Ultra-precision grinding and profile accuracy control system of high-precision roller screw

Abstract

The application discloses a high-precision roller screw super-precision grinding and profile precision control system and relates to the technical field of grinding processes; the system comprises a rigidity confirmation module, a parameter acquisition module and a parameter adjustment module; the rigidity confirmation module is used for acquiring the axial rigidity distribution and the axial position of a grinding head in a grinding process and finding the equivalent rigidity value corresponding to the axial position in the axial rigidity distribution according to the axial position; the parameter acquisition module is used for acquiring the load signal and the workpiece deflection in the grinding process, converting the workpiece deflection into the elastic deformation force based on the equivalent rigidity value, and obtaining the actual grinding contact force by deducting the elastic deformation force from the load signal; the parameter adjustment module is used for checking and correcting the actual grinding contact force, obtaining the corrected actual grinding contact force, and generating the real-time grinding parameter adjustment value in combination with the equivalent rigidity value; and the initial grinding module is used for completing the initial grinding; through the cooperative work of the multiple modules, the application constructs a complete grinding precision control process and improves the consistency of the profile precision of the screw.

Description

Technical Field

[0001] This invention relates to the field of grinding technology, and more specifically, to an ultra-precision grinding and contour accuracy control system for high-precision roller screws. Background Technology

[0002] In the ultra-precision grinding of high-precision roller screws, a closed-loop compensation control scheme based on load feedback is typically used to achieve sub-micron level contour accuracy control. This scheme is widely applied in the mass production of long and slender roller screws, and is particularly suitable for the manufacturing process of roller screws for industrial robots and precision machine tools where strict contour consistency requirements are necessary. In such machining scenarios, the roller screws often exhibit a large length-to-diameter ratio, requiring clamping and positioning at both ends or multi-point support. The helical groove contour is then machined using an ultra-precision grinding machine, while load detection signals are used to adjust and compensate grinding parameters in real time to ensure that the contour accuracy meets design standards.

[0003] The aforementioned load feedback-based compensation control technology uses the measured load signal as a key indicator of the amount of material removed from the grinding zone. A pre-defined removal function establishes a correspondence between the measured load and the amount of material removed. Then, based on the contour detection error, the feed rate, depth of cut, and other process parameters during the grinding process are dynamically adjusted to correct the contour error. The measured load is typically obtained through spindle current, feed axis servo load, power head force sensor, or table force measuring device. The control system assumes a fixed proportional relationship between the measured load and the actual contact pressure in the grinding zone, and this proportional relationship remains constant throughout the machining process, thus simplifying the calculation of the removal function and the implementation of the compensation algorithm.

[0004] However, for lead screw workpieces with long and slender structures, the measured load and the actual contact pressure in the grinding zone cannot maintain a stable correspondence. Due to the large length-to-diameter ratio of the lead screw workpiece and its relatively weak rigidity, the combined flexibility of clamping and support formed during the clamping process exhibits significant differences along the axial direction, while the local deflection changes with the axial position. In addition, the rolling clearance in the support structure and the liquid film bearing effect formed by the coolant during grinding further interfere with the contact state. These factors work together to cause the same measured load to correspond to different actual contact pressures and contact areas at different axial positions of the lead screw. This results in the transmission relationship between the measured load and the actual contact pressure dynamically changing with the axial position and machining conditions, breaking the preset assumption of a fixed proportional relationship between the two in the control system. Consequently, the removal function in the control system loses its accuracy, and the actual removal driving force in the grinding zone undergoes spatial distortion along the lead screw axis, leading to a series of consequences.

[0005] During the grinding process, contour errors exhibit significant segmented correlation characteristics, especially near support points and in areas with significant deflection changes. These contour errors recur and are difficult to suppress using existing compensation strategies. Because the compensation algorithm still calculates the removal amount based on a fixed proportional relationship, adjusting process parameters using the same compensation strategy easily leads to overcompensation in areas of weak rigidity and undercompensation in areas of strong rigidity. This results in decreased consistency in the lead screw contour accuracy, failing to meet the design requirements of high-precision roller screws. Such segmented errors reduce the yield rate of mass production, increase rework and scrap costs, prolong production cycle time, and may even cause problems such as fluctuating transmission accuracy, increased noise, and shortened service life when the machined lead screw is installed and put into service.

[0006] In view of this, the present invention proposes an ultra-precision grinding and contour accuracy control system for high-precision roller screws to solve the above problems. Summary of the Invention

[0007] To overcome the aforementioned deficiencies of the prior art and achieve the above objectives, the present invention provides the following technical solution: a high-precision roller screw ultra-precision grinding and contour accuracy control system, comprising:

[0008] The stiffness verification module is used to obtain the axial stiffness distribution and the axial position of the grinding head during the grinding process, and to find the equivalent stiffness value corresponding to the axial position in the axial stiffness distribution based on the axial position.

[0009] The parameter acquisition module is used to acquire load signals and workpiece deflection during the grinding process, convert the workpiece deflection into elastic deformation force based on the equivalent stiffness value, and then subtract the elastic deformation force from the load signal to obtain the actual grinding contact force.

[0010] The parameter adjustment module is used to obtain the support reaction force at each support point and use the support reaction force to check and correct the actual grinding contact force, so as to obtain the corrected actual grinding contact force; the grinding force deviation is calculated based on the corrected actual grinding contact force and the preset target contact force, and the real-time grinding parameter adjustment value is generated by combining the equivalent stiffness value.

[0011] The initial grinding module is used to correct the feed rate of the grinding head at the corresponding axial position in real time according to the real-time grinding parameter adjustment value, and to complete the initial grinding.

