JP2001356016A - Surveying instrument with magnetic encoder - Google Patents

Abstract

(57) [Summary] [Objective] To provide a surveying instrument equipped with a magnetic encoder capable of removing the influence of an external magnetic field. The total station includes a magnetic encoder and an external magnetic field detecting element that detects an external magnetic field acting on a magnetic sensor unit of the magnetic encoder.
31a, 131b) and a magnetic field generating member 231 for generating a magnetic field in a direction to cancel the external magnetic field acting on the magnetic sensor unit 54.
a, 131b) The magnetic sensor unit 5 detected by
The magnetic field generating member 2 cancels the external magnetic field acting on
31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor, and more particularly to a surveying instrument such as a total station and a theodolite equipped with a magnetic encoder for measuring a horizontal angle and a vertical angle.

[0002]

2. Description of the Related Art Some conventional surveying instruments such as a total station and a theodolite are equipped with an optical encoder as angle measuring means. The optical encoder includes a scale formed at a predetermined pitch in a circumferential direction, and a photo sensor for detecting passage of the scale.

As an angle measuring means similar to such an optical encoder, there is a magnetic encoder. A magnetic encoder usually has a division number N (N
(A positive integer), a multi-pole magnetized layer magnetized at an equal pitch is formed, and a magnetic sensor is provided so as to face the multi-pole magnetized layer. The magnetic sensor includes, for example, four magnetoresistive elements arranged at a pitch smaller than the pitch of the multipolar magnetized layer, and detects magnetism that changes with rotation of the magnetic drum as a change in the resistance value of the magnetoresistive element, In this configuration, the rotation angle of the magnetic drum is obtained based on the cycle of the change.

[0004] However, the magnetic encoder may generate an error under the influence of an extremely strong external magnetic field. In particular, the surveying instrument always uses it in an unspecified outdoor, and may receive an unspecified strong magnetism. . Therefore, in order to mount a magnetic encoder on a surveying instrument, it is preferable to provide some means for preventing an error due to the influence of external magnetism. (The geomagnetism is about 0.5G, so the effect is small.)

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and can eliminate the influence of external magnetism.
It is an object to provide a surveying instrument equipped with a magnetic encoder.

[0006]

SUMMARY OF THE INVENTION To achieve this object, the present invention provides an external magnetic field detecting means for detecting an external magnetic field acting on a magnetic sensor of the magnetic encoder in the surveying instrument, and a direction for canceling the external magnetic field acting on the magnetic sensor. Magnetic field generating means for generating a magnetic field of the type described above, and magnetic field control means for generating a magnetic field in the magnetic field generating means for canceling an external magnetic field acting on the magnetic sensor detected by the external magnetic field detecting means. .

The magnetic field control means energizes the magnetic field generating member in a forward direction when the detection value of the external magnetic field detection means exceeds a permissible value, and changes the detection value of the external magnetic field detection means in the energized state. Detecting, setting an energizing direction to the magnetic field generating member in accordance with the fluctuation, and further controlling an energizing amount to the magnetic field generating member such that a detection value of the external magnetic field detecting means is less than the allowable value. Then, the external magnetic field can be canceled. Further, the external magnetic field detecting means includes a pair of magnetic field detecting elements separated from each other along the direction in which the plurality of magnetoresistive elements are arranged, and a magnetic field arranged near each of the magnetic field detecting elements and canceled by the magnetic field generating means. And a permanent magnet for causing magnetic fields in parallel to each other to act on the corresponding magnetic field detecting elements. When the difference between the detection values of the pair of magnetic field detection elements exceeds an allowable value, the magnetic field control means controls the magnetic field generation member based on the difference between the pair of detection values so that the difference becomes smaller. By controlling the energization, the external magnetic field can be canceled.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a rear view showing a total station on which the magnetic encoder of the present invention is mounted, with a part cut away so that the main part of the magnetic encoder can be seen. FIG. 2 shows the total station so that the main part of the magnetic encoder can be seen. It is a side view which cuts and shows a part.

As is well known, the total station 11 includes a bottom plate 13 for mounting on a tripod or the like.
Leveling table (base) 1 supported by three leveling screws 15
7. A U-shaped frame (main body) 21 rotatably supported by the leveling table 17 via a vertical shaft 19 and having a pair of columns 21a, between the two columns 21a of the frame 21. Telescope 2 rotatably supported on a horizontal axis 23 via a horizontal axis 23
5 and so on. Note that the horizontal axis 23 is the collimating telescope 2
5 is fixed to the left and right sides and is rotatably supported by the two columns 21a of the gantry 21, but only the left horizontal shaft 23 is shown in FIG.

