A cam grinding lift error compensation method based on active axis position

Abstract

This invention belongs to the field of CNC machining technology and discloses a method for compensating the lift error in CNC cam grinding based on the position of the drive axis. The method includes the following steps: S1. Acquire the actual contour or lift data of the cam after machining, calculate the actual displacement sequences of the C-axis and X-axis controlling the relative motion between the cam and the grinding wheel during grinding, and calculate the displacement error sequence; S2. Based on the hysteresis characteristics of the machine tool's C-axis and X-axis response, correct the C-axis coordinates in the displacement error sequence to obtain the C-axis coordinate sequence; calculate the X-axis compensation value sequence; the C-axis coordinate sequence and the X-axis compensation sequence form the displacement compensation sequence; S3. Use the displacement compensation sequence to compensate for the preset theoretical displacement sequence, and use the compensated displacement sequence to machine the cam. This invention solves the problems of complex online control parameters, limited accuracy of error back-superposition compensation, and reliance on experience for trial cutting and adjustment in existing cam machining error compensation methods.

Description

Technical Field

[0001] This invention belongs to the field of CNC machining technology, and more specifically, relates to a method for compensating for CNC cam grinding lift error based on the position of the drive shaft. Background Technology

[0002] Cams are crucial components in automotive engines, textile machinery, and packaging machinery. Currently, the primary cam grinding method is XC-axis linkage grinding, where the C-axis acts as the driving axis, rotating the camshaft workpiece along its axial direction. The X-axis, as the driven axis, drives the grinding wheel to move closer to or away from the cam according to the X-axis displacement corresponding to the C-axis angle. During this process, the envelope trajectory of the grinding wheel is the cam's forming trajectory. However, in actual cam grinding, due to the complex cam profile and numerous influencing parameters, the process heavily relies on operator experience. Most machining solutions are based on "experience" and "trial cutting," resulting in low efficiency and inconsistent final machining accuracy.

[0003] Common cam machining error compensation techniques can be divided into two types: online control and offline compensation.

[0004] Online control involves real-time feedback compensation of the machining process based on sensor data during CNC machine tool operation. For example, in patent application CN201210073867.0, entitled "Three-Axis Linkage Contour Error Compensation Control Method for Cylindrical Cam Machining," the contour error between the actual position of the worktable detected by the sensor and the tool trajectory of the cylindrical cam contour line is calculated in a spatial rectangular coordinate system at each sampling cycle. This error is then converted to the machine tool coordinate system, and a scaling factor is introduced to obtain the contour error compensation amount for each axis. This compensation is then superimposed with a certain scaling coefficient and input to the servo actuators of each axis for contour error compensation control, thereby achieving online real-time compensation of contour errors. However, this method requires real-time conversion and calculation of compensation values ​​in each sampling cycle, placing high demands on the real-time computing capabilities of the CNC system.

[0005] Offline compensation involves compensating for actual errors in the workpiece during the next machining cycle. For example, the operator might use the lift error detected after cam machining to approximately superimpose it onto the cam lift curve, make local adjustments based on experience, and then regenerate the machining G-code for compensation. However, this method requires the operator to perform multiple trial cuts and adjust the G-code until the machining result meets the cam accuracy requirements. This method involves multiple trial cuts, is time-consuming, and relies heavily on the operator's experience.

[0006] For example, in the patent application CN201510157673.2 entitled "A CNC Cam Grinding Contour Error Compensation Control Method Based on Cycle to Cycle Feedback Control," the grinding information from the previous cycle, i.e., the contour error, is used to guide the grinding process of the current cycle between successive cycle control steps, taking into account the repetitive motion cycle characteristic of the cam machining process. This ensures that the grinding contour error is controlled within an allowable range, resulting in satisfactory grinding accuracy. Although this method solves the current situation of compensation based on experience, contour error measurement is required between each grinding cycle to update the CtC feedback controller parameters, making the process relatively complex and time-consuming. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method for compensating for the lift error in CNC cam grinding based on the position of the drive shaft. This method solves the problems of existing cam machining error compensation methods, such as the high requirements for the real-time computing power of the CNC system in online real-time compensation methods, the long time consumption of multiple trial cuts in offline compensation methods and reliance on the operator's experience, and the complexity and time consumption of CtC feedback control methods.

[0008] To achieve the above objectives, according to the present invention, a method for compensating for the lift error in CNC cam grinding based on the position of the drive shaft is provided, the method comprising the following steps:

[0009] S1 collects the actual contour or lift data of the cam after machining, calculates the actual displacement sequence of the C-axis and X-axis that control the relative motion between the cam and the grinding wheel during the grinding process, and uses the actual displacement sequence and the preset theoretical displacement sequence to calculate the displacement error sequence.

