US2956795A - Spring - Google Patents

Description

Oct. 18, 1960 Filed Nov. 21, 1958 E. E. FOSTER SPRING 4 Sheets-Sheet 1 6 INVENTOR.

[dz/()2 Elbafe j BY 6 ,M W M 5 Oct. 18, 1960 FOSTER 2,956,795

SPRING Filed NOV. 21, 1958 4 Sheets-Sheet 2 INVENTOR.

Oct. 18, 1960 E. E. FOSTER 2,955,795

SPRING Y Filed Nov. 21, 1958 4 Sheets-Sheet 3 Eda/m 27165551 BY Oct. 18, 1960 E. E. FOSTER 2,956,795

SPRING Filed Nov. 21, 1958 4 Sheets-Sheet 4 INVENTOR.

Fab/L n E 155166 United States Patent SPRING Edwin E. Foster, P.0. Box 714, Austin, Tex. Filed Nov. 21, 1958, Ser. No. 775,490

17 Claims. (Cl. 267- 1) This invention pertains to a spiral spring and in particular to a new and useful improvement in spiral springs and is a continuation-impart of application Serial No. 486,810, filed February 8, 1955, now abandoned.

Springs constructed of a flat band of a ribbon formed into a spiral coil have long been used as. a source of power in spring motors for use in tape measures, toys, sash balances, and the like. An example of one such spring that has enjoyed tremendous commercial success is shown in my Patent 2,609,191, issued September 2, 1952, and entitled Spring counterbalance. The spring shown in this patent is formed by pulling a ribbon over a die member having a relatively sharp radius.

This spring is characterized as a coil composed of a flat ribbon stressed to assume a plurality of tightly wound convolutions when the coil is in its reposed' condition. By tightly wound it is meant that the coils are in a substantially touching relationship. Thus the repose radius of curvature of the increment of ribbon forming each convolution with respect to the repose radius of curvature of the increment forming the preceding convolution may be less than, equal to, or slightly larger up to the thickness of the ribbon. The spring is further characterized by the fact that the ribbon may be unwound from the. coil so that it extends outwardly therefrom or so that it may be backwound into a coil consisting of a plurality of convolutions. Examples of the backwound spring are shown in my Patents 2,833,027 and 2,833,534, both issued on May 6, 1958. When a portion of the spring is unwound from the coiled condition, it will tend to return to the coiled condition.

I have discovered that by usinga ribbon having cross curvature the tendency of an extended portion of the spring disclosed in my Patent 2,609,191 to rewind into its convoluted condition may be increased or decreased a predetermined amount. In fact, by using different amounts of cross curvature the spring may be self-winding in that an extended portion of the ribbon will tend to. wind on the coil or may be self-extending in that a coiled portion of the ribbon will tend to uncoil or may be balanced in that the ribbon will remain unchanged from either extended or coiled conditions.

As a direct result of these discoveries it is possible to achieve numerous desirable effects by combining a cross curvature with the stresses inherent in springs of the type shown in my patent. For this reason a foremost feature and object resides in the provision of a spring which is especially suited for a myriad of uses.

While the spring shown in my Patent 2,609,191 has many advantages over the prior art springs, it does have certain characteristics which limit the manner in which it may be used. As was previously mentioned, when the spring is extended or backwound, it will tend to return to the forwardly wound condition. If the return is not carefully controlled and restrained, the unwound portion due to its instability will in many instances not return to its spiral form but will become entangled oftentimes in the form of a helix. For this reason it has been 2,956,795 Patented Oct. 18, 1960 necessary to use these springs in some type of motor in which the spring is confined.

I have also discovered that by using a ribbon having a cross curvature it is possible to retain the advantages of the aforementioned coil spring but in which the instability of the spring may be minimized. By using various amounts of cross curvature in combination with the stresses inherently present in this type of coil spring, it is possible to minimize or substantially eliminate any tendency for the coil ribbon when unwound to become entangled or to assume a configuration other than its normal spiral.

This and other objects of the invention will be apparent upon reading of the specification with reference to the following drawings:

In the drawings:

Figure 1 is a coil spring constructed according to my Patent 2,609,191 having a portion of the ribbon uncoiled and extending therefrom.

Figure 2 is a cross sectional view of the coil spring shown in Figure 1 taken along the lines 2-2.

Figure 3 is a front view of a coil spring composed of a ribbon having a cross sectional curvature, in which a portion of the ribbon has been. uncoiled and in which the concave side is toward the center of the coil.

Figure 4 is a cross sectional view of the coil spring shown in Figure 3 taken along the lines 44.

Figure 5 is a front elevational view of a coil spring constructed of a ribbon having a cross sectional curvature. in which the concave side is away from the center of the coil and in which a portion of the ribbon extends from the coil.

Figure 6 is a cross sectional view of the coil' spring shown in Figure 5 taken along the lines 66'.

