Household appliance, in particular an electrically operated household appliance

A household appliance, in particular an electrically operated household appliance, can be controlled using voice signals. In order to avoid malfunction, e.g. as a result of voice signals coming from a radio set and not from a user, a control program is configured in such a way that successive voice signals can only form a control command when the successive voice signals are input within a given time period.

BACKGROUND OF THE INVENTION
 FIELD OF THE INVENTION
 The invention relates to a household appliance, in particular an
 electrically operated household appliance.
 In household appliances, power is supplied to the electrical load or loads
 by mechanical actuators or control elements. The mechanical actuators or
 operating elements are located in the household appliance, so that the
 operator has to be at the location of the household appliance in order to
 actuate the operating elements. The operator therefore has to interrupt
 his current work and, if necessary, has to clean and to dry his hands.
 Furthermore, the actuation of household appliances often proves to be
 relatively troublesome for the disabled. A product for the rehabilitation
 sector is already known under the name "SICARE pilot" (available from the
 software vendor evosoft Softwarevertrieb GmbH, D-90411 Nuremberg/Germany),
 which includes a mobile device which converts spoken commands into
 signals. The signals are output by an infrared transmitter, for example
 for the control of television sets, video recorders, hi-fi systems,
 telephone and lighting, by radio transmitters, for example for the control
 of house doors, lifts, call and alarm systems, or by wire-bound
 interfaces, for example for the control of electrically driven wheelchairs
 and motor-adjustable beds. The known product, which is intended for
 physically disabled persons, permits the storage of a maximum of 64
 commands. The mobile device transmits the command for the desired action,
 for example "television on" automatically to the appropriate device via
 the previously selected interface. Each individual instruction can address
 a number of devices at the same time. The known product is trained to the
 individual speech pattern of one person, and therefore implements
 speaker-dependent speech recognition. Ideally, other persons are not
 capable of generating signals which control the devices from spoken
 commands. In the known product, the speech recognition is implemented by
 predefined words (e.g. "house", "light", "four", "minus") which must be
 spoken in accordance with a menu tree having a number of branches, however
 it is possible for the individual words to be spoken at any desired time
 interval. If, because of an indisposition of the physically disabled
 person, the speech input is aborted prematurely, it is possible that
 individual words, which are, for example, generated by a radio or
 television set and which are provided in the branch of the menu tree,
 which is to be dealt with after the speech input was aborted, can cause
 signals to be generated which control one or more devices. Such an
 inadvertent control of one or more devices, for example a wheelchair, can
 endanger the physically disabled person.
 The German patent document DE 38 03 220 discloses a household appliance
 having a program switching device. A phonetic control device is configured
 in such a way that code words or their speech pattern signals no longer
 called up or not called up for a long time are deleted from a speech
 pattern memory.
 The European patent document EP 0 031 144 discloses a heating appliance
 having a device for recognizing speech and having a device for generating
 artificial speech signals. In this heating appliance, a first speech
 recognition step (m-1) is carried out, and is followed by a step (m-2), in
 which an artificial speech signal is produced, which is further followed
 by a second speech recognition step (m-3).
 SUMMARY OF THE INVENTION
 It is accordingly an object of the invention to provide a household
 appliance which overcomes the above-mentioned disadvantages of the
 heretofore-known appliances of this general type and which provides a
 simple, reliable, and rapid speech-controlled operation for the household
 appliance.
 With the foregoing and other objects in view there is provided, in
 accordance with the invention, a household appliance configuration,
 including a household appliance, in particular an electrically operated
 household appliance, having operating functions and/or components, such as
 electrical load components; a first device, connected to the household
 appliance, for inputting at least two speech signals designating the
 operating functions and/or components of the household appliance; a second
 device, operatively connected to the first device, for recognizing the
 operating functions and/or components designated by the speech signals;
 and a third device, operatively connected to the second device, for
 converting the speech signals, after being recognized, into a given
 control command to operate the household appliance, the third device
 producing the given control command only when the speech signals are input
 in a sequence defined by a menu tree; and a controller having a control
 program and being assigned to at least one of the first, second, and third
 devices, the control program operating such that the speech signals, being
 input in a direct succession for selecting the operating functions and/or
 the components, cause a formation of the given control command only when
 the speech signals are separated in time by not more than a respective
 given first time period, the respective given first time period being a
 respective pause period, and are input within a respective given second
 time period.
