Patent Publication Number: US-7725223-B2

Title: Control arrangement for a propulsion unit for a self-propelled floor care appliance

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The instant application is a continuation-in-part of U.S. patent application Ser. No. 10/677,999 filed on Sep. 30, 2003 now abandoned, which is also incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention is directed to controls for a floor care appliance. Specifically, the present invention relates to a programmable control for controlling the movement of a self-propelled floor care appliance. More specifically, the present invention is directed to a programmable control that adjusts the speed of a floor care appliance in accordance with a preprogrammed response characteristic, such as a non-linear logistic function. 
   BACKGROUND OF THE INVENTION 
   It is known to produce a self-propelled upright vacuum cleaner by providing a transmission in the foot or lower portion of the vacuum cleaner for selectively driving at least one drive wheel in forward rotation and reverse rotation to propel the vacuum cleaner in forward and reverse directions over a floor. A handgrip is commonly mounted to the top of the upper housing in a sliding fashion for limited reciprocal motion relative to the upper housing as a user pushes and pulls on the handgrip to direct the movement of the vacuum cleaner  10 . A Bowden type control cable typically extends from the hand grip to the transmission for transferring the pushing and pulling forces applied to the hand grip by the user to the transmission, which selectively actuates a forward drive clutch and a reverse drive clutch of the transmission so as to propel the vacuum cleaner  10  in similar directions. 
   However, such arrangements provide little or no flexibility in providing for controlling the speed of the propulsion drive motor. That is, the vacuum cleaner typically tends to abruptly move forward and backward, in coordination with the movement of the handgrip. This results in a vacuum that is difficult for the average user to effectively control and maneuver. For example, in environments, such as a living room or bedroom, where the vacuum encounters many obstacles in its path it may be especially difficult for the user to exercise precise control so at to prevent the vacuum cleaner from colliding with such obstacles. Moreover, the abrupt movements of the vacuum cleaner may cause physical injury to the user of the vacuum cleaner as well. 
   Therefore, there is a need for a self-propelled vacuum cleaner that provides a programmable control system that can control the movement of the vacuum cleaner in accordance with various response characteristics. Furthermore, there is a need for a self-propelled vacuum cleaner that provides a programmable control system that controls the movement of the vacuum cleaner in accordance with a logistic function based response characteristic. In addition, there is a need for a self-propelled vacuum cleaner that includes a selection switch that allows an operator to select a desired response characteristic that is to be used to control the vacuum cleaner. Still yet, there is a need for a self-propelled vacuum cleaner that includes a response button that allows an operator to adjust the responsiveness of a particular response characteristic. 
   SUMMARY OF THE INVENTION 
   It is thus an object of the present invention to provide a self-propelled vacuum cleaner that may be controlled in accordance with movements of a handgrip maintained by the vacuum cleaner. 
   It is another object of the present invention to provide a self-propelled vacuum cleaner that moves in accordance with a logistic function based response characteristic. 
   It is yet another object of the present invention to provide a self-propelled vacuum cleaner that utilizes a lookup table maintained by a microprocessor, such that the lookup table maintains a plurality of predetermined digital Hall voltage levels that are each associated with a pulse width modulation (PWM) output level in accordance with the response characteristic. 
   It is still another object of the present invention to provide a self-propelled vacuum cleaner that utilizes a lookup table maintained by the microprocessor, such that the predetermined Hall voltage levels and pulse width modulation (PWM) output levels may be scaled, such that the mathematical relationship between the Hall voltage levels and the PWM output levels is retained. 
   These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements hereinafter described and claimed. 
   In general, a self-propelled floor care appliance comprises a drive motor to propel the floor care appliance over a surface to be cleaned. A Hall effect sensor is positioned in an operative relationship with a handgrip that is maintained by the floor care appliance. Based on the movement of the handgrip, the Hall effect sensor is configured to provide a corresponding Hall voltage. A microprocessor is configured to receive the Hall voltage from the Hall effect sensor, and also stores a response characteristic. The microprocessor supplies a pulse width modulation control signal to the drive motor based upon the Hall voltage and the response characteristic, so as to propel the floor care appliance over the surface to be cleaned. 
