US1779545A - Timer for electric circuits - Google Patents

Description

Oct. 28, 1930. A. R. JOHNSON TIMER FOR ELECTRIC CIRCUITS Filed Jan. 6, 1928 [/v VENTOR firaen E. Job/250M I the length of time an electric circuit is to be Patented Oct. 28, 1930 PATENT OFFICE ARDEN R. JOHNSON, OF ST. CHARLES, MISSOURI TIMER FOR ELECTRIC CIRCUITS Application filed January 6, 1928.

This invention relates to timers for electric circuits, and particularly to photographic print timers. It has for one of its ob ects providing means for automatically timing closed. The particular application of the timer in this case is to the exposure of sensitized photographic sheets to the light of an electric lamp. The invention has for a fur- 1O ther object providing means for enabling my invention Fig. 2 is an enlarged rear View of the apparatus with the rear side of the casing removed; Fig. 3 is a sectional new of the same along the line 3-3 of Fig. 2; and Fig. 4: is an enlarged sectional view along 25 the line 44 of Fig. 3.

The operation of the timing apparatus which I provide depends primarily on the swinging of a pendulum which, as 1t swings, closes and opens an electric circuit and this, in turn,operates an electric light to which the sensitized photographic sheet is exposed. 13y suitable adjustments, the time during whlch the current is passed through the lamp can be controlled, and the time of exposure thus can be made as little or as much as may be desired.

The apparatus, for convenience, is mounted in a casing 5 in the upper portion of which is a horizontally mounted supporting rod 6. To this rod is rotatably suspended a pendulum rod 7, and a pendulum bob 8 is fixed to the lower end of the rod. The length of the pendulum rod may be whatever is convenient for the particular use, but I prefer, ordinarily, a rod which is about twelve inches long from its point of suspension to the center of the pendulum bob; and the bob, in this instance, has a diameter of about two inches. However, it is to be understood that these Serial No. 244,825.

dimensions are not an essential part of my invention.

The pendulum, as described, has a time of complete oscillation of about one second. Any convenient means may be provided for releasing the pendulum and for stopping it after each complete oscillation has been made. I prefer, for the purpose, a pawl 10 which is pivoted to the pendulum rod and which has a tooth 11 which is adapted to coact with a pin 12 fixed to lever 13. This lever has its fulcrum 14 fixed to the side of the casing and it is resiliently held in the normal position indicated by a spring 15. Fixed to the fulcrum 141, preferably on the outside and on the front of the casing, is an operating arm 16. In order to release the pendulum the operator presses downwardly on the arm 16, a flange 17 being provided for this purpose. This rotates the lever 18 so as to carry the lower end to the right and bring the inclined surface 20 of the pawl against a projection 21, so that the pawl is forced upwardly with reference to the pin 12 and is released from coaction with the pin. This releases the pendulum and allows it to oscillate. But, ordinarily, as soon as the pendulum is released, the operator releases the arm 16 and the spring 15 forces the arm upwardly against a stop 28 and the lower end of the lever 13 is again brought back to normal position so that the pawl 10 again coacts with the pin 12 as soon as the pendulum has made a complete oscillation. Theinclined surface 20, coacting with the pin 12, raises the pawl upwardly as the pendulum returns until the pin passes off from the surface and is caught by the tooth 11.

The lamp 54 is used, as hereinafter described, for printing the photographs, and the means for controlling the light of the lamp comprise an electric circuit consisting of the wires 23 and 24. The wire 23 passes to the lamp 54: in the ordinary manner and the wire 24 passes to any suitable source of electric supply 25 and thence, by the wire 26, to the lamp. The wire 23 is electrically connected to a switch terminal 27 which is fixed toan arm 30. The arm 30 is rotatably mounted in any suitable manner. In this instance,

V I prefer to suspend it rotatably on the rod 6.

contact with the terminal 27 and the lamp circuit will be closed. Asth e arm 3Q is ro tatably mounted, when the" contact occurs the arm will be carried with the pendulum rod,

normally adjusted siti n, eeliersi e fier; described, and the contact between the terminals will be broken. Hence, the lamp Wlll be operated only during that portion ofthof complete oscillation that the two switch terminals are in contact In order to adjust the time of operation of the lamp, means are provided for varying. at will the position ofthe contact 27. I pre:

. fer, for this purpose, an arm 32, also rotatably mounted on the rod Gbutrigidiyfixed'to the arm 30 sov that the position of the arm 30 canbe controlled by the positionoi the arm 32.

the casing. The arm 35 is fixedto a segmen-v tal member 36 which is rotatably; suspendedby the rod 6, or in any other suitablemanner. Obviously, byfvarying the position. of

the member 36, the position oi..tl1e.'ro d.3O and, hence, of. the contact27, will be varied.

