Abstract:
An inner tub of a washing machine is rapidly braked during a portion of a deceleration phase following an extraction phase of an overall spin cycle. A controller establishes the braking operation over a critical speed band or resonant frequency zone during which excessive vibrations would be developed. The critical speed band is preferably determined based on one or more signals received from speed, load, and/or out-of-balance sensors.

Description:
BACKGROUND OF INVENTION 
   1. Field of Invention 
   The present invention pertains to the art of washing machines, and more particularly, to a control system for braking an inner tub of a washing machine through a critical speed range within which an out-of-balance condition could occur, such that the washing machine is not exposed to high vibration levels. 
   2. Discussion of Prior Art 
   Typical washing machines perform a wash cycle by agitating or tumbling a load of clothes bathed in a water or water/detergent solution within an inner tub. After the wash cycle has completed, a spin cycle, including an extraction phase and a deceleration phase, is required. Most machines perform this cycle by spinning the inner tub at a high rate such that centrifugal forces cause the water or water/detergent solution to separate from the clothes. After a predetermined period has elapsed, drive to the inner tub is disrupted whereby the inner tub is slowly brought to a stop. 
   It is well known in the art that, prior to the extraction or dehydration phase, the clothes can become unevenly distributed within the inner tub. During the extraction phase of the spin cycle, the uneven distribution of the clothes results in an out-of-balance condition which causes excessive vibration of the machine. For this reason, it is known to incorporate out-of-balance sensors in washing machines to determine the presence of such a condition which can be counteracted such that the effects caused by the vibrations are reduced. While these corrective measures are effective, they focus on the extraction phase of the spin cycle, as opposed to the deceleration phase of the cycle. However, during the deceleration phase, an out-of-balance condition can cause the machine to experience similar vibration problems as during the extraction phase of the spin cycle. Accordingly, based on at least these reasons, there exists a need in the art for a braking system which will effectively and efficiently reduce the effects of vibration on a washing machine, thereby enhancing the effective life of the machine and protecting its various components. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a system and method for effectively braking an inner tub or spinner of a washing machine following an extraction phase of a spin cycle to reduce the amount of time the inner tub is near the resonant frequency of the machine. Experience has shown that an out-of-balance condition will occur within a discrete or critical speed band during deceleration (assuming a generally consistent load size). Therefore, if the inner tub is caused to rapidly pass through the critical speed band during braking, the effects of high vibrations due to an unbalanced load is substantially eliminated. To this end, in accordance with the invention, a control system is incorporated into the washing machine to rapidly decelerate the inner tub through the critical speed band, preferably by applying a short burst of braking force, e.g., a pulsed braking force, to reduce the impact on electronic control components. 
   In accordance with the invention, an out-of-balance sensor is provided to sense the onset of an unbalance condition. The sensor will signal a controller which will operate a brake to rapidly decelerate the inner tub. More particularly, in one preferred embodiment, the controller is configured to intermittently operate the brake to slow the inner tub through the critical speed band such that component life can be extended. In another preferred embodiment, the brake control of the present invention is incorporated into systems having a mechanical brake. As mechanical braking systems are exposed to potential damage when subjected to excessive or extreme out-of-balance conditions, the present invention preferably provides for intermittent operation of the mechanical brake to aid in handling unbalanced loads. 
   In a still further preferred form of the embodiment, the control system of the present invention will “learn” the location of the critical speed band during a spin cycle in which an out-of-balance condition is likely to occur for any given load size. The location will be stored in a memory including a “look-up” table such that the control will activate the brake over a known discrete speed band in order to reduce the impact of an out-of-balance condition. 
   Based on the above, it should be apparent that the system of the present invention relies upon one or more specific dynamic variables of the washing machine in order to accurately and effectively control the braking of the inner tub, such that the washing machine is not exposed to excessive vibrations. In any event, additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a horizontal axis washing machine incorporating the braking control system of the present invention; and 
       FIG. 2  is a partially cut away view of a vertical axis washing machine, including a spherical spinner, multiple agitators and a direct drive system, incorporating the braking control system of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With initial reference to  FIG. 1 , an automatic horizontal axis washing machine incorporating the braking control system of the present invention is generally indicated at  2 . In a manner known in the art, washing machine  2  is adapted to be front loaded with articles of clothing to be laundered through a tumble-type washing operation. As shown, automatic washing machine  2  incorporates an outer cabinet shell  5  provided with a front door  8  adapted to extend across an access opening  10 . Front door  8  can be selectively pivoted to provide access to an inner tub or spinner  12  that constitutes a washing basket within which articles of clothing are laundered. 
