Wireless power supply system

Abstract

To provide a wireless power supply system that does not require adjustment or control for the position and angle of a power supply coil and a power reception coil when power is supplied to a rotating object, has a simple structure, and can always supply power wirelessly without interruption irrespective of the manner in which the power reception coil rotates with respect to the power supply coil.　Provided is a system for wirelessly supplying power to a rotating power supply object using PT symmetry, wherein: each of a power supply coil 11 and a power reception coil 21 is a solenoid-type or helical-type coil having magnetic poles at both ends; and when the power reception coil 21 is rotated with respect to the power supply coil 11, the power supply coil 11 and the power reception coil 21 are arranged so that a rotation center O of the power reception coil 21 approaches either one of two magnetic poles (201, 202) at the two ends of the power reception 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 JP 2020-106985 A JP 2022-121324 A JP 2014-532296 A JP 2009-164293 A

[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 embodiment 1 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) and the transmission power when the coils are arranged as shown in FIG. 4.

[0023] FIG. 1 is a schematic perspective view showing one specific example (an example in which the coils are arranged in the axial direction) in which a feeding coil and a receiving coil are built into a robot arm in a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to a first embodiment of the present invention.

[0024] FIG. 2 is a schematic perspective view showing a specific example (an example in which the coils are arranged in the axial direction) in which a feeding coil and a receiving coil are built into a robot arm in a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to a first embodiment of the present invention.

[0025] FIG. 3 is a schematic perspective view showing another specific example (an example in which the coils are arranged in the rotation direction) in which a feeding coil and a receiving coil are built into a robot arm in a wireless power feed system using a magnetic resonance method utilizing PT symmetry according to a first embodiment of the present invention.

[0026] FIG. 4 is an explanatory diagram showing an example of the schematic configuration of a feeding coil and a receiving coil used in a wireless power feed system using PT symmetry according to a second embodiment of the present invention. 13 is an explanatory diagram showing another example of the schematic configuration of a power supply coil and a power receiving coil used in a wireless power supply system utilizing PT symmetry according to embodiment 2 of the present invention. FIG. 14 is an explanatory diagram showing yet another example of the schematic configuration of a power supply coil and a power receiving coil used in a wireless power supply system utilizing PT symmetry according to embodiment 2 of the present invention. FIG. 15 is a perspective view schematically showing a coil structure for the wireless power feeder shown in FIG. 15. FIG. 14 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 embodiment 2 of the present invention, when the center of rotation O is located in one of two magnetic poles at both ends of the double-spiral power receiving coil shown in FIG. 13. FIG. 15 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 embodiment 2 of the present invention, when the center of rotation O is located in one of two magnetic poles at both ends of the hybrid-type power receiving coil shown in FIG. 15.15 is a schematic perspective view showing a specific example in which the hybrid-type power supply coil and power receiving coil shown in FIG. 15 are mounted on a wall surface of a metal robot arm in a wireless power supply system using a magnetic field resonance method utilizing PT symmetry according to a second embodiment of the present invention. FIG. 16 is an explanatory diagram showing an example of a schematic configuration of a power supply coil and power receiving coil used in a wireless power supply system using PT symmetry according to a third embodiment of the present invention. FIG. 17 is a diagram showing a positional relationship between coils in a case where the center of rotation O is located on one of two magnetic poles at both ends of the solenoid-type power receiving coil shown in FIG. 20 in a rotating power supply target in a wireless power supply system using PT symmetry according to a third embodiment of the present invention. FIG. 18 is a schematic perspective view showing a specific example in which the hybrid-type power supply coil and solenoid-type power receiving coil shown in FIG. 20 are mounted on a wall surface of a metal robot arm in a wireless power supply system using a magnetic field resonance method utilizing PT symmetry according to the third embodiment of the present invention.

[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] First Embodiment. 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 a first 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 wires) 111, 211 are wound around magnetic cores 100, 200 made of a soft magnetic material such as ferrite. Note that a single spiral coil (or pancake coil) with a spiral and circular shape is often used for wireless power supply. One of the features of the first embodiment 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" in either case means that the center of rotation O is not near the center (central portion) 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. The term "near the magnetic pole" defines the center of rotation O as being at the very end of the magnetic poles (201, 202) at both ends of the receiving coil 21, or at the center of the magnetic poles (201, 202). In other words, when the receiving coil 21 is viewed as a whole, the center of rotation O is located at a position offset near the magnetic poles (201, 202) at both ends. The same applies to the second and third embodiments.

