WO2018086872A1

WO2018086872A1 - Domestic appliance having a projection device, and method for the operation thereof

Info

Publication number: WO2018086872A1
Application number: PCT/EP2017/077125
Authority: WO
Inventors: Janet OWCZAREK; Ralph Pietruska; Martin Reichhuber; Umur Sener
Original assignee: BSH Hausgeräte GmbH
Priority date: 2016-11-14
Filing date: 2017-10-24
Publication date: 2018-05-17
Also published as: CN109963975B; EP3538702A1; CN109963975A; EP3538702B1; DE102016222256A1; PL3538702T3

Abstract

The invention relates to a domestic appliance (1) having a housing (2), having a treatment chamber (3) for articles which are to be treated, having a control unit (4) and having a door unit (5) for opening and closing the treatment chamber (3), wherein the door unit (5) has a central element (6) and a peripheral element (7), and the peripheral element (7) is arranged at least in a lower half of the door unit (5) and is arranged in front of the central element (6) such that the central element (6) and peripheral element (7) form an angle α ranging from 10° to 85°, and having a projection device (8), wherein the peripheral element (7) contains a projection surface (9) and the control unit (4) is designed so that information relating to a treatment program which can be carried out in the domestic appliance (1), or is being carried out therein, is presented in the form of an optical display (12), by means of the projection device (8), on the projection surface (9). The invention also relates to a method for operating said domestic appliance.

Description

Home appliance with projection device and

Procedure for its operation

The invention relates to a household appliance with a projection device and a method for its operation. More particularly, the invention relates to a domestic appliance having a housing, a treatment room for objects to be treated, a control unit and a door unit for opening and closing the treatment room, wherein the door unit has a central element and an edge element, and wherein the edge element at least in a lower half of the door unit is arranged and the central element is such upstream that the central element and edge element form an angle α in the range of 10 ° to 85 °, and a projection device, and a particularly suitable method for operating the household appliance. The visual display of information has become very important for a user-friendly operation of a household appliance. For the operation of household appliances such as washing machines, dryers or herds also increasingly touch-sensitive controls, especially external controls are used. Such a touch-sensitive operating device may be, for example, a smartphone or even a tablet computer. These generally have a touch screen, which combines a display device with an operating device. The operation of the household appliance then usually takes place via an app. Although in this way a quick operation of the household appliance is possible, the available on smartphones and tablet PCs touch screens are usually very small. However, the technology available in household appliances has become more and more sophisticated over the years and the operation has thus become more and more complex. The clear presentation of complex content on small touchscreens therefore presents a challenge. It would be desirable to additionally provide an option on a home appliance to display complex content over a larger area. But even in household appliances with a stationary operating device, also referred to as an operating unit, an improved display of information about the operation of the household appliance would make sense. Domestic appliances with a projected display of settings and setting options of the household appliance are already known.

The publication WO 2010/128729 A2 describes a washing machine, comprising a housing, which forms the external appearance of the washing machine and includes an opening. A drum is rotatably mounted within the housing and is loaded with laundry through the opening. The housing also has a door for opening and closing the opening, wherein a display unit is provided for displaying washing information on the door. The position of the display unit can correspond to the position of the opening.

The publication WO 2006/021936 A1 describes a household appliance comprising a housing, a door which is attached to the housing and allows a user access to the interior of the housing, and a window which is positioned on the housing and / or on the door and allowing a user to observe the interior of the housing. The household appliance also includes a control card, which allows the control of the household appliance. A display unit is mounted on the window which allows the user to simultaneously observe the interior of the housing through the window and the data provided by the control card.

The publication EP 1 489 364 A1 describes a cooking, refrigerating and / or washing appliance, in particular a household appliance such as a cooker, hob or extractor hood, with at least one projection device for projection of representable information about at least one function of this appliance on a projection surface. The projection of displayable information from connected devices is also disclosed. The projection surface may be formed on the same and / or another device and / or on a piece of furniture or devices accommodating the device and / or on a space accommodating the devices and / or furniture.

The publication DE 10 2012 103 684 A1 describes a display device in a household appliance in the form of a projector mounted in a housing of the household appliance. By means of the projector in operation a projection image on an outer surface projected to the housing, wherein the projector is associated with an optics, which causes at least one deflection for projecting from the projector light beams, so that the light rays are passed through an interior of a door element of the household appliance. A resulting projection image is projectable onto an inner surface of a viewing window of the door element. The optics comprises a light-guiding element which effects a projection of the projection image into a viewing area formed in the viewing window.

