Patent Publication Number: US-2006015284-A1

Title: Contaminant detecting touch sensitive element

Description:
BACKGROUND OF THE INVENTION  
      This invention relates generally to touch sensitive control interfaces, and more particularly, to touch sensor elements for environments vulnerable to spills and contaminants.  
      Due to their convenience and reliability, touch sensitive control interfaces are increasingly being used in lieu of mechanical switches for various products and devices. Touch sensitive control interfaces are used in a wide variety of exemplary applications such as appliances (e.g., stoves and cooktops), industrial devices such as machine controls, cash registers and check out devices, and even toys. The associated devices may be operated by pressing predefined areas of the interface with a finger, and typically include a controller coupled to the interface to operate mechanical and electrical elements of the device in response to user commands entered through the touch control interface.  
      Various types of touch technologies are available for use in touch control interfaces, including but not limited touch sensitive elements such as capacitive sensors, membrane switches, and infra-red detectors. It has been noted, however, that such touch sensitive elements are subject to inadvertent activation attributable to a foreign object or deposit that touches the interface in the vicinity of the touch sensitive elements. It has been observed, for example, that foreign materials splashed, spilled, deposited or otherwise accidentally applied to the control interface can actuate known touch sensitive elements. This is a particularly undesirable result when the touch sensitive elements are associated, for example, with an appliance heating element or a heavy piece of machinery, yet such splashes, spills, and unintentional application of foreign material are not uncommon to cooking environments and manufacturing environments.  
      U.S. Pat. No. 5,760,715 (the &#39;715 patent) describes one system which is designed to avoid erroneous activation of a touch sensitive element due to foreign objects or deposits. The &#39;715 patent describes a capacitive circuit formed through the touch sensitive element, the user, and the earth, and when the circuit is completed by a user a varying electric potential in the circuit triggers activation of the element and signals the controller to respond appropriately.  
      Despite safeguards of a system such as that described in the &#39;715 patent, substances splashed, spilled or otherwise applied to the touch sensitive interface may nonetheless activate a touch sensitive element without a conscious action of a user. For example, a spilled condiment such as ketchup has been observed to extend and distort the effective activation area of one or more touch sensitive elements of a control interface. Thus, when the interface is coated with ketchup, a touch outside the normal operating area of the touch sensitive element may be transmitted through the ketchup to the normal activation area and actuate an associated component or device. That is, a user may touch an area or region of the control interface that in a normal condition would not activate the touch sensitive element, but because of the presence of the ketchup or other foreign matter which does touch the normal activation region of the touch sensitive element, the touch sensitive element may nonetheless be activated. As such, the likelihood of an inadvertent actuation of a touch sensitive element may be greatly increased by the presence of such a spill on the interface. When the user attempts to wipe the ketchup from the interface, affected touch sensitive elements may be unintentionally activated.  
     BRIEF DESCRIPTION OF THE INVENTION  
      In an exemplary embodiment, a touch sensitive control interface for a controlled device is provided. The control interface comprises a panel defining an interface area configured to selectively input command instructions of an operator of the device. The panel comprises at least one primary touch sensor portion configured to receive a true operator command, and a secondary touch sensor portion proximate the activation area configured to detect a false operator command, for example, due to a presence of a contaminant.  
      In another exemplary embodiment, a touch sensitive control interface is provided. The interface comprises a plurality of touch sensitive areas configured to accept a user input. At least one of the touch sensitive areas comprises a primary activation area and a contaminant detection area surrounding the primary activation area.  
      In yet another exemplary embodiment, a touch sensitive control system for controlling a device is provided. The control system comprises an interface comprising at least one predefined primary touch sensitive activation area and a contaminant detection area adjacent the activation area, and a controller electrically connected to the interface and operatively responsive to the interface when the primary activation area is activated and when the contaminant detection are is not activated. The controller is programmed to prevent actuation of the device when the contaminant detection area is activated, regardless of the state of the primary activation area. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic block diagram of an exemplary touch sensitive control system for a device.  
       FIG. 2  is a top plan view of an exemplary control interface for the control system shown in  FIG. 1 .  
       FIG. 3  is an exemplary control algorithm executable by the control system shown in  FIG. 1 .  
       FIG. 4  is a top plan view of another embodiment of a control panel for the control system shown in  FIG. 1 .  
