A method and system for stall protection control of a main shaft of a numerical control machine tool

Abstract

The application discloses a numerical control machine tool spindle stall protection control method and system, and relates to the field of numerical control machine tool control. Three-phase current signals of a numerical control machine tool spindle driving motor, vibration acceleration signals of a spindle shell, and high-frequency acoustic emission signals collected within a spindle setting range are collected in real time. Based on tool spindle interface state judgment, cutting force disturbance judgment, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude, multi-feature linkage judgment is realized through a combination of preset threshold values. Based on the multi-feature linkage judgment result, hierarchical protection actions are executed to realize layered management and control of spindle stall risks. Through synchronous collection of multi-physical field signals and multi-feature linkage judgment, the application improves the accuracy of spindle stall early warning, effectively avoids false positives and false negatives, actively compensates for cutting force disturbance, realizes early intervention of stall hazards, and reduces the probability of stall occurrence.

Description

Technical Field

[0001] This invention relates to the field of CNC machine tool control technology, and in particular to a CNC machine tool spindle stall protection control method and system. Background Technology

[0002] The spindle is the core component of a CNC machine tool, and its operational stability directly determines the machining accuracy and production efficiency. During CNC machining, the spindle often faces various stall risks, including degradation of the tool-spindle interface stiffness, excessive cutting force disturbances, and abnormal spindle vibration. Degradation of the tool-spindle interface stiffness leads to decreased spindle rotation accuracy, while excessive cutting force disturbances disrupt the spindle's force balance. Both factors can cause spindle stall, resulting in tool damage, workpiece scrap, and in severe cases, damage to the spindle drive system, increasing equipment maintenance costs and production downtime.

[0003] Existing CNC machine tool spindle stall protection technologies mostly employ single-signal detection or complex model simulation, which have significant drawbacks. Single-signal detection methods can only monitor one type of stall hazard, resulting in low accuracy in early warning and a high risk of false alarms or missed alarms. Complex model simulation relies on high-performance computing platforms, leading to high implementation costs, complex operation, and difficulty in adapting to the retrofitting needs of existing CNC machine tools. Furthermore, its slow response speed makes it impossible to provide timely early warning and proactive intervention for stall precursors.

[0004] The existing protection technologies lack clear hierarchical logic, and the protection actions do not match the risk conditions, making it difficult to achieve layered control of stall risk and resulting in insufficient protection reliability. Therefore, there is an urgent need for a spindle stall protection technology that is simple in structure, easy to implement, provides accurate early warning, and offers reliable protection to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method and system for controlling spindle stall in CNC machine tools. The technical solution is as follows: A method for controlling spindle stall in a CNC machine tool includes the following steps: Step 1: Real-time acquisition of three-phase current signals of the CNC machine tool spindle drive motor, vibration acceleration signals of the spindle housing, and high-frequency acoustic emission signals acquired within the spindle set range; Step 2, Tool spindle interface status judgment: Inject a set high-frequency voltage signal into the current loop of the spindle driver. By responding to abnormal changes in the current amplitude, judge the stiffness degradation state of the tool spindle connection interface, set a stiffness degradation threshold, and execute early warning control if the threshold is exceeded. Step 3, Cutting force disturbance judgment: By identifying the correspondence between torque current and speed change during spindle acceleration and deceleration, the equivalent inertia of the system is identified. The cutting force disturbance is calculated by combining the instantaneous change of spindle torque current. When the cutting force disturbance exceeds the preset threshold, the disturbance compensation is calculated based on the cutting force disturbance and the compensation coefficient and introduced into the feed control loop as feedforward compensation. The feed control loop then performs compensation control. Step 4: Perform wavelet decomposition on the high-frequency acoustic emission signal, extract multiple core frequency bands within the set frequency range, and execute stall precursor warning control if the energy threshold of the characteristic frequency band is exceeded. Step 5: Based on the tool spindle interface state judgment, cutting force disturbance judgment, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude, multi-feature linkage judgment is achieved through preset threshold combinations. Step 6: Execute graded protection actions based on the multi-feature linkage judgment results to achieve layered control of spindle stall risk.

[0006] Optionally, in step 1, the high-frequency acoustic emission signal is collected within 50mm of the spindle housing, using an acoustic emission sensor with a resonant frequency of 150kHz and a sampling rate of not less than 2MHz; the three-phase current signal is collected by a three-phase current sensor, and the vibration acceleration signal is collected by a vibration acceleration sensor. All signals are collected synchronously for subsequent judgment steps.

[0007] Optionally, in step 2, the frequency of the high-frequency voltage signal is set to 1.4kHz-1.6kHz, and the amplitude is 1.5%-2.5% of the rated current of the spindle drive motor. Abnormal changes in the response current amplitude are determined by comparing it with the standard response current amplitude under normal operating conditions. When the deviation between the response current amplitude and the standard amplitude exceeds 20%, it is determined that the stiffness of the tool spindle connection interface has degraded. The stiffness degradation threshold is set to a 20% deviation in the response current amplitude. When this threshold is exceeded, early warning control is immediately executed. The early warning control is to issue an interface stiffness degradation early warning signal and simultaneously trigger the priority upgrade of subsequent multi-feature linkage judgments.

[0008] Optionally, in step 3, the cutting force disturbance is calculated by identifying the equivalent inertia of the system through the correspondence between torque current and speed changes during spindle acceleration and deceleration. Combined with the instantaneous change in spindle torque current The cutting force disturbance was calculated. ; ;in The pre-calibrated torque coefficient of the spindle drive motor, It is the rate of change of the principal shaft angular velocity. The tool radius is used; the preset threshold is the maximum allowable value of cutting force disturbance, pre-calibrated according to the CNC machine tool spindle model and cutting conditions; disturbance compensation amount. The calculation method is based on a preset ratio between the cutting force disturbance and the compensation coefficient. , It is the compensation coefficient. The value range is 0.3-0.5; the specific way to introduce feedforward compensation into the feed control loop is to input the disturbance compensation amount into the feedforward channel of the feed control loop, and the feed control loop performs compensation control, specifically by automatically reducing the feed speed by 10%-30% according to the disturbance compensation amount, so as to achieve active cancellation of cutting force disturbance.

