A method for realizing high-precision linear feed motion of large rotary table of machine tool

Abstract

The present invention relates to the manufacturing of mechanical equipment in the field of processing, and specifically to a method for realizing high-precision linear feed motion of a large rotary table of a machine tool. The method is realized through four steps: improving the mechanical precision of the feed shaft of the large rotary table of the machine tool, avoiding thermal deformation based on the structural characteristics of the rotary table, compensating for thermal deformation, and controlling the heat source. The present invention can be applied to vertical and horizontal five-axis machining centers, boring and milling machines, vertical turning and milling composite machining centers, and other types of equipment whose rotary tables can move along linear axes, thereby improving product precision and performance.

Description

Technical Field

[0001] The invention relates to mechanical equipment manufacturing in the field of processing, and in particular to a method for realizing high-precision linear feed motion of a large-scale turntable of a machine tool. Background Art

[0002] The turntable is a key functional component of vertical and horizontal five-axis machining centers, boring and milling machines, and vertical turning and milling compound machining centers. In addition to its own rotational motion, according to the structural and functional requirements of some large machine tools, the turntable also needs to be fed along the linear axis as a whole, which is the so-called "moving table" machine tool. The feed axis drives the turntable and the workpiece on the turntable to move as a whole, participating in the machine tool feeding, and its motion accuracy directly affects the overall accuracy performance of the machine tool.

[0003] Conventional high-precision feed shaft control methods generally improve feed shaft accuracy by controlling the assembly accuracy of the feed shaft, high-precision requirements for transmission parts such as the lead screw, and closed-loop feedback of the grating ruler. However, for higher precision requirements for machine tool motion, the impact of heat on machine tool accuracy must be considered. The precision control of traditional machine tool feed shafts is generally achieved through structural means such as improving the accuracy of the lead screw. The present invention specifically targets the structural layout and working conditions of large turntables, and achieves high-precision control of the feed shaft motion equipped with a large turntable through layout, structure, thermal elongation avoidance, thermal control, and thermal compensation. Summary of the invention

[0004] The invention provides a method for realizing high-precision linear feed motion of a large rotary table of a machine tool. The stable and high-precision operation of the machine tool is realized through the steps of structural design of the machine tool, heat control during operation, temperature collection and compensation, and avoidance of thermal deformation.

[0005] The technical solution of the present invention is as follows:

[0006] A method for realizing high-precision linear feed motion of a large rotary table of a machine tool comprises the following steps:

[0007] Step 1: Improvement of mechanical accuracy of feed axis of large rotary table of machine tool:

[0008] The overall structure of the bed adopts a thermally symmetrical design layout, the feed shaft adopts a symmetrical double-drive layout of the lead screw, and the lead screw is pre-stretched to avoid thermal elongation during the working process of the lead screw. The drive mode of the lead screw is that the lead screw is fixed and does not rotate, and the nut rotates. At the same time, the inertia of the transmission components is reduced through special design to improve the overall dynamic response performance;

[0009] Step 2: Avoid thermal deformation based on the structural characteristics of the turntable:

[0010] The rotary center of the turntable is used as the coordinate zero point of the feed axis. One end of a carbon fiber rod with a low linear expansion coefficient is fixed near the center of the turntable. The other end is supported by a bracket built with spring sheets to form a floating support. A grating ruler probe is installed on the floating support end. The low expansion coefficient of the carbon fiber rod is used to transmit the accurate position change of the coordinate zero point, avoiding the grating ruler detection error caused by thermal elongation due to temperature rise during the operation of the turntable casting body.

[0011] Step 3: Compensation for thermal deformation:

[0012] Three sets of temperature sensors are installed on the bed below the grating ruler to detect the temperature change of the bed near the grating ruler. By comparing the temperature with the base temperature and performing position compensation, the detection error caused by the asynchronous deformation of the glass grating of the grating ruler and the bed during temperature change due to the different linear expansion coefficients of the materials can be eliminated, thereby improving the detection accuracy.

