Tilt detecting device and rotary laser apparatus

The invention provides a tilt detecting device, in which a fixed member and a tilting plate are relatively rotatably provided via a pivot member, either one of the fixed member or the tilting plate is integral with the pivot member, comprising a tilt detecting unit provided on either of the fixed member or the tilting plate which relatively rotates with respect to the pivot member, and an angle detection pattern formed on the pivot member, wherein the tilt detecting unit comprises a light source for projecting an illumination light to the pivot member, a photodetection element for receiving the illumination light reflected by the pivot member, an optical system for projecting a pattern image to the photodetection element and an arithmetic unit for detecting a rotation of the pivot member based on a projecting position of the pattern image projected onto the photodetection element when the pivot member rotates.

BACKGROUND OF THE INVENTION

The present invention relates to a tilt detecting device and a rotary laser apparatus which is capable of detecting a tilt based on a pattern.

As a tilt detecting means for use in a tilt detecting device, an encoder such as a linear encoder or a circle encoder or the like is extensively used.

However, in order to make a tilt detection accuracy more accurate, a size of the encoder must be increased. Further, since a portion with a large moving amount must be determined as a detection target, an increase in size of a device itself is unavoidable. Therefore, it had been difficult to achieve both a miniaturization of the device and the improvement of the tilt detection accuracy.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a tilt detecting device and a rotary laser apparatus, which can achieve a miniaturization.

To attain the object as described above, a tilt detecting device according to the present invention, in which a fixed member and a tilting plate are relatively rotatably provided via a pivot member, either one of the fixed member or the tilting plate is integral with the pivot member, comprising a tilt detecting unit provided on either of the fixed member or the tilting plate which relatively rotates with respect to the pivot member, and an angle detection pattern formed on the pivot member, wherein the tilt detecting unit comprises a light source for projecting an illumination light to the pivot member, a photodetection element for receiving the illumination light reflected by the pivot member, an optical system for projecting a pattern image to the photodetection element and an arithmetic unit for detecting a rotation of the pivot member based on a projecting position of the pattern image projected onto the photodetection element when the pivot member rotates.

Further, in the tilt detecting device according to the present invention, the optical system comprises a polarizing plate disposed on an optical axis, a polarizing beam splitter and a quarter-wave plate, wherein the illumination light is projected to the pivot member via the polarizing plate, the polarizing beam splitter and the quarter-wave plate, and the pattern image reflected by the pivot member is received by the photodetection element via the quarter-wave plate and the polarizing beam splitter.

Further, in the tilt detecting device according to the present invention, the polarizing plate is a polarizing film formed on an incident surface of the polarizing beam splitter and the quarter-wave plate is a quarter-wave film formed on an exit surface of the polarizing beam splitter.

Furthermore, a rotary laser apparatus according to the present invention comprises a laser projector tiltably provided, deflecting a laser beam in a horizontal direction and projecting in rotary irradiation, a tilting unit for tilting the laser projector, and a tilt setting unit for setting a target tilt angle of the laser projector, wherein the tilt setting unit comprises a base plate orthogonal to an axis of the laser projector, a tilting plate provided tiltably with respect to the base plate via a pivot member, a tilt detector provided on the tilting plate for detecting a horizontality of the tilting plate, an angle detection pattern formed on the pivot member, and the tilt detecting unit as described in claim1provided on the tilting plate.

According to the present invention, the tilt detecting device, in which a fixed member and a tilting plate are relatively rotatably provided via a pivot member, either one of the fixed member or the tilting plate is integral with the pivot member, comprising a tilt detecting unit provided on either of the fixed member or the tilting plate which relatively rotates with respect to the pivot member, and an angle detection pattern formed on the pivot member, wherein the tilt detecting unit comprises a light source for projecting an illumination light to the pivot member, a photodetection element for receiving the illumination light reflected by the pivot member, an optical system for projecting a pattern image to the photodetection element and an arithmetic unit for detecting a rotation of the pivot member based on a projecting position of the pattern image projected onto the photodetection element when the pivot member rotates. As a result, a moving amount of the angle detection pattern is slight compared to a moving amount of the tilting plate, which contribute to a miniaturization of the photodetection element which receives the pattern image, a reduction in size and cost and the highly accurate detection of a tilt angle of the tilting plate.

