as a preliminary matter , it will readily be understood by one having ordinary skill in the relevant art (“ ordinary artisan ”) that the present invention has broad utility and application . furthermore , any embodiment discussed and identified as being “ preferred ” is considered to be part of a best mode contemplated for carrying out the present invention . other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure of the full scope of the present invention that is contemplated . moreover , many embodiments , such as adaptations , variations , modifications , and equivalent arrangements , will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention . accordingly , while the present invention is described herein in detail in relation to one or more embodiments , it is to be understood that this disclosure is illustrative and exemplary of the present invention , and is made merely for the purposes of providing a full and enabling disclosure of the present invention . the detailed disclosure herein of one or more embodiments is not intended , nor is to be construed , to limit the scope of patent protection afforded the present invention , which scope is to be defined by the claims and the equivalents thereof . it is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself . thus , for example , any sequence ( s ) and / or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive . accordingly , it should be understood that , although steps of various processes or methods may be shown and described as being in a sequence or temporal order , the steps of any such processes or methods are not limited to being carried out in any particular sequence or order , absent an indication otherwise . indeed , the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention . accordingly , it is intended that the scope of patent protection afforded the present invention is to be defined by the appended claims rather than the description set forth herein . additionally , it is important to note that each term used herein refers to that which the ordinary artisan would understand such term to mean based on the contextual use of such term herein . to the extent that the meaning of a term used herein - as understood by the ordinary artisan based on the contextual use of such term - differs in any way from any particular dictionary definition of such term , it is intended that the meaning of the term as understood by the ordinary artisan should prevail . furthermore , it is important to note that , as used herein , “ a ” and “ an ” each generally denotes “ at least one ,” but does not exclude a plurality unless the contextual use dictates otherwise . thus , reference to “ a picnic basket having an apple ” describes “ a picnic basket having at least one apple ” as well as “ a picnic basket having apples .” in contrast , reference to “ a picnic basket having a single apple ” describes “ a picnic basket having only one apple .” when used herein to join a list of items , “ or ” denotes “ at least one of the items ,” but does not exclude a plurality of items of the list . thus , reference to “ a picnic basket having cheese or crackers ” describes “ a picnic basket having cheese without crackers ”, “ a picnic basket having crackers without cheese ”, and “ a picnic basket having both cheese and crackers .” finally , when used herein to join a list of items , “ and ” denotes “ all of the items of the list .” thus , reference to “ a picnic basket having cheese and crackers ” describes “ a picnic basket having cheese , wherein the picnic basket further has crackers ,” as well as describes “ a picnic basket having crackers , wherein the picnic basket further has cheese .” referring now to the drawings , embodiments of the present invention are next described . the following description of the embodiments is merely exemplary in nature and is in no way intended to limit the invention , its implementations , or uses . turning now to the drawings , fig1 illustrates a perspective view of an automatic paper towel dispenser apparatus 10 in accordance with one embodiment of the present invention . the apparatus 10 dispenses common , readily available , perforated paper towels . furthermore , the apparatus has a learning capability , giving it the ability to detect and dispense towels of varying lengths , including full sheets , half sheets , multiple sheets , and abnormally sized sheets . therefore , a wide variety of perforated towels can be used with the apparatus , including any brand or length available at retail . fig2 is an isometric view of the apparatus 10 and fig3 is a perspective view of the apparatus 10 . fig2 shows the top drive mechanism 12 of the towel dispenser apparatus 10 . fig3 shows the apparatus with the front cover 14 removed , displaying the battery holder 16 and control circuitry 18 . preferably , the apparatus 10 may be powered by either batteries 20 ( as shown in fig3 ) or an ac / dc adapter 22 ( such as the one illustrated in fig1 ). the apparatus 10 is intended to be mounted under kitchen cabinetry , or on the underside of any sufficiently sized shelf . four screws 24 interface with thread inserts in the main structure of the dispenser 10 . installation involves drilling four holes , positioned with a supplied template . some features have been included to allow a level of installation customization . kitchen cabinets are constructed in a number of ways . if a recess exists under a cabinet , the dispenser can be mounted with the supplied spacers 13 . these spacers slide onto the screws . they can be stacked and combined to achieve three height offsets for the dispenser . furthermore , if spacers are used , a gap between the dispenser and underside of the cabinet may be visible from some angles . to address this aesthetic issue , trim tabs 50 have been designed into the exterior side covers of the apparatus 10 . these trim tabs 50 are simply molded with the side covers , and can be folded over or snapped off at scores 52 ( or otherwise bent ) as desired in order to accommodate spacing between the top panel of the apparatus and the bottom of the underside of the cabinet . as an alternative to the spacers , it is contemplated that a bracket may be used for mounting the dispenser . use of the device begins by deciding on the source of power . four d batteries 20 can be used to supply the necessary 6v input , or a 6v , 3 . 