[0012] The fine grinding module is used to obtain the contour error distribution of the workpiece after the initial grinding, form updated grinding control parameters based on the contour error distribution, and use the updated grinding control parameters to perform fine grinding on the workpiece to obtain the finished ball screw.

[0013] Furthermore, by using the equivalent stiffness value to perform a mechanical dimension conversion on the workpiece deflection, the elastic deformation effect caused by the comprehensive flexibility of the long and slender lead screw workpiece at the current axial position is mapped from the displacement domain to the force domain, thus obtaining the elastic deformation force.

[0014] Furthermore, the support reaction force is aligned with the load signal according to the sampling time, and the support reaction force of each support point is converted into a force component in the same direction as the load signal based on the force direction of the support point and the sensor installation direction, and then summed to obtain the resultant support reaction force.

[0015] Furthermore, during the time period when no grinding contact occurs, the baseline offset is calculated by recording the corresponding load signal and the resultant force of the support reaction force based on the same axial position. During the grinding process, the consistency residual is calculated by subtracting the resultant force of the real-time support reaction force from the real-time load signal and deducting the baseline offset. The consistency residual is then used to determine the rationality of the actual grinding contact force.

[0016] Furthermore, when the absolute value of the consistency residual exceeds the consistency threshold in multiple consecutive sampling periods, it is determined that correction is required. When the correction condition is met, the actual grinding contact force is adjusted, and the adjustment amount is the value of the consistency residual after being weighted by the verification weight coefficient, wherein the verification weight coefficient is determined based on the fluctuation level of the load signal and the support reaction force within the sliding time window.

[0017] Furthermore, the grinding force deviation is mapped to the feed compensation amount, so that the feed compensation amount and the grinding force deviation maintain a monotonic relationship in the same direction, and the amplitude of the feed compensation amount is limited to a preset allowable range by saturation constraint.

[0018] Furthermore, when the grinding force deviation is greater than 0, the feed compensation is set to a positive value and the feed rate is increased to increase the contact strength in the grinding zone and improve the material removal rate, so that the actual grinding contact force converges to the preset target contact force; when the grinding force deviation is less than 0, the feed compensation is set to a negative value and the feed rate is reduced to reduce the contact strength in the grinding zone and suppress the material removal rate, so that the actual grinding contact force converges to the preset target contact force.

[0019] Furthermore, there is a linear mapping relationship between the feed compensation amount and the grinding force deviation. The proportional coefficient of the linear mapping relationship is adaptively adjusted as the equivalent stiffness value changes. The proportional coefficient is defined as the compensation gain coefficient, which is used to characterize the change in feed compensation amount corresponding to a unit grinding force deviation.

[0020] Furthermore, based on the axial stiffness distribution statistics, the minimum and maximum values ​​of the equivalent stiffness are obtained, and the equivalent stiffness values ​​are normalized to obtain the stiffness factor. The stiffness factor is used to characterize the stiffness level of the current axial position relative to the entire axial stiffness range. When the stiffness factor is lower than the stiffness threshold, it is determined to be a weakly stiff region, and when the stiffness factor is higher than the stiffness threshold, it is determined to be a strongly stiff region.

[0021] Furthermore, in the weakly rigid region, the compensation gain coefficient is reduced according to a set reduction ratio, so that the absolute value of the feed compensation decreases as the stiffness factor decreases, thereby suppressing overcompensation; in the strongly rigid region, the compensation gain coefficient is increased according to a set increase ratio, so that the absolute value of the feed compensation increases as the stiffness factor increases, thereby suppressing undercompensation.

[0022] Compared with the prior art, the technical effects and advantages of the high-precision roller screw ultra-precision grinding and contour accuracy control system of the present invention are as follows:

[0023] The high-precision roller screw ultra-precision grinding and contour accuracy control system of the present invention obtains the axial stiffness distribution and the axial position of the grinding head through a stiffness confirmation module and finds the corresponding equivalent stiffness value; the parameter acquisition module collects load signals and workpiece deflection during grinding, converts the deflection into elastic deformation force based on the equivalent stiffness value, and subtracts it from the load signal to obtain the actual grinding contact force; the parameter adjustment module uses the support reaction force of each support point to check and correct the actual grinding contact force, calculates the grinding force deviation in combination with the preset target contact force, and then generates real-time grinding parameter adjustment values ​​based on the equivalent stiffness value; the initial grinding module corrects the grinding head feed in real time according to the adjustment value to complete the initial grinding; the fine grinding module obtains the contour error distribution after the initial grinding, forms updated grinding control parameters, and performs fine grinding.

[0024] This invention constructs a complete grinding precision control process through the collaborative work of multiple modules. It effectively solves problems such as the dynamic change of the measured load and the actual contact pressure transmission relationship in the grinding zone during the grinding of long and slender structure lead screws, the segmented correlation of contour error caused by inaccurate removal function, repeated errors near the support point and in the deflection change area, and overcompensation and undercompensation. It improves the consistency of lead screw contour precision, ensures that the finished lead screw meets the sub-micron precision requirements, improves the yield of mass production, reduces rework and scrap costs, shortens the production cycle, and makes the processed lead screw more stable in transmission precision, less noisy, and longer in service when installed. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the ultra-precision grinding and contour accuracy control system for a high-precision roller screw according to an embodiment of the present invention.