The publication EP 2 542 139 B1 describes a projector adapted for installation on a household appliance for projecting visual information onto a projection surface outside the household appliance. The projector has a focusing device that is adapted to focus a light beam that radiates from a light source onto the projection surface. The focusing device further comprises at least one fixing element, which is adapted for arranging the focusing device in at least two different focusing positions within the projector. The projector also includes at least one flexible, light-conducting cable connected to the at least one light source such that the light emitted by the light source is directed to a free cable end of the light-conducting cable from where it is projected onto the projection field , The free cable end is arranged in a housing, wherein the housing is arranged in a longitudinal direction adjustable in a carrier element.

Publications WO 2010/128729 A3 and US 2012/128729 A3 describe a washing machine which washes laundry using a mechanical force. The washing machine includes a display unit formed on a door to display information about the washing, thus enlarging the installation space for the display unit. In addition, in the event that the display unit comprises a touch screen, not only the input and display of washing information should be possible, but also the visual inspection of laundry in the drum can be achieved by the display unit.

The publication US 2012/0327201 A1 describes a user interface projected onto the surface of a domestic appliance which can be used for a selection concerning the operation of the household appliance. In the known household appliances, however, often shown in the door area, in particular projected information is not easily recognizable, especially when one considers that a user of the household appliance, such as a water-conducting household appliance such as a washing machine or a dryer, mostly from the top of the appliance looks. It would also be useful if the home appliance could provide improved information about set and adjustable treatment programs and their parameters.

Against this background, it was an object of the present invention to provide a household appliance with an improved display of information about a running or running in the home appliance treatment program. In particular, it should be possible to make the display of information on the display more user-friendly. The object of the invention was also to provide a method for operating such a household appliance.

The solution of this object is achieved according to this invention by a household appliance and a method suitable for operating the household appliance with the features of the corresponding independent claims. Preferred embodiments of the household appliance according to the invention and of the method according to the invention are listed in the respective dependent claims. Preferred embodiments of the household appliance according to the invention correspond to preferred embodiments of the method according to the invention and vice versa, even if this is not explicitly stated herein. The invention thus relates to a household appliance with a housing, a treatment room for objects to be treated, a control unit and a door unit for opening and closing the treatment room, wherein the door unit has a central element and a peripheral element, the edge element arranged at least in a lower half of the door unit and is disposed in front of the central element so that the central element and edge element form an angle α in the range of 10 to 85 °, and a projection device, wherein the edge element includes a projection surface and the control unit is arranged to use the projection device information about a feasible in the household appliance or expire treatment program as a visual display on the screen.

The edge element is preferably also arranged in an upper half of the door unit and most preferably encloses the central unit.

Central element and edge element may be separate elements or form a unit. Preferably, central element and edge element are designed in one piece. Central element and edge element can consist of the same or different materials. Preferably, however, the central element and edge element are designed differently, such that they differ in their optical properties. Preferably, the central element is at least partially transparent, while the edge element is preferably optimized for use with a projection device, for example by a projected visual display being particularly clearly perceptible.

The household appliance according to the invention contains a projection device. The projection device generally comprises a projector or a projector, as well as optical means for positioning the projection. Optical means are generally e.g. Reflectors, lenses and collimators. The positioning of the projector or projector within the housing of the household appliance is not limited according to the invention. However, in a preferred embodiment of the household appliance according to the invention, the projection device is arranged outside the treatment room in the housing above the door unit. In an alternative preferred embodiment of the household appliance according to the invention, the projection device is arranged outside the treatment room in an upper half of the door unit.

Moreover, a household appliance is preferred in which the edge element with an installation surface of the household appliance forms an angle β in the range of 10 ° to 80 °, preferably in the range of 20 ° to 70 °. It is assumed that a lower edge of the household appliance is generally parallel to the footprint of the household appliance and thus be used for the determination of the angle ß can. With regard to the arrangement of the door unit, in particular a lateral edge of the household appliance is used for this purpose.