[0009] Optionally, in step 4, the wavelet decomposition is divided into two layers of wavelet decomposition, with the frequency range set to 100kHz-225kHz. Four core frequency bands within this range are extracted, namely 100kHz-125kHz, 125kHz-150kHz, 150kHz-175kHz, and 200kHz-225kHz. The characteristic frequency band energy threshold is twice the average energy of the corresponding frequency band under normal cutting conditions. When the energy of any core frequency band exceeds the characteristic frequency band energy threshold, stall precursor warning control is executed. The warning control involves issuing a stall precursor warning signal and simultaneously adjusting the response speed of subsequent multi-feature linkage judgment.

[0010] Optionally, in step 5, the peak values ​​of the current harmonics are extracted by harmonic analysis of the three-phase current signals acquired in step 1, and the peak values ​​of the 5th and 7th harmonics are extracted; the vibration amplitude is obtained by amplitude analysis of the vibration acceleration signals acquired in step 1. The preset threshold combination is as follows: independent warning thresholds are set for the tool spindle interface stiffness degradation state, cutting force disturbance, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude. When any one type of feature exceeds the corresponding warning threshold, it is judged as low risk; when any two or more types of features exceed the corresponding warning threshold at the same time, it is judged as high risk.

[0011] Optionally, the graded protection action in step 6 is executed based on the multi-feature linkage judgment result in step 5, specifically divided into four levels, with the following correspondence: Level 1 protection: If only one type of feature exceeds the corresponding warning threshold, a protection action of reducing the feed rate by 30% will be executed; Level 2 protection: If the stiffness degradation of the tool spindle interface exceeds the threshold, or if the cutting force disturbance exceeds the threshold, a protection action will be executed to reduce the feed rate to 50% and the spindle speed to 20%. The action will automatically recover after execution. Level 3 protection: If any two or more characteristics exceed the corresponding warning threshold at the same time, the protection action of stopping the feed and actively short-circuiting the inverter to achieve electromagnetic braking will be executed. Press the reset button to restart. Level 4 protection: If the spindle speed drops by more than 30% / s, regardless of whether other characteristics are normal, synchronous electromagnetic braking, mechanical brake, and spindle directional shutdown protection actions will be executed, and the machine will restart after power failure and reset.

[0012] Optionally, the inverter active short-circuit method in the three-level protection and four-level protection: through the short-circuit control module built into the spindle driver, the lower bridge arm of the inverter is turned on and the upper bridge arm is turned off, so that the winding of the spindle drive motor is short-circuited to generate electromagnetic braking torque. When the spindle speed drops below 50 r / min, the short circuit is automatically released.

[0013] Optionally, step 7 is also included: after each stall protection action or early warning control is executed, record the characteristic threshold deviation under the current operating condition and adjust the early warning threshold of the corresponding characteristic. The threshold adjustment ranges from 5% to 10%, and only the warning threshold corresponding to the feature that triggered this warning or protection action is adjusted.

[0014] A CNC machine tool spindle stall protection control system is provided to implement a CNC machine tool spindle stall protection control method. The system includes a multi-physics field signal acquisition unit, a high-frequency signal injection unit, a signal processing unit, and a protection execution unit. The multiphysics signal acquisition unit includes a three-phase current sensor, a vibration acceleration sensor, and an acoustic emission sensor. The acoustic emission sensor is installed within a set range on the spindle housing and is used to acquire high-frequency acoustic emission signals. The three-phase current sensor is used to acquire the three-phase current signal of the spindle drive motor. The vibration acceleration sensor is used to acquire the vibration acceleration signal of the spindle housing. The high-frequency signal injection unit is integrated into the spindle driver and is used to inject a set high-frequency voltage signal into the current loop of the spindle driver, synchronously acquire the response current signal, compare the response current amplitude with the standard amplitude, and realize the tool spindle interface status judgment. The signal processing unit is a PLC programmable controller used to perform cutting force disturbance calculation, disturbance compensation conversion, acoustic emission signal wavelet decomposition, feature frequency band extraction, current harmonic peak extraction, vibration amplitude analysis, and multi-feature linkage judgment. The protection execution unit is connected to the signal processing unit and the spindle driver to receive multi-feature linkage judgment results, execute graded protection actions and threshold adjustments, including feed speed control, spindle speed control, inverter active short circuit control and mechanical brake control.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: This invention provides a CNC machine tool spindle stall protection control method and system. By synchronously acquiring multi-physics field signals and judging multiple features, it improves the accuracy of spindle stall early warning and effectively avoids false alarms and missed alarms. Through active compensation for cutting force disturbances, it realizes early intervention of stall risks and reduces the probability of stall occurrence. The graded protection actions are precisely matched with the risk status, realizing layered control of stall risk, and taking into account both protection reliability and production continuity; The system has a simplified structure, requires no high-performance computing platform, and can be directly adapted to the retrofit of existing CNC machine tools, reducing implementation costs; By adaptively adjusting the threshold, it can adapt to different cutting conditions, maintain stable protection accuracy over a long period of time, improve the overall safety and stability of CNC machine tool spindle operation, and reduce equipment damage and production downtime losses. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a CNC machine tool spindle stall protection control method according to the present invention.

[0017] Figure 2 This is a schematic diagram of the architecture of a CNC machine tool spindle stall protection control system according to the present invention; Figure 3 This is a flowchart of the spindle stall graded protection action logic of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings.

