Projector with tilt angle measuring device

A projector having a tilt angle measurement device is provided with: a projection device for projecting an image onto a projection surface; a tilt angle measurement device for calculating the tilt angle that is formed between the axis of projection of the projection device and the projection surface; and an image control unit for controlling the output image from the projection device in accordance with the tilt angle that is calculated and thus correcting distortion in the image that is projected onto the projection surface. The tilt angle measurement device includes: a light guide unit that is provided on the projection-side surface of the case of the projector and separated from the axis of projection in a prescribed direction; a photodetection element for photodetecting, by way of the light guide unit, reflected light from at least two points that are projected onto the projection surface; and a tilt angle calculation unit for calculating the tilt angle that is formed between the axis of projection of the projection device and the projection surface based on photodetection position information of the reflected light of the photodetection element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector, and more particularly, to a projector having a tilt angle measuring device for calculating the tilt angle of the optical axis of projection of the projection device of the projector and the projection surface.

2. Description of the Related Art

The rapid progress of liquid crystal technology and DLP (registered trademark) (Digital Light Processing) technology has been accompanied by advances in the development of more compact and more highly functional projectors. With this development, the use of projectors of the prior art having the purpose of image projection has expanded, and projectors are now receiving attention as large-sized display devices for taking the place of display-type televisions for home use.

However, in contrast with a display-type television, the image plane of a projector may be a screen or a wall, and the problem therefore arises of distortion in the image that results from the relation between the axis of projection of the projector and the projection surface. To provide a solution to this problem, Japanese Patent Laid-Open Publication No. 281597/97 discloses a method that includes a detection means for detecting the installation angle of the liquid crystal projector and a distance detection means for detecting the distance between the liquid crystal projector and the object of projection whereby the angle of the liquid crystal display unit is adjusted according to the angle that is calculated from the two detection results. In addition, Japanese Patent Laid-Open Publication No. 169211/01 discloses a distortion correction method in which: the light spot of a laser pointer for which the angle can be controlled is projected onto a curved screen; a dot image for measurement is generated and projected onto the screen from a projector, the image of the light spot and dot image is captured by a camera and their positions measured; and the dot image is shifted until the two points coincide, whereupon the picture element coordinates of the dot image in a frame memory are converted to the coordinates of the light spot on the input image and set in a coordinate conversion parameter memory. A liquid crystal projector is also disclosed in Japanese Patent Laid-Open Publication No. 197249/97 in which: an image pattern that is projected onto a screen is passed through a slit and received by a line sensor, whereupon the position of the reflected light of this image pattern is used to find the distance to the screen; the image pattern that is projected onto the screen is shifted on the screen and the tilt of the screen is found based on the shift of the position of the reflected light of the image pattern that is passed through the slit and received by the line sensor; and diagonal adjustment is realized by controlling a diagonal actuator to tilt the projector unit backward and forward.

Techniques have already been put into practical use whereby, if the tilt of a screen in perpendicular and horizontal directions with respect to the axis of projection of a projector is known, an image that is free of distortion can be projected onto a screen by converting coordinates in the frame memory of the projector. Thus, Japanese Patent Laid-Open Publication No. 5278/03 already discloses a projector in which, on the premise that the screen is installed perpendicularly, the tilt of the projector is detected by means of a gravity sensor, and the tilt in the perpendicular direction, which in particular tends to produce distortion, is measured and distortion then corrected in accordance with this tilt.

