Linear motor

Abstract

This linear motor reduces costs by decreasing the amount of permanent magnets used for driving, while enabling stable, highly efficient, long-distance transport. [Solution] The linear motor 100 comprises a movable element 20 having an armature and a stator 10. In the track of the movable element 20, the magnetic flux density generated in the acceleration section S1 is greater than the magnetic flux density generated in the constant velocity section S3, and a transition section S2 is provided in which the magnetic flux density gradually decreases from the acceleration section S1 to the constant velocity section S3.

Description

Technical Field

[0001] The present invention relates to a linear motor.

Background Art

[0002] A linear motor has a configuration including a mover provided with an armature and a stator in which a plurality of drive permanent magnets are arranged along the path of the mover. Since a linear motor can generate high thrust, it is widely used for applications that transport high-weight loads over long distances.

[0003] Conventionally, in order to prevent an increase in the counter electromotive voltage generated in the motor due to an increase in the speed of the mover, the number of turns of the winding of the coil of the armature was reduced, or current control was performed by weakening the field. However, in the former method, since the number of turns of the winding of the coil of the armature is reduced, the thrust generated by the linear motor decreases. In order to suppress the decrease in the thrust generated by the linear motor, it is necessary to increase the motor current, and there is a problem that it is necessary to increase the capacity of the amplifier that supplies the motor current. Also, in the latter method, it is necessary to flow a d-axis current that generates a magnetic flux in the opposite direction to the counter electromotive voltage of the linear motor by weakening field control. Since the d-axis current does not contribute to the thrust of the linear motor, losses increase by continuously flowing the d-axis current, and there is a problem that efficient transportation of the load is difficult. Furthermore, in both the former method and the latter method, there is a problem that the amount of use of the drive permanent magnets increases when transporting the load over a long distance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a linear motor in which the track of the movable element is divided into an acceleration / deceleration section and a non-driving section, and no permanent magnets for driving are placed in the non-driving section. This configuration reduces the amount of permanent magnets used for driving, thereby lowering costs, while enabling long-distance transport.

[0006] However, in the linear motor disclosed in Patent Document 1, there is a risk that cogging thrust and velocity fluctuations may increase due to the effects of end effects caused by changes in magnetic flux during the transition between the acceleration / deceleration section and the non-driving section.

[0007] Therefore, the purpose of this disclosure is to provide a linear motor that enables stable, highly efficient, long-distance transport while reducing costs by decreasing the amount of permanent magnets used for driving. [Means for solving the problem]

[0008] A linear motor relating to one aspect of this disclosure is It comprises a movable element having an armature and a stator, In the track of the aforementioned movable element, the magnetic flux density generated in the acceleration section is greater than the magnetic flux density generated in the constant velocity section. A transition section is provided in which the magnetic flux density gradually decreases from the acceleration section toward the constant velocity section. [Effects of the Invention]

[0009] According to this disclosure, it is possible to reduce costs by reducing the amount of permanent magnets used for driving, while enabling stable, highly efficient, long-distance transport. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of a linear motor according to the first embodiment of this disclosure. [Figure 2] Figure 2 is a schematic diagram of a linear motor according to Comparative Example 1. [Figure 3]Figure 3 is a comparison diagram of the armature coils of the movable element of the linear motor according to Comparative Example 1 and the armature coils of the movable element of the linear motor according to Comparative Example 2. [Figure 4] Figure 4 is a vector diagram illustrating the comparison between the current control of a linear motor according to Comparative Example 1 and the current control of a linear motor according to Comparative Example 3. [Figure 5] Figure 5 is a comparison diagram of the simulation results when the linear motor according to Comparative Example 3 and the linear motor according to the first embodiment of this disclosure are driven at high speed. [Figure 6] Figure 6 is a comparison diagram of the loss (copper loss) Wcu of a linear motor according to Comparative Example 3 and the loss (copper loss) Wcu of a linear motor according to the first embodiment of this disclosure. [Figure 7] Figure 7 is a comparison diagram of the magnet volume Vmag of a linear motor according to Comparative Example 2 and the magnet volume Vmag of a linear motor according to the first embodiment of this disclosure. [Figure 8] Figure 8 is a schematic diagram of a linear motor according to the second embodiment of this disclosure. [Figure 9] Figure 9 is an explanatory diagram of the end effects caused by changes in the length of the permanent magnet. [Figure 10] Figure 10(a) shows the measured cogging thrust waveform when the change in length ΔL of the permanent magnet is 0 mm. Figure 10(b) shows the measured cogging thrust waveform when the change in length ΔL of the permanent magnet is 10 mm. Figure 10(c) shows the measured cogging thrust waveform when the change in length ΔL of the permanent magnet is 20 mm. Figure 10(d) shows the measured cogging thrust waveform when the change in length ΔL of the permanent magnet is 30 mm. Figure 10(e) shows the measured cogging thrust waveform when the change in length ΔL of the permanent magnet is 40 mm. [Figure 11] Figure 11 is a graph showing the cogging thrust Fc as a function of the change in the length ΔL of the permanent magnet. [Figure 12] Figure 12 is a graph showing the cogging thrust Fc as a function of the rate of change r in the length of the permanent magnet. [Figure 13] Figure 13 is a schematic diagram of a linear motor according to the third embodiment of this disclosure.

