A short-stroke ultra-precision positioning platform for vertical motion

Abstract

This invention provides a short-stroke ultra-precision positioning platform for vertical motion, belonging to the field of manufacturing technology for micro-positioning structure devices. The novel Lorentz force motor in this invention generates a hyperbolic-shaped air gap magnetic field through a four-quadrant permanent magnet array structure of the mover assembly. This reduces electromagnetic thrust fluctuations, enabling linear changes in the control current and electromagnetic thrust of the controlled motor, reducing the control difficulty of the positioning platform and improving positioning accuracy. The novel magnetic bearing adopts a non-uniform width Halbach stator structure, enhancing the ability of magnetic lines of force to converge towards the mover permanent magnet, increasing the radial component of the air gap magnetic field, and thus increasing the levitation force of the magnetic bearing. The use of unequal permanent magnet widths and increased axial air gaps between axially and radially magnetized permanent magnets reduces the levitation stiffness, improving the positioning accuracy and low-frequency vibration isolation performance of the positioning platform. This invention enables nanometer-level positioning of the positioning platform within a millimeter-level motion stroke at high speed and high acceleration.

Description

Technical Field

[0001] This invention relates to a short-stroke ultra-precision positioning platform for vertical motion, belonging to the field of manufacturing technology of micro-positioning structure devices. Background Technology

[0002] Ultra-precision machining technology, as an important component of intelligent manufacturing, is widely used in high-end CNC machine tools, semiconductor chip processing equipment, biotechnology, and other fields. The vertically moving short-stroke ultra-precision positioning platform, as one of the key pieces of equipment in ultra-precision machining, relies on its speed and accuracy for achieving efficient production.

[0003] Short-stroke ultra-precision positioning platforms typically employ piezoelectric ceramics, electrostrictive, magnetostrictive materials, or Lorentz force motors for actuation. Solid-state actuators, represented by piezoelectric ceramics, electrostrictive, and magnetostrictive materials, offer advantages such as nanometer-level positioning accuracy and high resolution, with typical strokes ranging from tens to hundreds of micrometers. However, compared to Lorentz force motors, they also have significant limitations: First, their stroke is more limited, making them unsuitable for applications requiring larger strokes; second, these materials generally exhibit nonlinearity and hysteresis effects, and are prone to heat generation and thermal drift, requiring complex control algorithms for compensation, which increases the difficulty of control; furthermore, their load-bearing capacity is typically weaker, their driving voltage is higher (especially for piezoelectric ceramics), and they are more sensitive to the operating environment, posing challenges to long-term lifespan and reliability.

[0004] The Lorentz force motor utilizes the Lorentz force generated by a current-carrying coil in a constant magnetic field as the driving force for a positioning platform. Its stator assembly has no iron core structure, offering advantages such as simple structure, fast dynamic response, no cogging torque, and high linearity. The magnetic bearing utilizes the interaction between permanent magnets to offset the mass of the moving parts of the positioning platform, reducing the driving current of the Lorentz force motor, lowering copper losses, and reducing ambient temperature rise. It also offers advantages such as frictionless operation, noiseless operation, simple control, and adaptability to vacuum environments. However, existing Lorentz force motors and magnetic bearings suffer from large electromagnetic thrust fluctuations and high levitation stiffness, respectively, affecting the positioning accuracy and low-frequency vibration isolation performance of the positioning platform. This invention relates to a novel Lorentz force motor and a novel magnetic bearing structure for use on short-stroke ultra-precision positioning platforms with vertical motion, enabling nanometer-level positioning of the platform at high speed and high acceleration within millimeter-level motion strokes. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and to provide a short-stroke ultra-precision positioning platform for vertical motion.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A short-stroke ultra-precision positioning platform for vertical motion includes: a novel Lorentz force motor and a novel magnetic bearing;

[0008] The specific structure includes: Lorentz force motor assembly, magnetic bearing assembly, Lorentz force motor mover and magnetic bearing mover connector, support base, support column, support top plate, air bearing shaft, air bearing sleeve, air bearing sleeve and magnetic bearing mover connector, load disk mounting transition piece, load disk and grating assembly.

[0009] The Lorentz force motor assembly and the magnetic bearing assembly are connected by a Lorentz force motor mover and a magnetic bearing mover connector. The magnetic bearing assembly is mounted on a support base, which is connected to the support top plate via a support column. An air bearing sleeve is mounted on an air bearing shaft, and the air bearing sleeve is connected to the magnetic bearing assembly via an air bearing sleeve and a magnetic bearing mover connector. The load disk is connected to the air bearing sleeve via a load disk mounting transition piece and an air bearing sleeve and a magnetic bearing mover connector. The grating assembly includes: a grating ruler, a grating ruler connector, a reading head, and a reading head connector. The grating ruler and grating ruler connector of the grating assembly are mounted on the support column, and the reading head and reading head connector are connected to the air bearing sleeve.

