Abstract:
An elapsed time clock is incorporated into a part call tag for requesting replenishment of components used by workstations of a manufacturing facility. One or more transmission readers spatially distributed around the manufacturing facility detect a part call signal transmitted from the part call tag. A reader output processing subsystem processes part call signals detected by at least one of the tag transmission readers to recover information contained in the part call signal. A management processor associates the recovered information with a respective workstation, and what component is to be replenished. The elapsed time clock is reset when the part call tag is operated to transmit a part call signal, and thereby serves as a call tag ‘stop watch’—informing workstation personnel of the length of time that has elapsed since the last part call transmission from that tag.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application incorporates by reference, in its entirety, U.S. patent application Ser. No. 09/503,675, now U.S. Pat. No. 6,317,082, concurrently filed herewith and assigned to the same assignee as the present application. The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/120,122, filed Feb. 16, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to part/material replenishment for product manufacture and/or assembly systems and the like, and is particularly directed the use of an elapsed time clock in conjunction with the call tag employed in the wireless call tag-based material replenishment system described in the above-referenced co-pending Bacon et al application. The elapsed time clock serves essentially as a call tag ‘stop watch’, that is reset whenever a part replenishment call is made, and thereby functions to inform workstation personnel of the length of time that has elapsed since the last part call from that tag. 
     BACKGROUND OF THE INVENTION 
     As described in the above-referenced co-pending application, product manufacturers widely employ a technique, referred to as ‘pull manufacturing’, to replenish components or material required by an assembly line-side workstation in the course of its participation in the production of an item. In accordance with this resupply scheme, parts or material required by a line-side workstation are resupplied in response to a request or ‘call’ from the workstation to a remote storage management and distribution subsystem, which then retrieves some number of the requested part from a storage facility and delivers them to the requesting site. 
     Unfortunately, within most manufacturing environments, options for communicating material replenishment requests to those responsible for delivering the parts are considerably limited. A significant number of production facilities continue to employ traditional manual, labor-intensive routines, such as card-based methods. Others, which have attempted to incorporate upgraded communication methods, use hardwired subsystems, that are not only costly to install but, due to their inherent inflexibility, are expensive, time consuming, and labor intensive to retrofit or modify, as the needs and/or retooling of the plant are continually being updated and reconfigured. Although some wireless forms of call systems have been proposed, they are complex—requiring two-way communications with a line-side location—and are therefore very expensive to install and operate. 
     Pursuant to the invention described in the above-referenced co-pending application, shortcomings of conventional pull manufacturing replenishment systems are obviated by a wireless ‘call tag’ based system. In accordance with this call tag based scheme, diagrammatically shown in FIG. 1, advantage of the detection and signal processing infrastructure of the tagged object radio location system described in the U.S. Pat. No. 5,920,287, to D. Belcher et al (hereinafter referred to as the &#39;287 patent), by installing one or more ‘call tags’  16  at or in proximity of each plant workstation  13  of one or more assembly lines  15  within a manufacturing plant  12 . If a workstation employs different components, it is equipped with multiple call tags—one for each different part. 
     A respective call tag  16  may have a physical configuration, shown in FIG. 2 as including a housing  30 , that contains various input/output (I/O) units associated with the use of the call tag, such as a ‘part call’ push-button  32 , and an optical indicator  36 . The push-button  32  is employed by a (line-side) operator to trigger the operation (part call transmission) of the call tag. The optical indicator  36  may comprise a light emitting diode (LED), or the like, that is illuminated or flashed when a part replenishment call signal is transmitted by the call tag. 
     To initiate part replenishment, a line-side workstation operator simply pushes the tag&#39;s ‘call’ button  32 . This causes the call tag&#39;s internal RF transmitter to transmit a spread spectrum RF transmitter to transmit a spread spectrum RF signal burst that is encoded with the identification (e.g., serial number) of the call tag. At the same time, the call tag&#39;s optical indicator  36  (e.g., LED) is flashed to provide a visual indication that the ‘part call’ was transmitted. The transmitted RF burst is detected by one or more transmission readers  10  of a spatially distributed transmission burst detection and processing subsystem  24 . In addition to having the ability to perform tag geolocation processing of the type described in the &#39;287 patent, the signal processing subsystem  24  reads identification and other data conveyed in each call tag transmission. The call tag identification data is used by a resource management operator to access an asset management database  20 , which associates each call tag&#39;s identity with a part employed by the site where the call tag is located. This enables the resource management operator to specify what component is to be accessed from storage, so that the part may be delivered to the identified call tag&#39;s workstation. 
