Patent Publication Number: US-6903654-B2

Title: Automatic dispenser apparatus

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/160,863 filed Jun. 3, 2002, said application being pending at issuance of this patent, the entire content of which is incorporate herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention is related generally to dispenser apparatus and, more particularly, to apparatus for dispensing of sheet material. 
     BACKGROUND OF THE INVENTION 
     Apparatus for use in dispensing paper towel, personal care products and the like are often provided in public restrooms, commercial food preparation areas and similar settings in order to assist patrons and employees in maintaining personal hygiene. These dispensers are typically provided to supply the user with a product such as a sheet of paper towel. A lever, push bar or other device is commonly provided to actuate the dispenser. Product is dispensed when the user grasps and pulls the lever or presses her hand against the push bar or other actuator. These dispensers have proven to be reliable and cost effective and are completely satisfactory for their intended purpose. 
     In certain applications there has been a recent trend toward the use of automatic dispenser apparatus in place of, or in addition to, manually-operated dispensers. In theory, automatic dispensers operate by dispensing the towel in response to the proximity of the user and without contact between the user and the dispenser device. The dispenser detects the presence of the user (typically the user&#39;s hand) adjacent the dispenser housing and automatically discharges the towel in response to a signal generated by detection of the user. 
     It can be appreciated that there are benefits potentially associated with automatic dispenser apparatus. For example, automatic dispensers may limit the transfer of germs or other agents to the user&#39;s hand because the user is, in theory, not required to physically contact the dispenser device. The appearance and cleanliness of the dispenser may be enhanced through reduced physical contact between the dispenser and the user. This not only improves the appearance of the dispenser but has related benefits in terms of reducing the effort required to maintain the dispenser. Yet another potential benefit is that the dispenser may be more effective in controlling or limiting the amount of product dispensed from the device thereby providing uniform amounts of dispensed product and reducing waste. 
     Efforts have been made to develop automatic dispenser apparatus which utilize proximity sensors of various types to detect the presence of the user and to dispense in response to the presence of the user. One approach has been to utilize photoelectric dispensers of various types. Examples include U.S. Pat. No. 6,069,354 (Alfano et al.) and U.S. Pat. No. 4,786,005 (Hoffman et al.). For example, the dispenser apparatus of Alfano and Hoffman utilize reflectance-type infrared detection systems to actuate the dispenser. The user places his hand adjacent a localized infrared light generator and changes in light reflectance are detected by a photo transistor to generate a signal actuating the dispenser. Hoffman includes a further photo transistor detector provided to detect changes in ambient light resulting from the presence of the user&#39;s hand. 
     The generator and detector of Alfano are localized at a specific position on the front side of the dispenser while in the Hoffman dispenser these elements are located in a cavity formed in the dispenser housing where ambient light conditions can be controlled. None of these detection components are positioned at the location where the towel is dispensed, i.e., the position where the user&#39;s hand would naturally be expected to extend. As a result, these dispensers may not be ergonomic for all users. Further, such photoelectric-based systems may not operate properly in conditions of potentially variable ambient light, such as in a public restroom. Other examples of automatic dispensers utilizing photoelectric sensor devices include U.S. Pat. No. 6,293,486 (Byrd et al.), U.S. Pat. No. 6,105,898 (Byrd et al.) and U.S. Pat. No. 5,772,291 (Byrd et al.), U.S. Pat. No. 5,452,832 (Niada) U.S. Pat. No. 4,796,825 (Hawkins), U.S. Pat. No. 4,722,372 (Hoffman et al.) and U.S. Pat. No. 4,666,099 (Hoffman et al.). 
     Another approach has been to utilize detected changes in an electrical field as a means to actuate the dispenser. Examples include U.S. Pat. No. 6,279,777 (Goodin et al.), U.S. Pat. No. 5,694,653 (Harald), U.S. Pat. No. 4,921,131 (Binderbauer), U.S. Pat. No. 4,826,262 (Hartman et al.), U.S. Pat. No. 6,412,655 (Stützel et al.) and Canadian Patent Application Serial No. 2,294,820 (Stützel et al.). 
     For example, Hartman discloses an automatic cloth towel dispenser which dispenses clean cloth towel and takes up the soiled towel following use. Hartman utilizes a detection device which consists of a bulky, elongated coil which oscillates to generate a radio frequency field below the dispenser cabinet. The oscillator circuit is said to detect small changes in the RF field. Hartman requires unduly large components and may be prone to detection of false signals. Furthermore, such a system would likely be adversely affected by conditions of high humidity which are commonly encountered in environments where the dispenser might be expected to be located. 
     By way of further example, the dispenser apparatus of the Stützel patent describes what is called a capacitive sensor which includes a flat, two-dimensional pair of electrodes with very specific electrode surface area ratios and placement requirements. The electrodes are said to generate a rectified field. The patent asserts that placement of an object within 1.18″ of the dispenser will produce changes in capacitance which, when detected, are used to actuate the dispenser. Such a system is disadvantageous at least because the range of detection is limited and the location of the field is not ergonomic. The user is required to be extremely close to the dispenser, potentially resulting in unwanted contact between the user and the dispenser apparatus. 
     The dispenser of the Goodin patent requires a “theremin” antenna which is said to detect changes in capacitance as the user&#39;s hand approaches the dispenser. In response, a solenoid is actuated to dispense liquid soap. To eliminate the risk of false detection, a second sensor may be provided to independently detect the presence of the user&#39;s hand. The need for primary and secondary sensors suggests that the system is not entirely reliable. 
     There is also a need to provide improved control over dispenser operation which compensates for changes in battery voltage which occur over the life cycle of the batteries used to power the dispenser. Improved control is useful to ensure that the length of sheet material dispensed is consistent in each dispense cycle even as battery voltage decreases as the batteries become discharged. This need for improved dispenser control exists for all types of battery powered dispensers including for hands-free dispensers with a proximity detector input device and for dispensers which utilize an input device such as a contact switch to initiate a dispense cycle. 
     It would be a significant improvement in the art to provide automatic dispenser apparatus with an improved proximity sensor wherein the proximity sensor would positively detect the presence of a user without physical contact by the user and dispense in response to the detection, which would operate in an ergonomic manner by detecting the user at a range and position from the dispenser along which the user would be expected to place his or her hand or other body part, which would discriminate between signals unrelated to the presence of the user, which would be compact permitting use in small dispenser apparatus and avoiding interference with the operation of other dispenser components, which would operate reliably under a wide range of ambient light, humidity and temperature conditions which could include certain other optional features provided to enhance the operation of the dispenser and which would include an improved control apparatus. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide improved automatic dispenser apparatus overcoming some of the problems and shortcomings of the prior art. 
     One of the other objects of the invention is to provide improved automatic dispenser apparatus which dispenses without contact between the user and the dispenser. 
     Another object of the invention is to provide improved automatic dispenser apparatus which positively detects the presence of a user in proximity to the dispenser. 
     Yet another object of the invention is to provide improved automatic dispenser apparatus which discriminates between the proximity of the user and other objects. 
     Still another object of the invention is to provide improved automatic dispenser apparatus which has an improved design versus prior art dispensers. 
     Yet another object of the invention is to provide improved automatic dispenser apparatus which includes a proximity sensor which generates an ergonomically-positioned detection zone. 
     It is also an object of the invention to provide improved automatic dispenser apparatus which includes a compact proximity sensor. 
     An additional object of the invention is to provide improved automatic dispenser apparatus which would reliably operate across a range of ambient light, humidity and temperature conditions. 
     A further object of the invention is to provide improved automatic dispenser apparatus which dispenses uniformly over the operational life of the dispenser power source. 
     Another object of the invention is to provide an automatic dispenser apparatus and method which provides improved control over the length of sheet material dispensed. 
     These and other objects of the invention will be apparent from the following descriptions and from the drawings. 
     SUMMARY OF THE INVENTION 
     In general, the invention comprises automatic dispenser apparatus for dispensing sheet material and the like. An improved proximity detector is provided for detecting the presence of a user and, ultimately, for actuating the dispenser without contact between the user and the dispenser. The sensitivity of the proximity detector causes the dispenser to dispense in a reliable manner. Moreover, the dispenser is actuated in an ergonomic manner because the dispenser is actuated in response to placement of the user&#39;s hand at positions adjacent the dispenser where the user&#39;s hand might naturally be expected to placed to receive the dispensed product. 
     The dispenser apparatus and dispensing methods described herein provide instructions for improved dispenser operation and improved control over the sheet material dispensed throughout the life cycle of the dispenser power source. Such improved instructions are useful for controlling operation of battery powered dispensers generally, including hands-free dispensers which utilize a proximity detector to input a user dispense request and dispensers requiring human contact actuation, for example by manually pushing a contact switch form of input device. 
     Preferred forms of sheet material dispensers for use in practicing the invention may include mechanical components known in the art for use in dispensing sheet materials. Such sheet materials include, for example, paper towel, wipers, tissue, etc. Typical mechanical components may include drive and tension rollers which are rotatably mounted in the dispenser. The drive and tension rollers form a nip. The tension roller holds the sheet material against the drive roller and rotation of the drive roller draws sheet material through the nip and, ultimately, the sheet material is fed out of the dispenser. 
     The drive roller is rotated by motor drive apparatus in power transmission relationship with the drive roller. Power supply apparatus, also referred to herein as a power source, is provided to supply electrical power to the motor drive. The preferred power supply apparatus also supplies electrical power to the electrical components of the proximity detector and control apparatus of the inventive dispenser. 
     The preferred proximity detector provided to actuate the dispenser comprises a sensor and a signal detection circuit. The sensor has a capacitance which is changed by the presence of a user within a “detection zone” projecting outwardly from the dispenser. The signal detection circuit is operatively connected to the sensor and detects the capacitance change. 
     A control apparatus receives the detected frequency change and generates a signal used to actuate the motor drive apparatus to dispense the sheet material. The control apparatus may include additional features to enhance operation of the dispenser. 
     In a preferred embodiment, the sensor is mounted within the dispenser housing and is provided with first and second conductors. The conductors are configured and arranged to have a capacitance. Most preferably, the sensor has a three-dimensional geometry and the sensor three-dimensional geometry generates a generally arcuate detection zone. The term detection zone refers to a region about the sensor into which the user places his or her hand or other body part to bring about a detectable change in capacitance. The detection zone most preferably projects outwardly from the dispenser at positions where the user&#39;s hand would naturally be placed to receive a segment of dispensed sheet material from the dispenser. In this most preferred embodiment, the three dimensional sensor geometry is achieved by depositing the first and second electrodes on a substrate with a three-dimensional geometry so that the electrodes take on the shape of the substrate. 