5a ac / dc adapter 22 can be connected via a standard 5 mm input jack , as illustrated in fig1 . if the ac / dc adapter 22 is selected , power from the batteries 20 is interrupted , protecting the circuitry 18 from over voltage damage . specifically , plugging in the connector of the adapter into the housing of the dispenser apparatus 100 breaks the battery circuit , thereby preventing parallel connection of the batteries and ac / dc supply . an off the shelf dc jack with a ground interrupt loop , kobiconn 163 - mj21 - ex , provides this switching protection . fig7 - 9 are photographs showing steps in a sequence of installing toweling into an automatic paper towel dispenser apparatus 100 in accordance with an embodiment of the invention . fig1 a and 14b collectively illustrate a block diagram describing operational logic that is implemented in the automatic paper towel dispenser apparatus 100 ; and fig1 a is an electronic schematic diagram for control circuitry that may be utilized in automatic paper towel dispenser apparatus in accordance with at least one embodiment of the invention . fig1 b is an alternative electronic schematic diagram for control circuitry that may be utilized in automatic paper towel dispenser apparatus in accordance with at least one other embodiment of the invention , wherein , inter alia , a single position sensor is utilized . a latch mechanism is released to open apparatus 100 . this latch is operated by a sliding pull handle located on the underside of the front section of the dispenser . fig7 shows the apparatus 100 in the open position and ready to accept a roll of paper towels . the lower driver roller moves with the towel carrier . this feature greatly simplifies installation of the toweling . in conventional dispensers , tensioning devices and a convoluted feeding route need to be understood by the operator . in apparatus 100 , the operator simply installs a roll of towels with the first towel draped over the lower drive roller and closes the device . there is no requirement for the toweling to be threaded through any path defined by rollers and tensioning devices . included in the rotating towel carrier subassembly is a magnet that interfaces with a hall — effect transducer resident on the main circuit board . output from the hall - effect transducer notifies the micro controller of the position of the towel carrier door . each time the door is opened , the device is reset . upon closing the door , the microcontroller initiates a “ length learn ” program sequence . with particular regard to the “ length learn ” program sequence , the apparatus 100 first retracts the toweling until output from the “ s 1 ” positioning reflective ir sensor indicates that no paper is present , i . e ., that a leading edge of the toweling has been sensed . this reflective sensor is located at the front and top of the dispensing slot . it is mounted to the main circuit board , and protrudes through an opening that keeps it flush with the dispensing slot top surface . in at least some preferred implementations , a surface opposite the reflective sensor includes one or more holes or openings to prevent reflections off of dispenser components from being an issue . position of the towel &# 39 ; s edge has now been determined . preferably , a known length , such as twelve inches of paper towel , is then dispensed although a greater length may be dispensed , especially if the user desired dispensing of more than one towel at a time . the length of toweling that is dispensed is determined by driving the motor in the forward direction a predetermined number of encoder counts , or “ drive length units ”. length corresponds to counts . counts correspond to both edges of openings in a slotted wheel axially mounted to the top roller shaft . output from a slot type ir sensor , tt optek opb89it51z , is used by the microcontroller to count . in a preferred implementation , there are 32 counts per revolution with a 16 slot wheel . a pause in the program , referred to as the “ tear time interval ”, allows an operator to interact with the dispenser . towel length for all subsequent dispensing is determined by tearing off a length of towel at any desired perforated position . “ tear time interval ” concludes and the dispenser again retracts until the reflective ir sensor detects the leading edge of the toweling . while reversing , the microcontroller again uses the encoder to count openings in the slotted wheel , sometimes referred to as an encoder pinwheel . “ retract length units ”, reverse counts , are used to determine “ learned towel length ”, whereupon the “ length learn ” program sequence is completed . the learned towel length or l tl is determined by subtracting the retract length units or rlu from the drive length units or dlu . it further will be appreciated that technology other than an encoder pinwheel may be used as an alternative for measuring the extent to which the toweling is extended or retracted by the motor . for example , the technology conventionally found in an optical mouse may be utilized , which includes a tiny camera that takes thousands of pictures per second to determine position and speed . conventionally , the optical mouse uses a very small light emitting diode more commonly referred to as an led which is red in color . this led bounces