METHOD FOR USING THE SAME

Field of the Invention

The invention relates to a spring assembly useful in electrical switches, pressure sensors, latches, and other apparatus and methods of making and using the same, and most specifically to a spring assembly which is well suited for cost- effective electrical switching.

Background of the Invention A variety of switches, pressure sensors, and latches are known. Known switches come in a variety of shapes, sizes, and styles, which can be actuated in a variety of ways. One such variety includes membrane switches used in electrical switching. One type of membrane switch, shown in Figure 1, is a tactile membrane switch 2 which includes a flexible dome 4 which, when compressed, creates physical contact between two electrical contacts or electrodes 6, 8. The contact between the electrodes 6, 8 closes an electrical circuit (not shown). Closure ofthe circuit occurs when a sufficient force has been applied to the flexible dome 4 such that the dome 4 snaps downwardly forcing one electrical contact located beneath the dome 4 to move from one position (open circuit) into another position (closed circuit). The dome 4 can have an upwardly-concave shape when in the open circuit first position and can have a flatter shape when in the closed circuit second position. When depressed, the dome 4 can provide a tactile feedback to the person applying the depressing force.

The snap-action membrane switch 2 is mono-stable, meaning that the dome 4 can remain in an unstable position (downwardly-concave) only for a short period of time, after which the dome 4 will retract back (upwardly-concave up) to the stable position when the actuation force to the dome 4 is released. This action is

the result ofthe elasticity ofthe material used to make the dome 4 and the geometry ofthe dome 4 itself.

There are limitations regarding the use ofthe snap-action membrane switch 2, one of which is the mono-stability. If the quick retraction ofthe mono-stable switch is not desired, this switch 2 is ineffective, or is, at least, inefficient. Another limitation is that the spring force required to actuate the snap-action membrane switch 2 can change with repeated use, which can result in unintentional contact or difficulty in making contact. Furthermore, repeated use can finally result in the fracturing ofthe dome 4. Still further, the switch 2 is generally limited to low- voltage logic switching applications.

One type of power switch used for battery powered electronic equipment (e.g., a computer), although mechanically mono-stable, includes logic circuitry to electronically provide means for bi-stability. That is, this power switch can be pushed inwardly and released to power-up a computer and can be pushed inwardly and released again to power-down the computer. In addition to requiring the logic circuitry to electronically provide the bi-stability, this power switch continuously draws power from a power source to be effective.

Other types of switches, like light switches, may provide bi-stability (stable at both open and closed positions), but can be bulky taking up significant space. When efficient use of space is important, these switches are undesirable. In addition, known bi-stable switches can also be relatively complex and expensive.

Known switches fail to provide a combination of bi-stability, simplicity, reliability, compactness, cost-effectiveness, the ability to handle higher voltage levels than that used in logic switching applications, and the ability to perform without draining a power source, or a subset of this combination. In addition, known mechanical latches and known pressure sensors also fail to provide this combination or a subset thereof.

Summary of the Invention The present invention overcomes these problems by providing a spring assembly which is useful as a bi-stable electrical switch. The assembly includes a

first electrical contact and a second electrical contact. A buckleable member has a buckleable member first end portion, a buckleable member second end portion, and a buckleable member inner portion between the buckleable member first and second portions. The buckleable member first end portion is adjacent to at least one ofthe first and second electrical contacts. At least one end constraint is included for at least partially constraining at least one ofthe buckleable member first end portion and the buckleable member second end portion. An inner constraint means is positioned adjacent to the buckleable member inner portion. The inner constraint and the at least one end constraint cause the buckleable member to be moveable between a first buckled position and a second buckled position. The first and the second buckled positions are stable. The first and second electrical contacts are electrically disconnected when the buckleable member is in the first buckled position, and the first and second electrical contacts are electrically connected when the buckleable member is in the second buckled position. Another embodiment ofthe present invention is an apparatus useful as part of an electrical switch having a first electrical contact and a second electrical contact. The apparatus includes a flexible member and means for constraining the flexible member such that the flexible member is moveable between a first buckled position and a second buckled position, the first and second electrical contacts being electrically connected when the flexible member is in the second buckled position, and the first and second electrical contacts being electrically disconnected when the flexible member is in the first buckled position, the second buckled position being stable and the second buckled position being stable.

