Patent Publication Number: US-6698743-B2

Title: Determining when adhesive in a replaceable adhesive dispenser is nearly spent

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a divisional of copending application Ser. No. 09/837,648 filed on Apr. 18, 2001, which is a continuation-in-part of copending application Ser. No. 09/721,549, filed on Nov. 24, 2000. which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This invention relates to systems and methods of determining when adhesive in a replaceable adhesive dispenser is nearly spent. 
     BACKGROUND 
     Today, a variety of different bookbinding systems can deliver professionally bound documents, including books, manuals, publications, annual reports, newsletters, business plans, and brochures. A bookbinding system generally may be classified as a commercial (or trade) bookbinding system that is designed for in-line manufacturing of high quality volume runs or an in-house (or office) bookbinding system designed for short “on-demand” runs. Commercial bookbinding systems generally provide a wide variety of binding capabilities, but require large production runs (e.g., on the order of thousands of bindings) to offset the set-up cost of each production run and to support the necessary investment in expensive in-line production equipment. Office bookbinding systems, on the other hand, generally involve manual intervention and provide relatively few binding capabilities, but are significantly less expensive to set up and operate than commercial bookbinding systems, even for short on-demand production runs of only a few books. 
     In general, a bookbinding system collects a plurality of sheets (or pages) into a text body (or book block) that includes a spine and two side hinge areas. The bookbinding system applies an adhesive to the text body spine to bind the sheets together. A cover may be attached to the bound text body by applying an adhesive to the side hinge areas or the spine of the text body, or both. The cover of a typical commercial soft cover book generally is attached to the text body spine. The covers of hardcover books and some soft cover “lay flat” books, on the other hand, typically are attached to the side hinge areas of the text body and are not attached to the text body spines (i.e., the spines are “floating”). 
     Many different systems have been proposed for providing replaceable adhesive cartridges for bookbinding systems. 
     For example, U.S. Pat. No. 5,632,853 describes a desktop bookbinding device for binding a stack of sheets along a stack edge using a cold set aqueous adhesive. The desktop bookbinding device is an office system having a liquid adhesive storing compartment that is connected to a disposable, non-refillable liquid adhesive cartridge, which includes an applicator belt. The applicator belt applies liquid adhesive to the stack edge when a carriage drives the cartridge along the stack of sheets. 
     U.S. Pat. No. 4,540,458 describes a booklet binding system in which a set of sheets is delivered seriatim along a sheet path leading from an input station to an assembly station where a booklet is formed. As a sheet is moved along the path, a line of liquid adhesive is applied to one surface of the sheet adjacent to one side of the sheet. The adhesive dispensing system includes a replaceable, pressurizable cartridge of liquid adhesive. An emitter and a detector are located in the cartridge holder and are configured to provide a signal to a system controller that indicates that the level of liquid adhesive in the cartridge is above or below the lower end of the cartridge. In the assembly station, the sheets are jogged to align the sheets of the set and pressure is applied to the sheets over the line of liquid adhesive. When the entire set has been bound together into a booklet, the booklet is removed from the assembly station and delivered to an output station. 
     Still other bookbinding systems have been proposed. 
     SUMMARY 
     The invention features novel systems and methods of determining when adhesive in a replaceable adhesive dispenser is nearly spent. 
     In one aspect, the invention features a bookbinding system that includes a receptacle for receiving a plug-in cartridge housing of an adhesive dispenser containing a length of solid sheet adhesive wound into a roll, and an adhesive quantity interrogator that is configured to obtain an indication of the length of solid sheet adhesive remaining within the plug-in cartridge housing. 
     Embodiments in accordance with this aspect of the invention may include one or more of the following features. 
     In one embodiment, the adhesive quantity interrogator is configured to interrogate a memory device that is mounted on the plug-in adhesive cartridge and is programmed to store an indication of the length of solid sheet adhesive remaining within the plug-in cartridge housing. The adhesive quantity interrogator may be configured to store in the memory device an indication of the length of solid sheet adhesive remaining within the plug-in cartridge housing. 