     In preferred forms of the invention, the sensor first and second conductors each include a plurality of parallel conductor elements deposited on the substrate. Each plural element of the first conductor is conductively connected to each other element of the first conductor. And, each plural element of the second conductor is conductively connected to each other element of the second conductor. 
     The plural parallel conductor elements are most preferably arranged in an “interdigital” array in which the elements are in an alternating arrangement. More specifically, the plural parallel elements of the first conductor and the plural parallel elements of the second conductor are substantially parallel to each other. The elements are arranged so that the nearest element to each element in the first conductor plurality is an element of the second conductor plurality and the nearest element to each element in the second conductor plurality is an element of the first conductor plurality. 
     Referring next to the preferred signal detection circuit embodiment, such circuit is powered by the power supply apparatus and includes an oscillator and a differential frequency discriminator. The oscillator has a frequency which is affected by the sensor capacitance when a user&#39;s hand is in the detection zone. The differential frequency discriminator detects changes in the oscillator frequency so that the detected change can be acted upon by the control apparatus. The signal detection circuit is sufficiently sensitive to permit detection of the presence of a user within the detection zone at distances spaced meaningfully from the dispenser yet is also sufficiently insensitive to avoid false positive signals caused by the mere presence of a person or other object in the vicinity of the dispenser. 
     A preferred form of differential frequency discriminator used in the signal detection circuit includes a signal conditioning circuit, first and second averaging circuits and a comparator. A set point circuit may also be provided. Most preferably, the signal conditioning circuit is generated by a monostable multivibrator. The multivibrator is configured to produce two outputs. The first output is a first series of pulses. Each pulse is of a fixed duration, and the series of pulses has a frequency corresponding to the oscillator frequency. The second output is a second series of pulses which is the complement of the first series of pulses. 
     The preferred first averaging circuit averages the first series of pulses and generates an output which is referred to herein as a first average. The second averaging circuit averages the second series of pulses and generates an output which is referred to herein as a second average. 
     The preferred comparator is a first comparator which receives the first and second averages generated by the averaging circuits. The comparator compares the first average and the second average and produces an output which is referred to herein as a discriminator difference. The discriminator difference represents the difference between the second average and the first average and the discriminator difference output corresponds to the presence of the user within the detection zone. If the selection of parameters are not such that the averages are equal when a user is not present then a set point circuit is further provided which sets the discriminator difference substantially to zero when the user is not present in the detection zone. The discriminator difference is subsequently multiplied by a gain factor of the first comparator to produce an output. 
     A further advantage of the invention is that the signal detection circuit may include circuitry for setting a detection zone volume thereby permitting the detection zone to be expanded or contracted as appropriate. The terms tuned and detuned are also used herein to describe, respectively, the expanded and contracted detection zones. In such embodiments, the signal detection circuit is configured to generate a predetermined threshold reference signal provided to set the detection zone volume. A second comparator is provided to compare the output of the first comparator with the threshold reference signal. The second comparator then provides an output which is the difference between the threshold reference signal and the output from the first comparator. The difference is then multiplied by a gain factor of the second comparator. The detection zone volume may be expanded and contracted simply by changing the threshold reference signal thereby adjusting the magnitude of the frequency changes at which the logical output of the second comparator switches. 
     As will be explained, the proximity detector of the invention is unaffected by conditions of temperature and humidity typical of those encountered at locations where the invention is intended to be used, i.e., in public restrooms, commercial food preparation areas and similar settings. The proximity detector is unaffected by lighting conditions because it does not require an optical detection system. 
     Preferred embodiments of the control apparatus are powered by the power supply apparatus and are included to control actuation of the motor drive. The output of the second comparator is received by the control apparatus and, in response, the control apparatus actuates the motor for a predetermined time. It is most preferred, but not required, that the control apparatus is in the form of a programmable controller including preprogrammed instructions. 
     The control apparatus may also include additional features provided to enhance operation of the apparatus. For example, the control apparatus may include a timer controller which sets a minimum time duration of a capacitance change required to actuate the dispenser. A preferred time interval is 30 ms. The control apparatus may further include a blocking controller which limits dispenser actuation to a single cycle for each detected capacitance change. 
     The control apparatus may further include a power supply voltage compensation circuit provided to ensure consistent dispensing irrespective of any voltage drop in the batteries or other power source. The preferred compensation circuit provides a reference voltage proportional to a power supply voltage and controls the duration of motor drive actuation such that the dispensing of sheet material is substantially independent of changes in the power supply voltage. 
     A further preferred embodiment controls dispenser operation based on the power source output, preferably represented by the battery voltage under load. The dispenser control apparatus adjusts the timed duration of subsequent dispense cycles to provide consistent lengths of sheet material discharged from the dispenser. Such embodiment is useful to control the operation of any battery powered dispenser device. 
     The control apparatus may further include a sheet material length selector. Such a length selector may comprise a control for selecting one of several sheet material lengths to be dispensed, a length signal corresponding to the selected control setting, two or more preset length reference signals corresponding to preselected lengths of sheet material to be dispensed and a sheet length comparator which compares the length signal with the preset length reference signals to determine which sheet material length has been selected. It is most preferred that the preset length reference signals and the sheet length comparator are in the form of a programmable controller including preprogrammed instructions. 
     Preferred embodiments of the control apparatus may also include a low-power-supply alarm. Preferably, this component element of the control apparatus also comprises a programmable controller including preprogrammed instructions and the low-power-supply alarm is included in the programmable controller. The control apparatus preferably includes a first preset voltage level, a second preset voltage level, a power-warning comparator which compares the power supply voltage to the first and second preset voltage levels, an indicator which provides a warning signal when the power supply voltage is below the first preset voltage level and a lockout circuit which blocks the dispensing of sheet material when the power supply voltage is below the second preset voltage level. The low battery alarm may include an audible sound generator. 
     Further preferred embodiments include a counter which increments and decrements counts when the open circuit and/or loaded battery voltages are determined to be either above or below one or more thresholds. The counts are used to ensure that any low battery alarm is responsive to decreases in the battery voltage which occur near the end of the battery life cycle. 
     The invention is not limited to sheet material dispensers and may include other types of automatic dispenser apparatus which are to be actuated without contact by the user. For example, the invention may be used with automatic liquid material dispenser apparatus for use in dispensing liquid products such as soaps, shaving creams, fragrances and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate preferred embodiments which include the above-noted characteristics and features of the invention. The invention will be readily understood from the descriptions and drawings. In the drawings: 
         FIG. 1  is a perspective view of a preferred automatic dispenser apparatus according to the invention, such dispenser apparatus provided for dispensing sheet material. 
         FIG. 2  is a perspective view of the dispenser of  FIG. 1  with the housing cover removed. 
         FIG. 3  is another perspective view of the dispenser of  FIG. 1  also with the housing cover removed. 
         FIG. 4  is a perspective view of the front side of the dispenser frame. 
         FIG. 5  is another perspective view of the front side of the dispenser frame. 
         FIG. 6  is a perspective view of the rear side of the dispenser frame. 
         FIG. 7  is another perspective view of the rear side of the dispenser frame. 
         FIG. 8  is an exploded perspective view of the frame and certain preferred mechanical components mounted with respect to the frame. 
         FIG. 9  is a sectional view of the exemplary dispenser taken along section  9 — 9  of FIG.  1 . Sheet material is being dispensed from the primary roll. Certain hidden parts are shown in dashed lines. 
         FIG. 10  is a sectional view of the exemplary dispenser taken along section  9 — 9  of FIG.  1 . Primary roll sheet material is depleted and sheet material is being dispensed from the secondary roll following operation of the transfer mechanism. Certain hidden parts are shown in dashed lines. 
         FIG. 11  is an enlarged partial sectional view of the exemplary dispenser of  FIGS. 9 and 10 . Certain hidden parts are shown in dashed lines. 
         FIG. 12  is a rear perspective view of the rear side of the dispenser frame showing an exemplary three-dimensional sensor and the location at which the sensor is positioned within the dispenser. Certain parts are removed from the dispenser. The electrical components shown are illustrative only and are not intended to represent the actual components. 
         FIG. 13  is a perspective view the exemplary three-dimensional sensor of FIG.  12 . The electrical components shown are illustrative only and are not intended to represent the actual components. 
         FIG. 14  is a top plan view the exemplary three-dimensional sensor of FIG.  12 . The electrical components shown are illustrative only and are not intended to represent the actual components. 
         FIG. 15  is a graph demonstrating the directionally-oriented detection zone generated by an exemplary three-dimensional sensor. 
         FIG. 16  is a block diagram illustrating the general operation of the proximity detector and control apparatus of the invention. 
         FIGS. 17A-17D  are schematic diagrams showing the preferred electrical components of the control apparatus in accordance with the present invention. 
         FIG. 17E  is a schematic diagrams showing a sound emitter incorporated into the control apparatus in accordance with the present invention. 
         FIGS. 18A-18K  are graphs illustrating the operation of a differential frequency discriminator according to the invention. 
         FIGS. 19A-19E  are block diagrams showing the steps of a preferred method of dispensing according to the invention. 
         FIGS. 20A-20G  are block diagrams showing the steps of a preferred alternative method of dispensing according to the invention. 
         FIG. 21  is a graph showing the voltage of a representative alkaline battery cell over the life of the battery. 
         FIG. 22  is an exemplary battery power source output voltage trace during a dispense cycle. 
         FIG. 23  is an exemplary set of six sequential battery power source output voltage traces. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The mechanical components comprising preferred embodiments of an exemplary automatic dispenser in the form of a sheet material dispenser  10  will be described with particular reference to  FIGS. 1-14 . Dispenser  10  is of a type useful in dispensing paper towel. The invention may be practiced with other types of dispensers. Certain of the mechanical components of the exemplary dispenser  10  are also described in U.S. Pat. No. 6,250,530 (La Count et al.) which is assigned to the assignee of the present application. The disclosure of the La Count patent is incorporated herein by reference. 