       FIG. 5  is a top plan view of still another embodiment of a control panel for the control system shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  is a schematic block diagram of an exemplary touch sensitive control system  100  for a device  102 , which in various embodiments may be an appliance, an industrial machine or any other device in which a touch sensitive control interface is desirable, and for which inadvertent actuation of the device  102  is a concern.  
      In an exemplary embodiment, the control system  100  includes a controller  104  which may, for example, include a microcomputer or other processor  105  coupled to a user control interface  106  including one or more touch sensitive elements as described further below. An operator may enter control parameters, instructions, or commands and select desired operating algorithms and features of the device  102  via user interface input  106 . In one embodiment a display or indicator  108  is coupled to the controller  104  to display appropriate messages and/or indicators to the operator of the device  102  to confirm user inputs and operation of the device  102 . A memory  110  is also coupled to the controller  104  and stores instructions, calibration constants, and other information as required to satisfactorily complete a selected user instruction or input. Memory  110  may, for example, be a random access memory (RAM). In alternative embodiments, other forms of memory could be used in conjunction with RAM memory, including but not limited to flash memory (FLASH), programmable read only memory (PROM), and electronically erasable programmable read only memory (EEPROM).  
      Power to control system  100  is supplied to controller  104  by a power supply  112  configured to be coupled to a power line L. Analog to digital and digital to analog converters (not shown) are coupled to the controller  104  to implement controller inputs and executable instructions to generate controller outputs to operative components  114 ,  116 ,  118  and  120  of the device  102  according to known methods. While four components  114 ,  116 ,  118 , and  120  are illustrated in  FIG. 1 , it is recognized that greater or fewer components may be employed within the scope of the present invention.  
      In response to manipulation of the control interface  106 , the controller  104  monitors various operational factors of the device  102  with one or more sensors or transducers  122 , and the controller  104  executes operator selected functions and features according to known methods.  
       FIG. 2  is a top plan view of an exemplary control interface  106  for the control system  100  (shown in  FIG. 1 ). The interface  106  includes a panel  130  which defines an interface area  132  for manipulation by a user to enter control commands and instructions for the device  102  (shown in  FIG. 1 ). In different embodiments, the panel  130  may be mounted proximate the operative components  114 - 120  (e.g., heating elements) of the device  102  (such as in a cooking appliance), or the panel  130  may be located in a remote location from the components  114 - 120  (such as for moving components of an industrial machine).  
      The panel  130  further includes touch sensitive elements  134  and  136  (sometimes referred to as sensor element or sensors) and a periphery  135 ,  137  of the respective elements  134 ,  136  subdivide the panel interface area  132  into active areas  138  and inactive areas  140 . Specifically, an area outside the peripheries  135 ,  137  of the elements  134 ,  136  constitute inactive areas  140 , while an area within the peripheries constitutes the active portions or areas  138  of the sensor elements  134  and  136 . The active areas  138  of the touch sensitive elements  134  and  136  include first and second sensor portions, namely a primary activation area or portion  142  and a passive secondary activation area or portion  144 , sometimes referred to as a contaminant activation area, which may serve to identify inadvertent control inputs and prevent activation of a component  114 - 120  (shown in  FIG. 1 ) of a device  102  as explained below. In one embodiment the primary activation area  142  and the secondary activation area  144  are discrete portions of a single touch sensitive element, and the primary and secondary activation areas  142  and  144  are calibrated to different sensitivity levels. In another embodiment, the primary and secondary activation areas  142  and  144  are defined by discrete (i.e., different) touch sensitive elements.  
      Each of the primary activation areas  142  and the secondary areas  144  provide inputs to the controller  104  (shown in  FIG. 1 ), and each of the primary activation areas  142  are of a predetermined size and shape for convenient actuation with for example, a user&#39;s fingertip. The primary activation areas  142  of the respective touch sensitive elements  134  and  136  are marked with appropriate graphics or indicia to delineate the primary activation areas for the user. The secondary activation areas  144  in one embodiment are generally invisible or transparent to the user, although they may be marked or otherwise delineated if desired.  