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. For members having the same reference numerals as those already described in the description of the embodiments, the description thereof will be omitted for convenience of explanation. In addition, the dimensions of each member shown in the drawings may be different from the actual dimensions of each member for convenience of explanation.

[0012] In addition, the linear motor according to the embodiment of the present disclosure and the linear motor according to the reference example will be described as a linear motor driven by a three-phase alternating current system composed of U-phase, V-phase, and W-phase. Note that the linear motor according to the present embodiment is not limited to the three-phase alternating current system, and may be a linear motor driven by other systems.

[0013] <First Embodiment> (Overall Configuration of the First Embodiment) FIG. 1 is a schematic diagram of a linear motor 100 according to the first embodiment of the present disclosure. An upper view schematic diagram of the linear motor 100 is shown in the upper part of FIG. 1, and a side view schematic diagram of the linear motor 100 is shown in the lower part of FIG. 1.

[0014] The linear motor 100 includes a stator 10 and a mover 20. The stator 10 has a plurality of plate-shaped magnet rails 11 laid along the traveling direction X of the mover 20. The plurality of plate-shaped magnet rails 11 have substantially the same dimensions.

[0015] Each magnet rail 11 is provided with a plurality of plate-shaped permanent magnets 12. The plurality of permanent magnets 12 are arranged at equal intervals along the traveling direction X of the mover 20 on the upper surface of each magnet rail 11 and are attached with an adhesive or the like. The plurality of permanent magnets 12 are made of substantially the same magnetic material. In the example shown in FIG. 1, eight permanent magnets 12 are provided on each magnet rail 11.

[0016] The movable element 20 is positioned above the stator 10 and has an armature consisting of one or more coils 21. In the example shown in Figure 1, the armature consists of three coils 21. The armature is also connected to a drive amplifier (not shown). When the alternating current output from the drive amplifier flows through the coils 21 of the armature, a thrust F in the direction of the track X is obtained by the flux linkage from the multiple permanent magnets 12 of the stator 10. As a result, the movable element 20 is driven in the direction of the track X and moves a distance D along the upper surface of the multiple magnet rails 11 from the starting point S to the goal point G.

[0017] As shown in Figure 1, each magnet rail 11 and each permanent magnet 12 are, for example, both substantially rectangular parallelepipeds. Each permanent magnet 12 has a strip-like shape extending on the surface of the magnet rail 11 in a direction perpendicular to the direction of travel X. Multiple permanent magnets 12 of this shape are arranged along the direction of travel X. Here, for each permanent magnet 12, the dimension parallel to the path direction of the movable element 20 (path direction X) is defined as width W, the dimension in the direction opposite to the path direction of the movable element 20 is defined as thickness L, and the dimension in the direction perpendicular to the width W direction and the thickness L direction is defined as length L. In Comparative Examples 1 to 3, the second embodiment, and the third embodiment described later, the dimensions of the permanent magnet 12 are defined in the same manner as above.

[0018] To describe the detailed configuration of the linear motor 100 according to the first embodiment, we will first describe the configurations of the linear motor 100 according to Comparative Example 1, the linear motor 200 according to Comparative Example 2, and the linear motor 400 according to Comparative Example 3.

[0019] (Comparative Example 1) Figure 2 is a schematic diagram of a linear motor 200 according to Comparative Example 1. The upper part of Figure 2 shows a schematic top view of the linear motor 200, and the lower part of Figure 2 shows a schematic side view of the linear motor 200. Each magnet rail 11 of the linear motor 200 is provided with a plurality of plate-shaped permanent magnets 12'. The plurality of permanent magnets 12' have the same length L1. Note that the magnet rails 11 of the stator 10 and the movable part 20 are common to the magnet rails 11 of the stator 10 and the movable part 20 of the linear motor 100 according to the first embodiment, so their description is omitted.

[0020] In the linear motor 200 according to Comparative Example 1, the back electromotive force Ke generated in the armature of the movable element 20 increases as the speed V of the movable element 20 increases. As a result, the alternating current Ia flowing through the armature of the movable element 20 decreases, the thrust F generated in the movable element 20 decreases, and the maximum speed Vmax of the movable element 20 is limited. Therefore, in order to increase the speed of the linear motor, the linear motor 300 according to Comparative Example 2 and the linear motor 400 according to Comparative Example 3 have the configurations described below.