[0013] Step 4: Heat source control:

[0014] Thermal control of the heat source is achieved by water cooling the heat source of the lead screw, servo motor, and guide rail slider during operation.

[0015] Furthermore, the above-mentioned method for realizing high-precision linear feed motion of a large turntable of a machine tool, step 1 specifically includes: the bed adopts a fully thermally symmetrical design to ensure that the thermal deformation of the whole machine is uniform and stable, and two lead screw feed systems are symmetrically installed on the bed of the machine tool, the lead screw is composed of a lead screw body and a nut, one end of the lead screw body of each lead screw is fixed to the right support through a tightening sleeve, and the other end is a stretching end, which is connected to the left support through a limit key, and the stretching end is also provided with a disc spring group and a nut; a nut is installed in the middle of the lead screw, the nut is specially customized, and a positioning boss coaxial with the nut body is designed at the left end of the nut; the connecting flange and the nut are matched through the positioning boss and the connecting flange and the nut are combined together by screws, and the lubrication hole at the end of the nut is a through hole; a thrust bidirectional angular contact bearing is installed on the connecting flange; the inner ring of the thrust angular contact bearing and the connecting method The flange is in contact, the end is tightened by a nut, and the outer diameter is connected to the bearing support. A bolt through hole is designed on the outer ring of the thrust angular contact bearing. The inner ring is screwed together with the bearing support by screws, and the bearing support is connected to the turntable; the large pulley is connected to the connecting flange through a clamping sleeve, and the power input relies on the servo motor. A small pulley is installed on the shaft end of the servo motor, and the large pulley and the small pulley are connected by a circular arc toothed belt; when working, the power output by the servo motor is transmitted to the nut of the lead screw through the small pulley, the circular arc toothed belt, and the large pulley; at the same time, the nut rotates during the working process, and the conventional nut lubrication method cannot be completed, so two rotating sealing rings are provided on the outside of the connecting flange, and an independent space is formed between the two rotating sealing rings as a transmission channel for the nut lubricating oil. During lubrication, the lubricating oil reaches this independent space through the bearing support and enters the inside of the nut;

[0016] During the pre-stretching process of the screw, it is necessary to place a dial indicator on the fixed end of the screw and rotate the nut next to the disc spring group. During the rotation, the nut transmits the tensioning force to the screw body through the disc spring group, and the screw body is stretched. When the value of the dial indicator reaches the stretching requirement, the nut is locked. After the stretched screw expands due to temperature rise, the expansion force is offset by the stretching force, and the screw will not be thermally deformed, ensuring the precision and position stability of the screw during operation. The servo motor transmits the rotational power to the connecting flange through the large pulley and the small pulley, and the connecting flange transfers the power to the nut. During operation, the screw does not rotate, but the nut rotates, thereby driving the entire turntable component to move along the bed guide rail as a whole.

[0017] Furthermore, in the above-mentioned method for realizing high-precision linear feed motion of a large turntable of a machine tool, in step 2, one end of the carbon fiber rod is a fixed end, and the other end is a floating end. The fixed end is installed at the center of the turntable through a bracket, and the floating end extends to the end of the turntable. The grating ruler probe is installed on the floating end of the carbon fiber rod through a floating bracket supported by a spring sheet. When the turntable is working, the turntable body expands and stretches, but the probe installed at the floating end of the carbon rod can avoid the axial thermal elongation caused by the expansion of the turntable due to the action of the spring sheet, and the position change of the zero point of the center coordinate of the turntable is transmitted through the carbon fiber rod. In this way, the exact position of the turntable zero point is transmitted to the grating ruler probe, and the exact size of the turntable zero point is accurately read, and the accuracy of the feed axis is improved through the closed-loop feedback of the grating ruler.

