CN115242129B - Three-degree-of-freedom magnetic suspension moving platform and control method thereof - Google Patents

Abstract

The present invention discloses a three-degree-of-freedom magnetic levitation mobile platform and control method, including a levitation platform, a driving unit, a magnetic stator, a position detection magnet, a three-axis sensor and a base; the levitation platform includes a working platform and a levitation magnet placed on the working platform; the levitation magnet is composed of a plurality of cylindrical permanent magnets, and the levitation magnet is adsorbed on the working platform through an iron sheet base installed on the working platform; the driving unit and the magnetic stator can be detachably stacked up and down to form a levitation control component; the levitation control component is fixed on the base, relative to the number and position of the levitation magnet; the driving unit includes a driving coil for controlling the three-degree-of-freedom motion in space, and the driving coil does not contain a magnetic core or a permanent magnet; the position detection magnet and the three-axis sensor correspond in position and are fixed on the working platform and the base respectively. The present invention solves the problem of decoupling of motion in the horizontal and vertical directions of the magnetic levitation platform, and each part can be independently disassembled and replaced, which is easy to maintain.

Description

A three-degree-of-freedom magnetic suspension mobile platform and control method thereof

Technical Field

The invention relates to the technical field of magnetic suspension mobile platforms, and in particular to a magnetic suspension mobile platform capable of realizing three-degree-of-freedom movement and a three-degree-of-freedom control method thereof.

Background Art

Micro-motion tracking platforms play a vital role in today's mechanical processing, precision measurement and other fields. Traditional tracking platforms require multiple linear motors to drive, and inevitably have mechanical friction, guide defects and creeping phenomena, resulting in limited positioning accuracy, cumbersome disassembly steps and high maintenance costs. Pneumatic suspension in non-contact tracking platforms is a tracking method that uses air support to reduce friction, but pneumatic suspension methods are often more complex in structure and difficult to apply in vacuum environments.

The magnetic levitation platform has the advantages of high positioning accuracy, fast response speed, no friction, low heat generation, and compatibility with vacuum environment, which can meet the stringent requirements of micro-motion tracking. Its basic principle is to achieve the suspension and movement of the mover through the electromagnetic interaction force between the electromagnetic coil and the permanent magnet. Therefore, the combination of the electromagnetic coil and the permanent magnet is an important consideration for realizing the specific functions of the magnetic levitation platform. According to the composition of the mover, the magnetic levitation platform can be divided into a moving coil platform and a moving magnet platform: 1) The moving coil platform is to fix the electromagnetic coil in the mover. This solution is easy to implement, but it is necessary to consider how to solve the problem of powering the moving coil; 2) The mover of the moving magnet platform is composed of a permanent magnet or a permanent magnet array, and the stator is mostly composed of a coil array directly. If the stator is directly composed of a coil array, the coil array is required to provide the mover with suspension force and lateral translation force at the same time to achieve both suspension and movement. This involves a complex decoupling problem. If it is not handled properly, it will directly affect the robustness and accuracy of the system. In addition, when the platform is stably suspended, the coil still needs to provide all the suspension force to ensure the stable suspension of the platform, which increases the unnecessary power consumption of the coil. Therefore, some moving-magnet magnetic levitation platforms cross-arrange the electromagnetic coils and permanent magnets in the stator, or wind the electromagnetic coils around permanent magnets or magnetic cores to prepare excitation coils, and form an embedded structure. The permanent magnets in the stator provide suspension force while the excitation coils in the stator provide horizontal thrust. This can reduce coil heat loss while avoiding complex decoupling calculation problems.

Chinese invention patent CN102055382A discloses a repulsive magnetic suspension system, including a fixing device and a suspension part, which uses the electromagnetic force generated by the solenoid coil array containing permanent magnets in the fixing device to suspend and move the permanent magnet array in the suspension part. The system has a simple structure, but the solenoid array of the stator is embedded with the permanent magnet. If some electromagnetic coils in the solenoid array fail, it is not easy to maintain. Chinese invention patent CN108768214A discloses a six-degree-of-freedom controllable magnetic suspension mechanism and a six-degree-of-freedom control method thereof, which can arbitrarily control the suspension height, suspension angle, suspension rotation speed, etc. of the mover within a certain range, but the control coil in the stator surrounds the stator attraction magnet, which also has the problem of being inconvenient for maintenance. Chinese invention patent CN1819436A discloses a magnetic repulsion suspension device, including a suspension base and a suspension body. The suspension base is composed of permanent magnets arranged in a ring and an electromagnetic coil in the ring. The combined force generated by the two enables the magnetic suspension body to suspend above the base. However, the suspension body in the device is in a state of 360-degree free horizontal rotation, which conflicts with the requirement of the micro-tracking platform to avoid rotation. Chinese invention patent CN110677075A discloses a two-degree-of-freedom magnetic suspension device, which improves the problem of the existing push-down magnetic suspension device being difficult to place, greatly improves the suspension stability, and solves the problem of movement. However, the electromagnetic coil is wound on the magnetic core and forms an embedded structure with the permanent magnet array, which is inconvenient to maintain. In addition, the device lacks control over the rotational freedom of the suspension magnet, and there is uncertainty that the suspension magnet will spontaneously rotate around its own central axis during stable suspension or movement.

