AU2016385274B2

AU2016385274B2 - Dishwasher and controlling method thereof

Info

Publication number: AU2016385274B2
Application number: AU2016385274A
Authority: AU
Inventors: Sangsoo Lee
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2016-01-05
Filing date: 2016-11-23
Publication date: 2019-05-16
Anticipated expiration: 2036-11-23
Also published as: CN106963316A; EP3189764A1; CN106963316B; EP3189764B1; KR20170082033A; WO2017119605A1; AU2016385274A1; US20170188776A1

Abstract

Disclosed is a controlling method of a dishwasher (100) comprising a water supply step for supplying wash water, a preliminary washing step (S 120) for injecting the wash water to one or more dishes, a main washing step (S 130) for injecting the wash water mixed with washing liquid to the dishes, a rinsing step (S 140) for injecting the wash water to the dishes, and a heating step for heating the wash water in one or more of the preliminary washing step (S 120), the main washing step (S 130) and the rinsing step (S 140), wherein a heater sensing step for determining an operational state of a heater heating the wash water is performed in the heating step in a state where the circulation of wash water is stopped.

Description

DISHWASHER AND CONTROLLING METHOD THEREOF

Technical Field [1] Embodiments of the present disclosure relate to a dishwasher, more particularly, to a dishwasher which uses night-time electricity in performing a drying process which is the next step of the washing process , and a controlling method thereof.

Background [2] Generally, a dishwasher is the mechanism configured to wash and dry one or more dishes held therein by injecting wash water to the dishes at a high pressure. Specifically, wash water is injected in a washing tub where dishes are held at a high pressure and the injected wash water washes and clean out food scraps or contaminants from surfaces of dishes.

[3] Such a dishwasher is capable of filtering the food scraps contained in the wash water and reusing the used wash water. Also, the dishwasher has dishwashing detergent or liquid dissolved in the wash water to remove the food scraps smoothly and efficiently. The dishwashers capable of enhancing washing efficiency by raising the temperature of wash water or generating steam, using a heater, have been widely popular.

[4] Such the conventional dishwasher includes a case defining an exterior appearance; a washing tub provided in the case and defining a washing space for dishes; a driving unit provided in a lower portion of the washing tub and supplying, collecting, circulating and draining washing water for washing the dishes; lower/upper/top injecting nozzles injecting the washing water supplied by the driving unit to dishes; and lower/upper/top storage racks extractable between the lower/upper/top injection units within the washing tub and selectively accommodating dishes according to kinds and sizes of dishes.

[5] Each of the storage racks has a plurality of moving rollers installed in each lower surface and guide rails are provided in an inner wall of the washing tub. The guide rails guide the rollers for the storage racks to be retractable.

[6] Meanwhile, a user opens a door of the dishwasher to start dishwashing and takes out one of the storage racks arranged in the washing tub. Then, the user puts one or more dishes in the taken-out storage rack and pushes the storage rack before closing the door, to put the dishwasher into operation so as to wash the dishes.

[7] Hence, the user puts the dishwasher into operation and the driving unit is implemented to supply wash water to the upper/lower/top injection nozzles independently or simultaneously, to start the washing process for the dishes put in the lower/upper/top storage racks.

[8] Such the dishwasher controls wash water to be heated to facilitate the solution of dishwashing detergent which is mixedly supplied together with the wash water and soak

2016385274 27 Mar 2019 the food scraps stuck on the dishes for a long time, so that an overall dishwashing process can be performed smoothly.

[9] A conventional controlling method of such the dishwasher includes a preliminary washing step; a main washing step; a rinsing step; and a drying step. In the preliminary washing step, food scraps are soaked and a more reliable dishwashing process is able to be performed. Recently, a sterilizing step is further provided to irradiate ultraviolet rays to the dishes or heat the dishes at high temperatures the after the main washing step and the rinsing step, so as to restrain the propagation of germs or bacteria.