 In accordance with another feature of the invention, the controller is
 configured for carrying out a speaker-independent speech signal
 recognition or, alternatively, a speaker-dependent speech signal
 recognition.
 In accordance with a further feature of the invention, the first device is
 disposed separated from the household appliance and may in particular be
 integrated into a portable telephone terminal.
 In accordance with yet another feature of the invention, the first device
 has at least one microphone and is installed on a holding element, which
 damps structure-borne sound.
 In accordance with another feature of the invention, the first device
 includes an electric filter damping oscillations of frequencies below
 approximately 100 hertz and/or above approximately 5 kilohertz.
 In accordance with yet a further feature of the invention, the first,
 second, and third devices are a provided in place of mechanical operating
 elements for inputting control commands when actuated or in addition to
 the mechanical operating elements.
 With the objects of the invention in view there is also provided, a
 household appliance system, including a household appliance having
 operating functions and/or components, such as electrical load components;
 a first device for inputting at least two speech signals designating the
 operating functions and/or the components of the household appliance; a
 second device, operatively connected to the first device, for recognizing
 the operating functions and/or the components designated by the speech
 signals; a third device, operatively connected to the second device, for
 converting the speech signals, after being recognized, into a given
 control command to operate the household appliance, the third device
 producing the given control command only when the speech signals are input
 in a sequence defined by a menu tree; and a central computer connected to
 the household appliance, at least one of the first, second, and third
 devices being assigned to the central computer, the first, second, and
 third devices being configured such that the speech signals, being input
 in a direct succession for selecting the operating functions and/or
 components of the household appliance, cause a formation of the given
 control command only when the speech signals are separated in time by not
 more than a respective given first time period and are input within a
 respective given second time period, the central computer being
 connectable to further household appliances.
 With the objects of the invention in view there is further provided, in
 combination with a household appliance having components and operating
 functions, a speech-activated device including a first device for
 inputting at least two speech signals designating at least one of the
 components and operating functions of the household appliance; a second
 device, operatively connected to the first device, for recognizing the at
 least one of the components and operating functions designated by the
 speech signals; and a third device, operatively connected to the second
 device, for converting the speech signals, after being recognized, into a
 control command to operate the household appliance, the third device
 producing the control command only when the speech signals are input in a
 sequence defined by a menu tree; and a controller having a control program
 and being assigned to at least one of the first, second, and third
 devices, the control program operating such that the speech signals, being
 input in a direct succession for selecting the at least one of the
 components and operating functions of the household appliance, cause a
 formation of the control command only when the speech signals are
 separated in time by not more than a respective given first time period,
 being a respective pause period, and are input within a respective given
 second time period.
 With the objects of the invention in view there is additionally provided, a
 central computer system for at least one household appliance, the central
 computer system including a first device for inputting at least two speech
 signals designating operating functions and/or components of the at least
 one household appliance; a second device, operatively connected to the
 first device, for recognizing the operating functions and/or components
 designated by the speech signals; a third device, operatively connected to
 the second device, for converting the speech signals, after being
 recognized, into a control command to operate the household appliance, the
 third device producing the control command only when the speech signals
 are input in a sequence defined by a menu tree; and a central computer to
 be connected to the least one household appliance; and a controller having
 a control program and being assigned to at least one of the central
 computer, the first device, the second device, and the third device, the
 control program operating such that the speech signals, being input in a
 direct succession for selecting operating functions and/or components of
 the at least one household appliance, cause a formation of the control
 command only when the speech signals are separated in time by not more
 than a respective given first time period and are input within a
 respective given second time period.
