JPH0657051B2 - External magnetic field correction device for CRT - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention allows a CRT to be used in an environment with a large external magnetic field (for example, an environment used in a factory electromagnetic crane, a large electromagnet, a ship equipped with a degaussing device, etc.). The present invention relates to a CRT external magnetic field correction device that automatically corrects distortion of a display screen when used.

[Prior Art] A CRT display device displays characters or graphics on a CRT screen by deflecting an electron beam. Therefore, when a magnetic field from the outside is applied, the deflection position of the electron beam is disturbed, distortion (rotational distortion and distortion in the vertical or horizontal direction of the display screen) occurs, and the display image is disturbed.
For this reason, conventionally, as shown in FIG. 4, a shield case 1 having a high magnetic permeability such as permalloy is covered around the CRT. However, this method is effective against the external magnetic field B ₁ that enters the shield case at a right angle, but is unprotected against the external magnetic field B ₂ that enters perpendicularly to the CRT display surface.
Therefore, as shown in FIG. 5, the correction coil 2 is attached to a portion close to the CRT display surface, and a current for generating the correction magnetic field B ₃ so as to cancel the external magnetic field B ₂ is applied to this coil by an amplifier (AMP) 3 Was supplied from. Then, the magnitude of the correction magnetic field is adjusted by the volume 4 provided on the panel surface.

[Problems to be Solved by the Invention] However, in such a conventional method, since it is necessary to correct the magnetic field with the manual volume, it is not possible to afford the correction when the operator is busy with other operations. Further, it is effective for the rotational distortion due to the external magnetic field B ₂ which enters in the direction perpendicular to the CRT display surface, but as to the movement in the vertical / horizontal direction of the screen by the magnetic field B ₄ which enters at a certain angle as shown in FIG. Less effective.

There is also a method of attaching a magnetic sensor to detect this and correct the external magnetic field. However, even by this method, when the operator's artificial problem, for example, a metal such as a watch or a ring is brought close to the magnetic sensor, the magnetic sensor detects the concentration of the magnetic flux due to these metals and generates an unnecessary correction current, There is a problem that the direction of the external magnetic field cannot be detected.

[Means for Solving the Problems] In order to solve such problems, the present invention provides a plurality of magnetic sensors arranged around the CRT display surface at an angle that spreads outward, and the output of the magnetic sensor having the directivity. The direction and magnitude of the external magnetic field are detected based on the signal, and based on the result, a rotational distortion correction current is generated and supplied to the correction coil, and a vertical and horizontal movement correction current is generated and supplied to the main deflection coil of the CRT. It is something that is done.

[Operation] If the detected change in the external magnetic field is not artificial, a correction current is generated based on the detected result to cancel the external magnetic field. On the other hand, if the detected change in the external magnetic field is artificial, the change is ignored and the correction is not performed.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
5 _{1 to} 5 ₄ are magnetic sensors, which are displayed on the display screen 4 as shown in FIG.
It is attached to the corners, and its output signal is supplied to the comparison and determination circuit 12 via respective amplifiers _{(AMP) 10 1 ~10 4,} A / D converter 11 ₁ to 11 _4. The external magnetic field is generally considered to be a direct current magnetic field of about several Gauss, and the output generated by the magnetic sensor due to this magnetic field is extremely small. Therefore, the amplifier 10 performs voltage amplification about 1000 times. An output of about 20 to 30 mv can be obtained by this amplification. The input signal range of the A / D converter 11 is set to about 100 mv. Further, polarity data corresponding to the polarity of the output signal of the AMP 10, that is, the polarity of the detection signal of the magnetic sensor is added to the output data of the A / D converter 11.

