Dust extractor having automatic filter cleaning

Abstract

A dust extractor (500) comprises: - an inlet (IN1) to draw an air flow (AIR1) and dust particles (DUST1), - a filter (FIL1) to separate dust particles (DUST1) from the air flow (AIR1), - a filter cleaning unit (FCU1) to release separated dust particles (DUST1) from the filter (FIL1), and - a control system (SYS1) to control operation of the dust extractor (500), wherein the control system (SYS1) comprises at least one sensor (PSEN1) to detect an interruption (COM1) of the air flow (AIR1), and wherein the control system (SYS1) is arranged to change an operating mode (MODE1, MODE2) of the filter cleaning unit (FCU1) based on a detected interruption (COM1) of the air flow (AIR1).

Description

[0001] DUST EXTRACTOR HAVING AUTOMATIC FILTER CLEANING

[0002] FIELD

[0003] The present invention relates to a dust extractor.

[0004] BACKGROUND

[0005] A dust extractor may be used for removing dust particles e.g. at a workshop or at a construction site. The dust may be generated e.g. when material is processed by a power tool. The dust extractor causes suction to remove dust particles. The dust extractor may draw an air flow via a hose, so as to remove dust particles, which are carried by the air flow.

[0006] The dust extractor may comprise a filter to separate dust particles from the air flow. Dust particles collected on the filter may increase the pressure difference across the filter. Dust particles collected on the filter may reduce the air flow rate via the hose. The dust extractor may comprise a filter cleaning unit to remove collected dust particles from the filter. It is known that operation of the filter cleaning unit may be started e.g. by pushing a filter cleaning button of the dust extractor. In that case the user of the dust extractor may need to walk close to the dust extractor, in order to push the button of the dust extractor.

[0007] SUMMARY

[0008] An object is to provide a dust extractor. An object is to provide a method for extracting dust.

[0009] According to an aspect, there is provided a dust extractor (500), comprising:

[0010] - an inlet (IN1 ) to draw an air flow (AIR1 ) and dust particles (DUST 1 ),

[0011] - a filter (FIL1 ) to separate dust particles (DUST1 ) from the air flow (AIR1 ),

[0012] - a filter cleaning unit (FCU1 ) to release separated dust particles (DUST1 ) from the filter (FIL1 ), and - a control system (SYS1 ) to control operation of the dust extractor (500), wherein the control system (SYS1 ) comprises at least one sensor unit (PSEN1 ) to detect an interruption (COM1 ) of the air flow (AIR1 ), and wherein the control system (SYS1 ) is arranged to change an operating mode (MODE1 , MODE2) of the filter cleaning unit (FCLI1 ) based on a detected interruption (COM1 ) of the air flow (AIR1 ).

[0013] According to an aspect, there is provided a dust extractor of claim 1 .

[0014] Further embodiments are defined in the other claims.

[0015] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0016] The dust extractor may draw an air flow and dust particles e.g. via a suction hose. The dust extractor comprises a filter to collect the dust particles from the air flow. The dust particles collected on the filter may increase the flow resistance of the filter. The dust extractor comprises a filter cleaning unit to intermittently remove the collected dust particles from the filter. The filter cleaning unit may provide e.g. filter cleaning pulses, wherein the direction of the air flow across the filter may be temporarily reversed to release the collected dust particles. Alternatively, or in addition, the filter cleaning unit may release collected dust particles by shaking the filter.

[0017] The filter cleaning operations facilitate maintaining sufficient air flow rate in case of high dust concentration. On the other hand, the filter cleaning operation may generate acoustic noise and / or may temporarily disturb the air flow. The user of the dust extractor may wish to change a filter operating mode of the dust extractor between automatic repetitive filter cleaning and constant suction without filter cleaning. The dust extractor may have a first filter operating mode where the filter cleaning unit does not perform filter cleaning operations, and a second filter operating mode where the filter is automatically cleaned. The user may provide an instruction to the dust extractor to change the filter operating mode. The user may provide the instruction by interrupting the air flow of the inlet. The interruption of the air flow may be detected and used as an instruction for controlling the operating mode of the filter cleaning unit. The user may provide the instruction simply by blocking the inlet of the suction hose. The user may interrupt the air flow of the suction hose e.g. by hand. The control system of the dust extractor may be arranged to change the filter operating mode when the control system determines that the air flow is interrupted.

[0018] The user may provide the instruction for changing the filter operating mode simply by blocking the end of the suction hose. The user does not need to walk close to the dust extractor to change the filter operating mode. The dust extractor may enable using the suction hose as a pneumatic remote control device for changing operating mode of the dust extractor.

[0019] The user may first use the dust extractor in a filter operating mode where cleaning pulses are not generated. The user may at a later stage provide an instruction to start automatic filter cleaning when needed. Consequently, there may be less noise due to unnecessary filter cleaning. Consequently, there may be less drops in suction power due to unnecessary filter cleaning pulses.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the following examples, several variations will be described in more detail with reference to the appended drawings, in which

[0022] Fig. 1a shows, by way of example, a dust extractor connected to a power tool with a hose,

[0023] Fig. 1 b shows, by way of example, interrupting the air flow of the dust extractor,

[0024] Fig. 2a shows, by way of example, an operating mode where filter cleaning operations are not performed, Fig. 2b shows, by way of example, starting operation in an operating mode where filter cleaning operations are performed repetitively,

[0025] Fig. 2c shows, by way of example, starting operation in an operating mode where filter cleaning operations are not performed, and starting operation in an operating mode where filter cleaning operations are performed repetitively,

[0026] Fig. 2d shows, by way of example, starting operation in an operating mode where filter cleaning operations are performed repetitively based on measured pressure difference across the filter,

[0027] Fig. 3 shows, by way of example, starting operation in a temporary operating mode, where filter cleaning operations are performed repetitively during a predetermined time period, or where filter cleaning operations are performed based on a predetermined number of the filter cleaning operations,

[0028] Fig. 4a shows, by way of example, extending duration of a temporary operating mode,

[0029] Fig. 4b shows, by way of example, a situation where the duration of the temporary operating mode is not extended,

[0030] Fig. 5a shows, by way of example, temporal evolution of chamber pressure, and temporal evolution of fan inlet pressure,

[0031] Fig. 5b shows, by way of example, temporal evolution of chamber pressure,

[0032] Fig. 5c shows, by way of example, temporal evolution of pressure difference across the filter,

[0033] Fig. 5d shows, by way of example, temporal evolution of the air flow rate via the inlet, Fig. 6a shows, by way of example, a first operating mode where filter cleaning operations are not performed,

[0034] Fig. 6b shows, by way of example, a second operating mode where filter cleaning operations are performed repetitively at regular intervals,

[0035] Fig. 6c shows, by way of example, a third operating mode where filter cleaning operations are performed based on a detected pressure difference,

[0036] Fig. 7a shows, by way of example, temporal evolution of chamber pressure and temporal evolution of fan inlet pressure, in a situation where the inlet of the dust extractor is blocked,

[0037] Fig. 7b shows, by way of example, temporal chamber pressure, in the situation where the inlet of the dust extractor is blocked,

[0038] Fig. 7c shows, by way of example, temporal evolution of pressure difference across the filter, in the situation where the inlet of the dust extractor is blocked,

[0039] Fig. 8a shows, by way of example, changing an operating mode based on an interruption of the air flow,

[0040] Fig. 8b shows, by way of example, changing an operating mode based on an interruption of the air flow,

[0041] Fig. 8c shows, by way of example, changing an operating mode based on an interruption of the air flow,

[0042] Fig. 8d shows, by way of example, method steps for changing an operating mode based on an interruption of the air flow,

[0043] Fig. 9a shows, by way of example, starting operation in a temporary operating mode, and resuming operation in a normal operating mode, Fig. 9b shows, by way of example, method steps for starting operation in a temporary operating mode, and determining a duration of operation in the temporary operating mode,

[0044] Fig. 9c shows, by way of example, method steps for starting operation in a temporary operating mode, and determining a duration of operation in a temporary operating mode,

[0045] Fig. 10 shows, by way of example, a control system of the dust extractor,

[0046] Fig. 1 1 a shows, by way of example, in a three-dimensional view, a dust extractor, and

[0047] Fig. 1 1 b shows, by way of example, in a three-dimensional view, a dust extractor.

[0048] DETAILED DESCRIPTION

[0049] Referring to Figs. 1 a and 1 b, the control system SYS1 of the dust extractor 500 may be arranged to change the operating mode of the filter cleaning unit FCLI1 of the dust extractor 500 based on a pneumatic instruction COM1 , which is provided by temporarily interrupting the air flow AIR1 drawn via the inlet IN1 of the dust extractor 500. A user of the dust extractor may interrupt the air flow AIR1 e.g. by blocking the inlet IN0 or IN1. The symbol COM1 may refer to the interruption and to the instruction. The detected interruption of the air flow may be used as an instruction for controlling the operating mode of the filter cleaning unit of the dust extractor. The control system SYS1 of the dust extractor 500 may be arranged to change the operating mode of the filter cleaning unit FCLI1 based on the detected interruption COM1 of the air flow AIR1 .