[0021] (Comparative Example 2) The linear motor 300 according to Comparative Example 2 has a configuration in which the number of turns of the armature coil 21 of the movable element 20 is reduced. Figure 3 is a comparison diagram of the armature coil 21 of the movable element 20 of the linear motor 200 according to Comparative Example 1 and the armature coil 21 of the movable element 20 of the linear motor 300 according to Comparative Example 2. The left side of Figure 3 shows the waveform of the back electromotive force Ke when the number of turns of the armature coil 21 is large, as in Comparative Example 1, and the right side of Figure 3 shows the waveform of the back electromotive force Ke when the number of turns of the armature coil 21 is reduced, as in Comparative Example 2. As shown in Figure 3, by reducing the number of turns of the armature coil 21, the rise in the back electromotive force Ke generated in the armature can be suppressed. The configuration of the linear motor 300 according to Comparative Example 2 is the same as the configuration of the linear motor 200 according to Comparative Example 1 shown in Figure 2, except for the number of turns of the coil 21.

[0022] However, as in Comparative Example 2, reducing the number of turns in the coil 21 reduces the thrust F generated in the movable element 20, causing a decrease in the acceleration of the movable element 20. To prevent a decrease in the acceleration of the movable element 20, it is necessary to increase the alternating current Ia flowing through the armature of the movable element 20. Therefore, the capacity of the drive amplifier connected to the movable element 20 must be increased.

[0023] (Comparative Example 3) The linear motor 400 according to Comparative Example 3 is configured to suppress the rise in the back electromotive force Ke generated in the armature of the movable element 20 by field weakening control. Figure 4 is a vector diagram for comparing and explaining the current control of the linear motor 200 according to Comparative Example 1 and the linear motor 400 according to Comparative Example 3. The left side of Figure 4 shows a vector diagram of the dq axis coordinate when field weakening control is not performed, as in Comparative Example 1, and the right side of Figure 4 shows a vector diagram of the dq axis coordinate when field weakening control is performed, as in Comparative Example 3.

[0024] As shown in Comparative Example 1 on the left side of Figure 4, when field weakening control is not performed, the electrical angular velocity ω in the dq axis coordinate increases as the velocity V of the movable element 20 increases, and the back electromotive force Ke generated in the armature of the movable element 20 increases. Therefore, the armature voltage Va, which is the resultant vector of the voltage generated by the back electromotive force Ke and the inductance of the armature, becomes greater than or equal to the output voltage Vin of the drive amplifier.

[0025] On the other hand, when field weakening control is performed as in Comparative Example 3 on the right side of Figure 4, the increase in back electromotive force Ke associated with the increase in the speed V of the movable element 20 can be suppressed by flowing a d-axis current Id to generate a magnetic flux in the opposite direction to the magnetic flux generated by the permanent magnet. As a result, the armature voltage Va becomes less than or equal to the output voltage Vin of the drive amplifier, enabling the linear motor 400 to operate at higher speeds. Note that the configuration of the linear motor 400 in Comparative Example 3 is the same as the configuration of the linear motor 200 in Comparative Example 1 shown in Figure 2, except for the current control.

[0026] However, since the d-axis current Id does not contribute to the thrust F of the linear motor 400, continuing to flow the d-axis current Id increases losses, making efficient operation of the linear motor 400 difficult. In particular, losses due to the d-axis current Id tend to become a problem when the travel distance D is long.

[0027] Thus, in the linear motor 300 according to Comparative Example 2, the capacity of the drive amplifier connected to the movable element 20 needs to be increased, and in the linear motor 400 according to Comparative Example 3, efficient movement becomes difficult. Furthermore, in the linear motor 300 according to Comparative Example 2 and the linear motor 400 according to Comparative Example 3, when the travel distance D is long, the amount of permanent magnet 12 used increases in proportion to the travel distance D.

[0028] Therefore, the inventors investigated a linear motor configuration that reduces costs by lowering the amount of permanent magnets 12 used by adjusting the magnetic flux density from the stator 10 in the path of the movable element 20, while achieving stable, highly efficient, long-distance transport.

[0029] (Detailed configuration of the first embodiment) In the first embodiment of the present disclosure shown in Figure 1, the track of the movable element 20 is divided into an acceleration section S1, a constant velocity section S3, and a deceleration section S5. Furthermore, a transition section S2 is provided between the acceleration section S1 and the constant velocity section S3, and a transition section S4 is provided between the constant velocity section S3 and the deceleration section S5.

[0030] Here, the acceleration section S1 is a section of a predetermined length that includes the starting point S. The acceleration section S1 is a section in which a large thrust F is generated in the track direction X because the movable element 20 needs to be accelerated quickly from a stationary state to a predetermined speed. Because a large thrust F needs to be generated, a long permanent magnet of length L is used in the acceleration section S1. Furthermore, the deceleration section S5 is a section of predetermined length that includes the finish line G. Since the deceleration section S5 requires the movable element 20 to be quickly decelerated from a predetermined speed to a stationary state, a large thrust F is generated in the direction opposite to the track direction X. Similar to the acceleration section S1, a long permanent magnet of length L is used because a large thrust F needs to be generated. Furthermore, the constant-velocity section S3 is a section of predetermined length set between the acceleration section S1 and the deceleration section S5. In the constant-velocity section S3, the movable element 20 travels at a constant speed (constant velocity) at its maximum speed Vmax. In this constant-velocity section S3, since the movable element 20 travels a long distance at a constant speed (constant velocity), the thrust required in the direction X of the track is only a small thrust due to friction, and a permanent magnet with a shorter length L is used than in the acceleration section S1 and the deceleration section S5. Furthermore, in the transition section S2, the length L of the permanent magnet 12 is changed in steps to prevent an increase in cogging thrust and velocity fluctuations due to the effects of the end effect caused by a rapid change in the length L of the permanent magnet 12 when the movable element 20 moves from a predetermined speed to the maximum speed Vmax. Similarly, in the transition section S4, the length L of the permanent magnet 12 is also changed in steps to prevent an increase in cogging thrust and velocity fluctuations due to the effects of the end effect caused by a rapid change in the length L of the permanent magnet 12. Details of cogging thrust and velocity fluctuations will be described in the second embodiment.

