Rotation angle detecting apparatus and surveying instrument

A rotation angle detecting apparatus comprises a bearing holder, a rotation shaft rotatably supported by said bearing holder, a shaft portion space formed in said rotation shaft, a bearing holder space formed in said bearing holder, a first condenser lens in said shaft portion space and having an optical axis that coincides with a center line of said rotation shaft, a second condenser lens in said bearing holder space and on an extension of a center line of said rotation shaft, an angle detection pattern at a focal position of one of said first and said second condenser lens, and an image sensor at a focal position of the other of said condenser lens, wherein said image sensor detects a projection image of said angle detection pattern projected onto said image sensor, and a displacement of said projection image involved by the rotation of said rotation shaft is detected.

BACKGROUND OF THE INVENTION

The present invention relates to a rotation angle detecting apparatus for detecting a rotation angle and a surveying instrument for measuring an angle and a distance of an object to be measured.

A total station has become widespread as a surveying instrument for measuring an angle and a distance of an object to be measured in the civil engineering or construction field. The total station can highly accurately measure an angle and a distance of the object to be measured at from a short-distance to a long-distance, but an inexpensive and small total station with good mobility that is used at a site targeting a relatively short distance, e.g., the interior field etc. (which will be referred to as a mini total station hereinafter) has been recently demanded more.

As one of causes of an increase in price of the total station, there is a demand for high accuracy of an angle detection accuracy and a rotation accuracy.

An error of a measurement value due to an angular error is proportionate to a distance to a object to be measured, and hence an angular accuracy is demanded to a degree of a second. Therefore, a detection error of a rotation angle detecting apparatus and a rotation error (a tilt error involved by rotation on the rotational center) due to wobbling of a rotation shaft of a telescope for measurement which can be a cause of an angular error are strictly limited.

As a rotation angle detecting apparatus for use in a surveying instrument, an encoder has been conventionally adopted, and a highly accurate encoder is expensive. Further, it is difficult to set a rotation accuracy of a rotation shaft to a demanded accuracy, just by managing a processing accuracy of a lone component, and fine adjustment and fine finishing in an assembling state of the rotation shaft and a bearing holder are required, which results in expensiveness.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a rotation angle detecting apparatus that enables highly accurate angular detection with a simple structure and a surveying instrument using the rotation angle detecting apparatus.

To attain the above object, a rotation angle detecting apparatus according to the present invention comprises a bearing holder, a rotation shaft rotatably supported by the bearing holder, a shaft portion space formed in the rotation shaft, a bearing holder space formed in the bearing holder, a first condenser lens which is accommodated in the shaft portion space and has an optical axis that coincides with a centerline of the rotation shaft, a second condenser lens which is provided in the bearing holder space and also provided on an extension of a center line of the rotation shaft, an angle detection pattern provided at a focal position of one of the first condenser lens and the second condenser lens, and an image sensor provided at a focal position of the other of the first condenser lens and the second condenser lens, and in the rotation angle detecting apparatus, the image sensor detects a projection image of the angle detection pattern projected onto the image sensor, and a displacement of the projection image involved by the rotation of the rotation shaft is detected.

Further, in the rotation angle detecting apparatus according to the present invention, a reference position can be set on the image sensor, and a rotational displacement amount of the angle detection pattern with respect to the reference position is detected.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern is detected by the image sensor, a center position of an angle detection pattern image is detected based on the angle detection pattern, and a tilt angle of the rotation shaft is detected based on a deviation between the detected center position of the angle detection pattern image and the reference image on the image sensor and based on a focal length of the first condenser lens or the second condenser lens.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern has a line-segment pattern in which line segments extending in a radial direction are arranged on a total circumference at a predetermined angle pitch and a ring-like track formed of the line segments is provided.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern has a circular pattern of one circle or a plurality of concentric circles with the center of the angle detection pattern as a center.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern has a plurality of concentrically multiply-formed ring-like tracks.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern is detected when a detection line is set on the image sensor and a detection signal of the angle detection pattern is extracted from a signal obtained by scanning the detection line.

Further, in the rotation angle detecting apparatus according to the present invention, the detection line is a straight line which runs through the center of the angle detection pattern on the image sensor and is set to fall within the range including each track in accordance with each track in a direction orthogonal to each radius that equally divides the circumference as required.

