Cylindrical permanent magnet linear motor with bidirectional force output and control method thereof

Abstract

The application discloses a bidirectional force output cylindrical permanent magnet linear motor and a control method thereof, relates to the technical field of linear motors, and is suitable for a scenario with long diameter, short length, short stroke, large thrust and fast motor movement frequency. The bidirectional force output cylindrical permanent magnet linear motor comprises a pair of cylindrical permanent magnet linear motors which are the same in structure and are symmetrically arranged. Each cylindrical permanent magnet linear motor comprises a mover, a front end cover and a rear end cover arranged at two ends of the mover, a stator assembly and a winding assembly are arranged on the periphery of the mover, a grating ruler sensor reading head is fixedly arranged on the front end cover, and a grating ruler sensor corresponding to the position of the grating ruler sensor reading head is arranged on the shaft of the mover. The application is suitable for a bidirectional synchronous driving scenario with large diameter, short length, short stroke and high movement frequency. Under the premise of limiting the axial length, bidirectional synchronous reciprocating linear motion can still be realized at a high frequency.

Description

Technical Field

[0001] This invention relates to the field of linear motor technology, and in particular to a bidirectional cylindrical permanent magnet linear motor and its control method. Background Technology

[0002] A linear motor is a device that directly converts electrical energy into linear motion without the need for intermediate structures (such as lead screws, gears, etc.), and has advantages such as high speed, high acceleration, and high precision. A cylindrical linear motor is one structural form of linear motor. Currently, traditional cylindrical linear motors are usually single-output structures or achieve bidirectional motion through complex external mechanical mechanisms. This results in complex system structures, large size, high cost, slow response speed, and asymmetrical output, making them unsuitable for certain special application scenarios. Specifically: 1. It is impossible to achieve efficient and symmetrical bidirectional electromagnetic thrust within a compact cylindrical structure; 2. When outputting in both directions, the output characteristics (such as magnitude, phase, and stability) are inconsistent; 3. The output frequency adjustment is not flexible enough and the precision is not high enough to meet the requirements of precision vibration; 4. Reliance on mechanical reset leads to wear, lifespan, and noise issues. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a bidirectional cylindrical permanent magnet linear motor and its control method. This invention is suitable for bidirectional synchronous drive scenarios with large diameter, short length, short stroke, large thrust, and high motion frequency. Under the premise of limiting the axial length, it can still achieve high-frequency bidirectional synchronous reciprocating linear motion.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a bidirectional cylindrical permanent magnet linear motor suitable for scenarios with long diameter, short length, short stroke, large thrust, and high motor movement frequency, comprising: a pair of cylindrical permanent magnet linear motors with identical structures and symmetrical arrangement, each of the cylindrical permanent magnet linear motors including a mover, a front end cover and a rear end cover located at both ends of the mover, a stator assembly and a winding assembly located around the mover, a grating ruler sensor reading head fixedly mounted on the front end cover, and a grating ruler sensor corresponding to the position of the grating ruler sensor reading head mounted on the shaft of the mover.

[0005] As a further improvement of the present invention, the grating ruler sensor reading head is connected to the front cover via a sensor connection flange.

[0006] As a further improvement of the present invention, the stator assembly includes a first stator module, a second stator module, multiple third stator modules, a fourth stator module, and a fifth stator module installed sequentially; the winding assembly includes multiple first windings and multiple second windings, wherein the multiple first windings are disposed in stator slots between the first stator module and the second stator module, and between the fourth stator module and the fifth stator module, and the multiple second windings are disposed in stator slots between the second stator module and the third stator module, between the third stator module and the fourth stator module, and between adjacent third stator modules.

[0007] As a further improvement of the present invention, the mover includes a shaft, an N-pole permanent magnet, an S-pole permanent magnet disposed around the shaft, a linear bearing, and a stop block; the linear bearing includes a plastic bearing disposed between a shaft sleeve and a bearing sleeve.

[0008] As a further improvement of the present invention, a pair of cylindrical permanent magnet linear motors with identical structures and symmetrical arrangement are connected by screws, and the outer periphery of the pair of cylindrical permanent magnet linear motors is fixed with a housing by M4 screws.