[10] Two methods may be proposed for the drying step. The two methods include a circulation type drying method and an exhaustion type drying method. In the circulation type drying method, dishes are heated in the washing tub and moisture is evaporated from the dishes and changed into vapors and the vaporized air inside the washing tub is circulated and condensed in the dishwasher, so that the condensed water is drained outside. In the exhaustion type drying method, external dry air is sucked into the washing tub of the dishwasher and the dry air absorbs moisture from the vaporized air evaporated form the heated dishes and the moisture-containing humid air is exhausted outside so as to dry the dishes.

[H] However, the circulation type drying method out of the conventional controlling methods according to the related art has a disadvantage of a lower drying efficiency than the exhaustion type drying method in an aspect of drying efficiency.

[12] Meanwhile, the exhaustion type drying method out of the conventional controlling methods according to the related art also has a disadvantage of high energy consumption, even though it is proper to the dishwasher as the drying method. In the exhaustion type drying method, the wash water inside the sump is heated to a preset temperature in the rinsing step for rinsing the washed dishes after the main washing step and the temperature inside the washing tub rises high enough to evaporate the moisture from the dishes, only to make the overall drying step longer.

[13] In addition, users usually collect and put a relatively much amount of dishes in the dishwasher. In this instance, such a much amount of dishes are put in the dishwasher and the conventional dishwasher has a disadvantageously deteriorated drying condition for the dishes having being washed and dried/kept therein.

[13A] It is desired to address or ameliorate one or more disadvantages or limitations associated with the prior art, or to at least provide a useful alternative.

Summary [13B] In accordance with the present invention there is provided a controlling method of a dishwasher including a washing tub defining a space in which one or more dishes are placed, a storage unit movable from the washing tub, a driving unit provided in a lower

2016385274 27 Mar 2019 unit of the washing tub and injecting wash water to the storage unit, a door opening/closing the washing tub and including a drying module drying the dishes, the controlling method comprising:

a water supply step of supplying wash water to a dishwasher;

a washing step of washing one or more dishes using the supplied wash water;

a rinsing step of rinsing the washed dishes;

a drying step of drying the rinsed dishes;

a drying determining step for determining selection of a dry maintaining step after the drying step; and the dry maintaining step of intermittently drying the dishes to maintain a dried state of the dishes.

[13C] The present invention also provides a dishwasher comprising:

a washing tub in which one or more dishes are placed;

a storage unit;

a driving unit provided in the washing tub and injecting wash water to the storage unit; a door opening/closing the washing tub and comprising a drying module for drying the dishes and a manipulation unit comprises a dry maintaining button for operating a dry maintaining step for intermittently operating the drying module for a preset time period; and a controller intermittently operating the drying module for a preset time period according to user’s settings of the manipulation unit to maintain a dried state of the dishes separately from the drying step after the step of drying the dishes.

Brief Description of Drawings [14] Some embodiments are hereinafter described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[15] FIG. 1 is a perspective diagram illustrating a dishwasher in accordance with the present disclosure;

[16] FIG. 2 is a schematic diagram illustrating an internal structure of the dishwasher in accordance with the present disclosure;

[17] FIG. 3 is a diagram illustrating key parts of the dishwasher in accordance with the present disclosure; and [18] FIG. 4 is a flow chart illustrating the operation of the dishwasher in accordance with the present disclosure; and [19] FIG. 5 is a flow chart illustrating a dried condition containing step of the dishwasher in accordance with the present disclosure

2016385274 27 Mar 2019

Detailed Description [20] To overcome the disadvantages, the present disclosure may provide a dishwasher which is capable of keeping a dried condition of dishes, even if a user leaves the dishes in the dishwasher after a drying process after a washing process, and a controlling method thereof.

[21] Furthermore, the present disclosure may provide a dishwasher which is capable of performing a drying process for drying the dishes after a washing process at late nights when the dishwasher is not used, and a controlling method thereof.

[22] Still further, the present disclosure may provide a dishwasher which is capable of performing the drying process for drying the dishes after a washing process, using the night-time electricity which is relatively cheap, and a controlling method thereof.