[0026] Figure 2 This is an execution flowchart of the ultra-precision grinding and contour accuracy control system for a high-precision roller screw according to an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be described in detail, clearly, and completely below with reference to the accompanying drawings. It should be particularly noted that the specific embodiments below are only used to better illustrate and explain the technical solutions of the present invention, and are intended to enable those skilled in the art to better understand and implement the present invention, and should not be construed as limiting the scope of protection of the present invention. Without departing from the spirit and substance of the present invention, those skilled in the art can modify, adjust, or make equivalent substitutions based on the content disclosed in the present invention, and these should all be considered within the scope of protection of the present invention.

[0028] Example 1:

[0029] Please see Figure 1 and Figure 2 As shown, this embodiment discloses an ultra-precision grinding and contour accuracy control system for high-precision roller screws, including a stiffness confirmation module, a parameter acquisition module, a parameter adjustment module, a preliminary grinding module, and a fine grinding module. Each module is connected by wires and / or wirelessly to realize data transmission.

[0030] The stiffness verification module is used to obtain the axial stiffness distribution and the axial position of the grinding head during the grinding process, and to find the equivalent stiffness value corresponding to the axial position in the axial stiffness distribution based on the axial position.

[0031] The axial position is provided by the CNC system and represents the axial coordinate value of the current position of the grinding head. The machine tool outputs the axial position in real time via an encoder or straight ruler, thus providing a positional reference for subsequent stiffness indexing and error compensation calculations without adding additional acquisition devices. The axial stiffness distribution characterizes the equivalent stiffness value of the workpiece at various positions along the axial direction. Its equivalent stiffness value K is a directional stiffness defined along the direction of the grinding contact force. The direction of the grinding contact force is the direction of the contact force component used by the CNC system for closed-loop compensation calculations, ensuring that the equivalent stiffness value K is consistent in direction with the subsequently acquired workpiece deflection D. To achieve directional consistency, in the pre-calibration test, the applied known transverse load and the measurement direction of the workpiece deflection D are both consistent with the direction of the grinding contact force, and are completed under the same clamping and support methods, so that the axial stiffness distribution can reflect the comprehensive equivalent stiffness formed by the workpiece itself and the support method.

[0032] The axial stiffness distribution can be obtained through finite element simulation analysis or pre-calibration tests. In the pre-calibration test, the workpiece is kept stationary before machining, and a known transverse load is applied at different axial positions while the corresponding displacement is measured. Based on this, the equivalent stiffness value at each axial position is calculated, forming the axial stiffness distribution. This calibration process can be completed during the trial production stage, thus avoiding impact on the batch production cycle. Considering that the grinding contact point moves along the axial position while deflection measurement is usually obtained at a fixed measuring point, in order to match the equivalent stiffness value K with the structural response at the grinding contact point, the control system pre-establishes a positional mapping relationship between the displacement of the fixed measuring point and the displacement of the contact point, and stores the mapping relationship in association with the axial position. During machining, the corresponding mapping relationship is called according to the real-time axial position, and the workpiece deflection D measured at the fixed measuring point is converted into the equivalent deflection of the contact point and then combined with the equivalent stiffness value K for calculation. This ensures that the use of the equivalent stiffness value K remains closed and feasible even when the measuring point and the contact point do not coincide.

[0033] Furthermore, changes in clamping and support preload, support clearance, and temperature rise drift can cause the equivalent stiffness value K to deviate from the pre-calibrated state. To ensure the applicability of the axial stiffness distribution in batch processing, the control system performs consistency detection on the workpiece deflection D and the equivalent force signal during the no-load stroke stage after each clamping. Based on this, a stiffness correction coefficient is introduced to the axial stiffness distribution for periodic calibration. The stiffness correction coefficient is calculated by applying a preset amplitude feed perturbation during the no-load stage and measuring the corresponding change in workpiece deflection D. This allows the axial stiffness distribution to be updated as a whole with the clamping and temperature rise state without changing its relative axial distribution shape, thereby reducing the contact force reconstruction error caused by the drift of the equivalent stiffness value K and improving the stability and consistency of error compensation calculation.

[0034] Using the real-time acquired axial position as an index, the equivalent stiffness value K corresponding to the axial position is found in the axial stiffness distribution. This allows the comprehensive stiffness of the workpiece in the shaft segment where the grinding head is currently located to be explicitly introduced into the subsequent calculation process. Since long, slender workpieces with lead screws exhibit differences in comprehensive flexibility along the axial direction under conditions of clamping at both ends or multi-point support, and these differences lead to different local deformations and contact states corresponding to the same load input, matching the axial stiffness distribution by axial position and obtaining the equivalent stiffness value K enables the weak-rigid region to establish a mechanical parameter basis consistent with the actual working conditions for the stiffness level of the current shaft segment. This provides the necessary prerequisite for subsequently converting workpiece deflection into elastic deformation force based on the equivalent stiffness value K and further reconstructing the actual grinding contact force. Correspondingly, the introduction of the equivalent stiffness value K can suppress the systematic deviation caused by assuming a fixed proportional relationship between the measured load and the actual contact pressure, so that the load feedback closed loop has a consistent mechanical interpretation and compensation scale at different axial positions, reducing the risk of overcompensation and undercompensation near the support point and in areas with significant deflection changes, and improving the convergence consistency and stability of the profile error along the axial direction.

[0035] The parameter acquisition module is used to acquire load signals and workpiece deflection during the grinding process, convert the workpiece deflection into elastic deformation force based on the equivalent stiffness value, and then subtract the elastic deformation force from the load signal to obtain the actual grinding contact force.

[0036] The load signal is acquired by using a current sensor mounted on the grinding machine spindle or feed axis to obtain real-time grinding load information, which serves as the data source for force feedback during the grinding process. This signal reflects the total force in the grinding zone. The workpiece deflection is acquired by deploying high-precision displacement sensors, such as laser displacement sensors, near locations where the workpiece is prone to bending. These sensors measure the minute bending deformation of the workpiece in the grinding zone in real time, obtaining the deflection data caused by the grinding force.

