U.S. patent application number 13/156885 was filed with the patent office on 2012-02-09 for transportation vehicle system and charging method for the transportation vehicle system.
This patent application is currently assigned to MURATA MACHINERY, LTD.. Invention is credited to Takao HAYASHI.
Application Number | 20120032668 13/156885 |
Document ID | / |
Family ID | 45090910 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120032668 |
Kind Code |
A1 |
HAYASHI; Takao |
February 9, 2012 |
Transportation Vehicle System and Charging Method for the
Transportation Vehicle System
Abstract
A magnetic sensor array including a plurality of magnetic
sensors detects a phase regarding a magnetic pole of a magnetic
pole array including magnetic poles of N and S arranged
alternately. A pitch identification unit detects a pitch number of
the magnetic pole currently being detected by the magnetic sensor
array, in the magnetic pole array.
Inventors: |
HAYASHI; Takao;
(Inuyama-shi, JP) |
Assignee: |
MURATA MACHINERY, LTD.
Kyoto-shi
JP
|
Family ID: |
45090910 |
Appl. No.: |
13/156885 |
Filed: |
June 9, 2011 |
Current U.S.
Class: |
324/207.24 |
Current CPC
Class: |
Y04S 30/14 20130101;
B60L 53/65 20190201; B60L 58/12 20190201; B60L 53/30 20190201; Y02T
90/14 20130101; Y02T 90/169 20130101; Y02T 90/167 20130101; B60L
2200/26 20130101; Y02T 10/70 20130101; Y02T 10/7072 20130101; B60L
53/66 20190201; Y02T 90/16 20130101; G08G 9/00 20130101; Y02T 90/12
20130101 |
Class at
Publication: |
324/207.24 |
International
Class: |
G01D 5/244 20060101
G01D005/244 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2010 |
JP |
2010-178463 |
Claims
1. A magnetic pole detection system comprising: a magnetic pole
array including a plurality of magnetic poles of N and S arranged
alternately; a magnetic sensor array including a plurality of
magnetic sensors for detecting a magnetic pole of the magnetic pole
array; a phase detection head for detecting a phase regarding one
magnetic pole currently being detected by the magnetic sensor array
in the magnetic pole array according to a signal from the magnetic
sensor array; and a pitch identification unit for identifying a
pitch number of the magnetic pole currently being detected in the
magnetic pole array, based only on current detection data
regardless of historical detection data.
2. The magnetic pole detection system according to claim 1, further
comprising: a plurality of marks arranged in parallel with the
magnetic pole array, changing synchronously with the magnetic poles
of the magnetic pole array; and a mark sensor array including a
plurality of mark detection sensors provided in parallel with the
magnetic sensor array, the pitch detection unit identifying the
pitch number of the magnet pole in the magnet pole array based on a
combination of signals from the mark detection sensors.
3. The magnetic pole detection system according to claim 2, the
marks each being configured at least by the magnetic poles of the
magnet array extended in a first direction perpendicular to a
second direction in which the magnet poles of the magnet array are
arranged and magnetic poles of the magnet array un-extended in the
first direction.
4. The magnetic pole detection system according to claim 2, further
comprising an offset correction unit for converting data regarding
the pitch number of the magnetic pole in the magnetic pole array
into a reference position of each magnetic pole, and converting the
phase into a shift from the reference position to output an
absolute position.
5. A method of detecting a magnetic pole of a magnetic pole array
comprising magnetic poles of N and S arranged alternately with a
magnetic sensor array including a plurality of magnetic sensors,
the method comprising the steps of: detecting a phase regarding one
magnetic pole currently being detected by the magnetic sensor array
in the magnetic pole array by a phase detection head; and
identifying a pitch number of the magnetic pole currently being
detected in the magnetic pole array, by a pitch identification
unit, based only on current detection data regardless of historical
detection data.
6. The method according to claim 5, a plurality of marks being
arranged in parallel with the magnetic pole array, the marks
changing synchronously with the magnetic poles of the magnetic pole
array, a mark sensor array including a plurality of mark detection
sensors being provided in parallel with the magnetic sensor array,
the identifying step including identifying the pitch number of the
magnetic pole in the magnetic pole array based on a combination of
signals from the mark detection sensors.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a magnetic pole detection
system and a magnetic pole detection method, e.g., used for
detecting a position of a moving vehicle.