[0050] The filter cleaning unit FCLI1 of the dust extractor 500 may perform a filter cleaning operation by generating a filter cleaning pulse and / or by mechanically shaking the filter. The filter cleaning unit of the dust extractor 500 may have e.g. two or more of the following operating modes: a normal operating mode MODEO, a first operating mode MODE1 , a second operating mode MODE2, a third operating mode MODE3, and a temporary operating mode MODE4.

[0051] The control system SYS1 may be arranged to change the operating mode of the filter cleaning unit FCLI1 e.g. from a first operating mode MODE1 to a second operating mode MODE2 when the control system SYS1 determines that the air flow AIRI of the inlet IN1 is interrupted COM1.

[0052] The first operating mode MODE1 may be e.g. an operating mode MODE1 , where filter cleaning operations are not performed.

[0053] The second operating mode MODE2 may be e.g. an operating mode where filter cleaning operations are performed repetitively based on a timer. In particular, filter cleaning operations may be performed repetitively at regular intervals.

[0054] The third operating mode MODE3 may be e.g. an operating mode where filter cleaning operations are performed repetitively based on a measured pressure and / or based on a measured pressure difference.

[0055] The normal mode MODEO may be e.g. an operating mode, where filter cleaning operations are not performed. The temporary operating mode MODE4 may be an operating mode, which has a determined or predetermined duration. The duration of the temporary operating mode MODE4 may be e.g. in the range of 1 min to 10 min. The control system SYS1 may be arranged to stop operation in the temporary operating mode MODE4 at the end of the duration, and to start operation in the normal operating mode MODEO at the end of the duration. The filter cleaning unit FCLI1 may be arranged to repetitively perform filter cleaning operations in the temporary operating mode MODE4. The filter cleaning operations may be performed repetitively based on a timer, based on measured pressures and / or based on measured pressure differences.

[0056] The dust extractor 500 may be arranged to suck dust particles DUST 1 , which are carried by an air flow AIR1. The dust extractor 500 may comprise a rotating suction fan FAN1 to cause a partial vacuum p2, which in turn may draw the air flow AIR1 and the dust particles DUST1 through a hose HOSE1 connected to the inlet IN1 of the dust extractor 500. The dust extractor 500 may comprise a motor MOTOR1 for rotating the suction fan FAN1. The air flow AIR1 and the dust particles DUST1 may enter a dust chamber CHM1 of the dust extractor via the inlet IN1 . The dust chamber CHM1 may also be called as a tank.

[0057] The dust chamber CHM1 has a chamber pressure pi.

[0058] The dust extractor 500 comprises a filter FIL1 to separate dust particles DUST1 from the air flow AIR1. Dust particles DUST1 collected on the filter FIL1 may increase the flow resistance across the filter FIL1 . The increased flow resistance may reduce the maximum air flow rate QAIR, which can be provided via the inlet IN1. The dust extractor 500 comprises a filter cleaning unit FCLI1 for releasing collected dust particles DUST1 from the filter FIL1. The filter cleaning unit FCLI1 may release the collected particles DUST1 e.g. by shaking the filter FIL1 and / or by providing reversed air flow.

[0059] The filter cleaning unit FCLI1 may comprise e.g. an air valve VAL1 for providing temporarily reversed air flow. The valve VAL1 may be opened and closed by an actuator ACLI1 . The reversed air flow may blow the particles away from the filter FIL1 . The reversed air flow may be provided only for a short time, and the temporarily reversed air flow may be called e.g. as a filter cleaning pulse.

[0060] The released particles DUST1 may e.g. fall to the bottom of the inlet chamber CHM1.

[0061] The ambient pressure po denotes the pressure of the ambient atmosphere. The inlet chamber pressure pi denotes the pressure in the space between the inlet IN1 and the filter FIL1. The fan input pressure p2 denotes the pressure in the space SPC2 between the filter FIL1 and the suction fan FANI . The fan output pressure ps denotes the pressure between the suction fan FAN1 and the outlet OUT 1 of the dust extractor 500.

[0062] A power tool TOOL1 may be connected to the inlet IN1 of the dust extractor 500 with a suction hose HOSE1. Pressure near the power tool TOOL1 and at the outlet OUT1 of the dust extractor 500 may be substantially equal to the atmospheric pressure po. The inlet chamber pressure pi may also denote the upstream pressure of the filter FIL1 . The pressure difference po - pi may draw the dust-laden air flow AIR1 from the power tool TOOL1 to the inlet chamber CHM1 of the dust extractor 500 via the flexible hose HOSE1 .

[0063] The pressure difference po-pi between the ambient pressure po and the chamber pressure pi may draw the air flow AIR1 and the dust particles DUST 1 via the inlet IN1 into the dust chamber CHM1 . The suction fan FAN1 may draw the air flow AIR1 through the filter FIL1. The pressure difference P1-P2 (=APF) between the chamber pressure pi and the fan input pressure p2 may draw the air flow AIR1 through the filter FIL1. The filter FIL1 may separate the dust particles DUST1 from the air flow AIR1 such that the air flow AIR1 passing via the space SPC2 between the filter FIL1 and the fan FAN1 may be substantially free of dust particles DUST1. The fan FAN1 may generate a pressure difference P3-P2 (=APFAN) across the fan FAN1 .

[0064] The rotating fan FAN1 may cause the partial vacuum p2, which prevails between the filter FIL1 and the fan FANI . p2 denotes an upstream pressure of the fan FAN1 and downstream pressure of the particle separator FIL1. The pressure p2 may be the lowest pressure of the apparatus 1000. ps denotes a downstream pressure of the fan FAN1 . The maximum pressure difference (P3-P2) over the fan FAN1 may be e.g. in the range of 5 to 30 kPa. The downstream pressure of the fan FAN1 may be near to the ambient pressure po. The ambient pressure po is typically substantially equal to 101.3 kPa. The minimum absolute pressure P2 between the filter FIL1 and the fan FAN1 may be e.g. in the range of 70 kPa to 95 kPa.

[0065] The dust extractor 500 may also be called e.g. as a vacuum cleaner.

[0066] The control system SYS1 of the dust extractor 500 may comprise one or more sensors PSEN1 , PSEN2 for detecting the airflow AIR1 . The control system SYS1 of the dust extractor 500 may comprise one or more sensors PSEN1 , PSEN2 for detecting the flow rate QAIR of the air flow AIR1 .

[0067] For example, the dust extractor 500 may comprise a pressure sensor PSEN1 for measuring the inlet chamber pressure pi. The control system SYS1 may detect the flow rate QAIR based on the measured inlet chamber pressure pi. For example, if the inlet chamber pressure pi is lower than a first limit value, this may be an indication that the air flow rate QAIR into the chamber CHM1 is lower than a second limit value. For example, if the inlet chamber pressure pi is lower than the first limit value, this may be an indication that the air flow AIR1 is interrupted.

[0068] For example, the dust extractor 500 may comprise a first pressure sensor PSEN1 for measuring the chamber pressure pi, and a second pressure sensor PSEN2 for measuring the fan inlet pressure p2. The control system SYS1 may detect the flow rate QAIR based on the pressure difference Apr = P1-P2. For example, if the pressure difference P1-P2 is lower than a first limit value, this may be an indication that the air flow rate QAIR through the filter FIL1 is lower than a second limit value.

[0069] The response of the chamber pressure pi(t) to an interruption of the air flow AIR1 may be faster than the response of the fan inlet pressure P2(t). Detecting the air flow AIR1 by measuring the inlet chamber pressure pi may provide fast response.

[0070] Detecting an interruption COM1 of the air flow AIR1 may comprise measuring at least one pressure (pi,p2) prevailing in the dust extractor (500), and / or measuring a pressure difference (Apr, APFAN) prevailing in the dust extractor (500).

[0071] The dust extractor 500 may comprise a user interface LIIF1 for receiving user input from a user and / or for providing information to the user. For example, the user may set a default filter operating mode by using the user interface LIIF1 . For example, the user interface LIIF1 may provide a visual or audible indication of a current filter operating mode to the user.

[0072] The user may optionally set a target power value of the suction motor MOTOR1 by using the user interface LIIF1. The control system SYS1 may optionally comprise a sensor RPMSEN4 for measuring the rotation speed of the motor MOTOR1 and / or for measuring the rotation speed of the fan FAN1 . The sensor may provide an indication of the measured rotation speed of the fan.