[0037] It is necessary to clarify the physical meaning and acquisition link of the load signal. The load signal is not a direct extraction of the raw current or servo load display value from the machine tool sensors. Instead, it is an equivalent force signal obtained by force equivalence conversion of the raw quantities output by the spindle current, feed axis servo load, power head force sensor, or table force measuring device. This gives it force dimension and directional significance in control calculations. Force equivalence conversion is achieved using conversion coefficients and zero-bias parameters obtained through calibration: Under the condition that the machine tool is in the same clamping and support state and no material removal occurs, a known calibration force is applied in the grinding contact direction and the raw output is collected simultaneously. A linear mapping relationship between the raw output and the known calibration force is established, and the conversion coefficients and zero-bias parameters are obtained. During machining, the raw output is converted into a load signal in real time using this linear mapping relationship. This ensures that subsequent mechanical calculations related to workpiece deflection D and equivalent stiffness value K have a consistent dimensional basis, and the fixed bias of the sensing link is eliminated in the form of zero-bias parameters to avoid bias errors being mistakenly introduced into compensation calculations as changes in contact state.

[0038] After obtaining the load signal with mechanical dimensions, the elastic deformation force is obtained by mapping the workpiece deflection D to the equivalent stiffness value K. The equivalent stiffness value K represents the comprehensive equivalent stiffness along the grinding contact direction at the current axial position, and the workpiece deflection D is the structural displacement response measured in the same direction. Both satisfy the restoring force relationship under the linear elastic approximation. Here, the elastic deformation force... Instead of being defined as a result of the grinding contact force, it is defined as the equivalent force component of the structural restoring force caused by the comprehensive compliance of the long, slender lead screw workpiece in the sensing link. Its physical meaning is the contribution of the structural restoring force that the CNC system needs to overcome to maintain a given feed position and relative pose. Based on this definition, under the same force direction and the same sign convention, the load signal can be decomposed into the superposition of the grinding zone contact force component and the structural restoring force component according to the quasi-static equilibrium relationship within the sampling period, i.e. Therefore, the actual grinding contact force is obtained by subtracting the elastic deformation force from the load signal. With clear measurement link criteria, it is possible to separate the structural compliance effects that vary significantly with axial position from the equivalent force feedback, thus enabling... This provides a more stable representation of the mechanical quantities corresponding to the actual contact pressure in the grinding zone, thereby avoiding misinterpreting force changes caused by structural deformation as changes in the material removal state, which could lead to incorrect compensation directions. It also lays the foundation for subsequent... The closed-loop adjustment provides a consistent control scale across the axial direction, thereby suppressing overcompensation in the weak rigid region and undercompensation in the strong rigid region, and improving the convergence consistency of the profile error along the axial direction.

[0039] The parameter adjustment module is used to obtain the support reaction force at each support point and use the support reaction force to check and correct the actual grinding contact force, so as to obtain the corrected actual grinding contact force. Based on the corrected actual grinding contact force and the preset target contact force, the grinding force deviation is calculated, and the real-time grinding parameter adjustment value is generated by combining the equivalent stiffness value.

[0040] After obtaining the actual grinding contact force, the support reaction force at each support point is read and consistency verification and correction are performed. The support reaction force is obtained by installing force sensors at the clamping points at both ends of the lead screw or at the middle support point to collect the support reaction force of each support position on the workpiece during the grinding process. By recording the support reaction force, the load distribution caused by the workpiece's flexibility can be understood. Specifically, the support reaction force is aligned with the load signal according to the sampling time, and the support reaction force at each support point is converted into a consistent force component in the direction corresponding to the load signal based on the force direction of the support point and the sensor installation direction. The resultant force of the support reaction force is then summed. Subsequently, during the time period when no grinding contact occurs, the corresponding load signal and the resultant force of the support reaction force are recorded based on the same axial position, and the baseline offset is calculated. This baseline offset is used to characterize the steady-state offset introduced by non-grinding contact factors such as workpiece weight and coolant action in the sensing link. Then, during the grinding process, the consistency residual is calculated by subtracting the real-time support reaction force resultant force from the real-time load signal and subtracting the baseline offset. The consistency residual is used to determine whether the actual grinding contact force needs to be corrected. By utilizing the support system to directly observe the force distribution on the workpiece, the deviation of the actual grinding contact force caused by sensor proportional drift, changes in support gap, or changes in liquid film bearing capacity is constrained. This improves the estimation of the actual grinding contact force from single-channel inference to inference under multi-channel consistency constraints, thereby enhancing the reliability and stability of the contact force reconstruction.

[0041] When the absolute value of the consistency residual exceeds the consistency threshold over multiple consecutive sampling periods, correction is deemed necessary. The consistency threshold is adaptively determined based on the noise level of the current control loop. Specifically, the standard deviation of the consistency residual is calculated within the sliding time window, and the consistency threshold is derived accordingly. This allows the threshold to dynamically adjust with changes in measurement noise, avoiding unnecessary corrections triggered by instantaneous noise. When the correction condition is met, the actual grinding contact force is adjusted. The adjustment value is the weighted value of the consistency residual after verification weighting coefficients. These verification weighting coefficients are determined based on the fluctuation levels of the load signal and support reaction force within the sliding time window, giving higher weight to data with smaller fluctuations and higher stability during correction.