[0019] This invention discloses a method and system for preventing and controlling spindle stall in CNC machine tools.

[0020] Reference Figures 1-3 Example 1: A method for controlling spindle stall in a CNC machine tool, comprising the following steps: Step 1: Real-time acquisition of three-phase current signals of the CNC machine tool spindle drive motor, vibration acceleration signals of the spindle housing, and high-frequency acoustic emission signals acquired within the spindle set range; Step 2, Tool spindle interface status judgment: Inject a set high-frequency voltage signal into the current loop of the spindle driver. By responding to abnormal changes in the current amplitude, judge the stiffness degradation state of the tool spindle connection interface, set a stiffness degradation threshold, and execute early warning control if the threshold is exceeded. Step 3, Cutting force disturbance judgment: By identifying the correspondence between torque current and speed change during spindle acceleration and deceleration, the equivalent inertia of the system is identified. The cutting force disturbance is calculated by combining the instantaneous change of spindle torque current. When the cutting force disturbance exceeds the preset threshold, the disturbance compensation is calculated based on the cutting force disturbance and the compensation coefficient and introduced into the feed control loop as feedforward compensation. The feed control loop then performs compensation control. Step 4: Perform wavelet decomposition on the high-frequency acoustic emission signal, extract multiple core frequency bands within the set frequency range, and execute stall precursor warning control if the energy threshold of the characteristic frequency band is exceeded. Step 5: Based on the tool spindle interface state judgment, cutting force disturbance judgment, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude, multi-feature linkage judgment is achieved through preset threshold combinations. Step 6: Execute graded protection actions based on the multi-feature linkage judgment results to achieve layered control of spindle stall risk.

[0021] By adopting the above technical solution, six steps are executed sequentially: signal acquisition, tool spindle interface status judgment, cutting force disturbance judgment, acoustic emission signal processing, multi-feature linkage judgment, and graded protection action. These steps are seamlessly connected to form a complete spindle stall protection process, ensuring timely response and efficient coordination at each stage. Signal acquisition is the foundational step; all subsequent judgments and protection actions are based on the acquired signals. Interface status judgment and cutting force disturbance judgment target two core stall risks, achieving precise monitoring. Acoustic emission signal processing focuses on capturing stall precursors and providing early warnings. Multi-feature linkage judgment integrates various monitoring results to accurately determine the risk level. Graded protection actions execute corresponding measures according to the risk level, achieving closed-loop control. Through the coordinated efforts of multiple stages, a complete closed-loop control is formed from signal acquisition to protection execution, comprehensively monitoring various stall risks during spindle operation, achieving effective control of stall risks, breaking the limitations of single-stage monitoring, and improving the overall reliability and response speed of the protection system.

[0022] In Example 2, in step 1, the high-frequency acoustic emission signal is collected within 50mm of the spindle housing, using an acoustic emission sensor with a resonant frequency of 150kHz and a sampling rate of not less than 2MHz; the three-phase current signal is collected by a three-phase current sensor, and the vibration acceleration signal is collected by a vibration acceleration sensor. All signals are collected synchronously for subsequent judgment steps.

[0023] By adopting the above technical solution, the acquisition range of high-frequency acoustic emission signals is limited to within 50mm of the spindle housing. This range can accurately capture high-frequency stress wave signals generated during spindle operation, reducing external interference. An acoustic emission sensor with a resonant frequency of 150kHz and a sampling rate of no less than 2MHz is selected to ensure the capture of high-frequency signals related to spindle stall precursors. Combined with a three-phase current sensor and a vibration acceleration sensor, the three sensors work synchronously to achieve simultaneous acquisition of three-phase current, vibration acceleration, and high-frequency acoustic emission signals. The acquired signals are directly transmitted to the signal processing unit for subsequent judgment steps. Reasonable setting of sensor installation positions and parameters can effectively reduce external interference, ensure accurate and effective signal acquisition, provide reliable data support for subsequent judgment steps, guarantee the accuracy of judgment results, avoid misjudgments and omissions due to signal distortion, and lay the foundation for the stable operation of the entire protection system.

[0024] In Example 3, in step 2, the frequency of the high-frequency voltage signal is set to 1.4kHz-1.6kHz, and the amplitude is 1.5%-2.5% of the rated current of the spindle drive motor. Abnormal changes in the response current amplitude are determined by comparing it with the standard response current amplitude under normal operating conditions. When the deviation between the response current amplitude and the standard amplitude exceeds 20%, it is determined that the stiffness of the tool spindle connection interface has degraded. The stiffness degradation threshold is set to a 20% deviation in the response current amplitude. When this threshold is exceeded, an early warning control is immediately executed. The early warning control is to issue an interface stiffness degradation early warning signal and simultaneously trigger the priority upgrade of subsequent multi-feature linkage judgments.

[0025] By adopting the above technical solution, the frequency of the high-frequency voltage signal is set to 1.4kHz-1.6kHz, and the amplitude is 1.5%-2.5% of the rated current of the spindle drive motor. This parameter range ensures the sensitivity of signal detection without affecting the normal operation of the spindle drive system. By comparing the deviation of the response current amplitude with the standard response current amplitude under normal operating conditions, when the deviation exceeds 20%, it is determined that the stiffness of the tool spindle connection interface has degraded. The stiffness degradation threshold is set at a 20% deviation of the response current amplitude. When this threshold is exceeded, early warning control is immediately executed, and an interface stiffness degradation early warning signal is issued. Simultaneously, the priority of subsequent multi-feature linkage judgment is increased, accelerating the response speed of linkage judgment and timely capturing potential risks. After the high-frequency voltage signal is injected into the current loop, the change in the stiffness of the tool spindle connection interface will change the loop impedance, thereby affecting the response current amplitude. By measuring the amplitude deviation, the degree of stiffness degradation can be accurately judged, and interface hazards can be warned in advance, improving the safety of spindle operation and avoiding problems such as spindle vibration and stall caused by interface stiffness degradation.

