Projector

A projector is provided which includes a distance measuring unit which can accurately measure distances to a plurality of points on a surface of a screen using light rays. The projector of the invention has the distance measuring unit for measuring distances to the plurality of points on the surface of the screen, which includes a plurality of light ray units for irradiating light rays onto the screen and one light receiving element for receiving the light rays which are reflected on the surface of the screen, and a tilt angle calculation unit for calculating a tilt angle of the screen relative to the projector based on the distances to the plurality of points on the surface of the screen which are measured by the distance measuring unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application Nos. 2007-078754 filed on Mar. 26, 2007 and 2008-009834 filed on Jan. 18, 2008, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector.

2. Description of the Related Art

In these days, data projectors are used in many cases which projects an image displayed on the screen of a personal computer, an image carried on a video signal, and furthermore, an image carried on image data stored in a memory card or the like.

Many of the data projectors have a construction in which light emitted from a compact high-intensity light source, for which a metal halide lamp or extra-high pressure mercury vapor lamp is used, is converted into light beams of three primary colors by a color filter so as to be irradiated onto a display device such as a liquid crystal display device or a DMD (digital micromirror device) by a light source side optical system, and a image light beam that has passed through or been reflected by the display device is projected onto a screen via units or groups of lenses which constitute a projection side optical system having a zooming function.

In the projectors like this, there may occur a case where a keystone distortion in a projected image by a distance to the screen, a tilt angle of the screen and a projection angle, and in order to correct the keystone distortion (keystoning correction), a distance to the screen, a tilt angle of the screen and a projection angle need to be measured accurately. To make this possible, a distance measuring device needs to be provide on the projector.

SUMMARY OF THE INVENTION

The invention has been made in view of the situations described above and an objective thereof is to provide a projector having a distance measuring unit for measuring distances to a plurality of points on the surface of a screen accurately using rays of light.

According to a preferred embodiment of the invention, there is provided a projector with a distance measuring unit for measuring distances to a plurality of points on the surface of the screen, which includes a plurality of light ray units for irradiating light rays onto a screen and a light receiving element for receiving light rays reflected on a surface of the screen, and a tilt angle calculation unit for calculating a tilt angle of the screen relative to the projector based on the distances to the plurality of points on the surface of the screen which is measured by the distance measuring unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a best mode for carrying out the invention, there is provided a projector1which includes a light source unit, a light source side optical system for guiding light from the light source unit to a display device50, a display device50, and a projection side optical system for projecting an image projected from the display device50onto a screen, having a projector control unit for controlling the light source unit and the display device50.

In addition, the projector control unit includes a distance measuring unit for measuring distances to three points on a surface of a screen61, as well as an average distance to the screen61, a tilt angle calculation unit for calculating a tilt angle of the screen61relative to the projector1based on the distances to the plurality of points on the surface of the screen61, and a distortion correcting unit for creating image data for a projected image of which distortion is corrected based on the information measured by the distance measuring unit and the information calculated by the tilt angle calculation unit.

A distance measuring unit15, which functions as the distance measuring unit, includes three laser units53which irradiate leaser beams onto the screen61and one light receiving element54for receiving laser beams which have been reflected at the three points on the surface of the screen61and further includes a distance measuring substrate51to which an operation unit63for calculating a distance to the screen61from the reflected lights received by the light receiving element54, a laser unit control unit64for time-sharing controlling the laser units53, and the light receiving element54are fixed.

In addition, this distance measuring unit15includes a light receiving mirror barrel52which is made up of a cylindrical body which is formed into a frustum of circular cone and is made open in both end faces thereof and which is disposed on a circumferential edge of the light receiving element54for removing unnecessary light with the light receiving element54positioned in a central portion on a narrow open end thereof and a condenser lens55which is disposed in such a manner as to close a wide open end of the light receiving mirror barrel52and is adapted to gather as much of light reflected from the screen61as possible so as to direct it to the light receiving element54, and the three laser units53are disposed radially on an exterior surface of the light receiving mirror barrel52at intervals of an equal internal angle.