In a preferred embodiment of the household appliance according to the invention, in order to increase the contrast of the optical display, the edge element and / or the projection surface are darkened or colored at least in a partial region. The realization of the darkening or coloring is not restricted according to the invention. This may be a modification of the material of the edge element, for example glass in the case of a transmission change, but also an additional application of material, for example in the form of a coating or film.

According to the invention, a domestic appliance which contains a motion sensor which can detect the presence of a user in the vicinity of the domestic appliance is preferred, wherein the control unit is then set up to initiate a mode of operation of the projection apparatus predetermined for this case in the event of a detected presence. For example, it could be provided that a visual display only takes place when a user is nearby. In addition, the control unit and projection device could be coordinated so that the brightness and / or the contrast of the visual display of the presence and possibly the distance of the user from the household appliance are dependent. A motion sensor, in particular if this is designed as a camera and / or has a suitable associated software, can also be advantageously used for a gesture control of the household appliance. The "proximity" may be a fixed or adjustable by a user depending on the site size, where appropriate, the distance and / or size of the moving object (user) can be considered.

With regard to an advantageous networking of several household appliances, it is inventively preferred that the household appliance has a network interface, via which it can be integrated into a home network, which has at least a second home appliance. Then, the control unit is preferably configured to display on the household appliance according to the invention information about the second household appliance and / or running in the second household appliance program on the screen. According to the invention, a household appliance is preferred in which the door unit is at least partially transparent, so that it allows the observation of the treatment room by a user. Preferably, the central unit is at least partially, in particular completely, transparent, and the edge element substantially opaque, in particular completely opaque. In this case, the edge element is preferably designed such that an opaque part is suitable as a projection surface.

In a further preferred embodiment, the household appliance contains a light sensor, which can detect the light intensity Lu in an environment of the domestic appliance, and the control unit is set up to increase in brightness of the optical display and / or at a fall below a minimum value L _Um Exceeding a maximum value L _To increase the contrast of the optical display. The household appliance according to the invention generally has an internal and / or external operating unit.

In a preferred embodiment of the household appliance, an operating unit is arranged centrally on a front panel of the housing, wherein at least three touch-sensitive operating elements are arranged in the operating unit, of which at least two are designed as sliders. In this case, a first touch-sensitive operating element is preferably set up as a hierarchically higher operating element, which permits the selection of a treatment program to be carried out in the household appliance, and the at least two sliders are set up to allow setting of program parameters. In a preferred arrangement of the controls they are arranged in a row which forms a right angle with the sliders, which are generally designed as elongated sliders. Elongated sliders have elongated sensor elements, in the longitudinal direction of which an assigned parameter value changes continuously or suddenly, so that the parameter value can be adjusted by touching the elongated sensor element. The non-selected or selectable parameter values are then preferably displayed on the projection surface, ie in the optical display, optically reset, for example darker and / or smaller, and the selectability is blocked by the control device. There are basically two options for using the sliders. Thus, in a first possibility, a substantially locally fixed contact with an adjustment unit, in particular with a finger, that is to say no straight pulling or lateral movement, can be evaluated as a point-like contact. The location of the point-like actuation is then generally associated with a specific parameter value which is thereby set. In the second possibility, it is provided that a finger is applied for actuation and, above all, is moved in a pulling movement along the elongated sensor element. This operation is therefore beyond a point-like touch. Depending on the length and / or the starting point and end point of the operation or the pulling elongated movement, a corresponding parameter value is set. The elongated sensor element may, in particular, be a segmented slider which can be displaced by a contact, wherein the segments as such may be visible to a user or may follow one another continuously. Sliders present in the domestic appliance according to the invention are preferably arranged parallel to one another.

In general, in the household appliance according to the invention, there is also an operating element with which a set treatment program can be started, i. a starting element. If the operating elements are arranged in a row, the first touch-sensitive element and the starting element are preferably located at opposite ends of the row.

According to the invention, a domestic appliance is preferred in which display areas assigned to the operating elements are present on the optical display on the projection surface, wherein the display area assigned to an operating element in use is optically highlighted. In general, there is no equivalent on the optical display for the starting element. In a preferred embodiment of the household appliance, the door unit has a door sensor and the control unit is set up to switch off the optical display when the door unit is open. A household appliance according to the invention is a household appliance for the treatment of objects, but otherwise not limited. Such a household appliance may for example be a washing machine, a dryer, a washer-dryer, but also a microwave oven or a stove. For receiving and for treating the objects, the household appliance comprises a treatment room. If the household appliance is, for example, a washing machine, a dryer or a washer-dryer, then the treatment room can be a drum. If the appliance is a stove, then the treatment room can also be a furnace muffle. Preferably, the household appliance is a water-conducting household appliance, selected from the group consisting of washing machine, washer-dryer and dryer.