Further, according to the present invention, in the tilt detecting device, the optical system comprises a polarizing plate disposed on an optical axis, a polarizing beam splitter and a quarter-wave plate, wherein the illumination light is projected to the pivot member via the polarizing plate, the polarizing beam splitter and the quarter-wave plate, and the pattern image reflected by the pivot member is received by the photodetection element via the quarter-wave plate and the polarizing beam splitter. As a result, the pattern image is not reflected to the light source side, the illumination light from the light source is not received by the photodetection element and a tilt detecting operation of the tilting plate can be stabilized.

Further, according to the present invention, in the tilt detecting device, the polarizing plate is a polarizing film formed on an incident surface of the polarizing beam splitter and the quarter-wave plate is a quarter-wave film formed on an exit surface of the polarizing beam splitter. As a result, numbers of the components are reduced and a further miniaturization can be realized.

Furthermore, according to the present invention, the rotary laser apparatus comprises a laser projector tiltably provided, deflecting a laser beam in a horizontal direction and projecting in rotary irradiation, a tilting unit for tilting the laser projector, and a tilt setting unit for setting a target tilt angle of the laser projector, wherein the tilt setting unit comprises a base plate orthogonal to an axis of the laser projector, a tilting plate provided tiltably with respect to the base plate via a pivot member, a tilt detector provided on the tilting plate for detecting a horizontality of the tilting plate, an angle detection pattern formed on the pivot member, and the tilt detecting unit as described in claim1provided on the tilting plate. As a result, it is not necessary to provide a mechanism for detecting a tilt of the tilting plate, the number of the components are reduced, which contribute to a miniaturization.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A description will be given below on embodiments of the present invention by referring to the attached drawings.

First, referring toFIG. 1, a description will be given on a tilt detecting device according to a first embodiment of the present invention.

InFIG. 1, reference numeral1denotes a base plate as a fixed member and a part of the base plate1is shown inFIG. 1. Reference numeral2denotes a tilting plate as a movable part and the tilting plate2can be tilted with respect to the base plate1, and inFIG. 1, one part of the tilting plate2is shown. The tilting plate2is provided so as to rotate integrally with a pivot member3and can relatively tilt with respect to the base plate1.

The pivot member3is a sphere, and a hole is provided in the base plate1. A peripheral surface of the hole is a spherical surface so that the pivot member3can be fitted therein, and the hole functions as a spherical seat4of the pivot member3. Further, the pivot member3can be rotatably fitted on the spherical seat4and the tilting plate2rotates around the pivot member3as a supporting point. Further, when the pivot member3is fitted on the spherical seat4, a part of a lower portion of the pivot member3is adapted to be exposed to a lower side.

The tilt detecting device is for detecting a relative tilt between the base plate1and the pivot member3. The tilt detecting device is constituted of a tilt detecting unit5provided on the base plate1and an angle detection pattern6formed on the pivot member3.

A description will be given below on the tilt detecting unit5.

A light source7which emits an illumination light, e.g. an LED, is provided in a vertically upward direction. A projection lens9, a polarizing plate11, a polarizing beam splitter12, a quarter-wave plate13, a condenser lens14and the angle detection pattern6are disposed on a projection optical axis8of the light source7. Further, the projection optical axis8is set so as to pass through a center of the pivot member3.

The polarizing plate11has an optical characteristic of turning an illumination light emitted from the light source7, for instance, to an illumination light which is a P-polarized light, for instance. The polarizing beam splitter12has a polarization characteristic of allowing the light, which is the P-polarized light, to pass through and of reflecting the light which is the S-polarized light, for instance.