     Dispenser  10  preferably includes housing  11  and frame  13  mounted within an interior portion  15  of housing  11 . Housing  11  includes a front cover  17 , rear wall  19 , side walls  21 ,  23  and top wall  25 . Cover  17  may be connected to housing  11  in any suitable manner. As shown in  FIGS. 1-3 , cover  17  is attached for pivotal movement to housing  11  by means of axially aligned pins (not shown) in cover  17  configured and arranged to mate with a respective axially aligned opening  27 ,  29  provided in housing side walls  21  and  23 . Flanged wall surfaces  31 - 35  extend into cover  17  when the cover  17  is in the closed position shown in  FIG. 1  to ensure complete closure of the dispenser  10 . A lock mechanism  37  may be provided in cover  17  to prevent unauthorized removal of cover  17 . Cover  17  is opened, for example, to load rolls  39 ,  41  ( FIGS. 9-10 ) of sheet material in the form of a web into dispenser  10  or to service dispenser  10 . Housing  11  and cover  17  may be made of any suitable material. Formed sheet metal and molded plastic are particularly suitable materials for use in manufacturing housing  11  and cover  17  because of their durability and ease of manufacture. 
     Frame  13  and the principal mechanical components of exemplary dispenser  10  are shown in  FIGS. 2 and 3  in which cover  17  is removed from dispenser  10  and in  FIGS. 4-8  and  11  in which frame  13  is apart from housing  11 . Frame  13  is preferably positioned within a portion of housing interior  15  as shown in  FIGS. 2  and  3 . Frame  13  is provided to support the major mechanical and electrical components of dispenser  10  including the dispensable product discharge apparatus  43 , drive apparatus  45 , power supply apparatus  47 , proximity detector apparatus  49  and control apparatus  50 . Frame  13  is made of a material sufficiently sturdy to resist the forces applied by the moving parts mounted thereon. Molded plastic is a highly preferred material for use in manufacture of frame  13 . 
     Frame  13  includes a rear support member  51  (preferred frame  13  does not include a full rear wall), a first sidewall  53  having sidewall inner  55  and outer  57  surfaces, a second sidewall  59  having sidewall inner  61  and outer  63  surfaces and bottom wall  65 . Web discharge opening  67  is provided between web-guide surface  69  and tear bar  71 . Side walls  53  and  59  define frame front opening  73 . Housing rear wall  19  and frame walls  53 ,  59 ,  65  and  69  define a space  75  in which primary roll  39  can be positioned for dispensing or storage. 
     Frame  13  is preferably secured along housing rear wall  19  in any suitable manner such as with brackets  77 ,  79  provided in housing rear wall  19 . Brackets  77 ,  79  mate with corresponding slots  81  and  83  provided in frame rear support member  51 . Frame  13  may also be secured in housing  11  by mounting brackets  85 ,  87  provided along frame sidewall outer surfaces  57 ,  63  for mating with corresponding brackets (not shown) provided in housing  11 . Frame  13  may further be secured to housing  11  by means of fasteners  89 ,  91  positioned through housing sidewalls  21 ,  23 , bushings  93 ,  95  and posts  97 ,  99 . Frame  13  need not be a separate component and could, for example, be provided as an integral part of housing  11 . 
     The exemplary dispenser  10  may be mounted on a vertical wall surface (not shown) where dispenser  10  can be easily accessed by a user. As shown particularly in  FIGS. 2 and 3 , dispenser  10  could be secured to such vertical wall surface by suitable fasteners (not shown) inserted through slotted openings in rear wall  19  of which slots  101 - 105  are representative. Of course, dispenser  10  could be configured in other manners depending on the intended use of dispenser  10 . 
     The exemplary dispenser apparatus  10  includes apparatus for storing primary and secondary sources of sheet material  107 ,  109 . The sheet material in this example is in the form of primary and secondary rolls  39 ,  41  consisting of primary and secondary sheet material  111 ,  113  rolled onto a cylindrically-shaped hollow core  115 ,  117  having an axial length and opposed ends (not shown). Such cores  115 ,  117  are typically made of a cardboard-like material. As shown in  FIG. 9 , primary roll  39  sheet material  111  is being dispensed while secondary roll sheet material  113  is in a “ready” position prior to dispensing from that roll  41 .  FIG. 10  illustrates the dispenser  10  following a transfer event in which sheet material  113  from roll  41  is transferred to the nip  157  for dispensing from the dispenser  10  following depletion of primary roll  39  sheet material  111 . 
     It is very highly preferred that the rolls  39 ,  41  are stored in and dispensed from housing interior  15 . However, there is no absolute requirement that such rolls be contained within housing interior  15  or space  75 . 
     Turning now to the preferred apparatus  107  for storing primary web roll  39 , such storing apparatus  107  includes cradle  119  with arcuate support surfaces  121 ,  123  against which the primary roll  39  rests. Surfaces  121 ,  123  are preferably made of a low-friction material permitting primary roll  61  to freely rotate as sheet material  111  is withdrawn from roll  39 . 
     Referring further to  FIGS. 2-3  and  9 , there is shown a preferred apparatus  109  for storing secondary web roll  41 . Storing apparatus  109  includes yoke  125  attached in a suitable manner to housing rear wall  19 , such as by brackets  127 ,  129  formed around yoke  125 . Yoke  125  comprises arms  131 ,  133  and web roll holders  135 ,  137  mounted on respective arms  131 ,  133 . Arms  131  and  133  are preferably made of a resilient material so that they may be spread apart to receive respective ends of hollow core roll on which the secondary sheet material web is wound. 
     Persons of skill in the art will appreciate that support structure, other than cradle  119  and yoke  125  could be used to support primary and secondary web rolls  39 ,  41 . By way of example only, a single removable rod (not shown) spanning between walls  53 ,  59  or  21 ,  23  could be used to support rolls  39 ,  41 . As a further example, primary web roll  39  could simply rest on frame bottom wall  65  without support at ends of the core  115 . 
     A preferred discharge apparatus  43  for feeding sheet material  111 ,  113  from respective rolls  39 ,  41  and out of dispenser  10  will next be described. Such discharge apparatus  43  comprises drive roller  139 , tension roller  141  and the related components as hereinafter described and as shown particularly in  FIGS. 2-10 . 
     Drive roller  139  is rotatably mounted on frame  13  and includes a plurality of longitudinally spaced apart drive roller segments  143 ,  145 ,  147  on a shaft  149 . Drive roller  139  includes ends  151 ,  153  and drive gear  155  rigidly connected to end  153 . Drive gear  155  is part of the drive apparatus  45  which rotates drive roller  139  as described in more detail below. Segments  143 - 147  rotate with shaft  149  and are preferably made of a tacky material such as rubber or other frictional materials such as sand paper or the like provided for the purpose of engaging and feeding sheet material  111 ,  113  through a nip  157  between drive and tension rollers  139 ,  141  and out of the dispenser  10  through discharge opening  67 . 
     Shaft end  153  is inserted in bearing (for example, a nylon bearing)  159  which is seated in opening  161  in frame side wall  59 . Stub shaft  152  at shaft end  151  is rotatably seated on bearing surface  163  in frame first side wall  53  and is held in place by arm  167  mounted on post  97 . 
     A plurality of teeth  169  extend from guide surface  69  into corresponding annular grooves  172  around the circumference of drive roller outer surface  257 . The action of teeth  169  in grooves  172  serves to separate any adhered sheet material  111 ,  113  from the drive roller  139  and to direct that material through the discharge opening  67 . 
     The tension roller  141  is mounted for free rotation on a roller frame assembly  173 . Roller frame assembly  173  includes spaced apart side wall members  175 ,  177  interconnected by a bottom plate  179 . Roller frame assembly  173  is provided with arm extensions  181 ,  183  having axially-oriented inwardly facing posts  185 ,  187  which extend through coaxial pivot mounting apertures in frame sidewalls  53 ,  59  one of which  189  is shown in  FIG. 8  (the other identical aperture is hidden behind guide surface  69 ) pivotally mounting roller frame assembly  173  to frame  13 . Reinforcement members, such as member  191 , extend from the bottom plate  179  to an upstanding wall  193 . Bearing surfaces  186 ,  188  are located at the top of the side walls  175 ,  177  to receive respective stub shafts  170 ,  171  of tension roller  141  as described in detail below. 
     Tear bar  71  is either mounted to, or is integral with, the bottom of the roller frame assembly  173 . The tear bar  71  may be provided with tabs  203  and clips  205  for attachment to the bottom of the roller frame assembly  173  if the tear bar  71  is not molded as part of the roller frame assembly  173 . A serrated edge  207  is at the bottom of tear bar  71  for cutting and separating the sheet material  111 ,  113  into discrete sheets. 
     Roller frame assembly  173  further includes spring mounts  209 ,  211  at both sides of roller frame assembly  173 . Leaf springs  213 ,  215  are secured on mounts  209 ,  211  facing forward with bottom spring leg  217 ,  219  mounted in a fixed-position relationship with mounts  209 ,  211  and upper spring leg  221 ,  223  being mounted for forward and rearward movement. Cover  17 , when in the closed position of  FIG. 1 , urges springs  213 ,  215  and roller assembly  173  rearwardly thereby urging tension roller  141  firmly against drive roller  139 . 
     An optional transfer assembly  227  is mounted interior of tension roller  141  on bearing surfaces  229 ,  231  of the roller frame assembly  173 . Transfer assembly  227  is provided to automatically feed the secondary sheet material  113  into the nip  157  upon exhaustion of the primary sheet material  111  thereby permitting the sheet material  113  from roll  41  to be dispensed. The transfer assembly  227  is provided with a stub shaft  233  at one end in bearing surface  229  and a stub shaft  235  at the other end in bearing surface  231 . Each bearing surface  229 ,  231  is located at the base of a vertically-extending elongate slotted opening  237 ,  239 . Each stub shaft  233 ,  235  is loosely supported in slots  237 ,  239 . This arrangement permits transfer assembly  227  to move in a forward and rearward pivoting manner in the direction of dual arrows  241  and to translate up and down along slots  237 ,  239 , both types of movement being provided to facilitate transfer of sheet material  113  from secondary roll  41  into nip  157  after depletion of sheet material  111  from roll  39  as described below. 
     The transfer assembly  227  is mounted for forward and rearward pivoting movement in the directions of dual arrows  241 . Pivoting movement in a direction away from drive roller is limited by hooks  243 ,  245  at opposite ends of transfer assembly  227 . Hooks  243 ,  245  are shaped to fit around tension roller  141  and to correspond to the arcuate surface  247  of tension roller  141 . 
     A transfer mechanism  249  is positioned generally centrally of the assembly  227 . Transfer mechanism  249  includes a drive roller contact surface  250 , an arcuate portion  251  with outwardly extending teeth  253  which are moved against drive roller arcuate surface  257  during a transfer event as described below. A catch  256  is provided to pierce and hold the secondary sheet material  113  prior to transfer of the sheet material to the nip  157 . Opposed, inwardly facing coaxial pins  259 ,  261  are mounted on respective ends of transfer assembly  227  also to hold the secondary sheet material  113  prior to transfer to the nip  157 . Operation of transfer assembly  227  will be described in more detail below. 