[0010] S2 corrects the C-axis coordinates in the displacement error sequence based on the C-axis and X-axis response hysteresis characteristics of the machine tool to obtain the C-axis coordinate sequence; the X-axis compensation value sequence is calculated from the X-axis displacement error sequence in the displacement error sequence; the C-axis coordinate sequence and the X-axis compensation index sequence form the displacement compensation sequence;

[0011] S3 uses the displacement compensation sequence obtained in step S2 to compensate the preset theoretical displacement sequence in step S1, and uses the displacement sequence obtained after compensation to process the cam.

[0012] More preferably, after step S2, the coordinate compensation sequences corresponding to the C-axis and X-axis respectively need to be subjected to amplitude limiting and filtering processing.

[0013] More preferably, in step S1, the displacement error sequence is performed according to the following relationship:

[0014] C error =C cmd

[0015] X error =X actnew -X cmd

[0016] Among them, C error X error These represent the C-axis rotation coordinate sequence and the X-axis displacement error sequence, respectively; C cmd X cmd These represent the C-axis rotation coordinate sequence and the X-axis displacement sequence in the theoretical displacement sequence, respectively; X actnew Representing the actual displacement sequence in C cmd The new actual displacement sequence of the X-axis is obtained after interpolation calculation of the new C-axis rotation coordinates.

[0017] More preferably, in step S2, the C-axis coordinate sequence is performed according to the following relationship:

[0018] C comp1 =C error +ΔC

[0019] Among them, C comp1 Represents the C-axis coordinate sequence, C error Let C represent the C-coordinate sequence in the displacement error sequence, and ΔC represent the correction sequence from the C-coordinate in the displacement error sequence to the C-coordinate in the displacement compensation sequence.

[0020] More preferably, the correction sequence ΔC is performed according to the following relationship:

[0021] ΔC=(T C -T X )*V C

[0022] Among them, T C T represents the C-axis response lag time. X V represents the X-axis response lag time. C This indicates the C-axis rotation speed corresponding to the current C-axis coordinate.

[0023] More preferably, in step S2, the X-axis compensation value sequence is performed according to the following relationship:

[0024] X comp1 =-k*X error

[0025] Where k represents the compensation coefficient, X comp1 Represents the X-axis compensation value sequence, X error This represents the X-axis displacement error sequence in the displacement error sequence.

[0026] More preferably, in step S1, after obtaining the actual displacement sequence of the C-axis and X-axis, the actual displacement sequence needs to be interpolated to align it with the preset displacement sequence.

[0027] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0028] 1. This invention provides targeted compensation based on the dynamic response characteristics of the machine tool itself. Its compensation accuracy is higher than that of compensation methods that rely on human experience. It uses various data reflecting cam machining errors, and the output of the driven axis compensation based on the position of the driving axis can be applied to cam machining compensation in various forms. Compared with existing methods that are tied to specific detection devices or internal control parameters of the machine tool, it is more flexible, easier to adapt to various machining and detection schemes, and can be widely promoted.

[0029] 2. This invention takes into account the characteristic that the driven shaft follows the driving shaft during the XC linkage machining process of the cam. It utilizes the cam profile or lift data after machining and the dynamic response characteristics of the machine tool to calculate the driven shaft compensation value sequence with the driving shaft position as the index coordinate according to the compensation strategy. This compensation value sequence can be applied in various ways in subsequent cam machining, thereby effectively reducing the final machining lift error of the cam.

[0030] 3. This invention compensates for the lift error in CNC cam grinding, reducing the reliance on operator experience during cam machining and reducing material, labor, and time costs; it does not restrict the source of error data, and the application method of the output compensation sequence is unlimited; moreover, it has a higher compensation upper limit for calculating compensation values ​​based on the dynamic characteristics of the machine tool, and it is simple to operate and easy to promote. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of a CNC cam grinding lift error compensation method based on the position of the drive shaft, constructed according to a preferred embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the data at each stage in the process of calculating compensation value based on electronic control data according to a preferred embodiment of the present invention, wherein (a) is the theoretical displacement sequence and the actual displacement sequence, (b) is the displacement error sequence, (c) is the C-axis rotation speed sequence, and (d) is the displacement compensation sequence;

[0033] Figure 3 The diagram shows the effect before and after compensation of the cam using machine tool electronic control data according to a preferred embodiment of the present invention. (a) shows the theoretical profile of the cam, the actual profile of the cam before compensation, and the actual profile of the cam after compensation. (b) shows the cam lift error before compensation and the cam lift error after compensation.