Further, in the rotation angle detecting apparatus according to the present invention, the angle detection pattern is detected when a detection line is set on the image sensor and a detection signal of the angle detection pattern is extracted from a signal obtained by scanning the detection line, and the detection line is a straight line which runs through the center of the angle detection pattern on the image sensor and cuts across the circular pattern.

Further, in the rotation angle detecting apparatus according to the present invention, the detection line is a circle which is included in the track and has the center of the angle detection pattern on the image sensor as its center.

Further, a surveying instrument according to the present invention comprises a base unit, a frame rotatably provided on the base unit through a first rotation shaft having a vertical shaft center line, a telescope unit rotatably provided on the frame through a second rotation shaft having a horizontal shaft center line, a first rotation angle detecting apparatus which is provided between the first rotation shaft and the base unit and has the configuration according to claim1, and a second rotation angle detecting apparatus which is provided between the second rotation shaft and the mount and has the configuration according to claim1.

According to the present invention, the rotation angle detecting apparatus comprises a bearing holder, a rotation shaft rotatably supported by the bearing holder, a shaft portion space formed in the rotation shaft, a bearing holder space formed in the bearing holder, a first condenser lens which is accommodated in the shaft portion space and has an optical axis that coincides with a center line of the rotation shaft, a second condenser lens which is provided in the bearing holder space and also provided on an extension of a center line of the rotation shaft, an angle detection pattern provided at a focal position of one of the first condenser lens and the second condenser lens, and an image sensor provided at a focal position of the other of the first condenser lens and the second condenser lens, and in the rotation angle detecting apparatus, the image sensor detects a projection image of the angle detection pattern projected onto the image sensor, and a displacement of the projection image involved by the rotation of the rotation shaft is detected. As a result, a rotation angle of the rotation shaft can be measured without using an expensive encoder.

Further, according to the present invention, in the rotation angle detecting apparatus, a reference position can be set on the image sensor, and a rotational displacement amount of the angle detection pattern with respect to the reference position is detected. As a result, the reference position can be set an arbitrary position at an arbitrary timing, the rotation shaft and the bearing holder do not have to be mechanically set, and initial setting of the angle measurement can be facilitated.

Further, according to the present invention, in the rotation angle detecting apparatus, the angle detection pattern is detected by the image sensor, a center position of an angle detection pattern image is detected based on the angle detection pattern, and a tilt angle of the rotation shaft is detected based on a deviation between the detected center position of the angle detection pattern image and the reference image on the image sensor and based on a focal length of the first condenser lens or the second condenser lens. As a result, even if the rotation of the rotation shaft contains an error, a measurement value can be corrected by using the detected tilt angle. Even if an assembling accuracy of the rotation shaft is not high, the highly accurate measurement is possible, and a manufacturing cost can be reduced.

Further, according to the present invention, in the rotation angle detecting apparatus, the angle detection pattern is detected when a detection line is set on the image sensor and a detection signal of the angle detection pattern is extracted from a signal obtained by scanning the detection line. As a result, the detection line can be arbitrarily set, the detection lines may overlap each other, the positions or the numbers of the detection lines in the setting are not limited, and the setting can be configured in accordance with the measurement accuracy.

Furthermore, according to the present invention, the surveying instrument comprises a base unit, a frame rotatably provided on the base unit through a first rotation shaft having a vertical shaft center line, a telescope unit rotatably provided on the frame through a second rotation shaft having a horizontal shaft center line, a first rotation angle detecting apparatus which is provided between the first rotation shaft and the base unit and has the configuration according to claim1, and a second rotation angle detecting apparatus which is provided between the second rotation shaft and the mount and has the configuration according to claim1. As a result, an expensive encoder is not used, an error produced in the assembling of the rotation shaft and the bearing holder can be corrected by using a detection result of the rotation angle detecting apparatus, the assembling of the rotation shaft and the bearing holder is not costly, and the manufacturing cost can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will be given below on the embodiments of the present invention by referring to the drawings.

First, inFIG. 1AandFIG. 1B, description will be given on a rotation angle detecting apparatus according to an embodiment of the present invention.

