A double-working-condition interpolation switching control method of a multi-station flexible numerical control island

Abstract

The present application relates to the technical field of numerical control machining control, in particular to a double-working-condition interpolation switching control method of a multi-station flexible numerical control island. The numerical control island is composed of a plurality of multi-axis numerical control machining main machines and a shared workpiece transfer station, and is used to perform rough machining and finishing processes of workpieces. The method comprises the following steps: S1, parameter retrieval: after the main control FPGA determines the current base material type, the milling working condition parameter set and the polishing working condition parameter set corresponding to the base material are retrieved from the in-chip parameter storage unit of the power-on initialization. The FPGA executes interpolation point output at a preset interpolation period, the switching window is compressed from the millisecond level of the prior art to the sub-millisecond level, the smooth transition of the shaft parameters between the milling and polishing working conditions is realized, the fluctuation amplitude of the tool-workpiece contact force is reduced, and the surface vibration lines and stepped defects caused by step switching are further eliminated.

Description

Technical Field

[0001] This invention relates to the field of CNC machining control technology, specifically to a dual-condition interpolation switching control method for a multi-station flexible CNC island. Background Technology

[0002] In the composite machining process of a multi-station flexible CNC island, the same workpiece often needs to undergo two distinct machining conditions: milling and polishing. Milling removes material from the workpiece using carbide tools, requiring the spindle system to have high rigidity, high feed rate, and large cutting force capacity. Polishing, on the other hand, uses ultrasonic vibration or flexible grinding to finish the workpiece surface, requiring the spindle system to have low rigidity, high compliance, and precise amplitude control. The requirements for axis parameters differ significantly between these two conditions. When a workpiece moves from the milling station to the polishing station, or when the same machine switches between milling and polishing operations, the control system must reconfigure axis parameters such as spindle rigidity, feed rate, and ultrasonic amplitude. The smoothness of this switching process directly determines the quality and consistency of the machined surface.

[0003] It should be noted that the "spindle stiffness" mentioned in this application does not refer to the elastic modulus of the spindle structural material at the control level. The elastic modulus of a material is determined by the atomic bonding strength and is an inherent property of the material, which cannot be changed through electrical control. The "spindle stiffness" mentioned in this application refers to the equivalent contact stiffness of the force control loop of the spindle servo system, which is essentially a programmable gain coefficient inside the servo drive unit. This coefficient determines the magnitude of the driving torque output by the servo system per unit position error. When the gain coefficient is set higher, the contact force applied by the tool to the workpiece per unit deformation is larger, and the system exhibits "high stiffness" characteristics, suitable for milling. When the gain coefficient is set lower, the contact force is smaller for the same amount of deformation, and the system exhibits "low stiffness" characteristics, suitable for polishing. By modifying the stiffness gain value in the FPGA (Field-Programmable Gate Array) control output register, the equivalent contact stiffness of the spindle system can be adjusted and switched without changing the spindle mechanical structure.

[0004] Currently, CNC islands commonly employ a step-switching method when switching between milling and polishing modes. A step-switching refers to a sudden jump in control parameters from the milling parameter set to the polishing parameter set, or vice versa, at the moment of switching. This abrupt parameter change causes significant fluctuations in the spindle drive force and the tool-workpiece contact force during the switching instant. Taking the milling-to-polishing process of a typical thin-walled titanium alloy part as an example, the stable cutting force during the milling stage is approximately 8N to 12N. If the parameters jump abruptly during the switching instant, the cutting force fluctuation amplitude can reach ±2.5N, meaning the force fluctuation range is as high as 5N, nearly half of the stable cutting force. Such drastic force fluctuations leave visible milling marks on the surface of the thin-walled titanium alloy part, and form step-like surface defects on the polished surface of sapphire spheres. According to batch inspection statistics from existing production lines, this alone results in a 12.3% defect rate for workpiece surface steps, becoming one of the main bottlenecks restricting the improvement of the yield rate of composite machining.

[0005] It should be noted that removing the tool from the workpiece surface during the switching of operating conditions is not a feasible solution to the above problems. First, the relative positioning accuracy of the tool-workpiece in precision composite machining is at the micrometer level. When re-contacting after separation, the spindle thermal expansion, servo return backlash, and the contact pressure reconstruction process of the ultrasonic transducer will all cause the actual contact point to deviate from the original machining datum. The deviation can reach several to tens of micrometers, and the resulting contour error cannot be repaired by subsequent machining. Second, ultrasonic polishing requires the polishing head to maintain continuous contact with the workpiece surface and apply constant pressure. Once separated, the no-load resonance characteristics of the transducer change, and the time required to re-establish the contact pressure closed loop is much longer than the switching window itself. For brittle and hard materials such as sapphire and CVD diamond, the impact force at the moment of re-contact is enough to induce microcracks. Third, the tool lifting and re-entry actions themselves are accompanied by acceleration changes and additional force impacts, which actually introduce new sources of force fluctuations rather than eliminating them. Therefore, achieving a smooth transition of operating parameters while maintaining continuous tool-workpiece contact is the only feasible technical approach.

[0006] Further analysis reveals that the problems caused by step switching extend beyond force fluctuations themselves. The duration of the switching window directly determines the time during which force fluctuations affect the workpiece surface. In existing control methods, the parameter switching window is typically no less than 1 millisecond, meaning that the tool contacts the workpiece surface with uncontrolled force for 1 millisecond. However, the global force control performance of precision composite machining usually requires a force control response time within a few milliseconds. The switching process alone occupies a significant proportion of the force control time budget, severely squeezing the force control response margin during normal machining. For brittle and hard materials such as sapphire and CVD diamond, millisecond-level force loss of control is sufficient to induce microcracks and surface material damage, defects that cannot be repaired in subsequent processes.

[0007] Furthermore, shaft parameters are not constant during machining. Even if the stiffness gain coefficient of the force control loop remains unchanged, the bearing preload of the milling spindle will still experience creep drift under prolonged high-load operation due to the temperature of the cutting zone. For every 1°C increase in temperature, the bearing preload can change by approximately 0.3% to 0.5%, causing the actual equivalent contact stiffness of the spindle system to deviate from the preset value corresponding to the gain coefficient, resulting in physical stiffness disturbances. The polishing ultrasonic system is affected by base vibration, and the resonant frequency of the piezoelectric transducer shifts with changes in the vibration environment, with the shift reaching tens to hundreds of hertz, causing the polishing amplitude to deviate from the optimal operating point. Existing switching control methods do not simultaneously collect cutting zone temperature, polishing zone temperature, and base vibration data during switching, nor do they incorporate these environmental physical quantities into the control closed loop for synchronous correction of shaft parameters. This means that even if the parameters are correctly set at the moment of switching, the shaft parameters will deviate from the target value again after the operating condition switch due to temperature changes and vibration disturbances, resulting in long-term drift. After processing hundreds of workpieces in succession, the accumulated drift of the axis parameters is enough to deteriorate the dimensional consistency of the batch of workpieces, and the dimensional dispersion gradually increases.