   In accordance with another aspect of the present invention, a method for controlling the movement of a microprocessor controlled, motor driven vacuum cleaner in accordance with a movable handgrip comprises the steps of generating a digitized Hall voltage based upon the position of the handgrip. Next, the microprocessor is provided with a response characteristic. After the microprocessor is provided with a response characteristic, a pulse width modulation (PWM) control signal is generated, containing a pulse width modulation output level based on the position of the handgrip and the response characteristic. Finally, the motor is controlled in accordance with the PWM control signal, so as to propel the floor care appliance in accordance with the movement of the handgrip. 
   In accordance with yet another aspect of the present invention, a self-propelled floor care appliance controlled by a moveable handgrip comprises a drive motor to control the movement of the floor care appliance. A Hall effect sensor in operative communication with the handgrip is configured to generate a Hall voltage based on the movement of the handgrip. A microprocessor, which maintains a lookup table, is coupled to the Hall effect sensor. The lookup table associates a plurality of predetermined digital Hall voltage levels with predetermined pulse width modulation (PWM) output levels in accordance with a logistic response characteristic. Wherein the microprocessor outputs a pulse width modulation (PWM) control signal to the drive motor, such that the PWM control signal includes one of said PWM output levels associated with Hall voltage output by the Hall effect sensor in accordance with the lookup table. 
   A preferred exemplary self-propelled vacuum cleaner incorporating the concepts of the present invention is shown by way of example in the accompanying drawings without attempting to show all the various forms and modifications in which the invention might be embodied, the invention being measured by the appended claims and not by the details of the specification. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Embodiments of the invention, illustrative of several modes in which applicants have contemplated are set forth by way of example in the following description and drawings, which are particularly and distinctly pointed out and set forth in the appended claims. 
       FIG. 1  is a perspective view of a vacuum cleaner which includes the present invention; 
       FIG. 2  is the vacuum cleaner of  FIG. 1  with a partial cutaway portion of the housing with the handle in the in use position; 
       FIG. 3  is a cutaway portion of the upper handle with a partial cutaway portion of the handgrip showing the Hall effect sensor and magnet; 
       FIG. 4  is an electrical schematic of the control circuit having a programmable microprocessor for controlling a propulsion arrangement having a variable and user selectable response characteristic; 
       FIG. 5A  is a graphical display of the voltage generated by the Hall effect sensor that is input to the microprocessor as a function of time, according to the preferred embodiment of the present invention; 
       FIG. 5B  is a graphical display of the voltage applied to the propulsion motor as a function of time based upon the input to the microprocessor from the Hall effect sensor as shown in  FIG. 5A , according to the preferred embodiment of the present invention; 
       FIG. 5C  is a graphical display of the voltage applied to the propulsion motor as a function of time based upon the input to the microprocessor from the Hall effect sensor as shown in  FIG. 5A , according to an alternate embodiment of the present invention; 
       FIG. 5D  is a graphical display of the voltage applied to the propulsion motor as a function of time based upon the input to the microprocessor from the Hall effect sensor as shown in  FIG. 5A , according to another alternate embodiment of the present invention; 
       FIG. 6  is a graphical display of a response characteristic comprising a non-linear logistic function used to generate PWM signals based on the voltage output of the Hall sensor according to the position of the handgrip; and 
       FIG. 7  is a graphical display of a lookup table maintained by the microprocessor which represents a plurality of digital Hall voltage levels that are associated with corresponding discrete PWM output levels in accordance with the logistic function based response characteristic. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A self-propelled upright vacuum cleaner  10  is generally referred to by the numeral  10 , as shown in  FIG. 1  of the drawings. The vacuum cleaner  10  comprises a foot or lower engaging portion  100  that maintains an agitator (not shown) and an agitator chamber (not shown) that is formed in an agitator housing (not shown). The agitator chamber communicates with a nozzle opening (not shown), while the agitator rotates about a horizontal axis inside the agitator chamber, so as to loosen dirt from a floor surface. A suction airstream generated by a motor-fan assembly (not shown) draws the loosened dirt into a suction duct (not shown) located behind, and fluidly connected to the agitator chamber. The suction duct directs the loosened dirt to a dirt particle filtration and collecting system (not shown), which is positioned in an upper housing  200 . Freely rotating support wheels  6  (only one of which is visible in  FIG. 1 ) are located to the rear of the foot  100 . The foot  100  further includes a transmission  108  and drive wheels  110  for propelling the vacuum cleaner  10  in forward and reverse directions over a floor. A rotary power source, such as an electric motor  105 , provides rotary power to the transmission  108 . A suitable transmission for use with a self-propelled upright vacuum cleaner according to the present invention is disclosed in U.S. Pat. No. 3,581,591, the disclosure of which is herein incorporated by reference. 
