Abstract:
A switch device which includes a magnet movable within a passageway. A wire coil is provided about the passageway such that, as the magnet moves into the coil, a current is induced, thereby providing a signal pulse. The switch can be utilized for sensing changes in inertia, with a stopper opposing movement of the magnet unless the magnet imparts sufficient force against the spring biased stopper to allow the magnet to move along the passageway. The biasing force of the stopper can be adjusted to adjust the amount of force, acceleration or deceleration required for actuating the switch. The switch may also be utilized without the spring-biased stopper, with the magnet preloaded with a spring or weight, such that the switch automatically operates upon removal of a safety pin.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to switches and particularly to switches utilized for sensing a change in inertia. Certain aspects of the present invention are also applicable to switches utilized for purposes other than sensing a change in inertia. 
     2. Discussion of Background 
     Often it is desirable to sense a change in inertia for data gathering purposes and/or to initiate an automated sequence of events. For example, in one well-known application, an inertia switch can sense impact of a vehicle in order to actuate a safety device such as an air bag. In addition, in the context of rocketry and missiles, it can be desirable to determine the point at which a certain level of acceleration is attained in order to monitor the rocket or missile, as well as to initiate a sequence of controlled events which are to occur at a predetermined level of acceleration. An inertia switch may also be utilized in the shipping or automotive industries to indicate when predetermined acceleration levels are exceeded, for example in order to avoid excessive acceleration which may cause excessive loads on the engine. Inertia switches may also be utilized for armaments, such that detonation occurs upon impact, or a predetermined period after impact or after launch (e.g., in missile applications). 
     Typically, an inertia switch will include a mass which moves (i.e. moves relative to other portions of the switch) upon the application of a sufficient force/acceleration to the switch or the body to which the switch is attached. More particularly, when the switch attains a predetermined amount of acceleration, the mass within the switch will be moved to a position which either establishes or breaks an electrical contact in order to produce a signal. 
     U.S. Pat. No. 3,493,701 discloses an example of an inertia switch in which a magnet holds a ball in a seated position. When the switch encounters a predetermined amount of acceleration, the magnet will be insufficient to maintain the ball in the seated position, and the ball becomes unseated. Unseating of the ball will either break an electrical contact established in the seated position, or will establish a new electrical contact at a location other than the seated position. When functioning properly such an arrangement can provide an adequate indication of a change in inertia. However, it can be difficult to accurately maintain an exact magnetic force such that the ball is only unseated at a desired acceleration level. 
     In addition, the use of electrical circuit arrangements, in which contacts are established or broken upon acceleration, requires a voltage source which can increase the weight and complexity of the device. Additional monitoring or inspection is also required to ensure that the voltage source is functioning properly. Moreover, electrical contacts can often become oxidized or corroded, thereby diminishing the reliability of the switch. Such contacts are also susceptible to corrosion or dirt preventing proper contact. 
     Accordingly, a switch is desired which avoids the aforementioned shortcomings. Such a switch should be able to sense changes in inertia, or other conditions, without requiring a voltage source for producing a signal. In addition, the switch should be able to accurately sense changes in inertia without relying upon the establishment or breaking of electrical contacts within a circuit. The switch should also be reliable and inexpensive to build, and not susceptible to the production of an undesired signal as a result of vibration or other conditions which are not desired to be sensed. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a switch device which can reliably indicate a change of inertia. 
     It is another object of the present invention to provide an inertia switch having a rugged, yet inexpensive construction. 
     It is a further object of the present invention to provide a switch device which can produce an electrical pulse without requiring a separate voltage source. 
     It is a further object of the present invention to provide a switch device which produces a signal in response to movement of a movable object within the switch device, without requiring electrical contacts to sense the movement. 
     It is yet another object of the present invention to provide an inertia switch having a high natural frequency such that a signal is not inadvertently produced by random accelerations or vibrations. 
     It is a still further object of the present invention to provide an inertia switch which senses acceleration in one direction, and is not prone to inadvertent signaling as a result of accelerations or shocks in other than the selected direction. 
     These and other objects and advantages are attained in accordance with the present invention in the form of a switch device which utilizes an induced current produced within the switch. In particular, the present invention includes a housing having a passageway therein, with a magnet provided for movement along the passageway. When utilized for sensing changes in inertia, a stopper or restraint opposes movement of the magnet until the change in inertia is sufficient to overcome the opposing restraint force. Once the change in inertia of the magnet is sufficient to overcome the opposing force provided by the stopper, the magnet moves along the passageway and into a coil which is disposed about a portion of the passageway. As the magnet passes into the coil, a current is induced which thus provides a signal indicative of the change of inertia. 