The vertical shaft 19 is rotatably supported by a vertical bearing 27 fixed to the leveling table 17. The gantry 21 has a base 21b connecting the support portions 21a fixed to the upper end of the vertical shaft 19, and is supported by the vertical shaft 19 so as to be rotatable integrally. The horizontal shaft 23 is rotatably supported by a horizontal bearing 29 fixed to a pair of columns 21 a of the gantry 21. As described above, the collimating telescope 25 is pivotally supported on the gantry 21 via the horizontal shaft 23 so as to be vertically rotatable, and further supported on the leveling platform 17 via the gantry 21 and the vertical shaft 19 so as to be azimuthally rotatable. Have been.

Further, the magnetic encoder 4 is provided on the vertical axis 19 as a horizontal degree for measuring the rotation angle (horizontal angle) of the vertical axis 19 (the gantry 21, the collimating telescope 25) with respect to the leveling table 17.
The magnetic encoder 51 is mounted on the horizontal axis 23 as an altitude degree for measuring the rotation angle (altitude angle) of the horizontal axis 23 (collimation telescope 25) with respect to the gantry 21. These magnetic encoders 41 and 51 are closely opposed at predetermined intervals to magnetic drums 43 and 53 fixed to the shafts 19 and 23 and a multi-pole magnetized layer formed on the outer peripheral surface of the magnetic drums 43 and 53, respectively. A magnetic sensor unit 44 and a magnetic sensor unit 54 are provided.

Although not shown in detail, signal processing means for detecting the output signals of the magnetic sensor units 44 and 54 to obtain the rotation angles of the magnetic encoders 41 and 51, ie, the horizontal angle and the altitude angle. An electronic circuit 60 including means (see FIG. 4) is mounted on the base 21 b of the gantry 21. Then, the total station 11 is operated,
Operation panels 31 and 32 having a keyboard 31a for controlling and a display 31b for displaying basic data and distance measurement results input by the keyboard,
It is provided on both front and rear surfaces of the gantry 21 (see FIG. 2).

In FIGS. 1 and 2, reference numeral 33 denotes a handgrip for carrying the total station 11, and reference numeral 34 denotes a dustproof attached to the gantry 21 to protect the magnetic encoder 41 and a battery (not shown). The cover and reference numerals 35 and 36 are the collimating telescope 2 respectively.
5 is an eyepiece and an objective lens.

The configuration of the magnetic encoder according to the present embodiment will be described in more detail with reference to FIGS. Since the basic configurations of the magnetic encoders 41 and 51 are the same, the configuration of one magnetic encoder 51 will be described. Moreover, the magnetic sensor unit 5 according to the embodiment of the present invention
Each of the magnetic sensor units 4 and 55 has a plurality of magnetoresistive elements (see FIG. 3). However, since the magnetic sensor units 54 and 55 have the same configuration, only the configuration of one magnetic sensor unit 54 will be described. FIG. 3 shows each magnetic resistance element of the magnetic sensor unit 54 of the magnetic encoder 51 and the multipolar magnetized layer 53a.
FIG. 4 is a wiring diagram showing the connection of the magnetoresistive elements provided in the magnetic sensor unit 54. The magnetic sensor unit 54 is fixed to the angle 56, and is fixed to the gantry 21 via the angle 56.

The outer peripheral surface of the magnetic drum 53 has a division number N
(N is a positive integer) to form a multi-pole magnetized layer 53a magnetized at an equal pitch. The magnetic pole pitch (interval between pole boundaries) of the multipolar magnetized layer 53a is λ. This multi-pole magnetized layer 53
The magnetic sensor unit 54 is arranged so as to oppose a with a predetermined gap. The magnetic sensor 54 unit is
8 provided on the opposing surface of the planar substrate 54a and the planar substrate 54a facing the multipolar magnetized layer 53a at a pitch of λ / 4.
Magnetoresistive elements 4a1, 4b1, 4a2, 4b2, 4a
3, 4b3, 4a4, and 4b4. The magnetic sensor 54 unit includes the magnetoresistive elements 4a1 to 4a4, 4b1
4b4 is disposed so that a vertical line set substantially at the center thereof passes through the rotation center of the magnetic drum 53. That is, the magnetoresistive elements 4a1 to 4a4, 4b1 to 4b4 are arranged in parallel with the tangential direction of the magnetic drum 53. Note that, in this specification, the λ pitch is a unit related to the central angle, and
Indicates one magnetization pitch.