BACKGROUND ART
[0002] The inventors developed a system adopting a combination of a
magnetic pole array including a plurality of magnetic poles
arranged in a straight line, and a coil array including a plurality
of coils for detecting a position based on the magnetic pole array
(e.g., Patent Publication 1: JP2009-276827A). In the system, the
magnetic poles are arranged at the same pitch such that magnetic
poles of N and S are arranged alternately, i.e., the adjacent
magnetic poles have the opposite polarities N and S. The coil array
detects a phase based on the magnetic pole. In this approach, pitch
numbers of the magnetic poles in the magnetic pole array cannot be
determined from the coil array. In this regard, the signal from the
coil array changes cyclically for each of the magnetic poles.
Therefore, using this information, the number of cycles in which
the signal from the coil array changed is counted to determine the
pitch numbers of the magnetic poles. However, in the method, in the
case where data of the pitch numbers of the magnetic poles is lost
due to an instantaneous power failure or the like, restarting
operation becomes difficult.
[0003] Detection of the pitch numbers of the magnetic poles of the
magnetic pole array and detection of the phase relative to the
magnetic pole can be used, e.g., for controlling a linear motor, in
addition to detecting a position of a moving vehicle. For example,
a linear synchronous motor is used as the linear motor, the pitch
numbers of the magnetic poles of the magnetic pole array and the
phase relative to the magnetic pole are detected, and feedback
control is provided for the linear motor. In both of the control of
the linear motor and position detection of the moving vehicle, if
the pitch numbers of the magnetic poles in the magnetic pole array
are found without counting cycles of the signal, control can be
implemented without any significant troubles.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to make it possible to
identify a pitch of a magnetic pole in a magnetic pole array
without any data that requires storage of information such as a
repeat number of cycles.
[0005] The present invention relates to a magnetic pole detection
system including a magnetic pole array, a magnetic sensor array, a
phase detection head, and a pitch identification unit. The magnetic
pole array includes a plurality of magnetic poles of N and S
arranged alternately. The magnetic sensor array includes a
plurality of magnetic sensors for detecting a magnetic pole of the
magnetic pole array. The phase detection head detects a phase based
on one magnetic pole in the magnetic pole array. The pitch
identification unit identifies a pitch number of one magnetic pole
currently being detected by the magnetic sensor array, in the
magnetic pole array, based only on current detection data
regardless of historical detection data.
[0006] In the present invention, the pitch number of the magnetic
pole is identified regardless of data detected in the past, e.g.,
data indicating how many cycles of magnetic poles have been
counted. Therefore, the pitch number of the magnetic pole in the
magnetic pole array can be detected reliably without being affected
by a power failure or the like.
[0007] Preferably, the magnetic pole detection system further
includes a plurality of marks arranged in parallel with the
magnetic pole array and changing in units of magnetic poles of the
magnetic pole array, and a mark sensor array including a plurality
of mark detection sensors provided in parallel with the magnetic
sensor array. The pitch detection unit identifies a pitch number of
the magnetic pole in the magnetic pole array based on a series of
signals from the mark detection sensors. In this manner, the pitch
number of the magnetic pole can be identified based on a series of
signals from the marks arranged in parallel with the magnetic pole
array. Identification is not made based only on the signal from one
mark, but made based on the series of signals. Therefore, it is
acceptable that the amount of information from each mark is small.
Thus, the magnetic pole pitch number can be identified using simple
marks each having a small amount of information.
[0008] In particular, preferably, the marks are configured at least
by the magnetic poles of the magnet array extended in a first
direction perpendicular to a second direction in which the magnetic
poles of the magnet array are arranged and magnetic poles of the
magnet array un-extended in the first direction. In this manner,
the mark can be configured based on whether or not the magnetic
pole is extended or not. In the embodiment, by combining
information indicating whether the magnetic pole is extended or not
and the polarity of the magnetic pole, three types of the magnetic
poles can be identified by the marks. Alternatively, without
considering the polarity of the magnetic pole, there are only two
types of marks indicating whether the magnetic pole is extended or
not may be provided. In this case, the marks can be formed
integrally with the magnetic pole array, and the marks can be
configured simply. A portion detected by the magnetic sensor array
in the magnetic pole array is referred to as the first magnetic
pole array, and a portion detected by the mark sensor array is
referred to as the second magnetic pole array. It can be considered
that the first magnetic pole array and the second magnetic pole
array are arranged in parallel with each other in the longitudinal
direction of the magnetic pole array.
