US2145704A - Spring device - Google Patents

Description

J. K. WOOD SPRING DEVICE Jan. 31, 1939.

Original Filed May 9, 1935 4 Shets-Sheet 1 EYS BY ATTOR Jan. 31, 1939.

J. K. WOOD SPRING DEVICE Original Filed May 9, 1935 4 Sheets-Sheet 2 INVENTOR loaf/ 171 15 h/op.

BY ATTORNEYS J. K. WOOD SPRING DEVICE Jan 31, 1939.

4 Shets-Sheet 5 Original Filed May 1935 INVENTO'R JOSEP/l My: 000

ATTO RNEYS Jan. 31, 1939. J. K. WOOD 2,145,704

SPRING DEVICE Original-Filed May 9, 1935 4 Sheets-Sheet 4 INVENTOR fist-P /7Y av A-f'roRNEYs Patented Jan. 31, 1939 PATENT orrlcs SPRING DEVICE Joseph Kaye Wood, Mount Vernon, N. Y., assignor to General Spring Corporation, New York, N. Y., a corporation of New York Application May 9, 1985, Serial No. 20,511

Renewed November 23, 193'! 10 Claims.

This invention relates to a spring device and more particularly to a device in which the inherent action, i. e., load/deflection characteristic, of the spring is modified by a machine whereby the force of the spring is exerted upon a load throughout its travel in a manner which would be impossible in a directly acting spring. In a more specific scope my invention relates to a support in which the force of a spring is applied indirectly to the support of a moving load and the increases and decreases .of force exerted by the spring are compensated for by an automatic changing of the mechanical advantage or leverage of the spring upon the load. it Although I shall use the word load to refer to the load on the entire device, I have retained the commonly accepted phrase load/deflection ratio to describe the characteristic of the spring. Wherever, as in this phrase I refer to the load on the spring as distinguished from the load on the entire device, I shall endeavor to make this clear by the context. In order to distinguish between the characteristic of the spring and the combined characteristic of the spring together with a force-transmitting means through which it acts upon the load, I shall designate the latter as the pull/travel characteristic. This represents the plot of the force actually applied to the load through the force-transmitting means, against the position of the load. I have used the word pull" in this connection without reference to direction, that is to say to include a push as well as a pull. In referring to these characteristics I consider as positive the slope of the natural characteristic of the spring, that is to say the characteristic curve has a positive slope when the force exerted decreases upon movement or the load in the direction of the supporting force and increases when it is moved against the supporting force. A negative slope, of course, is the opposite, i. e., when the force increases upon movement in the direction of the supporting force and decreases upon movement against the supporting force.

One object of the invention is to simplify and to render more satisfactory and compact a device which may be used for affording constant sup-- port to a load, or desired varying support whether the variation is positive or negative. Another object of my invention is to provide for more complete and efiective compensation than has heretofore been possible, whereby the variation from the desired characteristic, e. g., constant support or any other desired variation of the support may be made so slight as to be insigniflcant from the point of view of practical requirements, (e. g. within an error 01' less than at all times).

The invention applies in general to spring devices in which a lever or other rotatable force 5 transmitting device is connected between the spring and the load, and the arms of which lever are disposed at such angles and lengths about the fulcrum as to vary the mechanical advantage between the spring and the load and thereby to 10 compensate at least in part for the variation in force exerted by the spring when it is deflected i. e., by extension or compression. This combination of spring and lever results in a force applied to the load which, with travel of the load, 15 varies along a curve which although not a true sine curve I shall refer to as sine-like by which I mean to indicate that it has sloping sides and rounded crest or hump similar to a true sine curve. This curve includes the factors of moan ment arm and extension of the spring both of which involve sine functions; but since the former has its maximum and minimum crests at positions corresponding to and 270 and is at 0 at 180 and 860 while, the extension or 5 spring reaction curve has its maximum at 180, is at 0 at the positions where the spring is relaxed and is imaginary for all negative values, each distorts the other and to a degree depending upon the positions at which the spring is m relaxed.

