CA2086893A1 - Projection type display apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An adjusting pattern is formed on a cathode-ray tube and this pattern is projected through a projection lens onto a photodetector installed on a screen frame. Based on the output of the photodetector that detects the projected image of the adjusting pattern, the characteristics of the cath-ode-ray tube are automatically adjusted with the adjusting pattern being adjusted to the optimum level.

Description

TITLE OF TIIE INVENTION
E'ROJECTION TYPE DISPLAY APPARATUS

BACKGROUND OF THE INVENTION

F:ield of the Invention Tne present invention rela-tes to a projection -type display apparatus which projeets image l.ight from a eatnode-ray tube (hereinafter abbrevia-te(l as CRT) through a projee-tion lens for p:rojectlorl Or an enlarged :imag~e onto a screen, and more partic;ularly to automatie adjustment o-f -the eharac-teristics of the CRT.

Description of Rela-ted Ar-t Adjustments speeially required -for the eharacteristics of -the CRTs used in projeetion type display apparatuses generally inelude -focus adjustments for effec-ting proper-foeusing on the screen, eonvergenee adjus-tments for correct-ing the separa-tion of eolors on the sereen, raster dis-tor-tion adjustments for eorree-ting raster distor-tions eaused when an eleetron beam is not eorreetly deflected for ras-ter seanning due to nonlinearity of deflection circuitry, ete., eu-toff adjustments for adjusting the euto-ff voltage at whicn lumineseent spots become invisible, and white balanee ad-justments for p:reventing blaek-and-white pietures -to be uniformly tinted.

Fig. 1 is a schemat;ic diagra~l of a prior art projec-tion -type disp1ay apparatus disclosed, for example, in Japanese Paten-t Applicatio~ Laicl Open No. 59-23684, relating to focus adjustment. In Fig. 1, the reference nllmeral l designa-tes a CRT having a phosphor screen 10. In front of the CRT 1 is a projec-tion lens 2 with A lens cover 21 fit over i-t. The Lens cover 21 i5 provided at i-ts center with a PIN pho-tocliode ~1 serving as a pho-tocletector for detecting the brightness of the phosphor screen 10 of -the CRT 1.
Next, the opera-tion of the above dispLay appara-tus wlll be described below. When using the projection -type display apparatus, the lens cover 21 is removed and image light from the CRT 1 is projected through the projec-tion lens 2 onto a screen (not shown) on which the resultin~ image is focused.
When making focus adjustments, a beam spot is emitted -to illuminate the cen-ter of the phosphor screen and the beam spot is detected by the PIN photodiode 41. Then, the focus vol-tage is adjus-ted by a focus adjusting circui-t (not shown~
with reference to the output of -the PIN photodiode 41 so tha-t the detec-ted brightness of the beam spot is reduced to the minimum level.
In the prior ar-t projection -type display apparatus, potentiometers for adjus-ting the cutoff and whi-te balance characteris-tics are provided -for each CRT. When adjusting the cu-to-ff and white balance charac-teristics, these potenti-~8~3~3 ometers are marlually adjus-ted, which are used -in combination wi-th special tes-t equipment respectively, so lhat proper values are obtained.
Furthermore, in the pl'iOI` ar-t projection -type d:isplay apparatus, convergence and raster distortion adjllstlllerlts are also made manua]]y as in the above adjustments.
Since the prior art projection -type display apparatus is constructed as describecl above, focus adjustment requires -the WOI'k to fit a ]ens cover, ancl the adjustment is possible only in the manufacturing process of the apparatus. The resultirlg problem is -tha-t~ even if the adjustment has been once made, devia-tion from the proper value may occur because o-f deterioration of the CRT characterist:ics with time, e-tc.
Another problem is that adjusting the cu-to-ff and whi-te balance characteristics requires special equipment built for the respective purposes, taking a lot of trouble for adjus-t-ment. Fur-thermore, the adjustment can only be made in the manufacturing process of the apparatus, and the problem here is also that, even if the adjus-tment has been once made, deviation from the proper value ma~ occur af-ter manufactur-ing because of various factors such as the de-terioration of the CRT phosphors, the temperature charac-teristics of compo-nents, etc.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a projection type d-isplay apparatus in which the various adjustments specially required fo.r the characteris-tics of the CRT can be made automatically w.itll the display apparatu6 in an assembled state.
It is another objec-t of the :inven-tion to provide a projection ty~pe display apparatus capable of being automa-ti-cally adjusted w:ithout requiring the use of special equip-ment.
The projec-tion -type display apparatus of the present invention includes a pattern forming means for forming an adjusting pattern on a CRT, a de-tecting means for de-tecting the projected image of the adjusting pattern, and an adjust-ing means for adius-ting the characteristics of the CRT on -the basis of the results of detection by the detecting means. Using the pattern forming means, an ad~justing pat-tern is formed on the screen of the CRT, and this adjusting pat-tern is projec-ted on-to the detecting means, based on -the output of which the characteristics of the CRT are au-toma-ti-cally adjusted with -the adjusting pattern being adjusted to optimum level.
To describe specifi.cally, focus adjustments, conver-gence adjustments, ras-ter distortion correc-tions, cutoff characteristic adjustments, white balance characteris-tic adjus-tmen-ts, etc. are automatically made. When -the detect-ing mearls is installecl ou-tside tlle effective image area of the screen, the characteris-tics Oe the CRT can be adjusted wi-thout inter-fering wi-th the normal imag~e clisplay.
The above and further objects and features of the invention will more flllly be apparent from -the following detailed description with accompanying drawings.

