Patent Publication Number: US-2022224256-A1

Title: Magnetic Levitation Gravity Compensation Device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The disclosure claims the priority of Chinese Patent Present invention No. 201910363230.7, filed on Apr. 30, 2019 and entitled “Magnetic Levitation Gravity Compensation Device”, and the priority of Chinese Patent Present invention No. 201910628291.1, filed on Jul. 12, 2019 and entitled “Magnetic Levitation Gravity Compensation Device”, which are incorporated herein in their entirety by reference. 
     TECHNICAL FIELD 
     The disclosure relates to the technical field of integrated circuit equipment manufacturing, and particularly relates to a long-stroke magnetic levitation gravity compensation device. 
     BACKGROUND 
     In recent years, as higher integration of large-scale integrated circuit devices demands higher precision of a workbench, especially motion precision of its vertical module, a motion stroke is increased year over year with the increasing demand of the workbench, such as lithographic equipment, film thickness detection equipment, etc. Thus, a vertical gravity compensation technology is also constantly updated iteratively. At present, three solutions are widely used in a gravity compensation device: a mechanical spring, an air flotation device and a magnetic levitation gravity compensation device. 
     U.S. Pat. No. 6,337,484B1 uses the air flotation device to compensate for gravity, and controls an air flow in a constant pressure chamber to be constant so as to output stable air buoyancy. However, it is difficult to design and manufacture the air flotation device. In addition, the air flow in the constant pressure chamber is required to keep stable at all times because system disorder will be caused once the air flow fluctuates. 
     An adjustable magnetic levitation gravity compensation device provided in CN201510091980.5 and CN201110299070.8 makes a magnetic field distributed more uniformly by changing strength of a mover magnetic field, and then outputs a magnetic levitation force with small fluctuation. However, these methods not only have complex magnetic circuit structures, but also have large fluctuation in output magnetic levitation force and a small vertical stroke of a mover. Moreover, a stroke of a mover in the patent is only ±2 mm, which is far from the application requirements. 
     Thus, a novel magnetic levitation gravity compensation device is needed urgently, which may overcome defects of a traditional magnetic levitation gravity compensation device, such as a short stroke and a complex structure, and may generate the magnetic levitation force with small fluctuation and high amplitude. 
     SUMMARY 
     The object of the disclosure is to provide a magnetic levitation gravity compensation device, which is long in stroke, simple in structure, high in amplitude of magnetic levitation force and small in fluctuation. 
     In order to achieve the above object, the disclosure provides a magnetic levitation gravity compensation device, the magnetic levitation gravity compensation device includes: 
     a first magnetic steel, the first magnetic steel is cylindrical; 
     a second magnetic steel, the second magnetic steel is cylindrical, and is arranged in the first magnetic steel and radially spaced from the first magnetic steel; and 
     at least one end magnetic steel, the at least one end magnetic steel is cylindrical, and is located on at least one of two axial ends of the second magnetic steel and axially spaced from the two axial ends of the second magnetic steel, a center line of the end magnetic steel is configured to coincide with a center line of the second magnetic steel, and a cylinder wall thickness of the end magnetic steel is smaller than a cylinder wall thickness of the second magnetic steel, 
     wherein a magnetization direction of the first magnetic steel is a radial direction, and a magnetization direction of the second magnetic steel and the end magnetic steel is an axial direction. 
     In an implementation mode, the magnetic levitation gravity compensation device includes: a first supporting member, the first supporting member is used for fixing the first magnetic steel; and a second supporting member, the second supporting member is used for fixing the second magnetic steel and the end magnetic steel, where the first supporting member and the second supporting member may axially move relative to each other. 
     In an implementation mode, the first supporting member is cylindrical, and the first magnetic steel is embedded in an inner peripheral surface of the first supporting member. 
     In an implementation mode, the second supporting member is columnar, and the second magnetic steel and the end magnetic steel are embedded in an outer peripheral surface of the second supporting member. 
     In an implementation mode, a spacing distance between the second magnetic steel and the end magnetic steel is 0.1 mm to 1.0 mm. 
     In an implementation mode, the first magnetic steel consists of an even number of radial magnetic steel blocks which are radially spaced from each other, and a pole-arc coefficient of single radial magnetic steel block ranges from 0.75 to 0.98. 
     In an implementation mode, each of two ends of the second magnetic steel is provided with one end magnetic steel. 
     In an implementation mode, at least one end of the second magnetic steel is provided with two or more end magnetic steels. 