A part of this curve adjacent the maximum load is substantially fiat, and it is possible by the utilization of the range of movement corresponding to this fiat part of the curve to make such 35 a spring device which exerts nearly a constant pull upon the load. If the movement of the load within the supported range is such that it can be accommodated by a small angular movement of the lever, the variation in the pull exerted AM by this device upon the load may be kept so slight as to be practically insignificant. With increased amplitude of movement of the'load it is necessary, if this principle alone is relied upon, to increase the leverage of the load upon the spring, and eventually a condition is reached in which a further increase in the length of the lever is objectionable, and in the interest of compact and economical design it is desirable to use a shorter lever and a greater angular movement 56, of the lever.

I have previously suggested the possibility under these conditions of ofisetting such increasedvariation, by varying the action of the levers or other force-transmitting means e. g. by

cams, slots, etc. It has been found diifcult, however, to design a suitable supplemental compensating device which would not add unduly either to the expense of manufacture or to the friction involved in the operation of the device.

I have now discovered that by application of a supplemental force-applying means, e. g., a spring, to the load either directly or through the interposition of suitable levers but without use of cams or other parts involving relatively high friction, a supplemental compensation may be attained which may hold the pull/travel characteristic of the entire device even more accu rately to that required than with the narrower range when no supplemental compensating means is used. This is accomplished with greatest simplicity. For example, in the preferred embodiment of my invention, the load/deflection characteristic of the spring is overcompensated during at least a part of its travel by a lever or other means for varying the mechanical advantage of the spring upon the load, and a second spring may be applied substantially directly to the load so that the resultant between the load/deflection characteristic of the supplemental spring and the load/travel characteristic of the entire device without the supplemental spring is substantially the characteristic desired.

In the accompanying drawings I have illustrated a preferred embodiment of my invention, various modifications thereof and graphs illustrating the operation of these devices, all of which I have chosen and presented herein with a view to explaining my invention fully to those skilled in the art, so that those skilled in the art may apply it under varied practical conditions and may readily understand how it may be modified and adapted to meet such varying conditions of practice. It is to be understood that these and the accompanying description are given for purposes of illustration and explanation and are not intended to limit the scope of this application.

In these drawings:

Figure 1 is a view in elevation of a constant support spring device.

Figure 2 is the same in side elevation.

Figure 3 is a view similar to Figure l but of a modified device and with one side of the symmetrical structure broken away.

Figure 4 is a view similar to Figure 3 of another modified device.

Figure 5 is a view in elevation and on a smaller scale of another device embodying my invention.

Figure 6 is a diagrammatic view of another device modified from that shown in Figures 1 to 3.

Figure 7 is a family of graphs representing the pull of the device upon the load in its various positions, each curve representing one of the three adjustment positions shown in Figure l with normal length of springs.

Figure 8 is a corresponding family of graphs for the modified construction shown in Figure 3 showing both the resultant and its components by which more perfect compensation is attained.

Figures 9 and 10 are graphs corresponding to those of Figures 7 and 8, but for the device of Figures 5 and 6 respectively and for only one adjustment position, showing both the resultant compensated curve and its components.

In Figures 1 and 2 I have illustrated a spring support adapted particularly for use as a hanger for high temperature equipment such as steam pipes, oil refinery piping, etc., in which cases equipment of great weight musiflbe supported so as to avoid lack or excess of support when relatively large expansion and contraction occurs. This hanger is designed to afford constant support for the load to relieve the supported apparatus of excessive stresses.

In this case the hanger is built around the frame 20, which is secured to a beam or other supporting member. A vertical member 22 of this frame provides a fulcrum at 23 for the pivoted levers 24; and at 25 forms a limiting shelf which would support the load, if through any mischance'the spring or levers or other parts of the device should become broken or overloaded. In the present case the shelf 25 is adapted to afford double security against complete release of the load in that it acts in the first instance upon the levers 24 being of such width that they strike against this at the bottom of their downward movement. In the second instance, if the levers or pivots thereof should have failed, the yoke 25, to which the load is secured through the bolt or rod 21, would engage the shelf 25 directly.

The levers 24 are limited in their upward movement when relieved of the load, by the T strut 28 against which their shoulders 29 strike at the upper limit of their travel.

The springs 30 are pivotally secured at their upper ends to the cross arm 2| and at their lower ends to the levers 24 by means of clevis bolts 3| and eye bolts 32 adjustably secured to the plugs 33 which are threaded into the ends of the springs.

