Abstract:
The present invention relates generally to manually controlling an apparatus and/or a multiplexer. More particularly, the present invention relates to controlling an apparatus and/or a multiplexer by signals that preferably include both proportional-output signals and rate-of-change signals. The signals may be generated by either tilt transducers or switches capable of producing an “on” and “off” signal. The signals may be used to control a primary apparatus connected to a control means and may alternatively be used to control a secondary apparatus connected to the same control means.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims benefit of priority to and is a continuation of U.S. Provisional Pat. Application Ser. No. 61/770,904, filed Feb. 28, 2013, and entitled METHOD AND SYSTEM FOR CONTROL OF APPARATUS (Lautzenhiser), which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to manually controlling an apparatus and/or a multiplexer. More particularly, the present invention relates to controlling an apparatus and/or a multiplexer by signals that preferably include proportional-output signals, rate-of-change signals, and open/closed output signals. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years there has been an increasing awareness of the importance, not only providing for the needs of handicapped persons, but also of utilizing them as productive members of society, rather than keeping them partially or wholly dependent upon others. 
         [0006]    Fortunately, this enlightened view has coincided with giant strides in technology, particularly electronics and computer-based technology, and this increase in technology has been reflected by giant strides in electrically-propelled wheelchairs. 
         [0007]    The prior art includes electrically-propelled wheelchairs in which control of start, stop, and steering has been achieved by manually-actuated X-Y transducers, commonly called “joysticks.” 
         [0008]    Lautzenhiser et al., in U.S. Pat. No. 4,906,906, issued 6 Mar. 1990, and in U.S. Pat. No. 4,978,899, issued 18 Dec. 1990, teach wheelchairs that are propelled by pulse-width-modulated voltages, that are dynamically braked by shorting the motors, that are made freewheeling without the expense and complexity of a clutch, and in which tremor control is provided, so that those who have hand tremors can easily and accurately control power wheelchairs. 
         [0009]    The prior art includes attempts to control wheelchairs by sipping or puffing on a tube. However, controllability of sip-and-puff units has been marginal, especially for those who depend upon a respirator or ventilator for breathing, since they can puff into a tube only while exhaling, and sipping is even more difficult. 
         [0010]    In U.S. Pat. No. 5,635,807, which issued on 3 Jun. 1997, Lautzenhiser teaches electric control systems that provide nonlinear relationships between X-Y mechanical inputs and resultant differential speeds of two propulsion motors. These nonlinear relationships between X-Y mechanical inputs and electrical outputs allow many handicapped persons, who otherwise would be limited to sip-and-puff systems, to control a wheelchair by joystick movement. 
         [0011]    Perhaps even more significantly, when a joystick is replaced with two tiny transducers or input devices that are mounted to a person&#39;s head, or to an other body member, these nonlinear relationships allow easy and accurate control of both speed and steering of power wheelchairs by means of body-component movements. For instance, a person who is paralyzed from the neck down can perform all control functions of an electrically propelled wheelchair except for connecting and disconnecting power to the system. 
         [0012]    In U.S. Pat. No. 5,635,807, Lautzenhiser also provides adjustable transducer sensitivity, steering sensitivity control that is adjustable, selectively-adjustable signal limiting so that maximum speeds can be selectively adjusted, and overrange shutdown. 
         [0013]    In U.S. patent application Ser. No. 09/652,395, filed 31 Aug. 2000, Lautzenhiser et al. teach a tilt-axis X-Y input device that may be mounted to a body component, such as the head or a hand of a user, null compensators that automatically compensate for errors in attaching the X-Y input device to a head or other body component, a null-width generator that adjustably provides a neutral zone to help an operator find and hold a neutral position, a turn-signal conditioner that provides easier control of turns including elimination of “fishtailing,” tremor control for those with body tremors, adjustable tilt-axis sensitivity to selectively match the motor skills of the user, and overrange shutdown as a safety feature. 
         [0014]    In the same patent, Lautzenhiser et al. teach control of a second device, such as a computer and its cursor, both of which may utilize voice-recognition technology to provide the required switching functions. 
         [0015]    Even with the great strides that have been provided by head and other body-component control of both speed and turns of power wheelchairs, much still needs to be accomplished. Many still are unable to control their own safety except by the use of a call button. Many are unable to control their own comfort and productivity needs, such as adjusting leg supports, head supports, backrests, heating, cooling, and lighting. And many are unable to control productivity devices, such as computers, and entertainment devices, such as radio or television. 
         [0016]    In the industry, apparatus for controlling safety, productivity, comfort, and entertainment devices have been called “Environmental Control Units” (ECU). Therefore, this terminology is used extensively in the detailed description. 
         [0017]    Furthermore, there are many individuals whose condition has left them unable to operate a power wheelchair using normal control methods. These individuals may have very limited control over their head and other body-member. For these individuals, using their head or single body-member to control both X and Y movement may be difficult or impossible. What is needed is a control method to enable individuals with extremely limited physical ability to control a power wheelchair or ECU using only a single range of motion in their head or other body-member. 
       BRIEF SUMMARY OF THE INVENTION 
       [0018]    The present invention includes rate-of-change control devices, timed-opportunity switches, and multiplexers. 
         [0019]    More particularly, the present invention provides rate-of-change control devices that actuate in response to adjustable rate-of-change thresholds, timed-opportunity switches that can be actuated by one or more appropriately-timed inputs, and multiplexers, that can be used by physically-handicapped persons to control such things as wheelchair and hospital bed positioning actuators, lighting, entertainment, communication, computer and productivity devices. 
         [0020]    The timed-opportunity switches and the multiplexers can be actuated by any type of momentary-contact switch. However, preferably, the rate-of-change control devices of the present invention are used in combination with mechanical-to-electrical transducers. 
         [0021]    With regard to the rate-of-change control devices, repeated ones of output signals, from transducers such as X-Y tilt sensors, are differentiated with respect to time, and then discriminated to provide rate-of-change switching functions that can be used to control start-up (power on) of power wheelchairs, to control additional external devices, and/or to provide a safety shutdown for power wheelchairs. Additionally, the rate-of-change control devices may be used to control wheelchair and hospital bed positioning actuators, lighting, entertainment, communication, computer and productivity devices 
         [0022]    If an input position of a mechanical-to-electrical transducer is “y,” then the output is equal to f(y). Thus, it is equally accurate to speak of differentiating the input or the output, although from a practical standpoint, the electrical output is differentiated. 
         [0023]    While highly successful results have been achieved by differentiating only once, thereby producing values that are a function of the velocity of the input “y,” alternately, the electrical outputs are differentiated twice, thereby providing values that are a function of the acceleration of the input “y.” 
         [0024]    The rate-of-change control devices have two basic advantages. One is that they can use the output of transducers, such as head-attached X-Y tilt sensors that are used to control speed and steering of wheelchairs, to provide switching functions. An other advantage is that the rate-of-change control devices are self-centering, or self-nulling. That is, they function by differentiating an output, and the differential of a constant is zero. Therefore, when an output of a transducer is constant, the rate-of-change control device does not produce an output. 
         [0025]    By differentiating signals generated by a two-axis transducer, such as an X-Y tilt sensor, two rate-of-change signals are produced for each axis, one for an increase in the output signal, and one for a decrease in the output signal. 
         [0026]    Preferably, the rate-of-change control device that is used with the timed-opportunity switch and the signal conditioner that is shown herein, produces a single switching output from the four rate-of-change signals. 
         [0027]    That is, switching occurs when any one of four rates-of-change is beyond a preselected threshold. For instance, when used with a head-attached X-Y input device, a nod of the head can be used to produce a logic “1” output, and returning the head to a level position can be used to produce a second logic “1” output. 
         [0028]    In a simplified embodiment of the rate-of-change control devices that are included herein, two rate-of-change switching outputs are produced in response to outputs from a single-axis transducer. One rate-of-change output is produced whenever the rate-of-change of an increasing output exceeds a predetermined magnitude. And, the other rate-of-change output is provided whenever the rate-of-change of a decreasing output exceeds a predetermined magnitude. However, this embodiment can be simplified further by eliminating one comparator. Then, only one output will be produced. 
         [0029]    In a slightly more complex embodiment of the rate-of-change control devices, two rate-of-change switching outputs are produced from a single-axis transducer, the two rate-of-change outputs are combined to produce a single switching output, and the single switching output is used to control a relay. 
         [0030]    In other embodiments of the rate-of-change control devices, switching outputs are produced that are combinations of one or more sequential rate-of-change signals. For instance, an “1” output can be made to equal A AND B, by holding A until B occurs, or visa versa. 
         [0031]    Or a logic “1” can be made to equal “A AND A,” where “A AND A” refers to two “A” signals that are sequential, and the first “A” signal is held until the second “A” signal occurs. 
         [0032]    Therefore, although only four logic “1” signals are available from a two-axis transducer, by using digital logic, a large number of logic outputs can be produced. 
         [0033]    One of the rate-of-change control devices, or any momentary-contact switch, may be used to initiate the timed-opportunity switch. If a switched signal is provided within a first window-of-opportunity, power is supplied to a first apparatus, such as an electrically-propelled wheelchair. Or, if a switched signal is provided within a second window-of-opportunity, the environmental control unit becomes controllable by the rate-of-change control device, or any momentary-contact switch. 
         [0034]    In an other application of the rate-of-change control devices, a rate-of-change signal exceeding a preset threshold will shut down the electrically-propelled wheelchair. This signal will occur in such instances as an X-Y transducer being knocked off of the head of a user, if some force jars the head of the user, and even if the cord from the X-Y transducer is given a sudden jerk. 
         [0035]    It is important to remember that a constant value, differentiated as a function of time, is zero. Therefore, no matter what constant output a transducer may produce when it is at null, or is not being actuated, dy/dt is zero. 
         [0036]    Therefore, while rate-of-change control devices have been shown and described in conjunction with proportional-output transducers that are used to control apparatus, such as a power wheelchair, the rate-of-change control devices of the present invention may be used with any transducer that will produce a change in output in response to an input. 
         [0037]    Further, since the neutral position of a transducer, that is used with the rate-of-change control device, is whatever input position the transducer has immediately preceding a rate-of-change that is of sufficient magnitude to cause switching, there is no requirement that the transducer have a neutral position, that its output be even relatively repeatable, that its output be even relatively free of drift, or that it be even relatively free of hysteresis. 
         [0038]    In another embodiment of the invention, motion control is provided through one or more switches. The switches can be any combination of switches including infrared, magnetic, mechanical, optical, proximity, ultrasonic or any type of switches capable of providing an open/closed output. A device, such as a powered wheelchair, may be operated optimally by 4 switches configured to provide motion control or alternatively by 3, 2 or 1 switch(es) similarly configured. Full control using fewer than four switches is enabled through the use of a set of one or more flip-flop circuits that allow the input from one or more of the switches to step through a series of control means. 
         [0039]    As defined herein, a rate-of-change control device includes a differentiator and whatever additional components may be required to perform the desired switching functions in response to an input received from a transducer. When a transducer is included with the rate-of-change control device, the combination is a rate-of-change switch. 
         [0040]    In a first embodiment, the invention provides a method which comprises: actuating a switch; disabling control of a device in response to the actuation of the switch; selectively actuating a transducer; generating a control signal in response to the actuation of the transducer; storing a voltage offset proportional to the control signal generated by the actuation of the transducer; enabling control of the device; selectively increasing or decreasing the voltage of the control signal; and operating the device using the control signal from the transducer wherein the signal is modified by the voltage offset. 
         [0041]    In a second embodiment, the invention provides an apparatus comprising: means, comprising first and second transducers that are connected to a powered wheelchair, for moving said powered wheelchair in X and Y direction in response to body member actuating said transducers; means for conditioning a control signal generated by the selective actuating of said transducers; means for storing and applying a voltage offset to the control signal; means for selecting control of either an external device or the powered wheelchair; and means for selectively increasing or decreasing the voltage of the control signal to enable operation one of a set of unique powered wheelchairs. 
         [0042]    In a third embodiment, the invention provides a method which comprises: actuating a switch; powering on a device in response to said actuation; if a specified number of input switches are connected to the device, operating the device in a first mode of operation by selectively operating at least one control switch connected to the device wherein the operation of the at least one control switch generates a control signal; if fewer than the specified number of input switches are connected to the device, selecting a second mode of operation in response to a unique operation of the at least one control switch connected to the device; selectively increasing or decreasing the voltage of the control signal; and operating the device in the second mode of operation by selectively operating the at least one control switch connected to the device. The switch used in this method may be either an active or a passive switch. 
         [0043]    In a fourth embodiment, the invention provides an apparatus comprising: means, comprising at least one active or passive switch that are connected to a powered wheelchair, for moving said powered wheelchair in X and Y direction in response to body member actuating said at least one active or passive switch; means, comprising at least one active or passive switch, for alternating control of the powered wheelchair between positive X, negative X, positive Y, and negative Y directions in response to body member actuating said at least one active or passive switch; means for conditioning a control signal generated by the selective actuating of said at least one active or passive switch; means for selecting control of either an external device or the powered wheelchair; and means for selectively increasing or decreasing the voltage of the control signal to enable operation one of a set of unique powered wheelchairs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    In order to facilitate a full understanding of the present invention, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present invention, but are intended to be exemplary and for reference. 
           [0045]      FIG. 1  is a block diagram of control circuitry that may be either analog or digital. 
           [0046]      FIG. 1A  is a block diagram of control circuitry operated by tilt transducers for control of a powered wheelchair or USP device; 
           [0047]      FIG. 2  is a block diagram of an alternate embodiment of control circuitry operated by one or more switches for control of a powered wheelchair or external device; 
           [0048]      FIG. 3  is a schematic drawing of input, orientation and inverting circuitry that are part of the control system in  FIG. 1 ; 
           [0049]      FIG. 4  is a schematic drawing of buffer and signal limiting circuitry that are part of the control system in  FIG. 1 ; 
           [0050]      FIG. 5  is a schematic drawing of over-range limiting circuitry that is part of the control system in  FIG. 1 ; 
           [0051]      FIG. 6  is a schematic drawing of over-rate limiting circuitry that is part of the control system in  FIG. 1 ; 
           [0052]      FIG. 7  is a schematic drawing of activation and delay circuitry that are part of the control system in  FIG. 1 ; 
           [0053]      FIG. 8  is a schematic drawing of a null width generator and signal conditioner that are part of the control system in  FIG. 1 ; 
           [0054]      FIG. 9  is a schematic drawing of a lockout circuit that is part of the control system in  FIG. 1 ; 
           [0055]      FIG. 10  is a schematic drawing of an X-Y input proportioning circuit that is part of the control system in  FIG. 1 ; 
           [0056]      FIG. 11  is a schematic drawing of a voltage offset and Z-axis circuit that is part of the control system in  FIG. 1 ; 
           [0057]      FIG. 12  is a schematic drawing of a system monitoring circuit that is part of the control system in  FIG. 1 ; 
           [0058]      FIG. 13  is a schematic drawing of an emergency stop circuit that is part of the control system in  FIG. 1 ; 
           [0059]      FIG. 14  is a schematic drawing of switch connection circuit that is part of the control system in  FIG. 2 ; 
           [0060]      FIG. 15  is a schematic drawing of a Y-axis conditioning circuit that is part of the control system in  FIG. 2 ; 
           [0061]      FIG. 16  is a schematic drawing of an X-axis conditioning circuit that is part of the control system in  FIG. 2 ; 
           [0062]      FIG. 17  is a schematic drawing of a flip-flop control circuit for selecting from forward, reverse, left and right control that is part of the control system in  FIG. 2 ; 
           [0063]      FIG. 18  is a schematic drawing of a flip-flop circuit for selecting from forward and reverse control that is part of the control system in  FIG. 2 ; 
           [0064]      FIG. 19  is a schematic drawing of a flip-flop circuit for selecting from left and right control that is part of the control system in  FIG. 2 ; 
           [0065]      FIG. 20  is a schematic drawing of a flip-flop circuit for selecting from Y-axis low and high speed control that is part of the control system in  FIG. 2 ; 
           [0066]      FIG. 21  is a schematic drawing of USP control circuitry comprising a universal signal port that is part of the control system in  FIG. 2 ; 
           [0067]      FIG. 22  is a schematic drawing of an active/standby circuit and a flip-flop reset circuit that are part of the control system in  FIG. 2 ; 
           [0068]      FIG. 23  is a schematic drawing of a rapid deceleration inhibitor that is part of the control system in  FIG. 2 ; 
           [0069]      FIG. 24  is a schematic drawing of a lock-out circuit that is part of the control system in  FIG. 2 ; 
           [0070]      FIG. 25  is a schematic drawing of a voltage offset and Z-axis circuit that is part of the control system in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0071]    The present invention will now be described in more detail with reference to exemplary embodiments as shown in the accompanying drawings. While the present invention is described herein with reference to the exemplary embodiments, it should be understood that the present invention is not limited to such exemplary embodiments. Those possessing ordinary skill in the art and having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other applications for use of the invention, which are fully contemplated herein as within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility. 
         [0072]    In each of  FIGS. 1 ,  1 A and  2 , the present invention is illustrated by a block diagram that generally capsulizes the previously discussed functions and intercomponent relationships of a preferred embodiment of the present invention, illustrating by functional blocks, how the present invention can be practiced using analog components, digital components, or a combination of analog and digital components. Then,  FIGS. 3 to 25  provide a detailed description of the present invention in embodiments constructed with analog and digital components. 
         [0073]    With reference now to  FIG. 1 , a first embodiment of the invention is depicted. The control device  100  comprises the control system  10 , the input transducers  30 , the powered wheelchair  40 , and may also optionally comprise an external device  50 . The control system  10  comprises a startup and delay controller  12 , a null compensator  14 , a turn control module  16 , an external device interface  18 , a voltage offset storer  20 , a signal conditioner module  22 , and a wheelchair interface module  24 . The control system  10  and its modules may comprise either analog or digital components. For example, the control system  10  may be either a microprocessor-based system or may be comprised of analog components such as op-amps, capacitors, resistors, and diodes for example. In a microprocessor configuration, the control system  10  will also comprise a memory to store information needed for the operation of its constituent modules. In an analog configuration, the control system  10  would comprise a set of circuits and discrete components configured to condition an input signal from input transducers  30  to provide for control of powered wheelchair  40  and/or external device  50 . 
         [0074]    With reference now to  FIG. 1A , an embodiment of the invention as shown in  FIG. 1 , control system  1000 , is depicted. The control system  1000  is comprised of separate X and Y signal input and conditioning channels. Y input comes from tilt transducer  1050   a  while X input comes from tilt transducer  1050   b . Signal input from transducers  1050   a  and  1050   b  goes through orientation buffer  1100   a  and  1100   b  respectively. Input for the X and Y axis control can be inverted using signal orientation selectors  1150   a  and  1150   b.    
         [0075]    Continuing to refer to  FIG. 1A , only one of the signal conditioners,  1950   a , will be described, since the signal conditioners  1950   a  and  1950   b  are identical. The signal conditioning performed by signal conditioners  1950   a  and  1950   b  may include tremor control, maximum speed limiting, soft starts, soft stops, signal proportioning, turn-signal conditioning, and/or null width adjustment which are taught herein by Lautzenhiser in U.S. Pat. No. 5,635,807 and/or by Lautzenhiser et al. in U.S. patent application Ser. No. 10/352,345, both of which are incorporated herein by reference. 
         [0076]    The system  1000  is powered on using power control  1300 . When the system  1000  is powered on using power control  1300 , the latch and delay controller  1350  is also activated. When the latch and delay controller  1350  is activated, the input voltage into the system  1000  is held at a neutral voltage until the input from the transducer  1050   a  is determined to be centered or within a determined null width. More specifically, a resistor biases the circuit high and switches between buffer  1770   a  and buffer/splitter  1425   a  is closed. The voltage downstream from the switch is held at a neutral signal voltage of 5 volts. Upstream from the switch a capacitor, in this embodiment a 6.8 μF 100 volt ceramic capacitor, stores an offset voltage from the tilt transducer  1050   a &#39;s input signal voltage. When the delay in the latch and delay controller  1350  times out it pulls the voltage on the circuit low, opening the switch between buffer  1770   a  and buffer/splitter  1425   a , and buffer/splitter  1425   a  begins to receive the voltage signals from the transducer  1050   a  that are offset by the voltage offset stored in the capacitor. Alternatively, an activator/detector module may be attached to a BNC connection port between buffer  1770   a  and buffer/splitter  1425   a . The activator/detector module detects any reclining or tilting of the seat of a powered wheelchair device. If the seat is reclined or tilted by the user, a switch is closed causing a neutral voltage of 5 volts to be sent downstream, halting user control. A new voltage offset is stored in a capacitor, and when the switch is opened the new voltage offset is applied to the input signal voltage from tilt transducer  1050   a.    
         [0077]    Before being routed by buffer/splitter  1425   a  the signal is processed by both the over-range limiter  1200  and over-rate limiter  1250 . The function of the over-range limiter  1200  is to halt signal input if the input signal is over a predetermined limit. The over-range limiter  1200  will send a signal to the lockout circuit  1650  if the input signal from either of the tilt transducers  1050   a  or  1050   b  is over an acceptable input range. The signal from the over-range limiter  1200  to the lockout circuit  1650  will be sent until the signal from the tilt transducers is back within the acceptable input range. The function of the over-rate limiter  1250  is to filter out unwanted or unsafe acceleration signals from either the X or Y input. The over-rate limiter  1250  will send a signal to the lockout circuit  1650  if rate of change in the input signal from the tilt transducers  1050   a  or  1050   b  is over an acceptable limit. 
         [0078]    The voltage signal from the buffer/splitter  1425   a  is limited by the signal limiter  1400   a  and  1450   a . If an external device is connected to the system  1000 , real time, unbuffered, input can be sent to the USP connected external device through real-time input circuit  1600   a . The voltage signal is simultaneously processed by the buffer  1760   a  and null width generator  1525   a.    
         [0079]    The null width generator  1525   a  receives a null width voltage from null width adjustment circuit  1500 . The null width voltage is used to specify a null width or “dead zone” wherein any voltage signal from the tilt transducer  1050   a  will be interpreted as “null” or neutral. The null width adjustment circuit  1500  can be used to adjust the upper and lower limits of the null width voltage to be used in comparisons by the null width generator  1525   a . The null width generator  1525   a  compares the signals from the buffer/splitter  1425   a , which has been limited by signal limiters  1400   a  and  1450   a , to the null voltage provided by the null width adjustment circuit  1500 . If the voltage signal is within the null voltage range, the null voltage generator  1525   a  will supply a null or neutral voltage signal, effectively ignoring the original voltage signal. If the voltage signal exceeds the limits of the null voltage the voltage signal will be further conditioned by the signal conditioner  1950   a . The null width generator  1525   a  may also be adapted to send a signal to a display device to provide a visual indication that the tilt transducer  1050   a  is in a centered or neutral position. 
         [0080]    The attack/decay conditioner  1575   a  provides for a rapid decay and return to neutral of the signal voltage when the tilt transducer  1050   a  begins to return to a centered position. This feature prevents over-steering and provides for rapid braking or deceleration. 
         [0081]    Still with reference to  FIG. 1A , the lockout circuit  1650   a  is represented as being connected to buffer  1760   a . However, in alternative embodiments, lockout circuit  1650   a  may also be directly connected to over-range limiter  1200 , over-rate limiter  1250 , watch dog circuit  1800 , and may also comprise an emergency stop circuit  1675 . When activated, the lockout circuit  1650   a  sends out a neutral voltage signal to return the output to a neutral state, bypassing any inputs from tilt transducer  1050   a.    
         [0082]    The voltage signal is then further buffered by buffer  1750   a  before being checked by watch dog circuit  1800 . The watch dog circuit  1800  functions as a system safeguard. If any circuits or modules upstream of the watch dog circuit  1800  malfunction, the watch dog circuit  1800  will determine that the voltage signal at the watch dog circuit is in an error state. If the voltage signal is in an error state, the watch dog circuit  1800  will send a signal to the emergency stop circuit  1675 , which will then activate the lockout circuit  1650   a . If the emergency stop circuit  1675  is activated by the watch dog circuit  1800  or through any other means, the entire system  1000  must be powered off and on to reset the emergency stop circuit  1675 . 
         [0083]    If the lockout circuit  1650   a  has not been activated and the voltage signal is not in an error state as determined by the watch dog circuit  1800 , the voltage signal is further conditioned by the X/Y proportioner  1850 . The X/Y proportioner  1850  compares the voltage signals from the transducers  1050   a  and  1050   b  representing control of the Y and X axes respectively. The purpose of the X/Y proportioner is to keep the device controlled by the system  1000  from performing undesirable turning or acceleration maneuvers. For example, if the signal voltage for control of the Y axis is in a high positive state for a high rate of forward motion, the X/Y proportioner  1850  will condition the signals for the Y signal voltage to prevent the signal voltage for the Y axis from also being in a high positive state. The Y input signal is conditioned non-linearly as a function of the X input signal, and the X input signal is not changed or reduced. This proportional conditioning prevents a device controlled by the system  1000  from “fishtailing” or performing other undesirable or unsafe actions. 
         [0084]    A final voltage offset is applied to the signal voltage by the final offset and Z-axis circuit  1900 . The offset to be applied is selectable by the user. The voltage offset allows the control system  1000  to be used with a variety of different devices to enable compatibility with a variety of different devices. The voltage offset and Z-axis circuit  1900  can also be used to supply a reference voltage signal for a “Z-axis” to be used with certain devices. 
         [0085]    With reference now to  FIG. 2 , a second embodiment of the invention, control system  2000 , is depicted. Control system  2000  is a power wheelchair drive control device with multiple input ports. The control system may utilize 4, 3, 2, or 1 switch(es) to provide user control of a powered wheelchair or other device. The control system  2000  comprises a set of one or more proximity switches, or any other switch that provides open/closed output for motion control, connected to one switch control  2100  which provide signal voltages which are used to operate one or more devices connected to control system  2000 . Through the use of one or more switches connected to switch control  2100 , a user may control a device connected to the system  2000  using only one axis, a single directional input on one axis, or any combination of a single directional input on one axis and both directional inputs on another axis. For example, a user may operate forward, reverse, left, and right control of a device connected to the control system  2000  using only a single switch connected to the switch control  2100  and may step through the control outputs until the desired control output is selected. A user may also operate left and right control using two switches, and use an other switch to operate forward and reverse control. 
         [0086]    Operation of the control system  2000  is enabled when the user operates a switch connected to the active/standby port on switch control  2100 . When this switch is operated, a signal is sent to the active/standby circuit  2400 . When the signal is received at the active/standby circuit  2400 , flip-flop circuits  2200 ,  2250 ,  2300 , and  2350  are reset to their starting state, and user control of the control system  2000  is enabled. However, no reset is performed if the flip flop circuits are in their default state. 
         [0087]    The user may connect one or more switches to switch control  2100  to enable control of a device connected to the control system  2000 . For motion control, a maximum of four (4) switches can be used. This can be any combination of switches including mechanical, proximity, ultrasonic, infrared, or any type of switches capable of providing an open/closed output. By selecting multiple switch ports, the control system  2000  can be operated with 3, 2, or 1 switch(es) for motion or device control in the event of a progressive illness such as ALS. The switch connectors, switch jacks and/or switch ports will accommodate and interface with both passive switches such as an Able Net Jelly Bean Twist 10033400, and active switches such as an Omron capacitive proximity sensor requiring a source of power such as E2K-F10MC1. If three or fewer switches are used, one or more of the input switches used for motion control are used to control motion in more than one direction. For example, a flip-flop circuit may be used to allow a single switch to step through the control outputs, and the resulting movement of the power wheelchair would step through forward and reverse and/or left and right motion control. Any combination of input switches may be used and the input switches may be placed anywhere on the user&#39;s body or wheelchair where the user has adequate body or body member control to operate the switches. 
         [0088]    In a two switch configuration for the Y axis, a first switch allows the user to control the +Y axis, and a second switch allows the user to control the −Y axis. If the first switch is operated by the user, a signal is sent from the switch control  2100  to Y-axis common control circuit  2600  for +Y axis control. In this state, input from the switch will be conditioned to provide +Y axis control. If the second switch is operated by the user, a signal is sent from the switch control  2100  to Y-axis common control circuit  2600  for −Y axis control. In this state, input from the second switch conditioned to provide only −Y axis control. 
         [0089]    In a single switch configuration for the Y axis, a switch allows the user to control either the + or −Y axis control by stepping through both control methods. In the default, or starting state, Y+/− flip-flop circuit  2300  provides for user control of the +Y axis. If the user operates the switch, a signal is sent from switch control  2100  to the Y+/− flip-flop circuit  2300  which switches to enable user control of the −Y axis. The next operation of the switch will return the Y+/− flip-flop circuit  2300  to the default state, providing user control of the +Y axis. 
         [0090]    User selection of X axis control is performed in a similar manner to Y axis control. The user may connect one or two switches to provide the user with + and −X axis control. In a two switch configuration for the X axis, a first switch allows the user to operate +X axis control, and a second switch allows the user to operate −X axis control. If the first switch is operated by the user, a signal is sent from the switch control  2100  to X-axis common control circuit  2650  for +X axis control. In this state, input from the first switch will be conditioned to provide +X axis control. If the second switch is operated by the user, a signal is sent from the switch control  2100  to X-axis common control circuit  2650  for −X axis control. In this state, input from the second switch conditioned to provide −X axis control. 
         [0091]    In a single switch configuration for the X axis, a switch allows the user to operate either + or −X axis control by stepping through both control methods. In the default, or starting state, X+/− flip-flop circuit  2350  provides for user control of the +X axis. If the user operates the switch, a signal is sent from switch control  2100  to the X+/− flip-flop circuit  2350  which switches to enable user control of the −X axis. The next operation of the switch will return the X+/− flip-flop circuit  2350  to the default state, providing user control of the +X axis. 
         [0092]    Still referring to  FIG. 2 , the user may also connect a single switch to switch control  2100  to enable +/−X and Y axis control through the use of a single switch. In this configuration, each operation of the switch steps through the control methods of +Y, +X, −Y, −X. The selection of the control method is performed by one switch control flip-flop circuit  2200 . In the default state, user control will be of the +Y axis through the default state of the Y+/− flip-flop circuit  2300 . Each operation of the switch connected to switch control  2100  will send a signal to one switch control  2200  that will step through the available control methods. The first operation of the switch will cause the one switch control  2200  to switch to the +X axis control through the X+/− flip-flop circuit  2350 . The second operation of the switch will cause the one switch control  2200  to switch back to the Y+/− flip-flop circuit  2300 , which will switch to −Y control, enabling control of the −Y axis. The third operation of the switch will cause the one switch control  2200  to switch to the X+/− flip-flop circuit  2350 , which will switch to the −X control, enabling control of the −X axis. A fourth operation of the switch will cause the one switch control  2200  to switch back to the default state, returning to the Y+/− flip-flop circuit  2300 , which will switch back to the default state of +Y axis control. Further operation of the switch will cause the system to continue step through the control methods in the manner specified above. 
         [0093]    Additional switches may be connected to switch control  2100  to enable additional features of the control system  2000 . A switch may be connected to switch control  2100  to enable control of the Y lo/hi flip-flop circuit  2250 . Operation of a switch connected to the Y lo/hi flip-flop circuit  2350  will enable the user the input higher values for the +Y control signal. In normal operation, the absolute value of the Y axis voltage signal is limited to a certain value. A user may wish to increase the limit to enable, for example, faster movement of a powered wheelchair when outdoors. If the switch connected to the Y lo/hi circuit  2250  is operated, the Y lo/hi circuit  2250  switches to the higher Y signal voltage limit value. A second operation of the switch will return the limit to the original, lower value, and additional operation of the switch will step through the signal voltage limits as described above. 
         [0094]    A switch may also be connected to switch control  2100  to enable control of an external device connected to USP control  2700 . Operation of a switch connected to USP control  2700  will provides the user with the ability to select between control of a powered wheelchair device and an external device connected to the control system  2000 . A switch may also be connected to switch control  2100  to enable an emergency stop feature. If a switch for an emergency stop feature is operated, lock-out circuit  2800  supplies the device connected to control system  2000  with a neutral voltage, disabling user control until the control system is powered off and on. 
         [0095]    Still with reference to  FIG. 2 , the lock-out circuit  2800  also contains a system monitor or “watch dog” feature that monitors the voltage signal output from all system components. If the voltage signal is outside of a specified range, the system monitor circuit will enable the lock-out circuit  2800  and will disable user control. 
         [0096]    A further control system  2000  safety feature is the rapid deceleration inhibitor  2750 . The rapid deceleration inhibitor  2750  prevents rapid deceleration via a rapid drop in signal from the +/−X or Y signal voltages due to the user operating a switch connected to switch control  2100 . This feature prevents, for example, rapid braking or overly sharp turning due to the user switching from forward to reverse control, or from forward to left control, by operating a switch connected to switch control  2100  while the voltage signal from an input switch is at a high absolute value. The rapid deceleration inhibitor  2750  is engaged whenever any control switch, e.g., forward, forward plus, forward/reverse, or reverse in Y-axis common control  2600 , is operated. When a control switch is operated, a switch in the Y-axis common control  2600  is opened, removing the resistor that enables a rapid bleed-off of the signal voltage out of the circuit. When a control switch is no longer operated, the switch is closed and the resistor is reconnected to the circuit, enabling a rapid bleed-off of the input signal voltage. In the Y-axis common control  2600  this prevents jerky motion and unwanted rapid deceleration. 
         [0097]    A final voltage offset is applied to the signal voltage by the final offset circuit  2900 . The offset to be applied is selectable by the user. The voltage offset allows the control system  2000  to be used with a variety of different devices. The voltage offset circuit  2900  can also be used to supply a reference voltage signal for a “Z-axis” necessary for the operation of certain devices. 
         [0098]    With reference now to  FIGS. 1A and 3 , with specific reference to  FIG. 3 , an exemplary embodiment of the input circuitry  300  for control system  1000  is depicted. A signal voltage comes from tilt transducers  1050   a  and  1050   b . Signal orientation selectors  1150   a  and  1150   b  provide for the inversion or switching of input signals from transducers  1050   a  and  1050   b . In this embodiment, the signal orientation selectors  1150   a  and  1150   b  are a set of dip switches that allow a user or technician to customize the control input by selecting the signal path based on user needs. The orientation &amp; inversion circuits  1100   a  and  1100   b  provide a user with the ability to change the orientation of the tilt transducers to suit the user. The signal voltage continues to signal conditioning circuits  1950   a  and  1950   b.    
         [0099]    For  FIGS. 4 ,  8  and  9 , reference is made to conditioning circuit  1950   a , however, similar or identical circuits are found in conditioning circuit  1950   b . With reference now to  FIGS. 1 and 4 , with specific reference to  FIG. 4 , buffering and limiting circuitry  400  is depicted. An input signal for system power comes from latch and delay circuitry  1350 . This input signal opens the solid state switch  1402   a . When the system is powered on, and the switch  1402   a  is closed, a signal offset is stored in the capacitor  1404   a . The input signal from buffer  1770   a  may be at, for example 2.4 volts. A neutral voltage of 5 volts is supplied when switch  1402   a  is closed. After a specified time-out period of 0-8 seconds, the switch  1402   a  opens, and the voltage offset is stored in the capacitor  1404   a . There is very little voltage leakage in capacitor  1404   a  and buffer  1770   a , which may be, for example, an LMC  6484  quad-rail precision amplifier. This enables the capacitor  1404   a  to hold its offset voltage for at least 24 hours. This voltage offset adjusts the input signal from the input circuitry  300  to compensate for however far off the input signal voltage is from the neutral voltage. The voltage offset allows the control system  1000  to be operated normally even if the tilt transducer  1050   a  or  1050   b  are not positioned in a perfect orientation on the user. The user may re-set the offset held in the capacitor  1404   a  by resetting the control system  1000 . The voltage offset signal from buffer  1770   a  and capacitor  1404   a  is sent to both over-range limiter  1200  and over-rate limiter  1250 . Signal limiters  1400   a  and  1450   a  limit the input signal. The reference for the signal limiters  1400   a  and  1450   a  is provided from voltage reference  402 , and the input voltage is sent through buffer and limiter  1425   a . The value limited signal is sent to both buffer  1760   a  and null width generator  1525   a.    
         [0100]    With reference now to  FIGS. 1A and 5 , with specific reference to  FIG. 5 , over-range limiter  1200  is depicted. An input voltage signal is sent to over-range limiter  1200  from buffers  1770   a  and  1770   b  for the Y and X input voltage signals respectively. Comparators  1204  check the input voltage signals against an upper and lower voltage limit. If the input voltage exceeds the upper or lower limit, over-range latch  1202  latches. When latched, lockout circuits  1650   a  and  1650   b  are activated, and a visual notification of an over-range is shown to the user through LED control  1010 . 
         [0101]    With reference now to  FIGS. 1A and 6 , with specific reference to  FIG. 6 , over-rate limiter  1250  is depicted. Input voltages for Y and X input are sent from buffers  1770   a  and  1770   b  respectively. Reference voltages are provided at reference voltage circuitry  1252 . If the rate through op amps and R/C circuits  1256  and  1254  is determined by comparators  1258  to be greater than the reference voltages  1252 , then a signal is sent from op amp  1260  to lockdown circuits  1650   a  and  1650   b  to return the voltage signal to neutral, overriding user control. A visual notification of an over-rate state is shown to the user through LED control  1010 . 
         [0102]    With reference now to  FIGS. 1A and 7 , with specific reference to  FIG. 7 , latch and delay circuit  1350  is depicted. The enable delay function provides a selectable delay time period ranging from 0 to 7 seconds. The delay period commences when the user activates a mode switch connected at connection port  1352 , and ends when an indicator LED darkens. The time delay allows a user an opportunity to comfortably and naturally position their head or other body member(s) before the system defines the user&#39;s neutral position. The higher the setting for the delay, the greater the time delay prior to tilt transducer activation. The switch is used to activate the system  1000  and to enable control of an external device in the USP port  1615 . If the switch is held closed for 3 seconds, control of the USP is activated. The user is given a visual notification of USP control at USP LED  1012 . The latch and delay circuit  1350  also delays the activation of over-range limiter  1200  and over-rate limiter  1250 . Delay inhibitor  1355  disables the delay when use of USP  1615  is activated. The signal from the latch and delay circuit is sent to the switch  1402   a  to enable user control. 
         [0103]    With reference now to  FIGS. 1A and 8 , with specific reference to  FIG. 8 , conditioning circuitry  800  is depicted. Conditioning circuitry  800  comprises null width adjustment  1500 , null voltage generator  1525   a , attack/decay conditioner  1575   a , buffer  1760   a , and R/C circuit  802 . Null width adjustment  1500  allows for an adjustable voltage limit for a null or neutral voltage. The upper and lower limit set at null width adjustment  1500  is used by null width generator  1525   a  to determine if the input signal from buffer  1425   a  is within the specified null voltage limit. The null voltage is useful if the user experiences tremors or cannot maintain a fixed center. Attack/decay conditioner  1575   a  provides for a rapid return to neutral to prevent oversteering. Or gates  804  activate a visual signal through LED control  1010  if the input signal voltage is determined to be centered. Real time signal control is provided by real-time input circuitry  1600   a  to the USP module. 
         [0104]    With reference now to  FIGS. 1A and 9 , with specific reference to  FIG. 9 , lockout circuit  1650   a  is depicted. If a signal is sent from attack/decay conditioner  1575   a , emergency stop circuit  1675 , over-rate limiter  1250 , over-range limiter  1200 , or if the USP control  1615 , switch  1652  is opened and a neutral voltage is sent to the control output. If a signal is not sent from one of the aforementioned circuits, the input signal voltage from buffer  1760   a  continues through buffer  1750   a  and is monitored by watch dog circuit  1800  and is proportioned at X/Y proportioner  1850 . 
         [0105]    Referring now to both  FIGS. 8 and 9 , the null width circuit  1525   a , attack/decay conditioner  1575   a , and lockout circuit  1650   a  are discussed in more detail. The set of comparators  1525  compares the adjustable null voltage from null width adjustment  1500  to determine if the input signal is within the specified voltage. If the signal is “centered” or within the null width or “neutral zone,” the user is given a visual indication and the switch  1652  is closed. While the switch  1652  is closed the control system outputs a neutral voltage to disable user control while the input is centered in the neutral zone. Any input signal voltage applied while in the neutral zone, but not exceeding the specified null width voltage, is stored in the R/C circuit  802 . The capacitor and resistor that make up the R/C circuit  802  will store and the slowly add or “bleeds off” the stored voltage into the input signal voltage to enable a more responsive control of the device connected to the control system  1000  until the stored voltage is reduced to 0 volts. The rate of the signal “bleed” into the input voltage is determined by the difference between the input voltage and the stored voltage in the R/C circuit  802 ; a greater difference will result in a faster addition of the stored voltage to the input signal voltage. The advantage to this configuration is that there is a full range of signal and no input signal is lost. The combination of the null width generator  1525   a  and the R/C circuit  802  provides for very smooth control by the control device  1000 ; it prevents jerky acceleration and turning of a powered wheelchair type device. Another important feature of this portion of the system is the rapid “snap back” or return to center of the input signal voltage once the user has returned the tilt transistor  1050   a  to its centered position. Once the input signal voltage returns to center as determined by the comparators in null width generator  1525   a , the switch  1652  is again closed and the neutral 5 volt signal is output by the system. Any stored voltage in the R/C circuit  802  is rapidly bled off. The return to neutral and rapid bleed off of the stored voltage provides for faster stopping, no oversteering, and helps prevent fishtailing of a powered wheelchair device. It should be noted that the similar circuit in signal conditioner  1950   b  provides for a more rapid bleed off of the stored voltage in the corresponding R/C circuit to provide for more responsive turning. Furthermore, this configuration allows for even a partial tilt of the tilt transducer  1050   a  to translate into a full control signal, further improving responsiveness and control. The neutral zone provided by the null width generator  1525   a  also allows a user to center the tilt transducers  1050   a  and  1050   b  for a period of time, for example 5-10 seconds, to access menu options or additional functions in the powered wheelchair connected to control system  1000 . 
         [0106]    With reference now to  FIGS. 1A and 10 , with specific reference to  FIG. 10 , X/Y proportioner  1850  is depicted. The Y input voltage signals from signal conditioners  1950   a  is conditioned proportionally by conditioners  1852  and  1854 . For example, if the signal voltage for control of the Y axis is in a high positive state for a high rate of forward motion, the X/Y proportioner  1850  will condition the signals for the Y signal voltage to prevent the signal voltage for the Y axis from also being in a high positive state. The Y input signal is conditioned non-linearly as a function of the X input signal, and the X input signal is not changed or reduced. This proportional conditioning prevents a device controlled by the system  1000  from “fishtailing” or performing other undesirable or unsafe actions. The conditioned signals are then returned to signal conditioners  1950   a  and  1950   b  to be sent to Y and X signal output. 
         [0107]    With reference now to  FIGS. 1A and 11 , with specific reference to  FIG. 11 , final offset and Z-axis circuit  1900  is depicted. The fully conditioned input voltage signals from signal conditioners  1950   a  and  1950   b , Y and X axis respectively, are modified by any specified voltage offset. The voltage offset is selected by using dip switches  1902 . If a Z-axis output is needed for operation of a particular device, an adjustable reference voltage can be supplied to Z-axis output  1904  by selecting the corresponding dip switch  1902 . The input voltage signals are sent to Y-drive and X-drive outputs after any offsets have been applied as selected through dip switches  1902 . 
         [0108]    With reference now to  FIGS. 1A and 12 , with specific reference to  FIG. 12 , watch dog circuit  1800  is depicted. Watch dog circuit  1800  is a system monitoring circuit that receives input from signal conditioners  1950   a  and  1950   b . If the signal from the conditioners is determined to exceed upper and lower limits by comparators  1802 , a signal is sent to emergency stop circuit  1675  to halt user control. 
         [0109]    With reference now to  FIGS. 1A and 13 , with specific reference to  FIG. 13 , emergency stop circuitry  1675  is depicted. Emergency stop circuitry  1675  allows for immediate shut down of the control system  1000  through the use of a switch connected to control port  1677  or from an input signal from watch dog circuit  1800 . In one embodiment, the port  1677  provides a ⅛ inch (3.5 mm) plug receptacle used to deactivate the system by either the user or a caregiver. The control system  1000  must be completely powered down to reset the emergency stop circuitry  1675 . Any commonly used mode or reset switch, such as a red Jelly Bean switch by Able Net® or similar switch could be used. If the switch connected to port  1677  is pressed or if a signal is received from the watch dog circuit  1800 , the lockout circuits  1650   a  and  1650   b  are activated. A visual signal of an emergency stop state is sent to the user through LED control  1010 . 
         [0110]    With reference now to  FIGS. 2 and 14 , with specific reference to  FIG. 14 , switch control  2100  is depicted. Switch control  2100  consists of a plurality of control ports  2100   a - 2100   j . The control ports allow a user or caregiver to connect one or more switches to enable selective control of a device connected to the control system  2000 . In a first embodiment, switches will be connected to forward port  2100   a , reverse port  2100   c , right port  2100   e , left port  2100   f , and active/standby port  2100   i . In a second embodiment, switches are connected to forward/reverse port  2100   d , right/left port  2100   g , and active standby port  2100   j . In a third embodiment, switches are connected to one switch control port  2100   h  and active/standby port  2100   i . Other combinations of switch connectivity are also possible. In any switch configuration, switches may also be connected to forward+ port  2100   b  and to USP control port  2100   j.    
         [0111]    With reference now to  FIGS. 2 and 15 , with specific reference to  FIG. 15 , Y-axis common control circuit  2600  is depicted. An input signal voltage is provided from switches  2100   a ,  2100   c , or from the flip flop circuit  2300 . User operation of a switch connected to forward port  2100   a  from switch control  2100  is initially conditioned at op amp  2602 . User operation of a switch connected to reverse port  2100   c  from switch control  2100  is initially conditioned at op amp  2604 . The input signal voltage from switches  2100   a  or  2100   c  is increased or decreased, “pulled up or down”, by the high side and low side resistors on the circuit. Rapid deceleration inhibitor  2750  closes switch  2610  when any switch connected to one switch control  2100  is open and not being operated by the user, enabling a rapid bleed-off of the input signal voltage. This rapid bleed-off of the input signal voltage prevents rapid deceleration or jerky control by providing a rapid bleed off of the input signal through a 3.01K ohm resistor on the circuit. USP control  2700  is connected to Y-axis common control  2600  so input voltage signals may be sent to an USP device connected to USP control  2700  If the system monitoring portion of the lock-out module  2800  determines that a system malfunction has occurred, or if the emergency stop portion of the lock-out module has been activated, the switch  2608  is opened so that only a neutral voltage is output by the Y-axis common control  2600 , locking out user control. Activation of the active/standby module  2400  will also open the switch  2608 . Conditioned input voltage signals are sent to final offset module  2900  for final voltage offset. 
         [0112]    With reference now to  FIGS. 2 and 16 , with specific reference to  FIG. 16 , X-axis common control circuit  2650  is depicted. An input signal voltage is provided from switches  2100   e ,  2100   f , or from flip-flop circuit  2350 . User operation of a switch connected to right control port  2100   e  from switch control  2100  is initially conditioned at op amp  2652 . User operation of a switch connected to left control port  2100   f  from switch control  2100  is initially conditioned at op amp  2654 . The input signal voltage from switches  2100   e  or  2100   f  is increased or decreased, “pulled up or down”, by the high side and low side resistors on the circuit. Rapid deceleration inhibitor  2750  closes switch  2610  when any switch connected to one switch control  2100  is open and not being operated by the user, enabling a rapid bleed-off of the input signal voltage. This rapid bleed-off of the input signal voltage prevents rapid deceleration or jerky control by providing a rapid bleed off of the input signal through a 3.01K ohm resistor on the circuit. USP control  2700  is connected to X-axis common control  2650  so input voltage signals may be sent to an USP device connected to USP control  2700 . If the system monitoring portion of the lock-out module  2800  determines that a system malfunction has occurred, or if the emergency stop portion of the lock-out module has been activated, the switch  2658  is opened so that only a neutral voltage is output by the X-axis common control  2650 , locking out user control. Activation of the active/standby module  2400  will also open the switch  2658 . Conditioned input voltage signals are sent to final offset module  2900  for final voltage offset. 
         [0113]    A difference between the control circuit  1000  in  FIG. 1  and the control circuit  2000  in  FIG. 2  is that the real time input module  1600   a  in control system  1000  is connected to a USP port and provides a real time voltage input signal to a device connected to the port while the control system  2000  cannot provide a real time input signal. The response rate of the voltage input signal in the control system  2000  is limited by the R/C circuits in depicted in  FIGS. 15 and 16  which is set by the physical limitations of the R/C circuits. 
         [0114]    With reference now to  FIGS. 2 and 17 , with specific reference to  FIG. 17 , one switch control circuit  2200  is depicted. When a signal from the one switch control port  2100   h  is received, switches  2206 ,  2208 , and  2210  are opened. The first operation of the one switch  2100   h  will cause a signal to be sent through op amp  2204  to Y+/− flip-flop circuit  2300  as though a switch connected to forward/reverse port  2100   d  had been operated. A second operation will cause a signal to be sent through op amp  2202  to X+/− flip-flop circuit  2300  as though a switch connected to left/right port  2100   g  had been operated. The one switch control flip-flop circuit  2200  is reset from a signal from flip-flop reset circuit  2450 . The functionality of one switch control circuit  2200  allows a user to step through X and Y inputs through the use of a single input switch  2100   h , providing users with limited body member control the ability to have full operation of a powered wheelchair device controlled by control system  2000 . 
         [0115]    With reference now to  FIGS. 2 and 18 , with specific reference to  FIG. 18 , a Y+/− flip-flop circuit  2300  is depicted. The Y+/− flip-flop circuit  2300  allows a user to select from either +Y-axis or −Y-axis control through the operation of switch  2100   d  or from a switch connected to one switch control  2200 . Switches  2306  and  2302  are opened in response to the signal from port  2100   d , providing the user with alternating +Y-axis and −Y-axis control. If the circuit  2300  is providing −Y-axis control, the user is given is visual indication through LED  2304 . The conditioned signal is sent to Y-axis common control circuit  2600 . 
         [0116]    With reference now to  FIGS. 2 and 19 , with specific reference to  FIG. 19 , a X+/− flip-flop circuit  2350  is depicted. The X+/− flip-flop circuit  2350  allows a user to select from either +X-axis or −X-axis control through the operation of switch  2100   g  or from a switch connected to one switch control  2200 . Switches  2356  and  2352  are opened in response to the signal from port  2100   d , providing the user with alternating +X-axis and −X-axis control. If the circuit  2350  is providing −X-axis control, the user is given is visual indication through LED  2304 . The conditioned signal is sent to X-axis common control circuit  2650 . 
         [0117]    With reference now to  FIGS. 2 and 20 , with specific reference to  FIG. 20 , a Y lo/hi flip-flop circuit  2250  is depicted. The Y lo/hi flip-flop circuit  2250  allows a user to select from either a low speed or high speed Y-axis control through the operation of switch  2100   b . Switches  2256  and  2252  are opened in response to the signal from port  2100   d , providing the user with alternating high and low speed Y-axis control. The conditioned signal is sent to Y-axis common control circuit  2600 . High speed Y-axis control increases the maximum input signal voltage, allowing a user a higher maximum Y-axis signal value, thus providing for faster movement of a device controlled by control system  2000 . 
         [0118]    With reference now to  FIGS. 2 and 21 , with specific reference to  FIG. 21 , USP control  2700  is depicted. USP control  2700  provides for user control of a device connected to the universal signal port. Power control circuitry  2702  provides power to the device connected to the USP control output  2704 . Input control signal voltages from Y-axis common control  2600  and X-axis common control  2650  also provide control signal voltages for the device connected to the USP control  2700 . Active/standby circuit  2400  is used to both enable and disable USP control  2700 . USP control is also connected to lock-out circuitry  2800  to provide protection against system faults. Power is provided to an USP device connected to the USP port through power connection  2710 . 
         [0119]    With reference now to  FIGS. 2 and 22 , with specific reference to  FIG. 22 , active/standby circuit  2400  and flip-flop reset circuit  2450  are depicted. The control system  2000  is powered on when a switch connected to port  2100   i  is operated. If the switch  2100   i  is held for a period of time, three seconds for example, then control of USP control  2700  is activated. A delay of 0-7 seconds may be applied before a user may begin control of either the USP control  2700  or of input circuits  2010  which comprise Y-axis common control  2600  and X-axis common control  2650  and also disarms the rapid deceleration inhibitor  2750  when input signals are received for forward/reverse or left/right motion. When the control system  2000  is powered on, one switch control  2200 , Y lo/hi flip-flop  2250 , Y+/− flip-flop  2300 , and X+/− flip flop  2350  are reset to their default states. 
         [0120]    With reference now to  FIGS. 2 and 23 , with specific reference to  FIG. 23 , rapid deceleration inhibitor  2750  is depicted. If any switch  2100   a ,  2100   b ,  2100   c ,  2100   d ,  2100   e ,  2100   f ,  2100   g , or  2100   h  connected to switch control  2100  is operated, a signal is sent from rapid deceleration inhibitor  2750  to corresponding Y-axis common control  2600  or X-axis common control  2650  to prevent rapid deceleration or turning due to input switching. 
         [0121]    With reference now to  FIGS. 2 and 24 , with specific reference to  FIG. 24 , lock-out circuit  2800  is depicted. Watch dog circuit  2810  is a system monitoring circuit that receives input from Y-axis common control  2600  and X-axis common control  2650 . If the signal from the common controllers is determined to exceed upper and lower limits by comparators  2812 , a signal is sent to emergency stop circuit  2820  to halt user control. Emergency stop circuitry  2820  allows for immediate shut down of the control system  2000  through the use of a switch connected to control port  2822  or from an input signal from watch dog circuit  2810 . In one embodiment, the port  2822  provides a ⅛ inch (3.5 mm) plug receptacle used to deactivate the system by either the user or a caregiver. The control system  2000  must be completely powered down to reset the emergency stop circuitry  2820 . Any commonly used mode or reset switch, such as a red Jelly Bean switch by Able Net® or similar switch could be used. If the switch connected to port  2822  is pressed or if a signal is received from the watch dog circuit  2810 , a signal is sent to Y-axis common control  2600  and X-axis common control  2650  opening a switch and causing a neutral voltage control signal to be output. A visual signal of an emergency stop state is sent to the user through LED control  2010 . 
         [0122]    With reference now to  FIGS. 2 and 25 , with specific reference to  FIG. 25 , final offset and Z-axis circuit  2900  is depicted. The fully conditioned input voltage signals from Y-axis common control  2600  and X-axis common control  2650 , are modified by any specified voltage offset. The voltage offset is selected by using dip switches in output signal selector circuit  2910 . If a Z-axis output is needed for operation of a particular device, an adjustable reference voltage can be supplied to Z-axis output  2920  by selecting the corresponding dip switch. The input voltage signals are sent to Y-drive and X-drive outputs after any offsets have been applied in offset circuitry  2930  as selected through output signal selector  2910 . 
         [0123]    While specific apparatus and method have been disclosed in the preceding description, it should be understood that these specifics have been given for the purpose of disclosing the principles of the present invention and that many variations thereof will become apparent to those who are versed in the art. Therefore, the scope of the present invention is to be determined by the appended claims and their respective recitations.