Furthermore, the distance measuring unit15also includes a reflection mirror56which is disposed in an interior of the light receiving mirror barrel52for reflecting towards the light receiving element54part of light which is incident on the light receiving mirror barrel52and which intersects a common optical axis of the light receiving mirror barrel52, the light receiving element54and the condenser lens55at a large angle, and this reflection mirror56is provided in the same number as the number of laser units53, that is, three so as to function as a light quantity adjusting unit. In addition, these three reflection mirrors56are made to pair up with the three laser units53, respectively, to make a predetermined pair and are disposed so that part of light that is emitted from the paired laser unit53, is then reflected on the surface of the screen61and is incident on the light receiving mirror barrel52is reflected thereby in the direction of the light receiving element54.

Hereinafter, an embodiment of the invention will be described based on the drawings. As is shown inFIG. 1, the projector1according to the embodiment of the invention includes a projection opening14and a distance measuring unit15which are provided in the vicinity of an end of a front plate12of a main body case, and a plurality of exhaust ports16from which air that has cooled or absorbed heat inside the case of the projector1is expelled are formed in such a manner as to extend from the vicinity of the projection opening14to the vicinity of the other end of the front plate12, and furthermore, although not shown, an Ir receiving unit is provided for receiving a control signal from a remote controller.

In addition, the projector1includes a key/indicator unit37and an audio output unit18which are provided on an upper plate11of the main body case, and included in this key/indicator unit37are keys and indicators such as a power supply switch key, a power indicator lamp which indicates whether a power supply is switched on or off, a lamp switch key which turns on a lamp of the light source unit, a lamp indicator which indicates whether the lamp is illuminated or not, and an overheat indicator which indicates that the light source unit overheats when it really occurs.

Furthermore, although not shown, on a back plate which constitutes a back side of the main body case of the projector1has an input/output connector unit where USB terminal, image signal inputting D-SUB terminal, S terminal, RCA terminal and the like are provided, as well as various types of terminals including a power supply adaptor plug and a memory card slot.

In addition, the projector1includes a plurality of intake ports19which are provided on each of a right-hand side plate13, which is a side plate of the main body case, and a left-hand side plate, and has front legs20which is adapted to extend and contract on a bottom plate, which constitutes a bottom side of the main body case, for adjusting a projection angle so as to project an image onto a screen with the projector1oriented upwards.

Additionally, the projector1has a power supply control circuit board which includes a lamp power supply circuit block or the like and a main circuit block which includes a project control unit in an interior thereof, and also includes a cooling fan for reducing the interior temperature of the projector1, a high-intensity light source unit including a halogen lamp which functions as a light source unit, a DMD (digital micromirror device) which functions as a display device for creating an image, a light source side optical system for gather as much of light from the light source unit as possible to direct it to the DMD, and a projection side optical system for projecting reflected light from the DMD onto a screen.

This DMD has a number of micromirrors which are arranged into a matrix and is adapted to reflect incident light which is incident from an incident direction which is tilted in one direction relative to a front direction in such a manner as to divide it into on-state light rays directed in the front direction and off-state light rays directed in an oblique direction by switching the tilt directions of the micromirrors so arranged so as to form an image. In other words, light incident on the micromirrors which are tilted in one tilt direction is reflected by the micromirrors in the front or “on” direction so as to be converted into on-state light rays, and light incident on the micromirrors which are tilted in the other tilt direction is reflected in the oblique or “off” direction by the micromirrors so as to be converted into off-state light rays, with the off-state light rays made to be absorbed by a light absorbing plate, so that the light rays reflected in the front direction effect bright indications while the light rays reflected in the oblique direction dark indications so as to form an image.

As is shown inFIG. 2, the projector control unit80of this projector1is such as to have a control unit38, an input/output interface22, an image transforming unit23, a display encoder24, a video RAM25, a display drive unit26, a tilt angle calculation unit46, and a distortion correcting unit47, and image signals of various standards which are inputted from an input/output connector unit21are sent to the image transforming unit23via the input/output interface22and a system bus (SB) so as to be converted to be unified into an image signal of a predetermined format which is suitable for display, whereafter the image signal is sent to the display encoder24.