Another embodiment ofthe present invention is a bi-stable spring apparatus which includes a member having a member first end portion, a member second end portion, and a member inner portion between the member first and second portions. The member is buckleable. The apparatus also includes means for constraining the member such that the member is moveable between a first buckled position and a second buckled position. The member first end portion is buckled downwardly when the member is in the second buckled position. The member second end portion is buckled downwardly when the member is in the first buckled position.

The member is stable when in the first buckled position and when in the second buckled position.

Another embodiment ofthe present invention is an apparatus useful for capturing a radiographic image. The apparatus includes a cassette housing and a radiographic imaging medium within the housing. A power supply is electrically connectable with the radiographic imaging medium. A bi-stable electrical switch is within the housing for functionally connecting the power supply to the radiographic imaging medium. The bi-stable electrical switch is moveable between a first stable buckled position, in which the power supply is functionally disconnected to the radiographic imaging medium, and a second stable buckled position, in which the power supply is functionally connected from the radiographic imaging medium.

Another embodiment includes a method useful for electrically connecting and disconnecting a first electrical contact and a second electrical contact. The method includes the step of providing a buckleable member having a buckleable member first end portion, a buckleable member second end portion, and a buckleable member inner portion between the buckleable member first and second portions. The buckleable member first end portion is adjacent to the first and second electrical contacts. Another step includes providing at least one buckleable member end constraint for at least partially constraining at least one ofthe buckleable member first end portion and the buckleable member second end portion. Another step includes providing an inner constraint positioned adjacent to the buckleable member inner portion. The inner constraint and the at least one buckleable member end constraint cause the buckleable member to be moveable between a first stable buckled position and a second stable buckled position. The first and second electrical contacts are electrically connected when the buckleable member is in the second stable buckled position and electrically disconnected when the buckleable member is in the first stable buckled position. Another step is applying a closing force to the buckleable member first end portion to move the buckleable member from the first stable buckled position to the second stable buckled position. Another step is applying an opening force to the buckleable

member second end portion to move the buckleable member from the second stable buckled position to the first stable buckled position.

Brief Description of the Drawings The foregoing advantages, construction, and operation ofthe present invention will become more readily apparent from the following description and accompanying drawings in which:

Figure 1 is a sectional perspective view of a known membrane switch; Figure 2 is an isometric schematic view of one embodiment of a spring assembly useful as a bi-stable electrical switch in a first stable buckled position, according to the present invention;

Figure 3 is a side schematic view ofthe spring assembly shown in Figure 2, the switch being in a second buckled position;

Figure 4 is a side schematic view ofthe spring assembly shown in Figure 2, but the switch is in a first buckled position;

Figure 5 is an isometric schematic view of another embodiment ofthe spring assembly shown in Figure 2;

Figure 6 is an isometric schematic view of another embodiment ofthe spring assembly shown in Figure 2, including a conductive member; Figure 7 is side schematic view of another embodiment ofthe spring assembly shown in Figure 2;

Figure 8 is an isometric view of another embodiment ofthe spring assembly shown in Figure 2, the assembly being within a first stable buckled position and one portion being unconstrained; Figure 9 is a side view ofthe assembly shown in Figure 8;

Figure 10 is a side view ofthe assembly shown in Figure 8; Figure 11 is a isometric view of a plurality of spring assemblies similar to the assembly shown in Figure 2;

Figure 12 is a isometric view ofthe spring assembly of Figure 2 shown as a part of a radiographic imaging cassette;

Figure 13 is a isometric view of an embodiment ofthe spring assembly useful as a part of a sensor;

Figure 14 is a isometric view of an embodiment ofthe spring assembly useful as a part of a latching apparatus which is shown in an unlatched position; Figure 15 is a isometric view ofthe embodiment shown in Figure 14, but where the latching apparatus is in a latched position;

Figure 16 is a side view of another embodiment ofthe spring assembly shown in Figure 2, the buckleable member being actuated by a piezoelectric component; and Figure 17 is an exploded isometric view of another embodiment ofthe spring assembly shown in Figure 2, the embodiment being constructed in a layered fashion.

Detailed Description of the Preferred Embodiments The present invention involves a spring assembly useful for switching applications (including electrical and mechanical switching), latching, and other applications. Figures 2-4 illustrate one embodiment of a spring assembly 10 which is useful as a bi-stable electrical switch 12. The switch 12 includes a base 14 which has a base upper surface 16. The base upper surface 16 has a base upper surface first portion 18 and a base upper surface second portion 20. The base 14 can include a first end slot 22 and a second end slot 24. Preferably, the first end slot 22 remains in the same position relative to the position ofthe second end slot 24.