     The drive and tension rollers  139 ,  141 , roller frame assembly  173 , transfer assembly  227  and related components may be made of any suitable material. Molded plastic is a particularly useful material because of its durability and ease of manufacture. 
     Referring now to  FIGS. 3-4 ,  6 - 9  and  11 , there are shown components of a preferred drive apparatus  45  for powering drive roller  139 . A motor mount  263  is mounted to inside surface  61  of frame side wall  59  by fasteners of which screw  265  is exemplary. A direct current geared motor  267  is attached to mount  263 . A suitable DC geared motor is the model 25150-14 50 motor available from Komocon Co. Ltd. of Seoul, Korea. Motor  267  is enclosed by motor housing  269  mounted over motor  267  to mount  263 . Motor  267  is preferably powered by four series-connected 1.5 volt D-cell batteries, two of which  271 ,  273  are shown in  FIGS. 9 and 10 . Optionally, motor  267  may be powered by direct current from a low-voltage transformer (not shown). 
     Motor  267  drives a power transmission assembly consisting of input gear  275  intermediate gear  276 , and drive gear  155 . Input gear  275  is mounted on motor shaft  279 . Input gear teeth  281  mesh with teeth  283  of intermediate gear  276  which is rotatably secured to housing  285  by a shaft  287  extending from housing  285 . Teeth  283  in turn mesh with drive gear teeth  289  to rotate drive gear  155  and drive roller  139 . 
     Housing  285  covers gears  155 ,  275  and  276  and is mounted against side wall outer surface  63  by armature  291  having an opening  293  fitted over post  99 . Bushing  95  secured between walls  23  and  59  by fastener  91  urges armature  291  against side wall outer surface  63  holding housing  285  in place. Further support for housing  285  is provided by pin  295  inserted through mating opening  297  in side wall  59 . 
       FIGS. 6-10  show a preferred power supply apparatus  47  for supplying electrical power to motor  267 . Power supply apparatus  47  has a power source output which may be the voltage or current produced by the power supply apparatus  47 . While the preferred power supply apparatus  47  is described in connection with dry cell batteries, such as batteries  271 ,  273 , it is to be understood that other types of power sources may be used in conjunction with the invention. Such power sources could include low voltage AC from a transformer or power from photovoltaic cells or other means. 
     Base  299  is mounted in frame  13  by mechanical engagement of base end edge surfaces  301 ,  303  with corresponding flanges  305 ,  307  provided along inner surfaces  55 ,  61  of respective walls  53 ,  59  and by engagement of tabs  306 ,  308  with slots  314 ,  316  also provided in walls  53 ,  59 . Tabs  310 ,  312  protruding from frame bottom wall  65  aid in locating base  299  by engagement with base bottom edge  309 . Base  299  and frame  13  components are sized to permit base  299  to be secured without fasteners. 
     Battery box  311  is received in corresponding opening  313  of base  311  and may be held in place therein by any suitable means such as adhesive (not shown) or by fasteners (not shown). Battery box  311  is divided into two adjacent compartments  315 ,  317  each for receiving two batteries, such as batteries  271 ,  273 , end to end in series connection for a total of four batteries. Positive and negative terminals and conductors (not shown) conduct current from the batteries to the drive, sensor and control apparatus  45 ,  49  and  50 . 
     Cradle  119  is removably attached to base  299  by means of tangs  319 ,  321 ,  323  inserted through corresponding openings  325 ,  327 ,  329  in base  299 . Cradle  119  includes a hollow interior portion  331  corresponding to the profile of battery box  311 . Cradle  119  receives battery box  311  therein when cradle  119  is attached to base  299 . Tangs  319 - 323  are made of a resilient material permitting them to be urged out of contact with base  299  so that cradle  119  may be removed to access battery box  311 , for example to place fresh batteries (i.e.,  271 ,  273 ) into battery box  311 . 
     The mechanical structure of a proximity detector apparatus  49  according to the invention will be now be described particularly with respect to  FIGS. 8-13 . Proximity detector  49  comprises circuit components  333  mounted on printed circuit board  335  (“PC board”) and a sensor  337  comprising first and second conductors  339 ,  341  deposited on substrate  343 . The circuit components  333  shown in the drawings are provided for illustrative purposes only and do not represent the actual components utilized in the invention. A detailed description of the actual circuit components and circuit operation will be provided below with respect to  FIGS. 16-19 . 
     PC board  335  on which components  333  are mounted is a rigid resin-based board with electrical conductors (not shown) deposited thereon between the appropriate components  333  as is typical of those used in the electronics industry. PC board  335  is mounted in frame  13  by attachment to housing  345 . Housing  345  has a hollow interior space  347  in which components  333  are received. PC board rear edge  349  is inserted in slot  351  and front edges of PC board  353 ,  355  are inserted in co-planar housing slots, one of which  357 , is shown in FIG.  11  and the other of which is a mirror image of slot  357 . Housing  345  includes a front opening  359  through which substrate  343  extends out of housing  345  toward the front of the dispenser  10 . As best shown in  FIGS. 8-11 , housing  345  is held in place along frame bottom wall  65  with housing rear wall  361  abutting base front wall  363  with tangs  365 ,  367  engaged with corresponding openings (not shown) in housing rear wall  361 . Housing front and rear legs  369 ,  371  rest on frame bottom wall  65 . 
     Substrate  343 , is preferably made of a thin flexible material, such as MYLAR®, polyamide, paper or the like for a purpose described in detail below. By way of example only, a preferred substrate thickness may be approximately 0.008″ thereby permitting the substrate to be shaped. Substrate  343  is initially die-cut, preferably in a trapezoidal configuration best shown in  FIGS. 12-14 . Substrate  343  is provided with a front edge  373 , a center  375  front corners  377 ,  379  side edges,  381 ,  383 , rear edge  385  and top  387  and bottom  389  surfaces. Substrate  343  is mechanically fastened along rear edge  385  to PC board  335  by solder joints at terminals  403 ,  405 . An adhesive or mechanical fasteners could additionally be provided to further join substrate  343  to PC board  335 . 
     Referring to  FIGS. 12-14 , sensor  337  consists of first and second conductors  339 ,  341  made of electrically-conductive copper or the like deposited on substrate  343 , preferably on substrate bottom  389  surface. Conductors  339 ,  341  are preferably deposited in the interdigital array shown in  FIGS. 12-14 . Specifically, first and second conductors  339 ,  341  each preferably include a plurality of parallel conductor elements  395 ,  397  deposited on substrate  343  each connected to respective main conductors  399 ,  401  which end in terminals  403 ,  405 . Each parallel element  395 ,  397  is connected such that each element  395  of the first conductor  339  is connected to every other first conductor element  395  and each element  397  of the second conductor  341  is connected to every other second conductor element  397 . Further, the parallel elements  395 ,  397  of each conductor  339 ,  341  are preferably arrayed such that elements  395 ,  397  alternate one after the other so that the nearest element  397  to each element  395  is an element  397  of the second conductor  341  and the nearest element  395  to each element  397  is an element  395  of the first conductor  399 . 
     Sensor  337  most preferably has a three-dimensional geometry and generates a detection zone  400  advantageously directed toward positions about dispenser  10  most likely to be contacted by the outstretched hand or body part of user positioned to receive sheet material  111 ,  113  from web discharge opening  67 . This advantageous result is achieved by providing substrate  343  and conductors  339 ,  341  with a pronounced arcuately-shaped architecture, preferably by bending the flexible substrate  343  and conductors  339 ,  341  so that substrate front corners  377 ,  379  and side edges  381 ,  383  are positioned above center portion  375  as shown in  FIGS. 12-14 . Clip  407  holds substrate  343  along the front edge  373  center portion  375 . Slots  411 ,  413  in ribs  414 ,  415  are above clip  407  and receive the substrate  343  therein. Front corners  377 ,  379  are held against walls  417 ,  419  at a position above slots  411 ,  413 . Conductors  339 ,  341  take on the three-dimensional configuration of substrate  343 . 
     Sensor  337  is not limited to the specific three-dimensional structure described above. Other types of three-dimensional architecture may be used. For example, substrate  343  could be configured in the form of a cylindrical tube with conductors  339 ,  341  deposited across the outer surface of the tube. Sensor  337  will function with a flat substrate  343  having conductors  339 ,  341  deposited on the flat substrate  343  and such sensors are within the scope of the invention. However, such sensors are disadvantageous because, for the same size sensor, the detection zone of a flat sensor is far more limited, particularly in width across the dispenser housing, than the detection zone  400  of the three-dimensional sensor  337 . 
       FIG. 15  is a two-dimensional representation of the three-dimensional volume of detection zone  400  generated by a the three-dimensional sensor  337  of a detuned proximity detector  49  and control  50  with the sensor  337  at the location shown in  FIGS. 9 and 10 . The location of dispenser housing  11  and sensor  337  within housing  11  are indicated. For purposes of  FIG. 15 , dispenser  10  was positioned along a vertical wall surface. Measurements were taken of dispenser actuation at points across the width of the dispenser bottom wall  65  at distances 12 cm and 15 cm from the wall. The outermost points along which dispenser actuation occurred are represented by the curves shown on FIG.  15 . 
     Curves  421 ,  423  represent the volume of the detection zone  400  provided by three-dimensional sensor  337  at locations 15 cm ( 421 ) and 12 cm ( 423 ) from the wall. As is apparent, the three-dimensional sensor  337  generates a shaped detection zone  400  which covers the region below the dispenser discharge opening central to the dispenser where a user would naturally place his or her hand to receive sheet material  111 ,  113  from discharge opening  67 . The boundaries of detection zone may be expanded or contracted (i.e., tuned or detuned) as described in detail below. 
     Referring now to  FIGS. 16-18 , those figures illustrate the components and operation of exemplary proximity detector apparatus  49  and control apparatus  50 .  FIG. 16  is a block diagram of the proximity detector  49  and control apparatus  50  in accordance with the present invention.  FIGS. 17A-17D  are schematic diagrams showing the electrical components of the proximity detector  49  and control apparatus  50  in accordance with the present invention.  FIGS. 18A-18K  comprise a series of idealized graphs which are used to describe operation of the differential frequency discriminator  509 . 