The display encoder24deploys the image signal sent thereto on the video RAM25for storage and creates a video signal from the contents stored in the video RAM25for output to the display drive unit26.

The display drive unit26, into which the video signal is inputted from the display encoder24, is such as to drive a display device50, which is a spatial optical modulator (SOM), at an appropriate frame rate in association with the image signal sent thereto, whereby by causing light from a light source unit62to be incident on the display device50via a light source side optical system70, a light image is formed by reflected light from the display device50, and the image so formed is then projected onto a screen, not shown, via the projection side optical system for display on the screen. In addition, a movable lens group97of the projection side optical system is such as to be driven by a lens motor42for zooming or focusing a projection lens.

An image compressing/expanding unit31enables a recording operation in which a luminance signal and a color difference signal of the image signal are data compressed through an operation such as ADTC and Huffman coding so as to be written sequentially on a memory card32which is a detachable recording medium and in a reproduction mode a display operation in which image data recorded on the memory card32is read out, and individual image data which make up a series of moving pictures are expanded one frame by one frame to send the data so expanded to the display encoder24via the image transforming unit23, so that the moving pictures are displayed based on the image data stored on the memory card32.

A distance measuring unit45is such as to measure distances to a plurality of points on the surface of the screen using a laser beam, which is one of light rays, so as to calculate an average distance to the screen, and the tilt angle calculation unit46is such as to calculate a tilt angle of the screen based on the distances to the plurality of points on the surface of the screen which were measured by the distance measuring unit45. In addition, the distance measuring unit45and the tilt angle calculation unit46transmit data measured or calculated to the distortion correcting unit47. In addition, the average distance to the screen which is calculated by the distance measuring unit45is such as to be used for focusing by the lens motor42.

The distortion correcting unit47is such as to correct the distortion of a projected image based on the data received from the distance measuring unit45and the tilt angle calculation unit46, transmit the image signal after the correction of distortion to the display encoder24via the image transforming unit23and display the projected image of which distortion has been corrected.

The control unit38is such as to govern the control of operations of circuits within the projector1and is made up of a CPU381, a ROM382in which operation programs such as various types of settings are stored in a fixed fashion and a RAM383which is used as a working memory.

Control signals of the key/indicator unit37, which is made up of main keys and indicators which provided on the upper plate11of the main body case are sent out directly to the control unit38, key control signals from the remote controller are received at the Ir receiving unit35, and code signals which are demodulated by an Ir processing unit36are sent to the control unit38.

In addition, a voice processing unit48is connected to the control unit38via a system bus (SB), and the voice processing unit48includes a sound source circuit such as a PCM sound source, whereby in a projection mode and a reproduction mode the voice processing unit48is adapted to convert voice data into analog signals and drive a speaker49to emit sound loudly.

The control unit38controls a power supply control circuit41, and this power supply control circuit41illuminates a discharge lamp of the light source unit when the lamp switch key is operated. Furthermore, the control unit38controls a cooling fan drive control circuit43, and this cooling fan drive control circuit43controls the rotation speed of the cooling fan based on temperatures detected by a plurality of temperature sensors provided on the light source unit or the like and keeps the cooling fan to rotate continuously by a timer even after the lamp of the lamp source unit has been switched off. In addition, the control unit38stops the light source unit depending upon the results of temperature detections by the temperature sensors and then switches off the power supply of the projector main body.

Next, the distance measuring unit15will be described which is disposed on the front plate12of the projector1for measuring distances to the screen by making use of laser beams. A general laser distance meter is such as to project a laser beam while switching it on and off at a predetermined frequency so as to calculate a distance from a difference in phase of the laser beam between when it is emitted and when received. However, since a tilt angle of the screen needs to be calculated in order for the distance measuring unit15to be used to correct the distortion of the projector1, an accurate correction cannot be attained only by measuring a distance to one point on the surface of the screen, and hence, distances to at least three different points on the surface of the screen need to be measured to measure a tilt angle of the screen. In addition, in the event that the three different points lie in a straight line, a tilt angle in only one direction, that is, in a horizontal direction or a vertical direction can be measured, and therefore, in order to obtain a tilt angle of a flat surface, distances to three points which do not lie in a straight line need to be measured.

