Wireless power-feeding system

Abstract

Provided is a wireless power-feeding system that has a simple structure and does not require adjustment or control with respect to the positions and angles of a power-feeding coil and a power-receiving coil when power is supplied to a rotating object, the wireless power-feeding system being capable of always supplying power wirelessly without interruption regardless of the manner in which the power-receiving coil rotates with respect to the power-feeding coil.　In a system for feeding power wirelessly to a rotating power feed object using PT symmetry, each of a power-feeding coil 11 and a power-receiving coil 21 is a solenoid-type or helical-type coil having magnetic poles at both ends. When the power-receiving coil 21 is rotated with respect to the power-feeding coil 11, the power-feeding coil 11 and the power-receiving coil 21 are arranged so that a rotation center O of the power-receiving coil 21 comes near one of two magnetic poles (201, 202) at the two ends of the power-receiving coil 21.

Description

Wireless Power Supply System

[0001] The present invention relates to a wireless power supply system for a rotating target that uses Parity-Time symmetry (hereinafter referred to as "PT symmetry").

[0002] There are several known contactless wireless power transfer technologies, including electromagnetic induction and magnetic resonance. Of these, electromagnetic induction wireless power transfer technology is used, for example, to charge mobile phones, and has coils arranged one above the other, essentially acting as an electrical transformer, with electricity flowing when the power transfer coil and power receiving coil are tightly attached.

[0003] However, with electromagnetic induction wireless power transfer technology, it is not possible to maintain a large distance between the power transfer coil and the power receiving coil, and even a slight misalignment or separation between the power transfer coil and the power receiving coil makes it impossible to charge or transfer power. This makes it difficult to apply this technology to artificial devices attached to the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0004] Furthermore, magnetic resonance wireless power transfer technology was developed at a university in the United States around 2006-2007, and is close to being put to practical use because it allows for a greater distance between the power supply coil and the power receiving coil compared to electromagnetic induction. However, it is sensitive in that it cannot be transferred unless the distance between the power supply coil and the power receiving coil is kept constant, and it cannot be transferred if the coils are closer or farther apart than that distance, or if they are at an angle. This also poses the problem of it being difficult to apply this technology to artificial devices attached inside the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0005] In order to solve such problems, for example, Patent Document 1 discloses a contactless power supply system using the magnetic resonance method, which uses a wireless power supply technology based on magnetic resonance and includes a control device that has the function of adjusting the positional relationship between a power supply coil and a power receiving coil and adjusting the angle, thereby supplying stable power to an artificial heart or the like.

[0006] Furthermore, for example, Patent Document 2 discloses a technology for a contactless power supply type rotation module used in a robot, in which a multi-joint robot having a first arm and a second arm has two contactless power supply parts to facilitate work such as attaching or adding arms, thereby enabling rotation and bending.

[0007] International Publication No. 2018 / 150678 Japanese Patent Application Laid-Open No. 2020-106985 Japanese Patent Application Laid-Open No. 2022-121324

[0008] Sid Assawaworrarit, Xiaofang Yu & Shanhui Fan, “Robust wireless power transfer using a nonlinear parity-time-symmetric circuit”, Nature, 15 JUNE 2017, volume 546, p.387-390Xianglin Hao, Ke Yin, Jianlong Zou, Ruibin Wang, Yuangen Huang, Xikui Ma & Tianyu Dong, “Frequency-Stable Robust Wireless Power Transfer Based on High-Order Pseudo-Hermitian Physics”, Phys. Rev. Lett. 2023, 130, 077202H. Ishida, T. Kyoden, and H. Furukawa, “Application of parity-time symmetry to low-frequency wireless power transfer system”, IEEJ J. Ind. Appl., 2022, vol.11, no.1, pp.59-68

[0009] However, in a contactless power transfer system using magnetic resonance as disclosed in, for example, Patent Document 1, it is necessary to provide a function for adjusting the distance and angle between the power supply coil and the power receiving coil so that they remain constant, which causes problems such as the power transmitting device becoming large in size and the need to constantly perform advanced control such as adjusting the positional relationship and angle between the coils, which places a burden on the control unit of the power transmitting device.In addition, there is also a problem that the advanced control function stops when the battery is replaced.

[0010] Furthermore, in a contactless power supply system for a robot arm as shown in Patent Document 2, for example, there is a problem that when supplying or receiving power to a rotating object, power cannot be supplied at a certain rotation angle. Also, since it is not possible to bend the tip of a single arm in any direction and rotate 360 ​​degrees in any direction, there is also a problem that if you want to rotate in any direction 360 degrees, a complex structure with multiple joints is required.

[0011] The present invention has been made to solve the above-mentioned problems, and has an object to provide a wireless power supply system that does not require adjustment or control of the positions and angles of the power supply coil and power receiving coil when supplying power to a rotating object, has a simple structure, and is capable of constantly supplying power wirelessly without interruption no matter how much the power receiving coil rotates relative to the power supply coil.

