Patent Publication Number: US-6667689-B1

Title: Silverware detector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND 
     1. Field of Invention 
     This invention relates to food handling equipment, specifically an apparatus that sounds an audible alarm whenever silverware is discarded with food and table refuse. 
     2. Description of Prior Art 
     Food preparers involved in restaurants, cafeterias, or catering services that provide silverware to their patrons face potential loss of such silverware during the cleanup process. Such silverware is easily mixed with food and paper refuse such that the silverware is discarded with the refuse. Such silverware is lost both accidentally as it is hidden with other refuse and sometimes deliberately by less than conscientious personnel. Silverware discarded with refuse is a serious problem in this industry. 
     There are numerous patents that describe devices that use magnets to attract and hold silverware as it flows with paper and food refuse down a chute or into a refuse container. These have no alarms and do not guarantee that lost silverware will be retrieved by less than conscientious personnel. Also, such devices will catch and hold silverware provided the flow and force used on the refuse is within range. Some known patents that deal with such magnetic devices with no alarms are as follows: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 U.S. Pat. No. 
                 Issue Date 
                 Inventor 
               
               
                   
                   
               
             
            
               
                   
                 3,149,066 
                 Sep. 15, 1964 
                 Ross 
               
               
                   
                 3,926,792 
                 Dec. 16, 1975 
                 Buford 
               
               
                   
                 4,367,138 
                 Jan. 4, 1983 
                 Kustas 
               
               
                   
                 4,494,657 
                 Jan. 22, 1985 
                 Oldenkamp 
               
               
                   
                 4,706,818 
                 Nov. 17, 1987 
                 Zutell et al. 
               
               
                   
                 4,782,970 
                 Nov. 8, 1988 
                 Edwards 
               
               
                   
                 6,129,213 
                 Oct. 10, 2000 
                 Edwards 
               
               
                   
                   
               
            
           
         
       
     
     Other patents exist that do employ alarms. The applicants are aware of the following references which disclose devices which are more relevant to this area of the art: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 U.S. Pat. No. 
                 Issue Date 
                 Inventor 
               
               
                   
                   
               
             
            
               
                   
                 4,632,253 
                 Dec. 30, 1986 
                 Stromgren et al. 
               
               
                   
                 4,742,339 
                 May 3, 1988 
                 Nelson Baziuk 
               
               
                   
                 5,538,143 
                 Jul. 23, 1996 
                 Pettersson 
               
               
                   
                 5,797,497 
                 Aug. 25, 1998 
                 Edwards 
               
               
                   
                 6,222,450 
                 Apr. 24, 2001 
                 Clements 
               
               
                   
                   
               
            
           
         
       
     
     U.S. Pat. No. 4,632,253 discloses a chute assembly with an inductive sensor and a flap door having two positions. Such an assembly appears to require a certain amount of cleaning and maintenance to keep the mechanism clean and operative. The power required to move a mechanical flap would likely make this unit less than ideal as far as being portable or having long battery life. Also, since this device senses aluminum and other nonferrous metals, adjustment is required for this device to differentiate silverware from silver paper. 
     U.S. Pat. No. 4,742,339 appears to overcome some of the limitations of U.S. Pat. No. 4,632,253 in that it uses an alarm to signal the presence of metal as opposed to a mechanical flap to capture such material. However, this invention is reported to trigger on all metal large enough to exceed an adjustable threshold level. Thus, adjustment is required to differentiate between tin foil and silverware. It would appear that larger metal articles whether they be tin foil or metal containers could trigger the circuit. 
     U.S. Pat. No. 5,538,143 appears to suffer from some of the same limitations as U.S. Pat. No. 4,632,253 in that the device has mechanical doors and a structure that does not lend itself to being easily portable or operating for long periods of time from batteries. The mechanical components appear to require maintenance and periodic cleaning. This device requires calibration to differentiate between cutlery and silver paper. 
     U.S. Pat. Nos. 5,797,497 and 6,222,450 also disclose metal detectors implying that they would be triggered by metal besides silverware. No differentiation is noted between ferrous and non-ferrous material implying that non-silverware metal in the refuse would likely provide a false trigger. 
     All current inventions fail to provide an apparatus that detects only silverware while ignoring all other metal, that is truly low maintenance, that is very portable with long battery life, that allows managers confidence that silverware is being detected independent of personnel involved, and that is very affordable due to simplicity of design. 
     SUMMARY 
     This Silverware Detector consists of a portable sensing mechanism that is installed on the top of a refuse container and can be easily moved from one refuse container to another. It senses magnetized silverware that falls into a refuse container along with other refuse. It ignores all other metal and non-metal objects. 
     The sensing mechanism uses magnetic field sensors to sense the falling magnetized silverware as it falls through an opening. 
     An electronic circuit triggered by the magnetic field sensors activates an alarm when silverware is detected. 
     OBJECTS AND ADVANTAGES 
     Accordingly, several objects and advantages of our invention are here provided. Our invention has the ability to differentiate between the silverware of interest and other metal objects be they ferrous or non-ferrous. Only magnetized silverware triggers the alarm providing for a very consistent and reliable means of detection. Also, our invention is mechanically simple with no moving parts that require cleaning or adjustment. Accordingly, our invention is light weight allowing easy movement from refuse container to refuse container. Our invention uses little electrical power allowing long operation on a set of batteries further enforcing our claim of portable operation with little periodic maintenance. The presence of a latched audible alarm allows security features that prevent unconscientious employees from ignoring silverware falling into the refuse container. 
    