[0026] In Example 4, step 3, the cutting force disturbance is calculated as follows: the equivalent inertia of the system is identified by the correspondence between the torque current and the speed change during the spindle acceleration and deceleration process. Combined with the instantaneous change in spindle torque current The cutting force disturbance was calculated. ; ;in The pre-calibrated torque coefficient of the spindle drive motor, It is the rate of change of the principal shaft angular velocity. The tool radius is used; the preset threshold is the maximum allowable value of cutting force disturbance, pre-calibrated according to the CNC machine tool spindle model and cutting conditions; disturbance compensation amount. The calculation method is based on a preset ratio between the cutting force disturbance and the compensation coefficient. , It is the compensation coefficient. The value range is 0.3-0.5; the specific way to introduce feedforward compensation into the feed control loop is to input the disturbance compensation amount into the feedforward channel of the feed control loop, and the feed control loop performs compensation control, specifically by automatically reducing the feed speed by 10%-30% according to the disturbance compensation amount, so as to achieve active cancellation of cutting force disturbance.

[0027] By adopting the above technical solution, the accuracy of inertia identification is ensured by analyzing the changes in torque current and speed during spindle acceleration and deceleration, combined with the equivalent inertia of the preset calculation logic identification system. The instantaneous change in spindle torque current is used to calculate the cutting force disturbance and disturbance compensation amount according to a preset formula. The compensation coefficient ranges from 0.3 to 0.5 and can be flexibly adjusted according to the spindle model and cutting conditions. The calculated disturbance compensation amount is introduced into the feedforward channel of the feed control loop. The feed control loop automatically adjusts the feed speed according to the compensation amount, achieving active compensation for cutting force disturbance. Cutting force disturbance causes instantaneous changes in spindle torque current. The magnitude of the disturbance can be accurately calculated using formulas. The compensation amount is then introduced into the feed control loop in advance through feedforward compensation to actively adjust the feed speed, offsetting the impact of cutting force disturbance and preventing spindle stall caused by the disturbance. This achieves a shift from passive protection to active disturbance rejection.

[0028] In Example 5, in step 4, wavelet decomposition is performed in two layers, with a set frequency range of 100kHz-225kHz. Four core frequency bands within this range are extracted: 100kHz-125kHz, 125kHz-150kHz, 150kHz-175kHz, and 200kHz-225kHz. The energy threshold of the characteristic frequency band is twice the average energy of the corresponding frequency band under normal cutting conditions. When the energy of any core frequency band exceeds the energy threshold of the characteristic frequency band, stall precursor warning control is executed. The warning control involves issuing a stall precursor warning signal and simultaneously adjusting the response speed of subsequent multi-feature linkage judgment.

[0029] By employing the above technical solution, a two-level wavelet decomposition is performed on the high-frequency acoustic emission signal. This decomposition level effectively extracts core frequency band features, simplifies the calculation process, and improves signal processing efficiency. Four core frequency bands within the 100kHz-225kHz frequency range are extracted, covering the high-frequency acoustic emission signals generated by spindle stall precursors. By comparing the energy of each core frequency band with a preset threshold, when the energy of any core frequency band exceeds the threshold, stall precursor warning control is immediately executed, issuing a stall precursor warning signal. Simultaneously, the response speed of subsequent multi-feature linkage judgments is adjusted to ensure timely response to potential stall risks. Before spindle stall, phenomena such as tool wear and microscopic material fracture will generate acoustic emission signals at specific frequencies. Wavelet decomposition can effectively extract these key feature frequency bands, and stall precursors can be judged by energy thresholds, achieving early warning and providing sufficient time for subsequent intervention and protection actions.

[0030] In Example 6, in step 5, the peak values ​​of the current harmonics are extracted by harmonic analysis of the three-phase current signals acquired in step 1, and the peak values ​​of the 5th and 7th harmonics are extracted; the vibration amplitude is obtained by amplitude analysis of the vibration acceleration signals acquired in step 1. The preset threshold combination is as follows: independent warning thresholds are set for the tool spindle interface stiffness degradation state, cutting force disturbance, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude. When any one type of feature exceeds the corresponding warning threshold, it is judged as low risk; when any two or more types of features exceed the corresponding warning threshold at the same time, it is judged as high risk.

[0031] By adopting the above technical solution, the peak values ​​of the 5th and 7th harmonics are extracted from the three-phase current signal acquired in step 1. The peak value changes of these two harmonics are closely related to abnormal spindle load and drive system failure, and can effectively reflect the spindle operating status. Vibration amplitude is extracted from the vibration acceleration signal, and the change in vibration amplitude can directly reflect abnormal spindle vibration. Independent warning thresholds are set for five types of features: tool spindle interface stiffness degradation state, cutting force disturbance, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude. Each threshold is pre-calibrated according to the spindle model and cutting conditions. The risk level is determined by the combination of thresholds. When any one type of feature exceeds the corresponding warning threshold, it is judged as low risk; when any two or more types of features exceed the corresponding warning threshold at the same time, it is judged as high risk. Multi-feature linkage can comprehensively reflect the spindle operating status, avoid the limitations of single feature judgment, accurately capture the synergistic effect of various stall risks, improve the accuracy of risk judgment, and provide a reliable basis for graded protection actions.