The base 14 can be an injection-molded part made of a variety of materials, such as polycarbonate or other injectable material. The base 14 could instead be a stamped metal component. Or, the base 14 could be made of materials used currently to make circuit board bases (e.g., glass-filled resins). The base 14 can function as a lower constraint which will be described further below.

A first electrical contact 26 is positioned on the base upper surface first portion 18. A second electrical contact 28 positioned on the base upper surface first portion 18. The second electrical contact 28 is electrically connectable to the first electrical contact 26 to close an electrical circuit (not shown). An example of a

circuit could include a battery and light bulb such that the light bulb can be energized and emit light when the first and second electrical contacts are connected.

An inner constraint 30 is positioned above the base upper surface 16, for example, between the base upper surface first portion 18 and the base upper surface second portion 20. The inner constraint 30 includes a inner constraint contacting surface 32 which is shown as being curved. The inner constraint 30 can be an injection-molded part and can be an extension ofthe injection-molded base. The inner constraint 30 can instead be a pin having, for example, a circular cross-section and being fixed in a position relative to the first and second end slots 22, 24. A buckleable or flexible member 34 for electrically connecting the first and second electrical contacts 26, 28 is positioned between the base upper surface 16 and the inner constraint 30. In this embodiment, the buckleable member 34 can be a conductive strip. The buckleable member 34 has a buckleable member first end portion 36, a buckleable member second end portion 38, and a buckleable member inner portion 40 between the buckleable member first and second end portions 36, 38. The buckleable member first end portion 36 is positioned adjacent to the first and second electrical contacts 26, 28. The buckleable member second end portion 38 being positioned adjacent to the base upper surface second portion 20. The buckleable member inner portion 40 is positioned adjacent to and slideable against the inner constraint contacting surface 32. The inner constraint 30 could be a pin having, for example, a circular cross-section and being fixed in a position relative to the first and second end slots 22, 24. Or, the pin could be rotatably mounted and include a center slot through which the buckleable member 14 could fit.

The buckleable member first end portion 36 includes a first buckleable member end 42 which is insertable within the base first end slot 22. The buckleable member second end portion 38 includes a second buckleable member end 44 which is insertable within the base second end slot 24. The slot height is preferably larger than the thickness ofthe buckleable member 34 so that the first and second end portions 36, 38 are at least somewhat free to move within the slot. However, the slot height can be such that the first and second end portions 36, 38 fit tightly within

the slots 22, 24. The slot shape is shown as being rectangular, although the walls forming the slot could be curved or angled differently.

As shown, the distance from the ends ofthe base first and second end slots 22, 24 is less than the length ofthe buckleable member 34 such that the buckleable member 34 is bowed when inserted into the base first and second slots 22, 24. In one embodiment where the buckleable member 34 is a 0.0055-thick strip of steel shimstock, the distance between the ends ofthe first and second end slots 22, 24 is approximately 3.57 centimeters (approximately 1.40 inches) and the length of the buckleable member 34 is approximately 3.64 centimeters (approximately 1.43 inches). Therefore, difference between the distance and the length is 0.07 centimeter (0.03 inch). For shimstock steel, it has been found if the distance-length difference is significantly less than 0.063 centimeter (0.025 inch), the buckleable member 34 becomes too flat to perform effectively. The distance-length difference can be at least as much as approximately 0.254 centimeter (0.1 inch) and still function. For other materials, the range for the distance-length difference may be different which could be determined by testing materials other than the shimstock steel (or the shimstock steel at different thicknesses, widths, lengths). As a result, the distance-length difference can be chosen to affect the distance which the buckleable member is depressed to cause movement from one buckled position to another.

The end slots 22, 24 are shown as being a particular distance above the surface ofthe base 14. The exact distance is not critical. Like other dimensions within the spring assembly 10, this slot-base distance can be chosen based on experimentation with the material choice and dimensions ofthe buckleable member 34 and the material choice (and other dimensions) ofthe base 14.

