WO2012132144A1

WO2012132144A1 - Charging platform

Info

Publication number: WO2012132144A1
Application number: PCT/JP2011/079619
Authority: WO
Inventors: 恭三寺尾
Original assignee: 三洋電機株式会社
Priority date: 2011-03-30
Filing date: 2011-12-21
Publication date: 2012-10-04
Also published as: JP2014116988A

Abstract

[Problem] To accurately detect the position of a power reception coil by means of echo signals guided by position detection coils. [Solution] In a charging platform, the position of the power reception coil (51) of a device (50) with built-in battery and placed on an upper surface plate (21) is detected by means of a position detection control device (14) and power is delivered by bringing a power transmission coil (11) close to the power reception coil (51) as a consequence of controlling a moving mechanism (13). The power detection control device (14) supplies a pulse signal from a detection pulse generating circuit (31) to a plurality of position detection coils (30) arranged on the upper surface plate (21) and determines the position of the reception coil (51) with an identification circuit (33) by receiving with a reception circuit (32) the echo signals guided by the position detection coils from the power reception coil (51). In the position detection control device (14), a portion of the position detection coils (30) disposed adjacent to one another is arranged so as to overlap with the adjacent position detection coil (30) and the position of the power reception coil (51) is determined on the basis of the level of the echo signal of the position detection coil (30) guiding the maximum level echo signal and the echo signals of the position detection coils (30) disposed on both sides of the aforementioned position detection coil (30) guiding the maximum level echo signal.

Description

Charging stand

The present invention relates to a charging stand on which a battery built-in device such as a battery pack or a mobile phone is placed on top and the power is transferred by electromagnetic induction to charge the built-in battery.

A charging stand has been developed that carries power from the power transmission coil to the power receiving coil by the action of electromagnetic induction and charges the internal battery. This charging stand incorporates a power transmission coil that is excited by an AC power source. A battery built-in device such as a battery pack or a portable device set on a charging base has a power receiving coil that is electromagnetically coupled to a power transmission coil of the charging base. The battery built-in device also has a built-in circuit for rectifying the alternating current induced in the power receiving coil and supplying the battery to the battery for charging. According to this structure, the battery pack can be charged in a non-contact state by placing the battery pack on the charging stand.

The above charging stand can be conveniently used by moving the power transmission coil to the position of the power reception coil. This is because the user can set the battery built-in device at a free position on the charging stand and charge the power receiving coil of the battery built-in device close to the power receiving coil. A charging stand has been developed to achieve this. (See Patent Document 1)

JP 2009-247194 A

The above charging stand includes a moving mechanism for moving the power transmission coil so as to approach the power receiving coil. In order to control the moving mechanism, a position detection controller for detecting the position of the power receiving coil and controlling the transfer mechanism is provided. In order to detect the position of the power receiving coil, the position detection controller fixes a plurality of position detection coils to the upper surface plate of the case on which the battery built-in device is placed. The position detection coils are fixed at regular intervals. A detection pulse generating circuit for supplying a pulse signal is connected to each position detection coil. When a pulse signal is supplied from the detection pulse generation circuit to the position detection coil, a resonance current flows through the resonance circuit formed by the receiving coil and the parallel capacitor by being excited by this pulse signal, and an echo is sent from the receiving coil to the position detection coil. A signal is output. Since the echo signal is output from the power receiving coil excited by the pulse signal, the echo signal is guided to the position detection coil with a certain time delay from the pulse signal. In order to receive this echo signal, a receiving circuit is connected to the position detection coil. The echo signal received by the receiving circuit is input to an identification circuit that detects the position of the receiving coil. The identification circuit determines the position of the power receiving coil from the level of the input echo signal.

The above position detection controller outputs a pulse signal to each position detection coil in turn by a detection pulse generation circuit. The identification circuit detects the position of the power receiving coil from the level of the echo signal induced in each position detection coil. This is because the echo signal induced in the position detection coil that is closest to the power receiving coil is the largest. As shown in FIG. 11, when the power receiving coil 151 is in the middle of the two position detection coils 130, as shown by the point B in the figure, the first X-axis position detection coil 130A and the second X-axis position The level of the echo signal induced in the detection coil 130A is the same. That is, in each X-axis position detection coil 130A, the level of the echo signal induced when the power receiving coil 51 is closest is the strongest, and the level of the echo signal decreases as the power receiving coil moves away. Therefore, it can be determined which X-axis position detection coil the power receiving coil is closest to which X-axis position detection coil has the strongest echo signal level. In addition, when an echo signal is induced in the two X-axis position detection coils, the echo signal is guided to the X-axis position detection coil in which direction from the X-axis position detection coil that detects a strong echo signal, It is possible to determine in which direction the power receiving coil is shifted from the X-axis position detection coil having a strong echo signal, and it is possible to determine the relative position between the two X-axis position detection coils based on the level ratio of the echo signal. For example, if the level ratio of echo signals of two X-axis position detection coils is 1, it can be determined that the power receiving coil is located at the center of the two X-axis position detection coils. If the level of the echo signal of one X-axis position detection coil is the highest and the level of the echo signal of the adjacent X-axis position detection coil is equal, it means that it is directly above the highest level X-axis position detection coil. In the meantime, it can be calculated by a quadratic or cubic equation between the higher level of the left and right echo signals and the strongest echo signal level.

The above position detection controller can detect the echo signal detected by the two position detection coils, that is, the position of the power receiving coil set between the two position detection coils relatively accurately. However, the leftmost end and the rightmost end have a drawback that the position of the power receiving coil set near the center of the position detecting coil cannot be detected accurately. In the state where the power receiving coil is set at the center portion of the position detection coil, the echo signal of the position detection coils on both sides becomes 0 level region (S), and no echo signal is induced in the position detection coils on both sides, and the power receiving coil This is because the position is determined only by the echo signal level of the position detection coil that is the maximum level. The echo signal at the maximum level varies not only with the position of the receiving coil relative to the position detection coil, but also with the size and inductance of the receiving coil, and the distance away from the top plate. If the position is determined, the position of the power receiving coil cannot be accurately detected. Further, as shown in FIG. 12, the level of the echo signal has a small amount of change in the peak vicinity region where the maximum level is reached, and the position cannot be accurately determined if the position of the power receiving coil is determined from that level.

Therefore, the charging stand of the cited document 1 has a drawback that the position of the power receiving coil cannot be accurately determined only by the position detecting coil. If the position of the power receiving coil cannot be accurately detected, the power transmitting coil cannot be brought close to the exact position of the power receiving coil, and the relative position between the power transmitting coil and the power receiving coil is shifted, so that power cannot be efficiently conveyed. In order to eliminate this adverse effect, the conventional charging stand is provided with a corrected position detection controller for more accurately detecting the position of the power receiving coil in order to more accurately detect the position of the power receiving coil.

In the above charging stand, the position detection controller roughly detects the position of the power receiving coil, brings the power transmission coil closer to the power receiving coil, and then the corrected position detection controller detects the position of the power receiving coil more accurately. The power transmission coil is moved closer to the power reception coil. The correction position detection controller controls the moving mechanism by accurately detecting the position of the power receiving coil from the oscillation frequency of the oscillation circuit using an AC power source that outputs an AC signal to the power transmission coil as a self-excited oscillation circuit. The correction position detection controller detects the oscillation frequency of the AC power supply by moving the power transmission coil. FIG. 13 shows the characteristic that the oscillation frequency of the self-excited oscillation circuit changes. This figure shows the change in the oscillation frequency with respect to the relative displacement between the power transmission coil and the power reception coil. As shown in this figure, the oscillation frequency of the self-excited oscillation circuit is set to be the highest at the position where the power transmission coil is closest to the power reception coil, and to be lowered as the relative position is shifted. Therefore, the corrected position detection controller can move the power transmission coil, stop at the position where the oscillation frequency is highest, and approach the power transmission coil to the power reception coil. This charging stand requires a dedicated circuit configuration for more accurately detecting the position of the power receiving coil in order to bring the power transmitting coil closer to the power receiving coil. For this reason, there exists a fault which a position detection controller becomes complicated and a manufacturing cost becomes high.

The present invention was developed for the purpose of solving the above disadvantages. An important object of the present invention is to provide a charging stand that can accurately detect the position of a power receiving coil with an echo signal induced in a position detecting coil and efficiently carry power by bringing the power transmitting coil close to the power receiving coil. There is.

Means for Solving the Problems and Effects of the Invention

The charging base of the present invention is a charging base for the battery built-in device 50 including the battery 52 that is charged by the power conveyed to the power receiving coil 51. This charging stand has a power transmission coil 11 connected to the AC power supply 12 and carrying electromotive force in the power receiving coil 51, and has a power transmission coil 11 and a top plate 21 on which the battery built-in device 50 is placed. The position of the power receiving coil 51 of the battery built-in device 50 mounted on the case 20, the moving mechanism 13 that is built in the case 20 and moves the power transmission coil 11 along the inner surface of the upper surface plate 21, and is detected. And position detection controllers 14 and 64 for controlling the moving mechanism 13 to bring the power transmission coil 11 closer to the power reception coil 51. The position detection controllers 14 and 64 include a plurality of position detection coils 30 arranged at predetermined intervals on the back side of the top plate 21, and a detection pulse generation circuit 31 that supplies a pulse signal as a position detection signal to the position detection coil 30. A receiving circuit 32 that receives an echo signal that is excited by the pulse signal supplied from the detection pulse generation circuit 31 to the position detection coil 30 and is induced from the power reception coil 51 to the position detection coil 30; And an identification circuit 32 for determining the position of the power receiving coil 51 from the received echo signal. The position detection controllers 14 and 64 are arranged such that a part of the position detection coil 30 formed by the position detection coil 30 adjacent to the adjacent position detection coil 30 is overlapped. The position of the power receiving coil 51 is determined from the position detection coil 30 from which the echo signal of the maximum level is induced and the level of the echo signal of the position detection coil 30 disposed on both sides thereof.

The charging base described above has a feature that the position of the power receiving coil can be accurately detected by an echo signal induced in the position detecting coil, and the power transmitting coil can be brought close to the power receiving coil to efficiently carry power. Position it over the charging stand is, while arranged to overlap the next position detection coil part of the position detection coil adjacent are disposed identification circuit, the maximum level of the echo signal is derived This is because the position of the power reception coil is determined from the detection coil and the level of the echo signal of the position detection coil disposed on both sides of the detection coil. By arranging a part of the position detection coils arranged adjacent to each other so as to overlap each other, as shown in FIG. 10, an area where the level of the echo signal induced in one position detection coil becomes the maximum level, that is, In the peak vicinity region, the level of the echo signal induced in the position detection coils arranged on both sides of the peak detection region can be increased, and the width of the zero level region of the echo signal of the position detection coil on both sides in the peak vicinity region can be reduced. Further, in the vicinity of the peak, the identification circuit determines the position of the receiving coil not only from the echo signal of the maximum level but also from the level of the echo signal induced in the position detection coils on both sides. The position of the power receiving coil can be determined more accurately.

In the charging stand according to the present invention, the position detection coil 30 is an elongated coil having a straight portion, and the adjacent position detection coils 30 are arranged so as to be displaced in a direction perpendicular to the longitudinal direction of the coils and adjacent to each other so as to overlap each other. Thus, the overlapping amount (d) of the position detection coils 30 can be set to 1/2 to 9/10 of the lateral width (W) of the elongated coil.
The above charging stand can accurately detect the position of the power receiving coil in the direction in which the elongated position detecting coils are arranged. In particular, it is possible to accurately detect the position of the power receiving coil by arranging the linear portions constituting the position detecting coil at equal intervals. In addition, by reducing the overlap amount (d) between adjacent position detection coils to be smaller than the lateral width (W) of the position detection coil, the level of the echo signals of the position detection coils on both sides in the peak vicinity region is increased to receive power. The position of the coil can be accurately detected.

In the charging stand of the present invention, the overlapping amount (d) of the position detection coils 30 adjacent to each other so that the position detection coils overlap with each other can be set to 2/3 of the lateral width (W) of the elongated coil.
In the above charging stand, the overlapping amount (d) of the position detection coils is set to 2/3 of the lateral width (W) of the coils, so that the position detection coils are efficiently arranged in an overlapping state, and the both sides of the peak vicinity region are arranged. The position of the power receiving coil can be accurately detected from the echo signal of the position detecting coil.

In the charging stand of the present invention, the position detection coil 30 has a plurality of X-axis position detection coils 30A that detect the position of the power receiving coil 51 in the X-axis direction, and a plurality of Y-axis position detection coils that detect the position in the Y-axis direction. 30B.
The above charging stand can accurately detect the positions in the X-axis direction and the Y-axis direction of the power receiving coil set on the upper surface plate by both the X-axis position detection coil and the Y-axis position detection coil. For this reason, this charging stand can set the device with a built-in battery at a free position in the X-axis direction and the Y-axis direction of the upper surface plate and allow the power transmission coil to approach the power reception coil.

In the charging stand of the present invention, the X-axis position detection coil 30A can be an elongated coil in the Y-axis direction, and the Y-axis position detection coil 30B can be an elongated coil in the X-axis direction.
The above charging stand can detect the positions of the receiving coil set on the top plate in the X-axis direction and the Y-axis direction over a wider range by widening the detection area of the X-axis position detection coil and the Y-axis position detection coil. .

It is a schematic perspective view of the charging stand concerning one Example of this invention. It is a schematic block diagram of the charging stand concerning one Example of this invention. It is a vertical longitudinal cross-sectional view of the charging stand shown in FIG. It is a vertical cross-sectional view of the charging stand shown in FIG. It is a circuit diagram which shows the position detection controller of the charging stand concerning one Example of this invention. It is a block diagram of the charging stand and battery built-in apparatus concerning one Example of this invention. It is the schematic which shows the state which the position detection coil shown in FIG. 5 overlaps. It is a figure which shows an example of the echo signal output from the receiving coil excited with the pulse signal. It is a circuit diagram which shows the position detection controller of the charging stand concerning the other Example of this invention. It is a figure which shows the level of the echo signal induced | guided | derived to the position detection coil of the position detection controller shown in FIG. It is a figure which shows the level of the echo signal induced | guided | derived to the position detection coil of the conventional charging stand. It is a figure which shows the level of the echo signal with respect to the relative position shift of a power transmission coil and a receiving coil. It is a figure which shows the change of the oscillation frequency with respect to the relative position shift of a power transmission coil and a receiving coil.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a charging stand for embodying the technical idea of the present invention, and the present invention does not specify the charging stand as follows. In addition, the member shown by the claim is not what specifies the member of embodiment. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the constituent members described in the embodiments are not intended to limit the scope of the present invention only to the description unless otherwise specified. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing. In addition, the contents described in some examples and embodiments may be used in other examples and embodiments.

1 to 6 show a schematic configuration diagram and a principle diagram of a charging stand. As shown in FIGS. 1 and 6, the charging stand 10 places the battery built-in device 50 on the charging stand 10 and charges the built-in battery 52 of the battery built-in device 50 by magnetic induction. The battery built-in device 50 includes a power receiving coil 51 that is electromagnetically coupled to the power transmitting coil 11. A battery 52 that is charged with electric power induced in the power receiving coil 51 is incorporated. Here, the battery built-in device 50 may be a battery pack.

FIG. 6 shows a circuit diagram of the battery built-in device 50. The battery built-in device 50 has a capacitor 53 connected in parallel with the power receiving coil 51. The capacitor 53 and the power receiving coil 51 constitute a parallel resonance circuit 54. The battery built-in device 50 of FIG. 6 includes a rectifier circuit 57 including a diode 55 that rectifies an alternating current output from the power receiving coil 51, a smoothing capacitor 56 that smoothes the rectified pulsating current, and an output from the rectifier circuit 57. And a charge control circuit 58 for charging the battery 52 with a direct current. The charge control circuit 58 detects the full charge of the battery 52 and transmits a full charge signal indicating that the battery 52 is fully charged to the charging stand 10. The charging stand 10 detects a full charge signal and stops charging.

As shown in FIGS. 1 to 6, the charging stand 10 includes a power transmission coil 11 that is connected to an AC power source 12 and conveys power to the power receiving coil 51, and the power transmission coil 11. A case 20 having an upper surface plate 21 on which the power receiving coil 51 is mounted, a moving mechanism 13 that is built in the case 20 and moves the power transmission coil 11 along the inner surface of the upper surface plate 21 to approach the power receiving coil 51, and the upper surface plate 21. And a position detection controller 14 that detects the position of the battery built-in device 50 to be mounted and controls the moving mechanism 13 to bring the power transmission coil 11 closer to the power receiving coil 51 of the battery built-in device 50. The charging stand 10 includes a power transmission coil 11, an AC power source 12, a moving mechanism 13, and a position detection controller 14 in a case 20.

The charging stand 10 charges the built-in battery 52 of the battery built-in device 50 by the following operation.
(1) When the battery built-in device 50 is placed on the upper surface plate 21 of the case 20, the position detection controller 14 detects the position of the battery built-in device 50.
(2) The position detection controller 14 that has detected the position of the battery built-in device 50 controls the moving mechanism 13 to move the power transmission coil 11 along the upper surface plate 21 with the moving mechanism 13, thereby Approach the power receiving coil 51.
(3) The power transmission coil 11 approaching the power reception coil 51 is electromagnetically coupled to the power reception coil 51 and carries AC power to the power reception coil 51.
(4) The battery built-in device 50 rectifies the AC power of the power receiving coil 51 and converts it into direct current, and charges the built-in battery 52 with this direct current.

The charging stand 10 that charges the battery 52 of the battery built-in device 50 through the above operation has the power transmission coil 11 connected to the AC power supply 12 built in the case 20. The power transmission coil 11 is disposed below the upper surface plate 21 of the case 20 and is disposed so as to move along the upper surface plate 21. The efficiency of power transfer from the power transmission coil 11 to the power reception coil 51 can be improved by bringing the power transmission coil 11 closer to the power reception coil 51. Therefore, the power transmission coil 11 is disposed below the top plate 21 and as close to the top plate 21 as possible. Since the power transmission coil 11 moves so as to approach the power reception coil 51 of the battery built-in device 50 placed on the upper surface plate 21, the power transmission coil 11 is disposed so as to be movable along the lower surface of the upper surface plate 21.

The case 20 containing the power transmission coil 11 is provided with a flat top plate 21 on which the battery built-in device 50 is placed on the top surface. The charging stand 10 shown in the figure is disposed horizontally with the entire top plate 21 as a flat surface. The upper surface plate 21 has such a size that various battery built-in devices 50 having different sizes and outer shapes can be placed thereon, for example, a quadrangle having a side of 5 cm to 30 cm, or a circle having a diameter of 5 cm to 30 cm. The charging stand according to the present invention can also charge a built-in battery in order by mounting a plurality of battery-equipped devices together so that the top plate is enlarged, that is, a size capable of simultaneously loading a plurality of battery-equipped devices. . The top plate can also be provided with a peripheral wall around it, and a battery built-in device can be set inside the peripheral wall to charge the built-in battery.

The power transmission coil 11 is wound in a spiral shape on a surface parallel to the upper surface plate 21 and radiates an alternating magnetic flux above the upper surface plate 21. The power transmission coil 11 radiates an alternating magnetic flux orthogonal to the upper surface plate 21 above the upper surface plate 21. The power transmission coil 11 is supplied with AC power from the AC power source 12 and radiates AC magnetic flux above the upper surface plate 21. The power transmission coil 11 can increase the inductance by winding a wire around a core 15 made of a magnetic material. The core 15 is made of a magnetic material such as ferrite having a high magnetic permeability, and has a bowl shape that opens upward. The core 15 of the pot-shaped has a shape that connects the cylindrical portion 15A to place the center of the transmitting coil 11 wound spirally, a cylindrical portion 15B which is disposed outside the bottom. The power transmission coil 11 having the core 15 can concentrate the magnetic flux to a specific portion and efficiently transmit power to the power reception coil 51. However, the power transmission coil does not necessarily need to be provided with a core, and may be an air-core coil. Since the air-core coil is light, a moving mechanism for moving it on the inner surface of the upper plate can be simplified. The power transmission coil 11 is substantially equal to the outer diameter of the power reception coil 51 and efficiently conveys power to the power reception coil 51.

The AC power supply 12 supplies, for example, high frequency power of 20 kHz to 1 MHz to the power transmission coil 11. The AC power supply 12 is connected to the power transmission coil 11 via a flexible lead wire 16. This is because the power transmission coil 11 is moved so as to approach the power reception coil 51 of the battery built-in device 50 placed on the upper surface plate 21. Although not shown, the AC power supply 12 includes an oscillation circuit and a power amplifier that amplifies the AC output from the oscillation circuit.

The power transmission coil 11 is moved by the moving mechanism 13 so as to approach the power reception coil 51. The moving mechanism 13 in FIGS. 1 to 4 moves the power transmission coil 11 along the upper surface plate 21 in the X-axis direction and the Y-axis direction to approach the power receiving coil 51. The moving mechanism 13 shown in the figure rotates the screw rod 23 by the servo motor 22 controlled by the position detection controller 14 to move the nut member 24 screwed into the screw rod 23, and the power transmission coil 11 is moved to the power receiving coil 51. To approach. The servo motor 22 includes an X-axis servo motor 22A that moves the power transmission coil 11 in the X-axis direction, and a Y-axis servo motor 22B that moves the Y-axis direction. The screw rod 23 includes a pair of X-axis screw rods 23A that move the power transmission coil 11 in the X-axis direction, and a Y-axis screw rod 23B that moves the power transmission coil 11 in the Y-axis direction. The pair of X-axis screw rods 23A are arranged in parallel to each other, driven by the belt 25, and rotated together by the X-axis servomotor 22A. The nut member 24 includes a pair of X-axis nut members 24A screwed into the respective X-axis screw rods 23A, and a Y-axis nut member 24B screwed into the Y-axis screw rods 23B. The Y-axis screw rod 23B is coupled so that both ends thereof can be rotated to a pair of X-axis nut members 24A. The power transmission coil 11 is connected to the Y-axis nut member 24B.

Furthermore, the moving mechanism 13 shown in the figure has a guide rod 26 disposed in parallel with the Y-axis screw rod 23B in order to move the power transmission coil 11 in the Y-axis direction in a horizontal posture. Both ends of the guide rod 26 are connected to the pair of X-axis nut members 24A and move together with the pair of X-axis nut members 24A. The guide rod 26 penetrates the guide portion 27 coupled to the power transmission coil 11 so that the power transmission coil 11 can be moved along the guide rod 26 in the Y-axis direction. That is, the power transmission coil 11 moves in the Y-axis direction in a horizontal posture via the Y-axis nut member 24 </ b> B and the guide portion 27 that move along the Y-axis screw rod 23 </ b> B and the guide rod 26 arranged in parallel to each other. To do.

In the moving mechanism 13, when the X-axis servo motor 22A rotates the X-axis screw rod 23A, the pair of X-axis nut members 24A move along the X-axis screw rod 23A, and the Y-axis screw rod 23B and the guide rod 26 is moved in the X-axis direction. When the Y-axis servo motor 22B rotates the Y-axis screw rod 23B, the Y-axis nut member 24B moves along the Y-axis screw rod 23B, and moves the power transmission coil 11 in the Y-axis direction. At this time, the guide part 27 connected to the power transmission coil 11 moves along the guide rod 26 to move the power transmission coil 11 in the Y-axis direction in a horizontal posture. Therefore, the rotation of the X-axis servomotor 22A and the Y-axis servomotor 22B can be controlled by the position detection controller 14, and the power transmission coil 11 can be moved in the X-axis direction and the Y-axis direction. However, the charging stand of the present invention does not specify the moving mechanism as the above mechanism. This is because any mechanism that can move the power transmission coil in the X-axis direction and the Y-axis direction can be used as the moving mechanism.

Furthermore, the charging stand of the present invention does not specify the moving mechanism as a mechanism that moves the power transmission coil in the X-axis direction and the Y-axis direction. That is, the charging stand of the present invention has a structure in which a linear guide wall is provided on the upper plate, and a battery built-in device is placed along the guide wall, and the power transmission coil can be moved linearly along the guide wall. Because it can be done. Although this charging stand is not shown, the power transmission coil can be moved linearly along the guide wall as a moving mechanism that can move the power transmission coil only in one direction, for example, the X-axis direction.

The position detection controller 14 detects the position of the battery built-in device 50 placed on the top plate 21. The position detection controller 14 in FIGS. 1 to 4 detects the position of the power receiving coil 51 built in the battery built-in device 50, and causes the power transmitting coil 11 to approach the power receiving coil 51.

As shown in FIG. 5, the position detection controller 14 generates a plurality of position detection coils 30 fixed to the inner surface of the upper surface plate 21, and generates a detection pulse for supplying a pulse signal as a position detection signal to the position detection coil 30. A receiving circuit 32 that receives an echo signal that is excited by a pulse of a position detection signal supplied from the detection pulse generation circuit 31 to the position detection coil 30 and is output from the power receiving coil 51 to the position detection coil 30; And an identification circuit 33 for determining the position of the power receiving coil 51 from the echo signal received by the receiving circuit 32.

The position detection coil 30 is composed of a plurality of rows of coils, and the plurality of position detection coils 30 are arranged on the back side of the top plate 21. The position detection coil 30 is fixed to the inner surface of the upper surface plate 21 and can be disposed on the back side of the upper surface plate 21. The position detection coil 30 includes a plurality of X-axis position detection coil 30A for detecting the X-axis direction position of the power receiving coil 51, and a plurality of Y-axis position detecting coil 30B for detecting the position of the Y-axis direction. The X-axis position detection coil 30A has a loop shape elongated in the Y-axis direction, and the plurality of X-axis position detection coils 30A are fixed to the inner surface of the upper surface plate 21 at a predetermined interval. The Y-axis position detection coil 30B has a loop shape elongated in the X-axis direction, and the plurality of Y-axis position detection coils 30B are fixed to the inner surface of the upper surface plate 21 at a predetermined interval.

The position detection coil 30 is arranged such that a part of the position detection coil 30 disposed adjacent to the position detection coil 30 is overlapped. The position detection coil 30 of the elongated coil is displaced in a direction orthogonal to the longitudinal direction of the coil, and the adjacent position detection coils 30 are arranged so as to overlap each other. The X-axis position detection coil 30A has an elongated loop shape having a linear portion extending in the Y-axis direction, and the plurality of X-axis position detection coils 30A are displaced in the X-axis direction by a predetermined amount of overlap. It arrange | positions on the back side of the upper surface plate 21 so that it may become (d). The Y-axis position detection coil 30B has an elongated loop shape having a linear portion extending in the X-axis direction, and the plurality of Y-axis position detection coils 30B are displaced in the Y-axis direction by a predetermined amount of overlap. It arrange | positions on the back side of the upper surface plate 21 so that it may become (d).

FIG position detection coil 30 of 5 are overlapping amount of the position detection coil 30 which can produce adjacent to overlap one another (d), and 2/3 of the width of the elongated coil (W). In other words, the position detection coils 30 adjacent to each other are arranged so as to be displaced in the lateral width direction of the coil by 1/3 of the lateral width (W) of the coil. As shown in FIG. 7, the position detection coil 30 has an area where two adjacent position detection coils 30 overlap each other with 2/3 of each position detection coil 30 (hatching A and hatching B in FIG. 7). display), and the three position detection coil 30 overlapping region of adjacent to each other, a third region of each position detection coil 30 (hatching a and the common portion of the hatching B in FIG. 7). In the illustrated position detection coil 30, the overlapping amount (d) between adjacent position detection coils 30 is 2/3 of the width (W) of the elongated coil, but the position detection coils are adjacent to each other so as to overlap each other. The overlap amount (d) between the position detection coils can be set to 1/2 to 9/10 of the lateral width (W) of the elongated coil.

A position detection coil in which the overlap amount (d) between adjacent position detection coils so as to overlap each other is ½ of the lateral width (W) of the coil is not shown, but two adjacent position detection coils overlap each other. The area is a half of each position detection coil. A position detection coil in which the overlap amount (d) between adjacent position detection coils so as to overlap each other is 3/4 of the lateral width (W) of the coil is not shown, but two adjacent position detection coils are not shown. The overlapping area of each position detection coil becomes a 3/4 area, and the overlapping area of the three position detection coils adjacent to each other becomes a 2/4 area of each position detection coil, and the four position detections adjacent to each other. A region where the coils overlap is a quarter of each position detection coil.

Further, the lateral width (W) of the position detection coil 30 is substantially equal to the outer diameter (D) of the power receiving coil 51, or is larger than the outer diameter (D), or is smaller than the outer diameter (D). is doing. The position detection coil 30 can detect the position of the power receiving coil 51 with higher accuracy by narrowing the center interval (d).

The detection pulse generation circuit 31 outputs a pulse signal to the position detection coil 30 at a predetermined timing. The position detection coil 30 to which the pulse signal is input excites the power receiving coil 51 that approaches with the pulse signal. The excited power receiving coil 51 outputs an echo signal to the position detection coil 30 with the energy of the flowing current. Accordingly, the position detection coil 30 located near the power receiving coil 51, as shown in FIG. 8, after the pulse signal is input, with a delay of a predetermined time, the echo signal from the receiving coil 51 is induced. The echo signal induced in the position detection coil 30 is output from the reception circuit 32 to the identification circuit 33.

The identification circuit 33 determines whether or not the power receiving coil 51 is approaching the position detection coil 30 using the echo signal input from the receiving circuit 32. When echo signals are induced in the plurality of position detection coils 30, the identification circuit 33 determines that the position detection coil 30 with the highest echo signal level is closest.

The position detection controller 14 shown in FIG. 5 connects each position detection coil 30 to the reception circuit 32 via the switching circuit 34. Since the position detection controller 14 switches the inputs in order and connects them to the plurality of position detection coils 30, the single reception circuit 32 can detect the echo signals of the plurality of position detection coils 30. However, an echo signal can also be detected by connecting a receiving circuit to each position detection coil.

The position detection controller 14 in FIG. 5 connects the plurality of position detection coils 30 in order with the switching circuit 34 controlled by the identification circuit 33 and connects to the receiving circuit 32. The detection pulse generation circuit 31 is connected to the output side of the switching circuit 34 and outputs a pulse signal to the position detection coil 30. The level of the pulse signal output from the detection pulse generation circuit 31 to the position detection coil 30 is extremely higher than the echo signal from the power receiving coil 51. The receiving circuit 32 has a limiter circuit 35 made of a diode connected to the input side. The limiter circuit 35 limits the signal level of the pulse signal input from the detection pulse generation circuit 31 to the reception circuit 32 and inputs the pulse signal to the reception circuit 32. An echo signal having a low signal level is input to the receiving circuit 32 without being limited. The receiving circuit 32 amplifies and outputs both the pulse signal and the echo signal. The echo signal output from the receiving circuit 32 is a signal delayed from the pulse signal by a predetermined timing, for example, several μsec to several hundred μsec. Since the delay time that the echo signal is delayed from the pulse signal is a fixed time, the signal after a predetermined delay time from the pulse signal is used as an echo signal, and the receiving coil 51 approaches the position detection coil 30 from the level of this echo signal. Determine whether or not.

The receiving circuit 32 is an amplifier that amplifies and outputs an echo signal input from the position detection coil 30. The receiving circuit 32 outputs a pulse signal and an echo signal. The identification circuit 33 determines whether or not the power reception coil 51 is set close to the position detection coil 30 from the pulse signal and echo signal input from the reception circuit 32. The identification circuit 33 includes an A / D converter 36 that converts a signal input from the reception circuit 32 into a digital signal. The digital signal output from the A / D converter 36 is calculated to detect an echo signal. The identification circuit 33 detects a signal input after a specific delay time from the pulse signal as an echo signal, and further determines whether the power receiving coil 51 is approaching the position detection coil 30 from the level of the echo signal.

The identification circuit 33 detects the position of the power receiving coil 51 in the X-axis direction by controlling the switching circuit 34 so that the plurality of X-axis position detection coils 30A are sequentially connected to the receiving circuit 32. Each time the identification circuit 33 connects each X-axis position detection coil 30A to the reception circuit 32, the identification circuit 33 outputs a pulse signal to the X-axis position detection coil 30A connected to the identification circuit 33, and a specific delay from the pulse signal. Whether or not the receiving coil 51 is approaching the X-axis position detection coil 30A is determined based on whether or not an echo signal is detected after the time. The identification circuit 33 connects all the X-axis position detection coils 30A to the reception circuit 32, and determines whether or not the power receiving coils 51 are close to the respective X-axis position detection coils 30A. When the power receiving coil 51 approaches one of the X-axis position detection coils 30A, an echo signal is detected in a state where the X-axis position detection coil 30A is connected to the reception circuit 32. Therefore, the identification circuit 33 can detect the position of the power receiving coil 51 in the X-axis direction from the X-axis position detection coil 30A that can detect an echo signal. In a state in which the power receiving coil 51 approaches across the plurality of X-axis position detection coils 30A, echo signals are detected from the plurality of X-axis position detection coils 30A. In this state, the identification circuit 33 determines the position of the power receiving coil 51 in the X-axis direction from the level of echo signals induced in the plurality of X-axis position detection coils 30A. Further, the identification circuit 33 similarly controls the Y-axis position detection coil 30Y to detect the position of the power receiving coil 51 in the Y-axis direction.

The identification circuit 33 controls the moving mechanism 13 from the position in the X axis direction and the position in the Y axis direction to be detected, and moves the power transmission coil 11 to a position approaching the power reception coil 51. The identification circuit 33 controls the X-axis servomotor 22 </ b> A of the moving mechanism 13 to move the power transmission coil 11 to the position of the power reception coil 51 in the X-axis direction. Further, the Y-axis servomotor 22B of the moving mechanism 13 is controlled to move the power transmission coil 11 to the position of the power reception coil 51 in the Y-axis direction.

As described above, the position detection controller 14 moves the power transmission coil 11 to a position approaching the power reception coil 51. Charging stand of the present invention may be charged after approaching the transmitting coil 11 in the position detection controller 14 to the receiving coil 51, a battery 52 to power carrier to the receiving coil 51 from the power transmission coil 11. However, the charging stand further accurately controls the position of the power transmission coil 11 to approach the power receiving coil 51, and then transports power to charge the battery 52.

Further, the position detection controller 64 shown in FIG. 9 causes the discrimination circuit 73 to detect the level of the echo signal induced in each position detection coil 30 with respect to the position of the power receiving coil 51, that is, each position as shown in FIG. A memory circuit 77 is provided for storing the level of an echo signal that is induced after a predetermined time has elapsed by exciting the detection coil 30 with a pulse signal. The position detection controller 64, as compared to the level of the echo signal to detect the level of the echo signal induced in each of the position detection coil 30, and stores the level of the detected echo signal in the storage circuit 77, The position of the power receiving coil 51 is detected.

The position detection controller 64 obtains the position of the power receiving coil 51 from the level of the echo signal induced in each position detection coil 30 as follows. FIG. 10 shows the level of the echo signal induced in the X-axis position detection coil 30A in a state where the power receiving coil 51 is moved in the X-axis direction, and the horizontal axis shows the position of the power receiving coil 51 in the X-axis direction. The vertical axis indicates the level of the echo signal induced in each X-axis position detection coil 30A. The position detection controller 64 detects the level of the echo signal induced in each X-axis position detection coil 30A, and obtains the position of the power receiving coil 51 in the X-axis direction. As shown in this figure, when the power receiving coil 51 is moved in the X-axis direction, the level of the echo signal induced in each X-axis position detection coil 30A changes.

For example, when the power receiving coil 51 is located between the first X-axis position detection coil 30A and the second X-axis position detection coil 30A, as shown by a point a in FIG. 10, the first X-axis position detection coil 30A. And the level of the echo signal induced in the second X-axis position detection coil 30A is the maximum and the same. Further, when the power receiving coil 51 is at a position deviated from the middle between the first X-axis position detection coil 30A and the second X-axis position detection coil 30A, the first X-axis position detection coil 30A and the second X-axis position The level ratio of the echo signal induced in the detection coil 30A changes. Therefore, the position of the power receiving coil 51 can be detected from the level ratio of echo signals induced in the first X-axis position detection coil 30A and the second X-axis position detection coil 30A.