[0073] An apparatus 1000 for extracting dust DUST1 may comprise the dust extractor 500 and a hose HOSE1 connected to the dust extractor 500. The hose HOSE1 may convey an air flow AIR1 and dust particles DUST1 to the dust extractor 500. The hose HOSE1 may convey an air flow AIR1 and dust particles DUST1 e.g. from a working area of a power tool TOOL1 to the dust extractor 500. The apparatus 100 may optionally comprise a tool TOOL1 . The tool TOOL1 may be e.g. a sander, a drilling machine, or a sawing machine.

[0074] The apparatus 1000 may be e.g. a surface processing apparatus. The surface processing apparatus 1000 may further comprise a power tool TOOL1 for processing a surface SRF1 of an object OBJ1. The power tool TOOL1 may be e.g. a rotary sander, an orbital sander or a belt sander. The power tool TOOL1 may comprise an abrasive article ABR1 , which comprises abrasive grains. The tool TOOL1 may comprise a supporting pad PAD1. The abrasive article ABR1 may be attached to the pad PAD1. The tool TOOL1 may comprise a motor MOTOR2 for causing a movement of the abrasive article ABR1 with respect to the surface SRF1 . The tool TOOL1 may comprise a motor MOTOR2 for causing rotary and / or oscillatory movement of the abrasive article ABR1 with respect to the surface SRF1 . Pressing the abrasive article ABR1 against the surface SRF1 may generate dust particles DUST 1 , which may comprise particles released from the surface SRF1 and / or particles released from the abrasive article ABR1 . The tool TOOL1 may comprise one or more openings OP1 for extracting the released particles DUST1 together with an air flow AIR1 . The dust extractor 500 may be arranged to draw the dust-laden air flow AIR1 via the openings OP1 and via a flexible hose HOSE1 to the inlet IN1 of the dust extractor 500.

[0075] The hose HOSE1 may operate as a flexible conduit for guiding the dust-laden air flow AIR1 . The hose HOSE1 may guide dust particles DUST1 together with the air flow AIR1 from a port PORT1 of the tool TOOL1 to the inlet IN1 of the dust extractor 500. The suction hose HOSE1 may be detachably connectable to the inlet IN1. The dust extractor 500 may be delivered to a user without the hose HOSE1. The dust extractor 500 and the hose HOSE1 may be delivered separately. The user may connect the hose HOSE1 to the inlet IN1 of the dust extractor 500.

[0076] Referring to Fig. 1 b, the user of the dust extractor 500 may temporarily interrupt the air flow AIR1 e.g. by blocking the inlet IN0 or IN1 with an obstacle BLC1 . The obstacle BLC1 may be e.g. the hand of the user, or a another suitable surface. IN0 denotes the inlet of the hose HOSE1 . In an embodiment, the hose HOSE1 , or an auxiliary unit connected to the hose HOSE1 , may comprise a manually operated valve for may temporarily interrupting the air flow AIR1 .

[0077] The control system SYS1 of the dust extractor 500 may be arranged to change the filter operating mode of the dust extractor 500 based on an instruction COM1 , which is provided by temporarily interrupting the air flow AIR1 , which passes via the inlet IN0, via the hose, and via the inlet IN1. The user may provide the instruction COM1 e.g. by blocking the inlet IN0 or IN1 .

[0078] For example, the dust extractor 500 may initially operate in a first filter operating mode, where the filter cleaning unit FCII1 does not perform any filter cleaning operations. The first filter operating mode may be suitable e.g. for a situation where the amount of generated dust is low, the air flow rate should be kept substantially constant, and acoustic noise generated by the dust extractor should be kept at a low level.

[0079] Next, the user may instruct the dust extractor to change filter operating mode from the first filter operating mode to a second filter operating mode, where the filter cleaning unit intermittently and automatically performs filter cleaning operations. The filter cleaning operations may be performed repetitively e.g. according to predetermined time intervals. The user may provide the instruction COM1 for changing the filter operating mode simply by blocking the inlet IN0 or IN1 . The second filter operating mode may be suitable e.g. for a situation where the amount of generated dust is higher.

[0080] In general, the control system SYS1 of the dust extractor 500 may be arranged to execute one or more method steps based on detected air flow rate QAIR of the inlet IN1. The user may provide one or more instructions to the control system SYS1 by modulating the airflow rate QAIR. The control system SYS1 may execute one or more method steps according to an instruction (COM1 ), which is provided by modulating the air flow rate QAIR. The control system SYS1 may execute an operation according to an instruction (COM1 ), which is provided by interrupting the air flow AIR1 . The user may provide a pneumatic instruction (COM1 ) to the control system SYS1 by modulating the air flow rate QAIR. Referring to Fig. 2a, the dust extractor 500 may be operated in a first operating mode MODE1 , where filter cleaning operations are not performed. The operation of the dust extractor 500 may be started e.g. at a time to. The suction air flow AIR1 may be started e.g. at a time to. The filter cleaning unit FCLI1 may be arranged to operate such that filter cleaning operations are not performed in the first operating mode MODE1 . The control system SYS1 of the dust extractor 500 may prevent filter cleaning operations in the first operating mode MODE1 .

[0081] Referring to Fig. 2b, operation in the first operating mode MODE1 may be stopped, and operation in the second operating mode MODE2 may be started based on a detected interruption COM1 of the air flow AIR1. The user may interrupt the airflow AIR1 of the dust extractor 500 at the time tic- The interruption COM1 of the air flow AIR1 may be detected at the time tic, and the operating mode may be changed based on the interruption COM1. The operating mode may be changed from the first mode MODE1 to the second mode MODE2.

[0082] The control system SYS1 may be arranged to change the operating mode of the filter cleaning unit FCLI1 from the first operating mode MODE1 to the second operating mode MODE2 when the control system SYS1 determines that the air flow AIRI of the inlet IN1 is interrupted COM1.

[0083] The first operating mode MODE1 may be a mode where filter cleaning operations are not performed. The filter cleaning unit FCLI1 may be arranged to repetitively perform filter cleaning operations PUi, PU2 in the second operating mode MODE2.

[0084] The filter cleaning unit FCLI1 may be arranged to perform a filter cleaning operation BPU1 at the start of the second mode MODE2, when the air flow is interrupted. The filter cleaning unit FCLI1 may be arranged to repetitively perform other filter cleaning operations PU2, PU3, PU4, PU5, PUe, PU7, PUs, ... at times t2c, tsc, c, tsc, tec, t?c, tsc, ■■■, when the air flow is not interrupted. The control system SYS1 may cause performing filter cleaning operations in the second operating mode MODE2 when the air flow is not interrupted. The control system SYS1 may cause performing filter cleaning operations PU2, PU3, PU4, ... e.g. at regular temporal intervals TFI . The time period TFI between consecutive filter cleaning operations (PU1, PU2) may be e.g. longer than 10 s. Performing filter cleaning operations at regular intervals may provide predictable and / or more reliable cleaning. Regular intervals may allow the user to synchronize his actions with the filter cleaning operations.

[0085] Referring to Fig. 2c, operation in the second operating mode MODE2 may be stopped, and operation in the first operating mode MODE1 may be started when an interruption COM1 is detected at a time tsc. Operation in the first operating mode MODE1 may be stopped, and operation in the second operating mode MODE2 may be started when an interruption COM1 detected at a time tec. TMODEI denotes a duration of operation in the first operating mode MODE1. TMODE2 denotes a duration of operation in the second operating mode MODE2. The symbols BPUi, BPUs, BPUe denote filter cleaning operations, which are performed when the air flow AIR1 is interrupted (COM1 ) at times tic, tsc, tec.

[0086] Referring to Fig. 2d, the filter cleaning pulses PU2, PU3, PU4, ... may also be performed based on a measured pressure difference or based on a measured pressure. In particular, the pressure difference App(t) across the filter FIL1 may increase with increasing amount of dust DUST 1 collected on the filter FIL1 . The dust extractor 500 may have an operating mode MODE3 where the control system SYS1 is arranged to cause performing a filter cleaning operation PU2, PU3, PU4, ... when the measured pressure difference App(t) across the filter FIL1 reaches a predetermined threshold value TRG1 .

[0087] Operation in the first operating mode MODE1 may be stopped, and operation in a third operating mode MODE3 may be started based on an interruption COM1 detected at a time tic- A first cleaning operation BPU1 may be performed when the air flow AIR1 is interrupted at a time tic- Other cleaning operations PU2, PU3, PU4, ... may be performed based on measured pressure (see also Fig. 6c). The temporal interval between consecutive cleaning operations may vary depending on the measured pressure. For example, the interval TFI between a first operation BPU1 and a second operation PU2 may be different from the interval TF2 between the second operation PU2 and a third operation PU3.