      In an exemplary embodiment, the touch sensitive elements  134  and  136  are capacitive touch sensing elements such as those described in U.S. Pat. No. 5,760,715, the disclosure of which is hereby incorporated by reference in its entirety. In alternative embodiments, the touch sensitive elements  134  and  136  are known membrane switch assemblies, infrared detectors, or other known tactile or touch switches familiar to those in the art. It is understood that the touch sensitive elements  134  and  136  may be arranged in any desired orientation relative to one another within the confines of the panel  130 , and greater or fewer touch sensitive elements may be employed in the panel  130  without departing from the scope of the present invention. It is further recognized that the benefits of the invention accrue to control systems having more than one control panel  130  with one or more touch sensitive elements, such as elements  134  and  136 .  
      In use, a user touches, such as with a finger, the primary activation area  142  to enter a user command, instruction or input to the controller  104  (shown in  FIG. 2 ), which, in turn, operates the applicable components  114 - 120  of the device  102  in accordance with the user input. User manipulation of the secondary or contaminant activation areas  144  will not operate the components  114 - 120  of the device  102 . The inactive area  140  is not responsive to user touch or manipulation and is ineffective to signal the controller  104  of the control system  100  (shown in  FIG. 1 ) in any manner. The secondary or contaminant activation areas are provided, as explained below, to appropriately address instances wherein a contaminant  148  may adversely affect the panel  130  and lead to inadvertent actuation of the device  102 .  
      For instance, considering the case of an appliance cooktop, the contaminant  148  may be, for example, ketchup which is splashed or spilled over the control panel  130  to form an irregularly shaped mass of contaminant  148  on the surface of the panel  130 . The contaminant  148  spans portions of each of the three regions or areas of the panel  130 . That is, the contaminant  148  extends across a portion of the inactive area  140 , a portion of the secondary activation area  144 , and the primary activation area  142  of the touch sensitive element  134 . The properties of the contaminant  148  may effectively extend the primary activation area  142  beyond its original periphery  150  to the portion of the secondary activation area  144  and even the portion of the inactive area  140  occupied by the contaminant  148 . For example, when the touch sensitive element  134  is a capacitive touch sensor, a capacitive circuit may be completed through the ketchup to the primary activation area  142  even though a user is touching an area outside of the primary activation area. That is, an area of the panel  130  that ordinarily would not signal the controller  104  of an input instruction may nonetheless, due to the presence of the contaminant  148 , activate the primary activation area  142  and signal the controller  104  to operate the device  102 .  
      The present invention provides a system to distinguish between a true control input wherein the user actually activates one of the primary activation areas  142  of the touch sensitive elements  134  and  136  and a false control input wherein an apparent activation of the primary activation area  142  and resulting signal to the controller  104  (shown in  FIG. 1 ) is attributable to the presence of a contaminant on the control interface  106 . In an illustrative embodiment, the secondary activation areas  144  of the touch sensitive elements  134  and  136  substantially surround and are complementary in shape to the primary activation areas  142 . It is anticipated, however, that the secondary activation areas  144  need not entirely surround the primary activation area  142  of the touch sensitive elements  136  or be a complementary shape to the primary activation areas  142  in alternative embodiments while still achieving at least some of the benefits of the invention.  
      The secondary activation areas  144  of the elements  134 ,  136  define a contaminant detection area proximate to or adjacent the primary activation areas  142 . As explained below, the secondary activation areas  144  may be used to determine the presence of a contaminant which touches the primary activation areas  142  and causes a false input to the controller  104 . By monitoring the secondary activation areas  144  in addition to the primary activation areas  142  of the touch sensitive elements  134  and  136 , the controller  104  may differentiate between true and false control inputs when the primary activation area  142  signals the controller  104 . Specifically, a true control input is entered only through the primary activation area  142 , and a false control input is entered through both of the primary activation area  142  and the secondary activation area  144  as explained below.  
       FIG. 3  is an exemplary control algorithm  170  executable, for example, by the controller  104  (shown in  FIG. 1 ) to distinguish true and false inputs from the control interface  106  (shown in  FIG. 1 ), and more specifically from the primary activation areas  142  of the touch sensitive elements  134  and  136  (shown in  FIG. 2 ). By distinguishing between true and false control inputs, inadvertent actuation of the components  114 - 120  (shown in  FIG. 1 ) of the device  102  (shown in  FIG. 1 ) is prevented and only properly entered control input instructions are recognized to operate the device  102 .  