[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 keeping the transmission power constant.

[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] Embodiment 2. Figure 13 is an explanatory diagram showing an example of the schematic configuration of a power supply coil 31 and a power receiving coil 41 used in a wireless power supply system utilizing PT symmetry according to embodiment 2 of the present invention, which are called double spiral coils. In wireless power supply devices, a coil known as a "DD coil" or "double D coil," in which two coils are wound spirally on a magnetic plate, is known as a coil that increases transmission distance and has high magnetic flux generation efficiency (see, for example, Figure 5 of Patent Document 4 and Patent Document 5). Furthermore, DD coils (double D coils) are used as the highest-performance electromagnetic coils for transmitting high power, such as wirelessly powering electric vehicles. Note that all coils will be referred to uniformly here as "double spiral coils."

[0079] 13( a) shows a state in which a power feeding coil 31 provided in a power feeding circuit and a power receiving coil 41 provided in a power receiving circuit face each other, and Fig. 13( b) is a side view of the power feeding coil 31 and the power receiving coil 41 shown in Fig. 13( a) when they are oriented horizontally with the sides facing each other facing up. As shown in Figs. 13( a) and 13(b), both the power feeding coil 31 provided in the power feeding circuit and the power receiving coil 41 provided in the power receiving circuit have a double-spiral coil structure in which double planar spiral coils 311 and 312, 411 and 412, each of which is formed by a spiral winding (e.g., a Litz wire) and forms a double spiral, are arranged on top of a magnetic core 100, 200 made of a soft magnetic material such as ferrite. The portions of the planar spiral coils 311, 312, 411, and 412 near the center where no coil is wound become the magnetic poles 101, 102, 201, and 202, respectively.

[0080] The coil structure shown in the first embodiment and the coil structure shown in the second embodiment are the same in terms of the general configuration of the feeding coil and receiving coil used in a wireless power transfer system utilizing PT symmetry, and when power is to be fed to a rotating object, the feeding coil and 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 feeding coil and receiving coil, has a simple structure, and can maintain uninterrupted and high transmission efficiency no matter how much the receiving coil rotates relative to the feeding coil, making it possible to always supply power wirelessly.

[0081] However, in the first embodiment, the power supply coil provided in the power supply circuit and the power receiving coil provided in the power receiving circuit were each a solenoid or helical coil with magnetic poles at both ends. However, as shown in FIGS. 10 to 12, when applying this to a robot arm, if the robot arm is made only of a metal that blocks magnetic fields, it has been found that magnetic flux leaks from the back of each coil and cannot be looped properly, resulting in a decrease in the magnetic coupling coefficient and preventing the effectiveness of wireless power supply from being achieved.

[0082] That is, when a power supply coil and a power receiving coil as shown in FIG. 4 in the first embodiment are attached inside or around a rotating object, if there is a metal plate on the back surface of each coil (the surface opposite the side where the power supply coil and the power receiving coil face each other), that is, if the rotating object is made entirely of metal, magnetic flux leaks from the back surface of each coil, the magnetic flux cannot be properly looped, and the AC magnetic field hits the metal plate, resulting in eddy current loss. It has been found that this eddy current loss not only reduces power transmission efficiency but also makes it impossible to preserve PT symmetry. In other words, the first embodiment is effective when the rotating object is made of a non-metallic material such as plastic, but if the rotating object is made entirely of metal, there is a risk that the effectiveness of wireless power transfer will not be achieved.

[0083] Therefore, in this second embodiment, the power feeding coil provided in the power feeding circuit and the power receiving coil provided in the power receiving circuit are each a double-spiral type ( FIG. 13 ) or hybrid type (see FIGS. 14 and 15 described below) coil with magnetic poles at both ends. In this case, even if there is metal on the back surface of the coil, the proportion of magnetic flux that self-loops on the back surface of the coil is very small. Therefore, it has been confirmed that when the power receiving coil is rotated relative to the power feeding coil or when the power feeding coil is rotated relative to the power receiving coil, PT symmetry can be preserved and power can be fed wirelessly at all times while maintaining constant transmitted power.