Figure 7 is a front elevational view of a coil spring somewhat similar to that shown in Figure 5 but in which the ribbon has a greater amount of cross sectional curvature.

Figure 8 is a cross-sectional view of the coil spring shown in Figure 7 taken along the lines 88.

Figure 9 is a cross sectional view taken along the lines 9-9 in Figure 10 of a modification of the spring embodying the invention.

Figure 10 is a front elevational view of the spring shown in Figure 9.

Figure 11 is a front elevational view of another modification of the spring embodying the invention.

Figure 12 is a cross sectional view taken along the lines 1212 in Figure 11.

Figure 13 is a diagrammatic illustration of a modification of the spring embodying the invention being constructed by backwinding the spring shown in Figure 3.

Figure 14 is a front elevational view of the spring embodying the invention when used as a tape measure.

Figure 15 is a plan view of the spring shown in Figure 14.

Figure 16 is a front elevational view in cross section of the spring when used as a tape measure mounted within a casing.

Figure 17 is a plan view of a measuring device constructed from a spring embodying the invention when fully extended.

Figure 18 is a side view of the measuring device shown in Figure 17 when partially wound.

Figure 19 is a cross sectional view of a brush holder for electrical apparatus, including one form of the spring embodying the invention.

Figure 20 is similar to Figure 19 but shows the spring in its extended form.

Figure 21 is a cross sectional view of a brush holder including a second form of the spring embodying the invention.

Figure 22 is similar to Figure 21 but showing the spring in its extended position.

Figure 23 is a front view in elevation of a retractable lamp support including one form of the spring embodying the invention.

Referring now to Figures 1 and 2, there is shown a spring constructed according to my Patent 2,609,191. This spring is characterized as a spiral coil composed of a plurality of tightly wound convolutions. The spring may be constructed of any one of suitable materials such as spring steel, brass, and the like. When this spring is constructed according to my patent, the ribbon used in the construction of the spring is found to contain residual stresses which result in the tightly wound convolutions and certain other benefical characteristics which will be described more fully later on.

Hereinafter the process of forming the coiled portion from the flat ribbon will be called stressing so that the length of the ribbon which has been subjected to the process will be called a stressed ribbon or portion and a length that has not will be called an unstressed ribbon or portion.

The coil spring shown in Figure 1 is generally denoted by the numeral and is constructed of a flat ribbon 12 having an unstressed portion 14 and a stressed portion 16. A cross-section 18 has been removed from the unstressed portion 14 to illustrate the fiat construction of the ribbon 12 used in the construction of the coil spring 10. A .length 20 of the stressed ribbon 16 has been unwound and extended from the coil 21, as shown in Figure l. The extended length 20 assumes a concave-convex crosssection 22 in which the concave side is toward the center of the coil. It is believed that this concave-convex crosssection is due to the stresses, particularly the residual stresses, within the coiled portion 16 of the ribbon 12. ,This concave-convex cross-section, which is believed to be due to the stresses within the ribbon 12 when unwound, will hereinafter be designated the natural cross-section in that it occurs notwithstanding the fact that the coil spring was, constructed from a ribbon having a substantially flat cross-section.

Referring now to Figure 2, it can be seenthat when the stressed'ribbon portion 16 of the ribbon 12 is in its reposed or wound condition, it has a substantially flat crosssection. In other words, as the ribbon is removed from the coil, it assumes the natural concave-convex crosssection but returns to its fiat cross-section when it is allowed to rewind on the coil.

Referring now to Figures 3 and 4, there is shown a coil spring generally denoted by the numeral 24. The coil spring 24 is constructed from a ribbon 26 stressed in the same manner as the ribbon shown in Figure 1 so as to form a coil 28 when in its reposed condition. At the end of the ribbon -26.is an unstressed portion 30. A crosssection 32 of the unstressed portion 30 shows that the ribbon 26 has beenprovided with a concave-convex crosssection, of which the concave side is toward the center of the coil 28. This concave-convex cross-section may be formed in any suitable manner such as a simple bending operation, die forming, and the like. i

This type of concave-convex cross-section will hereinafter be referred to as the formed cross-section as opposed to the natural cross-section which was heretofore mentioned with reference to Figures 1 and 2. The formed cross-section, as was mentioned previously, may be due to any one of numerous types of forming operations which may be imparted to the ribbon either prior to the coiling operation, concurrently with the coiling operation, or subsequent to the coiling operation. A stressed portion 34 of the ribbon 26 is shown in its extended form from the coil 28. A cross-section 36 reveals a concaveconvex cross-section having a somewhat greater radius of curvature than the cross-section 22 in Figure 1. One explanation for the greater amount of cross-sectional curvature is that the formed cross-section. showni t 4 cross-section 32 and the natural cross-section shown in the cross-section 22 are additive since they are in the same direction.