     In an implementation mode, an inner diameter of the end magnetic steel is not smaller than an inner diameter of the second magnetic steel, and an outer diameter of the end magnetic steel is not larger than an outer diameter of the second magnetic steel. 
     In an implementation mode, lengths of the first magnetic steel, the second magnetic steel and the end magnetic steel are La, Lb and Lc respectively, where Lb&gt;Lc. 
     In an implementation mode, an inner diameter of the second magnetic steel and an inner diameter of the end magnetic steel are Db and Dc respectively, and γl=Db/Dc, and γ 1  ranges from ⅛ to 1. 
     In an implementation mode, a stroke of the first supporting member and, the second supporting member axially moving relative to each other is S, λ 1 =La/Lb, λ 2 =Lc/Lb, and λ 1  ranges from ¼ to 1+2λ2−2S/Lb. 
     In an implementation mode, a stroke of the first supporting member and the second supporting member axially moving relative to each other is S, λ 2 =Lc/Lb, and λ 2  ranges from ¼ to ⅜. 
     In an implementation mode, a spacing distance between the first magnetic steel and the second magnetic steel is Rg, and Rg is not smaller than ten times a spacing distance between the second magnetic steel and the end magnetic steel. 
     The disclosure further provides a workbench, the workbench includes a workbench body, wherein a cavity is provided below the workbench body, and is used for accommodating the above magnetic levitation gravity compensation device. 
     In an implementation mode, the number of the cavities is three or four. 
     Compared with a magnetic levitation gravity compensation device in the related art, the magnetic levitation gravity compensation device of the disclosure may provide a high-amplitude magnetic levitation force, with small fluctuation of a magnetic levitation force in a long stroke. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a sectional schematic diagram of a magnetic levitation gravity compensation device according to the disclosure. 
         FIG. 2  shows a structural schematic diagram of the magnetic levitation gravity compensation device according to Embodiment 1 of the disclosure. 
         FIG. 3  shows a longitudinal sectional schematic diagram of a magnetization direction and a size of magnetic steel of the magnetic levitation gravity compensation device according to the disclosure. 
         FIG. 4  shows a schematic diagram of a magnetic line of force of the magnetic levitation gravity compensation device according to the disclosure. 
         FIG. 5  shows a curve of a magnetic levitation force of the magnetic levitation gravity compensation device according to the disclosure. 
         FIG. 6  shows a structural schematic diagram of the magnetic levitation gravity compensation device according to Embodiment 2 of the disclosure. 
         FIG. 7  shows a curie of fluctuation of the magnetic levitation force according to Embodiment 2 of the disclosure. 
         FIG. 8  shows a schematic diagram according to Embodiment 3 of the disclosure, wherein a cylinder bisecting a cylinder thickness of mover magnetic steel in a radial direction coincides with a cylinder bisecting a cylinder thickness of the end magnet steel in a radial direction. 
         FIG. 9  shows a schematic diagram according to Embodiment 4 of the disclosure, wherein inner diameters of the mover magnetic steel and the end magnetic steel are equal. 
         FIG. 10  shows a schematic diagram of the number of the end magnetic steel two according to Embodiment 5 of the disclosure. 
         FIG. 11  shows a single-point layout according to Embodiment 6 of the disclosure. 
         FIG. 12  shows a three-point layout according to Embodiment 6 of the disclosure. 
         FIG. 13  shows a four-point layout according to Embodiment 6 of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The exemplary embodiments of the disclosure are described in detail below in conjunction with the accompanying drawings so as to better describe objects, features and advantages of the disclosure. It should be understood that the embodiments shown in the accompanying drawings are not to limit the scope of the disclosure, but only to describe the spirit of the technical solution of the disclosure. 
     In the following description, in order to describe various disclosed embodiments, certain specific details are set forth to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the related art will recognize that embodiments may be implemented without one or more of these specific details. In other cases, well-known devices, structures and techniques associated with the disclosure may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. 
     Unless the context has other requirements, in the whole specification and claims, the word “including” and its variants, such as “comprising” and “having”, should be understood as an open and inclusive meaning, that is, should be interpreted as “including but not limited to.” 
     References to “an embodiment” or “one embodiment” throughout the specification mean that a particular characteristic, structure or feature described in conjunction with an embodiment is included in at least one embodiment. Therefore, “in an embodiment” or “in one embodiment” in various positions throughout the specification need not all refer to the same embodiment. In addition, specific characteristics, structures, or features may be combined in any mode in one or more embodiments. 