[0009] As a further improvement of the present invention, a connecting flange is connected to the side of the shaft near the front end cover by an M6 screw. The connecting flange is in contact with the outside world and serves as a thrust output.

[0010] The present invention also provides a control method for the bidirectional output cylindrical permanent magnet linear motor as described above, comprising the following steps:

[0011] Step 1: Construct a mathematical model of a permanent magnet synchronous linear motor;

[0012] Step 2: Using a relative / absolute hybrid control method, firstly, the two motors each form a complete control loop through their respective three-closed-loop control; then, synchronization control is achieved through a relative synchronization loop and an absolute position loop.

[0013] As a further improvement to the present invention, step 1 is specifically as follows:

[0014] Assumptions: Magnetic saturation, hysteresis, and eddy current losses are ignored; the three windings are symmetrically distributed in space, generating a sinusoidal magnetomotive force; the magnetic field generated by the permanent magnet is also sinusoidally distributed in the air gap; based on this, the mathematical model of the permanent magnet linear motor in the dq coordinate system is established, and the voltage equation is:

[0015] (1.1);

[0016] In the formula: , These represent the voltage and current components on the secondary d-axis, respectively. , These are the voltage and current components on the secondary q-axis, respectively. , These are the quadrature and direct-axis inductors, respectively. For secondary winding resistance, Let be the electric angular velocity of the motor; the conversion relationship between electric angle and velocity is:

[0017] (1.2);

[0018] In the formula: For initial speed, The polar distance is defined as:

[0019] (1.3);

[0020] in, This is the total movable length of the motor primary. It is the extreme logarithm;

[0021] In the dq coordinate system, the magnetic flux linkage is generated by both the current and the permanent magnet; the d-axis magnetic flux linkage is generated by the d-axis current. and permanent magnet magnetic flux Together they are generated, and the q-axis flux linkage is generated solely by the q-axis current. Therefore, the flux linkage expression is:

[0022] (1.4);

[0023] Electromagnetic power It equals the sum of the three-phase instantaneous power, expressed in the dq coordinate system as:

[0024] (1.5);

[0025] Substituting equations (1.1) and (1.2) and simplifying, we get:

[0026] (1.6);

[0027] The first part of Equation (1.6) represents copper loss, the second part represents the rate of change of magnetic field energy storage, which is reactive power, and the third part is air gap electromagnetic power.

[0028] set up (1.7);

[0029] For a linear motor, the relationship between electromagnetic thrust and air gap electromagnetic power is as follows:

[0030] (1.8);

[0031] Substituting equations (1.2), (1.4), and (1.7) into equation (1.8), the equations of motion for the permanent magnet synchronous linear motor are obtained as follows:

[0032] (1.9);

[0033] For surface-mounted permanent magnet synchronous linear motors, there are Then the electromagnetic thrust equation simplifies to:

[0034] (1.10);

[0035] definition Let be the thrust constant. Then, from equation (1.10), the motion equation of the permanent magnet synchronous linear motor is obtained as follows:

[0036] (1.11);

[0037] In the formula For load resistance, The coefficient of viscous friction, For initial speed, The total mass of the primary component and its load.

[0038] As a further improvement of the present invention, in step 2, the two motors each form a complete control loop through corresponding three-closed-loop control, as detailed below:

[0039] The output of the position loop is used as the input of the speed loop, and the output of the speed loop is used as the input of the current loop, with the current loop employing... control.

[0040] As a further improvement of the present invention, in step 2, the synchronization control is completed through a relative synchronization loop and an absolute position loop as follows:

[0041] Absolute position loop: Two motors each receive the same master position command and are controlled independently to ensure that they follow the reference position command in the general direction;

[0042] Relative synchronization loop: A synchronization controller is superimposed on the output of the absolute position loop, i.e., the speed command. Let the position signals fed back by the two motors be... ,but:

[0043] (1.12);

[0044] The obtained error signals are passed through the synchronous controller and then superimposed as one positive and one negative signal onto the final speed control command.

[0045] This invention solves the problem of the unavoidable increase in axial length of traditional motors to meet the requirements of high thrust and high precision. The thrust of the motor is directly related to the length of the effective magnetic field and the interaction between the coil. Given the limited axial length, how to generate a sufficiently large and stable bidirectional thrust within the effective axial space through electromagnetic design? This invention uses a 6-slot, 8-level slot configuration, increases the motor diameter to increase the number of coil turns, thus providing a sufficiently powerful and stable thrust. The stator modules and windings are installed step-by-step using a stepped splicing method, and the end covers and housing are installed using screw connections.