Referring now to Figure 4, it can be seen that the coiled ribbon, when in the reposed condition, assumes a substantially flat cross-section. In other words, the coiled portion of the ribbon assumes a concave-convex crosssection only when extended from the coil 28.

It has been found by actual test that the coil spring shown in Figures 3 and 4 is somewhat weaker than the coil spring shown in Figures 1 and 2, depending upon the amount of formed cross-curvature. This comparison is based on the restraining force necessary to prevent rewinding of an extended portion of the stressed ribbon.

One explanation for the difference between the two coil springs is that there is a certain amount of force required to flatten out the coiled ribbon as it moves from the extended condition to the coiled or repose condition. This force would tend to resist the movement from the uncoiled condition to the coiled condition. Assuming this explanation to be correct, it would then follow that the greater amount of cross-curvature to be flattened out, the greater the resistance and consequently the weaker the spring would be with regard to its tendency to rewind any extended portion. Thus the spring shown in Figure 3 would be somewhat weaker than the spring shown in Figure 1 since it has a greater cross sectional curvature, as is the case.

For convenience, hereinafter, the stresses which tend tocause the ribbon to assume a tightly wound configura' tion will be called a longitudinal component and the force required to flatten the cross curvature will be called the cross component.

It has been found that the spring shown in Figures 3 and 4 is subject to substantially the same disadvantage as the spring shown in Figures 1 and 2. This disadvantage being that when a portion of the stressed ribbon is extended from the coiled position and allowed to return in an uncontrolled manner, it will become entangled and not return to its spiral configuration. In other words, the spring shown in Figures 3 and 4 must be used in some type of spring motor in which it is restrained so as to prevent the aforementioned entanglement when moving from the uncoiled to coiled position.

Referring now to Figure 5, there is shown one modification of the coil spring embodying the invention generally denoted by the numeral 33. The coil spring 33 is constructed from a ribbon 40 stressed in such a manner as to form the coil 42 when in its reposed condition. A cross-section 44 of an unstressed portion 46 of the ribbon 40 is concave-convex with the concave side being away from the center of the coil 42. The cross-sectional curvature of the uncoiled portion 46 may be formed in any suitable manner, either prior to the stressing operation, currently therewith, or subsequent thereto, as was described previously. This cross-sectional curvature will be referred to as the formed cross-section as heretofore stated. A cross-section 48 of an extended portion 5% of the ribbon 40 reveals that a stressed portion has a substantially fiat configuration. One possible reason for the substantially flat cross-section is that the formed crosscurve is in the opposite direction to the natural crosscurve. In other words, the formed cross-curve would be subtractive from the natural cross-curve. If the formed cross-curve is substantially equal to the amount of the natural cross-curve, then it can be seen that a substantially flat cross-section would be formed when the stressed ribbon is extended from its coiled condition.

Referring now to Figure 6, it can be seen that when the stressed portion of the ribbon is in the coiled condition, it remains in a substantially flat cross-section. It has been found that the spring shown in Figure 5 is somewhat stronger than that shown in Figures 1 and 3. As was mentioned previously, it is believed that the amount of forv? 'cessary to restrain the stressed portion of the ribbon from moving from an extended position to a coiled condition is at least partially dependent on the amount of cross-curvature. Thus, the greater the amount of cross-curvature to be flattened out, the less the restraining force necessary to prevent the rewinding of an extended stressed portion. It would further follow that if there is substantially no cross-curvature to be flattened out, then the longitudinal component would be substantially undiminished. This conclusion would certainly appear to be congruous with the characteristics of Figure 5 in that the spring shown therein is considerably stronger than those shown in Figures 1 and 3.

Referring now to Figures 7 and 8, there is shown another modification of the spring embodying the invention. The spring generally denoted by the numeral 52 has been constructed from a ribbon 54 stressed for a sub-4 stantial portion of its length to form a plurality of tightly wound convolutions when in its reposed condition. A cross-section 56 taken from an unstressed portion 58 shows that the ribbon prior to stressing had a cross-sectional curvature in which the concave side was away from the center of the coil 60. The amount of crosssectional curvature as shown in the cross-section 56 is somewhat larger than the amount of cross-curvature shown in the cross-section 44 in Figure 5. A cross-section 62 taken from an extended portion 64 of the stressed ribbon shows a resultant cross-sectional curvature in which the concave side is away from the center of the coil. It will be noticed that the cross-curvature shown in cross-section 62 is somewhat less than that shown in the cross-section 56. This would appear to be the result of the opposing natures of the formed cross-section and the natural cross-section so that there is a subtractive relationship.

Referring now to Figure 8, it can be seen that the ribbon 54 when in the coiled condition has a substantially fiat cross-section. In other words, the cross-sectional curvature shown in the cross-section 62 must be flattened out as the ribbon is allowed to rewind from the extended condition to the coiled condition.