     Turning first to block diagram  FIG. 16 , proximity detector  49  includes an oscillator  501  with a sensor  337  in its feedback path  505 . As described in more detail below, oscillator  501  generates an oscillating voltage  551  ( FIG. 18A ) the frequency of which is affected by the electrical capacitance of sensor  337 . The capacitance of sensor  337  is changed by the presence of a user (e.g., a user&#39;s hand) in proximity to sensor  337 . A buffer  507 , well-known to those skilled in electronics, serves to isolate the operation of oscillator  501  from other parts of the circuitry. 
     Differential frequency discriminator  509  is configured to be sensitive to changes of the oscillator frequency and produce an output which is used by a processor, such as micro-controller  511 , to control motor drive  513  in order to dispense a length of sheet material. Micro-controller  511  controls the length of sheet material  111 ,  113  dispensed based on a signal from voltage compensation circuit  515  which is used to determine power source output (preferably voltage), and a signal from an optional sheet length adjustment control  517  provided to permit the operator to preselect a specific length of sheet material to be dispensed. 
     Central to operation of the proximity detector  49  shown in  FIG. 16  is the operation of frequency discriminator  509 . Discriminator  509  receives the output  551  from oscillator  501  and then processes that output  551  to detect very small changes in capacitance in the detection zone  400  resulting from the presence of the user&#39;s hand. 
     Operation of frequency discriminator  509  will be described in connection with  FIGS. 18A-18K . References to the schematic diagrams of  FIGS. 17A-17D  will be made as appropriate. 
     The following explanation will be useful in understanding the data represented by  FIGS. 18A-18K  provided to describe operation of the frequency discriminator  509 . In  FIGS. 18A-18K , each graph includes an upper horizontal dotted line  547  and a lower horizontal line  549 . Upper line  547  represents the logical high voltage level for the apparatus (about 3.3V for the circuits in FIGS.  17 A- 17 D), and lower line  549  represents the logical low voltage level for the apparatus (about 0 V for the circuits in  FIGS. 17A-17D , with one exception which will be noted later in the description of circuit operation). The graphs of  FIGS. 18A-18K  are somewhat idealized in that precise voltage levels are not shown, but the graphs completely represent the operation of frequency discriminator  509 .  FIGS. 18A-18I  have time as the horizontal axis (dependent variable), and  FIGS. 18J and 18K  have oscillator frequency decrease as the horizontal axis (dependent variable). 
     Referring now to  FIG. 18A , that figure shows a somewhat idealized representation of oscillator output  551 . A monostable multivibrator  521  ( FIG. 17C ) generates a first series of pulses  553  (shown in  FIG. 18B ) and a second series of pulses  555  (shown in  FIG. 18C ) which is the complement of first series  553 . In the embodiment of the apparatus being described, circuit parameters within multivibrator  521  are set such that the frequency of first series  553  is half the frequency of oscillator output  551 . (This frequency-halving is useful in this particular embodiment but not fundamental to the operation of discriminator  509 .) The width of the high portion  557  of first series  553  is adjusted by a set point circuit  523  ( FIG. 17C ) within monostable multivibrator  521  such that the high portion of each cycle is approximately one-half of each cycle when the user is not in the detection zone  400  of sensor  337 . Operation of multivibrator  521  is such that the width of high portion  557  remains unchanged when the frequency of oscillator output  551  changes. 
     First series  553  and second series  555  are averaged by a first averaging circuit  525  ( FIG. 17C ) and a second averaging circuit  527  respectively, generating a first average  559  and a second average  561  illustrated respectively in  FIGS. 18D and 18E . Since second series  555  is the complement of first series  553  and since the width of high portion  557  is about one-half of each cycle of series  553 , first average  559  and second average  561  are nearly equal to each other. 
     When a user comes into the proximity of sensor  337 , the sensor capacitance affects the oscillator  501  by lowering the frequency of oscillator output  551 . Because the width of high portion  557  remains constant, first average  559  decreases and second average  561  increases, as illustrated in exaggerated fashion in  FIGS. 18F-18I , which correspond to  FIGS. 18B-18E  respectively, and represent operation of discriminator  509  when a user is in the detection zone  400  proximate sensor  337 . First average  559  and second average  561 , by decreasing and increasing respectively with a decrease in the frequency of oscillator output  551 , result in highly sensitive detection of changes in the capacitance of sensor  337 . 
     Referring to  FIGS. 18J-18K , first average  559  and second average  561  are inputs to a first comparator  529  ( FIG. 17C ) which amplifies the difference between second average  561  and first average  559 , generating an output  563  of first comparator  529  as shown in FIG.  18 J. When no user is in detection zone  400 , the value of output  563  is at operating point  565  because set point circuit  523  is set such that first average  559  and second average  561  are nearly equal. When a user is present in detection zone  400 , output  563  goes high as shown at the right side of FIG.  18 J. Note that for first comparator  529  (FIG.  17 C), the logical low voltage level as indicated in  FIG. 18J  is about 1.5V, and the logical high voltage is 3.3V. 
     The proximity detector  49  may optionally be tuned or detuned to adjust the volume of the detection zone  400 . This result is accomplished through use of a second comparator  531  and a threshold reference signal  567  which may be set at a preselected voltage level corresponding to the size of the frequency change necessary for detection of the user within zone  400 . Referring then to  FIGS. 18J and 18K , second comparator  531  generates an output  566  which is the result of comparing output  563  of first comparator  529  with the threshold reference signal  567  (represented by the dotted line voltage level labeled  567  in FIG.  18 J). Output  566  in  FIG. 18K  is, therefore, the amplified difference between threshold reference signal  567  and output  563 . Second comparator  531  is configured such that output  566  is low when a user is in proximity of sensor  337  as shown in FIG.  18 K. 
     Operating point  565  represents no change in frequency (no user present) as indicated by the dotted line  570  correlating the signals of  FIGS. 18J-18K . When first comparator  529  output  563  becomes higher than threshold signal  567 , the presence of a user is indicated. This event (shown at the point labeled  569 ) occurs with a change in frequency indicated by dotted line  572  in  FIGS. 18J-18K . Thus, frequency change  572  represents the frequency change at which output  566  changes as a result of first comparator output  563  becoming higher than threshold signal  567 . Adjustment of the value of threshold reference signal  567  thereby adjusts the sensitivity of discriminator  509  to changes in oscillator frequency and thus in sensor capacitance. Therefore, higher levels of threshold reference signal  567  result in smaller detection zone  400  volumes since triggering requires a larger frequency change. 
     Threshold reference signal  567  also helps to reduce the sensitivity of discriminator  509  to changes in environmental conditions (temperature and humidity) by setting frequency change  569  outside of the range of frequency changes which expected variations of temperature and humidity would cause. This setting, combined with the differential nature of the discriminator and the selection of component values to set operating point  565 , all result in operation of discriminator  509  which is insensitive to the normal temperature and humidity variations expected at locations in which the dispenser normally would operate. 
     The schematic of  FIG. 17A  shows a power supply apparatus  47  for powering the dispenser  10 . Four 1.5V “D” cell batteries (such as batteries  271 ,  273 ) are connected in series at connector J 1 . The supply output of the battery-powered power supply apparatus  47  may comprise either the voltage, current or both provided by the batteries. Regulated power supply apparatus  47  receives the 6V electrical current from the batteries at connector J 1  and converts the voltage to 3.3V DC of regulated power output which is supplied to the remaining circuitry at the point represented by reference number  575 . Regulated power supply apparatus  47  is actually connected to the points labeled 3.3V throughout  FIGS. 17B-17D . The circuitry and operation of regulated power supply apparatus  47  is well-illustrated in FIG.  17 A and is known to those skilled in the art of electronic circuitry. 
       FIG. 17B  is a schematic of oscillator  501  which includes sensor  337 . Oscillator output  551  is found at the point in the circuit labeled  577 , which then provides output  551  to discriminator  509 , shown in  FIG. 17C  (also showing the point  577 ). The various circuits included in discriminator  509  have already been pointed out in the discussion above. Circuit elements labeled  579  (R 38  and R 37 ) are adjusted to set threshold signal  567 . 
     Output  566  of second comparator  531  is found at the point labeled  581 , such point being further found as an input to the schematic of  FIG. 17D  which shows micro-controller  511  and motor drive circuit  513 . Optional sheet material length selector  517  including control  585  and length signal found at the point labeled  587  set by selector  517 . Control  585  is shown as a connector configured to receive a jumper between a pair of neighboring pins, or no jumper, such connector being a common element known to those skilled in the art. 
     Also as shown in  FIG. 17D , a motor drive signal is available to the motor  267  (not shown in  FIG. 17D ) across the terminals of connector  514 . The duration of the signal determines the length of the sheet material selected  517  based on the power supply voltage level compensation at voltage compensation circuit  515 . 
     Method of Dispensing 
     Operation of exemplary automatic dispenser  10  and an exemplary method of dispensing will now be described. The method of dispensing will be adapted to the specific type of automatic dispenser apparatus utilized with the proximity detector. 
     The first step of the dispensing method involves loading the dispenser with product to be dispensed. For the sheet material dispenser  10 , such loading is accomplished with respect to dispenser  10  in the following manner. The dispenser cover  17  is initially opened causing roller frame assembly  173  to rotate outwardly about axially aligned pivot openings positioned in frame sidewall  53 ,  59  one of which is identified by reference number  189  (FIG.  8 ). The rotational movement of frame assembly  173  positions tension roller  141  and transfer assembly  227  away from drive roller  139  providing unobstructed access to housing interior  15  and space  75 . 
     When dispenser  10  is first placed in operation, a primary roll  39  of sheet material, such as paper toweling or tissue, may be placed on yoke  125  by spreading arms  131 ,  133  apart so as to locate the central portions of holders  135 ,  137  into roll core  117 . The sheet material  111  is positioned over drive roller  139  in contact with drive roller segments  143 - 147 . A fresh roll could be stored on cradle  119  awaiting use. Further, cradle  119  could be removed to insert fresh batteries into battery box  311 . Thereafter, cover  17  is closed as shown in FIG.  1 . Movement of cover  17  to the closed position of  FIG. 1  causes the leaf springs  213 ,  215  mounted on the roller frame assembly  173  to come in contact with the inside of cover  17  resiliently to urge the tension roller  141  into contact with sheet material  111  from roll  39  thereby ensuring frictional contact between the sheet material  111  and the drive roller  139  and, more particularly, drive roller segments  143 - 147 . The dispenser  10  is now loaded and ready for operation. 
     Subsequent steps involve the electrical components of the proximity detector and control apparatus  49 ,  50  and are illustrated in the block diagrams of  FIGS. 19A-19E . It would be expected that the instructions for execution of the steps are provided in the form of software code embedded on firmware provided, for example with micro-controller  511 . However, the instructions may be provided in other forms, such as in operating system software. 