[0018] Furthermore, in the above-mentioned method for realizing high-precision linear feed motion of a large turntable of a machine tool, in step 3, a vertical boss is designed in the middle of the bed, and the grating scale F is installed on the boss of the bed. Threaded holes are designed on the side elevation of the boss according to the length of the bed, and temperature sensors are installed in the threaded holes. There are three sensors (depending on the feed stroke, the number of sampling points can be increased according to the situation, not limited to three), which are respectively installed at the left end, middle and right end of the grating scale.

[0019] Furthermore, in the above-mentioned method for realizing high-precision linear feed motion of a large turntable of a machine tool, in step 4, a water-cooled servo motor is used as the servo motor; the screw body adopts a hollow design, and a water inlet joint and a water return joint are installed at both ends respectively, and cooling water is passed inside. The heat generated during the operation of the feed shaft is reduced in real time through continuous cooling water, and the overall thermal deformation of the feed system is suppressed. At the same time, because the feed shaft adopts a method in which the screw does not rotate and the nut rotates, the water-cooling joints at both ends of the screw are ordinary joints. There is no need to use a rotary joint at the end of the screw like traditional screw water cooling, which reduces costs and eliminates the problem of high failure rate of the rotary joint, thereby improving the reliability of the water cooling system. The mounting joint surface of the machine tool guide rail slider and the turntable base is designed with a groove, and a cooling pipeline is arranged in the groove. The friction heat during the movement of the slider and the guide rail is cooled by circulating cooling to prevent the temperature rise of the guide rail from affecting the overall thermal stability of the turntable.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention can be applied to vertical and horizontal five-axis machining centers, boring and milling machines, vertical turning and milling compound machining centers and other types of equipment whose rotary tables can move along linear axes, thereby improving product accuracy and performance.

[0022] 2. Good mechanical precision is the basis of overall precision control. All feedback and compensation in the later stage rely on good mechanical precision. Based on the characteristics of large turntables, the single-drive lead screw is considered to avoid the sway of the moving parts caused by the unilateral drive of large-sized moving parts, which affects the running precision. The lead screw feeding of the present invention adopts a double-screw symmetrical drive layout to avoid the sway of the moving parts caused by the unilateral drive of large-sized moving parts, which affects the running precision, and each lead screw adopts a pre-stretching design to offset the thermal deformation of the lead screw generated during the working process. The lead screw adopts a lead screw fixed and a nut rotating method. During the feeding process, the lead screw does not rotate, and fixed supports are used at both ends of the lead screw. There is no bearing rotation in the lead screw support, and no heat source is generated, which is convenient for reducing the heat source and improving the stability of the lead screw support. The tensioning end of the lead screw is designed with a disc spring group, and the tension value is easy to determine, and there is no need to determine the tension by matching the grinding adjustment pad. Different from the traditional design that the transmission mechanism is installed on the nut shaft diameter, the feature of the nut rotating mechanism of this scheme is that the transmission link is designed on the special end face of the nut, which will reduce the overall diameter of the transmission link, reduce the overall inertia of the rotating mechanism, and improve the dynamic responsiveness of the moving parts. At the same time, the overall structure is more concise, which improves the reliability of the entire transmission system. Figure 5 As shown, in order to facilitate the coaxiality of the nut with the connecting flange during assembly, it is necessary to add a positioning boss to the front end of the conventional ball screw nut, and at the same time meet the necessary coaxiality and end face runout requirements. In addition, unlike the conventional ball screw nut, the lubrication hole at the end is a threaded hole, and the lubrication hole at the end of the nut is a through hole.

[0023] 3. Since the feed shaft adopts the method of the screw not rotating but the nut rotating, the water cooling joints at both ends of the screw are ordinary joints, and there is no need to use a rotary joint, which reduces the cost, eliminates the problem of high failure rate of the rotary joint, and improves the reliability of the water cooling system.