[23] In accordance with the purpose of the embodiments, as embodied and broadly described herein, a controlling method of a dishwasher comprises a water supply step for supplying wash water to the dishwasher; a washing step for washing one or more dishes by using the wash water; a rinsing step for rinsing the washed dishes; a drying step for drying the rinsed dishes, and a dry maintaining step for intermittently drying the dishes to maintain a dried state of the dishes.

[24] The washing step may comprise a preliminary washing step for soaking food scraps or contaminants stuck on the dishes; and a main washing step for separating the food scraps or contaminants from the dishes.

[25] The controlling method of the dishwasher may further comprise a dry maintaining step for determining selection of the dry maintaining step after the drying step.

[26] The dry maintaining step may intermittently operate a drying module of the dishwasher for a preset time period.

[27] The operation time of the drying module may comprise a preset pause time and a preset duration time of the drying module which is shorter than the pause time.

[28] The dry maintaining step may end based on determination of the drying module operation ending condition.

[29] The drying module operation ending condition may comprise one of a user's operation ending input, opening of a door and staring of another washing course.

[30] In another aspect of the present disclosure, a dishwasher comprises a washing tub defining a space in which one or more dishes are paced; a storage unit movable from the washing tub; a driving unit provided in a lower unit of the washing tub and injecting wash water to the storage unit; a door opening/closing the washing tub and comprising a drying module drying the dishes; and a controller intermittently operating the drying module for a preset time period to maintain a dried state of the dishes placed in the washing tub.

4A

2016385274 27 Mar 2019 [31] The controller may operate the drying module after washing, rinsing and drying steps for the dishes to maintain the dried state of the dishes.

[32] The door may comprise a manipulation unit for controlling the dishwasher, and the manipulation unit may comprise a dry maintaining step for intermittently operating the drying module for a preset time period.

[33] The door may comprise a display unit displaying an operational state of the dishwasher, and the display unit comprises a dry maintaining lamp displaying that the drying module is intermittently operated for a preset time period.

[34] The embodiments may have following advantageous effects. The dishwasher is capable of keeping a dried condition of dishes, even if a user leaves the dishes in the dishwasher after a drying process after a washing process, and a controlling method thereof.

[35] Furthermore, the dishwasher is capable of performing a drying process for drying the dishes after a washing process at late nights when the dishwasher is not used, and a controlling method thereof.

[36] Still further, the dishwasher is capable of performing the drying process for drying the dishes after a washing process, using the night-time electricity which is relatively cheap, and a controlling method thereof.

[37] Referring to the accompanying drawings, exemplary embodiments of the present disclosure according to one embodiment of the present disclosure will be described in

WO 2017/119605 PCT/KR2016/013517 detail.

[38] Use of such terminology herein is merely intended to facilitate description of the specification, and the terminology itself is not intended to give any special meaning or function. In the present disclosure, that which is well-known to one of ordinary skill in the relevant art has generally been omitted for the sake of brevity.

[39] Regardless of numeral references, the same or equivalent components may be provided with the same reference numbers and description thereof will not be repeated. For the sake of brief description with reference to the drawings, the sizes and profiles of the elements illustrated in the accompanying drawings may be exaggerated or reduced and it should be understood that embodiments of a device or a controlling method presented herein are not limited by the accompanying drawings.

[40] First of all, a dishwasher in accordance with one embodiment of the present disclosure will be described in detail, referring to the accompanying drawings.

[41] FIG. 1 is a schematic diagram illustrating an internal structure of a dishwasher in accordance with the present disclosure. FIG. 2 is a perspective diagram illustrating a driving unit provided in the dishwasher. FIG. 3 is an exploded perspective diagram illustrating a heater assembly provided in the dishwasher.

[42] As shown in FIGS. 1, 2 and 3, the dishwasher 100 in accordance with the present disclosure includes a case 120 defining an exterior appearance thereof; a washing tub 130 installed in the case 120 and defining a washing space in which one or more dishes are washed, with an open front; a door 122 opening/closing the open front of the washing tub 130; a driving unit 140 provided in a lower portion of the washing tub 130 and supplying, collecting, circulating and draining wash water for washing the dishes; a plurality of storage units 150, 160 and 170 detachably provided in the washing tub 130 and having the dishes seated thereon; a plurality of injection units 132, 133 and 134 installed adjacent to the storage units 150, 160 and 170 and injecting the wash water for washing the dishes; a drying module 180 exhausting humid air inside the washing tub 130 outside the case 120; a controller 190 operating the dishwasher 100 by controlling the other components; and a control panel 123 connected to the controller 190 and controlling the components.