light off of a mouse pad or desk surface onto a cmos ( complementary metal oxide semiconductor ). in the context of the present invention , this same technology may be used to determine the extent of the toweling that is extended or retracted . in operation , the led produces a red light that is emitted onto the toweling surface . the light is reflected off the surface back to the cmos sensor . the cmos sensor sends each image that is reflected back to a dsp ( digital signal processor ) for analysis . using the thousands of images ( taken at hundreds of times per second ) that the cmos sends to the dsp for analysis , the dsp is able to detect both patterns and images and can determine if the toweling has moved , at what distance it has moved , and at what speed . yet another alternative technology includes that found in laser - based optical mice , which technology piggy backs off of the led optical mouse . the laser based optical mouse works similar to the led based optical mouse . it uses a laser instead of a led . the benefit is that because it uses a laser beam , the mouse can track much better , giving the user ultimately better response times , tracking and the ability for such a mouse to be used on even more surfaces . in the context of the present invention , it is believed that use of such laser technology would provide greater precision and accuracy in determining the extent of the toweling that is extended or retracted . furthermore , the housing in the area of the detection of the toweling surface preferably is dark and contrasts well with the toweling so as to better define the leading edge of the toweling for detection , whether the ir , optical or laser technology is used . after the ltl is learned , the operator engages the “ hand wave ” sensor to dispense a towel . the reflective ir sensor shown in the drawings is interfaced with through a lens located in the center of the front fascia panel . the sensor emitter and detector are mounted directly to the main circuit board . therefore , they do not move with the removable fascia panel . as a result , their placement , and proper installation of the fascia panel , is important to check for correct operation . after the “ length learn ” sequence is completed , the dispenser &# 39 ; s micro controller enters a program that constantly looks at the “ hand wave ” sensor for output . some level of ambient ir light is always present . also , people and objects may continually pass in front of the device with no intention of initiating towel dispensing . preferably , “ hand wave ” sensor output voltage is sampled and compared to avoid false initiation . the sample rate may be every 10 milliseconds , for example . when an operator or user intends to dispense a towel , “ hand wave ” sensor voltage is substantially higher than ambient for a determined number of samples . at this point the motor is driven forward the “ learned towel length ”. to accommodate possible additional towels being desired by the user , the program delays for one tenth of the “ tear time interval ”, then reviews the “ hand wave ” sensor output . if a hand is still present , the toweling is extended an additional l tl . this additional dispensing sub - sequence will continue until a hand is no longer detected by the “ hand wave ” sensor . when a hand is no longer detected by the “ hand wave ” sensor , the “ tear time interval ” is initiated , during which the operator is expected to tear off the desired paper towels from the dispensed toweling . after the “ tear time interval ”, the motor is driven in reverse until the positioning sensor “ s 1 ” again detects the leading edge ( i . e ., presumed new leading edge ) of the toweling . alternatively , the motor is driven forward the number of desired ltls ( e . g ., 1 ltl , 2 l tls , or 3l tls ), plus a predetermined additional extent . the predetermined extent may be , for example , a distance between the point at which the leading edge of the toweling is detected by the sensor , and a point exterior of the housing and proximate to area at which the toweling exits the housing . in accordance with this alternative , a line of perforations should be found each time a towel is dispensed at a point exterior of the housing and proximate the area at which the toweling exits the housing . as such , a small extent of the toweling following separation of the dispensed towels will be left extending outside of the housing and will be retracted back into the housing to the point at which the leading edge of the toweling is detected by the sensor . in accordance with this alternative , an operator will be able to clearly observe the particular line of perforations along which the tear is made . normal dispensing by the apparatus continues until all the towels on the roll have been dispensed , or until a dispensing error occurs . all errors result in the bi - color indicator led lighting red . an operator must open the device to reset the error condition . after any error , the “ length learn ” program will run again and the operator must teach the dispenser the desired dispense length . reliable paper feeding , without a specific paper to optimize the system around , is not trivial . variations in thickness , friction coefficient , strength , surface area , and cross section must all be accommodated . moreover , paper is removed by pulling with sufficient force to break the roll at a perforation , and this force also must be accommodated . several features have been designed to prevent malfunction , improve paper feed ability , and reliable operation . in particular , at least three main reliability features are provided in the apparatus 100 that are intended to prevent malfunction , improve paper feed ability , and reliable operation . furthermore , it should be understood that , while embodiments of the invention may