GB2126854A

GB2126854A - Electro-optical tube alignment

Info

Publication number: GB2126854A
Application number: GB08225703A
Authority: GB
Inventors: Philip Rangecroft Groves
Original assignee: Link Electronics Ltd
Current assignee: Link Electronics Ltd
Priority date: 1982-09-09
Filing date: 1982-09-09
Publication date: 1984-03-28
Also published as: GB2126854B

Abstract

To align the electron beam in a camera tube with the axial focusing field, the target bias is decreased so that only high energy electrons reach the target. The monitored target signal then shows shading, i.e. variation with position in the beam scan. The four corners of the target are monitored, the beam alignment being adjusted in X and Y directions independently by alignment coils to equalize the signals from the four corners. Scanning deflection may require simultaneous adjustment in the opposite sense.

Description

SPECIFICATION Electro-optical tube alignment The present invention relates to a method and apparatus for correcting electro-optical tube alignment, In a camera tube incident radiation is used to determine the current received per picture element on the camera tube target from a scanning electron beam. The electron beam is generated by gun assembly within the camera tube and is aligned with the focus field by magnetic fields produced by alignment coils. It is necessary for the alignment of the electron beam with the focus field to be optimised to minimise lateral energy components in the beam.

The conventional technique of camera tube - alignment consists of causing the electron beam to rotate with respect to the centre of the target.

Misalignment is manifest by the electron beam missing the centre of the target, as indicated by the camera tube image. Alignment corrections are effected so as to reduce the. This technique is generally inconvenient and inefficient.

The present invention seeks to mitigate these disadvantages.

According to a first aspect of the present invention there is provided apparatus for correcting electro-optical tube alignment comprising monitoring means for monitoring the shading of the tube image, adjustment means for decreasing the tube target bias voltage until a measurable shading is introduced in the tube image, as monitored by the monitoring means, and control means for varying the tube alignment until the monitoring means monitors a minimum average shading.

According to a second aspect of the present invention there is provided a method of correcting electro-optical tube alignment comprising the steps of reducing the tube target bias voltage so as to produce a measurable shading in the tube image and varying the tube alignment to determine minimum avarage tube image shading.

An embodiment of the present invention will now be described by way of example only.

It has been established that upon reducing the target bias voltage of a camera tube only high energy electron beams land on the target and this results in shading being exhibited by the camera tube image. The present invention utilises this fact in order to correct the alignment of the camera tube electron beam with the camera tube target.

Within a camera tube an electron beam is generated and impinges upon a camera tube target. The electron beam scans the target and picture element voltages are generated in accordance with radiation impinging upon the camera lens which is focused on to the target.

Alignment of the electron beam with the focus field is controlled by magnetic fields produced by alignment coils.

In order to optimise alignment of the electron beam with the focus field the target bias voltage is reduced so that only high energy electron beams land on the target. The reduction in bias voltage is such that a measurable shading is introduced into the camera tube image. The power supplies to the alignment coils is varied until a minimum avarage shading is obtained for ail field points within the camera tube image.

When this.is achieved the camera tube alignment is considered to be at an optimum.

In establishing the minimum average shading it is permissible to vary the alignment in one of two mutually perpendicular directions, the X-Y directions, until a minimum difference in shading is obtained between four picture elements, one from each of the corners of the image. The alignment is then varied in the other direction until the minimum difference in shading between the four corner picture elements is established.

When both alignment directions have been adjusted in this manner it is considered that the shading is equivalent to a minimum average shading.

When adjusting the camera tube alignment it may be necessary to compensate the camera tube scanning so that the sampling points remain within the sampling window. The required scanning compensation will often be equal and opposite to the correction applied to the alignment coils.

The above described operation is undertaken for each of the camera tubes present within a television camera.

Variations of the above embodiment will be evident to persons skilled in the art.

Claims

1. Apparatus for correcting electro-optical tube alignment comprising monitoring means for monitoring the shading of the tube image, adjustment means for decreasing the tube bias voltage so that a measurable shading is introduced on the tube image, as monitored by the monitoring means, and control means for varying the tube alignment until the monitoring means monitors a minimum avarage shading.

2. Apparatus as claimed in claim 1, wherein the monitoring means includes a detector for detecting the minimum difference in shading between picture elements from respective corners of the image, which minimum difference is considered to indicate the minimum average shading.

