Wireless Transmission of Photographs Part 4

[Ill.u.s.tration: FIG. 35.

M, motor; Y, isochroniser; F, clutch; A, machine; R, stylus; S, relay; X, gearing; O, circuit breaker; T, receiver; C, condenser; U, telephone relay; K, polarised relay; L, contact breaker; D, D^1, D^2, D^3, batteries; P, friction brake; B, B^1, double-pole two-way switches; N, N^1, N^2, single switches; W, key; E, electric clock; J, telephones.]

The drum measures 5 inches long by 2-1/8 inches diameter, and this takes a metal print 5 inches by 7 inches, which allows for a lap of about 1/4 inch.

In working, the print is wrapped tightly round the drum, being secured by means of a little seccotine smeared along one edge. Care must be taken that the edge of the lap draws away from the point of {78} the stylus and not towards it. A margin of bare foil, about 1/8 inch wide, should be left on the print at the commencing edge, the purpose of which will be explained later.

[Ill.u.s.tration: FIG. 36.]

_The Stylus._--As the drum of the machine travels laterally, by reason of the threaded shaft and bearing, the stylus must necessarily be a fixture.

It consists of a holder B, drilled to take a hardened steel point S, attached to the spring M. The spring is arranged to work in the guide F, which is provided with an adjusting screw W for regulating the pressure of the stylus upon the print; the pressure being sufficient to enable good contact to be made, but must not be heavy enough to scratch the soft foil.

The needle should present an angle of about 60 to the surface of the print, as this angle has been found to give the best results in working.

To eliminate any sparking that may take place at the point of make and break, due to the self-induction of the relay coils, a condenser C, about 1 microfarad capacity, should be connected across {79} the drum and stylus.

The complete stylus is given in the drawings, Figs. 37, 37_a_, and also in the diagrams Figs. 8 and 9.

[Ill.u.s.tration: FIG. 37.

Showing the arrangement for sliding the stylus to or from the machine.]

[Ill.u.s.tration: FIG. 37a.]

_The Relay._--As will be seen from the diagram, Fig. 38, this consists of two electro-magnets having very soft iron cores, the magnet M being wound in the usual manner, while the magnet N is wound differentially. The armature A is made as light as possible, and is pivoted at P, and when there is no current flowing through any of the coils, is held midway between the magnet cores by the two spiral springs S and T, which are under slight but equal tension. The connections are as follows. The wires from the winding on M are connected directly to the relay terminals F and H, as are also the wires from one winding on N. The other winding on N is connected in series with the battery C, ammeter B, and regulating resistance R. {80}

[Ill.u.s.tration: FIG. 38.]

When the circuit of the battery C is completed, the coil of N, to which it is connected, is energised, and the armature A is attracted against the stop V. When in this position the tension of the spring S is released, while the tension of the spring T is increased. As soon as the circuit of the battery D is completed by means of the metal line print on the transmitting machine, the current divides at the terminals F and H, a portion flowing through the magnet coil M, and a portion through the remaining winding on N. The current which flows through the winding on N produces a magnetising effect equal to that caused by the other winding on N, but since the two windings are of equal length and resistance, and since the current flowing through the two windings is of equal strength but in opposite directions, the result is to neutralise {81} the magnetising effects produced by each winding, and consequently no magnetism is produced in the cores.

The other portion of the current from D flows through the coil M, and it becomes magnetised at the same time that the coil N becomes demagnetised.

The armature A is attracted by M against the stop X, and this attraction is a.s.sisted by the spring T, which was under increased tension. The conditions of the springs are now reversed, the spring S being under increased tension, while the tension of the spring T is released.

As soon as the current from D is broken, the magnetism disappears from M, the neutralising current in N ceases, and N once more becomes magnetised, owing to the current which still flows through one winding from C; the armature is therefore again attracted by N, a.s.sisted by the spring S. The current flowing through the two windings of N must be perfectly equal, and the regulating resistance R, and ammeters B and B', are inserted for purposes of adjustment. The current from C must flow in a direction opposite to that which flows from D.

[Ill.u.s.tration: FIG. 39.

H, H', containers; M, mercury; E, paraffin oil; T, T', terminals; C, suspending rod; D, base; F, F', dipping rods.]