[0012] In order to achieve the above object, the present invention provides a wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), in which a power supply coil provided in a power supply circuit and a power receiving coil provided in a power receiving circuit are each a solenoid or helical coil with magnetic poles at both ends, and the power supply coil and the power receiving coil are arranged so that the center of rotation of the power receiving coil is near one of two magnetic poles at both ends of the power receiving coil, as a means for always wirelessly supplying power while preserving the PT symmetry and keeping the transmitted power constant when the power supply coil is rotated relative to the power supply coil.

[0013] According to the wireless power feed system of the present invention, in wireless power feed utilizing PT symmetry, when feeding power to a rotating object, the feed coil and the receiving coil are arranged so that the center of rotation of the receiving coil is near one of the two magnetic poles at either end of the receiving coil. This eliminates the need to adjust or control the positions and angles of the feed coil and the receiving coil, and the structure is simple. No matter how much the receiving coil rotates relative to the feed coil, power is transmitted uninterrupted and high transmission efficiency can be maintained, making it possible to always supply power wirelessly.

[0014] 2 is an explanatory diagram showing a schematic configuration of a power supply coil and a power receiving coil used in a wireless power supply system utilizing PT symmetry according to an embodiment of the present invention. It is a diagram showing the positional relationship between coils in a rotating power supply target in a wireless power supply system utilizing PT symmetry when the center of rotation O is located at the center of the power receiving coil. It is a diagram showing the relationship between the rotation angle θ and the magnetic coupling coefficient k when the coils are arranged as shown in FIG. ｍ 4 is a diagram showing the relationship between the rotation angle θ and the magnetic coupling coefficient k in the case where the center of rotation O is located at one of the two magnetic poles at both ends of the solenoid-type power receiving coil in a rotating power supply target in the wireless power supply system utilizing PT symmetry according to the first embodiment of the present invention. ｍ 2 is a graph showing the relationship between the rotation angle of two coils (a power supply coil and a power receiving coil) used in a wireless power supply system and the transmitted power. FIG. 3 is an explanatory diagram showing an example of the schematic configuration of a wireless power supply system. FIG. 4 is a graph showing the relationship between the rotation angle of two coils (a power supply coil and a power receiving coil) used in a wireless power supply system and the transmitted power. FIG. 5 is an explanatory diagram showing an example of the schematic configuration of a wireless power supply system. ｍ , critical magnetic coupling coefficient k ｍｃ、and an example graph of experimental results showing the relationship between the rotation angle of two coils (a feeding coil and a receiving coil).

[0033] FIG. 1 is a schematic perspective view showing one specific example (an example in which the coils are arranged in the axial direction) of a wireless power transfer system using a magnetic resonance method utilizing PT symmetry according to the first embodiment of the present invention, in which a feeding coil and a receiving coil are built into a robot arm.

[0034] FIG. 1 is a schematic perspective view showing another specific example (an example in which the coils are arranged in the rotation direction) of a wireless power transfer system using a magnetic resonance method utilizing PT symmetry according to the first embodiment of the present invention, in which a feeding coil and a receiving coil are built into a robot arm.

[0015] The present invention relates to a wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"). Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0016] First, we will explain wireless power transfer technology. There are several known wireless power transfer technologies, such as electromagnetic induction and magnetic resonance. Of these, electromagnetic induction wireless power transfer technology is used, for example, to charge mobile phones. In this technology, the coils are arranged one above the other, and, based on the same principle as a transformer, power can be transferred only when the distance (transmission distance) between the power transfer coil and the power receiving coil is very short.

[0017] However, because the transmission distance of electromagnetic induction wireless power transfer technology is short, at around a few millimeters, the distance between the power transfer coil and the power receiving coil cannot be large. Furthermore, even a slight misalignment or separation between the power transfer coil and the power receiving coil makes charging and power transfer impossible. In other words, because this technology is sensitive to misalignment, it is difficult to apply it to artificial devices attached inside the human body, such as artificial hearts, or to devices that rotate in multiple directions or have an axis that is misaligned, such as robotic arms.

[0018] Furthermore, magnetic resonance wireless power transfer technology has a long transmission distance of several centimeters to several meters, which allows for a greater distance between the power supply coil and the power receiving coil compared to electromagnetic induction, and it is close to being put to practical use. However, power cannot be transferred unless the distance between the power supply coil and the power receiving coil is kept constant, and if the coils are closer or further away than that distance, or if they are at an angle, the transmission efficiency decreases and the required power cannot be sent. In other words, this method is also vulnerable to positional misalignment, making it difficult to apply to devices that rotate in multiple directions or have an axis misalignment (rotating power supply targets), such as robot arms.

[0019] Furthermore, Patent Document 1 discloses a wireless power supply system that uses magnetic field resonance wireless power supply technology and is equipped with a control device that has the function of adjusting the positional relationship between the power supply coil and the power receiving coil, as well as adjusting the angle, to supply stable power to an auxiliary artificial heart, etc. According to this system, even if the position shifts up or down by a few centimeters due to human body movement, the control device adjusts the position each time by changing parameters, etc., to match the position shift.

[0020] However, this type of system requires functions to adjust the distance and angle between the power supply coil and the power receiving coil to a constant, which results in the control device (external device such as a power transmission device) becoming large-scale, and the need to constantly perform advanced control such as adjusting the positional relationship and angle between the coils places a burden on the control unit of the control device (external device such as a power transmission device).Another problem is that this advanced control function stops when the battery used to supply power to the external device is replaced.

