Thermal extension compensation method based on machine tool screw

Abstract

The invention relates to the technical field of machine tools, in particular to a machine tool screw rod-based thermal extension compensation method, which comprises the following steps of: acquiring a displacement reference value; collecting actual displacement values when the screw rotates at different moments; calculating a thermal extension value of the screw by using the displacement reference value and the displacement measured value; and calculating a compensation slope at the current moment by using the thermal extension value and the shaft travel value, and calculating a thermal extension compensation value at the next moment. The problem that efficiency and cost cannot be considered at the same time in an existing method is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of machine tools, and particularly relates to a thermal elongation compensation method based on a machine tool screw. Background Art

[0002] The transmission mechanism in the axial direction of a numerically controlled machine tool is mainly completed by a screw, which converts the rotational motion of the motor into a linear motion; and the screw is a slender member, and the temperature change has a great influence on it;

[0003] The axial control accuracy of the machine tool determines the accuracy of the machined product. Common methods to solve the influence of temperature on the screw include:

[0004] 1. Thermal machine: After the machine tool equipment is turned on, without machining the workpiece product, a thermal machine running-in program is carried out to make the temperature of the screw reach the thermal equilibrium state. After that, the thermal elongation of the screw will tend to be stable, and then the product machining is started;

[0005] 2. Install a grating scale and perform closed-loop control on the control axis. The grating scale is made of glass material, and its coefficient of thermal expansion is much smaller than that of the screw material;

[0006] 3. Perform constant temperature control on the screw, that is, cool the screw;

[0007] However, the thermal machine scheme reduces the production efficiency and the service life of the machine tool equipment; the cost of the scheme of installing a grating scale is high; and the constant temperature control system of the screw is complex. Summary of the Invention

[0008] Aiming at the deficiencies of the existing methods, the present invention compensates the stroke of the numerically controlled machine tool at different times by using the measured value of the displacement sensor, and reduces the influence of thermal elongation on the machining accuracy.

[0009] The technical solution adopted by the present invention is: a thermal elongation compensation method based on a machine tool screw includes the following steps:

[0010] Step 1: Obtain the displacement reference benchmark value;

[0011] Step 2: Collect the measured displacement values when the screw rotates at different times;

[0012] As a preferred embodiment of the present invention, a displacement sensor is used to measure the measured displacement value.

[0013] As a preferred embodiment of the present invention, the displacement sensor includes an eddy current displacement sensor.

[0014] As a preferred embodiment of the present invention, the machine tool of the screw includes: single-axis, three-axis, and five-axis.

[0015] Step 3: Calculate the thermal elongation value of the screw by using the displacement reference benchmark value and the measured displacement value;

[0016] As a preferred embodiment of the present invention, the formula for the thermal extension value is:

[0017] △L t =L t test -L r ;

[0018] Among them, L t test is the measured displacement value at time t, L r is the displacement reference value.

[0019] Step 4: Calculate the compensation slope at the current moment using the thermal extension value and the axis travel value, and use it to calculate the thermal extension compensation value at the next moment;

[0020] As a preferred embodiment of the present invention, the formula for the compensation slope is:

[0021] k t =△L t / L;

[0022] Among them, △L t is the thermal extension value at time t; L is the shaft travel value.

[0023] As a preferred embodiment of the present invention, the formula for the thermal extension compensation value is:

[0024] L t+1 b =X t+1 *tan(k t )*ɑ;

[0025] Among them, X t+1 is the mechanical coordinate system value of the stroke corresponding to the moment t+1, and ɑ is the compensation magnification.

[0026] As a preferred embodiment of the present invention, a thermal expansion compensation system based on a machine tool screw includes: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement a thermal expansion compensation method based on a machine tool screw.

[0027] As a preferred embodiment of the present invention, a computer readable medium stores computer program code, and when the computer program code is executed by a processor, a method for compensating for thermal extension of a machine tool screw is implemented.