include only one or two - or none - of these features , other embodiments of the invention may include all three of these features . the first reliability feature of the mechanism allows the upper drive roller to travel vertically . two springs hold the roller in its lowest position . when the towel carrier is closed , the lower drive roller dictates the upper drive roller &# 39 ; s position . this addresses different towel thicknesses that will tend to push the upper roller to slightly different positions . with the spring loaded drive roller , thickness variations throughout the roll are constantly accounted for . this also addresses inherent manufacturing dimensional variation , within tolerances , that otherwise affects feed reliability , especially when injected molding with plastics . the second reliability feature prevents unwanted movement of one or both rollers . both rollers in this dispenser are driven . they are directly linked together ( or directly interconnected ) by a pair of axially mounted end gears . these gears have fairly large and forgiving tooth geometry . this is important , because of the unique ability to separate the rollers during paper installation . opening the rollers enough for the entire roll to pass between them separates the gears completely . they must re - mesh , without damage or perceived difficulty , when the dispenser is closed . the third reliability feature is software based . during the “ tear time interval ” the motor has a percentage of the stall current applied in reverse . this applies force to the drive mechanism , preventing its movement , and allowing a very positive feel as the towel &# 39 ; s perforation is broken by the user pulling on the toweling portion extending from the housing . indeed , even slow and consistent pull on the extended toweling does not further extend toweling from the dispenser due , at least in part , to the application of reverse current . yet another automatic paper towel dispenser apparatus 200 in accordance with an embodiment of the invention is illustrated in fig1 a through 23b . operation and structure of apparatus 200 is similar to those disclosed above . of additional note , fig2 a and fig2 b illustrate the open area within the housing , over the space for receiving a roll of paper towels , into which area toweling that is retracted into the housing may be directed . moreover , if too much toweling is retracted into this area , the excess toweling likely falls out of the back of the apparatus , thereby avoiding possible jamming of the apparatus 200 . to this end , the back of the housing preferably is open when the door is closed , as shown in fig2 a and fig2 b . additional description of structure and functionality in accordance with one or more embodiments will now be provided , first with reference to the exemplary flowchart of fig2 , and then with reference to fig2 - 34 . in one or more embodiments , an automatic paper towel dispenser apparatus is configured to , after learning how long a paper towel of a paper towel roll is , dispense one or more paper towels via a dispensing opening . such dispenser apparatus includes a hand wave sensor configured to sense the wave of a user &# 39 ; s hand . the dispenser apparatus is configured such that , when a firsthand wave is detected at step 1002 , toweling begins to be advanced at step 1004 by providing current to a motor assembly configured to drive the dispensing of toweling . as the toweling is advanced , a leading edge of the toweling , i . e . a leading edge of the first paper towel , is detected at step 1006 by a reflective sensor the toweling travels past prior to passing through the dispensing opening . this reflective sensor preferably operates by determining whether emitted light is reflected by toweling , e . g . white toweling . following detection of this leading edge , an extent determined based on a learned length of toweling is advanced at step 1008 . the advancing of exactly this extent is preferably provided via use of a slot sensor . the slot sensor comprises an emitter , a detector disposed opposite the emitter , and a rotatable disc disposed therebetween . the rotatable disc includes a plurality of slots disposed therein . as toweling is advanced , the rotatable disc rotates , and , as the slots and non - slot sections pass between the emitter and receptor , light emitted by the emitter is intermittently received by the receptor . the slot sensor is configured to determine , based on the intermittent reception of light by the receptor , the amount of rotation of the rotatable disc , and thus the amount of toweling advanced . once , following detection of the leading edge , the desired extent of toweling based on a learned length of toweling has been advanced , current is drawn from the motor assembly to halt dispensing at step 1010 . in at least some embodiments , upon halting of dispensing , a perforated line separating the first paper towel from a next paper towel is disposed at , on , under , and / or proximate to the reflective sensor . in at least some other embodiments , an additional offset is added to or subtracted from a learned towel length such that such perforated line is disposed upstream of , or downstream of , the reflective sensor . preferably , the dispenser apparatus is further configured such that , following halting of dispensing , a first time period begins at step 1012 . this time period is preferably measured by a timer , and preferably lasts around one second . at any time prior to the end of this time period , a subsequent hand wave will trigger advancement of an additional extent of toweling based on a learned length . preferably , such a subsequent hand wave will also result in the resetting or restarting of the first time period , thereby providing additional time for yet another hand wave , although , in at