The adjustment of the force applied to the load by stretching or relaxing the springs between their pivots, e. g., by adjustment of the clevis bolts 3| or the eye bolts 32, may result in shifting the pull/travel curve of the device as a whole. If carried too far this may result in shifting the fiat portion near the maximum of the characteristic until it is partly or wholly out of the operating range, which range is then thrown into one of the steeper slopes of the curve, with consequent excessive variation in the force applied to the load near one end of or throughout the range of operation.

In order to provide for greater adjustment, and to avoid excessive spring deflection, a plurality of holes are provided, into any one of which the eye bolt 32 may be pinned. These holes are all positioned so as to maintain the centering of the pull/travel curve of the device. Additional adjustment may be effected by changing pivots 36 at which the load acts upon the levers, but without varying the angle at the fulcrum 23.

The load, as already described, in supported from the rod 2'l and the yoke 26, and the latter is in turn hung from the levers 24 by means of the swing links 35 pivoted upon the levers 24 at one end and upon the yoke 26 at the other.

The several adjusting positions, as well as the original position, may be determined, e. g., by the experimental method or by use of the formulae as set forth below.

In the case of the hanger or support adapted to afford substantially constant tension equal to its load, the device is designed and operated so as to bring the maximum of the pull/travel curve at substantially the center of the range of normal movement, and in order to produce as little effect as possible upon this curve due to variation of the moment arm at which the load hangs from the lever, the pivots 36 of the swing links 35 are advantageously placed so as to be on a horizontal level with the pivot 23 when at the center or their normal range of movement. The distance of these pivots 38 irom the fulcrum 23 depends upon the amplitude of movement required. As already stated, the greater the angular amplitude, the less perfect will be the com.- pensation, and accordingly the pivot holes 36 are preferably drilled as far from the pivot 23 as is consistent with the magnitude of the pull required to support the load and with other requirements of design.

In Figure '7, I have shown a group of three fragmentary curves, each representing the pull/travel curve of the device within the operating range for a given moment arm adjustment for the springs 38, i. e., each tor the connection of the eye bolt 32 to one of the holes in the end of the lever 23 with normal spring length. Intermediate curves may be obtained by varying the spring lengths. As will be observed from these curves, the permissible adjustment covers a substantial range, but at the cost 01' some sacrifice of full compensation.

In Figure 8, I have shown comparative curves illustrating a preferred method according to my invention of achieving supplemental compensation so as to give substantially perfect constant support to the load. In this case the curves a, b, and c are comparable to the curves a, b, and c of Figure 7, but as will be observed, have been shifted so that only the most horizontal part of each curve near its maximum is used, and that in the upper range of movement whereas the center of movement of the lever is at a point from which the left hand portion of the curve swings rapidly downward with objectionable variation in pull exerted upon load. The curve d at the bottom of this figure represents the load/deflection characteristic of a booster spring used to efiect supplemental compensation. The load/defiection rate of this spring (or springs) is chosen so as to give an upward angle from the horizontal substantially equal but opposite to the downward angle of the curve I). In order to make this comparison more apparent, I have transposed the curve d to the curve b where it is shown as d. At l) I have shown in dot-dash line the resultant of the curves b and (1, this being the actual pull/travel curve of the device as a whole when the booster spring is used and with the lever arm at its center adjustment. In curves at and c the same comparison has been indicated by the same types of lines. As will be observed, the curve a is not quite completely compensated, due to the greater slope of the left-hand portion of the curve a while the curve c is slightly overcompensated due to the lesser slope of its lefthand portion. I

It shouldbe noted that the graphs just discussed above are plotted with linear movement of the load up and down from the normal median position against the pull, or supporting efio'rt exerted on the load at each position. A substantially similar curve would result from plotting the angle at the pivot point of the lever which is defined by the points of attachment of the spring against the moment of the spring tension upon the lever. Although these curves are not identical, they are approximately concentric and illustrate the same fundamental principle involved in my invention, but it should be noted that in so far as they are comparable the curves shown on the accompanying drawings are reversed with respect to moment/angle curves plotted in the usual way, the steeper left-hand portion of the curve discussed above corresponding to the steeper right-hand portion of the usual curve plotted with angular instead of linear positions.

In Figure 3, I have shown a constructional mod iflcation of the device as shown in Figures 1 and 2 by which this supplemental compensation is attained. Essentially this change concerns only the levers 24 and the cross arm 2 I. To the latter has been added a cross-member lll, drilled as shown at 4| to engage the booster spring.