The distance measuring unit15of the embodiment is made up of the distance measuring unit45, and as is shown in FIGS.3and4, the distance measuring unit45includes a distance measuring substrate51, a light receiving element54fixed to the distance measuring substrate51, a light receiving mirror barrel52which is made up of a cylindrical body which is formed into a frustum of circular cone and is made open in both end faces thereof and which is disposed on a circumferential edge of the light receiving element54, three laser units53(light ray units) which are disposed radially in three directions on an exterior surface of the light receiving mirror barrel52for emitting laser beams, a condenser lens55which is disposed at a distal end portion of the light receiving mirror barrel52and three reflection mirrors56which are disposed radially in an interior of the light receiving mirror barrel52to function as light quantity adjusting units.

The distance measuring substrate51has an operation unit63for calculating distances to a plurality of points on the surface of the screen and an average distance from reflected light received by the light receiving element54and a laser units control unit64(a light ray units control unit) for time-sharing control the laser units53, and the light receiving element54is fixed to this distance measuring substrate51.

The light receiving element54is a highly sensitive light receiving element such as an avalanche photodiode for amplifying an optical signal by making use of avalanche multiplication phenomenon which is caused by an electron avalanche phenomenon and is such as to be used as a light receiving element in a commercially available laser distance meter, and the light receiving element54receives laser beams which are emitted from the laser units53and are then reflected on the surface of the screen to convert them into electric information and transmits the electric information so converted to the operation unit63possessed by the distance measuring substrate51.

The light receiving mirror barrel52is the cylindrical body formed into a frustum of circular cone, the frustum of circular cone being opened in an upper surface and a bottom surface thereof and is disposed to prevent unnecessary external light from being incident on the light receiving element54. The light receiving element54is disposed in a central portion of an end portion at a narrow open end, and the condenser lens55is disposed in such a manner as to close an end portion at a wide open end of the light receiving mirror barrel52. The light receiving mirror barrel52is disposed vertical relative to the distance measuring substrate51.

The laser units53each include a laser light source for emitting a laser beam, which is a straight line beam, in an interior thereof and are time-sharing controlled by the laser units control unit64on the distance measuring substrate51. Two laser units53and one laser unit53are disposed radially in upper positions and a lower position radially, respectively, on the exterior surface of the light receiving mirror barrel52at intervals of an equal internal angle. Since the laser units53are disposed radially on the exterior surface of the light receiving mirror barrel52at such intervals of an equal internal angle, the laser units53can emit laser beams towards different apexes of an arbitrary triangle on the surface of the screen61as is shown inFIG. 5.

The condenser lens55is a lens which is disposed in such a manner as to close the end portion at the wide open end of the light receiving mirror barrel52to gather as much of light from the surface of the screen61as possible so as to direct it towards the light receiving element54. Namely, the condenser lens55refracts light emitted from the laser units53and reflected on the surface of the screen61in such a manner as to be incident on the light receiving mirror barrel52so as to gather as much of the light as possible to direct it towards the light receiving element54so as to be incident thereon.

The three reflection mirrors56, which function as the light quantity adjusting units, are made to pair up with the three laser units53, respectively and are controlled to be tilted to allow part of light emitted by the mating laser units53and reflected on the screen61to be incident on the light receiving element54. The reflection mirrors56are fixed to an interior surface of the light receiving mirror barrel52in positions which are symmetrical with the laser units53relative to the center of the light receiving mirror barrel52.

In the distance measuring unit15that is configured as has been described heretofore, when comparing the intensity of reflection light with a projection distance of 5 m and the intensity of reflection light with a projection distance of 0.5 m, since the intensity of light is in inverse proportion to square of distance, in theory, the intensity of the latter should be something like 100 times that of the former. However, in case the intensity of the latter reflected light becomes 100 times that of the former reflected light in reality, in almost all light receiving elements, the light intensity surpasses a dynamic range which is a ratio of a least light intensity to a greatest light intensity.

