A measuring device and real-time compensation method for full-closed-loop spindle thermal expansion

Abstract

The present invention discloses a measuring device and real-time compensation method for thermal elongation of a fully closed-loop spindle. The measuring device comprises an electric spindle, a displacement sensor, a bracket, a single-chip microcomputer, a protocol converter and a numerical control system. The displacement sensor is fixedly mounted on the bottom of the rotating part of the electric spindle through the bracket. The sensor head of the displacement sensor faces the axial plane where the bottom of the rotating part of the electric spindle is located. The displacement sensor is sequentially connected to the numerical control system through the single-chip microcomputer and the protocol converter. The displacement data output by the displacement sensor is converted by the single-chip microcomputer and the protocol converter and input into the numerical control system. The numerical control system calculates the compensation value after receiving the displacement data, and realizes compensation for thermal elongation of the electric spindle by using the mechanical origin coordinate offset function. The method of the present invention is less affected by changes in the working environment temperature, cutting process conditions and surface conditions of the cutting workpiece. The flatness of the machined plane after compensation is within 10μm, the maximum compensation effect is 72%, and the closed-loop compensation effect is significant.

Description

Technical Field

[0001] The invention belongs to the technical field of spindle thermal elongation compensation methods, and in particular relates to a measuring device and a real-time compensation method for full-closed-loop spindle thermal elongation. Background Art

[0002] When the electric spindle is running at high speed, the bearing will heat up due to friction, and the motor will generate heat due to the coil current. This heat will be transferred to the various parts of the spindle through conduction, convection and radiation, causing the overall temperature of the electric spindle to rise. Since the electric spindle is directly connected to the tool, the thermal elongation caused by the temperature rise of the electric spindle will affect the processing accuracy. Therefore, it is necessary to compensate and control the thermal elongation of the electric spindle to further improve the processing accuracy and stability of the machine tool.

[0003] Temperature is directly related to the thermal elongation of the electric spindle. Therefore, establishing a prediction model based on the temperature-thermal elongation relationship of the electric spindle is a commonly used prediction and compensation method at home and abroad. In the public document "Research on Thermal Error Modeling and Compensation Methods of Electric Spindle under Complex Working Conditions", Wang Nan from Xi'an University of Technology used a hierarchical clustering method combined with gray correlation analysis to select the temperature key points on the electric spindle, and used the particle swarm algorithm to optimize the support vector regression to establish an adaptive thermal error prediction model of the electric spindle under complex and different working conditions. In the public document "Research on Thermal Error Testing and Compensation of Electric Spindle of Five-Axis Machining Center", Wen Mengfei from Beijing Information Science and Technology University proposed a WOA-SVR-based electric spindle thermal error optimization modeling method by optimizing temperature measurement points and comparing different thermal error prediction optimization models. An exponential function multivariate thermal error model was established. This model was used to compensate for thermal elongation on the CNC system, and idling experiments, plane processing experiments, and impeller blade processing experiments were carried out. In the open document "Thermal Elongation Test and Compensation of Electric Spindle in Vertical Machining Center", Wu Xiaojie tested and analyzed the temperature and thermal elongation of the electric spindle at different speeds, and established a thermal elongation prediction model based on multivariate linear regression theory. The CNC system calculates the compensation value based on the measured temperature value, and compensates the compensation value to the Z-axis drive to realize the thermal compensation function.