[0088] Performing cleaning operations based on measured pressure in the operating mode MODE3 may provide optimized cleaning. For example, cleaning pulses may be generated only when needed. Referring to Fig. 3, the filter cleaning unit FCLI1 may have a normal operating mode MODEO and a temporary operating mode MODE4.

[0089] Filter cleaning operations (PUi, PU2) are not performed in the normal operating mode MODEO. The control system SYS1 may change the operating mode of the filter cleaning unit FCLI1 from the normal operating mode MODEO to the temporary operating mode MODE4 e.g. based on a detected interruption COM1 of the air flow AIR1.

[0090] Operation in the temporary operating mode MODE4 may have a duration TMODE4. The control system SYS1 may be arranged to start operation in the normal operating mode MODEO at the end tE4 of the duration TMODE4. The filter cleaning unit FCII1 may be arranged to resume operation in the normal mode MODEO at the end tE4 of the duration TMODE4 of the temporary operating mode MODE4.

[0091] Operation in the temporary operating mode MODE4 may be stopped based on a timer signal. Operation in the temporary operating mode MODE4 may be stopped when the elapsed time of the temporary operating mode MODE4 reaches the determined duration of the temporary operating mode MODE4.

[0092] The control system SYS1 may stop operation in the temporary operating mode MODE4 without detecting an interruption of the air flow at the end tE4 of the duration TMODE4 of the temporary operating mode MODE4.

[0093] The dust extractor 500 may also be arranged to operate such that only a predetermined number (NPU) of cleaning operations are performed during operation in the temporary operating mode MODE4. Operation in the temporary operating mode MODE4 may be stopped when the counted number of the cleaning operations PU1, PU2 becomes equal to the predetermined number (NPU) of cleaning operations.

[0094] The temporary operating mode MODE4 may have a predetermined duration (TMIN4), or the duration (TMODE4) may be the time needed for performing the predetermined number (NPU) of filter cleaning operations PU1, PU2. Referring to Figs. 4a and 4b, the dust extractor 500 may have a passive normal operating mode MODEO, where an interruption COM1 of the air flow AIR1 occurring during operation in the normal operating mode MODEO does not cause a change of the operating mode. In other words, interruptions COM1 of the air flow AIR1 may be ignored. The dust extractor 500 may have a temporary operating mode MODE4, where an interruption COM1 of the air flow AIR1 may extend the duration of the temporary operating mode MODE4, and / or where an interruption COM1 of the air flow AIR1 causes performing a filter cleaning operation BPUi, BPU2. In the temporary mode MODE4, the filter cleaning unit FCU1 may perform filter cleaning operations based on detected interruptions COM1 of the air flow AIR1 . In the temporary operating mode MODE4, the dust extractor 500 may perform filter cleaning operations PU1, PU2 repetitively and / or based on a detected interruption COM1 of the air flow AIR1 .

[0095] The normal operating mode MODEO may be a passive mode, where the dust extractor 500 draws the air flow AIR1 , but the filter cleaning unit FCLI1 does not perform filter cleaning operations based on a detected interruption (COM1 ) of the air flow AIR1 .The dust extractor 500 may sometimes be used such that the air flow AIR1 via the hose HOSE1 is occasionally prevented even if the user does not intend to interrupt the air flow. Operating the dust extractor 500 in the passive normal operating mode MODEO may avoid performing unintentional filter cleaning operations in the passive normal operating mode MODEO.

[0096] The dust extractor 500 may start operation in the passive normal operating mode MODEO at the time to. Operation in the temporary operating mode MODE4 may be started at a time ts4 e.g. by giving user input SACT4 via a user interface LIIF1 . Operation in the temporary operating mode MODE4 may be stopped at the time tE4. Operation in the temporary operating mode MODE4 may have a duration TMODE4. The duration TMODE4 may have a predetermined minimum value TMIN4. The minimum value TMIN4 may be e.g. in the range of 30 s to 600 s.

[0097] Fig. 4a shows a situation where air flow AIR1 is interrupted during operation in the temporary operating mode MODE4. The control system SYS1 may be arranged to extend the duration TMODE4 when an interruption COM1 of the air flow AIR1 is detected during the operation in the temporary operating mode MODE4. The air flow AIR1 may be interrupted (COM1 ) at a time t2c and a time tsc. A modified end time tE4 of the temporary operating mode MODE4 may be determined by adding a temporal length TADD4 to the latest detected interruption time (e.g. tsc). The temporal length TADD4 may be e.g. in the range of 30 s to 600 s.

[0098] The filter cleaning unit (FCLI1 ) may be arranged to perform a filter cleaning operation (BPUi, BPU2, BPII3) when an interruption COM1 of the air flow AIR1 is detected during operation in the temporary operating mode MODE4.

[0099] Fig. 4b shows a situation where the air flow AIR1 is not interrupted during operation in the temporary operating mode MODE4. The duration TMODE4 is not extended, and the duration TMODE4 remains equal to the initial minimum value TMIN4. The dust extractor 500 may resume or start operation in the passive normal operating mode MODEO at the end tE4 of the temporary mode MODE4.

[0100] The dust extractor 500 does not perform a filter cleaning operation when the air flow AIR1 is interrupted during operation in the passive normal operating mode MODEO. An interruption COM1 after the end tE4 of the temporary mode MODE4 does not cause performing a filter cleaning operation. For example, an interruption COM1 at the time tic in the passive mode MODEO does not cause performing a filter cleaning operation. An interruption COM1 at the time tic in the passive mode MODEO does not cause extending the duration of the temporary mode MODE4.

[0101] Figs. 5a to 5d illustrate operation of the dust extractor and forming filter cleaning pulses PU1, PU2 in a situation where the air flow AIR1 of the inlet IN1 is not blocked by an obstacle BLC1 .

[0102] Fig. 5a shows, by way of example, temporal evolution of chamber pressure pi (t) and temporal evolution of fan inlet pressure P2(t). The amount of dust DUST1 collected on the filter FIL1 increases between times to and tic. The pressure difference Apr = pi(t)-p2(t) across the filter FIL1 increases between the times to and tic. A filter cleaning pulse PU1 may be started at the time tic.

[0103] Fig. 5b shows in more detail the temporal evolution of the chamber pressure pi(t) during the filter cleaning pulse PU1. The air valve VAL1 of the filter cleaning unit FCU1 is opened at the time tic so that ambient air AIR2 rapidly flows into the space SPC2 between the filter FIL1 and the fan FAN1 (see also Fig. 1 b). The fan inlet pressure p2 may be temporarily increased to a value, which is close to the ambient pressure po at the time tid- The pressure p2 in the space SPC2 may temporarily become higher than the inlet chamber pressure pi so that the direction of air flow through the filter FIL1 may be temporarily reversed. The reversed air flow through the filter Fill may increase also the inlet chamber pressure pi to a value, which is close to the ambient pressure po at the time tie. The air valve VAL1 of the filter cleaning unit FCLI1 is closed at the time tif. The fan FAN1 draws the air flow AIR1 so that the pressures pi(t) and P2(t) start to decrease after the time tif. The chamber pressure pi(t) may reach a minimum value at the time tig. The amount of dust DUST1 collected on the filter FIL1 may increase again between times tigand t2c. A second filter cleaning pulse PU2 may be provided between times t2c and t2g.

[0104] PMIN denotes the minimum possible value of the chamber pressure pi(t) in a situation where the air flow AIR1 via the inlet IN1 is interrupted. TLVO denotes a trigger level. It may be noticed that the chamber pressure pi (t) may remain higher than the trigger level TLVO when the inlet IN1 is not blocked.

[0105] Fig. 5c shows, by way of example, temporal evolution of the pressure difference Apr = pi(t)-p2(t) across the filter FIL1. APMAX denotes the maximum possible pressure difference, which is equal to po - PMIN. ApR2 denotes the pressure difference across the filter during the reverse flow of the filter cleaning pulse PU1.

[0106] Fig. 5d shows, by way of example, temporal evolution of the air flow rate QAIRC) via the inlet IN1 . QMAX denotes a maximum value of the air flow rate QAIRC). The air flow rate QAIRC) decreases between the times to and tic, with the increasing amount of dust DUST1 collected on the filter FIL1 . The air flow rate QAIRC) may be temporarily reduced during the filter cleaning pulses PU1, PU2, due to the temporarily increased chamber pressure pi(t).

[0107] Figs. 6a to 6c show different filter operating modes MODE1 , MODE2, MODE3 of the dust extractor 500. Fig. 6a shows a first filter operating mode MODE1 , where the filter cleaning unit FCU1 does not perform any filter cleaning operations. In particular, the control system SYS1 may be arranged to prevent filter cleaning pulses PU1 , PU2 during operation in the first filter operating mode MODE1. The duration TMODEI of operation in the first filter operating mode MODE1 may be e.g. longer than 200s, or even longer than 500 s.

