US2403628A

US2403628A - Television pickup control system

Info

Publication number: US2403628A
Application number: US532579A
Authority: US
Inventors: George L Beers
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1944-04-25
Filing date: 1944-04-25
Publication date: 1946-07-09
Anticipated expiration: 1963-07-09
Also published as: GB617872A

Description

July 9, 1946. s. L. BEERs TELEVISION PICKUP CONTROL SYSTEM Filed April 25, 1944 2 Sheets-Sheet 1 NNN wuQbOm .MQ mum.

` INVENTOR sans? L. sse/a5' U70/EME?.

July 9, 1946- G. L BEERs TELEVISION PICKUP coNTnonsYsTEM 2 Sheets-Sheet 2 Filed April 25, 1944 ATTORNEY.

Patented July 9, 1946 George L. Beers, Haddonfield, N. J.,

assgnor to Radio Corporation of America, a corporation of Delaware Application April 25, 1944, Serial No. 532,579

This invention relates to 'automatic control apparatus, and more particularly to control apparatus in which a control function is exercised in accordance with a selected series of values from which a control actuating value may be derived.

The invention is illustrated as being applied to a novel arrangement. for obtaining automatic focusing of a television camera. Automatic focusing systems, in order to be fully effective, must insure against the possibility of accidental focusing on an unimportant portion of the field of view, and moreover, itis desirable to provide -for selecting the portion ofthe field of view whichy in the opinion of a skilled operator, is the important portion, or the center of interest of the eld of view when it is considered as an artistic composition. The 'present invention has for its principal aim not only tc prevent inadvertent' focusing on unimportant portions or objects of the field of view, but to provide a positive means whereby a deiinite object or a desired portion of the eld of view will be automatically kept in focus and may be selected at will.

Another important object of the present invention is to provide a control system operable in response to a selectable control value.

A further object of the present invention is to provide means in a control system for selecting a. source of control values.

Still another object of the invention is to provide a novel motor control system fora reversing 16 Claims. (Cl. 178-7.2)

motor which will automatically insure operation in a desired direction.

y Still another object of the invention is to provide a novel arrangement for deriving a control signal.

,A still further object of the present invention is to provide novel means in a television pickup system for selecting the portion of the iield of view vfrom which a control signal or series of sig-r nals are to be derived.

Still further objects of the invention will become apparent and suggest themselves to those skilled in the art to which the invention is directed upon reading the following specification and claims in connection with the drawingsin which:

Fig. l is a schematic showing of a television `pickup system, including a television camera and a portion of the focusing equipment of the present invention;

,Figs 2 and 3 illustrate additional equipment which is associated with the focusing equipment of Fig. 1; and

Fig. 4 shows a slight modic tion of Figs. l and 2.

The television pickup system selected for purposes of illustration is more or less conventional and comprises a camera 9 (suggested in dotted .outline) housing a pickup tube I0 shown as being of thel storage type containing a light sensitive mosaic II and the usual auxiliary electrodes and electron emitters. These electrodes include the anode and the cathode for producing a cathode ray b'eam. The cathode ray beam deflecting means or yoke is indicated conventionallyv at I2 and may comprise horizontal and vertical deflecting coils for producing a scanning movement of the beam I4 which is directed onto the mosaic II to release a signal output therefrom'to a load circuit. The released signal output of the pickup tube I0 isl applied to a preamplifier I5 across a load resistor I6 in most conventional devices. After initial amplification and, if desirable or necessary, additional amplication, the signal is transmitted to a line amplifier I1. Reference numeral I8 indicates a sync signal generator of conventional form which generates suitable synchronizing and blanking signals, in known manner, and which is shown as being connected to the ray deflecting means I2 by way of conductors by way of conductors 34. The resulting composite sync and picture signal output of the amplifier I1 may be transmitted over any suitable transmission channel as 35 to a distribution point such as a radio transmitter.

The camera Sis equipped in the usual manner with a lens combination 36 suitable for imaging the scene, indicated conventionally at 38, on the mosaic II. The lens combination 36' is or may `be equipped with the usual iris diaphragm v(not shown) for stopping down the lens to obtain greater depth of focus when the televised scene v the mirror 42 together with an associated cathode ray tube 43 will be described indetail hereinafter.

of the pinion 41 by a focusing motor 49. Energization of the motor 48 is obtained under control of a derived signal in accordance with the invention in a manner to be later described.

