Visual measurement system and method for thermal error of multi-axis machine tool
阅读说明：本技术 多轴机床热误差的可视化测量系统及方法 (Visual measurement system and method for thermal error of multi-axis machine tool ) 是由 黄诺帝 华力 陈金超 张杨 朱利民 于 2021-07-28 设计创作，主要内容包括：本发明提供了一种多轴机床热误差的可视化测量系统及方法,包括热误差测试工件和对热误差测试工件进行加工的多轴机床；热误差测试工件设置在多轴机床上；热误差测试工件包括多个线性轴测试面、多个旋转轴测试面、设置在线性轴测试面上的参考槽和设置在旋转轴测试面上的参考槽；线性轴测试面的法向和对应的线性轴方向同向,旋转轴测试面的轴线方向和对应的旋转轴轴向同向。本发明提出的测量方法及系统可以用于所有构型的五轴机床,且能够得出五轴机床所有运动轴的热误差数据；通过对热误差测试工件表面加工槽,并根据加工槽的痕迹直接目视得到热误差,可视化效果高。(The invention provides a visual measurement system and a visual measurement method for thermal errors of a multi-axis machine tool, wherein the visual measurement system comprises a thermal error test workpiece and the multi-axis machine tool for processing the thermal error test workpiece; the thermal error test workpiece is arranged on the multi-axis machine tool; the thermal error test workpiece comprises a plurality of linear axis test surfaces, a plurality of rotating axis test surfaces, a reference groove arranged on the linear axis test surfaces and a reference groove arranged on the rotating axis test surfaces; the normal direction of the linear shaft testing surface is the same as the direction of the corresponding linear shaft, and the axial direction of the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft. The measuring method and the system provided by the invention can be used for five-axis machine tools with all configurations, and can obtain thermal error data of all motion axes of the five-axis machine tools; the thermal error is obtained by testing the surface processing groove of the workpiece through the thermal error and directly and visually observing the trace of the processing groove, and the visualization effect is high.)
1. A visual measurement system for thermal errors of a multi-axis machine tool is characterized by comprising a thermal error test workpiece (2) and the multi-axis machine tool for processing the thermal error test workpiece (2); the thermal error test workpiece (2) is arranged on a multi-axis machine tool; the thermal error test workpiece (2) comprises a plurality of linear axis test surfaces, a plurality of rotating axis test surfaces, a reference groove (8) arranged on the linear axis test surfaces and a reference groove (8) arranged on the rotating axis test surfaces; the normal direction of the linear shaft testing surface is the same as the direction of the corresponding linear shaft, and the axial direction of the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft.
2. Visual measurement system of thermal errors of a multi-axis machine tool according to claim 1, characterized in that the reference slots (8) on the test surface of the linear axis are parallel and equidistant grooves, the direction of the reference slots (8) on the test surface of the linear axis being horizontal or vertical.
3. Visual measurement system of thermal errors of a multi-axis machine tool according to claim 1, characterized in that the reference grooves (8) on the test surface of the rotating shaft are parallel grooves with equal arc length spacing, and the direction of the reference grooves (8) on the test surface of the rotating shaft is in the same direction as the axis direction of the corresponding test surface of the rotating shaft.
4. A visual measurement method for thermal errors of a multi-axis machine tool is characterized in that the visual measurement system for the thermal errors of the multi-axis machine tool, which is disclosed by any one of claims 1 to 3, is applied, and comprises the following steps:
step 1: defining a plurality of directions according to the configuration of the multi-axis machine tool, and designing a model of a thermal error test workpiece (2);
step 2: machining and manufacturing a thermal error test workpiece (2);
and step 3: planning paths of a cutter on the multi-axis machine tool on a test surface corresponding to each motion axis;
and 4, step 4: operating the multi-axis machine tool to process a thermal error test workpiece (2) according to a planned path at fixed time intervals from a cold state and recording the processing temperature;
and 5: the thermal error of each motion axis of the multi-axis machine tool under different temperature conditions is obtained according to the trace of the processing groove (10).
5. The visual measurement method of thermal error of multi-axis machine tool according to claim 4, characterized in that, when processing the thermal error test piece (2) in step 2, the multi-axis machine tool is required to be preheated sufficiently, the thermal error test piece (2) is obtained by milling, and then equidistant and parallel reference grooves (8) are processed on the test surface of the thermal error test piece (2) corresponding to each axis of the multi-axis machine tool.