It has been found that the strength of the spring shown in Figure 7 may be somewhat stronger than, equal to, or considerably weaker than the strength of the spring shown in Figure 1. The strength of the spring shown in Figure 7 depends upon the relationship of the cross component to the longitudinal component. If the amount of resultant cross curvature in Figure 7 is less than the natural cross curvature in Figure 1, then the former will be somewhat stronger. If the cross curvatures of the two springs are equal, then their strengths will be substantially equal. Finally, if the cross curvature in Figure 7 is greater than that shown in Figure 1, then the former will be weaker than the latter. As a matter of fact, the cross curvature may be of such an amount that it is substantially equal to the longitudinal component of the spring. In that instance it will take force of zero magnitude to maintain the spring in its extended condition. The stressed ribbon in this type of spring may be readily removed from the coil whereupon it will form the cross-sectional curvature. If it should be desired to rewind the stressed ribbon onto the coil, it is merely necessary to hold the coiled portion and apply a slight force toward the coil at the other end. If the coil is allowed to rotate, then the unwound stressed ribbon will readily wind onto the coil.

The cross-sectional curvature may also be of such an extent that it exceeds the longitudinal component of the coiled spring. In this type of spring the stressed portion will unwind by itself from the coiled condition. As a result it is necessary to provide some sort of brake or restraining means to prevent the stressed ribbon from unwinding from the coil. If it should be desired to rewind the stressed portion, it is then merely necessary to force the unwound end toward the coil with sufficient forceto overcome the cross component.

It has also been discovered that this spring has certain rather unique properties which permit various uses that will be described later on. This characteristic is the result of the stability imparted to the stressed ribbon by the cross-curvature. If the formed cross-section such as shown in Figure 7 is suflicient to form a resultant cross curvature, the resultant will tend to eliminate the tendency for the extended stressed ribbon when unrestrained to become entangled and for the free end to rotate about the coil. The stressed ribbon will readily wind upon the coil but will do it by means of rotating the coil so that the extended ribbon moves in a longitudinal direction toward the coil. The greater the amount of crosscurvature, the greater the stability.

It has also been found that the spring shown in Figure 7 when fully extended will tend to remain in its extended condition even if unrestrained. This tendency to remain in the extended condition is at least partially dependent upon the magnitude of the resultant cross curvature. If the resultant cross curvature is relatively large, the stability of the spring when in the extended condition will be greater than if it is relatively small for any given longitudinal component. When such a spring is in the extended condition, it may be recoiled by bending the ribbon in the direction of the coil so as to partially form a first convolution. if the spring is of the selfwinding type, then it will continue winding until all of the stressed ribbon has been wound into the coiled condition. If the spring is of the balanced or self-extending types, then it will be necessary to provide a slight force to wind the ribbon into the coiled condition.

The spring shown in Figure 7 has the further characteristic that an extended length of stressed ribbon will act as a cantilever and will support a considerable amount of weight. The load that may be supported without buckling is dependent upon the magnitude of the resultant cross curvature. The extended portion will also support a load acting in a longitudinal direction toward the coil without buckling. Again, the size of the load required to buckle the extended portion is dependent upon the magnitude of the cross curvature.

Referring now to Figures 9 and 10, there is shown another modification of the spring embodying the invention. In this modification the coil spring generally denoted by the numeral 70 is constructed of a ribbon 72 stressed to form a plurality of tightly wound convolutions. The stressing operation is substantially the same as that described with reference to Figures 1, 3, 5, and 7, and may be substantially the same as that described in my Patent 2,609,191. In the construction of this particular spring, However, there is one important difference which results in the barrel-shape configuration shown in Figure 9. This difference resides in the fact that the cross-sectional curvature is formed or at ieast partially formed contemporaneously with the stressing operation by stressing the ribbon 72 over a die having a curvature substantially the same as the desired cross-sectional curvature. In this type of forming the transverse center is stretched relative to the marginal portions of the ribbon so that the ribbon tends to assume the bowed-out condition as shown in Figure 9. This bowed-out condition is the result of the fact that the center tends to assume a greater radius of curvature than the marginal portions of the ribbon. When the ribbon is extended from the coiled condition, it can be seen that there are two strong longitudinal components tending to rewind it into the coiled condition. The first component is that which is imparted by the stressing operation and which is present in the springs previously described. The second component is the tendency for the center to assume a larger radius than the marginal portions which can be accomplished only when the spring is in a substantially circular or spiral form. Therefore, the second component in addition to the first component is tending to wind any extended portion of the stressed ribbon into the spiral condition. While there may be some tendency for the ribbon to flatten out when moving from the extended to the wound condition, it i believed that the cross component resisting any such flattening is relatively minor compared to these two strong longitudinal components. As a result of the additional force present in the springs shown in Figures 9 and 10', it has been found that this spring is much stronger than the springs described previously.