     Because of the effectively continuously dynamic character of assembly line production, including differences among production shifts and operator assignments, coupled with the ease with which the call tag system described above enables workstation personnel to request material replenishment (simply by pushing a button), system operators may not be particularly diligent in keeping track of replenishment orders. This can lead to duplicate and triplicate orders, as well as out of stock conditions. Moreover, a subsystem failure or an anomaly in the replenishment path, which could lead to assembly line slow down or interruption, may not be immediately noticed. It would be desirable, therefore, to know how recently a parts call has been made. Not only would this advise lineside personnel of the time of the call, but it would aid in determining maximum and minimum inventory levels to be stored lineside. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention this objective is fulfilled by an enhancement to the call tag-based replenishment system described in the above-referenced copending application, which is effective to continuously inform workstation personnel of the length of time that has elapsed since the last part call was made from a respective call tag. In particular, the present invention includes the incorporation into the call tag of an elapsed time clock, that is automatically reset in response to the call button being pushed, and thereby essentially operates as a part replenishment ‘stop watch’. 
     Even though experience of normal assembly line operation will customarily enable a workstation operator to anticipate when to expect parts delivery once a parts call has been made, the incorporation of a part call ‘stopwatch’ or elapsed time device into the call tag not only allows the lineside operator to determine if an expected delivery is late, but to confirm whether a call was actually made within a given time reference (e.g., an assembly line shift). While the elapsed time clock may be installed and operate as a stand-alone item, it is preferred that it be integrated with other components of the call tag, to facilitate ease of use. In accordance with a non-limiting embodiment of the invention, the call tag timer is arranged to be reset by the operation of the call tag&#39;s pushbutton. As a non-limiting example, the elapsed time may be displayed by way of a dedicated clock display on the call tag housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 diagrammatically illustrates the general architecture of the radio location call tag-based part/material replenishment system described in the above-referenced co-pending patent application; 
     FIG. 2 illustrates the general physical configuration of a part replenishment call tag employed in the system of FIG. 1; and 
     FIG. 3 is a block diagram of the circuitry contained in the call tag of FIG. 2, modified to incorporate an elapsed time call tag clock in accordance with the present invention and; 
     FIG. 4 shows the circuit architecture of the RF transceiver board of the call-tag diagram of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     Before describing in detail the elapsed time clock is enhancement to the wireless call tag-based material replenishment system of the above-referenced co-pending application, it should be observed that the invention resides primarily in what is effectively a prescribed arrangement of conventional communication circuits and associated digital signal processing components and attendant supervisory control circuitry therefor, that controls the operations of such circuits and components. Consequently, the configuration of such circuits components and the manner in which they are interfaced with other communication system equipment have, for the most part, been illustrated in the drawings by readily understandable block diagrams, which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the block diagram illustrations are primarily intended to show the major components of the system in a convenient functional grouping, whereby the present invention may be more readily understood. 
     As pointed out above, although an elapsed time clock enhancement to the call tag of FIG. 2 may be implemented as a stand-alone item, it is preferred that it be integrated with other components of the call tag, to facilitate ease of use and implementation. For this purpose, as shown in FIG. 3, which illustrates the functional architecture of the internal circuitry of the call tag described and shown in detail in the above identified copending application, an elapsed time clock  31 , such as one having a standard (six digit) twenty-four hour display  34 , may be installed in the call tag housing  30  as a discrete component, with a reset input  33  thereof coupled to the call tag&#39;s call pushbutton  32 . When employed in the physical configuration of the call tag shown FIG. 2, the elapsed time clock&#39;s display  34  may be mounted with a suitable window provided in the call tag housing  30 , so that the clock&#39;s elapsed time may be continuously viewable by line-side operator personnel. 
     The internal circuitry of the call tag includes a supervisory control processor  38  (e.g., controller board), with which I/O units such as pushbutton  32  and optical indicator  36  are coupled. Power for the call tag is supplied by a battery  39 . Coupled to the control processor  38  is an RF transceiver board  40 , having a transmit antenna  60  and a receive antenna  51 . The RF transceiver board  40  (shown schematically in FIG. 4 to be described) includes memory, which stores a multibit code identifying the (serial number of the) call tag, and auxiliary data. The call tag&#39;s transceiver circuitry is coupled to receive a transmit command from the call tag&#39;s control processor  38 , so that the call tag&#39;s transmitter may generate a ‘part call’ RF burst transmission containing its identification code and any optional data stored in memory, when triggered by the actuation of the call push button  32 . 
     In response to operation of the part call button  32 , the control processor  38  (e.g., micro-controller board) couples a part call command signal to the call tag&#39;s transmitter circuitry, which causes the tag&#39;s transceiver board  40  to transmit a prescribed number of sequential spread spectrum RF signal bursts encoded with the serial number of the call tag and part call status data downloaded by the call tag&#39;s microcontroller to memory. At the same time, the control processor  38  supplies a drive signal to the optical indicator  36  (e.g., LED), which is then illuminated or ‘flashed’ for a prescribed period of time (e.g., one second) to confirm to the operator that a ‘part call’ burst has been transmitted. A ‘part call’ RF burst is received by one or more of a plurality of transmission readers  10  that are distributed within and/or around the workstation production environment of the manufacturing plant and processed for replenishment of the part associated with the call tag, as described briefly above, and detailed in the above-referenced copending application. 
