Product Monitoring Device And System

Abstract

A product monitoring system including a releaseable locking device adapted to be secured to a product and actuatable between locked and unlocked positions. The locking device consists of a pair of movable members, one of which mounts a bimetallic member consisting of bimetal elements having different temperature coefficients of expansion, the bimetal elements being separated by an insulator. The locking device further includes a detent cooperatively associated with the bimetallic means to maintain the members in a locked position. The system further includes an electrifiable key for heating the bimetallic elements to effect displacement thereof relative to the detent to facilitate movement of the members to an unlocked position. Heating of the bimetallic member is accomplished by passing current through the two mutually insulated bimetallic elements in series. In a preferred form, electronic means are provided for automatically reducing the heating current to the bimetallic member and for lighting an indicator lamp when the bimetallic has been heated sufficiently to release the locking device, thereby protecting the bimetallic from overheating and informing the operator when to withdraw the locking device from the key.

Description

BACKGROUND OF THE INVENTION

The present invention relates to product monitoring devices and more specifically to a device selectively attachable to articles of merchandise having means for deterring unauthorized removal of the merchandise from, for example, store premises.

It is well known in merchandising that unauthorized removal of merchandise from supervised premises such as stores produces a significant loss to merchants. The removal is usually due to intentional theft or inadvertence.

Systems have been proposed in the prior art for enabling detection of unauthorized removal of products from premises by associating with the product some identifiable signal producing means which, when taken past a detection station without authorization, will produce a suitable alarm; for example, small radio transmitters, magnetic devices, and passive tuned electrical circuits have been secured in or on products for such purposes. In general, such known devices have several disadvantages or drawbacks. For example, it has been found that these devices are either of excessive bulk, expensive, inconvenient to attach to different types of goods, difficult to remove, and offensive to the buying public.

There is disclosed in a copending application Ser. No. 112,355, filed on Feb. 3, 1971, now U.S. Pat. No. 3,718,922, entitled "Product Monitoring Apparatus, System and Method," a product monitoring apparatus and system suitable for the above purposes. This system includes an electrically releaseable locking device secured to a product which is releaseable by application thereto of an electrically powered key. The locking device comprises a pair of relatively moveable members actuatable between a locking position and a release position and an elongated bimetallic element secured to one of the moveable members and which mounts a locking pin at its free end normally engageable in a keeper hole in the other moveable member. Heating of the bimetallic element causes it to deflect in a direction to withdraw the locking pin from the keeper hole. One of the members has a keyway within which the electrically powered key may be inserted to supply current to the bimetallic element.

Also, in the locking device of the above-cited copending application the heating current is passed through a portion of both of the mutually contacting metal strips of the bimetallic member in parallel, from two wires leading to a separate electrical connector. As a result, the heating of the strips is somewhat nonuniform and requires relatively high currents; also, separate soldering steps must be performed to connect the supply wires between bimetallic member and connector.

In the specific form of system disclosed in the above-identified application, the operator or check-out attendant connects the locking device to the electrified key for what is judged to be a time long enough to release the locking device. In order to make this time relatively short, the current supplied to the locking device by the key is relatively high, and in some cases when it is applied for too long a time there is danger of damaging the key; on the other hand, if the current is applied by the operator for too short a time the locking device will not be released.

With the foregoing in mind, it is an object of the present invention to provide a new and useful system for the detection of unauthorized removal of products from a predetermined location which is of comparatively simplified construction and includes a clip of simplified form readily attachable to articles of merchandise and an electrified key applicable to the locking clip to unlock the device and permit its removal from merchandise by authorized personnel.

Another object of the present invention is to provide such a system incorporating the locking clip and electrifiable key which is inexpensive and easy to employ, but difficult for the thief or shoplifter to defeat.

Another object is to provide a locking device for use on products which is difficult for a thief to unlock on the premises.

Another object is to provide such a locking device which is inexpensive and reliable in operation.

Another object is to provide a new and useful bimetallic member in which the heating thereof is more uniform, and can be accomplished with lower currents.

A further object is to provide means for preventing damage to the locking device due to overheating caused by too long an application of high current thereto.