[0034] Figure 4 The diagram shows the effect before and after compensation of the cam using data from a cam lift measuring instrument, constructed according to a preferred embodiment of the present invention. (a) shows the theoretical profile of the cam, the actual profile of the cam before compensation, and the actual profile of the cam after compensation. (b) shows the cam lift error before compensation and the cam lift error after compensation. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for compensating for the lift error in CNC cam grinding based on the position of the drive shaft. First, a trial cut of the cam is performed to obtain data reflecting the actual contour of the cam after grinding. The data is then processed to obtain the cam CX grinding displacement error sequence. The basic process is as follows:

[0037] S1 obtains the CX displacement error sequence

[0038] (1) The actual lift data (θ, L) of the cam after machining is collected using a cam lift measuring instrument. The lift-lift conversion formula f(R) in the reference is used to convert the lift data to the lift data. b R r R w The actual displacement sequence (C, θ, L) is calculated. act X act ), where the base circle radius R b =17mm, follower radius R r = 8.5mm, grinding wheel radius R w =220mm.

[0039] (2) The actual displacement sequence (C) act X act C is obtained by aligning using interpolation. cmd The actual displacement sequence after interpolation (C) is obtained cmd X newact ), and the theoretical displacement sequence (C) set in the cam machining process. cmd X cmd The displacement error sequence (C) is obtained by subtracting the values. error X error ), where C error =C cmd X error =Xactnew -X cmd The calculation results are as follows Figure 2 As shown.

[0040] Furthermore, (1) does not have strict requirements for the data reflecting the actual contour or actual lift of the cam after machining, but it needs to be able to accurately reflect the contour of the cam after machining, and the error between it and the actual contour of the cam should be within a reasonable range. Feasible data types include, but are not limited to, cam-specific testing instrument test data, CNC machine tool internal electrical control data, coordinate measuring machine test data, optical measuring instrument test data, etc.

[0041] Furthermore, in (2), there is no requirement for the actual displacement sequence and the theoretical displacement sequence to be aligned one-to-one on the C coordinate, but the displacement sequence must be able to truly reflect the theoretical and actual profiles of the cam. Under this premise, the one-to-one alignment of the actual grinding displacement sequence and the theoretical grinding displacement sequence on the C coordinate can be achieved by interpolation.

[0042] S2 obtains the coordinate compensation sequences corresponding to the C-axis and X-axis respectively.

[0043] After obtaining the displacement error sequence, simply adding the errors in reverse to the theoretical displacement sequence will result in a poor compensation effect due to the response lag caused by the inertia of each axis of the machine tool, deviating from the predetermined C-axis coordinate. Therefore, this method proposes a calculation method from the error sequence to the compensation value sequence, i.e., a compensation strategy, specifically for the machining characteristics of camshaft linkage. This compensation strategy includes processing the C-axis coordinate of the driving axis and processing the X-axis compensation value of the driven axis. The basic process is as follows:

[0044] (1) The response lag period T of the machine tool's C-axis and X-axis C T X And the C-axis speed sequence (C) set in the cam machining process v V c ) Calculate the C-axis coordinate sequence correction sequence ΔC from the error value to the compensation value. In this embodiment, T C =14ms, T X =13ms, obtained from the machine tool servo debugging report, C-axis speed sequence as follows: Figure 2 As shown, where C v C in the theoretical displacement sequence cmd Consistency, i.e., C v =C cmd The formula for calculating ΔC is ΔC=(T C -T X )*V C ;

[0045] Furthermore, there are no strict requirements for the C-axis and X-axis response hysteresis period parameters of the machine tool, but they must accurately reflect the hysteresis characteristics of the machine tool's C-axis and X-axis response. These parameters can be obtained, but are not limited to, from machine tool servo debugging reports or from analysis of CX-axis excitation response data under speed step signal input.

[0046] Furthermore, the distribution density of the C-axis rotation speed sequence on the C-axis cannot be too sparse, otherwise it will not be able to accurately reflect the C-axis rotation speed during cam machining.

[0047] (2) Based on the C coordinate sequence C in the error displacement sequence error The C-coordinate sequence C is used to calculate the initial compensation value sequence C in the C-axis coordinate correction sequence ΔC. comp1 Its calculation formula is C comp1 =C error +ΔC

[0048] (3) Set the compensation coefficient k, which is derived from the X-axis error sequence X in the displacement error sequence. error The X-axis compensation value sequence X in the initial compensation value sequence is calculated. comp1 Its calculation formula is X comp1 =-k*X error .

[0049] (4) In order to reduce the interference of high-frequency noise and outliers in the compensation value sequence on the machine tool motion control of cam grinding, the initial compensation value sequence (C) is further modified. comp1 X comp1 Amplitude limiting and filtering are performed to obtain the compensation value sequence (C). comp2 X comp2 In this embodiment, an upper limit for the compensation value abs(X) is set. comp1 )≤0.025mm, the filtering method is low-pass filtering with an upper limit of 200Hz, and the result is as follows Figure 2 As shown.

