US2662991A - Arc lamp regulating device - Google Patents

Description

Dec. 15, 1953 E. GRETENER ARC LAMP REGULATING DEVICE Filed Dec. 29, 1949 2 Sheets-Sheet J Dec. 15, 1953 E. GRETENER ARC LAMP REGULATING DEVICE 2 Sheets-Sheet 2 Filed D96. 29, 1949 v w W 0 z g 5 7 a i w i 3 n 5 t 4 m M Patented Dec. 15,1953

UNITED STATES PATENT orrlcs Claims priority, application Switzerland December 30, 1948 8 Claims. (Cl. 314--20) The present invention relates to an improved system for regulating the feed and position of the positive electrode of an arc lamp and more particularly, although not exclusively, of a high intensity lamp such as is used for the projection of motion pictures in cinemas. Such projection in many cases includes reproduction of sound from films. As stated, the invention is not, of course, limited to this precise use as it is also applicable to are lamps generally.

For the steady and proper projection of motion pictures it is of the utmost importance for the arc and, in particular, the positive crater of the arc, to be kept constantly in the focus of the illumination system, consisting for example, of a mirror or condenser lens system.

Systems have therefore been evolved for effecting the control of the carbon feed and regulating the arc position. Of particular interest is the present system in which an image of the arc is projected on to a radiation sensitive device such as a photo cell, bimetal or the like which, in turn, controls the carbon feed mechanisms. The radiation sensitive device is influenced by the difference in intensity of the arc and the incandescent ends of the electrodes. Because the arc and are flame occupy an appreciable space and, in addition, continually vary in intensity, it has been difficult to effect a very exact regulation as considerable variation in the position of the arc and are crater can take place before the feed control mechanism operates owing to lack of contrast in the radiation of the projected image.

A further disadvantage with the less expensive type of lamp is that the positive carbon is not rotated during burning and consequently the end burns unevenly and with a deep crater which adds to the difliculty of making the regulation system sensitive. The expense of the comparatively intricate mechanism necessary for rotating the carbon is often prohibitive and the rotating mechanism itself may be a source of trouble.

It is an object of the invention to provide an improved regulation system which overcomes these difficulties and, at the same time, attains an optimum sensitivity of the regulation system by producing the maximum light or radiation intensity contrast between the arc and the end of the positive electrode and maintaining a substantially vertical front to the burning end of the positive electrode without employing a carbon rotating mechanism.

One form of the present invention comprises a system for regulating the feed and position of the positive electrode of an arc lamp by projecting an image of the are at the end of the positive electrode on to a radiation sensitive device such as a photo electric cell and circuit to contrast the radiation of the projected image either with a standard or to obtain a differential value between images of the arc flame and the electrode end, which device, in turn, controls the feed mechanism.

According to the invention, the object above mentioned is achieved in part by making use of an arrangement wherein the contrast is enhanced by concentrating the arc and are flame into the space before the positive crater by means of a coaxial air stream which also serves to secure a substantially vertical front to the burning end of said electrode.

For the better understanding of the invention reference is made to the accompanying drawings, wherein like numerals refer to like parts throughout:

Fig. 1 illustrates schematically an arrangement as used in conjunction with an unblown arc.

Fig. 2 illustrates diagrammatically the light distribution curve of an unblown arc of the kind shown in Fig. 1.

Fig. 3 illustrates a plan view partly in section of one embodiment of an improved regulation system according to the present invention.

Fig. 4 illustrates diagrammatically the light distribution curve of a blown arc lamp as used according to the present invention.

Figs. 5 and 6 illustrate in elevation details of the carbon feed mechanism shown in Fig. 3.

Figs. 7 and 8 illustrate modifications of the circuit arrangement forming part of Fig. 3.

Fig. 9 illustrates a plan arrangement of the arc system when used in conjunction with the modification shown in Fig. 8, and

Fig. 10 illustrates a plan view of a further modification of the invention employing a bimetallic strip as the radiation sensitive device.

Fig. 1 of the accompanying drawings illustrates an unblown are light. The positive electrode is shown at H and the negative electrode at l2; the arc is struck between these two electrodes and the anode flame l3 burns upwards due to the usual thermal eifect. At the same time a deep crater I4 is formed in the positive electrode II and unless mechanism is employed for rotating the positive electrode the end thereof tends to burn unevenly and thus form a badly shaped arc.