The magnetic encoder 51 includes a magnetic drum 5
3 rotates, the magnetoresistive elements 4a1 to 4a4 that depend on changes in the magnetic field (lines of magnetic force) 3 generated by the multipolar magnetized layer 53a,
This is an incremental type magnetic encoder that detects a change in the resistance value of 4b1 to 4b4 and detects the rotation angle of the magnetic drum 53 at a λ / 4 pitch from the change in the resistance value. In addition,
An angle smaller than λ / 4 pitch is obtained by a so-called interpolation operation.

Eight magnetoresistive elements 4a1, 4b1, 4a
As shown in FIG. 3, 2, 4b2, 4a3, 4b3, 4a4, and 4b4 have an A phase including four magnetoresistive elements 4a1 to 4a4 and a B phase including four magnetoresistive elements 4b1 to 4b4. Divided. A-phase magnetoresistive elements 4a1, 4a2, 4a
3, 4a4 and B-phase magnetoresistive elements 4b1, 4b2, 4b
3 and 4b4 are arranged alternately, and the intervals between the magnetoresistive elements 4a1 to 4a4 and 4b1 to 4b4 of the same phase are equal pitches of λ / 2, and the intervals between adjacent magnetoresistive elements of other phases are λ / 4.
The pitch is equal to 4.

The A-phase and B-phase magnetoresistive elements 4a1 to 4a1 to
4a4, 4b1 to 4b4 are each bridge-connected as shown in FIG. That is, the serially connected magnetoresistive elements 4a1, 4a2 and 4a3, 4a4, the magnetoresistive elements 4b1, 4b2 and the magnetoresistive elements 4b3, 4b4 are connected in parallel, and the A-phase terminals e ₀ , e ₁ are connected between the series resistors. , And B
The phase terminals e ₀ ′ and e ₁ ′ are drawn out. Then, the electronic circuit 61 applies a constant voltage V between the bridge-connected magnetoresistive elements, and changes in voltages appearing at the A-phase terminals e ₀ and e ₁ and the B-phase terminals e ₀ ′ and e ₁ ′. The change of the magnetic field is detected based on (phase), and the rotation angle ω of the magnetic drum 53 is measured.

According to this embodiment, the resistance values a1, a2, a3, and a4 of the A-phase magnetoresistive elements 4a1 to 4a4 are represented by the following equations by the change in the magnetic field 3 acting by the rotation of the magnetic drum 53. Changes to a1 = R0 + Rsin (Nω) a2 = R0 + Rsin (Nω + π) = R0−Rsin (Nω) a3 = R0 + Rsin (Nω + 2π) = R0 + Rsin (Nω) a4 = R0 + Rsin (Nω + 3π) = R0−Rsin (Nω) , R0 is a resistance value in the absence of a magnetic field, R is a coefficient (resistance ratio), and N is a multipolar magnetized layer 5.
3a is the number of divisions.

Therefore, when the outputs of the terminal e ₀ and the terminal e ₁ are differentially amplified, the output Aout of the phase A is given by Aout = α × R × V / R0 × sin (Nω) (where α is the amplification factor ).

Since the B-phase magnetoresistive elements 4b1 to 4b4 are arranged shifted by .lambda. / 4 pitch with respect to the A-phase magnetoresistive elements 4a1 to 4a4, the outputs of the terminals e0 'and e1' are differentiated. After amplification, the B-phase output Bout is given by Bout = α × R × V / R0 × cos (Nω).

The A-phase output Aout and the B-phase output Bo
If the zero cross point of ut is detected, the rotation angle of the magnetic drum 53 can be detected in units of 360 / 4N (゜). That is,
The detection pitch is reduced to four times the division number N, and the resolution is increased. In the embodiment of the present invention, the output A of the A and B phases
By the following interpolation calculation based on out and Bout, the detectable detection pitch is made smaller than 1 / 4N, the number of detection pitches is increased, and the resolution is increased. tan ^-1 (Aout / Bout)

In order to correct the eccentricity error, a magnetic sensor unit satisfying the same condition as the phase position may be arranged at a position substantially 180 ° opposite to each magnetic sensor. In the illustrated total station, two magnetic sensor units 5 arranged at opposing positions shifted by 180 ° are provided.
The eccentricity error is corrected using the detection values of the magnetic sensor units 44 and 45 and 55.