Summary of the invention

In view of this, the present invention provides a magnetic levitation mobile platform that can realize three-degree-of-freedom movement and a three-degree-of-freedom control method thereof, realizes a magnetic levitation mobile platform without spontaneous rotation, solves the problem of decoupling of motion in the horizontal and vertical directions of the magnetic levitation platform, eliminates the electromagnetic coil required to provide passive suspension force to reduce the number of coils and coil power consumption, and at the same time, the electromagnetic coil in the stator has no magnetic core or permanent magnet inside, and the coil array and the magnet array are separated in space, and each part can be independently disassembled, assembled and replaced, which is easy to maintain.

In order to solve the above technical problems, the present invention is implemented as follows.

A three-degree-of-freedom magnetic suspension mobile platform, comprising: a suspension platform, a driving unit, a magnetic stator, a position detection magnet, a three-axis sensor and a base;

The suspension platform includes a working platform and a suspension magnet placed on the working platform; the suspension magnet is composed of a plurality of cylindrical permanent magnets stacked together, and the size of the magnets decreases from top to bottom; the suspension magnets are adsorbed on the working platform through an iron sheet substrate installed on the working platform;

The drive unit and the magnetic stator can be detachably stacked up and down to form a suspension control component; the suspension control component is fixed on the base, and is relative to the number and position of the suspension magnets; the drive unit includes a drive coil for controlling the three-degree-of-freedom motion in space, and the coil in the drive coil does not contain a magnetic core or a permanent magnet;

The position detection magnet and the three-axis sensor are located in corresponding positions and are fixed on the working platform and the base respectively.

Preferably, the position detection magnet is a bar magnet.

Preferably, the length direction of the position detection magnet is parallel to the x-axis or y-axis of the magnetic levitation mobile platform, the height direction is parallel to the z-axis, and the magnetization direction is along the z-axis; the center of the bar magnet coincides with the center of the working platform.

Preferably, the driving unit includes a driving coil array and a coil base platform; the driving coil array controls the vertical z-direction freedom movement and the horizontal x and y-direction freedom movement of the suspension platform, and ensures the stable suspension of the magnetic suspension platform; the driving coil array is fixed on the coil base platform, and the coil base platform is placed on the upper surface of the magnetic stator and can be disassembled and separated.

Preferably, the driving coil array in the driving unit consists of a z-direction freedom control coil and a group of x-direction and y-direction freedom control coils; the z-direction freedom control coil is arranged at the center of the coil base platform, and is responsible for controlling the vertical z-direction freedom of the suspension magnet; a group of coils responsible for controlling the x-direction and y-direction freedom are distributed in a circular symmetrical manner with the center of the z-direction freedom control coil.

Preferably, the group of coils responsible for controlling the x-direction and y-direction degrees of freedom is 3 or more; by changing the current in the coils, a suitable electromagnetic force is generated to achieve control of the horizontal x-direction and y-direction degrees of freedom of the suspension magnet.

Preferably, the magnetic stator adopts a circular permanent magnet or a permanent magnet array.

Preferably, the vertical projection of the center of the z-degree-of-freedom control coil in the driving unit above the magnetic stator on the plane where the magnetic stator is located is used as the center of the magnetic stator; if the magnetic stator adopts a circular permanent magnet, the center of the circular permanent magnet coincides with the center of the magnetic stator; if the magnetic stator adopts a permanent magnet array, the cylindrical permanent magnets are evenly arranged into a circular ring with the center of the magnetic stator as the center, forming a permanent magnet array.

The present invention also provides a three-degree-of-freedom control method for a magnetic levitation mobile platform, using the above three-degree-of-freedom magnetic levitation mobile platform; the method comprises:

According to the position state of the detection magnet monitored in real time by the three-axis sensor, the drive coils in the drive unit that control the x and y degrees of freedom movement are controlled separately, and electromagnetic force is applied to the suspension magnet to adjust it back to its initial equilibrium position, so that it is in a state of force balance in the horizontal x and y directions and maintained, thereby preventing the suspension work platform from rotating freely.

When movement in a certain direction is required, the target value of the platform displacement is changed first, and the actual position of the working platform in this direction is detected in real time by the three-axis sensor. According to the error between the target value and the actual position, the size and direction of the driving coil current corresponding to the direction are obtained, and an electromagnetic force is generated along the direction toward the target position to push the working platform toward the target position to achieve the displacement of the working platform.

