Abstract:
A door locking mechanism for an appliance provides a bolt that is biased by a spring but may be moved by a unidirectional actuator. A bi-stable mechanism blocks movement of the bolt at certain positions at successive actuations of the unidirectional actuator. In this way, energy need not be provided to the electromechanical actuator except periodically.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application 61/847,210 filed Jul. 17, 2013 and hereby incorporated by reference 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to clothes washing machines and the like, and specifically to a lid locking mechanism. 
       BACKGROUND OF THE INVENTION 
       [0003]    The spin cycle of a washing machine removes water centrifugally from wet clothes by spinning the clothes at high speed in a spin basket. In order to reduce the possibility of injury to the user during the spin cycle, it is known to use an electronically actuated lock for holding the washing machine lid in the closed position. U.S. Pat. Nos. 6,363,755; 5,823,017; and 5,520,424, assigned to the present assignee and hereby incorporated by reference, describe several locking mechanisms. Desirably, the locking mechanism minimizes projecting parts on the washing machine lid which might snag clothing or reduce access to the spin basket and is simply integrated into the washing machine housing. 
         [0004]    A signal indicating the state of the washing machine lid as opened or closed may be used to ensure the lid is closed before the lock is engaged. Such a signal may be provided by a switch communicating with the washing machine lid. Ideally such a switch could not be easily defeated, would operate reliably when used with other washing machine components with normal manufacturing tolerances, and would be resistant to contamination by water and dirt. 
         [0005]    U.S. Pat. No. 7,493,783, hereby incorporated by reference, describes a lid lock that can sense whether the lid is closed by distinguishing between an “over-travel” position of the lock bolt that can occur when the lock bolt is extended and the lid is up and so does not block the extension of the lock bolt, and an “engagement” position of the lock bolt that occurs when the lid is down and the lock bolt is received by the lid blocking overextension. A controller, by distinguishing between three electrical signals indicating, respectively, the unlock position, the over-travel position, and the lock position, can determine that the door is properly locked with the lid engaging the lock bolt. 
         [0006]    U.S. provisional application 61/711,418 filed Oct. 9, 2012, and hereby incorporated by reference, describes a lock bolt actuator employing a mechanical element responding to successive pairs of forward followed by reverse actuation from a bidirectional electric actuator, such as a motor, to provide three distinct lock bolt positions (unlock, lock and over-travel position) depending on the presence or absence of the lid. The lock position is blocked against retracting when an external inward force is applied on the bolt. A unique signal indicating that the bolt is either in the engaged position or over-travel position combined with controller logic allows the appliance controller to determine if the lid is closed and locked with only one binary signal. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides an improved lock bolt actuator that avoids the need for a bidirectional electrical actuator and which ensures full locking engagement between the bolt and lid despite bolt “bounce back”, lid spacing tolerances, and machine vibration. These benefits are obtained by incorporating a spring into the bolt mechanism that biases the bolt outward to fully engage the lid for a variety of bolt extensions and providing a two-state mechanical element that may alternatively release the bolt for a range of motion locking engagements or hold the bolt in the unlock position with successive unidirectional activations by a motor or solenoid. The ability to use a unidirectional actuator allows the actuator to be freely selected from among DC motors, AC motors, and solenoids. 
         [0008]    In one embodiment, the present invention provides an electric lock for a household appliance having a door where the door can be locked in a closed position by receipt of a bolt extending along an axis from an appliance frame into the door. The electric lock includes a housing to attach to the appliance frame and a bolt that may extend from the housing to a lock position to lock the door and retract into the housing to an unlock position to unlock the door. An electromechanical actuator operates to receive an electrical signal to apply a force to the bolt opposing a spring, the latter which may move the bolt when the electromechanical actuator is not actuated. A bi-stable mechanical linkage is attached to the bolt to hold the bolt at a stable position resisting movement by the spring and then to release the bolt from the stable position allowing movement by the spring with successive actuation of the electromechanical actuator. 
         [0009]    It is thus a feature of at least one embodiment of the invention to provide for a spring driven “homing” of the bolt when the electromechanical actuator is not actuated provide greater certainty in bolt position. 