BRIEF DESCRIPTION OF TIIE DR~WINGS

Fig. 1 is a schema-tic cliagram showing the construc-tion of a pI' i O I' art projection type display appara-tus.
Fig. 2 is a schematic sectional -view showing the construction of a projection type display apparatus accord-ing to -the invention.
Fig. 3 is a diagram showing images, such as focus adjusting pa-t-terns, formed on a CRT screen.
Fig. ~ is a diagram showing the locations of photode-tectors.
Fig. 5 is a schema-tic diagram showing a feedback system for focus adjllstment, convergence adjustment, and ras-ter distortion correction.
Fig. 6 is a schematic sectional view showing -the construction of a projection type display appara-tus accord-ing to another embodimen-t of -the invention.
Fig. 7 is a diagram showing images, such as cutoff and white balance adjus-ting pa-tterns, formed on a CRT

~ ~ 8 ~

screen.
Fig. 3 is a diagram showing the loca-tions of photode-tect~rs.
Fig. 9 is a schematic diagram showing a feedback sys-tem for cutof~ and whi-te balance adjustments.
Fig. 10 is a schematic sec-tional v:iew show:ing the construction of a projection type display apparatus accord-ing to a further embodiment of the inven-tion.

DESCRIPTION OF THE PRRFERRED FMBODIMENTS

The preferred embodiments o~ the presen-t invention will now be described below with reference to -the accompanying drawings.

(Embodiment 1) Fig. 2 is a schematic sectional view showing a pro-jection type display appara-tus according to one embodimen-t of the present inven-tion. A projec-tion lens 2 is mounted in front of the screen of a CRT 1~ and a screen 3 is installed at a dis-tance in fron-t of the projection lens 2. The screen 3 is supported at i-ts periphery by a screen frame 31. Pho-todetectors ~ having CCDs, etc. are moun-ted on -the surface of the screen frame on the same side as -the projected side of the screen 3.
In the projection type display apparatus of -the above ?3 ~ i~