[0009] Preferably, the magnetic pole detection system further
includes an offset correction unit for converting data regarding
the pitch number of the magnetic pole in the magnetic pole array
into a reference position of each magnetic pole, and converting the
phase into a shift from the reference position to output an
absolute position.
[0010] Further, the present invention relates to a method of
detecting a magnetic pole of a magnetic pole array including
magnetic poles of N and S arranged alternately with a magnetic
sensor array including a plurality of magnetic sensors. The method
comprises the steps of: [0011] detecting a phase based on one
magnetic pole in the magnetic pole array using a phase detection
head; and [0012] identifying a pitch number of one magnetic pole
currently being detected by the magnetic sensor array, in the
magnetic pole array, using a pitch identification unit, based only
on current detection data regardless of historical detection data.
In the specification, description regarding the magnetic pole
detection system is directly applicable to the magnetic pole
detection method.
[0013] Preferably, a plurality of marks are arranged in parallel
with the magnetic pole array, the marks change in units of magnetic
poles of the magnetic pole array, and a mark sensor array including
a plurality of mark detection sensors is provided in parallel with
the magnetic sensor array. The identifying step includes
identifying a pitch number of the magnetic pole in the magnetic
pole array based on a series of signals from the mark detection
sensors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] [FIG. 1]
[0015] FIG. 1 is a block diagram showing a magnetic pole detector
according to an embodiment.
[0016] [FIG. 2]
[0017] FIG. 2 is a diagram schematically showing a magnetic pole
array and output from a phase detection head.
[0018] [FIG. 3]
[0019] FIG. 3 is a plan view showing the magnetic pole array
according to the embodiment.
[0020] [FIG. 4]
[0021] FIG. 4 is a table showing determination of a central
position in a traveling direction of the phase detection head.
[0022] [FIG. 5]
[0023] FIG. 5 is a flow chart showing an algorithm of detecting an
absolute position according to the embodiment.
[0024] [FIG. 6]
[0025] FIG. 6 is a block diagram showing a moving vehicle system
utilizing the embodiment.
[0026] Hereinafter, an embodiment in the most preferred form for
carrying out the present invention will be described. The scope of
the invention shall be determined according to understanding of a
person skilled in the art based on the description of the claims in
consideration of the description of the specification and
techniques known in this technical field.
MOST PREFERRED EMBODIMENT
[0027] FIGS. 1 to 6 show an embodiment and its application. FIG. 1
shows a magnetic pole detector 2. The magnetic pole detector 2
includes a phase detection head 4 for detecting a phase relative to
each of magnetic poles of a magnetic pole array, and a pitch
determination circuit 6 for determining, i.e., identifying a pitch
number of a magnetic pole which is currently being detected
regardless of historical detection data, and an offset correction
unit 8. The phase detection head 4 includes an alternating current
power supply 10 and a coil array made up of a plurality of, e.g.,
four coils 11 to 14. The coils 11 to 14 are connected to resistors
R1 to R4, respectively. The coil array faces a magnetic pole array
30 shown in FIG. 3 to detect the phase based on the magnetic pole
in the magnetic pole array. Reference numerals P1 and P2 denote
operational amplifiers for collecting signals as shown in FIG. 1.
.alpha. denotes a phase relative to each magnetic pole of the
magnetic pole array. The output current of the alternating current
power supply 10 is expressed by sin .omega.t, and two signals of
sin .alpha..times.sin .omega.t and cos .alpha..times.sin .omega.t
are obtained from the operational amplifiers P1, P2. These signals
are processed by an operational amplifier circuit 16, e.g., by
delaying the phase of the signal of sin .alpha..times.sin .omega.t
by .pi./2 to produce sin .alpha..times.cos .omega.t. Then, by
adding sin .alpha..times.cos .omega.t to sin .alpha..times.sin
.omega.t, sin(.alpha.+.omega.t) is obtained by addition theorem.
The coil array is an example of a magnetic sensor array, and the
pitch determination circuit 6 is an example of a pitch
identification unit.