However, the method that is disclosed in Japanese Patent Laid-Open Publication No. 281597/97 requires mechanical adjustment of the angle of the liquid crystal display unit. The method disclosed in Japanese Patent Laid-Open Publication No. 169211/01 requires control of the angle of the laser pointer and therefore entails a complex structure. The method that is disclosed in Japanese Patent Laid-Open Publication No. 197249/97 requires shifting of the image pattern on the screen to detect the angle, and therefore cannot obtain the detection speed necessary for realizing distortion correction in real time. The method that is disclosed in Japanese Patent Laid-Open Publication No. 5278/03 assumes the perpendicular installation of the screen and therefore cannot provide accurate correction of distortion when the screen is not installed perpendicularly or when the screen is tilted in the horizontal direction with respect to the axis of projection of the projector.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a projector having a tilt angle measurement device for correcting image distortion; this projector being able to accurately measure the angle of tilt of a screen in the horizontal and vertical direction with respect to the axis of projection of the projector by means of a simple configuration.

A projector having a tilt angle measurement device according to the present invention includes a tilt angle measurement device for calculating the tilt angle between the axis of projection of the projector device and the projection surface, and controls the output image of a display unit in accordance with the calculated tilt angle to correct distortion of the image on the projection surface. The tilt angle measurement device includes: a light guide unit that is provided on the projection-side surface of the projector case separated from the axis of projection in a prescribed direction; a photodetection element for receiving, by way of the light guide unit, reflected light from at least two points that are projected onto the projection surface; and a tilt angle calculation unit that calculates the tilt angle between the axis of projection of the projection device of the projector and the projection surface based on photoreaction position information of the reflected light in the photodetection element.

In the first mode of the invention, the tilt angle measurement device is provided with: a laser pointer for projecting at least two spots onto the projection surface; a digital camera having a lens, which is the light guide unit, and a pickup element, which is the photodetection element; and an image-analyzing tilt angle calculation unit, which is the tilt angle calculation unit. A projection port of the laser pointer and the lens of the digital camera are provided on the irradiation-side surface of the projector. The laser pointer projects at least two points onto the projection surface for establishing each vertical and horizontal direction of the projection device. The lens of the digital camera is arranged at a prescribed spacing in the vertical and horizontal directions, from the projection ports of the laser pointer and is able to capture an image of the points on the projection surface. The image-analyzing tilt angle calculation unit, based on the captured image of the pickup element of the digital camera, analyzes the tilt angle between a line that joins points on the projection surface that have been captured by the digital camera, i.e., the photodetection position information, and the reference lines that indicate the vertical direction and horizontal direction of the projection device, and calculates the tilt angle between the axis of projection of the projection device and the projection surface based on this tilt angle.

The laser pointer may be three point-type laser pointers that project points, two line-type laser pointers that project lines, or one crossline-type laser pointer that project orthogonal lines.

The analysis of the tilt angle between the reference lines and the line that joins points that are captured by the digital camera, which is based on the captured image of the pickup element of the digital camera, may be realized by calculating the difference between the picture element numbers of the picture elements that correspond to the intersections of the two edges of the captured image and either of a pointing line or a line that joins points, and then calculating the tilt angle by means of a table that is created beforehand that relates differential picture element numbers to tilt angles.

In the second mode of the present invention, the projection device has a test pattern output function for projecting a planar beam from the projection lens along the reference plane in which the tilt angle is found such that a projected image of a line is formed on the projection surface. The tilt angle measurement device is provided with: a light guide unit; a pair of left and right linear-arranged pickup elements, which are the photodetection elements; and a photodetection position analyzing distance/tilt angle calculation unit, which is the tilt angle calculation unit. The light guide unit is provided on the projection-side surface of the projector case and is separated from the axis of projection in a direction that is orthogonal to the reference plane. The linear-arranged pickup elements are provided in the interior of the case and are arranged in a vertical direction to the left and right of a vertical centerline that is above the axis of projection with respect to the reference plane. The reflected light of the projected image of the line that is projected onto the projection surface is received by way of the light guide unit, and based on the information of the heights and difference in heights of the positions of photodetection of the reflected light in the left and right linear-arranged pickup elements, the photodetection position analyzing distance/tilt angle calculation unit calculates the distance between the projection lens and the projection surface and the tilt angle between the axis of projection of the projection device and the projection surface.

