Title:
Telautograph system
United States Patent 2269599


Abstract:
My invention relates to improved means and systems whereby writing or tracing movements of a body such as a pen, pencil or stylus in tracing a picture or design may be reproduced at a distance. Instruments and systems whereby writing at a distance is made visible are sometimes referred to...



Inventors:
Moodey, Hannah C.
Application Number:
US37190240A
Publication Date:
01/13/1942
Filing Date:
12/27/1940
Assignee:
RCA CORP
Primary Class:
Other Classes:
178/19.06
International Classes:
G08C21/00
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Description:

My invention relates to improved means and systems whereby writing or tracing movements of a body such as a pen, pencil or stylus in tracing a picture or design may be reproduced at a distance.

Instruments and systems whereby writing at a distance is made visible are sometimes referred to as telautograph instruments and systems, and while such arrangements have been proposed incorporating a cathode ray tube having a long 1i persistence luminescent screen on which the movements of the stylus are reproduced by a moving cathode ray beam, it has been customary to produce movements of the beam in the cathode ray tube directly from beam deflection po- 13 tentials applied to a resistance plaque or tablet.

For adequate sensitivity of beam deflection the potentials applied to the plaque or tablet are relatively high and become a hazard during use.

In addition, the sensitivity of reproduction may be relatively low and it is therefore an object of my invention to provide a system wherein high sensitivity may be obtained without danger or hazard to those operating the equipment.

Another object is to provide such a system wherein no apparatus having points or areas at high potential is exposed and it is a further object to provide a system including a resistance plaque wherein the power loss in the plaque is a minimum. In accordance with my invention I provide a low potential alternating current source which is applied to the writing plaque or tablet of relatively high resistance or semi-conducting material, and derive from this single potential source, 33 current or voltage pulses representative of the position of a stylus moving over the plaque or tablet. These and other objects, features and advantages of my invention will be apparent when taken with, the following description and accompanying drawing in which: Figure 1 is a schematic representation of a teleautograph system incorporating a cathode ray tube reproducing device, and Figure 2 is a schematic representation of a modified system for use in teleautograph apparatus.

As shown in Figure 1, I provide a resistance plaque or tablet 10 over which a conducting stylus II is moved, simulating a writing or tracing movement, such movement being indicative of the intelligence for which reproduction is desired at a distant receiving position. The plaque or tablet 10, which may be of rectangular form, is provided on two of its opposite sides with conductors 12 and 13 and on its other opposite sides with conductors I4-15. The conductors 12-15 do not extend entirely to the corners of the plaque 10 but are insulated one from the other except for conduction through the plaque or 80 tablet to produce mutually perpendicular voltage gradients across the central portion of the plaque such as the portion enclosed within the dashed lines 16. In accordance with my invention an alternating or pulsating current is applied to the opposite conductors such as between the conductors 12-13 and 14-15. Referring specifically to Figure 1, which shows one method of applying pulsating voltages to the conductors, -alternating voltage from a source 20 may be applied to two transformers 21 and 21' each of which is in series with a uni-directional current limiting device such as the diodes 22-23. The transformer 21 is provided with a secondary winding 24 and the transformer 21' is provided with a secondary winding 25, the winding 24 being connected across the opposite conductors 12-13 and the secondary winding 25 being connected across the other pair of opposite conSductors 14-15 of the plaque 10. In the operation of the above-described circuit, pulsating currents are applied alternately or sequentially to the conductors 12-13 and then to the conductors 14-15, these pulsating currents being displaced in phase by 180*. During one one-half cycle of the alternating current wave the diode 22 allows current flow in the secondary winding 24, and during the following half cycle the diode 23 allows current flow in the secondary winding 25.

The energized plaque or tablet in combination with the stylus II comprises the transmitting portion of the system, whereas the receiving portion, likewise shown in Figure 1, includes a cathode ray tube 30 having means to generate an electron beam, such as a conventional electron gun 31, a luminescent screen 32 preferably of material having relatively long time lag phosphorescent characteristics, and means such as two pair of deflection plates 33-34 and 35-36 to deflect the beam from the electron gun 31 over the luminescent screen 32. Magnetic deflection means may be utilized in place of the plates 33-36 if desired. In the showing of Figure 1 the stylus II is preferably connected directly to two of the deflection plates, such as the plates 34-35 which may be operated at ground potential, and to the input circuits of two amplifiers 40, 41 which may be of the triode type as shown. The input electrode of the amplifier 40 is connected to one of the plaque conductors, such as the conductor 12, and the input electrode, such as the grid 43 is connected to an adjacent plaque conductor 15. During operation the pulsating currents applied between the conductors 12-13 and 14-15 produce substantially mutually perpendicular equi-potential voltage gradients across the central portion of the plaque 10 so that upon movement of the stylus II in contact with' the central portion of the plaque 10 potentials applied to the stylus are substantially proportional to the distance over the surface of the plaque from the surrounding conductors. Signal pulses will be alternately applied to the amplifiers, such as the triodes 40 and 41, these impulses having a time and phase relationship equivalent to a displacement of 180°.