[0046] The beneficial effects of this invention are:

[0047] 1. Bidirectional symmetrical output: By controlling the symmetrical coil and magnetic field design, efficient, symmetrical bidirectional electromagnetic drive without mechanical reset is achieved, with a compact structure.

[0048] 2. Stable output: Through precise closed-loop control of the coil current, the output can be kept stable with minimal fluctuations under different strokes and speeds.

[0049] 3. The frequency is adjustable and the control is flexible. The output frequency depends only on the switching frequency of the current. It can realize high-frequency dynamic input tracking, stepless adjustment, and fast response speed. Attached Figure Description

[0050] Figure 1 This is a cross-sectional view of a cylindrical permanent magnet linear motor with bidirectional power output in an embodiment of the present invention;

[0051] Figure 2 This is a front view of a cylindrical permanent magnet linear motor with bidirectional power output in an embodiment of the present invention;

[0052] Figure 3 This is a top view of a cylindrical permanent magnet linear motor with bidirectional power output in an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram of the overall structure of the cylindrical permanent magnet linear motor with bidirectional power output in an embodiment of the present invention;

[0054] Figure 5 This is a block diagram of the FOC control in an embodiment of the present invention;

[0055] Figure 6 This is a displacement curve diagram in an embodiment of the present invention;

[0056] Figure 7 This is a speed curve diagram from an embodiment of the present invention;

[0057] Figure 8 This is a thrust curve diagram from an embodiment of the present invention;

[0058] Figure 9This is a diagram of the three-phase current curves in an embodiment of the present invention.

[0059] Figure label:

[0060] 1. Front cover; 2. Shaft; 3. N-pole permanent magnet; 4. S-pole permanent magnet; 5. Stop block; 6. Bushing; 7. Plastic bearing; 8. Bearing sleeve; 9. First stator assembly; 10. Second stator assembly; 11. Third stator assembly; 12. Fourth stator assembly; 13. Fifth stator assembly; 14. First winding; 15. Second winding; 16. Rear end cover; 17. Housing; 18. Connecting flange; 19. M6 screw; 20. M4 screw; 21. Sensor connecting flange; 22. Grating ruler sensor reading head; 23. Grating ruler sensor. Detailed Implementation

[0061] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0062] Example

[0063] like Figures 1-4 As shown, a bidirectional cylindrical permanent magnet linear motor is suitable for scenarios with long diameter, short length, short stroke, large thrust, and high motion frequency. It includes: a pair of cylindrical permanent magnet linear motors with identical structures and symmetrical arrangement. Each cylindrical permanent magnet linear motor includes a mover, a front end cover 1 and a rear end cover 16 located at both ends of the mover. The mover is surrounded by a stator assembly and a winding assembly. A grating ruler sensor reading head 22 is fixedly provided on the front end cover 1. A grating ruler sensor 23 corresponding to the position of the grating ruler sensor reading head 22 is provided on the shaft 2 of the mover.

[0064] Specifically, the grating ruler sensor reading head 22 is connected to the front cover 1 through the sensor connecting flange 21; a linear bearing is provided between the mover and the front cover 1, and the linear bearing includes a plastic bearing 7 disposed between the bushing 6 and the bearing sleeve 8.

[0065] In this embodiment, the stator assembly includes a first stator module 9, a second stator module 10, four third stator modules 11, a fourth stator module 12, and a fifth stator module 13 installed sequentially; the winding assembly includes multiple first windings 14 and multiple second windings 15, wherein the multiple first windings 14 are disposed in the stator slots between the first stator module 9, the second stator module 10, the fourth stator module 12, and the fifth stator module 13, and the multiple second windings 15 are disposed in the stator slots of the second stator module 10 and the third stator module 11, the third stator module 11 and the fourth stator module 12, and adjacent third stator modules 11; specifically, this embodiment includes two first windings 14 and five second windings 15.