   The upper housing portion  200  of the vacuum cleaner  10  is pivotally mounted to the foot  100  to allow pivotal motion from a generally upright latched storage position, as illustrated in  FIG. 1 , to an inclined pivotal operating position, as shown in  FIG. 2 . In one embodiment of the present invention, the vacuum cleaner  10  is similar to the indirect air bagless vacuum cleaner 10 disclosed in U.S. patent application Ser. No. 10/417,866, which is incorporated herein by reference. In an alternate embodiment of the present invention, the vacuum cleaner  10  may be a direct air vacuum cleaner or any other type of floor care appliance. 
   In one embodiment of the present invention, a handgrip  114  is slidably mounted to a handle stem  116  that is attached to the upper end of the upper housing portion  200 . This arrangement allows for limited reciprocal rectilinear motion of the handgrip  114  relative to the handle stem  116 , as illustrated by arrows F and R. The handgrip  114  controls the speed and direction of the drive wheels  110 , via motor  105  and transmission  108 , using an electronic switching arrangement. Shown in  FIG. 3 , the electronic switching arrangement comprises an analog linear Hall effect sensor  310  located in proximity to a magnet  305 . The Hall effect sensor  310  generates an analog Hall voltage, the magnitude of which corresponds to the position of the Hall effect sensor  310  in relation to the magnet  305 . The Hall voltage is input to a control circuit  400 , shown in  FIG. 4 , that maintains a microprocessor  450 , and associated electrical components to be discussed to control the speed and direction of the motor  105 . It should be appreciated that the microprocessor  450  may comprise an application specific or general purpose processor having the necessary combination of hardware, software, and memory to carryout the functions to be described below. In addition, the memory utilized by the microprocessor  450  could be comprised of non-volative memory or a combination of non-volatile memory and volatile memory. It should also be appreciated that while the voltage output by the Hall sensor  310  is an analog voltage, it is converted into a digital or discrete voltage level using known techniques to be discussed. Finally, returning to  FIG. 3 , the vacuum cleaner  10  includes a power switch  304  that is preferably located adjacent to the top of the handle stem  116 , near the handgrip  114 , for conveniently turning the vacuum cleaner  10  on and off. 
   During operation of the cleaner  10 , movement of the handgrip  114  in the direction of arrow F causes the microprocessor  450  to generate the necessary signals to propel the cleaner  10 , via the drive wheels  110 , in the direction of arrow F′. Similarly, movement of the handgrip  114  in the direction of arrow R, causes the microprocessor  450  to propel the vacuum cleaner  10 , via drive wheels  110 , in the direction of arrow R′. The speed by which the cleaner  10  is propelled in the forward F′ and reverse R′ directions is dependent on the position of the handgrip  114 , and on a pre-programmed response characteristic maintained by the microprocessor  450 . In other words, the movement speed and the responsitivity of the vacuum&#39;s movement to the actuation of the handgrip  114  is dictated by both the response characteristic and the position of the handgrip  114 , as it is moved during operation of the vacuum cleaner  10 . 
   The various response characteristics control the speed and responsiveness of the motor  105 , based on the position of the handgrip  114 . Specifically, response characteristics may embody a mathematical expression, function, or algorithm, and can be represented graphically as illustrated in  FIGS. 5B-5D , and  FIG. 6 , which will be more fully described herein below. In one aspect, as shown in  FIGS. 1-3 , a selection switch  470  coupled to the microprocessor  450 , may be provided to allow a user to select one of several possible response characteristics stored in the memory of the microprocessor  450  for use during operation of the vacuum cleaner  10 . For example, the microprocessor  450  may maintain a responsive response characteristic that is highly responsive for use when the vacuum cleaner  10  is used in tight areas, and a response characteristic having a smooth response may be used for when the vacuum cleaner  10  is used in large, open areas, for example. Furthermore, response characteristics can be initially programmed into the microprocessor  450  at the time of manufacturing or may be added later via a connection (not shown) to a computer (not shown) or computer network (not shown). It should also be appreciated that the response characteristics may be wirelessly transmitted from a computing device to the microprocessor  450 , if the microprocessor  450  is provided with a suitable receiver or transceiver configured to receive wireless signals therefrom. 