InFIG. 1, the reference numeral1denotes a rotation shaft which is an object to be measured with respect to a rotation angle measurement, and the rotation shaft1is freely rotatably supported by a bearing holder3via a bearing2.

A cylindrical shaft portion space4is formed at an end portion of the rotation shaft1so as to be concentric with a center line of the rotation shaft1, and a shaft end portion has a hollow structure. In the bearing holder3, a bearing holder space5is formed on an extended line of the shaft center line of the shaft portion space4. The bearing holder space5is concentric with the shaft portion space4, and the bearing holder space5and the shaft portion space4have the same diameter. Primary constituent elements of a rotation angle detecting apparatus6are accommodated in the shaft portion space4and the bearing holder space5.

A first condenser lens7is provided in the shaft portion space4, and a second condenser lens8is provided in the bearing holder space5. Each of the first condenser lens7and the second condenser lens8has a magnifying power of 1, and these lenses have the same focal length.

The first condenser lens7and the second condenser lens8have optical axes9aand9b, respectively, the optical axis9acoincides with the center line of the rotation shaft1, and the optical axis9bcoincides with the shaft center line of the bearing holder space5. Therefore, when the rotation shaft1does not have a tilt, the optical axis9aand the optical axis9bcoincide with each other on the same straight line.

In addition, it is preferable for the first condenser lens7and the second condenser lens8to have the same characteristics in order to prevent an image from being distorted.

An angle detection pattern11is provided on a bottom portion of the shaft portion space4, and the angle detection pattern11is placed at a focal position of the first condenser lens7. Further, an image sensor12is provided in the bearing holder space5, and the image sensor12is placed at a focal position of the second condenser lens8.

A light emitting unit for illuminating the angle detection pattern11is provided at an appropriate position of the bearing holder space5or the shaft portion space4. In the drawing, as an example, a light emitting unit13that is provided on the bottom portion of the shaft portion space4and illuminates the angle detection pattern11is shown.

As the image sensor12, for example, a CCD or a CMOS sensor as an aggregate of pixels etc. is used, and a position of each pixel can be specified on the image sensor12. Furthermore, a photodetection signal from the image sensor12is input to a signal processing unit14, and the signal processing unit14is configured to measure a rotation angle or a tilt (a tilt angle) of the rotation shaft1based on the photodetection signal.

FIG. 2shows an example of the angle detection pattern11.

A basic shape of the angle detection pattern11is a circle, and the center of the angle detection pattern11coincides with the optical axis of the first condenser lens7, i.e., the optical axis9a.

The angle detection pattern11is configured by a circular pattern15for centering provided at the central portion thereof and a line-segment pattern16arranged around the circular pattern15. The circular pattern15is a true circle described with a predetermined line width.

The line-segment pattern16has a configuration that line segments extending in the radial direction are arranged on a total circumference at a predetermined angle pitch, and a ring-like track is formed by using the line-segment pattern16. In the line-segment pattern16, identification line segments17provided at a plurality of predetermined positions are thick. An inner end and an outer end of the line-segment pattern16are placed on the circumferences which are concentric with the circular pattern15, respectively. Moreover, as shown in the drawing, the identification line segments17are not provided at the positions that equally divide the circumference, and detecting the positions of the identification line segment17enables detecting a rotation angle exceeding a pitch interval of the angle detection pattern11.

Description will be given below on an operation of the above-mentioned rotation angle detecting apparatus6.

The angle detection pattern11is projected onto the image sensor12with a relationship of 1:1 by the operations of the first condenser lens7and the second condenser lens8, and the image sensor12emits a signal corresponding to the received angle detection pattern11.

When the rotation shaft1rotates, the angle detection pattern11rotates integrally with the rotation shaft1, and a rotated angle detection pattern image is projected onto the image sensor12. Since the image sensor12emits the photodetection signal in accordance with each pixel, for example, when the line-segment pattern16and the identification line segment17move, the positions of the pixels receiving the lights of the line-segment pattern16and the identification line segment17change. Therefore, when the positional change of the pixels receiving the lights of the line-segment pattern16and the identification line segment17is detected based on the signals from the image sensor12, a rotation angle of the rotation shaft1with respect to the bearing holder3can be detected.

Next, description will be given on a situation where the rotation shaft1tilts with respect to the bearing holder3.

