Thermal displacement compensation device of motorized spindle, numerical control machine tool and compensation method of thermal displacement compensation device

Abstract

The invention discloses a thermal displacement compensation device of an electric spindle, a numerical control machine tool and a compensation method of the numerical control machine tool. The device comprises an eddy current displacement sensor and a compensation system. The eddy current displacement sensor comprises a probe and a post-stage processing circuit, the probe is provided with a first coil, a second coil and a multi-channel chip, the first coil is connected with a first inductance input channel of the multi-channel chip to output a first digital signal, and the second coil is connected with a second inductance input channel to output a second digital signal; the post-stage processing circuit converts the first digital signal into a first voltage signal and a pulse signal, and converts the second digital signal into a second voltage signal; and the compensation system performs temperature drift compensation on the first voltage signal according to the second voltage signal, and performs axial compensation on the motorized spindle by using the pulse signal and the compensated first voltage signal. According to the scheme, the accuracy of displacement measurement of the motorized spindle is improved, and the thermal displacement compensation effect of the spindle is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of numerically controlled machine tools, and in particular relates to a thermal displacement compensation device for an electric spindle, a numerically controlled machine tool and a compensation method thereof. Background Art

[0002] The electric spindle is a core component of CNC machine tools. When it is running, it will generate a lot of heat inside, causing thermal displacement at the tool at the front end of the spindle, thus affecting the processing accuracy.

[0003] In order to suppress the adverse effects of axial thermal displacement of the spindle, eddy current displacement sensors are usually used to detect the axial thermal displacement generated by the spindle in real time during operation and perform reverse compensation. Among them, the eddy current probe is an important component of the eddy current displacement sensor. It usually outputs an analog signal in the form of voltage or current, and its change is proportional to the change in the physical parameters of the object being measured, such as displacement. These analog signals can then be converted into digital signals by the data acquisition system for further processing and analysis. However, in actual operation, the measurement accuracy of the sensor is poor. The specific reasons are: the probe and the system are generally connected by a coaxial cable. The analog signal output by the probe is easily affected by factors such as bending of the signal cable, changes in electrical parameters, and vibration, resulting in a large noise output signal of the eddy current sensor; the heat generated by the spindle will cause the electromagnetic parameters of the sensor coil to change, causing the measurement signal to drift.

[0004] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a thermal displacement compensation device for an electric spindle, a CNC machine tool and a compensation method thereof, so as to solve the problem of poor measurement accuracy of eddy current displacement sensors in the prior art. By integrating and packaging a multi-channel chip and a coil inside a probe, outputting an inductance digital signal and connecting it to a post-processing circuit via a coaxial cable, the influence of cable bending and vibration on the signal during machine tool processing is reduced. At the same time, an additional coil is added to perform temperature compensation on the sensor, effectively solving the problem of poor measurement accuracy of the eddy current displacement sensor, ensuring the spindle thermal displacement compensation effect, and improving the measurement accuracy under harsh working conditions.

[0006] The present invention provides a thermal displacement compensation device for an electric spindle, comprising an eddy current displacement sensor and a compensation system; the eddy current displacement sensor comprises a probe and a post-processing circuit, the probe comprising a first coil, a second coil, and a multi-channel chip; the first coil is connected to a first inductance input channel of the multi-channel chip, for detecting the thermal displacement of the electric spindle and outputting a first digital signal; the second coil is connected to a second inductance input channel of the multi-channel chip, for detecting the temperature at the eddy current displacement sensor and outputting a second digital signal; the post-processing circuit is configured to convert the first digital signal into a first voltage signal and a pulse signal, and convert the second digital signal into a second voltage signal; the compensation system is configured to perform temperature drift compensation on the first voltage signal according to the second voltage signal, and to perform axial compensation on the electric spindle using the pulse signal and the first voltage signal after temperature drift compensation.

[0007] In some embodiments, the post-processing circuit includes an MCU, an optocoupler, and a DAC. The MCU is used to convert the first digital signal into a first voltage quantity and the second digital signal into a second voltage quantity. The optocoupler and the DAC are used to convert the first voltage quantity into the first voltage signal and the second voltage quantity into the second voltage signal.

[0008] In some embodiments, the multi-channel chip is an LDC1614 chip; among the four inductance input channels of the LDC1614 chip, the remaining two inductance input channels are connected to the proximity switch of the electric spindle, which is used to output a Boolean signal to determine the working status of the electric spindle.

[0009] In some embodiments, the probe has a stainless steel shell, the interior of which is filled with epoxy resin to fix the first coil, the second coil, and the multi-channel chip.

[0010] Matching the above-mentioned device, the present invention further provides a CNC machine tool, comprising: the thermal displacement compensation device of the electric spindle described above.

[0011] Matching the above-mentioned CNC machine tool, the present invention provides a compensation method for a CNC machine tool on another aspect, comprising: obtaining the first voltage signal, the pulse signal, and the second voltage signal; performing temperature drift compensation on the first voltage signal according to the second voltage signal; and performing displacement compensation on the electric spindle according to the pulse signal and the first voltage signal after temperature drift compensation.