To accommodate objects to be treated, the treatment room has an opening through which it can be equipped with objects. The objects are generally treated under the influence of certain process conditions, be it dry-warm process air in a dryer or heat in an oven or washing liquor in a washing machine. It is thus generally necessary that the treatment room can be closed during the treatment of objects. Therefore, the household appliance according to the invention has a door unit for opening and closing the treatment room. The design of such a door unit is not restricted in addition to the specifications according to the invention, but generally depending on the type of household appliance and the type of treatment that takes place in the treatment room, and thus the design of the treatment room. Thus, the door unit of a washing machine usually has the form of a preferably partially transparent porthole, whereas preferably also at least partially transparent door unit in an oven generally has a rectangular, flat shape. In any case, the material, thickness and shape of the door unit are dependent on the type of household appliance in which the door unit is used. According to the invention, the projection device and the projection surface are designed to display text, symbols, patterns and / or images in cooperation with the control unit of the household appliance. Texts include letters, numbers and special characters. The representation can be done both in colors, in grayscale and / or in black and white.

The invention also relates to a method for operating a household appliance with a housing, a treatment room for objects to be treated, a control unit and a door unit for opening and closing the treatment room, wherein the door unit has a central element and a peripheral element, and wherein the edge element at least in a lower half of the door unit is arranged and the central element is such that central element and edge element form an angle α in the range of 10 ° to 85 °, and a projection device, wherein the peripheral element includes a projection surface and the control unit is arranged to use the Projection device to present information about a running in the home appliance or running treatment program as a visual display on the screen, comprising the steps

(A) switching on the household appliance, wherein in a closed state of the door unit by means of the projection device on the projection surface is a visual display of information about a feasible or running in the home appliance treatment program;

(b) setting or changing the treatment program by selecting a control element from touch-sensitive controls arranged on a control unit for selecting a treatment program or for setting a program parameter; and

(C) visual display of preset or selected by a user by means of the controls settings of a treatment program or program parameters on the touch-sensitive controls associated display areas on the screen, wherein the one in use control located associated display area is highlighted.

The invention has numerous advantages. An optical display on the edge element can be designed over a large area and allows embodiments of the invention due to the also present at least partially transparent central element still simultaneously observing the interior of a treatment room by a user. In addition, on the surface of the edge element, which is comparatively larger in comparison to a display on a front panel, contents can be displayed in a pleasantly perceptible size. This is often not possible on small touchscreens, such as those found on smartphones or tablet PCs. In addition, a pleasant viewing angle is possible for a user in particular. A user can also immediately see, in embodiments of the invention, from a distance, which treatment programs and parameters are set. Finally, with the projection device in the edge element also warnings regarding a faulty operation of the device could be displayed, so that appropriate countermeasures could be taken. Even in a dark room, in the event of light failure or at nightfall, a large and easy-to-read display of contents or possibly warnings is an advantage. Last but not least, an enlarged display of contents on the visual display facilitates the operation of the household appliance for persons who are limited in their sight. Finally, the invention in embodiments is particularly well suited for use in a home network, which has several household appliances.

Further details of the invention will become apparent from the following description of non-limiting embodiments. Here, reference is made to FIGS. 1 to 4.

Figure 1 shows a perspective view of a washing machine as a first non-limiting embodiment of a household appliance according to the invention, wherein a projection device is arranged outside a treatment room in an upper half of the door unit.

Fig. 2 shows a side view of another washing machine as a non-limiting embodiment of a household appliance according to the invention, in which case a projection device outside a treatment room in

Housing is arranged above the door unit. Fig. 3 shows a front view from above of another washing machine as a non-limiting embodiment of a household appliance according to the invention, in which case a projection device is arranged outside a treatment room either in the housing above the door unit or in an upper half of the door unit and a visual display according to Setting a treatment program is done.

Fig. 4 shows a front view from above of the washing machine of Fig. 3, wherein a visual indication of a set treatment program in terms of its nature and the set parameters.