With the operations of the first condenser lens7and the second condenser lens8, a light ray that enters the first condenser lens7is projected onto the image sensor12so as to be parallel to the light ray by the second condenser lens8. Therefore, as shown inFIG. 1B, when the optical axis9aof the first condenser lens7tilts with respect to the optical axis9of the second condenser lens8, the angle detection pattern image projected onto the image sensor12is projected onto the image sensor12for an amount corresponding to the tilt of the optical axis9aof the first condenser lens7from a tilting direction. Therefore, the projected image is displaced on the image sensor12for an amount corresponding to the tilt.

Here, assuming that a displacement amount of the pattern image on the image sensor12is Δ, the tilt of the optical axis9aof the first condenser lens7is α, and a focal point of the second condenser lens8is f, tan α=Δ/f is achieved. Additionally, the center of the circular pattern15represents the center of the angle detection pattern11, detecting a position of each pixel of the image sensor12that receives the light of the circular pattern15enables determining the center of the circular pattern15, and determining a deviation between the center of the circular pattern15and the center of the yet-to-be-tilted circular pattern15enables determining the displacement amount Δ. Therefore, the tilt of the optical axis9aof the first condenser lens7, i.e., a tilt angle of the rotation shaft1can be detected based on a photodetection result of the image sensor12.

Since the rotation of the angle detection pattern11on the image sensor12or the displacement amount Δ of the center position of the angle detection pattern11can be detected in pixels of the image sensor12, the highly accurate measurement is possible.

Further, in the present embodiment, the rotation angle and the tilt of the rotation shaft1can be detected. When a measurement value is corrected based on the detected tilt, a measurement result excluding an influence of the tilt of the rotation shaft1can be obtained. Therefore, even if the rotation of the rotation shaft1includes an error, namely, even if the assembling of the rotation shaft1is not highly accurately carried out, an angle can be highly accurately detected.

It is to be noted that, in the foregoing embodiment, the image sensor12may be provided on the rotation shaft1side and the angle detection pattern11may be provided on the bearing holder3side.

FIG. 3shows a second example of the angle detection pattern11.

In the second example, the circular pattern15is configured by a plurality of (four in the drawing) concentric circles15ato15d. When the circular pattern15is configured by the plurality of circles15ato15d, and the centers of the respective circles15ato15dcan be obtained, and averaging the obtained center positions enables highly accurately determining the center position of the angle detection pattern11.

Furthermore, in the second example, besides the circular pattern15and the line-segment pattern16, a reference designation pattern18is provided. The reference designation pattern18is configured by three line segments18aand18bextending in the radial direction on a circumference having a diameter (a small diameter in the drawing) different from a diameter of the circumference where the line-segment pattern16is provided, the line segments18aand18bare arranged at an equal angle pitch, and the line segments18bat both sides are formed with a large line width. It is to be noted that the line segments18aand18bmay have the same line width.

Since the reference designation pattern18is provided, when a position of the reference designation pattern18is detected by the image sensor12at the start of measurement and the detected position is set as a reference position, an angle at a time of the measurement can be determined from a difference between the position of the reference designation pattern18at the time of measurement and the reference position. Furthermore, an infinitesimal rotation angle is detected based on a deviation between the line segments in the line-segment pattern16.

FIG. 4shows a third example of the angle detection pattern11.

The third example represents the case where the angle detection pattern11is a lattice pattern which is configured by a plurality of straight lines19as arranged to be orthogonal to each other at equal intervals. In the straight lines19, some of straight lines19ahave a large line widths, and the straight lines19aenable detecting the center of the angle detection pattern11and a reference position and also enable detecting a posture of the angle detection pattern11in a rotating direction.

FIG. 5shows a fourth example of the angle detection pattern11.

In the fourth example, the circular pattern15is configured by a plurality of (four in the drawing) concentric circles15ato15d, and the line-segment pattern16is configured by the fact that a plurality of (four in the drawing) tracks16a,16b,16c, and16dare concentrically multiply-arranged.

Like the line-segment pattern16shown inFIG. 2, each of the tracks16a,16b,16c, and16dhas a configuration that line segments21extending in the radial direction are arranged on the total circumference at a predetermined angle pitch.