A further object is to provide an indication to the operator of when current has been applied to the locking device for a time sufficient to release it.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, these and other objects are achieved by the provision of a system in which a locking device is secured to each product on the premises to be made secure against theft, and detecting stations are provided at one or more checkpoints on the premises so that if one attempts to remove a product having a locking device secured thereto past the checkpoint, an alarm indication will be given. The locking device is releasable by means of an electrified key maintained on the premises for this purpose, such as at a sales register, which key is effective when applied to the locking device to release it and permit the unchallenged removal of the product from the premises.

In one aspect of the invention, the locking device incorporates a bimetallic element which in its normal locking position prevents removal from the object and which in response to the electrical current supplied thereto from the key causing heating thereof, moves to a position permitting unlocking of the device and removal from the product.

More specifically, the locking device comprises a pair of pivotally connected members, one member mounting a bimetallic element and the other member having a detent which in the normal position of the bimetallic element locks the members in a closed position and which deflects upon application of current to a position out of the range of a detent to permit the members to be moved to a release position. The moveable members are formed with a socket within which the release key is engageable to supply current to the bimetallic element. The key incorporates a moveable shuttle which when inserted into the locking device is displaced to actuate a switch closing circuits to contacts of the key which engage contacts of the bimetallic element thereby effecting flow of current through the bimetallic element. Thus the locking device and key of the present invention are of a more simplified arrangement and are easily engaged with one another to effect unlocking of the locking device.

In another aspect of the invention, there is provided a bimetallic member comprising a pair of adjacent different bimetal elements mechanically joined to each other at least at two spaced-aparts points, an electrical interconnection between portions of the bimetal elements, a contact area on each of said elements for applying voltage between them, and insulating means electrically insulating said elements from each other between said contact area and said electrical interconnection, thereby to enable passage of current through said two elements in series in response to said applied voltage. Preferably the mutually insulated spaced-apart portions of the bimetal elements terminate in a connector socket to mate with a pair of corresponding connector elements in a key for supplying the heating current to the two bimetal elements in series.

In a further aspect of the invention, means are provided for automatically reducing the current supplied to said locking device by said key, after a period sufficient for the locking device to be operated to its release condition by the applied current, and preferably to provide an automatic indication that this time interval has passed. Preferably this is done by sensing the abrupt drop in voltage from the current source caused by current through the locking device when it is first plugged in and, after a suitable delay, inserting an impedance in series with the current path to reduce its intensity. This protects the locking device from overheating, and tells the operator when it is appropriate to release the key from the locking device.

BRIEF DESCRIPTION OF FIGURES

These and other objects and features of the invention will be more readily understood from a consideration of the following detailed description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a view of the locking device applied to an article of merchandise and the key about to be applied thereto to permit removal;

FIG. 2 is a similar view showing the locking device and key engaged;

FIG. 3 is a view of the locking device in the open position permitting release from the article of merchandise;

FIG. 4 is an enlarged side elevational view, the solid line position showing the device in a locked position and the broken line view showing the device in an open position, the view being partly in section to show the internal constructions of the locking device;

FIG. 5 is a plan view partly in section of the locking device;

FIG. 6 is a sectional view taken on line 6--6 of FIG. 4;

FIG. 7 is a view similar to FIG. 6 showing the locking device showing the relative position of the parts with the locking device in the open position;

FIG. 8 is a view taken on line 8--8 of FIG. 4;

FIG. 9 is a side elevational view partly in section of the electrified release key;

FIG. 10 is a plane view partly in section of the key;

FIG. 11 is an end view into the socket portion of the key;

FIG. 12 is a view partly in section of the engaged locking device and key;

FIG. 13 is a similar side view of the interengaged locking device and key;

FIG. 14 is an electrical schematic showing of the key and power supply circuit;

FIG. 15 is a fragmentary view of a modified form of locking device in accordance with the present invention;

FIG. 16 is a sectional view taken on line 16--16 of FIG. 15;

FIG. 17 is a perspective view of a system incorporating control means for providing indication to an operator that a locking device is conditioned for release; and

FIG. 18 is a schematic of the electric circuit for the control means.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT

Referring now to the drawings and particularly to FIGS. 1-3 thereof, there is illustrated a locking device generally designated by the numeral 10 adapted to be secured to articles of merchandise A and an electrifiable key 12 operable to permit actuation of the locking device to the open position (FIG. 3) to release it from the articles of merchandise A when desired. The locking device incorporates means to be described in detail hereinafter for effecting actuation of an alarm if the article with the locking device applied thereto is removed past a detection station.