[0010] The Lorentz force motor assembly and the magnetic bearing assembly are connected by a Lorentz force motor mover and a magnetic bearing mover connector. The stator assembly of the magnetic bearing assembly is mounted on a support base. The support base and the support top plate are connected by a support column. The air bearing sleeve is mounted on an air bearing shaft. The air bearing sleeve and the mover assembly of the magnetic bearing assembly are connected by the air bearing sleeve and the magnetic bearing mover connector. The load disk is connected to the air bearing sleeve and the magnetic bearing mover connector via a load disk mounting transition piece and the air bearing sleeve. The grating assembly includes: a grating ruler, a grating ruler connector, a reading head, and a reading head connector. The grating ruler and the grating ruler connector of the grating assembly are mounted on the support column, and the reading head and the reading head connector are connected to the air bearing sleeve.

[0011] The motor mover assembly consists of motor mover permanent magnets distributed in four quadrants at 45° angles and a motor mover yoke with magnetic conduction function. The motor mover permanent magnets adopt a rectangular structure and are magnetized along the thickness direction. The permanent magnet fixing blocks are pressed onto two motor mover permanent magnets and connected to the mover yoke by bolts to press the motor mover permanent magnets. The above structure includes four permanent magnet fixing blocks pressed onto the motor mover permanent magnets distributed in four directions respectively.

[0012] The magnetic bearing assembly consists of two parts: a stator assembly and a mover assembly. The stator assembly includes: a stator inner ring radial permanent magnet, a stator inner ring axial permanent magnet, a stator inner ring frame, a stator outer ring radial permanent magnet, a stator outer ring axial permanent magnet, a stator outer ring frame, and a stator base. In the stator assembly, two stator inner ring radial permanent magnets and one stator inner ring axial permanent magnet are fixed to the stator inner ring frame with structural adhesive. Two stator outer ring radial permanent magnets and one stator outer ring axial permanent magnet are fixed to the stator outer ring frame with structural adhesive. The stator inner ring frame and the stator outer ring frame are fixed to the stator base with bolts.

[0013] The mover assembly includes: a mover base, a mover coil, a mover permanent magnet, and a mover frame; in the mover assembly, the mover permanent magnet is fixed to the mover frame with structural adhesive, the two mover coils are fixed to the mover frame with a winding machine, and the mover frame is fixed to the mover base with bolts.

[0014] Furthermore, the permanent magnet of the motor rotor is made of neodymium iron boron (N35).

[0015] Furthermore, the yoke of the motor mover is made of electrical pure iron.

[0016] Furthermore, the permanent magnets in the magnetic bearing assembly are all neodymium iron boron (N35).

[0017] Furthermore, the novel Lorentz force motor exhibits smaller electromagnetic thrust fluctuations with vertical displacement, which can improve the positioning accuracy of the positioning platform. The formula for the electromagnetic thrust of the novel Lorentz force motor in relation to vertical displacement is as follows: Since the air gap magnetic field of this structure is nearly linearly distributed, i.e., k3 = 0, the electromagnetic thrust generated by the novel Lorentz force motor is almost unaffected by the vertical displacement Δz.

[0018]

[0019] Among them, the air gap magnetic field B y The expression is:

[0020] B y =k1·z+k3·z 3

[0021] Where k1 and k3 are the polynomial fitting coefficients of the air gap magnetic field, and z is the vertical position;

[0022] J p l is the coil current density. pm h is the effective length of the coil. c1 h c2 These represent the upper and lower boundary heights of the runway coil, respectively, w c1 w c2 Δz represents the width of the left and right boundaries of the runway coil, respectively, and Δz represents the vertical displacement of the Lorentz force motor mover.

[0023] Furthermore, the novel magnetic bearing exhibits low levitation stiffness with vertical displacement, which improves the positioning accuracy and low-frequency vibration isolation performance of the positioning platform. The formula for the levitation force of the novel magnetic bearing in relation to vertical displacement is as follows:

[0024]

[0025] The expressions for J1 and J2 in the formula are as follows:

[0026]

[0027] The levitation stiffness of a magnetic bearing is the rate of change of the levitation force with respect to the vertical displacement of the mover assembly, expressed as:

[0028]

[0029] Where r is the radial position and z is the axial position. Δz represents the levitation force of the novel magnetic bearing, and Δz represents the vertical displacement of the magnetic bearing.