The light source7, the projection lens9, the polarizing plate11, the polarizing beam splitter12, the quarter-wave plate13and the condenser lens14make up a projecting optical system15.

A focus lens17and a photodetection element18which is a two-dimensional sensor are disposed on a reflection optical axis16of The polarizing beam splitter12. As the photodetection element18, a profile sensor which is an aggregate of pixels is used, for instance.

In the profile sensor, the pixels are aligned in a matrix state and a position of an object in the profile sensor can be detected by only informations of each column, which the pixels belong, of two directions (an X direction, a Y direction) orthogonal to each other. Therefore, the profile sensor can easily detect a position of the object in the profile sensor without acquiring the information of all the pixels.

It is to be noted that a CCD or a CMOS sensor may be used as the photodetection element18, information of all the pixels may be acquired and a position of the object on the photodetection element18may be detected.

The photodetection element18outputs a photodetection signal to an arithmetic unit19and the arithmetic unit19calculates the position of the object based on the photodetection signal. Further, the arithmetic unit19calculates a displacement and a displacement direction of a position of the object, and detects a tilt angle and a tilt direction of the tilting plate2based on a calculation result.

The condenser lens14, the quarter-wave plate13, the polarizing beam splitter12, the focus lens17and the photodetection element18make up a photodetection optical system21. Further, the polarizing plate11and the quarter-wave plate13make up an optical isolator.

Next, a description will be given on the angle detection pattern6. The angle detection pattern6is formed on a lower surface of the pivot member3by a required method such as printing or engraving or the like.

For instance, as shown inFIG. 2, the angle detection pattern6has lands22arranged an a matrix fashion. Each land22has a different dimension in an X direction respectively and each land has a different dimension in a Y direction respectively. Therefore, the angle detection pattern6is configured so as to include a two-dimensional information of the X direction and the Y direction.

The illumination light emitted from the light source7is turned to a parallel luminous flux by the projection lens9, turned to the P-polarized light, for instance, in a process of passing through the polarizing plate11and transmitted through the polarizing beam splitter12. The illumination light, as transmitted through the polarizing beam splitter12passes through the quarter-wave plate13, is condensed by the condenser lens14and enters the lower surface of the pivot member3, i.e. the angle detection pattern6.

The reflection light reflected on the lower surface of the pivot member3, i.e. a pattern image of the angle detection pattern6, passes through the quarter-wave plate13again and is reflected by the polarizing beam splitter12. By the illumination light passing through the quarter-wave plate13twice, the P-polarized Light is changed to the S-polarized light.

An illumination light of the S-polarized light is reflected by the polarizing beam splitter12, and condensed on the photodetection element18by the focus lens17. Therefore, the condenser lens14and the focus lens17function as focus lenses for projecting the angle detection pattern6onto the photodetection element18.

It is to be noted that, as the focus lens17, a lens with high magnification such as a semi-spherical lens may be used. When a refractive power which enables forming an image on the photodetection element18is provided to the focus lens17alone, the condenser lens14can be omitted.

When the tilting plate2tilts and the pivot member3relatively rotates with respect to the tilt detecting unit5, the angle detection pattern6is relatively displaced with respect to the base plate1, i.e. the tilt detecting unit5. When the angle detection pattern6is displaced, a projecting position of a pattern image of the angle detection pattern6, which is received by the photodetection element18, changes. The arithmetic unit19calculates a displacement of the projecting position based on a photodetection signal from the photodetection element18and is capable of detecting a tilt of the tilting plate2based on a calculation result.

It is to be noted that the tilt of the tilting plate2may be detected based on a moving amount or a moving direction of the position of the pattern image on the photodetection element18after the tilt with respect to the position of the pattern image on the photodetection element18before the tilt. Further, a coordinate system and an origin point may be set on the photodetection element18and the tilt of the tilting plate2may be detected based on the position of the pattern image on the photodetection element18with respect to the origin point of the coordinate system.

