An electric spindle with error compensation and force feedback functions and control method thereof

Abstract

The present invention discloses an electric spindle with error compensation and force feedback functions and a control method thereof. The electric spindle includes a stator, a micro-displacement compensation actuator, a spindle, an electric spindle housing, and a cooling system; the stator includes a stator silicon steel sheet and a stator winding, and the spindle is composed of an output shaft, a spline sleeve, a hexagon socket head screw, a countersunk cross screw, a ball assembly, a rotor, a nut flange, a support shaft, and a pre-tightening bolt. The rotor includes a permanent magnet, a rotor silicon steel sheet, a rotor sleeve, and a rotor sleeve nut. The present invention adopts the above-mentioned electric spindle with error compensation and force feedback functions and a control method thereof, designs a micro-displacement compensation actuator according to the positive and negative effects of giant magnetostrictive materials, and integrates it inside the electric spindle, realizes thermal error compensation of the electric spindle and compensates for machining errors existing during axial machining operations of the electric spindle, and improves machining accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of precision machining, and in particular to an electric spindle with error compensation and force feedback functions and a control method thereof. Background Art

[0002] As the core component of high-precision machine tools, high-precision electric spindles have greatly improved the machining accuracy and efficiency of machine tools. The electric spindle is a structure that combines the machine tool spindle and the motor rotor into one. It consists of a stator, a rotor, a bearing, a housing and other parts. Its working principle is to use electromagnetic induction. When three-phase alternating current is passed through the stator, a rotating magnetic field is generated. The rotor rotates at high speed under the action of the rotating magnetic field. The rotor of the electric spindle rotates at high speed and transmits the rotational motion to the tool through the connecting parts. The tool contacts the workpiece under high-speed rotation for cutting. During the rotation process, the accuracy, rigidity and stability of the electric spindle play a vital role in the processing quality.

[0003] As the speed and power of the electric spindle increase, the electromagnetic heat generated between the stator and rotor inside the electric spindle and the heat generated by the friction of the bearings also increase, resulting in the electric spindle's axial thermal expansion becoming larger and larger as the working time increases. In addition, the vibration generated when the electric spindle is working causes processing errors when the electric spindle is performing axial processing operations. For some parts with required dimensions in the depth direction, the accuracy of the thermal expansion in the depth direction and the error compensation will seriously affect the processing accuracy. Therefore, it is proposed in the prior art to measure the thermal expansion of the electric spindle, and then compensate for the thermal expansion of the electric spindle in the axial direction, so as to ensure the processing accuracy of the machine tool. With regard to the error compensation for the axial direction of the electric spindle, the prior art uses the machine tool's own numerical control system to compensate for the thermal expansion of the electric spindle and the processing errors during the electric spindle processing, and does not start from the perspective of the error compensation mechanism.

[0004] For example, in the patent document entitled Intelligent Electric Spindle System for CNC Machine Tools with patent number CN111273605A, the error compensation module calculates the current compensation value based on the displacement signal from the displacement sensor collected by the data acquisition module and the spindle error model and outputs it to the CNC system of the CNC machine tool, and compensates for the deformation of the spindle through the error compensation function of the CNC system itself. Although this can reduce the machining error of the electric spindle, the CNC system of the machine tool is affected by the error of the ball screw mechanism itself when controlling the axial ball screw mechanism of the electric spindle for error compensation, and as the working time increases, the error of the ball screw mechanism increases due to wear and thermal deformation when performing axial error compensation of the electric spindle, which makes it difficult to meet the high-precision machining requirements of the electric spindle.

[0005] In order to overcome the shortcomings of the prior art, the present invention provides an integrated high-speed electric spindle with error compensation and force feedback functions and a control method thereof. A micro-displacement compensation actuator is designed based on the positive and negative effects of giant magnetostrictive materials and integrated inside the electric spindle, realizing thermal error compensation of the electric spindle and compensation for machining errors existing during axial machining of the electric spindle, thereby improving machining accuracy. Real-time monitoring of tool force during the working period of the electric spindle is realized, and feedback control of the axial machining operation of the electric spindle is realized according to the set tool force threshold, thereby extending tool service life and improving machining quality. Summary of the invention

[0006] The purpose of the present invention is to provide an electric spindle with error compensation and force feedback functions and a control method thereof. A micro-displacement compensation actuator is designed according to the positive and negative effects of a giant magnetostrictive material and integrated inside the electric spindle, thereby realizing thermal error compensation of the electric spindle and compensation for machining errors existing during axial machining operations of the electric spindle, improving machining accuracy, and realizing real-time monitoring of tool force during the working period of the electric spindle. According to a set tool force threshold, feedback control of the axial machining operations of the electric spindle is realized, thereby extending tool service life and improving machining quality.