[0108] Fig. 6b shows, by way of example, a second filter operating mode MODE2, where the filter cleaning unit FCLI1 repetitively performs filter cleaning operations. In particular, the control system SYS1 may control operation of the filter cleaning unit FCU1 so that the filter cleaning unit FCLI1 repetitively generates filter cleaning pulses PUi, PU2, PU3, PU4, ... The pulses may be generated at regular intervals TFI . The time period TFI between consecutive pulses PU1, PU2, PU3, PU4 may be e.g. in the range of 10 s to 200 s. In this operating mode, the maximum pressure difference across the filter FIL1 may depend on the concentration dust DUST1 of the air flow AIR1. For example, the pressure difference across the filter FIL1 may reach a value LV11 at the time tic. For example, the pressure difference across the filter FIL1 may reach a different value LV12 at the time t4c. In an embodiment, the length of the time period TFI may be selected e.g. by using the user interface LIIF1. The duration of operation in the second filter operating mode MODE2 may be e.g. longer than 200s, or even longer than 500 s. Operation in the second filter operating mode MODE2 may comprise e.g. generating five or more filter cleaning pulses PU1, PU2, PU3.

[0109] Fig. 6c shows, by way of example, a third filter operating mode MODE3, where the filter cleaning unit FCLI1 repetitively performs filter cleaning operations based on measured pressure difference ApF across the filter FIL1. In particular, the control system SYS1 may control operation of the filter cleaning unit FCLI1 so that the filter cleaning unit FCLI1 repetitively generates a filter cleaning pulse PU1, PU2, PU3, PU4 each time when the measured pressure difference ApF across the filter FIL1 reaches a predetermined threshold value TRG1. In this operating mode, the time interval TFI , TF2 between consecutive pulses PU1, PU2, PU3 may depend on the concentration of dust DUST1 in the air flow AIR1. In an embodiment, the threshold value TRG1 may be selected e.g. by using the user interface LIIF1. The duration of operation in the third filter operating mode MODE3 may be e.g. longer than 200s, or even longer than 500 s. Operation in the third filter operating mode MODE3 may comprise e.g. generating five or more filter cleaning pulses PUi, PU2, PU3.

[0110] Figs. 7a to 7c illustrate operation of the dust extractor in a situation where the air flow AIR1 is temporarily interrupted between times tia-tig, for example by using the user's hand BLC1 . The air flow AIR1 is not interrupted after the time tig.

[0111] Referring to Figs. 7a to 7c, the user may provide an instruction (COM1 ) to the dust extractor 500 by interrupting the air flow AIR1 at a time tia. The chamber pressure pi(t) and the fan inlet pressure P2(t) may fall close to the minimum pressure PMIN at the time tib- The control system SYS1 may detect the air flow AIR1 e.g. by monitoring the chamber pressure pi(t), by monitoring the fan inlet pressure P2(t), and / or by monitoring the pressure difference Apr across the filter FIL1 . If the chamber pressure pi(t) and / or the fan inlet pressure P2(t) falls below a threshold value TLV0, this may be an indication that the air flow AIR1 is interrupted. The control system SYS1 may determine at a time tDET that the instruction (COM1 ) has been provided by interrupting the air flow AIR1 of the inlet IN1.

[0112] For increased certainty, the control system SYS1 may also check whether the pressure pi (t) and / or P2(t) remains lower than the threshold value TLV0 for a time period, which is longer than a predetermined time period TSEC. In an embodiment, the control system SYS1 may be arranged to interpret the reduced pressure (pi(t),p2(t)) as the instruction (COM1 ) for changing filter operating mode only in a situation where the chamber pressure pi(t) and / or the fan inlet pressure P2(t) remains lower than the threshold value TLV0 for a time period, which is longer than a predetermined time period TSEC. The control system SYS1 may determine at a time tDET that the instruction (COM1 ) has been provided by interrupting the air flow AIR1 of the inlet IN1 . The length of the time period TSEC may be e.g. in the range of 1 s to 30 s.

[0113] The air flow AIR1 might sometimes be partially blocked also during normal use of the dust extractor, e.g. when vacuuming dust from a floor. The threshold value TLV0 and the time period TSEC may be selected such that normal use of the dust extractor is not likely to initiate a change of filter operating mode. The length of the time period TSEC may be e.g. longer than or equal to 5 s in order to reduce risk of accidental change of filter operating mode. For example, the user may first use the dust extractor without filter cleaning, and the user may later instruct the dust extractor 500 to start automatic repetitive filter cleaning by blocking the hose with his hand BLC1 for at least 5 s.

[0114] The control system SYS1 may be arranged change the filter operating mode of the dust extractor 500 based on the pneumatically received instruction COM1. For example, the control system SYS1 may change the operating mode from the first filter operating mode MODE1 to the second filter operating mode MODE2 based on the instruction COM1 , which may be determined to be received at the time tDET.

[0115] In addition to changing the filter operating mode, the control system SYS1 may optionally also control the filter cleaning unit FCLI1 so that a filter cleaning operation is performed at the start of operation in the next filter operating mode (MODE2). The control system SYS1 may control the filter cleaning unit FCLI1 to generate a filter cleaning pulse BPUi when the air flow AIR1 is interrupted. The chamber pressure pi (t) may reach the minimum pressure PMIN when the air flow AIR1 is interrupted, so that the magnitude of the reverse pressure difference APREV of the filter cleaning pulse BPUi may be greater than the magnitude of the reverse pressure difference APREV of the filter cleaning pulses PUi, PU2.

[0116] Referring to Fig. 8a, the dust extractor 500 may be arranged to start operation in a default filter operating mode e.g. when the power switch of the user interface is turned on. The default filter operating mode may be e.g. the first mode MODE1 . The dust extractor 500 may operate in the first filter operating mode MODE1 until the user provides the instruction COM1 by interrupting the air flow AIR1. The control system SYS1 may determine that the instruction COM1 is received at the time tDET. The control system SYS1 may change the operating mode from the first filter operating mode MODE1 to the second filter operating mode MODE2 based on the instruction COM1 . For example, the control system SYS1 may be arranged change the operating mode from MODE1 to MODE2. For example, the control system SYS1 may be arranged change the operating mode from MODE1 to MODE3. Referring to Figs. 8b and 8c, the control system SYS1 may be arranged change the operating mode each time when an instruction COM1 is provided by interrupting the air flow AIR1. For example, the control system SYS1 may be arranged change the operating mode from MODE1 to MODE2, and then from MODE2 to MODE1 . For example, the control system SYS1 may be arranged change the operating mode from MODE1 to MODE2, from MODE2 to MODE3, and from MODE3 back to MODE1 . For example, the control system SYS1 may be arranged change the operating mode from MODE1 to MODE3, from MODE3 to MODE2, and from MODE1 back to MODE1 .

[0117] Referring to Fig. 8d, an initial filter operating mode may be set in step 1010. The dust extractor 500 may be operated according to the current filter operating mode in step 1020. The status of the air flow AIR1 may be checked in step 1030. Operation in the current filter operating mode may be continued (step 1020) if the control system SYS1 determines that the air flow AIR1 is not interrupted. The control system SYS1 may change the filter operating mode if the control system SYS1 determines that the air flow is interrupted (step 1040). The dust extractor 500 may be operated in the next filter operating mode (step 1020).

[0118] Referring to Fig. 9a, the control system SYS1 may change the operating mode of the filter cleaning unit FCLI1 from the normal operating mode MODEO to the temporary operating mode MODE4 based on a detected interruption COM1 of the air flow AIR1 .

[0119] Alternatively, the control system SYS1 may be arranged to ignore the interruptions COM1 in a passive normal operating mode MODEO, so as to prevent unintentional change of operating mode. In that case, the control system SYS1 may be arranged to change the operating mode of the filter cleaning unit FCU1 from the passive normal operating mode MODEO to the temporary operating mode MODE4 based on a user input SACT, which is not received by detecting an interruption of the airflow AIR1 . The user input SACT may be received via a user interface LIIF1 of the dust extractor 500. The user input SACT may be received e.g. via a push button of the user interface LIIF1. The user input SACT may be received e.g. via a mobile phone, which is arranged to operate as a user interface LIIF1 of the dust extractor 500. Alternatively, the temporary operating mode MODE4 may be arranged to be a default operating mode in a situation where the power switch of the dust extractor 500 is turned on.

[0120] The temporary operating mode MODE4 may have a duration TMOD4. The temporary operating mode MODE4 may have a predetermined duration (e.g. TMIN4) or a determined duration. The duration TMOD4 may also be determined based on a predetermined number NPU of filter cleaning operations PUi, PU2. Operation in the temporary operating mode MODE4 may be continued until a predetermined number NPU of filter cleaning operations PU1, PU2 have been performed. The control system SYS1 may change the operating mode of the filter cleaning unit FCLI1 from the temporary operating mode MODE4 to the normal operating mode MODE4 based on a timer signal or based on a counter value.