The locking device and key of the present invention are particularly adapted for use in retail stores which typically include a main area for displaying articles of merchandise, and one or more checkout counters past which each customer must travel on his way to an exit in the store. These checkout counters are usually provided with a cash register. Also located at each checkout counter will be an electrifiable key 12 by means of which store personnel may release the locking device 10 from articles of merchandise as they are declared and paid for. At each exit there is located a detection station for detecting unauthorized removal of products and for producing an alarm indication of such unauthorized removal if an article of merchandise with the locking device 10 is taken past the exit, each protected product on the premises having a locking device 10 secured thereto.

The locking device, in the present instance, is illustrated as being applied to a fabric or the like and includes a pin which penetrates the goods to hold the locking device firmly in place. As illustrated, the locking device has a pair of pivot arms 16 and 18 which may be pivoted to the open position shown in broken lines in FIG. 4 after the device is unlocked so that it may then be removed from the product. When the arms are moved to the closed position as shown in solid lines in FIG. 4, the device snaps into its locked condition and can be released only by application of electric current thereto by the key 12. It is, of course, to be understood that the device may be applied to merchandise other than fabric. For example, the opening between the arms may encircle a cord of an appliance or the like. Additionally, in some instances, it may be more effective to place another element such as a wire or a chain to a portion of a product and to secure the protruding portions of the element to each other by means of the locking device.

The locking device 10 as mentioned above is such that its unauthorized removal past a detection station will sound an alarm. There are a variety of means by which this can be provided. For the purposes of the present description, it will be assumed that the locking device contains a magnet 20 and that the detection station includes appropriate magnetrometer apparatus for detecting the passage of a magnet past it.

As will be described in detail hereinafter, the requirement of a key of a particular configuration and the reguirement of a certain electrical current to release the locking device, make it difficult for a would-be thief or shoplifter to release the locking device. As will also be described in detail hereinafter, the locking device is preferably make in a simple, convenient and inexpensive form, particularly as to the locking and unlocking arrangement which, in accordance with the present invention, comprises a bimetallic element heated by the applied current in order to effect unlocking of the device.

Considering now more specifically the structural arrangement and details of the electrically releaseable locking device 10 in accordance with the present invention, the device comprises male and female jaw members 16 and 18 which are pivotally mounted to one another as at 22 so that the device may be selectively actuated between a closed or locking position [solid lines in FIG. 4] and an open or released position [broken lines in FIG. 4]. The members are preferably made of a plastic material and are of a simplified configuration so that they may be easily molded. The male member comprises a generally rectangular sidewall 30, top and bottom walls 32 and 34 respectively projecting from the inner edge of the sidewall and a pair of opposed end walls 36 and 38, one of which mounts the arm 16. The male member further includes a center partition 40 dividing the interior into two elongated compartments 42 and 44. The lower compartment 42 houses at least one conventional magnet 46 and the upper compartment 44 houses the bimetallic element 50.

The bimetallic element 50 as illustrated comprises a pair of thin elongated members 51 and 53 of different metals or alloys and having different temperature coefficients of expansion which are suitably secured together, for example, by welding at their outer ends, and are secured by means of a plastic button 52 to a wall portion 54 dividing the compartment 44 into an inner chamber 44a and an outer rear socket portion 44b. A strip 55 of insulating material is interposd between the members 51 and 53 of the bimetallic element 50, one of the members 51 being offset at its terminal rear portion to define one of a pair of spaced contacts 60 and 62 in the socket 56.

The female member comprises a generally rectangular sidewall 70 adapted to overlie the open portion of the compartments 42 and 44 of the male member in the assembled position and a top wall 72 coextensive with the sidewall 70 confronting and overlying the top wall 32 of the male member. The sidewall 70 has an opening 71 through which a button 73 on the center divider of the male member projects and which is adapted to be upset to provide the means for pivotally securing the members together. Note that the female member is open at its rear terminal portion to expose the socket 56 and form a portion of the sidewall of the socket. Additionally, the arms 16 and 18 of the male and female members are shaped in such a manner to provide a generally circular opening 75 through which a portion of an article of merchandise may be secured, for example, the chord of an electrical appliance.

