A temperature compensation-based precision control system for drilling and tapping machines

Abstract

The application discloses a drilling and tapping machine precision control system based on temperature compensation and relates to the technical field of machining precision control of numerical control machine tools, which comprises the following steps: collecting time domain temperature sequences of each monitoring point in a non-main shaft area of a drilling and tapping machine bed and time domain pressure pulsation sequences of an oil supply pipeline; constructing a cross-correlation function and extracting response delay time of each monitoring point; extracting an inflection point moment of a first derivative of the time domain temperature sequences and a valley moment of the pressure pulsation sequences, and obtaining an inflection point-valley time difference of each monitoring point; determining the monitoring point with equal response delay time and inflection point-valley time difference as a thermal-mechanical coupling response node; calculating a local thermal expansion displacement amount, calculating an elastic compression displacement amount based on a pressure pulsation value; synthesizing two projection components and a main shaft positive thermal elongation amount to obtain a comprehensive compensation amount, and superimposing the comprehensive compensation amount into a position command offset amount of a Z-axis servo driver. The application can identify and compensate the comprehensive influence of a thermal-mechanical coupling field induced by a hydraulic system on the Z-axis precision.

Description

Technical Field

[0001] This invention relates to the field of CNC machine tool machining accuracy control technology, and in particular to a drilling and tapping machine accuracy control system based on temperature compensation. Background Technology

[0002] Currently, thermal error compensation systems for drilling and tapping machines and vertical machining centers generally adopt the assumption of "single heat source," meaning that the main heat source of the machine tool is limited to components related to the spindle system. Based on this assumption, existing technologies typically collect temperature measurements at the front / rear bearings of the spindle and the motor housing to establish a linear or polynomial thermal expansion model with time as the independent variable and temperature rise as the dependent variable. Chinese invention patent application CN109085797A discloses a method for generating computer-controlled machine tool offsets unaffected by cycle time, estimating the machine tool offset based on temperature sensor measurements; Chinese invention patent TWI649648B discloses a machining machine thermal compensation control system and method, integrating tool speed into the temperature compensation model. However, both of these patents limit the heat source to the spindle and related transmission components, failing to consider the comprehensive impact of the hydraulic clamping system on the machine tool's spatial accuracy.

[0003] With the widespread adoption of high-pressure hydraulic clamping systems in modern drilling and tapping machines, the machine tools face a source of interference that existing models cannot handle during actual operation: when the internal seals of the hydraulic cylinder experience microscopic wear or there is micro-leakage in the pipeline, the high-pressure oil undergoes viscous shear dissipation through narrow throttling gaps, generating localized transient thermal shock. Simultaneously, pressure pulsations (±5%~±10%) during pressure holding induce time-varying elastic deformation of the structure. The thermal shock point of this thermo-mechanical coupled field is located on the bed or table bottom surface, causing the column to bend in the opposite direction, with Z-axis drift opposite to the positive thermal elongation direction of the spindle. Existing models completely fail to recognize this reverse component and typically classify temperature fluctuations in non-spindle areas simply as "ambient thermal noise" for filtering, resulting in the loss of effective characteristic signals and compensation failure. Currently, there is no technology to incorporate the pressure pulsations and leakage throttling temperature rise of the hydraulic clamp as independent feedforward factors into the compensation system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a temperature-compensated precision control system for drilling and tapping machines. The system aims to solve the problem that during the operation of the high-pressure hydraulic clamp of the drilling and tapping machine, the local thermal shock caused by micro-leakage in the hydraulic system and the structural force deformation caused by pressure pulsation create a thermo-mechanical coupling field, which causes the machine tool to produce spatial bending / tilting drift opposite to the direction of spindle thermal elongation. Existing compensation models based on a single temperature field of the spindle cannot identify and correct this dynamic disturbance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a temperature-compensated drilling and tapping machine precision control system, comprising:

[0006] Data acquisition module: used to acquire the time-domain temperature sequence of each monitoring point in the non-spindle area of ​​the drilling and tapping machine body, acquire the time-domain pressure pulsation sequence of the oil supply pipeline, and obtain the positive thermal elongation of the spindle at the current moment;

[0007] Delay Time Module: Used to construct a cross-correlation function based on the time-domain temperature sequence and time-domain pressure pulsation sequence of each monitoring point, extract the delay time corresponding to the peak value of the cross-correlation function, and obtain the response delay time of each monitoring point;

[0008] Time difference calculation module: used to calculate the first derivative of the time-domain temperature sequence, extract the inflection point when the sign of the first derivative changes, extract the valley value of the time-domain pressure pulsation sequence, and calculate the difference between the inflection point and valley value of each monitoring point to obtain the inflection point-valley time difference of each monitoring point.

[0009] Node determination module: Used to determine the monitoring points whose response delay time is equal to the inflection point-valley time difference as thermo-mechanical coupling response nodes, and extract the temperature difference of the thermo-mechanical coupling response node and the corresponding oil supply pipeline pressure pulsation value.

[0010] Displacement calculation module: used to calculate the local thermal expansion displacement of the thermo-mechanical coupling response node based on the temperature difference, project the local thermal expansion displacement onto the Z-axis to obtain the thermal expansion projection component, calculate the elastic compression displacement based on the pressure pulsation value, project the elastic compression displacement onto the Z-axis to obtain the elastic compression projection component.

[0011] The comprehensive compensation module is used to synthesize the elastic compression projection component and the thermal expansion projection component to obtain the composite displacement. The composite displacement is then combined with the positive thermal elongation of the spindle to obtain the comprehensive compensation amount. The module also obtains the current position command offset of the Z-axis servo drive, reverses the sign of the comprehensive compensation amount, and adds it to the position command offset to generate the compensated Z-axis motion command.

[0012] Furthermore, the acquisition of time-domain temperature sequences at various monitoring points in the non-spindle area of ​​the drilling and tapping machine body, the acquisition of time-domain pressure pulsation sequences in the oil supply pipeline, and the acquisition of the positive thermal elongation of the spindle at the current moment include:

[0013] Collect the output values ​​of the temperature sensors at each monitoring point, and calculate the absolute temperature value based on the output values;

[0014] Arrange the absolute temperature values ​​of the same monitoring point in order of sampling time to form the time-domain temperature sequence of that monitoring point;

[0015] The raw signal output by the pressure sensor is acquired, and the raw signal is subjected to AC coupling filtering to generate a time-domain pressure pulsation sequence of the oil supply pipeline.

[0016] Read the gap signal output by the spindle axial displacement sensor at the current moment, convert the gap signal into mechanical displacement based on the pre-calibrated displacement sensor characteristic curve, and calculate the difference between the mechanical displacement and the preset reference displacement recorded during cold tool setting to obtain the positive thermal elongation of the spindle at the current moment.

[0017] Furthermore, the construction of a cross-correlation function based on the time-domain temperature sequence and time-domain pressure pulsation sequence of each monitoring point, and the extraction of the delay time corresponding to the peak value of the cross-correlation function to obtain the response delay time of each monitoring point, includes:

[0018] Cross-correlation calculations are performed on the time-domain temperature sequence and the time-domain pressure pulsation sequence of the oil supply pipeline at each monitoring point to generate a temperature-pressure cross-correlation function sequence with the delay time as the independent variable;

[0019] Search for the maximum value of each temperature-pressure cross-correlation function sequence, and determine the delay time at the maximum value as the response delay time of that monitoring point.

[0020] Furthermore, the step of calculating the first derivative of the time-domain temperature sequence, extracting the inflection point when the sign of the first derivative changes, extracting the trough time of the time-domain pressure pulsation sequence, and calculating the difference between the inflection point time and the trough time time of each monitoring point to obtain the inflection point-trough time difference of each monitoring point includes:

[0021] Calculate the first derivative of the time-domain temperature sequence for each monitoring point with respect to time to generate the temperature change rate sequence for that monitoring point.

[0022] The sampling time at which the sign of the numerical value in the temperature change rate sequence of each monitoring point changes is detected, and the detected sampling time is determined as the inflection point time of the monitoring point;

[0023] Search for local minima in the time-domain pressure pulsation sequence of the oil supply pipeline, extract the sampling time corresponding to the local minima, and form a set of valley time moments;

[0024] For each monitoring point, the inflection point time of the monitoring point is compared with the valley time in the valley time set to obtain the inflection point-valley time difference of the monitoring point.