     The circuit architecture of the call tag&#39;s RF transceiver unit  40  is schematically illustrated in FIG. 4 as comprising a relatively coarse (RC) oscillator  41 , whose output is fed to a ‘slow’ pseudo random pulse generator  42 , a strobe pulse generator  44 , and a push button blink timer circuit  117 . The strobe generator  44  contains a timer  46  having a prescribed time-out duration (e.g., one-half second) and a (one-shot) delay circuit  48 , the output of which is a low energy (e.g., several microamps) receiver enable pulse having a prescribed duration (e.g., one-second wide). 
     The receiver enable pulse enables or strobes a relatively short range receiver  50 , such as a crystal video detector, which requires a very low amount of power compared to other components of the tag. Because the receiver enable pulse is very low power, it does not effectively affect the call tag&#39;s battery life. The duration of the receiver enable pulse produced by the strobe pulse generator  44  may be defined such that any low power signal transmitted by another device will be detected by the short range receiver  50 . 
     Where the call tag employs a common antenna that both transmits and receives (or, alternately, a transmitting antenna  60  along with a receiving antenna  15 ), the short range receiver  50  may have its input coupled to a receive port  52  of a transmit/receive switch  54 , a bidirectional RF port  56  of which is coupled to an antenna. The transmit/receive switch  54  has a transmit port  62  coupled to the output of an RF power amplifier  64 , which is powered up only during the relatively infrequent transmit mode of operation of the call tag. Alternatively, where the call tag employs separate transmit and receive antennas (as shown at  60  and  51  in the block diagram of FIG.  3 ), the crystal video receiver  50  may have its input coupled to a receive antenna  51 , as shown by broken lines. 
     The output of the ‘slow’ pseudo random pulse generator  42  is a series of relatively low repetition rate (for example, from tens of seconds to several hours), randomly occurring ‘blink’ pulses. These pulses are coupled to a high speed PN spreading sequence generator  73  via an OR gate  75  and an AND gate  76 , and serve to define when the call tag is to randomly transmit bursts of wideband (spread spectrum) RF energy (to be detected by the system readers) during its quiescent mode. In response to an enabling pulse, the high speed PN spreading sequence generator  73  generates a prescribed spreading sequence of PN chips. AND gate  76  has a second input hardwired via a pull-up resistor  77  to a battery supply voltage +V, and to a ‘BLINK_ON’ output from the microcontroller  38 . When the ‘BLINK_ON’ signal is at a logical ‘0’, AND gate  76  is disabled, placing the call tag in the ‘OFF’ mode, so that no spread signal will be transmitted. 
     The PN spreading sequence generator  73  is driven at the RF frequency output of a crystal oscillator  82 , which provides a reference frequency for a phase locked loop  84 , that is used to establish a prescribed output frequency (for example a frequency of 2.4 GHz, to comply with FCC licensing rules). The RF output of loop  84  is coupled to a first input  91  of a mixer  93 , the output  94  of which is coupled to RF power amplifier  64 . The power amplifier  64  is coupled to supply a transmitter operational state signal PA_ON to the control processor  38  (e.g., micro-controller) to indicate that the RF transceiver unit  40  has been ‘awakened’ and has ‘blinked’ an RF burst. The mixer  93  has a second input  95  coupled to output  101  of a spreading sequence modulation exclusive-OR gate  103 . A first input  105  of exclusive-OR gate  103  is coupled to receive the PN spreading chip sequence generated by PN generator  73 . A second input  107  of exclusive-OR gate  103  is coupled to receive respective bits of data stored in a memory  110 , which are clocked out by the PN spreading sequence generator  73 . 
     As a non-limiting example, the tag memory  110  may comprise a relatively low power, electrically alterable CMOS memory circuit, which stores a multibit word or code identifying the call tag. The memory circuit  110  may also store auxiliary data, that may be coupled thereto by an associated data logic circuit  109 . The data select logic circuit  109  is coupled to receive information supplied by the microcontroller  38 , such as a PUSH_BUTTON signal associated with the operation of the push button  32 , as well as data contained in a message that has been transmitted to the call tag from another wireless device, and has been decoded by a command and data decoder  112 , coupled in circuit with the output of the short range receiver  50  (e.g., crystal video receiver). 