[0121] Fig. 9b shows, by way of example, method steps for changing a filter operating mode based on a detected interruption COM1 of the air flow AIR1. Operation in the normal mode MODEO may be started in step 1110. The air flow AIR1 may be checked in the normal mode MODEO in step 1120. Operation in the normal mode MODEO may be continued if an interruption is not detected. The operating mode may be changed from the normal mode MODEO to the temporary mode MODE4 when an interruption COM1 of the air flow AIR1 is detected. Operation in the temporary mode MODE4 may be started in step 1130. The air flow AIR1 may be checked in the temporary mode MODE4 in step 1140. The duration of the temporary mode MODE4 may be extended in step 1150 when an interruption COM1 of the air flow AIR1 is detected in the temporary mode MODE4. The elapsed operating time in the temporary mode MODE4 may be compared with the determined duration of the temporary mode MODE4 in step 1160. Steps 1130, 1140, 1150 may be repeated if the elapsed time is shorter than the determined duration. Operation in the temporary mode MODE4 may be stopped and operation in the normal mode MODEO may be resumed at the end of the determined duration.

[0122] Fig. 9c shows, by way of example, method steps for changing a filter operating mode based on a detected interruption COM1 of the air flow AIR1 . The control system SYS1 may be arranged to ignore interruptions COM1 of the air flow AIR1 in the passive normal mode MODEO, so as to avoid unintentional change of operating mode. Operation in the passive normal mode MODEO may be started in step 1210. User input via a user interface UIF1 may be checked in step 1220. Operation in the passive normal mode MODEO may be continued if user input (SACT4) for changing the operating mode is not received. Operation in the temporary mode MODE4 may be started in step 1230 if user input (SACT4) for changing the operating mode is received.

[0123] The air flow AIR1 may be checked in the temporary mode MODE4 in step 1240. The duration of the temporary mode MODE4 may be extended in step 1250 when an interruption COM1 of the air flow AIR1 is detected in the temporary mode MODE4. The elapsed operating time in the temporary mode MODE4 may be compared with the determined duration of the temporary mode MODE4 in step 1260. Steps 1230, 1240, 1250 may be repeated if the elapsed time is shorter than the determined duration. Operation in the temporary mode MODE4 may be stopped and operation in the passive normal mode MODEO may be resumed at the end of the determined duration.

[0124] Fig. 10 shows, by way of example, a control system SYS1 of the dust extractor device 500. The control system SYS1 may comprise one or more pressure sensors PSEN1 , PSEN2, PSEN3 for measuring pressures pi, p2, ps. A pressure sensor PSEN1 may provide a pressure signal SPI indicative of the chamber pressure pi. A pressure sensor PSEN2 may provide a pressure signal SP2 indicative of the fan inlet pressure p2. A pressure sensor PSEN3 may provide a pressure signal Sps indicative of the downstream pressure ps. In an embodiment, a pressure sensor (e.g. PSEN3) may provide a pressure signal indicative of the pressure difference APFAN = P3-P2 across the fan FANI . In an embodiment, a pressure sensor (e.g. PSEN2) may provide a pressure signal indicative of the pressure difference ApF = P2-P1 across the filter FIL1 .

[0125] The control system SYS1 may comprise a control unit CNT1 for setting an operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4) based on the detected air flow AIR1 . The control unit CNT1 may be implemented e.g. by one or more data processors. The control system SYS1 may comprise a machine- readable memory MEM1 for storing computer program code PRG1 . The program code PRG1 , when executed by one or more processors of the control unit CNT1 may cause the control unit CNT1 to change the operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4) based on the detected air flow rate QAIR. The control system SYS1 may comprise a machine-readable memory MEM2 for storing one or more operating parameters PAR1 of the extractor device 500. The operating parameters PAR1 may specify e.g. an interval TFI between consecutive filter cleaning operations PUi, PlhThe control system SYS1 may comprise a timer for timing operations.

[0126] The control system SYS1 may comprise a user interface LIIF1 for receiving user input from a user. The user interface LIIF1 may also provide information to the user.

[0127] The dust extractor 500 may comprise a user interface LIIF1 for receiving user input from a user and / or for providing information to the user. For example, the user may set a default filter operating mode by using the user interface LIIF1 . For example, the user interface LIIF1 may provide a visual or audible indication of a current filter operating mode to the user.

[0128] The user interface LIIF1 may comprise an input device LIIF1 a for inputting a target power setting PTI . The user interface LIIF1 may comprise an input device UIF1 b for setting an initial operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4). The user interface LIIF1 may comprise an output device UIF1 c for providing an indication to the user. The output device UIF1 c may e.g. provide an indication of a current operating mode or indication of a selected operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4).

[0129] The control system SYS1 may comprise a flow measuring unit FSEN1 for measuring the air flow rate QAIR of the air flow AIR1 , which is drawn via the inlet IN1 by the fan FANI . The flow measuring unit FSEN1 may provide a flow rate signal SFLOW indicative of the measured air flow rate QAIR of the air flow AIR1 passing through the fan FAN1 . The control unit CNT1 may change the operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4) based on the flow rate signal SFLOW.

[0130] The control system SYS1 may comprise a flow detecting unit FCAL1 for providing a flow rate signal SFLOW to the control unit CNT1 . The flow rate signal SFLOW may be indicative of the detected flow rate QAIR. In an embodiment, the flow detecting unit FCAL1 may calculate the flow rate QAIR from the measured pressure difference P3-P2 and from the rotation speed NRPM of the fan FAN1. The flow detecting unit FCAL1 may be implemented e.g. by one or more data processors (PROC1 ). The flow detecting unit FCAL1 may be implemented e.g. by a calculation algorithm running on one or more data processors (PROC1 ).

[0131] The flow measuring unit FSEN1 may comprise one or more pressure sensors PSEN2, PSEN3 for measuring a pressure difference P3-P2 over the fan FANI . For example, a first pressure sensor PSEN2 may measure an upstream pressure P2 of the fan FAN1 . For example, a second pressure sensor PSEN3 may measure a downstream pressure ps of the fan FAN1 . Alternatively, a pressure difference sensor (e.g. PSEN2) may be arranged to measure the pressure difference P3-P2. The pressure sensor PSEN2 may form a pressure signal Sp2 indicative of the pressure p2 or the pressure difference P3-P2. The pressure sensor PSEN3 may form a pressure signal SPS indicative of the pressure ps.

[0132] The control system SYS1 may comprise a rotation speed indicator RPMSEN4 for providing a signal SRPM indicative of the rotation speed NRPM of the FANI . The control system SYS1 may be arranged to measure the flow rate QAIR by calculating the flow rate QAIR from the measured pressure difference P3-P2 and from the rotation speed NRPM of the fan FAN1 . The control system SYS1 may be arranged to measure the flow rate QAIR from one or more signals Sp2, Sps of the pressure sensors PSEN2, PSEN3 and from the rotation speed signal SRPM. The control system SYS1 may be arranged to calculate the flow rate QAIR by using the signals SRPM, SP2, SPS. The control system SYS1 may be arranged to calculate the flow rate QAIR from the measured pressure difference P3-P2 and from the rotation speed e.g. by using a regression function. Parameter values specifying the regression function may be stored in a memory (e.g. MEM2) of the control system SYS1 .

[0133] The fan FAN1 may be e.g. an axial fan and / or a centrifugal fan. The pressure difference APFAN = (P3-P2) over the fan FAN1 may depend on the air flow rate QAIR and on the rotation speed of the fan FAN1 . Consequently, the air flow rate QAIR may be calculated from the measured pressure difference (P3-P2) and from the rotation speed NRPM of the fan FAN1 . T1

[0134] The rotation speed indicator RPMSEN4 may form the rotation speed signal SRPM e.g. from a frequency of a driving electric current EC1 of the motor MOTOR1 . The rotation speed indicator RPMSEN4 may form the rotation speed signal SRPM e.g. from a commutation frequency of the motor MOTOR1. The rotation speed indicator RPMSEN4 may comprise a sensor for measuring the rotation speed of the motor MOTOR1 and / or to measure the rotation speed of the fan FAN1 .

[0135] The rotation speed signal SRPM may be indicative of the measured rotation speed of the motor MOTOR1 and / or indicative of the measured rotation speed NRPM of the fan FANI . The rotation speed of the fan FAN1 may be proportional to the rotation speed of the motor MOTOR1 . The rotation speed of the fan FAN1 may be equal to the rotation speed of the motor MOTOR1 . The rotation speed NRPM of the FAN1 may be determined from the rotation speed of the motor MOTOR1 . The rotation speed of the motor MOTOR1 may be determined from the rotation speed NRPM of the fan FAN1 , respectively.