Preferably, according to the error between the target value and the actual position, the magnitude and direction of the driving coil current corresponding to the direction are obtained, and an electromagnetic force is generated along the direction toward the target position to push the working platform toward the target position, so as to achieve the displacement of the working platform as follows:

The distance between the target value and the actual position of the platform is divided into several equally spaced target positions. The actual position is compared with the divided target positions to obtain error information, and then the magnitude and direction of the drive coil current corresponding to the direction are obtained, and an electromagnetic force is generated along the direction toward the target position to push the working platform toward the target position. Finally, the displacement of the working platform is achieved by a small-pitch stepping method.

Beneficial effects:

(1) The present invention provides a three-degree-of-freedom magnetic levitation mobile platform and a three-degree-of-freedom control method thereof, which utilizes a magnetic stator composed of permanent magnets and a driving coil to jointly realize stable suspension and three-degree-of-freedom motion of the platform. The driving coil is separated from the magnetic stator, the magnetic stator provides the main suspension force, and the driving coil provides the driving force, without the need for complex decoupling calculations: considering that the overall force on the suspension magnet can be divided into: passive force _Fm from the magnetic stator, active force _Fe from the driving coil after power is turned on, and the gravity mg of the suspension magnet itself, the linear motion of the suspension magnet at a certain suspension height includes two aspects: 1) the vertical components Fm_z _and Fe_z of _Fm and _Fe in the vertical _direction counteract the gravity mg of the suspension magnet to stabilize the suspension; 2) the horizontal _{components Fm_xy} and Fe_xy of _Fm and _Fe in the horizontal _direction drive the suspension magnet to move in the horizontal plane. Due to the existence of the force _Fm exerted _by the magnetic stator on the suspension magnet, within a certain range, Fm_z , _{Fe_z} and mg in the vertical direction reach a force balance, so there is no need to design a high-dimensional controller to control the movement in the vertical and horizontal directions respectively. It is only necessary to consider designing a controller in the horizontal plane to control the movement of the suspension magnet in the horizontal plane. In other words, since the magnetic stator provides the force _Fm , it is avoided to consider introducing more driving coils to increase _{the vertical component Fe_z} of _Fe so that Fe_z and mg reach a force balance in the vertical direction, and _at the same time, it is avoided to consider the _Fe decoupling problem involved in designing a high-dimensional controller to consider different coils passing different currents to simultaneously achieve force balance in the vertical direction and movement in the horizontal plane.

At the same time, it makes it easy to achieve motion decoupling of the entire mechanism, easy to achieve mobile motion control of the platform, and can effectively reduce the number and power consumption of driving coils.

(2) The suspension magnet of the present invention is composed of a plurality of cylindrical permanent magnets stacked together, and the size decreases from top to bottom. The stacking of multiple permanent magnets can increase the magnetic flux and enhance the magnetic force between the electromagnetic coil and the suspension magnet. Each suspension magnet is adsorbed on the iron sheet substrate, which plays the role of converging the magnetic flux, further enhancing the magnetic force between the electromagnetic coil and the suspension magnet. At the same time, the drive unit and the magnetic stator can be detached and stacked up and down, so that the drive unit is closer to the suspension magnet, which is conducive to increasing the magnetic force between the two. Through the above series of settings, even if a magnetic core or permanent magnet is not set in the drive coil, sufficient electromagnetic force between the drive coil and the suspension magnet can be guaranteed.

(3) The drive unit is spatially separated from the magnetic stator, and the drive coil does not contain a magnetic core or permanent magnet. It can be disassembled and replaced independently, making maintenance easy.

(4) In a preferred embodiment, the drive unit adopts a structure in which the drive coil array is arranged on a coil base platform, and the coil base platform is directly mounted on the upper surface of the magnetic stator, which is convenient for disassembly and separation, thereby making it easier to maintain.

(5) In a preferred embodiment, the drive coil array in the drive unit is composed of 5 coils, the z-direction freedom control coil is located at the center, and the outer 4 coils are distributed in a circular symmetric manner with the center of the z-direction freedom control coil as the center. This combination uses fewer coils and the control algorithm is relatively simple.

(6) In a preferred embodiment, the present invention uses a bar magnet as a position detection magnet, which can detect the rotation of the platform. Therefore, based on the detection feedback, combined with the design of multiple suspension magnets and corresponding control components of the platform, rotation suppression can be performed in a timely manner, so that the entire platform does not have spontaneous rotation. This is because if the suspension platform generates rotation in the xy plane, that is, rotation around a straight line parallel to the z- axis, the rotation will cause all or part of the suspension magnets to shift in the x- direction or y -direction, and the rotation will cause the length direction of the detection magnet to no longer be parallel to the x- axis (or y- axis), so that the spatial magnetic field distribution generated by the bar magnet changes, that is _, the x -direction magnetic field Bx and the y -direction magnetic field By at a certain point in space will change, and this change will be detected by the three-axis sensor, which transmits the data to the controller in real time. The controller controls the power of the coils in the drive unit that are symmetrically distributed in a ring according to the data, applies electromagnetic force to each suspension magnet, adjusts it back to the initial equilibrium position, and makes it in a state of force balance in the horizontal x- direction and y -direction and maintains it. When each suspension magnet is adjusted back to the initial equilibrium position, the detection magnet also returns to the initial position, and the length direction continues to remain parallel to the x- axis (or y -axis), so that the suspension work platform can be prevented from rotating freely. If a cylindrical magnet is used as a detection magnet, it is impossible to control the spontaneous rotation.