The measured tilt angle may be the tilt angle in the horizontal plane between the projection surface and the axis of projection; and the reference plane may be the horizontal plane that contains the axis of projection. In addition, the tilt angle measurement device may include a vertical tilt sensor for detecting the tilt angle of the axis of projection in the vertical plane that contains the axis of projection of the projector; and the output image of the display unit may be controlled by combining the tilt angle in the vertical plane, that is detected by this vertical tilt sensor, with the tilt angle in the horizontal plane that is calculated from the height and difference in the heights of the photodetection positions of the reflected light in the right and left linear-arranged pickup elements. The measured tilt angle may be the tilt angle in the vertical plane between the projection surface and the axis of projection, and the reference plane may be the vertical plane that contains the axis of projection.

The projection device may be provided with a focus adjustment unit for adjusting the focal point of the projection lens, and the focus adjustment unit may be controlled by the distance between the projection lens and the projection surface that is calculated in the photodetection position analyzing distance/tilt angle calculation unit.

The light guide unit may be a pinhole or an optical lens that is provided in the wall of the projector case.

Control of the output image of the display unit in accordance with the tilt angle between the projection surface and the axis of projection of the projection device may be realized by creating LSI control parameters from the correction values of the input image of the display unit that are calculated in advance for tilt angles and which then controls projector image processing LSI.

The projection device may be a liquid crystal projector that includes a liquid crystal display unit; or may be a DLP (registered trademark) projector that includes a DMD (Digital Micromirror Device) display unit, a color wheel, and a light source.

The ease of calculation of the tilt angle between the projection surface and the axis of projection of the projection device in the horizontal direction and vertical direction allows modification of the image that is projected onto a projection surface to the correct state by shifting the arrangement of picture elements of the image in the liquid crystal display unit.

This effect is obtained because the tilt angle measurement device includes: a light guide unit that is provided on the projection-side surface of the projector case and separated in a prescribed direction from the axis of projection; a photodetection element that receives, by way of the light guide unit, reflected light from at least two points that are projected onto the projection surface; and a tilt angle calculation unit that calculates the tilt angle between the projection surface and the axis of projection of the projection device based on photodetection position information of reflected light in this photodetection element.

The second mode further enables automatic focus adjustment. This capability is obtained because the distance between the projection lens and the projection surface can also be calculated simultaneously in the photodetection position analyzing distance/tilt angle calculation unit based on the photodetection position information of the reflected light in the photodetection element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the interest of facilitating understanding, identical constituent elements are referred to by the same names and reference numerals in all modes and working examples in each of the drawings of the present description.

The present explanation regards a case in which projector10is a liquid crystal projector, but the present invention can still be applied to a DLP (registered trademark) (Digital Light Processing) projector. In place of liquid crystal display unit22that is used for a liquid crystal projector, a DLP projector is normally provided with a DMD (Digital Micromirror Device) display unit, a color wheel, and a light source.

As shown inFIG. 1, projector10in the first mode of the present invention is provided with: projection device20that includes projection lens21and liquid crystal display unit22; image control unit23for controlling the image of liquid crystal display unit22; tilt angle measurement device30; and CPU (Central Processing Unit)60for controlling overall operations.

Tilt angle measurement device30is provided with: laser pointer40for projecting at least two points on the projection surface; digital camera50that includes lens51and pickup element52and image-analyzing tilt angle calculation unit53. As shown inFIG. 2AandFIG. 2B, the projection ports of laser pointers41and lens51of digital camera50are provided on the illumination-side surface of projector10. Laser pointers41project at least two points81onto projection surface70for establishing each of the vertical direction and horizontal directions of projection device20. Lens51of digital camera50is arranged at a prescribed spacing from the projection ports of laser pointers41in the vertical and horizontal direction and can capture images of points81of projection surface70. Based on captured image80of pickup element52of digital camera50, image-analyzing tilt angle calculation unit53analyzes the tilt angle between the lines that join points81of projection surface70, that are captured by digital camera50and reference lines that indicate the vertical and horizontal direction of projection device20as shown inFIG. 2C, and calculates the tilt angle between axis of projection27of projection device20and projection surface70based on this tilt angle. Image control unit23in accordance with the calculated tilt angle controls the output image of liquid crystal display unit22, and image distortion on projection surface70is thus corrected.