[0066] The moving part in this embodiment includes a shaft 2, an N-pole permanent magnet 3, an S-pole permanent magnet 4, a linear bearing, and a stop block 5 disposed around the shaft 2. In this embodiment, the permanent magnet is installed in an 8-petal configuration and bonded to the permanent magnet mounting groove of the shaft 2. In a specific implementation, the stator assembly is provided with connecting holes and winding connection channels. The copper wire of each winding in the winding assembly passes through the connecting holes and is led out through the winding connection channels. A pair of cylindrical permanent magnet linear motors with the same structure and symmetrical arrangement are connected by M4 screws, and a housing 17 is provided around the pair of cylindrical permanent magnet linear motors.

[0067] The following is about the combination Figures 1-4 Further explanation of this embodiment:

[0068] In this embodiment, a bidirectional output cylindrical permanent magnet linear motor has a linear bearing (composed of a bushing 6, a plastic bearing 7, and a bearing sleeve 8) placed in the front end cover 1 on the left side. The sensor connecting flange 21 and the front end cover 1 are connected using screws. The grating ruler sensor reading head 22 is mounted on the sensor connecting flange 21. The first winding 14 is placed in the stator slot of the first stator assembly 9. The first stator assembly 9 and the second stator assembly 10 are then joined together. A linear winding 14 is placed in the stator slot of the second stator assembly 10. The second winding 15 is assembled by connecting the second stator assembly 10 and the third stator assembly 11. The second winding 15 is placed in the stator slot of the third stator assembly 11, and so on. The first winding 14 is placed in the stator slot of the fourth stator assembly 12. The fourth stator assembly 12 is then assembled with the fifth stator assembly 13. The mover (composed of shaft 2, stop block 5, bushing 6, N-pole permanent magnet 3, and S-pole permanent magnet 4, which is potted with potting compound after installation) is then placed. The rear end cover 16 is installed at the end of shaft 2. The copper wires of the windings pass through the connecting holes and winding connection channels in sequence, and are welded together at the outlet according to the pattern of the three-phase windings. First, heat the soldering iron tip and apply a small amount of flux to the wire ends. Then, use the soldering iron to evenly coat the copper wire surface with solder. Twist the two tinned copper wires together. Dip the soldering iron tip in an appropriate amount of solder and heat the twisted area. Once the solder has completely melted and evenly coated the wire ends, remove the soldering iron and allow it to cool and solidify naturally. Finally, all copper wires will exit from the stator outlet. Assemble the right side in the same way, using the outer casing 17 and securing it with M4 screws 20.

[0069] For example Figure 1As shown, a grating ruler sensor 23 is fixedly mounted along the axial direction. The scale body of the grating ruler sensor 23 is fixed to the shaft 2 with a high-performance adhesive, ensuring no relative movement between it and the shaft 2, and enabling it to perform synchronous high-precision linear motion with the shaft 2. A grating ruler sensor reading head 22 is installed in the sensor connecting flange 21 in front of the front end cover 1, ensuring a 1mm gap between the reading head and the scale body of the grating ruler sensor 23. When the motor is powered on, the shaft 2 reciprocates linearly relative to the end cover, and the grating ruler sensor 23 fixed on the shaft 2 moves synchronously, while the grating ruler sensor reading head 22 fixed on the end cover remains stationary. The grating ruler sensor reading head 22 reads the scale lines on the moving grating ruler sensor 23 and outputs an electrical signal related to displacement in real time. An M6 screw 19 is used to connect the connecting flange 18 to the shaft 2. The connecting flange 18 is in contact with the outside environment, serving as a thrust output.

[0070] This embodiment also provides a control method for the bidirectional output cylindrical permanent magnet linear motor as described above, specifically including:

[0071] (1) Mathematical model of permanent magnet synchronous linear motor:

[0072] When establishing the mathematical model of the permanent magnet synchronous linear motor, the following assumptions are made:

[0073] (a) Neglecting magnetic saturation, hysteresis, and eddy current losses;

[0074] (b) The three windings are symmetrically distributed in space, and the resulting magnetomotive force is a sine wave;

[0075] (c) The magnetic field generated by the permanent magnet is also sinusoidally distributed in the air gap;

[0076] The mathematical model of the permanent magnet linear motor in the dq coordinate system is established as follows:

[0077] (1.1)

[0078] In the formula: , These represent the voltage and current components on the secondary d-axis, respectively. , These are the voltage and current components on the secondary q-axis, respectively. , These are the quadrature and direct-axis inductors, respectively. For secondary winding resistance, Let be the electrical angular velocity of the motor. The conversion relationship between electrical angle and velocity is:

[0079] (1.2)

[0080] In the formula For initial speed, The polar distance is defined as:

[0081] (1.3)

[0082] in This is the total movable length of the motor primary. It is an extreme logarithm.