Referring now to the equipment for generating a control signal and for the present more specically to Fig. 2, conductor 5| furnishes horizontal sync pulses for control of a sine wave ocillator 52 which runs at image line frequency. A phase shifter 53 of any known type is adjustable to shift the phase of the output of the oscillator 52.- A phase shift range of approximately 180 is desirable. One cycle of the output from the oscillator 52 is shown conventionally above the oscillator and the phase shifter. An amplifier 54 amplifies successive half cycles of the wave which are passed through a clipper stage 58. The clipped half wave, indicated at 58, is passed through a shaper and amplifier 8| which gives the half wave approximately the form shown at 82.

Vertical sync pulses from the sync Asignal generator i8 are applied over a conductor 84 to a sine wave oscillator 66. The output from this oscillator is passed to aphase shifter 81, and the equipment following this phase shifter comprising 4an amplifierv 88, a clipper stage 69, and a shaper A'pulse 12, similar to the pulse 62, appears in the output of the wave shaper and amplifier 1| but occurs in timed relationship with respect to the vertical sync' pulses supplied from the sync generator. A phase shift range of approximately 180 for the output of the oscillator 88 is also desirable. l

The

pulses

82 and 12 are combined in a conductor 14 including a coupling condenser 18 to provide an operating bias for the grid 18 of the cathode ray tube 43, and also an operating bias for a spot selector amplifier 18 which amplifles the image `signal output of the preamplifier I8. The operating biases of both' the cathode ray tube 43 and the amplifier 18 are adjustedso that the combined voltage of the pulses 62 and 12 causes with respect to the wave 88, for example, which.

these pieces of equipment to become operative when the pulses coincide in time.

The luminous spot generated inthe fluorescent screen 11 of the cathode ray tube 43 by the cathode ray beam 18 is thereby shiftable over the` face of the tube and is reected from the half silvered mirror 42 onto the ground glass viewing screen 44. It is preferred that' light'from the luminous spot is of low intensity so that it does notV obliterate any partof the image of the scene 38. It will be understood that the elements of the tube 43 are provided with the usual operating and biasing voltage connections (not shown);

The luminous spot produced by the beam 18 may be shifted to substantially any point on the screen 44 by manipulating the phase shifters 83 and 81, and when this is done the spot selector amplifier 18 passes the portion of the image s18- nal from the preamplifier I8 representing only this luminous spot. In this manner an identiniable portion of the picture signal appearing in the output of the spot selector lamplifier 'I8 may be selected .by manipulating the two ph'ase shiftcamera tube |8 representative of the chosen area during one interval of time to the high frequency response during the-next succeeding interval of time. The control circuits to be described for the motor 48 are so arranged that if the motor is moving the lens in a given direction to bringY it in focus on the desired area, the high frequency response in the second time interval lwill be greater than during the first time interval. Under this condition, the. control circuits are so arranged that the motor continues to move the lens in the same direction. When the high frequency response during the second interval of time is less than during the first interval, the control circuit will operate to reverse the motor.

The control signal which is applied to a relay 82 to determine direction of rotation of th'e motor is derived by the apparatus of Fig. 3 of the drawi ings. The higher frequency components of the selected portionof the image signal are passed by a high pass filter (Fig. l), and this high frequency signal is applied to the control electrodes 88 and 81 of

vacuum tubes

88 and 88 over a conductor 88. I

In order to set the time intervals of the suc. cessive high frequency response signals, an oscillator 92 is provided which may operate at any desired frequency. This frequency may be determined for example by the time required for the focusing motor to move the lens by an amount which is sufficient to produce a desired change in the high frequency output of amplifier 18 and filter 84. If a time intervalof high frequency response comparison is to be 11s of a second, for example, the oscillator 82 may be a 10 cycle oscillator. The output 84 of the oscillator 82, which',

if desired, may be of the sine wave form, is changed to square wave form 88 in a wave shaper 88. The waves 84 and- 88 are, it will be understood, not shown to scale along the time axis may be several thousand pulses per second.

'Ihe square wave output from the wave shaper 88 is applied to amplifiers |8| and |82. 'I'he voltage output wave of the amplifier I 8| is applied to the grid 88 of tube 88, and the output voltage of amplifier |82 is applied to the grid 81 of tube 88.- The voltage wave |88 may be considered as shifted in phase by from the voltage wave |81 or may be considered` as of reverse polarity. The

tubes

88 and 88 are so biased that they function to amplify the signals applied totheir grids over the conductor 88 during one half of each voltage wave. In this way tube 88 is caused to function during a desired series of spaced time intervals. -Tube 88 is, however, caused to function on the alternate timeintervals so that tubes I2 and |I4 supplied from the cyclically

operating amplifier tubes

88 and 88, serves to rectify the high frequency signals applied to the rectiiiers across resistors IIB and H3. The high frequency signals across resistor H8 are applied to rectiner ||4. 'I'he rectication of these signals by the tube H4 causes terminal |28- of resistor H8 to become' more negative with respect to terminal i 8. Likewise the high frequency signalsv applied with the stationary contacts of the relay 82.

versal of the position of the tongues'of eitherv i relay Awill cause to rectifier ||2 across resistor I3 causes terminal ||1 to become more negative with respect to terminal |I6. Thus, it will be seen that the potential between terminals |20 land I |1 may b'eeither positive or negative depending on the relative strength of the high frequency signals applied to rectiiiers I I2 and I I4.