The local circuit of the relay is completed by means of a copper dipper in mercury, somewhat resembling an ordinary mercury break, but modified to suit the present requirements. The arrangement will be seen from Fig. 39.

The whole of the {82} moving parts are made as light as possible, and for this reason the rod C and the dippers F, F' should be made as short as convenient. The containers H, H' are separate, of cast iron, and rectangular in shape. The dipper is of very thin copper tube--an advantage where alternating current is to be used--and is made adjustable for height on the suspending rod C. The leg F is of such a length that permanent contact is made with the mercury in the container H, while the leg F'

clears the surface of the mercury by about 1/4 inch, when the armature of the relay is in its normal position. To prevent undue churning of the mercury, which would necessarily take place if the dipper entered and left the mercury at each movement of the armature, a pointed ebonite plug is inserted in the end of the tube. This will be found to give good results at a high speed, the mercury being practically undisturbed, and the production of "sludge" reduced to a minimum. To prevent oxidation of the mercury, and to prevent arcing, the surface is covered with paraffin oil. If this is not sufficient to prevent arcing a condenser should be shunted across the {83} containers. The volume of mercury, and the area of the dippers, should be sufficient to carry the current used for a considerable period without heating up to any extent. An adjustable weight J is provided in order to balance the armature and dipping rod.

The remaining transmitting apparatus consists of the battery D^2 and the usual wireless apparatus. The double-pole two-way switch B' is to enable the photo-telegraphic set to be switched out and the hand key W switched in for ordinary signalling purposes. The battery D^2 should be about 12 volts.

RECEIVING APPARATUS

The wireless portion of the receiver is similar to that given in Fig. 22, is of the usual syntonic type, and comprises an oscillation transformer, S being the secondary, and P the primary; C' is a block condenser, and C a variable condenser. The detector D is of the carborundum crystal or electrolytic pattern. A two-way switch B is provided so that the relay U can be switched out and the telephones J switched in for ordinary receiving purposes. The relay U is a Brown's telephone relay.

[Ill.u.s.tration: FIG. 40.]

_The Receiver._--The magnified current from the relay U is taken to a special telephone receiver, the construction of which is given in Fig. 40.

The diaphragm F is about 2-1/2 inches diameter, and should be fairly thin but very resilient. Only one {84} [Ill.u.s.tration] [Ill.u.s.tration] coil is provided, and this should be wound with No. 47 S.S.C. copper wire for a resistance of about 2000 ohms. By using only one coil and therefore only one core, the movement of the diaphragm is centralised. To the centre of the diaphragm a light steel point is fastened, about 1/2 inch long, and provided with a projecting hook H. An enlarged view of this pin is given in Fig. 41. The movement of the diaphragm and consequently of the steel point P is communicated to a pivoted rod R, which is of special construction. A piece of aluminium tube 3-3/4 inches long, and of the section given at B, is bushed at one end with a piece of bra.s.s of the shape shown in Fig. 41a.

A stiff steel wire T about 1 inch long (20 gauge) is screwed into the end of Z, and carries a counterbalance weight C. A hardened {85} steel spindle, pointed at both ends, is fastened at D, and runs between two coned bearings, one of which is adjustable. The underside of Z is flattened, and a small coned depression is made for the reception of the pointed end of the pin. By means of the spring J the two pieces, Z and P, are held firmly together, at the same time allowing perfect freedom of movement. The bridge G is made from a piece of sheet aluminium placed in a slot cut in the tube R, the end of the tube being pressed tight upon G, and secured by means of a small rivet.

The optical arrangements are as follows. By means of the Nernst lamp L, and the lenses B and B', Figs. 42 and 43, a magnified shadow of G is thrown upon the screen J. When the shutter G is in its normal position (_i.e._ at rest), its shadow is just above the small hole in J, and light from L reaches the photographic film wrapped round the drum V of the machine.

[Ill.u.s.tration: FIG. 42.

J, screen; L, Nernst lamp; G, shutter; B, condensing lens; B_1, focussing lens.]