construction, an imagSe formecl on the screen of the CRT l is enlarged through the projection lens 2 and beamed in the form of projection 1.igh-t 110 onto -the screen 3 for viewing.
The diverging angle of the projecti.on l;.ght 110 is made wider than -the angle that just matches the screerl sir~e, so tha-t -the photodetectors 4 mounted outside the periphery o~
-the screen 3 can also be illumi.nated.
Fig. 3 shows the condiLion of an image eorme(l on the phosphor screen 10 of the CRT 1. An area 13 on the phosphor screen 10, wh:ich is projec-ted on-to -the screen 3, is smaller -than an image area 12, the ac-tual image area formed by ras-ter scanning on -the phosphor screen 10. In practice, this image area 12 is beamed toward the screen 3. This means -that part of the area on the phosphor screen 10 which is raster-scanned by an electron beam does no-t appear on the screen 3.
Outside ~he image area 12 on which an image is formed, a cross-shaped focus adj~s-ting pat-tern 1'l (hereinafter referred -to as the pattern 14) is formed, for example, by applying an outpllt of a character genera-tor to the CRT 1.
In Fig. 3, the pattern 14 is cen-tered on each side of the rectangular image area 12, tha-t is, a total of four patterns 14 are formecl.
Fig. 4 shows the screen 3 viewed from -the projecting side. As shown, on the screen frame 31 supporting the ~8~8~

screen 3 a,t the periphery thereof, four photo-letec-tors 'I are mounted correspondirlg in position and number -to the pat-terns l'l .
Fig. 5 shows a t`eeclback sys-tem for the projec-tion -type display apparatus wi-th regard -to one embodilllen-t of' the invention, except the por-tions indicclted by dot and dash type lines. In the figure, the numeral 7 indicates a t'OCllS
adjus-ting circuit f`or adj~lsting eOcus, ancl 6 is a microcom-pu-ter for controlling -the foc~ls adjusting~ circuit 7 on the basis of outputs fed from -the photode-tectors ~.
The pa-tterns l~ formed cn the phosphor screen lO of t~le CRT 1 are beamed through -t,he projection lens 2 and projected beamed in the'Porm of pro,jec-tion light 110 onto the pho-tode--tectors ~ moun-ted on the screen frame 31. ~ased on the outputs of the pho-todetectors ~1, the n~icrocomputer 6 con--trols the focus adjusting circuit 7 so as to mini~li2e the line width of each projec-ted pattern 14~ Wi-th this con-trol, a focus voltage for proper focusing is set in the fOCllS
adjusting circui-t 7, and -this focus voltage is applied -to the CRT 1.
In the illustrated e~ample, four focus adjusting pat--terns 1~ are used, but i-t will be appreciated that a single pattern may serve the purpose. Also, the number of patterns 1~ is made equal to -the number of photode-tec-tors ~, but the pho-todetectors ~ may be made fewer in number than the pat-terns l~1.

(Embodiment 2) ~ ig. 6 is a schemat:ic sec-tional view showing a pro-jection type display apparat11s using, for exampLe, three separate CRTs for red~ green, and blue colors, accorc~ing to ano-ther embodiment of the invention. In Fig. 6, -the same reference numerals as those in Fig. 2 desigrlate the same parts. Projection lenses 2a, 2b, and 2c are mounted in front of the screerls of -the three CRTs la, Ib, and Ic, respectively.
In this pr~ojection type display appara-tus, one of the -three primary color images, for example, formed on the CRT
la, is beamed through -the projec-tion lens 2a, where the enlarged image is projected in -the ~orm of projection light ll0a on-to -the screen 3. Obviously, the same applies to -the other CRTs lb, lc, projection lenses 2b, 2c, and projection light llOb, llOc. Thus, a full-color image is formed on the screen 3.
The feedback system for the above projection -type display apparatus is fundamentally the same as the one shown by solid lineæ in Fig~ 5. Tha-t is, in the configuration of Fig. 5, -the CRTs la, lb, and lc are generally repre-sented by the CRT l, and the focus adjusting circui-t 7 for adjus-ting focus is designed to ou-tput a separate adjusting signal for each of the CRTs la, lb, and lc.
Focu5 adjus-tment in such a -three--tube proJection type display appara-tus is performed separately ~or each of the CRTs ta, lb, and 1c, but clescrip-tion o~ the eOcus adjus-tment is omi-tted herein as it is in operation the same as thal;
described in connection wi-th the f`:irst embodiment.