Adjacent the forward end of the male member, the top wall and center partition are provided with aligned cutouts 80 and 82 respectively, and a tapered detent 84 is formed integrally with the sidewall of the female member which clears the pocket 85 formed by the cutouts to allow pivotal movement of the members. The bimetallic element 50 in the normal unheated position extends across the pocket 85 so that when the device is locked, the flat shoulder 86 of the detent engages under the bimetallic element 50 to prevent opening of the device or pivotal movement of the male and female members relative to one another. Now, when the bimetallic element 50 is heated, it is deflected to the position shown in broken lines shown in FIG. 5 out of the range of the detent 84, thereby permitting the male and female members to be pivoted about the pivot 22 to an open position. Of course, once the bimetallic element is cooled and returns to its normal position, the clip may be closed, the detent having a tapered front face 87 which springs the bimetallic element 50 inwardly to permit closing. However, when the detent 84 passes the position of the bimetallic element, it snaps back into place to securely lock the members in a closed position. Means described in more detail below is provided for controlledly passing a heating current electricity through the bimetallic element to selectively control actuation thereof as described above.

The details of the release key are best illustrated in FIGS. 9-11 inclusive. The key 100 comprises an elongated hollow housing 102 which, for purposes of ease of construction, is sectionalized in halves so that it may be made by a molding operation from a plastic material. The housing has a rear compartment 104 for mounting therein an on-off switch 106 and a forward compartment 110 for a pair of electrical contacts 112 and 114. In the present instance, the specific mounting for the contacts 112 and 114 includes a post member 116 formed integrally with the sidewall of the housing over which the contacts are mounted. An insulating member 120 which is disposed between the contacts 112 and 114 is also mounted on the post member 116. In the present instance, the key includes a movable shuttle 122 normally biased to an outer position by means of the spring biased pin 126 of the on-off switch 106. The shuttle, as illustrated, is shaped to straddle the contacts 112 and 114 and in its forwardmost position the front end of the shuttle lies flush with the outer terminal ends of the contacts in the manner illustrated in FIG. 9. The shuttle has a head portion 130 which engages a shoulder 132 in the housing to limit the forward position. The shuttle also mounts a shim 134 to insure proper contact with the pin 126. The shuttle 122 is formed with a projection 139 at its forward end engageable with the offset portion of the contacts to define a rear limit position (see FIG. 13). The forward end of the key has a generally rectangular shaped opening of a size to accommodate the locking device in the manner illustrated in FIGS. 12 and 13. Additionally, the contacts 112 and 114 are spaced apart laterally a distance so that when the locking device is inserted therein and the shuttle actuated rearwardly, the contacts engage in the socket in the locking device and make engagement with the outer terminal ends 60, 62 of the bimetallic element. In this position, the actuating pin 126 is depressed to an "on" position thereby closing the circuit to effect heating of the bimetallic strip which, as described previously, permits the locking device to be actuated to an open position. As illustrated in FIGS. 9 and 10, one of the contacts 112 is connected through a lead 140 to one of the contact arms of the switch 106 and the other contact 114 is connected to lead 142 to the control circuit C. Lead 144 connects the other contact of switch 106 to the circuit C.

The power control circuit C for the key as illustrated in FIG. 14 includes a main power supply 160, a switch 162 connected through lead 164 to one terminal of the power supply, the switch 162 being connected to one side of the primary of a transformer 170. The center tap of the secondary of the transformer is connected through electrical lead 142 to one of the contacts 114 of the key, and the lead 144 connects one terminal of the on-off switch 106 to the electrical lead 180 bridging rectifiers 182 and 184. The circuit also includes an indicator lamp 190 which is energized when the switch 162 is closed.

Considering now briefly the operation of the locking device and key in accordance with the present invention, assume that the locking device is applied to an article of merchandise as shown in FIG. 1 and that the article has now been selected by a purchaser and delivered to a checkout counter. Personnel at the checkout counter are in the control of the electrified keys. Assume that the switch 162 has been closed to condition the key for releasing the locking device. Under these circumstances, the locking device is inserted in the manner shown in FIG. 2 into the forward end of the key. The locking device and key are actuated relative to one another to displace the shuttle 122 rearwardly to actuate the on-off switch 106 thereby closing the circuit to the contacts 112 and 114. In this position, the contacts 60 and 62 engage the contacts 112 and 114 to complete the circuit to the bimetallic element 50 and effect flow of current through the two elements 51 and 53. After a predetermined short time period, this current heats the bimetallic element sufficiently to cause it to bend out of the range of the detent 84; the locking device may then be removed from the key and the jaw members 16 and 18 pivoted to an open position to remove it from the article of merchandise. Of course, as the locking device is removed from the key, the shuttle is biased to a forward position by the spring actuated plunger 126 thereby opening the circuit to the power for the contacts 112 and 114.