Figure 1 shows a perspective view of a washing machine 1 as a first non-limiting embodiment of a household appliance according to the invention, wherein a projection device 8 is arranged outside of a treatment room 3 in an upper half of a door unit 5. 3 thus means a closable by the door unit 5 treatment room. From the projection device 8, light rays emanate in the direction of a projection surface 9, which is contained in an edge element 7 of the door unit 5. 6 means a central element, which is designed here as a translucent circular glass pane. The door unit 5 thus has the form of a porthole here. On the projection surface 9 there is a not shown in detail optical display. 22 means a lateral edge of the washing machine 1 as a reference for the determination of the angle ß.

In the embodiment shown in FIG. 1, a control unit 14 is centrally arranged on a front panel 15, on which two punctiform touch-sensitive operating elements and three touch-sensitive sliders are indicated.

4 indicates a control unit and 10 a motion sensor.

2 shows a side view of a further washing machine 1 as a non-limiting embodiment of a household appliance according to the invention, in which case a projection device 8 is arranged outside a treatment space 3 in the housing 2 above the door unit 5. A central element 6 and an edge element 7 form an angle α in the range of 10 ° to 85 °. In addition, the edge element 7 and a footprint of the household appliance, for which purpose a base of the household appliance or a lateral edge 22 is used, an angle ß in the range of 20 ° to 70 °. 4 is a control unit, 10 is a motion sensor, 1 is a network interface, and 13 is a light sensor.

Fig. 3 shows a front view from above of another washing machine 1 as a non-limiting embodiment of a household appliance according to the invention, in which case a projection device not shown in detail outside a treatment room either in the housing above the door unit or in an upper half of the door unit is arranged and a visual display according to the setting of a treatment program. For this purpose, the display areas 19, 20 and 21 are shown on the projection surface 9 as a visual display in the lower area of the edge element 7, which here surrounds a transparent central element 6. The display areas 19, 20 and 21 extend substantially in a row from top to bottom. While the display areas 20 and 21 display only one value for a parameter at a time, a plurality of symbols are shown along the edge element 7 in the display area 19, with the symbol currently selected, shown in the middle, being illustrated brighter. The lighter-colored symbol represents a selected treatment program, while the optically reset, ie less brightly represented, icons for non-selected programs are available. The optical display shown in FIG. 3 therefore illustrates the case in which a treatment program is selected, wherein the values preset here for this treatment program by default (temperature 50 ° C., revolution number 800 rpm) can also be changed in a further adjustment step which is not shown here , To adjust touch-sensitive controls 16, 17, 18 are used in the embodiment shown here, which are included in a control unit 14 on a front panel 15 of the washing machine 1. The controls 16, 17, 18 are the display areas 19, 20, 21 associated with, so that the sequences of the setting on the Operating unit and the display of treatment program and program parameters on the optical display are the same.

23 means a starting element with which a treatment program finally selected and specified by parameter details can be started in the washing machine 1.

FIG. 4 shows a front view from above of the washing machine of FIG. 3, with an optical display 12 of a treatment program on the projection surface 9 which has already been selected and specified by parameter specifications, with regard to its type and the set parameters. The other reference numerals otherwise have the same meaning as in FIG. 3.

LIST OF REFERENCE NUMBERS

1 home appliance

2 housings

3 treatment room, drum

4 control unit

5 door unit

6 central element

7 edge element

8 projection device

9 projection surface

10 motion sensor

1 1 network interface

12 Optical display (on the projection screen)

13 light sensor

14 operating unit

15 front panel

16 first touch-sensitive control

17 second touch-sensitive control, slider

18 third touch-sensitive control, slider

19 first display area, associated with the first touch-sensitive control

20 second display area, the second touch-sensitive control associated

21 third display area, the third touch-sensitive control associated

22 lower edge of the household appliance, in particular lateral edge

23 start element

Claims

Domestic appliance (1) with a housing (2), a treatment room (3) for objects to be treated, a control unit (4) and a door unit (5) for opening and closing the treatment room (3), wherein the door unit (5) is a central element (6) and an edge element (7), and wherein the edge element (7) is arranged at least in a lower half of the door unit (5) and is disposed in front of the central element (6) such that the central element (6) and edge element (7) form an angle α in the range of 10 ° to 85 °, and a projection device (8), characterized in that the edge element (7) includes a projection surface (9) and the control unit (4) is arranged to be rotated by the projection device (8 ) Represent information about a in the household appliance (1) feasible or running treatment program as a visual display (12) on the projection surface (9).