     In some embodiments, the adhesive quantity interrogator comprises a sensor that is configured to sense when the solid sheet adhesive within the plug-in cartridge housing is nearly spent. 
     The sensor may be configured to optically sense when the solid sheet adhesive is nearly spent. For example, the sensor may be configured to sense when the solid sheet adhesive is nearly spent based upon a light signal transmitted toward a side of the roll of solid sheet adhesive. Alternatively, the sensor may be configured to sense when the solid sheet adhesive is nearly spent based upon a light signal transmitted toward an exposed surface of solid sheet adhesive. In some embodiments, the sensor is configured to sense when the solid sheet adhesive is nearly spent based upon a change in light response of the exposed surface of solid sheet adhesive. In other embodiments, the sensor is configured to sense when the solid sheet adhesive is nearly spent based upon detection of an information-containing symbol disposed on the exposed surface of the solid sheet adhesive. 
     In one embodiment, the sensor is configured to magnetically sense when the solid sheet adhesive is nearly spent based upon detection of a magnetic indicator that is disposed near an end of the solid sheet adhesive. 
     In another embodiment, the sensor is configured to physically sense when the solid sheet adhesive is nearly spent based upon contact between a probe and a surface of the roll of solid sheet adhesive. The probe preferably is configured to remain in contact with the surface of the roll of solid sheet adhesive by turning on a pivot. The sensor may be configured to sense the length of solid sheet adhesive remaining within the plug-in cartridge housing based upon an angle at which the probe turns on the pivot. The angle at which the probe turns on the pivot may be measured based upon an electrical resistance measurement. 
     In another aspect, the invention features an adhesive dispenser that includes a plug-in cartridge housing that is configured to plug into a receptacle of a bookbinding system, a length of solid sheet adhesive that is disposed within the plug-in cartridge housing and wound into a roll, and an indicator of the length of solid sheet adhesive remaining within the plug-in cartridge housing. 
     Embodiments in accordance with this aspect of the invention may include one or more of the following features. 
     The length indicator may comprise a memory device that is mounted on the plug-in adhesive cartridge and is programmed to store an indication of the length of solid sheet adhesive remaining within the plug-in cartridge housing. 
     The length indicator may comprise an interrogatable feature that is disposed on an exposed surface of the solid sheet adhesive. The interrogatable surface feature may comprise a change in light response of the exposed surface of solid sheet adhesive, an information-containing symbol disposed on the exposed surface of the solid sheet adhesive, or a magnetic indicator disposed near an end of the solid sheet adhesive. 
     Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic side view of a bookbinding system. 
     FIG. 2A is a diagrammatic perspective view of a text body formed by collecting and aligning a plurality of sheets. 
     FIG. 2B is a diagrammatic end view of the spinal portion of a text body formed by registering sheets with respect to two datum edges so that variations in sheet width dimension are accommodated in the spine edge of the text body. 
     FIG. 3 is a flow diagram of a method of binding sheets into a bound text body. 
     FIG. 4A is a diagrammatic perspective view of an adhesive dispensing system that incorporates a spot heater that is configured to tack a solid hot melt adhesive to a text body spine. 
     FIG. 4B is a diagrammatic perspective view of the adhesive dispensing system of FIG. 4A disposing a solid hot melt adhesive over a text body spine. 
     FIG. 4C is a diagrammatic perspective view of the spot heater of FIG. 4A tacking the dispensed solid hot melt adhesive to the text body spine and a cutting wheel cutting the tacked adhesive to width. 
     FIG. 4D is a diagrammatic perspective view of the adhesive dispensing system of FIG. 4A and a preformed solid hot melt adhesive tacked to the text body spine. 
     FIG. 5A is a diagrammatic front view of a cover with two strips of pressure sensitive adhesive applied to areas corresponding to the side hinge areas of a bound text body. 
     FIG. 5B is a diagrammatic end view of the cover of FIG. 5A being folded over the bound text body of FIG.  5 A. 
     FIG. 5C is a diagrammatic end view of an open bound book with a floating spine formed by attaching the cover of FIG. 5A to the bound text body of FIG.  5 A. 