[0084] Fig. 14 is an explanatory diagram showing another example of the schematic configuration of a power supply coil 31 and a power receiving coil 41 used in a wireless power supply system utilizing PT symmetry according to embodiment 2 of the present invention, which is a type of so-called hybrid coil. Similar to the double spiral type shown in Fig. 13 , Fig. 14 shows a coil structure in which two coils, namely, planar spiral coils 311 and 312, and 411 and 412, constituting a double spiral, are arranged slightly apart above magnetic cores 100 and 200 made of a soft magnetic material such as ferrite, and solenoid-shaped coil windings 111 and 211 are arranged between the two coils (311 and 312, and 411 and 412) in the same manner as Fig. 4 in embodiment 1, and are wound around magnetic cores 100 and 200 as axes. In this coil structure, the unwound portions near the centers of the planar spiral coils 311, 312, 411, and 412 also become the magnetic poles 101, 102, 201, and 202.

[0085] FIG. 15 is an explanatory diagram showing yet another example of the schematic configuration of power supply coil 31 and power receiving coil 41 used in a wireless power supply system utilizing PT symmetry in embodiment 2 of the present invention. FIG. 15 is also a type of so-called hybrid coil. In FIG. 15 , two spiral coils 321 and 322, 421 and 422 (stepped spiral coils 321 and 322, 421 and 422 constituting a double spiral) are wound diagonally from top to bottom around magnetic core 100, 200 made of a soft magnetic material such as ferrite, and the two coils 321 and 322, 421 and 422 are arranged a short distance apart. Similar to FIG. 14 , a single solenoid-shaped coil winding 111, 211 is arranged between the two coils (321 and 322, 421 and 422) and wound around magnetic core 100, 200 as an axis. In this coil structure, the unwound portions near the centers of the stepped spiral coils 321, 322, 421, and 422 also become the magnetic poles 101, 102, 201, and 202.

[0086] FIG. 16 is a perspective view schematically illustrating the coil structure for the wireless power feeder shown in FIG. 15 , showing only the power feed coil 31. That is, FIG. 15( b ) is a side view of FIG. 16 as viewed from the direction of arrow A. As shown in FIG. 16 , the magnetic core 100 is a magnetic body having a substantially rectangular parallelepiped shape, with its longest side in the X-axis direction, its depth in the Y-axis direction, and its shortest side in the Z-axis direction. The directions of the X-axis, Y-axis, and Z-axis are shown only in FIG. 16 and omitted in FIGS. 13 to 15 . However, the X-axis, Y-axis, and Z-axis are defined in FIGS. 13 to 15 in the same way as in FIG. 16 . The terms "upper" and "lower" refer to the positive and negative sides in the Z-axis direction, and the side where the power feed coil and power receiving coil face each other is considered to be the top.

[0087] Furthermore, the use of "approximately rectangular parallelepiped-shaped magnetic material" means that the material does not have to be strictly rectangular as long as it appears to be roughly rectangular overall, such as if each corner of the rectangular parallelepiped is slightly rounded, or if the intersecting edges are slightly diagonal rather than at right angles.

[0088] Here, two spiral coils 321 and 322, and 421 and 422 are spiral coils that form a double spiral. In FIG. 16 , of the two stepped spiral coils 321 and 322, coil 321 is arranged on the left side and coil 322 is arranged on the right side. The left coil 321 is stepped in the Z-axis direction so that the inner side (the side closest to the right coil 322) of coil 321 is located above the magnetic core 100 (the positive side in the Z-axis direction) and the outer side (the side farthest from the right coil 322) is located below the magnetic core 100 (the negative side in the Z-axis direction). The right coil 322 is stepped in the Z-axis direction so that the inner side (the side closest to the left coil 321) of coil 322 is located above the magnetic core 100 (the positive side in the Z-axis direction) and the outer side (the side farthest from the left coil 321) is located near the lower side (the negative side in the Z-axis direction) of the magnetic core 100.