[0012] In some embodiments, temperature drift compensation is performed on the first voltage signal based on the second voltage signal, including: obtaining a current temperature change based on a preset correspondence between the second voltage signal and the temperature change; determining a voltage error based on the current temperature change based on a preset temperature compensation model; and determining the difference between the first voltage signal and the voltage error as the first voltage signal after temperature drift compensation.

[0013] In some embodiments, displacement compensation is performed on the electric spindle based on the pulse signal and the first voltage signal after temperature drift compensation, including: obtaining the current thermal displacement compensation amount based on a preset correspondence between the first voltage signal and the thermal displacement compensation amount; judging whether the pulse signal is a high level or a low level; if the pulse signal is a high level, performing axial compensation according to the first direction and the current thermal displacement compensation amount; if the pulse signal is a low level, performing axial compensation according to the second direction and the current thermal displacement compensation amount; the first direction and the second direction are opposite directions.

[0014] In some embodiments, the method further includes: when the ambient temperature is a preset first temperature, using the current second voltage signal as a reference voltage; raising the ambient temperature from the preset first temperature to a preset second temperature, and obtaining a change in the second voltage signal during this process; fitting the change in the second voltage signal with the change in the ambient temperature to obtain a corresponding relationship between the second voltage signal and the temperature change.

[0015] In some embodiments, the method further includes: after the difference between the first voltage signal and the preset reference voltage is greater than a preset threshold, reacquiring the current voltage signal as the new reference voltage and resetting the displacement compensation count; the displacement compensation count is used to record the number of actions of the electric spindle displacement compensation and the numerical identifier of the accumulated compensation amount.

[0016] Therefore, the present invention provides a thermal displacement compensation device for an electric spindle, comprising an eddy current displacement sensor and a compensation system. The eddy current displacement sensor includes a probe and a post-processing circuit. The probe comprises a first coil, a second coil, and a multi-channel chip. The first coil is connected to a first inductance input channel of the multi-channel chip to output a first digital signal, and the second coil is connected to a second inductance input channel to output a second digital signal. The post-processing circuit converts the first digital signal into a first voltage signal and a pulse signal, and the second digital signal into a second voltage signal. The compensation system compensates for temperature drift of the first voltage signal based on the second voltage signal, and uses the pulse signal and the compensated first voltage signal to perform axial compensation on the electric spindle. Thus, by integrating the multi-channel chip and the coil into a probe, outputting an inductance digital signal and connecting it to the post-processing circuit via a coaxial cable, the influence of cable bending and vibration on the signal during machine tool processing is reduced. At the same time, a coil is added to perform temperature compensation on the sensor, effectively solving the problem of poor measurement accuracy of the eddy current displacement sensor, ensuring the spindle thermal displacement compensation effect, and improving measurement accuracy under harsh working conditions.

[0017] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of an embodiment of a thermal displacement compensation device for an electric spindle of the present invention;

[0020] Figure 2 This is a schematic diagram of the installation of the eddy current displacement sensor;

[0021] Figure 3 This is a schematic diagram of the installation section of the eddy current displacement sensor;

[0022] Figure 4 This is the flow chart of spindle thermal displacement compensation;

[0023] Figure 5 This is a schematic diagram of the pulse signal output by the eddy current displacement sensor;

[0024] Figure 6 is a schematic diagram of the relationship between the first voltage signal and the main shaft displacement;

[0025] Figure 7 This is the installation diagram of the spindle proximity switch;

[0026] Figure 8 This is a flow chart of the spindle thermal displacement compensation algorithm;

[0027] Figure 9 This is a structural diagram of the spindle thermal displacement compensation module;

[0028] Figure 10 This is a diagram illustrating the effect of spindle thermal displacement compensation;

[0029] Figure 11 This is a diagram illustrating the effect of temperature drift compensation;

[0030] Figure 12 FIG. 4 is a flow chart of an embodiment of a compensation method of the present invention.

[0031] In conjunction with the accompanying drawings, the reference numerals in the embodiments of the present invention are as follows:

[0032] 1-probe; 2-sensor bracket; 3-thermal displacement detection ring; 4-axis; 5-flange; 6-tool handle; 7-disc spring; 8-sensor disk; 9-proximity switch. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and corresponding drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] According to an embodiment of the present invention, a thermal displacement compensation device for an electric spindle is provided. The thermal displacement compensation device includes an eddy current displacement sensor and a compensation system. The eddy current displacement sensor includes a probe and a post-processing circuit. The probe includes a first coil, a second coil, and a multi-channel chip. The first coil is connected to a first inductance input channel of the multi-channel chip and is used to detect the thermal displacement of the electric spindle and output a first digital signal. The second coil is connected to a second inductance input channel of the multi-channel chip and is used to detect the temperature at the eddy current displacement sensor and output a second digital signal. The post-processing circuit is used to convert the first digital signal into a first voltage signal and a pulse signal, and the second digital signal into a second voltage signal. The compensation system is used to perform temperature drift compensation on the first voltage signal based on the second voltage signal, and to perform axial compensation on the electric spindle using the pulse signal and the first voltage signal after temperature drift compensation.