         [0010]    The electromechanical actuator may operate only to provide force counter to the force of the spring. 
         [0011]    It is thus a feature of at least one embodiment of the invention to permit use of a unidirectional actuator that may be more simply controlled with fewer control wires. 
         [0012]    The spring may move the bolt along the axis in extension and wherein the bi-stable actuator operates to release the bolt to extend beyond the unlock position upon a first actuation and following a first deactivation of the electromechanical actuator, and may hold the bolt at the unlock position upon a second actuation and following second deactivation of the electromechanical actuator. 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide a spring loading to the bolt that retains the bolt fully in the lock position despite possible actuator bounce back caused by impact of the bolt and the lid and through a range of lid location tolerances and during appliance vibration when the actuator is de-energized. 
         [0014]    In an alternative embodiment, the spring may move moves the bolt along the axis in retraction and the bi-stable actuator may operate to hold the bolt at the lock position upon a first actuation and following a first deactivation of the electromechanical actuator, and to release the bolt to retract to the unlock position upon a second actuation and following second deactivation of the electromechanical actuator. 
         [0015]    It is thus a feature of at least one embodiment of the invention to provide a bolt that will automatically retract when the door is not in the closed position. 
         [0016]    Upon release by the bi-stable mechanical linkage, the bolt may extend to an over-travel position beyond the lock position when the door is not in the closed position, whereas the bolt may extend only to the lock position when the door is in the closed position. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide a method of detecting lid closure using measured bolt extension. If the bolt extends to the over-travel position, it can be inferred that the lid is not closed. In this regard, the invention may eliminate the need for separate lid closure sensors or provide backup to such sensors 
         [0018]    The electric lock may include contacts providing an electrical signal distinguishing between whether the bolt is in the lock position or over-travel position. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide an electrical signal that may be used to lockout some appliance functions in the event that the lid is not closed. 
         [0020]    The contacts may be closed when the bolt is in the lock position and not when the bolt is in the over-travel position. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a system where contact failure indicates a door reducing the chance that such failure would promote unsafe appliance operation. 
         [0022]    The electric lock may include a controller providing the electric signal to the electromechanical actuator to operate the electromechanical actuator only to provide a force urging the bolt in retraction and not a force urging the bolt in extension. 
         [0023]    It is thus a feature of at least one embodiment of the invention to provide a system that may use unidirectional or bidirectional electromechanical actuators. In this regard, the invention allows greater flexibility in selecting an actuator and simplifies the generation of control voltages. 
         [0024]    The spring may be sized to move the bolt in extension from the unlock position when the electromechanical actuator is not activated and the bolt is not held by the bi-stable mechanical linkage at the unlock position. 
         [0025]    It is thus a feature of at least one embodiment of the invention to permit the electromechanical actuator to be turned off during most of the operating time of the appliance for power savings while retaining lock functionality. 
         [0026]    The bi-stable mechanical linkage may provide a track and track-follower fixed, respectively, to one of the bolt and housing, the track follower interacting with the track to stably hold the bolt against the spring in the unlock position upon the first actuation and following the first deactivation. 
         [0027]    It is thus a feature of at least one embodiment of the invention to provide for a simple bi-stable mechanism that permits a range of over-travel positions. 
         [0028]    The follower may be a tip of a flexible spring. 
         [0029]    It is thus a feature of at least one embodiment of the invention to provide a simple follower resistant to binding. 
         [0030]    The track may be a groove in the bolt. 
         [0031]    It is thus a feature of at least one embodiment of the invention to minimize the size of the housing by placing the track on the bolt itself. 
         [0032]    The electromechanical actuator may be an electric motor, for example, a DC permanent magnet motor. 
         [0033]    It is thus a feature of at least one embodiment of the invention to permit use of a rapid response low noise, energy efficient electromagnetic actuator. 
         [0034]    The contacts may include only a single contact, pair allowing determination only of whether the bolt is in the lock position so that the electrical signal distinguishes between whether the bolt is in the unlock position or over-travel position. 
         [0035]    It is thus a feature of at least one embodiment of the invention to reduce the wiring harness necessary between an electric lock and a controller. 