Due to the position ofthe inner constraint 30 and the base 14 (acting as a lower constraint) relative to the base first and second end slots 22, 24, the buckleable member 34 contacts and flexes about the inner constraint contacting surface 32. As a result, the buckleable member 34 is shown as being flexed into a generally S-shaped (or serpentine) configuration. The spring assembly 10 can be configured such that the radii ofthe arches ofthe buckleable member first and

second end portions 36, 38 are either larger and smaller than that shown making the S-shape more flat or more curved, respectively. When the S-shape is made flatter, the S-shape appears like a wavy I-shape. In addition, the spring assembly 10 can be configured such that one ofthe buckleable member portions has a smaller radius than the other portion (which is bowed in substantially an opposite direction). In fact, the spring assembly 10 can be configured such that one ofthe buckleable member end portions is curved to have a specific radius and the other end portion can be straighter, or flatter, or actually straight, or flat.

The buckleable member 34 can be repeatedly buckleable about the inner constraint 30 between a first stable buckled position, shown in Figures 2 and 4, and a second stable buckled position, shown in Figure 3. When in the second stable buckled position, the buckleable member first end portion 36 can be arched downwardly and contact the first and second electrical contacts 26, 28 while the buckleable member second end portion 38 can be arched upwardly away from the base upper surface second portion 20. When in the first stable buckled position, the buckleable member first end portion 36 can be arched upwardly away from the first and second electrical contacts 26, 28 while the buckleable member second end portion 38 can be arched downwardly more toward the base upper surface second portion 20. The buckleable member 34 is shown as having a first S-shape when in the first position and as having a second S-shape when in the second position. The first S-shape is shown as being a virtually a mirror image ofthe second S-shape. However, the first and the second S-shapes can have significantly different shapes. For example, the spring assembly 10 can be configured such that when the buckleable member 34, which has one curved end portion and one flat end portion, moves from one position to another, the flat end portion can become curved while the curved end portion can become flat (or curved in the opposite direction). Or, alternatively, the spring assembly 10 can be configured such that when the buckleable member 34, which has two curved end portions, moves from one position to another, one ofthe curved end portions becomes curved in the opposite

direction and the other curved end portion becomes flat (or curved, but flatter, in the opposite direction).

Because the buckleable member 34, as shown, can be conductive, the buckleable member first end portion 36 can electrically connect the first and second electrical contacts 26, 28 and close a related electrical circuit (not shown). The resistivity ofthe buckleable member 34 depends on what material the buckleable member 34 is made of. For example, the buckleable member 34 can be at least partially metallic, e.g., made of stainless steel. Or, the buckleable member 34 could generally be non-conductive, but coated with a thin conductive layer. When in the first stable buckled position, the buckleable member first end portion 36 is arched upwardly and does not contact the first and second electrical contacts 26, 28 while the buckleable member second end portion 38 is arched downwardly and against the base upper surface second portion 20. Consequently, the first and second electrical contacts 26, 28 are electrically disconnected and the related electrical circuit is opened.

When the buckleable member 34 is in the first stable buckled position, a closing force applied downwardly against the buckleable member first end portion 36 causes the buckleable member 34 to shift to the second stable buckled position. When the buckleable member 34 is in the second stable buckled position, an opening force applied downwardly against the buckleable member second end portion 38 causes the buckleable member 34 to shift to the first stable buckled position.

In addition to the bi-stability offered by the switch 12, the application of a force less than, for example, the opening force can cause the buckleable member first end portion 36 to be raised from the first and second electrical contacts 26, 28 thereby opening the related circuit. But, because this lesser force can be insufficient to shift the buckleable member 34 to the first stable buckled position, removing the lesser force results in the return ofthe buckleable member 34 and contact with the first and second electrical contacts 26, 28. Hence, the related circuit would again be closed.

The buckleable member 34 can provide a tactile indication when the application of an opening or closing force causes the buckleable member 34 to shift from one stable position to another. In other words, when a human user applies the opening or closing force to the buckleable member 34 with his or her finger, the user will feel a "snap" when a shift has occurred. In fact, the user can feel the downward snap ofthe buckleable member first end portion 36 while feeling the upward snap ofthe buckleable member second end portion 38, and vice versa. In addition, the buckleable member 34 provides an audible "snap" indication when a shift has occurred. The buckleable member 34 and the inner constraint 30 could be configured such that the inner constraint have a center slot through which the buckleable member 34 fits (not shown), rather than the buckleable member 30 contacting the outer surface ofthe inner constraint 30. In addition, the inner constraint could include the ability to rotate about its longitudinal axis (which lies in and out ofthe page on which Figure 2 rests). With this ability, a user could simply rotate a knob connected to the inner constraint to shift the buckleable member from position to position.