6. The visual measurement method for the thermal error of the multi-axis machine tool according to claim 4, wherein the planning of the path of the tool on the test surface corresponding to each motion axis in the step 3 includes a tool path planning for measuring the thermal error of a linear axis and a tool path planning for measuring the thermal error of a rotary axis.
7. The visual measurement method of the thermal error of the multi-axis machine tool according to claim 6, characterized in that the tool path when measuring the thermal error of the linear axis is a straight line and is perpendicular to the reference groove (8) on the test surface; the cutting depth of the tool is gradually reduced from an initial position (9) along the moving direction of the tool, and finally the tool is separated from the contact with the testing surface at a preset reference axis.
8. The visual measurement method of the thermal error of the multi-axis machine tool according to claim 6, characterized in that the tool path when measuring the thermal error of the rotating axis is a circular arc, and the tangential direction of the tool path is perpendicular to the reference groove (8) on the test surface; the cutting depth of the tool is set to decrease gradually in the direction of movement of the tool, starting from an initial position (9), and finally the tool is brought out of contact with the test surface at a predetermined reference axis.
9. The visual measurement method of the thermal error of the multi-axis machine tool according to claim 4, characterized in that, when the linear axis test surface of the thermal error test workpiece (2) is processed in the step 4, the normal direction of the linear axis test surface is the same as the axial direction of the corresponding linear axis; when the rotating shaft test surface of the thermal error test workpiece (2) is machined, the axial direction of the rotating shaft test surface is the same as the axial direction of the corresponding rotating shaft, the circular arc center of the planned cutter track is on the rotating shaft axis, and the axis of the rotating shaft test surface is offset by a certain distance relative to the rotating shaft axis.
10. Method for the visual measurement of thermal errors of a multi-axis machine tool according to claim 4, characterized in that in step 5, the reference grooves (8) are numbered sequentially from the initial position (9) of the tool in the direction of movement of the tool from small to large, and when no thermal error is present, the theoretical contact-free position (11) of the tool with the test surface is located at the programmed positionNumber N0At the reference groove (8), the thermal error of the motion axis is expressed as
ε＝d(N-N0)
Wherein d is the projection length of the theoretical cutter track between two adjacent reference grooves (8) in the cutting depth direction, and N is the number of the reference groove (8) corresponding to the actual contact position (12) where the machining groove (10) is separated from the test surface; ε is the thermal error of the axis of motion.
Technical Field
The invention relates to the technical field of machine tool thermal error measurement, in particular to a visual measurement system and method for thermal errors of a multi-axis machine tool.
Background
In precision and ultra-precision machining, the application of a five-axis machine tool is very wide, and the machining precision is directly influenced by the positioning error of the machine tool. Thermal errors caused by ambient temperature changes and heat generated during machine tool operation affect the positioning accuracy of the machine tool, and of the typical error sources of kinematic errors, thermo-mechanical errors, loads, power, motion control systems, etc., up to 75% of the overall geometric errors of the machined workpiece are caused by temperature effects. Therefore, the method has a significant meaning for predicting, measuring, analyzing and compensating the thermal error of the machine tool to improve the motion precision of the five-axis machine tool, and the measuring method of the thermal error is more important for evaluating the influence of the thermal error.
The current measuring methods related to the thermal error of the machine tool can be divided into two categories, namely non-machining measurement and machining measurement. The non-machining test method mainly uses an R test device, a ball bar instrument, an optical measurement device, and the like to measure thermal deformation and thermal error of a linear axis and a rotational axis. The optical measurement equipment is widely applied to thermal error identification in a non-mechanical processing measurement method, the laser interferometer can be used for measuring a thermally induced positioning error of a linear axis, the non-contact laser grating system can be used for evaluating the influence of the thermal error on a position error of a rotating axis, and the laser tracker can be used for evaluating the influence of the thermal error on a motion track error of a machine tool in the whole working space. Machining measurement is a method of measuring and evaluating thermal errors of a machine tool during actual machining. According to the measuring method, the measurement of the machined workpiece is completed through equipment such as a dial indicator or a coordinate measuring machine, so that the influence of the thermal error of the machine tool on the geometric shape of the workpiece can be reflected quantitatively, but the influence of the temperature on the positioning precision of the machine tool is difficult to obtain visually.