The above is the basic configuration of the total station to which the embodiment of the present invention is applied. The configuration which eliminates the influence of external magnetism, which is a feature of the embodiment of the present invention, will be described.

Each magnetic sensor unit 44, 45, 54,
55, each magnetic sensor unit 44, 45, 5
The magnetic drums 43, 5 detected by the magnetoresistive elements 4, 55
3, an external magnetic field detecting element 111, 121, 131, 141 for detecting an external magnetic field acting substantially in parallel with the magnetic field 3, and a magnetic field generating member 21 for generating a magnetic field for canceling the external magnetic field
1, 221 231 241 are arranged. In this embodiment, the external magnetic field detecting elements 111, 121, 13
The magnetic field generating members 211, 221, 2
31 and 241 are controlled to be energized.

Regarding the configuration of the external magnetic field detecting element and the magnetic field generating member, each magnetic sensor unit 44, 45, 54,
55, external magnetic field detecting elements 111, 121, 131, 14
1. Since the configurations of the magnetic field generating members 211, 221, 231, and 241 are the same, an embodiment applied to the magnetic sensor unit 54 shown in FIGS.

As shown in FIG. 5, the magnetic field 3 generated by the multi-pole magnetized layer 53a of the magnetic drum 53 is generated along the surface of the multi-pole magnetized layer 53a of the magnetic drum 53. Therefore, the external magnetic field 301 in the direction parallel to the magnetic field 3 of the multi-pole magnetized layer 53a has a great effect when the magnetic sensor unit 54 detects. Therefore, in the present embodiment, a pair of external magnetic field detecting elements 131 constituting the external magnetic field detecting element 131 is provided on the extension of the magnetic resistance element row of the magnetic sensor unit 54.
a and 131b are arranged. The magnetic drum 53 is cylindrical, and the magnetic sensor unit 54 is flat. Therefore, above an arbitrary distance position on the extension of the magnetic sensor unit 54, the distance from the magnetic drum 53 is large and the influence of the magnetic field 3 is almost eliminated. Therefore, since the external magnetic field detecting elements 131a and 131b are not affected by the magnetic field 3,
A magnetoresistive element can be used.

The magnetic field generating member 231 is arranged on the back side of the magnetic sensor unit 54. Magnetic field generating member 23
Numeral 1 comprises a U-shaped core 231a having a coil 231b wound in the center thereof, and is arranged so as to generate a magnetic field (lines of magnetic force) 4a parallel to the arrangement direction of the magnetoresistive elements when the coil 231b is energized. ing. External magnetic field detecting elements 111, 12 of other magnetic sensor units 44, 45, 55
1, 131, 141 and magnetic field generating members 211, 22
1, 231 and 241 have the same configuration.

An external magnetic field canceling control system for controlling the external magnetic field detecting element and the magnetic field generating member will be described with reference to FIG. In the present embodiment, the external magnetic field cancellation control system is provided separately from the angle measurement processing circuit. External magnetic field detecting elements 111, 121, 211, 221
Are detected and output by the control circuit (CPU) 6
1 is input. The CPU 61 calculates the strength of the external magnetic field based on each of the input detection signals, and if the strength is equal to or more than the allowable value, the external magnetic field generating member 2 that can cancel the detected external magnetic field.
11, 221, 231, and 241 are calculated.
Then, based on the calculated energization direction and current value, current is applied to the external magnetic field generation members 211, 221, 231, and 241 via the respective drive circuits 63a, 63b, 63c, and 63d. The above processing is repeated until the intensity of the detected external magnetic field becomes smaller than the allowable magnetic field.

The details of the external magnetic field canceling operation of the first embodiment will be described with reference to the flowchart shown in FIG. In this embodiment, when the power of the total station is turned on, an external magnetic field canceling process is started.

In this process, first, an external magnetic field is detected via the first external magnetic field detecting element (S101). Then, it is checked whether or not the detected absolute value of the external magnetic field is equal to or less than the absolute value of the allowable magnetic field (S103). If it is below, there is no need to cancel the external magnetic field, and the display of the angle measurement value on the display is permitted (S103;
Y, S105). Then, returning to S101, the detection processing of the external magnetic field is repeated for all the external magnetic field detection elements.