     The loaded dispenser  10  is now in the “start” state  601  illustrated in FIG.  19 A. While awaiting an input signal indicating the presence of a user, the dispenser firmware automatically restores calibration, initializes input/output and initializes timers and interrupt vectors, combined as step  603 . Upon completion of this step, the dispenser is in the “main” state  605 . In step  607 , the dispenser  10  then determines whether the low battery flag has been set during a previous dispensing cycle. Setting of the flag would indicate that the batteries have a low voltage between preset values as described below. If the flag is set, the dispenser is in state  609  and the dispenser activates a signal in the form of an LED which is cycled on and off (step  611 ) to indicate to the attendant that the batteries require replacement. If the batteries have a voltage above the threshold (state  613 ) and if no user is present, the dispenser will enter a “sleep mode” (state  615 ) to conserve energy. The dispenser does not enter sleep mode if the low battery flag is set. 
     When a person approaches the dispenser and a change in capacitance is detected by the frequency discriminator  509 , a “sensor interrupt” event (step  617 ) occurs. 
     In response to the sensor interrupt event  617 , dispenser  10  next attempts to determine whether the detection was true or false by filtering out false detection. In the sensor filter state  619  represented in FIG.  19 A and at the top of  19 B, dispenser  10  determines whether the detection responsible for the sensor interrupt event exceeded a time duration threshold which is 30 ms in this example (step  621 ). Detection for less than the threshold duration means that the signal was false and the dispenser is returned to the main state  605 . Detection in excess of the threshold indicates that the detection event is true (state  623 ). 
     A cascade of further steps occurs in response to a true sensor interrupt event. In step  625 , the A/D converter is initialized. The sheet material length to be dispensed and battery voltage corresponding to the length of sheet material to be dispensed are read and stored in memory (steps  627  and  629 ), and A/D conversion is then complete (step  633 ), resulting in state  635 . 
     Power supply voltage compensation circuit  515  is optionally provided to cause the dispenser to determine (step  637 ) whether the battery voltage is below a minimum voltage threshold (3.75V in this example) required to enable completion of a dispensing cycle. If the voltage is below the threshold then the dispenser is placed in a “lockout” condition (state  639 ) in which further mechanical operation is interrupted and the LED low battery flag is active (state  641 ). If the voltage is above the minimum threshold but below a secondary threshold (determined by step  643 ), lockout is avoided but the low battery flag is set (state  645 ). Detection of the low battery flag in an earlier step  607  results in actuation of the cycling LED indicator signal (state  611 ). If the voltage is above the secondary voltage threshold then any previous low battery flag is cleared in step  647 . The battery condition is stored (step  648 ) in memory, and the dispenser proceeds to the next steps if sufficient power is available. 
     If an optional sheet material length adjustment selector  517  ( FIGS. 16 and 17D ) is included, the control apparatus  50  will next determine the appropriate length of sheet material to be dispensed. The towel length reading is read (step  649 ) and then, in step  651 , is compared to three predetermined settings and set to the setting selected. Dispenser  10  is then in a state  653  ready for a voltage compensation step. 
     In step  655 , control apparatus  50  accesses a look-up table with stored motor run times corresponding each towel length and to the stored battery voltage in step  648 . Control apparatus  50  computes the dispense time (step  655 ), and generates a drive signal (step  656 ) which, when amplified by motor drive  513 , turns on the drive motor  267  rotating drive roller  139  and drawing sheet material  111  through nip  157  and out of dispenser  10  through discharge opening  67 . While the drive signal is being generated (step  656 ), the control apparatus  50  checks the low battery flag (step  657 ), blinks the low battery LED (state  659 ) if the low battery flag is set, and checks to see if the computed dispense time has been reached (step  661 ). When the dispense time has been reached, the drive signal is terminated and the motor  267  is turned off (step  663 ), a one second delay is inserted (step  665 ), and the dispenser is returned to main state  605 . The user may then separate the sheet  111  into a discrete sheet by lifting sheet  111  up and into contact with tear bar  71  serrated edge  207  tearing the sheet  111 . 
     After repeated automatic dispensing cycles, cover  17  is removed to permit replenishment of the sheet material. At this time, a portion of roll  39  remains and a reserve roll  41  of sheet material can be moved into position. As illustrated in  FIG. 9 , partially dispensed roll  39  (preferably having a diameter of about 2.75 inches or less) is now moved onto cradle  119  arcuate surfaces  121 ,  123 . Sheet material  111  extending from roll  39  continues to pass over drive roller  139 . 
     After primary roll  39  is moved to the position shown in  FIG. 9 , a fresh secondary roll  41  can be loaded onto yoke  125  as previously described. Sheet material  113  is then threaded onto the transfer assembly  227 . More specifically, sheet material  113  is urged onto catch  256  which pierces through the sheet material  113 . Sheet material  113  is further led under pins  259 ,  261  to hold sheet material  113  in place on the transfer assembly  227  as shown in FIG.  9 . Transfer assembly surface  250  rests against sheet material  111 . Surface  250  will ride along sheet material  111  without tearing or damaging material  111  as it is dispensed. The cover  17  is then closed to the position shown in FIG.  1 . 
     After further automatic dispensing cycles, sheet material  111  from primary roll  39  will be depleted. Upon passage of the final portion of sheet material  111  through nip  157 , transfer surface  250  will come into direct contact with arcuate surface  257  of drive roller  139 . Frictional engagement of drive roller segment  145  and surface  250  causes transfer assembly  227  to pivot rearwardly and slide up along slots  237 ,  239 . Movement of transfer assembly  227  as described brings teeth  253  along arcuate surface  251  into engagement with drive roller segment  145 . Engagement of teeth  253  with the frictional surface of segment  145  forcefully urges sheet material  113  held on catch  256  into contact with drive roller surface  257  causing sheet material  113  to be urged into nip  157  resulting in transfer to roll  41  as shown in FIG.  10 . Following the transfer event, transfer assembly  227  falls back to the position shown in FIG.  10 . Thereafter, sheet material  113  from roll  41  is dispensed until depleted or until such time as the sheet material rolls are replenished as described above. 
     The invention is directed to automatic dispenser apparatus generally and is not limited to the specific automatic dispenser embodiment described above. For example, there is no requirement for the dispenser to dispense from plural rolls of sheet material and there is no requirement for any transfer mechanism as described herein. The sheet material need not be in the form of a web wound into a roll as described above. The novel proximity detector  49  and control apparatus  50  will operate to control the discharge and drive apparatus  43 ,  45  of virtually any type of automatic sheet material dispenser, including dispensers for paper towel, wipes and tissue. 
     The novel proximity detector  49  will operate with automatic dispensers other than sheet material dispensers. For example, the proximity detector will operate to control automatic personal care product dispensers, such as liquid soap dispensers (not shown). In the soap dispenser embodiment, the power supply apparatus  47 , proximity detector  49  and control apparatus  50  components may be housed in an automatic soap dispenser apparatus. Discharge apparatus  43  and drive apparatus  45  may be a solenoid or other mechanical actuator. An appropriate fluid reservoir in communication with the solenoid or actuator (i.e.,  43  and  45 ) is provided to hold the liquid soap. The solenoid or other actuator discharges soap from the dispenser through a fluid-discharge port. The detection zone  400  is generated below the soap dispenser adjacent the fluid-discharge port. 
     Operation of the soap dispenser may include steps/states  601 - 647  and  656 - 665  and the corresponding apparatus described with respect to the dispenser  10 . (Steps  648 - 655  would not be relevant for the soap dispenser.) In the soap dispenser embodiment, the drive signal generated in response to a detected user (step  656  above) is available to the solenoid or other actuator in a manner identical to the manner in which the drive signal is generated in the dispenser embodiment  10 . Generation of the drive signal actuates the solenoid or other actuator to dispense a unit volume of soap from the soap dispenser spout into the user&#39;s hand. The programmed instructions in micro-controller  511  will be tailored to the specific type of soap dispenser being used, for example to limit the number of dispensing cycles per detection event and to limit the dwell time between dispensing cycles. 
     Further Method of Dispensing 
     The block diagrams of  FIGS. 20A-20G  illustrate an alternative embodiment of instructions for use in controlling the operation of dispenser  10 . The mechanical and electrical configuration of dispenser  10  used with the alternative instructions of  FIGS. 20A-20G  is identical to dispenser  10  previously described and such description of dispenser  10  is incorporated by reference. The instructions represented by the block diagram of  FIGS. 20A-20G  are typically provided for execution in the form of firmware embedded within a processor, such as micro-controller  511  of control apparatus  50 . 
     The alternative embodiment of  FIGS. 20A-20G  provides instructions for improved operation of dispenser  10  across the life cycle of the batteries (such as D-cell batteries, two of which are indicated by reference nos.  271  and  273 ). Preferably, four 1.5V series-connected alkaline D-cell batteries are used to power dispenser  10  including motor  267 . The output of the batteries is referred to herein as a power source output to indicate that a physical quantity (voltage or current) is measured to assess the state of the power supply. Such power source output is preferably expressed in terms of the voltage produced by the batteries. The power source output exists under both loaded and unloaded conditions. The instructions of  FIGS. 20A-20G  provide more accurate control over the length of sheet material  111  dispensed by dispenser  10  and provide for improved control over dispenser  10  operation as the power source output of the batteries diminishes across the battery life cycle. 
     As is known, batteries produce voltages which depend on many different factors, including the chemistry of the type of battery cells being used, the length of time between manufacture and use, the rate of discharge, temperature and duty cycles. By way of example,  FIG. 21  shows the changes in battery voltage of a representative 1.5V alkaline battery over the life cycle of the battery. The abscissa (time axis—time increasing from left to right) is not shown with a time scale since the purpose of the graph is only to illustrate the form of battery voltage vs. time as an alkaline battery is discharged. As shown in  FIG. 21 , after an initial voltage drop, the voltage of the 1.5V alkaline battery remains around 1.2V for an extended period of time, after which the voltage drops off rapidly as the battery approaches the end of its life cycle. 
     A challenge facing designers of battery powered dispensers is to ensure consistent operation of the dispenser as battery voltage decreases over the life cycle of the battery. One important object of dispenser operation is that the dispenser should discharge consistent lengths of sheet material over repeated dispense cycles. By consistent it is meant that the length of sheet material dispensed in repeated cycles is the approximately the same length. Put another way, the sheet material should be within a length range based on a preselected length. 