 The household appliance according to the invention has, instead of the
 mechanical operating elements or else in addition to these, a first device
 for the input of speech signals which designate operating functions of the
 household appliance, a second device for recognizing the operating
 functions designated by the speech signals, and a third device for
 converting the speech signals recognized into control commands to operate
 the household appliance. It is therefore possible for the household
 appliance also to be operated by operators who are not directly present at
 the location of the household appliance. A manual operation does not take
 place, so that the operator has his "hands free" during the operation of
 the household appliance. It is therefore possible for the operator, for
 example to prepare ingredients for preparing a meal and, at the same time
 to switch on a cook top or hob of a cooker. The formation or generation of
 undesired control commands is prevented by successive speech signals
 leading to the formation of a control command only when the successive
 speech signals are input in a defined sequence and within a
 predeterminable time. If these conditions are not met, no control command
 is formed. Furthermore, the speech-signal processing procedures are set
 back to the starting point of the processing sequence. If therefore the
 originally intended control command is to be formed, it is not the speech
 signals which are still missing which have to be input, instead all the
 specified speech signals have to be input within the defined sequence and
 within the predeterminable time.
 The speech recognition is preferably carried out in a speaker-independent
 manner and therefore permits the household appliances to be produced in
 large numbers without having to perform any modifications in order to make
 them operable for individual operators.
 A further advantageous embodiment of the household appliance according to
 the invention has is characterized in that the control program assigned to
 a controller is configured in such a way that the first device and/or the
 second device and/or the third device can be activated only after a
 mechanical operating element has been actuated. This has the advantage
 that a radio or television set, which may possibly run all week, cannot
 switch on the household appliance as a result of the purely random playing
 of "suitable" keywords.
 A further embodiment of the household appliance according to the invention
 has the advantage that devices which are used for the input of speech
 signals, for the recognition of the content of speech signals and for the
 conversion of control signals are used for a number of household
 appliances. Separate devices specific to the household appliance are
 therefore not necessary.
 Other features which are considered as characteristic for the invention are
 set forth in the appended claims.
 Although the invention is illustrated and described herein as embodied in a
 household appliance, in particular an electrically operated household
 appliance, it is nevertheless not intended to be limited to the details
 shown, since various modifications and structural changes may be made
 therein without departing from the spirit of the invention and within the
 scope and range of equivalents of the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring now to the figures of the drawings in detail and first,
 particularly, to FIG. 1 thereof, there is shown an exemplary embodiment of
 a household appliance 1 according to the invention, which is, for example,
 an electrically operated cooker with a built-in cook top or hob, and which
 has mechanical operating elements 2 which switch a power source P. The
 power source P is used to supply electrical power, for example to a
 built-in cook top having a first cooking area K1 (front left), a second
 cooking area K2 (back left), a third cooking area K3 (back right) and a
 fourth cooking area K4 (front right).
 Furthermore, the household appliance according to the invention has a first
 device 3, which is used for the input of speech signals and, in
 particular, is formed by a microphone fitted directly to the household
 appliance.
 As an alternative, it is possible to provide the device 3 separated from
 the household appliance and to provide it, for example, in a portable
 telephone terminal (cordless telephone; mobile telephone), such that the
 existing microphone of the telephone terminal has a dual function.
 The first device 3 for the input of speech signals is connected to a second
 device 41, known per se, for recognizing the operating functions
 designated by the speech signals, and this is in turn connected to a third
 device 42, known per se, for converting the speech signals recognized into
 control commands to operate the household appliance 1.
 The second device 41 and the third device 42 can be physically connected
 and, in circuit terms, can be formed by a device 4 or by a controller CPU
 (microprocessor).
 This controller can be formed by the second and third devices 41, 42 or can
 be assigned to these devices and to the first device 3. The controller is
 assigned a control program which, inter alia, is configured in such a way
 that successive speech signals lead to the formation of a control command
 only when successive speech signals (e.g. W1, W2, W3, W4 in FIG. 2), whose
 sequence is defined by a menu tree (FIG. 2), are input within a
 predeterminable time (T12=time between the beginning or the end of the
 input of one speech signal W1 and the beginning or the end of the input of
 a following speech signal W2).