As shown inFIG. 6, projector10in the second mode of the present invention is provided with: projection device20that includes projection lens21, focus adjustment unit26, and liquid crystal display unit22; image control unit23that controls liquid crystal display unit22; tilt angle measurement device30, and CPU60that controls overall operations.

Projection device20has a test pattern output function for projecting a planar light beam from projection lens21that follows reference plane28in which the tilt angle with respect to projection surface70is found such that a projected image of a line is formed on projection surface70. Tilt angle measurement device30is provided with pinhole54, a left-right pair of linear-arranged pickup elements55L and55R, and photodetection position analyzing distance/tilt angle calculation unit56. Pinhole54is provided on the projection-side surface of the case of projector10separated from axis of projection27in a direction that is orthogonal to reference plane28. Linear-arranged pickup elements55are provided inside the case and arranged in a vertical direction at equal spacing to the left and right of a centerline that is vertically above axis of projection27with respect to reference plane28. As shown inFIG. 7B, reflected light32from linear projected image84that is projected onto projection surface70is photodetected by way of pinhole54. Photodetection position analyzing distance/tilt angle calculation unit56calculates the distance from projection lens21of projector10to projection surface70and the tilt angle between axis of projection27of projection device20and projection surface70based on the information of the heights and difference of heights of the photodetection positions of reflected light32in the left-right pair of linear-arranged pickup elements55. Image control unit23corrects the image distortion on projection surface70in regard to the output image of liquid crystal display unit22in accordance with this calculated tilt angle. In addition, focus adjustment unit26is controlled based on the calculated distance from projection lens21to projection surface70, whereby the focus of projection lens21can be adjusted.

Explanation next regards the first working example of the first mode of the present invention. The configuration is identical to that of the above-described first mode, and explanation of the configuration is therefore omitted here. As shown inFIG. 2A, projector10is disposed on stand90and normally vertically tilted such that an image is projected upon projection surface70such as a screen or a wall. In this case, when projection is realized in which the axis of projection27of projection device20is orthogonal to projection surface70, the image plane of liquid crystal display unit22is enlarged and projected onto the projection plane without alteration, but the tilt of axis of projection27of projection device20with respect to projection surface70causes variation in the distance from projection lens21, this variation depends on the location when compared with a case in which axis of projection27is orthogonal to projection surface70, giving rise to the problem of distortion in the projected image plane due to, for example, the enlargement of the image plane at points that are more distant from projection lens21. Various designs have been employed to solve this problem, including those designs proposed in the above-described patent documents. If the tilt angle between the axis of projection27of projection device20and projection surface70can be accurately gauged in such a case, the image that is projected onto projection surface70can be modified to the correct form by shifting the arrangement of picture elements of the image of liquid crystal display unit22via means image control unit23, and the degree of shifting can be found numerically from the tilt angle.

The present invention takes as an object the accurate assessment of the tilt angle between the axis of projection27of projection device20and projection surface70, and tilt angle measurement device30that is described hereinbelow achieves this object.

In tilt angle measurement device30, as shown inFIG. 2B, three point-type laser pointers41a,41b, and41cand lens51of digital camera50having photodetection element52are arranged so as to be positioned at the apices of a square that surrounds projection lens21of projection device20. This arrangement need not be an accurate square.