Through the document retrieval discovery of the prior art, the Chinese invention patent document with the publication number of CN104999342A discloses an automatic thermal error measuring system and a measuring method thereof under the real cutting state of a numerical control machine tool, which comprises a temperature sensor for measuring the temperature value of a temperature sensitive point of the numerical control machine tool, wherein the output end of the temperature sensor is connected with the input end of a temperature acquisition unit; the on-line detection system for measuring the standard component outputs trigger signals in two paths, one path is sent to the numerical control system of the numerical control machine, the other path is sent to the coordinate acquisition unit for extracting the space coordinate of the numerical control machine, the output end of the numerical control system of the numerical control machine is connected with the input end of the coordinate acquisition unit, and the output ends of the coordinate acquisition unit and the temperature acquisition unit are connected with the input end of the PC. The thermal error data of the machine tool X, Y, Z in three directions can be obtained by measuring the preset point positions of the cuboid standard block by using the contact type measuring head respectively in the machine tool cold state and after running for a period of time, but the measuring method of the thermal error of the rotating shaft is not involved, and the result is in a numerical value form and is not visual enough.
The chinese patent publication No. CN111168469A discloses a five-axis numerical control machine spatial thermal error measurement system, in which three directions that are vertically intersected in a defined space are the X direction, the Y direction, and the Z direction, the five-axis numerical control machine spatial thermal error measurement system includes a measurement standard component that is used for being fixed on a workbench of a numerical control machine, and further includes a measuring head that is used for being fixed at a position of a spindle tool of the numerical control machine, the measurement standard component includes a standard ball head, and the standard ball head has a standard spherical surface that is used for being measured by the measuring head. The invention solves the technical problem that in the prior art, when a cuboid measurement standard component is applied to the thermal error measurement of a five-axis numerical control machine tool, if the measurement standard component generates a rotation angle, the thermal error value in other directions is influenced by a single thermal error. The thermal error data of the machine tool is obtained by measuring the distances from a plurality of standard balls to the sensors by the eddy current sensors respectively in a machine tool cold state and after the eddy current sensors run for a period of time, so that the problem that the measured thermal errors in different directions influence each other due to the inclination angle is solved, but the result is not visual enough, and the visualization effect is not good.
In view of the above-mentioned related technologies, the inventors consider that the above-mentioned method results are not intuitive enough and the visual effect is not good.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a system and a method for visually measuring the thermal error of a multi-axis machine tool.
The visual measurement system for the thermal error of the multi-axis machine tool comprises a thermal error test workpiece and the multi-axis machine tool for processing the thermal error test workpiece, wherein the thermal error test workpiece is arranged on the multi-axis machine tool; the thermal error test workpiece is arranged on a multi-axis machine tool; the thermal error test workpiece comprises a plurality of linear axis test surfaces, a plurality of rotating axis test surfaces, a reference groove arranged on the linear axis test surfaces and a reference groove arranged on the rotating axis test surfaces; the normal direction of the linear shaft testing surface is the same as the direction of the corresponding linear shaft, and the axial direction of the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft.
Preferably, the reference grooves on the linear axis test surface are parallel and equidistant grooves, and the direction of the reference grooves on the linear axis test surface is horizontal or vertical.
Preferably, the reference grooves on the rotating shaft testing surface are parallel grooves with equal arc length spacing, and the direction of the reference grooves on the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft testing surface.
The visual measurement method for the thermal error of the multi-axis machine tool provided by the invention comprises the following steps:
step 1: defining a plurality of directions according to the configuration of the multi-axis machine tool, and designing a model of a thermal error test workpiece;
step 2: processing and manufacturing a thermal error test workpiece;
and step 3: planning paths of a cutter on the multi-axis machine tool on a test surface corresponding to each motion axis;
and 4, step 4: operating the multi-axis machine tool from a cold machine state, processing a thermal error test workpiece according to a planned path at fixed time intervals, and recording the temperature during processing;
and 5: and obtaining the thermal error of each motion axis of the multi-axis machine tool under different temperature conditions according to the trace of the processing groove.
Preferably, when the thermal error test workpiece is processed in the step 2, the multi-axis machine tool is required to be fully preheated, the thermal error test workpiece is obtained by milling, and then equidistant and parallel reference grooves are processed on the test surface of the thermal error test workpiece corresponding to each axis of the multi-axis machine tool.
Preferably, the planning of the path of the tool on the test surface corresponding to each motion axis in step 3 includes tool path planning for measuring thermal errors of a linear axis and tool path planning for measuring thermal errors of a rotary axis.