   As is known in the art, inner tub  12  is formed with a plurality of holes  15  and multiple, radially inwardly projecting fins or blades  19  are fixedly secured to inner tub  12 . Inner tub  12  is mounted for rotation within an outer tub (not shown) which, in turn, is supported through a suspension mechanism (also not shown) within cabinet shell  5 . Inner tub  12  is mounted within cabinet shell  5  for rotation about a generally horizontal axis. A motor  27 , preferably constituted by a variable speed, reversible electric motor, is mounted within cabinet shell  5  and adapted to drive inner tub  12 . More specifically, inner tub  12  is rotated during both wash and rinse cycles such that articles of clothing placed therein actually tumble through either water, a detergent/water solution, or another washing fluid supplied within inner tub  12 . 
   The general construction and basic operation of washing machine  2  is known in the art and not considered an aspect of the present invention. Therefore, a full description of its construction will not be set forth here. However, for the sake of completeness, automatic washing machine  2  is also shown to include an upper cover  42  that provides access to an area for adding detergent, softeners and the like. In addition, an upper control panel  45 , including an LCD touch screen display  50 , is provided for manually setting a desired washing operation. 
   The present invention is particularly directed to the manner in which a rotational speed of inner tub  12  is controlled during a critical period following an extraction phase of a spin cycle. To this end,  FIG. 1  also illustrates one preferred control system embodiment in accordance with the present invention. As shown, washing machine  2  incorporates a central processing unit (CPU)  60  which preferably includes a memory  62 . As will also be detailed fully below, CPU  60  functions to regulate a brake control  65  for inner tub  12 . In the embodiment shown, CPU  60  is adapted to receive signals from an inner tub speed sensor  80  and an out-of-balance sensor  85 . As will also be detailed more fully below, CPU  60  actually functions to regulate brake control  65 , drive controls  90  and, at least indirectly, motor  27 . As further discussed more fully below, CPU  60  can receive signals from a load sensor as generally indicated at  92 . At this point, it should be noted that speed, out-of-balance, and load sensors for washing machines are well known in the art. In any event, the particular construction of each of these sensors is not important in connection with the present invention and therefore will not be detailed further here. 
   After the articles of clothing placed within inner tub  12  for laundering are subjected to a washing phase wherein the clothes will be tumbled within inner tub  12 , a spin cycle of an overall washing operation will be initiated. A similar spin cycle will also be performed following each rinse cycle. In any event, during an extraction or dehydration phase of each spin cycle, inner tub  12  will be rotated at relatively high speeds, e.g., speeds up to and exceeding 700 rpm as is known in the art, such that the water or water/detergent solution is caused to separate from the clothes. After extraction, a deceleration phase takes place wherein drive to inner tub  12  is terminated through drive control  90 . During the extraction phase, out-of-balance sensor  85  can be used to monitor for the onset of an out-of-balance condition. That is, if the clothes are unevenly distributed, out-of-balance sensor  85  will send a signal to CPU  60 . If the out-of-balance condition exceeds a predetermined threshold, CPU  60  can respond by modifying the operation of washing machine  2 , such as by lowering the maximum rotational speed for inner tub  12  for future cycles, as known in the art. 
   In any event, after the water or water/detergent solution is extracted from the clothing, a deceleration period for inner tub  12  is initiated. Therefore, motor  27  will be deactivated through drive control  90  and inner tub  12  is caused to decelerate. It is at this point that the present invention is actually employed. In accordance with the invention, as inner tub  12  decelerates, out-of-balance sensor  85  continuously monitors for the presence of an unbalanced condition. When out-of-balance sensor  85  detects an unbalanced condition during this deceleration phase, a signal is sent to CPU  60 . Essentially simultaneously with the receipt of the out-of-balance signal, CPU  60  will send a braking signal to brake control  65  in order to rapidly reduce the rotational speed of inner tub  12 . In general, experience has shown that a critical speed band will exist over an intermediate portion of the deceleration phase. It is during this portion that out-of-balance conditions are prevalent based on an average load and machine design parameters. In any event, as signals are continuously received from out-of-balance sensor  85 , brake control  65  need only be activated by CPU  60  through the critical speed band. 