FIGS. 15 and 16 show a modified form of locking device in accordance with the present invention. The device is similar in overall structural details and arrangement comprising male and female members 16a and 18a which are pivotally secured as at 22a so that the members may be actuated selectively between a closed or locking position and an open or release position. In the present instance pivotal movement of the members to the release position is controlled or limited by a rib 23a mounted on the inner face of the rectangular sidewall 70a of the female member 18a. Upon pivotal movement of the members to a release position the rib 23a engages the lower edge of the center partition 40a which divides the interior to define a lower compartment 42a for the magnet 46a. In this manner the rib 23a determines the maximum open position.

While the circuit arrangement illustrated in FIG. 14 may be utilized, as described above, to accomplish the purposes of the invention, if the locking device is inserted into the key for too long a period, the bimetallic element may be overheated and in some cases damaged. On the other hand, if the locking device is inserted into the key for too brief an interval, the bimetallic element will not be heated sufficiently to unlock the locking device. There is therefore a preferred range of time for applying current to the bimetallic member, which usually can be provided by an operator with appropriate care and experience. However, the apparatus now to be described with particular reference to FIGS. 17 and 18 prevents accidental overheating of the bimetallic element, indicates to the operator when the locking device has been unlocked and can be removed, and also provides an indication that the locking device has been inserted into the key long enough to release the locking device.

Referring first to FIG. 17, there is shown one suitable physical form of automatic release device in accordance with this feature of the invention, which suitably is placed on the counter at a checkout station so that the front face thereof faces the checkout attendant. A suitable AC supply line 200 terminates in a conventional three-pronged power plug 202, which in use is plugged into a conventional three-terminal power line socket in the store. The casing 204 contains the circuitry to be described with reference to FIG. 18. The release key 12 is connected by line 206 to the circuitry within casing 204. On the front of the casing 204 there are mounted a front-replaceable line current fuse 210, a line voltage indicating pilot lamp 212, a key-operated line current switch 214 and a timer lamp 216.

When power plug 202 is inserted into its appropriate receptacle and switch 212 turned to its on position, the pilot lamp 212 lights to show that the circuit is in operable condition; initially, the timer lamp 216 is extinguished. When the key 12 is inserted into the previously described locking device 10, current is supplied to the bimetallic member within locking device 10 for an appropriate length of time sufficient to operate the bimetallic without damaging it, and the current is then automatically terminated by the circuitry within casing 204. At the latter time, the timer lamp 216 is also automatically illuminated to indicate to the attendant that the locking device has been unlocked, and that the key can be removed and the clip detached from the article.

Referring now to FIG. 18 in which parts corresponding to those of FIG. 17 are indicated by corresponding numerals, the three wires of the power cable 200 comprise the ground line 230 and the two "hot" lines 232 and 234. Line 232 is connected to the series combination of fuse 210, line switch 214, current limiting resistor 238, and one end of the primary 240 of the iron core stepdown transformer 242. The opposite end of primary 240 is connected directly to line 234.

Pilot lamp 212 is connected directly between power line 234 and the junction of resistor 238 and switch 214, so as to be illuminated only when switch S1 is closed and fuse 210 is intact. Relay 243 is provided with contacts 244 and 245 which, when relay 243 is activated to the switch position shown in broken line by current through relay coil 250, short-circuit resistor 238 so that the entire line voltage is normally applied across the transformer primary 240. When there is no current through relay coil 250, the relay returns to its normal position, shown in full line, in which it shorts together the relay contacts 252 and 254, threby removing the short circuit across resistor 238 and connecting timer lamp 216 across the transformer primary 240, causing it to become illuminated. The manner in which the circuit operates to cause this operation of relay 240 will be described hereinafter in detail.