[0028] A counter 20 counts a clock signal (not shown). For example,
the counter 20 is reset when a zero crossing detector 18 or the
like detects that the phase of the output current from the
alternating current power supply 10 becomes 0. Though the zero
crossing detector 18 has been mentioned for the purpose of
explaining operation of the circuit, the zero crossing detector 18
may not be provided physically. For example, in the case where a
D/A converter or the like is used for the alternating current power
supply 10, the counter 20 should be reset when the input to the D/A
converter becomes zero. By counting a period of time, e.g., from
.omega.t=0 to .alpha..+-..omega.t=0, by the counter 20 based on sin
.omega.t, sin(.alpha..+-..omega.t)=0 or the like, a can be
determined. .alpha. is a phase relative to one magnetic pole. When
the center of the coil array 14 faces one end of the magnetic pole,
.alpha. becomes 0, and when the center of the coil array 14 faces
the other end of the magnetic pole, for example, .alpha. becomes
2.pi.. .alpha. represents a position at the center of the coil
array relative to the magnetic pole.
[0029] Though the coils 11 to 14 are provided for detection of the
phase of the magnetic pole in the embodiment, a magnetic sensor
array having a plurality other magnetic sensors such as hall
elements, magneto-resistive effect sensors, magneto-impedance
effect sensors arranged in an array may be provided. For example,
in the case where a set of four magnetic sensors or a set of two
magnetic sensors are arranged within the width of one magnetic pole
(one pitch) of the magnetic pole array, the phase relative to each
magnetic pole can be detected. The drive circuit shown in FIG. 1 is
merely an example. Various other circuits are known as circuits for
detecting the phase relative to the magnetic coil from the coil
array.
[0030] The logic circuit 24 includes a plurality of hall elements
22. For example, the number of the hall elements 22 is 5.
Alternatively, the number of the hall elements is 3, 7, 9, 1, or
the like. For the purpose of explanation, the hall elements are
denoted by alphabets A, . . . E. A plurality of the hall elements
22 are arranged in a line at the same pitch as the poles of the
magnetic pole array. A combination of signals that can be
determined uniquely depending on the position of the magnetic pole
array is outputted. In the embodiment, though the hall elements 22
can identify three types of states N, S, or no polarity in the
embodiment, it is sufficient that the hall elements 22 can identify
two types of the states, i.e., the presence or absence of the
magnetic pole. Further, instead of the hall elements, magnetic
sensors such as coils, magneto-resistive effect sensors,
magneto-impedance effect sensors may be used. If the magnetic
sensors such as the hall elements 22 are arranged densely in
comparison with the magnetic poles of the magnetic pole array,
e.g., at 1/2 pitch of the arrangement pitch the magnetic poles in
the magnetic pole array, temporal missing of the pitch number at
the time of passing a border between magnetic poles will not
occur.
[0031] The combination of signals from the five hall elements A to
E can be determined uniquely depending on the position on the coil
array. The logic circuit 24 stores a table or the like showing
correspondence between combinations of the signals from the
individual hall elements A to E and positions on the magnetic pole
array, and outputs the pitch number on the magnetic pole array,
i.e., the number of the magnetic pole pitch. The table is an
example of means for converting the combination of the signals from
the hall elements A to E into the magnetic pole pitch. The pitch
number of the magnetic pole is inputted to a controller 44 of a
linear motor 42 shown in FIG. 6.
[0032] An offset correction unit 8 converts data indicating which
magnetic pole array is currently being detected (in the case where
a plurality of magnetic pole arrays are present) and the pitch
number of the magnetic pole in the magnetic pole array into a
reference position in each magnetic pole, e.g., an absolute
position at an end of the magnetic pole. In the embodiment, this
conversion is referred to as the offset correction. For example,
the offset correction unit 8 stores an offset for each of the
magnetic poles, or an offset for each magnet array. Assuming that
the magnetic poles are arranged at an equal pitch in the magnet
array, the width of the magnetic pole is stored. The phase et of
the magnetic pole is represented by converting the ratio of the
shift of the current position relative to the reference position of
the magnetic pole which is currently being detected to the width of
the magnetic pole into an angle in a range of 0.degree. to
360.degree.. Further, the width of the magnet pole can be
determined based on a difference or the like between the offset of
the magnet which is currently being detected and the offset of the
next magnetic pole. The offset correction unit 8 outputs the
absolute position based on the combination of the ID (data
indicating which magnetic pole array is currently being detected in
the case where a plurality of magnetic pole arrays are present),
the pitch number of the magnetic pole which is currently being
detected, and the phase .alpha. in the magnetic pole. Further, in
the case where only the control of the linear motor is implemented,
the offset correction unit 8 is not required.