Such an image of the are (shown in dotted lines) is formed by an optical system l5 below a diaphragm 26 having a slit 21 through which light passes and influences a radiation sensitive device disposed beneath the diaphragm and controlling, in turn, the feed mechanism for the positive electrode.

The light distribution of an ordinary unblown are as shown in Fig. 1 follows approximately to the curve 18 shown in Fig. 2 in which the abscissa Iii-i6 indicates the relative position of the carbons and the ordinate l1-l1 indicates light intensity. It will be seen that comparatively large movements of the arc position can take place along the abscissa l6-i6 on each side of the ordinate l1-i 1 without any great or critical variation in light distribution. This, however, is a disadvantage as the most intense part of the arc is the crater M in the positive electrode II which consequently is likely to fall outside of focus of the illumination system as a whole. Such unblown arcs also tend to form a deep crater which becomes partly hidden by the electrode shell, thereby re iuc 'nq the intensit contra t.

It has been found necessary to select a definite part of the arc image for efiecting optimum regulation. If the are or are flame in front of the positive carbon is chosen for this purpose it is not possible .to achieve a high degree of accuracy because of the continual variations in the radiation intensity caused by the flickering of the flame and uneven ends of the carbons. The crater at the burning end of the positive carbon of such unblown arcs is also not very suitable because (a) not only does the end change shape during burning unless rotated, (b) the mechanism for doing which isan undesirable expense, but (0) the difference in intensity between the deep and partly hidden crater and the incandescent end of the carbon is not suflicient to obtain a definite and critical line of contrast demarcation which is necessary to satisfactorily afiect the radiation sensitive device and operate the feed mechanism is close correlation with the position of the arc crater.

These disadvantages are overcome in the present invention by using a concentric air-stream to concentrate the anode flame and are into the cylindrical spacein front of the positive crater in conjunction with the radiation sensitive device.

Fig. 3 illustrates one such improved arrangement. The positive carbon is again shown at H and the negative carbon at 12; the positive carbon II is supported by a positive head I9 with the crater H extending substantially beyond the edge thereof as shown in Figs. 3, 9 and 10. The positive head i9 is provided with a hollow space 20 into which compressed air is blown at 2|. This air issues out of the holes 22 and concentrates the arc and are flame in front of the positive crater M, the air and arc gasses shown at 23 being drawn or sucked away through a pipe at 24 around the negative carbon.

The anode flame fills up the space between the crater ll of the positive carbon Ii and the tip of the negative carbon l2 as a radiant lighting cylinder of concentrated and great light inten sity, the arc crater it being quite shallow and the crater edge square. This results not only in a relatively high contrast in radiation intensity between the end of the carbon II and the arc crater itself but also ensures that the end of the positive carbon burns evenly and with a substantially vertical front.

Fig. 4 illustrates this graphically and shows the light distribution curve of the are when formed and blown between the two electrodes II and I2 in accordance with the arrangement illustrated by Fig. 3. The abscissa l8-l6 again shows the relative positions of the carbons and the ordinate l1-l1 the light intensity value. It will be seen that the light reaches an intense critical peak adjacent the shallow crater H of the positive carbon II and falls of! very rapidly on either side. The sharply defined line of demarcation 25 corresponding to the end of the crater in the positive carbon II is particularly suitable for obtaining an exact and definite regulation of the positive carbon feed because of the contrast in intensity between the brilliant shallow unhidden crater l4 and the glowing end of the electrode itself. This sharply defined line of contrast is available for practical control purposes only where the crater in positive electrode ll extends substantially beyond any mounting means so that it is not shielded thereby and is freely available.

An image of the positive crater i4 is projected by the optical system 15 onto the slit 21 in the diaphragm 26 as shown in Fig. 3 and the radiation passing through the slit falls on a radiation sensitive device 28 illustrated by way of example only as a photo-electric cell. It will beappreciated that should the positive carbon ii burn back too far or be advanced too far by the feed mechanism the sharp peak of the light distribution curve in Fig. 4 will move away from the slit 21 with the consequential effect that the photopoint of the positive carbon with crater it protruding substantially therefrom. Consequently the current passing through the photocell will vary and these variations will control the carbon feed mechanism.