[0004] The temperature-based thermal elongation prediction model is mostly limited to evaluating the model prediction effect from the fitting accuracy of the theoretical level, and there are few studies on the actual machine effect. The reasons are that the data source for establishing the spindle thermal elongation model is not comprehensive, the robustness of the prediction model is poor, and the modeling data is greatly affected by the changes in the working environment temperature, cutting process conditions (cutting speed, cutting depth and feed speed) and cutting plane conditions. As a result, the spindle thermal elongation prediction data cannot meet the use requirements in actual tests, and even detailed jumping tool marks appear on the surface of the processed workpiece. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and provide a measuring device and compensation method for the thermal expansion of a full-closed-loop spindle. The measuring device is used to directly measure the error and deformation of the electric spindle of a machine tool, and the collected displacement data is sent to the machine tool CNC system. The mechanical origin offset function is used to perform real-time compensation for the coordinates in the CNC system to reduce the impact of errors and deformations on machining accuracy.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0007] The present invention first provides a measuring device for thermal expansion of a full-closed-loop spindle, comprising an electric spindle, a displacement sensor, a bracket, a single-chip microcomputer, a protocol converter and a numerical control system, wherein the displacement sensor is fixedly mounted on the bottom of a rotating portion of the electric spindle through the bracket, one end of the bracket is fixedly fixed to the lower end surface of a housing of the electric spindle through hot-melt adhesive, and the other end is internally fixedly mounted with a displacement sensor, the sensor head of the displacement sensor is directly facing the axial plane where the bottom of the rotating portion of the electric spindle is located, the displacement sensor is sequentially connected to the numerical control system through a single-chip microcomputer and a protocol converter for communication, the single-chip microcomputer is used to convert an analog signal output by the displacement sensor into a digital signal through analog-to-digital conversion, and transmit the displacement data to the protocol converter using the Modbus protocol, the protocol converter is used to transmit the received displacement data to the numerical control system through the Profinet protocol, and after receiving the displacement data, the numerical control system uses a mechanical origin coordinate offset function to realize compensation for thermal expansion of the electric spindle.

[0008] Specifically, the bracket is fixedly provided with a jet port around the position of the displacement sensor head, and a gas flow channel is correspondingly arranged inside the bracket. One end of the gas flow channel is connected to the jet port, and the other end is connected to the gas source. The jet port ejects airflow when the electric spindle is working, thereby blowing away the cutting fluid and chips around the displacement sensor head.

[0009] Preferably, the displacement sensor is an eddy current displacement sensor, the resolution of the eddy current displacement sensor is 1 / 80000; the measurement range is 0.1mm~0.5mm; and the sampling time is 1s.

[0010] On the basis of the above technical solution, the present invention also provides a method for real-time compensation of thermal expansion of a full-closed-loop spindle using the above measuring device, comprising the following steps:

[0011] Step S1, fix the displacement sensor inside the bottom end of the bracket, and use hot melt adhesive to stick the top end of the bracket to the workbench, move the electric spindle, and make the measured end face of the electric spindle close to the sensor head of the displacement sensor;

[0012] Step S2, using a standard measuring ruler to measure the distance between the displacement sensor and the measured end face of the electric spindle, and adjusting the distance between the displacement sensor and the measured end face of the electric spindle to 1 mm;

[0013] Step S3, set the working coordinate system X=0mm, Y=0mm, Z=1mm; move the electric spindle so that its Z-axis coordinate reaches 0.1mm, and record the AD value of the displacement sensor at this time, then gradually increase the Z-axis coordinate by 0.01mm each time, collect and record the corresponding AD value of the displacement sensor until the Z-axis coordinate reaches 0.4mm;

[0014] Step S4: Use the cftool toolbox in Matlab software to fit the AD value collected by the displacement sensor with the displacement value of the measured end face of the electric spindle to obtain the displacement value of the measured end face of the electric spindle. And displacement sensor AD value The fitting expression of

[0015] Step S5: Based on the fitting expression obtained in step S4, the numerical control system calculates the compensation value according to the received displacement data, and uses the mechanical origin coordinate offset function to achieve real-time compensation for the thermal expansion of the electric spindle.

[0016] Specifically, in step S2, the distance between the displacement sensor and the measured end face of the electric spindle is adjusted to 1 mm, and the adjustment process is as follows:

[0017] Use a measuring ruler with a standard thickness of 1mm, insert it into the gap between the displacement sensor and the measured end face of the electric spindle, and gradually adjust the gap distance until a certain resistance can be felt when plugging and unplugging the measuring ruler, thereby confirming that the distance between the displacement sensor and the measured end face of the electric spindle is 1mm.

[0018] Furthermore, the displacement value of the measured end face of the electric spindle in step S4 is And displacement sensor AD value The fitting expression is:

[0019] .

[0020] Specifically, the mechanical origin coordinate offset function described in step S5 is used to compensate for the thermal elongation of the electric spindle. After inspection, it was found that after compensating for the thermal elongation of the spindle according to the method of the present invention, the flatness of the processed plane was within 10 μm, and the maximum compensation effect reached 72%.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention designs a fully closed-loop spindle thermal expansion measuring device, which can directly measure the error and deformation of the machine tool electric spindle, and convert the collected displacement data and send it to the machine tool CNC system. By using its mechanical origin offset function, the coordinates in the CNC system are compensated in real time, thereby reducing the impact of errors and deformation on processing accuracy.