[0008] Regarding production line configuration adaptability, existing axis parameter switching control programs are only written for a single type of production line layout (usually circular), and lack the ability to identify and adapt to different hardware topologies such as multi-center symmetrical configurations or H-type linear configurations. Once the production line layout changes, the switching program needs to be rewritten entirely, resulting in a long debugging cycle, and it is impossible to achieve a unified deployment of a single switching control scheme in production scenarios where multiple configuration production lines coexist.

[0009] Currently available axis parameter switching control schemes are all designed for single machining conditions, or are only applicable to the transition of cutting parameters between different milling stages, or only applicable to amplitude adjustment between different polishing stages. The industry currently lacks an integrated switching control method that can simultaneously cover two different physical conditions—milling and polishing—achieve smooth parameter transitions through interpolation, synchronously correct through linkage with temperature and vibration sensor signals, and adapt to multi-configuration CNC island production line layouts. This technological gap directly limits the simultaneous improvement of surface quality consistency and long-term operational stability in composite precision machining. Summary of the Invention

[0010] This invention aims to solve the following problems existing in the prior art: Firstly, the abrupt switching between milling and polishing conditions causes significant fluctuations in the tool-workpiece contact force, resulting in surface defects and a decrease in yield. Secondly, during and after the switching process, the drift of shaft parameters caused by the temperature in the cutting zone and the vibration of the base was not corrected synchronously, resulting in insufficient long-term machining stability. Third, the switching control program is only adapted to a single production line configuration and lacks the ability to adapt to multiple hardware topologies.

[0011] To achieve the above objectives, the present invention provides a dual-condition interpolation switching control method for a multi-station flexible CNC island, wherein the CNC island consists of multiple multi-axis CNC machining hosts and a shared workpiece transfer station, and is used to perform roughing and finishing operations on the workpiece. The method includes: S1. Parameter Retrieval: After determining the current substrate type, the main control FPGA (Field-Programmable Gate Array) retrieves the milling condition parameter set and polishing condition parameter set corresponding to the substrate from the on-chip parameter storage unit initialized upon power-on. The parameter set includes at least the target stiffness value of the cutting force control channel and the target amplitude value of the ultrasonic vibration control channel corresponding to each machining condition stage. The target stiffness value is the equivalent contact stiffness value corresponding to the stiffness gain coefficient of the force control loop of the spindle servo system. S2. Dual-channel configuration: The axis control path of each machining host is divided into two physically isolated hardware closed loops: a cutting force control channel and an ultrasonic vibration control channel. The cutting force control channel is responsible for the output control of spindle speed, feed rate and cutting force. The ultrasonic vibration control channel is responsible for the independent control of the amplitude, frequency and polishing dwell time of the ultrasonic transducer. Each channel has its own independent servo drive unit and feedback sensor. S3, Interpolation Switching: When the preset working condition switching conditions are met, while the tool and workpiece are in contact, the FPGA uses the stiffness value and amplitude value in the current control output register as the starting value and the target stiffness value and target amplitude value corresponding to the next working condition stage retrieved by S1 as the ending value. It performs interpolation calculations within the preset interpolation period according to the preset interpolation model, outputs the stiffness value of the cutting force control channel and the amplitude value of the ultrasonic vibration control channel respectively, and outputs them directly to the corresponding servo drive unit or ultrasonic power supply unit through the hardware digital-to-analog conversion port of the FPGA. S4. Temperature and Vibration Coupling Correction: During and after the switching process, the FPGA synchronously corrects the stiffness and amplitude values ​​output by S3 based on the real-time collected cutting zone temperature, polishing zone temperature, and base vibration signal. The stiffness correction factor is calculated based on the real-time temperature of the cutting zone and then superimposed on the stiffness value of the cutting force control channel output by S3. The amplitude correction factor is calculated based on the real-time temperature of the polishing zone and superimposed on the amplitude value of the ultrasonic vibration control channel output by S3. The vibration compensation factor is calculated based on the vibration amplitude of the base, and then superimposed on the feed rate output value of the cutting force control channel and the amplitude output value of the ultrasonic vibration control channel. The main frequency component is extracted by performing spectrum analysis on the vibration signal of the base. If the difference between the main frequency component and the nominal frequency of the ultrasonic resonance is within the preset frequency threshold, the ultrasonic resonance frequency is shifted from the nominal frequency to avoid the main frequency of the base vibration. Among them, the correction factors of the first three corrections are combined in a multiplicative manner to affect the output value of the corresponding channel.

[0012] Further, in step S1, after the main control FPGA is powered on, it also reads the hardware identification code of each workstation and the EtherCAT protocol slave topology register, and automatically identifies the current production line configuration and matches the corresponding workpiece transfer path according to preset judgment conditions; the preset judgment conditions include: if a single transfer workstation is detected and there are multiple processing workstations distributed at equal angular intervals, and the distance from each processing workstation to the transfer workstation is equal, it is determined to be a circular configuration; if multiple transfer workstations are detected to be angularly symmetrically distributed and the processing host is grouped to correspond to each transfer workstation, it is determined to be a multi-transfer symmetrical configuration; if the processing host is detected to be arranged at equal intervals along the linear guide rail and there is no fixed transfer workstation, it is determined to be an H-shaped linear configuration.

[0013] Furthermore, in step S3, the preset interpolation model is a linear interpolation model: Cutting force control channel: K(t) = K_start + (t / T) × (K_end - K_start) Ultrasonic vibration control channel: A(t) = A_start + (t / T) × (A_end - A_start) Where T is the preset interpolation period, and t∈[0,T]; K_start and A_start are the current stiffness and amplitude values ​​before the switch, respectively; K_end and A_end are the target stiffness and target amplitude values, respectively; K(t) and A(t) are the stiffness output value and amplitude output value at time t during the interpolation process, respectively; the feed rate scales synchronously with the stiffness output value within the interpolation period.