The lower edge ofLthe segmental member.

r and 31 will be relatively positioned sothat they will be in contact for one second. during the swing of the pendulum. Or, if the pointer points to the line 41, the terminals will be in contactior half a second. Hence, by

positioning the pointer with reference to the scale between the Zero 11116 and theone.sec.

0nd line, the fraction of a second of time desired to operate thelamp will be obtained.

Ifit is desired -to operatethe' la'mp more than onesecond with the apparatus described herewith, the operator can hold the arm 16 down and the'pendulum will then maketwo complete oscillations, or as many complete oscillations as may be desired. However, it several oscillations are required, it may be necessary forthe operator t o'j relejase the arm after two'or three oscillations sojwas to give the pendulum an additional impulse. It will-be understood that in increasing the length of time beyond one second; any addi- The arm 32crosse's a slot,33.in the cas ing. Passing through this slot. and. under; the arm 32, thus suspending the arm, is a. fia nge34; fixed to another arm. 35 'outsidexof' tional fraction of a second may be obtained by suitably adjusting the position of the contact 27. For instance, if a second and a half is required, the pointer would be set for about, three-fourths of asecond so that, during two oscillations, the total time that the lamp, would be operated wouldbe a second anjd a half a m Although there is some lag in the intensity ofthe light, after the closing of the terminals o ftliecircuit,whichaffects the effect of a the, light onthe sensitized paper, yet, ordibut, on the return, the rod 30 'will stopatits narilytliisis compensated for by the lag in the dyingdownoithe light when the contacts are broken. s6 that, for ordinary lights at least, this lagis immaterial,

The. particular application of myinv en-v tionin this case is to the printing of photo.-

other reasons, and for this-purposeiI provide in, the casing an opening 46 across whichlare, mounted strips of selected IlGgablVBSflQllllDI'lS:

ing, inthisinSfiaI Ce, strips 46, 47 and i8 The negative 48 is more densethan the others and the, negative LT -is more so than the negative 16; Back otthis opening, I place alamp. 50.

This lamp maybe supported in suitable I manner 5 for example, by meanj of abra cket 51, in the front of the openingj52 in the rear side of the casing. Obviously, the; operator in iron; of. the caS ihgZwiIL Zbe. able tofobser ve.

the effect of the an the different. nega tives 1 6,- 4? and 4 8, and thefinteiisityfof the light will vary with reference to the relative densities of the negatives.

Any sutable means may be usedior, exposing the sensitized puatst the light when. the

timer is used for photographic:purposes; I prefer to use the following described 'ratus, Theprinting lamp Misenclosedia a, cas ng 53. Abovev the printing lamp, is'

mounted a .trans aarent plate :55 on which is placedthe negative. 56' and the sensitized paper- 52, m any prdinary manner.

In determiningjthe time or exposure de sired, the operatorplaces the negative on the platebfiand compares the {intensity or the light which reaches his eye through thenegm tive with. the intensity of the light passing through the negatives 46, 1-? and d8, 'Ihee iposure necessary for a ,p articular negative showing ,a light intensity wh ch corresponds tothelight intensity of one of thenegatives 46, 47 and48nvillbe the same as the time experimentally, determined for that ,particu; lar negativei' For instance, ifthe time exp'erimentally determined for the particular negaawisw e second,- and the lightintensit y through this negative, say 48, corresponds to the negative undertest, the exposure of the sensitiiedsheetwould be,one sec-.

ond;- In this mannenthe operator can readily determine the approximate time, and a little experience will indicate to him the exact time required for the exposure.

It will be obvious, that, having once set the apparatus for exposing a definite length of time, as many prints may be taken as may be desired without any resetting of the apparatus, as it is arranged to maintain any adjusted position indefinitely. For instance, although'the member 36 is rotatably mounted in the rod 6, a spring 60 brings the segment firmly against the wall of the casing but yields sufliciently to allow suitable rotation of the segment for a new adjustment. By means of the nut 61., the compression of the spring may be made suiiiciently great to prevent any misplacement of the segmental member by the operation of the device and, hence, when the apparatus is once set for a certain time, there will be no change which would tend to vary the time of the exposure.

I claim as my invention:

1. A timer comprising a pendulum adapted to open and close an electric circuit as it oscillates, means for oscillating said pendulum, said means comprising a pawl pivoted to said pendulum, a pivoted arm, a pin fixed to said arm and adapted to coact with said pawl when the pendulum is rotated to one side of a vertical line passing through its point of support, and means for releasing said pawl from coaction with said pin.

2. A timer comprising a pendulum adapted to open and close an electric circuit as it oscillates, means for oscillating said pendulum, said means comprising a pawl pivoted to said pendulum, a pivoted arm, a pin fixed to said arm and adapted to coact with said pawl when the pendulum is rotated to one side of a vertical line passing through its point of support, and means for releasing said pawl from coaction with said pin, said releasing means comprising means for moving said pin further away from said line, and means for releasing said pawl from said pin.

In testimony whereof, I hereunto set my hand.

ARDEN R. JOHNSON.

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