[0136] The motor MOTOR1 may be e.g. an asynchronous or synchronous electric motor. The motor MOTOR1 may be e.g. an alternating current motor or a direct current motor. The motor MOTOR1 may be e.g. an universal motor. The motor MOTOR1 may be e.g. brushless direct current motor.

[0137] The control system SYS1 may comprise a motor driving unit MDLI1 for providing one or more electric currents EC1 to the motor MOTOR1 according to motor control signal SMOTORI . The motor driving unit MDLI1 may comprise e.g. power transistors and / or thyristors for providing the electric currents EC1 for the motor MOTOR1. The motor driving unit MDLI1 may provide one or more electric currents EC1 in response to a motor control signal SMOTORI . The control unit CNT1 may form the motor control signal SMOTORI based on the measured air flow rate QAIR.

[0138] In an embodiment, the rotation speed indicator SEN3 may determine the rotation speed of the fan FAN1 from the motor control signal SMOTORI and / or from the frequency of the one or more electric currents EC1 .

[0139] The dust extractor device 500 may comprise a dust chamber CHM1 for guiding the dust-laded air flow AIR1 from the inlet IN1 to the dust separator FIL1 and / or for collecting the separated dust DUST1. The dust extractor device 500 may comprise an air flow chamber CHM2 for guiding the air flow AIR1 from the fan FAN1 to the outlet OLIT1 .

[0140] The control unit CNT1 may be implemented e.g. by executing program code PRG1 by one or more data processors PROC1 of the control system SYS1 . Also the flow detecting unit FCAL1 may be implemented by executing program code by one or more data processors PROC1 of the control system SYS1 . In an embodiment, one or more data processors PROC1 may be arranged to carry out data processing for the control unit CNT1 and also for the flow detecting unit FCAL1 .

[0141] The control system SYS1 may qualitatively detect whether the air flow AIR1 is interrupted or not by monitoring at least one of the following: inlet chamber pressure pi, fan inlet pressure p2, pressure difference P2-P1 across the filter FIL1 , pressure difference APFAN = P3-P2 across the fan FAN1 , rotation speed NRPM of the fan FANI . A pressure pi or P2 which is lower than a limit value may be an indication of interrupted air flow AIR1. A pressure difference (P2 - pi) which is lower than a limit value may be an indication of interrupted air flow AIR1. A pressure difference (ps - P2) which is higher than a limit value may be an indication of interrupted air flow AIR1 . The control system SYS1 may be arranged to detect that the air flow AIR1 is interrupted e.g. if the pressure difference (P2 - pi) becomes lower than a limit value. The control system SYS1 may be arranged to detect that the air flow AIR1 is interrupted e.g. if the pressure difference (ps - P2) becomes higher than a limit value. The control system SYS1 may be arranged to detect an interruption COM1 of the air flow AIR1 based on a detected change of an internal pressure pi,p2 of the dust extractor 500, based on a detected change of a pressure difference Apr across the filter and / or based on a detected change of pressure difference APFAN across the fan FAN1 .

[0142] In an embodiment, the rotation speed of the fan FAN1 may also increase when the air flow AIR1 is interrupted. The motor MOTOR1 may be e.g. an universal motor, the torque needed to rotate the fan FAN1 may decrease when the air flow AIR1 is interrupted, and the rotation speed of the universal motor may increase when the torque needed to rotate the fan FAN1 is decreased. A rotation speed NRPM, which is higher than a limit value, may be an indication of an interrupted air flow AIR1. The control system SYS1 may be arranged to detect an interruption COM1 of the air flow AIR1 e.g. if the rotation speed NRPM becomes higher than a limit value. An interruption COM1 may be detected based on an increase of the rotation speed NRPM. The control system SYS1 may be arranged to detect an interruption COM1 of the air flow AIR1 based on a detected increase of the rotation speed NRPM of the fan FAN1 .

[0143] The control system SYS1 may also be arranged to measure the air flow rate QAIR. For example, the control system SYS1 may be arranged to calculate the air flow rate QAIR from the measured pressure difference APFAN = P3-P2 over the fan FAN1 and from the measured rotation speed of the fan FAN1 .

[0144] Detecting an interruption COM1 of the air flow AIR1 may comprise providing an indication (SRPM) of a rotation speed (NRPM) of the fan (FAN1), measuring a pressure difference (APFAN) across the fan (FAN1), and calculating the flow rate (QAIR) of the airflow (AIR1 ) from the rotation speed (NRPM) and from the measured pressure difference (APFAN). The calculated flow rate (QAIR) may be compared with a threshold value in order to determine whether the air flow is interrupted or not. The control system SYS1 may be arranged to detect an interruption COM1 of the air flow AIR1 based on a detected change of a calculated flow rate QAIR, wherein the control system SYS1 may be arranged to calculate the flow rate QAIR from the measured pressure difference APFAN across the fan FAN1 , and from the measured rotation speed NRPM of the fan FAN1 .

[0145] The dust extractor 500 comprises the filter cleaning unit FCII1 . The control unit CNT1 may send a control signal SACUI to the actuator ACII1 of the filter cleaning unit according to the operating mode of the dust extractor 500. The control unit CNT1 may cause performing a filter cleaning operation e.g. by sending a control signal SACUI to the actuator ACII1 of the filter cleaning unit FCII1 . The actuator ACU1 may e.g. open and / or close an air valve VAL1 of the filter cleaning unit. The actuator ACII1 may e.g. mechanically shake the filter FIL1 .

[0146] The control system SYS1 may comprise a communication unit RXTX1 e.g. for sending data to an external user interface (LIIF1 ) and / or for receiving user input via an external user interface (LIIF1 ). The external user interface (LIIF1 ) may be implemented e.g. by running an application on a mobile phone. The control system SYS1 may receive user input from an external user interface via the communication unit RXTX1 for setting an operating mode.

[0147] Referring to Fig. 11 a, the dust extractor 500 may comprise one or more input devices UIF1 a, UIF1 b for receiving user input. The dust extractor 500 may comprise an input device UIF1 a for inputting a target power setting of the motor MOTOR1 . The dust extractor 500 may comprise an input device LIIF1 b for setting an initial operating mode (MODEO, MODE1 , MODE2, MODE3, MODE4). The dust extractor 500 may comprise one or more output devices UIF1 c e.g. for providing an indication of a current operating mode. The dust extractor 500 may comprise one or more output devices UIF1 c e.g. for providing an indication of a selected operating mode. The output device UIF1 c may comprise e.g. buzzer or a loudspeaker for providing an audible alarm signal. The output device UIF1 c may comprise e.g. a lamp for providing a visual alarm signal.

[0148] SX, SY, and SZ denote orthogonal directions.

[0149] Referring to Fig. 11 b, the dust extractor 500 may optionally comprise e.g. an electric socket SOC1 for distributing electric power e.g. for the power tool TOOL1 . The dust extractor 500 may comprise an input device UIF1d for setting an operating mode of the dust extractor 500. For example, the dust extractor 500 may have a first operating mode where the dust extractor 500 operates continuously, and the dust extractor 500 may have a second operating mode where the dust extractor 500 operates only when electric power is drawn from the socket SOC1 .The socket SOC1 may also be called as an electric connector.

[0150] The dust extractor 500 may optionally comprise an input device UIF1 e e.g. for starting operation in the active mode MODE4 and / or for starting operation in the normal mode MODEO. The input device UIF1 e may comprise e.g. a push button. The human user may manually push the button so as to provide user input via the input device UIF1 e.

[0151] The dust extractor 500 has an inlet IN1 for connecting with the dust hose HOSE1 . The dust extractor 500 may have an outlet OUT 1 for discharging the substantially particle-free air flow AIR1 into ambient air, after the dust particles DUST1 have been separated from the air flow AIR1 . The input device UIF1a, LIIF1 b, LIIF1 d, and / or UIF1 e may be implemented e.g. by a rotary handle, by a sliding handle, and / or by one or push buttons.

[0152] In an embodiment, the dust extractor may comprise e.g. a keypad or a touch screen for receiving user input. In an embodiment, the user interface LIIF1 (UIF1 a, UIF1 b, UIF1 c, UIF1d, UIF1 e) may also be implemented e.g. by an application running on a mobile phone. The (mobile) user interface LIIF1 may communicate with the dust extractor 500 e.g. via wireless communication.

[0153] In an embodiment, the control system SYS1 may also change target power setting of the suction motor MOTOR1 . The control system SYS1 may be arranged to change a target power setting (PTI) of the suction motor MOTOR1 based on the detected air flow rate via the inlet. The control system SYS1 may change target power setting of the suction motor MOTOR1 from a first power value to a second power value when the control system SYS1 detects that the air flow AIR1 is interrupted. The control system SYS1 may be arranged to change the target power setting based on a detected interruption COM1 of the air flow AIR1. For example, the user may first use the dust extractor with at a low power setting without performing filter cleaning operations, and the user may later instruct the dust extractor to increase power setting and / or change filter operating mode to automatic filter cleaning by interrupting the air flow AIR1 , e.g. with his hand BLC1 .