[0021] For this reason, there is a strong demand for a wireless power transfer system that does not require adjustment or control of the positions and angles of the power transfer coil and power receiving coil for a rotating target, and that can supply power wirelessly without interruption no matter how much the power receiving coil rotates relative to the power transfer coil. Experiments and verifications have been conducted repeatedly on various wireless power transfer methods, but at present no system suitable for practical use has been found.

[0022] One type of wireless power transfer method is a wireless power transfer technology that utilizes parity-time symmetry (hereinafter referred to as "PT symmetry"). In a wireless power transfer system that utilizes PT symmetry, even if the transmission distance changes or if a positional shift occurs between the power transfer coil and the power receiving coil, the transmitted power is always kept constant as long as PT symmetry is maintained. In other words, a wireless power transfer system that utilizes PT symmetry replaces the AC power supply in conventional magnetic field resonance wireless power transfer technology with an inverter that behaves electrically in the same way as a negative resistor, that is, an inverter that behaves as a negative resistor.

[0023] This is a well-known technique, as disclosed in, for example, Patent Document 3. To explain it in more detail, an inverter that behaves as a negative resistance is an inverter whose switching frequency and voltage amplitude are not fixed in advance, has a circuit configuration in which the switching frequency is determined by the apparent resonant frequency of the wireless power feed circuit as seen from the output end of the inverter, and has a switching frequency that quickly responds to changes in the apparent resonant frequency of the wireless power feed circuit, which may change due to changes in the transmission distance or positional misalignment of the coil. Here, the wireless power feed circuit refers to a circuit that includes a power transmitting resonant circuit, a power receiving resonant circuit, and all subsequent circuits connected thereto. Furthermore, since the power transmitting resonant circuit and the power receiving resonant circuit interact with each other, the apparent resonant frequency refers to the actual resonant frequency that takes this interaction into account.

[0024] However, conventional wireless power transfer systems utilizing PT symmetry are driven at high frequencies of approximately 1 to 3 MHz, and therefore require the use of air-core coils as the power transfer coil and the power receiving coil, which necessitates large coil dimensions, thereby limiting the applications in which they can be used. Specifically, the coil dimensions in conventional wireless power transfer systems utilizing PT symmetry are approximately 60 cm in diameter (see Non-Patent Document 1). Furthermore, due to the high frequency, placing a metal object (conductive object) around the power transfer coil and the power receiving coil reduces transmission efficiency due to eddy current loss generated in the conductive object. Therefore, it was impossible to apply this technology to a rotating target.

[0025] In order to solve the problems with conventional wireless power transfer systems that utilize PT symmetry, one of the applicants of the present invention invented a wireless power transfer device that utilizes PT symmetry, which uses a low frequency of 100 kHz or less, resulting in little reduction in transmission efficiency even when metal objects are placed in the vicinity, and can maintain high transmission efficiency even when the transmission distance changes or the coil is misaligned.The device also enables the power transfer coil and power receiving coil to be made smaller, making it suitable for use in a variety of applications, and the applicant filed a patent application for this in 2021 (see Patent Document 3).

[0026] The present invention was arrived at through repeated experiments and trial and error in order to apply the technology of the wireless power feeder utilizing PT symmetry of the prior patent application 3 to wireless power feeding to a rotating power feed target. Note that in the embodiments of the present invention, a robot arm will be described as an example of a rotating power feed target.

[0027] When considering power supply to a robot arm as a rotating power supply target, it is desirable to supply power to the end of the arm's joints and have it perform various delicate tasks. In this case, it is desirable for the arm to be able to bend in multiple directions and rotate itself. This "rotation" makes it difficult to supply power via a wired cord. Also, when tilting in multiple directions, wireless power supply using a cylindrical coil is not possible.

[0028] Therefore, in this embodiment of the present invention, we will assume that both the power supply coil and the power receiving coil are solenoid coils or helical coils with magnetic poles at both ends, and will sequentially describe structures and circuits that were invented through repeated trial and error experiments to ensure that wireless power supply to a power supply target (robot arm) that bends in multiple directions and rotates itself is always possible. Note that solenoid coils and helical coils are well known, so detailed description will be omitted, but in this embodiment of the present invention, coils that are coupled by a spatial magnetic field generated in the radial direction of the coil are called solenoid coils, and coils that are coupled by a magnetic field generated in the axial direction of the coil are called helical coils.

[0029] Embodiment 1. FIG. 1 is an explanatory diagram showing the schematic configuration of a power supply coil 11 and a power receiving coil 21 used in a wireless power supply system utilizing PT symmetry according to an embodiment of the present invention. As shown in FIG. 1( a), the power supply coil 11 provided in the power supply circuit and the power receiving coil 21 provided in the power receiving circuit are both solenoid coils in which windings (e.g., Litz wire) 111, 211 are wound around magnetic cores 100, 200 made of a soft magnetic material such as ferrite. Note that a spiral coil (or pancake coil) with a circular spiral shape is often used for wireless power supply. One of the features of the present invention is that this coil is a solenoid coil or a helical coil with magnetic poles at both ends. Furthermore, using a solenoid coil or a helical coil with a soft magnetic material as a core in this way allows for a small coil size, making it possible to install the coil inside a small power supply target.