[0031] In the acceleration section S1 and the deceleration section S5, multiple permanent magnets 12 with a length L1 are provided on the magnet rail 11. In the constant velocity section S3, multiple permanent magnets 12 with a length L2 are provided on the magnet rail 11, where length L2 is smaller than length L1. Furthermore, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11, with a length L gradually decreasing from L1 to L2 as you move from the acceleration section S1 to the constant velocity section S3. Similarly, in the transition section S4, multiple permanent magnets 12 are provided on the magnet rail 11, with a length L gradually increasing from L2 to L1 as you move from the constant velocity section S3 to the deceleration section S5. Note that in all sections S1 to S5, the width W and thickness T of each permanent magnet 12 provided on the magnet rail 11 are equal, and they are made of the same material.

[0032] Incidentally, the magnetic flux density acting on the movable element 20 is determined by the magnitude of the magnetic force emitted by the permanent magnet 12 and the distance between the permanent magnet 12 and the movable element 20 (here, the distance between the permanent magnet 12 and the movable element 20 in the opposing directions). In the first embodiment shown in Figure 1, the distance between the permanent magnet 12 and the movable element 20 does not change throughout the entire track.

[0033] On the other hand, the magnitude of the magnetic force emitted by the permanent magnet 12 is proportional to the size (volume) of the permanent magnet 12. In the transition section S2, as described above, multiple permanent magnets 12 are arranged such that the length L gradually decreases from L1 to L2 from the acceleration section S1 to the constant velocity section S3. In other words, in this transition section S2, the magnitude of the magnetic force emitted by the permanent magnet 12 gradually decreases.

[0034] Therefore, in the transition section S2, the magnetic flux density acting on the movable element 20 gradually decreases from the acceleration section S1 to the constant velocity section S3. In other words, the transition section S2 is a section set so that the acceleration acting on the movable element 20 gradually decreases from the acceleration section S1 to the constant velocity section S3.

[0035] Similarly, in the transition section S4, multiple permanent magnets 12 are arranged such that their length L gradually increases from L2 to L1 as you move from the constant velocity section S3 to the deceleration section S5, so that the magnetic flux density acting on the movable element 20 gradually increases. In other words, the transition section S4 is a section set up so that the deceleration acting on the movable element 20 gradually increases as you move from the constant velocity section S3 to the deceleration section S5.

[0036] As a result, in the track of the movable element 20, the magnetic flux density from the stator 10 generated in the transition section S2 gradually decreases from the acceleration section S1 to the constant velocity section S3, and the magnetic flux density from the stator 10 generated in the transition section S4 gradually increases from the constant velocity section S3 to the deceleration section S5.

[0037] In the acceleration section S1, a large magnetic flux density of a constant magnitude acts on the movable element 20, so a constant acceleration acts on the movable element 20, and the movable element 20 quickly reaches a predetermined speed. In the deceleration section S5, a large magnetic flux density of a constant magnitude acts on the movable element 20, so a constant deceleration (negative acceleration) acts on the movable element 20, and the movable element 20 quickly comes to a stop.

[0038] Furthermore, in the constant-velocity section S3, the thrust required to keep the movable element 20 moving at a constant speed is only a small amount of friction. For this reason, the magnetic flux density acting on the movable element 20 in the constant-velocity section S3 is smaller than that acting in the acceleration section S1 and the deceleration section S5. This constant-velocity section S3 is often set to be a long section. By using a short permanent magnet of length L in this long constant-velocity section S3, the amount of magnets required is greatly reduced.

[0039] (Comparative study of the first embodiment and the comparative example) Figure 5 is a comparison diagram of the simulation results when the linear motor 400 according to Comparative Example 3 and the linear motor 100 according to the first embodiment of this disclosure are driven at high speed. The simulation waveform of Comparative Example 3 is shown on the left side of Figure 5, and the simulation waveform of the first embodiment of this disclosure is shown on the right side of Figure 5. In Figure 5, the horizontal axis represents time t [s], and the vertical axis represents, from top to bottom, the velocity V [m / s] of the movable element 20, the U-phase current Iu [A], the d-axis current Id [A], the q-axis current Iq [A], and the travel distance D [m] of the movable element 20. The U-phase current Iu refers to the current of one phase of the three-phase alternating current flowing through the armature of the movable element 20.