 Furthermore, the control program can be configured in such a way that if
 successive speech signals (e.g. W1, W2) are input outside the
 predeterminable time (T12) or if the speech signal input is aborted (e.g.
 no input of W3 and W4), a control command is formed only when all the
 speech signals needed to form a control command are then actually input
 again in the defined sequence within the respectively predeterminable time
 (T12 in relation to W1, W2; T23 in relation to W2, W3; T34 in relation to
 W3, W4 in FIG. 2).
 The speech signal recognition is preferably carried out in a
 speaker-independent manner. However, it can also be carried out in a
 speaker-dependent manner in particular in a speaker-group-dependent
 manner. The speech of adults exhibits speech characteristics which
 distinguish them from the speech characteristics of children. In this
 embodiment of the household appliance according to the invention, children
 can be excluded from actuating the household appliance.
 The control program can also be configured in such a way that the first
 and/or the second and/or the third device can be activated only after a
 mechanical operating element 2 has been actuated. In this case, the
 mechanical operating element 2 is a special key, switch, or button, whose
 actuation causes a command to be formed which indicates that a control of
 the household appliance by speech signals is to be carried out. The actual
 control, for example of a specific temperature of a cooking area of a cook
 top, is not carried out with this special key; instead, the control is
 prepared or set up as a result of the actuation of the special key. In
 particular, immediately after the household appliance has been switched
 off, the first and/or the second and/or the third device can be activated
 only after such a mechanical operating element 2 (special key) has been
 actuated.
 In this case, after the household appliance has been previously switched
 off, the household appliance can be activated by speech signals only when
 the mechanical operating element has been actuated beforehand. In this
 case, provision may be made for this actuation to be enabled only within a
 predeterminable time period following the switching off.
 Furthermore, pauses (Tt in FIG. 2) of different length between the speech
 signals can be set.
 The second device 41 may also recognize the speech signals, which have been
 input, in a speaker-dependent manner. This makes it possible to authorize
 only specific persons, for example only the adult members of a household,
 to actuate the household appliance.
 In the present exemplary embodiment, the household appliance has a number
 of electrical load elements (K1, K2, K3, K4), which can be controlled
 individually through the use of speech signals.
 The speech signals preferably include a sequence of predeterminable
 "keywords" which are to be spoken in particular in a sequence defined by a
 menu tree. One example of such a menu tree is illustrated in FIG. 2. The
 structure of this sequence depends on the grammar of the language in which
 the keywords are spoken.
 The words illustrated in FIG. 2, such as "cook top" and "cooking area" can
 be replaced for the use of the cook top by sequences of sounds of any
 desired form, so that, for example, even operators with impaired speech
 can control household appliances according to the invention in a simple
 way.
 In the exemplary embodiment illustrated in FIG. 2, each sequence of
 keywords begins with the word "cook top" (W1) as an address to the
 household appliance to be controlled. The function "cooking area" (W2, 1st
 alternative) or "griddle" (W2, 2nd alternative) is then spoken, the
 functions "griddle" and "cooking area" being considered intuitively as
 independent of one another, corresponding to normal domestic use, even if
 they are used in the same area on the cook top. Following the selection of
 the function "cooking area" or "griddle", the operator selects, through
 the use of the keyword "1" or "2" or "3" or "4" (W3, 1st, 2nd, 3rd or 4th
 alternative), the location on the cook top (front left; back left; back
 right; front right) on which the cooking area is to carry out actions. As
 an example of alternative keywords, instead of a number, the designation
 "front left", "back left", "back right" or "front right" can also be
 spoken.
 After the function "coking area" or "griddle" and the precise designation
 of the location on the cook top have been specified in this way, the
 action desired of the relevant cooking area is specified by a further
 keyword (W4).