, A resistor I I8 and a condenser ||9 serve to switch arm |53 of a rotary switch |54. The switch arm is connected to one terminal of the operating coil of the polar relay |24. Alternate average the successive pulses rectified -by the rectiiers `I|2 and ||4 so as toy obtain an averaging eifect. Thus, -theterminal IIII likewise becomes either positive or negative with respect to terminal I|1 as the relative strength of the high frequency signals applied to rectiflers ||2 and'` I I4 is varied.

The polarity changes appearing at the point IIIl are applied over a conductor I9 to the relay 82. This Arelay is a polar relay so. constructed that its contact tongue or tongues remain in the position assumed prior to de-energization.

tongues requires a change in direction in the current passing through the relayoperating coil.

Reversal of the position of its contact tongue or The motor 449 is energized from a suitable 'the type which requires a reversal in the direction of the current applied to its operating coil before the position of its contact tongues is reversed. f

These relays are connected as shown so as to serve as reversing switches for the motor 49. A make contact |26 and a break contact |28 of the relay 82 are connected to one conductor, and a make contact |29 and a break contact |3| are connected to the other line conductor. The conductors |33 and |34 are connected to the motor eld |22 `through contact tongues |36 and |31 of the relay |24, the stationary contacts of which are wired in the manner explained in connection the motor 49 to reverse its/direction of rotation. If, however, the position of the tongues of both relays is reversed, then the motor will continue to operate in the same direction as will be obvious from an inspection of Fig. l of the drawings. While relays have been shown, illustratively, to accomplish this purpose, it will be understood that other means may be employed.

To insure operation of the focusing control of the invention so that the camera will be brought into focus upon starting the system, normally closed limit switches |4| and |42 are provided which cooperate mechanically with suitable means such as the projections |43 and |44 on a movable part of the support 46 for the lens combinations 36 and 4|. These limit switches are connected across the source 2I in series with the operating coil of a relay |41 and are opened upon over travel of the lens support 46. The break contact. |48 of the relay 4|41 energlzes the operating coil of a stepping magnet |49 when either of the limit switches I4I or |42 is opened. I'he stepping magnet is provided with a pawl I5| cooperating with Aa ratchet |52 which intermittently drives the contact studs |56 over which the switch arm |53 is stepped are connected toA a suitable power source of negative polarity indicated at |51. The contact studs |59 are connected to a suitable power source of positive polarity indicated by reference character 6|. The rotary switch |54 together with its stepping magnet |49 may be oi' any well known construction, such as the usual telephone minor switch.

From the lforegoing vit win-be obvious that upon Y each over travel of the support 46, for example toward the left, as viewed in Fig. 1, switch |42 will be opened resulting in de-energization.. of the relay |41. When this occurs, the stepping magnet |49 is energized to step the switch arm |53 to the next -successive -contact stud, or as `shown in Fig. 1 by way of illustration, 'onto a contact stud |56 connected to the negative 'source |51. The position of the contact tongues |36 and |31 with the polar relay |24A will be reversed to reverse the direction of rotation of the motor 49. After the motor has operated in a reverse direction for a period of time, the switch 42 will be reclosed resulting in vde-energization of the relay |41 and release of the pawl I5|which will be returned to its linitial position by a spring |63. The motor 49 will continue to operate until the lensl combination 36 brings the image of the scene 38 substantially into focus on the light sensitive 'surface of the mosaic IIof the cathode ray tube I0.

While control relays and polar relays employed as reversing switches have been shown, illustratively, it will be understood that electronic` switching means, operating in response to the signals at the terminal III! to control the motor.

may be employed.v

All of the equipment involved in this system except the motor 49, the cathode ray tube43, and the controls for the

phase Shifters

53 and 61 which move the pattern on the oscillograph tube 43, may be located at a monitoring control station at a point more or less remote from the camera 9. If so desired, the control for selecting the desired area may be operated by observing th'e image on a monitoring image tube (not shown) Aat a supervisory control point; The motor for. driving the pinion 41 will usually be located in the camera housing and the control relay equipment 'may be separately vmounted and housed.. Itwill be understood that parts of the equipment located near the camera 9 lwill preferably be shielded so as to prevent interference with the television signal generating equipment.