[0035] Eddy current displacement sensor is the core component for detecting thermal displacement and temperature. Its installation position is as follows: Figure 2 、 Figure 3As shown, the eddy current displacement sensor is arranged outside the main shaft, the sensor probe 1 is installed in the fixed bracket 2, the fixed bracket is installed on the main shaft flange 5, the detection surface of the probe 1 is fixed on the thermal displacement detection ring 3, the detection surface size is generally 10 mm, and the end jump is about 2 microns.

[0036] Eddy current displacement sensors consist of a probe and a post-processing circuit. The probe, the sensor's detection front end, integrates a primary coil, a secondary coil, and a multi-channel chip. These three components are packaged in a specific structure to ensure stable operation even in high-speed spindle rotation and cutting fluid environments. The post-processing circuit converts and processes the signals detected by the coils, ultimately outputting an electrical signal that can be recognized by the compensation system.

[0037] In some embodiments, the probe has a stainless steel shell, the interior of which is filled with epoxy resin to fix the first coil, the second coil, and the multi-channel chip.

[0038] The probe housing is threaded and can be secured to the sensor bracket with a nut. Made of stainless steel, it resists mechanical shock and provides electromagnetic shielding. The probe interior contains two coils, a multi-channel chip, a coil resin mount, and an aviation plug connector. The probe is filled and secured with epoxy resin, ensuring stable inductance detection while also improving insulation and thermal conductivity. The coils measure 5.4mm in diameter and 1.8mm in height; the multi-channel chip measures 4.1mm*4.1mm*0.8mm. The coils are placed directly above the chip. Two enameled wires at the beginning and end of each coil connect to the chip's two input pins. The chip's five output pins connect to the post-processing circuitry via coaxial cable. The overall probe package measures 8mm in diameter and 15mm in length.

[0039] The first coil is directly connected to the first inductance input channel of the multi-channel chip. When the electric spindle operates at high speed, axial thermal displacement due to bearing friction and motor heat generation causes a change in the gap between the first coil and the front end of the spindle, which in turn causes a change in the coil's inductance. The multi-channel chip detects this change in inductance and outputs a first digital signal representing the raw data of the thermal displacement.

[0040] The second coil is connected to the second inductance input channel of the multi-channel chip. Ambient temperature changes (such as the spindle's temperature rise being transmitted to the sensor) cause the second coil's electromagnetic parameters (such as inductance and resistance) to drift. The multi-channel chip detects these changes and outputs a second digital signal reflecting the sensor's ambient temperature.

[0041] The main function of the multi-channel chip is to collect the inductance signals of different coils through multiple inductance input channels and convert them into digital signal outputs, including converting the first analog signal into a first digital signal and the second analog signal into a second digital signal.

[0042] After receiving the first digital signal and the second digital signal output by the multi-channel chip, the post-processing circuit performs a two-stage conversion, including converting the first digital signal into a first voltage signal and a pulse signal, and converting the second digital signal into a second voltage signal. The first voltage signal and the second voltage signal are analog quantities, and the analog signals are used to indicate the compensation direction. The converted signal is transmitted to the compensation system through a shielded cable to avoid the influence of electromagnetic interference of the spindle on the signal. The pulse signal is as follows: Figure 5 As shown, if inc is high, it means that the spindle needs to be controlled to lift up, and if it is low, it means that the spindle needs to be controlled to move down; one pulse of plus represents a compensation of one micron. The relationship between the first voltage signal and the thermal displacement is as follows: Figure 6 As shown, the displacement d is obtained by fitting the formula and inversely deducing the voltage v.

[0043] The compensation system is the control and execution core of the device. After receiving the signal output by the sensor, it performs temperature drift compensation on the thermal displacement detection signal. According to the processed signal, the electric spindle is controlled to perform axial compensation, thereby first eliminating the influence of temperature on measurement accuracy, and then offsetting the processing error caused by thermal deformation, ensuring higher processing accuracy.

[0044] Temperature drift compensation calculates the impact of temperature changes on the first voltage signal based on the second voltage signal, then corrects the first voltage signal to ensure it truly reflects the thermal displacement of the electric spindle, rather than a false signal caused by temperature interference. Axial compensation combines the corrected first voltage signal with the pulse signal to control the electric spindle's feed system to perform axial reverse compensation to offset thermal deformation.