[0032] In Example 7, the graded protection action in step 6 is executed based on the multi-feature linkage judgment result in step 5, specifically divided into four levels, with the following correspondence: Level 1 protection: If only one type of feature exceeds the corresponding warning threshold, a protection action of reducing the feed rate by 30% will be executed; Level 2 protection: If the stiffness degradation of the tool spindle interface exceeds the threshold, or if the cutting force disturbance exceeds the threshold, a protection action will be executed to reduce the feed rate to 50% and the spindle speed to 20%. The action will automatically recover after execution. Level 3 protection: If any two or more characteristics exceed the corresponding warning threshold at the same time, the protection action of stopping the feed and actively short-circuiting the inverter to achieve electromagnetic braking will be executed. Press the reset button to restart. Level 4 protection: If the spindle speed drops by more than 30% / s, regardless of whether other characteristics are normal, synchronous electromagnetic braking, mechanical brake, and spindle directional shutdown protection actions will be executed, and the machine will restart after power failure and reset.

[0033] By adopting the above technical solution, based on the risk level determined by multi-feature linkage, four levels of protection actions are executed. Different protection measures correspond to different risk levels, and the execution conditions and specific operations of each protection action are clearly defined. Level 1 protection targets low-risk states, adjusting only the feed speed to avoid affecting production; Level 2 protection targets specific low-risk hazards, adjusting the feed speed and spindle speed to automatically resume production after the hazard is resolved; Level 3 protection targets high-risk states, stopping the feed and executing electromagnetic braking to prevent the risk from escalating; Level 4 protection targets emergency stall states, executing dual braking and directional shutdown to minimize equipment damage. The graded protection can flexibly adjust the protection intensity according to the risk level, balancing spindle safety and production continuity, avoiding over-protection that could affect production efficiency, while ensuring rapid response in high-risk and emergency states, achieving effective risk control.

[0034] Example 8, Inverter active short circuit method in three-level protection and four-level protection: The short circuit control module built into the spindle driver controls the lower bridge arm of the inverter to be turned on and the upper bridge arm to be turned off, so that the winding of the spindle drive motor is short-circuited to generate electromagnetic braking torque. When the spindle speed drops below 50 r / min, the short circuit is automatically released.

[0035] By adopting the above technical solution, the short-circuit control module built into the spindle driver eliminates the need for additional hardware, reducing implementation costs. It controls the lower bridge arm of the inverter to be on and the upper bridge arm to be off, short-circuiting the spindle drive motor windings and rapidly generating electromagnetic braking torque for rapid spindle deceleration. A speed threshold of 50 r / min is set; when the spindle speed drops below this threshold, the short circuit is automatically released, preventing damage caused by excessive motor braking and ensuring the safety and reliability of the braking process. The inverter's active short circuit can quickly generate electromagnetic braking torque proportional to the rotor speed, achieving rapid spindle deceleration. It can quickly curb spindle stalling trends, preventing equipment damage caused by stalling. The speed threshold control prevents overheating damage to the motor windings due to prolonged short circuits, ensuring the rationality and safety of the braking process.

[0036] Example 9 also includes step 7: after each stall protection action or early warning control is executed, record the characteristic threshold deviation under the current operating condition and adjust the early warning threshold of the corresponding characteristic. The threshold adjustment ranges from 5% to 10%, and only the warning threshold corresponding to the feature that triggered this warning or protection action is adjusted.

[0037] By adopting the above technical solution, after each warning or protection action is executed, the system automatically records the characteristic threshold deviation under the current working condition, clarifying the magnitude of the deviation and the corresponding characteristic; the warning threshold of the corresponding characteristic is adjusted in a range of 5%-10%, and the adjustment range can be flexibly adapted to changes in working conditions; only the warning threshold of the corresponding characteristic that triggered the current warning or protection action is adjusted, without affecting the threshold settings of other characteristics, simplifying the adjustment process and reducing maintenance difficulty. Through adaptive threshold adjustment, the system can automatically optimize the warning threshold according to different cutting conditions, tool wear status, workpiece material changes, and other factors, without the need for complex model updates and manual intervention, maintaining stable protection accuracy over a long period of time, and improving the system's adaptability and reliability.

[0038] Example 10: A CNC machine tool spindle stall protection control system, used to implement a CNC machine tool spindle stall protection control method. The system includes a multi-physics field signal acquisition unit, a high-frequency signal injection unit, a signal processing unit, and a protection execution unit. The multiphysics signal acquisition unit includes a three-phase current sensor, a vibration acceleration sensor, and an acoustic emission sensor. The acoustic emission sensor is installed within a set range on the spindle housing and is used to acquire high-frequency acoustic emission signals. The three-phase current sensor is used to acquire the three-phase current signal of the spindle drive motor. The vibration acceleration sensor is used to acquire the vibration acceleration signal of the spindle housing. The high-frequency signal injection unit is integrated into the spindle driver and is used to inject a set high-frequency voltage signal into the current loop of the spindle driver, synchronously acquire the response current signal, compare the response current amplitude with the standard amplitude, and realize the tool spindle interface status judgment. The signal processing unit is a PLC programmable controller used to perform cutting force disturbance calculation, disturbance compensation conversion, acoustic emission signal wavelet decomposition, feature frequency band extraction, current harmonic peak extraction, vibration amplitude analysis, and multi-feature linkage judgment. The protection execution unit is connected to the signal processing unit and the spindle driver to receive multi-feature linkage judgment results, execute graded protection actions and threshold adjustments, including feed speed control, spindle speed control, inverter active short circuit control and mechanical brake control.