The levers 24 have been redesigned with a shifting of the pivots 36 and 37 so as to eifect the shifting of the maxima of the curves as shown in the graphs already discussed and according to the principles and formulae more fully set forth below.

In the present case this has been achieved primarily by moving the pivot 36 to a substantial angle above the horizontal so that the moment of the load upon the lever is varied substantially throughout the operating range, but a similar effect can be obtained by a shifting of the pivots 37 or 3i or by suitable change of the springs 30.

Finally the booster spring 42 has been-secured at one end to the cross-member 40 and at the other through the tum-buckle 43 and the slip connection 44 to the pivot $5 on the lever 26a.

In order to give the maximum effect to the booster spring and to minimize the efiect of changing moment of the booster spring upon the lever 24a, (thus giving the straight-line relation as shown in Figure 8) the pivot 45 is positioned so that at the middle of the lower half of the travel of the lever 24a the line through the center of the pivots 45 and 23 will be substantially perpendicular to the axis of the booster spring 42. In this, as in the other figures, the device is shown at the center of its range.

This perpendicular relationship is at the center of the second half of the travel because by means of the slip connection Ml the booster spring is not brought into action until substantially the beginning of the lower half of the travel. This is made clear on the graph in Figure 8 at which it will be observed that during the upper half of the travel the relatively flat nature of the unmodified pull/travel curve is utilized and the booster spring comes into action only at approximately the median, i. e., at the beginning of the lower hall of the travel.

Instead of the turnbuckle connection as shown in Figure 3 a spring with plugs threaded into the ends may be used exactly as shown for the spring 30, except for the slotted eye bolt 44 replacing the simple eye bolt 32. When the turnbuckle is used as shown, the slot is not essential since the eyes of the spring and turnbuckle permit it to break in the middle and bend outwardly without offering any resistance.

In these figures adjustment is provided by means of the slot 46 and the bolt 41 instead of by a series of holes 31 as in Figure 1. This form of adjustment is preferable to the several holes of Figure 1, because it provides a continuous adjustment to meet any required condition; whereas that of Figure 1 requires intermediate adjustments by merely stretching the spring for a given pivot-to-plvot length. It will be understood, of course, that these two means are alternative and not essentially tied up with the other differences between these figures. It is important, however, when adjusting the pivot 3'1! to make a corresponding adjustment of the turnbuckle t3, and if a series of holes were provided as in the case illustrated in Figure 1 it would ordinarily be all;

preferable to substitute a plate with corresponding holes in place of the turnbuckle 43 or some other means for making definite equivalent adjustments of the tension of the booster spring corresponding to the changes in the position of the pivots 31. With the screw adjustment equivalent scales may be marked oil e. g., on the parts 46 and 44 to assist in balancing the adjustments.

In Figure 5, I have shown a device which differs from the construction described above in two important ways which are not essentially dependent upon one-another, but either of which may be used 'alone with the other features of my invention.

The first diiference is the fact that the spring 30:: instead of being anchored to a fixed support is connected at each end to one of the levers 24a so that each lever 24a serves as anchoring means for the other. In this case, as will be apparent, since the springs move with the movement of the levers 24a and angle between the springs and the levers will change difierently with changing posi tion of the levers as compared with the case illustrated in Figures 1 to 3. The experimental determination of the design as described below need not be essentially affected by this difference, but the theoretical calculation oi this design will be afiected.

The decision whether to use a fixedly anchored spring construction as shown in Figures 1 to 3 or this double construction as shown in Figure 5, will depend primarily upon space consideration, and it should be understood that .the pivots 230 may be spaced apart or identical, according to the space conditions imposed upon the design.

The second important difference in the construction illustrated in this figure as compared with that illustrated in Figures 1 to 3 is that in this case the design has been so chosen as to throw the range of operation completely away from the maximum point of the pull/travel curve of the device without the'booster spring, and into the steep, relatively straight portion of its curve.

- The slope of this curve has been balanced by a booster spring acting throughout the entire range of operation and having a load/deflection rate equivalent to but opposite to the slope of this curve. In Figure 9, I have shown the pull/travel curve of the device without the booster at a; the load/deflection curve of the booster spring at b; and the resultant pull/travel curve of the entire device with the booster spring at c.