In operation of the automatic control system of theinvention for focusing the television camera 9 on a particular portion of a iield of view or scene 38, the camera. man operating the camera 9 would manipulate -the control of each

phase shifter

53 and 61 until light from the luminous spot produced by the cathoderay beam 18 is superimposed on the portion of the image appearing in the ground glass screen 44 on which the camera is tofocus. If the equipment is already in operation, the camera will, before the shift of the luminousspot occurs, have been focused on some portion of the scene 38. However. in the event that the equipment has just been placed in operation, the camera may be quickly brought to focus if the camera man observes that the lens f 36 is moving in a ydirec-tion away from its posi- 7 of the lens to be reversed immediately. This is accomplished by energization of the operating coil of the stepping magnet |49 to change the polarity of current iiowin'g through the winding of the polar relay |24.

With the area of the scene upon which the camera. is to focus selected, as stated previously the high frequency response representative of this area during one interval of time is compared to the high frequency response during a. succeeding interval of time. This is accomplished by the biases applied to the grids 86 and 81 of the

tubes

88 and 89 respectively from the oscillator 92. The time interval is preferably such that the lens can move between half cycles of the wave from this oscillator.- If it is assumed that the motor 48 is moving the lens 36 in the direction to bring it in focus on the desired area, the high frequency response during the second interval will be greater vthan during the iir'st interval of time. Under this condition the polarity at the point |||l is unchanged, and the motor 49 continues to rotate to move the lens 36 inthe same direction.

Ifthe high frequency response during a succeeding interval of time is less than during a preceding interval, the polarity at the .point I I will a reverse causing the polar relay 82 to reverse the motor.. By this arrangement, the lens 36 will move back and forth through a very narrow range centered about the position of optimum focus. This variation in lens position will not be observable bythe television audience since the loss Vof high frequency response which it produces may be very small, for example, less than per cent, and the camera, pickup tube, and amplifier system can -be designed with materially greater resolution capabilities than will -be obtained from the complete television system including the receiver. It is doubtful that a skilled cameraman could focus a television camera with this degree of accuracy merely by observing the image of the scene 38 in the ground glass view finder 44.

In the foregoing example it was assumed that the initial relationship between the high frequency signals applied to

amplier tubes

88 and 88 and the motion of the lens was such that either the lens moved in the direction to bring the desired scene in focus or that the camera operator used the switch |63 to cause the lens to move in the desired direction. Assuming now that when the initial relationship between the high frequency signals applied to the

amplifier tubes

88 and 89 and the motion of the lens is such that the lens moves away from the in focus position, the camera operator does not resort to the use of the switch |63. In this case the lens will move to the end of its travel and either the reversing' switch |4| or |42 will -be operated to reverse'the direction of lens motion. 'I'he relationship bei tween the Ihigh frequency signals applied to the iinder screen 44.

The high pass lter 84 is the same as that' shown lon Fig. l of the drawings; When lens 36 is tovbe moved manually in accordance with the mode of operation now tube set forth, the connection to the

tubes

88 and 89,may be omitted. as well as the driving motor and the motor control apparatus. However, it will be understood that the modified arrangement of Fig. 4 Shows a system including thespot selecting equipment in addition to the usual studio and console equipment.

IA rectifier |80 recties the high frequency output representing the picture area Selected in the manner described above by operating the phase Shifters 53 and 6l'. The output of the rectifier appearing across the load resistor I8! is applied to the grid 10 of the oscillograph I3 so that the spot produced by the beam 18 is brightest when the lens 36 is in focus on the selected spot. Combining the area indicator on the nder screen with the feature of changing the brightness of the spot .serving as the area indicator shows the camera operator that the particular spot selected is in focus while he is observing the entire scene included by the camera.

As an alternative a meter |83 either at the camera or at a remote point may be used to indicate when the camera is in focus on the selected area. f

As the sensitivity ofl television pickup tubes is increased, it becomes possi-ble to pick up television images at light levels which are insufficient to provide in a conventional view finder an image which is of suicient brightness to enable the camera. operator to focus the camera on the desired scene by observing the resolution in the visual image. Under these conditions the arrangement illustrated in Fig. 4 is particularly effective since the variation in brightness of the focus indicating spot or the meter indication depends entirely on the signals derived from the pickup tube. Any increase in the sensitivity of pickup tubes therefore automatically provides a corresponding increase in sensitivity of the focus indicating Spot.