[0154] The control system may respond to a detected interruption of the air flow e.g. by changing an operating mode or extending duration of operation in a temporary operating mode. Extending the duration means that the change of the temporary operating mode back to the normal operating mode is delayed based on the detected interruption. The control system SYS1 may also perform a cleaning operation in response to a detected interruption. For increased reliability, the control system may be arranged to change the operating mode only if the air flow AIR1 is interrupted for a time period (TINT) which is longer than a predetermined value (TSEC). The length of the time period TSEC may be e.g. in the range of 1 s to 30 s. The control system SYS1 may also ignore an interruption of the air flow in a passive operating mode, so as to avoid unintentional change of operating mode. Operating modes of the filter cleaning unit may be selected e.g. from the following list: first operating mode MODE1 , second operating mode MODE2, third operating mode MODE3, normal operating mode MODEO, temporary operating mode MODE4. The normal operating mode MODEO may be active or passive.

[0155] The above-mentioned operating modes may be summarized e.g. as follows:

[0156] Active normal operating mode MODEO: no cleaning operations; operating mode is changed to a temporary mode in response to a detected interruption; operating mode is not changed until an interruption is detected.

[0157] Passive normal operating mode MODEO: no cleaning operations; operating mode is not changed in response to a detected interruption; operating mode is not changed until user input is received via the user interface; operating mode is changed to a temporary mode in response to the user input.

[0158] First operating mode MODE1 : no cleaning operations; operating mode is changed in response to a detected interruption; operating mode is not changed until an interruption is detected.

[0159] Second operating mode MODE2: cleaning operations are performed repetitively; cleaning operations are timed based on a timer signal (e.g. at regular intervals); operating mode is changed in response to a detected interruption; operating mode is not changed until an interruption is detected.

[0160] Third operating mode MODE3: cleaning operations are performed repetitively; cleaning operations are timed based on a measured pressure value (e.g. when pressure difference across filter reaches a threshold value); operating mode is changed in response to a detected interruption; operating mode is not changed until an interruption is detected.

[0161] Temporary operating mode MODE4: cleaning operations are performed repetitively and / or in response to an interruption; repetitive cleaning operations may be timed based on a timer signal or based on a measured pressure value; duration may be extended in response to a detected interruption; operation is changed back to the normal mode at the end of the determined duration. The control system may control operation of the dust extractor. The control system may control operation of the filter cleaning unit. The dust extractor may perform a filter cleaning operation such that the control system causes the filter cleaning unit to perform the filter cleaning operation. The control system may perform a filter cleaning operation such that the control system causes the filter cleaning unit to perform the filter cleaning operation. The "filter operating mode" may refer to the "operating mode of the filter cleaning unit". The "operating mode of the dust extractor" may refer to the "operating mode of the filter cleaning unit".

[0162] For the person skilled in the art, it will be clear that modifications and variations of the devices and methods according to the present invention are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the invention, which is defined by the appended claims.

Claims

CLAIMS1 . A dust extractor (500), comprising:- an inlet ( I N 1 ) to draw an air flow (AIR1 ) and dust particles (DUST 1 ),- a filter (FIL1 ) to separate dust particles (DUST1 ) from the air flow (AIR1 ),- a filter cleaning unit (FCU1 ) to release separated dust particles (DUST1 ) from the filter (FIL1 ), and- a control system (SYS1 ) to control operation of the dust extractor (500), wherein the control system (SYS1 ) comprises at least one sensor (PSEN1 ) to detect an interruption (COM1 ) of the air flow (AIR1 ), and wherein the control system (SYS1 ) is arranged to change an operating mode (MODE1 , MODE2) of the filter cleaning unit (FCU1 ) based on a detected interruption (COM1 ) of the air flow (AIR1 ).

2. The dust extractor (500) of claim 1 , wherein the control system (SYS1 ) is arranged to change the operating mode of the filter cleaning unit (FCU1 ) from a first operating mode (MODE1 ) to a second operating mode (MODE2) when the control system (SYS1 ) determines that the air flow (AIR1 ) of the inlet (IN1 ) is interrupted (COM1 ).

3. The dust extractor (500) of claim 2, wherein filter cleaning operations (PUi, PU2) are not performed in the first operating mode (MODE1 ), and wherein the filter cleaning unit (FCU1 ) is arranged to repetitively perform filter cleaning operations (PU1, PU2) in the second operating mode (MODE2).

4. The dust extractor (500) according to any of the claims 1 to 3, wherein the control system (SYS1 ) is arranged to change the operating mode only if the air flow (AIR1 ) is interrupted for a time period (TINT) which is longer than a predetermined value (TSEC).

5. The dust extractor (500) according to any of the claims 1 to 4, wherein the control system (SYS1 ) is arranged to detect an interruption (COM1 ) of the airflow (AIR1 ) based on a detected increase of a rotation speed (NRPM) of a fan (FAN1 ).

6. The dust extractor (500) according to any of the claims 1 to 5, wherein the control system (SYS1 ) is arranged to detect an interruption (COM1 ) of the airflow(AIR1 ) based on a detected change of an internal pressure (pi,p2) of the dust extractor (500), and / or based on a detected change of a pressure difference (App, APFAN) of the dust extractor (500).

7. The dust extractor (500) according to any of the claims 1 to 6, wherein the control system (SYS1 ) is arranged to detect an interruption (COM1 ) of the airflow (AIR1 ) based on a detected change of a calculated flow rate (QAIR), wherein the control system (SYS1 ) is arranged to calculate the flow rate (QAIR) from a measured pressure difference (APFAN) across a fan (FAN1 ), and from a measured rotation speed (NRPM) of the fan (FAN1 ).

8. The dust extractor (500) according to any of the claims 1 to 7, wherein the filter cleaning unit (FCLI1 ) has a normal operating mode (MODEO) and a temporary operating mode (MODE4), wherein operation in the temporary operating mode (MODE4) has a duration (TMODE4), wherein the control system (SYS1 ) is arranged to start operation in the normal operating mode (MODEO) at the end (tE4) of the duration (TMODE4), and wherein filter cleaning operations (PUi, PU2) are not performed in the normal operating mode (MODEO).

9. The dust extractor (500) of claim 8, wherein the duration (TMODE4) is a predetermined duration (TMIN4), or wherein the duration (TMODE4) is the time needed for performing a predetermined number (NPU) of filter cleaning operations (PU1, PU2).

10. The dust extractor (500) of claim 8 or 9, wherein the control system (SYS1 ) is arranged to extend the duration (TMODE4) when an interruption (COM1 ) of the air flow (AIR1 ) is detected during the operation in the temporary operating mode (MODE4).11 . The dust extractor (500) according to any of the claims 8 to 10, wherein the filter cleaning unit (FCLI1 ) is arranged to perform a filter cleaning operation (BPU1) when an interruption (COM1 ) of the air flow (AIR1 ) is detected during operation in the temporary operating mode (MODE4).

12. The dust extractor (500) according to any of the claims 8 to 11 , wherein an interruption (C0M1 ) of the air flow (AIR1 ) detected during operation in the normal operating mode (MODEO) does not cause a change of the operating mode.

13. The dust extractor (500) according to any of the claims 1 to 12, wherein the filter cleaning unit (FCLI1 ) is arranged to release separated dust particles (DUST1 ) by shaking the filter (FIL1 ) and / or wherein the filter cleaning unit (FCLI1 ) is arranged to release separated dust particles (DUST1 ) by generating filter cleaning pulses (PU).

14. The dust extractor (500) according to any of the claims 1 to 13, wherein the control system (SYS1 ) is arranged to change a target power setting (PTI) of a suction motor (MOTOR1 ) based on a detected interruption (COM1 ) of the air flow (AIR1 ).

15. A method for extracting dust (DUST1 ) by using a dust extractor (500), the dust extractor (500) comprising an inlet (IN1 ), a filter (FIL1 ), and a filter cleaning unit (FCLI1 ), the method comprising:- drawing an air flow (AIR1 ) and dust particles (DUST 1 ) via the inlet (IN1 ),- separating dust particles (DUST1 ) from the air flow (AIR1 ) by using the filter (FIL1 ),- releasing dust particles (DUST 1 ) from the filter (FIL1 ) by using the filter cleaning unit (FCUI ),- detecting an interruption (COM1 ) of the air flow (AIR1 ), and- changing an operating mode (MODE1 , MODE2) of the filter cleaning unit (FCU1 ) based on the detected interruption (COM1 ) of the air flow (AIR1 ).

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