[0024] 4. Due to the structural limitations of the large turntable, in order to facilitate adjustment and maintenance, the grating ruler probe can only be installed on the outside of the turntable. The distance between the grating ruler probe and the linear axis coordinate zero point, that is, the turntable rotation center, is relatively far. The fixed end of the carbon fiber rod with a low linear expansion coefficient is installed at the center of the turntable through a bracket, and the floating end extends to the end of the turntable. The grating ruler probe is installed on the floating end of the carbon fiber rod through the bracket. In this way, the exact position of the turntable zero point is transmitted to the grating ruler probe, and the exact size of the turntable zero point is accurately read. The closed-loop feedback of the grating ruler improves the accuracy of the feed axis, avoiding the grating ruler detection error caused by thermal elongation caused by the temperature rise of the turntable when the probe is installed at the end of the turntable.

[0025] 5. Heat is inevitably generated during the operation of the machine tool due to factors such as movement friction and cutting heat. Heat will cause thermal deformation of machine tool parts, and the detection elements will also be thermally deformed when heated. The deformation of the detection elements themselves will also cause errors. The temperature sensor detects the temperature change of the bed near the grating scale. By comparing it with the base temperature, the detection error caused by the asynchronous deformation of the glass grating of the grating scale and the large machine tool bed due to the different linear expansion coefficients of the materials during temperature changes is eliminated.

[0026] 6. The water-cooled design of the servo motor, ball screw, and guide rail slider can reduce the heat generated during the operation of the feed axis in real time and suppress the overall thermal deformation of the feed system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an illustration of the overall structural layout of the present invention;

[0028] Figure 2 It is a cross-sectional view of the structure of the lead screw and the nut drive of the present invention;

[0029] Figure 3 The present invention is a floating probe installation structure based on a carbon fiber rod;

[0030] Figure 4 This is a top view of the turntable mechanism without the bed of the present invention;

[0031] Figure 5 This is an enlarged top view of the probe floating installation mechanism;

[0032] Figure 6 This is the end requirement diagram of the ball screw nut;

[0033] Figure 7 This is a schematic diagram of the cooling of the guide rail slider.

[0034] Among them: A-bed; B1-right screw support mechanism; B2-left screw support mechanism; C-turntable; D-right screw drive mechanism; E-water-cooled servo motor; F-grating ruler; G-temperature sensor; 100-water inlet connector; 101-right support; 102-screw body; 103-nut; 104-connecting flange; 105-rotating seal ring a; 106-rotating seal ring b; 107-thrust angular contact bearing; 108-bearing support; 109-positioning boss; 112-large pulley; 114-small pulley; 115-arc toothed belt; 117-limit key; 118-left support; 119-disc spring assembly; 121-rotating nut; 122-return joint; 123-cooling pipeline; 124-guide rail slider; 201-fixed bracket; 202-connecting seat a; 203-connecting rod a; 204-carbon fiber rod; 205-connecting rod b; 206-probe seat; 207-spring sheet; 208-pressure block; 209-adjustment pad; 210-connecting seat b; 211-grating ruler probe; 212-floating bracket; 213-floating end. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and by way of examples, but the present invention is not limited to the following examples.

[0036] A method for realizing high-precision linear feed motion of a large rotary table of a machine tool comprises the following steps

[0037] Step 1: Improvement of mechanical accuracy of feed axis of large rotary table of machine tool:

[0038] like Figure 1 As shown in the figure, the overall structure of the bed adopts a thermally symmetrical layout. The turntable C is installed on the guide rail of the bed A. The left screw support mechanism B2 and the right screw support mechanism B1 are fixed on the bed A. Each screw support mechanism is equipped with a screw drive mechanism, such as the right screw drive mechanism D. The right screw drive mechanism D is concentric with the right screw support mechanism B1 and is installed on the side of the turntable C. A water-cooled servo motor E is installed at the tail end of the right screw drive mechanism D. The screw support mechanism, the screw drive mechanism and the water-cooled servo motor E are completely symmetrically installed with the center of the turntable to form a turntable dual-drive mechanism. The stability of the linear movement of the large turntable is ensured by the symmetrical screw dual drive. During the feeding process, the dual feed axes adopt the master-slave control mode, with one feed axis as the main one and the other feed axis following synchronously to ensure the stable operation of the feeding motion.