[0040] In the linear motor 400 according to Comparative Example 3, as shown on the left side of Figure 5, high-speed driving of the movable element 20 with a maximum speed Vmax = 5 m / s is achieved by field weakening control. However, while the movable element 20 is being driven, the d-axis current Id is constantly flowing at approximately -3A to -4A due to the field weakening control.

[0041] In contrast, in the linear motor 100 according to the first embodiment, as shown on the right side of Figure 5, high-speed driving of the movable element 20 with a maximum speed Vmax = 5 m / s is achieved even without field weakening control. Furthermore, no d-axis current Id flows while the movable element 20 is being driven.

[0042] Figure 6 is a comparison diagram of the loss (copper loss) Wcu of the linear motor 400 according to Comparative Example 3 and the loss (copper loss) Wcu of the linear motor 100 according to the first embodiment of this disclosure. The loss (copper loss) Wcu of the linear motor 400 according to Comparative Example 3 is shown on the left side of Figure 6, and the loss (copper loss) Wcu of the linear motor 100 according to the first embodiment is shown on the right side of Figure 6.

[0043] As explained above, in the linear motor 400 according to Comparative Example 3, a d-axis current Id flows constantly due to field weakening control, whereas in the linear motor 100 according to the first embodiment, no d-axis current Id flows. As a result, as shown in Figure 6, the loss (copper loss) Wcu of the linear motor 100 according to the first embodiment is reduced compared to the loss (copper loss) Wcu of the linear motor 400 according to Comparative Example 3.

[0044] Figure 7 is a comparison diagram of the magnet volume Vmag of the permanent magnet 12' of the linear motor 300 according to Comparative Example 2 and the magnet volume Vmag of the permanent magnet 12 of the linear motor 100 according to the first embodiment of this disclosure. The magnet volume Vmag of the linear motor 300 according to Comparative Example 2 is shown on the left side of Figure 7, and the magnet volume Vmag of the linear motor 100 according to the first embodiment is shown on the right side of Figure 7. Note that the magnet volume Vmag represents the total volume of the permanent magnets 12 arranged on each magnet rail 11 of the linear motor.

[0045] In the linear motor 300 according to Comparative Example 2, as shown in Figure 2, each magnet rail 11 is provided with a plurality of plate-shaped permanent magnets 12' having substantially the same length L1. Therefore, the magnet volume Vmag of the permanent magnets 12 increases in proportion to the travel distance D of the movable element 20.

[0046] In contrast, in the linear motor 100 according to the first embodiment, as shown in Figure 1, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11, with their length L gradually decreasing from L1 to L2 from the acceleration section S1 to the constant velocity section S3. In the constant velocity section S3, multiple permanent magnets 12 with a length L2 smaller than length L1 are provided on the magnet rail 11. As a result, when the constant velocity section, where the velocity V of the movable element 20 is constant, is long, the magnet volume Vmag of the linear motor 100 according to the first embodiment is significantly reduced compared to the magnet volume Vmag of the linear motor 300 according to Comparative Example 2, as shown in Figure 7.

[0047] Furthermore, the magnet volume Vmag of the permanent magnet 12' of the linear motor 300 according to Comparative Example 2 and the magnet volume Vmag of the permanent magnet 12' of the linear motor 400 according to Comparative Example 3 are substantially the same. Therefore, the magnet volume Vmag of the linear motor 100 according to the first embodiment is significantly reduced compared to the magnet volume Vmag of the linear motor 400 according to Comparative Example 3.

[0048] As described above, in the linear motor 100 according to the first embodiment, the length of the permanent magnet 12 is gradually reduced in the transition section S2 provided from the acceleration section S1 to the constant velocity section S3, thereby gradually reducing the magnetic flux density on the track of the movable element 20. Furthermore, in the transition section S4 provided from the constant velocity section S3 to the deceleration section S5, the length of the permanent magnet 12 is gradually increased, thereby gradually increasing the magnetic flux density on the track of the movable element 20. This makes it possible to reduce the losses (copper losses) Wcu and the magnet volume Vmag of the linear motor 100. In other words, a linear motor 100 that can transport over long distances with high efficiency and low losses can be realized while reducing costs by reducing the amount of permanent magnet 12 used.

[0049] <Second Embodiment> Figure 8 is a schematic diagram of a linear motor 500 according to the second embodiment of this disclosure. The upper part of Figure 8 shows a schematic top view of the linear motor 500, and the lower part of Figure 8 shows a schematic side view of the linear motor 500. In the second embodiment, only the differences from the first embodiment will be described, and the same parts will not be described.

[0050] In the example shown in Figure 8, four permanent magnets 12 are provided on each magnet rail 11'. Each magnet rail 11' is, for example, roughly rectangular in shape, and the length LX is defined as the length of each magnet rail 11' in the same direction as the length L of the permanent magnet 12.

