JPH0388586A - Crt type projector - Google Patents

Abstract

PURPOSE:To correct the distortion on a screen generated by an S-shaped distortion, a vertical pincushion distortion and a right and left pincushion distortion by an equal distance projection system lens by placing the equal distance projection system lens (ftheta lens) as a projection lens in front of a fluorescent screen of a CRT. CONSTITUTION:In an equal distance projection system lens (ftheta lens) placed as a projection lens in front of a fluorescent screen 1 of a CRT, mapping height Y becomes Y=f.theta as a focal distance (f) of the lens against a beam deflection angel theta. Accordingly, a beam scanning speed on a screen 3 is constant against the deflection angle theta of a deflecting system (deflecting yoke) 4 of a beam. Therefore, when a deflecting speed of the deflection is set to a constant value (a deflecting current is set to a saw tooth current), an image having no distortion is obtained on the screen 3. That is, even when a radius R of the fluorescent screen 1 of the CRT does not coincide with a radius(r) from the deflection center of an electron beam to the fluorescent screen, since the deflection angle thetais proportional to a size on the screen 3 as it is, an S-shaped distortion, a vertical pincushion distortion and a right and left pincushion distortion are not generated.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a CRT (Cathode Ray Tube) projector, and in particular, the present invention relates to a CRT (Cathode Ray Tube) type projector, in particular when the electron beam emitted from an electron gun is
The present invention relates to a CRT type projector that can correct the distortion of an image projected onto a screen through RT using an equidistant projection lens (fθ lens) and project a distortion-free image onto the screen.

"Prior Art" In a conventional CRT projector, an image projected on a phosphor screen of a CRT is magnified by a lens and projected onto a screen.

In the above method, the radius of the phosphor screen of the CRT is large compared to the radius from the center of deflection of the electron beam to the phosphor screen, so various distortions appear in the screen image.

The main distortions and correction methods will be briefly explained.

(a), S-shaped distortion As shown in Figure 2, the radius R of the fluorescent screen 1 of a CRT (in the case of a projector, the screen that serves as the fluorescent screen is flat and is often R-(g)). (displayed as R=oo)
is larger than the radius r from the electron beam deflection center O to the phosphor screen 1; The amount of beam movement increases. Therefore, as shown in FIG. 3, the horizontal and vertical linearity of the image on the phosphor screen 1''2 is small at the center and large at the periphery, resulting in an S-shaped distortion.

In order to correct the above S-shaped distortion, as shown in Figure 4,
A deflection current was applied to reduce the amount of deflection in the periphery of the phosphor screen 1.

This deflection current resonates with a capacitor inserted in series with the horizontal deflection coil, generating a waveform that operates across the capacitor.

(b) The distance from the deflection center point O of the vertically pin-distorted CRT to the phosphor screen 1 becomes longer toward the periphery. Therefore, the deflection of the electron beam is necessarily greatest at the four corners of the image. For this reason, the raster 5 of the phosphor screen 1 has a pincushion shape constricted in the middle, as shown in FIG. 5(a), and vertical pin distortion occurs.

In order to correct the above-described vertical pin distortion, a vertical deflection current waveform as shown in FIG. 5(b) is used.

In order to obtain such a waveform, for example, a saturable rear lid type transformer may be used.

Further, as another correction means, distortion may be corrected by manipulating the magnetic field distribution of the deflection yoke instead of correcting the deflection current. However, this method has the disadvantage that astigmatism of the beam spot occurs due to distortion of the magnetic field distribution.

(C) Before left and right pin distortion (Ex) As explained in the section, the distance from the deflection center point O of the CRT to the phosphor screen 1 becomes longer as it gets closer to the periphery.Therefore, the deflection of the electron beam inevitably Generally, the four corners of the image are the largest.Therefore, the raster 6 of the phosphor screen 1 is as shown in Fig. 6(a).
), it becomes a pincushion shape with a constriction in the middle, and left and right bottle distortion occurs.

In order to correct the above left and right bin distortion, a horizontal deflection current waveform as shown in FIG. 6(b) is used.

As a means for obtaining such a waveform of the horizontal deflection current, a saturable rear-bottom transformer is used or a diode modulation method is used as in the previous section (b). Also,
A deflection yoke may also be used.