(7) The present invention provides a method for advance adjustment control, which divides the distance between the final target value and the actual position into several equally spaced target positions, compares the actual position with the divided target positions in turn to obtain error information, and performs multiple small step adjustments based on the error to reach the target position. The advance adjustment method can effectively improve the control quality of the controlled object with a large time lag.

In summary, the present invention utilizes the magnetic force between the suspension platform and the permanent magnets in the magnetic stator to generate suspension force, and utilizes the driving unit to achieve the stability of the platform and three-degree-of-freedom motion, thereby greatly reducing the power consumption of the coil, and has the characteristics of simple structure, easy disassembly and maintenance, high stability, and vacuum compatibility. It can be widely used in micromachining or other occasions that require a frictionless, vacuum environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a three-degree-of-freedom magnetic levitation mobile platform according to an embodiment of the present invention.

FIG. 2 is a front view of a three-degree-of-freedom magnetically suspended mobile platform according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a suspension platform according to an embodiment of the present invention (top view).

FIG. 4 is a schematic diagram (top view) of a driving unit according to an embodiment of the present invention.

FIG5 is a schematic diagram of a magnetic stator, a three-axis sensor and a base according to a first embodiment of the present invention.

FIG6 is a control method for advance regulation according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of a system composed of a three-degree-of-freedom magnetic suspension mobile platform and a control part of the present invention.

FIG8 is a schematic structural diagram of a three-degree-of-freedom magnetic levitation mobile platform in Embodiment 2 of the present invention.

FIG9 is a schematic diagram of the structure of a three-degree-of-freedom magnetic levitation mobile platform in Embodiment 4 of the present invention.

FIG. 10 is a schematic diagram of the forces acting on the float in the horizontal plane in the fourth embodiment of the present invention.

Among them, 1. working platform, 2. iron sheet base, 3. suspension magnet, 4. position detection magnet, 5. driving coil, 6. coil base platform, 7. permanent magnet array, 8. three-axis sensor, 9. base, 10. z-direction degree of freedom control coil, 11. x-direction degree of freedom control coil, 12. y-direction degree of freedom control coil.

DETAILED DESCRIPTION

The present invention discloses a magnetic levitation mobile platform capable of realizing three-degree-of-freedom movement, the magnetic levitation mobile platform comprising a levitation platform, a driving unit, a magnetic stator, a position detection magnet, a three-axis sensor and a base. The levitation platform comprises a working platform and a levitation magnet placed on the working platform. The levitation magnet is composed of a plurality of cylindrical permanent magnets stacked together, and the size is continuously reduced from top to bottom; the levitation magnet is adsorbed on the working platform through an iron sheet substrate installed on the working platform.

The drive unit and the magnetic stator can be separated and stacked up and down to form a suspension control component. The suspension control component is fixed on the base, relative to the number and position of the suspension magnets; the drive unit includes a drive coil that controls the three degrees of freedom movement in the vertical z direction, the horizontal x direction and the horizontal y direction, and the coil in the drive coil does not contain a magnetic core or a permanent magnet.

The position detection magnet and the three-axis sensor correspond to each other and are fixed on the working platform and the base respectively, so that the position and posture detection of the suspension platform can be realized.

It can be seen that the present invention utilizes the magnetic force between the suspension platform and the permanent magnets in the magnetic stator to generate suspension force, and utilizes the driving unit to achieve the stability of the platform and three-degree-of-freedom movement, which greatly reduces the power consumption of the coil, and has the characteristics of simple structure, easy disassembly and maintenance, high stability, and vacuum compatibility. It can be widely used in micromachining or other occasions that require a frictionless, vacuum environment.

Secondly, the suspension magnet of the present invention is composed of a plurality of cylindrical permanent magnets stacked together, and the size is continuously reduced from top to bottom. The stacking of multiple permanent magnets can increase the magnetic flux, and can enhance the magnetic force of the electromagnetic coil and the suspension magnet. Each suspension magnet is adsorbed on the iron sheet substrate, and the iron sheet substrate plays the role of converging the magnetic flux, further enhancing the magnetic force of the electromagnetic coil and the suspension magnet. At the same time, the drive unit and the magnetic stator can be detachably stacked up and down, so that the drive unit is closer to the suspension magnet, which is conducive to increasing the magnetic force between the two. Through the above series of settings, even if a magnetic core or permanent magnet is not set in the drive coil, sufficient electromagnetic force between the drive coil and the suspension magnet can be guaranteed. Moreover, the drive unit and the magnetic stator are separated in space, and can be independently disassembled and replaced, which is easy to maintain.