[0051] In the acceleration section S1 and the deceleration section S5, multiple magnet rails 11' with length LA are laid. In the constant velocity section S3, multiple magnet rails 11' with length LB are laid, where length LB is smaller than length LA. Furthermore, in the transition section S2, multiple magnet rails 11' are laid from the acceleration section S1 to the constant velocity section S3, with length LX gradually decreasing from LA to LB. Similarly, in the transition section S4, multiple magnet rails 11' are laid from the constant velocity section S3 to the deceleration section S5, with length LX gradually increasing from LB to LA.

[0052] Furthermore, in the acceleration section S1 and the deceleration section S5, multiple permanent magnets 12 with length L1 are provided on the magnet rail 11'. Also, in the constant velocity section S3, multiple permanent magnets 12 with length L2 are provided on the magnet rail 11'. Here, length L2 is smaller than length L1. Moreover, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11' in which length L gradually decreases from L1 to L2 as you move from the acceleration section S1 to the constant velocity section S3. Similarly, in the transition section S4, multiple permanent magnets 12 are provided on the magnet rail 11' in which length L gradually increases from L2 to L1 as you move from the constant velocity section S3 to the deceleration section S5.

[0053] In other words, as the length L of the permanent magnet 12 gradually decreases from L1 to L2 as you move from the acceleration section S1 to the constant speed section S3, the length LX of the multiple magnet rails 11' also gradually decreases from LA to LB. Similarly, as the length L of the permanent magnet 12 gradually increases from L2 to L1 as you move from the constant speed section S3 to the deceleration section S5, the length LX of the multiple magnet rails 11' also gradually increases from LB to LA. This makes it possible to combine stators with a product lineup that varies the length of the magnet rails 11' and the length of the permanent magnets 12 according to the travel distance D. In other words, there is no need to newly manufacture stators with the length of the permanent magnets changed while keeping the length of the magnet rails the same, which can reduce the manufacturing cost of the linear motor 500.

[0054] Figure 9 is an explanatory diagram of the end effect caused by the change in the length of the permanent magnet 12. As shown in Figure 9, when the length of multiple permanent magnets 12 changes from L1 to L2, the amount of magnetic flux Φ linked to the coil 21 decreases by the amount of magnetic flux from the outer ends of both ends in the direction of length L2 of the permanent magnet 12 (the area shown by the dashed line in Figure 9). In this way, when the change in magnetic flux is large, a cogging thrust Fc is generated in the movable element 20 due to the effect of the end effect, causing fluctuations in the velocity V of the movable element 20 and resulting in unstable transport.

[0055] Figure 10(a) shows the measured waveform of the cogging thrust Fc when the change in length ΔL of the permanent magnet 12 is 0 mm. Figure 10(b) shows the measured waveform of the cogging thrust Fc when the change in length ΔL of the permanent magnet 12 is 10 mm. Figure 10(c) shows the measured waveform of the cogging thrust Fc when the change in length ΔL of the permanent magnet 12 is 20 mm. Figure 10(d) shows the measured waveform of the cogging thrust Fc when the change in length ΔL of the permanent magnet 12 is 30 mm. Figure 10(e) shows the measured waveform of the cogging thrust Fc when the change in length ΔL of the permanent magnet 12 is 40 mm. Note that the change in length ΔL of the permanent magnet 12 is, for example, when the length L1 of the permanent magnet 12 shown in Figure 9 is 65 mm and the length L2 of the permanent magnet 12 is 55 mm, the change ΔL is 65 mm - 55 mm = 10 mm.

[0056] As shown in Figures 10(a) to (e), as the change in the length ΔL of the permanent magnet 12 increases from 0 mm to 40 mm, the amplitude of the cogging thrust Fc increases in the vicinity of the region where the length L of the permanent magnet 12 changes (the section where the travel distance D is from 250 mm to 400 mm).

[0057] Figure 11 is a graph showing the cogging thrust Fc as a function of the change in length ΔL of the permanent magnet 12. Figure 12 is a graph showing the cogging thrust Fc as a function of the rate of change r of the length of the permanent magnet 12. For example, if the length L1 of the permanent magnet 12 shown in Figure 9 is 65 mm and the length L2 of the permanent magnet 12 is 55 mm, then the rate of change r is 55 mm / 65 mm = 0.85.

[0058] As shown in Figure 11, the cogging thrust Fc monotonically increases from 12N to 100N as the change in the length ΔL of the permanent magnet 12 increases from 0 mm to 40 mm. Also, as shown in Figure 12, the cogging thrust Fc monotonically decreases from 100N to 12N as the rate of change r of the length of the permanent magnet 12 increases from 0.38 to 1.0. From this, it can be seen that if the length L of the permanent magnet 12 changes rapidly, the amplitude of the cogging thrust Fc increases, causing the velocity V of the movable element 20 to fluctuate greatly.