Various alterations and modifications may be made in the present invention without departing from the spirit' and scope thereof, and it is desired that any and all such modications be considered within the purview of the present invention as dened by the hereinafter appended claims. l

Having nowdescribed the invention, what is -claimed and desired to be secured by Letters Patent is the following:

1. In a television system, means for focusing a scene upon a light responsive area, means for focusing the scene on a viewing area, means for selecting a desired portion' of the image of said scene appearing on the viewing area, and means for causing said focusing means to automatically bring the desired portion of said scene in focus.

2. In a television system, means for focusing a scene upon a light responsive area, means for focusing the scene on' a viewing area, means for selecting a desired portion of the image of said scene appearing on the viewing area, means for producing signals indicative of said desired portion of said scene, and means for utilizing said signals to vary said focusing means.

3. In a television system, means for focusing a scene upon a light responsive area, means for selecting a desired portion of said scene, means for producing electrical potentials, the relative polarities of which are indicative of said desired portion of said scene, and means for utilizing said potentials to vary said focusing means.

4. In a television system, means for focusing a scene upon a light responsive area. means for obtaining a visual image of said scene to indiother visual focus indication superimposed on said visual image.

visual focus indication which can be viewed simulcomparison to which said controlling .element is responsive. and means to -actuate the controlling element in accordance with said characteristic whereby. the derived energy is maintained at a maximum.

l2. A control system comprising controlled and controlling elements. mean's for deriving energy representing the direction of movement of the 6. In 4a television system, means ,for focusing a scene upon a light responsive area, vmeans for producing a variation in the resolution of a visual image in response to'a focusing variation,

and. additional visual means for producing a manifestation of the displacement of a particular area in the depthof the scene whereby to enable resolution of the particular area on said` light responsive area.

7. In a television system. means vfor focusing a scene on a light responsive area, means for producing a variation in the resolution of a vise ual image in response to focusing variations, and means for producing an additional indication related to the resolution of the visual image.

8. In va television system, means for focusing a -scene on a light responsive area, means f or producing a variation in the resolution of a visual image in response to focusing variations, means for producing a cathode ray stream, means for producing a visual indication under control of said stream, and means whereby said last named means is responsive to said focusing means.

9. In a television system, means for focusinga scene on a light responsive area, means for producing a variation in the resolution of a visual image in response to focusing variations, an indicating instrument, and mns for producing a change in `the indication of said instrument in response to operation of said focusing means.

10. In a television system. means for focusing a scene on a light responsive area, means for producing a variationin the resolution of a vis# ual image in response to focusing variations, means for producing signalsl representing a portion of said visual image. said signals varying in .response to focusing variations, a rectifier for rectifying said signals, and an indicating` instru-4 ment responsiveto the change in current through said rectifier which occurs upon' variation of the.

focus.

ll. A control system comprising controlled and controlling elements, means for deriving energy representing the position of the controlled element during a given time interval, means for deriving energy proportional to a successive position during a succeeding time interval, means for comparing the values of the derived energies,

means for obtaining a characteristic from said controlled element duringa given time interval,

means for deriving energy during a succeeding time interval proportional' to continued movement, means for comparing the'values of the derived energies. means ior. iiatainingl a characteristic from said comparison toAwhich said controlling element is responsive. and means to actuate the controlling element in accordance qwith said characteristic.

13. In a television system, means for focusing a light imagev of a subject upon a light responsive,

area, means for scanning the light responsive area, means-for developing electrical energies in accordance with the light intensity of the elemental areas scanned, means for dividing the developed electrical energies into increments separated by time intervals, means for comparing successive increments to determine 'the difference in frequency components ofthe successive in crements, and means for varying the focusing means in accordance with said comparison means. 14. In a television system. power driven means for focusing alight image of a subiect'upon a light -f responsive. area, means for scanning the light responsive area, means for developing electrical energies in accordance with the light intensity of the elemental areas scanned, means for dividing the developed electrical energies into increments separated by time intervals, means for comparing successive increments to determine occurrence of a change in frequency components of successive groups of increments, means for producingxa --characteristic signal upon occurrence of a change in frequency components of successive groups.' and means for varying the focusing 'means in Y accordance with said characteristic' signal.

v15. In a television system, means for focusing a scene upon alight responsive area, means for producing electrical eifects, characteristics of which are indicative of said scena-and means for automatically causing said characteristics to vary in a. desired relationship in response to the actuation of said focusing means.

r16. In ya television system, means a scene upon a light responsive area, means for producing electrical potentials the relative polarities of which are indicative of said scene, and

means forv automaticallycausing the polarity of said potentials to vary in a desired relationship -mean5.

in response to the actuation of said focusing Gnomz: L. sanas.

for focusing