     FIG. 6 is a diagrammatic front view of a cover with a single strip of pressure sensitive adhesive applied to an area corresponding to the spine and side hinge areas of the bound text body of FIG.  5 A. 
     FIG. 7 is a diagrammatic front view of a cover with multiple strips of pressure sensitive adhesive applied to an area corresponding to the spine and side hinge areas of the bound text body of FIG.  5 A. 
     FIG. 8A is a diagrammatic side view of a plug-in adhesive dispenser for applying solid pressure sensitive adhesive film to a book cover. 
     FIG. 8B is a diagrammatic side view of an adhesive dispensing mechanism of the plug-in adhesive dispenser of FIG. 8A, including a supply spool supporting a roll of a sheet adhesive formed from a solid pressure sensitive adhesive film composition disposed on a carrier ribbon, and a take-up spool configured to reel-in spent carrier ribbon. 
     FIG. 9 is a block diagram of a bookbinder that includes a receptacle for receiving a plug-in cartridge housing of an adhesive dispenser and an adhesive quantity interrogator. 
     FIG. 10 is a block diagram of an adhesive quantity interrogator that is configured to interrogate a memory device that is attached to a plug-in cartridge housing of an adhesive dispenser. 
     FIG. 11 is a diagrammatic perspective view of a plug-in cartridge housing having a window through which a sensor may optically sense when a length of solid sheet adhesive is nearly spent. 
     FIG. 12 is a diagrammatic perspective view of a plug-in cartridge housing containing a length of solid sheet adhesive having an interrogatable feature disposed near one end. 
     FIG. 13 is a diagrammatic perspective view of a plug-in cartridge housing containing a length of solid sheet adhesive having an information-containing symbol disposed near one end. 
     FIG. 14A is a diagrammatic side view of a roll of solid sheet adhesive and a sensor that is configured to sense when the adhesive is nearly spent based upon contact between the sensor and a surface of the roll of adhesive. 
     FIG. 14B is a diagrammatic side view of the roll of adhesive and sensor of FIG. 14A after a substantial length of the solid sheet adhesive has been dispensed from the roll. 
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
     Referring to FIG. 1, in one embodiment, a bookbinding system  10  includes a printer  12  and a finisher  14 . Bookbinding system  10  may be implemented as a desktop or office bookmaking system designed to satisfy on-demand bookbinding needs. Printer  12  may be a conventional printer (e.g., a LaserJet® printer available from Hewlett-Packard Company of Palo Alto, Calif., U.S.A.) that includes a supply tray  16  that is configured to hold a plurality of sheets (e.g., paper sheets), and a print engine  18  that is configured to apply markings onto the sheets received from supply tray  16 . Finisher  14  includes a sheet collector  20  and a bookbinder  22 . Bookbinder  22  includes a sheet binder that is configured to bind the text body sheets to one another, and a cover binder that is configured to attach a cover to the bound text body. In operation, sheets are fed from supply tray  16  to print engine  18 , which prints text, pictures, graphics, images and other patterns onto the sheets. The printed sheets are fed to sheet collector  20 , which collects and aligns the sheets into a text body  24  with an exposed spine bounded by two exposed side hinge areas. The text body  24  is conveyed to bookbinder  22 . The sheet binder binds the sheets of text body  24 , and the cover binder attaches a cover to the bound text body to produce a bound book  26  with a floating spine or an attached spine. 
     Referring to FIGS. 2A and 2B, text body  24  includes a plurality of sheets and is characterized by a front end  28 , two sides  30 ,  32  and a spinal area (or spine)  34 , which is located opposite to front end  28 . Spine  34  is bounded by two side hinge areas  36 ,  38 . Text body  24  may be characterized by a height dimension  40 , a width dimension  42 , and a thickness dimension  44 . As shown in FIG. 2B, the spinal area exposed for adhesive penetration may be increased before adhesive is applied by registering and aligning text body sheets  54  with respect to two datum edges. In particular, sheets  54  preferably are aligned with reference to front end  28  of text body  24  and one of the two text body sides  30 ,  32  so that variations in sheet dimensions are accommodated in the text body width dimension  42  of spinal area  34 . As a result, the spinal surface area exposed for adhesive penetration is greater than if all of the sheets  54  were registered and aligned with respect to spine edge  34 . Upon cooling, the hot melt adhesive re-solidifies and binds the sheets  54  into a bound text body. A variety of different hot melt adhesive compositions may be used to bind the text body sheets, including a conventional paper-backed hot melt sheet adhesive that may be dispensed from a roll and may be obtained from Minnesota Mining and Manufacturing Company (3M), of St. Paul, Minn., United States. 