[0039] By adopting the above technical solution, the system consists of four units: a multi-physics signal acquisition unit, a high-frequency signal injection unit, a signal processing unit, and a protection execution unit. Each unit has a clear division of labor and works collaboratively. The multi-physics signal acquisition unit is responsible for the synchronous acquisition of various signals, providing basic data for the system. The high-frequency signal injection unit is integrated into the spindle driver, realizing high-frequency signal injection and response current acquisition, and completing the tool spindle interface status judgment. The signal processing unit uses a PLC programmable controller to perform various calculation and judgment tasks such as cutting force disturbance calculation, disturbance compensation conversion, and acoustic emission signal wavelet decomposition, and is the core control unit of the system. The protection execution unit communicates with the signal processing unit and the spindle driver, receives multi-feature linkage judgment results, and accurately executes graded protection actions and threshold adjustments, including feed rate control, spindle speed control, inverter active short-circuit control, and mechanical brake control. The collaborative work of each unit achieves full-process automation of signal acquisition, processing, judgment, and protection. The structure is simplified and the operation is reliable. It does not require high-performance computing equipment and can be directly adapted to existing CNC machine tool retrofits, reducing implementation costs and debugging difficulty, and ensuring stable and efficient system operation.

[0040] The following specific embodiments illustrate the implementation principle of the present invention: To address the spindle stall protection requirements of a certain type of vertical machining center, a complete CNC machine tool spindle stall protection control method and system is developed. This system enables stall monitoring, early warning, and graded protection throughout the entire spindle operation process. It is suitable for the machining center's spindle drive motor with a rated power of 15kW and a rated speed of 8000r / min. It can effectively avoid stall risks caused by loose tool spindle connection, sudden changes in cutting force, and abnormal spindle vibration, ensuring equipment operation safety and production continuity.

[0041] The CNC machine tool spindle stall protection control system consists of a multi-physics field signal acquisition unit, a high-frequency signal injection unit, a signal processing unit, and a protection execution unit. Each unit works in concert to complete the entire process of automated control from signal acquisition to protection execution. No additional high-performance computing equipment is required, and it can be directly adapted to the existing structure of the vertical machining center, reducing the cost of modification and debugging.

[0042] The multi-physics signal acquisition unit includes a three-phase current sensor, a vibration acceleration sensor, and an acoustic emission sensor. The acoustic emission sensor is installed within 50mm of the spindle housing, using a model with a resonant frequency of 150kHz and a sampling rate of 2.2MHz, to acquire high-frequency acoustic emission signals during spindle operation. The three-phase current sensor is connected to the power supply circuit of the spindle drive motor to acquire the motor's three-phase current signal. The vibration acceleration sensor is fixed on the spindle housing near the bearing to acquire the vibration acceleration signal of the spindle housing. The three sensors start acquiring data synchronously and transmit the real-time signals to the signal processing unit to provide accurate data support for subsequent judgment steps.

[0043] The high-frequency signal injection unit is integrated into the spindle driver of this machining center. During operation, it injects a high-frequency voltage signal into the current loop of the spindle driver. The frequency of this high-frequency voltage signal is set to 1.5kHz, and the amplitude is set to 2.0% of the rated current of the spindle drive motor. After the signal is injected, the high-frequency signal injection unit synchronously acquires the response current signal in the loop and compares the response current amplitude with the pre-calibrated standard response current amplitude under normal operating conditions. The amplitude deviation is used to determine the stiffness degradation state of the tool-spindle connection interface. When the deviation of the response current amplitude from the standard amplitude exceeds 20%, it is determined that the stiffness of the tool-spindle connection interface has degraded. An early warning control is immediately executed, and an interface stiffness degradation early warning signal is issued. At the same time, the priority of subsequent multi-feature linkage judgments is increased to accelerate the response speed.

[0044] The signal processing unit uses a PLC programmable controller to handle the processing, calculation, and judgment of various signals. The specific execution flow is as follows: First, the three-phase current signal, vibration acceleration signal, and high-frequency acoustic emission signal are synchronously received and preprocessed to remove external interference noise from the signals; then, the cutting force disturbance is judged, and the equivalent inertia of the system is identified by the correspondence between torque current and speed changes during spindle acceleration and deceleration. Combined with the instantaneous change in spindle torque current According to the formula Calculate the cutting force disturbance, where The pre-calibrated torque coefficient of the spindle drive motor, The spindle angular velocity change rate is denoted by r, and the tool radius is denoted by r. The maximum allowable value for cutting force disturbance is preset to be 30% of the rated cutting force of the machining center. When the calculated cutting force disturbance exceeds this threshold, the following applies: Calculate the disturbance compensation amount, where the compensation coefficient k is 0.4. Input the disturbance compensation amount into the feed forward channel of the feed control loop. The feed control loop automatically reduces the feed speed by 20% to achieve active cancellation of cutting force disturbance.

[0045] The signal processing unit simultaneously performs two-level wavelet decomposition on the high-frequency acoustic emission signal, sets the frequency analysis range to 100kHz-225kHz, and extracts four core frequency bands within this range: 100kHz-125kHz, 125kHz-150kHz, 150kHz-175kHz, and 200kHz-225kHz. It calculates the energy value of each core frequency band and compares it with twice the average energy value of the corresponding frequency band under normal cutting conditions. When the energy of any core frequency band exceeds the threshold, it executes stall precursor warning control, issues a stall precursor warning signal, and simultaneously adjusts the response speed of the multi-feature linkage judgment.

[0046] In addition, the signal processing unit performs harmonic analysis on the three-phase current signal, extracting the peak values ​​of the 5th and 7th harmonics, and performs amplitude analysis on the vibration acceleration signal to obtain the vibration amplitude. Independent warning thresholds are set for the tool spindle interface stiffness degradation state, cutting force disturbance, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude. The current harmonic peak value warning threshold is set to 1.8 times the corresponding harmonic peak value under normal operating conditions, and the vibration amplitude warning threshold is set to 0.5g. Multi-feature linkage judgment is achieved through preset threshold combinations. When any one type of feature exceeds the corresponding warning threshold, it is judged as low risk; when any two or more types of features simultaneously exceed the corresponding warning threshold, it is judged as high risk.