Since, as is clearly evident from an examination of the graph, the booster spring 42a acts throughout the entire range of operation, the slip connection 44 is not used in this case and the pivots Ma and 45a are positioned so that the spring 42a is perpendicular to the line between 45a and 23a at the center of the range of operation.

In this case no adjustment has been shown, but it will be understood, of course, that the princ'iples of adjustment are the same and that similar adjustment may be provided in this case as in the cases illustrated in Figures 1 to 3.

In Figures 6 and 10, I have illustrated diagrammatically an arrangement adapted for compensation to produce substantially constant support when the other slope of the characteristic curve is utilized. In such case the characteristic of a spring directly applied to a load would be such as to. magnify instead of to correct the variation in tension. It is necessary therefore to modify the action oi the booster spring in this case, and this is done by applying the tension of the booster spring between the pivots 36 so that as the lever passes through its median position the spring passes dead center and its action is reversed. The result of this is illustrated graphically in Figure 10 in which a is the curve of the device without the booster, b is the curve of the efiect of the booster on the load and c the resultant. Essentially in this case the levers 24 are utilized to over-compensate 'the characteristic of the booster spring 42b.

Obviously where this construction is used the particular design would have to be modified somewhat from that illustrated in Figures 1 to 4 by placing the link 35 outside of the levers 24 so as to permit the spring 42b moving above and below the pivot 23.

In Figure 4, I have illustrated still another compensating construction adapted to compensate the symmetrical curve when the maximum is at the median position of the levers 24. This requires a reversal of the slope of the load displacement curve representing the action of the booster spring on the load, and this reversal in the present instance is attained by the use of two springs, one of which comes into action on the second half of the movement by overbalancing the action of the first.

The member 50, pivoted at is pivotally secured at 52 to one end of the booster spring 53,

the other end of which is anchored at 54. A

second arm of the member at right angles to 52 is pivotally secured at 55 to a link 56 pivoted to the lever 24 at 51.

Through a lost motion connection 58 the member 50 engages a second pivoted member 50 rotatable about the same pivot 5i and having a second arm 6| at an angle to the first equal to 180 minus the angle described by the pivot 55 in the complete operating range of the device. At 62 the arm 61 is connected to a second booster spring 63, the opposite end of which is pivotally connected at 54. A stop 64 limits the movement of the arm 6|.

In operation when the lever 24 is moved downwardly from its uppermost position as shown in this figure the spring 53 is at first extended by the movement of the member 50 about the pivot 5i, thus the force of the spring 53 tends to support the load, but with a decreasing moment, as the dead center position is approached. During this movement the pivot 55 has been moving through the lost motion range 58 with respect to the member which has remained stationary without any action upon the lever 24 or the load. As the dead center position is passed, however, the spring 53 reverses its action tending to push down on the lever 24 instead of assisting it'in the support of its load, but at this same point the spring 53 comes into action by the contacting of 55 on .60 and this spring being chosen to overbalance the effect of the spring 53 results in an increasing support for the lever 24 against its load as the spring 53 is extended.

In this figure I have illustrated only one side of the device, i. e., operating on only one of the levers 24. Of course, it is possible to apply the entire compensation thus to one of the levers, but ordinarily I prefer to make the device symmetrical, duplicating the same construction on the opposite side of the device and proportioning the springs so that each provides one half of the necessary compensation.

Regarded in another way this construction illustrated in Figure 4 is a special case of the booster principle oi- Figure 3. In this case the spring 30 alone has its maximum strength at the center of its range of operation, but when the effective force of the spring 52 is added to that of the spring 30 the maximum is shifted to one side. Thus the spring 52 has an effect similar to the shifting of the pivot 36 in Figure 3, as compared with Figure 1, and the lost motion connection 58-60 acts in the same way as the lost motion connection 44-45 in Figure 3 to bring If it is desired to produce an operating characteristic having a positive or negative slope, arrangements such as those shown in Figures and 6 may be used, but with the compensation less or more than would give a substantially horizontal characteristic in the operative range and if an irregular curve is required one ormore supplemental or booster devices may be brought into action at the point or points where change of slope is required, e. g., as in the case illustrated in Figure 8.