The pivot member3has no restriction in its rotating direction and can freely rotate in two directions of X and Y, and the photodetection element18can detect a two-dimensional displacement of the angle detection pattern6. Therefore, as the tilting directions in the tilt detecting device, the X direction, the Y direction, and a composite direction of X and. Y can be detected, respectively.

When a driving unit for tilting the tilting plate2is provided on a movable part, i.e. the tilting plate2, the tilting plate2is capable of being tilted at an arbitrary tilt angle by she driving unit based on a tilt detection result of the tilt detecting device.

FIG. 3shows a tilt detecting device according to a second embodiment of the present invention. InFIG. 3, what are equivalent to components as shown inFIG. 1are referred by the same symbol, and detailed description thereof will be omitted.

In the tilt detecting device as shown. InFIG. 3, a pivot member3is provided on a fixed side. The pivot member3is integrated with a supporting pole23as a fixed member. A tilting plate2is capable of relatively rotating around the pivot member3as a supporting point in two horizontal directions with respect to the pivot member3.

A tilt detecting unit5is provided on the tilting plate2side, and the tilting plate2and the tilt detecting unit5are integrated with each other. Therefore, the tilt detecting unit5is provided so as to be able to relatively rotate with respect to the pivot member3. By tilting the tilting plate2, she tilting plate2and the tilt detecting unit5integrally tilt with respect to the pivot member3.

An angle detection pattern6is formed on the pivot member3. Further, when the tilting plate2relatively rotates with respect to the fixed member, the pivot member3relatively rotates with respect to the tilt detecting unit5, which is the same as the first embodiment. Since the tilting plate2and the tilt detecting unit5tilt integrally, the angle detection pattern6relatively rotates and is relatively displaced with respect to the tilt detecting unit5.

Similarly toFIG. 1, the illumination light is projected to the angle detection pattern6from a light source7through a projecting optical system15. A pattern image of the angle detection pattern6is projected onto a photodetection element18through a photodetection optical system21.

Therefore, the angle detection pattern6is displaced with respect to the photodetection element18. Further, based on a displacement of the angle detection pattern6with respect to the photodetection element18, a tilt of the tilting plate2can be detected.

When a driving unit for tilting the tilting plate2is provided on a movable part, i.e. the tilting plate2, the tilting plate2can be tilted at an arbitrary tilt angle by the driving unit based on a tilt detection result of the tilt detecting device.

Referring toFIG. 4andFIG. 5, a description will be given on one example of a surveying instrument to which she tilt detecting device is applied. InFIG. 4andFIG. 5, what are equivalent to components as shown inFIG. 3are referred by the same symbol, and detailed description thereof will be omitted. Further, in the description as given below, a rotary laser apparatus24will be exemplified as a surveying instrument, and the description will be given on a case where the tilt detecting device is provided on a tilt setting unit of the rotary laser apparatus24.

In the rotary laser apparatus24, a tilting plate2is a movable part and a tilt detecting unit5is provided on the tilting plate2.

A concave portion26with a truncated conical shape is formed at a center of a casing25and a support seat27is formed at a center of the concave portion26. The support seat27is provided by forming a circular through-hole28in the concave portion26and forming smoothly raised protuberances29at respective positions trisecting an inner periphery of the through-hole28.

A laser projector31which emits an illumination light is inserted into the through-hole28, and a head portion32of the laser projector31is supported by the support seat27. A lower portion of the head portion32is a spherical surface portion32aformed into a spherical surface shape, and the laser projector31is tiltably supported with respect to a perpendicular when the spherical surface portion32aslidably abuts on the protrusion29.

A motor seat33extending in the horizontal direction is provided on the head portion32and a scanning motor34is mounted on the motor seat33. A gear35is fitted into an output shaft of the scanning motor34and the gear35meshes with a scanning gear36(to be described later).