[0039] like Figure 1 , 2As shown, two screw feed systems are symmetrically installed on the machine tool bed A. The screws are composed of a screw body 102 and a nut 103. One end of the screw body 102 of each screw is fixed to the right support 101 through a tightening sleeve as a fixed end, and the other end is a stretching end, which is connected to the left support 118 through a limit key 117. The stretching end is also provided with a disc spring group 119 and a nut 121; a nut 103 is installed in the middle of the screw, as shown in FIG. Figure 6 As shown, a positioning boss 109 coaxial with the main body of the nut 103 is designed at the left end of the nut 103; the connecting flange 104 cooperates with the nut 103 through the positioning boss, and the connecting flange 104 and the nut 103 are screwed together; a thrust angular contact bearing 107 is installed on the connecting flange 104; the inner ring of the thrust angular contact bearing 107 contacts with the connecting flange 104, and the end is tightened by a nut, the outer diameter of the thrust angular contact bearing 107 is connected to the bearing support 108, and the outer ring of the thrust angular contact bearing 107 is designed with a bolt through hole, and the inner ring is screwed together with the bearing support 108 by screws, and the bearing support 108 is connected to the turntable C; the large pulley 112 is connected to the connecting flange 104 through a tightening sleeve The power input relies on the water-cooled servo motor E, and a small pulley 114 is installed on the shaft end of the water-cooled servo motor E. The large pulley 112 and the small pulley 114 are connected by a circular arc toothed belt 115. When working, the power output by the water-cooled servo motor E is transmitted to the nut 103 of the lead screw through the small pulley 114, the circular arc toothed belt 115, the large pulley 112; at the same time, the nut 103 is rotating during the working process, and a rotating sealing ring a105 and a rotating sealing ring b106 are provided on the outer side of the connecting flange 104. An independent space is formed between the two rotating sealing rings as a transmission channel for the lubricating oil of the nut 103. When lubricating, the lubricating oil reaches this independent space through the bearing support 108 and enters the inside of the nut 103.

[0040] During the pre-stretching process of the lead screw, a dial indicator needs to be placed at the fixed end of the lead screw, and the rotating nut 121 next to the rotating disc spring group 119 is rotated. During the rotation process, the rotating nut 121 transmits the tensioning force to the lead screw body 102 through the disc spring group 119, and the lead screw body 102 is stretched. The stretching amount K should follow K≥α.TL. Among them, α is the linear expansion coefficient of the lead screw, T is the temperature rise of the lead screw from room temperature to the thermal stability state of this type of machine tool, and L is the total length of the lead screw support span. When the value of the dial indicator reaches the stretching requirement, the rotating nut 121 is locked. After the stretched screw expands due to temperature rise, the expansion force is offset by the stretching force, and the screw will not be thermally deformed, ensuring the precision and position stability of the screw during operation. The water-cooled servo motor E transmits the rotational power to the connecting flange 104 through the large pulley 112 and the small pulley 114, and the connecting flange 104 transfers the power to the nut 103. During operation, the screw does not rotate, but the nut 103 rotates, thereby driving the entire turntable component to move along the bed guide rail as a whole.

[0041] Step 2: Avoid thermal deformation based on the structural characteristics of the turntable:

[0042] like Figure 1 , 3 4, one end of the carbon fiber rod 204 is a fixed end, and the other end is a floating end 213, the connection seat a202 of the fixed end is installed on the fixed bracket 201, the fixed bracket 201 is installed in the center of the turntable C, and the floating end 213 extends to the end of the turntable C; the carbon fiber rod 204 is a hollow carbon rod, and the two ends are respectively bonded to the connecting rod a203 and the connecting rod b205 by AB glue; the connecting rod b205 is installed in the clamping hole of the probe seat 206, and the carbon fiber rod 204 is supported by the floating bracket 212 of the spring sheet 207 to install the grating ruler probe 211 on the floating end 213 of the carbon fiber rod 204, and the spring sheet 207 is pressed by four blocks 208. The spring sheet 207 is made of 65Mn spring steel and is installed vertically to ensure good rigidity in the up and down directions and good elasticity in the axial direction of the carbon fiber rod 204; the floating bracket 212 is installed on the outer end face of the turntable C, and the connecting seat b210 is installed on the floating bracket 212 through the adjustment pad 209. When the turntable C is working, the turntable body expands and stretches. The setting of the spring sheet 207 can not only play a stable supporting role for the carbon fiber rod 204 and the grating ruler probe 211, but also avoid the axial thermal elongation caused by the expansion of the turntable C, and transmit the position change of the zero point of the center coordinate of the turntable through the carbon fiber rod 204. In this way, the accurate position of the zero point of the turntable is transmitted to the grating ruler probe 211, and the accurate size of the zero point of the turntable is accurately read, and the accuracy of the feed axis is improved through the closed-loop feedback of the grating ruler.

[0043] Taking a 2000mm turntable as an example, the distance from the rotation center to the installation position of the probe is about 1000mm. When the turntable generates an overall temperature rise of about 5°C during operation, the turntable base is made of cast iron, and its linear expansion coefficient is 0.000012mm / °C. At this time, the thermal expansion from the turntable axis to the probe position is: 0.000012×1000×5=0.06mm. This error will cause inaccurate grating scale detection position, and the gradual expansion of the turntable during the temperature rise will also cause instability in the grating scale probe monitoring data. The above-mentioned carbon rod with a low linear expansion coefficient caused by the distance between the turntable coordinate zero point and the grating scale probe detection point circumvents this problem. The linear expansion coefficient of conventional carbon fiber is one order of magnitude lower than that of steel. For example, the thermal expansion coefficient of T300 carbon fiber is 0.00000074, which is about 1 / 16 of that of steel and is a negative value. The measurement error of the grating ruler probe using T300 carbon fiber rod as the support rod due to thermal deformation is 0.00000074×1000×5=-0.0037mm, which is much smaller than the position accuracy error requirement of the machine tool. In addition, the carbon fiber rod is an outsourced part, and its thermal expansion coefficient depends on the ratio of carbon fiber to resin when the carbon fiber rod is made. Among them, the thermal expansion coefficient of carbon fiber is negative, and the linear expansion coefficient of resin is positive, although the carbon fiber rod has a low thermal expansion coefficient as a whole. However, through a reasonable ratio, the carbon fiber with negative thermal expansion properties is combined with the resin matrix with positive thermal expansion coefficient, and the thermal expansion coefficient of the specially customized carbon fiber rod can be close to zero. This makes it easy to obtain higher accuracy than ordinary carbon fiber rods when using this structure. But this depends on the technical level of the carbon fiber rod manufacturer. Given the difference in linear expansion coefficient between carbon fiber rods and cast iron materials, beneficial effects can be achieved even with conventional carbon fiber rods.

[0044] Step 3: Compensation for thermal deformation:

[0045] like Figure 1 , 4 As shown in , 5, a vertical boss is designed in the middle of the bed A, and the grating ruler F is installed on the boss of the bed. Threaded holes are designed on the side surface of the boss according to the length of the bed, and temperature sensors G are installed in the threaded holes. There are three temperature sensors G (depending on the feed stroke, the number of sampling points can be increased according to the situation, not limited to three), which are installed at the left end, middle and right end of the grating ruler F respectively. Figure 1 The temperature sensor G shown in the figure is the left sensor. The specific working steps are as follows: First, laser accuracy detection is performed before the machine tool leaves the factory, and the temperature under the current machine tool detection state is set as temperature T1. Laser detection is performed under the current temperature state to form the current qualified accuracy data of the machine tool. When processing workpieces, the overall temperature of the machine tool will change due to changes in ambient temperature and during the operation of the machine tool. Figure 4The three temperature sensors G shown in the figure read the temperature data, and the average value is set as the current machine tool temperature T2. Taking the overall temperature rise as an example, the temperature rise will cause the overall length of the machine tool in the feed direction to become longer. The linear expansion coefficient of the large part of the bed is set to α1, and the linear expansion coefficient of the glass grating in the grating ruler is set to α2. The machine tool movement distance is L1, and the temperature correction coefficient is k. Then, when the turntable moves linearly for a distance of L1, the grating ruler detection accuracy error δ≈(α1-α2)·k(T1-T2)·L1 caused by the difference in the linear expansion coefficient between the grating ruler F and the bed. During the feed movement of the machine tool, the error compensation is performed in real time through system calculation to improve the linear motion position accuracy of the turntable.