[0014] Further, in step S4, the temperature-based stiffness correction factor γ_stiff=1-|T_actual_cut-T_target_cut|×k_temp_cut, where T_actual_cut is the measured temperature of the cutting zone, T_target_cut is the target temperature of the cutting zone, and k_temp_cut is the temperature-based stiffness drift coefficient corresponding to the current substrate. The temperature-based amplitude correction factor γ_amp=1-|T_actual_pol-T_target_pol|×k_temp_pol, where T_actual_pol is the measured temperature of the polishing zone, T_target_pol is the target temperature of the polishing zone, and k_temp_pol is the temperature-based amplitude drift coefficient corresponding to the current substrate; The vibration-based amplitude compensation factor δ_vib=1-(V_actual_RMS / V_ref)×β, where V_actual_RMS is the multi-axis resultant root mean square value of the base vibration, V_ref is the vibration reference value corresponding to the current substrate, and β is the vibration-based machining parameter attenuation coefficient; δ_vib is simultaneously superimposed on the feed rate output value of the cutting force control channel and the amplitude output value of the ultrasonic vibration control channel; In the vibration-based resonant frequency offset correction, fast Fourier transform is performed on the base vibration signal to extract the maximum amplitude frequency component f_vib_main. If |f_vib_main-f_nominal|≤Δf_threshold, the offset ultrasonic resonant frequency f_new=2×f_nominal-f_vib_main+δ, where f_nominal is the nominal ultrasonic resonant frequency, Δf_threshold is the preset frequency threshold, δ takes a positive value when f_vib_main<f_nominal, and δ takes a negative value when f_vib_main≥f_nominal, so as to maintain a preset safety distance between the offset resonant frequency and the main frequency of the base vibration.

[0015] Further, the method further comprises: generating a global time base inside the FPGA, and realizing clock synchronization of all spindle servo drive units and ultrasonic power supply units in a master-slave station periodic time calibration manner through the distributed clock mechanism of the EtherCAT protocol; the interpolation switching start moments of all stations are aligned to the same distributed clock synchronization edge; the interpolation operation result directly drives the servo unit and the ultrasonic power supply through the FPGA hardware digital-to-analog conversion port, and there is no intermediate processing link for transfer in the signal link.

[0016] Further, the method further comprises: dividing a plurality of independent storage blocks in the FPGA on-chip parameter storage unit according to the substrate type, and realizing physical interlocking between the blocks by a hardware address decoder; when the main control FPGA accesses any substrate block, the hardware automatically blocks the chip select signals of the remaining blocks, so as to ensure that only the authorized milling condition parameter set and polishing condition parameter set of a single substrate can be read; inside the same substrate block, the cutting force control parameters and the ultrasonic vibration control parameters are stored in separate partitions independently without overwriting each other.

[0017] Furthermore, the hardware address decoder implements physical interlocking in the following specific way: the main control FPGA outputs the corresponding block base address to the address bus according to the current substrate type, the hardware address decoder determines the target block according to the high address bit of the address bus, sets the chip select signal of the block, and automatically blocks the chip select signals of all other substrate blocks; within the same substrate block, the cutting force control parameters and ultrasonic vibration control parameters are further divided into independent sub-blocks for separate storage, and each sub-block is enabled uniformly according to the chip select signal of its respective substrate block, and the sub-blocks can be accessed simultaneously.

[0018] Furthermore, the substrate includes titanium alloy, infrared optical glass, alumina ceramic, copper alloy, CVD diamond, sapphire and quartz glass. Each substrate has an independent milling condition parameter set and polishing condition parameter set storage block in the FPGA on-chip parameter storage unit. The temperature-based stiffness drift coefficient, temperature-based amplitude drift coefficient, vibration reference value and vibration-based processing parameter attenuation coefficient of each substrate are set respectively.

[0019] Furthermore, the multi-axis CNC machining host is a five-axis CNC machining host; the roughing process includes a rough milling stage, and the finishing process includes semi-finish milling, ultrasonic finishing, precision micro-hole machining, ultrasonic polishing, and mirror polishing stages; in the rough milling stage, the cutting force control channel sets the spindle equivalent contact stiffness to 100% to 120% of the nominal value; in the semi-finish milling and ultrasonic finishing stages, the spindle equivalent contact stiffness is gradually reduced to 70% to 90% of the nominal value; in the precision micro-hole machining stage, the spindle equivalent contact stiffness is reduced to 50% to 70% of the nominal value; in the ultrasonic polishing stage, the ultrasonic vibration control channel sets the ultrasonic amplitude to 80% to 100% of the nominal value; in the mirror polishing stage, the ultrasonic amplitude is reduced to 60% to 80% of the nominal value.

[0020] Furthermore, when multiple CNC islands are arranged in series, the main control FPGA of each CNC island completes the timing coordination between CNC islands through the EtherCAT protocol bus, and the interpolation switching start time of each CNC island is kept synchronized at the cross-island level, realizing cross-island interpolation switching synchronous control.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This application uses an FPGA to execute interpolation point output with a preset interpolation period, compressing the switching window from the millisecond level of existing technologies to the sub-millisecond level, realizing a smooth transition of axis parameters between milling and polishing conditions, reducing the fluctuation amplitude of tool-workpiece contact force, and further eliminating surface ripples and step-like defects caused by step switching.

[0022] By simultaneously performing four corrections—temperature-based stiffness correction, temperature-based amplitude correction, vibration-based resonance correction, and vibration-based amplitude correction—during the switching process and the continuous machining process after the switching is completed, the temperature drift in the cutting zone and the vibration interference of the base are incorporated into the real-time closed-loop compensation, thus solving the problem of long-term drift of shaft parameters leading to the deterioration of the dimensional consistency of batch workpieces in the prior art.

[0023] By employing a mirror mapping and safety margin strategy in vibration-based resonance correction, the offset ultrasonic resonant frequency maintains a safe distance from the dominant vibration frequency of the base under all operating conditions, effectively avoiding the risk of resonance caused by the coupling between the ultrasonic resonant frequency and the dominant vibration frequency of the base.

[0024] After the FPGA is powered on, it automatically reads the EtherCAT protocol slave topology register and identifies circular, multi-transfer symmetrical, or H-shaped linear configurations. The purpose of configuration identification is not only to match the workpiece transfer path, but also to determine the range of hosts participating in distributed clock synchronization and the synchronization timing reference. This enables cross-host coordination at the interpolation switching trigger time to be uniformly executed on multi-configuration production lines, thereby achieving a universal deployment of a switching control scheme in production scenarios where multiple configuration production lines coexist.

[0025] By using the FPGA's on-chip parameter storage unit to store parameters according to substrate type through hardware interlocking, the milling / polishing process parameters and temperature and vibration correction coefficients of each substrate are independently fixed and protected by the chip select signal at the hardware level. This physically eliminates parameter misreading and cross-over, ensuring process safety in multi-material mixed-line production scenarios.