The signal supplied to the comparison / determination circuit 12 compares the detection time of the magnetic sensors 1 to 4 with the level. It consists of a firmware-controlled microprocessor and peripheral circuits. The comparison / determination circuit 12 ignores the detection signal generated from only one magnetic sensor as being due to an artificial cause, and compares the levels of only the detection signals detected from the four magnetic sensors at substantially the same time, By adding the polarity data, the component (6th
B _{cz in the} figure) and a component parallel to the CRT display surface (B in FIG. 6)
_cx-y ). The comparison / determination circuit generates rotational distortion correction data for the component B _cz , and the vertical / horizontal direction for the component B _cx-y ).
Generate lateral movement correction data.

By comparing the detection outputs of the four magnetic sensors, C
The component (B _cz ) perpendicular to the RT display surface and the component (B _cx-y ) parallel to the RT display surface can be divided into the directivity of the magnetic sensor and the periphery of the CRT display surface with an angle extending outward. To be achieved.

When the magnetic sensors are mounted in this way, in FIGS. 1 and 6, each magnetic sensor (5 _{1 to} 5 _{4 in} FIG. ₁ ) outputs substantially the same output with respect to a magnetic field perpendicularly entering the CRT surface. . In this case, the comparison / determination circuit 12 of FIG. 1 outputs B _cz correction (rotational distortion correction) data.

For a magnetic field entering the CRT display surface at an angle,
The output of each magnetic sensor is not the same depending on the directivity of the magnetic sensor and the mounting angle, and a sensor in which the directivity of the magnetic sensor and the direction of the external magnetic field are matched outputs a large output. In this way, the comparison and determination circuit 12 performs the B _cz correction,
(B _cx-y ) correction (vertical / horizontal movement correction) data is also output.

The rotational distortion correction data is converted into an analog signal by the D / A converter 13 shown in FIG. 1 and amplified by the amplifier 14, and a current (about several amperes) necessary to generate a sufficient correction magnetic field in the correction coil 15 is generated. Supply. The vertical / horizontal movement correction data is converted into analog signals (X, Y correction signals) by the D / A converters 16 ₁ and 16 ₂ , amplified by the deflection amplifier 17, and supplied to the main deflection coil 18.

The timing of these operations is shown in FIG. 2, and the firmware control flow of the comparison / determination circuit 12 is shown in FIG. 2 (a) to (d) are output signals of the magnetic sensors 5 _{1 to} 5 ₄ , and the sensor output of the signal "a" is an output of only a certain sensor, so it is ignored as an artificial one, and the correction is performed. not going. However, if a magnetic field is applied in the direction perpendicular to the CRT display surface in the area indicated by the range A, output signals are generated from all four magnetic sensors, so that as shown in FIG. Occurs. As a result, the operation of canceling the external magnetic field is performed, the magnetic field acting on the magnetic sensor is reduced, and the signal detected by each magnetic sensor is reduced, as shown by the alternate long and short dash line in FIGS. 2 (a) to (d). .

On the other hand, when an external magnetic field enters the CRT display surface from below in the range B, the detection amount of each sensor differs depending on its position as shown in FIGS. 2 (a) to (d). Depending on the level of this detection signal, a rotational distortion correction current as shown in FIG. 2 (e) and an X correction signal as shown in FIG. 2 (f) are generated. The magnetic field is corrected by this signal, and the current detected by the magnetic sensor gradually decreases as shown by the alternate long and short dash line in FIGS. Range C shows an example in which the absolute value of the external magnetic field is equal to that of range B, but the directions are opposite.

These controls are performed according to the procedure of the flowchart shown in FIG. First, the detection operation is started in step 100, the detection data of the magnetic sensors (MSG) 1 to 4 is fetched in step 101, and the detection data is compared in step 102. As a result, when it is determined in step 103 that the detection signals of the magnetic sensors 1 to 4 are temporally aligned, the respective detection signals are compared in step 104, polarity data is added, and the direction of the external magnetic field is determined.

This determination is performed as follows, for example.

(A) When the absolute values of the outputs of the magnetic sensors 5 _{1 to} 5 ₄ are almost the same ... The external magnetic field is determined to be perpendicular to the CRT display surface and the rotational distortion correction data is output.