When, however, signals are sent out from the transmitting apparatus, the magnified current from the relay U energises the coil of the special telephone S, attracting the diaphragm F, and consequently giving movement to the pivoted rod R. As by means of the optical arrangements a {86} magnified movement as well as a magnified image of G is thrown upon the screen J, the shadow of G will, when the telephone S is actuated, cover the hole in the screen, and prevent any light from reaching the film on V, until current from the relay U ceases to flow. Therefore, when the stylus of the transmitter traces over a conducting strip on the metal print, no light reaches the film on V, but when tracing over an insulating strip the shadow of G on the screen J rises, and the light from L reaches the film.

By this means a positive picture is received, which is a great advantage where the photographs are required for reproduction. Atmospherics would be represented by irregular transparent marks on the film after development, and these can be easily eradicated by retouching.

[Ill.u.s.tration: FIG. 43. E, ebonite screen; F, focussing lens; G, shutter; O, condensing lens; L, Nernst lamp.]

The drum of the machine moves laterally 1/75th of an inch per revolution, and the hole in the screen is 1/90th of an inch in diameter. As the screen J is not in direct contact with the film, the slight diffusion of the light that takes place will produce {87} a mark of about the right thickness.

With a movement of the diaphragm of only 1/40000th of an inch, the actual movement of G will be 1/4000th of an inch. If the optical arrangements have a magnifying power of 100, then the movement of the shadow upon the screen will be 1/40th of an inch, which will be ample to cover the aperture.

The aluminium rod R, minus the counter-weight, can be made to weigh not more than 12 grains. It is necessary to enclose the optical parts in a light tight box, indicated by the dotted lines in Fig. 43, in order to prevent any extraneous light from reaching the film.

_The Contact Breaker._--The contact breaker (L, Fig. 35), as will be seen from Fig. 44, consists of an electro-magnet N, the windings of which are connected with the battery B and the polarised relay K. The armature which is supported by the spring G carries a contact arm A, which in its normal position makes permanent contact with the contact screw T, and completes the circuit between the relay K and the telephone relay U (Fig. 35). As soon as the transmitter sends out the first signal, the magnified current from the telephone relay actuates the relay K, which in turn completes the circuit of the contact breaker. Directly the armature M has been attracted, the contact with T is broken, and A makes fresh contact with the screw H, by means of the spring Z {88} fastened to the underside of A. The armature, once it has been attracted, is held in permanent contact with H by the catch S, independent of the magnets N. As soon as contact is made with H, the clutch (F, Fig. 35) circuit is completed, and the circuit of the relay K is broken. When the circuit of the clutch F is broken by means of the circuit breaker C on the machine (Fig. 36), the stop S is pulled back by hand, allowing the contact arm A to rise, and again make fresh contact with the contact screw T.

[Ill.u.s.tration: FIG. 44.]

DRIVING APPARATUS

_The Friction Brake._--This consists of a steel disc A, Fig. 45, about 2-1/2 inches diameter and 3/8 inch or 1/2 inch wide on the face, secured to the main shaft of the driving motor. The arm H, pivoted at C, carries at one end the curved block B, which is faced with a pad of tow F. The other extremity is pivoted to the steel rod P, which slides {89} [Ill.u.s.tration]

in holes bored in the standards J. One end of the rod P is screwed with a fine thread, about 75 to the inch, and is fitted with a regulating wheel T, by means of which the block B can be made to press upon the disc A with any required degree of pressure. A fairly stiff steel spring R is placed upon the rod P, between one standard J and the collar N. As the speed of the driving motor is slightly in excess of that required by the machine, the block B, by means of the wheel, is made to press upon the disc A, setting up friction which reduces the motor speed until the isochroniser indicates that the correct working speed has been attained.

_The Clutch_.--The details of this will be seen from Figs. 46 and 47. It consists of a steel shaft coned at both ends running between two countersunk bearings, one of which is adjustable. This shaft carries the two portions of the clutch A and B, the portion A being a fixture on the shaft, and the portion B running free upon it. The portion B is a gun-metal casting bored to run accurately upon the steel shaft. A soft iron annular ring is fastened to the face.

[Ill.u.s.tration: FIG. 46.

E, spindle; R, bobbins; P, iron cores; D, copper rings; T, brushes; N, back plate; V, front plate; J, gearing; S, spring; H, collar; Z, iron ring; F, fixed bearing; C, insulating bush.]