Preferably, the tool path when measuring the thermal error of the linear axis is a straight line and is perpendicular to the reference groove on the test surface; the cutting depth of the tool is gradually reduced along the moving direction of the tool from the initial position, and finally the tool is separated from the test surface at the preset reference axis.
Preferably, the tool path when measuring the thermal error of the rotating shaft is an arc, and the tangential direction of the tool path is perpendicular to the reference groove on the test surface; the cutting depth of the tool is set to gradually decrease along the moving direction of the tool from the initial position, and finally the tool is separated from the test surface at the predetermined reference axis.
Preferably, when the linear axis test surface of the thermal error test workpiece is processed in the step 4, the normal direction of the linear axis test surface is the same as the axial direction of the corresponding linear axis; when the rotating shaft test surface of the thermal error test workpiece is machined, the axial direction of the rotating shaft test surface is the same as the axial direction of the corresponding rotating shaft, the circular arc center of the planned cutter track is on the axis of the rotating shaft, and the axis of the rotating shaft test surface is offset by a certain distance relative to the axis of the rotating shaft.
Preferably, in the step 5, the reference grooves are numbered sequentially from small to large along the moving direction of the tool from the initial position of the tool, and when no thermal error is caused, the theoretical contact-breaking position of the tool and the test surface is numbered as N0The thermal error of the moving axis is expressed as
ε＝d(N-N0)
D is the projection length of a theoretical cutter track between two adjacent reference grooves in the cutting depth direction, and N is the number of the reference groove corresponding to the position where the machining groove is actually separated from the test surface; ε is the thermal error of the axis of motion.
Compared with the prior art, the invention has the following beneficial effects:
1. the measuring method and the system can be used for five-axis machine tools with all configurations, and can obtain thermal error data of all motion axes of the five-axis machine tool;
2. the thermal error is tested by processing the groove on the surface of the workpiece, and the thermal error is directly obtained by visual observation according to the trace of the processing groove, so that the visual effect is high;
3. the invention adopts a mechanical processing method to measure the thermal error, has simple cutter track, does not depend on redundant measuring equipment, does not need to process a large number of microstructures, has high efficiency, saves the cost and reduces the influence of cutting force on the measuring result.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of a five-axis machine tool;
FIG. 2 is a schematic view of a thermal error test workpiece model;
FIG. 3 is a schematic diagram of a linear axis thermal error measurement method;
FIG. 4 is a schematic diagram of a C-axis thermal error measurement method;
FIG. 5 is a schematic view of the A-axis thermal error measurement method;
FIG. 6 is a schematic diagram of a linear axis thermal error measurement method without tilting the tool;
FIG. 7 is a first schematic view of a C-axis thermal error measurement method without tilting the tool;
FIG. 8 is a second schematic view of a C-axis thermal error measurement method without tilting the tool.
Reference numerals:
initial position 9 of 1Z-axis test surface 5 of five-axis machine tool
Thermal error test workpiece 2C axis test surface 6 processing tank 10
Theoretical contact position 11 that breaks away from of X axle test face 3A axle test face 7
The Y-axis test surface 4 actually moves away from the contact position 12 with reference to the groove 8
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The embodiment of the invention discloses a visual measurement system for thermal errors of a multi-axis machine tool, which comprises a thermal error test workpiece 2 and the multi-axis machine tool for processing the thermal error test workpiece 2, as shown in fig. 1 and fig. 2; the thermal error test workpiece 2 is arranged on a multi-axis machine tool; the thermal error test workpiece 2 comprises a plurality of linear axis test surfaces, a plurality of rotating axis test surfaces, a reference groove 8 arranged on the linear axis test surfaces and a reference groove 8 arranged on the rotating axis test surfaces; the normal direction of the linear shaft testing surface is the same as the direction of the corresponding linear shaft, and the axial direction of the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft. The reference grooves 8 on the linear axis test surface are parallel and equidistant grooves, and the direction of the reference grooves 8 on the linear axis test surface is horizontal or vertical. The reference grooves 8 on the rotating shaft testing surface are parallel grooves with equal arc length intervals, and the direction of the reference grooves 8 on the rotating shaft testing surface is the same as the axial direction of the corresponding rotating shaft testing surface.