     Referring to FIG. 3, in one sheet binding embodiment, text body  24  may be bound as follows. An adhesive dispensing system disposes a solid hot melt adhesive over text body spine  34  (step  60 ). A spot heater tacks the dispensed adhesive to the text body spine (step  62 ). The adhesive dispensing system cuts the adhesive to width, leaving a preformed solid hot melt adhesive tacked to text body spine  34  (step  64 ). An adhesive heater heats the preformed solid hot melt adhesive to a temperature at or above the melting temperature of the adhesive (step  66 ). The melted adhesive conforms to the exposed surface features of spinal area  34  and flows into spaces between the ends of sheets  54 . An adhesive former forms the melted adhesive to text body spine  34  (step  68 ). An adhesive cooler cools the formed adhesive until the adhesive re-solidifies to bind the text body sheets into a bound text body (step  70 ). The resulting bonds between text body sheets  54  are greater than the bonds that would have been formed had the sheets been registered and aligned at spine edge  34 . Next, a cover is attached to the bound text body to form a bound book with a floating spine or an attached spine (step  71 ). 
     As shown in FIGS. 4A-4D, in one embodiment, an adhesive dispensing system  72  includes a cartridge housing  74  that includes a supply spool  76  supporting a roll of a paper-backed solid hot melt adhesive  78 . Cartridge housing  74  may plug into a corresponding receptacle in bookbinder  22  of finisher  14 . Hot melt adhesive  78  is dispensed through a guide slot  80  formed in housing  74 . Opposed drive wheels  82 ,  84  draw hot melt adhesive  78  through guide slot  80 . Adhesive dispensing system  72  also includes a spot heater  86  that is configured to heat one or more localized areas of hot melt adhesive  78  to a temperature that is sufficient to tack the adhesive to text body spine  34 . Spot heater  86  includes an elongated clamp  88  that supports one or more exposed spaced-apart heating elements (e.g., conventional heating strips or resistive wires). The spacing between heating elements may be on the order of 1-4 cm. A cutting wheel  90  is configured to cut hot melt adhesive  78  to width by traversing a cutting edge of a cutter bar  92 . 
     As shown in FIG. 4B, in operation, adhesive dispensing system  72  is brought into contact with a clamping system (not shown) that holds text body  24  in place. Drive wheels  82 ,  84  dispense hot melt adhesive  78  over text body spine  34  to a desired width. In one embodiment, an optical sensor may be configured to stop drive rollers  82 ,  84  upon detection of when the leading edge of hot melt adhesive  78  has passed over text body spine  34  by a desired amount. Referring to FIG. 4C, after hot melt adhesive  78  has been disposed over text body spine  34 , spot heater  86  clamps hot melt adhesive  78  to text body spine  34  and cutting wheel  90  cuts hot melt adhesive  78  to width. Spot heater  86  holds hot melt adhesive  78  in place while the adhesive is being cut and applies sufficient heat and pressure to tack the adhesive to text body spine  34  at one or more locations. After hot melt adhesive  78  has been tacked in place, the heating elements of spot heater  86  may be turned off and adhesive dispensing system  72  may be withdrawn (FIG.  4 D). The tack bond holds the resulting preformed hot melt adhesive  94  to text body spine  34  with sufficient force to prevent preformed hot melt adhesive  94  from becoming displaced during subsequent processing steps and to prevent the sheets of text body  24  from moving. 