Domestic appliance (1) according to claim 1, characterized in that the central element (6) and edge element (7) are designed in one piece.

Domestic appliance (1) according to one of claims 1 to 2, characterized in that the projection device (8) outside the treatment chamber (3) in the housing (2) above the door unit (5) is arranged.

Domestic appliance (1) according to one of claims 1 to 2, characterized in that the projection device (8) outside the treatment chamber (3) in an upper half of the door unit (5) is arranged.

Domestic appliance (1) according to one of claims 1 to 4, characterized in that the edge element (7) forms an angle ß in the range of 10 ° to 80 ° with a footprint of the household appliance (1).

Domestic appliance (1) according to one of claims 1 to 5, characterized in that the household appliance (1) contains a motion sensor (10), the Presence of a user in the vicinity of the household appliance (1) can determine, and the control unit (4) is arranged to cause a detected presence in this case predetermined operation of the projection device (8).

Domestic appliance (1) according to one of claims 1 to 6, characterized in that the household appliance (1) has a network interface (1 1), via which it can be integrated into a home network having at least a second household appliance.

Domestic appliance (1) according to one of claims 1 to 7, characterized in that the door unit (5) is at least partially transparent, so that it allows the observation of the treatment room (3) by a user.

Domestic appliance (1) according to one of claims 1 to 8, characterized in that the household appliance (1) contains a light sensor (13) which can detect the light intensity Lu in an environment of the household appliance (1), and the control unit (4) is to increase in a brightness of the optical display (12) and / or on exceeding a maximum value L _Um ax to increase the contrast of the optical display (12) when falling below a minimum value L _Um .

Domestic appliance (1) according to one of claims 1 to 9, characterized in that an operating unit (14) is arranged centrally on a front panel (15) of the housing (2), wherein in the operating unit (14) at least three touch-sensitive operating elements (16, 17,18) are arranged, of which at least two are designed as a slider (17,18).

Domestic appliance (1) according to claim 10, characterized in that a first touch-sensitive control element (16) is arranged as a hierarchically higher control element, which allows the selection of a household appliance (1) treatment program and the at least two sliders (17,18) are set up to allow the setting of program parameters. Domestic appliance (1) according to claim 10 or 1 1, characterized in that on the optical display (12) the control elements (16,17,18) associated display areas (19,20,21) are present, wherein the one in use control (16,17,18) associated display area (19,20,21) is optically highlighted.

Domestic appliance (1) according to one of the preceding claims, characterized in that the door unit (5) has a door sensor and the control unit (4) is arranged to switch off the optical display (12) when the door unit (5) is open.

Domestic appliance (1) according to one of the preceding claims, characterized in that the household appliance (1) is a water-conducting household appliance, selected from the group consisting of washing machine, washer-dryer and dryer.

Method for operating a domestic appliance (1) with a housing (2), a treatment room (3) for objects to be treated, a control unit (4) and a door unit (5) for opening and closing the treatment room (3), wherein the door unit ( 5) has a central element (6) and an edge element (7), and wherein the edge element (7) is arranged in a lower half of the door unit (5) and precedes the central element (6) such that the central element (6) and edge element (7) forming an angle α in the range of 10 ° to 85 °, and a projection device (8), wherein the edge element (7) includes a projection surface (9) and the control unit (4) is arranged to be rotated by the projection device (8 ) Display information about a treatment program that can be carried out or run in the household appliance (1) as a visual display (12) on the projection surface (9),

comprising the steps

(A) switching on the household appliance (1), wherein in a closed state of the door unit (5) by means of the projection device (8) on the projection surface (9) is a visual display (12) of information about an executable or running in the home appliance treatment program; and (b) setting or changing the treatment program by selecting an operating element from touch-sensitive operating elements (15, 16, 17) arranged on an operating unit (13) for selecting a treatment program or for setting a program parameter; and

(c) optical display (12) of preset or selected by a user by means of the controls (15,16,17) settings of a treatment program or by program parameters on the touch-sensitive controls (15,16,17) associated display areas (18,19,20 ) on the projection surface (9), the display area (18, 19, 20) assigned to a control element (15, 16, 17) in use being optically highlighted.