[0083] In the dq coordinate system, the magnetic flux linkage is generated by both the current and the permanent magnet; the d-axis magnetic flux linkage is generated by the d-axis current. and permanent magnet magnetic flux Together they are generated, and the q-axis flux linkage is generated solely by the q-axis current. Therefore, the flux linkage expression is:

[0084] (1.4)

[0085] Electromagnetic power It equals the sum of the instantaneous power of the three phases, which can be expressed in the dq coordinate system as:

[0086] (1.5)

[0087] Substituting equations (1.1) and (1.2) and simplifying, we get:

[0088] (1.6)

[0089] Equation (1.6) is divided into three parts: the first part represents the copper loss, the second part represents the rate of change of magnetic field energy storage, which is the reactive power, and the third part is the air gap electromagnetic power.

[0090] (1.7)

[0091] For a linear motor, the relationship between electromagnetic thrust and air gap electromagnetic power is as follows:

[0092] (1.8)

[0093] Substituting equations (1.2), (1.4), and (1.7) into equation (1.8), the equations of motion for the permanent magnet synchronous linear motor are obtained as follows:

[0094] (1.9)

[0095] For surface-mounted permanent magnet synchronous linear motors, there are Then the electromagnetic thrust equation can be simplified to:

[0096] (1.10)

[0097] definition Let be the thrust constant. Then, according to equation (1.10), the thrust of the cylindrical permanent magnet linear motor is only related to the q-axis current. Relatedly, the motion equations of the permanent magnet synchronous linear motor can be obtained as follows:

[0098] (1.11)

[0099] In the formula For load resistance, The coefficient of viscous friction, For initial speed, The total mass of the primary component and its load.

[0100] (2) Dual-motor synchronous control scheme:

[0101] like Figure 5 As shown, Figure 5 This is a block diagram of a three-loop FOC control system for a permanent magnet synchronous linear motor, consisting of a position loop, a speed loop, and a current loop, from the outside in. The output of the position loop serves as the input to the speed loop, and the output of the speed loop serves as the input to the current loop. The current loop uses... control.

[0102] To achieve synchronous control of the two motors, a hybrid relative / absolute control system is employed. First, each motor undergoes a corresponding three-loop control to form a complete control circuit. Then, synchronization control is achieved through relative position loops and absolute position loops.

[0103] Absolute position loop: Two motors each receive the same master position command and are controlled independently, ensuring that they follow the reference position command in the general direction.

[0104] Relative synchronization loop: A synchronization controller is superimposed on the output of the absolute loop, i.e., the speed command. Let the position signals fed back by the two motors be... ,but:

[0105] (1.12)

[0106] This error signal is passed through a synchronous controller (usually a proportional controller P) and then superimposed with one positive and one negative signal onto the final speed control command.

[0107] The following simulation of the dual-motor synchronous control of a permanent magnet synchronous linear motor further illustrates this embodiment:

[0108] A simulation model was built in MATLAB / Simulink. Based on the FOC position-velocity-current three-loop control circuit, an absolute / relative hybrid controller was designed. The simulation time was 0.4s. The solver used was ode45 with variable step size and a tolerance of 10. -3Other parameters use default values.

[0109] The simulation uses no-load start-up and position loop control. The input signal is set to a sinusoidal signal with an amplitude of 15mm and a frequency of 10Hz. At 0.2s, a load of 100N is applied to motor 1 and a load of 200N is applied to motor 2. The performance of the control system is verified by measuring the position, speed, output thrust, and current waveforms.

[0110] like Figure 6 As shown, in the displacement dimension, the system exhibits excellent tracking accuracy and synchronization performance. Throughout the entire motion cycle, both motors exhibit sinusoidal tracking with the same amplitude. Notably, there is a phase lag, which is due to the controller's execution time and the inertia of the motors themselves. At 0.2s, when the two motors are subjected to an asymmetrical load impact, the two motors show almost no positional deviation, and no obvious steady-state error or synchronization error is observed. This indicates that the designed control strategy has strong anti-interference and synchronization capabilities.