[0033] FIG. 2 is a graph showing the relationship between the
arrangement of the magnetic poles in a magnetic pole array and
output from a phase detection head. For example, the magnetic pole
array 30 is made up of 20 magnetic poles. The magnetic poles are
arranged at the same pitch such that magnetic poles of N and S are
arranged alternately, i.e., the adjacent magnetic poles have the
opposite polarities N and S. The magnetic poles has the same size
in a direction in which the magnetic poles are arranged. The pitch
between the magnetic poles, i.e., the interval between the central
lines of the adjacent magnetic poles is referred to as the pitch of
the magnetic pole. The phase detection head cannot recognize which
magnetic pole is currently being detected, and outputs the phase
relative to the magnetic pole which is currently being detected, as
a phase, e.g., in a range of 0.degree. to 360.degree..
[0034] FIG. 3 shows structure of a magnetic pole array 30. The
magnetic pole array 30 is formed by combining long magnets 36 each
having a large size in a direction perpendicular to the
longitudinal direction of the array 30 and short magnets 38 each
having a small size in the direction perpendicular to the
longitudinal direction of the array 30. For example, the number of
the magnets 36, 38 is 20 in total. The pitches at the magnetic
poles are identified into three types of polarities, i.e., the
polarity of N at the long magnet, the polarity of S at the long
magnet, and no polarity at the short magnet. The short magnet
having the reduced size does not show any polarity at the position
where the long magnet protrudes. Identification of three types of
polarities are used as magnetic marks. The hall elements are mark
sensors for detecting these marks. If the types of five pitches are
detected by the five hall elements of the pitch determination
circuit, there are 3.sup.5 possible combinations of possible
signals. After inappropriate signals are eliminated from the
combinations, for example, several tens to 100 arrangements of the
magnetic pole pitches can be identified. Therefore, the pitch
number on the magnetic pole array can be identified uniquely based
on the combination of the outputs from the five hall elements. It
should be noted that even if the number of pitches in the magnetic
pole array 30 is increased, the pitch number can be identified
uniquely by increasing the number of hall elements.
[0035] The magnets 36, 38 of the magnet pole array 30 are arranged
such that the adjacent magnets 36, 38 have the opposite polarities.
Further, the long magnets 36 have the same size in the longitudinal
direction of the array 30, and have different sizes in the
direction perpendicular to the longitudinal direction of the array
30. It can be considered that the magnetic pole array 30 is formed
by arranging a first magnetic pole array 32 and a second magnetic
pole array 34 in parallel with each other in a moving direction of
the moving vehicle. The first magnetic pole array 32 is the
secondary side of the linear motor, and used for detecting the
phase in the magnetic pole using the phase detection head. The
second magnetic pole array 34 identifies the pitch number in the
magnetic pole array using the magnetic sensors such as the hall
elements. The first magnetic pole array 32 is present in a portion
below a border line indicated by arrows shown in FIG. 3, and the
second magnetic pole array 34 is present in a portion above the
border line.
[0036] In this manner, the first magnetic pole array 32 and the
second magnetic pole array 34 are provided in parallel with each
other, and the three types of states, i.e., polarities of N, S, and
no polarity in the second magnetic pole array 34 are detected,
e.g., by the five hall elements. The second magnetic pole array 34
is formed by combining the long magnets 36 and the short magnets 38
to simplify the structure of the array 30. The magnetic poles used
in the second magnetic pole array 34 and the magnetic poles used in
the first magnetic pole array 32 may be separated physically.
[0037] If the length of the magnetic pole array 30 is increased
much more, and the second magnetic pole array 34 is formed as one
line array as shown in FIG. 3, it may become difficult to identify
the pitch number of the magnetic pole. In such a case, the second
magnetic pole array 34 should have two or more lines. For example,
long magnets, middle magnets, and short magnets are arranged such
that the second magnetic pole array 34 includes magnet poles
arranged in two parallel lines. In the line adjacent to the first
magnetic pole array 32, the long magnets and the middle magnets are
considered as the same, and are distinguished from the short
magnets. In the next line, the long magnets are distinguished from
the middle magnets and the short magnets. In the embodiment, the
magnetic pole array 30 is the secondary side of the linear motor.