         [0036]    Alternatively, the electric lock may include second contacts providing an electrical signal distinguishing between whether the bolt is in the unlock position or over travel position. 
         [0037]    It is thus a feature of at least one embodiment of the invention to positively identify the location of the bolt between the lock, unlock, and over-travel positions. 
         [0038]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a perspective view of a top loading washing machine suitable for use with the present invention showing a strike opening on a side of the opened lid of the washing machine and an electric lock having a bolt for engaging the same when the lid is closed and showing a controller on the console; 
           [0040]      FIG. 2  is a fragmentary cutaway of the portion of the lid and washing machine near the bolt of  FIG. 1  showing support of a locking mechanism beneath a lid well; 
           [0041]      FIG. 3  is a simplified top plan view of the bolt of  FIG. 2  extending through a wall of the lid well to engage a strike of the lid and illustrating an unlock position, lock position, and over-travel position of the bolt and further showing corresponding states of an electrical switch having multiple contacts connected to the bolt to provide an indication of bolt position both in the unlock position and lock position; 
           [0042]      FIG. 4  is a perspective view of an electric motor and rack and pinion mechanism for extending and retracting the bolt and showing a track and wire-follower controlling a resting position of the bolt in two states; 
           [0043]      FIG. 5  is a diagram of the position of the track and bolt with respect to the wire-follower for a full retraction (unlock) state; 
           [0044]      FIG. 6  is a figure similar to  FIG. 5  showing a position of the track and bolt after a first unidirectional actuation from the state of  FIG. 5 ; 
           [0045]      FIG. 7  is a figure similar to  FIGS. 5 and 6  after cessation of the unidirectional actuation with the bolt in a full extension engaged (lock) state with the lid such as accommodates a variety of lid housing separations; 
           [0046]      FIG. 8  is a figure similar to  FIGS. 5 ,  6 , and  7  showing a return of the track and bolt to the full retraction (unlock) state with a second unidirectional actuation; 
           [0047]      FIG. 9  is a figure similar to  FIG. 5  showing over-travel of the bolt after the first unidirectional actuation of  FIG. 6  when the lid is open; 
           [0048]      FIG. 10  is a flowchart of a program executed by the controller for control of the electric lock of  FIGS. 5-9 ; 
           [0049]      FIG. 11  is a figure similar to that of  FIG. 5  showing alternative track designed for use with a retraction spring showing the bolt in the unlock position; 
           [0050]      FIG. 12  is a figure similar to that of  FIG. 7  showing the bolt in the lock position; 
           [0051]      FIG. 13  is a figure similar to  FIG. 9  showing the bolt in the over travel position; and 
           [0052]      FIG. 14  is a figure similar to that of  FIG. 10  showing a program executed by the controller for control of the electric lock of  FIGS. 11-13 . 
           [0053]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0054]    Referring now to  FIG. 1 , an appliance  10 , such as a top loading washing, machine suitable for use with the present invention, includes a lid  12  opening upward about a horizontal lid hinge axis  13 . The lid hinge axis  13  is positioned near the top rear edge of a housing  14  of the appliance  10  so that a front edge  16  of the lid  12  may raise and lower to expose and cover an opening  20  through which clothing may be inserted into the spin basket. The present invention may also be used with a frontloading washing machine or other similar appliances  10  as will be understood from the following description. 
         [0055]    An electric lock  17  may be attached to the housing  14  and may provide for a bolt  30  that may be extended from the housing  14  into a strike opening  26  in the lid  12  to lock the lid  12  when the lid  12  is closed, conversely, an electric signal may retract the bolt  30  into the housing  14  to allow the lid  12  to be freely opened after locking. 
         [0056]    The electric lock  17  may communicate electrically via at least one conductive circuit  15  to a controller  21 , for example, positioned at a rear console of the housing  14 . The controller  21  may also provide for electrical communication with various user controls  23  as is understood in the art and with electrical machinery  25  such as an agitator motor or the like to control the same. In this regard, the controller  21  may provide an electronic processor for executing an appliance control program held in a non-transient media such as computer memory. 