In the embodiment of the invention illustrated by Fig. 3 the light sensitive device 28 isconnected to the control grid 29 of a multigrid electron discharge tube 30 such as a glow lamp or the like. The voltage supply for the discharge tube 38 is applied at 31. Tworesistances 32 and 33 are suitably chosen to apply a constant voltage on the stabilising grid 35 of the discharge tube 39, which has the effect of eliminating disturbances otherwise caused by any fluctuations in the voltage 3I and enables the glow discharge tube til to operate consistently. The current from the anode 35 of the discharge tube 30 flows through the coil of an electro-magnetic system 36, shown in Fig. 5, controlling a clutch 31, shown in Fig. 6, which, in turn, controls the drive of the positive carbon feed mechanism 38.

The arrangement shown in Fig. 3 operates so that the crater I4 is always held at the focus of the illumination system. This may be accomplished as follows:

The positive carbon I i is fed in known manner at substantially; or slightly faster than, its normal burning rate by means of the feed mechanism 38. As already mentioned, an image of the arc crater i4 is formed at the slit 21 and falls upon the cell 28 which, at a predetermined light or radiation intensity, allows sufficient current to flow through it to influence the control grid 29 which also, at a predetermined value triggers the electron glow discharge tube 30 which forms a discharge between the main electrodes or disengaged, according to the method of carbon feed employed, to feed, or stop feeding, the

carbon.

For example, the positive carbon feed mechanism and the regulation system may be arranged so that should the end of the carbon and therefore the image of the crater H be advanced beyond the slit 21 and the comparatively dark end of the carbon H be focused on the cell 28 its current would drop so that, in turn, the discharge tube 30 would cease to glow and the failure of the discharge between electrodes 85 and 39 would prevent current flowing through the magnet coil 4|). This action would release the armature 42 which momentarily stops the carbon feed mechanism until the arc burns back into position again.

Due to the comparatively sharp line of demarcation 25 between the arc crater l4 and the end of the electrode II with a blown arc, a characteristic absent from an unblown arc, the system can be arranged so as to be very sensitive and in practice keep the arc crater |4 virtually constantly at one focus of lens I5.

Fig. 6 illustrates details of the form of clutch which it is preferred to use in conjunction with the present invention. The clutch device comprises a small shaft 44 which is rotated at a constant speed by a suitable source of power such as a small synchronous motor (not shown). The shaft 44 is mounted in bearing 45 and extends as far as the end 45. A further shaft 41 mounted in bearing 48 and co-axial with the shaft 44 has its end 49 positioned closely adjacent to the end 46 of the shaft 44. The shaft 41 is connected to, and drives, the feed mechanism 38 when it is coupled to the shaft 44. The coupling between the two shafts is effected by means of a spring 43 which is coiled partly round the end of the shaft 41 and partly round the end of the shaft and normally grips both shafts sufficiently tightly to transmit torque from the driving shaft 44 to the driven shaft 41. However, in order to control the clutch the spring 43 is provided with an elongated end 58 which is engaged or disengaged by the hooked end 5| of the armature 42 according to the position of the latter.

It is, of course, only a matter of design whether the hooked end SI of the armature 42 engages the end 50 of the spring 43 when the armature 42 is attracted by the magnet 4| or when it is not attracted and is free therefrom.

The arrangement shown in Figs. 5 and 6 issuch that when the armature 42 is released its end 5| engages and holds the end 58 and the spring 43 against clockwise rotation. The shaft 44 will still continue to rotate but spring 48 will not then transmit any torque to the shaft 41 which will become stationary and no longer drive the carbon feed mechanism 38.

Alternatively, of course, the electro-magnet system 4|, 42 can be reversed in position and operation so that the clutch operates in the reversed manner, that is to say, so that when the armature 42 is released it is held free from the end 50 of 6 the spring 48, whilst the feed mechanism 88 continues to operate, and hook 8| only engages the end 58 of the spring 48 to stop the feed 38 when armature 42 is attracted by the magnet 4|.