[43] The washing tub 130, the driving unit 140 and the injection units in the structure of the dishwasher 100 mentioned above may be equal to or similar to corresponding components of the conventional dishwasher in accordance with the related art. Accordingly, detailed description thereof will be omitted.

[44] Meanwhile, the storage units 150, 160 and 170 are able to be taken out from the internal space toward the open front of the washing tub 130. The plurality of the storage units 150, 160 and 170 includes a first storage unit 150 provided in a lower portion of the washing tub 130 and having relatively large dishes stored therein; a

WO 2017/119605 PCT/KR2016/013517 second storage unit 160 provided over the first storage unit 150 and having relatively small dishes stored therein; and a third storage unit 170 provided in an upper portion of the washing tub 130 and having tableware stored therein.

[45] The plurality of the injection units 132, 133 and 134 are configured to inject wash water to the dishes and tableware stored in the plurality of the storage units 150, 160 and 170. The plurality of the injection units 132, 133 and 134 includes a lower injection unit 134 provided in the lower portion of the washing tub 130 and injecting wash water to the first storage unit 150; an upper injection unit 133 provided between the first storage unit 150 and the second storage unit 160 and injecting wash water to the first and second storage units 150 and 160; and a top injection unit 132 provided in an upper portion of the washing tub 130 and injecting wash water to the third storage unit 170 or the second storage unit 160.

[46] Meanwhile, the door 122 is configured to open and close the open front of the washing tub 130 mentioned above. A hinge (not shown) is provided in a lower portion of the open front so that the door 122 can be rotary on the hinge.

[47] A handle (128) for opening the door 122 and a control panel 123 for controlling the dishwasher 100 are provided in an outer surface of the door 122.

[48] The drying module 180 for exhausting internal air of the washing tub 130 is provided in an inner surface of the door 122. The drying module 180 includes a drying path 184 provided in the inner surface of the door 122 and in communication with the washing tub 130 to guide a flow path of air to the outside of the dishwasher 100; and a drying fan 182 provided on the drying path 184 and blowing the air along the drying path. Such the drying module 180 may be selectively operated according to one of preset operation courses (for example, a drying course) which is selected by the user.

[49] The controller 190 may be implemented to control the overall operation of the dishwasher 100 and to operate each of the units provided in the dishwasher according to setting modules of the dishwasher 100. For example, the controller 190 may implement control for a conventional dishwashing course and a dry maintaining course configured to maintaining a dried state of dishes. The controller 290 may include an auxiliary timer 192 for time-based control of the dishwasher 100.

[50] The control panel 123 may be an upper portion of the door 122 and includes a manipulation unit 124 for controlling the operation of the dishwasher 100; and a display unit 126 displaying operation states of the dishwasher 100.

[51] The manipulation unit 124 and the display unit 126 are linked to the controller 190 mentioned above to control the operation of the dishwasher or display the operation states of the dishwasher 100.

[52] In this instance, the manipulation unit 124 has a plurality of buttons and the buttons serve as the input means for operating the dishwasher, so that the user can select a

WO 2017/119605 PCT/KR2016/013517 dishwashing course, dishwashing reservation time. Moreover, the manipulation unit 124 may include a dry maintaining button 125 for operating a dry maintaining step (S200, see FIG. 4) as the illustrated embodiment of the present disclosure.

[53] The display unit 126 is configured to display the information about the dishwasher which is set through the manipulation unit 124, and includes a plurality of LEDs and LCDs which are arranged serially. Diverse dishwashing information such as dishwashing states, time and so on may be displayed to the user, using flickering of LEDs and LCDs. Moreover, the display unit 126 may further include a dry maintaining operation lamp 127 for noticing to the selection of the dry maintaining step (S200) to the user in case the dry maintaining step (S200, see FIG. 4) is set to start through the manipulation unit 124 by the user.

