinate dispersion, L avg is the average radius of curvature.

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