[0007] To achieve the above-mentioned objectives, the present invention provides an electric spindle with error compensation and force feedback functions, including a stator, a micro-displacement compensation actuator, a spindle, an electric spindle housing, and a cooling system; the stator includes a stator silicon steel sheet and a stator winding, the spindle consists of an output shaft, a spline sleeve, a hexagon socket head screw 1, a countersunk cross screw, a ball assembly, a rotor, a nut flange, a support shaft, and a pre-tightening bolt; the electric spindle housing includes an electric spindle housing assembly 1, an electric spindle housing assembly 2, an electric spindle housing assembly 3, a hexagon socket head screw 2, and a hexagon socket head screw 3; the rotor includes a permanent magnet, a rotor silicon steel sheet, a rotor sleeve, and a rotor sleeve nut; the rotor silicon steel sheets are stacked and installed on the rotor sleeve, and are threadedly connected to the rotor sleeve nut by a set screw 1 to axially fix the rotor silicon steel sheets, and the permanent magnet The body circumference is evenly installed in the rotor silicon steel sheet slot, the micro-displacement compensation actuator includes a giant magnetostrictive rod, a magnetic block, a coil bracket, an excitation coil, and an induction coil, the excitation coil and the induction coil are wound on the coil bracket, the giant magnetostrictive rod is arranged inside the coil bracket, and magnetic blocks are arranged at both ends of the giant magnetostrictive rod; one end of the output shaft is a stepped shaft, the support shaft is a stepped shaft, one end of which is provided with an internal threaded hole and threadedly connected with a pre-tightening bolt, and the support of the electric spindle housing component three is obtained through a deep groove ball bearing, and a conductive slip ring is arranged on the support shaft, the conductive slip ring is axially installed on the support shaft and is fixed to the end face of the electric spindle housing component three by screws, the electric spindle housing component one and the electric spindle housing component three are located at both ends of the electric spindle housing component two, and are connected respectively by using a second hexagon socket head screw and a third hexagon socket head screw.

[0008] Preferably, the cooling system is composed of a cooling groove with sealing rings at both ends installed coaxially opposite to the second electric spindle housing component, and a coolant inlet is provided on the outer surface of the second electric spindle housing component close to the output shaft side, and a coolant outlet is provided on the side away from the output shaft.

[0009] Preferably, one side of the output shaft is supported by the electric spindle housing assembly 1 through the outer ring plane bearing, and four keys are evenly arranged in the circumferential direction of the other side of the output shaft, and each key is symmetrically provided with a rectangular groove 1 on two axial sides, and threaded through holes are provided at both ends of the rectangular groove 1, and the ball assembly is installed in the rectangular groove 1 on the side of each key and fixed by a countersunk cross screw; the output shaft with the ball assembly installed is matched with the spline sleeve for shaft key, and the spline sleeve is provided with a countersunk threaded hole in the circumferential direction and is threadedly connected with the rotor sleeve by a hexagon socket cylindrical head screw 1, so that the rotor torque is transmitted to the output shaft through the spline sleeve, the outer end face of the magnetic block at one end of the giant magnetostrictive rod is tightly fitted with the stepped shaft at one end face of the output shaft, and the magnetic block at the other end of the giant magnetostrictive rod is tightly fitted with the pre-tightening bolt, and the pre-tightening bolt and the support shaft with an internal thread at one end form a threaded pair, and tightening the pre-tightening bolt provides a pre-tightening force for the micro-displacement compensation actuator while providing a supporting force for one end of the giant magnetostrictive rod.

[0010] Preferably, a disc spring is provided at one end of the spline sleeve, and a plane thrust ball bearing is provided between the disc spring and the outer ring plane bearing.

[0011] Preferably, the nut flange is axially mounted on the support shaft and axially fixed to the support shaft by means of two set screws, and four countersunk threaded holes are evenly opened in the circumferential direction on the nut flange surface, which are threadedly fixed to the rotor sleeve nut by means of four hexagon socket head screws.

[0012] Preferably, the coil bracket is in an I-shape, wherein a rectangular groove 2 is axially provided on one end face to facilitate the excitation coil and the induction coil leads, a through hole is provided inside the rotor sleeve nut, and a rectangular groove 3 is provided on the flange end face along the radial direction.