     Changes in battery voltage over the life cycle of the battery may adversely affect the consistency of the length of sheet material  111  discharged. This problem occurs because, as the power source output decreases, the motor  267  powering drive roller  139  runs more slowly (i.e., at decreased revolutions per minute). As battery voltage decreases over the life cycle of the batteries, the motor  267  is required to run for a longer time duration in order to dispense a consistent length of sheet material  111 . By way of further example, battery voltage under load could increase if the dispenser  10  is moved from a location that is relatively cold to a location which is relatively warm. Such voltage increase may cause inconsistent lengths of sheet material  111  to be discharged from dispenser  10 . 
     Because of the complex relationship between voltage and the various parameters which affect voltage, the inventors found that measurements of battery voltage under both unloaded and loaded conditions can yield reliable assessments of battery state. As set forth in the control sequence depicted in  FIGS. 20A-20G , the dispenser  10  monitors battery state in both unloaded and loaded conditions to provide improved controlled operation of the dispenser  10  as battery voltage changes over the life cycle of the batteries. Among other things, the control sequence depicted in  FIGS. 20A-20G  compensates for decreasing battery voltage by generally increasing the time duration of motor  267  operation to enable the dispenser  10  to discharge a consistent length of sheet material  111  over many successive dispense cycles. The control sequence generally decreases the time duration of motor  267  operation when the voltage under load increases. 
     In the preferred embodiment, the change in the time duration of motor  267  operation occurs in the next dispense cycle; the motor run time for the then-occurring dispense cycle is predetermined and is not changed as described below. The then-occurring dispense cycle refers to the dispense cycle then taking place responsive to a user dispense request initiated by actuation of a user input device. In this example the input device is proximity detector  49 . The preceding dispense cycle refers to the dispense cycle immediately before the then-occurring dispense cycle while the next dispense cycle refers to the next sequential dispense cycle after completion of the then-occurring dispense cycle. 
     Referring then to  FIG. 20A , upon power-up, the loaded dispenser  10  enters the “start” state  701 . The control sequence automatically restores calibration, initializes input/output and initializes timers and interrupt vectors, all of these steps are combined in  FIG. 20A  as step  703 . Upon completion of step  703 , the instructions of step  705  blink LED 2  (see  FIG. 17D ) to indicate that step  703  is complete and further to indicate what version of the firmware code is present in micro-controller  511 . (As shown in  FIG. 20A , the blinking pattern of blink-blink-pause-blink indicates such a firmware version.) Before reaching the “main” state  721 , control apparatus  50  now sequences through a series of steps (steps  709 - 719 ) in order to determine the condition of the batteries at the time of power-up and before motor  267  operation. Using the analog-to-digital conversion (A/D) feature of micro-controller  511 , control apparatus  50  obtains the “open-circuit” (i.e., unloaded circuit voltage) battery voltage in step  707 . In step  709 , control apparatus  50  determines if the open-circuit battery voltage is below a preset voltage threshold V 1  (in  FIG. 20A , V 1  is 4.5V). (Note that throughout the block diagrams of  FIGS. 20A-20G , elements of the diagram shown as diamonds indicate that a determination is being made with two possible outcomes—“YES” or “NO”. In each such case, the “YES” determination is labeled as XXXa and the “NO” determination is labeled as XXXb, where XXX is the number referring to the specific determining step in question.) 
     If the open-circuit voltage is below V 1  (determination  709   a ) in step  709 , control apparatus  50  enters continuous loop  711 . The instructions of continuous loop  711  blink LED 2  to indicate that the battery is in a low-voltage state and trap the dispenser in this loop, thereby preventing further operation of dispenser  10 . 
     A “NO” determination  709   b  at step  709  enables determination step  713  to occur. In step  713 , control apparatus  50  determines if the open-circuit battery voltage is below a preset voltage threshold V 2  (in  FIG. 20A , V 2  is 5.3V). If the open-circuit voltage is below V 2  (determination  713   a ) in step  713 , control apparatus  50  sets a “low open-circuit voltage” flag (logical variable within micro-controller  511 ) in step  715  to indicate that the battery is in a partially-discharged condition. If the open-circuit voltage is not below V 2  (determination  713   b ) in step  713 , control apparatus  50  clears the “low open-circuit voltage” flag in step  717 . 
     In step  719  the control apparatus  50  sets the initial value of voltage V b     —     load  to a preset initial value. Step  719  only occurs during the power up sequence. The initial value of V b     —     load  is 6.6V, a level selected to be above the battery voltage of fresh batteries. With these power-up steps complete, control apparatus  50  enters its “main” state  721 , which represents the point in the logic sequence of  FIGS. 20A-20G  through which the control loop passes each dispense cycle of the loop during dispenser operation. 
     “Main” state  721  is shown at the bottom of FIG.  20 A and at the top of FIG.  20 B. Referring to  FIG. 20B , following the entry of control apparatus  50  into “main” state  721 , step  723  determines if either of the two low battery voltage flags is set. The two low battery voltage flags are the “low open-circuit voltage” flag of step  715  and the “low V b     —     load ” flag (V b     —     load  is battery voltage under load) discussed in step  797  below. The two flags are either “set” or “cleared” as described above in the context of the low open-circuit voltage flag. The low V b     —     load  flag is “cleared” during step  703  of the power-up sequence just described. If either low battery voltage flag is in the “set” state at step  723  (determination  723   a ), control apparatus  50  enters a loop which instructs LED 2  to blink at step  725 , indicating a low-battery condition within the dispenser  10 . Step  727 , a determination as to whether or not a sensor interrupt (from proximity detector  49 ) has occurred, is also part of this loop. As long as a sensor interrupt is not received from proximity detector  49  (determination  727   b ), LED 2  continues to blink and the dispenser continues to monitor proximity detector  49  at step  727 . 
     If neither low-battery-voltage flag is in the “set” state at step  723  (determination  723   b ), control apparatus  50  enters a different loop represented by steps  729  and  731  in FIG.  20 B. Subsequent to determination  723   b , control apparatus  50  enters sleep mode (or state)  729 , which in the case of this embodiment, is provided as a built-in feature of micro-controller  511 . In sleep mode, micro-controller  511  lowers its power consumption and waits until an interrupt signal is received, at which point micro-controller  511  is said to “wake”, returning to normal operation at the point in the sequence at which it entered “sleep” mode. Upon micro-controller  511  being “wakened”, step  731  determines if the received interrupt is a sensor interrupt (signal from proximity sensor  49 ). If it is not, determination  731   b  returns micro-controller  511  to sleep mode  729 . 
     If the result of either determination step  727  or determination step  731  is “YES” (determination  727   a  or determination  731   a ), the dispenser control sequence proceeds to a sensor filter at step  733 . A sensor interrupt occurs when a person approaches the dispenser and a change in capacitance is detected by the frequency discriminator  509 , causing proximity detector  49  form of input device to produce the sensor interrupt signal. The detected change in capacitance represents the user&#39;s request that the dispenser discharge a length of sheet material  111 . The presence of the sensor interrupt event indicates that the then-occurring dispense cycle has been commenced by the user dispense request. 
     In response to the sensor interrupt event as determined by step  727  or step  731 , dispenser  10  next determines whether the detection event was true or false by filtering out false detection events based on the duration of the sensor interrupt signal. Sensor filter entry step  733  is shown at the bottom of FIG.  20 B and at the top of FIG.  20 C. At determination step  735 , dispenser  10  determines whether the detection responsible for the sensor interrupt event is valid by determining whether the event has a duration which exceeds a preset time duration threshold, which in this example is 30 milliseconds. Detection for less than the duration threshold (determination  735   b ) is interpreted to mean that the signal was false, and control apparatus  50  is returned to the “main” state  721 . Detection in excess of the threshold (determination  735   a ) indicates that the detection event is true. 
     The alternative embodiment of instructions for use in controlling the operation of dispenser  10  is not limited to use in a “hands-free” dispenser utilizing an input device in the form of proximity detector  49 . For example, proximity detector  49  could be replaced with an input device in the form of a push button contact switch (not shown) located at a convenient location along, for example, front cover  17  of dispenser housing  11 . Manual contact between the user and the push button contact switch would close the switch and generate the sensor interrupt event as determined by step  727  or step  731 . In such an embodiment, step  735  would act as a debounce step responsive to closure of the push button contact switch by the user. Generation of the sensor interrupt event with the push button contact switch would initiate the then-occurring dispense cycle. 
     After a “YES” determination following step  735  (a “true” sensor interrupt event), the control sequence of control apparatus  50  proceeds with a cascade of further steps. In step  737 , the A/D converter is initialized. Using the A/D converter of micro-controller  511 , the sheet material length to be dispensed (represented by an analog voltage at pin  7  of micro-controller  511 — see  FIG. 17D ) and the open-circuit battery voltage are read and stored in memory (steps  739  and  741  respectively). Step  743  ends A/D conversion. Step  743  is shown at the bottom of FIG.  20 C and the top of FIG.  20 D. 
     Referring now to  FIG. 20D , using the open-circuit voltage measurement captured in step  741 , control apparatus  50  compares this measurement with preset voltage threshold V 1 , in this example 4.5V (step  747 ). If it is determined that the open-circuit battery voltage is below V 1  (determination  747   a ), control apparatus  50  enters continuous loop  749 . The instructions of continuous loop  749  blink LED 2  to indicate that the battery is in a low-voltage state and trap the dispenser in this state, thereby preventing further operation of the dispenser. A further comparison (determination  747   b ) is performed in step  751 , comparing the open-circuit battery voltage with preset voltage threshold V 2 , in this example 5.3V. In step  751 , if the open-circuit voltage is below V 2  (determination  751   a ), control apparatus  50  sets the “low open-circuit voltage” flag in step  753  to indicate that the battery is in a partially-discharged condition. If the open-circuit voltage is not below V 2  (determination  751   b ), control apparatus  50  clears the low open-circuit voltage flag in step  755 . Following step  753  or step  755 , the control sequence of the dispenser proceeds to set the length of towel to be dispensed. The block diagram element  757  labeled “A” in  FIGS. 20D and 20E  simply represents a convenient waypoint in the description of the control sequence. 
     Referring to  FIG. 20E , the control sequence continues in step  759  by recalling the towel length voltage previously stored in step  739  and then in the group of steps labeled  761  and in a fashion similar to steps  651  in  FIG. 19D , determines the selected towel length (“short”, medium”, or “long”) from the stored towel length voltage (stored after an A/D conversion in step  739 ) by comparing this voltage with preset voltage thresholds (in  FIG. 20E , 0.75V and 2.25V). 