[0042] Taking a continuous data stream as an example, the dispersion of the consistency residual sequence within the sliding time window corresponds to a consistency threshold of 6N (Newtons). In the subsequent five sampling periods, the absolute values ​​of the consistency residuals are 7N, 8N, 9N, 8N, and 7N, respectively, satisfying the condition that the consistency threshold is exceeded for five consecutive sampling periods, thus requiring correction. Within this sliding time window, the load signal fluctuation amplitude is 12N, and the support reaction force fluctuation amplitude is 5N. Therefore, the support reaction force corresponds to a higher verification weight coefficient, which is set to 0.7. Based on this verification weight coefficient, the target adjustment amount after weighting the consistency residuals is 6N. However, due to the constraint of the maximum change, the actual grinding contact force is adjusted by 2N in the first sampling period, then by 2N in the second sampling period, and then by 2N in the third sampling period. After a cumulative adjustment of 6N, the consistency residuals fall back to 3N and are below the consistency threshold. The control system then exits the adjustment state and continues subsequent compensation control. This fine-tuning ensures that the corrected actual grinding contact force is consistent with the observed support force in a statistical sense, thereby offsetting the bias effect of non-grinding contact factors such as workpiece weight and coolant action on the contact force estimation, reducing the contact force estimation error near the support point and in areas with significant deflection changes, and improving the stability and consistency of contact force-based compensation control across the entire axial range.

[0043] Preset target contact force The ideal grinding force level, determined based on process experiments or historical stable production conditions, is used to characterize the desired contact state while meeting surface integrity and material removal efficiency requirements. Grinding force deviation is calculated. This allows the deviation of the current contact state of the grinding zone from the target state to be quantified into a single control deviation signal, thereby providing a unified closed-loop driving quantity for the real-time correction of subsequent grinding process parameters.

[0044] Real-time grinding parameter adjustment values ​​are generated based on the sign and amplitude of the preset target contact force. These values ​​are used at least for real-time correction of the feed rate and can optionally be used for synchronous correction of the depth of cut. Specifically, the grinding force deviation is mapped to a feed compensation amount, ensuring that the feed compensation amount and the grinding force deviation maintain a monotonic relationship in the same direction. The amplitude of the feed compensation amount is limited within a preset allowable range by saturation constraints to avoid overcorrection caused by transient disturbances. The feed compensation amount is updated on a sampling period of 10 milliseconds, and the feed rate change ratio of a single update is limited to ±5% of the original planned feed rate, while the cumulative change ratio is limited to ±20% of the original planned feed rate. This ensures a fast closed-loop response while reducing the impact of frequent and large changes in feed rate on the machining process.

[0045] When the grinding force deviation is greater than 0, it indicates that the actual grinding contact force is lower than the preset target contact force, the true contact pressure in the grinding zone is insufficient, and the material removal is too small. The feed compensation is set to a positive value, and the feed rate is increased to increase the contact strength in the grinding zone and improve material removal, causing the actual grinding contact force to converge towards the preset target contact force. The feed rate is increased using a graded proportional adjustment mechanism: when the absolute value of the grinding force deviation does not exceed 5% of the preset target contact force, the feed rate is increased by 2%; when the absolute value of the grinding force deviation is greater than 5% but not more than 10% of the preset target contact force, the feed rate is increased by 4%; when the absolute value of the grinding force deviation is greater than 10% of the preset target contact force, the feed rate is increased by 5%, and is constrained by the feed rate change ratio of each update. By increasing the feed rate in stages according to the deviation amplitude, the material removal in the grinding zone increases with the degree of deviation, prompting the actual grinding contact force to return to the preset target contact force, while avoiding compensation overshoot caused by excessively high feed increments under small deviation conditions.

[0046] When the grinding force deviation is less than 0, it indicates that the actual grinding contact force is higher than the preset target contact force, suggesting a tendency for cutting overload and a high risk of local overcutting. Therefore, the feed compensation is set to a negative value, and the feed rate is reduced. The feed rate reduction also employs a graded proportional adjustment mechanism: when the absolute value of the grinding force deviation does not exceed 5% of the preset target contact force, the feed rate is reduced by 2%; when the absolute value of the grinding force deviation is greater than 5% but not more than 10% of the preset target contact force, the feed rate is reduced by 4%; and when the absolute value of the grinding force deviation is greater than 10% of the preset target contact force, the feed rate is reduced by 5%, and is constrained by the feed rate change ratio of each update. By reducing the feed rate in stages according to the deviation amplitude, the amount of material removed from the grinding zone decreases with the degree of deviation, prompting the actual grinding contact force to return to the preset target contact force and reducing the risk of cumulative deviation in material removal due to excessively high contact force. Through the above-mentioned unidirectional adjustment mechanism, the actual grinding contact force fluctuates stably around the preset target contact force, avoiding the long-term accumulation of contact force deviation into segmented drift of profile error, thus directly contributing to suppressing overcompensation and undercompensation of the long and slender lead screw along the axial direction.

[0047] To eliminate the torsional effect of the axial comprehensive flexibility difference of long and slender workpieces on the compensation amplitude, the feed compensation amount is calculated in conjunction with the equivalent stiffness value K. The proportional coefficient that maps the grinding force deviation to the feed compensation amount is adaptively adjusted with the change of the equivalent stiffness value K. The proportional coefficient is defined as the compensation gain coefficient, which is used to characterize the change in feed compensation amount corresponding to a unit grinding force deviation. This allows different axial positions to obtain a feed correction amplitude that matches their mechanical constraints under the same grinding force deviation conditions, avoiding overcompensation of weak rigid shaft sections and undercompensation of strong rigid shaft sections caused by using a fixed compensation ratio.