(B) When the absolute output values of the magnetic sensors 5 ₂ and 5 ₄ are larger than the absolute output values of the magnetic sensors 5 ₁ and 5 ₃ ... The external magnetic field is determined to be in the downward direction of the CRT, and the rotational distortion correction data and the X value are determined.
Outputs direction correction data.

(C) When the absolute output values of the magnetic sensors 5 ₃ and 5 ₄ are larger than the absolute output values of the magnetic sensors 5 ₁ and 5 ₂ ... The external magnetic field is determined to be in the right direction of the CRT, and the rotational distortion correction data and Y are determined.
Outputs direction correction data.

(D) The absolute value of the output of the magnetic sensor 5 ₄ is the magnetic sensor 5 ₁ ,
When it is larger than any of the absolute output values of 5 ₂ and 5 ₃
..It is determined that the external magnetic field is in the lower right direction of the CRT and the rotation correction data and the X and Y direction movement correction data are output.

(E) The polarities of the rotational distortion correction data, the X-direction movement correction data, and the Y-direction movement correction data of (a) to (d) are determined according to the polarity of the detection signal of the magnetic sensor.

By the above processing, the correction data is output in step 105, the operations of step 105 and step 106 are repeated, the level of the correction data that minimizes the absolute value of the detection data of each magnetic sensor is searched, and step 107
The correction data that minimizes the absolute value of the detection data of each magnetic sensor is held for a certain period. If there is a change in the detection data of each magnetic sensor in step 108, step 10
Return to 0. If there is no change, the process returns to step 107, and the correction data of the same level is held for a certain time again.

If it is determined in step 103 that the detection signals of the magnetic sensors 5 _{1 to} 5 ₄ are not aligned in time, step 10
As shown in Fig. 9, if one sensor outputs a detection output independently, ignore it as being due to an artificial cause, and
Return to 100.

By performing such processing, the external magnetic field from any direction can be canceled.

When a correction current is applied to the correction coil, a magnetic field generated by the correction coil enters the magnetic sensor. However, when a correction current is applied, a magnetic field that normally cancels the external magnetic field is generated, resulting in a small detection output. The correction data is output until this detection output does not become smaller than a certain limit. When the detection data becomes minimum, the external magnetic field and the correction magnetic field are in equilibrium, so the correction data is held. After a certain period of time, the external magnetic field changes, and when this equilibrium state is broken, the detection operation is repeated again.

[Effects of the Invention] As described above, according to the present invention, the magnetic sensor having directivity is arranged around the CRT display surface, and when the output signals thereof are simultaneously generated, the level difference is detected and the polarity data is added. Then, a correction current is generated to supply the rotational distortion correction current to the correction coil arranged in the CRT and the vertical / horizontal movement correction current to the main deflection coil of the CRT. There is an external magnetic field because it can automatically correct the external magnetic field that comes in from and does not react to artificial magnetic field changes.
Even if it fluctuates, there is an effect that it is possible to always display in a state where the influence of the external magnetic field is greatly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform chart of each part, FIG. 3 is a flowchart of a control operation for canceling a magnetic field, and FIGS. 4 to 6 are for explaining the influence of an external magnetic field. FIG. 1 ...... shield _case, 5 1 to 5 ₄ ...... magnetic sensor, 12
…… Comparison judgment circuit, 15 …… Correction coil.

Claims (1)

[Claims] 1. A CR for supplying a correction current for canceling an external magnetic field to a correction coil when an external magnetic field acts on a CRT.
In the external magnetic field correction device of T, when the magnetic sensors having a plurality of directivities are arranged around the CRT display surface at a distance from each other and the outputs of the magnetic sensors change at the same time, the change amount, the polarity and the change of the output. External magnetic field specification detecting means for detecting the magnitude and direction of a magnetic field acting from the outside from the state, and a rotational distortion correction current is generated and supplied to the correction coil based on the detection result of the external magnetic field specification detecting means. And a correction current generating unit for generating a vertical / horizontal movement correction current and supplying it to the main deflection coil of the CRT.