[0046] Step 4: Heat source control:

[0047] like Figure 2 , 7 The servo motor adopts a water-cooled servo motor E; the screw body 102 adopts a hollow design, and the water inlet joint 100 and the return joint 122 are installed at both ends respectively. Cooling water flows inside the screw body 102. The heat generated during the operation of the feed shaft is reduced in real time through continuous cooling water, thereby suppressing the overall thermal deformation of the feed system. At the same time, because the feed shaft adopts a method in which the screw does not rotate and the nut 103 rotates, the water-cooling joints at both ends of the screw are ordinary joints. There is no need to use a rotary joint at the end of the screw like traditional screw water cooling, which reduces costs and eliminates the problem of high failure rate of the rotary joint, thereby improving the reliability of the water cooling system. The mounting joint surface of the machine tool guide rail slider 124 and the turntable C base is designed with a groove, and a cooling pipeline 123 is arranged in the groove. The friction heat generated during the movement of the slider and the guide rail is cooled by circulating cooling to prevent the temperature rise of the guide rail from affecting the overall thermal stability of the turntable.

[0048] The above description is only a preferred implementation example of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A method for realizing high-precision linear feed motion of a large rotary table of a machine tool, characterized in that: The following steps are involved: Step 1: Improvement of mechanical accuracy of feed axis of large rotary table of machine tool: The overall structure of the bed adopts a thermally symmetrical design layout, the feed axis adopts a symmetrical double-drive layout of the lead screw, and each set of lead screws is pre-stretched. The drive mode of the lead screw is that the lead screw is fixed and does not rotate, and the nut rotates; The bed adopts a full thermal symmetry design to ensure that the thermal deformation of the whole machine is uniform and stable. The two screw feed systems are symmetrically installed on the machine bed. The screw consists of a screw body and a nut. One end of the screw body of each screw is fixed to the right support through a tightening sleeve, and the other end is a stretching end, which is connected to the left support through a limit key. The stretching end is also provided with a disc spring group and a nut; a nut is installed in the middle of the screw, and a positioning boss coaxial with the nut body is designed at the left end of the nut; the connecting flange and the nut are matched through the positioning boss and the connecting flange and the nut are screwed together; a thrust bidirectional angular contact bearing is installed on the connecting flange; the inner ring of the thrust angular contact bearing is in contact with the connecting flange, the end is pressed by a nut, and the outer diameter is connected to the bearing support The outer ring of the thrust angular contact bearing is designed with a bolt through hole, the inner ring is screwed together with the bearing support, and the bearing support is connected to the turntable; the large pulley is connected to the connecting flange through a tightening sleeve, the power input depends on the servo motor, a small pulley is installed on the shaft end of the servo motor, and the large pulley and the small pulley are connected through a circular arc toothed belt; when working, the power output by the servo motor is transmitted to the nut of the lead screw through the small pulley, the circular arc toothed belt, and the large pulley; at the same time, the nut is rotating during the working process, and two rotating sealing rings are arranged on the outside of the connecting flange. An independent space is formed between the two rotating sealing rings as a transmission channel for the nut lubricating oil. During lubrication, the lubricating oil reaches this independent space through the bearing support and enters the inside of the nut; During the pre-stretching process of the screw, a dial indicator needs to be placed on the fixed end of the screw to rotate the rotating nut next to the disc spring group. During the rotation process, the rotating nut transmits the tensioning force to the screw body through the disc spring group, and the screw body is stretched. When the value of the dial indicator reaches the stretching requirement, the rotating nut is locked. After the stretched screw expands due to temperature rise, the expansion force is offset by the stretching force, and the screw will not be thermally deformed, ensuring that the precision position of the screw is stable during operation. The servo motor transmits the rotational power to the connecting