    
     Further objects and advantages of our invention will become apparent from a consideration of the drawings and ensuing description. 
     DRAWINGS 
     FIG. 1 is an overview drawing showing the invention as it would appear to a user. 
     FIG. 2 is a cut-away view showing only the sensor positions in the main enclosure. 
     FIG. 3 is a more detailed drawing of one of the magnetic field sensors showing a linear Hall Effect integrated circuit and its related flux collectors. 
     FIG. 4 is a block and symbol diagram showing the basic electrical and electromechanical components of the invention. 
     FIG. 5 is a schematic of the circuitry contained in electronic monitor circuit  32  shown as a block diagram in FIG.  4 . 
     
       
         
           
               
             
               
                   
               
               
                 REFERENCE NUMERALS IN DRAWINGS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 18 
                 silverware detector 
                 20 
                 funnel assembly 
               
               
                 22 
                 refuse container 
                 24 
                 front magnetic field sensor 
               
               
                 26a/26b 
                 flux collector 
                 28 
                 rear magnetic field sensor 
               
               
                 30 
                 Hall Effect IC 
                 32 
                 electronic monitor circuit 
               
               
                 34 
                 position sensor 
                 36 
                 batteries 
               
               
                 38 
                 power key switch 
                 40 
                 audible alarm 
               
               
                 42 
                 silverware 
                 44 
                 rear magnetic field 
               
               
                 46 
                 front magnetic field 
                   
                 sensor interface 
               
               
                   
                 sensor interface 
                 48 
                 position sensor input 
               
               
                 50 
                 alarm output 
                 52 
                 switch power input 
               
               
                 54 
                 rear channel amplifier 
                 56 
                 front channel amplifier 
               
               
                 58 
                 threshold detector 
                 60 
                 bi-stable latch 
               
               
                 62 
                 reset signal line 
                 64 
                 alarm driver 
               
               
                 66 
                 power supply 
                 68 
                 low battery oscillator 
               
               
                 70 
                 max peak signal line 
                 72 
                 min peak signal line 
               
               
                 74 
                 low battery signal line 
                 76 
                 voltage reference circuit 
               
               
                   
               
            
           
         
       
     
    
    