[0026] The beneficial effects listed above are not exhaustive of all advantages. Other potential beneficial effects and detailed technical implementation methods will be further disclosed in the embodiments or other descriptive sections of this application. Attached Figure Description

[0027] Figure 1 This is a flowchart of the workflow of this application. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments. Example

[0029] This embodiment provides a dual-condition interpolation switching control method for a multi-station flexible CNC island. The CNC island consists of six five-axis CNC machining centers and a shared workpiece transfer station, used to perform roughing and finishing operations on infrared optical glass workpieces. The entire control system is centered on a main control FPGA, which uses a Xilinx Zynq-7000 series SoC chip. Its programmable logic section runs various control algorithms, and the processing system section is responsible for the EtherCAT protocol master station stack. Each machining center communicates with the main control FPGA via the EtherCAT protocol bus, forming a distributed real-time control network.

[0030] The method includes the following steps: S1, Hardware Topology Recognition and Substrate Locking After the main FPGA is powered on, it first scans all slave devices via the EtherCAT protocol bus, reading the hardware identification code (Vendor ID, Product Code) and slave topology register (ESC, EtherCAT SlaveController, EtherCAT slave controller register, such as the topology information in registers 0x0000-0x0004) of each slave. Based on the read hardware identification code, the FPGA indexes the absolute coordinates and relative distance of each station from the on-chip pre-stored station geometry configuration table, and automatically identifies the current production line configuration according to preset judgment conditions, combined with the slave connection order reflected in the topology register.

[0031] The determination logic in this embodiment is as follows: if a single transfer station is detected (i.e., only one transfer station slave station), and there are six processing stations distributed at equal 60° intervals, with each processing station 1200mm from the transfer station, then it is determined to be a circular configuration; if three transfer stations are detected symmetrically distributed at 120° angles, and the six processing machines are arranged in groups of two corresponding to each of the three transfer stations, then it is determined to be a multi-transfer symmetrical configuration; if six processing machines are detected arranged along a linear guide rail at equal intervals of 800mm, and there are no fixed transfer station slave stations, then it is determined to be an H-shaped linear configuration. The production line layout in this embodiment satisfies the first condition, and the FPGA automatically configures the system as a circular configuration and loads the corresponding workpiece transfer path table.

[0032] After configuration recognition is completed, the FPGA obtains the current substrate type (in this embodiment, "infrared optical glass") from the human-machine interface. The human-machine interface is connected to the FPGA via a serial communication interface. After the operator selects the substrate type on the interface, the FPGA outputs the corresponding block base address to the internal address bus according to the substrate type. The hardware address decoder sets the chip select signal of the substrate block and blocks the other substrate blocks. The FPGA retrieves the milling and polishing parameter sets corresponding to the infrared optical glass from the selected blocks.

[0033] The on-chip parameter storage unit of the FPGA is Block RAM (on-chip block random access memory). Its power-on contents are automatically loaded by the configuration bitstream (configuration file used to initialize on-chip logic and storage contents when the FPGA is powered on) in the external QSPI Flash, realizing the solid storage of parameters and automatic power-on recovery, taking into account both the non-volatile preservation requirements of parameters and the high-speed access requirements of the FPGA.

[0034] The milling condition parameter set includes: a target stiffness value of 3000 N / mm for rough milling, 2400 N / mm for semi-finish milling, 2100 N / mm for ultrasonic finishing, and 1500 N / mm for precision micro-hole machining. The polishing condition parameter set includes: a target amplitude value of 8 μm for ultrasonic polishing and 5 μm for mirror polishing. The target stiffness value is the equivalent contact stiffness value corresponding to the stiffness gain coefficient of the force control loop of the spindle servo system.

[0035] S2, Dual-channel physical isolation configuration: The FPGA divides the axis control path of each machining host into two hardware closed loops: the cutting force control channel and the ultrasonic vibration control channel.

[0036] The cutting force control channel consists of the following hardware: a first servo drive unit (driving five-axis servo motors of X / Y / Z / A / C), a first feedback sensor group (optical scales and rotary encoders for each axis), and a first signal conditioning circuit (differential signal receiver and filter). This channel is responsible for converting the spindle speed command, feed rate command, and cutting force command output by the FPGA into current loop control quantities for each axis motor, while simultaneously feeding back the actual position and speed of each axis to the FPGA.

[0037] The ultrasonic vibration control channel consists of the following hardware: a second servo drive unit (ultrasonic power supply unit, including a PWM inverter and impedance matching network), a second feedback sensor group (ultrasonic transducer voltage / current sensor and laser vibrometer), and a second signal conditioning circuit (lock-in amplifier). This channel independently controls the amplitude (0-15μm continuously adjustable), frequency (nominal value 20kHz, adjustable range 19kHz-21kHz), and polishing dwell time (0.1s-10s adjustable) of the ultrasonic transducer.

[0038] The power ground, signal ground, and shielding layers of the two channels are independently isolated from each other, eliminating electromagnetic interference from the high-current PWM noise of the cutting force control channel to the ultrasonic vibration control channel. The two channels are powered by independent isolated DC-DC power modules, and the signals are optically isolated before entering the FPGA's independent I / O Bank, ensuring complete physical layer isolation.

[0039] S3, Interpolation Switching Operation: In this embodiment, the condition switching is determined by a position triggering method: when the tool tip position fed back by the grating ruler of each axis reaches the preset switching position (0.5mm away from the current machining surface), the FPGA determines to initiate the condition switching from the semi-finish milling stage to the ultrasonic finishing stage. The preset condition switching condition can also be that the cutting force change rate exceeds a preset threshold, or the machining time reaches the preset switching time.

[0040] The FPGA starts with a preset interpolation period T = 200μs. Internally, the FPGA uses a 100MHz (10ns period) hardware clock as a reference and triggers an interpolation operation every 10 clock cycles (i.e., every 100ns) via an internal counter, performing 2000 interpolation point outputs within a single interpolation period. It should be noted that the 100ns here is the FPGA's internal interpolation operation step, which is a separate time mechanism from the 100μs distributed clock synchronization period of the EtherCAT protocol bus in S5 (described later). These two mechanisms are coordinated through the FPGA's internal global time base and serve two different control dimensions: interpolation smoothness and multi-master synchronization accuracy.

[0041] During each interpolation operation, the FPGA reads the current value of the cutting force control channel stiffness, K_start = 2385 N / mm, and the current value of the ultrasonic vibration control channel amplitude, A_start = 0.3 μm, from the current control output register (previously in the semi-finish milling stage, the ultrasonic amplitude remained at the residual level). It also reads the target values ​​for the next working condition, K_end = 2100 N / mm and A_end = 8.0 μm, from the working condition parameter set retrieved from S1. The interpolation point output value is calculated using the linear interpolation model. K(t)=2385+(t / 200)×(2100-2385) A(t)=0.3+(t / 200)×(8.0-0.3) The value t increases from 0 to 200 in microseconds, with a step size of 0.1 microseconds. It should be noted that a step size of 0.1 microseconds corresponds to a time step size of 100ns, which is consistent with the mechanism inside the FPGA that uses a 10ns clock as a reference and triggers an interpolation operation every 10 clock cycles.