In response to the alternating voltage at its primary, transformer 242 produces across its secondary 260 a voltage which is supplied directly to the release key 12 over lines 262 and 264, contained in cable 206 of FIG. 17. For example, with a 110-volt AC line supply connected to leads 232 and 234, the voltage across transformer secondary 260 may be about 3 volts rms when the release key is not connected to the locking device.

In general, the remainder of the circuit provides the following function. When switch 214 is closed, current flows through relay coil 250 to produce direct connection between contacts 244 and 245. When the locking device is then inserted into the release key 212, the resultant current load, which may be of the order of 13 amperes, causes the voltage across transformer secondary 260 to drop abruptly, for example from about 3 volts to about 2 volts rms. The circuit senses the occurrence of this drop in secondary voltage, provides a suitable delay (typically about 3 seconds) during which heating of the bimetallic occurs, and then causes the current through relay coil 250 to be terminated, which operates the relay to remove the short-circuit across resistor 238. This inserts resistor 238, typically of 500 ohm value, in series with the transformer primary 240, thereby greatly reducing the current supplied to the bimetallic, typically from about 13 amperes to about 4 amperes, by way of example. The latter level of current is entirely safe for the bimetallic and will not cause it to be damaged.

The functions of sensing the drop in voltage across secondary 260, providing a predetermined delay, and then deactuating the relay 250 are accomplished as follows. The alternating voltage across secondary 260 is passed through coupling capacitor 270 to a voltage doubling and rectifying circuit of generally conventional form consisting of diode rectifier 272 and 274 and capacitor 276; a resistor 278 is provided in parallel with capacitor 276 to permit the voltage across the latter capacitor to drop rapidly when the transformer secondary voltage drops abruptly in response to a load across it, due to plugging in of the locking device. Line 280 connected to the lower end of capacitor 276 is the reference voltage line for the remainder of the circuit.

The rectified and doubled voltage on line 282 serves as the supply voltage source for three semiconductor devices 284, 286 and 288, and also serves to supply the above-mentioned abrupt drop in voltage to the base of the silicon controlled switch 284 by way of the series circuit comprising resistor 290, capacitor 292 and resistor 294 connected to the reference voltage line 280.

The silicon controlled switch device 284 is of a known type which is turned on by a positive pulse supplied to its base and remains in its on condition until switched to its opposite, or off, position by a negative pulse, in which latter state it will remain until turned on again. Thus when the entire circuit is initially turned on by closing of the line switch 214, the voltage on line 282 searches positively, typically to about 7 volts DC, and this surge acts through resistor 290 and capacitor 292 to turn on device 284. Capacitor 292 is sufficiently large to pass such relatively rapid voltage surges sufficiently to turn on device 284, but is sufficiently small in value to prevent device 284 from being turned on by relatively slow changes in voltage due, for example, to slow changes in the AC line voltage.

Electrode 298 of device 284 is connected through adjustable resistor 300 to supply line 282, and the other electrode 302 thereof is connected to the reference voltage line 280. When device 284 is in its normal on condition, electrode 298 thereof is held at a low positive potential.

Timing capacitor 206 is arranged with one of its terminals connected directly to the reference voltage line 280 and its other terminal connected through resistors 310 and adjustable resistor 312 to the positive line 282. Accordingly, the upper plate of capacitor 306 tends to charge to the supply voltage level. However, this upper plate is also connected to electrode 298 of device 284 through diode rectifier 312 and resistor 314, the anode of rectifier 312 being connected directly to the upper plate of capacitor 306. The latter circuit of resistor 314 and diode rectifier 312 thus prevents capacitor 306 from charging up appreciably above the reference voltage when device 284 is on.

Transistor 286 is of the pnp type, having its base connected through resistor 316 to the upper plate of timing capacitor 306, having its emitter connected through resistor 318 to the positive supply line 282, and having its collector connected to the reference line 280 through relay coil 250 of relay 243. A capacitor 320 is preferably connected between base and collector of transistor 286 to suppress tendencies toward oscillation in the circuit, and a camping diode 322 is connected across relay coil 250 to suppress undesired transients caused by switching of the current through relay coil 250.