[0045] The structure of the thermal displacement compensation device is as follows Figure 1As shown, the compensation system includes a thermal compensation model, a CNC system PLC, and a driver. The eddy current displacement sensor's probe consists of a coil and a multi-channel chip. The coil senses the gap change caused by thermal displacement of the electric spindle. The multi-channel chip converts the coil inductance signal into a digital signal, which is transmitted via a coaxial cable to acquire thermal displacement and temperature-related signals. The post-processing circuit receives the digital thermal displacement signal transmitted by the probe and performs signal conversion to provide a usable signal for subsequent compensation control. Based on the output signal of the post-processing circuit and a temperature drift compensation algorithm, the thermal compensation model calculates the thermal displacement to be compensated and establishes the logic linking thermal displacement and compensation control. The CNC system PLC receives the thermal displacement compensation output by the thermal compensation model as a control command source, sending a compensation control signal to the driver. The driver, receiving the command from the CNC system PLC, drives the electric spindle's actuator to complete the thermal displacement compensation operation and ensure the machining accuracy of the electric spindle. The spindle is the target of thermal displacement generation and compensation. Thermal displacement caused by high-speed operation is compensated by the driver to maintain stable machining conditions.

[0046] When the spindle is running, the tool holder will continuously generate thermal displacement downward, that is, the detection surface will continue to approach the sensor probe. As the spindle runs longer, the rate of thermal displacement of the tool holder tends to be flat, until it stabilizes at a certain position. The sensor detects the axial thermal displacement of the spindle in real time during machining, calculates the compensation amount according to the thermal displacement compensation model, and the PLC controls the spindle to perform axial compensation. There are two communication methods between the sensor and the CNC system: digital communication (pulse) and analog communication (voltage). The compensation process is as follows: Figure 4 As shown in the figure, the CNC IO board is used to receive the pulse signal output by the displacement sensor, is responsible for the transmission and preliminary processing of the pulse digital signal, and transmits the signal to the PLC control module; the analog IO board is used to receive the voltage signal output by the displacement sensor, condition and convert the voltage signal, adapt it to the input requirements of the PLC control module, and then transmit it to the PLC.

[0047] This invention integrates a multi-channel chip and coil within a sensor probe, which outputs a digital inductance signal. This probe is connected to the post-processing circuit using a coaxial cable. During machine tool processing, the digital signal is less susceptible to cable bending, vibration, and other factors than the analog signal, resulting in better spindle thermal displacement compensation. The addition of a coil probe also provides temperature compensation for the sensor, further improving the displacement sensor's measurement accuracy under harsh conditions such as machine tool processing, ensuring superior compensation and increasing the yield rate of test piece processing.

[0048] In some embodiments, the post-processing circuit includes an MCU, an optocoupler, and a DAC. The MCU is used to convert the first digital signal into a first voltage quantity and the second digital signal into a second voltage quantity. The optocoupler and the DAC are used to convert the first voltage quantity into the first voltage signal and the second voltage quantity into the second voltage signal.

[0049] The MCU, optocoupler, and DAC jointly complete the conversion from digital signals to voltage signals. Specifically, the MCU receives the first digital signal and the second digital signal output by the multi-channel chip and converts them into the first voltage and the second voltage using a built-in algorithm. For example, the MCU can linearly map the first digital signal (range 0-65535) to a first voltage of 0-3.3V. The optocoupler acts as an electrical isolation device to prevent the influence of strong electromagnetic interference from the spindle on subsequent signals, while converting the digital voltage output by the MCU into a signal that can drive the DAC. The DAC receives the digital voltage after optocoupler isolation and converts it into an analog voltage signal, for example, converting a 0-3.3V digital voltage into a 0-10V analog voltage signal to adapt to the input requirements of the compensation system. That is, the digital signal output by the multi-channel chip is transmitted to the MCU, which converts it into a voltage. After the optocoupler isolates the voltage, the DAC converts it into a voltage signal. At the same time, the MCU outputs a pulse signal according to the direction of change of the first voltage. In addition, the post-processing circuit also includes a power supply unit for powering chips such as the MCU and LDC1614. The total power supply is the 24V voltage output by the CNC system.

[0050] The digital voltage is converted into an analog voltage signal through the DAC, which is compatible with the standard analog input interface of the CNC system without the need for additional customized hardware. The isolation function of the optocoupler can completely isolate the circuits on the probe side from the compensation system side, ensuring the calculation accuracy of temperature drift compensation. The high processing speed of the MCU can meet the real-time requirements of signal conversion.

[0051] In some embodiments, the multi-channel chip is an LDC1614 chip; among the four inductance input channels of the LDC1614 chip, the remaining two inductance input channels are connected to the proximity switch of the electric spindle, which is used to output a Boolean signal to determine the working status of the electric spindle.

[0052] Specifically, the LDC1614 chip itself has four inductance input channels, two of which are used to receive the analog inductance of the two coils, and the other two can be connected to the proximity switch of the spindle to obtain the working status of the spindle, which includes broaching, no knife, and loosening the knife. Specifically, the first channel of the LDC1614 chip is connected to the first coil, detects the inductance change corresponding to the thermal displacement of the electric spindle, and outputs a first digital signal; the second channel is connected to the second coil, detects the inductance change corresponding to the ambient temperature, and outputs a second digital signal; the third and fourth channels are connected to the proximity switch sensor disk of the electric spindle, and output Boolean signals (high level / low level) by detecting the position change of the sensor disk. Figure 7 As shown, three proximity switches 9 are provided on the induction disk 8 .