[0089] These two stepped spiral coils 321 and 322 are arranged at a slight distance in the X-axis direction, and one coil winding (solenoid coil) 111, 211 is arranged between these two spiral coils 321 and 322, wound multiple times around the magnetic core 100 as its axis so that the coils do not overlap in the Y-axis and Z-axis directions.

[0090] The coil structures shown in Figures 14 and 15 are coil structures that the applicant of the present application has devised as an application of Figure 13, and are also disclosed in International Patent Application PCT / JP2023 / 44946 by the applicant of the present application. Both of these coil structures, which include a double spiral coil and a solenoid coil, will be referred to as "hybrid coils."

[0091] Generally, the shape of the coil used for wireless power supply is often a spiral, circular single spiral coil (or pancake coil), but one of the features of the second embodiment of the present invention is that the coil is a double spiral coil with magnetic poles on both ends, or a hybrid coil. By using a double spiral coil or hybrid coil that uses a soft magnetic material as a core in this way, the coil can be made small in size, and therefore can be installed inside a small power supply target.

[0092] However, as described above, in the first embodiment, 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. However, as shown in FIGS. 10 to 12 , when applying this to a robot arm, if the robot arm is made only of a metal that blocks magnetic fields, it has been found that magnetic flux leaks from the back of the coil and cannot be effectively looped, resulting in a decrease in the magnetic coupling coefficient and preventing the effectiveness of wireless power supply from being achieved.

[0093] Therefore, in this second embodiment, the power feeding coil provided in the power feeding circuit and the power receiving coil provided in the power receiving circuit are each a double-spiral or hybrid coil having magnetic poles at both ends. In this case, even if there is metal on the back surface of the coil, the proportion of magnetic flux that self-loops on the back surface of the coil is very small. Therefore, it has been confirmed that when the power receiving coil is rotated relative to the power feeding coil, or when the power feeding coil is rotated relative to the power receiving coil, PT symmetry can be preserved and wireless power can always be fed while maintaining constant transmitted power.

[0094] 17 is a diagram showing the positional relationship between coils when the center of rotation O is located at one of the two magnetic poles at both ends of the double spiral type power receiving coil shown in FIG. 13 in a rotating power supply target in a wireless power supply system utilizing PT symmetry according to the second embodiment of the present invention. As in FIG. 4 of the first embodiment, the magnetic coupling coefficient k ｍ An example of a coil arrangement in which the value of the power supply coil 31 does not become 0 (zero) is shown in Fig. 17. In Fig. 17, the power supply coil 31 is shown in the foreground and the power receiving coil 41 is shown in the background, which is the opposite of that shown in Fig. 4, and the power receiving coil rotates relative to the power supply coil.

[0095] As in Fig. 4 in the first embodiment, the state in which the axis 31L of the power supply coil 31 and the axis 41L of the power receiving coil 41, shown by dashed lines, are parallel is defined as a rotation angle of 0 degrees, and the angle between the two axes is defined as a rotation angle θ (this also applies to Fig. 18 , which will be described later). Also in Fig. 17 , the dashed line shows the power receiving coil before rotation, in which the axis 31L of the power supply coil 31 and the axis of the power receiving coil (the dashed power receiving coil does not show a symbol or axis) are parallel before rotation. The power receiving coil after being rotated by the rotation angle θ around one of the two magnetic poles at both ends of the power receiving coil 41 (magnetic pole 202 in the example shown in Fig. 17 ) is the power receiving coil 41 shown by the solid line (this also applies to Fig. 18 , which will be described later).

[0096] Although not shown, in the case of the positional relationship of the coils as shown in FIG. 17, 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 41, the magnetic coupling coefficient k 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.

[0097] In this way, the power supply coil 31 and the power receiving coil 41 are arranged so that the center of rotation of the power receiving coil 41 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 41. Therefore, when the power receiving coil 41 is rotated relative to the power supply coil 31, 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 keeping the transmission power constant.