[0030] J1 and J2 are the equivalent current densities of the upper and lower sides of the moving permanent magnet under the equivalent current method, respectively; R(1) and R(2) are the inner and outer diameters of the moving permanent magnet, respectively; B r-sec Let denoted as the radial component of the magnetic flux density of the stator assembly of the magnetic bearing in space, and 2H be the height of the mover permanent magnet, μ. r M is the relative permeability of the permanent magnet. s For the coercivity of permanent magnets, H av1 H av2 These represent the average magnetic field strengths of the gravitational and repulsive half-regions of the permanent magnet, respectively.

[0031] Furthermore, the novel magnetic bearing adopts a non-uniform width Halbach stator structure, and adjusts the levitation force magnitude and levitation force stiffness according to the requirements of levitation force and levitation force stiffness by adjusting the structural parameters of the axially magnetized permanent magnets and the radially magnetized permanent magnets of all permanent magnets in the stator assembly (including: radial permanent magnets in the inner ring of the stator, axial permanent magnets in the inner ring of the stator, radial permanent magnets in the outer ring of the stator, and axial permanent magnets in the outer ring of the stator) and the air gap size between them.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention provides a short-stroke ultra-precision positioning platform for vertical motion, which includes a novel Lorentz force motor and a novel magnetic bearing. These features have advantages on the ultra-precision positioning platform, namely, smaller electromagnetic force fluctuations and smaller levitation stiffness, resulting in higher positioning accuracy and vibration isolation performance.

[0034] The novel Lorentz force motor of this invention generates a hyperbolic air gap magnetic field through a four-quadrant permanent magnet array structure of the mover assembly. This reduces electromagnetic thrust fluctuations, enables linear changes in the control current and electromagnetic thrust of the controlled motor, greatly reduces the control difficulty of the positioning platform, and improves positioning accuracy.

[0035] This invention's novel magnetic bearing employs a non-uniform Halbach stator structure, enhancing the ability of magnetic field lines to converge towards the mover permanent magnet, increasing the radial component of the air gap magnetic field, and thus increasing the magnitude of the magnetic bearing's levitation force. This allows it to generate a large levitation force while maintaining a relatively small levitation stiffness within the vertical displacement range. Furthermore, the magnitude and stiffness of the levitation force can be more flexibly adjusted by modifying structural parameters such as the height and width of the axially magnetized permanent magnets and the radially magnetized permanent magnets, as well as the size of the air gap between them, according to the required levitation force and stiffness.

[0036] The present invention adds two annular coils to the radially magnetized permanent magnet of the moving part of the novel magnetic bearing. Based on the linear distribution of coil current and dynamic levitation force, the magnitude of the combined levitation force can be increased and the stiffness of the combined levitation force can be reduced by adjusting the magnitude of the coil current at different vertical movement positions.

[0037] This invention relates to a novel Lorentz force motor and a novel magnetic bearing for use on a short-stroke ultra-precision positioning platform for vertical motion. This enables nanometer-level positioning of the platform at high speed and high acceleration within a millimeter-level motion stroke. Using the aforementioned short-stroke ultra-precision positioning platform with the novel Lorentz force motor and magnetic bearing, and in conjunction with a composite nonlinear feedback active disturbance rejection control (NAM-CNFADRC) algorithm based on a nominal auxiliary model, a steady-state error of up to 20 nm within a ±2 mm motion stroke can be achieved in specific experimental tests using a 10 nm resolution readhead. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0039] Figure 2 This is a schematic diagram of a novel Lorentz force motor structure for a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0040] Figure 3 This is a schematic diagram of a novel magnetic bearing structure for a short-stroke ultra-precision positioning platform with vertical motion according to the present invention.

[0041] Figure 4 This is a partially enlarged view of the grating assembly of a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0042] Figure 5 This is a two-dimensional schematic diagram of a novel Lorentz force motor for a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0043] Figure 6 This is a schematic diagram of the magnetic field distribution of a novel Lorentz force motor for a short-stroke ultra-precision positioning platform with vertical motion according to the present invention.

[0044] Figure 7 This is a schematic diagram showing the displacement of the air gap magnetic field and electromagnetic thrust of a novel Lorentz force motor with vertical motion in a short-stroke ultra-precision positioning platform of the present invention.

[0045] Figure 8 This is a two-dimensional schematic diagram of a novel magnetic bearing for a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0046] Figure 9 This is a schematic diagram of the magnetic field distribution of a novel magnetic bearing in a short-stroke ultra-precision positioning platform for vertical motion according to the present invention.

[0047] Figure 10 This is a schematic diagram showing the levitation force and levitation stiffness of a novel magnetic bearing in a short-stroke ultra-precision positioning platform for vertical motion as a function of vertical motion displacement according to the present invention.