[0030] As shown in FIG. 1B , the magnetic core 100 (or 200) has magnetic poles 101, 102 (or 201, 202) of a generally rectangular parallelepiped shape on both ends, i.e., on both ends other than the portion around which the winding 111 (or 211) is wound (the portion surrounded by the dashed line in FIG. 1B ), on which no winding is wound. The magnetic poles 101, 102, 201, 202 are formed so that the area of ​​the facing surface when the power supply coil 11 and the power receiving coil 21 are facing each other (the area of ​​both end portions in the upper (back) view of FIG. 1B ) is larger than the area of ​​the other surfaces of the magnetic poles. This increases the magnetic coupling coefficient when the power supply coil 11 and the power receiving coil 21 are facing each other, thereby enabling the transmission distance of the coils to be increased and widening the tolerance for coil misalignment.

[0031] Here, we will explain the magnetic coupling coefficient between two coils. When the positions of the two coils change, such as when the distance or angle between the two coils changes, the magnetic coupling coefficient k ｍ The magnetic coupling coefficient k between the two coils changes. ｍbecomes smaller as the transmission distance between the two coils becomes longer, and also becomes smaller when the positional misalignment of the coils becomes larger. Conversely, as the distance between the two coils becomes shorter, the magnetic coupling coefficient k ｍ becomes large, and when they come close enough to touch, it approaches 1. In other words, the magnetic coupling coefficient k ｍ takes a value between 0 and 1.

[0032] As described above, the power supply coil 11 and the power receiving coil 21 used in the wireless power supply system utilizing PT symmetry in the embodiment of the present invention are each a solenoid coil or a helical coil having magnetic poles at both ends. The embodiment of the present invention provides a means for maintaining PT symmetry and constantly supplying power wirelessly while maintaining constant transmission power when the power receiving coil is rotated relative to the power supply coil.

[0033] 2 is a diagram showing the positional relationship between coils in a rotating power supply target in a wireless power supply system using PT symmetry when the center of rotation O is located at the center of the power receiving coil. Also, FIG. 3 is a diagram showing the relationship between the rotation angle θ and the magnetic coupling coefficient k when the coils are arranged as shown in FIG. ｍ 2 shows the relationship between the rotational center O of the power receiving coil 21 and the axis 21L of the power supply coil 11. In a conventional robot arm, as shown in Fig. 2, the rotational center O of the power receiving coil 21 is generally located near the center of the power receiving coil 21. Here, the state in which the axis 11L of the power supply coil 11 and the axis 21L of the power receiving coil 21, shown by the dashed dotted lines in Fig. 2, are parallel to each other is defined as a rotational angle of 0 degrees, and the angle between the two axes is defined as a rotational angle θ (this also applies to Fig. 4, which will be described later).

[0034] 2 shows the power receiving coil before rotation, and before rotation, the axis 11L of the power feeding coil 11 and the axis of the power receiving coil (the symbol and axis are not shown for the power receiving coil shown in dashed line) are parallel. The power receiving coil after being rotated by a rotation angle θ around the vicinity of the center of this power receiving coil is shown as power receiving coil 21 by solid line.

[0035] In the case of the coil arrangement shown in FIG. 2 , that is, when the rotation center O is located near the center of the receiving coil 21, the magnetic coupling coefficient k ｍ It can be seen that the magnetic coupling coefficient k ｍ When becomes 0 (zero), power supply becomes impossible even with wireless power supply using PT symmetry. Therefore, it is not possible to constantly supply power to a robot arm that can rotate 360 ​​degrees and move it. Therefore, in order to make it move in a complex manner, the magnetic coupling coefficient k ｍ It was necessary to use a multi-joint robot arm that could move within a range that did not reach 0 (zero), that is, in this case, within a range that did not reach plus or minus 90 degrees.

[0036] To solve this problem, the applicant of the present invention has determined that the magnetic coupling coefficient k ｍ The present invention was arrived at through repeated experiments and trial and error to devise a coil arrangement that would prevent the value of θ from becoming 0 (zero) and to enable wireless power supply to a rotating power supply target.

[0037] In this way, the magnetic coupling coefficient k ｍ An example of a coil arrangement in which the magnetic coupling coefficient k does not become 0 (zero) is shown in Fig. 4. Fig. 4 is a diagram showing the positional relationship between coils in a rotating power supply target in a wireless power supply system utilizing PT symmetry according to the first embodiment of the present invention, when the center of rotation O is located at one of two magnetic poles at both ends of a solenoid-type power receiving coil. Fig. 5 is a diagram showing the relationship between the rotation angle θ and the magnetic coupling coefficient k when the coils are arranged as shown in Fig. 4. ｍ FIG.

[0038] 2, the power receiving coil 21 is shown by a broken line in Fig. 4, and before rotation, the axis 11L of the power feeding coil 11 and the axis of the power receiving coil (the symbol and axis are not shown for the power receiving coil shown in broken line) are parallel to each other. The power receiving coil 21 shown by a solid line is the power receiving coil 21 after being rotated by a rotation angle θ around one of the two magnetic poles at both ends of the power receiving coil 21 (magnetic pole 202 in the example shown in Fig. 4).