[0025] Furthermore, the search for local minima of the time-domain pressure pulsation sequence of the oil supply pipeline, extracting the sampling times corresponding to the local minima, forms a set of valley times, including:

[0026] The first derivative of the time-domain pressure pulsation sequence of the oil supply pipeline with respect to time is obtained to generate a pressure change rate sequence.

[0027] The zero-crossing points in the pressure change rate sequence where the pressure changes from negative to positive are detected, and the sampling time corresponding to the zero-crossing point is determined as the pressure pulsation trough time.

[0028] All pressure pulsation trough moments are collected to form a trough moment set.

[0029] Furthermore, the step of identifying monitoring points whose response delay time is equal to the inflection point-valley time difference as thermo-mechanical coupling response nodes, and extracting the temperature difference of the thermo-mechanical coupling response node and the corresponding oil supply pipeline pressure pulsation value, includes:

[0030] For each monitoring point, if there is a time difference in the inflection point-valley time difference that is equal to the response delay time of the monitoring point, then the monitoring point is marked as a thermo-mechanical coupling response node, and the valley time corresponding to the equal time difference is determined as the matching valley time of the thermo-mechanical coupling response node.

[0031] For the time-domain temperature sequence of the thermo-mechanical coupling response node, the absolute temperature value of the thermo-mechanical coupling response node at the inflection point is extracted. The difference between the absolute temperature value at the inflection point and the absolute temperature value at the initial sampling point in the time-domain temperature sequence of the thermo-mechanical coupling response node is calculated to obtain the temperature difference of the thermo-mechanical coupling response node.

[0032] From the time-domain pressure pulsation sequence of the oil supply pipeline, extract the pressure pulsation value corresponding to the matching valley moment of the thermo-mechanical coupling response node, and use it as the oil supply pipeline pressure pulsation value corresponding to the thermo-mechanical coupling response node.

[0033] Furthermore, the step of calculating the local thermal expansion displacement of the thermo-mechanical coupling response node based on the temperature difference, projecting the local thermal expansion displacement onto the Z-axis to obtain the thermal expansion projection component, and calculating the elastic compression displacement based on the pressure pulsation value, projecting the elastic compression displacement onto the Z-axis to obtain the elastic compression projection component, includes:

[0034] Retrieve the preset constant set obtained during the calibration phase of the hydraulic clamping system of the drilling and tapping machine, and read from the preset constant set the material linear expansion coefficient of the machine tool base component at the thermo-mechanical coupling response node, the equivalent heat conduction length of the thermo-mechanical coupling response node along the temperature gradient direction, the hydraulic action area of ​​the hydraulic clamping unit at the thermo-mechanical coupling response node, the contact stiffness of the machine tool base component at the thermo-mechanical coupling response node along the force direction, the unit vector of the force direction, and the unit direction vector of the Z-axis of the drilling and tapping machine;

[0035] The known spatial coordinates of all monitoring points and the absolute temperature values ​​at the same sampling time are collected to form a spatial temperature point set;

[0036] Three-dimensional temperature field gradient estimation is performed on the set of spatial temperature points, and the gradient vector at the spatial coordinates of the thermo-mechanical coupling response node is determined as the temperature gradient vector.

[0037] The unit vector of the temperature gradient vector is defined as the direction of the temperature gradient.

[0038] The local thermal expansion displacement is obtained by multiplying the material's coefficient of linear expansion, the equivalent thermal conduction length, and the temperature difference.

[0039] The temperature gradient direction is multiplied by the unit direction vector of the drilling rig's Z-axis to obtain the direction cosine of the temperature gradient direction relative to the Z-axis.

[0040] The thermal expansion projection component is obtained by multiplying the local thermal expansion displacement with the direction cosine of the temperature gradient relative to the Z-axis.

[0041] The time-varying force is obtained by multiplying the pressure pulsation value of the oil supply line with the hydraulic action area.

[0042] Divide the time-varying force by the contact stiffness to obtain the elastic compressive displacement.

[0043] The direction cosine of the force direction relative to the Z-axis is obtained by taking the dot product of the unit vector of the force direction with the unit direction vector of the drilling machine's Z-axis.

[0044] The elastic compression projection component is obtained by multiplying the elastic compression displacement by the direction cosine of the force direction relative to the Z-axis.

[0045] Furthermore, the composite elastic compression projection component and the thermal expansion projection component are used to obtain a composite displacement. This composite displacement is then combined with the positive thermal elongation of the main shaft to obtain a comprehensive compensation amount, including:

[0046] The composite displacement is obtained by performing an algebraic summation on the elastic compression projection component and the thermal expansion projection component.

[0047] The combined compensation amount is obtained by performing an algebraic sum of the composite displacement and the positive thermal elongation of the main shaft at the current moment.

[0048] Furthermore, the step of obtaining the current position command offset of the Z-axis servo driver, inverting the sign of the comprehensive compensation amount, and adding it to the position command offset to generate the compensated Z-axis motion command includes:

[0049] The offset of the position command currently sent to the Z-axis servo drive is read through the Z-axis servo control loop of the drilling machine's CNC system.

[0050] Invert the comprehensive compensation amount to obtain the compensation amount with the reversed sign;

[0051] The compensation amount is added to the position command offset to obtain the compensated position command offset.

[0052] Write the compensated position command offset into the command register to generate the compensated Z-axis motion command.

[0053] The present invention provides a temperature-compensated precision control system for drilling and tapping machines, the advantages of which are mainly reflected in the following aspects:

[0054] 1. This invention, by introducing cross-correlation analysis between the time-domain pressure pulsation sequence of the oil supply pipeline and the time-domain temperature sequence of multiple points in the non-spindle region of the machine tool, can accurately identify the thermo-mechanical coupling response nodes induced by changes in the hydraulic system state in the time domain. Compared with the existing technology that simply classifies and filters out temperature fluctuations in the non-spindle region as environmental thermal noise, this invention utilizes the matching determination of the delay time corresponding to the peak value of the cross-correlation function and the time difference between the inflection point of the temperature change rate and the pressure trough value to effectively distinguish the thermo-mechanical coupling response signal from environmental random noise, avoiding compensation failure caused by the erroneous filtering of effective characteristic signals.

[0055] 2. This invention projects the local thermal expansion displacement and elastic compression displacement of the thermo-mechanical coupling response node onto the Z-axis and synthesizes them with the positive thermal elongation of the spindle to form a unified spatial comprehensive compensation amount, which is then superimposed on the position command offset of the Z-axis servo drive. Compared with existing time-series compensation models based on a single temperature field of the spindle, this invention can simultaneously compensate for the positive thermal elongation of the spindle and the reverse bending / tilting drift induced by the hydraulic system, solving the defect of existing models that completely "blindly ignore" the reverse component. By superimposing the comprehensive compensation amount with reversed sign onto the position command offset, closed-loop control of the Z-axis repeatability accuracy is achieved, effectively controlling the deterioration of the Z-axis comprehensive accuracy under conditions such as precision thread diameter machining and deep hole stepped drilling. Attached Figure Description

[0056] Figure 1 This is a functional block diagram of a temperature-compensated precision control system for a drilling and tapping machine according to the present invention.

[0057] Figure 2 This is a flowchart of the delay time extraction process of the present invention;

[0058] Figure 3 This is a flowchart of the thermo-mechanical coupling response node determination process of the present invention;

[0059] Figure 4 This is a flowchart of the Z-axis projection component calculation process of the present invention. Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] Please see Figures 1-4 This invention provides a temperature-compensated precision control system for drilling and tapping machines, comprising the following steps:

[0062] Data acquisition module: used to acquire the time-domain temperature sequence of each monitoring point in the non-spindle area of ​​the drilling and tapping machine body, acquire the time-domain pressure pulsation sequence of the oil supply pipeline, and obtain the positive thermal elongation of the spindle at the current moment;

[0063] In this embodiment, the acquisition of time-domain temperature sequences of various monitoring points in the non-spindle area of ​​the drilling and tapping machine body, the acquisition of time-domain pressure pulsation sequences of the oil supply pipeline, and the acquisition of the positive thermal elongation of the spindle at the current moment include:

[0064] The output values ​​of the temperature sensors at each monitoring point are collected, and the absolute temperature value is calculated based on the output values.