     After the towel length determination is complete, the control sequence proceeds with voltage compensation, the start of which is represented by step  763  shown at the bottom of FIG.  20 E and the top of FIG.  20 F. The voltage compensation step  763  results in operation of the motor  267  such that the dispenser  10  discharges a consistent length of sheet material  111  in successive dispensing cycles even as battery voltage fluctuates over the life cycle of the batteries. 
     Referring then to  FIG. 20F , the control sequence next determines (in step  765 ) the dispense time for the then-occurring dispense cycle. The control sequence utilizes a look-up table, preferably prestored in micro-controller  511 . The use of look-up tables is common practice for those skilled in the use of micro-controller-based systems. The look-up table contains a series of motor run time values corresponding to the various towel lengths (in this example, “short”, medium”, or “long”) and to intervals of average V b     —     load  values along the full range of expected values for V b     —     load . By way of example only, the motor run time values for a “long” length of sheet material  111  (e.g., ideally about 14 inches long) may range from a minimum of 0.671 seconds to a maximum of 1.643 seconds, the motor run time values for a “medium” length of sheet material  111  (e.g., ideally about 12 inches long) may range from a minimum of 0.576 seconds to a maximum of 1.409 seconds while the motor run time values for a “short” length of sheet material  111  (e.g., ideally about 10 inches long) may range from a minimum of 0.479 seconds to a maximum of 1.174 seconds. 
     Each motor run time value corresponds to an interval of average V b     —     load  value for each of the three choices of sheet material  111  lengths. The average V b     —     load  is a stored value (stored in micro-controller  511  memory) calculated near the end of the preceding dispense cycle as described in connection with step  775  below. Operation of the motor  267  for the motor run time corresponding to the interval in which the stored average V b     —     load  falls, results in discharge of the desired length of sheet material from the dispenser  10 . In general, the motor run time is of a shorter duration when the batteries are at the beginning of their life cycle and the average V b     —     load  is greater and is of a longer duration near the end of the battery life cycle and the average V b     —     load  is decreased. Under normal operating conditions, there is little change in the motor run time in sequential dispense cycles as alkaline batteries typically operate for in excess of 50,000 dispense cycles. 
     In step  765 , the control apparatus accesses the look-up table and the stored average V b     —     load . A motor run time is then determined for the then-occurring dispense cycle. In this example, the motor run time is based on the stored average V b     —     load  from the preceding dispense cycle. Voltage measurements determined during the then-occurring dispense cycle do not affect the motor run time of the then-occurring dispense cycle. 
     Referring next to steps  767  through  773 , such steps cooperate to run motor  267  for the motor run time in the then-occurring dispense cycle as determined in step  765  and to blink LED 2  if either of the low voltage flags is set. In a dispense-time loop (steps  767 - 773 ), step  767  turns motor  267  on, step  769  determines if either low flag is set, step  771  blinks LED 2  if either flag is set (determination  769   a ), and, after determination  769   b , step  773  determines if the dispense time is complete. If the dispense is not complete (determination  773   b ), the loop continues by branching back to step  767 . If the dispense time is complete (determination  773   a ), the control sequence exits the dispense-time loop, moving to step  775  at which a measurement of V b     —     load  (i.e., power source output under load) is taken as discussed below in connection with FIG.  20 F. 
       FIG. 22  is provided to graphically illustrate the preferred point in the then-occurring dispense cycle at which the V b     —     load  measurement is obtained in step  775 . Referring to the exemplary battery power source output voltage trace of  FIG. 22 , dispense time (determined in step  765 ) within a dispense cycle spans the time between 0.00 seconds and about 0.70 seconds on the time axis of the graph. At the point marked T m  at the end of this trace is the time at which the power source output measurement of step  775  is taken, just prior to turning motor  267  off in step  801 . Note that although there are numerous steps in the control sequence between steps  773  and  801 , the length of time required for an instruction to be completed within a typical micro-controller is extremely short (typically a few micro-seconds or less) compared to the overall dispense time. By obtaining the power source output measurement of V b     —     load  at the end of the dispense time, “corrupting” the measurement of V b     —     load  with the drop in battery voltage caused by the acceleration of the roll of towel (seen at the beginning of the trace in  FIG. 22 ) is avoided. The measurement of V b     —     load  is stored in memory of micro-controller  511 . 
     Referring now to  FIG. 20G , the control sequence next determines the battery voltage to estimate remaining battery life so that the operator can be alerted if the batteries are near the end of their life cycle. The control sequence continues with step  777  which is a comparison of this measurement of V b     —     load  with a preset voltage threshold V 3  (in  FIG. 20G , V 3  is 3.3V). If V b     —     load  is not below V 3  (determination  777   b ) in step  783 , control apparatus  50  decrements a lock-out counter (internal variable within micro-controller  511 ) by one count in step  783 , and the control sequence continues to step  785 . If V b     —     load  is below V 3  (determination  777   a ), control apparatus  50  increments the lock-out counter by one count (step  779 ) and in step  781  checks to see if the count in the lock-out counter is equal to a preset value (in  FIG. 20G , this preset value is 19). If this count is equal to the preset value (determination  781   a ), the dispenser is locked out from further operation in step  787 . If the count is not equal to the preset value (determination  781   b ), the control sequence continues on to step  785 , during which V b     —     load  is compared with yet another preset voltage threshold V 4  (in  FIG. 20G , V 4  is 4.0V). If V b     —     load  is below V 4  (determination  785   a ), a low-battery counter is incremented by one count (step  791 ), and if V b     —     load  is not below V 4  (determination  785   b ), the low-battery counter is decremented by one count (step  789 ). Step  793  is a comparison of the low-battery counter to yet another preset value (in  FIG. 20G , this preset value is also  19  although it is not required that these two counter preset values be equal). The comparison of step  793  is used to set or clear the low V b     —     load  flag, with a “YES” (determination  793   a ) causing the low V b     —     load  flag to be set and a “NO” (determination  793   b ) causing the low V b     —     load  flag to be cleared. 
     The use of the lock-out and the low-battery counters enables reliable assessment of battery condition by assuring that (1) lock-out occurs only if the value of V b     —     load  is persistently below preset threshold V 3  and that (2) low battery indication is made (blinking LED 2 ) only when V b     —     load  is persistently below preset threshold V 4 . In other words, dispenser  10  is shut down only when it is determined that V b     —     load  is repeatedly below a preset very low threshold V 3 , and the low-battery indication is made only when it is determined that the battery is getting near to the end of its life cycle, that is when V b     —     load  is repeatedly and consistently below preset threshold V 4  which is not as low as V 3 . In this way, anomalous V b     —     load  measurements which may occur due to some outside interference with dispenser operation will not be misinterpreted as an indication of battery condition. 
     Following the setting or clearing of the low V b     —     load  flag in steps  795 - 797 , the measured value of V b     —     load  is averaged in step  799  with its previous (stored) value, and this average value (i.e., the average V b     —     load ) is stored in place of the previously-determined average V b     —     load  value. The average V b     —     load  determined in the then-occurring dispense cycle is the new stored value for the next iteration through the control loop triggered by the next valid user request for a length of sheet material  111 . Put another way, the stored average V b     —     load  is used to determine the motor run time in step  765  of the next dispense cycle; such stored average V b     —     load  does not affect the then-occurring dispense cycle. 
     Referring again to  FIG. 22 , the averaging which takes place in step  799  serves to smooth out the determination of dispense times, decreasing the sensitivity of value of the dispense time to the noise which typically is present in the battery voltage signal due to motor operation. The uneven trace of  FIG. 22  illustrates the variations which can occur in the battery voltage of a dispenser. 
     In this example, for the first dispense cycle after a power-up sequence, the stored value of average V b     —     load  is the initial value of voltage V b     —     load  which is the preset value to which V b     —     load  is set in step  719 . (In  FIG. 20A , the initial value of V b     —     load  is 6.6V.) As a result of the average V b     —     load  determination in step  799 , the average V b     —     load  approaches the actual V b     —     load  within about 5 or 6 dispense cycles resulting in dispense cycles of sufficient time duration to dispense the desired length of sheet material. 
       FIG. 23  illustrates the effect of the averaging determination of step  799  for six sequential dispense cycles following power up.  FIG. 23  is a graph showing the voltage traces of six sequential representative dispense cycles  807   a  through  807   f . As with  FIG. 22 , the voltage traces shown in  FIG. 23  each correspond to battery voltage during motor  267  operation during a dispense cycle. Dispense cycle  807   a  is the first dispense cycle following power up with fresh batteries. The motor run time of dispense cycle  807   a  is of a shorter time duration than the time duration of dispense cycles  807   b  through  807   f . The shorter time duration of dispense cycle  807   a  is the result of V b     —     load  being preset, in this example, to 6.6V. In the averaging step  799  of dispense cycles  807   a  through  807   f , the average V b     —     load  is decreased from the preset 6.6V to the actual V b     —     load  (about 6V for fresh alkaline batteries) resulting in a longer motor run time determination in step  765  and longer time duration dispense cycles  807   b  through  807   f . Dispense cycles  807   e  and  807   f  have near identical time durations indicating that the average V b     —     load  determination in step  799  is approaching the actual V b     —     load . 
     Since the dispense time has passed, motor  267  is turned off in step  801 . The final step of the dispense cycle is step  803  which is a delay for a preset period of time (in  FIG. 20G , this preset time is one second). Also during step  803 , if the low battery flags require that the LED 2  is blinking, such blinking is carried out. After the completion of the preset period of delay, the control sequence within control apparatus  50  returns to the “main” state  721  to begin its sequence of operation once again. 
     Low battery LED indicator lights, such as visible indicator LED 2  (FIG.  17 E), are extremely common in battery-powered devices. One disadvantage of such LED indicators is that, in common practice, the energized state of the LED is not always synonymous with a low battery condition and could be misinterpreted to mean that the dispenser  10  is powered and ready for operation, rather than to signify that the batteries are near the end of their life cycle. As shown in the schematic of  FIG. 17E , LED 2  may be replaced with an audible sound emitter as a low battery indicator. One such audible sound emitter is a magnetic buzzer  809  available from CUI, Inc., Beaverton, Oreg. as part number CEM-1205C. Generation of an audible sound is more likely to be associated with a low battery state and a need to service the dispenser than an indicator light because such sounds are typically associated with a device that requires some sort of service. 
     The dispenser apparatus of the invention may be made of any suitable material or combination of materials as stated above. Selection of the materials will be made based on many factors including, for example, specific purchaser requirements, price, aesthetics, the intended use of the dispenser and the environment in which the dispenser will be used. 
     While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention.