Position sensor arrangement for detecting a signal after a time delay from the zero crossing of the AC power source

In order to supply water into a water tank mounted on a train, a position detecting apparatus and method is developed for assisting connection of the tube coupler of the water tank with the tube coupler attached to the working terminal of a robot placed on the ground. Either one of the train and the working terminal of the robot is provided with a target circuit composed of a target coil and a capacitor connected in parallel while the other is provided with an excitation circuit, a sensor coil and a detector. The excitation circuit is provided with a power coil driven by an AC power source for generating magnetic field to induce current in a target coil. The magnetic flux center line of the sensor coil is orthogonal to that of the power coil so that the sensor coil does not sense the magnetic field generated by the power coil but senses only the magnetic field generated by the target coil. The output level of the sensor coil corresponds to the relative positions of the target coil and the sensor coil. The detector detects the output level of the sensor coil having a predetermined phase difference from the output of the AC power source. Thus, the position detection can be carried out under poor environment, and also the arrangement can be simplified since the target circuit requires no power source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a position detecting apparatus and method 
which are preferably used in e.g. a robot to position an object. 
2. Description of the Related Art 
In order to automatically supply water from the ground to a water tank 
mounted on a train, the following technique has been proposed. A robot is 
movably set in the neighborhood of a prescribed train stopping position, 
and a tube coupler for water supply attached to the working terminal of 
this robot is automatically connected with the tube coupler of the water 
tank mounted on the train to supply water to the water tank. An example of 
a position detecting method performing such a technique is as follows. 
Either one of the working terminals of the train and the robot is provided 
with a spot light source for emitting light therefrom. The other is 
provided with a semiconductor PSD (position sensing device), as available 
from Hamamatsu Photonics Limited at Hamamatsu city in Shizuoka, Japan, 
having a planar light receiving surface for detecting the two-dimensional 
position of the light emitted from the spot light source. Thus, the two 
tube couplers can be connected in a state that they are precisely 
positioned in a relationship from each other. However, this method has the 
following defects. 
(1) Since the position is detected optically, detection error or detection 
impossibility may occur in poor environment. 
(2) Power sources are required for both the light spot and the position 
detecting device. This is very disadvantageous since fewer power sources 
are preferable. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a position detecting 
apparatus with improved resistance to environment and a simplified 
structure with fewer power sources, and a position detecting method using 
this apparatus. 
In order to attain the above object, in accordance with one aspect of the 
present invention, there is provided a position detecting apparatus 
comprising a target circuit composed of a target coil and an impedance 
device connected with each other, an excitation circuit composed of a 
power coil shiftable in a relative position relationship with the target 
coil and an AC power source for driving the power coil connected with one 
another, a sensor coil integrated with the power coil so that the magnetic 
flux center line of the power coil is orthogonal to that of the sensor 
coil, and means for detecting the level of the output of the sensor coil 
having a predetermined phase difference from an AC power source. 
The position detecting apparatus may be characterized in that the impedance 
element is a capacitor and the resonance frequency of the target circuit 
is equal to that of output frequency of the AC power source. 
The position detecting apparatus according to the present invention may 
also be characterized in that a pair of sensor coils the magnetic flux 
center lines of which are orthogonal to each other are provided, and the 
sensor means are provided respectively for each sensor coil. 
The position detecting apparatus according to the present invention may be 
characterized in that the output level of the sensor coil having a 
predetermined phase difference from the output of the AC power source is 
detected within a range where maximum values with opposite polarities are 
obtained. 
In accordance with another aspect of the present invention, there is 
provided a position detecting method for detecting a relative position 
relationship between a first object and a second object using a position 
detecting apparatus comprising a target circuit attached to the first 
object and composed of a target coil and an impedance element connected 
with each other, an excitation circuit attached to the second object and 
composed of a target coil and a power coil shiftable in a relative 
position relationship with the target coil and an AC power source for 
driving the power coil connected with one another, a sensor coil 
integrated with the power coil so that the excitation center line of the 
power coil is orthogonal to that of the sensor coil, and means for 
detecting the level of the output of the sensor coil having a 
predetermined phase difference from an AC power source within a range 
where its maximum levels with opposite polarities can be obtained, the 
method comprising the steps of shifting said first object and said second 
object so that they are located in said range, and shifting said first and 
second object so that the output level of the sensor coil having the 
predetermined phase difference from the output of the AC power source 
becomes zero on the basis of the output from the detecting means. 
In accordance with the present invention, in order to detect relative 
positions of a first and a second object, a target circuit is attached to 
the first object, an excitation coil, and a sensor coil and detecting 
means are attached to the second object. The target coil of the target 
circuit is excited by the magnetic field from the power coil driven by the 
AC power source for the excitation coil. The target coil is connected with 
the impedance element such as a capacitor or a resistor so that the target 
circuit may resonate at the same frequency as the output frequency of the 
AC power source. The magnetic field generated by the target coil due to 
crossing of its magnetic flux from the power coil is detected by the 
sensor coil. The detecting means detects the output level from the sensor 
coil having a prescribed phase difference from the output of the AC power 
source for driving the power coil. Thus, the relative position 
relationship between the sensor coil and the target coil corresponding to 
the output level of the sensor coil can be detected. 
Since the magnetic flux center line of the power coil is orthogonal to that 
of the sensor coil, it is possible to prevent the sensor coil from being 
affected by the magnetic field of the power coil. Also, since the target 
circuit requires no power source, the structure of the position detecting 
apparatus can be simplified. Further, since the position detection is 
carried out using the magnetic couplings between the power coil and the 
target coil and between the target coil and the sensor coil, the position 
detecting apparatus has a more excellent resistance to poor environment 
than the optical construction according to the prior art described above. 
When a pair of sensor coils are used, the position of the target coil can 
be detected two-dimensionally. 
Further, in the present invention, the output level of the sensor coil 
having the prescribed phase difference from the output of the AC power 
source varies linearly for the change in the position relationship between 
the target coil and the sensor coil within a range where its maximum 
values with opposite polarities are obtained, so that the position 
detection can be made precisely. 
In accordance with the position detection method according to the present 
invention, at first, the first object and said second object are shifted 
so that the level of the output of the sensor coil having a predetermined 
phase difference from an AC power source is located within a range between 
the maximum levels with opposite polarities, and then, these objects are 
shifted so that the output level of the sensor coil becomes zero on the 
basis of the output from the detecting means. Thus, the target coil and 
the sensor coil are positioned so that the first and the second object can 
be positioned precisely.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a simplified perspective view showing the principle of the 
position detecting apparatus according to the present invention. The first 
object e.g. a vehicle 34 as shown in FIG. 15, whose two-dimensional 
position is to be detected, is provided with a target circuit 3 composed 
of a target coil 1 and a capacitor 2 (impedance element) connected in 
parallel with each other. The working terminal 38 of a second object, e.g. 
a robot 27 as shown in FIG. 15 is provided with an excitation coil 4 and a 
pair of sensor coils 5 and 6. It should be noted in FIG. 1 that the target 
coil 1 has a coil strand wound in a circular shape in an X - Y plane, and 
its magnetic flux center line is coincident with a Z-axis. 
In operation, the excitation circuit 4 generates an induction current in 
the target coil 1. The change in the magnetic field due to this induction 
current is sensed or detected by the pair of sensor coils 5 and 6. The 
relative positions of the first and the second object are sensed on the 
basis of the outputs from the sensor coils 5 and 6. 
The excitation coil 4 is composed of a power coil 7 and an AC power source 
8 for driving the power coil which are connected with each other. The 
target circuit may be considered an inductance modifying mechanish. The 
output frequency of the AC power source 8 may be e.g. 30 kHz. The power 
coil 7 has a coil strand wound in a circle, and its magnetic flux center 
line is a straight line 9. The sensor coils 5 and 6 along the X-axis and 
the Y-axis respectively are arranged integrally with the power coil 7. The 
sensor coils 5 and 6 have coil strands wound in a circle in a plane 
orthogonal to each other. The line 9 is a line perpendicular to the X - Y 
plane. The magnetic flux center line of the sensor coil 5 is a straight 
line in parallel to the X-axis, and that of the sensor coil 6 is a 
straight line in parallel to the Y-axis. The sensor coils 5 and 6 have 
substantially the same structure. In a state where the line 9 is 
perpendicular to the X - Y plane and so in parallel to the Z-axis, the 
shift amount .DELTA.X in the X-direction can be sensed or detected on the 
basis of the output from the sensor coil 5 as described thereafter, and 
the shift amount .DELTA.Y are connected on the basis of the sensor coil 6. 
FIG. 2 is a simplified front view showing the state where the line 9 is 
coincident with the Z-axis. All the radiuses of the target coil 1, the 
sensor coils 5 and 6 and the power coil 7 may be equal. Since the magnetic 
flux center line 9 of the power coil 7 is orthogonal to the magnetic flux 
center line 10 of the sensor coil 5, the sensor coil 5 does not sense the 
magnetic field generated by the power coil 7. Likewise, since the line 9 
is orthogonal to the magnetic flux center line 11 of the sensor coil 6, 
the sensor coil 6 does not sense the magnetic field generated by the power 
coil 7. 
FIG. 3 is a perspective view showing a part of the arrangement of the 
position detecting apparatus shown in FIG. 1. As seen from FIG. 3, the 
pair of sensor coils 5 and 6, and the power coil 7 are wound on a bobbin 
12. This bobbin 12 is made of a non-magnetic material such as synthetic 
resin. On the other hand, the target coil 1 is wound on a bobbin 13 made 
of a non-magnetic material. 
FIG. 4 is a block diagram showing the electrical arrangement relative to 
the sensor coils 5 and 6, and the power coil 7. In operation, the output 
from the AC power source 8 for driving a power coil 7 is supplied to a 
zero crossing detecting circuit 14. The output voltage waveform of the AC 
power source 8 is shown in graph (1) of FIG. 6 and its zero crossing 
points are indicated by times t1, t2 and t3. The outputs from the sensor 
coils 5 and 6 are sent to sample-hold circuits 15 and 16. 
FIG. 5A is a plan view of the target coil 1, power coil 7 and sensor coil 5 
viewed from the perpendicular direction of the X - Z plane. The output 
waveform from the sensor coil 5 varies at positions designated by 
reference numerals 5a to 5e. The reference numerals 5a to 5e will be also 
used to specify the sensor coil itself at the respective positions. The 
sensor coil 5c represents the state where it is located on the Z-axis 
which is the magnetic flux center line of the target coil 1. The power 
coil 7 is shown only when the sensor coil 5 is located at the position 5a. 
When the sensor coil 5 is at the positions 5a and 5d, it produces the 
waveform indicated by 75 in graph (2) of FIG. 6. When the sensor coil 5 is 
at the positions 5b and 5e, it produces the waveform indicated by 76 in 
the graph (2). On the other hand, when the sensor coil 5 is at the 
position 5c, the output from the sensor coil 5 is zero indicated by 
numeral 74 in the graph (2). This is also true in the shift of another 
sensor coil 6 in the Y-direction. 
The zero crossing detecting circuit 14 supplies a zero-crossing signal as 
shown in graph (3) of FIG. 6 to a delay circuit 17 through a line 18. The 
delay circuit 17 delays the rising edge of the zero crossing signal 
received through the line 18 by a period W1 and provides a signal shown in 
graph (4) of FIG. 6 to the pulse generating circuit 19. The pulse 
generating circuit 19 provides a pulse shown in graph (5) of FIG. 6 to a 
line 20 with a pulse width of e.g. 200 ns or longer starting from time t4 
elapsed from time t2 by the period W1, so as to supply top sample-hold 
circuits 15 and 16 as a command. The sample-hold circuit 15 holds the 
output from the sensor coil 5 after the time t4 as shown in graph (8) of 
FIG. 6. In response to the pulse passing through the line 20, an A/D 
converter 21 converts the output held by the sample-hold circuit 13 into a 
digital value during a period W2 (e.g. shorter than 9 .mu. sec) starting 
from time t5. The output from the A/D converter 21 is supplied to a 
processing circuit 22 (which may be realized by a microcomputer) during 
the period from time t6 to time t7. Likewise, the sample-hold circuit 16 
is provided for another sensor coil 16. The output from the sample-hold 
circuit 16 is converted into a digital value by an A/D converter 23. The 
digital output from the A/D converter 23 is supplied to the processing 
circuit 22. The processing circuit 22 is connected with a memory 24. The 
signals representative of the shift amounts .DELTA.X and .DELTA.Y 
calculated by the processing circuit 22 are supplied to a water supply 
robot processing circuit 52 from a communication interface 25 through a 
line 26 as described later. A clock signal generating circuit 32 supplies 
a clock signal to the A/D converters 21 and 23 to control the operation 
thereof. 
FIG. 5B shows the output voltage level of the sensor coil 5 having a fixed 
phase difference from the output voltage of the AC power source 8 supplied 
to the power coil 7 when the sensor coil 5 is shifted in the X-direction 
along the positions 5a to 5e in FIG. 5A. The phase difference is due to 
the impedance of the sensor coil 5. The output from the sensor coil 5 
having the fixed phase difference from the AC power source 8 is desired to 
be in its maximum value so that the sensitivity can be in maximum, but it 
is not indispensable. If the sensor coil 5 is on the Z-axis, in FIG. 5B, 
the output level of the sensor coil 5 is zero as indicated by reference 
symbol P0. With the Z-direction fixed, the output level changes linearly 
in the range between the positions P1 and P2 in the X-direction. In such a 
range from P1 to P2, the position relationship between the target coil 1 
and the sensor coil 5 can be precisely detected. Further, in order to 
adjust the relative position relationship between the target coil 1 and 
the sensor coil 5, their positions may be detected in a range between P3 
and P4. The feedback control can adjust the position relationship between 
the target coil 1 and the sensor coil 5 on the basis of the sign of the 
detected signals. Now referring to FIGS. 7 to 12, an explanation will be 
given of the reason why, when the relative positions of the target coil 1 
and the sensor coil 5 change, the output level of the sensor coil 5 having 
a fixed phase difference from the output of the AC power source 8 changes 
as shown in FIG. 5B. 
When reference to FIG. 7, according to Bio Savart's Law, the intensity 
.DELTA.H of the magnetic field at the point P due to the current vector I 
flowing through a conductive line 28 can be written by 
##EQU1## 
.DELTA.H represents the minute magnetic field at the point P generated by 
the current I at a minute portion .DELTA.L of the conductive line apart 
from the point P by a distance d, and .theta. represents an angle formed 
by the minute portion .DELTA.L and a straight line OP. The direction of 
the magnetic field depends on Ampere's right screw law. Therefore, 
assuming that as shown in FIG. 8 and FIG. 9 which is a plan view of FIG. 
8, the conductive line 29 is a circle laid in the X - Y plane, the 
intensity H of the magnetic field generated at the point P owing to the 
current I along the entire conductive line 29 can be expressed by 
##EQU2## 
where r is a radius of the conductive line 29 which comes in contact with 
a tangent line 30 at a contact point O1, a is a distance between the 
center O of the circle and the point P, b is a distance between the point 
P and the contact point O1, .phi. is an angle formed by the radial line 
connecting the center O with the contact point O1 and the X-axis, and 
.PSI. is an angle formed by the straight line connecting the contact point 
with the point P and the tangent line 30. 
Therefore, in FIG. 10 the intensit H.sub.pt of the magnetic field due to 
the power coil 7 at the center Pt of the target coil 1 can be expressed by 
##EQU3## 
where n1 is the number of windings of the power coil 7, I1 is the current 
supplied to the power coil 7, r1 is the radius of the power coil 7 and 
z.sub.pt is the distance from the center Pt of the target coil 1 to the 
plane of the power coil 7. 
Further, in FIG. 11, the intensity H.sub.ps of the magnetic field due to 
the target coil 1 at the center Ps of the sensor coil 5 can be expressed 
by 
##EQU4## 
where n2 is the number of windings, r2 the radius of the target coil 1 and 
z.sub.ts is the distance from the center Ps of the sensor coil 5 to the 
plane of the target coil 1. 