[0013] A control method for an electric spindle with error compensation and force feedback functions, the control method is implemented based on a single-chip microcomputer control system, the control method includes a displacement error compensation control method and a force feedback control method, the displacement error compensation control method and the force feedback control method cannot be performed at the same time, the displacement error compensation control method includes negative displacement error compensation and positive displacement error compensation, and the prerequisite for negative displacement error compensation is that the giant magnetostrictive rod is already in an extended state;

[0014] Negative displacement error compensation includes the following steps:

[0015] The first step is to set the error threshold according to the machining accuracy requirements;

[0016] The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value;

[0017] In the third step, the error value is substituted into the existing magnetostrictive inverse model as input, and the error compensation current signal is output;

[0018] In the fourth step, the micro-displacement compensation actuator receives the error compensation current signal, reduces the magnetic field generated by the excitation coil, and the disc spring pushes the output shaft to move in the negative direction to perform negative displacement error compensation;

[0019] In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement.

[0020] Positive displacement error compensation includes the following steps:

[0021] The first step is to set the error threshold according to the machining accuracy requirements;

[0022] The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value;

[0023] The third step is to bring the error value into the existing magnetostriction inverse model as an input value and output the error compensation current signal;

[0024] In the fourth step, the micro-displacement compensation actuator receives the error compensation current signal, increases the magnetic field generated by the excitation coil, and pushes the output shaft to move in the positive direction to perform positive displacement error compensation;

[0025] In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement.

[0026] The force feedback control method comprises the following steps:

[0027] The first step is to set the tool force threshold during the machining process according to the selected machining tool and the material of the workpiece;

[0028] In the second step, the induction coil senses the internal magnetic field generated when the giant magnetostrictive rod is subjected to force, causing the induced electromotive force to change, playing the role of a force feedback sensor. The force feedback sensor monitors the axial force exerted on the tool during the machining process in real time and uses it as the force input value.

[0029] In the third step, the single chip control system receives the force input value and compares it with the threshold value;

[0030] Step 4: When the force input value is less than or equal to the force threshold, the electric spindle continues to perform processing operations. Otherwise, the single-chip control system outputs a current signal to the micro-displacement compensation actuator, causing it to enter a negative displacement error compensation mode, and the giant magnetostrictive rod is shortened, thereby reducing the axial force on the output shaft.

[0031] Step 5: Repeat steps 2, 3 and 4 until the axial force on the output shaft is within the force threshold range.

[0032] The advantages and positive effects of the electric spindle with error compensation and force feedback functions and the control method thereof described in the present invention are:

[0033] 1. The present invention designs a micro-displacement compensation actuator based on the forward and reverse effects of giant magnetostrictive materials and integrates it inside the electric spindle, thereby realizing thermal error compensation of the electric spindle and compensating for machining errors existing during axial machining of the electric spindle, thereby improving machining accuracy.

[0034] 2. The present invention realizes real-time monitoring of the tool force during the working period of the electric spindle, and realizes feedback control of the axial processing operation of the electric spindle according to the set tool force threshold, thereby extending the service life of the tool and improving the processing quality.

[0035] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the structure of the electric spindle of the present invention;

[0037] Figure 2 This is a schematic diagram of the installation of the rear axle parts of the electric spindle of the present invention;

[0038] Figure 3 This is an exploded view of the output shaft and the spline sleeve of the present invention;

[0039] Figure 4 A schematic diagram of a coil support of the present invention;

[0040] Figure 5 This is a schematic diagram of the nut flange of the present invention;

[0041] Figure 6 This is a schematic diagram of the rotor sleeve nut of the present invention;

[0042] Figure 7 It is a schematic diagram of the negative displacement and positive displacement error compensation control method of the electric spindle of the present invention;

[0043] Figure 8 It is a schematic diagram of the force feedback control method of the present invention.

[0044] Reference numerals

[0045] 1. Output shaft; 2. Electric spindle housing assembly 1; 3. Outer ring plane bearing; 4. Plane thrust ball bearing; 5. Disc spring; 6. Hexagon socket head screw 1; 7. Spline bushing; 8. Rotor bushing; 9. Stator winding; 10. Electric spindle housing assembly 2; 11. Cooling groove; 12. Stator silicon steel sheet; 13. Permanent magnet; 14. Set screw 1; 15. Rotor bushing nut; 16. Nut flange; 17. Set screw 2; 18. Conductive Slip ring; 19. Support shaft; 20. Electric spindle housing assembly three; 21. Deep groove ball bearing; 22. Pre-tightening bolt; 23. Hexagon socket head screw two; 24. Coil bracket; 25. Magnetic block; 26. Induction coil; 27. Excitation coil; 28. Giant magnetostrictive rod; 29. ​​Sealing ring; 30. Rotor silicon steel sheet; 31. Hexagon socket head screw three; 32. Countersunk cross screw; 33. Ball assembly; 34. Hexagon socket head screw four. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0047] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] Example