Referring now to Figures 11 and 12, there is shown another coil spring generally denoted by the numeral 76. The coil spring 76 is constructed of a. ribbon 78 which has been stressed by pulling it over a die in the manner previously described. In this instance, however, the die is provided with a cross curvature so that the marginal portions of the ribbon 78 are stretched more than the center portion. As a result of this die the coil assumes the shape shown in Figure 12. This spring has characteristics somewhat similar to that shown in Figures 9 and 10 in that there are two strong longitudinal components which provide the spring force. The first component is due to the stress imparted to the ribbon by pulling it over the die and the second component is due to the fact that the marginal portions are stressed more than the center so that the ribbon has a strong tendency to assume its coiled condition. While there may be some flattening of the cross-section as the ribbon moves from the extended position to the coiled condition, it would appear that any cross component inherent in this flattening will be subordinate to the aforementioned longitudinal components.

Referring now to Figure 13, there is shown another modification of the spring embodying the invention generally denoted by the numeral 80. The spring 80 is constructed by backwinding a spring substantially the same as that shown in Figures 3 and 4 in the manner shown in my Patents 2,833,027 and 2,833,534. The forwardly wound spring is indicated by the numeral 82 and is constructed from a spring ribbon 84 which has a formed cross-section in which the concave side is toward the center of the coil 82. When the ribbon 84 is extended from its coiled condition, it assumes a concave crosssection 86 as shown in the drawing. As the extended portion 85 approaches the backwound coil 80, the cross curvature is substantially flat as indicated by the crosssection 88. The spring 80 is characterized by the fact that if unrestrained, it will rapidly expand until it returns to the forwardly wound condition. For this reason the coil spring 80 is restrained in its backwound condition and is used in a spring motor, such as a drum having a concentric shaft in which the force is the result of the expansion of the coil. Since the cross component resists coiling, it would assist the expansion of the stressed ribbon. Thus, it can be seen that the longitudinal component normally present in the coil 80 would be somewhat complemented by the cross component. Thus, when the spring or coil 80 is allowed to expand from a wound to an unwound condition, the amount of total work derived from this expansion is increased a substantial amount by the cross-curvature.

Referring now to Figures 14 and 15, there is shown a tape measure generally denoted by the numeral 90, constructed from a spring embodying the invention. The

spring in this instance is substantially the same as that shown in Figure 7, having been constructed from a ribbon having a formed cross curvature. The formed crosscurvature was substantially greater than the natural crosscurvature of the stressed ribbon so as to provide :a resultant cross-curvature in which the concave side is away from the center of the coil 94 as shown in the cross-section 96. The resultant cross-curvature is of sufficient magnitude to impart the desired stability to the extended portion of the stressed ribbon. Thus the free end 98 of the extended ribbon when unrestrained will not tend to rotate around the coil 94.

In one preferred form of the tape measure 90, 'the relationship of the resultant curvature to the longitudinal component is such that the spring is self-winding. Thus, when the end 98 is left unrestrained and the coil 94' is allowed to rotate about its axis, the extended portion of the ribbon 92 will move in a longitudinal direction toward the coil 94. This type of arrangement'provides a convenient measuring tape which does not necessitate the use of a casing and other mechanical apparatus to facilitate its use.

In a preferred form the measuring tape is provided with spaced null points at which the longitudinal component and the cross component are substantially in balance. The purpose of these null points is to permit the user of the tape to extend a desired length of the tape and then leave the coil 94 unrestrained without rewinding the entire length of the extended ribbon until it is so desired. These null points may be placed at any suitable intervals such as indicated schematically at the 12-inch and 24-inch marks in Figure 15. The null points may be accomplished in any one of several manners. For example, they may be the result of di mirrishing the longitudinal component so that it becomes substantially equal to the cross component. It may further be the result of increasing the cross-curvature so that the cross component is substantially equal to the longitudinal component or thirdly it may be the result of varying both the longitudinal and the cross components until they are substantially equal. In any event when the coil 94 reaches one of the null points 100, it will tend to remain at that point until given a slight additional impetus to continue the rewinding operation.

Referring now to Figure 16, there is shown a slight modification of the tape measure. In this modification the tape measure includes a spring 104 having suitable indicia printed thereon and which is constructed from a ribbon 106, having a formed cross-curvature of sufficient magnitude to provide a resultant cross-curvature in which the concave side is away from the center of the coil 108. The resultant cross-curvature as shown in the cross-section 109 is of sufiicient magnitude to provide the stability necessary to the operation of the tape measure. As was mentioned previously with reference to the tape measure shown in Figure 14, the relationship of the cross components and the longitudinal components may be varied with respect to each other so that the ribbon 106 is selfwinding, self-extending, or is in a substantially balanced condition. The coil 108 is disposed within a casing 110, having a slot 112 through which passes the extended portion of the ribbon 106. If the ribbon is to be self-extending or self-retracting, it may be desirable to provide the null points 100 as described with reference to Figure 15.