[0028] Beneficial effects of the present invention:

[0029] 1. Compared with the installation of grating scale, the hardware cost is significantly reduced and the assembly process and maintenance design are simple;

[0030] 2. Compared with the screw constant temperature control method, it solves the immaturity and lack of domestic hollow screw manufacturing processes, and is restricted by others in terms of hardware and technology; detecting the thermal elongation is used to solve the "stuck neck" problem for domestic machine tools. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flowchart of the thermal elongation compensation method for the machine tool screw of the present invention;

[0032] Figure 2 is a schematic structural diagram of the machine tool screw of the present invention;

[0033] Figure 3 is the cold machine accuracy data of the X-axis of the present invention;

[0034] Figure 4 is the non-thermal elongation compensation accuracy data of the X-axis hot machine of the present invention;

[0035] Figure 5 is the thermal elongation compensation accuracy data of the X-axis hot machine of the present invention;

[0036] Figure 6 is the cold machine accuracy data of the Y-axis of the present invention;

[0037] Figure 7 is the non-thermal elongation compensation accuracy data of the Y-axis hot machine of the present invention;

[0038] Figure 8 is the thermal elongation compensation accuracy data of the Y-axis hot machine of the present invention;

[0039] Figure 9 is the cold machine accuracy data of the Z-axis of the present invention;

[0040] Figure 10 is the non-thermal elongation compensation accuracy data of the Z-axis hot machine of the present invention;

[0041] Figure 11 is the thermal elongation compensation accuracy data of the Z-axis hot machine of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The present invention will be further described below in conjunction with the drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner, so it only shows the components related to the present invention.

[0043] As Figure 1 shown, a thermal elongation compensation method based on a machine tool screw includes the following steps:

[0044] Step 1: Obtain the displacement reference benchmark value;

[0045] Before the machine tool commissioning, based on high-precision requirements, screw pitch compensation is usually required. However, if the precision requirement is of a lower level, pitch compensation can be skipped and the displacement reference datum value can be captured directly. After the screw pitch compensation is completed, the screw is run slowly, and the maximum and minimum values of the detection data fed back by the displacement sensor are confirmed. The average value of the maximum and minimum values is calculated to obtain the displacement reference datum value.

[0046] The displacement reference datum value can also be set according to experience.

[0047] Step 2: Collect the measured displacement values when the screw rotates at different times.

[0048] As Figure 2 shown, the stepper motor drives the screw to rotate. A displacement sensor bracket is installed at the end face of the screw, and the displacement sensor is fixed on the displacement sensor bracket. The probe of the displacement sensor faces the end face of the screw. Usually, the center of the probe and the center of the end face of the screw are located on the same horizontal plane and the probe end face is aligned with the plane position of the end face of the screw to improve the displacement detection accuracy.

[0049] Since the screw material is generally 50CrMo4 or 4150 (GCr15), its expansion coefficient is 11.75 (10^-6 mm / mm / ℃); assuming the screw length is 1000 mm, when the temperature rises by 1℃, the elongation of the screw is 11.75 micrometers (μm).

[0050] Since the screw is a moving part and rotates, non-contact measurement must be used. An eddy current displacement sensor is used to measure the elongation of the screw (i.e., the measured displacement value); when installing the displacement sensor, the distance between the probe and the end face of the screw needs to be adjusted. The numerical control system is used to obtain the distance between the displacement sensor and the end face of the screw so that the feedback data is within the preset range value. Since the distance between the probe and the end face of the screw will affect the accuracy of the measurement data, this distance needs to be adjusted to make the displacement sensor meet the measurement accuracy requirements.

[0051] Different times can be custom-set. For example, measure once every 100 ms.

[0052] Figure 2 The figure is a schematic diagram of an X-axis single-axis machine tool, and it also includes: machine tools such as X / Y / Z three-axis and five-axis.

[0053] When it is a three-axis machine tool, 3 displacement sensors are installed on the opposite side of the end face of the screw corresponding to each axis.

[0054] This embodiment takes the screw of an X single-axis machine tool as an example for illustration.

[0055] The numerical control system can adopt Siemens 828D / 840D. Since the measured value of the displacement sensor is an analog value, the analog value needs to be converted into floating-point displacement data.

[0056] Step 3: Calculate the thermal elongation value of the screw at the current moment;

[0057] △L t = L t test - L r ;

[0058] where, △L t is the thermal elongation value at time t, L t test is the measured displacement value at time t, and L r is the displacement reference benchmark value.

[0059] t is the current moment, and t + 1 is the next moment;

[0060] For example: The displacement reference benchmark value is 0.5 mm;

[0061] When t = 100 ms, it corresponds to the 1st measurement, and L 100 test = 0.5177 mm; then △L = 0.0177 mm.