"Problems to be Solved by the Invention" As described in the conventional technology, various distortions that occur have been dealt with by manipulating electric circuits and deflection yoke magnetic field distribution.
The method of correcting using an electric circuit requires the use of a saturable rear cover, an output diode, etc., and has the problem of increasing the circuit scale. Furthermore, the method of manipulating the magnetic field distribution of the deflection yoke has the problem of producing beam astigmatism.

This invention addresses the above-mentioned problems, and uses an electric circuit using a saturable rear lid, an output diode, etc. to reduce the magnetic field distribution of the deflection yoke, which is caused by beam astigmatism. To provide a CRT type projector capable of projecting a distortion-free image onto a screen without any operation.

"Means for solving the problem" In order to solve the above problem, in this invention, CR
This CRT type projector enlarges and projects an image of T on a screen, and is characterized in that an equidistant projection type lens (fθ lens) is disposed as a projection lens in front of the fluorescent screen of the CRT.

``Function'' In the embodiment shown in FIG. 1, an equidistant projection lens (f
θ lens), the mapping height Y with respect to the beam deflection angle θ
is the focal path Hf of the lens, and Y=f·θ. Therefore, the beam scanning speed on the screen 3 is constant with respect to the deflection angle θ of the beam deflector (deflection yoke) 4.

Therefore, if the deflection velocity is kept constant (the deflection current is made into a sawtooth waveform), an image without distortion can be obtained on the screen 3.

"Embodiment" Next, an embodiment of the CRT type projector according to the present invention will be described in detail with reference to FIG.

In Figure 1, CRT is a cathode ray tube, 1 is a fluorescent screen of CRT, 2 is an equidistant projection lens (fθ lens), 3 is a screen, 4 is a deflector (deflection yoke) built into the CRT, and 0 is an electron beam. is the center of deflection.

The equidistant projection type lens 2 intentionally gives distortion aberration by uniform velocity spot scanning in proportion to the deflection angle θ, and is arranged as a projection lens in front of the fluorescent screen 1 of the CRT, as shown in Fig. 1. , for the deflection angle θ of the beam deflector 4,
The scanning speed of the beam on the screen 3 is kept constant.

By using the equidistant projection lens 2 described above, the image deflected by the angle θ, regardless of the position of the screen 3, is
The image is projected onto the screen 3 at a size of f·θ.

In other words, even if the radius R of the CRT's phosphor screen 1 does not match the radius r between the electron beam deflection center and the phosphor screen, the deflection angle θ is directly proportional to the size on the screen 3, so the S-shape described above is maintained. No distortion, vertical bin distortion, or left/right pin distortion occurs.

In the embodiment shown in FIG. 1, an equidistant projection lens (f
θ lens), the mapping height Y with respect to the beam deflection angle θ
is the focal length f of the lens, and Y=f·θ. Therefore, the beam scanning speed on the screen 3 is constant in terms of the deflection angle θ of the beam deflector (deflection yoke) 4.

Therefore, if the deflection velocity is kept constant (the deflection current is made into a sawtooth waveform), a distortion-free image on the screen 3 can be obtained.

"Effects of the Invention" As described above, the CRT type projector according to the present invention
uses an equidistant projection type lens as a projection lens, and the distortion on the screen caused by S-shaped distortion, vertical pin distortion, and left and right bin distortion is corrected by the equidistant projection type lens.

Therefore, compared to correction using an electric circuit, the number of circuits can be reduced and the size and weight can be reduced. Furthermore, astigmatism can be eliminated compared to the case where the deflection yoke is used.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of distortion correction by a CRT type projector according to the present invention, Fig. 2 is a diagram of the principle of distortion generation in a CRT, Fig. 3 is image linearity of S-shaped distortion, and Fig. 4 is correction of three-character distortion. Figure 5 (a) + (b) is a waveform diagram of upper and lower pin distortion and its correction waveform diagram, Figure 6 (a). (b) is a diagram of left and right bin distortion and its waveform.・Phosphor screen ・Equidistance projection lens ・Screen ・Deflector ・Cathode ray tube ・Deflection center point

Claims (1)

[Claims] (1) A CRT that enlarges and projects the CRT image onto a screen.
In the CR type projector, an equidistant projection type lens (fθ lens) is arranged as a projection lens in front of the fluorescent screen of the CRT.
T type projector.