[0048] Figure 11 This is a schematic diagram of the steady-state error of a short-stroke ultra-precision positioning platform for vertical motion according to the present invention, combined with a composite nonlinear feedback active disturbance rejection control (NAM-CNFADRC) algorithm based on a nominal auxiliary model.

[0049] The reference numerals in the diagram represent: Lorentz force motor assembly 1, motor stator base 1-1, motor stator support rod 1-2, motor stator coil 1-3, motor stator coil frame 1-4, motor mover yoke 1-5, motor mover permanent magnet 1-6 and permanent magnet fixing block 1-7, magnetic bearing assembly 2, mover base 2-1, mover coil 2-2, mover permanent magnet 2-3, mover frame 2-4, stator inner ring radial permanent magnet 2-5, stator inner ring axial permanent magnet 2-6, stator inner ring frame 2-7, stator... Outer ring radial permanent magnet 2-8, stator outer ring axial permanent magnet 2-9, stator outer ring frame 2-10, stator base 2-11, Lorentz force motor mover and magnetic bearing mover connector 3, support base 4, support column 5, support top plate 6, air bearing shaft 7, air bearing bush 8, air bearing bush and magnetic bearing mover connector 9, load plate mounting transition piece 10, load plate 11, grating assembly 12, including grating ruler 12-1, grating ruler connector 12-2, reading head 12-3, reading head connector 12-4. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiments.

[0051] like Figures 1 to 11 As shown, the vertical motion short-stroke ultra-precision positioning platform involved in this embodiment includes:

[0052] The purpose of this invention is to design a novel Lorentz force motor and a novel magnetic bearing for application on a short-stroke ultra-precision positioning platform with vertical motion. The electromagnetic thrust fluctuations generated by the Lorentz force motor directly affect the positioning accuracy of the positioning platform, according to Newton's second law F=ma and the formula for uniformly accelerated linear motion. A simple calculation shows that when the system is an open-loop system, if the load mass m is 2.5 kg, the motor thrust fluctuation F is 10 mN, and the thrust duration t is 10 ms, then the deviation s between the actual and planned positions will be 200 nm. The positioning accuracy will not reach the nanometer level. Therefore, sufficiently small electromagnetic thrust fluctuations are necessary to achieve ultra-high precision positioning. The levitation stiffness generated by the magnetic bearing affects the low-frequency vibration isolation performance of the positioning platform, and the natural frequency of the positioning platform... Then the levitation stiffness K of the magnetic bearing z The smaller the value, the greater the levitation force. The larger the value, the smaller the system's natural frequency, and the better the low-frequency vibration isolation performance. For example... Figure 10 As shown, the average levitation force is 25.84 N, the maximum levitation stiffness is 75 N / m, and the natural frequency of its positioning platform is... Compared to traditional magnetic bearings, it has a smaller natural frequency. Therefore, when a new structure of Lorentz force motor and magnetic bearing is designed with small electromagnetic thrust fluctuations and levitation stiffness, the positioning accuracy and low-frequency vibration isolation performance of the positioning platform can be improved.

[0053] Example 1

[0054] This invention designs a novel Lorentz force motor and a novel magnetic bearing based on the objectives of small electromagnetic thrust fluctuation and small suspension stiffness, respectively, and applies them to a short-stroke ultra-precision positioning platform for vertical motion. The system composition of the short-stroke ultra-precision positioning platform for vertical motion includes: a Lorentz force motor assembly 1, a magnetic bearing assembly 2, a Lorentz force motor mover and magnetic bearing mover connector 3, a support base 4, a support column 5, a support top plate 6, an air bearing shaft 7, an air bearing bush 8, an air bearing bush and magnetic bearing mover connector 9, a load disk mounting transition piece 10, a load disk 11, and a grating assembly 12; the grating assembly 12 includes a grating ruler 12-1, a grating ruler connector 12-2, a reading head 12-3, and a reading head connector 12-4.

[0055] like Figure 1As shown, the Lorentz force motor assembly 1 and the magnetic bearing assembly 2 are connected by the Lorentz force motor mover and the magnetic bearing mover connector 3. The stator assembly of the magnetic bearing assembly 2 is mounted on the support base 4. The support base 4 and the support top plate 6 are connected by the support column 5. The air bearing sleeve 8 is mounted on the air bearing shaft 7. The air bearing sleeve 8 and the mover assembly of the magnetic bearing assembly 2 are connected by the air bearing sleeve and the magnetic bearing mover connector 9. The load disk 11 is connected to the load disk mounting transition piece 10 and the air bearing sleeve and the magnetic bearing mover connector 9 and the air bearing sleeve 8. The grating assembly 12 includes: grating ruler 12-1, grating ruler connector 12-2, reading head 12-3 and reading head connector 12-4. The grating ruler 12-1 and grating ruler connector 12-2 of the grating assembly 12 are mounted on the support column 5, and the reading head 12-3 and reading head connector 12-4 are connected to the air bearing sleeve 8.