[0053] Since only two channels can output Boolean signals, assuming they are channel A and channel B, the state definition and signal combination can be set as follows: in the broaching state, the spindle tool is clamped, the induction disk is in the near-field position, channel A outputs a high level, and channel B outputs a low level; in the tool-free state, the spindle has no tool, the induction disk is in the mid-field position, and both channel A and channel B output a low level; in the tool-releasing state, the spindle tool is released, the induction disk is in the far-field position, channel A outputs a low level, and channel B outputs a high level.

[0054] When the proximity switch sensor disk undergoes axial displacement depending on the spindle tool status, the inductance of the detection coils connected to the third and fourth channels changes: When the tool is pulled, the sensor disk is closest, the inductance of Channel A's coil increases sharply, and the output is high, while the inductance of Channel B's coil remains unchanged and the output is low. When the tool is not in use, the sensor disk is centered, the inductance of both channel coils is at an intermediate value, and both output a low. When the tool is released, the sensor disk is farthest, the inductance of Channel B's coil increases sharply, and the output is high, while the inductance of Channel A's coil remains unchanged and the output is low. By utilizing the remaining channels of the LDC1614 to detect working conditions, the device eliminates the need for additional sensors and reduces both cost and size. Using a combination of Boolean signals instead of three channels allows coverage of all necessary states without adding hardware, adapting to the real-time status feedback requirements of high-speed spindle machining.

[0055] The technical solution of the present invention provides a thermal displacement compensation device for an electric spindle, comprising an eddy current displacement sensor and a compensation system. The eddy current displacement sensor includes a probe and a post-processing circuit. The probe comprises a first coil, a second coil, and a multi-channel chip. The first coil is connected to a first inductance input channel of the multi-channel chip to output a first digital signal, and the second coil is connected to a second inductance input channel to output a second digital signal. The post-processing circuit converts the first digital signal into a first voltage signal and a pulse signal, and the second digital signal into a second voltage signal. The compensation system compensates for temperature drift of the first voltage signal based on the second voltage signal, and uses the pulse signal and the compensated first voltage signal to perform axial compensation on the electric spindle. Thus, by integrating the multi-channel chip and the coil within the probe, outputting an inductance digital signal and connecting it to the post-processing circuit via a coaxial cable, the effect of cable bending and vibration on the signal during machine tool processing is reduced. At the same time, an additional coil is added to perform temperature compensation on the sensor, effectively solving the problem of poor measurement accuracy of the eddy current displacement sensor, ensuring the spindle thermal displacement compensation effect, and improving measurement accuracy under harsh working conditions.

[0056] According to an embodiment of the present invention, a CNC machine tool corresponding to the thermal displacement compensation device of the electric spindle is also provided. The CNC machine tool may include: the thermal displacement compensation device of the electric spindle described above.

[0057] Since the processing and functions implemented by the CNC machine tool of this embodiment basically correspond to the embodiments, principles and examples of the device, for any details not fully described in this embodiment, please refer to the relevant descriptions in the aforementioned embodiments and will not be repeated here.

[0058] The technical solution of the present invention provides a thermal displacement compensation device for an electric spindle, comprising an eddy current displacement sensor and a compensation system. The eddy current displacement sensor includes a probe and a post-processing circuit. The probe comprises a first coil, a second coil, and a multi-channel chip. The first coil is connected to a first inductance input channel of the multi-channel chip to output a first digital signal, and the second coil is connected to a second inductance input channel to output a second digital signal. The post-processing circuit converts the first digital signal into a first voltage signal and a pulse signal, and the second digital signal into a second voltage signal. The compensation system compensates for temperature drift of the first voltage signal based on the second voltage signal, and uses the pulse signal and the compensated first voltage signal to perform axial compensation on the electric spindle. Thus, by integrating the multi-channel chip and the coil within the probe, outputting an inductance digital signal and connecting it to the post-processing circuit via a coaxial cable, the effect of cable bending and vibration on the signal during machine tool processing is reduced. At the same time, an additional coil is added to perform temperature compensation on the sensor, effectively solving the problem of poor measurement accuracy of the eddy current displacement sensor, ensuring the spindle thermal displacement compensation effect, and improving measurement accuracy under harsh working conditions.

[0059] According to an embodiment of the present invention, a compensation method for a CNC machine tool is also provided, such as Figure 12 FIG2 is a flow chart of an embodiment of the method of the present invention. The compensation method for a CNC machine tool may include steps S110 to S130.

[0060] In step S110 , the first voltage signal, the pulse signal, and the second voltage signal are acquired.

[0061] The first voltage signal, pulse signal, and second voltage signal are all generated by the post-processing circuit of the eddy current sensor. The first voltage signal reflects the thermal displacement of the electric spindle, the pulse signal is used to indicate the direction of thermal displacement compensation, and the second voltage signal reflects the temperature change at the eddy current displacement sensor.

[0062] In step S120 , temperature drift compensation is performed on the first voltage signal according to the second voltage signal.

[0063] Since temperature changes can cause the coil inductance to drift, the drift error needs to be calculated and eliminated using a preset model to ensure that the first voltage signal truly reflects the thermal displacement.