[0050] S3 Compensation Processing

[0051] After obtaining the grinding displacement compensation sequence, this compensation sequence can be applied to subsequent cam grinding processes in various ways. In this embodiment, it is superimposed on the theoretical displacement sequence, and the compensation result is as follows: Figure 3 As shown.

[0052] The application of compensation value sequences in the cam grinding process includes, but is not limited to, superimposing them into the theoretical displacement sequence, using the data interpolation module inside the CNC system to calculate the compensation value of the driven shaft corresponding to the current position of the driving shaft in real time and inputting it into the position control quantity of the driven shaft.

[0053] like Figure 2 As shown, for ease of description, the sub-figures are numbered (a)-(d) from top to bottom. Figure 2 In (a), the difference between the theoretical displacement sequence and the actual displacement sequence after interpolation alignment can be used to obtain the sub-displacement. Figure 2 The mid-displacement error sequence, combined with the C-axis and X-axis response lag time and Figure 2 From the C-axis rotational speed sequence and compensation coefficients in (c), the initial displacement compensation sequence can be obtained. After amplitude limiting and filtering, the sub-displacement compensation sequence can be obtained. Figure 2 The displacement compensation sequence of (d) in the middle.

[0054] like Figure 3 As shown, using electronic control data as the initial data source, and after compensation according to the method described in this invention, the cam lift error can be effectively reduced. The cam profile before and after compensation is as follows: Figure 3 As shown in (a), the lift error before and after compensation is as follows: Figure 2 As shown in (b)

[0055] like Figure 4 As shown, using the test results of a dedicated cam lift testing instrument as the initial data source, and after compensation according to the method described in this invention, the cam lift error can be effectively reduced. The cam profile before and after compensation is as follows: Figure 4 As shown in (a) and (b), the lift error before and after compensation is shown in the following sub-figures.

[0056] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for compensating for lift error in CNC cam grinding based on the position of the drive shaft, characterized in that, The method includes the following steps: S1 collects the actual contour or lift data of the cam after machining, calculates the actual displacement sequence of the C-axis and X-axis that control the relative motion between the cam and the grinding wheel during the grinding process, and uses the actual displacement sequence and the preset theoretical displacement sequence to calculate the displacement error sequence. S2 Based on the response hysteresis characteristics of the machine tool's C-axis and X-axis, the C-axis coordinates in the displacement error sequence are corrected to obtain the C-axis coordinate sequence; the X-axis compensation value sequence is calculated from the X-axis displacement error sequence in the displacement error sequence; the C-axis coordinate sequence and the X-axis compensation value sequence form a displacement compensation sequence. S3. The displacement compensation sequence obtained in step S2 is used to compensate the theoretical displacement sequence preset in step S1, and the cam is processed using the displacement sequence obtained after compensation. In step S2, the C-axis coordinate sequence is performed according to the following relationship: Corrected sequence Perform according to the following formula: The X-axis compensation value sequence is determined according to the following formula: in, Represents the C-axis coordinate sequence. This represents the C-coordinate sequence in the displacement error sequence. This represents the correction sequence from the C-coordinate in the displacement error sequence to the C-coordinate in the displacement compensation sequence. Indicates the C-axis response lag time. Indicates the X-axis response lag time. This indicates the C-axis rotation speed corresponding to the current C-axis coordinate. Indicates the compensation coefficient. Represents the X-axis compensation value sequence. This represents the X-axis displacement error sequence in the displacement error sequence.

2. The method for compensating for CNC cam grinding lift error based on the position of the drive shaft as described in claim 1, characterized in that, After step S2, the C-axis coordinate sequence and the X-axis compensation value sequence also need to be subjected to amplitude limiting and filtering.

3. A method for compensating for CNC cam grinding lift error based on the position of the drive shaft as described in claim 1 or 2, characterized in that, In step S1, the displacement error sequence is performed according to the following relationship: in, , These represent the C-axis rotation angle coordinate sequence and the X-axis displacement error sequence in the displacement error sequence, respectively. , These represent the C-axis rotation coordinate sequence and the X-axis displacement sequence in the theoretical displacement sequence, respectively. Indicates the actual displacement sequence as The new actual displacement sequence of the X-axis is obtained after interpolation calculation of the new C-axis rotation coordinates.

4. The method for compensating for CNC cam grinding lift error based on the position of the drive shaft as described in claim 1, characterized in that, In step S1, after obtaining the actual displacement sequence of the C-axis and X-axis, it is necessary to interpolate the actual displacement sequence to align it with the preset displacement sequence.

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