The output of pulsating wave form, from the amplifier 40 is applied to the deflection plates 33-34 of the tube 30, in series with a uni-direc- 1C tional current limiting device, such as the diode 50. Similarly, the output from the amplifier 41 is applied to the deflection plates 35-36 through a uni-directional current limiting device, such as the diode 51. 1! From the foregoing description it will be apparent that the potentials applied between the opposite conductors on the plaque 10 may be relatively low, such as a peak-to-peak value of volts which cannot possibly cause injury to 2' the operator but which is nevertheless sufficient to control the amplifiers 40-41 and supply high deflecting potentials to the cathode ray tube through the diodes 50-51.

From the foregoing description it will be ap- 2 preciated that the voltages applied across the plaque may be of very small values and need not be sufficient in and of themselves to deflect the electron beam in the tube 30. Since the voltages are small such as 10 volts or less and further 3 since the potentials are intermittently applied, the power loss in the plaque or tablet 10 is a minimum. It will also be apparent that alternate pulsations of voltage similar to the pulsations appearing across the plaque 10 and varying 3 in amplitude in accordance with the position of the stylus on the plaque will be applied to the deflection plates of the cathode ray tube 30.

Thus if the alternating current supply is a 60cycle supply, 60 voltage surges will be applied 4 between the deflection plates 33-34, and similarly, 60 voltage surges will be applied across 35-36 in alternate succession, these voltage surges being representative in amplitude of the position of the stylus II on the plaque 10. The electron beam of the cathode ray tube 30 will therefore be displaced from a neutral position in two mutually perpendicular directions 60 times per second. However, such operation is disadvantageous and further in accordance with my invention I connect across the plates 33-34 means to damp the pulsations, such as the time constant circuit comprising the resistor 5: and condenser 53, and a second time constant circuit comprising the resistor 54 and condenser 55 in parallel across the plates 35-36. The absolute values of these resistor-condenser combinations are dependent upon the frequency of the alternating current supply applied to the transformer 21. Thus, the time constants provided by these combihations should be sufficiently long to smooth the pulsations appearing across the respective diodes 50-51, but also the time constants should be sufficiently short to follow the writing speed or movement of the stylus over the central area of the plaque 10. Values of 250,000 ohms and 0.1 microfarad are satisfactory with an alternating current supply of 60 cycles.

The system shown in Figure 1 is particularly advantageous for use with cathode ray tubes having only two free deflection plates wherein two of the plates are operated at a single potential, such as at a potential of one of the electron gun electrodes. When utilizing tubes of the type wherein all four deflection plates are provided with leads extending without the cathode ray tube envelope, the system of Figure 2 may be used. Referring to Figure 2, the plaque or tablet, together with the conductors partially surrounding the tablet, are similar to those described in connection with Figure 1, and an alternating current potential is applied across opposite conductors of the plaque through the writing stylus. Thus the writing stylus 11 is connected in series with a low potential alternating current source, such as the secondary winding of a transformer 60, the stylus being connected the stylus being connected through the transformer secondary through resistors 61-62 having a value of resistance which is high with respect to the resistance of the plaque 10 to the opposite conductors 12-13, and to the conductors 14-15 through similar resistors 63-64. In this arrangement four amplifiers must be uti0 lized, the input electrodes of which are directly connected to the plaque conductors. Thus the control electrodes, such as the grids of the amplifiers 65-66, may be connected to the opposite conductors 12-13, and similarly, the grids of the 5 amplifiers 67-68 connected to the other opposite conductors 14-15. The output electrodes of the amplifiers 65-66 are connected through unilateral conducting devices such as the diodes 69-10 to the deflection plates 33-34 of the 0 cathode ray tube 30 and the output electrode of the amplifiers 67-68 are connected through the diodes 71-72 to the other pair of deflection plates 35-36. As in the circuit of Figure 1 I utilize two time constant circuits comprising 5 resistors 80-80' and condensers 81-81', except that I connect these resistors and condensers between each of the plates 33-34 and ground.

Similar resistors 82-82' and condensers 83-83' are connected between the other plates 35-36 .0 and ground. As explained above the value of these elements depend upon the alternating supply frequency and the values given in connection with the circuit of Figure 1 are satisfactory in the circuit of Figure 2.

5 While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no )0 means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth 53 in the appended claims.

I claim: 1. In a telautograph system a resistance tablet having substantially uniform lateral resistance over an exposed area, means to apply potentials aii across said tablet comprising two pairs of electrodes the electrodes of each pair being on opposite sides of said tablet, an electrically conducting stylus adapted to move over in contact with said tablet simulating a writing motion, means to o.i apply a pulsating electric potential of the same frequency of pulsation in two directions across said tablet effective to produce pulsating potential drops across said tablet when said stylus is in contact therewith, a plurality of thermionic am70 plifiers having input and output electrodes, connections between at least two of said electrodes on adjacent sides of said tablet and the input electrodes of two of said amplifiers, a cathode ray tube including means to generate an electron 75 beam and a luminescent screen, means to deflect the said electron beam in one direction over said luminescent screen, means to deflect the beam in another direction over said luminescent screen, and connections between each of said two lastmentioned means and said two amplifiers to deflect said beam in accordance with the position of said stylus on said tablet.