[0047] The protection execution unit establishes a communication connection with the signal processing unit and the spindle driver, receives the multi-feature linkage judgment results, and executes four-level protection actions. The specific action logic is as follows: Level 1 protection is for low-risk states, i.e., when only one type of feature exceeds the corresponding warning threshold, it executes a protection action to reduce the feed speed by 30% to maintain the normal spindle speed and not affect production continuity; Level 2 protection is for situations where only the tool spindle interface stiffness degradation state exceeds the threshold, or only the cutting force disturbance exceeds the threshold, it executes a protection action to reduce the feed speed to 50% and reduce the spindle speed by 20%. When the hidden danger is eliminated, the system automatically restores to the normal operating parameters; Level 3 protection is for high-risk states, i.e., when any two or more types of features exceed the corresponding warning threshold at the same time, it executes a protection action to stop the feed and actively short-circuit the inverter to achieve electromagnetic braking. The system can only be restarted after the operator presses the reset button; Level 4 protection is for emergency stall states. If the spindle speed drops suddenly by more than 30% / s, regardless of whether other features are normal, electromagnetic braking and mechanical brake are executed simultaneously to control the spindle to stop in a directional manner. The system can only be restarted after power is cut off and reset.

[0048] Among them, the inverter active short-circuit method in the three-level protection and four-level protection is implemented through the short-circuit control module built into the spindle driver. Specifically, it controls the lower bridge arm of the inverter to be turned on and the upper bridge arm to be turned off, so that the winding of the spindle drive motor is short-circuited to generate electromagnetic braking torque. When the spindle speed drops below 50 r / min, the system automatically releases the short circuit to avoid damage caused by excessive braking of the motor.

[0049] This case also features an adaptive threshold adjustment function. After each stall protection action or early warning control is executed, the system automatically records the characteristic threshold deviation under the current operating condition and adjusts the early warning threshold of the corresponding feature that triggered the early warning or protection action by an 8% increment, without adjusting the threshold settings of other features. This simplifies the adjustment process and eliminates the need for manual intervention. For example, if an early warning is triggered due to the cutting force disturbance exceeding the threshold, the system only adjusts the early warning threshold for the cutting force disturbance. Subsequent monitoring is performed based on the new threshold to ensure the stability of protection accuracy during long-term operation and adapt to the needs of different cutting conditions, tool wear states, and workpiece material changes.

[0050] After implementation in this case, the safety and stability of the vertical machining center's spindle operation were significantly improved, successfully avoiding three potential spindle stall risks: once due to tool loosening causing degradation of the tool-spindle interface stiffness, the system promptly issued an early warning and executed secondary protection, adjusting the feed rate and spindle speed to prevent increased spindle vibration; once due to a sudden change in cutting quantity causing excessive cutting force disturbance, the system reduced the feed rate through feedforward compensation to offset the disturbance; and once due to abnormal acoustic emission signals generated by tool wear, the system issued an early stall warning, allowing operators to replace the tool in time and prevent stalling. Simultaneously, the tiered protection design balanced equipment safety with production continuity, avoiding over-protection that impacted production efficiency. The threshold adaptive adjustment function reduced manual maintenance costs, and the overall protection system demonstrated fast response speed and accurate judgment, fully meeting the actual operational needs of the machining center.

[0051] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling spindle stall protection in CNC machine tools, characterized in that, Includes the following steps: Step 1: Real-time acquisition of three-phase current signals of the CNC machine tool spindle drive motor, vibration acceleration signals of the spindle housing, and high-frequency acoustic emission signals acquired within the spindle set range; Step 2, Tool spindle interface status judgment: Inject a set high-frequency voltage signal into the current loop of the spindle driver. By responding to abnormal changes in the current amplitude, judge the stiffness degradation state of the tool spindle connection interface, set a stiffness degradation threshold, and execute early warning control if the threshold is exceeded. Step 3, Cutting force disturbance judgment: By identifying the correspondence between torque current and speed change during spindle acceleration and deceleration, the equivalent inertia of the system is identified. The cutting force disturbance is calculated by combining the instantaneous change of spindle torque current. When the cutting force disturbance exceeds the preset threshold, the disturbance compensation is calculated based on the cutting force disturbance and the compensation coefficient and introduced into the feed control loop as feedforward compensation. The feed control loop then performs compensation control. Step 4: Perform wavelet decomposition on the high-frequency acoustic emission signal, extract multiple core frequency bands within the set frequency range, and execute stall precursor warning control if the energy threshold of the characteristic frequency band is exceeded. Step 5: Based on the tool spindle interface state judgment, cutting force disturbance judgment, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude, multi-feature linkage judgment is achieved through preset threshold combinations. Step 6: Execute graded protection actions based on the multi-feature linkage judgment results to achieve layered control of spindle stall risk.

2. The CNC machine tool spindle stall protection control method according to claim 1, characterized in that, In step 1, the high-frequency acoustic emission signal is collected within 50mm of the spindle housing, using an acoustic emission sensor with a resonant frequency of 150kHz and a sampling rate of no less than 2MHz; the three-phase current signal is collected by a three-phase current sensor, and the vibration acceleration signal is collected by a vibration acceleration sensor. All signals are collected synchronously for subsequent judgment steps.

3. The CNC machine tool spindle stall protection control method according to claim 2, characterized in that, In step 2, the frequency of the high-frequency voltage signal is set to 1.4kHz-1.6kHz, and the amplitude is 1.5%-2.5% of the rated current of the spindle drive motor. Abnormal changes in the response current amplitude are determined by comparing it with the standard response current amplitude under normal operating conditions. When the deviation between the response current amplitude and the standard amplitude exceeds 20%, it is determined that the stiffness of the tool spindle connection interface has degraded. The stiffness degradation threshold is set to a 20% deviation in the response current amplitude. When this threshold is exceeded, early warning control is immediately executed. The early warning control is to issue an interface stiffness degradation early warning signal and simultaneously trigger the priority upgrade of subsequent multi-feature linkage judgments.