Then, in this embodiment, to cope with this problem, in the distance measuring unit15, the condenser lens55is adjusted such that reflected light reflected on the surface of a screen61which lies a long distance therefrom is incident on the center of the light receiving element54while reflected light reflected on the surface of a screen61which lies a short distance therefrom is irradiated onto the reflection mirrors56, and furthermore, the reflection mirrors56are adjusted such that part of the reflected light which is made to be incident on the reflection mirrors56is allowed to be incident on the light receiving element54while bundles of rays of the remaining reflected light are prevented from being incident on the light receiving element54, whereby the intensity of the reflected light reflected from the short distance is made to stay on the order 10 times the intensity of the reflected light reflected from the long distance. Thus, measuring various distances is enabled by adjusting the reflection mirrors56in the way described above.

Next, the function and operation of the distance measuring unit15will be described which is configured as has been described above. In the case of the screen61being positioned in a long distance from the projector1, laser beams emitted from the laser units53and reflected on the surface of the screen61are, as shown inFIG. 4, irradiated onto the condenser lens55, and then are refracted by the condenser lens55in such a manner as to be directed towards the light receiving element54to thereby be incident on the vicinity of the center of the light receiving element54.

On the other hand, in the case of the screen61being positioned in a short distance from the projector1, laser beams emitted from the laser units53and reflected on the surface of the screen61are, as shown inFIG. 6, irradiated at large angles relative to the optical axis of the condenser lens55, and are then refracted by the condenser lens55towards the reflection mirrors56to be divided into light which is to be reflected by the reflection mirrors56towards the light receiving element54and light which is not incident on the light receiving element54, whereby part of the reflected light is allowed to be incident on the light receiving element54.

The light receiving element54which has received the reflected light reflected from the screen61transmits electric information produced from the light so received to the operation unit63possessed by the distance measuring substrate51, the operation unit63then calculates distances to the respective points on the surface of the screen61and an average distance to the screen61which is a distance to a center of the three points from the electric information so received, and the tilt angle calculation unit46calculates a tile angle of the screen61based on the data calculated by the operation unit63.

Thus, by calculating the distance to and tilt angle of the screen61based on the distances from the three different points on the surface of the screen61, an accurate distance to and tilt angle of the screen61can be obtained, whereby an accurate distortion correction can be implemented in the distortion correcting unit47. In addition, since the average distance to the screen61which is the distance to the center of the three points is calculated, an image beam projected from the projection lens can be focused substantially on the center of a projected image.

According to the projector1of the embodiment, by including the distance measuring unit15which has the plurality of laser units53and the single light receiving element54which receives a bundle of laser beams which are emitted from the plurality of laser units53and reflected on the surface of the screen, the necessity is obviated of disposing a plurality of distance measuring units15to obtain distances from the different points on the surface of the screen and disposing a driving mechanism to drive the distance measuring units15so disposed, whereby distances to a plurality of points on the surface of the screen can easily be obtained even with a small projector.

In addition, since unnecessary light which is incident on the light receiving element54can be removed by disposing the light receiving mirror barrel52and a bundle of rays of light which is reflected on the surface of the screen61to thereby be incident on the light receiving mirror barrel52can be made to be incident on the light receiving element54by providing the condenser lens55, highly accurate distance measurement can be enabled even though the quantity of laser beam emitted from the laser units53is small and a reduction in amount of consumed electricity can be realized.

Additionally, by forming the light receiving mirror barrel52into the cylindrical body having the shape of a frustum of circular cone which is opened in both the end faces with the wide open end disposed at the light incident end, and disposing the plurality of laser units53radially on the exterior surface of the light receiving mirror barrel52, reflected light is allowed to be incident on the light receiving mirror barrel52from the end having a wide open area, and hence, the quantity of light incident on the light receiving mirror barrel52can be increased.