[0023] 2. The present invention provides a real-time compensation method for thermal expansion of a fully closed-loop spindle. The cftool toolbox in the Matlab software is used to fit the AD value of the displacement sensor with the displacement value of the measured end face of the electric spindle. The numerical control system calculates the compensation value for the received displacement data according to the fitting formula, thereby utilizing the mechanical origin coordinate offset function to achieve real-time compensation for the thermal expansion of the electric spindle. Compared with the traditional method of establishing a spindle thermal expansion model to predict the compensation value, the method of the present invention is less affected by changes in the working environment temperature, cutting process conditions (cutting speed, cutting depth and feed speed) and surface conditions of the cutting workpiece. The flatness of the machined plane after compensation is within 10 μm, the maximum compensation effect is 72%, and the closed-loop compensation effect is significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a structural schematic diagram of a fully closed-loop spindle thermal elongation measuring device of the present invention;

[0026] Figure 2 Schematic diagram of the communication process between the eddy current displacement sensor and the numerical control system in an embodiment of the present invention;

[0027] Figure 3 is the displacement value of the measured end face of the electric spindle obtained in the embodiment of the present invention And displacement sensor AD value The fitting curve diagram of

[0028] Figure 4 It is the display interface of the spindle thermal elongation compensation software in the embodiment of the present invention;

[0029] Figure 5 This is a comparison chart of the flatness measurement results when testing the compensation effect in an embodiment of the present invention.

[0030] In the figure: 1. Electric spindle; 2. Displacement sensor; 3. Bracket. DETAILED DESCRIPTION

[0031] In order to facilitate those of ordinary skill in the art to understand and implement the present invention, the following detailed description is given to each step of the method proposed by the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0032] Example

[0033] like Figure 1 As shown, the present invention provides a measuring device for thermal elongation of a full-closed-loop spindle, comprising an electric spindle 1, a displacement sensor 2, a bracket 3, a single-chip microcomputer, a protocol converter and a numerical control system, wherein the displacement sensor 2 is fixedly mounted on the bottom of the rotating part of the electric spindle 1 through the bracket 3, one end of the bracket 3 is fixedly fixed to the lower end surface of the outer shell of the electric spindle 1 by hot-melt adhesive, and the displacement sensor 2 is fixedly mounted inside the other end, and the sensor head of the displacement sensor 2 is directly opposite to the axial plane where the bottom of the rotating part of the electric spindle 1 is located; as shown Figure 2 As shown, the displacement sensor 2 is connected to the numerical control system in communication via the single-chip microcomputer and the protocol converter in turn. The single-chip microcomputer is used to convert the analog signal output by the displacement sensor 2 into a digital signal through analog-to-digital conversion, and transmit the displacement data to the protocol converter using the Modbus protocol. The protocol converter is used to transmit the received displacement data to the numerical control system through the Profinet protocol. After receiving the displacement data, the numerical control system uses the mechanical origin coordinate offset function to compensate for the thermal expansion of the electric spindle 1.

[0034] The bracket 3 is fixedly provided with a jet nozzle around the position of the sensor head of the displacement sensor 2, and a gas flow channel is arranged inside the bracket 3 accordingly. One end of the gas flow channel is connected to the jet nozzle, and the other end is connected to an air inlet pipe. The jet nozzle ejects airflow when the electric spindle 1 is working, thereby blowing away the cutting fluid and chips around the sensor head of the displacement sensor 2.

[0035] The displacement sensor 2 is an eddy current displacement sensor, which is usually composed of a power supply, a coil and a sensor head. When the power supply is energized, the coil will generate a high-frequency alternating electromagnetic field, which will penetrate the metal surface being tested to form eddy currents. When the metal being tested is displaced, the induction of the eddy current will change, thereby changing the characteristics of the electromagnetic field. The sensor head can detect this change, and by measuring the change in the electromagnetic field, the displacement of the object being tested can be determined. The resolution of the eddy current displacement sensor selected in this embodiment is 1 / 80000; the measuring range is 0.1mm~0.5mm; the specific parameters are shown in Table 1 below.

[0036] Table 1. Specific parameters of eddy current displacement sensor .