A prism holder38is rotatably provided on the head portion32via a bearing37and an axis of the prism holder38coincides with an axis of the laser projector31. The scanning gear36is fitted into the prism holder38and the scanning gear36meshes with the gear35. It is arranged so that the prism holder38can rotate with a vertical shaft center as a center by the scanning motor34and a rotating unit39is constituted by the prism holder38, the scanning gear36, and the like. Further, a pentagonal prism41is provided in the prism holder38, and the pentagonal prism41is adapted to deflect and emit the illumination light emitted from the laser projector31in a horizontal direction through a projection window42.

Further, a base plate43is fixed to a lower end of the laser projector31. The base plate43has an approximately right-angled triangular shape and is orthogonal to the axis of the laser projector31. The supporting pole23is erected near a right-angled top portion of the base plate43and the pivot member3is fixed to an upper end of the supporting pole23.

The tilting plate2with a right-angled L-shaped form is arranged on an upper part of the base plate43and a conical spherical surface seat44is formed on an L-shaped top portion on the back side of the tilting plate2. The pivot member3is fitted on the spherical surface seat44, and the supporting pole23supports the top portion of the tilting plate2via the pivot member3. The tilting plate2is capable of pivot-movement with the pivot member3as the center.

Further, the tilt detecting unit5is provided immediately above the pivot member3of the tilting plate2. The tilt detecting unit5tilts integrally with the tilting plate2, and is adapted to relatively tilt with respect to the angle detection pattern6as formed on an upper surface of the pivot member3.

Further, bubble tubes45and46which are tilt detectors which detect the horzontality are provided on the tilting plate2so as to cross each other at a right angle. The bubble tubes45and46are capacitance detection type electric bubble tubes and configured to output electric signals corresponding to tilt angles with reference to a horizontal plane.

The base plate43, the tilting plate2, the tilt detecting unit5, the bubble tubes45and46and the angle detection pattern6make up a tilt setting unit.

Further, a spring47is provided between the tilting plate2and the base plate43, presses the spherical surface seat44to the pivot member3and biases the tilting plate2in a clockwise direction inFIG. 3.

A bearing plate48is disposed in a middle portion of the laser projector31and the bearing plate48extends from the laser projector31in the horizontal direction. At positions forming a triangle which has the supporting pole23of the base plate43as a vertex, tilting screws49and51are rotatably erected. The upper ends of the tilting screws49and51are rotatably supported by the bearing plate48, respectively.

A lower end portion of the tilting screw49protrudes downward from the base plate43. A tilting gear52is fitted into the protruding lower end portion of the tilting screw49and the tilting gear52meshes with a tilting gear53to be described later. Similarly, a lower end portion of the tilting screw51protrudes downward from the base plate43. A tilting gear54is fitted into the protruding end portion of the tilting screw51and the tilting gear54meshes with a tilting gear55to be described later.

A tilting nut56is screwed to the tilting screw49and on the tilting nut56, a nut pin57with a circular-shaped cross section is provided to protrude in a horizontal direction. A tilting pin58is provided to protrude from an end face of the tilting plate2on the tilting screw49side and the tilting pin58abuts on the nut pin57. Further, two parallel guide pins59are stretched over between the base plate43and the bearing plate48. The guide pins59slidably sandwich the tilting pin58and restrict a rotation of the tilting plate2in the horizontal direction, and the guide pins59allow the rotation of the tilting pin58in an up-and-down direction and around an axis of the tilting pin58as a center.

Further, a tilting nut61is screwed to the tilting screw51and a nut pin62with a circular-shaped cross section is provided to protrude on the tilting nut61. A tilting pin63is provided to protrude from an end face of the tilting plate2on the tilting screw51side and the tilting pin63abuts on the nut pin62.

A leg pillar64is provided on a lower surface of the base plate43in a suspending manner, and a motor base65is fixed via the leg pillar64. Tilt angle setting motors66and67as pulse motors are provided on an upper surface of the motor base65. The tilting gear53is fitted and fixed on an output shaft of the tilt angle setting motor66, the tilting gear55is fitted and fixed on an output shaft of the tilt angle setting motor67, and the tilting gears53and55are meshed with the tilting gears52and54, respectively.