[0049] An electric spindle with error compensation and force feedback functions, including a stator, a micro-displacement compensation actuator, a spindle, an electric spindle housing, and a cooling system. The stator includes a stator silicon steel sheet 12 and a stator winding 9. The spindle is composed of an output shaft 1, a spline sleeve 7, a hexagon socket head screw 16, a countersunk cross screw 32, a ball assembly 33, a rotor, a nut flange 16, a support shaft 19, and a pre-tightening bolt 22. The electric spindle housing includes an electric spindle housing assembly 1 2, an electric spindle housing assembly 2 10, an electric spindle housing assembly 3 20, a hexagon socket head screw 2 23, and a hexagon socket head screw 3 31. The electric spindle housing assembly 1 2 and the electric spindle housing assembly 3 20 are located at both ends of the electric spindle housing assembly 2 10, and are connected using the hexagon socket head screw 2 23 and the hexagon socket head screw 3 31 respectively.

[0050] The rotor includes a permanent magnet 13, a rotor silicon steel sheet 30, a rotor sleeve 8, and a rotor sleeve nut 15. The rotor silicon steel sheet 30 is stacked and installed on the rotor sleeve 8, and is threadedly connected with the rotor sleeve nut 15 through a set screw 14 to axially fix the rotor silicon steel sheet 30. The permanent magnet 13 is evenly installed in the groove of the rotor silicon steel sheet 30. The micro-displacement compensation actuator includes a giant magnetostrictive rod 28, a magnetic block 25, a coil support 24, an excitation coil 27, and an induction coil 26. The excitation coil 27 and the induction coil 26 are wound on the coil support 24, wherein the induction coil 26 acts as a force feedback sensor. A giant magnetostrictive rod 28 is arranged inside the coil support 24, and magnetic blocks 25 are arranged at both ends of the giant magnetostrictive rod 28.

[0051] The support shaft 19 is a stepped shaft, one end of which is provided with an internal threaded hole threadedly connected to a pre-tightening bolt 22, and is supported by the electric spindle housing assembly 3 20 through a deep groove ball bearing 21. The conductive slip ring 18 is axially mounted on the support shaft 19 and fixed to the end face of the electric spindle housing assembly 3 20 by screws.

[0052] The cooling system is composed of a cooling groove 11 with sealing rings 29 at both ends and the electric spindle housing component 10 installed coaxially. The outer surface of the electric spindle housing component 10 is provided with a coolant inlet on the side close to the output shaft 1 and a coolant outlet on the side away from the output shaft 1.

[0053] One end of the output shaft 1 is a stepped shaft, and one side of the output shaft 1 is supported by the electric spindle housing assembly 2 through the outer ring plane bearing 3. Four keys are evenly arranged in the circumferential direction on the other side of the output shaft 1. Each key is symmetrically provided with a rectangular groove 1 on two axial sides, and threaded through holes are provided at both ends of the rectangular groove 1. The ball assembly 33 is installed in the rectangular groove 1 on the side of each key and fixed by a countersunk cross screw 32; the output shaft 1 equipped with the ball assembly 33 is matched with the spline sleeve 7 for shaft key, and the spline sleeve 7 is provided with a countersunk threaded hole in the circumferential direction and is threadedly connected with the rotor sleeve 8 by a hexagon socket head screw 6, so that the rotor torque is transmitted to the output shaft 1 through the spline sleeve 7. In addition, the ball assembly 33 can realize the axial movement of the output shaft 1 in the keyway inside the spline sleeve 7, which is to prepare for the axial error compensation of the micro-displacement compensation actuator. The outer end face of the magnetic block 25 at one end of the giant magnetostrictive rod 28 is closely fitted with the stepped shaft at one end face of the output shaft 1, and the magnetic block 25 at the other end of the giant magnetostrictive rod 28 is closely fitted with the pre-tightening bolt 22. The pre-tightening bolt 22 forms a thread pair with the support shaft 19 with an internal thread at one end. Tightening the pre-tightening bolt 22 provides pre-tightening force for the micro-displacement compensation actuator and provides support force for one end of the giant magnetostrictive rod 28. A disc spring 5 is provided at one end of the spline sleeve 7, and a plane thrust ball bearing 4 is provided between the disc spring 5 and the outer ring plane bearing 3.