If the absolute value of the detected external magnetic field is not less than the absolute value of the allowable magnetic field (S103; N), even if the angle is measured in this state, the error is large, and the display of the angle measurement value on the display 31b is prohibited. (S107). First, a specified current is caused to flow in the coil in the forward direction (S109), and an external magnetic field is detected by inputting the output signal of the external magnetic field detecting element (S11).
1) Check whether the detected magnetic field has increased (S1)
13).

When the magnetic field has increased (S113;
Y) Since a magnetic field is generated in the coil in the same direction as the external magnetic field, a current is applied in a direction opposite to the forward direction of the coil to detect the magnetic field, and the current is gradually increased until the detected magnetic field becomes equal to or less than the allowable magnetic field. (S117).
Then, when the detected magnetic field becomes equal to or smaller than the allowable magnetic field, the current supply state is maintained, and the process returns to S101.

When the magnetic field has not increased, a magnetic field is generated in the coil in a direction to cancel the external magnetic field.
The magnetic field detection is repeated while gradually increasing the forward current value (S115). Then, when the detected magnetic field becomes equal to or smaller than the allowable magnetic field, the current supply state is maintained, and the process returns to S101. The above process is repeated for all the magnetic sensor units.

In steps S115 and S117 to S101, since the detected magnetic field returns to a state below the allowable magnetic field, display of the angle measurement value is normally permitted. Therefore, the angle measurement values obtained by the subsequent angle measurement processing are displayed on the display 31b. Thus, the operator can know the value measured by the display 31b in a state where the influence of the external magnetic field is canceled.

In the above-described embodiment, only the strength of the external magnetic field is detected by the external magnetic field detecting element, and the direction of energization is detected based on the detection result of the external magnetic field detecting element that changes when the magnetic field generating member is energized. Met. next,
An embodiment of an external magnetic field detecting element capable of detecting not only the intensity of the external magnetic field but also the direction of the external magnetic field will be described. 9 and 10 show an embodiment applied to the magnetic sensor unit 55.

In this embodiment, a pair of magnetic direction detecting elements 14 separated from the magnetic sensor unit 55 in a position closer to the gantry 21 in parallel with the direction in which the magnetoresistive elements are arranged.
2a and 142b are arranged. Further, a pair of permanent magnets 143 a and 143 b are fixed at positions facing the external magnetic field detecting elements 142 a and 142 b via a non-magnetic body 145. These permanent magnets 143a, 143b
Are arranged such that the lines of magnetic force are generated in a direction substantially parallel to the direction of the external magnetic field that affects the angle measurement, and that the polarities are opposite to each other. That is, the external magnetic field detecting element 14
2a and 142b are permanent magnets 143a and 143 in a normal state.
b, the action of the magnetic fields 5a and 5b. Magnetic fields 5a, 5
b, when an external magnetic field in the same direction as any of the magnetic fields 5a and 5b is present, the magnetic fields in the same direction are multiplied and increased, and the magnetic fields in the opposite directions are canceled and reduced. Therefore, by detecting a change in the detection signal of the external magnetic field detection elements 142a and 142b, the direction and intensity of the magnetic field can be known.

The other magnetic sensor units 44, 4
External magnetic field detecting elements 112a, 112b, 122a, 122 similar to the direction detecting elements 142a, 142b
b, 132a, 132b and a corresponding pair of permanent magnets are provided. Also, each pair of direction detecting elements 112
a and 112b, 122a and 122b, 132a and 132
b and the detection signals of 142a and 142b
1 is input. The control circuit 61 detects the direction and intensity of the external magnetic field from the magnitude relationship between the pair of detection signals, and in the direction in which the detection signals become equal, via the drive circuits 63a to 63d, the magnetic field generation members 211, 221, 231 and 241. To generate a magnetic field, and the magnetic field cancels out the external magnetic field.

The details of the operation for canceling (cancelling) the external magnetic field in the second embodiment will be described with reference to the flowchart shown in FIG. In this embodiment, when the power of the total station is turned on, the external magnetic field cancel processing starts.