Returning to embodiment shown in Figures 1-4, the magnitude ofthe opening force and the magnitude ofthe closing force necessary to shift the buckleable member 34 can depend on the material choice and dimensions ofthe buckleable member 34, the radius ofthe bow ofthe buckleable member first end portion 36 and the buckleable member second end portion 38, the position ofthe inner constraint 30 relative to the base first and second end slots 22, 24. In one embodiment, a person could apply sufficient force to shift the buckleable member 34 between first and second stable buckled positions using his or her finger. For a shimstock steel buckleable member having a length of approximately 3.64 centimeters (approximately 1.434 inches) and a width of approximately 0.7 centimeter (approximately 0.275 inch), a suitable thickness could be approximately 0.014 centimeter (approximately 0.0055 inch). The distance between the end ofthe first end slot 22 and the end ofthe second end slot 24, the position ofthe inner constraint 30, and the length ofthe buckleable member 34 is one way of

determining the degree to which the buckleable member 34 is flexed and the force required when moving the buckleable member 34 between positions.

The switch 12 can be designed so that the magnitude ofthe opening force and magnitude ofthe closing force are either approximately equal or unequal to each other. For some uses, a difference can be beneficial. For example, the switch 12 can be designed such that shifting from a first position to the second can be accomplished with a relatively small force while shifting from the second position back to the first can be "discouraged" by the requirement of a significantly greater force. To provide the switch 12 such that different opening and closing forces are required, several approaches can work. First, the buckleable member 34 can be made thicker in the buckleable member first end portion 36 than in the buckleable member second end portion 38. Or, when a buckleable member 34, having a constant thickness and width, remains in one position for an extended period of time such that it creeps and naturally "prefers" to remain or to move to that prefened position. Or, the buckleable member could be preformed or positioned within the spring assembly such that the curvature ofthe buckleable member first and second end portions is different. Or, a spring (not shown) can be added below the buckleable member first end portion 36 or the buckleable member second end portion 38 to apply an upward force to that portion.

Rather than relying on a difference in force to "discourage" the shifting from one position to another, a rigid wall 46 A could be included as shown in Figure 5. The rigid wall 46A can prevent a user from pressing on the buckleable member second end portion 38A (hidden). The rigid wall 46 A could include a wall hole 48 A leading to the buckleable member second portion 38 A which could be penetrated by a specially designed tool or key (not shown) which could apply the requisite opening force to the buckleable member second end portion 38 A. With this scheme, only a user (or a machine) possessing the tool or key could shift the buckleable member 34A back to the first stable buckled position. Figure 6 illustrates another embodiment of a bi-stable electrical switch 12B.

In this embodiment, the buckleable member 34B need not be conductive due to the

inclusion of a conductive member 50B positioned between the buckleable member first end portion 36B and the first and second electrical contacts 26B, 28B. As such, the buckleable member 34B and the conductive member 50B together make up the actuator ofthe switch 12B. The conductive member 5 OB can act as one ofthe electrical contacts (not shown) by being electrically connected to the previously mentioned circuit (e. g., the electrical circuit including the Ught bulb and the battery). Similarly, when the conductive member SOB is replaced in the circuit by a conductive buckleable member 34B, the buckleable member 34B can effectively be the second electrical contact by being electrically connected to the circuit.

The conductive member 5 OB can act as one ofthe electrical contacts (not shown) by being electrically connected to the previously mentioned circuit (e. g., the electrical circuit including the Ught bulb and the battery). Similarly, when the conductive member 50B is replaced in the circuit by a conductive buckleable member 34B, the buckleable member 34B can effectively be the second electrical contact by being electrically connected to the circuit.

Figure 7 illustrates another embodiment in which the buckleable member need not be conductive. The second electrical contact 28C is shown as being positioned above the first electrical contact 26C. The first and second electrical contacts 26C, 28C can be positioned in this way by being constructed similarly to known membrane switches. The second electrical contact 28C could include an upper layer having a bottom surface on which a silver ink circuit is located. The first electrical contact 26C could simUarly include a lower layer having a top surface on which another silver ink circuit is located. The silver ink circuits can be produced by silk-screening a silver ink onto a plastic film, such as a mylar film. The upper and lower layers can be spaced apart from one another by a middle layer which has a hole through which the first and second electrical contacts 26C, 28C can communicate. The middle layer allows contact between the upper and lower layers (and the first and second electrical contacts 26C, 28C) through the hole when a sufficiently large force is apphed to the three layers to compress the middle layer

or cause the upper and/or lower layers to flex such that the silver ink surfaces make contact.