Assuming again that device 284 is on, the low voltage maintained at the upper plate of timing capacitor 306 provides a base voltage for transitor 286 causing the latter device to operate in its conducting, or on, condition. The other transistor 288 of the pnp type is connected to transistor 286 to form therewith a Darlington pair; thus the base of transistor 288 is connected to the emitter of transistor 286, the emitter of transistor 288 is connected directly to the positive supply line 282, and the collector of transistor 288 is connected to the collector of transistor 286 so as to contribute to the current through coil 250 when the two transistors are turned on. More particularly, when transistor 286 is on, its emitter voltage is held at a low value such as to hold transistor 288 also on, and both transistors contribute to the current through the relay coil.

Accordingly, it will be seen that when the entire system is first turned on, all of the semiconductor devices 284, 286 and 288 will be in their on condition, and there will be current through relay coil 250 holding it in the position for which resistor 238 is short circuited.

Now when the locking device is plugged into the release key, the resultant current through the bimetallic causes the voltage across transformer secondary 260 to drop by about 1 volt rms and causes the DC voltage on supply line 282 to drop by about 2 volts DC, in an abrupt manner. This negative surge is coupled to the base of device 284 and causes it to change to its off state. As a result, electrode 298 of device 284 assumes a voltage substantially equal to that on positive supply line 282, typically about 5 volts, which cuts off conduction in rectifier 312 and permits timing capacitor 306 to charge through resistors 310 and 312. The values of the latter timing capacitor and charging resistors are so selected that, after the desired timing interval (typically about 3 seconds), capacitor 306 is charged sufficiently positively to turn off transistors 286 and 288 and terminate the current relay coil 250. This causes relay 243 to switch to its opposite condition in which current limiting resistor 238 is no longer short circuited and lamp 216 is turned on. The removal of the short circuit across resistor 238 immediately reduces the current to the bimetallic in the locking device to about one-fourth its original value, thus protecting it from damage, and the lighting of the lamp 216 informs the operator that the locking device can be removed from the key and open.

When the locking device is removed from the key, the termination of the load current causes the DC voltage on line 282 to surge to its original value of about 7 volts in this example, which surge is coupled through resistor 290 and capacitor 292 to the base of device 284 to turn it on again. This in turn turns on transistors 286 and 288, produces current through relay coil 250, and returns the relay contacts to their original position in which resistor 238 is short circuited and timing lamp 216 is extinguished, ready for another subsequent operation.

There is thereby provided a system which automatically reduces the current through the bimetallic after the locking device has been plugged into the key for a predetermined length of time, thereby to protect it from overheating and possible damage, and also automatically provides an indication to the operator that the locking device has been released and should be removed from the key for opening and removal from the article.

Claims

What is claimed is:

1. In a product monitoring system a releasable locking device adapted to be secured to a product, said locking device including a pair of relatively movable members operable between locked and unlocked positions, bimetallic means in one of said members consisting of a pair of bimetal elements having different temperature coefficients of expansion separated by insulating means, detent means mounted in the other of said members and cooperatively associated with said bimetallic means to maintain said members in a locked position; an electrifiable key adapted to be connected to a suitable source of electrical power, means for passing an electrical heating current from said key through said bimetal elements in series thereby to heat the same and effect displacement out of the range of said detent means to permit movement of said members to an unlocked position; means for producting an electrical signal indicative of the initiation of current flow from said key to said locking device upon connection of said key to said locking device and means responsive to said electrical signal for automatically reducing the current supplied to said locking device at the end of a predetermined time interval.

2. A releasable locking device adapted to be secured to a product comprising a pair of relatively movable members, bimetallic means mounted in one of said members comprised of at least a pair of elongated elements having different temperature coefficients of expansion, detent means mounted in a fixed position in the other member and cooperatively associated with said bimetallic means to maintain said members in a locked position, said bimetallic means upon application of an electrical current to heat the same operable to be displaced out of the range of said detent means to permit movement of said members to an unlocked position.

3. A releasable locking device as claimed in claim 2 including means pivotally connecting said movable members and wherein said detent is located remote from said pivotal connection.

4. A releasable locking device as claimed in claim 2 wherein said movable members encapsulate said detent and bimetallic means so that members can be actuated from a locked to an unlocked position only by application of electric current to said bimetallic means.

5. A releasable locking device as claimed in claim 2 wherein the terminal ends of the elements of said bimetallic means form a pair of spaced contacts in a socket portion formed at one end of said members.