Furthermore, when the power receiving coil 51 is in the center of the second X-axis position detection coil 30A, that is, in the area A in FIG. 10, the level of the echo signal induced in the second X-axis position detection coil 30A is , Become the strongest. However, when the power receiving coil 51 is in the A region, the level variation of the echo signal with respect to the movement distance of the power receiving coil 51 in the X-axis direction is small, and the level of the echo signal varies depending on other factors. When 51 is in the A region, if the position of the power receiving coil 51 is determined only by the level of the echo signal induced in the second X-axis position detection coil 30A, it cannot be accurately determined. Therefore, the identification circuit 33, when in this region, the second not only echo signals induced in the X-axis position detection coil 30A, the first X-axis position detection coils 30A and the third X-axis position detection coil The position of the power receiving coil 51 is also determined from the level of the echo signal induced by 30A. When the power receiving coil 51 is located at the center of the second X-axis position detection coil 30A, the levels of the echo signals induced in the first X-axis position detection coil 30A and the third X-axis position detection coil 30A are equal. Alternatively, the level of the echo signal becomes 0 level. Accordingly, the identification circuit 33 is applied to the first X-axis position detection coil 30A and the third X-axis position detection coil 30A in a state where the echo signal induced in the second X-axis position detection coil 30A is at the maximum level. If the levels of the induced echo signals are equal or both are 0 level, it is determined that the power receiving coil 51 is located at the center of the second X-axis position detection coil 30A. When the position of the power receiving coil 51 is slightly shifted from the center portion of the second X-axis position detection coil 30A, an echo signal that is induced in the first X-axis position detection coil 30A and the third X-axis position detection coil 30A. The level of changes. When the power receiving coil 51 is displaced toward the first X-axis position detection coil 30A, the level of the echo signal induced in the first X-axis position detection coil 30A is induced in the third X-axis position detection coil 30A. It becomes larger than the level of the echo signal. Therefore, in this state, the identification circuit 33 accurately detects the position of the power receiving coil 51 from the level ratio of echo signals induced in the first X-axis position detection coil 30A and the second X-axis position detection coil 30A. can do. This is because as the power receiving coil 51 moves toward the first X-axis position detection coil 30A, the level of the echo signal induced in the first X-axis position detection coil 30A increases. On the other hand, when the power receiving coil 51 is shifted to the third X-axis position detection coil 30A side, the level of the echo signal induced in the third X-axis position detection coil 30A is changed to the first X-axis position detection coil 30A. It becomes larger than the level of the induced echo signal. Therefore, in this state, the identification circuit 33 can accurately detect the position 51 of the power receiving coil from the level ratio of echo signals induced in the second and third X-axis position detecting coils 30A. This is because as the power receiving coil 51 moves toward the third X-axis position detection coil 30A, the level of the echo signal induced in the third X-axis position detection coil 30A increases.

As described above, the identification circuit 33 does not determine the position of the power receiving coil 51 only from the echo signal of the position detection coil 30 at the maximum level when the echo signal is at the maximum level. The position of the power receiving coil 51 is determined in consideration of echo signals induced in the position detection coils 30 on both sides of the position detection coil 30 that detects the maximum level echo signal. Accordingly, the position of the power receiving coil 51 in the area A, which is the central portion of the position detection coil 30, can accurately detect even a slight deviation from the center of the position detection coil 30 at the maximum level.

The identification circuit 73 stores in the storage circuit 77 the level and level ratio of the echo signal induced in each X-axis position detection coil 30A with respect to the position of the power receiving coil 51 in the X-axis direction. When the power receiving coil 51 is placed, an echo signal is induced in one of the X-axis position detection coils 30A. Therefore, the identification circuit 73 detects that the power receiving coil 51 has been placed by an echo signal induced in the X-axis position detection coil 30 </ b> A, that is, that the battery built-in device 50 has been placed on the charging stand 10. Furthermore, the level and the level ratio of the echo signal induced in one of the X-axis position detection coil 30A, as compared to the level and the level ratio stored in the storage circuit 77, the position of the X-axis direction of the power receiving coil 51 Is accurately determined.

The above shows a method in which the identification circuit 73 detects the position of the power receiving coil 51 in the X-axis direction from the echo signal induced in the X-axis position detection coil 30A, but the position of the power receiving coil 51 in the Y-axis direction is also X. In the same manner as in the axial direction, it can be detected from the echo signal induced in the Y-axis position detection coil 30B.

When the identification circuit 73 detects the positions of the power receiving coil 51 in the X-axis direction and the Y-axis direction, the position detection controller 64 moves the power transmission coil 11 to the position of the power receiving coil 51 with the position signal from the identification circuit 73. Let
When the echo signal having the waveform as described above is detected, the identification circuit 73 of the charging stand can recognize and identify that the power receiving coil 51 of the battery built-in device 50 is mounted. When a waveform different from the waveform of the echo signal is detected and identified, the power supply can be stopped assuming that a device other than the power receiving coil 51 (for example, a metal foreign object) of the battery built-in device 50 is mounted. When the waveform of the echo signal is not detected or identified, the power supply coil 51 of the battery built-in device 50 is not mounted and power is not supplied.

Charging stand 10 is in a state of being close to the power transmission coil 11 and controls the moving mechanism 13 in the position detection controller 14, 64 to the receiving coil 51, and supplies the AC power to the power transmission coil 11 with an alternating current power source 12. The AC power of the power transmission coil 11 is transferred to the power reception coil 51 and used for charging the battery 52. When the battery built-in device 50 detects that the battery 52 is fully charged, it stops charging and transmits a full charge signal to the charging stand 10. The battery built-in device 50 can output a full charge signal to the power receiving coil 51, transmit this full charge signal from the power receiving coil 51 to the power transmission coil 11, and transmit full charge information to the charging stand 10. The battery device 50 outputs an AC signal of a frequency different from the AC power source 12 to the receiving coil 51, the charging stand 10 can detect the full charge by receiving the AC signal at the transmitting coil 11. Further, outputs a signal that the battery device 50 is modulated by the full charge signal a carrier wave of a specific frequency to the receiving coil 51, the charging stand 10 receives the carrier wave of a specific frequency, detects a full-charge signal by demodulating the signal You can also Furthermore, the battery built-in device can also transmit full charge information by wirelessly transmitting a full charge signal to the charging stand. The battery built-in device has a built-in transmitter that transmits a full charge signal, and the charging stand has a built-in receiver that receives the full charge signal. The position detection controller 14 shown in FIG. 6 incorporates a full charge detection circuit 17 that detects the full charge of the built-in battery 52. The full charge detection circuit 17 detects a full charge signal output from the battery built-in device 50 to detect full charge of the battery 52.