[0039] Here, the use of the term "near the magnetic pole" means that the center of rotation O is not near the center (central part) of the receiving coil 21 as shown in Fig. 2, but is located at a position offset from the center of the receiving coil 21, and the term "near the magnetic pole" defines that the center of rotation O may be at the very end of the magnetic poles (201, 202) at both ends of the receiving coil 21, or may be around the center of the magnetic poles (201, 202). In other words, when viewing the receiving coil 21 as a whole, the center of rotation O is located at a position offset near the magnetic poles (201, 202) at both ends.

[0040] That is, FIG. 4 shows the positional relationship of the coils when the center of rotation O is located at one of the two magnetic poles (201, 202) at both ends of the receiving coil 21, and FIG. 5 shows the relationship between the rotation angle θ and the magnetic coupling coefficient k in the positional relationship of the coils in FIG. ｍ Here, although the change varies slightly depending on the shape of the coil and the position of the center of rotation, as the rotation angle θ increases, the magnetic coupling coefficient k ｍ 2 and 4 have the same tendency that the magnetic coupling coefficient k decreases. However, in the case of the positional relationship of the coils as shown in FIG. 4, that is, when the center of rotation O is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21, as shown in FIG. ｍ It is possible to eliminate the rotation angle at which θ becomes 0. In this state, by utilizing PT symmetry, it is possible to make the transmitted power constant at any rotation angle θ.

[0041] In this way, the power supply coil 11 and the power receiving coil 21 are arranged so that the center of rotation of the power receiving coil 21 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21. Therefore, when the power receiving coil 21 is rotated relative to the power supply coil 11, the magnetic coupling coefficient k ｍ Since ≠ 0 (zero) is not achieved, it is possible to maintain PT symmetry and constantly supply power wirelessly while maintaining constant transmission power.

[0042] Here, we will explain existing wireless power transfer technologies again. Wireless power transfer using a magnetic field includes electromagnetic induction and magnetic resonance. Fig. 6 is a graph showing the relationship between the rotation angle of two coils (a power transfer coil and a power receiving coil) used in a wireless power transfer system and the transmitted power, with Fig. 6(a) showing the case of the electromagnetic induction method and Fig. 6(b) showing the case of the magnetic resonance method.

[0043] In the case of the electromagnetic induction method, the magnetic coupling coefficient k ｍ As the rotation angle of the two coils decreases, the power that can be transmitted (transmission power) also decreases. Therefore, as shown in the graph in Figure 6(a), the relationship between the rotation angle of the two coils and the transmission power is such that the transmission power is greatest when the rotation angle is 0 (zero), and the transmission power decreases as the rotation angle increases.

[0044] In the case of magnetic resonance, a specific magnetic coupling coefficient k ｍ When the magnetic coupling coefficient k is a certain value, the power supply circuit and the power receiving circuit resonate and become strongly coupled. ｍ Therefore, the relationship between the rotation angle of the two coils and the transmission power is such that the transmission power is greatest at a certain rotation angle, and the transmission power decreases as the rotation angle deviates from that angle, as shown in the graph in Figure 6(b).

[0045] As such, both methods have in common the fact that the transmitted power changes as the rotation angle changes. In practical applications, it is necessary to supply a constant amount of power to the load (device) attached to the power receiving side, so it is undesirable for the transmitted power to change depending on the rotation angle. Therefore, some method of power control is required to keep the transmitted power constant.

[0046] Here, the system configuration of a wireless power supply system will be described. Fig. 7 is an explanatory diagram showing an example of a schematic configuration of a wireless power supply system, and Fig. 7(a) shows a typical system configuration when power control is performed using existing technology. Fig. 7(b) shows an example of a system configuration when PT symmetry is used (without a repeater), and Fig. 7(c) shows another example of a system configuration when PT symmetry is used (with a repeater).

[0047] When power control is performed using existing methods, the system configuration shown in Figure 7(a) is considered. This system configuration requires sensors for detecting voltage and current values ​​in the power supply circuit and power receiving circuit, wireless communication equipment for feeding back the detected values ​​on the power receiving side to the power control unit on the power supply side, and a computer for performing arithmetic processing of the detected values ​​in the power control unit. However, if the angular velocity of rotation is fast, power control cannot keep up with that speed, and it is predicted that power control will be difficult with this configuration.

[0048] One factor that reduces the response speed of power control is the time delay that occurs in the wireless communication devices and computers mentioned above. If it were possible to perform power control using a method that does not use communication devices or computers, it would be possible to improve the response speed. Therefore, in this invention, a physical law called PT symmetry is used. As mentioned above, when PT symmetry is used, the physical phenomenon is that the transmitted power is proportional to the magnetic coupling coefficient k ｍ Therefore, even if the rotation angle changes, the transmitted power remains constant, achieving the objective. This method does not require the communication equipment or computer described above, so if there is no repeater, the system configuration shown in Figure 7(b) can achieve power control with a fast response speed.

