GB1559586A - Television systems - Google Patents

Description

(54) TELEVISION SYSTEMS (71) We, ENGLISH ELECTRIC VALVE COMPANY LIMITE, a British Company, of 106 Waterhouse Lane, Chelmsford, Essex Cml 2QU, do hereby declare the invention, for which we pray a patenL may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to television systems, and concerns in particular certain aspects of such systems as can be used to produce images representative of optical information of a kind which cannot readily be appreciated by the unaided human eye.

Studio television cameras usually include a monitor screen enabling the operator to see the picture his camera is generating, and in general these monitor screens are in essence merely a small television receiving -set built into the camera body. The camera as a whole is therefore somewhat more bulky, heavy, expensive, and powerconsuming than it need be-both camera and monitor each contains its own line scanning and scan synchronisation equipment-and, indeed, portable T. V. cameras usually employ a simpler optical viewer rather like the through-the-lens system used on modern photographic equipment. This is satisfactory for optical T. V. cameras-that is, cameras sensitive to visible light, and providing a picture accordingly-but is clearly quite inadequate for lonv light T. V. cameras, or for T. V.-type cameras sensitive to other regions of the electromagnetic spectrum-thus, for example, the ultraviolet (UV) or infra-red (tR) regions-for the unaided human eye cannot perceive radiation of these types. Accordingly, if an operator of one of these sorts of camera is to have a proyer picture of what his camera is seeing, he needs to have a monitor set.

However, there is a clear need for a camera/monitor assembly which is smaller, lighter, cheaper, and less power-consumin than the current conventional equipment, and the invention seeks to provide such an assembly by furnishing camera-monitor apparats having a scanning and scan synchronising arrangement of a quite different, and much simpler, variety.

In one aspect, therefore, this invention provides a television system including : a camera tube and a monitor tube mounted in fixed relationship with each other, each containing means for generating an electron beam ; means for producing a magnetic field which is common to both the camera tube and the monitor tube for deflecting in synchronism the two electron beams ; and means for producing rotation of the magnetic field relative to the camera tube and the monitor tube.

The camera tube may be adapted to produce video signals representative of the ultra-violet or the infra-red content of a viewed scheme, or it may be adapted to view scenes under very low levels of illumination.

The invention is primarily intended for use with an infra-red vidicon camera tube of the thermal-imaging or pyro-electric type. however, since this type of tube has a target (the output signal generating part) which does not produce a signal when in a steady state condition, but only gives an output when actually being heated up or cooled down under the influence of the presence or absence of infra-red irradiation, the tube is usually associated with a shutter device operating so as regularly to interrupt the incoming infra-red and thus cause the tube to provide a fresh output. If the shutter interrupts often enough, the tube's output appears to be"constant". Accordingly, when the camera tube in the system of the invention is one of this sort of infra-red vidicon tube, then an optical shutter is arrange to rotate in the optical path of the vidicon camera tube in synchronism with the rotation of the magnetic field.

According to a second aspect of this invention, a television system mcludes : an infra-red sensitive vidicon camera tube of the thermal-imaging or pyro-electric type mounted side by side with a monitor tube ; a rotatable optical shutter arrange to interrupt the optical path of the camera tube as it rotates, and shaving an axis of rotation which is between the camera tube and the monitor tube ; and a rotatable deflection coil arrange to rotate around the camera tube and the monitor tube on the same axis as and in synchronism with the optical shutter.

Preferablv, the axes of the camera tube and the monitor tube, and the axis of rotation of the optical shutter and the deflection coil are all parallel to each other.

The rotatable deflection coil is convenient ly carried by a rotatable hollow cylinder which is mechanically coupled to and driven with the rotatable optical shutter.

Advantageously, adjustment is provided for setting the angular position of the deflection coil relative to the optical shutter.

The invention is further described, by way of example, with reference to the drawings accompanying the Provisional specification, in which : Figure 1 shows a section view through a television system in accordance with the invention ; Figlxres 2 and 3 show alternative configur- ations for a rotatable shutter used with the system ; and Figllres v d 5 are explanatory diagrams.

Referring to Figure 1, there is shown therein a television camera system arrange to produce an image of the infra-red content of a viewed scene. A pyro-electric vidicon camera tube I receives an image of the viewed scene via a lens 2 which passes only the infra-red, or thermal, radiation, and which blocks out the normal visible light.

The image received by the camera tube l is converted into a vide signal and passed (by means not shown) to a monitor tube 3 which produces a reconstituted image at its phosphor screen 4.

As is knovcw, pyro-electric vidicon camera tubes respond to changing level of irradiation, and a rotatable mechanical shutter 5 is provideLl betxecn the lens and the camera tube to modlllate (or chop) the image as it rotâtes. The camera tube 1 contains a target material of cristal which is usually poled to give a positive signal from areas that are svarming up and a negative signal from areas that are cooling down. Thc use of an aperture rotating shutter conveniently pro- duces the required temperature cycle, and the largest output signal is obtained immedi- ately before the state of the shutter changes.

The negative signal is inverted electronically, (by means not shown) so that a display of constant polarity is seen on the screen 4.

The shutter 5 may be provided with a single aperture 6 as shown in Figure 2 or with two apertures 7 as shown in Figure 3.

The cross-hatched portions represent portions of the shutter which are opaque, and it will be appreciated that the shutter shown in Figure 3 is both dynamically and statically balance, and is for that reason to be preferred.