Furthermore, since the driving coil is separated from the magnetic stator, the magnetic stator provides the main suspension force and the driving coil provides the driving force, there is no need to perform complex decoupling calculations, making it easy to achieve motion decoupling of the entire mechanism, easy to achieve mobile motion control of the platform, and can effectively reduce the number and power consumption of the driving coils. Specifically: Considering that the overall force of the suspension magnet can be divided into: passive force _Fm from the magnetic stator, active force _Fe from the driving coil after power is turned on, and the gravity mg of the suspension magnet itself, the linear motion of the suspension magnet at a certain suspension height includes two aspects: 1) The vertical components _{Fm_z and} Fe_z of Fm and _Fe in the vertical direction counteract the gravity mg of the suspension _magnet to stabilize the suspension; 2) _The horizontal components Fm_xy and _{Fe_xy} of _Fm and _Fe in the horizontal direction drive the suspension magnet to move in the horizontal plane. Due to the existence of the force _Fm exerted _by the magnetic stator on the suspension magnet, within a certain range, Fm_z , _{Fe_z} and mg in the vertical direction reach a force balance, so there is no need to design a high-dimensional controller to control the movement in the vertical and horizontal directions respectively. It is only necessary to consider designing a controller in the horizontal plane to control the movement of the suspension magnet in the horizontal plane. In other words, since the magnetic stator provides the force _Fm , it is avoided to consider introducing more driving coils to increase _{the vertical component Fe_z} of _Fe so that Fe_z and mg reach a force balance in the vertical direction, and _at the same time, it is avoided to consider the _Fe decoupling problem involved in designing a high-dimensional controller to consider different coils passing different currents to simultaneously achieve force balance in the vertical direction and movement in the horizontal plane.

Furthermore, by using bar magnets as position detection magnets, the rotation of the platform can be detected. Therefore, based on the detection feedback, combined with the design of multiple suspension magnets and corresponding control components of the platform, rotation suppression can be performed in time to prevent the spontaneous rotation of the entire platform. This is because if the suspension platform generates rotation in the xy plane, that is, rotation around a straight line parallel to the z- axis, the rotation will cause all or part of the suspension magnets to have positional displacement in the x- direction or y -direction, and the rotation will cause the length direction of the detection magnet to no _longer be parallel to the x -axis (or y- axis), so that the spatial magnetic field distribution generated by the bar magnet changes, that is, the x- direction magnetic field Bx and the y -direction magnetic field By at a certain point in space will change, and this change will be monitored by the three-axis sensor, which transmits the data to the controller in real time. The controller controls the power of the coils in the periphery of the drive unit in a circular symmetrical distribution separately according to the data, applies electromagnetic force to each suspension magnet, adjusts it back to the initial equilibrium position, and makes it in a state of force balance in the horizontal x- direction and y -direction and maintains it. When each suspension magnet is adjusted back to the initial equilibrium position, the detection magnet also returns to the initial position, and the length direction continues to remain parallel to the x- axis (or y- axis), thus preventing the suspension work platform from rotating freely.

The present invention is described in detail below with reference to the accompanying drawings and embodiments.

Embodiment 1

The suspension platform of this embodiment adopts a long strip structure, and two suspension magnets are arranged on the edge. Correspondingly, two suspension control components are also installed on the base, corresponding to the suspension magnets.

1 to 6, the three-degree-of-freedom magnetic suspension mobile platform of the first embodiment of the present invention includes a suspension platform, a drive unit, a magnetic stator, a position detection magnet 4, a three-axis sensor 8 and a base 9. The suspension platform includes a working platform 1 and two groups of suspension magnets 3 placed on the edge of the working platform 1, and a position detection magnet 4 fixed to the center of the working platform. Each suspension magnet 3 is fixed to the suspension platform by installing an iron sheet base 2 at a corresponding position of the working platform 1 so that the magnet is adsorbed to the center of the iron sheet base by magnetic force.

For each group of suspension magnets 3, a suspension control assembly consisting of a group of drive units and a group of magnetic stators is configured below them. The drive unit includes a drive coil array and a coil base platform 6. The drive coil array controls the vertical z-direction freedom movement of the suspension platform and the horizontal x and y-direction freedom movement, and ensures the stable suspension of the magnetic suspension platform. The drive unit is located above the magnetic stator part, wherein the drive coil array is fixed on the coil base platform 6, and the coil base platform 6 is placed on the upper surface of the magnetic stator and can be disassembled and separated. This stacking method, firstly, makes the drive unit closer to the suspension magnet, which is conducive to increasing the magnetic force between the two, and secondly, separates the drive unit from the magnetic stator in space, and can be disassembled and replaced independently, which is easy to maintain.

The magnetic stator is composed of a circular permanent magnet or a permanent magnet array 7 , and each magnetic stator is fixed on a base 9 together with a three-axis sensor 8 below the position detection magnet 4 .