[0056] like Figure 2 As shown, the Lorentz force motor assembly 1 includes two parts: a motor stator assembly and a motor mover assembly. The motor stator assembly includes: a motor stator base 1-1, a motor stator support rod 1-2, a motor stator coil 1-3, and a motor stator coil frame 1-4. The motor stator assembly has two racetrack-shaped motor stator coils 1-3, which are wound onto the motor stator coil frame 1-4 by a winding machine. The motor stator coil frame 1-4 is connected to the motor stator support rod 1-2 by bolts, and the motor stator support rod 1-2 is connected to the motor stator base 1-1 by bolts.

[0057] The motor mover assembly consists of motor mover permanent magnets 1-6 distributed in four quadrants at 45° angles and a motor mover yoke 1-5 with magnetic conduction function. The motor mover permanent magnets 1-6 adopt a rectangular structure and are magnetized along the thickness direction. The permanent magnet fixing blocks 1-7 press onto two motor mover permanent magnets 1-6 and are connected to the mover yoke 1-5 by bolts to press the motor mover permanent magnets 1-6 tightly. The above structure includes four permanent magnet fixing blocks 1-7 pressing onto the motor mover permanent magnets 1-6 distributed in four directions respectively.

[0058] like Figure 3As shown, the magnetic bearing assembly 2 includes two parts: a stator assembly and a mover assembly. The stator assembly includes: a stator inner ring radial permanent magnet 2-5, a stator inner ring axial permanent magnet 2-6, a stator inner ring frame 2-7, a stator outer ring radial permanent magnet 2-8, a stator outer ring axial permanent magnet 2-9, a stator outer ring frame 2-10, and a stator base 2-11. In the stator assembly, two stator inner ring radial permanent magnets 2-5 and one stator inner ring axial permanent magnet 2-6 are fixed to the stator inner ring frame 2-7 with structural adhesive. Two stator outer ring radial permanent magnets 2-8 and one stator outer ring axial permanent magnet 2-9 are fixed to the stator outer ring frame 2-10 with structural adhesive. The stator inner ring frame 2-7 and the stator outer ring frame 2-10 are fixed to the stator base 2-11 with bolts.

[0059] The mover assembly includes: a mover base 2-1, a mover coil 2-2, a mover permanent magnet 2-3, and a mover frame 2-4; in the mover assembly, the mover permanent magnet 2-3 is fixed to the mover frame 2-4 with structural adhesive, the two mover coils 2-2 are fixed to the mover frame 2-4 with a winding machine, and the mover frame 2-4 is fixed to the mover base 2-1 with bolts.

[0060] This short-stroke ultra-precision positioning platform for vertical motion utilizes the vertical Lorentz force generated by a Lorentz force motor to drive the load disk up and down. To reduce the driving current of the Lorentz force motor, a magnetic bearing generates a constant upward levitation force to compensate for the moving mass of the positioning platform's components. In this invention, an air bearing is used to provide constraints in the X and Y horizontal directions of the positioning platform, ensuring that the platform can only move vertically along a single degree of freedom in the Z direction. Furthermore, replacing traditional mechanical bearings with non-contact air bearings improves the positioning accuracy, reduces mechanical friction, and extends the platform's service life. To achieve ultra-high precision positioning, this invention employs a high-precision, low-expansion coefficient indium steel ruler in conjunction with a high-speed, high-resolution reading head to form a feedback system.

[0061] The stator assembly of this novel Lorentz force motor features two racetrack-shaped coils, while the mover assembly comprises permanent magnets distributed at 45° angles across four quadrants and a magnetically conductive yoke. The permanent magnets have a rectangular structure and are magnetized along their thickness. This novel Lorentz force motor achieves a hyperbolic air gap magnetic field by distributing permanent magnets in all four quadrants. This effectively reduces the variation of the Lorentz force generated by the energized coils with the moving position, reduces thrust fluctuations caused by changes in the relative positions of the stator and mover, and enables linear changes in the control current and electromagnetic thrust of the controlled motor. This significantly reduces the control difficulty of the positioning platform and improves positioning accuracy.