[0049] Furthermore, as described in Non-Patent Document 2, PT symmetry can be preserved even when a repeater coil is placed between a power feed coil in a power feed circuit and a power receiving coil in a power receiving circuit. In practice, a capacitor is connected to the repeater coil, forming a resonant circuit. If this resonant circuit is called a repeater, a system configuration including the repeater shown in FIG. 7(c) can also be envisioned. As will be described later, this configuration is envisioned when applying wireless power transfer using PT symmetry to a multi-joint robot arm. Note that a requirement for a resonator is that the natural resonant frequency of the repeater matches the natural resonant frequencies of the power feed circuit and the power receiving circuit. Here, the natural resonant frequency refers to the resonant frequency of the resonator alone.

[0050] Next, the limit value (critical angle) of the rotation angle will be explained. When the magnetic coupling coefficient becomes smaller than a certain value, the PT symmetry cannot be preserved. In other words, there exists a limit (critical) magnetic coupling coefficient at which the PT symmetry can be preserved. In this way, the condition for preserving the PT symmetry is the magnetic coupling coefficient k ｍ The critical magnetic coupling coefficient k indicates the limit value (critical value) of ｍｃ This critical magnetic coupling coefficient k ｍｃ The formula and theoretical explanation are publicly known as described in, for example, Patent Document 3 and Non-Patent Document 3, and therefore a detailed explanation will be omitted here.

[0051] And, as mentioned above, when PT symmetry is preserved, the magnetic coupling coefficient k ｍ Even if the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ If the value of k is less than 0.001, the PT symmetry cannot be maintained and it becomes difficult to keep the transmitted power constant. ｍ is the critical magnetic coupling coefficient k ｍｃ If the value falls below this, the transmitted power drops significantly, making wireless power supply practically difficult.

[0052] FIG. 8 shows the relationship between the magnetic coupling coefficient k and the rotation angle θ when the power receiving coil shown in FIG. 2 is rotated around the center of the power receiving coil. ｍ, critical magnetic coupling coefficient k ｍｃ、 8 is a graph of experimental results showing the relationship between the rotation angle of the two coils (the power supply coil and the power receiving coil) shown in FIG. 2 and the transmission power and the magnetic coupling coefficient, where the horizontal axis represents the rotation angle and the vertical axis represents the transmission power and the magnetic coupling coefficient.

[0053] In the example of FIG. 8, as shown by the dashed line in the graph, the critical magnetic coupling coefficient k ｍｃ is 0.039. The critical magnetic coupling coefficient k ｍｃ is a constant that is specific to each system. On the other hand, the magnetic coupling coefficient k ｍ is a variable, and the magnetic coupling coefficient k ｍ tends to decrease as the rotation angle θ of the two coils increases. The black circles in the graph represent the experimental results of the transmitted power, and the solid line represents the magnetic coupling coefficient k ｍ The numerical calculation results are shown.

[0054] In the example shown in FIG. 8, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ In this case, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ Since PT symmetry is maintained up to a rotation angle of 70 degrees, where the value of the magnetic coupling coefficient k is larger than θ, the transmission power is maintained at a roughly constant value (approximately 18 W in this example). After that, when the rotation angle θ exceeds 70 degrees, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ Since the value is smaller than , the PT symmetry cannot be preserved and the transmission power drops significantly.

[0055] In practical applications, it is desirable to make the critical angle as large as possible. If PT symmetry can be maintained at any rotation angle θ, the transmitted power can be kept constant even when the receiving coil is rotated one revolution (360 degrees). This makes it possible to wirelessly power a continuously rotating target. However, except for the present invention, there have been no examples of successful continuous power supply over 360 degrees using a pair of solenoid coils or helical coils.

[0056] In this way, by using a pair of solenoid coils or helical coils, the power supply coil 11 and the power receiving coil 21, there is an advantage that the installation space is small, making it suitable for application to a robot arm, etc. Another advantage is that it can accommodate simultaneous movement of two rotation axes (11L and 21L).

[0057] Next, regarding a method for increasing the critical angle, the relationship between the rotation angle θ and the magnetic coupling coefficient k shown in FIGS. 3 and 5 is ｍ As shown by the broken line in FIG. 3, when the arrangement of the two coils is as shown in FIG. 2, the critical magnetic coupling coefficient k ｍｃ If is set to 0.1, the PT symmetry can be maintained up to a rotation angle of 44 degrees. ｍｃ The critical angle when is 0.1 is 44 degrees. Note that this graph is also line-symmetric for the rotation angle in the negative direction, so PT symmetry is actually preserved within the range of ±44 degrees (88 degrees in total).

[0058] Furthermore, as shown by the dashed line in FIG. 3, if the critical magnetic coupling coefficient k ｍｃ If the critical angle is 0.05, the PT symmetry is maintained up to ±66 degrees (total 132 degrees). Therefore, in order to increase the critical angle, the critical magnetic coupling coefficient k ｍｃ can be made smaller.

[0059] critical magnetic coupling coefficient k ｍｃ A method for reducing the critical angle will be described later. One method for increasing the critical angle is to reduce the magnetic coupling coefficient k ｍ The aim is to keep the value of as large as possible. This can be achieved by adjusting the coil arrangement. This is the coil arrangement shown in Fig. 4, but see Fig. 5, which is a graph showing the case where the center of rotation O is located at one of the magnetic poles (201 or 202) of the receiving coil 21.