[54] Next, referring to the accompanying drawings, the operation of the dishwasher in accordance with the illustrated embodiment of the present disclosure will be described. Each of the components which will be described later should be understood in reference to the description and drawings mentioned above.

[55] FIG. 4 is a flow chart illustrating the operation of the dishwasher in accordance with the present disclosure.

[56] First of all, the user puts one or more dishes in the storage units 121, 122 and 123 of the dishwasher and then starts a washing process by selecting a dish-washing button (not shown) provided in the manipulation unit 124. In this instance, the user may additionally select a course for maintaining a dried state of the dishes after the drying course, using the dry maintaining button 125 provided in the manipulation unit 124.

[57] Meanwhile, the controller 190 shown in FIG. 4 is implemented to start a water supply step (SI 10) for supplying water to the driving unit 140 of the washing tub 130. Once the water supply step (SI 10) finishes, a preliminary washing step (S120) for soaking food scraps or contaminants containing on the dishes starts.

[58] After the preliminary washing step (S120), a main washing step (S130) for injecting the wash water mixed with dishwashing detergent to remove the food scraps or contaminants from the dishes starts, then, once the main washing step (SI30) finishes, a rinsing step (S140) starts and then a drying step (S150) for drying the dishes starts after the rinsing step (S140), only to complete the dishwashing process.

[59] Before the main washing step (SI30) starts after the preliminary washing step (S120), a drainage step for draining the wash water injected and collected during the preliminary washing step starts. The wash water is pumped by a washing pump (not shown) mounted in the driving unit 140 and injected into the washing tub 130 via the injection units 132, 133 and 134. The wash water injecting process is repeatedly performed for a preset time period.

[60] A wash water injecting frequency is preset and the main washing step (SI30) is

WO 2017/119605

PCT/KR2016/013517 performed until the preset injection frequency. After the main washing step (S130), the rinsing step (S140) starts. The wash water supplied during the main washing step (S130) is drained before the rinsing step (S140) starts.

[61] Meanwhile, the drying step (SI50) for removing the food scraps or contaminants from the dishes starts after the rinsing step (S140) finishes. In the drying step (S150), hot or heated air is supplied to the washing tub 130 and evaporates moisture from the dishes. The air changed into hot humid air is exhausted outside the dishwasher 100 by the drying module 180.

[62] The water supply step (SI 10), the preliminary washing step (S120), the main washing step (S130), the rinsing step (S140) and the drying step (S150) are said to be similar to the steps of the conventional dishwasher so that detailed description of each step can be omitted.

[63] Meanwhile, the controller 190 determines whether the dry maintaining step (S200) is selected by the user (S160), after the drying step (S150). In this instance, the controller 190 controls the dishwashing process to finish, if determining that the dry maintaining step (S200) is selected by the user. For example, the controller 190 may control the dishwasher 100 to be turned off or in a standby state as the overall dishwashing process is complete.

[64] When the user sets to operate the dry maintaining step (S200), the controller 190 starts the dry maintaining step (S200) as an additional step after the drying step (S150). At the same time, the controller 190 controls the dry maintaining step lamp 127 of the display unit provided in the control panel 123 to display that the dry maintaining step (S200) is being performed.

[65] Hereinafter, referring to FIG. 5, the dry maintaining step (S200) will be described in detail. FIG. 5 is a flow chart illustrating the dry maintain step of the dishwasher.

[66] The dry maintain step (S200) is configured to maintain a dried state of the dishes inside the washing tub 130 by periodically operating the drying module 180 according to the user's selection, if the dishes having being washed and dried are remaining in the washing tub 130. Such the dry maintaining step (S200) may be performed for a preset time period in the daytime or nighttime. The dry maintaining step (S200) may end according to a preset operation time, a dishwasher condition and the user's selection.

[67] As shown in FIG. 5, the dry maintaining step (S200) is selected by the user and then the controller 190 is implemented to operate the dry fan 182 of the drying module 180 intermittently for a preset time period (S210).