Laser beams49from the three point-type laser pointers41a,41b, and41cconnect with points81a,81b, and81con projection surface70.FIG. 2Crepresents captured image80when points81a,81b, and81con projection surface70are captured by pickup element52of digital camera50. The upper portion of projection surface70tilts away from laser pointer41a, and in the image of pickup element52, that is captured at a position, that is separated in a horizontal direction from laser pointer41aas well as laser pointer41b, point81aof laser pointer41ais therefore displayed at a position that is farther to the right than point81bof laser pointer41bin the figure. Similarly, although not shown in the figure, the left side of projection surface70is tilted away from laser pointer41b, and in the image of pickup element52, that is taken at a position that is vertically separated from laser pointer41bas well as laser pointer41c, point81bof laser pointer41bis therefore displayed at a position that is higher than that of point81cof laser pointer41c.

In image-analyzing tilt angle calculation unit53, the position of each point in captured image80is analyzed based on its picture element position, and the tilt angle between axis of projection27of projection device20and projection surface70in both the vertical and horizontal direction is calculated by means of a prescribed calculation formula, and the result is supplied as output to image control unit23. Based on these tilt angles, image control unit23uses a prescribed calculation formula to shift the arrangement of the picture elements of the image of liquid crystal display unit22and thus modify the image that is projected onto projection surface70to the correct form.

In the first working example of the first mode, three point-type laser pointers41a,41b, and41cand lens51of digital camera50that has pickup element52are each arranged so as to be positioned at the apices of a square that surrounds projection lens21of projection device20. In the second working example of the first mode, however, as shown inFIG. 3AandFIG. 3B, one line-type laser pointer42athat projects a vertical pointing line is arranged at a position that is horizontally symmetrical with the position of lens51of digital camera50around the vertical centerline of projection lens21, and one line-type laser pointer42cthat projects a horizontal pointing line is arranged at a position that is vertically symmetrical with the position of lens51of digital camera50around the horizontal centerline of projection lens21.

Line-type laser pointers42aand42care laser pointers that can display lines and are often found among high-class laser pointers, and these line-type laser pointers42aand42cirradiate projection surface70as pointing lines82aand82c. The tilt angle may therefore be calculated in image-analyzing tilt angle calculation unit53by analyzing the picture element positions of pointing lines82aand82cin captured image80that is shown inFIG. 3C. It is also possible for example to acquire the picture element positions of the intersections of the two edges of captured image80with each of pointing lines82aand82c, calculate the difference in the picture element numbers of the two picture element positions, and then compute the tilt angle through the use of a table that has been prepared in advance that correlates differential picture element numbers with tilt angles, whereby the process can be simplified over the first working example.

As shown inFIG. 4, image-analyzing tilt angle calculation unit53acquires differential picture element number information from captured image80of pickup element52for vertical differential picture element number86and horizontal differential picture element number87(Step S1), and based on this differential picture element number information, generates the tilt angle between the axis of projection27of projection device20and projection surface70(Step S2). Image control unit23receives the generated tilt angle and generates LSI control parameters (Step S3) and controls image processing LSI for the projector (Step S4), whereby input image24is corrected to become output image25on liquid crystal display unit22. This output image25, when projected onto projection surface70, becomes an image that approximates input image24.

In the second working example of the first mode, two line-type laser pointers42aand42cwere arranged at positions that are horizontally and vertically symmetrical to lens51of digital camera50around the vertical center line and horizontal center line, respectively, of projection lens21, but in the third working example of the first mode, one crossline-type laser pointer43is arranged at a position that is symmetrical to lens51of digital camera50on a diagonal line with projection lens21of projection device20that is interposed, as shown inFIGS. 5A and 5B.

Crossline-type laser pointer43is a laser pointer that is capable of displaying a crossline and that is found in high-level laser pointers, and this crossline-type laser pointer43irradiates pointing lines83onto projection surface70that are similar to the pointing lines in the second working example of the first mode. The picture elements of pointing lines83in captured image80that are shown inFIG. 5Cmay then be analyzed in image-analyzing tilt angle calculation unit53to calculate the tilt angle, or, as described hereinabove, the differences in the picture element numbers at the picture element positions of the intersections of both edges of captured image80with pointing lines83, may be calculated and the tilt angle then calculated through the use of a table that has been prepared in advance that correlates the differential picture element numbers with tilt angles.