[0064] In some embodiments, in step S120, the specific process of performing temperature drift compensation on the first voltage signal based on the second voltage signal includes: obtaining the current temperature change based on a preset correspondence between the second voltage signal and the temperature change; determining the voltage error based on the current temperature change based on a preset temperature compensation model; and determining the difference between the first voltage signal and the voltage error as the first voltage signal after temperature drift compensation.

[0065] Specifically, the second voltage signal collected in real time is converted into the corresponding temperature change. For example, if the second voltage signal is 3V, the corresponding temperature change is 20°C, that is, the current temperature is 20°C higher than the normal temperature of 20°C. According to the preset temperature compensation model, the voltage error is calculated in combination with the current temperature change. The temperature compensation model is such as the linear model ΔU=k×Δt fitted by the experiment, where k is the temperature coefficient. For example, when the temperature change is 20°C, the voltage error is 1V. The first voltage signal is subtracted from the above voltage error to obtain the first voltage signal after temperature drift compensation. For example, if the original first voltage signal is 5V and the voltage error is 1V, the compensated signal is 4V, which more truly reflects the actual thermal displacement of the electric spindle. By eliminating the voltage drift caused by temperature, the accuracy of thermal displacement detection is ensured.

[0066] In some embodiments, a process is also included to determine the correspondence between the second voltage signal and the temperature change, which specifically includes: when the ambient temperature is a preset first temperature, using the current second voltage signal as a reference voltage; raising the ambient temperature from the preset first temperature to the preset second temperature, and obtaining the change in the second voltage signal during this process; fitting the change in the second voltage signal with the change in the ambient temperature to obtain the correspondence between the second voltage signal and the temperature change.

[0067] Specifically, the first temperature is preset to 20°C, that is, normal temperature environment, and the second voltage signal currently output by the second coil is recorded as the reference voltage U T0 , which is the reference zero point for subsequent temperature change calculations. Then, the temperature is raised from 20°C to the preset second temperature (60°C), and the corresponding second voltage signal U is recorded every fixed temperature interval (such as 5°C). T , record U at 25℃ T =1.2V, at 30℃ T =1.4V, until 60℃. Calculate the change of the second voltage signal and the change of the ambient temperature at each temperature point. The change of the second voltage signal is U T -U T0 The ambient temperature change is t-20°C. A linear fit is then used to determine the corresponding relationship between the second voltage signal and the temperature change. This quantitative relationship between the second voltage signal and temperature change resolves the issue of coil inductance drift caused by temperature changes.

[0068] In step S130 , displacement compensation is performed on the electric spindle according to the pulse signal and the first voltage signal after temperature drift compensation.

[0069] The compensation system combines the corrected first voltage signal with the pulse signal and sends a compensation instruction to the drive system of the electric spindle to control the spindle to perform reverse displacement along the axial direction, ultimately offsetting the influence of thermal deformation on machining accuracy. The compensation effect of temperature drift compensation is as follows: Figure 11 As shown, Figure 11 (a) Before compensation, Figure 11 (b) is after compensation. The compensation effect of displacement compensation is as follows Figure 10 As shown, Figure 10 (a) is cutting heat compensation. The cutting thermal elongation of the rear end face is reduced by 50μm. Figure 10 (b) is no-load thermal compensation. After compensation, the machine tool warm-up time is greatly shortened, and the spindle can be started from cold and put into processing directly.

[0070] In some embodiments, in step S130, the specific process of performing displacement compensation on the electric spindle according to the pulse signal and the first voltage signal after temperature drift compensation includes: obtaining the current thermal displacement compensation amount based on a preset correspondence between the first voltage signal and the thermal displacement compensation amount; judging whether the pulse signal is a high level or a low level; if the pulse signal is a high level, performing axial compensation according to the first direction and the current thermal displacement compensation amount; if the pulse signal is a low level, performing axial compensation according to the second direction and the current thermal displacement compensation amount; the first direction and the second direction are opposite directions.

[0071] The corresponding relationship between the first voltage signal and the thermal displacement compensation amount is as follows: Figure 6 As shown in the figure, this relationship is obtained by calibration at room temperature, such as 1V voltage corresponds to 10μm compensation. At the same time, the level state of the pulse signal is judged. If the pulse signal is high, the compensation direction is determined to be the first direction, and the spindle is controlled to move up; if the pulse signal is low, the compensation direction is determined to be the second direction, and the spindle is controlled to move down. Based on the determined compensation direction and thermal displacement compensation amount, the compensation system sends instructions to the drive mechanism of the electric spindle to control the spindle to move the corresponding distance in the corresponding direction. For example, when the thermal displacement compensation amount is 30μm and the pulse signal is high, the spindle is driven to lift 30μm to offset the processing error caused by thermal deformation. The compensation direction is clearly distinguished by the level state of the pulse signal, and the compensation amount is quantified by the voltage signal, realizing closed-loop compensation with controllable direction and precise value.