2. In a telautograph system a resistance plaque having substantially uniform resistance over an exposed area, two pairs of conductors, the conductors of each pair,being connected to opposite sides of said plaque, a stylus adapted to move over and contact said plaque simulating a writing motion, means to apply a pulsating electric potential of the same frequency of pulsation between said stylus and each of said conductors, a plurality of thermionic amplifiers having input and output electrodes, a connection between the input electrode of one amplifier and one of said conductors and a connection between the input electrode of another of said amplifiers and another of said conductors adjacent said first-mentioned conductor, a cathode ray tube having two pair of deflection plates, connections between the output electrode of each of said amplifiers and a plate of each of said pairs of plates and a rectifier interposed in each of said last-mentioned connections to apply to said plates potentials representative of the position of said stylus on said resistance plaque.

3. In a telautograph system a resistance plaque having a substantially uniform resistance' over an exposed area, four conductors electrically connected to said plaque adjacent the periphery. thereof forming two pairs of conductors, the conductors of one pair facing each other and the conductors of the other pair facing each other, a stylus adapted to be moved over and make contact with said plaque, means to energize said resistance plaque with pulsating currents and produce mutually perpendicular equi-potential voltage gradients across the central portion of said plaque, which voltage gradients vary in absolute value due to said pulsating current, a plurality of amplifiers having input and output circuits, a connection between said stylus and the input circuits of said amplifiers, a connection between each of two adjacent conductors and said input circuits to complete said input circuits through said resistance plaque, a cathode ray tube having electron beam forming means and a luminescent target, dual means to deflect said beam over said target and connections between said each of said dual means and a corresponding one of said amplifier output circuits.

4. A system as claimed in claim 3 including a time constant circuit including a resistor and capacitor connected across each of said dual means, each of said time constant circuits being of a value to provide a time constant sufficiently long to smooth the pulsations occuring at the frequency of said pulsating current and sufficiently short to follow the movement of said stylus over the central portion of said plaque.

5. In a telautograph system a resistance plaque, 6 having an extended area, four conductors surrounding said area providing two pairs of two conductors each, the conductors of each pair being on opposite sides of said area, a writing stylus adapted to move over and contact said plaque, a source of alternating current, a pair of transformers with their primary windings connected across said source, a uni-directional current limiting device in series with each transformer connected to allow intermittent pulsating current to flow in alternate transformers, connections between the secondary winding of each transformer and a different pair of said conductors, a plurality of alternating current amplifiers having input and output electrodes, a connection between the input electrodes of at least two of said amplifiers and one conductor of each pair of conductors, a cathode ray tube having means to generate an electron beam and a target adapted to be impinged by said beam, dual beam deflection means to sweep said-beam over said target in mutually perpendicular directions and a connection between the output electrode of each of said two amplifiers and a corresponding one of said dual deflection means to deflect said beam over said target in accordance with the movement of said stylus over said plaque.

6. The system claimed in claim 5 including a resistor and condenser connected in parallel across each of said dual deflection means to cause said beam to follow the movement of said stylus and prevent return of said beam to an undeflected position during the time no current is flowing in one or the other of said transformers.

7. In a telautograph system a pair of transformers having high voltage primary windings and low voltage secondary windings, means to impress an alternating current potential across the primaries of each transformer means associated with each of said transformers to limit the current flow alternately in each transformer to alternate half cycles of the impressed alternating current potential, a resistance plaque, two pairs of conductors surrounding and in contact with four sides of 'said resistance plaque, a stylus adapted to move over and make contact with said plaque and derive a pulsating signal representative of the position of said stylus on said plaque, means including a plurality of amplifiers to amplify said pulsating signal, and cathode ray tube means connected to said. plurality of amplifiers to produce a visual representation of the movement of said stylus over said plaque.

8. In a telautograph system a resistance plaque, four conductors conductively associated with said plaque, a stylus adapted to move and make contact with said plaque, a low potential alternating current potential source connected in series with said stylus and each of said four conductors, four thermionic amplifiers each having input and output electrodes, a connection between each of said conductors and an input electrode of a corresponding amplifier, a cathode ray tube including means to generate an electron beam and a luminescent screen, two pairs.of deflection plates to deflect said beam over said screen, a connection between each of the plates of said pairs of plates and the output electrode of a corresponding amplifier and a uni-directional current limiting device in series with the connection be5 tween each of said plates and the said corresponding amplifier output electrodes.

9. A system as claimed in claim 8 including a time constant circuit comprising a resistor and condenser connected in parallel between each o0 of said deflection plates and an input electrode of said amplifiers.

HANNAH C. MOODEY.