Furthermore, by disposing the reflection mirrors56which function as the light quantity adjusting units, part of the bundle of rays of light which is incident on the light receiving mirror barrel52but is not incident on the light receiving element54due to the light being so incident at the large angle with respect to the optical axis of the condenser lens55and the light receiving element54as when the screen61is placed in the short distance from the projector1can be made to be incident on the light receiving element54while the remaining part of the bundle of rays of light is not allowed to be incident on the light receiving element54, whereby the intensity of the reflected light can be adjusted, thereby making it possible to enable accurate measurement of various distances from a short distance to a long distance. In addition, the quantity of light can be adjusted easily by making the reflection mirrors56to pair up with the laser units53, respectively.

Additionally, by disposing the three laser units53so as to irradiate laser beams to apexes of an arbitrary triangle on the surface of the screen61, the tilt angle of the flat surface which is the screen61can be measured accurately, whereby the distance to the screen61and the tilt angle of the screen61which are used in correcting distortion can be measured to obtain accurate numerical values.

In addition, since the distance measuring unit15includes the distance measuring substrate51having thereon the operation unit63and the laser units control unit64, when disposing the distance measuring unit15on the projector1, the necessity is obviated of separately providing a substrate for controlling the distance measuring unit15and hence, the distance measuring unit15can easily be disposed on the projector1.

Next, a modified example of the invention will be described. While in the embodiment, the reflection mirrors56are used as the light quantity adjusting units, in a distance measuring unit15of this modified example, as is shown inFIGS. 7 and 8, short distance lenses59are incorporated in a condenser lens55in such a manner as to be situated on radial straight lines between laser units53which are provided radially on an exterior surface of a light receiving mirror barrel52and the center of the light receiving mirror barrel52, and the short distance lenses59so provided are made to function as light quantity adjusting units.

By incorporating the short distance lenses59in the condenser lens55as the light quantity adjusting units in the way described above, part of light which is reflected from the screen61which is placed a short distance and is incident on the light receiving mirror barrel54at a large angle with respect to the optical axis of the condenser lens55and a light receiving element54can be made to be incident on the light receiving element54via the short distance lenses59as is shown inFIG. 9, and almost all the reflected light which passes through the remaining portion of the condenser lens55where no short distance lenses59are incorporated is not allowed to be incident on the light receiving element54, whereby a difference in light intensity between reflected light from the screen61placed in a short distance and reflected light from the screen61placed in a long distance can be reduced, enabling accurate measurement of various distances.

While in the embodiment, the three laser units53are used, the invention is not limited to this particular number, provided that three or more laser units are provided, and the more laser units are provided, the more accurate tilt angle of the screen61can be obtained. However, the increase in the number of laser units53makes the tilt angle calculation complex, which makes, in turn, the correction of distortion complex. Due to this, it is most efficient to obtain a tilt angle of the screen61from three different points on the flat plane.

In addition, while in the embodiment, the laser units53are illustrated as two of them being disposed on the upper portion of the light receiving mirror barrel52and the remaining one being disposed on the lower portion thereof, the invention is not limited to this particular arrangement of the laser units53. However, since the projector1of the embodiment projects an image onto the screen61from below towards obliquely upwards, a projected image is distorted wide towards the top and narrow towards the bottom, and hence, it is appropriate in obtaining a tilt angle of the screen61that the two laser units are disposed on the upper portion and the one laser unit is disposed on the lower portion of the light receiving mirror barrel52.

Additionally, while in the embodiment, the distances to the screen are measured by making use of the laser beam, which is one of light rays, the invention is not limited to the laser beam, and hence, any light ray may be adopted, provided that the light ray is such that the light ray is emitted towards an object while being modulated using a reference signal which is transmitted at a predetermined frequency so as to measure a distance to the object by detecting a difference in phase between a light receiving signal which signals the reception of light returning from the object and the reference signal. For example, a light emitting element such as an LED can be adopted, provided that light emitted can be modulated and irradiate onto an object, and light ray units made up of such light emitting elements can be used in place of the laser units53.

In addition, the invention is not limited to the embodiment and modified example that have been described heretofore but can freely be modified or improved variously without departing from the spirit and scope of the invention.