(Embodiment 3) The third embocliment hereina-fter described concerrls a three-tube projection type displ&y apparatus wherein conver-gence adjustmen-ts are made au-toma-tically. The outline of the -feedback system used for this purpose is indica-ted by a one-dot and dash -type line in Fig. 5. O-therwise, -the con-struc-tion o-f -the apparatus is the same as tha-t shown in Fig.
6.
~ eferring primarily to Figs. 5 and 6, we will de-scribe how convergence adjustments are made. The same patterns 14 as shown in Fig. 3 are formed ho-th on the CRT
lb and on -the CRT la (or lc), and -these patterns 1~ are simul-taneously projected onto the pho-todetectors 4. Based on the ou-tpu-ts of the photode-tec-tors 4, the microcompu-ter 6 detects any misalignment between -the projected images of the pat-terns 1'1 on each photodetec-tor 4 and controls the gain of a convergence adjus-ting circui-t 8 -to correc-t the misalign-ment. The convergence adjus-ting circuit 8 OUtplltS conver-f~

gence acljusting signals -to the CRTs lb and la (or lc) to correct the separation of col.ors. Correc-ti.ng color separa--tion between the CRTs lb an(l la and between the CRTs lb and lc -resul$s in correcting misconvergence of all -the CRTs la, lb, and lc, and -thus, proper convergence adJustment is matle -~or the projec-tion type display apparatus.

(Embodiment ~) The fourth embodlment hereinafter described concerns a three-tube projection type d.isplay apparat-us wherein ras-ter distort:ion correc-tions are made automatical.ly, The outli.ne of -the feedback system used ~or this purpose is indicated by a two-dot and dash -type line in Fig. 5. O-therwise, the construction o~ -the ap-paratus is the same as tha-t shown in Fig. 6. Raster distortion corrections are made separately and sequentially ror each o-~ the CRTs la, lb, and lc. As in ~ocus ad,justment, the pat-terns 14 as shown in Fig. 3 are beamed onto the photodetectors ~. Based on -the outputs o:t' the photodeteotors ~1 the microcompu-ter 6 detects how much the projected images on the photode-tectors ~ are deviated from the required proper position, and controls the gain o~
a raster dis-tortion correc-ting circui-t 9 -to correct the deviations. The raster distortion correcting circui-t 9 outputs a raster distortion correction signal to any CRTs la, lb, or lc on which ras-ter dis-tortion has been detec-ted.

.

Raster distortiorl i.s -thus correcl;ed.
It will be :recognized tha-t automatic raster correc-tion can be appl;.ed not only to three--tube sys-tems but also to one-tube systems and -that raster correc-t:ion carl be made along with foc~ls adjustmen-t.
In the firs-t to t,he ~ourth ernbodiments, patterns 1~ of cross sh~pe are used, but i-t wil]. be appreciated that -t;he shape of the pa-ttern may be o~` spo-t or s-traight line.
In the case of a p:rojection type display apparatus using a mul-tiple CRTs, the configura-tions o-f the second and third embodiments may be combined to produce a system where-in both the focus and convergence adjustments are au-tomati-cally made wi-th the microcomputer 6 con-trolling the focus adjusting circuit 7 and the convergence adjusting circuit 8.
Furthermore, the configuration of -the -fourth embodiment may also be incorporated -to add -the raster dis-tor-tion correc-tion function.