In this process, first, an external magnetic field is detected via the first pair of direction detecting elements (S20).
1). Then, it is checked whether or not the absolute value of the difference between the one detected magnetic field a and the other detected magnetic field b detected by the pair of external magnetic field detection elements is equal to or less than the absolute value of the allowable magnetic field (S203). If it is below, there is no need to cancel the external magnetic field, and the display of the angle measurement value on the display 31b is permitted (S203; Y, S205). And S
Returning to 201, one detection magnetic field a and the other detection magnetic field b
S201 to S20 while the absolute value of the difference
Step 5 is repeated.

If the absolute value of the difference between the detected external magnetic fields is not smaller than the absolute value of the permissible magnetic field (S203; N), an error is large even if the angle is measured in this state. The display is prohibited (S207).

Next, the magnitude relationship between the detected magnetic field a and the detected magnetic field b is checked (S209). If the detected magnetic field a is larger, the external magnetic field has the same direction as the external magnetic field 302 shown in FIG. Then, a current is caused to flow in the forward direction that generates a magnetic field in the opposite direction to the magnetic field 5a, and the current value is adjusted such that the difference between the detected magnetic fields a and b is equal to or smaller than the allowable magnetic field (S21)
1). When the magnetic field becomes equal to or smaller than the allowable magnetic field, the process returns to S201.

If the detected magnetic field a is not larger, the external magnetic field is opposite to the external magnetic field 302 shown in FIG. 10, so that a current flows through the coil 243 in the reverse direction to generate a magnetic field in the direction of the magnetic field 5a. The current value is adjusted so that the difference b is equal to or less than the allowable magnetic field (S213). When the magnetic field becomes equal to or smaller than the allowable magnetic field, the process returns to S201. In addition, the above processing,
Repeat for all magnetic sensor units.

In steps S211 and S213 to S201, the difference between the detected magnetic fields a and b returns when the difference between the detected magnetic fields is equal to or smaller than the allowable magnetic field. Thereafter, display of the angle measurement value is permitted. Therefore, the angle measurement values obtained by the subsequent angle measurement processing are displayed on the display 31b. Thus, the operator can know the value measured by the display 31b in a state where the influence of the external magnetic field is canceled.

As described above, according to the embodiment of the present invention,
If an external magnetic field that affects the measurement accuracy is detected and such an external magnetic field is detected, the coil is energized to generate a magnetic field that cancels out the external magnetic field. A highly accurate angle measurement that is not affected by a strong external magnetic field can be performed.

In the second embodiment, since the direction of the external magnetic field is also detected, even when the external magnetic field changes, the effect of the external magnetic field can be quickly removed to maintain the measurement accuracy.

The embodiment of the present invention applied to a total station has been described above.
It goes without saying that the present invention can be applied to other surveying instruments such as transit and auto level.

[0048]

As is clear from the above description, the present invention
Detects an external magnetic field that is a cause of the detection error of the magnetic sensor of the magnetic encoder mounted on the surveying instrument, and generates a magnetic field that cancels the external magnetic field in the magnetic field generating member, so that predetermined accuracy is maintained even in extremely strong magnetic fields. it can.

[Brief description of the drawings]

FIG. 1 is a rear view showing a total station equipped with a magnetic encoder to which the present invention is applied, with a part cut away so that a main part of the magnetic encoder can be seen.

FIG. 2 is a side view showing the total station with a part cut so that a main part of a magnetic encoder can be seen.

FIG. 3 is an enlarged view for explaining a relationship between a magnetic drum and a magnetic sensor of the magnetic encoder.

FIG. 4 is a circuit diagram showing an example of a connection of a magnetoresistive element of the magnetic encoder.

FIG. 5 is a partially cutaway front view showing the configuration of the first embodiment of the magnetic sensor, the external magnetic field detecting element, and the magnetic field generating member of the magnetic encoder.

FIG. 6 is a sectional view taken along the line VI-VI in FIG. 5;

FIG. 7 is a block diagram illustrating a circuit configuration according to the first embodiment.

FIG. 8 is a diagram showing, in a flowchart, main operations in the first embodiment.

FIG. 9 is a partially cutaway front view showing the configuration of a magnetic sensor, an external magnetic field detecting element, and a magnetic field generating member of the magnetic encoder according to a second embodiment.

FIG. 10 is a sectional view taken along the line XX in FIG. 9;

FIG. 11 is a block diagram showing a circuit configuration according to the second embodiment.