         [0057]    Referring now to  FIG. 2 , in this example, when the lid  12  is in the closed position, it may sit within a lid well  18  having vertical walls  32  surrounding vertical walls  22  of the lid  12  and having a horizontal ledge  19  on which the lower surface of the lid  12  may rest. A vertical wall  22  of the lid  12  near a front edge  16  of the lid  12  provides a strike plate  24  having a strike opening  26 . 
         [0058]    Referring also to  FIG. 3 , the strike opening  26  is sized to receive a leading edge  28  of a lateral extension  40  of a bolt  30  passing horizontally out of a lock housing  33  of the electric lock  17  when the lock housing  33  is a fixed to the housing  14  behind the vertical wall  32 . The bolt  30  may extend from the lock housing  33  along an axis  62  through an opening in the vertical wall  32  of the lid well  18  opposite the strike plate  24  when the lid  12  is closed. When the leading edge  28  of the bolt  30  is engaged in the strike opening  26 , the lid  12  may not be raised vertically as indicated by arrow  36  as a result of the lower edge of the strike opening  26  interfering with a lower face of the leading edge  28 . This extension of the bolt  30  will be called the lock position or lock state. 
         [0059]    When the lid  12  is closed, the leading edge  28  of the bolt  30  may be blocked from further extension by a stop  34  attached to the lid  12  behind the strike opening  26 . When the lid  12  is open, however, the leading edge  28  may move further in extension to an over-travel position as will be described. 
         [0060]    Referring now to  FIG. 3 , as will be discussed in detail below, the bolt  30  communicates via a side arm  46  (shown schematically in  FIG. 3 ) with a contact set  52 . The contact set  52  provides a two-throw switch in which a pole  54  (attached to the side arm  46 ) interconnects between respective terminals  56   a,    56   b,  and  56   c  fashioned on the upper surface of the printed circuit board contact support element  70  (shown in  FIG. 4 ) fixed with respect to the housing  25 . 
         [0061]    Terminals  56   a  and  56   b  are joined by the conductive pole  54  in a lock position (B) in which the leading edge  28  engages the bolt hole  26  abutting the stop  34  but disconnects between terminals  56   a  and  56   b  and interconnects between respective terminals  56   c  and  56   b  in the unlock position (A) when the leading edge  28  is removed from the bolt hole  26 . In an over-travel position (C) where the leading edge extends beyond the lock position not stopped by the stop  34  when the door  12  is open, the pole  54  also connects to terminal  56   a  and  56   b.  Accordingly, the unlock position can be uniquely identified, but the lock position and the over-travel position cannot be positively distinguished by means of signals conveyed over separate conductors  59  attached to terminals  56   a  and  56   c  (and a common conductor attached to terminal  56   b ) conveying two signals of lock signal  96  and unlock/over-travel signal  91 . 
         [0062]    In a second embodiment, the contact set  52  implements a two-throw switch in which a pole  54  interconnects between respective terminals  56   a  and  56   b  in the lock position (B) in which the leading edge  28  engages the strike opening  26  abutting the stop  34 . Terminals  56   a  and  56   b  are otherwise disconnected when the bolt  30  is in other positions including both the unlock position (A) when the leading edge  28  is removed from the strike opening  26  and the over-travel position (C) where the leading edge extends beyond the lock position not stopped by the stop  34  when the lid  12  is open. In one embodiment, the contact set  52  comprises only terminals  56   a  and  56   b.  In this embodiment, only a lock position can be positively determined and the over-travel and unlock positions cannot be distinguished by terminals  56   a  and  56   b.    
         [0063]    In a third embodiment, a terminal  56   c  may be added where the pole  54  connects terminal  56   c  and terminal  56   b  only when the bolt is in the unlock position (A). It will be appreciated that this added terminal  56   c  allows the position of the bolt to be positively located in any one of the positions (A), (B) and (C). Accordingly, each of the lock, unlock, and over-travel positions can be positively determined and distinguished. 