A braking device of some suitable sort, such as those commonly used in connection with power driven tape measures may also be used to control the movement of the coil 108 in the extended portion of the ribbon. The inner end of the ribbon 106 is provided with the lug 114 which prevents the entire length of the ribbon from being withdrawn from the casing 110. Thus it can be seen that this invention provides a simple, lightweight con struction consisting essentially of two elements, namely, the ribbon 186 and the casing 1110.

Referring now to Figures 17 and 18, there is shown another application of the spring embodying the invention. In this particular instance the spring is designed to be used as a short tape measure or a yardstick. The yardstick consists of a ribbon having a formed crosssection in which the concave face was away from the coil 152 and which has been longitudinally stressed in the manner previously described. The formed cross-section was of sufiicient magnitude to provide a resultant crosscurvature having the concave side away from the center of the coil 152 as shown in the cross-sections 154 and 156. The relationship of the cross component to the lon gitudinal component may be such that the spring or yard- 9 stick is self-winding, self-extending, or in balance. In any event it has been found that the ribbon 150 may be pulled out to the fully extended position as shown in Figure 17. Even though the ribbon 150 is of the self-winding type, the cross component will impart suflicient stability to prevent the rewinding until the operator so desires once the ribbon is in the fully extended condition. This re- Winding may be accomplished by simply bending one end of the ribbon 150 in the direction in which it is normally coiled. If the tape is self-winding, then the rewinding may be completed by leaving either the free end or the coil unrestrained. On the other hand, if the tape should be the self-extending or balanced type, then it will be necessary to provide suificient force to overcome the cross component. When this is done, the ribbon 150 will readily form the coil 152 due to the longitudinal stresses originally imparted to the ribbon, even though the cross component normally exceeds the longitudinal component.

Referring noW to Figures 19 and 20, there is shown a further application of the spring embodying the invention. This application consists of a brush holder for maintaining carbon brushes and the like into contact with elec trical armatures. The brush holder 120 includes a casing 124 adapted to 'slidingly receive the carbon brush 126. A self-extending spring, generally denoted by the numeral 128, is disposed within the casing 124. The spring 128 is constructed of a ribbon 130 stressed for a substantial portion of its length, and includes a formed crosssection in which the concave side is away from the center of the coil 134. The formed cross-curvature is substantially larger than the natural cross-curvature so as to provide a resultant cross-curvature of substantial magnitude. In fact, the resultant cross-curvature provides a cross component of suflicient force to overcome the longitudinal component and thus provide a self-extending spring. The free end 132 of the ribbon 130 may be unstressed and is adapted to abut the end of the casing 124. The coil 134 of the spring 128 is positioned so as to abut the end of the brush 126 in the manner shown in the drawings. As the brush is worn off by the armature 122, it is maintained in engagement therewith by the force of the spring. In this manner the spring 128 maintains the brush 126 in constant engagement with the armature 122. When it is desired to replace the brush 126, it is merely necessary to remove the old brush and insert a new one and force it inwardly until the spring is in its fully wound condition as shown in Figure 19. Notwithstanding the fact that the cross component is somewhat larger than the longitudinal component, the spring may be readily coiled as a result of the longitudinal stressing operation. It is merely necessary to provide a sufficient force in inserting the new brush 126 to overcome the cross component. The spring 128 may be such that it completely unwinds when the brush 126 is removed or may be provided with a short section at the end 136 which does not completely unwind, even when the brush is removed. The latter feature is accomplished by varying the longitudinal component and the cross component with respect to each other, so that the former is somewhat stronger than the latter so as to provide a self-winding spring. Even though the brush is removed, the end 136 will remain in a wound or coiled condition so as to preform a part or all of a first convolution.

Referring now to Figures 21 and 22, there is shown a modification of the brush holder, generally denoted by the numeral 140. In this modification the free end 144 of the spring 142 is afiixed to the end of the brush 126 and the coiled portion 146 abuts the end of the casing 124. The cross component is somewhat larger than the longitudinal component of the stressed ribbon so that the spring is self-extending. Thus the brush 126 is maintained in constant engagement with the armature 122. The brush 126 may be replaced by simply removing it from the casing 124 and placing a new one so as to engage the end 144 and then forcing it inwardly until the spring 142 is in its coiled condition.