[0054] When the micro-displacement compensation actuator performs positive displacement error compensation, the giant magnetostrictive rod 28 begins to extend under the action of the magnetic field generated by the excitation coil 27. Because one end of the giant magnetostrictive rod 28 is supported by the pre-tightening bolt 22, the giant magnetostrictive rod 28 pushes the magnetic block 25, thereby pushing the output shaft 1 to extend, thereby achieving compensation for the positive displacement error; when the micro-displacement compensation actuator performs negative displacement error compensation, the pre-tightening force provided by the pre-tightening bolt 22 and the thrust provided by the giant magnetostrictive rod 28 that originally maintains the extended state (before the micro-displacement compensation actuator performs negative displacement error compensation, the giant magnetostrictive rod 28 is already in an extended state to ensure that the disc spring 5 is in a compressed state), so that the disc spring 5 is in a compressed state, and in order to prevent the disc spring 5 from rubbing against the outer ring plane bearing 3 when the output shaft 1 rotates, a plane thrust ball bearing 4 is added between the two, reducing the current passed into the excitation coil 27, so that the giant magnetostrictive rod 28 is shortened under the spring force of the disc spring 5, thereby shortening the output shaft 1, thereby achieving negative displacement error compensation.

[0055] The nut flange 16 is axially mounted on the support shaft 19 and axially fixed to the support shaft 19 by means of a set screw 17, and four countersunk threaded holes are evenly opened in the circumferential direction on the surface of the nut flange 16, which are threadedly fixed to the rotor sleeve nut 15 by means of a hexagon socket head screw 34, thereby providing support for the electric spindle rotor together with the output shaft 1.

[0056] The coil support 24 is in an I-shape, and a rectangular groove 2 is axially provided on one end face thereof to facilitate the lead-in of the excitation coil 27 and the induction coil 26. A through hole is provided inside the rotor sleeve nut 15, and a rectangular groove 3 is provided on the flange end face of the nut 16 along the radial direction, so that the coil on the coil support 24 can lead the wire to the conductive slip ring 18 through the rectangular groove 3 and the through hole.

[0057] A control method for an electric spindle with error compensation and force feedback functions, the control method is implemented with a single-chip microcomputer control system as a carrier, the single-chip microcomputer control system belongs to the prior art and will not be described here. The control method includes a displacement error compensation control method and a force feedback control method, the displacement error compensation control method and the force feedback control method cannot be performed at the same time, the displacement error compensation control method includes negative displacement error compensation and positive displacement error compensation, and the prerequisite for negative displacement error compensation is that the giant magnetostrictive rod 28 is already in an extended state. Set the extension direction of the output shaft 1 to the positive direction and positive displacement, and the shortening direction of the output shaft 1 to the negative direction and negative displacement.

[0058] Negative displacement error compensation includes the following steps:

[0059] The first step is to set the error threshold according to the machining accuracy requirements;

[0060] The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value;

[0061] In the third step, the error value is substituted into the existing magnetostrictive inverse model as input, and the error compensation current signal is output;

[0062] Step 4: The micro-displacement compensation actuator receives the error compensation current signal, reduces the magnetic field generated by the excitation coil 27, and the disc spring 5 pushes the output shaft 1 to move in the negative direction to perform negative displacement error compensation;

[0063] In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement.

[0064] The working principle of the micro-displacement compensation actuator is as follows: when the micro-displacement compensation actuator performs positive displacement error compensation, the giant magnetostrictive rod 28 begins to extend under the action of the magnetic field generated by the excitation coil 27. Since one end of the giant magnetostrictive rod 28 is supported by the pre-tightening bolt 22, the giant magnetostrictive rod 28 pushes the magnetic block 25, thereby pushing the output shaft 1 to extend, thereby achieving positive displacement error compensation; when the micro-displacement compensation actuator performs negative displacement error compensation, the pre-tightening force provided by the pre-tightening bolt 22 and the pre-tightening force provided by the giant magnetostrictive rod 28 that originally maintains the elongated state are Thrust (before the micro-displacement compensation actuator performs negative displacement error compensation, the giant magnetostrictive rod 28 is already in an extended state, ensuring that the disc spring 5 is in a compressed state), so that the disc spring 5 is in a compressed state and in order to prevent the disc spring 5 from rubbing against the outer ring plane bearing 3 when the main shaft rotates, a plane thrust ball bearing 4 is added between the two to reduce the current passed into the excitation coil 27, so that the giant magnetostrictive rod 28 is shortened under the spring force of the disc spring 5, thereby shortening the output shaft 1 and realizing negative displacement error compensation.

[0065] Hysteresis nonlinear model (magnetostriction positive model)

[0066] In the theoretical model of ferromagnetic material JA magnetization, the relationship between the magnetization intensity M and the external magnetic field H is as follows:

[0067]

[0068] Where: H e is the effective magnetic field of the magnetic material; H = nI is the external magnetic field; α is the domain wall interaction coefficient of the ferromagnetic material; a is the shape factor of the ferromagnetic material; M an is the hysteresis-free magnetization of the ferromagnetic material; M s is the saturation magnetization; M rev is the reversible magnetization; M irr is the irreversible magnetization intensity; δ is a symbolic constant, when dH / dt<0, δ=-1; when dH / dt>0, δ=1; k is the irreversible loss coefficient; c is the reversible component coefficient. δ M To remove the negative magnetic susceptibility parameter, it is expressed as

[0069]

[0070] The magnetostriction coefficient λ and elongation ΔL of the giant magnetostrictive rod under the action of the magnetic field should be

[0071]

[0072] Where: λ is the magnetostriction coefficient of the ferromagnetic material; λ sis the saturation magnetostriction coefficient; ΔL is the elongation of the giant magnetostrictive rod; L is the original length of the giant magnetostrictive rod. Equations (1) and (3) constitute the displacement hysteresis nonlinear model of the micro-motion part. The output displacement of the micro-motion part can be obtained from the input current I.