[0037] When using eddy current displacement sensors to measure the thermal elongation of the spindle, the sensor needs to be calibrated. The main purpose is to determine the relationship between the sensor output signal and the actual displacement to ensure the accuracy of the measurement results. Different application scenarios and processing requirements often require the use of spindles made of different materials. When using spindles made of different materials, in order to ensure processing accuracy and equipment performance, the electric spindle also needs to be calibrated again. The specific steps of sensor calibration and compensation process for the electric spindle are as follows:

[0038] Step S1, fix the displacement sensor 2 inside the bottom end of the bracket 3, and use hot melt adhesive to stick the top end of the bracket 3 to the workbench, move the electric spindle 1, and make the measured end face of the electric spindle 1 close to the sensor head of the displacement sensor 2;

[0039] Step S2, using a standard measuring ruler to measure the distance between the displacement sensor 2 and the measured end surface of the electric spindle 1, and adjusting the distance between the displacement sensor 2 and the measured end surface of the electric spindle 1 to 1 mm;

[0040] Use a measuring ruler with a standard thickness of 1 mm, insert the measuring ruler into the gap between the displacement sensor 2 and the measured end face of the electric spindle 1, and gradually adjust the gap distance until a certain resistance can be felt when the measuring ruler is pulled out and inserted, thereby confirming that the distance between the displacement sensor 2 and the measured end face of the electric spindle 1 is 1 mm;

[0041] Step S3, set the working coordinate system X=0mm, Y=0mm, Z=1mm; move the electric spindle 1 so that its Z-axis coordinate reaches 0.1mm, and record the AD value of the displacement sensor 2 at this time, then gradually increase the Z-axis coordinate by 0.01mm each time, collect and record the corresponding AD value of the displacement sensor 2 until the Z-axis coordinate reaches 0.4mm;

[0042] Step S4: Use the cftool toolbox in Matlab software to fit the AD value collected by the displacement sensor 2 with the displacement value of the measured end face of the electric spindle 1 to obtain the displacement value of the measured end face of the electric spindle 1. And displacement sensor 2AD value The fitting expression of

[0043] like Figure 3 The figure shows the displacement value of the measured end face of the electric spindle obtained in this embodiment. And displacement sensor AD value The fitting curve diagram is obtained by using the cftool toolbox in Matlab software to obtain the fitting expression of the fitting curve:

[0044] .

[0045] Step S5: After the calibration is completed according to the above steps, the displacement data measured by the eddy current sensor can be obtained through the above formula; the obtained displacement data is processed as follows: Figure 2 The communication process shown is input into the CNC system. After receiving the displacement data, the CNC system uses the mechanical element origin coordinate offset function to compensate for the thermal elongation of the electric spindle. In this embodiment, the Siemens system is taken as an example, and the compensation software interface designed is as follows Figure 4 shown.

[0046] In order to better describe the measuring device and compensation method of the present invention, a specific workpiece plane processing experiment is taken as an example to further illustrate the technical effects of the present invention.

[0047] Experimental equipment and parameter description: The 7075 aluminum alloy plane was processed, and the flatness error before and after the spindle thermal elongation compensation was tested with a plane milling cutter with a tool diameter of 10mm. The processing plane was a square plane with a side length of 180mm. The speed was set to 17000r / min, the step distance was 0.2mm, and the feed speed was 4000mm / min.

[0048] Experimental process: Use a micrometer to measure the flatness of the machined surface at a straight line every 10 mm along the machining direction, for a total of 18 points. Figure 5 Shown is a schematic diagram of the flatness measurement results of the processed plane before and after compensation.

[0049] Depend on Figure 5 It can be seen from the grid lines that due to the existence of thermal elongation of the electric spindle, the absolute value of the flatness of the machining plane before compensation increases continuously as the machining proceeds. Figure 5 It can be seen from the dotted line that the absolute value of the flatness of the machined plane after compensation also shows an upward trend, but after compensation, the flatness of the machined plane is maintained within 10μm, and the maximum compensation effect is about 72%, indicating that the spindle thermal elongation measurement device and the corresponding compensation method provided by the present invention have a significant closed-loop compensation effect on the electric spindle.