[0060] In the case of the coil arrangement shown in FIG. 4, if the critical magnetic coupling coefficient k ｍｃ is 0.05 (the dashed line in FIG. 5), the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃSince the rotation angle does not fall below ±180 degrees, it is possible to preserve PT symmetry up to ±180 degrees (a total of 360 degrees), and the receiving coil can be rotated continuously.

[0061] As described above, the critical angle can be increased by adjusting the arrangement (positional relationship) of the power supply coil 11 and the power receiving coil 21. Specifically, the critical angle is narrowest when the center of rotation O is located at the center of the power receiving coil 21, as shown in Fig. 2, whereas the critical angle is widest when the center of rotation O is located at one of the magnetic poles (201 or 202) of the power receiving coil 21, as shown in Fig. 4.

[0062] That is, as shown in FIG. 4 , if the power supply coil 11 and the power receiving coil 21 are arranged so that the center of rotation O of the power receiving coil 21 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21, the critical angle can be increased and the range of rotation angle and transmission distance in which PT symmetry can be preserved can be expanded. Therefore, when the power receiving coil 21 is rotated relative to the power supply coil 11, it becomes possible to always supply power wirelessly while preserving PT symmetry and keeping the transmission power constant.

[0063] Next, the results of an experiment conducted using an actual device with a repeater-less system configuration utilizing PT symmetry as shown in Fig. 7(b) will be described with reference to Fig. 9. Fig. 9 shows the magnetic coupling coefficient k versus the rotation angle when the power receiving coil is rotated around one of the two magnetic poles at both ends as shown in Fig. 4. ｍ , critical magnetic coupling coefficient k ｍｃ、 10 is a graph showing experimental results showing the relationship between the frequency and the transmission power.

[0064] 9 is a graph showing the relationship between the rotation angle of the two coils (the power supply coil and the power receiving coil) shown in FIG. 4 and the transmission power and the magnetic coupling coefficient, where the horizontal axis represents the rotation angle and the vertical axis represents the transmission power and the magnetic coupling coefficient. The dashed line in the graph indicates the critical magnetic coupling coefficient k ｍｃ (=0.039), the black circles indicate the experimental results of the transmitted power, and the solid line indicates the numerical calculation results of the magnetic coupling coefficient.

[0065] As shown in Figure 9, the experimental results confirmed that the transmission power was kept almost constant over a rotation angle of ±180 degrees (a total of 360 degrees). In addition, the magnetic coupling coefficient k ｍ is the critical magnetic coupling coefficient k ｍｃ (=0.039), and it was confirmed that the PT symmetry was maintained over 360 degrees, resulting in constant transmitted power. Furthermore, it was confirmed that constant transmitted power was achieved even when the coil was rotated continuously for more than one revolution. Until now, there had been no example of 360-degree rotation (successful continuous power supply) using a pair of solenoid coils or helical coils.

[0066] As described above, it has been confirmed not only through theoretical considerations but also through experiments that the present invention is effective and has great advantages.

[0067] Here, as an application example of the present invention, its applicability to various types of robot arms will be described. The joints of a robot arm may have degrees of freedom for rotation around multiple axes. Fig. 10 is a schematic perspective view showing a specific example in which a power supply coil and a power receiving coil are built into a robot arm (an example in which the coils are arranged in the axial direction) in a wireless power supply system using magnetic resonance and utilizing PT symmetry according to the first embodiment of the present invention.

[0068] FIG. 10( a) shows a state in which a forearm incorporating a power receiving coil 21 is connected to an upper arm incorporating a power supply coil 11, and the forearm from the elbow (joint) onward rotates 360 degrees around the upper arm. FIG. 10( b) shows that the forearm can rotate 360 ​​degrees in the plane indicated by the arrow relative to the fixed upper arm. FIG. 10( c) shows that the forearm can also rotate 360 ​​degrees on another plane. FIG. 10( d) also shows that the forearm can rotate 360 ​​degrees on another plane. In other words, the forearm can rotate 360 ​​degrees in all directions. FIG. 10( e) shows that the forearm is incorporated into a robot arm having a hand-like grasping part at its tip.

[0069] As shown in Figure 10, we assume that a pair of coils is placed at the elbow joint of a robot, and power is supplied from the upper arm to the forearm by wireless power supply. Since the forearm faces in various directions depending on the situation, the magnetic coupling coefficient k between the coils ｍ Therefore, it is difficult to keep the transmission power constant with existing technology. Therefore, there is no invention of a method or device for wirelessly supplying constant power using a set of coils in a system that rotates simultaneously in multiple axial directions. However, in this device that preserves PT symmetry, the magnetic coupling coefficient k ｍ Even if the critical magnetic coupling coefficient k ｍｃ If the power does not fall below this level, the transmitted power can be kept constant regardless of the direction or angle of the arm.

[0070] Therefore, by using the device of the present invention, it is possible to wirelessly transmit a constant amount of power in various directions that are expected as the rotation axis of a robot arm, such as those shown in Figures 10(a) to 10(e). Furthermore, constant power can be achieved even when multiple axes of rotation are performed simultaneously. Furthermore, a coil arrangement that is common to all expected rotation directions is one in which the power supply coil and the power receiving coil are arranged so that the center of rotation of the power receiving coil is located near one of the two magnetic poles at both ends of the power receiving coil.