Alternatively, the magnetic pole array 30 may be provided
separately from the secondary side of the linear motor, or may be
used for recognizing the position of the moving vehicle regardless
of the linear motor.
[0038] FIG. 4 shows a pattern of outputs from the hall elements A
to E. The output pattern shows the relationship between the center
of the phase detection head and the pitch number of the magnetic
pole which faces the center of the detection head. Based on the
layout of the second magnetic pole array 34 shown in FIG. 3, a
signal for uniquely defining the magnet pole detected by the phase
detection head as shown in FIG. 4 is obtained.
[0039] FIG. 5 shows processing in the embodiment. The pitch number
of the magnetic pole in the magnet array is detected by the hall
element array. In the coil array, the phase relative to the magnet
pole which is currently being detected is determined. Based on
combination of these items of data, the absolute position of the
moving vehicle is determined. Further, based on the relationship
between the pitch number of the magnetic pole and the phase, a
control signal for controlling the linear motor is generated.
[0040] FIG. 6 shows a moving vehicle 40 utilizing the embodiment. A
plurality of magnetic pole arrays 30 are arranged along a travel
route of the moving vehicle 40. For example, a linear motor 42 is a
linear synchronization motor or the like. Portions of the first
magnetic pole arrays in the magnetic pole arrays 30 are used as the
secondary side. By a magnetic pole detector 2, a relative position
relative to the magnet pole array 30 is determined. Then, the
linear motor 42 is controlled by the controller 44, and the
absolute position of the moving vehicle 40 is determined. Further,
data indicating which magnetic pole array is currently being
detected is stored in a flash memory or the like to prevent loss of
the data by a power failure. In the case of determining the
absolute position at an arbitrary position, the interval between
the adjacent magnetic pole arrays 30 is reduced. Further, in the
case where only the control of the linear motor 42 is intended,
calculation of the absolute position is not required. In the
embodiment, though the linear motor 42 and the magnetic pole
detector 2 are provided on the moving vehicle 40, alternatively,
the linear motor 42 and the magnetic pole detector 2 may be
provided on the ground, and the magnetic pole array 30 may be
provided on the moving vehicle. The moving vehicle is not limited
to a transportation vehicle such as an overhead traveling vehicle
or a rail vehicle. For example, the moving vehicle may be a
transfer apparatus, a head of a working machine or a transportation
apparatus for transporting a workpiece.
[0041] In the embodiment, the following advantages are obtained.
[0042] (1) It is possible to determine the pitch number of the
magnetic pole of the magnetic pole array 30 which is currently
being detected, and provide feedback control for the linear motor.
[0043] (2) The magnetic pole array 30 can be configured simply by
combining the long magnets 36 and the short magnets 38 for
providing the first magnetic pole array 32 and the second magnetic
pole array 34. [0044] (3) In the case of determining the pitch
number in the longer magnetic pole array, the second magnetic pole
arrays 34 should be arranged in parallel with each other in two or
more lines, or the number of magnetic sensors such as the hall
elements should be increased.
[0045] It should be noted that the hall elements A to E may be
arranged in a direction perpendicular to a direction in which
magnetic poles of the magnet pole arrays are arranged, and a
magnetic mark, an optical mark or the like having an amount of data
corresponding to 5 bits may be provided for each of the magnetic
poles. However, in this case, the marks realized simply by
combining the long magnets 36 and the short magnets 36 need to be
replaced by twenty types of marks inefficiently. The components
such as the computation circuit 16, the counter 20, the logic
circuit 24, the offset correction unit 8 or the like may be
provided as discrete circuits. Alternatively, these components may
be provided as computer structure made up of hardware and
software.
DESCRIPTION OF THE NUMERALS
[0046] 2: magnetic pole detector
[0047] 4: phase detection head
[0048] 6: pitch determination circuit
[0049] 8: offset correction unit
[0050] 10: alternating current power supply
[0051] 11 to 14: coil
[0052] 16: computation circuit
[0053] 18: zero crossing detector
[0054] 20: counter
[0055] 22: hall element
[0056] 24: logic circuit
[0057] 30: magnetic pole array
[0058] 32: first magnetic pole array
[0059] 34: second magnetic pole array
[0060] 36: long magnet
[0061] 38: short magnet
[0062] 40: moving vehicle
[0063] 42: linear motor
[0064] 44: controller
[0065] R1 to R4: resistor
[0066] P1, P2: operational amplifier
* * * * *