     Preformed hot melt adhesive  94  may be processed to bind text body  24  by a compact, multi-function sheet binder, as described in U.S. Ser. No. 09/776,251, filed Feb. 3, 2001. In particular, the multi-function sheet binder is configured to melt the preformed hot melt adhesive, form the melted adhesive, and actively cool the formed hot melt adhesive. A cover may be attached to the resulting bound text body as follows. 
     Referring to FIGS. 5A-5C, in one embodiment, a solid pressure sensitive adhesive film is applied to a cover  108  as two strips  110 ,  112  in cover areas  114 ,  116  that correspond to side hinge areas  36 ,  38  of text body  24 . Pressure sensitive adhesive strips  110 ,  112  are spaced apart by a width dimension  118  that is at least as wide as the thickness dimension  44  of text body spine  34 . As shown in FIG. 5B, cover  108  is aligned with respect to the same datum edges used to align the sheets of text body  24 , cut to size, and folded over the bound text body  24 . Cover  108  preferably is scored along a pair of score lines  120 ,  122  to allow cover  108  preferentially to fold over spinal area  34  of text body  24 . Pressure is applied to cover areas  114 ,  116  to activate pressure sensitive adhesive strips  110 ,  112  and, thereby, attach cover  108  to text body  24 . As shown in FIG. 5C, the resulting perfectly bound book  26  has a floating spine that enables the book  26  to lay flat when opened. 
     As shown in FIGS. 6 and 7, text body  24  may be bound to cover  108  with an attached spine construction by applying a solid pressure sensitive adhesive film to a cover area  124  that corresponds to text body spine  34 . The solid pressure sensitive adhesive film may be applied as a single continuous strip  126  over cover areas  114 ,  116 , and  124  (FIG.  6 ), or in a series of multiple strips  128 ,  130 ,  132  over cover areas  114 ,  116 , and  124  (FIG.  7 ). 
     As used herein, “pressure sensitive adhesives” refer to a class of adhesive compositions that are applied with pressure and generally do not undergo a liquid to solid transition in order to hold materials together. Pressure sensitive adhesives may be solvent-free natural or synthetic resins characterized by the rapid wetting of a surface to form an adhesive bond upon contact with the surface under pressure. 
     Referring to FIGS. 8A and 8B, in one embodiment, pressure sensitive adhesive strips may be applied to cover  108  by an adhesive dispenser  140  that includes a plug-in cartridge housing  142  and an adhesive dispensing mechanism  143 . Cartridge housing  142  may plug into a corresponding receptacle in bookbinder  22  of finisher  14 . In some embodiments, multiple adhesive dispensers  140  may be stacked and loaded into bookbinder  22 . The plug-in receptacle is located on a positioning mechanism that draws adhesive dispenser  140  across selected areas of cover  108 . Adhesive dispensing mechanism  143  includes a take-up spool  144 , a supply spool  146 , an application roller  148 , and a guide roller  150 . Supply spool  146  is disposed within plug-in cartridge housing  142  and is configured to support a roll of sheet adhesive (or adhesive tape)  154  that includes a pressure sensitive adhesive composition disposed on a carrier ribbon  152 . Take-up spool  144  is configured to reel-in spent carrier ribbon  152 . In operation, application roller  148  is placed against a surface of cover  108 . Take-up spool  144  and supply spool  146  are coupled by a gear coupling mechanism. The gear coupling mechanism is configured so that take-up spool  144  reels in spent carrier ribbon  152  at a speed that is greater than the feed speed of supply spool  146 , even when the winding diameter of carrier ribbon  152  on take-up spool  144  becomes greater than the winding diameter of adhesive tape roll  154 . Excessive tension between take-up spool  144  and supply spool  146  is relieved by a conventional clutch mechanism between the gears of take-up spool  144  and supply spool  146 . As adhesive dispenser  140  is drawn across the cover surface in a direction indicated by arrow  158 , the tack properties of the pressure sensitive adhesive between application roller  148  and the cover surface releases a film of pressure sensitive adhesive from carrier ribbon  154  onto the cover surface. 