     As used in this specification and the appended claims, the singular forms “a” and “the” include meanings of plural referents unless there are clear and additional stipulations herein. It should be pointed out that the term “or” is usually used in its meaning including “and/or”, unless there are clear and additional stipulations herein. 
     In the following description, in order to clearly show the structure and working mode of the disclosure, many directional words will be used to describe it, but words such as “front”, “rear”, “left”, “right”, “outside”, “inside”, “outward”, “inward”, “on” and “under” should be understood as convenient words, but should not be understood as limiting words. 
     It should be noted that relational terms in the claims and specification of the disclosure such as first and second are only used to distinguish one entity or operation from another entity or operation without necessarily requiring or implying any actual relation or order between such entities or operations. 
     The disclosure aims to overcome defects of a short stroke and a complex structure of a traditional magnetic levitation gravity compensation device, and provides a magnetic levitation gravity compensation device, which has a long stroke so as to provide a high-amplitude magnetic levitation force with small fluctuation, thus being applied to a workbench requiring high-precision vertical movement. With reference to the drawings, a magnetic levitation gravity compensation device according to the disclosure is described below. 
       FIG. 1  shows sectional schematic diagram of a magnetic levitation gravity compensation device  100  according to the disclosure. As shown in  FIG. 1 , the device  100  includes: a first magnetic steel  101 , a second magnetic steel  102 , and end magnetic steels  103   a  and  103   b.  Wherein the first magnetic steel  101  is cylindrical, and the second magnetic steel  102  is also cylindrical and sleeved with the first magnetic steel  101  and is radially spaced from the first magnetic steel  101  by a certain distance. Both of the end magnetic steels  103   a  and  103   b  are cylindrical and located in two axial ends of the second magnetic steel  102  respectively, and the end magnetic steels  103   a  and  103   b  are axially spaced from the two axial ends of the second magnetic steel  102  by a certain distance respectively. By additionally arranging the end magnetic steels  103   a  and  103   b  at the two axial ends of the second magnetic steel  102 , distribution of a magnetic line of force between the first magnetic steel  101  and the second magnetic steel  102  may be adjusted, so that a magnetic levitation force with small fluctuation in a long stroke of the first magnetic steel  101  and the second magnetic steel  102  axially moving relative to each other is achieved. It should be understood that only one axial end of the second magnetic steel  102  may be provided with the end magnetic steel  103   a  or  103   b  without departing from the scope of the disclosure. Center lines of the end magnetic steels  103   a  and  103   b  coincide with a center line of the second magnetic steel  102 , and cylinder wall thicknesses of the end magnetic steels  103   a  and  103   b  are smaller than a cylinder wall thickness of the second magnetic steel  102 . Wherein a magnetization direction of the first magnetic steel  101  is a radial direction, and magnetization directions of the second magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are an axial direction. The above magnetic steel arrangement and magnetization direction may generate a magnetic levitation force when the first magnetic steel  101  moves relative to the second magnetic steel  102  and the end magnetic steels  103   a  and  103   b.    
     In order to achieve the above arrangement, a first supporting member and a second supporting member are arranged, wherein the first supporting member is used for fixing the first magnetic steel  101 ; and the second supporting member is used for fixing the second magnetic steel  102  and the end magnetic steels  103   a  and  103   b,  the first supporting member and the second supporting member may be capable of axially moving relative to each other. In practice, one of the first supporting member and the second supporting member is fixed relative to the workbench, while the other one of the first supporting member and the second supporting member is fixed relative to a bracket of the workbench, so that when the workbench is driven by a driving device to move vertically relative to the bracket, a weight of the workbench and a supporting body thereof may be compensated by means of the magnetic levitation force generated between the first magnetic steel  101  and the second magnetic steel  102  as well as the end magnetic steels  103   a  and  103   b,  that is, between the first supporting member and the second supporting member, thus achieving more precise control over vertical movement of the workbench. Hereinafter, the disclosure is described by taking as an example that the first supporting member is fixed relative to the bracket of a workbench and the second supporting member is fixed relative to the workbench. It should be understood that an embodiment, in which the second supporting member is fixed relative to the support of the workbench and the first supporting member is fixed relative to the workbench, is also within the scope of the disclosure. 