       Bolt with Extension Biasing 
       [0064]    Referring now to  FIG. 4 , the bolt  30  may be driven along axis  62  in an retraction direction  67  by means of a rack gear  64  positioned on a lower surface of the bolt  30  driven by a pinion  66  turned by an electromechanical actuator  68  such as a DC motor operating in a unidirectional mode and capable of applying a force on the bolt  30  urging it to retract along axis  62  in the retraction direction  67  away from the lid  12  (as shown in  FIG. 3 ). In this regard, the DC motor may receive only a single polarity of voltage, for example, a DC voltage or a DC signal derived from an AC signal after it is rectified by a diode  71  (as shown). It will be appreciated that the electromechanical actuator  68  may alternatively be an AC motor (with the diode  71  removed), electrical solenoid, or other known electromechanical actuators. 
         [0065]    As will be described in more detail below, the bolt  30  may also attach to a spring  57  between the bolt  30  and the housing  14  urging the bolt  30  in an extension direction opposite the retraction direction  67  along axis  62 . The spring  57  may be, for example, a helical compression spring and may exert a force on the bolt  30  sufficient to move the bolt  30  to override the electromechanical actuator  68  when the latter is not electrically actuated. That is, the spring  57  may overcome the frictional forces presented by the un-energized electromechanical actuator  68  and other interconnecting and supporting structures. It will likewise be appreciated that the electromechanical actuator  68 , when actuated by an electrical current, may overcome the force of the spring  57  and any friction of the interconnecting mechanism and support structure. 
         [0066]    Referring still to  FIG. 4 , side arm  46  communicating between the bolt  30  and the contact set  52  may extend from a lower surface of the bolt  30  and pass in cantilevered fashion under a contact support element  70  forming part of the contact set  52  described above. A track  72  formed by a groove on the under surface of the bolt  30  receives an upwardly extending pin  74  being part of a wire form  75  attached to a housing  14  that may flex laterally generally perpendicular to axis  62 . The pin  74  fits in the groove of the track  72  to constrain motion of the bolt  30  as driven by the actuator  68 . When the motion of the bolt  30  in the retraction direction  67  is constrained by the pin  74 , as discussed below, the electromechanical actuator  68  may simply stall for a short period of time and is current limited (for example, by internal resistance) to allow the stall condition to be accommodated. In this way the actuator  68  may be driven in an “open-loop fashion” by an appliance controller  21  (shown in  FIG. 1 ). 
         [0067]    Referring now to  FIG. 5 , with the bolt  30  in the unlock position  76 , fully withdrawn from the lid  12 , the pin  74  will be at a distal end of the bolt  30  and the track  72 . The bolt  30  will be biased outward along axis  62  (opposite the retraction direction  67 ) by the spring  57  but will not move outward because the pin  74  presses stably against a trough  77  of the track  72 . At this position, the pole  54  connects to terminal  56   b  but not to terminal  56   a  and so a lock signal is not provided to the appliance controller. The track  72  provides a series of ledges  79  that enforce one-way travel of the pin  74  through the track  72  by causing the pin  74  to spring upward as it passes over the ledge  79  so that reverse travel is blocked by the ledge wall. 
         [0068]    Referring to  FIG. 6 , a pulse of current on the electromechanical actuator  68  (shown in  FIG. 4 ) provided by a central controller  21  will then cause the bolt  30  to move in the retraction direction  67  moving the pin  74  away from its resting position on the trough  77  up to a right-hand side  80  of the track  72  as indicated by the dotted line. Pole  54  is still disconnected from terminal  56   a.    
         [0069]    Referring to  FIG. 7 , when the current to the electromechanical actuator  68  ceases, the spring  57  urges the bolt  30  outward and the pin  74  drops from the right-hand side  80  down a central track  81  of the track  72  passing to the rear of the bolt  30  allowing the bolt  30  to extend along axis  62  until it hits the stop  34  in the lid  12  at an lock position  83 . The spring biasing ensures that the bolt  30  is fully extended into the strike opening  26  regardless of slight tolerance variations and removing any “bounce back” which can occur with motorized actuators in which flexure and/or inertia cause the bolt to retract slightly after bottoming on the stop  34 . The central track  81  extends by a tolerance stack-up distance  82  allowing this full extension of the bolt  30  into the strike opening  26  for a variety of different separations between the lid  12  and the housing vertical wall  32 . Terminal  56   a  is sized so that pole  54  connects terminal  56   a  to terminal  56   b  for the full extent of the tolerance stack-up distance  82  to provide a lock signal throughout this range. 