[0062] like Figure 5 and Figure 6As shown, the working principle of the new Lorentz force motor is that the conductor of the energized coil generates a Lorentz force in the constant magnetic field produced by the permanent magnet. The magnitude and direction of the Lorentz force motor can be changed by adjusting the magnitude and direction of the coil current. The effective magnetic field of the new Lorentz force motor starts from the N poles of permanent magnets No. 1 and No. 3, passes through the air gap, reaches the S poles of permanent magnets No. 2 and No. 4, and then returns to the S poles of permanent magnets No. 1 and No. 3 through the magnetic yoke, forming a closed loop. The electromagnetic thrust generated by the interaction of the effective magnetic field passing through the stator coil and the energized coil is described.

[0063] Based on the magnetic field distribution of the novel Lorentz force motor, it can be concluded that the air gap magnetic field exhibits an approximately linear relationship with the vertical displacement, expressed as follows:

[0064] B y (y,z)=k1·z+k3·z 3

[0065] Where k1 and k3 are the polynomial fitting coefficients of the air gap magnetic field, and z is the vertical position.

[0066] Therefore, the expression for the electromagnetic thrust obtained by the two runway coil stators within the vertical motion range is:

[0067]

[0068] J p l is the coil current density. pm h is the effective length of the coil. c1 h c2 These represent the heights of the upper and lower edges of the runway coil, respectively, w c1 w c2 Δz represents the width of the left and right sides of the runway coil, respectively, and Δz represents the vertical displacement of the Lorentz force motor mover.

[0069] As can be seen from the formula, under ideal conditions, when k3 = 0, i.e., when the air gap magnetic field is completely linearly distributed, the electromagnetic thrust generated by the energized coil is... The electromagnetic thrust is unaffected by the displacement Δz. Furthermore, the novel Lorentz force motor of this invention generates an air gap magnetic field that is closer to a linear change than that of a traditional Lorentz force motor, providing a driving force with smaller electromagnetic thrust fluctuations for the positioning platform.

[0070] The thrust fluctuation of a Lorentz force motor is defined as the ratio of the difference between the maximum and minimum electromagnetic thrust during the vertical motion stroke to the average electromagnetic thrust during the motion stroke:

[0071]

[0072] like Figure 7 As shown, the electromagnetic thrust fluctuation is calculated using the formula. It has smaller electromagnetic thrust fluctuations compared to traditional Lorentz force motors;

[0073] The permanent magnets 1-6 of the motor mover are made of neodymium iron boron (N35), which has a large magnetic energy product. The yoke 1-5 of the motor mover is made of electrical pure iron, which has good magnetic permeability. This allows it to generate a large air gap magnetic field in space. Furthermore, this new type of Lorentz force motor obtains a hyperbolic air gap magnetic field by distributing permanent magnets in all four quadrants. This effectively reduces the change of Lorentz force generated by the energized coil with the moving position, reduces the thrust fluctuation caused by the change of the relative position of the stator and mover, and makes the control current and electromagnetic thrust of the controlled motor change linearly. This greatly reduces the control difficulty of the positioning platform and improves the positioning accuracy.

[0074] The novel magnetic bearing consists of two parts: a stator assembly and a mover assembly. The stator assembly comprises permanent magnets arranged in a non-uniform width Halbach array, consisting of an inner ring and an outer ring. Each ring comprises two radially magnetized permanent magnets, one axially magnetized permanent magnet, and a stator frame. The Halbach array permanent magnets in the stator assembly enhance the ability of magnetic field lines to converge towards the mover permanent magnet, increasing the radial component of the air gap magnetic field and thus increasing the levitation force of the magnetic bearing. The use of non-uniform permanent magnet widths and the increase in the axial air gap between the axially and radially magnetized permanent magnets are used to reduce the levitation stiffness. The mover assembly consists of a radially magnetized permanent magnet, two symmetrically distributed annular coils, and a mover frame.

[0075] The working principle of the new magnetic bearing follows the objective law of like-polarity repulsion and unlike-polarity attraction. The two radial permanent magnet rings on the upper layer of the stator attract the moving permanent magnet ring, while the two radial permanent magnet rings on the lower layer of the stator repel the moving permanent magnet ring. Similarly, the axial permanent magnets in the middle layer of the stator attract the moving permanent magnet ring. Therefore, when the stator assembly is fixed, the moving assembly experiences a vertically upward static levitation force. Two annular coils are added to the moving assembly of the new magnetic bearing. The combined air gap magnetic field generated by all the permanent magnets in the stator and moving assembly, combined with the energized annular coils, will generate a vertical dynamic levitation force in the moving assembly. Adjusting the magnitude and direction of the coil current can regulate the magnitude and direction of the dynamic levitation force, thereby increasing or decreasing the magnitude of the combined levitation force and compensating for the reduced stiffness of the combined levitation force.