Next, a description will be given on a tilting unit which tilts the laser projector31.

Tilting arms68and69are orthogonally extended in a horizontal direction from the head portion32of the laser projector31. It is to be noted that inFIG. 4, the tilting arm68alone is shown and the illustration of the tilting arm69is omitted. The tilting arms68and69pierce through a conical surface of the concave portion26, are positioned in the casing25, and have engaging pins71and72provided to protrude on forward ends. It is to be noted that, inFIG. 4, the engaging pin71alone is shown and the illustration of the engaging pin72is omitted.

Each of the engaging pins71and72is formed into a cylindrical shape and a positional relationship is determined in such a manner that axes of the engaging pins71and72are orthogonal to each other and included in a plane running through a center of the spherical surface portion32a. Further, either one of the engaging pins71and72, e.g. regarding the engaging pin71, a movement in a horizontal direction is restricted and can move only in an up-and-down direction.

Shelf boards73and74are provided on an inner wall of the casing25, a tilt motor75is provided on the shelf board73and a tilt motor76(not shown) is provided on the shelf board74. Further, a driving gear77is fitted and fixed on a rotary shaft of the tilt motor75and a driving gear78(not shown) is fitted and fixed on a rotary shaft of the tilt motor76.

A screw shaft79orthogonal to the engaging pin71is mounted between a ceiling portion of the casing25and the shelf board73. A driven gear81is fitted into the screw shaft79and the driving gear77meshes with the driven gear81. A slide nut82is screwed to the screw shaft79, a pin83is provided to the slide nut82in protruding state, and the pin83and the engaging pin71are slidably abutted.

Similarly, a screw shaft (not shown) orthogonal to the engaging pin72is mounted between the ceiling portion of the casing25and the shelf board74and a driven gear (not shown) as meshed with the driving gear78is fitted into the screw shaft. Further, a slide nut (not shown) having a pin (not shown) provided to protrude is screwed to the screw shaft and the pin and the engaging pin72are slidably abutted.

A spring peg84is provided between the ceiling portion of the casing25and the two screw shafts and a spring85is provided in a tensioned state between the spring peg84and the laser projector31. The spring85biases the laser projector31in a clockwise direction with the support seat27as a center inFIG. 4.

InFIG. 4, reference numeral86denotes a battery box which accommodates a battery for driving the rotary laser apparatus24. Further, a main body87of the rotary laser apparatus24as described above is provided on a tripod (not shown) via a leveling bolt88. Further, reference numeral89denotes a glass window which surrounds a periphery of the prism holder38.

Next, a description will be given as to a case where, in the rotary laser apparatus24, a projecting direction of the illumination light emitted from the laser projector31is tilted.

First, a relative tilt between the tilting plate2and the base plate43is set to be 0 based on a detection result of the tilt detecting unit5. That is, the tilting plate2and the base plate43are set to be parallel. At this time, a projecting position of a pattern image as obtained by the illumination light, which is emitted from the light source7of the tilt detecting unit5and reflected by the angle detection pattern6, is an origin point, e.g. the center, of the photodetection element18. The axis of the laser projector31is orthogonal to the tilting plate2.

Next, the tilt motors75and76are driven based on the detection results of the bubble tubes45and46and the laser projector31is tilted. By tilting the laser projector31, the bubble tubes45and46are in a condition where the horizontality can be detected and the leveling of the laser projector31is carried out. In this condition, the laser projector31becomes vertical (the axis of the laser projector31is vertical).

After the leveling of the laser projector31, the tilting plate2is tilted based on an inputted tilt value. For instance, the tilt angle setting motor66is driven with number of steps corresponding to the tilt value and the tilting plate2is tilted at an angle as desired in a direction opposite to a direction in which the laser projector31is to be tilted. By tilting the tilting plate2, the tilt detecting unit5relatively rotates with respect to the pivot member3. Therefore, the pattern image projected on the photodetection element18moves and a tilt angle of the tilting plate2can be detected based on a position of the pattern image.