In this embodiment, the drive coil array in the drive unit is composed of 5 coils, and the coils do not contain magnetic cores or permanent magnets. The central position coil 10 is a z-direction freedom control coil, which is responsible for controlling the vertical z-direction freedom of the suspension magnet. The peripheral coils are symmetrically distributed in a ring with the center of the coil 10 as the center, and the center is located on the x-axis or y-axis respectively: the two coils with the center located on the x-axis are the x-direction freedom control coils 11, which are responsible for controlling the horizontal x-direction freedom of the suspension magnet; the two coils with the center located on the y-axis are the y-direction freedom control coils 12, which are responsible for controlling the horizontal y-direction freedom of the suspension magnet.

The magnetic stator is composed of a circular permanent magnet or a permanent magnet array 7. The central position coil in the driving unit above the magnetic stator is the z-direction freedom control coil 10, and the vertical projection of its center on the plane where the magnetic stator is located is taken as the center of the magnetic stator. If a circular permanent magnet is used, the center of the circular permanent magnet coincides with the center of the magnetic stator. If a permanent magnet array is used, the permanent magnet array is evenly arranged into a circular ring with the center of the magnetic stator as the center.

The suspension magnet 3 is composed of multiple cylindrical permanent magnets stacked together, and the size decreases from top to bottom. The stacking of multiple permanent magnets can increase the magnetic flux and enhance the magnetic force of the electromagnetic coil and the suspension magnet. Each suspension magnet is fixed to the suspension platform by installing an iron sheet base 2 at the corresponding position of the suspension platform so that the magnet is adsorbed to the center of the iron sheet base by magnetic force. The iron sheet base plays the role of converging magnetic flux, further enhancing the magnetic force of the electromagnetic coil and the suspension magnet.

The detection magnet 4 is a bar permanent magnet with a length of a, a width of b, and a height of c. The length direction is parallel to the x-axis or y-axis, the height direction is parallel to the z-axis, and the magnetization direction is along the z-axis. The center of the bar magnet coincides with the center of the suspension platform. The three-axis sensor 8 is located directly below the detection magnet 4.

The working process of the three-degree-of-freedom magnetic levitation mobile platform of the present invention is as follows: the repulsion between the levitation magnet 3 and the magnet array 7 is used to generate a levitation force in the vertical direction; the three-axis sensor 8 obtains the actual position of the xyz three-degree-of-freedom of the working platform 1 by detecting the magnetic field change of the position detection magnet (4); a closed-loop control calculation is performed after subtracting the target value to obtain the magnitude and direction of the corresponding drive coil array current; the magnetic field generated after the drive coil array is energized is superimposed on the original magnetic field, and finally acts on the levitation magnet 3 to realize the stable levitation and three-degree-of-freedom movement of the working platform 1.

The working principle of stable suspension of the working platform 1 is as follows: taking the motion analysis along the x- axis direction as an example, first, the actual position of the platform in space is the same as the target value, and it is in the equilibrium position during stable suspension. However, the external interference force and the passive offset force generated by the magnet array 7 on the suspension magnet 3 will cause the working platform 1 to deviate from the equilibrium position. At the same time, the sensor detects the offset position of the working platform 1 in the x-direction in real time, and obtains the error information by comparing it with the target position of stable suspension. Then, the magnitude and direction of the current of the two sets of drive coils in the x-direction are obtained through the advance adjustment control method, and an electromagnetic force along the x-direction is generated to ensure the force balance of the working platform 1 in the x-direction, thereby realizing stable suspension of the working platform 1. In addition, if the suspension platform generates a rotation in the xy plane, that is, it rotates around a straight line parallel to the z-axis, the rotation will cause all or part of the suspension magnet 3 to be offset in the x direction or the y direction, and the rotation will cause the length direction of the detection magnet 4 to no longer be parallel to the x-axis (or y-axis), so that the spatial magnetic field distribution generated by the bar magnet changes, that is, the x-direction magnetic field Bx and the y-direction magnetic field By at a certain point in space will change, and this change will be monitored by the three-axis sensor 8, and the error information will be obtained by comparing with the magnetic field corresponding to the target position of stable suspension, and then the size and direction of the driving coil current in the x-direction and y-direction will be obtained through the advance adjustment control method, and the electromagnetic force along the x-direction and y-direction will be generated to adjust the suspension magnet 3 back to the initial position, so that the detection magnet 4 also returns to the initial position, and the length direction continues to remain parallel to the x-axis (or y-axis), so that the suspension work platform 1 can be prevented from rotating freely, and the stable suspension of the work platform 1 can be achieved.

The working principle of the movement of the working platform 1 is that, on the basis of stable suspension, taking the motion analysis along the x-axis direction as an example, firstly, the target value of the platform displacement is changed, and the actual position of the working platform 1 in the x-direction is detected in real time by the sensor, and the distance between the final target value and the actual position of the platform is divided into several equally spaced target positions, and the actual position is compared with the divided target position to obtain the error information, and then the magnitude and direction of the current of the two groups of driving coils in the x-direction are obtained through the advance adjustment control method, and an electromagnetic force is generated along the x-direction toward the target position, pushing the working platform 1 toward the target position, and finally realizing the displacement of the working platform 1 by a small-pitch stepping method.