   A schematic view of the control circuit  400  for providing and controlling the power supplied to the motor  105  in accordance with various response characteristics is shown in  FIG. 4 . Specifically, the control circuit  400  includes a 120V AC (alternating current) power source  405  that is connected to a full Wheatstone bridge  407  to convert the AC power into 170V DC (direct current) power. A 220 uF smoothing capacitor  409  smooths the 170V DC power delivered from the bridge  407 . A 2.2K ohm resistor  411 , and a Zener diode  413  having a 33V zener voltage, clamps the voltage across its terminals to 33V, which is input to a voltage regulator  415 , which outputs a regulated 15V DC that is supplied to an H-Bridge motor driver  423 . The H-Bridge motor driver  423  is of a well known type using MOSFETS (metal-oxide field effect transistors) to control the current supplied to the motor  105 . The 15V DC output from the 15V voltage regulator  415  is input to a 5V voltage regulator  417 , which outputs a regulated 5V DC to the microprocessor  450 . The analog Hall voltage output from the Hall effect sensor  310 , determined by the relative position of the handgrip  114 , is input to pin  451  of the microprocessor  450 , whereby it is digitized into a digital or discrete voltage level via an analog-to-digital converter or ADC. In addition to digitizing the Hall voltage, the microprocessor  450  analyzes the magnitude of the digitized voltage level of the Hall voltage so as to determine which direction the handgrip  114  is moved. Specifically, the ADC may utilize 8 bits to represent the analog Hall voltage of as one of 256 discrete voltage levels, for example. However, an 8-bit ADC is not required for the operation of the present invention, as the ADC may utilize any number of bits. Moreover, as the number of bits utilized by the ADC increases, so does the precision and the smoothness in which the handgrip  114  is able to control the forward F′ and reverse R′ movement of the vacuum cleaner  10 . It should be appreciated that the ADC may be maintained as a discrete component, separate from the microprocessor  450 , or may be directly integrated within the logic and circuitry of the microprocessor  450 . 
   Continuing with the discussion of the control circuit  400 , a charge pump circuit charges the external capacitors  432 ,  433  between the output pins OUT 1  and OUT 2 , and the VB 1  and VB 2  pins. Capacitors  432 ,  433  provide suitable voltage to the high side driver circuit so as to drive the high side MOSFET of the H-bridge  423 . The charging process occurs when the output voltage is low. A pair of resistors  429 ,  431  and a pair of diodes  433 ,  434  form a current limiting circuit that limits the current flowing to pins VB 1  and VB 2 . A resistor  427  connected to the low side output pin LS is used as a current sense to determine if a stall of the motor  105  has occurred during operation of the vacuum cleaner  10 . If a motor stall has occurred, then the control circuit  400  shuts down the motor  105 . An RC network comprised of a resistor  425  and a capacitor  426  has the ability to shut down the control circuit  400  if the current through the control circuit  400  reaches a fixed level. The varying current in the control circuit  400  charges and discharges the RC network, and when the RC network reaches a predetermined level based upon component selection, the control circuit  400  shuts down. A pair of current limiting resistors  421 ,  422  limit the current between the forward F and reverse R outputs on the microprocessor  450 , and the inputs L1 and L2 on the H-Bridge motor driver  423 . In an embodiment of the present invention, the values of the various components may be as follows: capacitor  409 =220 uF; resistor  411 =2.2K ohm; diode  413 =33V zener diode voltage; capacitor  419 =0.1 uF; diodes  433 ,  434 =200V, 1 amp; resistors  429 ,  431 =30 ohm; capacitors  432 ,  433 =4.7 uF; resistors  421 ,  422 =10K ohm; resistor  427 =0.25 ohm; resistor  425 =1M ohm; and capacitor  426 =220 uF. In addition, these values should not be construed as limiting as the components used to form the control circuit  400  may comprise different electrical values and ratings than that of the example previously discussed, without affecting the operation of the control circuit  400 . 
     FIG. 5A , shows the varying Hall voltage that is input to the microprocessor  450 , as the handgrip  114  is moved from the neutral position to the maximum forward speed position F, and to the maximum reverse speed position R. Specifically, when the handgrip  114  is in the neutral position, the Hall effect sensor  310  outputs a Hall voltage of approximately 2.5 volts. As the handgrip  114  is moved from the neutral position to the maximum forward position in the direction F, the Hall voltage increases in a substantially linear manner from 2.5 volts to a maximum of approximately 5 volts, thus indicating the maximum forward speed of the vacuum cleaner  10 . Alternatively, as the handgrip  114  is moved from the neutral position of 2.5 volts to the maximum reverse position in the direction R, the Hall voltage decreases in a substantially linear fashion from 2.5 volts to 0 volts, thus indicating the maximum reverse speed of the vacuum cleaner  10 . The microprocessor  450 , in response to the receipt of the various Hall voltages described, generates a PWM control signal based on the preprogrammed response characteristics shown in  FIGS. 5B-5D  to control the movement of the vacuum cleaner  10 . 
     FIGS. 5B-5D  depict various response characteristics that may be utilized by the vacuum cleaner  10  in accordance with the concepts of the present invention. Thus, each of the response characteristics  5 B- 5 D determines the particular responsiveness that is delivered by the motor  105  in response to movements of the handgrip  114 . Therefore, for a given Hall voltage identified in  FIG. 5A , the microprocessor  450  generates an associated PWM control signal in accordance with one of the response characteristics  5 B- 5 D that is being used. In accordance with the response characteristic shown in  FIG. 5B , as the handgrip  114  is moved linearly in the forward direction F, the Hall voltage begins to increase to a maximum of 5V, while the voltage of the PWM control signal applied to the motor  105  via the microprocessor  450  rises proportionally, and begins to smooth off as the maximum voltage of 170 volts is applied to the motor  105 . As the handgrip  114  is pulled back in the reverse direction R, the Hall voltage begins to drop back to a low of 2.5 volts (neutral) as the handgrip  114  returns to the neutral position. As the handgrip  114  is pulled further into the reverse direction R, the Hall voltage drops from 2.5 volts (neutral) to a low of 0 volts when the handgrip  114  is in the maximum reverse speed position. The microprocessor  450  pulse width modulates the voltage carried by the PWM control signal to the motor  105  via the H-bridge motor driver  423 , so that the voltage delivered to the motor  105  will first begin to drop in a smooth manner and then proportionally based on the position of the handgrip  114  as it is pulled from the forward speed position towards the neutral position. 
   Similarly, the microprocessor  450  pulse width modulates the voltage carried by the PWM control signal to motor  105 , so that the voltage delivered to the motor  105  increases proportionally during the travel of the handgrip  114  in the reverse direction R, and begins to smooth off as the maximum of 170 volts is reached. If the handgrip  114  is moved from the neutral position in a linear manner, as shown in  FIG. 5A , the response of the motor  105  will be linear for the majority of the travel of the handgrip  114 , except as the handgrip  114  approaches the maximum forward and reverse operating speeds as seen in  FIG. 5B . If the handgrip  114  is not moved from the neutral position in a linear fashion, as demonstrated by the portion of the line graph to the right in  FIG. 5A , the response of the motor  105  will not be linear as it approaches operating speed as demonstrated by the portion of the line graph to the right in  FIG. 5B . 
   In an alternate embodiment of the present invention, and referring now to  FIG. 5C , the microprocessor  450  can be programmed with a response characteristic to pulse width modulate the voltage carried by the PWM control signal to the motor  105 , via the H-bridge  423 , so that the voltage increases linearly to operating speed, as the handgrip  114  is moved in the forward F or reverse R directions. Once the handgrip  114  is in the fully forward or reverse positions, the voltage delivered to the motor  105  is then capped at a peak voltage and will stay at that voltage until the handgrip  114  is released, at which time the voltage will drop in a linear fashion until it reaches zero. If the handgrip  114  is not moved in a linear fashion in the forward F and reverse R directions (as demonstrated by the right portion of  FIG. 5C ) the microprocessor  450  still pulse width modulates the voltage applied to motor  105  via the H-bridge  423  so that the voltage increases linearly to the operating speed and will remain constant until the handgrip  114  is moved again in either direction. 
   In another embodiment of the present invention, the microprocessor  450  may be programmed with a response characteristic that generates the response shown in  FIG. 5D , which will be discussed in detail below. As the handgrip  114  is moved linearly in the forward F or reverse R directions, the microprocessor  450  pulse width modulates the voltage carried by the PWM control signal to the motor  105 , so that the voltage increases linearly at a higher rate towards operating speed, but is smoothed slightly just before operating speed is reached. Once operating speed is reached, the voltage remains constant until the handgrip  114  is released, at which time the voltage will begin to drop smoothly at first but then decreases in a linear fashion until it reaches zero. If the handgrip  114  is not moved in a linear fashion in the forward and reverse directions (as demonstrated by the right portion of  FIG. 5D ) the microprocessor  450  still pulse width modulates the voltage carried by the PWM control signal to the motor  105 , so that the voltage increases at the same aforesaid linear rate, but is smoothed just before the operating speed is reached. The voltage will remain constant until the handgrip  114  is moved again in either direction, at which point the voltage will either smoothly increase or decrease before increasing or decreasing at the aforesaid linear rate. Although specific examples of the various response characteristics having different responses or response attributes that may be used to control the operation of the motor  105  have been disclosed, there are many other possible response characteristics that may be programmed into the memory of the microprocessor  450 . For example, various response attributes may be comprised of different rates of acceleration and deceleration, such as exponential or linear rates, of the movement of the cleaner  10 , in response to the movements of the handgrip  114 . 
   The response characteristics discussed with respect to  FIGS. 5B-5D  while shown as graphs, are embodied as lookup tables maintained by the memory of the microprocessor  450 . The lookup table contains a range of predetermined digital Hall voltage levels that are each associated with a specific PWM output level or magnitude, carried by the PWM control signal control signal to the motor  105 . As such, the microprocessor  450  is able to lookup the voltage level to be applied to the motor  105  based on the particular Hall voltage generated by the position of the handgrip  114 . 
   In another embodiment of the present invention, two Hall effect sensors with a single magnet could be utilized as a triggering mechanism having two voltages, which are input to the microprocessor  450  for controlling the motor voltage and direction. Alternately, instead of a moving handgrip, a wheel sensor (not shown) could be utilized to detect the movement of the cleaner suction nozzle when the user pushes or pulls on the cleaner handgrip  114 . The wheel sensor could sense the speed and detect both the amount of force transmitted to the suction nozzle via the handle and produce a representative voltage, which is input to the microprocessor  450 . The microprocessor  450  may then use pulse width modulation on L1, L2, H1 and H2 to control direction and speed of motor M. Of course microprocessor  450  can be programmed with any desired response characteristic to provide a desired output to the motor  105  based on the position of the handgrip  114 . 
   In another embodiment of the present invention, a graphical depiction of a response characteristic based upon a non-linear logistic function is referred to by the numeral  500  as shown in  FIG. 6  of the drawings. The logistic function may be defined by the equation: 
               tanh   ⁡     (   t   )       =         ⅇ   t     -     ⅇ     -   t             ⅇ   t     +     ⅇ     -   t             ,         
which is also referred to in the art as the hyperbolic tangent function. Specifically, the response characteristic  500  of  FIG. 6  shows the change of the PWM (pulse width modulation) output level with respect to change in Hall voltage due to the movement of the handgrip  114 . In other words, the logistic response characteristic  500  determines the level (or percentage) of pulse width modulation (PWM) that the PWM control signal will use to drive the motor  105  based on the value of the Hall voltage, so as to control the movement of the vacuum cleaner  10  in forward F′ and reverse R′ directions. It should be appreciated that an increase in PWM output level corresponds to an increase in motor speed, while a decrease in PWM output level corresponds to a decrease in motor speed.
 
   In general, the logistic function is used to model natural phenomena, such as bacterial growth, human population growth and the like. Thus, due to the ability of the logistic function to model naturally occurring phenomena, its use as a response characteristic, provides the user with a natural and fluid control to the movement of the self-propelled vacuum cleaner  10  as it is moved in forward F′ and reverse R′ directions by the handgrip  114 . 
   For example, as the handgrip  114  is moved in the forward direction F from the neutral position  510 , the Hall voltage initially increases, such that various regions that determine the PWM output level of the microprocessor  450  are encountered. Specifically, when the analog Hall voltage is between 2.5V and 3.25V the forward starting region  520  is encountered, whereby a slow exponential increase in motor speed is provided. When the Hall voltage increases between 3.25V and 4.25V, the forward linear region  540  is encountered, whereby a linear change in motor speed is provided. Finally, when the Hall voltage is between 4.25V and 5V the forward saturation region  560  is encountered, such that the linear response in motor speed is terminated by a gradual exponential decay, as the maximum forward speed of the motor  105  is attained. Correspondingly, as the handgrip  114  is moved in the reverse direction R, the Hall voltage decreases, such that between 2.5V and 1.75V the reverse starting region  530  is encountered, whereby a slow exponential increase in reverse motor speed is provided. As the Hall voltage decreases between 1.75V and 0.75V the reverse linear region  550  is encountered, whereby a linear change in motor speed is provided. Finally, when the Hall voltage decreases to between 0.75V and 0V the reverse saturation region  570  is encountered such that the linear response in motor speed is terminated by a gradual exponential decay, as the maximum reverse speed of the motor  105  is attained. 
   Prior to discussing the effects that the response characteristic  500  has on the responsiveness of the movement of the vacuum  10  in response to a user&#39;s control, a brief discussion of the operation of the vacuum cleaner  10  will be provided. During operation of the vacuum cleaner  10 , the magnitude of the digitized Hall voltage generated in a manner previously discussed varies linearly, at a given rate, based upon the position of the handgrip  114 . Next, as the Hall voltage changes due to the movement of the handgrip  114 , the regions  520 - 570  of the logistic response characteristic  500  are processed by the microprocessor  450 . Thus, the microprocessor  450  accesses the lookup table and identifies the PWM output level associated with the specific Hall voltage currently being generated by the handgrip  114 . Once the PWM output level is identified, the microprocessor  450  sends a forward or reverse PWM control signal having the identified PWM output level to the motor  105  to propel the vacuum cleaner  10 . 
   The process of generating a PWM output level for a specific Hall voltage is completed by a lookup table maintained by the microprocessor  450 . Specifically, the lookup table maintains a plurality of digital Hall voltage levels, each of which are related to a specific PWM output level that is established in accordance with the logistic response characteristic  500 . By maintaining the Hall voltage levels in a lookup table, the microprocessor  450  can scale the number of Hall voltage levels used, so that different levels of responsiveness with different maximum PWM output levels can be created, while still retaining the specific mathematical characteristics defined by the logistic function  500 . In one aspect, a response button  590  coupled to the microprocessor  450  as shown in  FIG. 5  may be used to initiate the re-scale of the number of Hall voltage levels used by the lookup table. In other words, the number of digital voltage levels used by the lookup table may be increased or decreased as desired by the actuation of the response button  590 . 
     FIG. 7  graphically shows an exemplary lookup table using the response characteristic  500  for forward and reverse movements of the vacuum cleaner  10 . Moreover,  FIG. 7  shows the logistic function based relationship between a plurality of digitized Hall voltage levels (0 to 256) and each digital PWM output level (0 to 256) that is associated therewith. For the purposes of clarity, due to the inherent operation of the H-bridge motor driver  423 , the reverse response characteristics  600 B,  610 B, and  620 B are discontinuous with the forward response characteristics  600 A,  610 A, and  620 A maintained by the lookup table. However, it should be apparent from  FIG. 7  that when moving the handgrip  114  in the reverse direction R, the vacuum cleaner begins to move in the reverse direction R′, and when the handgrip  114  is moved in the forward direction F, the vacuum cleaner  10  begins to move in the forward direction F′. Continuing, un-scaled forward and reverse response characteristics  600 A and  600 B based on the logistic response characteristic  500  shown in  FIG. 6 , illustrates the response that is generated when the lookup table utilizes 128 Hall voltage levels to represent both the forward F and reverse R movements of the handgrip  114 . In contrast, response characteristics  610 A and  610 B show the response that is generated when the lookup table is re-scaled, and only 64 Hall voltage levels are used to represent the forward F and reverse R movements of the handgrip  114 . By scaling the lookup table in such a manner, the maximum PWM output level is decreased by half, while the responsiveness has increased, as compared to the un-scaled response characteristics  600 A and  600 B that each use 128 discrete Hall voltage levels as previously discussed. As such, the vacuum cleaner  10 , is only able to be propelled in the forward F′ and reverse R′ directions at half the speed that would be possible using the un-scaled response characteristics  600 A,  600 B. Moreover, the resealing process performed by the microprocessor  450 , is completed such that the mathematical relationship established by logistic function  500  is retained by the response characteristics  610 A and  610 B. In other words, the scaled response characteristics  610 A and  610 B retain the exponential increase in the starting regions  520 , 530 , the linear ramp in the linear regions  540 , 550 , and the exponential decay in the saturation regions  560 , 570  of the original response characteristic  500  shown in  FIG. 6 . 
   In addition to resealing the hyperbolic tangent function, it may also be modified by multiplying the hyperbolic tangent function, tanh(t), by a coefficient Z, such that: 
             Z   ·     tanh   ⁡     (   t   )         =     Z   ·           ⅇ   t     -     ⅇ     -   t             ⅇ   t     +     ⅇ     -   t           .             
The use of the coefficient Z allows the logistic function  500  to be altered to provide modified PWM output level responses, as needed to allow the vacuum cleaner  10  to be controlled more efficiently when operated under specific operating conditions. For example, if the vacuum cleaner  10  is being used to vacuum small areas or various types of carpet, the logistic function  500  could be altered to achieve a customized response characteristic that is suited for use in tight or cramped areas. Moreover, the modification of the logistic function by a suitable coefficient Z, allows the user to tailor the responsiveness of the vacuum cleaner&#39;s movement to the actuation of the handgrip  114  according to the user&#39;s vacuuming technique and physical size and ability. For example, as shown in  FIG. 7 , by providing a suitable coefficient Z, forward and reverse response characteristics  620 A and  620 B may be created to provide a responsiveness that is approximately 50% slower than that of the un-scaled forward and reverse response characteristics  600 A and  600 B. Thus, it is contemplated that the response button  590  may provide various positional settings that allows a user of the vacuum cleaner  10  to select the particular coefficient Z used to alter the PWM output levels generated by the logistic function  500 .
 
   The following discussion will set forth the particular operation of the vacuum cleaner  10  using the logistic response characteristic  500 , as the user actuates the handgrip  114  to move the vacuum cleaner  10  in forward F′ and reverse R′ directions. Although the following discussion relates to the use of the logistic response characteristic  500  as shown in  FIG. 6 , it should be appreciated that the microprocessor  450  controls the motor  105  in accordance with the response characteristic  500  by utilizing the lookup table values comprising the digitized PWM output levels and digitized Hall voltage levels that embody the response characteristic  500  as previously discussed. 
   Initially, before the vacuum cleaner  10  is put into operation, the handgrip  114  rests in a neutral position  510 . Additionally, the following discussion makes reference to PWM output levels in terms of percentage values. As such, an increase in the PWM output level percentage corresponds to an increase in motor speed, while a decrease in the PWM output level percentage corresponds to a decrease in motor speed. In neutral, the Hall sensor  310  outputs a voltage of approximately 2.5V, which corresponds to a PWM output signal having a PWM output level of approximately 0%. As the user urges the handgrip  114  in the forward direction F, within the forward starting region  520 , the PWM output level slowly increases in an exponential manner, until it reaches a PWM level of approximately 25%, causing the vacuum cleaner  10  to slowly move forward. As the handgrip  114  continues to be moved forward, the forward linear region  540  is reached, where user adjustments to the movement of the handgrip  114  results in a linear response or change in motor speed and corresponding vacuum cleaner movement. If the user continues to move the handgrip  114  forward, he or she eventually reaches the end of the linear region, which corresponds to a PWM level of approximately 75%. With continued forward movement of the handgrip  114 , the forward saturation region  560  is reached, whereby the linear rate of increase provided by the forward linear region  540  begins to slowly decay in an exponential manner, until a maximum PWM level of 100% is delivered to the motor  105 , causing the vacuum cleaner  10  to move full speed in the forward direction F′. 
   Alternatively, when the handgrip  114  is moved from the neutral position  500 , in the reverse direction R, the reverse starting region  530  is encountered whereby, the PWM output level slowly increases in an exponential manner, until it reaches a PWM level of approximately 25%. As the handgrip  114  is continued to be moved in the reverse direction R, the reverse linear region  550  is reached, where adjustments to the movement of the handgrip  114  result in a linear response or change in motor speed and movement of the vacuum cleaner  10 . If the user continues to move the handgrip  114  in the reverse direction R, he or she eventually reaches the end of the reverse linear region  550 , which corresponds to a PWM output level of approximately 75%. With continued movement of the handgrip  114  in the reverse direction R, the reverse saturation region  570  is reached, whereby the linear rate of increase provided by the reverse linear region  550  begins to slowly decay in an exponential manner, until a maximum PWM level of 100% is delivered to the motor  105 , causing the vacuum cleaner  10  to move full speed in the reverse direction R′. 
   It will, therefore, be appreciated that one advantage of one or more embodiments of the present invention is that a self-propelled vacuum cleaner may be controlled via movements of a handgrip. Yet another advantage of the present invention is that the self-propelled vacuum cleaner utilizes a logistic function based response characteristic to provide a natural and fluid movement of the vacuum cleaner in response to the movements of the handgrip. Still another advantage of the present invention is that a lookup table stored by the microprocessor, and maintained by the self-propelled vacuum cleaner, may be scaled as desired so as to create a variety of response characteristics.