[0098] 18 is a diagram showing the positional relationship between coils when the center of rotation O is located at one of the two magnetic poles at both ends of the hybrid-type power receiving coil shown in FIG. 15 in a rotating power supply target in a wireless power supply system utilizing PT symmetry according to the second embodiment of the present invention. In the hybrid-type coil shown in FIG. 15 as well, the magnetic coupling coefficient k ｍ An example of a coil arrangement in which does not become 0 (zero) is shown in FIG.

[0099] 2, 4, and 17, the broken line in Fig. 18 shows the power receiving coil before rotation, and before rotation, the axis 31L of the power feeding coil 31 and the axis of the power receiving coil (the symbol and axis are not shown for the broken line power receiving coil) are parallel. Furthermore, the power receiving coil after being rotated by a rotation angle θ around one of the two magnetic poles at both ends of the power receiving coil 41 (magnetic pole 202 in the example shown in Fig. 18) is the power receiving coil 41 shown by the solid line.

[0100] Although not shown here, in the case of the positional relationship of the coils as shown in FIG. 18, 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 41, the magnetic coupling coefficient k 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.

[0101] In this way, the power supply coil 31 and the power receiving coil 41 are arranged so that the center of rotation of the power receiving coil 41 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 41. Therefore, when the power receiving coil 41 is rotated relative to the power supply coil 31, 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 keeping the transmission power constant.

[0102] That is, as shown in FIGS. 17 and 18 , similar to the first embodiment shown in FIG. 4 , the second embodiment of the present invention is characterized in that 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.

[0103] In this way, the power supply coil 31 and the power receiving coil 41 are arranged so that the center of rotation of the power receiving coil 41 is located near one of the two magnetic poles (201, 202) at both ends of the power receiving coil 41. This allows 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 keeping the transmission power constant.

[0104] 19 is a schematic perspective view showing a specific example in which the hybrid-type power supply coil and power receiving coil shown in Fig. 15 are attached to the wall surface of a metal robot arm in a wireless power supply system using magnetic field resonance and utilizing PT symmetry according to embodiment 2 of the present invention. In Fig. 19, the robot arm that is the rotation target is made entirely of metal, and the hybrid-type power supply coil and power receiving coil shown in Fig. 15 are arranged on the wall surface of the metal robot arm so that the center of rotation of the power receiving coil is located near one of the magnetic poles.

[0105] 19 shows that the power supply coil 31 is fixed to the robot arm 5 and the power receiving coil 41 is fixed to the robot arm 6, but because the power receiving coil 41 needs to be attached so as to face the power supply coil 31, the power receiving coil 41 is shown fixed to a coil attachment frame 7 attached to the robot arm 6. Note that the hybrid coil shown in FIG. 15 normally uses a coil former for winding and fixing the coil, but in FIG. 19, the coil former is omitted to make it easier to see that the hybrid power supply coil 31 and power receiving coil 41 shown in FIG. 15 are attached.

[0106] When the rotational object is not made solely of metal, i.e., when it is made of a material other than metal, such as resin, or when it partially contains metal, PT symmetry can be preserved even when a coil is built into the rotational object (robot arm) as shown in FIGS. 10 to 12 in the first embodiment. However, when the rotational object is made solely of metal, the built-in coil results in a state where the entire periphery is surrounded by metal, which may prevent PT symmetry from being preserved. Therefore, in such cases, by attaching the power supply coil and power receiving coil of the second embodiment to the wall surfaces of the rotationally symmetric robot arms 5 and 6, as shown in FIG. 19, PT symmetry can be reliably preserved and wireless power can be constantly transferred wirelessly. The experimental results for this specific example confirmed that PT symmetry is preserved and efficient wireless power transfer is possible even when a metal robot arm is rotated.

[0107] As described above, according to the wireless power feed system of the second embodiment of the present invention, as in the first embodiment, 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 for adjustment or control of 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.

[0108] In the second embodiment of the present invention, a robot arm has been described as an example of a rotating target to be powered, but the present invention is not limited to a robot arm and can be applied to any rotating target to which wireless power supply is required, such as a multi-joint arm stand on the tip of which a light bulb, camera, monitor, etc. Furthermore, according to the second embodiment, compared to the first embodiment, even if the rotating target to be powered is made of only metal, PT symmetry can be preserved and wireless power can be supplied efficiently.

[0109] Furthermore, in the second 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.