         [0070]    Referring now to  FIG. 8 , a second pulse of current on the actuator  68  will again cause the bolt  30  to move in the refraction direction  67  causing the pin  74  to pass upward to a left-hand lobe  84  of the track  72  and pole  54  to break contact between terminals  56   a  and  56   b  interrupting the lock signal as is appropriate. Cessation of the current to the electromechanical actuator  68  allows the spring  57  to urge the bolt outward so that the pin  74  returns again to the trough  77  as shown in  FIG. 5 . 
         [0071]    It can be seen therefore that successive unidirectional actuations of the actuator  68  when the lid  12  is closed can cause a cycling of the bolt  30  between an unlock position  76  and lock position  83  and that full extension of the bolt  30  into the strike opening  26  may be ensured for a variety of different manufacturing dimension variations. 
         [0072]    Referring now to  FIG. 9 , if the lid  12  is not closed or if the end of the bolt  30 , for example, is broken off, after cessation of the retraction direction  67  of  FIG. 6 , the bolt  30  will pass outward unimpeded by the stop  34  as driven by spring  57  to beyond the lock position  83 . This is allowed because of continuation of central track  81  substantially beyond the distance required for the bolt  30  to extend to the lock position  83 . The result is that the pole  54  moves beyond terminal  56   a,  again, breaking any lock signal so as to indicate to the central controller  21  that the lid  12  is not properly locked. 
         [0073]    A further actuation of the actuator  68 , however, will bring the bolt  30  back to the position shown in  FIG. 8  and it may return, to the position of  FIG. 5  provided the bolt  30  and the track  72  are preserved. 
         [0074]    The pin  74  has been described below as if it is moving relative to the bolt  30  for convenience of description, although in fact, it is the bolt  30  that is moving. 
         [0075]    After extension, the bolt  30  may be manually pressed fully in but will no longer indicate a locking, the pin simply moving along the upper right-hand side  80 . In this way the actuation of the washing machine may be inhibited in a manner that is difficult to defeat. Generally the lock signal may be used to prevent a starting of an appliance motor such as a washtub motor or the like. 
         [0076]    Referring now to  FIGS. 3 ,  4  and  10 , as noted above, the controller  21  may include a processor executing a stored program  100  held in computer memory in a non-transient form. The controller  21  may await a lock command from another portion of the program  100 , typically triggered by activation of the appliance  10  through user controls  23 . When a lock command is detected as indicated by decision block  102 , the controller  21  may provide a signal to the electromechanical actuator  68  causing it to apply retraction force in direction  67  to the bolt  30  and then to release that force so that the bolt  30  is moved by the force of the spring  57  in a push/release cycle indicated by process block  104 . 
         [0077]    Following process block  104 , at decision block  106 , the controller  21  may check terminal  56   a  to determine if the bolt  30  is in the locked position based on a lock signal received through a single electrical circuit formed with terminals  56   a  and  56   b.  In normal operation, a lock signal will be present and the program  100  proceeds to process block  108  to wait for an unlock command, for example, from another part of the program  100  timing out a wash cycle. Upon receiving the unlock command, the program  100  proceeds to a push/release block  110  identical to process block  104 , which causes a retraction of the bolt  30  as described above. 
         [0078]    At subsequent decision block  112 , program  100  checks to ensure that no lock signal is present (as would be typical), and if this is the case, after the first push/release operation of process block  104  proceeds again to decision block  102  to wait for new lock command. 
         [0079]    If at decision block  106  no lock signal is received after the push/release of process block  104 , two possibilities exist. One is that the bolt  30  is in the over-travel position (C) and the other is that the bolt  30  is in the retraction position (A) having previously been in the over-travel position, for example, as a result of a power failure or the like which interrupted a previous cycling. To resolve this ambiguity, process block  114  may initiate an additional push/release cycle. The lock signal is then checked at subsequent decision block  116  and if a lock has now been attained, the program proceeds to decision block  108 . 
         [0080]    If at decision block  116  a lock signal is not present, or if after decision block  112  the lock signal is present, the program  100  proceeds to an error state  118  where functionality of the appliance  10 , for example, starting of the agitator motor  25  or the like, is inhibited based on a conclusion that the lid  12  cannot be locked or unlocked as the case may be. 