[0076] like Figure 8 and Figure 9As shown, the effective magnetic field of the novel magnetic bearing originates from the N pole of permanent magnet 1, passes through the axial air gap to permanent magnets 2 and 3, then originates from permanent magnet 3, passes through the radial air gap to permanent magnet 6, then passes through the axial permanent magnets to permanent magnets 5 and 4, and finally passes through the radial air gap to the S pole of permanent magnet 1, forming a closed loop. The radial magnetic field passing through the mover assembly interacts with the mover permanent magnet, generating an upward levitation force. The novel magnetic bearing uses a Halbach array of permanent magnets, which, compared to traditional magnetic bearings, adds four radially magnetized permanent magnets, enhancing the ability of magnetic field lines to converge towards the mover permanent magnet, increasing the radial component of the air gap magnetic field, and thus increasing the magnitude of the magnetic bearing's levitation force.

[0077] The formulas for calculating the static levitation force and levitation stiffness of the new magnetic bearing are as follows:

[0078]

[0079] The expressions for J1 and J2 in the formula are as follows:

[0080]

[0081] The levitation stiffness of a magnetic bearing is defined as the rate of change of the levitation force with respect to the vertical displacement of the mover assembly, expressed as:

[0082]

[0083] Where r is the radial position and z is the axial position. Δz represents the levitation force of the novel magnetic bearing, and Δz represents the vertical displacement of the magnetic bearing.

[0084] J1 and J2 are the equivalent current densities of the upper and lower sides of the moving permanent magnet under the equivalent current method, respectively; R(1) and R(2) are the inner and outer diameters of the moving permanent magnet, respectively; B r-sec Let denoted as the radial component of the magnetic flux density of the stator assembly of the magnetic bearing in space, and 2H be the height of the mover permanent magnet, μ. r M is the relative permeability of the permanent magnet. s For the coercivity of permanent magnets, H av1 H av2 These represent the average magnetic field strengths of the gravitational and repulsive half-regions of the permanent magnet, respectively.

[0085] This embodiment relates to a novel Lorentz force motor and a novel magnetic bearing for use on a short-stroke ultra-precision positioning platform for vertical motion, enabling nanometer-level positioning of the platform at high speed and high acceleration within a millimeter-level motion stroke. Figure 11As shown, the vertical motion short-stroke ultra-precision positioning platform with the above-mentioned Lorentz force motor and magnetic bearing, combined with the composite nonlinear feedback active disturbance rejection control (NAM-CNFADRC) algorithm based on the nominal auxiliary model, can achieve a maximum steady-state error of 20nm within a motion stroke of ±2mm in specific experimental tests using a 10nm resolution reading head.