[0059] Therefore, in the linear motor 500 according to the second embodiment, as shown in Figure 8, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11', whose length L gradually decreases from L1 to L2 as you move from the acceleration section S1 to the constant velocity section S3. Similarly, in the transition section S4, multiple permanent magnets 12 are provided on the magnet rail 11', whose length L gradually increases from L2 to L1 as you move from the constant velocity section S3 to the deceleration section S5. In other words, in the transition sections S2 and S4, the amount of change ΔL of the length L of the permanent magnets 12 is reduced, and the rate of change r of the length L is made as close to 1 as possible. This makes it possible to suppress the cogging thrust Fc that occurs when the movable element 20 moves from the acceleration section S1 to the constant velocity section S3, and from the constant velocity section S3 to the deceleration section S5. In other words, it is possible to reduce the amount of permanent magnets used for driving and reduce costs while enabling stable, highly efficient, long-distance transport.

[0060] In the linear motor 100 according to the first embodiment shown in Figure 1, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11, with their length L gradually decreasing from L1 to L2 as they move from the acceleration section S1 to the constant velocity section S3. In the transition section S4, multiple permanent magnets 12 are provided on the magnet rail 11, with their length L gradually increasing from L2 to L1 as they move from the constant velocity section S3 to the deceleration section S5. Therefore, in the transition sections S2 and S4, the magnetic flux density acting on the movable element 20 changes gradually, which suppresses the cogging thrust Fc that occurs when the movable element 20 moves from the acceleration section S1 to the constant velocity section S3, and from the constant velocity section S3 to the deceleration section S5. In other words, it is possible to reduce the amount of permanent magnets used for driving, thereby reducing costs, while enabling stable, highly efficient, long-distance transport.

[0061] <Third Embodiment> Figure 13 is a schematic diagram of a linear motor 600 according to the third embodiment of this disclosure. The upper part of Figure 13 shows a schematic top view of the linear motor 600, and the lower part of Figure 13 shows a schematic side view of the linear motor 600. In the third embodiment, only the differences from the first embodiment will be described, and the same parts will not be described.

[0062] As shown in Figure 13, each magnet rail 11 is provided with a plurality of plate-shaped permanent magnets 12''. The plurality of permanent magnets 12'' have approximately the same length L1 from the acceleration section S1 to the deceleration section S5. In addition, a gap δ1 is provided from the track of the movable element 20 to the permanent magnet 12'' in the acceleration section S1 and the deceleration section S5. The gap δ is the distance from the bottom surface of the movable element 20 located directly above the permanent magnet 12'' to the top surface of the permanent magnet 12''. In addition, a gap δ2 is provided from the track of the movable element 20 to the permanent magnet 12'' in the constant velocity section S3. Here, gap δ2 is larger than gap δ1. Furthermore, in the transition section S2, the magnet rail 11 and permanent magnets 12'' are arranged so that the gap δ gradually increases from δ1 to δ2 from the acceleration section S1 to the constant velocity section S3. Similarly, in the transition section S4, the magnet rail 11 and permanent magnets 12'' are arranged so that the gap δ gradually decreases from δ1 to δ2 from the constant velocity section S3 to the deceleration section S5.

[0063] With the above configuration, in the transition section S2, the gap δ increases from the acceleration section S1 to the constant velocity section S3, so the magnetic flux density gradually decreases. Similarly, in the transition section S4, the gap δ decreases from the constant velocity section S3 to the deceleration section S5, so the magnetic flux density gradually increases. In other words, the amount of magnetic flux Φ linked to the coil 21 changes by the amount of the change in gap δ. Thus, in this third embodiment as well, the magnetic flux density acting on the movable element 20 in the constant velocity section S3 is reduced compared to the magnetic flux density acting in the acceleration section S1 and the deceleration section S5. For this reason, similar to the first and second embodiments, the amount of magnetic flux φ linked to the coil 21 is reduced in the constant velocity section S3, and the increase in back electromotive force Ke accompanying the increase in speed V is suppressed, thereby increasing the maximum speed. In the third embodiment as well, in the transition section S2, the magnetic flux density acting on the movable element 20 is gradually reduced from the acceleration section S1 to the constant velocity section S3. Therefore, as in the first and second embodiments, the increase in cogging thrust Fc that occurs when the movable element 20 moves from the acceleration section S1 to the constant velocity section S3, and from the constant velocity section S3 to the deceleration section S5, can be suppressed. Furthermore, in the third embodiment, the magnetic flux acting on the movable element 20 in the constant velocity section S3 is reduced compared to the linear motor 200 of Comparative Example 1. As a result, the cogging thrust Fc in the constant velocity section S3 is reduced compared to the linear motor 200 of Comparative Example 1, and the speed is stabilized. Furthermore, according to the third embodiment, since the length of the magnet rail 11 and the length of the permanent magnet 12'' are the same throughout the entire section, there is no need to newly manufacture stators with different lengths of magnet rail 11 and permanent magnet 12'', and the manufacturing cost of the linear motor 600 can be reduced.

[0064] While embodiments of this disclosure have been described above, it goes without saying that the technical scope of this disclosure should not be interpreted restrictively by the description of these embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications to the embodiments are possible within the scope of the invention described in the claims. The technical scope of this disclosure should be determined based on the scope of the invention described in the claims and the scope of its equivalents.