I have referred above to the importance, in the design of devices embodying my invention, of properly proportioning various factors relative to one another. Ihese are essentially:

lc=the load/deflection ratio of the spring 30.

a=the distance from the pivot 23 to the anchoring point at of the spring 3|] (in embodiments such as Figures 1 to 4 and 6) or N=the distance between the two pivots 23a (in embodiments such as Figure 5) b=the distance between the pivot centers 23-3'l or 2ta-3la I C=the angle between a-b or N-b H=the relaxed length of the spring and its connections, i. e., the distance between the pivot centers 3l3l or tic-4W0, when the spring is just relaxed.

With these factors the moment M of the spring M on the pivoted member 24 can be calculated from the formulae:

when one end of the spring is anchored; and

M=kb sin C(N-H2b cos 0) when both ends of the spring are connected to the pivoted member. When several springs are used as in Figure 1, they may be considered as one in these formulae by adding their load/deflection ratios or they may be taken separately and their moments added.

Plotting M against C with any given values of k, b, H and a or N will give the characteristic moment/angle curve, which as discussed above is substantially similar to the pull/travel characteristic, travel being expressed angularly rather than linearly, and the moment of the load being proportional to the pull. By diiferentiating this equation with respect to C and equating it to the desired slope the proper proportions may be determined. Some of the variables will be fixed for convenience or requirements of strength,

etc.; and given these, the other or others may be proportioned as required by these formulae.

Instead of thus calculating the moment, a test device may be constructed and the moment or pull determined experimentally and plotted for various positions in its travel, after which the desired slope can be readily chosen from the curve and the device set up to operate in the range of travel in which that slope pccurs.

In all of this we have considered only the moment of the spring 30 or the lever 24, disregarding the compensating device and the mo ment of the load upon the lever 24-.

If, as in Figures 1, 2, and 4, the load is pivoted on a horizontal line through the pivot of the member 24 at the center of its range of movement, and operates through only a very small range of movement, then the variations of moment or the load can be disregarded with only slight error and the moment M considered equivalentto the pull; but, if, as shown in Figures 3 and 5, the load is pivoted at an oblique angle to the direction of its action, then, of course, its moment also should be considered and the supporting effort calculated by the moments equation =Lr where M as before is the moment of the spring 30 on the member 24, L is the load and r is the moment arm at which the load acts upon the member 24.

If the booster 42 or other supplemental compensating device does not act. at the same angle to the line through its pivot and that of the member M as the angle of action of the load to the line of its pivot and the pivot of M, then again its moment M (e. g., calculated by the same formulae as for the spring 30) must be added to the moment in the above equation, which thus becomes M+M'=Lr. So long as those angles remain the same the booster may be considered as acting directly upon the load.

Although I have shown in the drawings and described above diverse forms and modifications of my invention, it will be observed in all of these that the supplemental compensating is performed by springs or weights operating directly upon the load or through simple pivotal connections which involve relatively little friction as compared with sliding cams, etc. In fact, although in the case illustrated in Figure 5, the force of the booster springs could have been applied directly to the load, it has been found equally emcient and much more practicable to apply it toa pivot on the lever 2t, and when this is done, the friction of the device is not significantly increased, and the compensation is made nearly perfect without any objectionable results.

What I claim is:

1. A device for exerting a substantially constant force between a support and a load movable vertically within a limited range which comprises a frame, a lever pivoted on said frame, spring means carried by said support, means connecting the load to said lever, means connecting the spring means to a point angularly spaced about the pivot of said lever from the point at which the load is connected, whereby the ratio of the moment arm of the spring means to the moment arm of the load on said lever varies with movement of the lever, said lever being positioned so that a movement of the lever while the load is within said limited range, produces a change in means upon the lever due to said movement of the lever, whereby the net result of such movement within said limited range is to decrease the force exerted upon the load from the spring means as the force exerted by the spring means upon the lever increases and vice versa, auxiliary spring means adapted to exert a compensating force upon the load which increases and decreases respectively at a rate which approximates the average rate of decrease and increase respectively of the force from the first-named spring means exerted upon the load by said lever, means for anchoring one end of the auxiliary spring means, and means for connecting the other end of the auxiliary spring means to the load.

2. A device for exerting a substantially constant force as defined in claim 1 in which the lever is positioned relative to the load so that, near the mid-point of its limited range, the ratio of the moment arm of the first named spring means tothat of the load changes, with an increment of motion of the lever, by an amount substantially proportional but opposedto so as to counterbalance the change in the force of the first-named spring means on said lever, whereby the force exerted from said spring means upon the load remains substantially unchanged, and the means for connecting the auxiliary spring means to the load is adapted to release the load from said auxiliary spring means from the position with the load at the top of the range until after said position of counterbalance change has been passed.