Figure 7 also shows a flexible covering 56C. The flexible covering 56C could be used to protect, seal, and/or hide the spring assembly from view and could even have graphics, such as "ON" and "OFF', positioned above the buckleable member first end portion 36C and the buckleable member second end portion 38C, respectively.

Figures 8-10 illustrate another embodiment of a bi-stable electrical switch 12D. In this embodiment, one end ofthe buckleable member 34D need not be constrained within a base first end slot in contrast to the embodiment shown in

Figure 2. The buckleable member second end portion 38D is not secured allowing it to move upwardly when the buckleable member first end portion 36D is arched downwardly as in the second buckled position, as shown in Figure 9. A force appUed downwardly against the upwardly flexed buckleable member second end portion 38D returns the buckleable member 34D to the first buckled position.

In this embodiment, the buckleable member inner portion 40D is shown as not being constrained by a curved surface as previously shown, but constrained by being pinned or riveted to the base 14D. Other mechanical constraints would also work including the use of screws, nails, adhesives, and the like. Another variation shown within this embodiment is that the buckleable member first end 42D is not held within a base end slot. Instead, the buckleable member first end 42D is attached to a top surface of an end ofthe base 14D (by, for example, an adhesive). The buckleable member first end 42D could, instead, be looped (not shown) such that the looped end could be slipped over and constrained by a base end pin (not shown).

Furthermore, this embodiment includes a lever 52D between the buckleable member 34D and the base 14D which pivots when the buckleable member 34D moves between the two positions. The addition ofthe lever 52D can allow the pinned buckleable member to be made of a greater range of materials. This embodiment points out that many constructions ofthe present invention are contemplated.

Another embodiment ofthe switch 12 could include a member (not shown), such as a waU, positioned above the buckleable member second end portion 38. This waU could be positioned relative to the buckleable member second end portion 38 to prevent the buckleable member 34 from moving far enough to snap into the second buckled position. Consequently, the second buckled position is, in fact, unstable, and the buckleable member 34 will return to the first stable buckled position when the force appUed to the buckleable member 34 is removed. This allows for a momentarily closed circuit which could be used for flashlights or other such uses. And, this allows for a momentarily closed circuit within higher voltage appUcations than known membrane switches. If the wall (not shown) could be moved such that it no longer interferes with the movement ofthe buckleable member second end portion 38, the user could convert the apparatus 10 from a mono-stable apparatus into a bi-stable apparatus.

Another embodiment ofthe switch 12 (not shown) could include the opening and closing of two electrical circuits, rather than one as previously discussed. In this case, when the buckleable member is in one position, it could close one circuit by connecting two contacts within a first circuit and it could open another circuit by disconnecting two contacts within a second circuit. When in the second position, the buckleable member could disconnect the two contacts ofthe first circuit and connect the two contacts ofthe second contact. The alternating closure ofthe two circuits could be similarly accomphshed (not shown) by connecting a common wire (i.e., ground) to the center ofthe spring and having an electrical contact at each side ofthe base. Then, one circuit would be broken and the other made when the spring goes back and forth between positions. The above-mentioned embodiments show that the spring assembly 10 is a relatively simple apparatus and, consequently, can be relatively cost-effective. Another advantage is that the spring assembly 10 can made relatively large, like a light switch, or can be made relatively small, such as a computer dipswitch array. The embodiment shown in Figures 2-4 is useful for "finger" actuation and be sized as previously noted.

Figure 11 illustrates the use of several smaU switches 12E in a smaU dipswitch anay 58E. The small switches 12E can be, for example, up to five to ten times smaller (or even smaller) than the previously described finger-actuated embodiment and can be useful, for example, in computers, other electronic devices, and on circuit boards.

With the ability to be made with a very low profile (thickness), the spring assembly 10 can be surface-mounted and not interfere with the motion of other objects. (The spring assembly 10 is shown with a relatively high profile and can be made with a significantly lower profile, i.e., thinner.) This can allow for easier assembly and retrofitting. Also, a conventional Ught switch, such as the one housed in an electrical box and fit into the wall of a bedroom or bathroom, can be replaced by a Ught switch using the spring assembly 10 such that the electrical box may not be necessary (nor the effort to fit the box into the waU).