[0086] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A short-stroke ultra-precision positioning platform for vertical motion, characterized in that, include: Lorentz force motor assembly (1), magnetic bearing assembly (2), Lorentz force motor mover and magnetic bearing mover connector (3), support base (4), support column (5), support top plate (6), air bearing shaft (7), air bearing bushing (8), air bearing bushing and magnetic bearing mover connector (9), load plate mounting transition piece (10), load plate (11) and grating assembly (12); The Lorentz force motor assembly (1) and the magnetic bearing assembly (2) are connected by the Lorentz force motor mover and the magnetic bearing mover connector (3). The stator assembly of the magnetic bearing assembly (2) is mounted on the support base (4). The support base (4) and the support top plate (6) are connected by the support column (5). The air bearing bush (8) is mounted on the air bearing shaft (7). The air bearing bush (8) and the mover assembly of the magnetic bearing assembly (2) are connected by the air bearing bush and the magnetic bearing mover connector (9). The load disk (11) is mounted on the load disk. The transition piece (10) and the air bearing bush and the magnetic bearing mover connector (9) are connected to the air bearing bush (8). The grating assembly (12) includes: grating ruler (12-1), grating ruler connector (12-2), reading head (12-3) and reading head connector (12-4); the grating ruler (12-1) and grating ruler connector (12-2) of the grating assembly (12) are mounted on the support column (5), and the reading head (12-3) and reading head connector (12-4) are connected to the air bearing bush (8); The Lorentz force motor assembly (1) includes two parts: a motor stator assembly and a motor mover assembly. The motor stator assembly includes: a motor stator base (1-1), a motor stator support rod (1-2), a motor stator coil (1-3), and a motor stator coil frame (1-4). The motor stator assembly has two racetrack-shaped motor stator coils (1-3). The two racetrack-shaped motor stator coils (1-3) are wound onto the motor stator coil frame (1-4) by a winding machine. The motor stator coil frame (1-4) is connected to the motor stator support rod (1-2) by bolts. The motor stator support rod (1-2) is connected to the motor stator base (1-1) by bolts. The motor mover assembly consists of motor mover permanent magnets (1-6) distributed in four quadrants at 45° angles and a motor mover yoke (1-5) with magnetic conduction function. The motor mover permanent magnets (1-6) adopt a rectangular structure and are magnetized along the thickness direction. The permanent magnet fixing blocks (1-7) press onto two motor mover permanent magnets (1-6) and are connected to the mover yoke (1-5) by bolts to press the motor mover permanent magnets (1-6) tightly. The above structure includes four permanent magnet fixing blocks (1-7) pressing onto the motor mover permanent magnets (1-6) distributed in four directions respectively. The magnetic bearing assembly (2) consists of two parts: a stator assembly and a mover assembly. The stator assembly includes: a stator inner ring radial permanent magnet (2-5), a stator inner ring axial permanent magnet (2-6), a stator inner ring frame (2-7), a stator outer ring radial permanent magnet (2-8), a stator outer ring axial permanent magnet (2-9), a stator outer ring frame (2-10), and a stator base (2-11). In the stator assembly, two stator inner ring radial permanent magnets (2-5) and one stator inner ring axial permanent magnet (2-6) are fixed to the stator inner ring frame (2-7) with structural adhesive. Two stator outer ring radial permanent magnets (2-8) and one stator outer ring axial permanent magnet (2-9) are fixed to the stator outer ring frame (2-10) with structural adhesive. The stator inner ring frame (2-7) and the stator outer ring frame (2-10) are fixed to the stator base (2-11) with bolts. The mover assembly includes: a mover base (2-1), a mover coil (2-2), a mover permanent magnet (2-3), and a mover frame (2-4); in the mover assembly, the mover permanent magnet (2-3) is fixed to the mover frame (2-4) with structural adhesive, the two mover coils (2-2) are fixed to the mover frame (2-4) with a winding machine, and the mover frame (2-4) is fixed to the mover base (2-1) with bolts; The magnetic bearing assembly (2) adopts a non-equal width Halbach stator structure, and adjusts the magnitude and stiffness of the levitation force by adjusting the structural parameters of the axially magnetized permanent magnet, the radially magnetized permanent magnet, and the air gap between them, according to the requirements of levitation force and levitation stiffness.

2. The short-stroke ultra-precision positioning platform for vertical motion according to claim 1, characterized in that, The permanent magnet (1-6) of the motor rotor is made of neodymium iron boron (N35).

3. The short-stroke ultra-precision positioning platform for vertical motion according to claim 1, characterized in that, The motor mover yoke (1-5) is made of electrical pure iron.

4. The short-stroke ultra-precision positioning platform for vertical motion according to claim 1, characterized in that, The permanent magnets in the magnetic bearing assembly (2) are all neodymium iron boron N35.

5. A short-stroke ultra-precision positioning platform for vertical motion according to claim 1, characterized in that, The formulas for the electromagnetic thrust and vertical displacement of the Lorentz force motor assembly (1) are as follows: Since the magnetic field of the air gap of the structure is close to linear distribution, i.e., k3=0, the electromagnetic thrust generated by the Lorentz force motor assembly (1) is almost unaffected by the vertical displacement Δz. Among them, the air gap magnetic field B y The expression is: Where k1 and k3 are the polynomial fitting coefficients of the air gap magnetic field, and z is the vertical position; J p Let l be the coil current density. pm h is the effective length of the coil. c1 h c2 These represent the upper and lower boundary heights of the runway coil, respectively, w c1 w c2 Δz represents the width of the left and right boundaries of the runway coil, respectively, and Δz represents the vertical displacement of the Lorentz force motor mover.

6. The short-stroke ultra-precision positioning platform for vertical motion according to claim 1, characterized in that, The formulas for the levitation force and vertical displacement of the magnetic bearing assembly (2) are as follows: The expressions for J1 and J2 in the formula are as follows: The levitation stiffness of a magnetic bearing is the rate of change of the levitation force with respect to the vertical displacement of the mover assembly, expressed as: Where r is the radial position and z is the axial position. Δz represents the levitation force of the magnetic bearing assembly, and Δz represents the vertical displacement of the magnetic bearing. J1 and J2 are the equivalent current densities of the upper and lower sides of the moving permanent magnet under the equivalent current method, respectively; R(1) and R(2) are the inner and outer diameters of the moving permanent magnet, respectively; B r-sec Let denoted as the radial component of the magnetic flux density of the stator assembly of the magnetic bearing in space, and 2H be the height of the mover permanent magnet, μ. r M is the relative permeability of the permanent magnet. s For the coercivity of permanent magnets, H av1 H av2 These represent the average magnetic field strengths of the gravitational and repulsive half-regions of the permanent magnet, respectively.

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