(Embodiment 5) The fifth embodiment o-f -the invention hereinaf-ter described concerns a projection -type display appara-tus wherein whi-te balance and cutoff characteristics are auto-ma-tically adjusted. The ou-tline of the cons-truc-tion of the apparatus is the same as that shown in Fig. 6.
Fig. 7 shows the condi-tion of an image formed on the 1~

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phosphor screen 10 of each of the CRTs la, lb, and Ic. An area 13 on the phosphor screen, which is projected on-to the screen 3, is smaller than an image area 12, -the ima~e area actually formed by raster scanning on the phosphor screen 10. Therefore, some part of the area scanned by an electron beam on the phosphor screen lO does not appear on the screen 3.
In this marginal area, cutoff/white balance adjus-ting patterns 15 (hereinafter referred to as the pat-terns 15) are formed at the same positions as the patterns 1~ of Fig. 3 by using, for example, a charac-ter generator. Each pa-t-tern 15 consists of two vertical lines, for example, a black line and a color line of one of the three primary colors (for example, red for the CRT la, blue for the CRT lb, and green for the CRT lc). A total of four patterns 15 are formed on the phosphor screen 10 of each of the CRTs la, lb, and lc.
Fig. 8 is a diagram showing the screen 3 viewed from the projecting side. Four pho-todetectors ~ are moun-ted on the screen frame 31 in positions and in number corresponding ~o -the pat-terns 15 shown in Fig. 7.
~ ig. 9 shows a feedback system for the projection display apparatus according to the fifth embodiment. In Fig. 9, the same parts as those shown in Figs. 5 and 6 are designated by the same numerals. The microcompu-ter 6 compu-tes the amount of con-trol, based on -the outputs of the pho-tocletectors ~I, to op-timize the cutoff and white balance charac-teristics. '['he numeral 16 designates a cutof'f' adjust-ing circuit for outputl;ing cu-toff signa:Ls respec-tively to adjust the cu-to-ff cha-racteristics of the CRTs la, Ib, and Ic under -the control o:f the microcompu-ter 6, and the numeral 'L7 shows a white balance adjusting circu:it, also unde:r the control of the m:icrocomputer G, ~or ou-tputtin~ wh:ite balance adjus-ting s:ignals respectivel.y -to adjust the white ba]ance character:istics of the CRTs la, Ib, ancl lc.
The pat-terns 15 formed on the CRT la are beamed through -the projection lens 2a and projec-ted in the fortn o-f projec-tion ligh-t llOa on-to the photodetec-tors ~. The patterns 15 -formed on the'CRTs lb and lc are also projected on the photodetec-tors ~ in the same manner. The projected images of the pat-terns 15 from -the respective CRTs la, lb, and lc are superimposed one on top of another on each photodetec-tor ~; -these superimposed images are combined -to form an image of black and whi-te vertical lines when cutoff and white balance are proPerly adjusted.
Based on -the outputs of the pho-tode-tectors ~ on which the projected images of -the patterns 15 are superimposed as described above, the microcomputer 6 recognizes informa-tion about cutoff and white balance deviations -from -the proper values, and con-trols -the cu-toff adjusting circui-t 16 and -the white balance adjusting circuit 17 so as to correc-t -the 1~

3 ~ '~

deviations, i.e. so tha-t the projected pa-t-terns on each pho-todetector ~ I`orm an image of blaclc and white lines.
Under -the cont.rol of the miclocompllte:r 6; the correc--tion vol-tages applied to the cutoff adjus-ting circuit :16 and the white balance adjusting circuit 17 are ~ar:ied. Accord-ingly, the cu-toff adjust:ing circuit 16 outputs cu-to-rf ad-jUSti.llg s:ignals to the CRTs .La, Ib, and lc to op-tim:ize thei.-r cu-toff charncteristics, and the white balance adjus-ting circui-t 17 ou-tputs white balance adjusting signa~s -to the CRTs la, lb, and lc to optimize their white balance charac-teris-tics. With such a feedback loop, the correction volt-ages are se-t. 60 as to optimize -the respect;ive values.
In -the i.llus-tra-ted example, four patterns 15 are used, but it will be appreciated -that a single pat-tern may serve the purpose. Also, each pa-ttern 15 has two vertical lines, bu-t o-ther appropria-te forms may be used. Further, the number o:f pat-terns 15 per CRT is made equal -to -the number of photodetectors, but the photodetectors may be made ~ewer i~
number than the patterns L5.