Further, the angle pitches of the respective line segments21a,21b,21c, and21dconfiguring the tracks16a,16b,16c, and16dslightly differ for each of the tracks16a,16b,16c, and16d, and detecting a phase relationship of the respective line segments21a,21b,21c, and21damong the tracks enables determining a rotational position. In the fourth example, since a rotational position of the angle detection pattern11is uniquely determined based on the phase relationship between the respective line segments21a,21b,21c, and21d. Therefore, like the first example (seeFIG. 2), some of line segments21do not have to be thickened. Furthermore, since an inner end and an outer end of each of the line segments21on each track are placed on the respective circumferences, by detecting the inner end and the outer end of the line segments21, the circles can be detected, and hence a center position can be detected based on the detected circles. Therefore, the circular pattern15can be omitted.

It is to be noted that the various kinds of angle detection patterns11can be considered, and this pattern is not restricted to the above-described example.

Next, description will be given on a method for detecting an angle and a center by using the above-mentioned pattern.

First, by referring toFIG. 6, description will be given on a first example of the method for detecting an angle and a center. Additionally, the first example will be described by using the fourth angle detection pattern11shown inFIG. 5.

Based on the signals emitted from all the pixels constituting the image sensor12, the respective line segments21a,21b,21c, and21dof the respective tracks16a,16b,16c, and16dcan be recognized, and a rotation angle and a center of the angle detection pattern11can be determined. However, description will be given below on a method for more easily detecting an angle and a center.

FIG. 6shows an angle detection pattern image11′ projected on the image sensor12. Further, the center of the angle detection pattern image11′ shown in the drawing coincides with the center of the image sensor12.

To acquire a photodetection signal from the image sensor12, a scan line is set at a predetermined position, the scan line is scanned, and the outputs from the pixels on the scan line are acquired. In regard to the setting of the scan line, each angle detection line22for angle detection and each center detection line23for center detection are set.

First, each angle detection line22is set to be orthogonal to a radius that equally divides the circumference (equally divides the circumference into eight pieces) and to be included in each of the tracks16a,16b,16c, and16d. Therefore, according to the first method, the circumference is divided into eight pieces, and the number of the tracks is four, and there are the 32 angle detection lines22.

Then, each of two center detection line23that runs through the center of the image sensor12is set so as to cut across the circular pattern15. It is preferable for the two center detection lines23to be orthogonal to each other.

In a case of detecting an angle, when each angle detection line22is scanned, the signals of the pixels at the positions where the angle detection line cuts across the line segments21can be obtained. For example, giving a description on the angle detection lines22ato22d, when the angle detection line22ais canned, every time the angle detection line cuts across the line segment21, a detection signal for the line segment21is obtained, and a position of a pixel that outputs the detection signal can be identified on the image sensor12.

Subsequently, when the angle detection line22bis scanned, likewise, every time the angle detection line cuts across the line segment21, a detection signal for the line segment21is obtained, and a position of the pixel that outputs the detection signal can be identified on the image sensor12. Furthermore, in regard to the angle detection line22cand the angle detection line22d, the detection signals of the line segments21can be sequentially obtained, and the positions of the detection signals can be identified on the image sensor12.

When the detection signals obtained by scanning the angle detection lines22ato22dare compared among the angle detection lines22ato22d, phase differences among the respective angle detection lines22ato22dcan be detected, and further, a rotation angle of the angle detection pattern11with respect to a reference position of the image sensor12can be detected based on the phase differences.

The rotation angle can be detected by one pair of angle detection lines22that cut across one radius, but detecting an angle by using another pair or a plurality of pairs of angle detection line22and averaging the detection results can further improve a measurement accuracy. Further, when a result obtained by the one pair of angle detection lines22and a result obtained by another pair of angle detection lines22having a 180° different phase with respect to the one pair of angle detection lines22are averaged, an error produced due to, e.g., the pattern collapse etc. can be canceled out.

The angle detection lines22to be set are not physically set on the image sensor12, but they are virtual lines used at a time of extracting the signals, and hence the angle detection lines22adjacent to each other may overlap each other. Therefore, the angle detection lines22that cut across the infinitely divided radiuses can be set in theory. Moreover, the larger the number of the divided radiuses is, i.e., the larger the number of the pairs of angle detection lines22is, the higher the measurement accuracy is improved.

