US 3853062 A Abstract The distance traversed by a spin-stabilized projectile is determined by a pendulum attached inside the fuze of the projectile so that each complete swing of the pendulum is equal or proportional to one complete revolution of the spinning shell. The distance traversed by the projectile is determined from reading of the number of complete cycles (frequency) made by the pendulum which, in turn, is equal to the number of revolutions of the spinning shell.
Claims available in Description (OCR text may contain errors) Mute States tet 1 1111 3,53,862 Cole Dec. 110, 1974 DEVICE FOR MEASURING DISTANCE OF 1,992,278 2/1935 Aliquo 102/83 TRAVEL BY A PROJECTXLE 3,297,948 1/1967 Kohler 102/70.2 R 3,353,487 11/1967 Perryman l02/70.2 R [75] Inventor: Lewis C. Cole, Chester, NJ. [73] Assignee: The United States of America as primary Examiner samuel Feinberg represented the Secretary of the Assistant Examiner-C. T. Jordan Army, Washington, DC. Attorney, Agent, or FirmEdward J. Kelly; Herbert 22 Filed; 23 1973 Berl; A. V1ctor Erkklla [21] Appl. No.: 336,663 Related US. Application Data Continuation-impart of Ser. No. 159,374, July 2, 1971, abandoned US. Cl. 102/70.2 R, 102/70 R lint. Cl F426 9/00, F420 ll/OO Field of Search lO2/70.2 R, 70 R, 79, 82, References Cited UNITED STATES PATENTS l0/l924 Hawkins 102/83 [5 7] ABSTRACT The distance traversed by a spimstabilized projectile is determined by a pendulum attached inside the fuze of the projectile so that each complete swing of the pendulum is equal or proportional to one complete revolution of the spinning shell. The distance traversed by the projectile is determined from reading of the number of complete cycles (frequency) made by the pendulum which, in turn, is equal to the number of revolutions of the spinning shell. 6 Claims, 5 Drawing Figures PAIENTEU mu: 1 0mm SETTER OUTPUT COUNTER PENDULUM DEVICE FOR MEASURING DISTANCE OF TRAVEL BY A PROJECTILE The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon. This is a continuation-in-part of Application Ser. No. 159,374, filed July 2, 1971, now abandoned. BACKGROUND OF THE INVENTION 1. Prior Art The devices which have heretofore been employed in a projectile to determine the distance traversed by the projectile have been of the type which measure the distance in accordance with elementary laws of physics. According to these well-established principles, the distance traversed by a projectile is the product of the velocity of the projectile and its time of travel and may be represented by the following equation: where s is the distance, in feet, traversed by the projectile, v is the velocity of the projectile in feet per second, and t is the time, in seconds, required for the projectile to travel the distance s. The disadvantages of the devices which are based upon this method of determination of the distance traversed by a projectile are immediately apparent from an inspection of the foregoing equation since the velocity of the projectile is not constant but rather, it is an average value which is affected by environmental conditions which may vary considerably from one time to another and from one location to another. Accordingly the distance measured using the devices which have heretofore been employed is necessarily an estimation, at best, and it is extremely difficult to preselect the exact distance which a projectile is required to travel. The uncertainties and the inherent inaccuracies which are associated with this method or means of measuring such distances are obvious limitations in those instances where accurate measurements are required and/or when the projectile is required to travel a predetermined distance with a high degree of accuracy. Accordingly, the need for a device or means which would permit accurate measurement of such distances and/or which would permit the selection of the distance of travel of a projectile in advance is readily apparent and highly significant particularly in the armament field. 2. Summary of the Invention This invention contemplates providing a means for accurate determination of the distance traversed by'a projectile. In one aspect, the present invention relates to a device which is capable of measuring the distance traversed by a projectile from the number of revolutions of the spinning shell of the projectile. In another aspect, the present invention is directed to a device which permits the selection of a predetermined distance which a projectile is desired to travel. In still another aspect, this invention is concerned with providing such a device for projectiles wherein the function of the device is unaffected by the velocity of the projectile. These and other aspects of this invention will be more clearly comprehended from the following de- BRIEF DESCRIPTION OF THE DRAWINGS The understanding of the present invention will be facilitated by reference to the accompanying drawings wherein like numerals are employed to designate like parts. In the drawings: FIG. I is a side view, partly in section, of a fuze embodying the principles of this invention; FIG. 2 is a side view, partly in section, of a projectile containing the fuze shown in FIG. 1, and FIG. 3 is a diagram illustrating the mathematical relationship between the frequency of the pendulum swings and the revolutions of the projectile. FIG. 4 is a blocked diagram illustrating one method of the operation of the device of this invention. FIG. 5 is a diagrammatic view of a fuze of this invention containing a double ended pendulum. DETAILED DESCRIPTION OF THE INVENTION It has now been unexpectedly discovered that by incorporating a novel device (to be hereinafter described) into the fuze of a projectile, the distance traversed by the projectile can be measured accurately from the number of revolutions of the spinning shell of the projectile. It has further been discovered that the device employed herein can be preset for a predetermined distance of travel by the projectile with high degree of accuracy. Basically, the principles of this