     As explained above, in some embodiments, the respective cartridge housings  74 ,  142  for the solid hot melt sheet adhesive  78  and the pressure sensitive adhesive tape  152  are configured to plug into respective receptacles in bookbinder  22  of finisher  14 . In these embodiments, bookbinder  22  may be configured to obtain automatically an indication of the length of solid sheet adhesives remaining within each of the plug-in cartridge housings  74 ,  142 . Bookbinder  22  also may be configured to replace automatically an exhausted adhesive dispenser with a new adhesive dispenser of an adhesive stack that has been loaded into bookbinder  22  based upon a signal received from a sensor. After each of the loaded adhesive dispensers has been exhausted, bookbinder  22  may display a notice indicating that another adhesive dispenser stack should be loaded into the system. 
     As shown in FIG. 9, bookbinder  22  may include a receptacle  170  that is configured to receive a plug-in cartridge housing  172  of an adhesive dispenser (e.g., hot melt adhesive dispenser  74  or pressure sensitive adhesive dispenser  142 ) that contains a length of solid sheet adhesive  174  wound into a roll  176 . Bookbinder  22  also includes an adhesive quantity interrogator  178 , which is configured to obtain an indication of the length of solid sheet adhesive  174  remaining within the plug-in cartridge housing  172 . Based upon this length indication, bookbinder  22  may determine whether a sufficient amount of adhesive  174  is available to complete a current binding job, or whether the adhesive dispenser should be replaced. 
     Referring to FIG. 10, in one embodiment, a memory device  180  (e.g., a 256-bit 1-WIRE™ EEPROM available from Dallas Semiconductor of Dallas, Tex. U.S.A.) is mounted on plug-in cartridge housing  172  and adhesive quantity interrogator  178  includes a read/write module  182  that is configured to read information from and write information to memory device  180 . Adhesive quantity interrogator  178  also includes a sensor  184  that is configured to obtain an indication of the length of solid sheet adhesive  174  dispensed from cartridge housing  172 , and a controller  186  that is configured to control the operation of read/write module  182  and to communicate with bookbinder  22 . In operation, memory device  180  initially may be programmed to store the length of adhesive contained in an unused adhesive cartridge. During use, controller  184  may update the length value stored in memory device  180  based upon an indication of the length of adhesive used obtained by sensor  184 . As a result, the length of adhesive  174  remaining within cartridge housing  172  may be stored in memory device  180  and updated each time adhesive is dispensed. When the length value stored in memory device  180  is smaller than the length of adhesive needed to complete a particular binding job, controller  186  sends to an adhesive loading system of bookbinder  22  a signal  188  indicating that the adhesive dispenser should be replaced. In this way, adhesive quantity interrogator ensures that a current binding job may be completed properly. In addition, because an indication of the length of adhesive remaining is stored with adhesive cartridge  172 , partially used adhesive cartridges may be inserted into bookbinder  22  and adhesive quantity interrogator  178  readily may determine the length of adhesive available for binding. This approach avoids the need to store adhesive availability information in a memory device of bookbinder  22 . In addition to adhesive length information, memory device  180  also may be programmed to store other information, including an identifier corresponding to the type of adhesive contained within cartridge  172 , an indication of the age of the adhesive, and quality control tracking information, such as an identifier corresponding to the location where the adhesive cartridge was manufactured and the manufacturing lot number. 
     Sensor  184  may obtain an indication of the length of solid sheet adhesive  174  dispensed from cartridge housing  172  directly, for example, by reading a rotary encoder that is coupled to the adhesive dispensing drive mechanism, or indirectly, for example, by obtaining a measurement of separation between clamps holding text body  24  while the text body sheets are being bound together by hot melt adhesive dispensed from adhesive dispenser  74 . 