[0042] The feed rate scales synchronously with the stiffness output value within the interpolation period: the feed rate for semi-finish milling before switching is 600 mm / min, and the feed rate for ultrasonic finishing after switching is 528 mm / min (scaled according to a ratio of 2100 / 2385, 600×2100 / 2385=528.3 mm / min). The feed rate is updated synchronously at each interpolation point.

[0043] The stiffness output value and feed rate value calculated by the FPGA at each interpolation point are output to the first servo drive unit of the cutting force control channel through a 16-bit digital-to-analog converter port (i.e., DA port, Digital-to-Analog). The amplitude output value is output to the ultrasonic power supply unit of the ultrasonic vibration control channel through a 16-bit digital-to-analog converter port.

[0044] During the entire 200-microsecond interpolation period, the measured fluctuation of the contact force between the tool and the workpiece was ±0.15N, which is better than the control target of ±0.3N.

[0045] The following illustrates a cross-condition interpolation example for switching from ultrasonic finishing to ultrasonic polishing. In this embodiment, the precision micro-hole machining stage is optional depending on the workpiece type. When the workpiece does not require micro-hole machining, the switch can be made directly from ultrasonic finishing to ultrasonic polishing. Before switching, the ultrasonic finishing stage has K_start = 2100 N / mm and A_start = 8.0 μm; after switching, the ultrasonic polishing stage has K_end = 1800 N / mm and A_end = 10.0 μm. Within a 200 microsecond interpolation period, the stiffness smoothly decreases from 2100 N / mm to 1800 N / mm, the amplitude smoothly increases from 8.0 μm to 10.0 μm, and the feed rate scales proportionally. The tool and workpiece maintain contact throughout the entire process, and the contact force fluctuation is controlled within ±0.3 N.

[0046] S4, Temperature-Vibration Coupling Bidirectional Drift Correction: During the dual-mode switching process and the subsequent continuous processing, four correction processes run synchronously. Among them, the temperature-based stiffness correction, temperature-based amplitude correction, and vibration-based amplitude correction factors act on the output value of the corresponding channel in a multiplicative superposition manner; the vibration-based resonance correction independently performs frequency offset and does not participate in the multiplicative superposition.

[0047] (a) Temperature-based stiffness correction. An NTC (Negative Temperature Coefficient) thermistor temperature sensor (thermal time constant ≤200ms, installed at the spindle bearing housing in the cutting zone) outputs the real-time temperature value T_actual_cut, which is directly connected to the FPGA's underlying I / O pins via a 16-bit ADC (Analog-to-Digital Converter) with a sampling frequency of 10kHz. Based on the substrate type "infrared optical glass" locked by S1, the FPGA reads the temperature-based stiffness drift coefficient k_temp_cut = 0.004 / ℃ corresponding to the substrate from the on-chip parameter storage unit. The target temperature of the cutting zone is T_target_cut = 22℃.

[0048] Assuming that at a certain moment T_actual_cut = 25℃, then: γ_stiff=1-|25-22|×0.004=1-0.012=0.988 If the calculated γ_stiff is lower than the preset stiffness correction lower limit γ_stiff_min=0.80, γ_stiff is locked at 0.80. The function of this lower limit locking is to prevent system instability caused by excessive stiffness correction under extreme temperature conditions.

[0049] Multiply γ_stiff by the stiffness value output from S3 (for example, 2100N / mm currently) to obtain the corrected stiffness value=2100×0.988=2074.8N / mm, which is superimposed to the output of the digital-to-analog conversion port.

[0050] (b) Temperature-based amplitude correction. The NTC thermistor temperature sensor is installed at the horn of the ultrasonic transducer in the polishing zone, and outputs T_actual_pol in real time. The FPGA reads k_temp_pol=0.003 / ℃ from the parameter storage unit. The target temperature of the polishing zone T_target_pol=20℃.

[0051] Assume that at a certain moment T_actual_pol=22℃, then: γ_amp=1-|22-20|×0.003=1-0.006=0.994 If the calculated γ_amp is lower than the preset amplitude correction lower limit γ_amp_min=0.85, γ_amp is locked at 0.85.

[0052] Multiply γ_amp by the amplitude value output from S3 to obtain the corrected amplitude value.

[0053] (c) Vibration-based resonance correction. The piezoelectric acceleration sensor is installed on the base of each main unit, and the three-axis composite signal is subjected to 256-point real-time spectrum analysis through the FFT (Fast Fourier Transform) module to extract the maximum amplitude frequency component f_vib_main. The nominal ultrasonic resonance frequency f_nominal=20000Hz, and the preset frequency threshold Δf_threshold=±200Hz.

[0054] If the analysis shows that f_vib_main=19880Hz, which satisfies |19880-20000|=120Hz≤200Hz, it is determined that the resonance frequency offset needs to be performed. Since f_vib_main=19880Hz<f_nominal=20000Hz, δ=+300Hz is taken.

[0055] f_new=2×20000-19880+300=40000-19880+300=20420Hz |f_new-f_vib_main|=|20420-19880|=540Hz, the safety distance is greater than 300Hz, which meets the vibration damping requirements.

[0056] The FPGA writes f_new into the DDS (Direct Digital Synthesis) frequency register of the ultrasonic power supply unit via SPI (Serial Peripheral Interface) to complete the resonant frequency shift.

[0057] If analysis in another sampling period yields f_vib_main=20150Hz, satisfying |20150-20000|=150Hz≤200Hz, and since f_vib_main=20150Hz≥f_nominal, we take δ=-300Hz.

[0058] f_new=2×20000-20150+(-300)=40000-20150-300=19550Hz |f_new-f_vib_main|=|19550-20150|=600Hz, with a safety spacing greater than 300Hz.

[0059] If the analysis shows f_vib_main = 20300Hz, and |20300-20000| = 300Hz > 200Hz, the triggering condition is not met. Therefore, the resonant frequency shift will not be performed this time, and f_nominal will remain unchanged. It should be noted that the actual sampling rate of the vibration sensor is 100kHz, corresponding to a frequency resolution of approximately 390Hz for a 256-point FFT. Although this resolution is numerically greater than the 200Hz range of Δf_threshold, the purpose of the FFT analysis is to quickly capture the approximate position of the dominant vibration frequency of the base to trigger the frequency shift decision. Subsequent high-precision tuning of the DDS frequency register (tuning resolution better than 1Hz) ensures that the resonant frequency after the shift accurately meets the safety clearance requirements.