[0048] Specifically, the minimum and maximum equivalent stiffness values ​​Kmin and Kmax are obtained based on the axial stiffness distribution statistics. A stiffness factor S is then calculated based on the equivalent stiffness value K, with the formula S = (K - Kmin) / (Kmax - Kmin). This stiffness factor characterizes the stiffness level of the current axial position relative to the entire axial stiffness range. When Kmax equals Kmin, the stiffness factor is set to 0.5 to avoid a denominator of 0 and to maintain scheduling continuity. A stiffness threshold of 0.5 is set to ensure a balanced division between weak and strong stiffness regions on the normalized scale and to be insensitive to extreme stiffness points. Regions with a stiffness factor less than 0.5 are classified as weakly stiff, while those with a stiffness factor greater than or equal to 0.5 are classified as strongly stiff.

[0049] In the weakly rigid region, the workpiece is more prone to elastic deformation, and the same feed correction is more likely to cause abrupt changes in the contact state. To limit the compensation amplitude and suppress overcompensation in the weakly rigid region, the control system achieves compressed scheduling of the feed compensation amount by reducing the compensation gain coefficient. Specifically, the grinding force deviation is... Mapped to feed compensation amount When adopted The compensation gain coefficient G(K) is limited to between Gmin and Gmax, where Gmin and Gmax are the minimum and maximum possible values ​​of the compensation gain coefficient, respectively, and Gmax is determined based on the machine tool's dynamic capabilities as the maximum allowable feed compensation amount within a single sampling period. Deviation from the maximum allowable grinding force The ratio, Gmin is taken as To ensure that the compensation gain coefficient in the weakly rigid region is significantly lower than that in the strongly rigid region and to avoid excessive sensitivity of the compensation amount to elastic deformation, a stiffness threshold is set to 0.5, and the compensation gain coefficient is linearly adjusted using a stiffness factor. When the stiffness factor is less than 0.5, the compensation gain coefficient is set to... ,in The intermediate possible values ​​for the compensation gain coefficient are: This causes the compensation gain coefficient in the weak rigid region to converge toward Gmin as the stiffness factor decreases, and the absolute value of the feed compensation decreases as the stiffness factor decreases. This quantitatively compresses the compensation in the weak rigid region, reducing the risk of overcompensation caused by excessive compensation near the support point and in areas with significant deflection changes.

[0050] In the rigid region, due to the smaller impact of structural deformation and the more predictable effect of the same feed correction on the contact state, the control system amplifies the feed compensation by increasing the compensation gain coefficient to improve the convergence speed of grinding force deviation and suppress undercompensation, in order to improve the convergence speed of grinding force deviation and suppress undercompensation. When the stiffness factor is greater than or equal to 0.5, the compensation gain coefficient is set to... This design allows the compensation gain coefficient to converge towards Gmax as the stiffness factor increases, and also increases the absolute value of the feed compensation amount with increasing stiffness factor. This quantitatively enhances the compensation amount in the strong rigidity region, reducing the risk of undercompensation due to insufficient material removal in the strong rigidity shaft section. By scheduling the compensation gain coefficient based on the equivalent stiffness value K, the feed correction at different axial positions has a consistent mechanical scale, avoiding overcompensation in the weak rigidity shaft section and undercompensation in the strong rigidity shaft section when using a fixed compensation ratio. This improves the convergence consistency and stability of the profile error along the axial direction.

[0051] The initial grinding module is used to correct the feed rate of the grinding head at the corresponding axial position in real time based on the real-time grinding parameter adjustment value, and to complete the initial grinding.

[0052] Will The feed control module of the CNC grinding machine is used to correct the feed amount of the grinding head at the current axial position in real time, thereby forming a machine tool feed command stream after real-time compensation. Specifically, when generating the feed command for the current position, the CNC grinding machine reads the corresponding... This is then superimposed on the original planned feed command to obtain a compensated feed command, causing the actual feed amount of the grinding head at that axial position to differ from the original planned feed amount. Adjusting in the same direction changes the instantaneous contact state between the grinding wheel and the workpiece, and corrects the material removal amount in real time; when the CNC grinding machine uses the depth of cut as the feed control value, the feed control module will... The new cutting depth is obtained by superimposing the new depth of cut onto the original planned depth of cut, and the grinding head is then driven to execute the compensated cutting depth trajectory accordingly. As the grinding head moves continuously along the workpiece axis, the CNC grinding machine repeats the process according to the sampling cycle. Superposition and command update enable the compensated feed command to change dynamically with the axial position, thereby continuously converging the actual grinding contact force along the axial direction towards the preset target contact force and maintaining it within the allowable fluctuation range. This reduces the spatial distortion of material removal caused by differences in axial comprehensive compliance and suppresses the segmented accumulation of contour error.

[0053] The fine grinding module is used to obtain the contour error distribution of the workpiece after the initial grinding, form updated grinding control parameters based on the contour error distribution, and use the updated grinding control parameters to perform fine grinding on the workpiece to obtain the finished ball screw.