     The data select logic circuit  109  is preferably implemented in gate array logic and is operative to append any data received from an external radio source to that stored in memory  110 . It may also selectively filter or modify data output by the command and data decoder  112 , as downloaded from an external radio source. When a wireless (RF) transmission from an external radio source is received, the call tag&#39;s identification code stored in memory  110  is coupled to a ‘wake-up’ comparator  114 , which compares the bit contents of the received message with the stored call tag identification code. 
     If the two codes match, the comparator  114  generates an output signal, which is used to cause any data contained in the incoming message to be decoded by the command and data decoder  112 , and written into tag memory  110  via the data select logic circuit  109 . The output of comparator  114  is coupled through an OR gate  116 , OR gate  75  and an AND gate  76  to the enable input of PN generator  73 . In response, the call tag&#39;s transmitter generates a response RF burst, in the same manner as it ‘blinks’ a PN spreading sequence transmission containing its identification code and any data stored in memory  110 , as described above. 
     The OR gate  116  is also coupled to a push button blink timer circuit  117 , which is operative to generate a prescribed (repetitive) timing signal in response to the control processor  38  (e.g., microcontroller or controller board) detecting the operation of the push button  32  and supplying a transmit command signal PUSH_BUTTON. As a non-limiting example, the transmit command timing signal may comprise a series of enabling pulses  119  (e.g., three in the example shown), which cause the transmitter unit to emit a sequence of ‘part call’ RF bursts (e.g., at a rate of one enabling pulse every three seconds), each of which contains a call tag identification code and any optional data stored in memory  110 . 
     When a component is in need of replenishment, a line-side workstation operator, who would typically be a human operator (although a robotic operator could perform the same function), simply pushes the ‘call’ button  32 . In response to operation of the call button, the call tag&#39;s microcontroller  38  generates a PUSH_BUTTON command signal, which is coupled to the timer circuit  117  and to the data select logic circuit  109 , as described above. The timer circuit supplies a series of ‘blink’ enabling pulses  119  to the OR gate  116  and thereby through OR gate  75  and the AND gate  76 . Coupling the PUSH_BUTTON signal to the data select logic circuit  109  for storage into the tag memory  110  causes a ‘button pushed’ status code to be appended to the call tag&#39;s identification code in order to distinguish a part call from a random blink (which normally has no push-button-associated status bits asserted). 
     The generation of a plurality of enabling pulses  119  by the timer circuit  117  serves to enhance communication reliability. Each enabling pulse causes the call tag to transmit a spread spectrum RF signal burst encoded with the identification (e.g., serial number) of the call tag and part call status data downloaded by the call tag&#39;s microcontroller to memory  110  through the data select logic  109 . At the same time, the microcontroller  38  supplies a drive signal to the LED indicator  36 , which is then illuminated or ‘flashed’ for a prescribed period of. time (e.g., one second) to confirm to the operator that a ‘part call’ burst has been transmitted. 
     The ‘part call’ RF burst emitted by the call tag is received by at least one and typically a plurality of burst emission readers  10  that are distributed within and/or around the workstation production environment of the manufacturing plant. The architecture and operation of the tag readers  10  and associated correlation-based, RF signal processors corresponds to that shown and described in the above-referenced &#39;287 patent. 
     Suffice it to say that the use of correlation-based RF signal processors with the spatial distribution of multiple readers facilitates determining which spread spectrum signals transmitted by a call tag and received by a respective reader is a first-to-arrive transmission, so that an accurate determination can be made of the location of the call tag and therefore the destination of the delivery of the parts request in the call may be confirmed. 
     In addition to determining call tag location, (identification and status) data read out of the call tag&#39;s memory and superimposed on the call tag transmission is downloaded to the asset management data base  20 , and linked therefrom to personal computer  26 , which is programmed to display call tag location and associated parameter data in a form customized for the user&#39;s application. As pointed out above, in the case of line-side part replenishment, the decoded data may be displayed on a floor plan map of the manufacturing plant, to facilitate assimilation of information relating to the workstations&#39; part replenishment requests and line-side delivery of those parts from storage. 
     Whether or not the outputs of the transmission readers are used to locate the call tag, the call tag identity (such as a call tag serial number) and any other (e.g., call status) data that was conveyed in the call tag&#39;s replenishment transmission burst is coupled to the asset management database  20 , which associates the identification data with a particular part employed by the workstation where the call tag is located. As described in the &#39;675 application, this allows the resource management operator to specify what component is to be accessed from storage, so that the requested part may be delivered to the identified call tag&#39;s associated workstation. For part call completion verification and inventory tracking purposes, a record of each part request and delivery transaction may be forwarded from the resource management processor to a (fixed or mobile) data terminal associated with the plant&#39;s parts storage area. A part delivery operator may then clear or reset the request once the material has been delivered to the workstation that originated the replenishment request. 
     While we have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.