The charging stand 10 on the upper surface plate 21 on which a plurality of battery built-in devices 50 can be placed is fully charged by sequentially switching the batteries 52 of the plurality of battery built-in devices 50. The charging stand 10 first detects the position of the power receiving coil 51 of any of the battery built-in devices 50, makes the power transmitting coil 11 approach the power receiving coil 51, and fully charges the battery 52 of the battery built-in device 50. To do. When the battery 52 of the battery built-in device 50 is fully charged and the full charge detection circuit 17 receives the full charge signal, the position detection controller 14 is set to a second position different from the battery built-in device 50. The position of the power receiving coil 51 of the battery built-in device 50 is detected, and the moving mechanism 13 is controlled to bring the power transmitting coil 11 closer to the power receiving coil 51 of the second battery built-in device 50. In this state, power is transferred to the battery 52 of the second battery-equipped device 50, and the battery 52 is fully charged. Further, when the battery 52 of the second battery built-in device 50 is fully charged and the full charge detection circuit 17 receives the full charge signal from the second battery built-in device 50, the position detection controller 14 further performs the third operation. detects the receiving coil 51 of the battery device 50 of the receiving coil 51 of the third battery device 50 controls the moving mechanism 13 is brought closer to the transmitting coil 11, the battery 52 of the battery device 50 Fully charge. As described above, when the plurality of battery built-in devices 50 are set on the top plate 21, the battery built-in devices 50 are sequentially switched to fully charge the built-in battery 52. The charging stand 10 stores the position of the fully-charged battery built-in device 50 and does not charge the battery 52 of the fully-charged battery built-in device 50. When it is detected that the batteries 52 of all the battery built-in devices 50 set on the top plate 21 are fully charged, the charging stand 10 stops the operation of the AC power supply 12 and stops the charging of the batteries 52. Here, in the above embodiment, the charging is stopped when the battery 52 of the battery built-in device 50 is fully charged. However, the charging may be stopped when the battery 52 reaches a predetermined capacity. .

The above moving mechanism 13 moves the power transmission coil 11 in the X-axis direction and the Y-axis direction to move the power transmission coil 11 to a position closest to the power receiving coil 51. In the present invention, the movement mechanism is in the X-axis direction. The power transmission coil is moved in the Y-axis direction and the position of the power transmission coil is not specified as a structure for approaching the power reception coil, and the power transmission coil can be moved in various directions to approach the power reception coil.

The charging stand according to the present invention can be suitably used not only for charging a mobile phone or a portable music player but also for charging an assist bicycle or an electric vehicle.

DESCRIPTION OF SYMBOLS 10 ... Charge stand 11 ... Power transmission coil 12 ... AC power supply 13 ... Moving mechanism 14 ... Position detection controller 15 ... Core 15A ... Cylindrical part 15B ... Cylindrical part 16 ... Lead wire 17 ... Full-charge detection circuit 20 ... Case 21 ... Top plate 22 ... Servo motor 22A ... X-axis servo motor 22B ... Y-axis servo motor 23 ... Screw rod 23A ... X-axis screw rod 23B ... Y-axis screw rod 24 ... Nut material 24A ... X-axis nut material 24B ... Y-axis nut material 25 ... Belt 26 ... Guide rod 27 ... Guide portion 30 ... Position detection coil 30A ... X-axis position detection coil 30B ... Y-axis position detection coil 31 ... Detection pulse generation circuit 32 ... Reception circuit 33 ... Identification circuit 34 ... Switching circuit 35 ... Limiter circuit 36 ... A / D converter 5 ... Battery built-in device 51 ... Receiving coil 52 ... Battery 53 ... Condenser 54 ... Parallel resonance circuit 55 ... Diode 56 ... Smoothing capacitor 57 ... Rectifier circuit 58 ... Charge control circuit 64 ... Position detection controller 73 ... Identification circuit 77 ... Storage circuit 130 ... Position detection coil 130A ... X-axis position detection coil 151 ... Receiving coil

Claims

A charging stand for a battery built-in device (50) including a battery (52) to be charged with power carried by the power receiving coil (51),
A power transmission coil (11) connected to the AC power source (12) and carrying the electromotive force to the power reception coil (51), and the power transmission coil (11) are incorporated, and a battery built-in device (50) is provided on the upper surface. A case (20) having an upper surface plate (21) to be mounted, and a moving mechanism (13) built in the case (20) to move the power transmission coil (11) along the inner surface of the upper surface plate (21); The position of the power receiving coil (51) of the battery built-in device (50) placed on the upper surface plate (21) is detected and the moving mechanism (13) is controlled so that the power transmitting coil (11) becomes the power receiving coil (51). A charging stand comprising a position detection controller (14; 64) to be approached,
The position detection controller (14; 64) has a plurality of position detection coils (30) arranged at predetermined intervals on the back side of the upper surface plate (21), and pulses as position detection signals to the position detection coil (30). A detection pulse generator circuit (31) for supplying a signal, and a pulse signal supplied from the detection pulse generator circuit (31) to the position detection coil (30) and excited by a pulse signal supplied from the power reception coil (51) to the position detection coil (30) Receiving circuit (32) for receiving the echo signal induced in the, and an identification circuit (33) for determining the position of the receiving coil (51) from the echo signal received by the receiving circuit (32),
The position detection coil (30) is disposed so as to overlap a part of the position detection coil (30) adjacent to the position detection coil (30),
The identification circuit (33) includes a position detection coil (30) from which an echo signal of the maximum level is induced, and a receiving coil (51) from the level of the echo signal of the position detection coil (30) disposed on both sides thereof. A charging stand characterized by determining the position of the battery.
The position detection coil (30) is an elongated coil having a straight portion, and the adjacent position detection coil (30) is arranged in a position shifted in a direction orthogonal to the longitudinal direction of the coil,
The charging stand according to claim 1, wherein the overlapping amount (d) of the position detection coils (30) adjacent to each other so as to overlap each other is 1/2 to 9/10 of the lateral width (W) of the elongated coil.
The overlap amount (d) between the position detection coils (30) adjacent to each other so that the position detection coils (30) overlap with each other is 2/3 of the lateral width (W) of the elongated coil. Charging stand.
The position detection coil (30) has a plurality of X-axis position detection coils (30A) for detecting the position of the power receiving coil (51) in the X-axis direction, and a plurality of Y-axis position detection coils for detecting a position in the Y-axis direction. The charging stand according to any one of claims 1 to 3, further comprising (30B).
The charging stand according to claim 4, wherein the X-axis position detection coil (30A) is a coil elongated in the Y-axis direction, and the Y-axis position detection coil (30B) is a coil elongated in the X-axis direction.