 Between the speaking of two keywords there is a pause, which is designated
 by Tt in FIG. 2. The pause is used to separate the keywords clearly from
 one another, if required, and at the same time to define a time limit
 after which the following word must be spoken at the latest. If the second
 word is not spoken or not spoken in time, then this is recognized as an
 error. Such an incomplete sequence of speech signals or keywords does not
 lead to the formation of a control command and therefore does not lead to
 any action on the cook top; a so-called time-out occurs. This is also true
 if the sequence of keywords continues to be spoken correctly after a time
 limit has been exceeded.
 In the case of such an error, the appropriate sequence of keywords W1, W2,
 W3, W4 for the control of the household appliance (here: cook top) must be
 spoken again from the beginning.
 An erroneous operation of the cook top, which might possibly be caused, for
 example, by a sequence of words of an accidental conversation or of a
 radio or television transmission in the background, is not to be expected
 in the case of the sequence of method steps provided in accordance with
 the invention, since the probability that precisely the prescribed
 keywords are said in precisely the provided sequence in precisely the
 prescribed time relation is extremely low.
 The operational safety of the cook top can be ensured by further special
 measures. In order to prevent that a switched-off cook top, for example,
 cannot be switched on, for example by a radio playing for several weeks,
 which accidentally specifies a suitable combination of keywords, according
 to one exemplary embodiment of the present invention, a switched-off cook
 top is prepared or initialized for the input of speech signals by a manual
 actuation of a mechanical operating element 2. If this input of speech
 signals does not take place within a specific time, then the operating
 logic formed by the above-mentioned devices of the household appliance
 returns into its quiescent state or sleep mode again and cannot be put
 into operation by an accidental combination of keywords.
 If, immediately following the speaking of a sequence of keywords, actions
 are to be initiated in a further cooking area on the cook top, then it is
 not necessary to speak the keyword "cook top" if the time of a time-out Tt
 defined for this has not yet elapsed. It is immediately possible for a new
 cooking area to be selected by the appropriate keyword. The procedure is
 similar when a number of actions are to be carried out on one cooking
 area. One example of this is the sequence of keywords "cook top--cooking
 area--front left--on--zone--start cooking"; it switches on the front left
 cooking area with the additional zone and sets the initial cooking surge.
 If at least one heating element of the cook top is in operation, then the
 actuation of the mechanical operating element (safety switch) is not
 necessary before each further spoken control of the cook top, since it can
 be assumed that a person authorized to operate the cook top is in the room
 and, as previously, is monitoring the safe function of the cook top.
 The circuit configuration illustrated in FIG. 3 includes a central computer
 CC and a number of household appliances A1, . . . , An. Each household
 appliance Ax (x=1, . . . n) can have a local control system ALCx. The
 household appliances are connected to the central computer CC via an
 installation bus IB. The local control systems of the household appliances
 can control the household appliances in each case through the use of a
 control program which, for example, is stored in the respective household
 appliance. The local household appliance control systems can also be
 controlled on the basis of a control program which is assigned to the
 central computer CC.
 The central computer CC is assigned a first device 3 for the input of
 speech signals, which designate operating functions of at least one
 household appliance, as well as a second device 41 for recognizing the
 operating functions (speech signal contents) designated by the speech
 signals, as well as a third device 42, which converts recognized speech
 signal contents into control commands to operate at least one household
 appliance.
 The exemplary embodiment of a household appliance A1 according to the
 invention as illustrated schematically in FIG. 4, which, for example, is
 an electrically operated cook top, has mechanical operating elements 2
 which switch a power source P. Instead of one or more mechanical operating
 elements 2, other operating elements, such as contact switches, can also
 be provided.
 The power source P is used to supply electrical power, for example to a
 cook top having a first cooking area K1 (front left), a second cooking
 area K2 (back left), a third cooking area K3 (back right), and a fourth
 cooking area K4 (front right).