[0072] In some embodiments, the method further includes: after the difference between the first voltage signal and the preset reference voltage is greater than a preset threshold, reacquiring the current voltage signal as the new reference voltage and resetting the displacement compensation count; the displacement compensation count is used to record the number of actions of the electric spindle displacement compensation and the numerical identifier of the accumulated compensation amount.

[0073] Specifically, the preset threshold can be set to 0.5V. When the difference between the first voltage signal and the preset reference voltage is greater than 0.5V, it indicates that the spindle has switched speeds. The sensor output voltage undergoes a step change, and the original reference voltage no longer accurately reflects the current thermal displacement reference. The current voltage signal must be re-acquired as a new reference voltage. Specifically, the new reference voltage is acquired at the moment the spindle speed switches. For example, if the original reference voltage is 2V, if the first voltage signal rises to 2.6V (a difference of 0.6V greater than the 0.5V threshold), 2.6V is used as the new reference voltage. The displacement compensation count is a numerical identifier that records the number of displacement compensation actions performed by the electric spindle and the cumulative compensation amount. For example, each count corresponds to 1μm of compensation, and a cumulative count of 50 times represents a cumulative compensation of 50μm. When the reference voltage is reset, the compensation amount corresponding to the original count no longer matches the thermal displacement state under the new reference. At this time, the count is reset to ensure that the count value is synchronized with the current thermal displacement compensation requirements. By resetting the reference voltage and displacement compensation count, the problem of nonlinear thermal displacement changes caused by sudden changes in the spindle operating conditions is resolved, ensuring the stability of machining accuracy.

[0074] Figure 8 This is a flow chart of the spindle thermal displacement compensation algorithm, as shown in Figure 8 As shown, the method includes:

[0075] Step 1: At a certain moment, the first voltage V1 is collected, and it is judged whether V1-V0 is greater than m. If it is greater than m, 1 micron is compensated; at the next moment, the first voltage V2 is collected, and it is judged whether the difference between V2-V0 is greater than m*2. If it is greater than m*2, 1 micron is compensated; at the next moment, the first voltage V3 is collected, and it is judged whether the difference between V3-V0 is greater than m*3. If it is greater than m*3, 1 micron is compensated; and so on. n , judge V n If the difference between Vn and V0 is greater than m*n, proceed to step 2; otherwise, repeat step 1.

[0076] Step 2: Determine whether the spindle is compensated upward or downward. If the pulse signal is high, the spindle is controlled to move upward, and if the pulse signal is low, the spindle is controlled to move downward. Then, according to the compensation direction, the compensation is performed in steps of 1 micron. Figure 5 As shown, each pulse of plus represents compensation of 1 micron, and inc represents the compensation direction.

[0077] Step 3: When the spindle switches speed, the output voltage of the sensor changes stepwise. Set the speed switching threshold. The program determines the voltage at the next moment minus the voltage at the previous moment (V n +1)-(V n ) is greater than the threshold, obtain the new initial displacement voltage V V0 Replace the initial V0, and set n to 1, and continuously collect the voltage VVn , start a new round of arithmetic progression compensation.

[0078] In some embodiments, the present invention further provides a spindle thermal displacement compensation module, such as Figure 9 As shown in the figure, the spindle thermal displacement compensation module includes a spindle thermal displacement detection sensor, a spindle thermal displacement compensation algorithm, a sensor-to-CNC system communication solution, a spindle proximity switch, a spindle status detection host computer, and a spindle fault diagnosis and life prediction module. The spindle thermal displacement detection sensor collects spindle thermal displacement data, providing the module with basic information about thermal deformation. The spindle thermal displacement compensation algorithm receives sensor data and, after calculation, outputs a compensation strategy. The sensor-to-CNC system communication establishes a data transmission channel, allowing signals such as thermal displacement collected by the sensor to be transmitted to the CNC system and compensation instructions to be transmitted back, ensuring information exchange. The spindle proximity switch monitors the spindle's operating status and assists in adapting thermal displacement compensation to different operating conditions. The spindle status detection host computer aggregates and displays information such as spindle thermal displacement and compensation progress for easy monitoring. Spindle fault diagnosis and life prediction uses data such as thermal displacement to predict spindle failures and estimate lifespan, expanding module functionality and facilitating equipment operation, maintenance, and management. By integrating multiple energy supplies into the spindle thermal displacement compensation module, the module can help improve the spindle's machining accuracy, enhance the spindle's intelligence level, and facilitate transplantation to machine tools of different models and specifications.

[0079] Since the processing and functions implemented by the method of this embodiment basically correspond to the embodiments, principles and examples of the aforementioned CNC machine tool, for any details not fully described in this embodiment, please refer to the relevant descriptions in the aforementioned embodiments and will not be repeated here.