[0054] The method for obtaining the contour error distribution is as follows: Using an online measuring device, such as a laser contour scanner or stylus measuring system mounted on a machine tool, the contour of the spiral groove is scanned along the lead screw axis after grinding to obtain contour error data for each axial position of the workpiece. The contour error distribution reflects the deviation of the actual machined contour from the design requirements. After the initial grinding, the online measuring device is used to perform contour detection on the workpiece to obtain the contour error distribution along the axial direction. The contour error distribution is then compared with the design contour to determine the out-of-tolerance axial region. Specifically, the online measuring device outputs contour error values ​​corresponding to the axial position according to a preset axial sampling interval. The contour error values ​​are arranged into an error sequence according to the axial position, and the contour error distribution is calculated based on the target contour value of the design contour at the corresponding axial position. Subsequently, the absolute value of the contour error distribution is compared with the out-of-tolerance threshold. When the absolute value is greater than the out-of-tolerance threshold, the axial position is determined to belong to the out-of-tolerance axial region. The out-of-tolerance threshold is set to 0.5 of the maximum allowable error based on the design tolerance requirements. When the maximum allowable error is 10 micrometers, the out-of-tolerance threshold is set to 5 micrometers. This allows the out-of-tolerance judgment to expose residual errors in advance while meeting the design tolerance, and to reserve compensation margin for finishing and grinding. This avoids insufficient or delayed compensation caused by triggering correction only when the tolerance limit is approached.

[0055] Taking a lead screw workpiece with an axial length of 1200 mm as an example, the online measuring device outputs 1201 data points for axial positions, increasing from 0 mm to 1200 mm. The contour error value is the deviation of the actual machined contour from the design contour, expressed in micrometers. The contour error values ​​at axial positions of 0 mm, 100 mm, 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, 700 mm, 800 mm, 900 mm, 1000 mm, 1100 mm, and 1200 mm are 2 micrometers, 3 micrometers, 4 micrometers, 6 micrometers, 7 micrometers, 5 micrometers, 3 micrometers, 2 micrometers, 4 micrometers, 6 micrometers, 5 micrometers, 3 micrometers, and 2 micrometers, respectively. The online measuring device arranges the contour error values ​​of all data points along the entire axis into an error sequence according to their axial positions, obtaining the contour error distribution. After obtaining the contour error distribution, it is aligned and compared with the design contour to determine the out-of-tolerance axial region. Taking the aforementioned data as an example, the profile error value at an axial position of 300 mm is 6 micrometers, the profile error value at an axial position of 400 mm is 7 micrometers, the profile error value at an axial position of 500 mm is 5 micrometers, and the profile error value at an axial position of 900 mm is 6 micrometers. The absolute value of the profile error distribution corresponding to the above axial positions is greater than 5 micrometers. Therefore, the control system determines the axial positions corresponding to 300 mm to 400 mm and 900 mm as out-of-tolerance axial regions and outputs the out-of-tolerance axial regions to generate a compensation correction list.

[0056] After identifying the out-of-tolerance axial region, the error value corresponding to the out-of-tolerance axial region is converted into the amount of material to be removed to generate a compensation correction list. The material removal amount is taken as the inverse vector of the error value and quantified according to the resolution of the machine tool feed axis, so that the subsequent finishing grinding can add or reduce the material removal amount at the corresponding axial position to offset the residual error. Adjacent and consecutive out-of-tolerance axial positions are merged into the same out-of-tolerance axial region, and the starting axial position, ending axial position and corresponding material removal amount are recorded for each out-of-tolerance axial region to improve the executability of the compensation correction list and reduce the frequency of CNC parameter updates.

[0057] Based on the compensation correction list, axial segmented compensation settings for finishing grinding are generated, and a process correction plan for secondary grinding is formulated accordingly. Specifically, the starting axial position, ending axial position, and material removal amount corresponding to each out-of-tolerance axial region in the compensation correction list are read, and the material removal amount is converted into a compensation amount that needs to be superimposed on the original planned machining command during the finishing grinding stage. The compensation amount includes feed rate correction amount and depth of cut correction amount. The feed rate correction amount is the increment or decrement superimposed on the original planned feed rate during finishing grinding, in millimeters per minute, used to change the material removal amount by changing the relative motion per unit time. The depth of cut correction amount is the increment or decrement superimposed on the original planned cutting depth during finishing grinding, in micrometers, used to change the material removal amount by changing the radial relative position of the grinding wheel and the workpiece. The material removal amount is mapped to the feed rate correction amount and the depth of cut correction amount in the same direction. When the material removal amount requires additional removal, the feed rate correction amount is set to decrease the feed rate or the depth of cut correction amount is set to increase the depth of cut. When the material removal amount requires reduced removal, the feed rate correction amount is set to increase the feed rate or the depth of cut correction amount is set to decrease the depth of cut. This allows the finishing grinding to produce a material removal change that cancels out the residual error at the corresponding axial position.

[0058] To ensure the stability and feasibility of CNC execution, the feed rate correction or depth of cut correction is quantized according to the resolution of the machine tool's feed axis, and adjacent and continuous out-of-tolerance axial regions are merged to reduce the number of compensation segments and avoid trajectory jitter caused by frequent switching. Simultaneously, a transition segment length is set for each out-of-tolerance axial region, allowing the compensation amount to change continuously with a linear ramp when entering and exiting the out-of-tolerance axial region, thereby avoiding transient load impacts and local overcutting caused by abrupt changes in feed or depth of cut commands. The transition segment length is determined based on the machine tool's acceleration constraints as the minimum axial distance required to achieve the compensation amount change under given acceleration constraints, ensuring that the compensation trajectory meets the machine tool's dynamic performance and reduces the impact on production cycle time. After completing the above mapping, quantization, merging, and continuous processing, the axial position range and compensation amount corresponding to each out-of-tolerance axial region are written into the CNC program or compensation table to form updated grinding control parameters, enabling the CNC system to automatically call the corresponding compensation amount according to the axial position during finishing grinding.