     The switch may also be utilized as a mechanical sensor device in which the magnet is preloaded with a spring or weight. Upon removal of a stopping pin, the magnet is fired along the passageway and into the coil, again producing a signal with the induced current. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily understood from the following detailed description, particularly when considered in conjunction with the drawings, in which: 
     FIG. 1 is a sectional view of an inertia switch device in accordance with the present invention, with the switch in a non-fired or non-actuated position; 
     FIG. 2 is a sectional view of the switch device of FIG. 1 in the fired condition; 
     FIG. 3 is a sectional view of a switch device in accordance with the present invention, which may be utilized for purposes other than sensing changes in inertia; and 
     FIG. 4 depicts a switch device of the present invention having alternative features to the FIG. 1 embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like numerals designate identical or corresponding parts, FIG. 1 depicts a switch which can be utilized for sensing inertia. The switch includes a housing 1 which may be formed, for example, of a molded plastic or machined aluminum. In addition, as discussed hereinafter, the housing may be formed of, or include, a magnetic-shielding material depending upon the application. A passageway 20 extends within the housing, and forms a path of movement for a magnet or firing mass 3. FIG. 1 shows the magnet 3 in the non-actuated or non-fired position. In order to prevent inadvertent firing or actuation of the switch, a pin 10a extends into a hole 10 in order to block movement of the magnet along the passageway. Thus, it can be ensured that the switch is not inadvertently actuated during transport or installation. The pin 10a is readily removable when it is desired to utilize the switch for sensing inertia. 
     Partially disposed in the passageway 20 is a stopper 4. The stopper 4 can take the form of a sphere as shown in FIG. 1, however, it may also take the form of a wedge or other shape having an inclined surface 4a which contacts the magnet. Preferably, the stopper is formed of a light-weight non-magnetic material, such as nylon. 
     The stopper should have a light weight, such that it is not subject to inertial forces, particularly inertial forces perpendicular to the passageway 20. The stopper 4 is connected to a spring 5, which in turn is connected to or at least in contact with a screw or plug 6. In the rest position (or when the inertial force of the magnet is insufficient to move the stopper), the spring holds the stopper at a position in which it at least partially projects into the passageway 20. When the magnet 3 applies a sufficient force to the stopper 4, the stopper is pushed into the channel 9 in opposition to the spring 5. It is important that the stopper 4 includes an inclined surface 4a, such that the force of the magnet (against the surface 4a in a direction along the passageway 20) produces a component force normal to the passageway 20 in opposition to the spring 5. The plug 6 is preferably threaded, such that the amount of force required to move the stopper out of the passageway 20 can be varied, thereby varying the amount of force required to move the stopper into the channel 9 in opposition to the spring 5. In addition, the threaded plug mounting allows the spring and stopper arrangement to be replaced, also to vary the amount of force required to actuate the switch. 
     At the lower end of FIG. 1, a coil of wire is provided as shown at 7. The coil has an annular configuration, with the passageway 20 extending through the center of the coil. The coil is connected to external wiring 21 such that the signal produced by the coil is provided to external circuitry. The wires 21 can be connected to posts or terminals mounted on the housing, or other suitable electrical coupling devices. The wires 21 may also be provided with terminals 21a to allow for easy and secure connection to appropriate circuitry. For example, the signal can be provided to a central processing unit in order to initiate a sequence of events upon receipt of the signal. Preferably, the passageway 20 will include one or more ports 11, 12 to allow for the inlet and outlet of any gas which may be present in the passageway 20, so that differential pressure forces in the passageway 20 will not hinder movement of the magnet 3. 
     The port 12 is formed in a threaded plug 8, and also allows for resetting of the switch device. In particular, after firing of the switch device, a rod may be inserted into the port 12 to return the magnet to its non-actuated position. The plug 8 also allows for removal and replacement of the magnet. This can allow replacement with a magnet of a different mass, thereby changing the acceleration necessary for actuating the switch. As an alternative to the use of port 12 for resetting, a magnet may also be utilized to move the magnet 3 to the non-fired position as will be discussed hereinafter with reference to FIG. 4. 
     Since the switch relies upon induction for producing a signal, it may be desirable to include a magnetic shielding material in the housing 1, thereby preventing inadvertent inductance of a current in coil 7. Alternatively, a magnetic shield can be formed about the housing as represented by the broken line 22 in FIG. 1. 
     FIG. 2 shows the arrangement of FIG. 1 after firing. In operation, the switch is mounted upon a device for which inertia sensing is desired. The pin 10a is removed such that only the stopper 4 opposes movement of the magnet 3. When the switch (or the body upon which the switch is mounted) encounters a sudden impact, acceleration or deceleration, the magnet will urge the stopper 4 into the channel 9, allowing the magnet to continue movement along the passageway 20 and into the coil 7. The acceleration must occur over a finite amount of time necessary to move the stopper into the channel 9. As the magnet passes into the coil 7, a current is induced in the coil, thereby providing a signal pulse to the wires 21. 
     As should be readily apparent, the foregoing construction provides an inertia switch of a rugged, simple construction which is easy and inexpensive to build. In addition, due to the low mass, the switch has a very high natural frequency, and thus is not subject to inadvertent firing as a result of random vibrations or accelerations. In addition, since the stopper 4 has a low weight/mass, forces normal to the passageway 20 will not cause movement of the stopper 4 into the channel 9. 