flange through the large pulley and the small pulley, and the connecting flange transfers the power to the nut. During operation, the screw does not rotate, but the nut rotates, thereby driving the entire turntable component to move along the bed guide rail as a whole; Step 2: Avoid thermal deformation based on the structural characteristics of the turntable: The rotary center of the turntable is used as the coordinate zero point of the feed axis. One end of a carbon fiber rod with a low linear expansion coefficient is fixed near the center of the turntable. The other end is supported by a bracket built with spring sheets to form a floating support. A grating ruler probe is installed on the floating support end. The low expansion coefficient of the carbon fiber rod is used to transmit the accurate position change of the coordinate zero point, avoiding the grating ruler detection error caused by thermal elongation due to temperature rise during the operation of the turntable casting body. Step 3: Compensation for thermal deformation: Three sets of temperature sensors are installed on the bed below the grating ruler to detect the temperature change of the bed near the grating ruler. By comparing the temperature with the base temperature and performing position compensation, the detection error caused by the asynchronous deformation of the glass grating of the grating ruler and the bed during temperature change due to the different linear expansion coefficients of the materials can be eliminated, thereby improving the detection accuracy. The specific working steps are as follows: First, laser precision detection is carried out before the machine tool leaves the factory. The temperature in the current machine tool detection state is set as temperature T1. Laser detection is carried out under the current temperature state to form the current qualified precision data of the machine tool. When the workpiece is processed, the overall temperature of the machine tool will change due to changes in ambient temperature and the operation of the machine tool. The temperature data is read through three temperature sensors G, and the average value is set as the current machine tool temperature T2. Taking the overall temperature increase as an example, the temperature increase will cause the overall length of the machine tool in the feed direction to become longer. The linear expansion coefficient of the large part of the bed is set to α1, the linear expansion coefficient of the glass grating in the grating ruler is set to α2, the machine tool movement distance is L1, and the temperature correction coefficient is k. When the turntable moves linearly for a distance of L1, the grating ruler detection accuracy error δ≈(α1-α2)·k(T1-T2)·L1 caused by the difference in the linear expansion coefficient of the grating ruler F and the bed, during the feed movement of the machine tool, the error compensation is carried out in real time through system calculation to improve the linear motion position accuracy of the turntable; Step 4: Heat source control: Thermal control of the heat source is achieved by water cooling the heat source of the lead screw, servo motor, and guide rail slider during operation.

2. The method for realizing high-precision linear feed motion of a large-scale rotary table of a machine tool according to claim 1, characterized in that: In step 2, one end of the carbon fiber rod is a fixed end and the other end is a floating end. The fixed end is installed at the center of the turntable through a fixed bracket, and the floating end extends to the end of the turntable. The grating scale probe is installed on the floating end of the carbon fiber rod through a floating bracket supported by a spring sheet. In this way, the exact position of the turntable zero point is transmitted to the grating scale probe, and the exact size of the turntable zero point is accurately read. The accuracy of the feed axis is improved through the closed-loop feedback of the grating scale.

3. The method for realizing high-precision linear feed motion of a large-scale rotary table of a machine tool according to claim 1, characterized in that: In step 3, the number of the temperature sensors can be increased according to the length of the grating scale.

4. The method for realizing high-precision linear feed motion of a large-scale rotary table of a machine tool according to claim 1, characterized in that: In step 4, a water-cooled servo motor is used as the servo motor; the lead screw body adopts a hollow design, with a water inlet joint and a water return joint installed at both ends respectively, and cooling water flows inside, which can reduce the heat generated during the operation of the feed shaft in real time and suppress the overall thermal deformation of the feed system.

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