[0073] The magnetostrictive inverse model is derived from the existing magnetostrictive positive model. According to the magnetostrictive positive model, the displacement under any current can be calculated. Through the magnetostrictive positive model, the relationship between current and displacement is established, and then the neural network algorithm is learned. Conversely, when the neural network algorithm measures a known displacement, the current value is deduced by comparing the positive model data.

[0074] Positive displacement error compensation includes the following steps:

[0075] The first step is to set the error threshold according to the machining accuracy requirements;

[0076] The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value;

[0077] The third step is to bring the error value into the existing magnetostriction inverse model as an input value and output the error compensation current signal;

[0078] In the fourth step, the micro-displacement compensation actuator receives the error compensation current signal, increases the magnetic field generated by the excitation coil 27, and pushes the output shaft 1 to move in the positive direction to perform positive displacement error compensation;

[0079] In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement.

[0080] The force feedback control method comprises the following steps:

[0081] The first step is to set the tool force threshold during the machining process according to the selected machining tool and the material of the workpiece;

[0082] In the second step, the induction coil 26 senses the internal magnetic field generated when the giant magnetostrictive rod 28 is subjected to force, causing the induced electromotive force to change, and plays the role of a force feedback sensor. Based on the piezomagnetic equation established by the self-sensing mechanism and combined with Faraday's law of electromagnetic induction, a mathematical model of the current-magnetic field-force three-field coupling is established and a force feedback sensor is designed to achieve real-time monitoring of the tool force during the working period of the electric spindle. The force feedback sensor monitors the axial force exerted on the tool during the machining process in real time and uses it as the force input value;

[0083] In the third step, the single-chip control system receives the force input value and compares it with the threshold value. According to the set tool force threshold value, feedback control of the electric spindle axial processing operation is realized to extend the tool life and improve the processing quality.

[0084] Step 4: When the force input value is less than or equal to the force threshold, the electric spindle continues to perform processing operations. Otherwise, the single-chip control system outputs a current signal to the micro-displacement compensation actuator, causing it to enter a negative displacement error compensation mode, and the giant magnetostrictive rod 28 is shortened, thereby reducing the axial force on the output shaft 1.

[0085] Step 5: Repeat steps 2, 3 and 4 until the axial force on the output shaft 1 is within the force threshold range.

[0086] The piezomagnetic equation of the giant magnetostrictive rod working under constant temperature conditions is:

[0087] ε=s H σ+λH(4)

[0088] B=λσ+μ σ H(5)

[0089] In the formula: ε, σ, H, B, λ, s H , μ σ They are respectively the strain, stress, magnetic field intensity, magnetic flux density, magnetostrictive strain coefficient, compliance coefficient under constant magnetic field and magnetic permeability under constant stress of giant magnetostrictive material.

[0090] Solve H from equation (4) and substitute it into equation (5), and we get:

[0091]

[0092] ε=ΔL / L (7)

[0093] Where: L and ΔL are the initial length and length change of the giant magnetostrictive rod, respectively.

[0094] ΔL can be calculated using the magnetostriction model based on magnetization intensity, namely:

[0095]

[0096] Where: E, μ0 and B0 are the elastic modulus, magnetic permeability in vacuum and initial magnetic flux density of the giant magnetostrictive rod respectively.

[0097] The strain of giant magnetostrictive material is:

[0098]

[0099] Substituting equation (9) into equation (6), we get

[0100]

[0101] The relationship between stress and external load is σ=F e / Ar Substituting into equation (10), the relationship between external load and magnetic flux density is obtained as follows:

[0102]

[0103] Where: F e and A r are the external load on the giant magnetostrictive rod and the cross-sectional area of ​​the giant magnetostrictive rod respectively.

[0104] From formula (11), we can see that the magnetic flux density inside the giant magnetostrictive rod after being subjected to an external load consists of two parts: the first part is the external load F e The first part is the change of magnetic flux density caused by the action; the second part is the initial magnetic flux density inside the giant magnetostrictive rod before it is subjected to the external load.