[0062] Step 4: Calculate the thermal elongation compensation value at the next moment using the compensation slope at the current moment;

[0063] The formula for the compensation slope value k t is:

[0064] k t = △L t / L;

[0065] where, △L t is the thermal elongation value at time t; L is the axis travel value, and the axis travel value is usually set as the screw length;

[0066] Then, when t = 100 ms, k 100 = 0.0177 / 1000;

[0067] The formula for the thermal elongation compensation value at the next moment t + 1 = 200 ms is:

[0068] L t+1 b = X t+1 * tan(k t ) * ɑ;

[0069] where, X t+1 is the mechanical coordinate system value corresponding to the travel at the (t + 1)th moment, and ɑ is the compensation magnification.

[0070] Keep executing sequentially until the machine tool processing task ends.

[0071] Actual measurements show that in machine tool equipment, the displacement reference value of the corresponding axis and the actual measured displacement value are not necessarily in a 1:1 relationship. It may be > 1 or < 1, depending on the actual working conditions. To obtain more accurate compensation, the present invention introduces a variable compensation ratio ɑ. Through the action of the compensation ratio, k is corrected to obtain a more practical slope, and this slope value is transmitted to the corresponding axis window of the numerical control system to update the slope. Actual tests show that the introduction of the compensation ratio can greatly improve the axial position accuracy. Since the compensation ratio needs to be custom-set, this definition is made in the open parameters.

[0072] Such as Figures 3 - 11 As the comparison accuracy data of the X / Y / Z three axes on the same machine tool, it can be found that without thermal compensation intervention, each axis has a large thermal expansion value in the hot machine state compared to the cold machine state. With thermal compensation intervention, the full-stroke accuracy can be effectively controlled, and there is an improvement of nearly one order of magnitude compared to the full-stroke accuracy without thermal compensation. With a small economic cost, a great improvement in the accuracy of machine tool equipment is achieved, and it has great application prospects.

[0073] The present invention obtains the elongation of the screw rod, sends the elongation to the numerical control system, and evenly compensates the elongation to the entire axial stroke of the screw rod through the numerical control system to achieve precision control.

[0074] Through this method, the axial accuracy can be well controlled, and the accuracy can be controlled within 0.02 mm under all-weather and full-stroke conditions. That is, in the ideal state, a certain linear axis needs 10 million pulses to complete the full stroke. Without thermal expansion, 10 million pulses are a fixed value when completing the full stroke. When there is thermal expansion compensation, the number of pulses required to complete the full stroke is a variable value.

[0075] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A thermal elongation compensation method based on a machine tool screw, characterized in that, Including the following steps: Step 1, obtaining a displacement reference benchmark value; Step 2, collecting the measured displacement values when the screw rotates at different times; Step 3, calculating the thermal elongation value of the screw using the displacement reference benchmark value and the measured displacement value; Step 4, calculating the compensation slope at the current moment using the thermal elongation value and the shaft stroke value, and using it to calculate the thermal elongation compensation value at the next moment.

2. The thermal elongation compensation method based on a machine tool screw according to claim 1, wherein The formula for the thermal elongation value is: △L t = L t test - L r ; Among them, L t test is the measured displacement value at time t, and L r is the displacement reference benchmark value.

3. The thermal elongation compensation method based on a machine tool screw according to claim 2, wherein The formula for the compensation slope is: k t = ΔL t / L; Among them, △L t is the thermal elongation value at time t; L is the shaft stroke value.

4. The thermal extension compensation method based on a machine tool screw according to claim 3, wherein, The formula for the thermal elongation compensation value is: L t+1 b = X t+1 * tan(k t ) * ɑ; Among them, X t+1 is the mechanical coordinate system value corresponding to the stroke at the (t + 1)-th moment, and ɑ is the compensation magnification factor.

5. The thermal extension compensation method based on a machine tool screw according to claim 1, wherein Measuring the measured displacement value using a displacement sensor.

6. The thermal elongation compensation method based on a machine tool screw according to claim 1, characterized in that, The displacement sensor includes an eddy current displacement sensor.

7. The thermal extension compensation method based on a machine tool screw according to claim 1, wherein, The machine tools of the screw include: single-axis, three-axis, five-axis.

8. Thermal extension compensation system based on a machine tool screw, characterized in that, Including: A memory for storing instructions executable by a processor; A processor for executing the instructions to implement the thermal elongation compensation method for a machine tool screw as described in any one of claims 1-7.

9. A computer-readable medium storing computer program code, characterized in that, The computer program code implements the thermal elongation compensation method for a machine tool screw as described in any one of claims 1-7 when executed by the processor.

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