     DESCRIPTION 
     FIG. 1 depicts a specific embodiment of silverware detector  18  as it appears lifted off of its final mounting location on the top of refuse container  22 . 
     FIG. 2 shows more detailed information regarding the sensing components of silverware detector  18 . Funnel assembly  20  contains an integral circular conduit for collecting and channeling refuse into refuse container  22 . Funnel assembly  20  also provides for refuse container sealing by covering the top of refuse container  22  to prevent easy access to the inside of the container without first removing funnel assembly  20  from refuse container  22 . Silverware  42  shows the travel path of silverware and also refuse as it flows through the circular funnel into refuse container  22 . Funnel assembly  20  also houses front magnetic field sensor  24 , rear magnetic field sensor  28 , and position sensor  34 . In addition funnel assembly  20  houses and supports all components of silver detector  18  shown in FIG.  1 . Funnel assembly  20  is made from a non-magnetic material such as a moldable plastic. 
     FIG. 3 shows more detail regarding magnetic field sensor  24  and  28 . Magnetic field sensors  24  and  28  are assemblies each consisting of a Hall Effect IC  30  and a flux collector  26   a  and a flux collector  26   b . In this embodiment, Hall Effect IC  30  is a linear integrated circuit identified specifically as Allegro A3515EUA. Hall Effect IC  30  is sandwiched between flux collector  26   a  and flux collector  26   b  such that its sensing element is in the center of the gap formed by the two flux collectors  26   a  and  26   b . Flux collectors  26   a  and  26   b  are made from ferrous material having low reluctance to magnetic flux. 
     Again referring to FIG. 2, front magnetic field sensor  24  and rear magnetic field sensor  28  are mounted on opposite sides of funnel assembly  20  refuse opening. Both magnetic field sensors  24  and  28  are mounted on the outside of the refuse funnel wall protected from the flow of refuse. A front magnetic field sensor interface  46  provides power to front magnetic field sensor  24  as well as transmits an analog signal from front magnetic field sensor  24 . A rear magnetic field sensor interface  44  likewise does the same for rear magnetic field sensor  28 . Front magnetic field sensor  24  and rear magnetic field sensor  28  are arranged such that their axial centers are approaching 90 degrees to each other when referencing the front view of FIG.  2 . Funnel assembly  20  height restrictions may prevent an ideal 90 degree angle between the two magnetic field sensors. When viewed from the top, front magnetic field sensor  24  and rear magnetic field sensor  28  each wrap approximately half way around the circular funnel. 
     FIG. 2 also shows position sensor  34  mounted on funnel assembly  20  such that the electrical switch associated with position sensor  34  opens its contacts when funnel assembly  20  is installed on refuse container  22 . Alternatively, this switch closes its contacts when funnel assembly  20  is removed from refuse container  22 . A position sensor input  48  serves as an interface to position sensor  34  conveying specifically its switch contact state to an electronic monitor circuit  32  shown in FIG.  4 . 
     FIG. 4 shows electronic monitor circuit  32  interfacing to front magnetic sensor  24  through front magnetic sensor interface  46 . Similarly, for back magnetic sensor  28  and for position sensor  34 . An audible alarm  40  interfaces to electronic monitor circuit  32  through an alarm output  50 . Audible alarm  40  is a low current piezoelectric alarm. Batteries  36  and a power key switch  38  provide power to electronic monitor circuit  32  through a switch power input  52 . Specifically for this embodiment, batteries  36  are four “D” cells wired in a combination series—parallel configuration to provide a nominal 3.0 volts. Power is switched on and off using power key switch  38 . Power key switch  38  has two positions—off and on. Key switch  38  includes a key that is removable in both positions. 
     FIG. 5 shows in schematic format the details contained in electronic monitor circuit  32  shown in FIG.  4 . Two amplifier channels referred to as a rear channel amplifier  54  and a front channel amplifier  56  are associated with rear magnetic field sensor  28  and front magnetic field sensor  24  respectively. Each amplifier consists of two operational amplifiers provided in this specific embodiment by a LM324A quad operational amplifier integrated circuit package. Amplifiers  54  and  56  each amplify the small signals from their respective magnetic field sensor. Each amplifier has a frequency bandpass that corresponds with the expected velocity range of silverware falling through funnel assembly  20 . 
     Using conventional diode circuits, a max peak signal line  70  follows the maximum DC voltage signal coming from rear channel amplifier  54  and front channel amplifier  56 . Likewise, a min peak signal line  72  follows the minimum DC voltage signal from the two amplifier channels. Each of these two signals is fed into a threshold detector  58 . A reference voltage generated by a voltage reference circuit  76  is used as the reference threshold for threshold detector  58 . Threshold detector  58  in this specific embodiment is built around two operational amplifiers from the LM324 quad integrated circuit package. When the voltage on max peak signal line  70  exceeds the reference voltage, a bi-stable latch  60  is set. Likewise, when the voltage on min peak signal line  72  drops below the reference voltage, bi-stable latch  60  is also set. 
     Latch  60  in this specific embodiment is built around one operational amplifier from the LM324 quad integrated circuit package. 
     Min peak signal line  72  can also be biased low by position sensor  34  closing its contacts. This takes place when funnel assembly  20  is removed from refuse container  22 . This biasing of min peak signal line  72  will also cause threshold detector  58  to set bi-stable latch  60 . 
     Bi-stable latch  60 , when set, causes alarm driver  64  to energize audible alarm  40 . Driver  64  is a NPN bi-polar transistor. The only way to reset bi-stable latch  60  is to power silverware detector  18  off using power key switch  38  shown in FIG.  4 . Upon power on of the unit, a reset signal line  62  insures that bi-stable latch  60  is in the reset state—that is, alarm driver  64  and audible alarm  40  off. 