Since it is difficult to calculate the current flowing through the target 
coil 1. Equation (6) can be obtained using the intensity H.sub.pt of the 
magnetic field in Equation (4) corresponding to it. 
Assuming that y=0 and z=r, H.sub.ps is calculated in the range where x lies 
between 0 and +3r. FIG. 12 is a graph showing the comparison between the 
calculated values and actually measured values. It is assumed in FIG. 12 
that the position relationship of the coils related to the coordinate 
system corresponds to FIGS. 7 to 11. The actually measured values are 
expressed by a unit so that the peak voltage generated in the sensor coil 
5 is 1, while the calculated values are represented by the profile 
corresponding to the unit. As seen, the calculated values coincide with 
the actually measured values to a considerable degree. The graph of FIG. 
12 corresponds to the figure located right from the point P0 in FIG. 5B 
and the figure located left from the point P0 is point-symmetrical to it 
with respect to the origin point 0. Thus, the characteristic of FIG. 5B is 
obtained by detecting the output level (e.g. peak value) of the sensor 
coil 5 having a prescribed phase difference (e.g. 180.degree.) from the 
output of the AC power source 8 owing to the impedance of the coil. 
Therefore, if the distance in the Z-direction is known, the shift amount 
.DELTA.X can be calculated on the basis of the output of the sensor coil 
5. Such a characteristic as shown in FIG. 5 is previously stored in the 
memory 24 in FIG. 4. The processing circuit 22 calculates the shift amount 
.DELTA.X from the output of the sensor coil 5 on the basis of the 
characteristic stored in the memory 24. Although the above explanation was 
made for the sensor coil 5, the shift amount .DELTA.Y can be calculated 
from the output of the sensor coil 6 in the same manner. If .DELTA.X and 
.DELTA.H are fixed, .DELTA.Z can be calculated in the similar manner. 
The technical idea of the present invention will be explained in both cases 
where (1) the target coil is stationary, and (2) it moves freely. 
In the case of (1), with the relationship between the voltage from the 
sensor coil 5 or 6 and the moving distance of the sensor coils previously 
stored as a table in the memory 24, the values on the table is compared 
with the measured voltage from the sensor coil 5 or 6, then the distances 
.DELTA.X, .DELTA.Y and .DELTA.Z to the target coil 1 can be known. For 
example, in FIG. 13, if the voltage while the position of the sensor coil 
5 or 6 moves in the order of Q1 .fwdarw. Q2 .fwdarw. Q3 is compared with 
the values on the table stored in the memory 24, .DELTA.X, .DELTA.Y and 
.DELTA.Z can be obtained as described above. 
In the case of (2), i.e. where the target coil 1 moves freely, the 
technique in the case of (1) cannot be carried out. In the case of (2), 
the sensor coils 5 and 6 and the power coil 7 are caused to follow the 
target coil 1 by e.g. a motor in the directions of arrows 64 and 65. Thus, 
if .DELTA.X and .DELTA.Y comes in a certain permissible range, those in 
the X-direction and the Y-direction are regarded as located on the center 
axis of the target coil 1, then the center of target coil 1 is searched 
while they approach the target coil 1 in the Z-direction as indicated by 
an arrow 66. Namely, if it is decided that the sensor coils 5 and 6 and 
the power coil 7 may follow the movement of the target coil 1, the former 
are moved gradually in the direction of the arrow 66. The water supply 
robot 27 shown in FIG. 15 can be realized by the technique relative to the 
case of (2) taking the swing of a vehicle 34 into consideration. 
FIG. 15 is a perspective view of the water supply robot 27 incorporating 
the position detecting apparatus according to the present invention 
explained with reference to FIGS. 1 to 12. A water tank 35 is mounted on 
the body 34 of a train 33, and the tube coupler 36 which is a water supply 
opening connected with the water tank 35 is fixed to the body 34. Also the 
target coil 1 is fixed to the body 34 in the neighborhood of the tube 
coupler 36. The target coil 1 is connected with the capacitor 2 in the 
manner described above. In order that the tube coupler 37 of the robot 27 
is connected with the tube coupler 36 to automatically supply water, the 
power coil 7 and sensor coils 5 and 6 as well as the tube coupler are 
fixed to the working terminal 38 of the water supply robot 27. The water 
supply robot 27 is composed of a truck 40 which is movable on a rail 39 
provided on the ground and plural arms 41 mounted on the truck 40. The 
rail 39 is provided in the neighborhood of the position where the train 33 
stops along the rail 42 on which the train travels. 