[0110] Embodiment 3. Fig. 20 is an explanatory diagram showing an example of the schematic configuration of a power supply coil 31 and a power receiving coil 21 used in a wireless power supply system utilizing PT symmetry according to embodiment 3 of the present invention. Fig. 20 shows an example in which the hybrid-type coil described in Figs. 15 and 16 of embodiment 2 is used as the power supply coil 31, and the solenoid-type coil described in embodiment 1 is used as the power receiving coil 21. In this way, the power supply coil and the power receiving coil do not necessarily have to have the same shape, and embodiment 3 is a combination of embodiment 1 and embodiment 2.

[0111] In other words, this third embodiment is an example of a pattern in which one of the power supply coil and the power receiving coil is the solenoid type or helical type coil described in the first embodiment, and the other is the double spiral type or hybrid type coil described in the second embodiment.

[0112] As shown in FIG. 20 , the power supply coil 31 provided in the power supply circuit may be a double-spiral or hybrid coil having magnetic poles at both ends, and the power receiving coil 21 provided in the power receiving circuit may be a solenoid or helical coil having magnetic poles at both ends, or conversely, the power supply coil may be a solenoid or helical coil having magnetic poles at both ends, and the power receiving coil may be a double-spiral or hybrid coil having magnetic poles at both ends.

[0113] 21 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 embodiment 3 of the present invention, when the center of rotation O is located at one of two magnetic poles at both ends of solenoid-type power receiving coil 21 shown in FIG. 20. As with FIG. 4 in embodiment 1 and FIGS. 17 and 18 in embodiment 2, the magnetic coupling coefficient k ｍAn example of a coil arrangement in which the value of the power supply coil 31 does not become 0 (zero) is shown in Fig. 21. In Fig. 21, similarly to Figs. 17 and 18, the power supply coil 31 is shown in the foreground and the power receiving coil 21 is shown in the background, and the power receiving coil 21 is assumed to rotate with respect to the power supply coil 31.

[0114] 4 of the first embodiment and FIGS. 17 and 18 of the second embodiment, the state in which the axis 31L of the power supply coil 31 and the axis 21L of the power receiving coil 21, shown by the dashed dotted lines, are parallel is defined as a rotation angle of 0 degrees, and the angle between the two axes is defined as a rotation angle θ. Also in FIG. 21 , the broken line shows the power receiving coil before rotation, in which the axis 31L of the power supply coil 31 and the axis of the power receiving coil (the broken line power receiving coil does not show a symbol or axis) are parallel before rotation. The power receiving coil after being rotated by the 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. 21 ) is the power receiving coil 21 shown by the solid line.

[0115] Although not shown here, in the case of the positional relationship of the coils as shown in FIG. 21, 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, the magnetic coupling coefficient k 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.

[0116] In this way, the power supply coil 31 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 31, 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 keeping the transmission power constant.

[0117] That is, as shown in FIG. 21 , similarly to the first embodiment shown in FIG. 4 and the second embodiment shown in FIGS. 17 and 18 , the third embodiment of the present invention is characterized in that 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.

[0118] In this way, the power supply coil 31 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. This allows 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 keeping the transmission power constant.

[0119] Here, we will explain the advantages of using a solenoid or helical coil as one of the receiving coil and the feeding coil, and a double spiral or hybrid coil as the other, as in this embodiment 3. First, a solenoid or helical coil has the advantage of being simple in structure and requiring fewer coil turns, resulting in an overall light weight. Furthermore, by using a double spiral or hybrid coil as the other coil, as described in embodiment 2, even if the rotating object is entirely made of metal and there is metal on the back surface of the coil, the magnetic flux leaking from the back surface of the double spiral or hybrid coil is not very large.

[0120] 22 is a schematic perspective view showing a specific example in which the hybrid-type power supply coil and solenoid-type power receiving coil shown in Fig. 20 are attached to the wall surface of a metal robot arm in a magnetic field resonance-based wireless power supply system utilizing PT symmetry according to embodiment 3 of the present invention. In Fig. 22 , the robot arm that is the rotation target is made entirely of metal, and the back surface of the hybrid-type power supply coil 31 shown in Fig. 20 is placed on the wall surface of the metal robot arm 5. The solenoid-type power receiving coil 21 is placed on the wall surface of the robot arm 6 that rotates relative to the robot arm 5 so as to face the power supply coil 31 attached to the robot arm 5, and the center of rotation of the power receiving coil 21 is located near one of the magnetic poles of the power receiving coil 21.