[0060] After the drive frequency shifts, the ultrasonic power supply automatically adjusts the drive voltage duty cycle at the shifted frequency point to compensate for the amplitude change, based on the pre-stored transducer impedance-frequency characteristic calibration data. This ensures that the actual amplitude remains at the target level consistent with the current corrected δ_vib and γ_amp. This compensation mechanism is executed after the frequency shift in S4(c) is triggered. The required calibration data is pre-stored by the ultrasonic power supply unit during initial configuration. The compensation action works in conjunction with the vibration-based amplitude correction in S4(d) to achieve precise amplitude adjustment.

[0061] (d) Vibration-based amplitude correction. The FPGA calculates the triaxial vibration composite root mean square value V_actual_RMS. The vibration reference value V_ref=0.5mm / s corresponding to the infrared optical glass and the vibration-based processing parameter attenuation coefficient β=0.35 are read from the parameter storage unit.

[0062] Assuming V_actual_RMS = 0.3 mm / s at a certain moment, then: δ_vib=1-(0.3 / 0.5)×0.35=1-0.21=0.79 The preset compensation lower limit of the infrared optical glass is δ_min = 0.15. Since δ_vib = 0.79 > 0.15, the lower limit locking is not triggered.

[0063] Using a multiplicative superposition method, the temperature correction factor and the vibration compensation factor are applied together to the corresponding channels: The corrected feed rate = 528 × γ_stiff × δ_vib = 528 × 0.988 × 0.79 = 412.2 mm / min Corrected amplitude = 8.0 × γ_amp × δ_vib = 8.0 × 0.994 × 0.79 = 6.28 μm Among them, γ_stiff acts on the cutting force control channel (including feed rate output value), γ_amp acts on the ultrasonic vibration control channel (including amplitude output value), and δ_vib acts on both the feed rate output value and amplitude output value of the two channels. The three correction factors are coupled and corrected in a multiplicative superposition manner on their respective channels.

[0064] S5, Global Synchronous Time Base and Hardware Direct Drive Output: The FPGA internally uses a 1GHz counter as the global time base source, which is distributed to all six spindle servo drive units and six ultrasonic power supply units via the EtherCAT protocol's distributed clock (DC) mechanism. The EtherCAT protocol master station (FPGA processing system) sends an ARMW (Auto-Increment Read Multiple Write) frame every 100μs, reads the DC time register of each slave station, calculates the offset between each slave station's clock and the FPGA's global time base, and writes the compensated offset into each slave station's DC System Time Offset register. Each slave station generates a synchronization interrupt based on the compensated local DC time at the Sync0 signal (EtherCAT protocol distributed clock synchronization signal, period 250μs). It should be noted that the 1GHz counter here is the FPGA's internal timestamp counter, used to generate a high-precision time base; while 100MHz is the system clock frequency of the FPGA's programmable logic, used for interpolation and other logic processing—the two clock domains are different but are coordinated and synchronized through the FPGA's internal MMCM (Mixed-Mode Clock Manager) module.

[0065] The DC Sync0 signals of all six spindle servo drive units and ultrasonic power supply units are aligned to the same distributed clock synchronization edge. The start time of interpolation switching is strictly aligned to this synchronization edge, ensuring that the axis parameter outputs of the six main units maintain nanosecond-level synchronization accuracy at the moment of switching.

[0066] The final results of the interpolation calculation (stiffness value, feed rate, amplitude value) are directly output through the parallel digital-to-analog converter port of the FPGA programmable logic. The signal path is: FPGA register → parallel digital-to-analog converter → analog voltage signal → analog input port of the servo drive unit / ultrasonic power supply unit. There is no intermediate processor (such as DSP, MCU) to relay the signal. The total delay from updating the internal register of the FPGA to establishing the analog voltage at the digital-to-analog converter port does not exceed 2 microseconds.

[0067] The stiffness setpoint output from the FPGA digital-to-analog converter port is mapped to the stiffness gain coefficient of the force control loop in the servo drive unit. This coefficient determines the magnitude of the torque output by the servo system under unit position error, thereby realizing the adjustment of the equivalent contact stiffness of the spindle system.

[0068] S6. Separate storage based on material and process: The FPGA's on-chip Block RAM (initialized by the configuration bitstream in the external QSPI Flash after power-on, achieving parameter-fixed storage, totaling 640KB) is divided into seven independent blocks according to substrate type, with the following base address allocations: Titanium Alloy (0x00000–0x13FFF, 80KB), Infrared Optical Glass (0x18000–0x2BFFF, 80KB, with a 16KB isolation band between each block), Alumina Ceramic (0x30000–0x43FFF), Copper Alloy (0x48000–0x5BFFF), CVD Diamond (0x60000–0x73FFF), Sapphire (0x78000–0x8BFFF), and Quartz Glass (0x90000–0xA3FFF). Each block is 80KB, with a base address interval of 96KB (including the 16KB isolation band).

[0069] The hardware address decoder determines the target block based on the high-order address bits of the address bus. When the FPGA accesses the infrared optical glass block, the address decoder outputs an enable signal to the Block RAM enable port of that block, while automatically pulling down the enable port levels of the other six blocks. This interlocking mechanism ensures that only one substrate block can be read physically at a time—interlocking between blocks allows for parallel access to sub-blocks within a block.

[0070] Within the same substrate block, cutting force control parameters (working condition parameter set, k_temp_cut, V_ref, β, γ_stiff_min) and ultrasonic vibration control parameters (target amplitude value, k_temp_pol, δ_min, γ_amp_min) are further divided into independent sub-blocks for separate storage. Each sub-block is enabled uniformly according to the enable signal of its respective substrate block, and sub-blocks can be accessed simultaneously through different address offset ranges. When S3 performs interpolation calculations, the FPGA can simultaneously read K_end from the cutting force sub-block and A_end from the ultrasonic vibration sub-block, meeting the requirement of simultaneous dual-channel output.

[0071] Examples of parameters for different substrates The table below lists example values ​​of key correction coefficients for different substrates, all of which are embedded in the FPGA's on-chip Block RAM and automatically loaded by the configuration bitstream upon power-up: Titanium alloy 0.005 0.004 0.8 0.35 0.75 0.80 0.15 Infrared optical glass 0.004 0.003 0.5 0.35 0.80 0.85 0.15 alumina ceramics 0.003 0.002 0.3 0.40 0.85 0.90 0.10 copper alloy 0.006 0.005 1.0 0.30 0.70 0.75 0.20 CVD diamond 0.002 0.002 0.2 0.45 0.90 0.90 0.10 sapphire 0.003 0.002 0.3 0.40 0.85 0.90 0.10 Quartz glass 0.004 0.003 0.5 0.35 0.80 0.85 0.15 Process Stages and Parameter Settings The reference parameter values ​​(nominal values) measured under standard working conditions are: nominal value of spindle equivalent contact stiffness 3000 N / mm, nominal value of ultrasonic amplitude 10 μm, and nominal value of feed rate 600 mm / min, all of which are fixed in the FPGA on-chip Block RAM (loaded by configuration bit stream after power-on).