[0105] According to Faraday's law of electromagnetic induction:

[0106]

[0107] Where: N is the number of turns of the coil; A is the cross-sectional area of ​​the coil; U is the induced voltage; t is the time.

[0108] Determine the relationship between the induced voltage in the coil and the external load:

[0109]

[0110] The present invention integrates a micro-displacement compensation actuator with the spindle on the electric spindle rotor, so that the spindle on the rotor can move axially relative to the electric spindle stator. Under the premise that the axial error compensation performed by the ball screw controlled by the machine tool's own numerical control system cannot meet the high-precision machining requirements, the micro-displacement compensation actuator can perform high-precision error compensation independently of the error compensation of the numerical control system itself, thereby realizing independent compensation for the thermal expansion of the spindle and compensation for machining errors existing during the axial machining operation of the electric spindle.

[0111] When the electric spindle housing of the present invention is axially fixed, the micro-displacement compensation actuator integrated on the spindle can be used as a feeding mechanism to drive the spindle to undergo axial micro-displacement (micrometer level) to achieve independent high-precision axial feeding processing operations. The internal energy dissipation of the electric spindle working for a long time will cause the spindle temperature to rise, which will in turn cause the thermal elongation of the spindle. The micro-displacement compensation actuator can perform negative displacement compensation, so that the spindle on the rotor is displaced in the opposite direction of the thermal elongation to perform error compensation. As the electric spindle works for a long time, the internal bearings of the spindle produce gaps due to friction, resulting in a lower axial preload force of the spindle. The micro-displacement compensation actuator extends the giant magnetostrictive rod 28 to make up for the gap caused by the bearing friction and compensate for the spindle preload force. The electric spindle integrated with the micro-displacement compensation actuator can realize the compensation of the positioning difference of the electric spindle to the workpiece before processing, the compensation of thermal errors during processing, and the compensation of the spindle axial preload force, meet the micron-level processing requirements, and achieve high-precision processing.

[0112] Therefore, the present invention adopts the above-mentioned electric spindle with error compensation and force feedback functions and its control method, designs a micro-displacement compensation actuator according to the positive and negative effects of the giant magnetostrictive material, and integrates it inside the electric spindle, realizes the thermal error compensation of the electric spindle and compensates for the machining error existing in the axial machining operation of the electric spindle, and improves the machining accuracy. In addition, based on the piezomagnetic equation established by the self-sensing mechanism and combined with Faraday's law of electromagnetic induction, a mathematical model of the current-magnetic field-force three-field coupling is established and a force feedback sensor is designed to realize real-time monitoring of the tool force during the working period of the electric spindle, and realize feedback control of the axial machining operation of the electric spindle according to the set tool force threshold, thereby extending the tool life and improving the machining quality.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. An electric spindle with error compensation and force feedback functions, characterized in that: It includes a stator, a micro-displacement compensation actuator, a spindle, an electric spindle housing, and a cooling system; the stator includes a stator silicon steel sheet and a stator winding, the spindle consists of an output shaft, a spline sleeve, a hexagon socket head screw 1, a countersunk cross screw, a ball assembly, a rotor, a nut flange, a support shaft, and a pre-tightening bolt; the electric spindle housing includes an electric spindle housing component 1, an electric spindle housing component 2, an electric spindle housing component 3, a hexagon socket head screw 2, and a hexagon socket head screw 3; the rotor includes a permanent magnet, a rotor silicon steel sheet, a rotor sleeve, and a rotor sleeve nut; the rotor silicon steel sheets are stacked and installed on the rotor sleeve, and are threadedly connected to the rotor sleeve nut by a set screw 1 to axially fix the rotor silicon steel sheets; the permanent magnets are evenly installed in the rotor silicon steel sheet slots circumferentially. The micro-displacement compensation actuator comprises a giant magnetostrictive rod, a magnetic block, a coil bracket, an excitation coil, and an induction coil. The excitation coil and the induction coil are wound on the coil bracket. The giant magnetostrictive rod is arranged inside the coil bracket, and magnetic blocks are arranged at both ends of the giant magnetostrictive rod; one end of the output shaft is a stepped shaft, and the support shaft is a stepped shaft, one end of which is provided with an internal threaded hole and threadedly connected with a pre-tightening bolt, and the support of the electric spindle housing component three is obtained through a deep groove ball bearing, and a conductive slip ring is arranged on the support shaft, and the conductive slip ring is axially installed on the support shaft and fixed to the end face of the electric spindle housing component three by screws, and the electric spindle housing component one and the electric spindle housing component three are located at the two ends of the electric spindle housing component two, and are connected respectively by using a second hexagon socket head screw and a third hexagon socket head screw; The cooling system is composed of a cooling groove with sealing rings at both ends and coaxially installed with the second electric spindle housing component. The outer surface of the second electric spindle housing component is provided with a coolant inlet on the side close to the output shaft and a coolant outlet on the side away from the output shaft; One side of the output shaft is supported by the electric spindle housing assembly through the outer ring plane bearing, and four keys are evenly arranged in the circumferential direction of the other side of the output shaft, and each key is symmetrically provided with a rectangular groove one on two axial sides, and threaded through holes are provided at both ends of the rectangular groove one, and the ball assembly is installed in the rectangular groove one on the side of each key and fixed by a countersunk cross screw; the output shaft with the ball assembly installed is matched with the spline sleeve for shaft key, and the spline sleeve is provided with a countersunk threaded hole in the circumferential direction to be threadedly connected with the rotor sleeve by a hexagon socket cylindrical head screw one, so that the rotor torque is transmitted to the output shaft through the spline sleeve, the outer end face of the magnetic block at one end of the giant magnetostrictive rod is tightly fitted with the stepped shaft at one end face of the output shaft, and the magnetic block at the other end of the giant magnetostrictive rod is tightly fitted with the pre-tightening bolt, and the pre-tightening bolt and the support shaft with an internal thread at one end form a threaded pair, and tightening the pre-tightening bolt provides a pre-tightening force for the micro-displacement compensation actuator while providing a supporting force for one end of the giant magnetostrictive rod; The nut flange is axially installed on the support shaft and is axially fixed to the support shaft by a second set screw, and four countersunk threaded holes are evenly opened in the circumferential direction on the nut flange surface, and are threadedly fixed to the rotor sleeve nut by a fourth hexagon socket head screw.