FIG. 16 is a side view of the water supply robot 27. The plurality of arms 
41 and the working terminal 38 are displaced so that the relative 
positions of the target coil 1 and the sensor coils 5 and 6 on the X - Y 
plane are detected, and their shift amount in Z-direction is detected by a 
limit switch 45. Thus, the tube couplers 36 and 37 are connected with each 
other. 
FIG. 17 is an enlarged side view of the neighborhood of the tube couplers 
36 and 37, and coils 1, 5, 6 and 7. The tube coupler 37 is connected with 
a flexible tube 43 so that water is supplied by pressure in the state 
where the tube couplers 36 and 37 are connected with each other. The train 
body is provided with a protrusion 44 to be sensed, and the working 
terminal 38 is provided with the limit switch 45 serving as a detecting 
means. When the limit switch comes into contact with the protrusion 45 in 
the state where the tube couplers 36 and 37 are connected with each other, 
the switching manner is changed so that the connecting state of the tube 
couplers 36 and 37 is detected. The two-dimensional positions on the X - Y 
plane can be sensed with the aid of the coils 1, 5, 6 and 7, and the shift 
amount in the Z-direction can be sensed with the aid of the protrusion and 
the limit switch 45. 
FIG. 18 shows the relative arrangements of the tube couplers 36 and 37 and 
coils 1, 5, 6 and 7 in the state where the tube couplers 36 and 37 are 
connected with each other, the Z-axis (FIG. 1) which is the magnetic flux 
center line coincides with that of the power coil 7, and the center of 
each of the sensor coils 5 and 6 is located on the magnetic flux center 
line 9. Thus, in this embodiment, the distance a between the axis line of 
the tube coupler 36 and the magnetic flux center line of the target coil 1 
is set to be equal to the distance between the tube coupler 37 and the 
magnetic flux center line 9 of the power coil 7. 
FIG. 19 is a block diagram showing the arrangement relative to a water 
supply robot 27. The train 34 is composed of a plurality of vehicle bodies 
34a, 34b, 34c, . . . The corresponding components are designated with 
suffixes a, b, . . . , and the components expressed in general are 
designated with no suffix. 
FIG. 20 is a flowchart for explaining the operation of the arrangement 
shown in FIG. 19. First, when the train reaches the place (e.g. a station) 
where the water supply robot 27 is located (step s1), an operator presses 
the start switch 47 (steps s2). Then, the data receiving circuit 50 
connected with a host computer 49 receives the position information of the 
water supply inlet 36 transmitted e.g. by radio from a data transmission 
circuit 48 and stores it in the host computer 49 (s3). The water supply 
robots 27a and 27b are provided with processing circuits 52a and 52b 
which can be realized by computers for controlling the corresponding 
robots, respectively. If water tanks 35a filled to the brim with water are 
detected by water-brimming detecting means 53a and 53b. The detected 
outputs are supplied to the corresponding processing circuits 52a and 52b. 
In step s4, the host computer 49 supplies the position information of the 
tube couplers 36a and 36b to the processing circuits 52a and 52b through a 
line 51. Thus, the processing circuits 52a and 52b move the water supply 
robots 27a and 27b along the rail 39 so that the sensor coils 5a and 5b 
attached to each of working terminals enter the range between P1 and P2 
shown in FIG. 5B expressed relatively to the target coils 1a and 1b. The 
water supply robots 27a and 27b may be moved into the range between P3 and 
P4 in place of the range between P1 and P2. 