[0072] In this embodiment, rough machining includes a rough milling stage, and finish machining includes five stages: semi-finish milling, ultrasonic finish machining, precision micro-hole machining, ultrasonic polishing, and mirror polishing. The precision micro-hole machining stage is optional; when the workpiece does not require micro-hole machining, the process can be directly switched from ultrasonic finish machining to ultrasonic polishing. The parameter settings for each stage are as follows: Rough milling stage: The cutting force control channel sets the spindle equivalent contact stiffness to 120% of the nominal value (i.e., 3600 N / mm), the feed rate to 120% of the nominal value (i.e., 720 mm / min), and the ultrasonic vibration control channel is not enabled.

[0073] Semi-finish milling stage: The spindle equivalent contact stiffness is set to 90% of the nominal value (2700 N / mm), the feed rate is set to 100% of the nominal value (600 mm / min), and the ultrasonic vibration control channel operates with a residual amplitude of 0.3 μm.

[0074] Ultrasonic finishing stage: spindle equivalent contact stiffness is set to 70% of the nominal value (2100 N / mm), feed rate is set to 88% of the nominal value (528 mm / min), and ultrasonic amplitude is set to 80% of the nominal value (8 μm).

[0075] Precision micro-hole machining stage (optional): The spindle equivalent contact stiffness is set to 50% of the nominal value (1500 N / mm), and the ultrasonic amplitude is set to 70% of the nominal value (7 μm).

[0076] Ultrasonic polishing stage: The ultrasonic amplitude is set to 100% of the nominal value (10μm), and the spindle equivalent contact stiffness is set to 60% of the nominal value (1800N / mm).

[0077] Mirror polishing stage: The ultrasonic amplitude is set to 60% of the nominal value (6μm), and the spindle equivalent contact stiffness is set to 50% of the nominal value (1500N / mm).

[0078] Each host has a built-in multi-axis switching macro program (running in the user macro program storage area of ​​the CNC system), which serves as the upper-level scheduling logic for the aforementioned dual-channel configuration. Based on the current station type parsed from the M function code instructions, the macro program automatically determines the channel combination to be enabled (cutting force channel only, ultrasonic vibration channel only, or both channels enabled simultaneously) and axis configuration (three-axis linkage or five-axis linkage), and sends the configuration instructions to the FPGA for execution.

[0079] During the execution of the method: the EtherCAT protocol communication buses of the milling station and the polishing station are independent and physically shielded to prevent crosstalk between different stations; the zoned constant temperature chamber maintains the temperature of the cutting zone at 22℃ (target temperature of the cutting zone) and the temperature of the polishing zone at 20℃ (target temperature of the polishing zone), and the target temperature is the set control temperature of the constant temperature chamber; each processing host is equipped with an independent double-layer vibration isolation base.

[0080] When multiple CNC islands are connected in series to form a flexible production line (for example, three CNC islands sequentially complete the entire process of rough milling, finishing, and polishing of infrared optical glass), the main control FPGAs of each CNC island are interconnected via an EtherCAT protocol bus. After completing its machining process, the upstream CNC island sends a workpiece transfer completion signal and machining status data to the FPGA of the downstream CNC island via the EtherCAT protocol. The interpolation switching start time of each CNC island is kept synchronized at the cross-island level. When the workpiece flows out of the first CNC island and enters the switching determination position of the second CNC island, the FPGA of the second CNC island performs interpolation switching with reference to the global time base offset of the first CNC island, realizing cross-island interpolation switching synchronous control and eliminating the timing uncertainty introduced by workpiece transfer between islands.

[0081] The above description is only a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of the present invention.

Claims

1. A dual-condition interpolation switching control method for a multi-station flexible CNC island, wherein the CNC island comprises multiple multi-axis CNC machining hosts and a shared workpiece transfer station, used to perform roughing and finishing operations on the workpiece; characterized in that, The method includes: S1. Parameter Retrieval: After the main control FPGA determines the current substrate type, it retrieves the milling condition parameter set and polishing condition parameter set corresponding to the substrate from the on-chip parameter storage unit initialized upon power-on. The parameter set includes at least the target stiffness value of the cutting force control channel and the target amplitude value of the ultrasonic vibration control channel corresponding to each machining condition stage. The target stiffness value is the equivalent contact stiffness value corresponding to the stiffness gain coefficient of the force control loop of the spindle servo system. S2. Dual-channel configuration: The axis control path of each machining host is divided into two physically isolated hardware closed loops: a cutting force control channel and an ultrasonic vibration control channel. The cutting force control channel is responsible for the output control of spindle speed, feed rate and cutting force. The ultrasonic vibration control channel is responsible for the independent control of the amplitude, frequency and polishing dwell time of the ultrasonic transducer. Each channel has its own independent servo drive unit and feedback sensor. S3, Interpolation Switching: When the preset working condition switching conditions are met, while the tool and workpiece are in contact, the FPGA uses the stiffness value and amplitude value in the current control output register as the starting value and the target stiffness value and target amplitude value corresponding to the next working condition stage retrieved by S1 as the ending value. It performs interpolation calculations within the preset interpolation period according to the preset interpolation model, outputs the stiffness value of the cutting force control channel and the amplitude value of the ultrasonic vibration control channel respectively, and outputs them directly to the corresponding servo drive unit or ultrasonic power supply unit through the hardware digital-to-analog conversion port of the FPGA. S4. Temperature and Vibration Coupling Correction: During and after the switching process, the FPGA synchronously corrects the stiffness and amplitude values ​​output by S3 based on the real-time collected cutting zone temperature, polishing zone temperature, and base vibration signal. The stiffness correction factor is calculated based on the real-time temperature of the cutting zone and then superimposed on the stiffness value of the cutting force control channel output by S3. The amplitude correction factor is calculated based on the real-time temperature of the polishing zone and superimposed on the amplitude value of the ultrasonic vibration control channel output by S3. The vibration compensation factor is calculated based on the vibration amplitude of the base, and then superimposed on the feed rate output value of the cutting force control channel and the amplitude output value of the ultrasonic vibration control channel. The main frequency component is extracted by performing spectrum analysis on the vibration signal of the base. If the difference between the main frequency component and the nominal frequency of the ultrasonic resonance is within the preset frequency threshold, the ultrasonic resonance frequency is shifted from the nominal frequency to avoid the main frequency of the base vibration. Among them, the correction factors of the first three corrections are combined in a multiplicative manner to affect the output value of the corresponding channel.

2. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, In step S1, after the main control FPGA is powered on, it also reads the hardware identification code of each station and the EtherCAT protocol slave topology register, and automatically identifies the current production line configuration and matches the corresponding workpiece transfer path according to preset judgment conditions. The preset judgment conditions include: if a single transfer station is detected and multiple processing stations are distributed at equal angular intervals, and the distance from each processing station to the transfer station is equal, it is determined to be a circular configuration; if multiple transfer stations are detected to be angularly symmetrically distributed and the processing host is grouped to correspond to each transfer station, it is determined to be a multi-transfer symmetrical configuration; if the processing host is detected to be arranged at equal intervals along the linear guide rail and there is no fixed transfer station, it is determined to be an H-shaped linear configuration.

3. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, In step S3, the preset interpolation model is a linear interpolation model: Cutting force control channel: K(t) = K_start + (t / T) × (K_end - K_start) Ultrasonic vibration control channel: A(t) = A_start + (t / T) × (A_end - A_start) Where T is the preset interpolation period, t∈[0,T]; K_start and A_start are the current stiffness and amplitude values ​​before switching, respectively; K_end and A_end are the target stiffness and target amplitude values, respectively; K(t) and A(t) are the stiffness output value and amplitude output value at time t during the interpolation process, respectively; the feed rate scales synchronously with the stiffness output value within the interpolation period.

4. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, In step S4: The temperature-based stiffness correction factor γ_stiff = 1 - |T_actual_cut - T_target_cut| × k_temp_cut, where T_actual_cut is the measured temperature of the cutting zone, T_target_cut is the target temperature of the cutting zone, and k_temp_cut is the temperature-based stiffness drift coefficient corresponding to the current substrate. The temperature-based amplitude correction factor γ_amp=1-|T_actual_pol-T_target_pol|×k_temp_pol, where T_actual_pol is the measured temperature of the polishing area, T_target_pol is the target temperature of the polishing area, and k_temp_pol is the temperature-based amplitude drift coefficient corresponding to the current substrate. The vibration-based amplitude compensation factor δ_vib = 1 - (V_actual_RMS / V_ref) × β, where V_actual_RMS is the root mean square value of the multi-axis composite vibration of the base, V_ref is the vibration reference value corresponding to the current substrate, and β is the vibration-based machining parameter attenuation coefficient; δ_vib is simultaneously superimposed on the feed rate output value of the cutting force control channel and the amplitude output value of the ultrasonic vibration control channel; In the vibration-based resonant frequency offset correction, Fast Fourier Transform is performed on the base vibration signal to extract the maximum amplitude frequency component f_vib_main. If |f_vib_main-f_nominal|≤Δf_threshold, the offset ultrasonic resonant frequency f_new=2×f_nominal-f_vib_main+δ, where f_nominal is the nominal ultrasonic resonant frequency, Δf_threshold is the preset frequency threshold. δ takes a positive value when f_vib_main<f_nominal, and δ takes a negative value when f_vib_main≥f_nominal, so as to maintain a preset safety distance between the offset resonant frequency and the main vibration frequency of the base.

5. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, The method further comprises: generating a global time base inside the FPGA, and realizing clock synchronization of all spindle servo drive units and ultrasonic power units through a periodic time calibration mode of master and slave stations via the EtherCAT protocol distributed clock mechanism; aligning the interpolation switching start moments of all stations to the same distributed clock synchronization edge; the interpolation operation results directly drive the servo units and the ultrasonic power through the FPGA hardware digital-to-analog conversion ports, with no intermediate processing link transfer in the signal link.

6. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, The method further comprises: dividing the on-FPGA parameter storage unit into a plurality of independent storage blocks according to base material types, and realizing physical interlock between the blocks by a hardware address decoder; when the main control FPGA accesses any base material block, the hardware automatically masks the chip select signals of the remaining blocks, ensuring that only the authorized milling condition parameter set and polishing condition parameter set for a single base material can be read; within the same base material block, the cutting force control parameters and the ultrasonic vibration control parameters are stored in separate partitions independently without overwriting each other.

7. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 6, characterized in that, The specific manner for the hardware address decoder to realize physical interlock is: the main control FPGA outputs the corresponding block base address to the address bus according to the current base material type, the hardware address decoder judges the target block according to the high-order address bits of the address bus, asserts the chip select signal of this block, and automatically masks the chip select signals of all other base material blocks at the same time; within the same base material block, the cutting force control parameters and the ultrasonic vibration control parameters are further divided into independent sub-blocks for separate storage, each sub-block is uniformly enabled along with the chip select signal of the affiliated base material block, and the sub-blocks can be accessed simultaneously.

8. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, The base materials include titanium alloy, infrared optical glass, alumina ceramics, copper alloy, CVD diamond, sapphire and quartz glass. Each base material has an independent storage block for the milling condition parameter set and the polishing condition parameter set in the on-FPGA parameter storage unit, and the temperature-based stiffness drift coefficient, temperature-based amplitude drift coefficient, vibration reference value and vibration-based machining parameter attenuation coefficient of each base material are set respectively.

9. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, The multi-axis CNC machining host is a five-axis CNC machining host; the roughing process includes a rough milling stage, and the finishing process includes a semi-finish milling, ultrasonic finishing, precision micro-hole machining, ultrasonic polishing, and mirror polishing stage; in the rough milling stage, the cutting force control channel sets the spindle equivalent contact stiffness to 100% to 120% of the nominal value; in the semi-finish milling and ultrasonic finishing stages, the spindle equivalent contact stiffness is gradually reduced to 70% to 90% of the nominal value; in the precision micro-hole machining stage, the spindle equivalent contact stiffness is reduced to 50% to 70% of the nominal value; in the ultrasonic polishing stage, the ultrasonic vibration control channel sets the ultrasonic amplitude to 80% to 100% of the nominal value; in the mirror polishing stage, the ultrasonic amplitude is reduced to 60% to 80% of the nominal value.

10. The dual-condition interpolation switching control method for a multi-station flexible CNC island according to claim 1, characterized in that, When multiple CNC islands are arranged in series, the main control FPGA of each CNC island completes the timing coordination between CNC islands through the EtherCAT protocol bus. The start time of interpolation switching of each CNC island is kept synchronized at the cross-island level, realizing cross-island interpolation switching synchronous control.

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