Specifically, as shown in Figure 6, a digital controller is used to implement the system's analog-to-digital conversion, control algorithm implementation, PWM (pulse width modulation) wave generation, and control of the output voltage direction. The front-stage three-axis sensor detects the position of the suspended platform, i.e., the float, and outputs an amplified voltage signal. The analog-to-digital conversion is then performed using the MCU chip of the digital controller, and the error value is compared with the reference position value. The PWM waveform corresponding to the duty cycle is then output through the calculation of the control algorithm. Finally, the drive circuit is controlled to generate the corresponding drive coil current, including the size and direction, to generate the corresponding driving force. An optocoupler isolation module is added between the digital controller and the drive circuit to reduce the reverse impact of the drive circuit.

Digital control is achieved by programming the STM32F407ZGT6 high-performance MCU. The software part of the STM32 microprocessor chip mainly designs the algorithm for the required functions. The advance correction PD control link is implemented on the STM32 microcontroller chip.

Embodiment 2

Referring to FIG. 7 , FIG. 4 and FIG. 6 , the suspension platform of this embodiment adopts a three-arm structure. A suspension magnet 2 is arranged at the edge of each arm, and a position detection magnet 4 is arranged at the center of the three-arm structure. Accordingly, for each group of suspension magnets 3, a group of driving units and a group of magnetic stators are arranged below them. The rest of the structure and working principle are similar to those of the specific implementation case 1.

Embodiment 3

In the first and second embodiments, the driving unit is composed of five driving coils 5. In practice, more driving coils may be used to form the driving unit.

For example, the drive unit has 1+n+m drive coils. "1" refers to a z-direction freedom control coil 10, which is set at the center of the coil base platform 6 and is responsible for controlling the vertical z-direction freedom of the suspension magnet. "n" refers to n x-direction freedom control coils 11, which are distributed in a circular symmetry with the center of the z-direction freedom control coil, and are responsible for controlling the horizontal x-direction freedom of the suspension magnet. "m" refers to m y-direction freedom control coils 12, which are distributed in a circular symmetry with the center of the z-direction freedom control coil, and are responsible for controlling the horizontal y-direction freedom of the suspension magnet.

The values of m and n may be the same or different. The diameters of the circle formed by the n x-direction freedom control coils 11 and the circle formed by the m y-direction freedom control coils 12 may be the same or different.

Taking m=n=3 as an example, three x-direction degree of freedom control coils 11 and three y-direction degree of freedom control coils 12 are alternately arranged to form a regular hexagon.

Embodiment 4

In this embodiment, as shown in FIG. 9 , four driving coils 5 are used to form a driving unit.

The center position coil 10 is a z-direction freedom control coil, and the centers of the three outer coils form an equilateral triangle, and the center of the equilateral triangle coincides with the center of the center position coil. The three outer coils control the movement of the suspension magnet in the horizontal plane.

Specifically, as shown in Figures 9 and 10, the horizontal plane where the center point of the coil is located is the reference plane, and the center points A, B, and C of the three peripheral coils A , B , and C form an equilateral triangle, and the center point O of the equilateral triangle ABC is the coordinate origin, and OA is the y- _axis direction. Assume that the side length of the equilateral triangle ABC | AB |= a , the coordinates of the vertical projection point P1 of the _center of the initial position of the suspension magnet on the reference plane _are P1 ( x1 , y1 ), and the suspension magnet is moved to the _target position. The coordinates of _the vertical projection point P2 of the center of the target position float on the reference plane _are P2 ( x2 , y2 ). The vertical projections of the attraction of the three electromagnetic coils on the _suspension magnet on the reference plane are _FA , _FB , _{and FC} respectively, and the resultant force of the three attractions is _FP = _FA + _FB + _FC .

The coordinates of the three points A , B , and C are , , ,vector , , , so we have:

in , , They represent _FA , _FB , The size of , Represent the x- axis and y- axis unit vectors respectively.

Adjustment , , , so that _FP = _FA + _FB + _FC can move the float from _point P1 to _point P2 .

For example, when satisfy When , where the coefficient , The suspension magnet can be moved from _point P1 to _point P2 . The controller changes the magnitude and direction of the current in coils A, B, and C according to the position deviation signal, and generates appropriate electromagnetic forces _FA , _FB , and _FC respectively. The resultant force _FP = _FA + _FB + _FC can move the float from _point P1 to _point P2 .

When the float is required to be stable at _point P2 , if the float position deviates from _point P2 due to external disturbances, the sensor will detect the actual position of the platform, and obtain error information by comparing it with the target position of stable suspension. The current size and direction of each drive coil are obtained through the advance adjustment method to adjust the , , , so that _FP = _FA + _FB + _FC, the float can be adjusted back to the target stable position _point P2 .

The advantage of this solution is that fewer drive coils are used.