The invention is not restricted to the precise circuit arrangement shown in Fig. 3 which is presented by way of example. Fig. 7 illustrates one alternative arrangement and is equivalent to the arrangement shown in Fig. 3 except that the cell 28 is replaced by a balancing resistance 88 and 8| and the discharge tube is provided with a cold cathode 82 which is made radiation sensitive and takes the place of the cell 28. The image of the arc crater I4 is projected through the slit 21 on to the cold cathode 62 which becomes electron emissive at a definite light or radiation value, whereupon the discharge tube 38 becomes conducting and operates the electro-magnet 4| in the same manner as described with reference to Fig. 3.

Fig. 8 illustrates a further alternative arrangement to that shown in Fig. 3 and provides two photo-cells 10 and 1|. This arrangement has the advantage that it provides a very high sensitivity to small contrasts at the end of the burning electrode I The two photo-electric cells act as a potentiome er in a differential arrangement and actuate the gas discharge tube 30. As shown in Fig. 9. the light source is imaged on the two cells 1|) and 1| which are situated behind a diaphragm14 having two slits 15 and 16. The arrangement is such that in the correct position of the are an image of the end of the carbon II is projected on one cell 10 and an image of the concentrated arc light or crater H on the other cell 1|.

The controlling action of this arrangement is no longer based on the actual difference in in tensity of the illumination but only on the relative differences of the illumination density on' both the cells 10 and 1|. Very small changes in the relative light intensity falling upon the cells 10 and 1| are sufficient to produce a very high change in the voltage on the grid 12 of the discharge tube 80 of Fig. 8 which is triggered accordingly.

Fig, 10 illustrates a still further embodiment of the invention. Whilst this embodiment operates in the same way as that shown in Fig. 3 thepell 28 is replaced by a different radiation sensrtire device comprising a bimetallic strip 80 which is deflected in well-known manner according to the momentary intensity of the radiation falling upon it and may be connected as a regulation device for the carbon feed.

In order to increase the contrast effect of the are image a colour selective system may be em ployed and may consist, for example, of a filter 8| which may be introduced into the beam between the arc and its image as shown in Figs. 3, 7, 8 and 9 and which may be an infra-red filter which eliminates a higher percentage of the radiation from the glowing end of the electrode than from the actual arc crater. Again, the filter 8| may be an absorption filter or it may be a reflection filter which allows the short-wave radiation to pass through and reflects the long-wave radiation.

In a further modification the surface of the bimetallic strip 88 may be coloured to enhance the radiation selective action; for example, a rei colouring or a gold coating absorbs the short wave radiation and produces a higher reflection of the long-wave radiation.

A colour selective filter 8| may, of course, be

introduced in the beam between the arc and its image formed on the radiation sensitive element as shown in Fig. 10 in order to intensify still further the contrast of the projecting image.

Finally, the cathodes of the photo-cells 28, I and II used in the embodiments described above may be made colour selective, for example, by using a potassium coating which is particularly sensitive to short-wave radiation.

The foregoing disclosure is presented by way of example and is not to be taken as limiting. The invention is set forth in the following claims which are intended to cover such other forms as may fairly and properly be regarded as falling within the spirit of the invention.

I claim:

1. In a regulating device for high intensity are lamps, a frame member, a negative electrode, a positive electrode, air projecting means surrounding said positive electrode said positive electrode protruding substantially from said air projecting means toward said negative electrode, said air projecting means directing from the rear towards the arcing end of said positive electrode an air blast which surrounds the arc discharge as a substantially concentric hollow tube of air slightly converging towards said negative electrode, concentrating the anode flame coaxially with said electrode and causing said are to burn with a substantially flat positive crater disposed at right angles to the axis of the carbon and yielding a critical light distribution characteristic curve having a peak ordinate with a value at least twice that of the effective base thereof and providing a high contrast of brilliancy at the separation edge of said positive electrode between said electrode and said are said high contrast separation edge being unobstructed by said air projecting means, radiation sensitive means, radiation condensing means mounted to focus an image of the said separation edge on said sensitive means, and carbon positioning means controlled by said radiation sensitive means, whereby the position of said separation edge with respect to said frame member is maintained with great precision.