[0121] 22, the power receiving coil 21 is fixed to the robot arm 6. However, since the power receiving coil 21 needs to be attached so as to face the power supply coil 31, the power receiving coil 21 is shown fixed to a coil attachment fixing frame 7 attached to the robot arm 6, similar to the power receiving coil 41 in FIG. 19.

[0122] When the rotational symmetry is not made solely of metal, i.e., when the rotational symmetry is made of a material other than metal, such as resin, or when metal is partially used, PT symmetry can be preserved even when a coil is built into the rotational symmetry robot arm, as shown in Figures 10 to 12 in the first embodiment. However, when the rotational symmetry is made solely of metal, the built-in coil results in a state where the entire periphery is surrounded by metal, making it impossible to preserve PT symmetry. Therefore, in such cases, by attaching the power supply coil and power receiving coil of the third embodiment to the wall surface of the rotational symmetry robot arm, as shown in Figure 22, it is possible to achieve a reduction in weight while preserving PT symmetry and constantly transmitting wireless power. The experimental results for this specific example confirmed that PT symmetry is preserved and wireless power can be transmitted efficiently even when a metal robot arm is rotated.

[0123] That is, as in this third embodiment, when one of the power supply coil and power receiving coil used in a wireless power supply system utilizing PT symmetry is a solenoid or helical coil and the other is a double spiral or hybrid coil, the overall weight of the coil can be reduced, and even if the rotational symmetry is made of metal and there is metal on the back of the double spiral or hybrid coil, it is possible to preserve PT symmetry and always supply power wirelessly while maintaining a constant transmission power.

[0124] As described above, according to the wireless power feed system of the third embodiment of the present invention, as in the first and second embodiments, 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 for adjustment or control of 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.

[0125] Note that in the third embodiment of the present invention, the rotating target to be powered is not limited to a robot arm, and can be any rotating target requiring wireless power supply, such as a multi-joint arm stand with a light bulb, camera, monitor, or the like attached to its tip. Furthermore, compared to the first embodiment, the third embodiment can preserve PT symmetry and efficiently supply power wirelessly even if the rotating target to be powered is made of metal only. Furthermore, compared to the second embodiment, the third embodiment has the advantage of being lightweight overall, since either the power supply coil or the power receiving coil is a solenoid or helical coil.

[0126] Furthermore, in the third 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.

[0127] It should be noted that within the scope of the present invention, the embodiments may be freely combined, or any of the components of the embodiments may be modified, or any of the components of the embodiments may be omitted.

[0128] 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.

[0129] 11, 31 Power supply coil 11L, 31L Axis of power supply coil 11, 31 21, 41 Power receiving coil 21L, 41L Axis of power receiving coil 21, 41 100, 200 Magnetic core 101, 102, 201, 202 Magnetic pole 111, 211 Winding (solenoid coil) 311, 312, 411, 412 Planar spiral coil constituting double spiral 321, 322, 421, 422 Stepped spiral coil constituting double spiral 5, 6 Robot arm 7 Fixing frame for mounting coil

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.

3. 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 double-spiral or hybrid coils 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 the two magnetic poles at both ends of the power receiving coil.

4. 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 double-spiral type or hybrid type 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 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.

5. A wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), wherein one of the power supply coil provided in the power supply circuit and the power receiving coil provided in the power receiving circuit is a solenoid or helical coil having magnetic poles at both ends, and the other coil is a double spiral or hybrid 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 near one of the two magnetic poles at both ends of the power receiving coil.

6. A wireless power supply system for a rotating target that utilizes Parity-Time symmetry (hereinafter referred to as "PT symmetry"), wherein one of the power supply coil provided in the power supply circuit and the power receiving coil provided in the power receiving circuit is a solenoid or helical coil having magnetic poles at both ends, and the other coil is a double spiral or hybrid 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 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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