     Hereinafter, for convenience of description, the first magnetic steel  101  is referred to as stator magnetic steel  101  and the second magnetic steel  102  is referred to as mover magnetic steel  102 . In an embodiment shown in  FIG. 1 , the first supporting member is a stator base  104 , the second supporting member is a mover shaft  105 . The stator base  104  is cylindrical, the stator magnetic steel  101  is embedded in an inner peripheral surface of the stator base  104 , and the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are embedded in an outer surface of the mover shaft  105 , and the stator magnetic steel  101  and the mover magnetic steel  102  are spaced from each other without mechanical connection therebetween. Wherein the mover shaft  105  may be of an integrated structure, or may be assembled from a mover shaft first portion  105   a  and a mover shaft second portion  105   b  as shown in  FIG. 1 , wherein a longitudinal section of the mover shaft first portion  105   a  is T-shaped, and the mover shaft second portion  105   b  and the mover shaft first portion  105   a  are assembled by means of threads. The assembling structure makes it possible to install or remove the end magnetic steel  103   b  as required, a magnetization direction of the stator magnetic steel  101  is a radial direction, and magnetization directions of the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are an axial direction. As shown in  FIG. 3 , an arrow direction in  FIG. 3  represents a magnetization direction of magnetic steel, the magnetization direction of the stator magnetic steel  101  is radially outward, and the magnetization directions of the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are consistent and axially downward; and in the same way, accordingly, the magnetization direction of the stator magnetic steel  101  may also be radially inward, while the magnetization directions of the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are axially upward. 
     In addition, a certain spacing distance  6  is provided between the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b,  which facilitates adjustment on fixing and assembling of a mover magnetic field and the magnetic steel. Wherein a value of spacing distance δ is selected depending on a stroke, and preferably ranges from 0.1 mm to 1.0 mm in general. 
       FIG. 2  shows a structural schematic diagram of Embodiment 1 of the disclosure. In  FIG. 2 , each of the stator magnetic steel  101 , the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  is of a cylindrical structure, and the end magnetic steels  103   a  and  103   b  are equal in shape and size. As shown in  FIG. 3 , lengths of the stator magnetic steel  101 , the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are La, Lb and Lc respectively, a mover magnetic steel outer diameter  1021  and an end magnetic steel outer diameter  1031  are represented by Dob and Doc respectively, a mover magnetic steel inner diameter  1022  and an end magnetic steel inner diameter  1032  are represented by Db and Dc respectively, and a unilateral air gap between the stator magnetic steel  101  and the mover magnetic steel  102  is represented by Rg. Axial lengths Lb and Lc of the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  are unequal, and generally Lb&gt;Lc. 
     As shown in  FIG. 3 , radial thicknesses of the end magnetic steels  103   a  and  103   b  are smaller than a radial thickness of the mover magnetic steel  102 . A radial position relation between the end magnetic steels  103   a  and  103   b  and the mover magnetic steel  102  is that outer diameters of the end magnetic steels  103   a  and  103   b  may be slightly larger than a outer diameter of the mover magnetic steel  102 , while inner diameters of the end magnetic steels  103   a  and  103   b  may be slightly smaller than a inner diameter of the mover magnetic steel  102 . In an embodiment, the outer diameters of the end magnetic steels  103   a  and  103   b  are not larger than the outer diameter of the mover magnetic steel  102 , while the inner diameters of the end magnetic steels  103   a  and  103   b  are not smaller than the inner diameter of the mover magnetic steel  102 . 
     The radial position relation generally has three solutions: (1) the mover magnetic steel outer diameter  1021  and the end magnetic steel outer diameter  1031  are equal, and the mover magnetic steel inner diameter  1022  and the end magnetic steel inner diameter  1032  are unequal; (2) the mover magnetic steel outer diameter  1021  and the end magnetic steel outer diameter  1031  are unequal, and the mover magnetic steel inner diameter  1022  and the end magnetic steel inner diameter  1032  are equal; (3) the mover magnetic steel outer diameter  1021 , the mover magnetic steel inner diameter  1022 , the end magnetic steel outer diameter  1031  and the end magnetic steel inner diameter  1032  are unequal, and a distance between the inner diameter of the mover magnetic steel  102  and the inner diameter of the end magnetic steel  103  is equal to a distance between the outer diameter of the mover magnetic steel  102  and the outer diameters of the end magnetic steels  103   a  and  103   b,  that is, a cylinder bisecting a cylinder thickness of the mover magnetic steel  102  in a radial direction coincides with a cylinder bisecting a cylinder thickness of the end magnetic steel in a radial direction. 