After the water supply robots 27a and 27b are moved to the range designated 
by step s4, their arms 41a and 41b are moved so that the target coil 1 on 
the X - Y plane is sensed by the sensor coils 5 and 6 until the position 
P0 in FIG. 5B is located in step s5. Thus, the magnetic flux center lines 
of the target coils 1a and 1b coincide with the magnetic flux center line 
9 of the power coil 7 so that the centers of the sensor coils 5 and 6 are 
located on the above magnetic flux center line 9. In step s6, the water 
supply robots 27a and 27b further move their arms 41a and 41b to push the 
tube couplers 37a and 37b for water supply into the tube couplers 36a and 
36b at the water supply inlets. The connecting state of the tube couplers 
36 and 37 is detected by the limit switch 45. After the tube couplers 36 
and 37 have been connected, in step s7, the water supply robot 27 starts 
to supply water. 
In step s8, the water brimming is detected by the water-brimming detecting 
means 53 for the water tanks 35 attached to the vehicle bodies 34a and 34b 
of the train 33, and this water brimming information is supplied to the 
processing circuit 52. Namely, it is data-transferred from the detecting 
means 53 through the target coil and the power coil 7 using the technique 
of frequency modulation. 
In step s9, the water supply by the water supply robot 27 is stopped at 
obtaining the water-brimming information. The arms 41 is moved to 
disconnect the tube couplers 36 and 37 from each other. The information of 
completion of water supply is supplied to the host computer 49 through the 
processing circuit 52. 
In step s10, when the host computer 49 detects that water supply from all 
the water supply robots 27 has been completed, it displays the completion 
of water supply on a monitor display means 54. The information of 
supplying water is also displayed on the monitor display means 54. 
Finally, in step s11, the operator recognizes the completion of water 
supply in accordance with the displayed content on the monitor display 
means 54. Thus, all the operations for water supply are completed. 
The present invention can be not only put into practice in relation to the 
water supply robot, but also applied to many other technical fields 
including connecting works on electronic circuit substrates such as 
connecting of jumper wires by a robot, automatic couplers which permits 
vehicle bodies to be coupled on a curve rail, detection of positions of 
works by a robot, non-contact limit switches, and rendezvous docking 
devices for space devices. 
As described hitherto, in accordance with the present invention, using a 
target coil of a target circuit composed of the target coil and an 
impedance element connected with each other, the magnetic field generated 
owing to a power coil of an excitation coil composed of the power coil and 
an AC power source is detected, the magnetic field due to the target coil 
is sensed by a sensor coil, the output level of the sensor coil having a 
predetermined phase difference from the AC power source is detected by a 
detecting means, and so the relative position relationship between the 
target coil and the sensor coil can be detected corresponding to the above 
output level of the sensor coil. Therefore, the present invention has 
improved tolerance to poor environment as compared with the optical 
arrangement according to the prior art, and has no fear of detection 
impossibility and erroneous detection. Further, the target circuit 
requires no power source according to the present invention so that the 
arrangement can be simplified, and the present invention can be applied to 
a wide variety of technical fields. 
Further, in accordance with the present invention, if a capacitor is used 
as the impedance connected with the target coil of the target circuit, and 
the resonance frequency of the target circuit is caused to be coincident 
with the output frequency of the AC power source, the detecting 
sensitivity can be improved. 
In accordance with the present invention, if the a pair of sensor coils are 
arranged in such a manner that the magnetic flux centers of the sensor 
coils are orthogonal to each other, the two-dimensional position relative 
to the target coil can be detected. 
Further, in accordance with the present invention, if the detecting means 
detects the output level of the sensor coil having a predetermined phase 
difference from the output of the AC power source, in a range between its 
maximum values with opposite polarities, the relative position 
relationship between the target coil and sensor coil linearly corresponds 
to the output level of the sensor coil so that the position detection can 
be precisely performed. 
Further, in accordance with the present invention, under the condition that 
the target circuit is provided to a first object and the excitation 
circuit, the sensor coil(s) and the detecting means are provided to a 
second object, the first object and the second object are shifted to enter 
the above range, and thereafter the first and the second object are 
shifted so that the output level of the sensor coil having a predetermined 
phase difference becomes zero based on the output from the detecting 
means. Thus, the relative positions of the target coil and the sensor 
coil, that is, the positions of the first object and the second object can 
be detected precisely.