     Referring to FIG. 11, in one embodiment, plug-in cartridge housing  172  includes a pair of windows  190 ,  192  through which a sensor  194  may optically sense when the solid sheet adhesive  174  is nearly spent. In particular, sensor  194  may include a transmitter  196  (e.g., a light-emitting diode) and a receiver  198  (e.g., a photodetector) that are disposed on opposite sides of cartridge  172 . Transmitter  196  and receiver  198  are positioned with respect to adhesive roll  176  such that light emitted from transmitter  196  is detected by receiver  198  only after the amount of adhesive  174  remaining within cartridge  172  has dropped below a selected level (e.g., below 10% of the original unused adhesive quantity). Controller  186  or, alternatively, a controller of bookbinder  22 , may be coupled to receiver  198  to determine when a light signal is detected by receiver  198 . When such a signal is detected, bookbinder  22  may automatically replace the spent adhesive dispenser with a new adhesive dispenser of an adhesive stack that has been loaded into bookbinder  22 , or bookbinder  22  may display a notice indicating that another adhesive dispenser stack should be loaded into the system. 
     In another embodiment, sensor  194  may include a single transceiver module that is configured to transmit light through window  190  and to detect light that reflects from the exposed side of adhesive roll  176 . When reflected light is no longer detected, bookbinder  22  may automatically replace the spent adhesive dispenser with a new adhesive dispenser of an adhesive stack that has been loaded into bookbinder  22 , or bookbinder  22  may display a notice indicating that another adhesive dispenser stack should be loaded into the system. 
     As shown in FIG. 12, in another embodiment, solid sheet adhesive  174  includes an exposed feature  200  that may be interrogated by a sensor  202 . Feature  200  may be disposed near the end (e.g., at the 10% remaining mark) of the length of sheet adhesive  174  so that sensor  202  may sense when adhesive  174  is nearly spent. In one embodiment, interrogatable feature  200  may correspond to a change in the light response of the exposed surface of adhesive  174  (e.g., a region of different color or a region of different light reflectivity). In this embodiment, sensor  202  may be implemented as a conventional light transceiver module. In another embodiment, interrogatable feature  200  may correspond to a change in the magnetic response of the exposed surface of adhesive  174  (e.g., a magnetic strip). In this embodiment, sensor may be implemented as a conventional magnetic field sensor. 
     Referring to FIG. 13, in one embodiment, interrogatable feature  200  corresponds to an information-containing symbol  204  that may be read by an optical reader  206 . Symbol  204  may be a conventional information-based indicium (e.g., a one- or two-dimensional bar code) that consists of a pattern of light and dark regions-disposed on the exposed surface of adhesive  174 , and optical reader  206  may be a conventional optical reader (e.g., an optical scanner or a bar code reader). Symbol  204  may be oriented along the length of adhesive  174  as shown, or symbol  204  may be oriented along the width of adhesive  174 . Symbol  204  may be disposed near one end of the length of adhesive  174  or a plurality of such symbols may be disposed periodically along the length of adhesive  174 . Symbol  204  may store information relating to the amount of adhesive remaining within cartridge  172 , as well as other information, including an identifier corresponding to the type of adhesive contained within cartridge  172 , an indication of the age of the adhesive, and quality control tracking information, such as an identifier corresponding to the location where the adhesive cartridge was manufactured and the manufacturing lot number. 
     Referring to FIGS. 14A and 14B, in another embodiment, a sensor  210  is configured to physically sense when the solid sheet adhesive  174  is nearly spent based upon contact between a probe  212  and a surface of the roll  176  of adhesive  174 . In particular, probe  212  is configured to turn on a pivot  214  and is coupled to a turn angle marker  216 , which may be read by a meter  218 . In operation, one end of probe  212  is biased against the surface of adhesive roll  176 . The angle at which probe  212  turns on pivot  214  and, consequently, the location on turn angle marker  216  where meter  218  reads the turn angle, is determined by the size of adhesive roll  176 . As adhesive  174  is dispensed from roll  176 , roll  176  becomes smaller and the angle measured by meter  218  varies. Angle marker  216  and meter  218  may be calibrated so that meter  218  may generate an indication of the amount of adhesive remaining based upon the measured turn angle. In one embodiment, angle marker  216  may be implemented as a potentiometer, and meter  218  may be implemented as an ohmmeter. In another embodiment, angle marker  216  may be implemented as an optical strip containing angle information encoded in a pattern of light and dark regions across the exposed surface, and meter  218  may be implemented as a conventional optical reader. 
     Other embodiments are within the scope of the claims.