     The device also requires no external power or voltage source, and thus is not subject to failure resulting from an ineffective voltage source, and does not require monitoring or inspection of the voltage source. In addition, no electrical contacts are required for sensing the switching, since the current is induced as the magnet passes into the coil. The device is also easy to reset, utilizing the port 12, and the safety pin 10a prevents inadvertent actuation during transport or mounting. 
     The inertia switch may also be utilized to determine maximum attained acceleration levels. For example, a bank of switches may be mounted upon a body, with each switch requiring a different acceleration level for firing. The maximum acceleration attained is approximated by the highest acceleration switch fired. An acceleration versus time profile can also be obtained by recording the time at which the various switches are fired. It should be noted that the present invention need not utilize a magnetic firing member or mass 3 (i.e., the firing member 3 need not be magnetic), or a coil 7 if the only concern is to determine the maximum acceleration attained (i.e., without requiring the production of a signal or time information). Thus, a plurality of switches can be utilized to determine a maximum acceleration attained simply by inspection of the switches after the acceleration/deceleration event under consideration. The inspection can be, for example, visual via one of the ports 11, 12; by an additional inspection port; or by providing a construction that can be readily opened or disassembled for visual inspection. 
     The construction of FIGS. 1 and 2 is also advantageous in that it is not susceptible to inadvertent switching by acceleration other than in a single direction. Due to the low mass of the stopper, accelerations normal to the passageway 20 will not cause firing. In addition, acceleration in the opposite direction of that being sensed merely urges the magnet upward against the housing. 
     An alternate embodiment of the present invention may also be utilized for applications other than sensing inertia. For example, as shown in FIG. 3, the magnet 3 may simply be preloaded utilizing a spring 13 or a weight (not shown). In this arrangement, removal of the pin 10a allows the magnet 3 to be fired along the passageway 20 by the preloaded spring 13. This arrangement can be desirable as a manual signaling device (where the pin 10a is simply moved to produce a signal), or for producing a signal upon the occurrence of a mechanical event. For example, in the context of an alarm device, the pin 10a may be connected to a door or window, such that movement of the door or window causes removal of the pin and thus fires the switch. 
     Referring now to FIG. 4, an embodiment depicting alternate features of the present invention is shown. It is to be understood that any of the alternate features shown in FIG. 4 may be utilized separately or in combination in the embodiments depicted in FIGS. 1 and 3. If the switch device is to be utilized in an environment in which cleanliness cannot be guaranteed, it may be desirable to provide a hermetically enclosed switch. Accordingly, in the FIG. 4 arrangement, the ports 11, 12 are omitted and the interior of the switch device is hermetically sealed. In order to avoid adverse effects created by differential pressures within the passageway 20 as the magnet or firing member 3 moves therealong, a channel 30 is preferably provided, with the channel 30 extending from an upper portion of the passageway 20 to a lower portion. Thus, the channel 30 acts to equilibrate pressures along the passageway 20, with the hermetic sealing ensuring movement of the magnet or firing member is not hindered by the accumulation of dirt or debris. 
     Still referring to FIG. 4, as mentioned earlier, the port 12 of the FIG. 1 arrangement is not essential in resetting the magnet or firing member 3. Alternatively, a magnet M may be provided which is of sufficient strength such that it draws the firing member 3 from the lower end of the passageway 20 to the upper end to thereby reset the switch. If the firing member 3 is a magnetic member, a magnet may also be provided at the lower end of the housing 1, with the magnet at the lower end of the housing repelling the magnet 3. As mentioned earlier, the switch of the present invention may be utilized with a firing member 3 which is not a magnet, with the coils 7 omitted, where it is not necessary to provide an instantaneous signal of firing. With this type of arrangement, a magnet M for resetting can nevertheless be utilized, however, the firing member 3 must be of a magnetic material, even if it is not a magnet. 
     In accordance with yet another feature shown in FIG. 4, a tapered or shouldered portion 9a is provided at an end portion of the channel 9 which is adjacent passageway 20. This arrangement is desirable in maintaining a positively defined rest position for the stopper 4. In particular, the tapered portion 9a forms an aperture which communicates the channel 9 and the passageway 20, with the aperture smaller than the diameter of the stopper 4. As a result, the stopper 4 cannot inadvertently enter the passageway 20. The use of a tapered or shouldered section 9a provides even greater flexibility from a force adjustment standpoint, since adjustment of the threaded plug 6 will not excessively protrude the stopper 4 to a position at which it may prevent firing movement of the magnet 3, since the tapered portion 9a positively defines the rest position of the stopper 4. However, adjustment of the plug 6 will continue to change the amount of compression or load between the plug 6 and the stopper 4, and therefore, adjustment of the plug 6 will continue to vary the amount of force required to move the stopper 4 completely out of the passageway 20 and into the channel 9. Thus, the tapered or shouldered arrangement at the portion of the channel 9 adjacent passageway 20 provides improved reliability while retaining, and even enhancing, the flexibility of the stopper and spring assembly for use in detecting a variety of acceleration levels. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.