The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims (8)

1. A three degree of freedom magnetic levitation mobile platform comprising: the device comprises a suspension platform, a driving unit, a magnetic stator, a position detection magnet (4), a triaxial sensor (8) and a base (9);

The suspension platform comprises a working platform (1) and a suspension magnet (3) arranged on the working platform (1); the suspension magnet (3) is formed by superposing a plurality of cylindrical permanent magnets, and the size of the suspension magnet is continuously reduced from top to bottom; the suspension magnet (3) is adsorbed on the working platform (1) through an iron sheet substrate (2) arranged on the working platform (1);

The driving unit and the magnetic stator are stacked up and down in a detachable way to form a suspension control assembly; the suspension control assembly is fixed on the base (9) and is opposite to the number and the positions of the suspension magnets (3); the driving unit comprises a driving coil (5) for controlling the spatial three-degree-of-freedom motion, and a magnetic core or a permanent magnet is not contained in the coil in the driving coil (5); the drive unit comprises a drive coil array and a coil base platform (6); the driving coil array controls the vertical z-direction freedom degree movement and the horizontal x-direction and y-direction freedom degree movement of the suspension platform, and ensures the stable suspension of the suspension platform; the driving coil array is fixed on a coil base platform (6), and the coil base platform (6) is placed on the upper surface of the magnetic stator and can be detached and separated;

The position detection magnet (4) and the triaxial sensor (8) are corresponding in position and are respectively fixed on the working platform (1) and the base (9); the position detection magnet (4) is a bar magnet.

2. A magnetically levitated mobile platform according to claim 1, characterized in that the length direction of the position detection magnet (4) is parallel to the x-axis or the y-axis of the magnetically levitated mobile platform, the height direction is parallel to the z-axis and the magnetization direction is along the z-axis direction; the center of the bar magnet coincides with the center of the working platform (1).

3. A magnetic levitation mobile platform as defined in claim 1, wherein the driving coil array in the driving unit is composed of one z-direction degree of freedom control coil and a set of x-direction, y-direction degree of freedom control coils; the z-direction degree-of-freedom control coil is arranged in the center of the coil base platform (6) and is responsible for controlling the vertical z-direction degree of freedom of the levitation magnet; and a group of coils responsible for controlling the degrees of freedom in the x direction and the y direction are distributed in annular symmetry with the center of the circle center of the control coil of the degree of freedom in the z direction.

4. A magnetic levitation mobile platform according to claim 3, wherein the set of coils responsible for controlling the degree of freedom in x-direction and y-direction is 3 or more; and the degree of freedom of the horizontal x direction and the y direction of the levitation magnet is controlled by changing the current in the coil to generate proper electromagnetic force.

5. A magnetic levitation mobile platform according to claim 3, wherein the vertical projection of the center of the z degree of freedom control coil in the drive unit above the magnetic stator in the plane of the magnetic stator is used as the center of the magnetic stator; if the magnetic stator adopts a circular ring permanent magnet, the center of the circular ring permanent magnet coincides with the center of the magnetic stator; if the magnetic stator adopts a permanent magnet array, the cylindrical permanent magnets are uniformly arranged into a circular ring by taking the center of the magnetic stator as the center of a circle, so as to form the permanent magnet array.

6. A magnetic levitation moving platform according to any of claims 1-5, characterized in that the magnetic stator employs a circular ring permanent magnet or an array of permanent magnets (7).

7. A three-degree-of-freedom control method of a magnetic suspension mobile platform is characterized by comprising the following steps of: a three-degree-of-freedom magnetic levitation mobile platform according to any of claims 1-6; the method comprises the following steps:

According to the position state of the detection magnet (4) monitored in real time by the triaxial sensor (8), a driving coil (5) for controlling the motion of the degrees of freedom of x and y in a driving unit is independently controlled, electromagnetic force is applied to a suspension magnet, the suspension magnet is adjusted back to an initial balance position, and the suspension magnet is kept in a state of being in stress balance in the horizontal x direction and the y direction, so that the suspension working platform (1) is prevented from freely rotating;

When the working platform moves along a certain direction, the target value of the platform displacement is changed, the actual position of the working platform (1) in the direction is detected in real time through a triaxial sensor (8), the magnitude and the direction of the driving coil current corresponding to the direction are obtained according to the error between the target value and the actual position, the electromagnetic force which faces the target position along the direction is generated, and the working platform (1) is pushed to move towards the target position, so that the displacement of the working platform (1) is realized.

8. The method of claim 7, wherein: according to the error between the target value and the actual position, the magnitude and the direction of the driving coil current corresponding to the direction are obtained, electromagnetic force which faces the target position along the direction is generated, and the working platform (1) is pushed to move towards the target position, so that the displacement of the working platform (1) is realized as follows:

Dividing the distance between the target value and the actual position of the platform into a plurality of equidistant target positions, comparing the actual position with the divided target positions to obtain error information, further obtaining the magnitude and the direction of the driving coil current corresponding to the direction, generating electromagnetic force along the direction towards the target positions, pushing the working platform (1) to move towards the target positions, and finally realizing the displacement of the working platform (1) by a small-spacing stepping method.