least some embodiments , this is not the case . in this way , a user is able to trigger dispensing of any number of paper towels that they wish , via , for example , that number of hand waves , or by continually leaving their hand in front of the hand wave sensor until a desired number of paper towels have been dispensed . in an embodiment , during this first time period , an indicator disposed proximate the hand wave sensor displays a first color , e . g . red . preferably , following expiration of this first time period , a second time period begins . this second time period is preferably also measured by a timer , and preferably lasts around four seconds . during this second time period , hand waving by the user does not trigger the dispensing of any additional paper towels . in an embodiment , during this second time period , an indicator disposed proximate the hand wave sensor displays a second color , e . g . orange . this second time period is intended to allow a user to tear off one or more dispensed paper towels . it will be appreciated that , when a user goes to tear off one or more dispensed paper towels , force applied by the user could cause the withdrawal of additional toweling from the dispenser apparatus , barring any mechanism for the prevention of such additional withdrawal . in an embodiment , the slot sensor is utilized in combination with the motor assembly to mitigate , or prevent , any such withdrawal , via the use of a “ fight sequence ”. preferably , the slot sensor is utilized to determine whether additional toweling has been withdrawn , via the detection of rotation of the rotatable disc of the slot sensor . in the event of such rotation , current , having an opposite polarity to that described hereinabove ( sometimes referred to herein as reverse polarity current ), is preferably provided to the motor assembly to return the slot sensor to its prior position ( e . g . the position it was in prior to rotation of the slot sensor caused by a user attempting to tear off one or more dispensed paper towels ). the second time period is represented by step 1016 . upon expiration of the second time period , the reflective sensor disposed proximate the dispensing opening determines whether or not toweling is sensed at step 1018 . if the reflective sensor senses toweling , then the toweling is retracted by providing reverse polarity current to the motor assembly at step 1020 . the toweling is preferably retracted until the reflective sensor no longer senses toweling . following this , the dispenser apparatus is ready to once again detect a user &# 39 ; s initial hand wave at step 1002 . fig2 - 34 illustrate an exemplary dispensing sequence for a paper towel dispenser apparatus in accordance with one or more embodiments of the invention . fig2 illustrates a paper towel dispenser apparatus . to dispense toweling , a user triggers a hand wave sensor of the dispenser apparatus using their hand , as illustrated in fig2 . upon detecting the user &# 39 ; s hand via the hand wave sensor , the dispenser apparatus dispenses a learned towel length . after dispensing the learned towel length , the dispenser apparatus determines whether the user &# 39 ; s hand is still present , or if the user has waved his hand again . if so , the dispenser apparatus dispenses an additional learned towel length . in this way , a user can effect dispensing of multiple learned towel lengths by leaving his hand in front of the hand wave sensor , as illustrated in fig2 - 29 . once the user ceases triggering the hand wave sensor via their hand , then the dispenser apparatus will cease dispensing additional learned towel lengths . upon this occurring , the dispenser apparatus will begin waiting a tear time interval , thereby allowing the user to tear off one or more sheets of dispensed toweling . fig3 illustrates a user tearing off a single sheet of dispensed toweling after dispensing a plurality of sheets of toweling . upon expiration of the tear time interval , the sheets that were dispensed , but not tom off by the user , are retracted back into the dispenser apparatus , as illustrated in fig3 - 34 . based on the foregoing description , it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application . many embodiments and adaptations of the present invention other than those specifically described herein , as well as many variations , modifications , and equivalent arrangements , will be apparent from or reasonably suggested herein , without departing from the substance or scope of the present invention . accordingly , while the present invention has been described herein in detail in relation to one or more preferred embodiments , it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention . the foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments , adaptations , variations , modifications or equivalent arrangements , the present invention being limited only by the claims appended hereto and the equivalents thereof .
a towel dispenser includes a housing , a sensor , and a motor assembly that causes in response to a hand : a leading edge of the toweling to be extended from the housing a multiple of a predetermined unit length , optionally plus a further extent that is less than pul ; and then to be retracted . the motor assembly ceases retracting based on sensing the leading edge of the toweling . pul is set in a length learn sequence by : retracting the toweling until a leading edge of the toweling is sensed ; advancing the toweling a preset extended length greater than at least a distance between immediately adjacent lines of perforations in the toweling ; retracting the toweling until a leading edge of the toweling is sensed while measuring a length by which the toweling is retracted ; and determining the difference between the preset extended length and the measured retracted length .