[0080] According to the technical solution of this embodiment, the thermal displacement compensation device of the electric spindle includes an eddy current displacement sensor and a compensation system; the eddy current displacement sensor includes a probe and a post-processing circuit, the probe having a first coil, a second coil, and a multi-channel chip, the first coil being connected to the first inductance input channel of the multi-channel chip to output a first digital signal, and the second coil being connected to the second channel to output a second digital signal; the post-processing circuit converting the first digital signal into a first voltage signal and a pulse signal, and the second digital signal into a second voltage signal; the compensation system performing temperature drift compensation on the first voltage signal according to the second voltage signal, and performing axial compensation on the electric spindle using the pulse signal and the compensated first voltage signal. Thus, by integrating the multi-channel chip and the coil into the probe, outputting the inductance digital signal and connecting it to the post-processing circuit via a coaxial cable, the influence of cable bending and vibration on the signal during machine tool processing is reduced, and a coil is added to perform temperature compensation on the sensor, effectively solving the problem of poor measurement accuracy of the eddy current displacement sensor, ensuring the spindle thermal displacement compensation effect, and improving the measurement accuracy under harsh working conditions.

[0081] In summary, it is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed.

[0082] The foregoing description is merely an embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of the claims.

Claims

1. A thermal displacement compensation device for an electric spindle, characterized in that: The thermal displacement compensation device includes an eddy current displacement sensor and a compensation system; the eddy current displacement sensor includes a probe and a post-processing circuit; the probe includes a first coil, a second coil, and a multi-channel chip; The first coil is connected to the first inductance input channel of the multi-channel chip, and is used to detect the thermal displacement of the electric spindle and output a first digital signal; the second coil is connected to the second inductance input channel of the multi-channel chip, and is used to detect the temperature at the eddy current displacement sensor and output a second digital signal; The post-processing circuit is used to convert the first digital signal into a first voltage signal and a pulse signal, and convert the second digital signal into a second voltage signal; The compensation system is used to perform temperature drift compensation on the first voltage signal according to the second voltage signal, and to perform axial compensation on the electric spindle using the pulse signal and the first voltage signal after temperature drift compensation.

2. The thermal displacement compensation device of the electric spindle according to claim 1, characterized in that: The post-processing circuit includes an MCU, an optocoupler, and a DAC. The MCU is used to convert the first digital signal into a first voltage quantity and the second digital signal into a second voltage quantity. The optocoupler and the DAC are used to convert the first voltage quantity into the first voltage signal and the second voltage quantity into the second voltage signal.

3. The thermal displacement compensation device of the electric spindle according to claim 1 or 2, characterized in that: The multi-channel chip is an LDC1614 chip; among the four inductance input channels of the LDC1614 chip, the remaining two inductance input channels are connected to the proximity switch of the electric spindle, and are used to output a Boolean signal to determine the working status of the electric spindle.

4. The thermal displacement compensation device of the electric spindle according to any one of claims 1 to 3, characterized in that: The probe adopts a stainless steel shell, and the interior is filled with epoxy resin to fix the first coil, the second coil, and the multi-channel chip.

5. A CNC machine tool, characterized in that: include: The thermal displacement compensation device of the electric spindle according to any one of claims 1 to 4.

6. A compensation method for a CNC machine tool as claimed in claim 5, characterized in that: include: acquiring the first voltage signal, the pulse signal, and the second voltage signal; performing temperature drift compensation on the first voltage signal according to the second voltage signal; Displacement compensation is performed on the electric spindle according to the pulse signal and the first voltage signal after temperature drift compensation.

7. A compensation method for a CNC machine tool as claimed in claim 6, characterized in that: Performing temperature drift compensation on the first voltage signal according to the second voltage signal includes: Acquiring a current temperature variation based on a preset correspondence between the second voltage signal and the temperature variation; Determining a voltage error according to the current temperature change based on a preset temperature compensation model; A difference between the first voltage signal and the voltage error is determined as the first voltage signal after temperature drift compensation.

8. A compensation method for a CNC machine tool as claimed in claim 6, characterized in that: Performing displacement compensation on the electric spindle according to the pulse signal and the first voltage signal after temperature drift compensation, comprising: Obtaining a current thermal displacement compensation amount based on a preset correspondence between the first voltage signal and the thermal displacement compensation amount; Determining whether the pulse signal is a high level or a low level; If the pulse signal is at a high level, axial compensation is performed according to the first direction and the current thermal displacement compensation amount; If the pulse signal is at a low level, axial compensation is performed according to the second direction and the current thermal displacement compensation amount; the first direction and the second direction are opposite directions.

9. A compensation method for a CNC machine tool as claimed in claim 7, characterized in that: Also includes: When the ambient temperature is a preset first temperature, using the current second voltage signal as a reference voltage; Raising the ambient temperature from a preset first temperature to a preset second temperature, and obtaining a change in the second voltage signal during this process; The variation of the second voltage signal is fitted with the variation of the ambient temperature to obtain a corresponding relationship between the second voltage signal and the variation of the temperature.

10. A compensation method for a CNC machine tool as claimed in claim 8, characterized in that: Also includes: After the difference between the first voltage signal and the preset reference voltage is greater than a preset threshold, the current voltage signal is reacquired as the new reference voltage, and the displacement compensation count is reset; the displacement compensation count is used to record the number of actions of the electric spindle displacement compensation and the numerical identifier of the accumulated compensation amount.

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