Explanation next regards the first working example of the second mode of the present invention. The configuration of this mode is identical to that of the above-described second mode and is therefore omitted here.

In contrast with a case in which projection surface70is orthogonal to the axis of projection27, when projection surface70, such as a screen or wall, is inclined with respect to the axis of projection27as shown inFIG. 7BandFIG. 7C, the distance of projection surface70from projection lens21varies by position, and because the image therefore expands at positions that are more distant from projection lens21, the problem of distortion arises in the projected image. In this case, if the tilt angle between the axis of projection27of projection device20and projection surface70can be accurately gauged, the image that is projected onto projection surface70can be modified to the correct form by shifting the arrangement of picture elements of the image of liquid crystal display unit22by means image control unit23, and the degree of shifting can be found numerically from the tilt angle.

Projection device20includes a test pattern output function for projecting a planar beam from projection lens21along reference plane28in which the tilt angle with projection surface70is to be found such that projected image84of a straight line is formed on projection surface70. As shown inFIG. 7D, projection beam31is reflected in a vertical direction as reflected beam32that is centered on projected image84. As shown inFIG. 7A, pinhole54of tilt angle measurement device30is provided in the projection-side surface of the case of projector10at a distance from the axis of projection27in a direction that is orthogonal to reference plane28. In addition, linear-arranged pickup elements55L and55R are provided vertically inside the case with the linear-arranged pickup elements55L and55R being equally spaced to the left and right of a vertical line above the axis of projection27with respect to reference plane28. In regard to reflected beam32from linear projected image84that is projected onto projection surface70, linear-arranged pickup elements55L and55R photodetect the reflected light32that is incident by way of pinhole54. If projection surface70is assumed to be perpendicular to the axis of projection27as shown inFIG. 7D, the positions of photodetection, (i.e., the heights, in linear-arranged pickup elements55L and55R that are positioned vertically and arranged in left-right symmetry) will be equal on the left and right. If projection surface70recedes as far as the position of projection surface70′, however, reflected beam32that passes through pinhole54will shift to the position that is shown by the chain line, and the photodetection positions in linear-arranged pickup elements55L and55R will be lower. Thus, based on the photodetection positions in linear-arranged pickup elements55L and55R, the distance between projection lens21and projection surface70can be calculated through the use of a table that has been prepared in advance.

When projection surface70is perpendicular to the axis of projection27as shown inFIG. 7D, the positions of detection in both linear-arranged pickup elements55L and55R will be the same height, but if projection surface70is tilted horizontally with respect to the axis line of axis of projection27in reference plane28as shown inFIG. 7BandFIG. 7C, the height of the photodetection positions in the left and right linear-arranged pickup elements55L and55R will differ. However, the average height will be the height of reflected beam32in the perpendicular direction in the axis of projection27that is produced by projected beam31, and the distance between projection lens21and projection surface70can therefore be calculated by means of this average height.

When projection surface70is horizontally tilted with respect to the axis line in reference plane28as shown inFIGS. 7B and 7C, the heights of the photodetection positions in left and right linear-arranged pickup elements55L and55R will differ as shown in the figures, but as described hereinabove, these heights correspond to the distances between projection lens21and the points of reflection in projected image84of reflected beams32that are incident to linear-arranged pickup elements55L and55R. Accordingly, finding the difference in these heights enables the finding of an approximate value of the difference in distance between projection lens21and each of input beam reflection points85in projected image84of reflected beams32that are incident to linear-arranged pickup elements55L and55R. The spacing between these input beam reflection points85can be calculated from: the spacing between left and right linear-arranged pickup elements55L and55R, the distance between pinhole54and the line that joins the left and right linear-arranged pickup elements, and the distance between pinhole54and reflection surface70that approximates the distance between projection lens21and reflection surface70. Accordingly, the tilt angle within, reference plane28between the axis of projection27and projection surface70can be calculated from: the distance between input beam reflection points85, and the difference between the distances between projection lens21and each of the input beam reflection points85in projected image84of reflected beams32that are incident to linear-arranged pickup elements55L and55R. Distortion in the image on projection surface70is corrected by controlling at image control unit23over the output image of liquid crystal display unit22in accordance with the tilt angles that are thus calculated. In addition, the focus of projection lens21can also be adjusted by controlling focus adjustment unit26based on the distance that has been calculated between projection lens21and projection surface70.