[0050] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A real-time compensation method for thermal expansion of a fully closed-loop spindle, characterized in that: A device for measuring thermal expansion of a fully closed-loop spindle comprises an electric spindle (1), a displacement sensor (2), a bracket (3), a single-chip microcomputer, a protocol converter and a numerical control system, wherein the displacement sensor (2) is fixedly mounted on the bottom of the rotating part of the electric spindle (1) via the bracket (3), one end of the bracket (3) is fixedly fixed to the lower end surface of the outer shell of the electric spindle (1) by hot-melt adhesive, and the other end of the bracket has the displacement sensor (2) fixedly mounted inside, the sensor head of the displacement sensor (2) faces the axial plane where the bottom of the rotating part of the electric spindle (1) is located, the displacement sensor (2) is sequentially connected to the numerical control system via the single-chip microcomputer and the protocol converter, the single-chip microcomputer is used to convert the analog signal output by the displacement sensor (2) into a digital signal through analog-to-digital conversion, and transmit the displacement data to the protocol converter using the Modbus protocol, The protocol converter is used to transmit the received displacement data to the numerical control system through the Profinet protocol. After receiving the displacement data, the numerical control system uses the mechanical origin coordinate offset function to realize compensation for the thermal expansion of the electric spindle (1); the bracket (3) is fixedly provided with an air jet around the position of the sensor head of the displacement sensor (2), and a gas flow channel is arranged inside the bracket (3) correspondingly. One end of the gas flow channel is connected to the air jet and the other end is connected to the gas source. When the electric spindle (1) is working, the air jet ejects air flow, thereby blowing away the cutting fluid and chips around the sensor head of the displacement sensor (2); the displacement sensor (2) is an eddy current displacement sensor, and the resolution of the eddy current displacement sensor is 1 / 80000; the measurement range is 0.1 mm to 0.5 mm; and the sampling time is 1 s; Based on the above-mentioned measuring device, the real-time compensation method for full-closed-loop spindle thermal expansion comprises the following steps: Step S1, fix the displacement sensor (2) inside the bottom end of the bracket (3), and use hot melt adhesive to glue the top end of the bracket (3) to the workbench, move the electric spindle (1), and make the measured end face of the electric spindle (1) close to the sensor head of the displacement sensor (2); Step S2, using a standard measuring ruler to measure the distance between the displacement sensor (2) and the measured end surface of the electric spindle (1), and adjusting the distance between the displacement sensor (2) and the measured end surface of the electric spindle (1) to 1 mm; Step S3, setting the working coordinate system X=0mm, Y=0mm, Z=1mm; moving the electric spindle (1) so that its Z-axis coordinate reaches 0.1mm, and simultaneously recording the AD value of the displacement sensor (2) at this time, and then gradually increasing the Z-axis coordinate by 0.01mm each time, collecting and recording the corresponding AD value of the displacement sensor (2), until the Z-axis coordinate reaches 0.4mm; Step S4: Use the cftool toolbox in Matlab software to fit the AD value collected by the displacement sensor (2) with the displacement value of the measured end face of the electric spindle (1) to obtain the displacement value of the measured end face of the electric spindle (1). and displacement sensor (2) AD value The fitting expression of ; The displacement value of the measured end face of the electric spindle (1) and displacement sensor (2) AD value The fitting expression is: ； Step S5: Based on the fitting expression obtained in step S4, the numerical control system calculates the compensation value according to the received displacement data, and uses the mechanical origin coordinate offset function to achieve real-time compensation for the thermal expansion of the electric spindle (1).

2. The real-time compensation method for thermal expansion of a fully closed-loop spindle according to claim 1, characterized in that: In step S2, the distance between the displacement sensor (2) and the measured end face of the electric spindle (1) is adjusted to 1 mm. The adjustment process is as follows: A measuring ruler with a standard thickness of 1 mm is inserted into the gap between the displacement sensor (2) and the end face of the motorized spindle (1) to be measured, and the gap distance is gradually adjusted until a certain resistance can be felt when the measuring ruler is inserted or removed, thereby confirming that the distance between the displacement sensor (2) and the end face of the motorized spindle (1) to be measured is 1 mm.

3. The real-time compensation method for thermal expansion of a fully closed-loop spindle according to claim 1, characterized in that: In step S5, the mechanical origin coordinate offset function is used to compensate for the thermal elongation of the electric spindle (1), and the flatness of the machined surface after compensation is within 10 μm.

Images