[0111] like Figure 7 As shown, in the velocity dimension, the velocity response curve is smooth and highly coincides with the displacement command, demonstrating good velocity control performance. During sudden load changes, the velocity curve exhibits the expected brief decrease, but the velocity quickly recovers to stability, demonstrating the significant dynamic adjustment effect of the velocity loop. Furthermore, the two velocity curves remain highly consistent throughout the entire process, indicating that the system does not sacrifice dynamic performance for synchronization, but rather achieves coordination in both dynamic and steady-state processes.

[0112] like Figure 8 and Figure 9 The figure shows the thrust output and current curves of the motor, directly reflecting the inherent effort of the control system. Under no-load conditions, the thrust mainly overcomes the system's inertial force and friction. When the load is suddenly increased, the controller reacts quickly, and the thrust output changes accordingly. The change in thrust precisely matches the load force, demonstrating the speed and accuracy of the current loop. The curve recovers quickly after the load is increased, indicating good overall system stability.

[0113] In summary, this synchronous control system demonstrates excellent performance in terms of high precision, high dynamics, and strong robustness in the three dimensions of displacement, velocity, and thrust when faced with high-frequency dynamic commands and asymmetrical load disturbances, successfully achieving the core control objectives of accurate tracking and stable synchronization.

[0114] This embodiment, considering technical indicators such as volume, cost, and response speed, designs a bidirectional cylindrical linear motor. First, based on a clearly defined application scenario, the core performance indicators such as thrust, speed, and accuracy are determined to design the motor body, including electromagnetic simulation, structural design, and scheme verification. Then, a corresponding control algorithm is designed to achieve precise control of the motor. Specifically, the bidirectional cylindrical linear motor is suitable for scenarios with long diameter, short length, short stroke, and high motion frequency. The motor includes a housing, stator blocks, permanent magnets, shaft, linear bearings, front cover, rear cover, windings, screws, etc. In terms of design, a 6-slot, 8-level slot configuration is used. Screws are used to connect the end cover to the housing. A stepped splicing method is used to systematically assemble the stator blocks and end covers, while simultaneously placing the windings. Copper wires pass sequentially through connecting holes, winding connection channels, and finally exit at the outlet. The design of linear motors follows a systematic multiphysics iterative process. First, core performance indicators such as thrust, speed, and accuracy should be clearly defined based on the application scenario. Then, electromagnetic design is carried out, using finite element method (FEM) software for detailed electromagnetic field simulation and optimization. Simultaneously, the control system is built and simulated in MATLAB / Simulink for verification. Based on this, a prototype is manufactured, and performance is verified against simulation results through testing. Finally, the design is optimized and solidified based on the test and experimental results, completing the closed-loop development from requirements to a qualified product.

[0115] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A cylindrical permanent magnet linear motor with bidirectional power output, characterized in that, Suitable for scenarios involving long diameter, short length, short stroke, high thrust, and high motor frequency, this product includes: a pair of identical and symmetrically arranged cylindrical permanent magnet linear motors connected by screws, with an outer shell fixed to the periphery of each motor using M4 screws. Each cylindrical permanent magnet linear motor includes a mover, a front end cover and a rear end cover at both ends of the mover, and a stator assembly and a winding assembly surrounding the mover. The stator assembly includes a first stator module, a second stator module, and multiple winding modules installed sequentially. The third stator assembly, the fourth stator assembly, and the fifth stator assembly; the winding assembly includes multiple first windings and multiple second windings, wherein the multiple first windings are disposed in the stator slots between the first stator assembly, the second stator assembly, the fourth stator assembly, and the fifth stator assembly, and the multiple second windings are disposed in the stator slots between the second stator assembly and the third stator assembly, the third stator assembly and the fourth stator assembly, and adjacent third stator assemblies; a grating ruler sensor reading head is fixedly provided on the front end cover, and a grating ruler sensor corresponding to the position of the grating ruler sensor reading head is provided on the shaft of the mover.