     In addition, it should be understood that the end magnetic steels  103   a  and  103   b  may also be different from each other, for example, one or more of the outer diameters, the inner diameters, the cylinder thicknesses or heights thereof may be different from each other. 
     It should be noted that in an embodiment shown in  FIG. 3 , the mover magnetic steel outer diameter  1021  and the end magnetic steel outer diameter  1031  are equal, while the mover magnetic steel inner diameter  1022  and the end magnetic steel inner diameter  1032  are unequal. 
     In the embodiment as shown in  FIG. 3 , three size ratios are defined as λ 1 =La/Lb, λ 2 =Lc/Lb, γ 1 =Db/Dc, which relate to the fluctuation of the magnetic levitation force and also change with a stroke and an amplitude of a magnetic levitation device. Assuming that a total stroke of the magnetic levitation device is S, a value range of λ 1  is preferably [¼, 1+2λ2−2S/Lb] according to the stroke; and a value of λ 2  relates to the number Nt of blocks (as described below) of the end magnetic steel, when Nt=1, a value range of λ 2  is preferably [¼, ⅜]. Generally, a value of γ 1  relates to the fluctuation of the magnetic levitation force, and considering processing difficulty and an assembly process of the magnetic steel, a value range of γ 1  is preferably [⅛, 1]. In addition, the unilateral air gap Rg between the stator magnetic steel  101  and the mover magnetic steel  102  also affects strength of a magnetic field to a certain extent, and further affects an amplitude and fluctuation degree of the magnetic levitation force. Generally, a value of the unilateral air gap Rg varies with the amplitude of the magnetic levitation force, and the value of the unilateral air gap Rg is preferably larger than or equal to 10δ. 
       FIG. 4  shows a schematic diagram of a magnetic line of force of the magnetic levitation gravity compensation device of the above embodiment. According to a distribution track of the magnetic line of force and a principle that like magnetic poles repel each other, it may be inferred that gravity of the mover shaft  105  and a carrier thereof as well as the mover magnetic steel  102  and the end magnetic steels  103   a  and  103   b  is compensated by the magnetic levitation force generated by magnetic field interaction among the mover magnetic steel  102 , the end magnetic steels  103   a  and  103   b  and the stator magnetic steel  101 , and radial thrust generated by the stator magnetic steel  101  against the mover magnetic steel  102  and the end magnetic steel  103   a  and  103   b  is a group of forces with equal amplitudes and uniformly distributed along a circumference, so the mover shaft  105  may always float in a center of the stator magnetic steel  101  by means of the magnetic levitation force. Through electromagnetic simulation, a curve of the magnetic levitation force generated by interaction between a magnetic field of the mover magnetic steel and a magnetic field of the stator magnetic steel may be obtained. As shown in  FIG. 5 , an amplitude of the magnetic levitation force in  FIG. 5  ranges from 38.13 N to 38.97 N with the small fluctuation of 1.08% in a stroke range of 25 mm, which is basically close to a fluctuation degree of a traditional magnetic levitation gravity compensation device in the stroke range of ±2 mm. 
       FIG. 6  shows a structural schematic diagram of the magnetic levitation gravity compensation device  200  according to Embodiment 2 of the disclosure. The magnetic levitation gravity compensation device  200  includes a stator magnetic steel, a mover magnetic steel  202 , and end magnetic steels  203   a  and  203   b.  The embodiment is basically consistent with Embodiment 1 except that considering magnetization of the stator magnetic steel and difficulty of a processing technology, the stator magnetic steel may be replaced with a group of blocky radially magnetized magnetic steels  201   a,    201   b,    201   c  and  201   d  in a circumferential direction. In order to eliminate a radial unbalanced force in the embodiment, the number N of blocks of the stator magnetic steels is usually even, and N=4 in the embodiment. It should be noted that a value of N is not limited to a value in the embodiment, but may also be extended to other even numbers, such as six and eight, according to the inner and outer diameters of the stator magnetic steel. 
     An pole-arc coefficient α of the radially magnetized magnetic steels  201   a,    201   b,    201   c  and  201   d  is a ratio of a polar arc length to a polar distance, and experience shows that the pole-arc coefficient α of the stator magnetic steels  201   a,    201   b,    201   c  and  201   d  generally ranges from 0.75 to 1.0, and the pole-arc coefficient α of the stator magnetic steel  201   a  may be equivalently represented by a pitch angle θ between the stator magnetic steel  201   a  and the stator magnetic steel  201   b.  When N takes different values, a value range of the pitch angle θ is generally [0°, 30°]. The pole-arc coefficient α of each block of magnetic steels may be adjusted by adjusting the pitch angle θ of adjacent blocks of magnetic steels in a circumferential direction, so as to increase or decrease a total volume of the stator magnetic steel and adjust the amplitude of the magnetic levitation force. 