Referring now to Figure 23, there is shown a still further application of the spring embodying the invention. In this instance the spring is used as a support means for the adjustable type lamps. The lamp generally denoted by the numeral is of any conventional type and is provided with the knob 162 for facilitating adjustment by the user. The lamp 160 is connected to a source of elec trical energy by means of the cord 164 which is wound on the reel generally denoted by the numeral 166. The lamp 166 is adapted to be supported from the ceiling 168 or the like by means of a pair of coil springs 170, each of which is similar to the spring shown in Figure 7. The springs are interwound in the manner shown in Figure 23, with the free end of one spring being afiixed to the fixture 172 which is in turn secured to the ceiling 168. The free end of the other spring is affixed to the lamp 160. Each of the springs is constructed of a ribbon 174 having a formed cross curvature of sufficient magnitude to provide a resultant cross curvature in which the concave side is away from the center of the coil 176, as shown in the cross-sections 178. The relationship of the cross component to the longitudinal component is such that the springs would ordinarily be self-winding when their ends are unrestrained. However, the difference between the two components is substantially equal to the total weight of the lamp 161 In this manner when the lamp is unsupported other than by the springs 170, the springs are in a substantially balanced condition. If the user should partially lift the lamp 160, then the springs will retrieve in the manner previously described. On the other hand, if the user should pull downwardly upon the lamp 160, the springs 170 will uncoil until the additional downward force is removed. This arrangement provides a sturdy but economical support for retractable lamps.

It should be kept in mind that the invention contemplates springs constructed of a ribbon having a varying amount of cross-sectional curvature as well as of a ribbon having a constant amount of cross-sectional curvature. A varying amount of cross-sectional curvature may be particularly desirable where it is necessary to have a variable amount of strength either self-extending or selfwinding. One example of this type of spring is illustrated in the tape measure shown in Figures 14 and 15 having the null points 100. As was stated previously, the crosssectional curvature may be varied until it substantially balances the longitudinal component so as to provide the null point.

A variable cross-section may also be used in certain instances to construct a spring having a constant strength from a ribbon which has been longitudinally stressed a varying amount. Such a spring could be constructed by varying the cross-sectional curvature an amount dependent upon the amount of longitudinal stress. Thus any variation in longitudinal stress could be offset by the cross curvature so as to result in a substantially constant force spring.

Although certain specific applications of the springs embodying the invention have been disclosed in the specification, it is to be understood that this is merely by way of example and not to be construed in any manner as a limitation. For example, the spring may be used as a supporting arm for such devices as telephones, irons, and the like. The spring also may be used in the construction of toys and other types of spring devices. It is contemplated that certain modifications of the springs embodying the invention may be made within the scope of the claims without departing from the spirit of the in vention.

What is claimed is:

1. A coiled spring comprising a ribbon having a formed concaveconvex cross-section, permanently stressed into a plurality of tightly wound convolutions when said stressed ribbon is in repose, each of said convolutions engaging the preceding convolution when said stressed ribbon is in repose, the convex side of said concave-convex cross-section facing towards the center of the coiled spring.

2. A coiled spring comprising a ribbon having a formed concave-convex cross-section, permanently stressed into a plurality of tightly wound contiguous convolutions when the stressed ribbon is in repose, the convex side of said concave-convex cross-section facing towards the center of the coiled spring.

3. A coiled spring comprising a ribbon having a formed concave-convex cross-section, permanently stressed into a plurality of tightly wound convolutions when said stressed ribbon is in repose, each of said convolutions engaging the preceding convolution when said stressed ribbon is in repose, the convex side of said concave-convex cross-section facing towards the center of the coiled spring, said stressed ribbon having a substantially flat cross-section when in repose.

4. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of tightly wound contiguous convolutions when in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency to assume a concave-convex cross-section in which the convex side is toward the center of the coil.

5. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions when in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency when extended to assume a concave-convex cross-section in which the convex side is toward the center of the coil, said ribbon being forced to assume a substantially flat cross-section when said extended portion is wound into its coiled condition, the flattening of said concave-convex cross-section forming a cross stress component in opposition to said tendency to return to said convoluted condition resulting from the longitudinal stress component.

6. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions when in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency when extended to assume a concave-convex cross-section in which the convex side is toward the center of the coil, said ribbon being forced to assume a substantially flat cross-section when said extended portion is wound into its coiled condition, the flattening of said concave-convex cross-section forming a cross stress component in opposition to said tendency to return to said convoluted condition resulting from the longitudinal stress component, said cross stress component being dependent upon the magnitude of cross-sectional curvature when said stressed ribbon is in the extended condition.

7. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions when in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause 'said stressed ribbon to return to its convoluted condition,

said stressed ribbon also formed to have a tendency when extended to assume a concave-convex cross-section in which the convex side is toward the center of the coil, said ribbon being forced to assume a substantially flat cross-section when said extended portion is wound into its coiled condition, the flattening of said concave-convex cross-section forming a cross stress component in opposition to said tendency to return to said convoluted condition resulting from the longitudinal stress component, said cross stress component being dependent upon the magnitude of cross-sectional curvature when said stressed ribbon is in the extended condition, said cross stress component being substantially smaller than said longitudinal stress component whereby said stressed ribbon when in the extended position is self-coiling.

8. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions when in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency when extended to assume a concave-convex cross-section in which the convex side is toward the center of the coil, said ribbon being forced to assume a substantially flat cross-section'when said extended portion is wound into its coiled condition, the flattening of said concave-convex cross-section forming a cross stress component in opposition to said tendency to return to said convoluted condition resulting from the longitudinal stress component, said'cross stress component being dependent upon the magnitude of cross-sectional curvature when said stressed ribbon is in the extended condition, said cross stress component being substantially equal to said longitudinal stress component whereby said stressed ribbon when unrestrained will remain in the extended position or the convoluted condition.

9. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency when extended to assume a concave-convex cross-section inwhich the convex side is toward the center of the coil, said ribbon being forced to assume a substantially flat cross-section when said extended portion is wound into its coiled condition, the flattening of said concave-convex cross-section forming a cross stress component in opposition to said tendency to return to said convoluted condition resulting from the longitudinal stress component, said cross stress component being dependent upon the magnitude of cross-sectional curvature when said stressed ribbon is in the extended condition, said cross stress component being substantially greater than said longitudinal stress component whereby said stressed ribbon when in its convoluted condition is self-extending.

10. A coil spring comprising a ribbon permanently longitudinally stressed into a plurality of contiguous convolutions with each convolution engaging the preceding convolution when said stressed ribbon is in repose, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency to assume a concave-convex crosssection in combination with the natural concave-convex cross-section in which the convex side of the formed 13 concave-convex cross-section is the concave side of the natural concave-convex cross-section.

11. A coil spring comprising a ribbon permanently longiturinally stressed into a plurality of contiguous convolutions with each convolution engaging the preceding convolution, When said stressed ribbon is in its reposd condition, said stressed ribbon having a longitudinal stress component when extended from its convoluted condition, said longitudinal stress component tending to cause a natural concave-convex cross-section in said stressed ribbon and further tending to cause said stressed ribbon to return to its convoluted condition, said stressed ribbon also formed to have a tendency to assume a concave-convex cross-section, said natural concave-convex cross-section being substantially equal and opposite to said formed concave cross-section so that said stressed ribbon has a substantially fiat cross-section when in its extended position.

12. A coil spring comprising a ribbon permanently stressed into a plurality of tightly wound convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when in repose, said ribbon formed to have a tendency to assume a concave convex cross-section, with the convex side of said ribbon adjacent the preceding inner convolution in the coil spring.

13. A coil spring comprising a ribbon permanently stressed into a plurality of tightly wound convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when in repose, said ribbon formed to have a tendency to assume a concave-convex cross-section, the concave side of said stressed ribbon being adjacent the preceding convolutions when the stressed ribbon is in repose, said stressed ribbon being at least partially backwound and maintained from its reposed position so that a coil spring is formed in which the convex side of said stressed ribbon is adjacent the preceding convolutions of said backwound portion of said stressed ribbon, said backwound portion tending to return to said reposed position when unrestrained.

14. A coil spring comprising a ribbon permanently stressed into a plurality of tightly wound convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when said stressed ribbon is in repose, said stressed ribbon formed to have a tendency to assume a concave-convex cross-section throughout its length, the concave side of said stressed ribbon being adjacent the preceding convolutions when said stressed ribbon is in repose, said stressed ribbon being backwound and maintained from its reposed position so as to form a coil spring in which the convex side of said stressed ribbon is adjacent the inner convolutions, said stressed ribbon tending to return when unrestrained from its backwound position to said reposed position.

15. A coil spring comprising a ribbon permanently stressed into a plurality of tightly wound convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when said stressed ribbon is in repose, said stressed ribbon formed to have a tendency to assume a concave-convex cross section, the central portion of said cross-section being stretched more than the marginal portions of said cross-section so that said stressed ribbon when in repose has a concave-convex cross-section.

16. A coil spring comprising a ribbon permanently stressed into a plurality of contiguous convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when said stressed ribbon is in repose, said stressed ribbon formed to have a tendency to assume a concave-convex cross section, the central portion of said cross-section being stretched relative to the marginal portions of said cross-section so that said stressed ribbon when in repose has a concave-convex cross-section.

17. A coil spring comprising a ribbon permanently stressed into a plurality of contiguous convolutions when in repose, each of said convolutions tightly engaging the preceding convolution when said stressed ribbon is in repose, said stressed ribbon formed to have a tendency to assume a concave-convex cross-section, the marginal portions of said cross-section being stretched more than the central portion of said cross-section so that said stressed ribbon when in repose has a concave-convex cross-section.

References Cited in the file of this patent UNITED STATES PATENTS 198,179 Anderson Dec. 18, 1877 1,922,921 Anderson Aug. 15, 1933 1,977,546 Fornelius Oct. 16, 1934 2,622,700 Geyer Dec. 23, 1952 FOREIGN PATENTS 802,363 Germany Feb. 8, 1951

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