[0065] For example, in the linear motor 100 according to the first embodiment, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11 such that the length L of the permanent magnets 12 gradually decreases from L1 to L2 as you move from the acceleration section S1 to the constant velocity section S3. Here, it is sufficient that the size of the permanent magnets 12 gradually decreases, not just the length L of the permanent magnets 12, as you move from the acceleration section S1 to the constant velocity section S3, so that the magnetic flux density on the track of the movable element 20 decreases. For example, the thickness T of the permanent magnets 12 shown in Figure 1 may gradually decrease. Alternatively, multiple permanent magnets 12 may be provided on the magnet rail 11 such that the residual magnetic flux density of the permanent magnets gradually decreases as you move from the acceleration section S1 to the constant velocity section S3. The same applies to the transition section S4.

[0066] Furthermore, in the linear motor 100 according to the first embodiment and the linear motor 500 according to the second embodiment, in the constant-velocity section S3, the thrust required for the movable element 20 to travel in the track direction X is only a minute thrust due to friction. In addition, by providing transition sections S2 and S4, the cogging thrust Fc due to the end effect can be reduced. Therefore, permanent magnets 12 do not need to be provided on the magnet rail 11 in the constant-velocity section S3. This further reduces the amount of permanent magnets used for driving and thus reduces costs.

[0067] Furthermore, a configuration combining the linear motor 100 according to the first embodiment, the linear motor 500 according to the second embodiment, and the linear motor 600 according to the third embodiment described above may also be used. For example, in the transition section S2, multiple permanent magnets 12 are provided on the magnet rail 11 such that the length L of the permanent magnets 12 gradually decreases from L1 to L2 as you move from the acceleration section S1 to the constant velocity section S3. Also, in the transition section S4, multiple permanent magnets 12 may be provided on the magnet rail 11 such that the length LX of the multiple magnet rails 11 gradually increases from LB to LA as the length L of the permanent magnets 12 gradually increases from L2 to L1 as you move from the constant velocity section S3 to the deceleration section S5.

[0068] Furthermore, while the above-described embodiments have explained linear motors having a movable element that runs on a magnet rail, the present invention is not limited thereto. For example, the present invention can also be applied to a magnetic attraction force canceling type linear motor in which the armature (movable element) is provided so as to straddle the magnet rail, and the armature moves relative to the magnet rail while straddling it. Alternatively, the present invention can also be applied to a magnetic attraction force canceling type linear motor in which the armature (movable element) moves relative to the magnet rail between two magnet rails arranged opposite each other. In a magnetic attraction force canceling type linear motor, two magnetic attraction forces generated in opposing directions between the armature (movable element) and the magnet rail cancel each other out, so no magnetic attraction force is generated in the linear motor as a whole. [Explanation of Symbols]

[0069] 10: Stator 11, 11': Magnetic rail 12, 12', 12'': Permanent magnets 20: Mover 21: Coil 100, 200, 300, 400, 500, 600: Linear motor S1: Acceleration section S2, S4: Transition section S3: Constant speed section S5: Deceleration section

Claims

1. A linear motor comprising a movable element having an armature and a stator, In the track of the aforementioned movable element, the magnetic flux density generated in the acceleration section is greater than the magnetic flux density generated in the constant velocity section. A linear motor characterized by having a transition section in which the magnetic flux density gradually decreases from the acceleration section toward the constant velocity section.

2. In the track of the aforementioned movable element, multiple magnetic rails, each equipped with multiple permanent magnets, are laid out. The linear motor according to claim 1, wherein at least one magnet rail is provided in the transition section between the acceleration section and the constant velocity section such that the magnetic flux density gradually decreases from the acceleration section to the constant velocity section.

3. The linear motor according to claim 2, wherein the size of the plurality of permanent magnets provided on the magnet rail in the transition section gradually decreases from the acceleration section to the constant velocity section.

4. Each of the multiple permanent magnets provided on the magnet rail in the transition section has a width that is parallel to the path direction of the movable element, a thickness that is in the direction opposite to the path of the movable element, and a length that is perpendicular to the width direction and the thickness direction. The linear motor according to claim 3, wherein the lengths of the plurality of permanent magnets gradually decrease from the acceleration section to the constant velocity section.

5. Each of the multiple permanent magnets provided on the magnet rail in the transition section has a width that is parallel to the path direction of the movable element, a thickness that is in the direction opposite to the path direction of the movable element, and a length that is in the direction perpendicular to the width direction and the thickness direction. The linear motor according to claim 3, wherein the thickness of the plurality of permanent magnets gradually decreases from the acceleration section toward the constant velocity section.

6. The linear motor according to claim 2, wherein in the transition section, the gap from the track of the movable element to each of the plurality of permanent magnets provided on the magnet rail gradually increases from the acceleration section to the constant velocity section.

7. The linear motor according to claim 2, wherein in the transition section, the residual magnetic flux density of the plurality of permanent magnets provided on the magnet rail gradually decreases from the acceleration section to the constant velocity section.

8. The linear motor according to claim 4, wherein in the transition section, the length of the magnet rail gradually decreases as the length of the plurality of permanent magnets gradually decreases from the acceleration section to the constant velocity section.

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