Another advantage ofthe spring assembly 10 is that it is capable of being used in high voltage appUcations. Typical membrane switches have silk-screened contacts which Umit cunent to that of logic control levels. The switch 10 can handle much higher cunent levels because the current can travel through the buckleable member 34 which can have a higher cunent carrying capabiUty than silk- screened contacts. Figure 12 illustrates the use ofthe bi-stable electrical switch 12F as a part of a radiographic imaging cassette 60F capable of capturing and storing a radiographic image. An example of a radiographic imaging cassette which could employ the switch 12F is disclosed in U. S. Patent Apphcation Serial No. 08/220,899. Within the radiographic imaging cassette 60F, the switch 12F is useful for closing a circuit which connects a power supply (e.g., batteries, not shown) to an imaging medium (not shown). The power supply can apply a voltage, which can be relatively high, across the imaging medium to aUow the medium to capture and retain an x-ray- generated image. The switch 12F can be mounted to an endcap 62F ofthe cassette tray which is sUdeable in and out ofthe cassette shell 64F. A membrane or other cover (not shown) could be included within the cassette 60F to conceal the switch 12F and/or to protect the switch from fluids. The keyhole approach shown in

Figure 5 could be used if it were desired to only aUow a person (or a conesponding mechanism) with a "key" to control the voltage within the cassette 60F.

The spring assembly 10 can also be useful for sensing. For example, the spring assembly 10 shown in Figure 2 could be positioned within an automobile (not shown) to sense a collision and cause an airbag to inflate, stop the flow of gasoline within the automobUe, or sense the sequence of collision impacts when the rear of a first automobile is struck by a second automobile and the front ofthe first automobile strikes a third automobile.

Another use for such as a sensor is within a machine which transports articles along a pathway (not shown). One embodiment for this could include a spring assembly 10 for sensing when an article begins to inadvertently move from the pathway but before the article is jammed within the machine, or in some way damaged by moving from the pathway. To do this, the spring assembly 10 could be positioned along the pathway, for example, adjacent to a pathway guide. When moving from the pathway, the article would strike and move the pathway guide which, in turn, strikes the spring assembly 10 causing the buckleable member 34 to shift positions. The spring assembly could, again, close an electrical circuit to signal the machine to stop transporting ofthe article. The movability ofthe guide could allow for easier removal ofthe article when the machine is shut down and could be easily repositioned along the pathway.

The spring assembly 10 could be used purely as an indicator rather than a part of a circuit. For example, the spring assembly could be positioned on an inside wall of a shipping container (not shown) to indicate when the wall of a shipping container has experienced some external impact. Another embodiment ofthe spring assembly is shown in Figure 13. The spring assembly 10G is within an enclosure 66G which includes an aperture 68G. The aperture 68G is covered by a flexible membrane 70G. The aperture 68G and the flexible membrane 70G are positioned above the buckleable member first end portion 36G (which is hidden behind the waUs ofthe enclosure 66G) such that the flexible member 70G can contact the buckleable member first end portion 36G and shift the buckleable member 34G to the second buckled position when the flexible

membrane 70G is sufficiently deflected toward the buckleable member 34G. This embodiment could be useful for sensing a differential between the pressure inside the enclosure 66G and the pressure outside the enclosure 66G. The enclosure 66G could be airtight such that an increase in pressure outside the enclosure 66G would cause the flexible member 68G to deflect inwardly and force the buckleable member 34G to the second buckled position. This pressure-sensing application could be useful for informing a SCUBA diver when he or she has reached a particular depth (exterior pressure increases with depth).