FIG. 12 is a flowchart showing main operations in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Total station (surveying instrument) 13 Bottom plate 15 Leveling screw 17 Leveling table 19 Vertical axis 21 Mount 23 Horizontal axis 25 Collimated telescope 27 Vertical bearing 29 Horizontal bearing 31b Display (display means) 41 51 Magnetic encoder 43 53 Magnetic drum (rotation) 53a Multi-pole magnetized layer 44 54 First magnetic sensor unit (detecting means) 45 55 Second magnetic sensor unit (detecting means) 4a1, 4a2, 4a3, 4a4 A-phase magnetic resistance element 4b1, 4b2, 4b3, 4b4 B-phase magnetoresistive element 61 Control circuit (magnetic field control means) 63a 63b 63c 63d Drive circuit 111 121 131 141 External magnetic field detecting element 211 221 231 241 Magnetic field generating member 211b 221b 231b 241b Coil

Claims (9)

[Claims] 1. A surveying instrument equipped with a magnetic encoder, comprising: an external magnetic field detecting means for detecting an external magnetic field acting on a magnetic sensor of the magnetic encoder; and an external magnetic field acting on the magnetic sensor. Magnetic field generating means for generating a magnetic field in a canceling direction; and magnetic field control means for generating, in the magnetic field generating means, a magnetic field for canceling an external magnetic field acting on the magnetic sensor detected by the external magnetic field detecting means. A surveying instrument equipped with a magnetic encoder. 2. A surveying instrument equipped with a magnetic encoder according to claim 1, wherein said magnetic field control means detects an external magnetic field by said external magnetic field detection means before said magnetic encoder operates, and controls said magnetic field generation means. A surveying instrument equipped with a magnetic encoder that generates a magnetic field. 3. A surveying instrument equipped with the magnetic encoder according to claim 1, wherein the magnetic encoder is rotatably supported by a fixed portion of the surveying instrument, and is a multi-pole magnetized magnetized at an equal pitch on an outer peripheral surface. A magnetic drum having a plurality of layers, wherein the magnetic sensor is mounted on the fixed portion, and a plurality of magnetic sensors are arranged at predetermined intervals in parallel with a tangential direction of the magnetic drum so as to face a multi-pole magnetized layer of the magnetic drum. A surveying instrument equipped with a magnetic encoder equipped with a magnetoresistive element. 4. A surveying instrument equipped with a magnetic encoder according to claim 1, wherein said magnetic field generating means is disposed behind said plurality of magnetoresistive elements, and generates a magnetic field substantially parallel to an arrangement direction of said magnetoresistive elements. A surveying instrument equipped with a magnetic encoder that has a coil to generate. 5. A surveying instrument equipped with a magnetic encoder according to claim 4, wherein said external magnetic field detecting means is equipped with a magnetic encoder arranged on an extension of an arrangement direction of said plurality of magnetoresistive elements. . 6. A surveying instrument equipped with a magnetic encoder according to claim 5, wherein said magnetic field control means forwardly moves said magnetic field generating member when a detection value of said external magnetic field detection means exceeds an allowable value. Detecting a change in the detection value of the external magnetic field detection means in the energized state, setting a direction of energization to the magnetic field generating member in accordance with the change; A surveying instrument equipped with a magnetic encoder that controls the amount of current supplied to the magnetic field generating member so as to be less than or equal to. 7. A surveying instrument equipped with a magnetic encoder according to claim 4, wherein said external magnetic field detecting means comprises: a pair of magnetic field detecting elements separated from each other along an arrangement direction of said plurality of magnetoresistive elements; Placed near the magnetic field detection element,
A surveying instrument equipped with a magnetic encoder including a permanent magnet for applying a magnetic field substantially parallel to the magnetic field canceled by the magnetic field generating means and in the opposite direction to the corresponding magnetic field detecting element. 8. A surveying instrument equipped with a magnetic encoder according to claim 7, wherein said magnetic field control means is adapted to detect said pair of detected values when a difference between detected values of said pair of magnetic field detecting elements exceeds an allowable value. A surveying instrument equipped with a magnetic encoder that controls energization of the magnetic field generating member based on the difference between the two. 9. A surveying instrument equipped with the magnetic encoder according to claim 1, further comprising display means for displaying a surveying value, wherein a value detected by the magnetic field detecting element is within a predetermined allowable range. A surveying instrument equipped with a magnetic encoder that does not display a surveying value when it does not fit inside.