Additionally, the number of division and the number of the pairs of angle detection lines22can be appropriately set in accordance with the demanded measurement accuracy. That is, for example, when a high accuracy is demanded, the number of division and the number of the pairs of angle detection lines22are increased. When a high accuracy is not demanded, the number of division and the number of the pairs are reduced.

Subsequently, in case of determining a center of the angle detection pattern image11′, each center detection line23is scanned. When the center detection line23is scanned, every time the center detection line cuts across the circles15ato15d, the detection signals for the line segments21are obtained, and a center position of the angle detection pattern image11′ can be determined based on the obtained signals.

The determined center position of the angle detection pattern image11′ is compared with the reference position of the image sensor12. When the optical axis9a(the rotation shaft1) tilts, a deviation is determined, and a tilt angle of the optical axis9ais determined based on the deviation. When the number of circular patterns15is increased and the number of center detection lines23is increased, many detection values can be obtained, and a detection accuracy can be improved.

Next, inFIG. 7, description will be given on a second example of the angle detecting method. Further, the second example will be explained by using the second angle detection pattern11shown inFIG. 3. It is to be noted thatFIG. 7Bshows the linearly developed angle detection pattern11.

A position of the pixel constituting the image sensor12is identified using a polar coordinate system, and a scan line25of the angle detection is determined as a circle. As to the scan line25, an angle detection line25aset to be equal to a reference circle of the line-segment pattern16(a circle that runs through an intermediate point between an inner end and an outer end of the line-segment pattern16) and a reference position detection line25bset on a circle running through the reference designation pattern18are set.

A reference position of the reference designation pattern18on the image sensor12is compared with a position of the reference designation pattern18obtained by scanning the reference position detection line25b, and by this composition, a rotation angle of the angle detection pattern11is determined.

Further, in regard to the detection of an angle that is not greater than a pitch of the line-segment pattern16, the signals of the line-segment pattern16corresponding to 360° are determined, the obtained detection signal of each line segment is multiplied by sin(2πn/360θ) and cos(2πn/360θ), and a phase in the pitch is determined based on a proportional relation of a sin component and a cos component.

Each ofFIG. 8andFIG. 9shows a case where the rotation angle detection apparatus6is embodied in a total station30as a surveying instrument.

A base unit33is provided on a leveling unit31through leveling screws32. A frame34is mounted on the base unit33, and a telescope unit35including an optical system is supported on the frame34. A distance measuring unit (not shown) is provided inside the telescope unit35. The distance measuring unit is configured in such a manner that a distance measuring light is projected to an object to be measured from the telescope unit35, the distance measuring light reflected on the object to be measured is received, and the distance measurement based on the received reflection light is carried out.

The base unit33can be leveled to be horizontal by the leveling screws32. Moreover, the frame34is rotatable with a vertical shaft center line as a center, and the telescope unit35can rotate with a horizontal shaft center line as a center. Additionally, an operation input portion37having a display unit36is provided on the frame34, and an operating state of the total station30, a measurement value of a distance to the object to be measured, or the like is displayed in the display unit36.

A frame base38is provided on an upper surface of the base unit33, and a bearing holder39protruding upward is provided at the center of the frame base38. A horizontal rotation shaft41is rotatably attached and engaged with the bearing holder39via a bearing42, and a housing43of the frame34is fixedly attached to the horizontal rotation shaft41. The frame base38constitutes a part of the base unit33that supports the housing43and has a function as a lower cover that closes a lower opening of the housing43.

A horizontal rotary gear44is fixedly attached to the bearing holder39, and a horizontal rotary drive gear45is engaged with the horizontal rotary gear44. The horizontal rotary drive gear45is fixedly attached to an output shaft of a horizontal rotary motor46. When the horizontal rotary drive gear45is rotated by the horizontal rotary motor46, the housing43rotates with the horizontal rotation shaft41as a center in a horizontal direction via the horizontal rotary gear44. It is designed so that the horizontal rotary motor46is fixedly attached to the housing43, and the horizontal rotary motor46and the housing43are designed so as to integrally rotate.