[0059] The CNC grinding machine performs finish grinding based on updated grinding control parameters. During the axial movement of the grinding head, the CNC system calls the corresponding axial segment compensation setting according to the real-time axial position. This axial segment compensation setting is superimposed on the original planned feed command or the original planned cutting depth command, enabling the grinding head to achieve targeted material removal adjustments in each out-of-tolerance axial region and to continuously change the compensation amount within the transition section to maintain machining stability. Simultaneously, during the finish grinding process, load signals and workpiece deflection are continuously acquired, and actual grinding contact force calculations and real-time corrections are performed. This gives the finish grinding not only feedforward segment compensation capabilities based on the compensation correction list but also closed-loop adaptive capabilities based on actual grinding contact forces. This eliminates residual contour errors while suppressing compensation mismatch caused by differences in axial overall compliance. Through the synergy of feedforward segment compensation and closed-loop real-time correction, the risks of overcompensation and undercompensation near support points and in areas with significant deflection changes can be reduced, improving the convergence consistency of contour errors along the axial direction and enhancing consistency and stability in batch production.

[0060] The final product is a finished ball screw with a profile accuracy that meets the submicron level requirements. The profile error along the axial direction is corrected and consistent, so that the profile accuracy of the ball screw helical groove meets the design standards and improves the yield rate of mass production.

[0061] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0062] In conclusion, the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision roller screw ultra-precision grinding and contour accuracy control system, characterized in that, include: The stiffness verification module is used to obtain the axial stiffness distribution and the axial position of the grinding head during the grinding process, and to find the equivalent stiffness value corresponding to the axial position in the axial stiffness distribution based on the axial position. The parameter acquisition module is used to acquire load signals and workpiece deflection during the grinding process, convert the workpiece deflection into elastic deformation force based on the equivalent stiffness value, and then subtract the elastic deformation force from the load signal to obtain the actual grinding contact force. The parameter adjustment module is used to acquire the support reaction force at each support point and use the support reaction force to check and correct the actual grinding contact force, thus obtaining the corrected actual grinding contact force. Based on the corrected actual grinding contact force and the preset target contact force, the grinding force deviation is calculated, and the real-time grinding parameter adjustment value is generated by combining the equivalent stiffness value. The support reaction force is aligned with the load signal according to the sampling time, and the support reaction force at each support point is converted into a force component consistent with the direction of the load signal according to the force direction of the support point and the sensor installation direction, and then summed to obtain the resultant force of the support reaction force. During the time period when no grinding contact occurs, the corresponding load signal and the resultant force of the support reaction force are recorded based on the same axial position, and the baseline offset is calculated. During the grinding process, the consistency residual is calculated by subtracting the resultant force of the real-time support reaction force from the real-time load signal and deducting the baseline offset. The consistency residual is used to judge the rationality of the actual grinding contact force. When the absolute value of the consistency residual exceeds the consistency threshold in multiple consecutive sampling periods, it is determined that correction is required. When the correction condition is met, the actual grinding contact force is adjusted. The adjustment amount is the value of the consistency residual after being weighted by the verification weight coefficient, where the verification weight coefficient is determined based on the fluctuation level of the load signal and the support reaction force within the sliding time window. The initial grinding module is used to correct the feed rate of the grinding head at the corresponding axial position in real time according to the real-time grinding parameter adjustment value, and to complete the initial grinding. The fine grinding module is used to obtain the contour error distribution of the workpiece after the initial grinding, form updated grinding control parameters based on the contour error distribution, and use the updated grinding control parameters to perform fine grinding on the workpiece to obtain the finished ball screw.

2. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 1, characterized in that, By using the equivalent stiffness value to perform a mechanical dimension conversion on the workpiece deflection, the elastic deformation effect caused by the comprehensive flexibility of the long and slender lead screw workpiece at the current axial position is mapped from the displacement domain to the force domain, thus obtaining the elastic deformation force.

3. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 1, characterized in that, The grinding force deviation is mapped to the feed compensation amount, so that the feed compensation amount and the grinding force deviation maintain a monotonic relationship in the same direction, and the amplitude of the feed compensation amount is limited to a preset allowable range by saturation constraint.

4. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 3, characterized in that, When the grinding force deviation is greater than 0, the feed compensation is set to a positive value and the feed is increased to increase the contact strength in the grinding zone and improve the material removal rate, so that the actual grinding contact force converges to the preset target contact force. When the grinding force deviation is less than 0, the feed compensation is set to a negative value and the feed is reduced to reduce the contact strength in the grinding zone and suppress the amount of material removed, so that the actual grinding contact force converges to the preset target contact force.

5. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 4, characterized in that, There is a linear mapping relationship between the feed compensation amount and the grinding force deviation, and the proportional coefficient of the linear mapping relationship is adaptively adjusted as the equivalent stiffness value changes. The proportional coefficient is defined as the compensation gain coefficient, which is used to characterize the change in feed compensation corresponding to a unit grinding force deviation.

6. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 5, characterized in that, The minimum and maximum values ​​of the equivalent stiffness are obtained based on the axial stiffness distribution statistics. The equivalent stiffness values ​​are then normalized to obtain the stiffness factor. The stiffness factor is used to characterize the stiffness level of the current axial position relative to the entire axial stiffness range. When the stiffness factor is lower than the stiffness threshold, it is determined to be a weakly stiff region. When the stiffness factor is higher than the stiffness threshold, it is determined to be a strongly stiff region.

7. The ultra-precision grinding and contour accuracy control system for high-precision roller screws according to claim 6, characterized in that, In the weakly rigid region, the compensation gain coefficient is reduced according to the set reduction ratio, so that the absolute value of the feed compensation decreases as the stiffness factor decreases, thereby suppressing overcompensation; in the strongly rigid region, the compensation gain coefficient is increased according to the set increase ratio, so that the absolute value of the feed compensation increases as the stiffness factor increases, thereby suppressing undercompensation.

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