A method for visually measuring thermal errors of a five-axis machine tool 1 can be used for measuring thermal errors of five-axis machine tools 1 of all configurations, so that the five-axis machine tool 1 with a rotating shaft on both a spindle side and a workpiece side shown in fig. 1 is selected in the embodiment to explain the content of the invention in detail, and the design of a thermal error test workpiece 2 is as follows: according to the configuration of the five-axis machine tool 1, three pairwise orthogonal directions in the space are defined as an X direction, a Y direction and a Z direction, which correspond to the movement directions of an X axis, a Y axis and a Z axis in the five-axis machine tool 1, as shown in fig. 1. The axial directions of the A axis and the C axis of the machine tool respectively correspond to the X direction and the Z direction. The designed thermal error test piece 2, as shown in fig. 2, includes three linear axis test faces, two rotational axis test faces and a reference groove 8 on each test face. The linear axis testing surface is an X-axis testing surface 3, a Y-axis testing surface 4 and a Z-axis testing surface 5 which are three planes which are orthogonal pairwise. In the actual machining test, the normal direction of the linear axis test surface should be adjusted to be the same direction as the corresponding linear axis direction, and the reference grooves 8 on the linear axis test surface are a series of parallel grooves with equal spacing, and the direction is generally horizontal or vertical. The rotating shaft testing surface is a C-axis testing surface 6 and an A-axis testing surface 7 which are two cylindrical surfaces. In the actual machining test, the axial direction of the rotating shaft test surface is adjusted to be in the same direction as the corresponding rotating shaft axial direction, and the reference grooves 8 on the rotating shaft test surface are a series of parallel grooves with equal arc length intervals, and the direction of the grooves is in the same direction as the axial direction of the corresponding test surface. In particular, the radius of the A-axis test surface 7 should be equal to the distance from the tool tip point to the axis of rotation of the A-axis.
The embodiment of the invention also discloses a visual measurement method for the thermal error of the multi-axis machine tool, which comprises the following steps as shown in fig. 1 and fig. 2:
step 1: according to the multi-axis machine tool configuration, a plurality of directions are defined, and a model of the thermal error test workpiece 2 is designed. According to the configuration of the five-axis machine tool 1, the X direction, the Y direction and the Z direction are defined, and a model of the thermal error test workpiece 2 is designed. The thermal error test piece 2 includes three linear axis test faces, two rotational axis test faces and a reference groove 8 on each test face. The linear axis testing surface is an X-axis testing surface 3, a Y-axis testing surface 4 and a Z-axis testing surface 5 which are three planes which are orthogonal pairwise. The reference grooves 8 on the linear axis test surface are a series of parallel, equally spaced grooves oriented generally horizontally or vertically. The rotating shaft testing surface is a C-axis testing surface 6 and an A-axis testing surface 7 which are two cylindrical surfaces. The reference grooves 8 on the test surface of the rotating shaft are a series of parallel grooves with equal arc length spacing, and the direction of the grooves is the same as the axial direction of the corresponding test surface. In particular, the radius of the A-axis test surface 7 should be equal to the distance from the tool tip point to the axis of rotation of the A-axis.
According to the configuration of the five-axis machine tool 1, three pairwise orthogonal directions in a space are defined as an X direction, a Y direction and a Z direction, and a model of a thermal error test workpiece 2 is designed.
Step 2: the thermal error test piece 2 is machined and manufactured. When the thermal error test workpiece 2 is machined, the multi-axis machine tool is required to be fully preheated, the thermal error test workpiece 2 is obtained through milling, and then equidistant and parallel reference grooves 8 are machined on the test surface of the thermal error test workpiece 2 corresponding to each axis of the multi-axis machine tool. When the thermal error test workpiece 2 is machined, the machine tool is required to be fully preheated so as to eliminate the influence of heat on the geometric precision of the test workpiece in the preheating process. Firstly, a test workpiece is obtained through milling, and then a series of equidistant parallel reference grooves 8 are machined on the workpiece test surface corresponding to each shaft of the machine tool.
The thermal error tests the manufacturing of the workpiece 2. The machine tool is required to be fully preheated so as to eliminate the influence of heat on the geometric accuracy of the tested workpiece in the preheating process. Then clamping the aluminum alloy blank on a workbench for milling to obtain a test workpiece, and processing a series of parallel reference grooves 8 with equal distance on the workpiece test surface corresponding to each shaft of the machine tool.