invention and the device employed herein are applicable to the so-called spin-stabilization projectiles as compared to the other types of projectiles which are commonly known in the art as fin-stabilized projectiles. Examples of spinstabilized projectiles for which the device of this invention is particularly suitable include guns of various calibers, rifles, etc., and similar armaments, whereas finstabilized projectiles generally include darts, mortar shells and the like. The device of this invention (a pendulum or the like) is simply incorporated into the fuze of the projectile so that the frequency of the pendulum is determined by the frequency of the spinning projectile as will be hereinafter described in further detail. Referring now to the drawings and particularly to FIGS. 1 and 2, there is shown a fuze I mounted in the forward part of projectile 3 in the usual manner as shown in FIG. 2 and the direction of the revolutions of the spinning shell of the projectile is indicated by the curved arrows around its longitudinal axis. Also shown in FIGS. 1 and 2 is a pendulum consisting of a swing arm 5, one end of which is attached to the center of the fuze by a pin 7 or by any other suitable means and the other end of which is integrally attached to a ballor disc-like object 9. This will permit measurement of the distance traversed by the projectile from a reading of the frequency of the pendulum since the frequency of the pendulum (f,,) is equal to the frequency of the shell (f Stating it differently, each complete swing cycle of the pendulum as employed herein is equal or proportional to one complete revolution of the fuze. This one-to-one relationship can be demonstrated mathematically in connection with FIG. 3 by the following equations: wherein f 11) frequency of the pendulum L length of pendulum g acceleration due to spin force field. For small angle 6 r the radial distance from the end of the pendulum to the spin axis, w spin of round in radians per second, f frequency of spinning round in revolutions per second. It can be seen from the figure that for small angle 0, L r and the force field out due to spin can be given by g =r W2 which is equal to r times the'quantity (271-11 Substituting for L and g in the equation forfl, it cari be seen that the equation reduces to the following: From the above relationship it can be seen that the frequency of the pendulum is equal to the frequency of the projectile, that is, the pendulum makes one complete swing cycle for each revolution of the projectile. For a larger angle 0, a proportionality between pendulum cycles/projectile revolutions can be calculated. Thus, for example, it can be shown by a rigorous mathematical analysis that when 1, 99.997 pendulum cycles equal I00 projectile revolutions, while when 0 =30, 97 pendulum cycles equal 100 projectile revolutions. This can be compensated by suitably adjusting the number of revolutions preselected by the setter. When a projectile containing a fuze of the present invention is fired, the resultant setback force compels the pendulum to the start position, which is the start of the swing, as shown in FIG. 1. The instant the projectile leaves the gun muzzle, the setback force drops to zero, as is well known according to Newtons law F m a, since acceleration (a) is zero whereby the (setback) force (F) on the projectile mass (m) is also zero. Simultaneously, the pendulum, thus free of setback force, begins to swing in response to the centrifugal force generated by the spin of the projectile, which at that instant is at a maximum, and swings in a longitudinal plane with the pivot point at pin 7 on the spin axis of the fuze, performing one complete swing cycle, i.e., p to p and back to p, for each revolution of the projectile, as mathematically shown above with reference to FIG. 3. Accordingly, since the setback force drops to zero and the projectile spin rate is essentially maximum at the instant the projectile exits from the gun muzzle, the invention provides an instantaneous attainment of the one to one relationship between pendulum oscillation cycles to projectile revolutions, and hence achieves an accurate count of the distance by the number of projectile revolutions. Thus, from the number of revolutions that the projectile has made, as counted by the pendulum cycles, the distance traversed by the projectile can be readily determined, since the distance per each revolution of the spinning projectile is the product of the twist of the projectile times its caliber and is independent of the initial projectile velocity, as is know in the art, viz. distance/revolution caliber/twist For example. for a 105 mm round fired in a gun having a l in twist, the projectile can be expected to travel 6.9 feet per revolution. For measuring short distances, i.e., when there is a negligible change in projectile velocity to spin rate, the distance traversed is determined by the caliber and rifling twist. For long distances, when this relationship does not hold, it will be necessary to establish experimentally a ratio of the number of projectile revolutions to the position (distance) of the projectile to provide the necessary relationship, e.g., as would be used in a firing table similar to that currently done with time fuz- While in the centrifugal force field of the spinning projectile, the pendulum tends to damp out, i.e., suffer a decrease of swing amplitude, due to friction forces. This reduction of amplitude has a slight effect on the ratio of pendulum cycles to projectile revolutions due to change in angle 0, which can be mathematically determined as noted above. If the pendulum damps out too rapidly for the desired application, energy may be added to compensate for loss in known manner, e.g., by a main spring or electromagnetically, as used in clock mechanisms. Thus, the novel pendulum arrangement for counting the number or projectile revolutions provides a valuable advance in the art in that it is relatively simple and economical in construction, and automatically