3. A device for exerting a substantially constant force as defined in claim 1 in which the lever is positioned relative to the load so that, throughout said limited range of movement of the load, the ratio of moment arm of the firstnamed spring means to moment arm of the load respectively on the lever changes at a rate more than proportional to and opposed to the change in the force of the first-named spring means on the lever, whereby the force exerted on the load from said spring means decreases as the force of the spring means itself increases and viceversa and the means for connecting the auxiliary spring means to the load is effective throughout said limited range to increase or decrease the distortion of the auxiliary spring means by every movement of the load within said range.

4. A device for exerting a substantially constant force as defined in claim 1 in which the means for connecting the auxiliary spring means to the load includes the same lever to which the first-named spring means is connected and the means connecting the load to said lever.

5. A device for exerting a substantially constant force as defined in claim 1 in which the first-named spring means and the auxiliary spring means are both anchored to the frame.

6. A device for exerting a substantially constant force as defined in claim 1 in which two pivoted levers adapted to swing in opposite directions, each connected to the load are used and at least one of the spring means is connected between said levers so that each serves to .anchor said spring means with respect to the other.

7. A device for exerting a force regulated to a load movable within a limited range which comprises a frame, a lever pivoted on said frame, spring means, means connecting the load to said lever, means connecting the spring to a point angularly spaced about the pivot of said lever from the point at which the load is connected,

whereby the mechanical advantage of said lever with respect to the action of said spring means on the load varies with movement of the lever, said lever being positioned relative to the load and the spring means so that the mechanical advantage is decreased by a given movement within said limited range so far as to overbalance the increase in the force of the spring means upon the lever by distortion due to said movement, whereby the net result is a decrease in the supporting force exerted upon the load from said spring means, a second spring means,

means for anchoring one end of said second spring means, and means connecting the other end of said second spring means to the load so that said second spring means acts upon the load with increasing supporting force adapted to compensate for departure from the load of the force applied thereto from the first-named spring means, and the stiffness and distortion of said spring means respectively being such that the force applied to the load from the second spring means is approximately equal to the difference between the load and the force applied thereto by the lever from the first-named spring means throughout said limited range.

8. A device as defined in claim '7 in which the lever for the second-named spring means is positioned so that it passes through dead center within said limited range of movement whereby on one side thereof the spring acts in support of the load and on the other side pushes against the load, and the connecting means for the firstnamed spring means is adapted to provide for the increase in force of its spring means which results from movement of the load through at least a part of thelimited range to be at least partially effective in support of the load, whereby to counter-act the opposite change of the force effective from the second-named spring means through its lever.

9. A spring support for a load movable through a limited range, of the type having a frame, primary spring means to exert a supporting force, a member adapted to transmit force from the spring means to the load with mechanical advantage which varies with movement of the memher so that, in at least a part of said limited range, the force applied to the load from said primary spring means decreases as the force exerted by the spring itself increases, and a supplemental spring means adapted to apply to the load a force which increases at approximately the same rate throughout its effective range as that at which the force applied to the load from the primary spring decreases, which support is characterized by means for adjusting the primary spring to increase or decrease the mean force exerted thereby within said limited range and for adjusting the mean angle at which said spring acts on said force transmitting member,

through a limited range, of the type having a frame, primary spring means to exert a supporting force, a member adapted to transmit force from the spring means to the load with mechanical advantage which varies with movement of the member so that, in at least a part of said limited range, the force applied to the load from said primary spring means decreases as the force exerted by the spring itself increases, and a supplemental spring means adapted to apply to the load a force which increases at approximately the same rate throughout its efiective range as that at which the force applied to the load from the primary spring decreases, which support is characterized by the fact that the primary spring and its force transmitting memher are adapted to exert during an initial portion near one end of said limited range a. force upon the load which closely approximates that required by the load, and within said limited portion of the operating range the eifect of variation of mechanical advantage overbalances the effect of deflection of the primary spring so that the force exerted thereby upon'the load stops increasing and begins to decrease, and the supplemental spring is connected to the load through a. lost motion connection, whereby it does not become effective until said initial portion of the operating range has been passed.

JOSEPH KAYE WOOD.

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