And step 3: and planning paths of the tool on the test surface corresponding to each motion axis on the multi-axis machine tool, namely planning motion tracks of the tool on the test surface corresponding to each motion axis. And planning paths of the cutter on the test surface corresponding to each motion axis, wherein the paths comprise cutter path planning for measuring thermal errors of linear axes and cutter path planning for measuring thermal errors of rotary axes. The tool path when measuring the thermal error of the linear axis is a straight line and should be perpendicular to the reference groove 8 on the test surface; the cutting depth of the tool is gradually reduced in the direction of movement of the tool, starting from an initial position 9, and finally the tool is out of contact with the test surface at a predetermined reference axis. The tool path when measuring the thermal error of the rotating shaft is a circular arc, and the tangential direction of the tool path is vertical to the reference groove 8 on the test surface; the cutting depth of the tool is set to decrease from the initial position 9 in the direction of movement of the tool and finally the tool is brought out of contact with the test surface at the predetermined reference groove 8. And planning the path of the cutter on the test surface corresponding to each motion axis.
And planning the motion tracks of the cutter on different test surfaces. The direction of movement of the tool is perpendicular to the direction of the reference groove 8, in which direction the cutting depth of the tool gradually decreases until it separates from the workpiece. The surface of the test piece will leave a trace of the machined groove 10 from deep to shallow.
And 4, step 4: and operating the machine tool from a cold state, machining the test workpiece according to the planned track at fixed time intervals, and recording the machining temperature. And operating the multi-axis machine tool to start from a cold state, testing the workpiece 2 according to the planned path machining thermal error at fixed time intervals, and recording the machining temperature.
When the linear axis test surface of the thermal error test workpiece 2 is processed, the normal direction of the linear axis test surface is the same as the axial direction of the corresponding linear axis; when the rotating shaft test surface of the thermal error test workpiece 2 is machined, the axial direction of the rotating shaft test surface is the same as the axial direction of the rotating shaft corresponding to the rotating shaft test surface, the circular arc center of the planned cutter track is on the axis of the rotating shaft, the axis of the rotating shaft test surface is deviated from the axis of the rotating shaft by a certain distance, and the distance meets the requirement of the cutter track on the cutting depth.
When the machining groove 10 on the test surface is machined, the cutter shaft direction needs to incline at a certain angle, and the certain angle comprises 45 degrees. For a five-axis machine tool 1 with two rotating shafts on the side of a workbench, the axial direction of the tool cannot be directly inclined, and the measuring method can be expanded. When measuring the thermal error of the linear axis without tilting the tool, the machining groove 10 on the test surface should be machined on the tilted plane. When measuring the C-axis thermal error without tilting the tool, there are 2 options: and replacing the cylindrical surface with a conical surface to be used as a C-axis thermal error testing surface, or controlling the movement of an A (or B) axis of the machine tool to enable the C axis to incline.
And 5: and obtaining the thermal error of each motion axis of the multi-axis machine tool under different temperature conditions according to the trace of the processing tank 10. According to the trace of the machining groove 10, the thermal error of each motion axis of the five-axis machine tool 1 under different temperature conditions can be directly obtained by visual observation. Numbering the reference grooves 8 from the initial position 9 of the cutter to the big in turn along the movement direction of the cutter, wherein the reference grooves 8 corresponding to the theoretical contact-separating position 11 of the cutter and the test surface are numbered N when no thermal error is caused0Then the thermal error of the moving axis is expressed as
ε＝d(N-N0)
Wherein d is the projection length of the theoretical cutter track between two adjacent reference grooves 8 in the cutting depth direction, and N is the number of the reference groove 8 corresponding to the actual contact position 12 where the machining groove 10 is separated from the test surface; ε is the thermal error of the axis of motion.