A lower end portion of the horizontal rotation shaft41is hollow, and a hollow portion forms a first shaft portion space47. A horizontal angle detection pattern48and a horizontal first condenser lens49are accommodated in the first shaft portion space47, and the horizontal angle detection pattern48and the horizontal first condenser lens49are provided on a shaft center line of the horizontal rotation shaft41.

A shaft portion holder51is provided on a lower surface of a central portion of the frame base38, and a shaft centerline of the shaft portion holder51coincids with the shaft center line of the horizontal rotation shaft41. A bearing holder space52that is a cylindrical concave portion is formed in the shaft portion holder51from an upper surface side, a horizontal second condenser lens53and a horizontal image sensor54are accommodated in the bearing holder space52, and the horizontal second condenser lens53and the horizontal image sensor54are provided on the shaft center line of the shaft portion holder51.

The horizontal angle detection pattern48, the horizontal first condenser lens49, the horizontal second condenser lens53, and the horizontal image sensor54constitute primary portions of a horizontal rotation angle detecting apparatus55for detecting a horizontal angle.

A vertical rotation shaft56extending in the horizontal direction from both left and right ends is provided to the telescope unit35, the vertical rotation shaft56is supported in the housing43via a bearing57, and the telescope unit35can rotate with the vertical rotation shaft56as a center in the vertical direction.

A vertical rotary gear58is fixedly attached to one end of the vertical rotation shaft56, and a vertical rotary drive gear59is engaged with the vertical rotary gear58. The vertical rotary drive gear59is fixedly attached to an output shaft of a vertical rotary motor61. When the vertical rotary motor61is driven, the telescope unit35is rotated with the vertical rotation shaft56as a center via the vertical rotary drive gear59and the vertical rotary gear58.

A second shaft portion space62that is concentric with the vertical rotation shaft56is formed at the other end portion of the vertical rotation shaft56, a vertical angle detection pattern63and a vertical first condenser lens64are accommodated in the second shaft portion space62, and the vertical angle detection pattern63and the vertical first condenser lens64are provided on a shaft center line of the vertical rotation shaft56.

A cylindrical holder support65is protruded inward so as to be concentric with the other end portion of the vertical rotation shaft56, and a shaft portion holder66is fitted at an end portion of the holder support65. A bearing holder space67that is concentric with the shaft center line of the vertical rotation shaft56is formed in the shaft portion holder66, and a vertical second condenser lens68and a vertical image sensor69are accommodated in the bearing holder space67. The vertical second condenser lens68and the vertical image sensor69are provided on the shaft center line of the vertical rotation shaft56.

The vertical angle detection pattern63, the vertical first condenser lens64, the vertical second condenser lens68, and the vertical image sensor69constitute primary portions of a vertical rotation angle detecting apparatus71for detecting a vertical angle (an elevation angle).

The total station30is leveled by the leveling screws32. After the leveling, the total station30is set as a reference position.

Then, to make the telescope unit35perform sighting with respect to a object to be measured, the horizontal rotary motor46is driven to rotate the housing43in the horizontal direction. A horizontal rotary angle of the housing43is detected by the horizontal rotary angle detecting apparatus55. Further, the shaft shifting (a tilt of the shaft) of the horizontal rotation shaft41is simultaneously detected, and the horizontal angle detected by the horizontal rotation angle detecting apparatus55is corrected based on the detected shaft shifting.

Further, the vertical rotary motor61is driven, and the telescope unit35is rotated in the vertical direction. A vertical rotation angle of the telescope unit35is detected by the vertical rotation angle detecting apparatus71, and the shaft shifting of the vertical rotation shaft56is detected at the same time. Likewise, the vertical angle detected by the vertical rotation angle detecting apparatus71is corrected based on the detected shaft shifting.

When the sighting of the telescope unit35is completed, a distance measuring light is emitted from the telescope unit35, a distance to the object to be measured is measured, and a horizontal angle and an elevation angle are measured by the horizontal rotation angle detecting apparatus55and the vertical rotation angle detecting apparatus71at the same time.

In the surveying instrument according to the present embodiment, a horizontal angle and an elevation angle can be highly accurately measured without using an expensive encoder, the horizontal rotation angle detecting apparatus55and the vertical rotation angle detecting apparatus71do not require a fabrication accuracy, the manufacture is inexpensively enabled, and a fabrication cost of the surveying instrument can be reduced.