     Power applied to the circuitry of electronic monitor circuit  32  is regulated by a power supply  66 . Power supply  66  in this specific embodiment is a switching power supply built around a Linear Technology LT1173CN8-5 integrated circuit. Power supply  66  maintains its output voltage near 5.0V as the battery input voltage available at a switched power input  52  varies. Power supply  66  also drives a low battery signal line  74  such that when in a low battery condition will enable a low battery oscillator  68 . This oscillator in this specific embodiment is built around one operation amplifier from the LM324 quad integrated circuit package. Oscillator  68  will drive alarm driver  64  such that audible alarm  40  will pulse when a low battery condition exists. 
     OPERATION—FIGS.  2 ,  4 ,  5   
     Silverware  42  mixed with other refuse is directed to refuse container  22  via funnel assembly  20 . The magnetic field associated with silverware  42  having been previously magnetized causes a signal change in one or both magnetic field sensors  28  and  24 . The near orthogonal structure of magnetic field sensors  28  and  24  each with its extended flux collectors  26   a  and  26   b  is such that silverware  40  can not fall past magnetic field sensor  24  or magnetic field sensor  28  without producing a perturbation in one of the sensors. When silverware  40  is falling in such a position and direction to produce almost no flux change in one of the magnetic field sensors due to symmetry of the flux collectors  26   a  and  26   b , the opposite magnetic field sensor with its near orthogonal set of flux collectors will be in optimum position to sense the passing magnetic field. Hall Effect IC  30  in both magnetic field sensor  28  and magnetic field sensor  24 , is a linear Hall Effect device that is biased such that the output signal line is at ½ of its supply voltage with no magnetic field. Changes in magnetic flux density in magnetic field sensor  28  and magnetic field sensor  24  due to the passage of magnetized silverware will cause a perturbation in the output voltage signal of these magnetic field sensors. All other material not magnetized, whether metal or non-metal, falling through funnel assembly  20  will not cause output voltage signal perturbations. 
     The two voltage signals from magnetic field sensor  28  and magnetic field sensor  24  are separately amplified through two independent amplifier channels, rear channel amplifier  54  and front channel amplifier  56 . The bandpass of these amplifiers is such that only signal perturbations in the frequency range corresponding to silverware  42  passing through the funnel assembly  20  are amplified. Voltage perturbation signals having frequencies below and above the bandpass frequency range are not amplified to the same level. 
     Diodes couple the outputs from rear channel amplifier  54  and front channel amplifier  56  to threshold detector  58 . Amplified signal perturbations will cause amplifier output voltages above and below the bias voltage of the amplifiers. The bias voltage is generated by voltage reference circuit  76 . Max peak signal line  70  will show the maximum peak of the perturbation above the reference voltage while min peak signal line  72  will show the minimum peak of the perturbation below the reference voltage. Either a perturbation from amplifier  54  or amplifier  56  resulting in a voltage above the reference voltage or a perturbation resulting in a voltage below the reference voltage will trigger threshold detector  58 . 
     When a signal perturbation causes threshold detector  58  to trigger, bi-stable latch  60  is set. This set state biases alarm driver  64  on, which in turn activates audible alarm  40  through alarm output  50 . Bi-stable latch  60  remains set until silverware detector  18  is powered off. 
     Additionally, removing funnel assembly  20  from the refuse container  22  will cause position sensor  34  to close its contacts. Position sensor input  48  in turn causes min peak signal line  72  to be biased such that threshold detector  58  will set bi-stable latch  60 . This drives alarm driver  64  on, which in turn causes audible alarm  40  to sound continuously. 
     When the unit is powered on, reset signal line  62  insures that bi-stable latch  60  is initialized in the reset state—that is, alarm driver  64  off resulting in audible alarm  40  off. Power key switch  38  works in conjunction with this circuitry during power on to provide an alarm reset function. 
     Power supply  66  provides regulated voltage to all circuitry in electronic monitor circuit  32 . When the battery voltage approaches a low level where power supply  66  can no longer provide voltage regulation, low battery signal line  74  enables low battery oscillator  68  which in turn cycles alarm driver  64  on and off causing the audible alarm  40  to pulse on and off. This signals the operator of a low battery voltage condition. 
     CONCLUSION 
     Thus this invention provides a very portable, low maintenance, and cost effective device that will detect only silverware that has been magnetized allowing all other refuse whether metallic or otherwise to pass with no false triggering. 
     Although the above description contains many specific implementations, these should not be constructed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment. Other variations are possible. For example, the sensing cavity need not be circular. Rectangular openings as well as other variations are possible. The flux collector design need not be made from round stock but can use other shape variations. Such collectors need not necessarily wrap around the sensing cavity nor be orthogonal to each other. If the sensing cavity is small enough, it is possible that only one assembly of sensor and flux collectors would de required. Also, other variations in circuitry can be used to sense perturbations in the voltage from the linear magnetic sensor. The alarm can be momentary not requiring operator intervention for reset. Also, reset could be achieved through other methods other than the key switch shown such as a momentary switch or a keypad. Other alarms could be employed beside the audible alarm indicated.