The portion A consists of a gun-metal casting {90} [Ill.u.s.tration] bored a tight fit for the shaft E, secured by means of a set screw. The two magnet cores P are screwed into the front plate V, which is also of gun-metal, and after the bobbins R have been slipped on, the shanks of the cores are pa.s.sed through holes drilled in the f.l.a.n.g.e N of the main casting and held in place with nuts. The faces of both A and B must be turned perfectly square with the shaft, so that they run accurately together. The portion B is {91} kept in contact with A by means of a spring S, the pressure being regulated by the collar H. Current is taken to the magnets by means of the two insulated copper rings D mounted upon the body of A. The gear-wheels on both portions have teeth of very fine pitch, the number of teeth on each being regulated by the speed of the driving motor and the required machine speed. Connection with the circuit breaker L and the battery B^2 is made with the collecting rings D by the brushes T. The complete connections are given in the diagram Fig. 51.

_The Isochroniser._--This is a device for ensuring the correct speed regulation of the driving motors, and is shown in detail in Fig. 48. It comprises two portions, one portion being rotated at a definite speed by electrical means, and the other portion rotated by the driving motor.

The main portion consists of a metal tube N, bushed at both ends, the bottom end of the tube being arranged to work on ball-bearings. An ebonite bush C carries three copper rings T, T^1, T^2, and the brushes R, R^1, R^2 are in electrical contact with them. The ebonite plate J, 3-1/2 inches diameter, is secured to the top end of N, and carries a contact piece Q, shown separate at E. As will be seen this is a block of ebonite with three contacts arranged on the top surface. The middle contact P is 1/64th of an inch wide, and the contacts P^1 {92} and P^2 are placed on either side at a distance of 1/16 inch; the contact strips P^1, P^2 carry the bra.s.s pins D, which are about 1/16 inch diameter, and s.p.a.ced 3/8 inch apart. A connecting wire is carried from the contact P to the copper ring T, another from P^1 to T^1, and one from P^2 to T^2.

[Ill.u.s.tration: FIG. 48.

N, bra.s.s tube; S, bushes; G, ball-bearing; H, gear-wheel; T, T^1, T^2, copper rings; C, insulating block; R, R^1, R^2, brushes; J, ebonite disc; Q, contact block; D, metal pins; O, pulley, P, P^1, P^2, contact plates; K, needle; Z, spring; W, steel rod; E, countersunk bearing.]

The bushes S are bored a running fit for the steel rod W (shown separate at A), which is coned at both ends, and runs between two countersunk bearings, the bottom bearing E being fixed while {93} the top bearing (not shown) is adjustable. A needle K is fastened near the end of the rod W, and attached to this needle is the spring Z, which presses lightly but firmly upon the contact block Q. To provide a level surface for Z to work over, the s.p.a.ces between the contact pieces are filled in with an insulating material, and the whole surface finished off perfectly smooth. The spring Z is 1/8 inch wide for portion of its length, but at the point where it presses upon Q it is reduced in width to 1/64th of an inch (see Fig. 48). The driving arrangements are as follows. A counter-shaft Q, Fig. 51, fitted with a grooved pulley, is run in bearings parallel with the shaft W, and is connected by suitable gearing to the shaft of the driving motor, so that the needle K makes one revolution in about 2-1/2 seconds. A belt pa.s.sing over the pulleys connects the two shafts, and the tension of the belt is regulated by means of an adjustable jockey pulley.

The tube N, carrying the disc J, must be rotated at a fixed speed, and this is accomplished in the following manner. An ordinary electric clock impulse dial, actuated from a master clock, is connected by suitable gearing H, so that the tube N makes exactly one revolution in 2 seconds; it being possible to adjust an electric clock of the "Synchronome" type, so that it only gains or loses about 1 second in 24 hours, and this provides {94} an accuracy sufficient for all practical purposes. The connections are given in Fig. 49, and the face of the instrument in Fig. 50. It will be seen that a connecting wire is run from the steel spindle W to one terminal each of the lamps L, L^1, L^2, and from the other terminal of the lamps to one terminal of the batteries J, the battery comprising a set of three 4-volt acc.u.mulators. The other terminals of the batteries are joined one to each of the brushes R, R^1, R^2.

[Ill.u.s.tration: FIG. 49.]