4. The CNC machine tool spindle stall protection control method according to claim 3, characterized in that, In step 3, the cutting force disturbance is calculated by identifying the equivalent inertia of the system through the correspondence between torque current and speed changes during spindle acceleration and deceleration. Combined with the instantaneous change in spindle torque current The cutting force disturbance was calculated. ; ;in The pre-calibrated torque coefficient of the spindle drive motor, It is the rate of change of the principal shaft angular velocity. The tool radius is used; the preset threshold is the maximum allowable value of cutting force disturbance, pre-calibrated according to the CNC machine tool spindle model and cutting conditions; disturbance compensation amount. The calculation method is based on a preset ratio between the cutting force disturbance and the compensation coefficient. , It is the compensation coefficient. The value range is 0.3-0.5; the specific way to introduce feedforward compensation into the feed control loop is to input the disturbance compensation amount into the feedforward channel of the feed control loop, and the feed control loop performs compensation control, specifically by automatically reducing the feed speed by 10%-30% according to the disturbance compensation amount, so as to achieve active cancellation of cutting force disturbance.

5. A CNC machine tool spindle stall protection control method according to claim 4, characterized in that, In step 4, wavelet decomposition is performed in two layers, with a frequency range of 100kHz-225kHz. Four core frequency bands within this range are extracted: 100kHz-125kHz, 125kHz-150kHz, 150kHz-175kHz, and 200kHz-225kHz. The energy threshold of the characteristic frequency band is twice the average energy of the corresponding frequency band under normal cutting conditions. When the energy of any core frequency band exceeds the energy threshold of the characteristic frequency band, stall precursor warning control is executed. The warning control involves issuing a stall precursor warning signal and simultaneously adjusting the response speed of subsequent multi-feature linkage judgments.

6. The CNC machine tool spindle stall protection control method according to claim 5, characterized in that, In step 5, the peak values ​​of the current harmonics are extracted by harmonic analysis of the three-phase current signals acquired in step 1, and the peak values ​​of the 5th and 7th harmonics are extracted; the vibration amplitude is obtained by amplitude analysis of the vibration acceleration signals acquired in step 1. The preset threshold combination is as follows: independent warning thresholds are set for the tool spindle interface stiffness degradation state, cutting force disturbance, acoustic emission characteristic frequency band energy, current harmonic peak value, and vibration amplitude. When any one type of feature exceeds the corresponding warning threshold, it is judged as low risk; when any two or more types of features exceed the corresponding warning threshold at the same time, it is judged as high risk.

7. A CNC machine tool spindle stall protection control method according to claim 6, characterized in that, In step 6, the graded protection actions are executed based on the multi-feature linkage judgment results of step 5, and are specifically divided into four levels, with the following correspondence: Level 1 protection: If only one type of feature exceeds the corresponding warning threshold, a protection action of reducing the feed rate by 30% will be executed; Level 2 protection: If the stiffness degradation of the tool spindle interface exceeds the threshold, or if the cutting force disturbance exceeds the threshold, a protection action will be executed to reduce the feed rate to 50% and the spindle speed to 20%. The action will automatically recover after execution. Level 3 protection: If any two or more characteristics exceed the corresponding warning threshold at the same time, the protection action of stopping the feed and actively short-circuiting the inverter to achieve electromagnetic braking will be executed. Press the reset button to restart. Level 4 protection: If the spindle speed drops by more than 30% / s, regardless of whether other characteristics are normal, synchronous electromagnetic braking, mechanical brake, and spindle directional shutdown protection actions will be executed, and the machine will restart after power failure and reset.

8. A CNC machine tool spindle stall protection control method according to claim 7, characterized in that, The active short-circuit method for inverters in the three-level and four-level protection is as follows: The short-circuit control module built into the spindle driver controls the lower bridge arm of the inverter to be turned on and the upper bridge arm to be turned off, so that the winding of the spindle drive motor is short-circuited to generate electromagnetic braking torque. When the spindle speed drops below 50 r / min, the short circuit is automatically released.

9. A CNC machine tool spindle stall protection control method according to claim 8, characterized in that, It also includes step 7, which records the characteristic threshold deviation under the current operating condition after each stall protection action or early warning control is executed, and adjusts the early warning threshold of the corresponding characteristic. The threshold adjustment ranges from 5% to 10%, and only the warning threshold corresponding to the feature that triggered this warning or protection action is adjusted.

10. A CNC machine tool spindle stall protection control system, characterized in that, To implement the CNC machine tool spindle stall protection control method as described in claim 9, the system includes a multi-physics field signal acquisition unit, a high-frequency signal injection unit, a signal processing unit, and a protection execution unit; The multiphysics signal acquisition unit includes a three-phase current sensor, a vibration acceleration sensor, and an acoustic emission sensor. The acoustic emission sensor is installed within a set range on the spindle housing and is used to acquire high-frequency acoustic emission signals. The three-phase current sensor is used to acquire the three-phase current signal of the spindle drive motor. The vibration acceleration sensor is used to acquire the vibration acceleration signal of the spindle housing. The high-frequency signal injection unit is integrated into the spindle driver and is used to inject a set high-frequency voltage signal into the current loop of the spindle driver, synchronously acquire the response current signal, compare the response current amplitude with the standard amplitude, and realize the tool spindle interface status judgment. The signal processing unit is a PLC programmable controller used to perform cutting force disturbance calculation, disturbance compensation conversion, acoustic emission signal wavelet decomposition, feature frequency band extraction, current harmonic peak extraction, vibration amplitude analysis, and multi-feature linkage judgment. The protection execution unit is connected to the signal processing unit and the spindle driver to receive multi-feature linkage judgment results, execute graded protection actions and threshold adjustments, including feed speed control, spindle speed control, inverter active short circuit control and mechanical brake control.

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