[68] For example, when the preset operation time of the dry maintaining step (S200) is set as 6 hours, the dry fan 182 is operated for ten minutes after thirty minutes of a pause time. The controller 190 operates the frying fan 182 repeatedly for the preset operation time period (six hours).

WO 2017/119605 PCT/KR2016/013517 [69] The preset operation time of dry maintaining step (S200), the pause and duration time of the dry fan 182 may be variable according to operational conditions of the dry fan 182.

[70] Simultaneously with that, the controller 190 senses an ending condition of the dry maintaining step during the pause and duration time of the dry fan 182 (S220). In other words, the dry maintain step (S200) may finish according to a specific condition. For example, when sensing the user's manipulation (for example, canceling of the dry maintaining step (S200), starting of another washing step, opening of the door 122 provided in the dishwasher during the dry maintaining step (S200), the controller 190 may forcibly end the dry maintaining step (S200).

[71] Unless satisfying the finishing conditions of the dry maintaining step (S200), the controller 190 determines whether the preset operation time of the dry mainlining step passes (S230).

[72] When it is determined that the preset operation time of the dry maintaining step (S200) does not passes, the controller 190 keeps the intermittent operation of the dry fan being operated in the dry maintaining step (S200). When the operation time of the dry maintaining step (S200) is up to the preset time period, the controller 190 finishes the dry maintaining step (S200).

[73] According to the controlling method of the dishwasher mentioned above, the dried state of the dishes having been under the dishwashing process or kept in the dishwasher may be maintained efficiently, so that the user can be provided with use convenience.

[74] According to the dishwasher and the controlling method thereof in accordance with the present disclosure as mentioned above, unnecessary power consumption may be prevented when sensing an abnormal state of the heater provided in the dishwasher and the operational state of the heater may be rapidly sensed.

[75] The foregoing embodiments are merely exemplary and are not to be considered as limiting the present disclosure. The present teachings can be readily applied to other types of methods and apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be considered broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes ίο

2016385274 27 Mar 2019 and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the appended claims.

[76] Throughout this specification and the claims which follow, unless the context requires otherwise, the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[77] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A controlling method of a dishwasher including a washing tub defining a space in which one or more dishes are placed, a storage unit movable from the washing tub, a driving unit provided in a lower unit of the washing tub and injecting wash water to the storage unit, a door opening/closing the washing tub and including a drying module drying the dishes, the controlling method comprising:

a water supply step of supplying wash water to a dishwasher;

a washing step of washing one or more dishes using the supplied wash water;

a rinsing step of rinsing the washed dishes;

a drying step of drying the rinsed dishes;

a drying determining step for determining selection of a dry maintaining step after the drying step; and the dry maintaining step of intermittently drying the dishes to maintain a dried state of the dishes.
2. The controlling method of claim 1, wherein the washing step comprises:

a preliminary washing step of soaking food scraps or contaminants stuck on the dishes; and a main washing step of separating the food scraps or contaminants from the dishes.
3. The controlling method of claim 1, wherein the operation time of the drying module comprises a preset pause time and a preset duration time of the drying module which is shorter than the pause time.
4. The controlling method of claim 1, wherein the dry maintaining step ends based on determination of a drying module operation ending condition.
5. The controlling method of claim 4, wherein the drying module operation ending condition comprises one of a user's operation ending input, opening of a door, and starting of another washing course.
6. A dishwasher comprising:

a washing tub in which one or more dishes are placed;

2016385274 27 Mar 2019 a storage unit;

a driving unit provided in the washing tub and injecting wash water to the storage unit;

a door opening/closing the washing tub and comprising a drying module for drying the dishes and a manipulation unit comprises a dry maintaining button for operating a dry maintaining step for intermittently operating the drying module for a preset time period; and a controller intermittently operating the drying module for a preset time period according to user’s settings of the manipulation unit to maintain a dried state of the dishes separately from the drying step after the step of drying the dishes.
7. The dishwasher of claim 6, wherein the door comprises:

a display unit displaying an operational state of the dishwasher, wherein the display unit comprises a dry maintaining lamp displaying that the drying module is intermittently operated for a preset time period.