2. The bidirectional output cylindrical permanent magnet linear motor according to claim 1, characterized in that, The grating ruler sensor reading head is connected to the front cover via a sensor connection flange.

3. The bidirectional output cylindrical permanent magnet linear motor according to claim 1, characterized in that, The moving element includes a shaft, an N-pole permanent magnet, an S-pole permanent magnet disposed around the shaft, a linear bearing, and a stop block; the linear bearing includes a plastic bearing disposed between a shaft sleeve and a bearing sleeve.

4. The bidirectional output cylindrical permanent magnet linear motor according to claim 1, characterized in that, A connecting flange is connected to the side of the shaft near the front end cover by an M6 screw. The connecting flange is in contact with the outside and serves as the thrust output.

5. A control method for a bidirectional cylindrical permanent magnet linear motor as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Construct a mathematical model of a permanent magnet synchronous linear motor; Step 2: Using a relative / absolute hybrid control method, firstly, the two motors each form a complete control loop through their respective three-closed-loop control; then, synchronization control is achieved through a relative synchronization loop and an absolute position loop.

6. The control method for the bidirectional output cylindrical permanent magnet linear motor according to claim 5, characterized in that, Step 1 is described in detail as follows: Assumptions: Magnetic saturation, hysteresis, and eddy current losses are ignored; the three windings are symmetrically distributed in space, generating a sinusoidal magnetomotive force; the magnetic field generated by the permanent magnet is also sinusoidally distributed in the air gap; based on this, the mathematical model of the permanent magnet linear motor in the dq coordinate system is established, and the voltage equation is: （1.1）； In the formula: , These represent the voltage and current components on the secondary d-axis, respectively. , These are the voltage and current components on the secondary q-axis, respectively. , These are the quadrature and direct-axis inductors, respectively. For secondary winding resistance, Let be the electric angular velocity of the motor; the conversion relationship between electric angle and velocity is: （1.2）； In the formula: For initial speed, The polar distance is defined as: （1.3）； in, This is the total movable length of the motor primary. It is the extreme logarithm; In the dq coordinate system, the magnetic flux linkage is generated by both the current and the permanent magnet; the d-axis magnetic flux linkage is generated by the d-axis current. and permanent magnet magnetic flux Together they are generated, and the q-axis flux linkage is generated solely by the q-axis current. Therefore, the flux linkage expression is: （1.4）； Electromagnetic power It equals the sum of the three-phase instantaneous power, expressed in the dq coordinate system as: （1.5）； Substituting equations (1.1) and (1.2) and simplifying, we get: （1.6）； The first part of Equation (1.6) represents copper loss, the second part represents the rate of change of magnetic field energy storage, which is reactive power, and the third part is air gap electromagnetic power. set up (1.7); For a linear motor, the relationship between electromagnetic thrust and air gap electromagnetic power is as follows: （1.8）； Substituting equations (1.2), (1.4), and (1.7) into equation (1.8), the equations of motion for the permanent magnet synchronous linear motor are obtained as follows: （1.9）； For surface-mounted permanent magnet synchronous linear motors, there are Then the electromagnetic thrust equation simplifies to: （1.10）； definition Let be the thrust constant. Then, from equation (1.10), the motion equation of the permanent magnet synchronous linear motor is obtained as follows: （1.11）； In the formula For load resistance, The coefficient of viscous friction, For initial speed, The total mass of the primary component and its load.

7. The control method for the bidirectional output cylindrical permanent magnet linear motor according to claim 6, characterized in that, In step 2, each of the two motors is controlled by a corresponding three-closed-loop system to form a complete control loop, as detailed below: The output of the position loop is used as the input of the velocity loop, and the output of the velocity loop is used as the input of the current loop, with the current loop employing... control.

8. The control method for the bidirectional output cylindrical permanent magnet linear motor according to claim 7, characterized in that, In step 2, synchronization control is achieved through a relative synchronization loop and an absolute position loop, as follows: Absolute position loop: Two motors each receive the same master position command and are controlled independently to ensure that they follow the reference position command in the general direction; Relative synchronization loop: A synchronization controller is superimposed on the output of the absolute position loop, i.e., the speed command. Let the position signals fed back by the two motors be... ,but: （1.12）； The obtained error signals are passed through the synchronous controller and then superimposed as one positive and one negative signal onto the final speed control command.

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