Referring now toFIG. 8, explanation next regards the steps for amending the output image of liquid crystal display unit22based on the photodetection positions, in linear-arranged pickup elements55that are arranged as a left/right pair, of reflected beams32from the test pattern projection image on projection surface70.

Photodetection position analyzing distance/tilt angle calculation unit56calculates the distance to left input beam reflection point85based on the height of the photodetection position in left linear-arranged pickup element55L (Step S11), calculates the distance to right input beam reflection point85based on the height of the photodetection position in right linear-arranged pickup element55R (Step S12), and then calculates the average value of the distance to reflection surface70(Step S13).

Photodetection position analyzing distance/tilt angle calculation unit56next acquires the difference in heights of the photodetection positions in left and right linear-arranged pickup elements55L and55R (Step S14), and based on the average value of the distance to reflection surface70and the difference in heights of the photodetection positions in left and right linear-arranged pickup elements55L and55R, generates the tilt angle between optical axis27of projection device20and projection surface70by performing an arithmetic operation or by referring to a table (Step S15).

Image control unit23receives the generated tilt angle and generates LSI control parameters (Step S16), and controls image processing LSI for the projector (Step S17), whereby input image24is corrected to become output image25on liquid crystal display unit22. This output image25is an image that approximates input image24when projected onto projection surface70. Focus servomotor of focus adjustment unit26can be controlled by means of the average value of the distance to reflection surface70to enable adjustment of the focal point of projection lens21to projection surface70.

Explanation up to this point has concerned the measurement of the tilt angle in the horizontal direction, but using pinhole54and linear-arranged pickup elements55at positions that are rotated 90° around axis of projection27enables measurement of the tilt angle in the vertical direction.

In addition, in the explanation up to this point, the light guide unit was a pinhole, but the same measurement can be realized if the light guide unit is an optical lens. When convex lens59is used as shown inFIG. 9, reflected beam32from projection surface70is incident to linear-arranged pickup elements55similar to reflected beam32from projection surface70when pinhole54is used.

As shown inFIG. 10, the configuration and operation of the second working example of the second mode are identical to the first working example of the second mode except for tilt angle measurement device30of vertical tilt sensor57, which is a tilt sensor (G-sensor) that employs an acceleration detection element that is also used in, for example, centering when setting up the machine, and which precisely measures tilt angle with respect to the direction of gravity and supplies the result as numerical data. Identical constituent elements are therefore given the same reference numerals and redundant explanation of these parts is omitted here.

Tilt angle in the vertical direction that is detected by vertical tilt sensor57is applied as input to photodetection position analyzing distance/tilt angle calculation unit56. In photodetection position analyzing distance/tilt angle calculation unit56, tilt angle in the horizontal direction is calculated by means of photodetection position information that is measured by the pair of linear-arranged pickup elements55and combined with the tilt angle in the vertical direction that is detected by vertical tilt sensor57and supplied as output to image control unit23. Image control unit23adds the tilt in the vertical and horizontal directions and generates LSI control parameters. In this case as well, the same process is carried out as described in the first working example when convex lens59is used in place of pinhole54in the light guide unit. It is to be understood, however, that although the characteristics and advantages of the present invention have been set forth in the foregoing description, the disclosure is illustrative only, and changes may be made in the arrangement of the parts within the scope of the appended claims.