A similar embodiment could be used to sense acceleration or deceleration rather than pressure. This variation could involve the use of a movable mass (not shown) positioned on or above the buckleable member first end portion 36G. When the buckleable member 34G is in the first buckled position and the mass is sufficiently accelerated (or decelerated), movement ofthe mass relative to the buckleable member 34G could apply downward pressure to the buckleable member first end portion 36G and shift the buckleable member 34G to the second buckled position. If properly positioned within an automobile, a sufficiently large. change in the velocity ofthe automobile (due to, for example, a collision with another automobile) could actuate the spring assembly 10G and cause an airbag to open (and/or a fuel pump to stop). Other safety-related uses and non-safety related use for this acceleration sensor are envisioned. In addition, this embodiment (and the pressure sensing embodiment) could include, for example, a keyed arrangement such as that shown in Figure 5. With this keyed arrangement, the spring assembly 10G could, in essence, provided a tamperproof record of the event which caused the actuation ofthe spring assembly 10G. Figures 14 and 15 schematicaUy iUustrate another embodiment ofthe spring assembly 1 OH as a part of a latching apparatus 72H. The spring assembly 10H includes a latching member 74H which is attached to or positioned adjacent to the buckleable member first end portion 36H. The spring assembly 10H is operatively coupled to the top of a first component 76H. The first component 76H includes a first latching depression 77H through the latching member 74H can pass when the buckleable member is shifted to the first position. A second component 78H is

sUdeable adjacent to the first component 76H and includes a second latching depression 80H which can be mateable with the latching component 74H.

Figure 14 shows the latching apparatus in a first position in which the latching member 74H and the latching depression 80H are not mateable. Figure 15 shows the latching apparatus 72H in a second position in which the latching member 74H and the latching depression 80H are mateable. When mateable, the buckleable member 34H can be shifted such that the latching member 74H move downwardly and fit within the latching depression 80H. When the latching member 74H is within the latching depression 80H, the second component 78H can not shde relative to the first component 76H. From the description of this latching embodiment, it is apparent that several other latching embodiments and many appUcations are envisioned. Also, many means (including those previously described for shifting the buckleable member 34 within the electrical switch embodiments) could be employed to shift the buckleable member 34H within the latching apparatus 72H.

To this point, the spring assembly 10 has been described as being actuated by the application of a force to the buckleable member 34 by some object, such as a person's finger for a Ught switch application, a small tool to move a small dipswitch array, or a automobile bumper for an airbag application. Another way of applying a force to the spring assembly 10J could involve a piezoelectric component 82 J, as shown in Figure 16. Positioned as shown, the piezoelectric component 82 J could be made to expand when an electric cunent is passed through it to the point where the piezoelectric component 82 J forces the buckleable member 34 J to shift from one position to the other. This embodiment could be used as an electrical fuse/circuit breaker (not shown) such that when a higher than desirable cunent is passing through a circuit (to which the piezoelectric component 82J is connected), the piezoelectric component 82 J can force the buckleable member 34 J to shift and open the circuit by disconnecting the two electrical contacts 26J, 28J.

Still another way of actuating the spring assembly 10 could involve the use of bi-metal technology. For example, a strip of activated bi-metal (not shown) could be attached to portions ofthe buckleable member 34 such that selective heat

appUcation to the activated bi-metal could cause thermal expansion ofthe strip and the shifting ofthe buckleable member 34. Or, an activated bi-metal member (not shown) could be operatively coupled to the inner constraint 30 such that, when heated, bi-metal member would move the inner constraint 30 toward, for example, the buckleable member second end portion 38. This could cause the buckleable member 34 to shift from one position to another.

The exploded illustration of still another construction ofthe apparatus is shown in Figure 17. This embodiment is shown as including five components. The lower component 84K can be a silver ink circuit on a mylar film, like that previously described. The second component is the buckleable member 34K. The third component 86K is a layer of material, such as another mylar layer which includes a third component aperture 88K. The length ofthe aperture 88K can be shghtly less than the length ofthe buckleable member 34K. The fourth component 90K is another layer, which, again, can be a mylar layer. The fourth component 90K includes two fourth component apertures 92K which are separated by a middle separating portion 94K (which acts similarly to inner constraint 30). The fifth component 96K can be a flexible material, such as another layer of mylar film. When the five components are sandwiched together by, for example, adhesive, the buckleable member 34K is held in a buckled state and is buckleable between two positions by applying, for example, finger pressure to the fifth component 96K above the fourth component holes 92K. The middle separating portion 94K functions similarly to the previously described inner constraint 30. This embodiment is one example of a simple and low profile construction.

The above embodiments are only a few ofthe ways in which the present invention can be constructed and used. Other uses involve the use ofthe spring assembly within dashboard or domeUght switches in automobiles. Other constructions or embodiments could include the a buckleable member 34 which is made-up of a mechanical linkage, rather than a flexible strip spring. These many uses and many constructions indicate the significant breadth ofthe present invention.