 The first device 3 for the input of speech signals (FIG. 3) can be
 integrated into a household appliance, as is illustrated in FIG. 4 for the
 household appliance 1. The first device 3 is formed in particular by at
 least one microphone fitted directly to the household appliance, the
 microphone or the microphones is or are preferably aligned with the
 probable whereabouts of the sound source (head of the speaker). A number
 of microphones make it possible to monitor various zones with maximum
 sensitivity. The microphone or microphones can also be disposed at other
 locations, for example in addition to the location (for example kitchen)
 of the household appliance, also at another location (for example living
 room).
 The first device 3 is connected to the local control system ALC1, which is
 further connected to the central computer CC (FIG. 3) and the cook top
 (K1, K2, K3, K4). Furthermore, the local control system ALC1 can be
 connected to the operating elements 2, in order to perform control
 procedures on the basis of actuations of the operating elements 2.
 The microphone or microphones have directional characteristics. The lobe of
 maximum sensitivity is located at the probable height of the head of the
 operator. Through the use of microphone diaphragms, which are fitted to
 the microphone such that they can be moved and/or replaced, the
 directional characteristics of the microphone can be matched to the
 conditions in the respective room. The microphone or the microphones are
 installed on a holding element which does not transmit structure-borne
 sound. A number of microphones make it possible to monitor different zones
 with maximum sensitivity.
 The first device 3 can also have an electric filter, which attenuates
 oscillations with frequencies below about 100 hertz and/or oscillations
 above about 5 kilohertz. The filter is in particular a bandpass filter,
 which attenuates oscillations with frequencies below about 100 hertz and
 oscillations above about 4 or 5 kilohertz.
 Furthermore, the first device 3 can be assigned a device which measures
 acoustic interference, in particular electrical signals which represent
 the acoustic interference. The first device 3 can also be assigned a
 device which compares the measured acoustic interference, in particular
 electrical signals which represent the acoustic interference, with
 electric useful acoustic signals (desired signals). This permits
 interference to be eliminated automatically.
 The first device 3 can be disposed to be physically separate from the
 second device 41 for recognizing the operating functions designated by the
 speech signals, the first device 3 being connected to the second device
 41, for example by a shielded cable. The devices 3 and 41 can be
 connectable to each other without wires, for example via an infrared
 connection. The microphone is installed on a holding element which damps
 structure-borne sound or oscillations.
 The device 3, which can be disposed separated from the central computer CC
 (FIG. 1) or from a household appliance, is embodied, for example, as a
 portable telephone terminal (cordless telephone; mobile telephone).
 By contrast, the second device 41 for recognizing the operating functions
 designated by the speech signals, and the third device 42 for converting
 the speech signals recognized into control commands to operate a household
 appliance (e.g. A1) are preferably disposed in or in the vicinity of the
 central computer CC.
 The control program assigned to the central computer CC is configured, in a
 manner corresponding to the control program already described with
 reference to FIG. 2, in such a way that successive speech signals lead to
 the formation of a control command only when successive speech signals W1,
 W2, W3, W4 (cf. FIG. 2) are input within a predetermined time T12, T23,
 T34 (FIG. 2).
 If successive speech signals are input outside the predeterminable time, or
 if the input of the speech signals is aborted, a control command is formed
 only when all the speech signals needed to form a control command are
 input again in the defined sequence and successive speech signals are
 input again within the predeterminable time periods (T12, T23, T34).
 After having been switched off, a household appliance can be activated by
 speech signals only after the (mechanical) operating element is actuated.
 In this case, provision may be made for this actuation to be enabled only
 within a predeterminable time period.
 Furthermore, the control may be configured such that the control of the
 household appliance or the formation of a control command can be activated
 by speech signals only after inputting a given number, for example
 "three".
 Likewise, pauses of different length between the speech signals can be
 predetermined.
 The speech signal recognition is preferably carried out in a
 speaker-independent manner, but the speech signal recognition can also be
 carried out in a speaker-dependent manner through the use of the second
 device 41, so that it becomes possible to authorize only specific persons,
 for example only the adult members of a household, to actuate the
 household appliance.