(Embodiment 6) Fig. 10 is a schematic sectional view of a reflec-tion-type projection display apparatus which projects a CRT
image onto a projection screen by using a reflec-tion mirror.
A mirror 18 is mounted in -the path of the projection ligh-t 6 ~ ~

1l0 to reflec-t the proJection l:ight llO. Otherwise, -the construction is the same as -that of the direct pl~ojec-tion type display apparatus; the same parts as those in ~i~s. 2 and 6 are designated by the same numerals, and description of such parts ls omitted herein. I-t wiL1 be appreclated that each of the above embodiments can also be applied to the reflection--type projection display ap-paratus of Fig.
10, in which case the same erfects as described above can also be obtained.
In each of the above embodimen-ts, the photodetectors are ins-talled outside -the ef~ective image area of -the pro-jection screen, bu-t i-t will be apprecia-ted -that the same effec-ts as described in each of the above embodimen-ts can be obtained if the photodetectors are installed inside -the effective image area of the projection screen, for example, on the periphery of -the screen.
Any of the above-described projection type display apparatuses do no-t require special CRT adjustments in the manufac-turing process) and the adjus-tments are automatically made any time after -the apparatus is ins-talled in place.
As described above, according to the projection type display apparatus of the invention, adjusting pa-tterns are formed on the CRT screen, and -the projected images of these pa-tterns are detected by pho-tode-tectors, based on the out-puts of which -the CRT characteris-tics are adjusted. This ~6~3 enables foclls:irlg or ot,her charact:,eri.sti.c,s such as cutoff and white balance to be adjustecl autolllatica:LIy, the effect be:ing tha-t the per-formance o~ the projection apparatus is not a~fec-ted by environmental conditions or de-teriorat:ion with time .
As -thi.s invention may be emboclied in seve:ral :f`orllls withollt cleparting ~rom -the spirit of essential characteris-tics thereof, the presen-t embodimen-t is -therefore i.l.lustra-tive and not restrictive, since the scope of the :inven-t.ion is defined by the appended claims ra-ther -than by tlle de-scription preceding -them, and all changes that fall within metes and bounds of -the claims, or equivalence of sllch metes and bounds thereof are therefore in-tended to be embraced by the claims.

Claims (10)

1. A projection type display apparatus comprising:
a cathode-ray tube for forming an image;
a projection lens for enlarging and projecting the image formed on the cathode-ray tube;
a screen for displaying the enlarged image;
pattern forming means for forming an adjusting pattern on said cathode-ray tube;
detecting means for detecting the projected image of the adjusting pattern; and adjusting means for adjusting the characteristics of said cathode-ray tube on the basis of the detection result by said detecting means.

2. A projection type display apparatus as set forth in Claim 1, wherein said adjusting means includes means for adjusting focus.

3. A projection type display apparatus as set forth in Claim 1, wherein said adjusting means includes means for adjusting convergence.

4. A projection type display apparatus as set forth in Claim 1, wherein said adjusting means includes means for correcting raster distortion.

5. A projection type display apparatus as set forth in Claim 1, wherein said adjusting means includes means for adjusting cutoff and white balance characteristics.

6. A projection type display apparatus as set; forth in Claim 1, wherein said cathode-ray tube is provided in multi-ple number.

7. A projection type display apparatus as set forth in Claim 7, wherein said adjusting means includes means for adjusting focus and means for adjusting convergence.

8. A projection type display apparatus as set forth in Claim 7, wherein said adjusting means further includes means for correcting raster distortion.

9. A projection type display apparatus as set forth in Claim 1, wherein said detecting means is disposed outside the effective image area of said screen.

10. A projection type display apparatus as set forth in Claim 1, further comprising a mirror installed between said projection lens and said screen.