      Upon power up of the control system  100  (shown in  FIG. 1 ), at step  172  the controller enters a main control loop or algorithm which initializes program parameters, prepares the device for use, and then enters a dwell state awaiting user input or instruction through the control interface  106 . At step  174 , the controller then determines whether an input has been entered via the control interface  106 , or more specifically from any of the touch sensitive elements in the interface  106 , such as the elements  134  and  136 . The input may be determined, for example, by scanning the touch sensitive elements  134  and  136  for inputs, awaiting a signal from the touch sensitive elements  134  and  136 , or by another known method.  
      If an input is detected from one of the touch sensitive elements  134  or  136 , then at step  176  the controller determines whether the primary activation area  142  of the respective element  134  or  136  was activated to signal the controller. If the primary activation area  142  is not activated, the controller returns to the main control algorithm and ignores the input. This scenario may occur, for example, if a user inadvertently touches the secondary containment area  144  but not the primary activation area  142 . This situation may also occur due to the presence of a contaminant  148 , but is considered harmless if the contaminant does not affect the primary activation area  142 .  
      If the primary activation area  142  was activated, at step  178  the controller determines whether the secondary or contaminant area  144  of the respective touch sensitive element is also activated to signal the controller. If both the primary activation area  142  and the secondary contaminant area  144  of the respective touch sensitive element  134  or  136  are activated, an input is considered a false input possibly attributable to a contaminant  148  (shown in  FIG. 2 ) on the panel  130  (shown in  FIG. 2 ) of the controller interface  106 , and at step  180  the controller denotes a contaminant error in, for example, the controller memory  110  (shown in  FIG. 1 ). After denoting the error, the controller returns to the main control algorithm and awaits another input from one of the switches  134  or  136 . The controller does not respond to the detected input in this circumstance wherein both the primary activation area  142  and the secondary or contaminant area  144  actuated in one of the touch sensitive elements  134  or  136 .  
      If the primary activation area  142  was activated but the secondary contaminant area  144  was not activated, the input is considered true and at step  182  the controller enters a sub-control algorithm in response to the selected input instruction. Thus, the respective component  114 - 120  of the device  102  is actuated in accordance with the input instruction or command. Once the sub-control algorithm is entered, at step  184  the controller checks whether the sub-control algorithm is complete, and if so, the controller returns to the main control algorithm. If the sub-control algorithm is not complete, the controller returns to the sub-control algorithm.  
      Having now described the invention, it is believed that those in the art could readily adapt the teaching of the above description with appropriate modification for use in various devices to provide an appropriate safeguard against inadvertent actuation or operation device components. It is believed that the methodology of the above-described control system could be implemented without further explanation.  
       FIGS. 4 and 5  illustrate alternative embodiments of control panels  200  and  250 , respectively, which may be used in lieu of the control panel  106  (shown in  FIGS. 1 and 2 ) in the system  100  (shown in  FIG. 1 ) to prevent inadvertent actuation of a device  102  according to the above methodology.  
      Control panel  200 , for example, illustrates three touch sensitive elements  204 ,  206 , and  208  of various shapes and sizes and defining primary activation areas or portions  208 ,  210 , and  212  respectively. Each of the elements  204 ,  206 ,  208  are surrounded by a secondary contaminant detection area which encompasses each of the elements  202 ,  204 ,  206  and thereby forms a protective region around the switches which may be used to detect contaminants as described above. Thus, unlike the control panel  130  (shown in  FIG. 2 ) which includes secondary activation areas corresponding to each of the primary activation areas of each of the touch sensitive elements, the control panel  200  employs a single contaminant detection area with a plurality of touch sensitive elements  202 ,  204 , and  206 .  
      As noted above, the secondary activation area  214  may be defined by the same or different touch sensitive elements as the primary activation areas  208 ,  210 ,  212 .  
      In the control panel  250  of  FIG. 5 , a first touch sensitive element  252  includes multiple primary activation areas  254 , and a second touch sensitive element  256  includes multiple primary activation areas  258 . The touch sensitive elements  252  and  256  and the respective primary activation areas  254  and  258  are surrounded by a contaminant detection area  260 . The secondary contamination detection area  260  may be defined by the same or different touch sensitive elements as the elements  252  and  256 .  
      While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.