[0065] Specifically, monitoring points refer to multiple measurement locations on the surface of the non-spindle area of ​​the drilling machine body, where temperature sensors are pre-installed by means of thermally conductive adhesive or threaded fixing. Temperature sensors refer to K-type thermocouples or PT100 resistance thermometers that convert the physical quantity of temperature into an electrical signal.

[0066] The output value refers to the original electrical signal generated by the temperature sensor in response to temperature changes at the measured point. For thermocouples, this is the thermoelectric potential; for RTDs, it is the resistance value. Calibration conversion refers to converting the output value into an absolute temperature value in degrees Celsius or Kelvin, based on the calibration table provided by the temperature sensor manufacturer or a signal-temperature mapping curve calibrated by a metrology institution. This mapping curve has been calibrated at multiple points using a standard temperature source and stored in the parameter table of the CNC system before sensor installation.

[0067] The absolute temperature values ​​of the same monitoring point are arranged in order of sampling time to form the time-domain temperature sequence of that monitoring point.

[0068] Specifically, the sampling time refers to the time coordinate at which the temperature data acquisition card samples the sensor output value according to a pre-set constant sampling period. The sampling period is set to 1 second to ensure the capture of the rapid temperature rise process caused by hydraulic shock. Arranging by sampling time sequence means that the absolute temperature values ​​obtained at the same monitoring point at various sampling times are arranged into a one-dimensional data vector according to the chronological order. Each data element in the vector is associated with a unique sampling time. After time-series processing, the absolute temperature values ​​of each monitoring point form a discrete numerical sequence with the sampling time as the horizontal axis and the absolute temperature as the vertical axis, which completely records the temperature evolution trajectory of the measuring point over a continuous time period.

[0069] The raw signal output by the pressure sensor is acquired, and AC coupling filtering is performed on the raw signal to generate a time-domain pressure pulsation sequence of the oil supply pipeline.

[0070] Specifically, a pressure sensor refers to a piezoresistive or piezoelectric sensing element installed in the oil supply line of a hydraulic clamp to convert the instantaneous pressure of the oil into a standard current signal or voltage signal. The original signal refers to the mixed electrical signal directly output by the pressure sensor, which includes a steady-state pressure component and a dynamic pulsation component.

[0071] AC-coupled filtering refers to using a high-pass digital filter or analog DC blocking capacitor with a cutoff frequency of 0.5Hz to filter out the steady-state pressure component from the original signal, retaining only the dynamic pressure fluctuation component with a frequency higher than the cutoff frequency. The filter cutoff frequency is set according to the hydraulic pump plunger frequency and the natural frequency of the pipeline. The time-domain pressure pulsation sequence refers to the sequence of dynamic pressure fluctuation values ​​arranged in order of sampling time after AC-coupled filtering; the values ​​of this sequence are expressed in megapascals (MPA). The original pressure signal from the oil supply pipeline is acquired by a pressure sensor and AC-coupled filtering is applied to obtain pressure pulsation time-series data containing only the fluctuation component.

[0072] Read the gap signal output by the spindle axial displacement sensor at the current moment, convert the gap signal into mechanical displacement based on the pre-calibrated displacement sensor characteristic curve, and calculate the difference between the mechanical displacement and the preset reference displacement recorded during cold tool setting to obtain the positive thermal elongation of the spindle at the current moment.

[0073] Specifically, the spindle axial displacement sensor refers to an eddy current displacement sensor installed at the end of the spindle sleeve or the rear end of the spindle motor to measure the axial position change of the spindle relative to a fixed reference point on the machine tool column. The gap signal refers to the voltage value output by the sensor that is proportional to the axial position of the spindle.

[0074] The pre-calibrated displacement sensor characteristic curve refers to the mapping relationship curve established by using a laser interferometer or dial indicator as a standard displacement gauge when the spindle is cold, applying a known axial displacement to the spindle and recording the corresponding output voltage of the sensor, and establishing the mapping relationship curve based on multiple sets of displacement-voltage data through least squares linear fitting. This curve has been calibrated during the machine tool assembly and debugging stage and stored as equipment parameters in the non-volatile memory of the CNC system.

[0075] Cold setting of machine tools refers to the tool setting operation performed after the machine tool has been powered on and left to stand for more than 4 hours, with the temperature difference between the front bearing of the spindle and the ambient temperature not exceeding ±1℃. At this time, the axial thermal expansion of the spindle is considered zero. The preset reference displacement refers to the mechanical displacement value obtained by converting the output voltage of the axial displacement sensor during cold setting through the characteristic curve. This value is stored in the system register as the reference zero point for calculating the thermal expansion.

[0076] The difference is calculated by subtracting the preset reference displacement from the mechanical displacement calculated by the characteristic curve at the current moment. The difference is the axial positive thermal elongation of the spindle from the cold state to the current moment due to the heating of the spindle motor windings and the friction of the bearings.

[0077] Delay Time Module: Used to construct a cross-correlation function based on the time-domain temperature sequence and time-domain pressure pulsation sequence of each monitoring point, extract the delay time corresponding to the peak value of the cross-correlation function, and obtain the response delay time of each monitoring point;

[0078] In this embodiment, the step of constructing a cross-correlation function based on the time-domain temperature sequence and the time-domain pressure pulsation sequence of each monitoring point, and extracting the delay time corresponding to the peak value of the cross-correlation function to obtain the response delay time of each monitoring point includes:

[0079] Cross-correlation calculations are performed on the time-domain temperature sequence and the time-domain pressure pulsation sequence of the oil supply pipeline at each monitoring point to generate a temperature-pressure cross-correlation function sequence with the delay time as the independent variable.

[0080] Specifically, cross-correlation is a mathematical method in digital signal processing used to quantify the relationship between the similarity of two discrete-time series as a function of relative time shift. The time-domain temperature series refers to the vector of absolute temperature values ​​at each monitoring point arranged in order of sampling time, while the time-domain pressure pulsation series refers to the vector of dynamic pressure fluctuation values ​​in the oil supply pipeline arranged in order of sampling time after AC coupling filtering. Both have the same sampling period and sequence length to ensure the mathematical validity of the cross-correlation operation.

[0081] During the calculation, the time-domain pressure fluctuation sequence is kept stationary as a reference sequence. The time-domain temperature sequence is successively shifted left or right by one sampling interval relative to the pressure sequence. After each shift, the sum of the products of corresponding points in the overlapping time domain of the two sequences is calculated. This sum of products is the cross-correlation coefficient under that shift amount, and the unit of the shift amount is the number of sampling intervals. The temperature-pressure cross-correlation function sequence refers to the discrete numerical sequence composed of cross-correlation coefficients corresponding to each shift amount arranged in ascending order of the shift amount. Each data point in this sequence represents the degree of linear correlation between pressure fluctuations and temperature fluctuations at a specific delay time.

[0082] Search for the maximum value of each temperature-pressure cross-correlation function sequence, and determine the delay time at the maximum value as the response delay time of that monitoring point.

[0083] Specifically, the search for the maximum value refers to comparing three consecutive data points in a temperature-pressure cross-correlation function sequence using a sliding window. When the cross-correlation coefficient of the middle data point is greater than the cross-correlation coefficients of its left and right adjacent points, the middle point is determined to be a local maximum. The point with the largest cross-correlation coefficient among all local maximum points is determined as the global maximum. If there are multiple consecutive points with the same maximum value in the sequence, the delay time in the middle of these points is taken as the delay time corresponding to the final maximum value.

[0084] The delay time at the global maximum refers to the horizontal coordinate delay corresponding to the global maximum point. This delay is measured in seconds and is equal to the number of translation sampling points corresponding to the global maximum point multiplied by the sampling period. The response delay time refers to the time lag between the occurrence of a pressure pulsation event in the oil supply pipeline and the moment when the temperature response at that monitoring point reaches its strongest correlation with the pressure pulsation. Physically, this lag represents the time it takes for pressure energy to be converted into heat energy through viscous dissipation and conducted along the machine tool's foundation components from the leakage source to the monitoring point. By extracting the delay time corresponding to the global maximum of the temperature-pressure cross-correlation function sequence, the dynamic response lag of each monitoring point relative to the pressure pulsation in the oil supply pipeline is obtained. This lag serves as the time reference for subsequent determination of thermo-mechanical coupling response nodes.

[0085] Time difference calculation module: used to calculate the first derivative of the time-domain temperature sequence, extract the inflection point when the sign of the first derivative changes, extract the valley value of the time-domain pressure pulsation sequence, and calculate the difference between the inflection point and valley value of each monitoring point to obtain the inflection point-valley time difference of each monitoring point.

[0086] In this embodiment, the step of calculating the first derivative of the time-domain temperature sequence, extracting the inflection point when the sign of the first derivative changes, extracting the trough time of the time-domain pressure pulsation sequence, and calculating the difference between the inflection point time and the trough time of each monitoring point to obtain the inflection point-trough time difference of each monitoring point includes:

[0087] Calculate the first derivative of the time-domain temperature sequence for each monitoring point with respect to time to generate the temperature change rate sequence for that monitoring point.

[0088] Specifically, the first derivative refers to the rate of change of a continuous function along the time axis at a given point. For a time-domain temperature sequence obtained through discrete sampling, the central difference method is used to calculate the approximate value of the first derivative at each sampling point. The central difference formula is: the derivative at the current sampling point equals the temperature value at the next sampling time minus the temperature value at the previous sampling time, divided by twice the sampling period. The first and last points of the sequence are calculated using forward and backward differences respectively. The time-domain temperature sequence refers to the vector of absolute temperature values ​​of each monitoring point arranged in the order of sampling time, with each data point in the sequence corresponding to a unique sampling time.

[0089] A temperature change rate sequence refers to a discrete numerical sequence composed of approximate first-order derivative values ​​calculated using the central difference method at each sampling point, arranged in chronological order of sampling time. The unit of this sequence is degrees Celsius per second. By converting discrete temperature sampling data into a temperature change rate sequence at each time point using the central difference method, this sequence reflects the dynamic trend of temperature rising or falling over time, providing a numerical basis for subsequent inflection point detection.

[0090] The sampling time at which the sign of the numerical value in the temperature change rate sequence of each monitoring point changes is detected, and the detected sampling time is determined as the inflection point of the monitoring point.

[0091] Specifically, a change in the sign of a numerical value refers to the approximate value of the first derivative between two adjacent sampling points in the temperature change rate sequence changing from positive to negative or vice versa. A positive value indicates that the temperature is in an upward phase, and a negative value indicates that the temperature is in a downward phase. The detection method is to start from the second data point in the temperature change rate sequence and compare the sign of the current point with that of the previous sampling point. If the signs are different, the sampling time of the current point is recorded as the inflection point. If there is a sampling point between two adjacent points where the approximate value of the first derivative is zero, the zero point is skipped, and the sampling time corresponding to the first sampling point after the zero point whose sign is different from that before the zero point is taken as the inflection point.

[0092] The inflection point refers to the sampling moment when the sign of the temperature change rate reverses. This moment corresponds to the turning point where the temperature time-domain curve changes from rising to falling or from falling to rising. By detecting the change in the sign of adjacent sampling points in the temperature change rate sequence, the time position of the directional turning point in the temperature evolution process of each monitoring point can be accurately located.

[0093] Search for local minima in the time-domain pressure pulsation sequence of the oil supply pipeline, extract the sampling time corresponding to the local minima, and form a set of valley time points.

[0094] Specifically, a local minimum refers to a pressure pulsation value at a sampling point in a time-domain pressure pulsation sequence that is simultaneously less than the pressure pulsation values ​​of its left and right adjacent points. This point corresponds to a trough position on the pressure pulsation curve. The search method is to start from the second data point in the time-domain pressure pulsation sequence and compare the value of the current sampling point with the values ​​of its previous and next sampling points one by one. If the value of the current point is less than the values ​​of the previous and next points, it is determined to be a local minimum point. If there are multiple consecutive equal minimum points in the sequence, the sampling time in the middle of these equal points is taken as the representative time of the trough position.

[0095] The valley value time set refers to the time series set formed by summarizing the sampling times corresponding to all detected local minimum points. The elements in this set are arranged in chronological order of sampling times, and each element corresponds to the time point when the pressure pulsation in the oil supply pipeline occurs once a pressure trough. By comparing the numerical relationship of three adjacent sampling points in the pressure pulsation sequence point by point, all the trough positions of the pressure fluctuation in the oil supply pipeline are identified, forming a time stamp set of the periodic decrease times of the pressure pulse.

[0096] For each monitoring point, the inflection point time of the monitoring point is compared with the valley time in the valley time set to obtain the inflection point-valley time difference of the monitoring point.

[0097] Specifically, the difference operation refers to taking the inflection point detected at the same monitoring point as the minuend and subtracting each valley point in the valley point set. Each subtraction operation yields a time difference in seconds. The physical meaning of this difference is the time interval between the sampling time when the direction of temperature change changes and the sampling time when the pressure in the oil supply pipeline reaches a trough. A positive difference indicates that the inflection point is later than the corresponding valley point, and a negative difference indicates that the inflection point is earlier than the corresponding valley point.

[0098] The inflection point-valley time difference refers to the numerical set formed by summing up all the above difference calculation results. Each element in this set corresponds to the time distance between the inflection point time of the corresponding monitoring point and a certain pressure valley time. By successively subtracting the inflection point time of each monitoring point from each valley time in the valley time set, the time interval set between the inflection point time and each pressure valley is obtained. This set is used for subsequent consistency comparison with the response delay time to screen thermo-mechanical coupling response nodes.

[0099] In this embodiment, the search for local minima of the time-domain pressure pulsation sequence of the oil supply pipeline, and the extraction of the sampling times corresponding to the local minima to form a set of valley times, includes:

[0100] The first derivative of the time-domain pressure pulsation sequence of the oil supply pipeline with respect to time is obtained to generate a pressure change rate sequence.

[0101] Specifically, the time-domain pressure pulsation sequence refers to the dynamic pressure fluctuation value vector of the oil supply pipeline arranged in the order of sampling time after AC coupling filtering. Each data point in this sequence corresponds to a unique sampling time. The first derivative is calculated for the discrete sequence using the central difference method. The central difference formula is: the derivative of the current sampling point equals the pressure pulsation value at the next sampling time minus the pressure pulsation value at the previous sampling time, divided by twice the sampling period. The first and last points of the sequence are calculated using forward difference and backward difference, respectively.

[0102] The pressure change rate sequence refers to a discrete numerical sequence composed of the first derivative values ​​calculated using the central difference method at each sampling point, arranged in chronological order of sampling time. The unit of this sequence is megapascals per second. By using the central difference method, discrete pressure pulsation sampling data is converted into a pressure change rate sequence at each time point. This sequence reflects the dynamic trend of pressure increase or decrease in the oil supply pipeline over time.

[0103] The zero-crossing points in the pressure change rate sequence that change from negative to positive are detected, and the sampling time corresponding to the zero-crossing point is determined as the pressure pulsation trough time.

[0104] Specifically, negative values ​​in the pressure change rate sequence indicate that the oil supply line pressure is in a decreasing phase, while positive values ​​indicate that the pressure is in a rising phase. A change from negative to positive indicates that the pressure has shifted from decreasing to increasing. The zero-crossing position refers to the critical position in the pressure change rate sequence where the numerical signs of two adjacent sampling points change from negative to positive. The detection method is to start from the second data point in the pressure change rate sequence and compare the numerical signs of the current point with those of the previous sampling point. If the value of the previous sampling point is negative and the value of the current point is positive, then a zero-crossing position is determined to exist between the adjacent points, and the sampling time of the current point is determined as the pressure pulsation trough time. If there is a sampling point with a value exactly zero, then the sampling time of that zero point is taken as the trough time, and the search continues.

[0105] The trough moment of pressure pulsation refers to the sampling moment corresponding to the turning point where the pressure pulsation curve of the oil supply pipeline changes from a downward to an upward trend. This moment corresponds to the trough position of the pressure fluctuation. By detecting the position where adjacent sampling points in the pressure change rate sequence change from negative to positive signs, each trough moment of the pressure pulsation waveform of the oil supply pipeline can be accurately located.

[0106] All pressure pulsation trough moments are collected to form a trough moment set.

[0107] Specifically, "aggregation" refers to arranging all detected pressure pulsation trough moments in chronological order of sampling time. The trough moment set refers to the time-series data set formed by summarizing all the aforementioned trough moments, where each element corresponds to a specific moment when a pressure pulsation trough occurred. By storing the successively detected pressure trough moments as an ordered set, a complete time-stamped sequence of pressure troughs is provided for subsequent subtraction with the inflection point moments of each monitoring point.

[0108] Node determination module: Used to determine the monitoring points whose response delay time is equal to the inflection point-valley time difference as thermo-mechanical coupling response nodes, and extract the temperature difference of the thermo-mechanical coupling response node and the corresponding oil supply pipeline pressure pulsation value.

[0109] In this embodiment, the step of determining the monitoring point whose response delay time is equal to the inflection point-valley time difference as a thermo-mechanical coupling response node, and extracting the temperature difference and corresponding oil supply pipeline pressure pulsation value of the thermo-mechanical coupling response node, includes:

[0110] For each monitoring point, if there is a time difference in the inflection point-valley time difference that is equal to the response delay time of the monitoring point, then the monitoring point is marked as a thermo-mechanical coupling response node, and the valley time corresponding to the equal time difference is determined as the matching valley time of the thermo-mechanical coupling response node.

[0111] Specifically, the inflection point-valley time difference refers to the set of time intervals obtained by subtracting the inflection point time of each pressure valley time from the inflection point time of the monitoring point. The response delay time refers to the time shift corresponding to the maximum value of the cross-correlation function between the temperature sequence and the pressure pulsation sequence of the oil supply pipeline at the monitoring point. The determination of equal time differences adopts an absolute error tolerance comparison method, with the tolerance threshold set to half the sampling period. That is, when the absolute value of the difference between the inflection point-valley time difference and the response delay time is less than or equal to half a sampling period, the two are considered equal. The sampling period is determined by a constant sampling interval preset by the data acquisition card.

[0112] Thermo-mechanical coupling response nodes refer to monitoring points that meet the above tolerance comparison conditions. The temperature change characteristics of these nodes have a deterministic causal relationship with the pressure pulsation event in the oil supply pipeline over time. The matching valley moment refers to the specific pressure valley moment corresponding to the equal time difference. This moment marks the time position of the pressure trough that is causally related to the temperature inflection point of the monitoring point on the time axis. By introducing a tolerance comparison judgment method, nodes with a deterministic time-delay causal relationship with the pressure pulsation in the oil supply pipeline are screened from all monitoring points, and the time correspondence between the temperature inflection point of the node and the specific pressure trough is established.

[0113] For the time-domain temperature sequence of the thermo-mechanical coupling response node, the absolute temperature value of the thermo-mechanical coupling response node at the inflection point is extracted. The difference between the absolute temperature value at the inflection point and the absolute temperature value at the initial sampling point in the time-domain temperature sequence of the thermo-mechanical coupling response node is calculated to obtain the temperature difference of the thermo-mechanical coupling response node.

[0114] Specifically, the inflection point refers to the sampling moment when the sign of the numerical value in the temperature change rate sequence reverses, and the absolute temperature value at the inflection point refers to the temperature sampling value corresponding to that moment. The initial sampling moment refers to the sampling time corresponding to the first data point in the time-domain temperature sequence. This moment is usually selected at the beginning of the machine tool's current operating cycle and in the cold state before the hydraulic system has started pressurizing. The determination condition is that after the machine tool is powered on, it has been allowed to stand for a sufficient period of time to allow the temperature of each component to reach equilibrium with the ambient temperature. The absolute temperature value at the initial sampling moment refers to the actual temperature value measured at that monitoring point at that initial moment, which serves as the reference zero point for the temperature difference calculation at that node.

[0115] The difference calculation is implemented using subtraction. The absolute temperature value at the inflection point is subtracted from the absolute temperature value at the initial sampling point to obtain the temperature difference value. The unit of the temperature difference value is degrees Celsius. The temperature difference refers to the result of this difference calculation, and its physical meaning is the net temperature change at the monitoring point from the initial sampling time to the time when the temperature inflection point occurs. The formula is as follows:

[0116]

[0117] In the formula, The temperature difference at the thermo-mechanical coupling response node is expressed in degrees Celsius. The absolute temperature value at the inflection point, in degrees Celsius, is read directly from the time-domain temperature series; The absolute temperature value at the initial sampling time, in degrees Celsius, is taken as the first data value of the time-domain temperature sequence. The effective temperature rise amplitude generated by the thermo-mechanical coupling response node under the action of pressure pulsation event is quantified by subtracting the temperature at the inflection point from the temperature at the initial time.

[0118] From the time-domain pressure pulsation sequence of the oil supply pipeline, extract the pressure pulsation value corresponding to the matching valley moment of the thermo-mechanical coupling response node, and use it as the oil supply pipeline pressure pulsation value corresponding to the thermo-mechanical coupling response node.

[0119] Specifically, the time-domain pressure pulsation sequence refers to the dynamic pressure fluctuation value sequence arranged in the sampling time order after AC coupling filtering of the oil supply pipeline. Each data point in this sequence corresponds to a unique sampling time and stores the corresponding pressure pulsation value. The matching valley moment refers to the valley moment determined when the time difference between the inflection point and the valley moment is equal to the response delay time after tolerance comparison. This moment has a definite time delay relationship with the temperature inflection point of the thermo-mechanical coupling response node on the time axis.

[0120] Extraction involves searching the time-domain pressure pulsation sequence based on the matching valley time. If the matching valley time falls exactly on a sampling time, the pressure pulsation value of that sampling point is directly read. If the matching valley time is between two adjacent sampling times, a linear interpolation method is used to calculate the pressure pulsation value corresponding to that time. The oil supply pipeline pressure pulsation value refers to the actual dynamic pressure fluctuation value existing in the oil supply pipeline at the matching valley time. This value, expressed in megapascals, represents the specific amplitude of the pressure excitation event that causes the temperature response at the monitoring point. Based on the matching valley time, time indexing and interpolation are performed in the time-domain pressure pulsation sequence to obtain the pressure fluctuation amplitude that is causally related to the temperature inflection point of the thermo-mechanical coupling response node.

[0121] Displacement calculation module: used to calculate the local thermal expansion displacement of the thermo-mechanical coupling response node based on the temperature difference, project the local thermal expansion displacement onto the Z-axis to obtain the thermal expansion projection component, calculate the elastic compression displacement based on the pressure pulsation value, project the elastic compression displacement onto the Z-axis to obtain the elastic compression projection component.

[0122] In this embodiment, the calculation of the local thermal expansion displacement of the thermo-mechanical coupling response node based on the temperature difference, the projection of the local thermal expansion displacement onto the Z-axis to obtain the thermal expansion projection component, and the calculation of the elastic compression displacement based on the pressure pulsation value, the projection of the elastic compression displacement onto the Z-axis to obtain the elastic compression projection component, includes:

[0123] Retrieve the preset constant set obtained during the calibration phase of the hydraulic clamping system of the drilling and tapping machine, and read from the preset constant set the material linear expansion coefficient of the machine tool base component at the thermo-mechanical coupling response node, the equivalent heat conduction length of the thermo-mechanical coupling response node along the temperature gradient direction, the hydraulic action area of ​​the hydraulic clamping unit at the thermo-mechanical coupling response node, the contact stiffness of the machine tool base component at the thermo-mechanical coupling response node along the force direction, the unit vector of the force direction, and the unit direction vector of the Z-axis of the drilling and tapping machine.

[0124] Specifically, the preset constant set refers to the set of fixed parameters obtained through actual measurement and theoretical calculation of the hydraulic clamping system of the drilling and tapping machine during the machine tool assembly and debugging phase. This set is stored in the non-volatile memory of the CNC system for retrieval during subsequent compensation calculations. The material linear expansion coefficient refers to the thermal expansion characteristic parameter of the material of the base component where the node is located. It is obtained from the national standard material handbook based on the material grade of the cast iron or steel used in the machine tool base component and entered into the calibration document.

[0125] The equivalent heat conduction length refers to the equivalent heat conduction distance from the high-pressure oil leakage thermal shock point along the internal heat conduction path of the machine tool base component to the monitoring point. This parameter is obtained during the calibration phase through finite element thermal simulation calculations based on the geometry of the base component and the location of the heat source. The hydraulic action area refers to the effective pressure-bearing area of ​​the oil pressure acting on the piston end face or the force-bearing surface of the worktable in the hydraulic clamping unit. This area is calculated from the piston diameter of the hydraulic cylinder using the formula for the area of ​​a circle.

[0126] Contact stiffness refers to the force required for a unit elastic deformation of the base component where the node is located in the direction of the hydraulic clamping force. This stiffness is calculated during the calibration phase by applying a known load to the clamping surface and measuring the corresponding deformation using a displacement sensor. The unit vector of the force direction refers to the direction vector of the hydraulic clamping force acting on the machine tool base component. This vector is determined and normalized during the calibration phase based on the installation azimuth angle of the hydraulic clamping unit. The unit direction vector of the drilling and tapping machine's Z-axis refers to the unit vector in the positive direction of the Z-axis in the machine tool coordinate system. This vector is set by the machine tool manufacturer and stored in the CNC system parameter table.

[0127] The known spatial coordinates of all monitoring points and the absolute temperature values ​​at the same sampling time are collected to form a spatial temperature point set.

[0128] Specifically, the known spatial coordinates refer to the three-dimensional position coordinates of each temperature monitoring point in the three-axis machine tool coordinate system. These coordinates are obtained and recorded in the system parameter table using the machine tool probe or manual tool setting when arranging the monitoring points. The absolute temperature value at the same sampling time refers to the temperature value obtained by calibration and transformation at each monitoring point within the current calculation cycle. All temperature values ​​must correspond to the same sampling time. If the sampling times of each monitoring point are inconsistent, the synchronization of the spatial temperature field will be disrupted, and the gradient estimation results will produce significant errors.

[0129] A spatial temperature point set refers to a data set formed by combining the three-dimensional spatial coordinates of each monitoring point with its corresponding absolute temperature value. Each element in this set contains information in two dimensions: spatial location and temperature.

[0130] Three-dimensional temperature field gradient estimation is performed on the set of spatial temperature points, and the gradient vector at the spatial coordinates of the thermo-mechanical coupling response node is determined as the temperature gradient vector.

[0131] Specifically, three-dimensional temperature field gradient estimation refers to calculating the rate of change of the temperature field in various directions in space based on the temperature values ​​at discrete spatial points. The implementation method is as follows: First, the irregularly distributed set of spatial temperature points is mapped to temperature values ​​on regular grid nodes using the inverse distance weighted interpolation method. Then, the central difference calculation is performed on each grid node in the X, Y, and Z directions to obtain the three components of the temperature gradient at that node. Finally, the spatial coordinates of the thermo-mechanical coupling response node are substituted into the interpolation grid to perform bilinear interpolation to obtain the temperature gradient vector at that point.

[0132] The gradient vector is a vector composed of the rates of change of the temperature field at a certain point along the three coordinate axes in space. The direction of this vector points to the direction of the fastest temperature increase, and its magnitude reflects the degree of temperature change in that direction. The gradient vector at the spatial coordinates of the thermo-mechanical coupling response node is the temperature gradient vector at that point obtained by interpolating the three-dimensional coordinates of the thermo-mechanical coupling response node into the spatial temperature field gradient estimation result.

[0133] The unit vector of the temperature gradient vector is defined as the direction of the temperature gradient.

[0134] Specifically, the unit vector of the temperature gradient vector refers to the vector obtained by dividing the temperature gradient vector by its own magnitude. This vector has a magnitude of 1 and its direction is exactly the same as the original direction of the temperature gradient vector. The sum of the squares of the components of this unit vector is 1. The temperature gradient direction refers to the spatial direction in the temperature field where the temperature rises the fastest, and this direction is uniquely determined by the unit vector of the temperature gradient.

[0135] The local thermal expansion displacement is obtained by multiplying the material's coefficient of linear expansion, equivalent thermal conduction length, and temperature difference.

[0136] Specifically, the multiplication operation refers to multiplying the material's linear expansion coefficient, equivalent thermal conduction length, and temperature difference sequentially. The resulting product is the linear thermal expansion displacement along the temperature gradient direction, measured in millimeters. Local thermal expansion displacement refers to the free expansion length of the base component along the temperature gradient direction caused by temperature rise at the thermo-mechanical coupling response node.

[0137] The temperature gradient direction is multiplied by the unit direction vector of the drilling rig's Z-axis to obtain the direction cosine of the temperature gradient direction relative to the Z-axis.

[0138] Specifically, the dot product operation refers to the sum of the products of corresponding components of two vectors. The result is a scalar, and its value is equal to the product of the magnitudes of the two vectors multiplied by the cosine of the angle between the two vectors. The dot product of the temperature gradient direction and the unit direction vector of the drilling rig's Z-axis is the direction cosine of the temperature gradient direction relative to the Z-axis. This value is between -1 and 1, and its positive or negative sign reflects the sharpness or bluntness of the angle between the temperature gradient direction and the positive direction of the Z-axis.

[0139] The thermal expansion projection component is obtained by multiplying the local thermal expansion displacement with the direction cosine of the temperature gradient relative to the Z-axis.

[0140] Specifically, the multiplication operation refers to multiplying the local thermal expansion displacement by the cosine of the temperature gradient direction relative to the Z-axis. The resulting product is the projected length of the thermal expansion displacement in the Z-axis direction. The thermal expansion projection component refers to the contribution of the thermal expansion displacement caused by the temperature rise at the thermo-mechanical coupling response node in the Z-axis direction. This value is a scalar, and its sign is determined by the angle between the temperature gradient direction and the positive direction of the Z-axis.

[0141] The time-varying force is obtained by multiplying the pressure pulsation value of the oil supply line with the hydraulic action area.

[0142] Specifically, the oil supply line pressure pulsation value refers to the actual dynamic pressure fluctuation value existing in the oil supply line at the matching trough moment. This value is extracted from the time-domain pressure pulsation sequence and is measured in megapascals (MPA). The hydraulic action area refers to the effective pressure-bearing area of ​​the hydraulic clamping unit acting on the piston end face or the force-bearing surface of the worktable, measured in square millimeters. The time-varying force refers to the clamping force fluctuation value that varies with time, obtained by multiplying the pressure pulsation value by the hydraulic action area. This force is a periodically changing dynamic load and is measured in Newtons (N).

[0143] Dividing the time-varying force by the contact stiffness yields the elastic compressive displacement.

[0144] Specifically, division refers to dividing the time-varying force value by the contact stiffness value. The quotient is the elastic compressive deformation of the contact surface under the action of the time-varying force, measured in millimeters. Elastic compressive displacement refers to the instantaneous elastic compressive or springback deformation length of the machine tool base component under the action of hydraulic clamping force fluctuations.

[0145] The direction cosine of the force direction relative to the Z-axis is obtained by performing a dot product operation between the unit vector of the force direction and the unit direction vector of the drilling rig's Z-axis.

[0146] Specifically, the unit vector of the force direction refers to the normalized unit vector obtained by normalizing the direction vector of the hydraulic clamping force acting on the machine tool base components. The sum of the squares of the components of this vector is 1. The dot product of the force direction and the unit direction vector of the drilling machine's Z-axis is the direction cosine of the force direction relative to the Z-axis. This value is between -1 and 1, and its sign reflects the sharpness or bluntness of the angle between the force direction and the positive direction of the Z-axis.

[0147] The elastic compression projection component is obtained by multiplying the elastic compression displacement by the direction cosine of the force direction relative to the Z-axis.

[0148] Specifically, the multiplication operation refers to multiplying the elastic compressive displacement by the direction cosine of the force's direction relative to the Z-axis. The resulting product is the projected length of the elastic compressive displacement along the Z-axis. The elastic compressive projection component refers to the contribution of the elastic compressive deformation of the machine tool's base components caused by fluctuations in hydraulic clamping force along the Z-axis. This value is a scalar, and its sign is determined by the angle between the force's direction and the positive Z-axis direction. The formula for calculating the thermal expansion projection component is as follows:

[0149]

[0150] In the formula, This represents the projected component of thermal expansion, in millimeters. The coefficient of linear expansion of the material of the machine tool base component at the thermo-mechanical coupling response node is given in degrees Celsius and can be found in the national standard material handbook based on the material grade of the base component. The equivalent heat conduction length of the thermo-mechanical coupling response node along the temperature gradient direction, in millimeters, is obtained during the calibration phase through finite element thermal simulation calculations based on the geometry of the basic components and the location of the heat source. The temperature difference at the thermo-mechanical coupling response node is expressed in degrees Celsius, representing the difference between the absolute temperature at the inflection point of the node and the absolute temperature at the initial sampling point. The direction cosine of the temperature gradient direction relative to the Z-axis is dimensionless and is obtained by the dot product of the unit vector of the temperature gradient and the unit direction vector of the Z-axis.

[0151] The comprehensive compensation module is used to synthesize the elastic compression projection component and the thermal expansion projection component to obtain the composite displacement. The composite displacement is then combined with the positive thermal elongation of the spindle to obtain the comprehensive compensation amount. The module also obtains the current position command offset of the Z-axis servo drive, reverses the sign of the comprehensive compensation amount, and adds it to the position command offset to generate the compensated Z-axis motion command.

[0152] In this embodiment, the composite elastic compression projection component and the thermal expansion projection component are used to obtain a composite displacement. This composite displacement is then combined with the positive thermal elongation of the spindle to obtain a comprehensive compensation amount, including:

[0153] The composite displacement is obtained by performing an algebraic summation on the elastic compression projection component and the thermal expansion projection component.

[0154] Specifically, algebraic summation refers to the mathematical operation of adding two scalars with positive and negative signs according to their signs. A positive sign indicates that the component acts in the positive direction of the Z-axis, and a negative sign indicates that it acts in the negative direction of the Z-axis. The difference between algebraic summation and ordinary arithmetic addition is that the original positive and negative signs of each component must be preserved during the operation, and the absolute values ​​cannot be simply added together. The elastic compression projection component refers to the projection value of the elastic compression deformation of the machine tool base components caused by fluctuations in hydraulic clamping force in the Z-axis direction. The thermal expansion projection component refers to the projection value of the thermal expansion displacement of the thermo-mechanical coupling response node caused by temperature rise in the Z-axis direction. Both are scalars with signs.

[0155] The composite displacement refers to the combined displacement value in the Z-axis direction obtained by performing an algebraic summation operation on the elastic compression projection component and the thermal expansion projection component. This value simultaneously includes the combined effects of the expansion displacement caused by thermal effects and the compression displacement caused by force effects on the spatial position of the Z-axis.

[0156] The combined compensation amount is obtained by performing an algebraic sum of the composite displacement and the positive thermal elongation of the main shaft at the current moment.

[0157] Specifically, the positive thermal elongation of the spindle at the current moment refers to the axial elongation of the spindle system along the positive Z-axis caused by the heating of the spindle motor windings and the frictional heat generated by the bearings. This value is calculated in real time by the spindle axial displacement sensor based on the cold reference. The composite displacement reflects the comprehensive influence of the hydraulically induced thermal-force coupling field on the Z-axis position of the machine tool's basic components. The positive thermal elongation of the spindle reflects the influence of the spindle's own thermal expansion on the Z-axis position of the tool.

[0158] The comprehensive compensation amount refers to the final result obtained by algebraically summing the synthetic displacement amount and the positive thermal elongation of the spindle. This result characterizes the total drift of the tool relative to the workpiece in the Z-axis direction caused by the combined effect of the spindle thermal elongation and the hydraulically induced thermal-force coupling field at the current moment.

[0159] In this embodiment, obtaining the current position command offset of the Z-axis servo driver, inverting the sign of the comprehensive compensation amount, and adding it to the position command offset to generate the compensated Z-axis motion command includes:

[0160] The offset of the position command currently sent to the Z-axis servo drive is read through the Z-axis servo control loop of the drilling machine's CNC system.

[0161] Specifically, the Z-axis servo control loop refers to the control loop composed of a digital PID controller and its peripheral signal processing unit used in the CNC system to achieve closed-loop control of the Z-axis position. This loop runs once in each servo cycle. The position command offset refers to the additional correction value included in the position loop setpoint of the Z-axis servo control loop. The initial value of this offset is determined by the tool setting reference value at the beginning of the machining cycle and is stored in the position command data area of ​​the dual-port RAM of the CNC system's NC kernel before compensation is superimposed. Reading refers to obtaining the value of the position command offset within the current sampling cycle using the CNC system's internal variable access functions, indexed by the variable name or register address.

[0162] Invert the comprehensive compensation amount to obtain the compensation amount with the reverse sign.

[0163] Specifically, the inversion operation involves multiplying the value of the comprehensive compensation by -1. The result is the inverted compensation, whose absolute value is equal to the comprehensive compensation but with the opposite sign. A positive comprehensive compensation indicates tool drift along the positive Z-axis, while a negative one indicates drift along the negative Z-axis. To ensure the effectiveness of negative feedback compensation, the correction applied to the position command must be opposite to the drift direction; therefore, the inversion operation must be performed. The inverted compensation is the correction value obtained by reversing the sign of the comprehensive compensation, and its unit is millimeters.

[0164] The offset of the position command is obtained by adding the inverted sign compensation amount to the position command offset amount.

[0165] Specifically, the addition operation refers to algebraically adding the value of the inverted compensation amount to the value of the position command offset according to their respective signs. This operation is performed once by the central processing unit of the CNC system in each servo cycle. The compensated position command offset is the new offset generated by superimposing the inverted compensation amount and the original position command offset. This value replaces the original position command offset for subsequent servo control. This addition operation directly modifies the additional correction term in the position loop setpoint, thereby achieving real-time correction of the Z-axis comprehensive drift without changing the interpolation trajectory master setpoint.

[0166] Write the compensated position command offset into the command register to generate the compensated Z-axis motion command.

[0167] Specifically, the instruction register refers to the storage unit in the NC kernel of the CNC system used to store the final Z-axis position instruction value for the current servo cycle. This register is read at the beginning of each servo cycle and converted into a pulse train or analog voltage signal, which is then output to the Z-axis servo driver. The write instruction, through the memory assignment operation of the CNC system, transfers the compensated position instruction offset to the aforementioned storage unit, overwriting the original position instruction offset value in the storage unit.

[0168] The compensated Z-axis motion command refers to the complete Z-axis position command data containing the compensated position command offset. This data is output to the Z-axis servo driver via the CNC system fieldbus or analog interface, and the driver drives the servo motor to perform positioning motion according to the command.

[0169] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0170] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0171] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A temperature-compensated precision control system for drilling and tapping machines, characterized in that, include: Data acquisition module: used to acquire the time-domain temperature sequence of each monitoring point in the non-spindle area of ​​the drilling and tapping machine body, acquire the time-domain pressure pulsation sequence of the oil supply pipeline, and obtain the positive thermal elongation of the spindle at the current moment; Delay Time Module: Used to construct a cross-correlation function based on the time-domain temperature sequence and time-domain pressure pulsation sequence of each monitoring point, extract the delay time corresponding to the peak value of the cross-correlation function, and obtain the response delay time of each monitoring point; Time difference calculation module: used to calculate the first derivative of the time-domain temperature sequence, extract the inflection point when the sign of the first derivative changes, extract the valley value of the time-domain pressure pulsation sequence, and calculate the difference between the inflection point and valley value of each monitoring point to obtain the inflection point-valley time difference of each monitoring point. Node determination module: Used to determine the monitoring points whose response delay time is equal to the inflection point-valley time difference as thermo-mechanical coupling response nodes, and extract the temperature difference of the thermo-mechanical coupling response node and the corresponding oil supply pipeline pressure pulsation value. Displacement calculation module: used to calculate the local thermal expansion displacement of the thermo-mechanical coupling response node based on the temperature difference, project the local thermal expansion displacement onto the Z-axis to obtain the thermal expansion projection component, calculate the elastic compression displacement based on the pressure pulsation value, project the elastic compression displacement onto the Z-axis to obtain the elastic compression projection component. Comprehensive compensation module: used to synthesize the elastic compression projection component and the thermal expansion projection component to obtain the composite displacement, and then combine the composite displacement with the positive thermal elongation of the main shaft to obtain the comprehensive compensation. Obtain the current position command offset of the Z-axis servo drive, reverse the sign of the comprehensive compensation amount and add it to the position command offset to generate the compensated Z-axis motion command.

2. The temperature-compensated precision control system for drilling and tapping machines according to claim 1, characterized in that, The process involves collecting the time-domain temperature sequence of each monitoring point in the non-spindle area of ​​the drilling and tapping machine bed, collecting the time-domain pressure pulsation sequence of the oil supply pipeline, and obtaining the positive thermal elongation of the spindle at the current moment, including: Collect the output values ​​of the temperature sensors at each monitoring point, and calculate the absolute temperature value based on the output values; Arrange the absolute temperature values ​​of the same monitoring point in order of sampling time to form the time-domain temperature sequence of that monitoring point; The raw signal output by the pressure sensor is acquired, and the raw signal is subjected to AC coupling filtering to generate a time-domain pressure pulsation sequence of the oil supply pipeline. Read the gap signal output by the spindle axial displacement sensor at the current moment, convert the gap signal into mechanical displacement based on the pre-calibrated displacement sensor characteristic curve, and calculate the difference between the mechanical displacement and the preset reference displacement recorded during cold tool setting to obtain the positive thermal elongation of the spindle at the current moment.

3. The temperature-compensated precision control system for drilling and tapping machines according to claim 1, characterized in that, The method involves constructing a cross-correlation function based on the time-domain temperature sequence and time-domain pressure pulsation sequence of each monitoring point, extracting the delay time corresponding to the peak value of the cross-correlation function, and obtaining the response delay time of each monitoring point, including: Cross-correlation calculations are performed on the time-domain temperature sequence and the time-domain pressure pulsation sequence of the oil supply pipeline at each monitoring point to generate a temperature-pressure cross-correlation function sequence with the delay time as the independent variable; Search for the maximum value of each temperature-pressure cross-correlation function sequence, and determine the delay time at the maximum value as the response delay time of that monitoring point.

4. The temperature-compensated precision control system for drilling and tapping machines according to claim 1, characterized in that, The process of calculating the first derivative of the time-domain temperature sequence, extracting the inflection point when the sign of the first derivative changes, extracting the trough time of the time-domain pressure pulsation sequence, and calculating the difference between the inflection point time and the trough time time of each monitoring point to obtain the inflection point-trough time difference for each monitoring point includes: Calculate the first derivative of the time-domain temperature sequence for each monitoring point with respect to time to generate the temperature change rate sequence for that monitoring point. The sampling time at which the sign of the numerical value in the temperature change rate sequence of each monitoring point changes is detected, and the detected sampling time is determined as the inflection point time of the monitoring point; Search for local minima in the time-domain pressure pulsation sequence of the oil supply pipeline, extract the sampling time corresponding to the local minima, and form a set of valley time moments; For each monitoring point, the inflection point time of the monitoring point is compared with the valley time in the valley time set to obtain the inflection point-valley time difference of the monitoring point.

5. The temperature-compensated drilling and tapping machine precision control system according to claim 4, characterized in that, The search for local minima of the time-domain pressure pulsation sequence of the oil supply pipeline, extracting the sampling times corresponding to the local minima, forms a set of valley times, including: The first derivative of the time-domain pressure pulsation sequence of the oil supply pipeline with respect to time is obtained to generate a pressure change rate sequence. The zero-crossing points in the pressure change rate sequence where the pressure changes from negative to positive are detected, and the sampling time corresponding to the zero-crossing point is determined as the pressure pulsation trough time. All pressure pulsation trough moments are collected to form a trough moment set.

6. The temperature-compensated drilling and tapping machine precision control system according to claim 4, characterized in that, The step of identifying monitoring points whose response delay time is equal to the inflection point-valley time difference as thermo-mechanical coupling response nodes, and extracting the temperature difference and corresponding oil supply pipeline pressure pulsation value of the thermo-mechanical coupling response node, includes: For each monitoring point, if there is a time difference in the inflection point-valley time difference that is equal to the response delay time of the monitoring point, then the monitoring point is marked as a thermo-mechanical coupling response node, and the valley time corresponding to the equal time difference is determined as the matching valley time of the thermo-mechanical coupling response node. For the time-domain temperature sequence of the thermo-mechanical coupling response node, the absolute temperature value of the thermo-mechanical coupling response node at the inflection point is extracted. The difference between the absolute temperature value at the inflection point and the absolute temperature value at the initial sampling point in the time-domain temperature sequence of the thermo-mechanical coupling response node is calculated to obtain the temperature difference of the thermo-mechanical coupling response node. From the time-domain pressure pulsation sequence of the oil supply pipeline, extract the pressure pulsation value corresponding to the matching valley moment of the thermo-mechanical coupling response node, and use it as the oil supply pipeline pressure pulsation value corresponding to the thermo-mechanical coupling response node.

7. The temperature-compensated precision control system for drilling and tapping machines according to claim 6, characterized in that, The local thermal expansion displacement of the thermo-mechanical coupling response node is calculated based on the temperature difference, and the local thermal expansion displacement is projected onto the Z-axis to obtain the thermal expansion projection component. The elastic compression displacement is calculated based on the pressure pulsation value, and the elastic compression displacement is projected onto the Z-axis to obtain the elastic compression projection component, including: Retrieve the preset constant set obtained during the calibration phase of the hydraulic clamping system of the drilling and tapping machine, and read from the preset constant set the material linear expansion coefficient of the machine tool base component at the thermo-mechanical coupling response node, the equivalent heat conduction length of the thermo-mechanical coupling response node along the temperature gradient direction, the hydraulic action area of ​​the hydraulic clamping unit at the thermo-mechanical coupling response node, the contact stiffness of the machine tool base component at the thermo-mechanical coupling response node along the force direction, the unit vector of the force direction, and the unit direction vector of the Z-axis of the drilling and tapping machine; The known spatial coordinates of all monitoring points and the absolute temperature values ​​at the same sampling time are collected to form a spatial temperature point set; Three-dimensional temperature field gradient estimation is performed on the set of spatial temperature points, and the gradient vector at the spatial coordinates of the thermo-mechanical coupling response node is determined as the temperature gradient vector. The unit vector of the temperature gradient vector is defined as the direction of the temperature gradient. The local thermal expansion displacement is obtained by multiplying the material's coefficient of linear expansion, the equivalent thermal conduction length, and the temperature difference. The temperature gradient direction is multiplied by the unit direction vector of the drilling rig's Z-axis to obtain the direction cosine of the temperature gradient direction relative to the Z-axis. The thermal expansion projection component is obtained by multiplying the local thermal expansion displacement with the direction cosine of the temperature gradient relative to the Z-axis. The time-varying force is obtained by multiplying the pressure pulsation value of the oil supply line with the hydraulic action area. Divide the time-varying force by the contact stiffness to obtain the elastic compressive displacement. The direction cosine of the force direction relative to the Z-axis is obtained by taking the dot product of the unit vector of the force direction with the unit direction vector of the drilling machine's Z-axis. The elastic compression projection component is obtained by multiplying the elastic compression displacement by the direction cosine of the force direction relative to the Z-axis.

8. The temperature-compensated precision control system for drilling and tapping machines according to claim 1, characterized in that, The composite elastic compression projection component and the thermal expansion projection component are used to obtain a composite displacement. This composite displacement is then combined with the positive thermal elongation of the main shaft to obtain a comprehensive compensation amount, including: The composite displacement is obtained by performing an algebraic summation on the elastic compression projection component and the thermal expansion projection component. The combined compensation amount is obtained by performing an algebraic sum of the composite displacement and the positive thermal elongation of the main shaft at the current moment.

9. A temperature-compensated precision control system for drilling and tapping machines according to claim 8, characterized in that, The process of obtaining the current position command offset of the Z-axis servo drive, inverting the sign of the comprehensive compensation amount, and adding it to the position command offset to generate the compensated Z-axis motion command includes: The offset of the position command currently sent to the Z-axis servo drive is read through the Z-axis servo control loop of the drilling machine's CNC system. Invert the comprehensive compensation amount to obtain the compensation amount with the reversed sign; The compensation amount is added to the position command offset to obtain the compensated position command offset. Write the compensated position command offset into the command register to generate the compensated Z-axis motion command.

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