 In the exemplary embodiment illustrated in FIG. 4, the household appliance
 1 has a number of electric load elements K1, K2, K3, K4, which can be
 controlled individually or in specific combinations (K2 and K3) by speech
 signals.
 The speech signals preferably include a sequence of predeterminable
 "keywords", which have to be spoken in particular in a defined sequence.
 The structure of this sequence depends on the grammar of the language in
 which the keywords are spoken. The words such as "cook top", "cooking
 area" can be replaced during the use of the cook top by sequences of
 sounds of any desired configuration, so that, for example, even operators
 with impaired speech can control the household appliances in a simple way.
 Each sequence of keywords starts with the word "cook top" as an address to
 the household appliance itself. Then, the function "cooking area" or
 "griddle" has to be named, the function "griddle" and "cooking area" being
 considered intuitively as independent of each other, corresponding to
 normal domestic use, even if they are used in the same area on the cook
 top.
 Following the selection of the function "cooking area" or "griddle", the
 operating person selects, through the use of the keyword "1" or "2" or "3"
 or "4", the location on the cook top (front left; back left; back right;
 front right) on which the cooking area is to carry out actions. As an
 example of alternative keywords, instead of a number, the designation
 "front left", "back left", "back right" or "front right" can also be
 spoken.
 After the function "cooking area" or "griddle" and the precise designation
 of the location on the cook top have been specified in this way, the
 action desired of the relevant cooking area is specified by a further
 keyword, for example "higher" for electrical power to be supplied or
 increased in steps, for example.
 Between the speaking of two keywords there is a pause, which is designated
 in FIG. 2 by Tt. The pause is used to separate the keywords clearly from
 one another if required and, at the same time, to define a time limit
 after which the following word must be spoken at the latest. If the second
 word is not spoken or is not spoken in good time, then this is recognized
 as an error. Such an incomplete sequence of speech signals or keywords
 does not lead to the formation of a control command, and therefore does
 not lead to any action on the cook top; a so-called time-out occurs. This
 is also true when the sequence of keywords continues to be spoken
 correctly after a time limit has been exceeded. The pauses can have
 different lengths.
 For any action on the cook top, the appropriate sequence of keywords must
 be spoken again from the beginning.
 An erroneous operation of the cook top, as could be expected, for example,
 from a sequence of words of a random conversation or from a radio or
 television transmission in the background, is extremely unlikely in the
 case of the sequence of method steps provided according to the invention,
 since the probability that precisely the prescribed keywords occur in
 precisely the prescribed sequence in precisely the prescribed time
 relation is extremely low.
 As already described for a single household appliance with reference to
 FIG. 2, the operational safety of the cook top can be ensured by further
 special measures. In order that, for example, a switched-off cook top or
 any other household appliance connected to the central computer CC cannot
 be switched on, for example by a radio playing for several weeks, which
 specifies a randomly suitable combination of keywords, as already
 described, according to one exemplary embodiment of the present invention
 a completely switched-off household appliance is prepared or initialized
 for the input of speech signals before being switched on, through the use
 of the manual actuation of a mechanical operating element. If this
 operation does not take place within a specific time period, then the
 operating logic formed by the above-mentioned devices of the household
 appliance change back again into their quiescent state and cannot be put
 into operation by a random combination of keywords.
 If, immediately after speaking a sequence of keywords, actions are to be
 initiated in a further cooking area on the cook top, then saying the
 keyword "cook top" is not necessary if the time of a time-out Tt defined
 for this has not yet elapsed. It is then immediately possible for a new
 cooking area to be selected by the appropriate keyword.
 The procedure is similar when a number of actions are to be carried out on
 one cooking area. One example of this is the sequence of keywords "cook
 top--cooking area--front left--on--zone--start cooking". It switches on
 the front left cooking area with the additional zone and sets the initial
 cooking surge. If at least one heating element of the cook top is in
 operation, an actuation of the mechanical operating element (safety
 switch) is then not necessary before each further speech operation of the
 cook top, because it can be assumed that a person authorized to operate
 the cook top is in the room and, as before, is monitoring the safe
 function of the cook top.