[0071] Another possible application is wireless power feeding that preserves PT symmetry in a two-joint or multi-joint robot arm or multi-joint robot by using a repeater formed by the aforementioned repeater coil and capacitor. Figure 11 shows a specific example of a magnetic field resonance type wireless power feed system that utilizes PT symmetry in the first embodiment of the present invention, in which a feed coil and a receive coil are built into the robot arm, where the system is applied to a two-joint robot arm with a repeater.

[0072] In this way, even in the case of a multi-joint robot arm in which three or more arms are connected, by placing a repeater with a resonator in the middle as shown in Fig. 11, wireless power supply is possible, and the arm can be bent in all directions and rotated 360 degrees (even allowing movement involving 360 degrees of rotation), thereby improving convenience. However, according to the present invention, wireless power supply is always possible even for a power supply target that requires 360 degrees of rotation, so for example, in the case of a robot arm, there is no need for it to be multi-jointed, and since it can be bent in all directions and rotated 360 degrees with a single joint, there is also the advantage that the arm structure is simplified.

[0073] 10, the coil is arranged in the direction of the axis (rotation axis) of the robot arm (the power receiving coil 21 is arranged so that the coil axis is in the same direction as or parallel to the axis (rotation axis) of the robot arm), but the same effect can be obtained even if the coil is arranged in the direction of rotation of the robot arm (the power receiving coil 21 is arranged so that the coil axis is perpendicular to the axis (rotation axis) of the robot arm), as shown in Fig. 12. Fig. 12 is a schematic perspective view showing another specific example (an example in which the coils are arranged in the rotation direction) in which a power feeding coil and a power receiving coil are built into a robot arm in a wireless power feeding system using magnetic field resonance and utilizing PT symmetry according to the first embodiment of the present invention.

[0074] Fig. 12(a) is a diagram showing the state in which the power supply coil 11 is built into a robot arm having a hand-like gripping part at the tip, and Fig. 12(b) is a partial enlarged view of Fig. 12(a). Compared with Fig. 10(e), it can be seen that the coil arrangement is different, but the arrangement shown in Fig. 12 is the same in that the power supply coil 11 and the power receiving coil 21 are arranged so that the center of rotation of the power receiving coil 21 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 21.

[0075] As described above, according to the wireless power feed system of the first embodiment of the present invention, in wireless power feed utilizing PT symmetry, when power is fed to a rotating object, the feed coil and the receive coil are arranged so that the center of rotation of the receive coil is located near one of the two magnetic poles at either end of the receive coil. This eliminates the need to adjust or control the positions and angles of the feed coil and the receive coil, and the structure is simple. Furthermore, no matter how much the receive coil rotates relative to the feed coil, high transmission efficiency can be maintained without interruption, making it possible to always supply power wirelessly.

[0076] In the first embodiment of the present invention, a robot arm has been described as an example of a rotating object to be powered, but the present invention is not limited to a robot arm and can be applied to any object that is a rotating object that requires wireless power supply, such as a multi-joint arm stand on the tip of which a light bulb, camera, monitor, etc. is mounted.

[0077] Furthermore, in the first embodiment of the present invention, the description has been given assuming that the power receiving coil rotates relative to the power feeding coil (this pattern is thought to be the most common), but this is not necessarily limited to this pattern and the present invention can also be applied to a power feeding target in which the power feeding coil rotates relative to the power receiving coil. That is, as a means for always feeding power wirelessly while maintaining PT symmetry and keeping the transmitted power constant when the power feeding coil is rotated relative to the power receiving coil, the power feeding coil and the power receiving coil may be arranged so that the center of rotation of the power feeding coil is near one of the two magnetic poles at both ends of the power feeding coil.

[0078] It should be noted that, within the scope of the present invention, any of the components of the embodiments may be modified or omitted.

[0079] The wireless power supply system of the present invention can be applied to various power supply targets that rotate, such as robot arms and articulated arm stands.

[0080] 11 Power supply coil 11L Axis of power supply coil 11 21 Power receiving coil 21L Axis of power receiving coil 21 100, 200 Magnetic core 101, 102, 201, 202 Magnetic pole 111, 211 Winding

Claims

1. A wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), wherein the power supply coil provided in the power supply circuit and the power receiving coil provided in the power receiving circuit are each a solenoid or helical coil having magnetic poles at both ends, and as a means for always wirelessly supplying power while maintaining a constant transmission power by preserving the PT symmetry when the power receiving coil is rotated relative to the power supply coil, the power supply coil and the power receiving coil are arranged so that the center of rotation of the power receiving coil is located near one of two magnetic poles at both ends of the power receiving coil.

2. A wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), wherein the power supply coil provided in the power supply circuit and the power receiving coil provided in the power receiving circuit are each a solenoid or helical coil having magnetic poles at both ends, and as a means for always wirelessly supplying power while maintaining a constant transmission power and preserving the PT symmetry when the power supply coil is rotated relative to the power receiving coil, the power supply coil and the power receiving coil are arranged so that the center of rotation of the power supply coil is located near one of the two magnetic poles at both ends of the power supply coil.

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