The rotatable shutter 5 is rigidly attache to a short cylinder 8 of light plastics material which carries a deflection coil pair (not shown) for deflecting the electron beams of the camera tube 1 and the monitor tube 3, both of which are provided with their own focus coils 9 and 10. It will be seen that the axes of the camera tube 1 and the monitor tube 3 are parallel to each other, and dispose symmetrically on either side of and parallel to the axis of the shutter 5. The axis of the cylinder 8 coincides, of course, with that of the shutter 5, and the two are rotated by a small electric motor I1 which is coupled to the shutter 5 by a shaft 12. The motor rotates the shutter 5 and the cylindrer 8 at a speed of about 500 r. p. m. to 1500 r. p. m. but the actual speed is not critical.

The operaton of the television system is explained with reference to Figures 4 and 5, in which the camera tube 1, the monitor tube 3 and the lens 2 are referenced as before. Both focus coils 9 and 10 produce magnetic fields which are poled in the same sense ; the direction of the magnetic fields are shown by the two arrows 41 and 42. The magnetic deflection field for the camera tube I and the monitor tube 3 is produced by the same set of deflection coils (not shown) mounted on the cylinder 8, so that both electron beams are deflected by a common magnetic field. The lines 43 and AA represent the respective paths of the two electron beams in the absence of a magnetic deflection field produced by the rotatable magnetic deflection coils.

The steads-offset deflection towards the axis of the shaft 12 can be achieved by separate (permanent magnet) fiels, or by applving a steady field (downwards in the draina), via a further pair of deflection coils (also not shown) which are held sta tionary relative to the camera tube 1 and the monitor tube 3. Application of a magnetic deflection field in the direction represented by arrows 4z and 46 causes the electron beams to scan the pyro-electric target (in the case of the camera tube) and the phosphor screen (in the case of the monitor tube) in the direction represented by the arrows 47 and 48 respectively.

An a. c. scanning field at a frequency of about 5kHz to 10 kHz is applied to the deflector coils to produce rapid scanning by the electron beams. The scan waveform can be triangular or sinusoidal, and it is arrange that the scan waveform deflects the beam 43 in the camera tube 1 upwards, and the electron beam 44 in the monitor tube 3 downwards, on the positive-going part of the waveform, and back to the offset position as the scan field returns to zero.

The negative part of the waveform is ineffective as the electron beams are off the screens.

Rotation of the magnetic field about the axis of the shaft 12 causes the electron beams to scan the pattern shown in Figure 5.

The shutter 5 is, of course, synchronised to the rotation of the magnetic deflection coils since both are mechanically coupled together, and the aperture in the shutter are arrange such that the electron beam scans a portion of the pyro-electric target at the time when it is generating the largest signal, as described previously. By providing a certain degree of angular adjustment for the magnetic deflection coils in relation to the apertures of the shutter, the generation of the largest signals can be optimise.

The signal arising from the closed part of the shutter is inverted and added to that from the open part, and it is this resulting video waveform which is used to modulate the monitor tube 3.

The reproduced display is superimposed on a raster pattern as shown in Figure 5, but even though the can lines are closer together at the top than at the bottom, no picture distortion results, as the scan pattern on the camera tube 1 is similar.

The operation as described has been based on the use of a shutter as shown in Figure 2 and a single pair of magnetic deflection coils. However, for a shutter as shown in Figure 3, two pairs of deflection coils at right angles are provided (gain, not shown), and the deflection waveform is switched from one pair to the other to give a continuous scan. The scan waveform gener ator can be stationary and supply the rotat able deflection coils via slip-rings, or it can rotate with the coils, in which latter case slip-rings need be provided to carry only a d. c. supply curent.

The present invention provides a compact self-contained unit, in which no external synchronising arrangements are required. If it is required to supply a signal to an external monitor, linc synchronising pulses can be extracted from the scan waveform, and field pulses from a suitable pics-off on the rotatable cylinder S.

WHAT WE CLAINI TS : 1. A television system including : a camera tube and a monitor tube mounted in fixed relationship with each other, each containing means for generating an electron beam ; means for producing a magnetic field which is common to both the camera tube and the monitor tube for deflecting in synchronism the two electron beams ; and means for producing a rotation of the magnetic field relative to the camera tube and the monitor tube.

Claims (1)

1. 2. A television system as claimed in claim 1 and wherein the camera tube is adapted to produce video signals representative of the ultra-violet or the infra-red content of a viewed scene.

   3. A television system as claimed in clam 1 and wherein the camera tube is adapted to produce video signals representative of scenes viewed under very low levels of illumination.

   4. A television system as claimed in claim 1 and wherein the camera tube is an infra-red vidicon camera tube having an optical shutter arrange to rotate in the optical path of the vidicon camera tube in synchronism with the rotation of the magnetic field.

   5. A television system including : an infra-red sensitive vidicon camera tube of the thermal imaging or pyro-electric type mounted side by side with a monitor tube ; a rotatable optical shutter arrange to interrupt the optical path of the camera tube as it rotates, and shaving an axis of rotation which is between the camera tube and the monitor tube ; and a rotatable deflection coil arrangeei to rotate around the camera tube and the monitor tube on the same axis as and in synchronism with the optical shutter.

   6. A television system as claimed in claim 5 and wherein the axes of the camera tube and the monitor tube, and the axis of rotation of the optical shutter and the deflection coil, are all parallel to each other.

   7. A television system as claimed in claim 6 and wherein the rotatable deflection coil is carried by a rotatable hollow cylinder which is mechenically coupled to and driven with the rotatable optical shutter.

   8. A television system as claimed in claim 7 and wherein adjustment is provided for setting the angular position of the deflection coil relative to the optical shutter.

   9. A television svstem substantially as illustrated and described with reference to the drawings accompanying the Provisional specification.