After tilting the tilting plate2, the tilt motor75is driven and the laser projector31is tilted in the direction in which the laser projector31is to be tilted until the bubble tubes45and46detect the horizontality. At this time, since the tilt detecting unit5and the pivot member3tilt integrally, a tilt detecting result of the tilting plate2provided by the tilt detecting unit5is maintained.

When the bubble tubes45and46detect the horizontality, the tilt setting of the laser projector31is completed and the tilt setting in the projecting direction of the illumination light is completed. In this condition, by rotating the pentagonal prism41by the scanning motor34via the prism holder38, a reference plane tilted in a predetermined direction at an angle as desired can be formed.

As described above, in this embodiment, the angle detection pattern6is formed on the pivot member3which serves as a supporting point when the tilting plate2tilts and a tilt angle of the tilting plate2can be detected based on a relative moving amount of the angle detection pattern6with respect to the tilt detecting device.

Therefore, the moving amount of the angle detection pattern6is considerably smaller than a moving amount of a forward end side of the tilting plate2. As a result, compared with a case where the moving amount of the tilting plate2is detected directly, the photodetection element18for receiving the pattern image of the angle detection pattern6can be decreased in size and manufacturing costs can be reduced.

Further, in the present embodiment, since the tilt angle of the tilting plate2is detected based on a projecting position of the pattern image of the angle detection pattern6, a size of a device does not have to be increased for higher accuracy such as a conventional encoder. Therefore, the tilt detecting device can be miniaturized and the tilt can be detected highly accurately.

Further, in the present embodiment, the angle detection pattern6is formed on the pivot, member3by printing, engraving and exposure, or the like, and a photodetecting position on the photodetection element18of the pattern image reflected by the angle detection pattern6is merely detected. Therefore, there is no need to additionally provide a mechanism for detecting and number of components can be reduced.

Further, in the present embodiment, the angle detection pattern6is formed on a spherical object by printing, engraving, or the like. Therefore, when an environmental temperature varies, the expansion and contraction become approximately point-symmetrical and an error can be minimized.

Further, in the present embodiment, the polarizing plate11and the quarter-wave plate13constitute an optical isolator. Therefore, the reflection light in a specific polarizing direction alone is received by the photodetection element18, a reduction in light amount can be suppressed, the pattern image can be detected with a sufficient light amount and a tilt detecting accuracy of the tilt detecting device, can be further improved.

Further, in the present embodiment, the pattern image reflected by the angle detection pattern6is totally reflected by the polarizing beam splitter12. Therefore, the pattern image is not transmitted through the polarizing beam splitter12and does not reach the light source7side, the illumination light from the light, source7is not received by the photodetection element18and the operation of the tilt detecting device can be stabilized.

Further, in the present embodiment, the condenser lens14is provided on the projection optical axis8, and the illumination light, which is turned to a parallel luminous flux by the projection lens9, can be condensed with respect to the angle detection pattern6. Therefore, even in a case where the light intensity is decreased in a process of passing through the polarizing plate11, the pattern image of the angle detection pattern6having a sufficient light intensity can be projected to the photodetection element18.

It is to be noted that, in the present embodiment, the polarizing plate11and the quarter-wave plate13are provided on the projection optical axis8and the polarizing plate11and the quarter-wave plate13constitute the optical isolator, but it may be so arranged that a polarizing film with a polarization characteristic of transmitting a light which is a P-polarized light alone, for instance, may be vapor-deposited on an incident surface of the polarizing beam splitter12, a quarter-wave film may be vapor-deposited on an exit surface of the polarizing beam splitter12and the polarizing beam splitter12alone may constitute the optical isolator. In this case, the polarizing plate11and the quarter-wave plate13can be omitted and the tilt detecting device can be further miniaturized.

Further, if an S/N ratio does not become a problem, the optical isolator can be omitted.