     In the embodiment, considering the amplitude and the fluctuation of the magnetic levitation force comprehensively, a group of optimal topological structures are recommended, wherein the number N of circumferential blocks of the stator magnetic steel is 4, the pitch angle θ of the magnetic steel is 5°, and the pole-arc coefficient α of the magnetic steel is 17/18. A curve of the fluctuation of the magnetic levitation force obtained through simulation is shown in  FIG. 7 . It may be seen from  FIG. 7  that the amplitude of the magnetic levitation force of Embodiment 2 fluctuates from 36.13 N to 36.91 N in the stroke range, with a very small fluctuation rate of 1.09%. 
       FIG. 8  shows a structural schematic diagram of the magnetic levitation gravity compensation device  300  according to Embodiment 3 of the disclosure. The magnetic levitation gravity compensation device  300  includes a stator magnetic steel (not shown), a mover magnetic steel  302  and an end magnetic steel  303   a.  In the embodiment, the cylinder bisecting the cylinder thickness of the mover magnetic steel  302  in the radial direction coincides with the cylinder bisecting the cylinder thickness of the end magnet steel  303   a  in the radial direction. 
       FIG. 9  shows a structural schematic diagram of the magnetic levitation gravity compensation device  400  according to Embodiment 4 of the disclosure. The magnetic levitation gravity compensation device  400  includes a stator magnetic steel (not shown), a mover magnetic steel  402  and an end magnetic steel  403   a.  Wherein an end magnetic steel inner diameter  4032  and a mover magnetic steel inner diameter  4022  are equal, and an end magnetic steel outer diameter  4031  and a mover magnetic steel outer diameter  4021  are unequal. 
       FIG. 10  shows a structural schematic diagram of the magnetic levitation gravity compensation device  500  according to Embodiment 5 of the disclosure. The magnetic levitation gravity compensation device  500  includes a stator magnetic steel (not shown), a mover magnetic steel  502 , and end magnetic steels  503   a  and  503   c,  wherein the end magnetic steel at one axial end of the mover magnetic steel  502  is axially blocky. According to the stroke of the magnetic levitation gravity compensation device and the fluctuation of the magnetic levitation force, the number Nt of unilateral blocks may be adjusted. In the above embodiments, Nt=1, but Nt is not limited to 1, and may also be larger than 1. Generally, the more the number Nt of unilateral blocks of the end magnetic steel, the more uniform distribution of a magnetic field provided by the mover magnetic steel  502  and the end magnetic steel, and the more stable the curve of the magnetic levitation force. In the embodiment, a solution that the number Nt of blocks of the end magnetic steel is 2 is shown. In addition, in the embodiment, an end magnetic steel inner diameter  5032  and a mover magnetic steel inner diameter  5022  are unequal, and an end magnetic steel outer diameter  5031  and a mover magnetic steel outer diameter  5021  are equal. It should be understood that the other axial end of the mover magnetic steel  502  may also be provided with a single block of end magnet steel or axially blocky end magnetic steel. Other radial position relations between the end magnetic steel and the mover magnetic steel  502  may be used without departing from the scope of the disclosure. 
       FIGS. 11-13  show a bottom view of a workbench using the magnetic levitation gravity compensation device according to the disclosure. A cavity is provided below the workbench body, and is used for accommodating a magnetic levitation gravity device according to the disclosure. Wherein a number of the cavity below the workbench may be one, as shown in  FIG. 11 , may also be three for regular triangle arrangement for example to form a three-point layout, and, as shown in  FIG. 12 , may also be four for square arrangement to form a four-point layout. 
     The exemplary embodiments of the disclosure have been described in detail above, but it should be understood that aspects of the embodiments may be modified to provide additional embodiments by using aspects, features and concepts of various patents, applications and publications, if necessary. 
     In view of the above detailed description, these and other changes may be made to the embodiments. Generally speaking, terms used in the claims should not be regarded as limited to the specific embodiments disclosed in the specification and claims, but should be understood as including all possible embodiments together with all the equivalent ranges of these claims.