       Bolt with Retraction Biasing 
       [0081]    Referring again to  FIG. 4 , in an alternative embodiment, the bolt  30  may be driven along axis  62  in an extension direction  67 ′ by means of the rack gear  64  with the DC motor operating in a unidirectional mode but capable of applying a force on the bolt  30  urging it to extend along axis  62  in the extension direction  67 ′ (shown in  FIG. 11 ) toward from the lid  12  (as shown in  FIG. 3 ). Again, the DC motor may receive only a single polarity of voltage, for example, a DC voltage or a DC signal derived from an AC signal after it is rectified by a diode  71  (as shown). It will be appreciated that the electromechanical actuator  68  may alternatively be an AC motor (with the diode  71  removed), electrical solenoid, or other known electromechanical actuators. 
         [0082]    In this embodiment, the bolt  30  may also attach to a spring  57 ′ between the bolt  30  and the housing  14  urging the bolt  30  in a retraction direction opposite the extension direction  67 ′ along axis  62 . The spring  57  may be, for example, a helical extension spring and may exert a force on the bolt  30  sufficient to move the bolt  30  to override the electromechanical actuator  68  when the latter is not electrically actuated. That is, the spring  57  may overcome the frictional forces presented by the un-energized electromechanical actuator  68  and other interconnecting and supporting structures. It will likewise be appreciated that the electromechanical actuator  68 , when actuated by an electrical current, may overcome the force of the spring  57  and any friction of the interconnecting mechanism and support structure. 
         [0083]    Referring now to  FIG. 11 , with the bolt  30  in the unlock position  76 , fully withdrawn from the lid  12 , the pin  74  will be at a distal end of the bolt  30  and the track  72 . The bolt  30  will be biased inward along axis  62  (opposite the extension direction  67 ′) by the spring  57  but will not move inward because the pin  74  presses stably against a trough  77 ′ of the track  72 ′. At this position, the pole  54  connects to terminal  56   b  but not to terminal  56   a  and so a lock signal is not provided to the appliance controller. Again, the track  72 ′ provides a series of ledges  79  that enforce one-way travel of the pin  74  through the track  72 ′ by causing the pin  74  to spring upward as it passes over the ledge  79  so that reverse travel is blocked by the ledge wall. 
         [0084]    Referring to  FIG. 12 , a pulse of current on the electromechanical actuator  68  (shown in  FIG. 4 ) provided by a central controller  21  will then cause the bolt  30  to move in the extension direction  67 ′ moving the pin  74  away from its resting position on the trough  77  down a right-hand side  80  of the track  72  as indicated by the dotted line. Pole  54  is still disconnected from terminal  56   a.  When the current to the electromechanical actuator  68  ceases, the spring  57  urges the bolt  30  inward and the pin  74  moves upward to be captured by trough  86  preventing further retraction. 
         [0085]    Alternatively, referring now to  FIG. 13 , if the lid  12  is not closed or if the end of the bolt  30 , for example, is broken off, after cessation of the retraction direction  67 ′ upon a pulse of current to the electromechanical actuator  68 , the bolt  30  will pass outward unimpeded by the stop  34  to beyond the lock position  83 . This is allowed because of continuation of central track  81  substantially beyond the distance required for the bolt  30  to extend to the lock position  83 . The result is that the pole  54  moves beyond terminal  56   a,  again breaking any lock signal so as to indicate to the central controller  21  that the lid  12  is not properly locked. 
         [0086]    Upon cessation of the current to the electromagnetic actuator  68 , the pin  74  will move back to his position shown in  FIG. 11  with the bolt  30  fully retracted. In this way the bolt  30  is protected from damage when the lid  12  is closed. 
         [0087]    Referring now to  FIGS. 3 ,  4  and  14 , stored program  100  executed by the controller  21  may operates similarly to that described with respect to  FIG. 10  with the exception that if after the lock actuation of process block  104 , there is no lock signal per decision block  106 , and error may be entered into immediately without the need to retract the bolt  30  which is automatically retracted by the force of the spring  57 ′ 
         [0088]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. 
         [0089]    Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.