   Most preferably, the signals received from out-of-balance sensor  85  reflect an incipient out-of-balance condition such that an actual state of unbalance need never actually be reached. In accordance with the embodiment of  FIG. 1 , activation of the brake preferably constitutes altering the operation of motor  27 . More specifically, motor  27  is either operated in reverse, or at a speed substantially lower than the current speed of rotation of inner tub  12 , in order to rapidly reduce the rotational speed of inner tub  12  through the speed range that exhibits the out-of-balance condition. Regardless, instead of simply allowing inner tub  12  to coast to a stop or applying some constant braking force, the present invention assures that the speed of inner tub  12  is rapidly reduced through the critical speed band or range during which an out-of-balance condition would exist. 
   Although CPU  60  could operate in accordance with the invention based only on the signals received from out-of-balance sensor  85  for a current washing operation, speed sensor  80  also preferably sends signals representative of the speed at which the unbalanced condition occurs. In accordance with a preferred embodiment of the invention, the unbalance and speed signals are stored in non-volatile memory  62  for later use. That is, the stored information is used in connection with the invention to better determine an incipient unbalanced condition. In general, as indicated above, a substantially consistent critical speed range will be established for an average load size and a given washing machine construction/operation. In any event, by storing this information, CPU  60  can actually contain a “look-up” table used to anticipate an out-of-balance condition and take pre-unbalance measures to avoid the condition. 
   Of course, tests could be simply run for a particular washing machine, with CPU  60  having pre-stored in memory  62  the critical speed range for the application of rapid deceleration. Therefore, CPU  60  effectuates braking when inner tub  12  approaches an unbalanced state based on “learned” parameters, with these parameters either being learned in pre-testing prior to selling washing machine  2  to a consumer or during actual use by the consumer. As indicated above, CPU  60  can also receive signals from and store in memory  62  the weight of a particular washing load. In this case, over time, CPU  60  will acquire a plurality of speed and load parameters which relate to sensed out-of-balance parameters. This information can readily be used to identify a particular critical speed band for rapid braking dependent on the weight of the load. Therefore, in this manner, a critical speed band can be established for discrete load weights such that braking is achieved without exposing the machine to any undue vibration. 
   As indicated above, the preferred embodiment disclosed with reference to  FIG. 1  controls motor  27  to establish the required braking. However, other braking arrangements could be equally employed.  FIG. 2  depicts a vertical axis washing machine  100  which utilizes another type of braking arrangement. As the general structure and operation of washing machine  100  are known in the art (details being found in U.S. Pat. Nos. 5,829,277 and 6,220,063 which are incorporated herein by reference), these details will not be reiterated here. However, washing machine  100  is shown to include a generally spherical inner tub  110 , a substantially spherical outer tub  111 , and a control panel  113 . A pair of agitators  115  are mounted within inner tub  110  and are provided to cause clothes  120  to effectively shift within inner tub  110  during a washing operation. Inner tub  110  is drivingly connected to a motor  130  through a driveshaft  135 . More importantly, in connection with the present invention, washing machine  100  is shown to include a mechanical braking system including a brake disc  145  and a brake caliper  150 . 
   In a manner corresponding to that set forth with respect to the first embodiment described above, washing machine  100  can be controlled to rapidly brake through a critical speed band or range during a deceleration phase of a spin cycle. Due to the directly analogous structure and function with the embodiment of  FIG. 1 , common reference numerals have been utilized in  FIG. 3  to depict the corresponding structure. In any event, the main difference between the embodiment of  FIG. 1  and that of  FIG. 3  is that brake control  65  controls caliper  150  in the latter embodiment. Since, in all other respects, the two embodiments are the same, a complete reiteration of the overall operation will not be provided here. Instead, it is simply important to note that the invention can be applied to both vertical and horizontal axis washing machines and the braking function can be performed in various ways. Therefore, it should be realized that the examples set forth herein are not intended to limit the methods of or structure for braking that can be used in connection with the present invention. It should also be realized that the braking operation can be achieved through the use of a consistent or uniform braking force, or an intermittent force could be applied through the critical period. In any event, the invention is only intended to be limited by the scope of the following claims.