6. A releasable locking device as claimed in claim 2 wherein said bimetallic means are secured to said one member in a manner defining a flexible portion operable when disposed in one position in the path of said detent to maintain said members locked and displaceable when heated by current to a second position out of the path of said detent to permit movement of said members to an unlocked position.

7. A releasable locking device as claimed in claim 6 wherein said detent has a tapered portion operable when said members are in an unlocked position and said flexible portion is in said one position to displace said flexible portion when said members are actuated to the locked position.

8. An electrifiable key for actuating a releasable locking device having bi-metallic means controlling unlocking of the locking device comprising an enclosed housing, at least one pair of spaced contacts in said housing, a shuttle movable in said housing between a forward limit position and a rearward limit position, biasing means normally urging said shuttle to said forward limit position, switch means adapted to be connected to a suitable source of electrical power, said shuttle movable in one direction to said rearward limit position by the locking device when engaged therewith to actuate said switch to close the circuit to the electrical power source producing flow of an electrical current through said contacts to the bimetallic means, said switch means being open when said shuttle is in said forward limit position.

9. An electrifiable key as claimed in claim 8 wherein said housing has a recess at one end into which the locking device may be inserted to engage said shuttle.

10. An electrifiable key as claimed in claim 8 wherein said switch actuator is spring biased and normally maintains said shuttle in a forward limit position.

11. An electrifiable key as claimed in claim 10 wherein said contacts are mounted in a fixed position and wherein said shuttle is mounted for movement relative thereto between the forward limit position wherein the contacts are covered by said shuttle and the rearward limit position wherein said contacts are exposed.

12. In a bimetallic device comprising a pair of adjacent bimetal elements having different temperature coefficients of expansion and means securing said elements to each other mechanically at least at two spaced-apart points, the improvement comprising means electrically interconnecting portions of said elements to each other, a contact area on each of said elements for applying a voltage between said elements, and insulating means electrically insulating said elements from each other between said contact areas and said electrically interconnected portions of said elements, thereby to enable passage of current through said elements in series in response to said applied voltage.

13. A bimetallic device comprising:

a pair of adjacent bimetal stips having different temperature coefficients of expansion;

junction means electrically and mechanically joining said strips together at one of their ends;

an insulating strip of material between said bimetal strips to maintain them insulated from each other except at said one ends thereof; and

fastening means insulatedly securing said bimetal strips together at a point spaced from said junction means, with said insulating strip between them.

14. A bimetallic device according to claim 13, in which the portion of said bimetal strips on the side of said fastneing means opposite from said junction means diverge to provide spaced-apart connector elements.

15. A bimetallic device according to claim 13, comprising a casing for supporting said bimetallic strips, said casing surrounding said connector elements and providing a socket for receiving a plug to apply a voltage between said connector elements.

16. In a system comprising a locking device adapted to be attached to articles and releasable therefrom in response to a predetermined magnitude of electrical current supplied thereto from an electrified key for a predetermined time interval, said locking device being subject to damage in the event said current is supplied thereto for a time interval substantially longer than said predetermined time interval, the improvement comprising:

means for producing an electrical signal indicative of the initiation of current flow from said key to said locking device upon connection of said key to said locking device; and

means responsive to said electrical signal for automatically reducing the current supplied to said locking device at the end of said predetermined time interval.

17. In the system of claim 16, indicator means and means for automatically actuating said indicator means at the end of said predetermined time interval.

18. A system in accordance with claim 16, comprising a source of said current, and in which said means for producing said electrical signal said initiation of current flow comprises means for producing an abrupt decrease in the voltage of said source in response to said initiation of current flow; means for connecting an impedance in series with the current path from said source to said key in response to said decrease in voltage thereby to reduce said current; and means for delaying said reduction of said current with respect to the time of said decrease in voltage by an amount substantially equal to said predetermined time interval.

19. A system in accordance with claim 18, in which said means for connecting an impedance in series comprises relay means having a first position in which said impedance means is in series with said current path and having a second position in which it is not, and in which said delaying means comprises timing capacitor means and a control circuit therefor responsive to said decrease in voltage to initiate charging of said capacitor means, said control circuit being responsive to increases in said voltage to discharge said capacitor means.

20. A system in accordance with claim 19, comprising indicator lamp means, and means for illuminating said lamp means only when said relay means is in said first position.