The method for measuring the thermal error of the linear axis comprises the following steps: the present embodiment selects the Z-axis thermal error measurement method, e.g.As shown in fig. 3, for a detailed description. The thermal error measurement method for the X-axis and the Y-axis is the same. First, the Z-axis test surface 5 is made normal to the Z-axis direction. Second, a theoretical tool path is planned that is free of thermal error effects. The theoretical tool path is a straight line and should be perpendicular to the reference groove 8, so the direction of the reference groove 8 of the Z-axis test surface 5 is selected as the X direction, and the tool motion direction is the Y direction. The tool is therefore only involved in movement in both the Y-axis and Z-axis. The cutting depth of the tool at the initial position 9 is set, the cutting depth gradually decreases along the tool movement direction, and finally the tool is separated from the contact with the Z-axis test surface 5. Numbering the reference grooves 8 from the initial position 9 to the big along the moving direction of the cutter in turn, wherein when no thermal error is caused, the number of the reference groove 8 corresponding to the theoretical contact-separating position 11 of the cutter and the Z-axis test surface 5 is N0. And finally, operating the five-axis machine tool 1 at intervals to process the Z-axis test surface 5 according to a preset theoretical tool path, so as to obtain a series of processing grooves 10 on the Z-axis test surface 5. The thermal error in the Z-axis direction can be expressed as:
εz＝d(Nz-N0)
wherein d is the projection length of the theoretical tool path between two adjacent reference grooves 8 in the cutting depth direction, NzThe reference groove 8 number, ε, corresponding to the actual out-of-contact position 12 of the machining groove 10 with the Z-axis test surface 5zIs the thermal error in the Z-axis direction.
The measuring method of the thermal error of the rotating shaft comprises the following steps: the method of measuring the thermal error of the C-axis is shown in fig. 4. First, the axis direction of the C-axis test surface 6 is made to be the Z direction, and the direction of the reference groove 8 thereon is made to be the Z direction. Second, a theoretical tool path is planned that is free of thermal error effects. The theoretical tool path is a circular arc with the same radius as the C-axis test surface 6, and the tangential direction of the theoretical tool path at the reference axis 8 is orthogonal to the direction of the reference axis 8. The depth of cut of the tool in the initial position 9 is set, which decreases gradually in the direction of movement of the tool and determines the theoretical release contact position 11 of the tool with the C-axis test surface 6. And finally, operating the five-axis machine tool 1 at intervals to process the C-axis test surface 6 according to a preset theoretical tool path, so as to obtain a series of processing grooves 10 on the C-axis test surface 6. In actual machining, the five-axis machine tool 1 only moves along the C axis, and the machined groove 10 is obtained through equivalent turning operation, so that the arc center of the theoretical tool path is on the C axis, and the axis of the C-axis test surface 6 is offset from the C axis by a distance to meet the requirement of the theoretical tool path on the cutting depth. The reference groove 8 is used for comparing the theoretical separation position 11 and the actual separation position 12 of the machining groove 10 and the C-axis test surface 6, and the radial positioning error of the C-axis under the heat influence can be obtained.
The measurement method of the thermal error of the a-axis is shown in fig. 5. In the measurement, the axis direction of the a-axis test surface 7 is the X direction, and the direction of the reference groove 8 thereon is the X direction. The remaining measurement principles and steps are similar to the measurement method of the C-axis thermal error.
The thermal error measurement method in the above embodiment can be directly applied to the orthogonal five-axis machine tool 1 of any structure. Note that, when machining the groove 10 on the test surface, the arbor direction needs to be inclined by 45 degrees. However, for the five-axis machine tool 1 configured with two rotation axes on the table side, the tool axis direction cannot be directly tilted, and the embodiment needs to be expanded. To measure the thermal error in the Y-direction, the test should be performed on an inclined plane, as shown in fig. 6. The result is affected by thermal errors in the X and Z directions, but in principle it is possible to separate them by measuring the thermal error in the Z direction. When measuring the C-axis thermal error without tilting the tool, there are 2 options: a conical surface is used as a C-axis thermal error testing surface instead of a cylindrical surface, as shown in fig. 7, or the A (or B) axis of the machine tool is controlled to move so that the C axis is inclined, as shown in fig. 8.
The method can measure the thermal errors of the three linear axes and the two rotating axes of the five-axis machine tool 1 without other measuring equipment or instruments, the visualization effect of the measurement result is good, and the influence of the temperature on the positioning precision of the machine tool can be evaluated by visual observation.
According to the invention, the corresponding thermal error test workpiece 2 is designed according to the configuration of the five-axis machine tool 1, so that the method can be used for measuring the thermal errors of the five-axis machine tool 1 with all configurations, and can obtain the thermal error data of all motion axes. Through processing reference groove 8 in advance on thermal error test work piece 2 for the thermal error can directly be seen and obtained, and visual effectual. By a mechanical processing test method, the actual processing path and the theoretical path are compared with the theoretical contact position 11 separated from the processing surface relative to the processing surface to obtain the thermal error data of each motion axis, expensive measuring equipment is not relied on, a complex microstructure does not need to be processed, the measuring efficiency is improved, the measuring cost is saved, and the influence of cutting force on the measuring result is reduced.
In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.