compensates for variations in muzzle velocity for short dis tances and also tends to compensate for such error in long distance applications, thereby providing a fuze better adapted to battlefield conditions. The frequency of the pendulum can be measured by any known means such as, for example, by a photocell, electronically, or by mechanical means such as, for example, a ratchet wheel of the type employed in pendulum clocks, and the like. In all cases, the means employed for reading the frequency of the pendulum (and hence the number of revolutions of the spinning shell of the projectile) may be suitably connected to the pendulum so-as to provide a convenient means for determining the number of revolutions of the spinning shell of the projectile. In operation, and in accordance with one embodiment of the invention, the pendulum is connected to a counter (not shown in FIGS. 1 and 2 but illustrated in block diagram in FIG. 4 for the sake of simplicity) which requires, say, (n) counts (revolutions) for activating the fuze. The setter shown in FIG. 4 is mechanically or electrically connected to the counter and is designed to put in the compliment, i.e., (n-a) counts and the pendulum is set to put in (a) counts. In a preferred embodiment, the pendulum is employed in conjunction with a photoelectric cell counter connected by electric circuits to a digital count totalizer (setter), which produces a current pulse for initiating the fuze when the count totals the preselected number of counts (revolutions). In this case there are two counts for each pendulum cycle per projectile revolution, since the pendulum arm cuts the light beam twice during one pendulum cycle, i.e., once when it swings from p to p and once .when it returns from p to p (see FIG. 3). Accordingly, While the present invention has heretofore been described with a certain degree of particularity, it must be emphasized that the device described herein and the principles of its operation are both susceptible of various modifications and/or revisions without departing from the basic character of this invention. For example, the device employed herein may be employed in the socalled S&A (safety and arming) rotating a detonator in line or in any other application where the frequency of the pendulum is proportional to the spin velocity of a spinning shell. This may be accomplished by the use of the well-known Coriollos Force which would rotate a can, barrel, or any other similar device containing the pendulum and the detonator. While a single ended pendulum has been shown in FIGS. 1 and 2, any pendulum means can be employed for the purpose of this invention. Thus, a double ended pendulum 10, comprising a bar having equal weights 9 and 9 attached at each end of swing arms 5 and 5' of said bar and mounted so as to pivot at its midpoint 7 corresponding to its center of gravity, may be utilized to reduce the effects of eccentric spin (where the pivot point is off the spin axis) as well as to minimize generally the forces on the pivot and thereby reduce the friction forces on the pendulum. In all cases, the pendulum means is attached to the center (rotating axis) of the fuze mounted in the projectile and is connected to a mechanical, electronic or any other suitable means for reading the number of frequencies. Hence, the device of this invention provides a convenient means for presetting the distance a projectile is desired to travel. Since, as was previously mentioned, the function of the device is independent of the velocity of the projectile, such distances can be preset and measured independently from changes in environmental conditions. I wish it to be understood that I do not desire to be limited to the exact method and detail of construction described for obvious modifications will occur to persons skilled in the art. What is claimed is: l. A device for determining the distance traversed by a spin-stabilized projectile having a spinning shell, which device comprises, in combination, a fuze element coaxially mounted in said projectile, pendulum means attached to said fuze element and adapted to oscillate therein in response to the centrifugal force generated by said spinning shell so that the frequency of cycles of said pendulum means is proportional to the revolutions of said spinning shell of said projectile, and means for determining the frequency of oscillation of said pendulum means. 2. A device as in claim 1 wherein said pendulum comprises a swing-arm having two ends, one end being pivotably attached to the center of said fuze element and the other end being attached to a discor ball-like object. 3. A device as in-claim 1 wherein the means for determining the frequency of oscillation of said pendulum means comprises a photoelectric cell. 4. A device as in claim 1, wherein the means for determining the frequency of oscillation of said pendulum means comprises a ratchet or escape wheel. 5. A device as in claim 1, wherein the pendulum is a double ended pendulum. 6. A method for presetting the distance of traverse of a spin-stabilized projectile having a spinning shell and a fuze element which method comprises: 1. mounting in said fuze element a pendulum means adapted to oscillate therein in response to the centrifugal force generated by said spinning shell so that the frequency of the oscillation cycles of said pendulum means is proportional to the number of revolutions of said spinning shell of said spinstabilized projectile; 2. associating said pendulum means with a counting means for determining the frequency of oscillation of said pendulum means and adapted to activate said fuze element at a predetermined number of oscillations of said pendulum means; 3. connecting said counting means to a setting means; and 4. adjusting the setting means to cause activation of said fuze element at a predetermined number of oscillations of said pendulum means corresponding to the preset distance of traverse of said projectile. Patent Citations
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