2. In a regulating device for high intensity are lamps, mounting means, a negative electrode, a

- positive electrode, air projecting means surrounding said positive electrode said positive electrode protruding substantially from said air projecting means toward said negative electrode, said air projecting means directing from the rear towards the arcing end of said positive electrode an air blast which surrounds the arc discharge as a substantially concentric hollow tube of air slightly converging towards said negative electrode, concentrating the anode flame coaxially with said electrode and causing said arc to burn with a substantially fiat positive crater disposed at right angles to the axis of the carbon and yielding a very critical light distribution characteristic curve having a peak ordinate with a value at least two and a half times that of the effective base thereof and providing a high contrast of brilliancy at the separation edge of said positive electrode between said electrode and said arc said high contrast separation edge being unobstructed by said air projecting means, a photoccll, radiation condensing means to focus the said separation edge on said photocell, a voltage divider, a cold-cathode gas discharge tube having its control grid connected to said photocell and having its stabilizing grid connected to a suitable tapping point of said voltage divider connected 8 to the cathode and the anode terminals of said discharge tube, and carbon positioning means controlled by said discharge tube, whereby the position of said separation edge with respect to said mounting means is maintained with great precision.

3. In a regulating device for high intensity are lamps, a negative electrode, a positive electrode. air projecting means surrounding said positive electrode said positive electrode protruding substantially from said air projecting means toward said negative electrode, said air projecting means directing from the rear towards the arcing end of said positive electrode an air blast which surrounds the arc discharge as a concentric hollow cone of air slightly converging towards said negative electrode, concentrating the anode flame coaxially with said electrode and causing said are to burn with a substantially flat positive crater disposed at right angles to the axis of the carbon and yielding a highly sensitive light distribution characteristic curve having a critical peak ordinate with a value at least two and a half times that of the eflective base thereof and providing a high contrast of brilliancy at the separation edge of said positive electrode between said electrode and said are said high contrast separation edge being unobstructed by said air projecting means, a cold-cathode gas discharge tube with radiation sensitive cathode, radiation condensing means to focus the said separation edge on said radiation sensitive cathode, a voltage divider, the stabilizing grid of said discharge tube being connected to a suitably chosen tapping point of a said voltage divider connected to the cathode and anode terminals of said discharge tube, and carbon positioning means controlled by said discharge tube whereby the position of said separation edge with respect to the stationary part of said lamp is maintained with great precision.

4. The combination set forth in claim 1, in which the radiation sensitive means are made selectively responsive to radiation, yielding higher efficiency for radiation emitted by said arc but lower efliciency to radiant heat emitted by said positive electrode, whereby the effect of contrast of brllliancy of said separation edge is further increased.

5. The combination set forth in claim 1. a radiation selective filter between said arc and said radiation sensitive means and transmitting relatively short wave radiation emitted by said arc, but ejecting relatively long wave radiant heat emitted by said positive electrode, whereby the eflect of brilliancy contrast of said separation edge is further increased.

6. In means to regulate high intensity are lamps, a positive electrode, a negative electrode, air blast means surrounding one of said electrodes to project a blast of air around an are between said electrodes and toward the other electrode to concentrate the arc flame between said electrodes as a short cylindrical, brilliant light source, radiation sensitive means, means to focus radiation on said radiation sensitive means and means to position one of said electrodes in response to a signal from said radiation sensitive means, said radiation sensitive means being selectively responsive to radiation, yielding higher emciency for radiation emitted by said arc and lower efficiency to radiant heat mitted by said positive electrode, whereby the effect of contrast of brilliancy of said separation edge is further increased.

7. In means to regulate high intensity are 5 trodes as a short cylindrical brilliant light source, radiation sensitive means, means to focus radiation on said radiation sensitive means and means to position one of said electrodes in response to a signal from said radiation sensitive means, said radiation sensitive means being selectively responsive to radiation, yielding higher efficiency for radiation emitted by said are and lower efficiency to radiant heat emitted by said positive electrode, whereby the efiect of contrast of brilliancy of said separation edge is maximized.

8. The combination set forth in claim 2, a second photo cell having its anode connected to the 10 cathode of the first photo cell and an apertured light shielding means positioned between said electrodes and said photo cells.

EDGAR GRETENER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,078,913 Fleming et a1 Nov. 18, 1913 2,107,148 Gretener Feb. 1, 1938 2,136,670 Brenkert Nov. 15, 1938 2,150,014 Walter Mar. 7, 1939 2,160,490 Strong May 30, 1939 2,469,664 Murch May 10, 1944 FOREIGN PATENTS Number Country Date 240,541 Switzerland Dec. 31, 1945

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