3. Apparatus as claimed in claim 2, wherein the control means and detector operate so that the alignment is varied in one of two mutually perpendicular directions until the minimum difference is detected and the alignment is then varied in the other direction until the minimum difference is again detected.

4. Apparatus as claimed in any preceding claim including scanning compensation means for compensating the scanning of the camera tube during alignment correction.

5. A television camera including the apparatus of any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electro-optical tube alignment The present invention relates to a method and apparatus for correcting electro-optical tube alignment, In a camera tube incident radiation is used to determine the current received per picture element on the camera tube target from a scanning electron beam. The electron beam is generated by gun assembly within the camera tube and is aligned with the focus field by magnetic fields produced by alignment coils. It is necessary for the alignment of the electron beam with the focus field to be optimised to minimise lateral energy components in the beam. The conventional technique of camera tube - alignment consists of causing the electron beam to rotate with respect to the centre of the target. Misalignment is manifest by the electron beam missing the centre of the target, as indicated by the camera tube image. Alignment corrections are effected so as to reduce the. This technique is generally inconvenient and inefficient. The present invention seeks to mitigate these disadvantages. According to a first aspect of the present invention there is provided apparatus for correcting electro-optical tube alignment comprising monitoring means for monitoring the shading of the tube image, adjustment means for decreasing the tube target bias voltage until a measurable shading is introduced in the tube image, as monitored by the monitoring means, and control means for varying the tube alignment until the monitoring means monitors a minimum average shading. According to a second aspect of the present invention there is provided a method of correcting electro-optical tube alignment comprising the steps of reducing the tube target bias voltage so as to produce a measurable shading in the tube image and varying the tube alignment to determine minimum avarage tube image shading. An embodiment of the present invention will now be described by way of example only. It has been established that upon reducing the target bias voltage of a camera tube only high energy electron beams land on the target and this results in shading being exhibited by the camera tube image. The present invention utilises this fact in order to correct the alignment of the camera tube electron beam with the camera tube target. Within a camera tube an electron beam is generated and impinges upon a camera tube target. The electron beam scans the target and picture element voltages are generated in accordance with radiation impinging upon the camera lens which is focused on to the target. Alignment of the electron beam with the focus field is controlled by magnetic fields produced by alignment coils. In order to optimise alignment of the electron beam with the focus field the target bias voltage is reduced so that only high energy electron beams land on the target. The reduction in bias voltage is such that a measurable shading is introduced into the camera tube image. The power supplies to the alignment coils is varied until a minimum avarage shading is obtained for ail field points within the camera tube image. When this.is achieved the camera tube alignment is considered to be at an optimum. In establishing the minimum average shading it is permissible to vary the alignment in one of two mutually perpendicular directions, the X-Y directions, until a minimum difference in shading is obtained between four picture elements, one from each of the corners of the image. The alignment is then varied in the other direction until the minimum difference in shading between the four corner picture elements is established. When both alignment directions have been adjusted in this manner it is considered that the shading is equivalent to a minimum average shading. When adjusting the camera tube alignment it may be necessary to compensate the camera tube scanning so that the sampling points remain within the sampling window. The required scanning compensation will often be equal and opposite to the correction applied to the alignment coils. The above described operation is undertaken for each of the camera tubes present within a television camera. Variations of the above embodiment will be evident to persons skilled in the art. Claims

5. A television camera including the apparatus of any preceding claim.

6. A method of correcting electro-optical tube alignment comprising the steps of reducing the tube target bias voltage to produce a measurable shading in the tube image and varying the tube alignment to determine minimum average tube image shading, which is considered to indicate optimum tube alignment.

7. A method as claimed in claim 6, comprising the step of establishing the minimum difference in shading between picture elements from respective corners of the tube image, which condition is considered to indicate minimum average tube image shading.

8. A method as claimed in claim 7, comprising the steps of establishing the minimum difference in shading by varying alignment in one of two mutually perpendicular directions and subsequently determining minimum difference in shading by varying the alignment in the other direction.

9. A method as claimed in any of claims 6 to 8, including the step of compensating the camera tube scanning during alignment correction.

10. Apparatus for correcting electro-optical tube alignment substantially as hereinbefore described.

11. A method of electro-optical camera tube alignment substantially as hereinbefore described.