2. The electric spindle with error compensation and force feedback function according to claim 1, characterized in that: A disc spring is arranged at one end of the spline shaft sleeve, and a plane thrust ball bearing is arranged between the disc spring and the outer ring plane bearing.

3. The electric spindle with error compensation and force feedback function according to claim 1, characterized in that: The coil bracket is in an I-shape, and a rectangular groove 2 is opened in the axial direction on one end face to facilitate the excitation coil and the induction coil lead wire. A through hole is opened inside the rotor sleeve nut, and a rectangular groove 3 is opened in the radial direction on the flange end face of the nut flange.

4. A control method for an electric spindle with error compensation and force feedback functions according to any one of claims 1 to 3, the control method is implemented based on a single-chip microcomputer control system, and is characterized in that: The control method includes a displacement error compensation control method and a force feedback control method, the displacement error compensation control method and the force feedback control method cannot be performed at the same time, the displacement error compensation control method includes negative displacement error compensation and positive displacement error compensation, and the prerequisite for negative displacement error compensation is that the giant magnetostrictive rod is already in an extended state; Negative displacement error compensation includes the following steps: The first step is to set the error threshold according to the machining accuracy requirements; The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value; The third step is to substitute the error value as input into the existing magnetostriction inverse model and output the error compensation current signal; In the fourth step, the micro-displacement compensation actuator receives the error compensation current signal, reduces the magnetic field generated by the excitation coil, and the disc spring pushes the output shaft to move in the negative direction to perform negative displacement error compensation; In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement. Positive displacement error compensation includes the following steps: The first step is to set the error threshold according to the machining accuracy requirements; The second step is to obtain the error value according to the existing electric spindle error detection device and use it as an input value; The third step is to substitute the error value as input into the existing magnetostriction inverse model and output the error compensation current signal; In the fourth step, the micro-displacement compensation actuator receives the error compensation current signal, increases the magnetic field generated by the excitation coil, and pushes the output shaft to move in the positive direction to perform positive displacement error compensation; In the fifth step, the error detection device detects the error compensation result. If the compensation result is less than or equal to the error threshold, the error compensation is completed. Otherwise, the process returns to the first step until the compensation result meets the error requirement. The force feedback control method comprises the following steps: The first step is to set the tool force threshold during the machining process according to the selected machining tool and the material of the workpiece; In the second step, the induction coil senses the internal magnetic field generated when the giant magnetostrictive rod is subjected to force, causing the induced electromotive force to change, playing the role of a force feedback sensor. The force feedback sensor monitors the axial force exerted on the tool during the machining process in real time and uses it as the force input value. In the third step, the single chip control system receives the force input value and compares it with the threshold value; Step 4: When the force input value is less than or equal to the force threshold, the electric spindle continues to perform processing operations. Otherwise, the single-chip control system outputs a current signal to the micro-displacement compensation actuator, causing it to enter a negative displacement error compensation mode, and the giant magnetostrictive rod is shortened, thereby reducing the axial force on the output shaft. Step 5: Repeat steps 2, 3 and 4 until the axial force on the output shaft is within the force threshold range.

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